ec-dossier-polyurethanes

EUROPEAN
C OATINGS
PRESENTED BY
dossierwww.european-coatings.com
74 RESIN MODIFIER
Polycaprolactones – resin modifiers
that enhance physical properties
39 BIO-BASED CROSSLINKERS
70% of carbon content of a new hardener for
PUR coatings is provided by biomass.
POLYURETHANES
The best technical papers on polyurethane
coatings published in the European Coatings Journal
within the past three years.
2016

EDITORIAL2
EUROPEAN COATINGS JOURNAL 2016
Source:Taiga/Fotolia
THE ROLLS-ROYCE
OF BINDERS!
Polyurethanes are the binders of choice for formulating high-performance
coating and adhesive systems. They possess unique chemical and mechanical
resistance, a high level of gloss and much more besides. PUR coatings and
adhesives are always evolving and developing and there are countless
products on the market. As a formulator, you need to be au fait with the latest
advances in research and development. Such knowledge is rarely to be found
in a single package. European Coatings Journal is about to change that. This
thematic dossier is bursting with information on polyurethanes that we
have compiled for you. In it you will find all the relevant technical papers on
polyurethanes that have been published in European Coatings Journal over
the last three years. Now there’s a welcome development!
If you are looking for more information about polyurethanes, I heartily
recommend European Coatings 360°, a knowledge database which gives
you access to all technical books, conference proceedings, and videos from
European Coatings, in addition to the journal content. Why not try out
the 360° knowledge hub by signing up for a free 14-day online trial at
www.european-coatings.com/360. 
Enjoy reading!
Join our Group
“European Coatings Industry”
Dr. Sonja Schulte
Editor-in-Chief
T +49 511 9910-216
sonja.schulte@vincentz.net

A fancy car, a pair of sport shoes, and a parquet floor may be completely
different products, but they do have one thing in common: They are often
protected by lacquer coatings or held together with adhesives made from
raw materials from Covestro.
A global production network
We produce our raw materials in three major facilities in Europe, America,
and Asia. The segment also operates nine technical centers for solutions
adapted to individual customer needs. We can thus guarantee a consistently
high and stable quality for our clients everywhere all over the world.
New Possibilities through Polymer Expertise
Coatings, Adhesives, and
Specialties from Covestro
Sustainability along
the entire value chain
We are already searching today for
solutions to the most important
questions of tomorrow: How can
we, together with our partners,
develop visions for the entire value
chain? How can we, in cooperation
with them, transform these visions
into reality? And how can chemistry
help us to enable growth based on
environmentally friendly and
resource-saving products and
technologies? We find answers
through close cooperation with our
customers, as well as through a
clear focus on their markets.
Diverse applications
The Covestro segment Coatings, Adhesives, Specialties (CAS) develops
and produces aliphatic and aromatic isocyanate and derivatives of this,
as well as polyurethane dispersions. These raw materials are necessary for,
among other things, the production of innovative lacquer coatings and
sealants, as well as for elastomers and high-quality films, and for cosmetics,
textiles, and medical goods. The main areas of application are the
fields of transport and traffic, construction, wood processing, and
furniture production.
About Covestro
Covestro is one of the world’s
leading providers of high-quality
polymer materials and application
solutions for many sectors of
modern life. Our portfolio comprises,
among other things, intermediate
products for polyurethane foams
(PUR segment) and the high-perfor-
mance plastic polycarbonate (PCS)
segment, as well as raw materials for
lacquer coatings, adhesives, and
sealants (CAS segment).
Covestro AG
Kaiser-Wilhelm-Allee 60
51373 Leverkusen

CONTENTS4
Source:Freepik-www.flaticon.com
Source:stokkete-Fotolia.com
Source:lumachina99-Fotolia.com
6 MARKET REPORT
The PU Market in the focus
10 TOP INDUSTRY MOVE
Covestro: New heavy weither is stepping in
12 NANOTECHNOLOGY
Can agglomeration of nanosilica in
coatings be benficial?
Ismail Abay Mesur Eren et al.,
Betek Boya ve Kimya San. A.S..
18 NANOTECHNOLOGY
Reactive polyurethane nanoparticles create
high-performance adhesives
Klaus-Uwe Koch, Westfälische Hochschule
Recklinghausen.
24 BIO-BASED RAW MATERIALS
Polyols for PUD prepared with various levels of
renewable conten.
Joel Neale, Perstorp.
TOP INDUSTRY
MOVE
Covestro: New
heavy weighter is
stepping in
10
BIO-BASED HARDENER
New polyurethane
crosslinkers.
30
46CROSSLINKER
Accelerate curing and add value.
30 BIO-BASED HARDENER
New polyurethane crosslinkers with significant
bio-based content.
Gesa Behnken et al., Covestro.
36 RADIATION CURING
Novel water-based UV-PUD for
robust single-coat mirror effect.
Michel Tielemans et al., Allnex.
40 RADIATION CURING
Water-based UV-PUD finishes offer enhanced
resistance properties.
Laurie Morris, Alberdingk Boley.
46 CROSSLINKER
Using crosslinking agents to accelerate curing
and add value.
Christof Irle and Jan Weikard, Covestro.

5CONTENTS
Source:EricGevaert-Fotolia.comSource:sociopat_empat-Fotolia.com
Source:Pyast-Fotolia.com
DILUENTS
Cutting VOCs
and preserving
performance
68
FLOOR COATINGS
Covering the cracks
78
ISOCYANATE-FREE PUR
Taming the Michael Addition
reaction
82
52 NON-ISOCYANATE CROSSLINKING
Novel PU chemistry combines rapid cure with
extended pot-life.
John Agryopoulos et al., The Dow Chemical Company.
58 AUTOMOTIVE COATINGS
Novle polyols improve performance of melamine
crosslinked coatings.
Ravi Ravichandran and John Florio, King Industries.
64 HARDENERS
Getting on with acrylics
Mauri Usai, S.A.P.I.C.I. Spa.
68 DILUENTS
Cutting VOCs and preserving performance
Tim Miller and Kwyne Pugh, Vertellus Specialities
Materials.
74 REACTIVE DILUENTS
Polycaprolactones - resin modifiers enhancing
physical properties.
Pär Jörgensen, Perstorp.
78 FLOOR COATINGS
Covering the cracks
Matthias Wintermantel et. al., Bayer MaterialScience
82 ISOCYANATE-FREE
Taming the Michael Addition reaction
R. Brinkhuis et al., Nuplex Resins.
90 TEXTILE COATINGS
Versatile and environmentally friendly
Willie Corso and Rolf Irnich, Bayer MaterialScience
94 METAL COATINGS
DTM acrylic polyol for 2K PUR coatings
eliminates etch primer.
Gautam Haldankar and Alan Woosley,
Nuplex Resins.
100 ADDITIVES
Enhancing the performance of water-borne
coatings.
Detlef Burgard and Marc Herold, Bühler Group.
Source cover: mekcar - Fotolia.com

6
POLYURETHANES
Source:BayerMS
THE PU
MARKET IN
THE FOCUS
Grand View Research on trends, challenges and
developments until 2020. By Anshuman Bahuguna
The global polyurethanes market was 16,432 kilo tons in 2014.
Recovery of major industries post economic recession in North
America and Europe has had a positive impact on the polyure-
thanes market. Production of essential raw materials such as
MDI and TDI has increased gradually and their prices are ex-
pected to remain stable during the forecast period until 2020.
Rigid PU foams demand in 2014 stood at 4,295.8 kilo tons with
MDI and TDI consumption in its production was 2,974.8 kilo
tons and 59.0 kilo tons respectively. Increasing demand for insu-
lation materials particularly in construction is expected to drive
rigid PU foams demand. By 2020, global PU demand is expected to
reach 22,058.4 kilo tons, registering a CAGR of 5.0 % over the fore-
cast period. With raw material supply expected to be stable and
increasing capacity utilization, PU spot prices are projected to re-
main consistent over the forecast period. However, prices in North
America and Europe are expected to be relatively higher than Asia
Pacific region. Pricing disparity can be attributable to manufactur-
ing conditions in Asian markets and cheap raw material prices in
the region. Other components that highly impact production cost
such as transportation costs, cheap labour and favourable gov-
ernment policies are favourable for production landscape in Asia
Pacific.
REGULATORY SCENARIO IS EXPECTED TO HAVE A POSITIVE
IMPACT ON THE MARKET
The global PU market value chain consists of highly integrated com-
panies (from raw material production to PU production). There is a
considerable presence of suppliers in the market who ensure con-
sistent MDI, TDI, PTMEG and additive supply for independent PU
manufacturers. Major companies in the market include BASF SE,
The Dow Chemical Company, Huntsman Corp., Mitsui Chemicals
Inc. and Bayer MaterialScience. In U.S., OSHA and ACGIH have not
established regulatory policies such as exposure limits and carci-
nogenicity levels for polyurethanes. Favourable regulatory scenario
is expected to have a positive impact on the market. High aware-
ness regarding environmental effects of conventional polymers
among consumers has led to development of bio-based products
as substitutes for conventional products. However, high econo-
mies of scale and undeveloped production processes associated
with bio-based products’ manufacturing are expected to ensure
continuous demand for their conventional counterparts. Growing
importance for bio-based PU is expected to provide opportunities
to market participants over the forecast period.
WATERBORNE PU COATINGS ARE EXPECTED TO
WITNESS HIGH DEMAND
PU coatings, particularly waterborne PU coatings, are expected
to witness high demand over the forecast on account of its in-
creasing application in automotive, floor coatings and industrial
finishing. In line with regulatory framework around the globe, wa-
terborne coatings contain low VOCs. Considering the tightening
policies pertaining to VOC impact on environment, waterborne PU
coatings are touted to gain more preference than solvent borne
coatings. Two component PU coatings (2K coatings) are gaining ac-
ceptance in textile intermediates and fiber glass sizing. 2K coatings
possess oxidative drying and radiation curing capabilities, which
is a major factor driving its demand in the above stated applica-

7POLYURETHANES
tions. PU coatings are expected to gradually replace traditional
solventborne coatings in automotive and construction industries
due to its strong demand for plastic glass coating, floor coating,
pipeline coating and wood coating applications. Global PU coat-
ings demand was estimated at 2,304.0 kilo tons in 2014. On ac-
count of the above mentioned factors, PU coatings consumption
is expected reach 3,124.4 kilo tons by 2020, registering a CAGR of
5.2 % from 2014 to 2020.
FOOTWEAR IS A MAJOR APPLICATION
SEGMENT FOR PU ADHESIVES
High demand for polyurethane adhesives for automotive, electronics
and construction applications in Southeast Asian markets is expected
to be a major factor contributing to the overall market growth. Ma-
jor industry participants are shifting their production capabilities to
Asia Pacific in order to capture the growing demand in the region.
Favourable regulatory framework and high performance properties
have led to replacement of conventional adhesives by PU adhesives.
Global PU adhesives demand was estimated at 1,268.3 kilo tons in
2014. Footwear is a major application segment for PU adhesives. With
major footwear companies increasing viewing Asian markets particu-
larly Vietnam, Thailand, Bangladesh and Indonesia a better produc-
tion destinations. Major footwear companies such as Nike and Adidas
(along with its subsidiaries) have outsourced their products to sub-
contract manufacturers in China, Indonesia and Vietnam. Increasing
footwear production in these regional markets is expected to drive PU
adhesives demand over the forecast period. Global consumption of
PU adhesives is expected to reach 1,671.0 kilo tons by 2020 with Asia
Pacific accounting for 48.3 % demand.
Product 2014 2020 CAGR (2014 – 2020)
Rigid Foams 4,295.8 5,844.3 5.2%
Flexible Foams 6,395.4 8,540.6 4.9%
Coatings Adhesives
Sealants
2,304.0 3,124.4 5.2%
1,268.3 1,671.0 4.7%
Elastomers 1,830.0 2,439.1 4.9%
Others 338.6 439.0 4.4%
Total 16,432.2 22,058.4 5.0%
Table 1: Global PU market demand CAGR, by product,
2014 2020 (Kilo Tons) Source: Grand View Research, Inc.
NEARLY HALF OF THE PU DEMAND IS
CONSUMED IN ASIA PACIFIC
Asia Pacific is a major regional polyurethanes market and accounted
for 47.3 % of the total market volume in 2014. The market in the re-
gion is largely driven by high demand for rigid PU foams and coatings
in construction industry. Increasing construction spending and rapid
urbanization rates in emerging markets of the region such as China
and India have led to large scale infrastructure projects being taken
up by both public and private entities. With increasing construction
in commercial real estate and residential real estate, rigid PU foams
are expected to witness significant demand. Additionally, high per-
formance of PU coatings (architectural, industrial, plastic and wood
coatings) compared to epoxy coatings is expected to further drive its
demand in the region. Moreover, PU coatings in Asia Pacific are priced
at USD 2.41 per kg compared to USD 2.86 per kg in Europe and USD
2.81 per kg in North America. With increasing presence of PU coat-
ings manufacturers in the region, abundant raw material availability
and relatively low pricing, the market in the region is heading towards
being export oriented. MDI and TDI consumption in Asia Pacific stood
at 1,818.9 kilo tons and 629.7 kilo tons in 2014 respectively with PU
foams (rigid flexible), coatings and adhesives being major products
manufactured.
PU DEMAND IS EXPECTED TO BE THE STRONGEST IN
AUTOMOTIVE AND ELECTRONICS
Major end-use industries such as automotive, electronics and furni-
ture are expected to witness high PU demand over the forecast pe-

POLYURETHANES8
riod. PU demand is expected to be the strongest in automotive and
electronics (5.3 % CAGR from 2014 to 2020). Major PU products that
find application in automotive industry include flexible PU foams, PU
coatings, PU adhesives and TPU. Flexible PU foams have been tradi-
tionally been used for seating, armrests and headrests of automo-
biles. PU coatings and adhesives find application in floor, glass and
wood coatings; and automotive component assembly respectively.
Increasing automotive production in Asian markets of China, Japan,
Korea and India is expected to drive the aforementioned PU products’
demand. Additionally, increasing automotive sales in Mexico and Bra-
zil along with complementing automotive production in U.S. for these
markets is expected to further drive PU market growth. PU demand
for automotive applications was 1,566.0 kilo tons in 2014 and is ex-
pected to reach 2,136.5 kilo tons by 2020. PU foams are widely used
in electronic components for encapsulation due to its abrasion resist-
ance and insulation properties.
Increasing electronics production in Korea, China, Japan and U.S. is
a major factor driving PU demand in electronic components manu-
facturing. The market for electronics was estimated at 2,084.9 kilo
tons in 2014. Other significant demand for PU products is expected
to be from construction industry which employs these products for
a plethora of applications such as insulation, adhesion, coating and
architectural aesthetics. The market for construction is expected to
grow at a CAGR of 4.9 % over the forecast period. 
REFERENCE
The information in this article is based on the
report: “Polyurethane (PU) Market Analysis By
Product, By End-use And Segment Forecasts To 2020” by Grand View Re-
search, Inc.
Rachel Brown
Grand View Research, Inc
T +1 415 349 0058
rachel@
grandviewresearch.com
FIG. 1: Global PU demand by end-use industry, 2014 2020
(Kilo Tons) Source: Grand View Research, Inc.
FIG. 2: Global PU demand CAGR by region, 2014 2020 (Kilo Tons)
Source: Grand View Research, Inc.

www.covestro.com
Covestro is an independent, globally leading provider of polymer solutions.
In the field of coatings, adhesives, and specialties, we operate an international
network of cutting-edge production plants. By producing the same high
standard at every site throughout the world, we ensure that our customers
are able to apply their formulations globally standardized. For efficiency and
reliable quality in every region.
What can we invent for you? www.inventing-for-you.com
INVENTING
POLYMER STANDARDS
FOR YOU
CovestroDeutschlandAG,D-51365Leverkusen·COV00080648

10
TOP INDUSTRY MOVE
IS A SPIN OFF A NEW IDEA?
To what extent investors will aim at Covestro as a possible target re-
mains uncertain. But Bayer already has experience in spinning off
a business unit. Ten years ago Bayer spun off parts of its specialty
chemicals business. The company operates as Lanxess in the mar-
ket and is now a listed company. Back in the days there were some
doubts in the market whether Lanxess could be successful. Measured
by the low expectations restructuring plans turned into a success
story. This might serve as a blue print.
WHAT ARE THE FIGURES FOR THE BUSINESS?
In brief: the business is doing better now. In 2014, the business unit
recorded sales of EUR 11.8 billion (28% of Bayer‘s total turnover) and
accounted for 13% of the profits (EUR 1.09 billion). The figures for the
COVESTRO: NEW HEAVY
WEIGHTER IS STEPPING IN
Bayer’s intention to spin off the polymer division was announced in 2014. Since 1 September, 2015 Bayer
MaterialScience is operating under the Covestro name. This is the fourth largest chemical company in Europe at the
start. What you need to know about this industry move. By Damir Gagro.
The company is now legally and economically independent,
but will remain a 100 % subsidiary of Bayer AG. Bayer wants to
float Covestro on the stock market by mid-2016 at the latest in
order to concentrate exclusively on the life sciences business-
es. Market experts expect it will be the largest stock market
entry in Germany for more than 15 years.
The independence is supposed to allow the new company to do
things faster and be more courageous and commercialise
things at a faster speed. Bayer intends to focus on its Life Science
business units: HealthCare and CropScience. Investors have re-
portedly demanded this move in the past. By spinning off the Ma-
terialScience business unit, it does not have to compete any more
with the two other business units for investments within the parent
company. Covestro will have direct access to capital for its future
development.

11TOP INDUSTRY MOVE
“The separation from Bayer
gives us a unique opportunity
to concentrate on and further
develop our leading positions in
our polymer business.“
Daniel Meyer
Head of the Coat-
ings, Adhesives,
Specialties Busi-
ness Unit (CAS) at
Covestro
3 questions to Daniel Meyer
Isn’t the new name a disadvantage as BMS was well established
in the market? Bayer has decided to focus in the future entirely on its
Life Science businesses and position itself as a world-leader in the field
of human, animal and plant health. The separation from Bayer and the
thereby connected independence gives us as Covestro a unique opportu-
nity to concentrate on and further develop our leading positions in our
polymer business. Covestro will be able to bear in global competition more
quickly, effectively and flexibly. The name Covestro reflects the identity of
the new company.
Why do you expect the business to be thriving now as it is inde-
pendent? We are a world-leading polymer producer and expect to con-
tinue our course of growth. According to independent research institutes
our markets will grow stronger than the world economy (GDP) in the years
to come. This development is expected to be backed by macro trends such
as climate change, rising mobility and intensifying urbanisation. Covestro
aims to capture this industry growth by offering and continuing to develop
products and solutions to meet these trends and the needs of its markets
and industries.
What is the initial strategy for the coatings and adhesives related
business within Covestro? Independence gives us the exciting oppor-
tunity to deploy our strengths even more rapidly, effectively and flexibly
in the global competitive arena. Our business unit CAS (Coatings, Adhe-
sives and Specialties) is positioning itself as high-end solution provider to
complex customer industries, unlocking above-average growth potential.
Its market-driven innovation capability and customer proximity help to
create new application space and maintain its leadership positions in dif-
ferent markets. At the ECS this year, CAS presented two interesting innova-
tions in the field of polyurethanes: first PDI, an entirely new isocyanate,
70% of whose carbon content comes from biomass without generating
any direct competition for food production. Second, a new thermolatent
hardener that enables energy and cost-efficient mixed material coating for
the automotive industry. Our CAS business holds global leading and de-
fendable positions in an industry with distinct barriers to entry. Its strong
financial profile due to high margin resilience and low requirements for
capital expenditure is a solid platform for future business expansion.
Source:Name-Seite/Anbieter
second quarter 2015 show an increase in turnover to EUR 3.2 billion
(+11%) and profits hiked from EUR 109 million to EUR 278 million.
Covestro supplies key industries around the world, such as the auto-
motive, construction and electronics sectors, as well as the furniture,
sporting goods and textiles industries. Products include raw materi-
als for polyurethane foam. The company also produces polycarbon-
ates, which are also very versatile materials for automotive compo-
nents, roof structures, medical devices and much more. Rounding
out the portfolio are specialty chemicals, including raw materials for
coatings, adhesives and films.
WHY COVESTRO?
The name Covestro comes from a combination of words that the
company believes reflect its new identity. The letters “C” and “O”
come from collaboration, while “Vest” signifies the company is well
invested in state-of-the-art manufacturing facilities. The final letters,
“Stro”, show the company is strong in the areas of innovation, the
market, and its workforce. Accompanying the new name is a brand
logo for Covestro. Even if the name sounds odd at first sight, enter-
prises want their business name to be sticky. They want people to
hear it once and have it stick in their minds. Common names do not
stick. They’re hard to remember – and they are harder to find online.
WHO WILL RUN COVESTRO?
Covestro is managed by a four-member board of management.
Members of the Board under CEO Patrick Thomas are Frank H. Lutz
(Finance, Labor Director), Dr Klaus Schaefer (Production and Tech-
nology) and Dr Markus Steilemann (Innovation). 

FACTS FIGURES ABOUT COVESTRO
Annual sales: EUR 11.7 billion
Employment: 14,200 people
Production sites around the globe: 30

12
NANOTECHNOLOGY
Source:agvisuell-Fotolia.com
A QUESTION OF
REINFORCEMENT
Can agglomeration of nanosilica particles in coatings be beneficial? By Ismail Abay Mesut Eren, Sezgin San,
Hakan Askun and Murat Orbay, Betek Boya ve Kimya San A.S.
Nanosilica has been added to waterborne 2K PU varnishes and
paints to examine its effects on properties. Additions of 5 %
were beneficial, provided the additive was pre-mixed rather
than added in the let-down stage. Silica agglomerates had a
different appearance from those reported elsewhere, and the
silica was preferentially distributed at the top surface, thus in-
creasing its effects on surface properties.
An extensive amount of coatings industry research is now devoted
to environmentally-friendly materials, due to the VOC restrictions
imposed in developed countries. When switching from solventbased
binders, their waterbased (WB) counterparts seem to be the most
widely applicable solutions. One-component (1K) and two-component
(2K) waterbased polyurethane coatings certainly compete with their
solventbased versions in the parquet and furniture industry.
Unfortunately, the mechanical strength and stiffness of these films
has been found to be inferior to solvent-based ones. Well-known
side reactions with water (or later with atmospheric humidity) con-
sume isocyanate groups to give carbamic acid, dissociating to form
amine groups which will use up another isocyanate group intended
to form urethane or allophanate linkages. Thus, various additives to
compensate for the deficiency have been sought. As discussed below,
nanosilica was among the best, although agglomeration and uniform
dispersion can be a problem.
PROBLEMS IN FORMULATING WATERBORNE 2K SYSTEMS
The work presented here is a small part of a more detailed project,
perhaps similar to those carried out worldwide on improving the
properties of WB 2K polyurethane wood coatings. The aim was to
find a suitable dispersion/emulsion + hardener combination from the
commercially available ones, which when applied on particle board or

13NANOTECHNOLOGY
RESULTS AT A GLANCE
 Side reactions can impair the properties of water-based 2K
polyurethane varnishes and paints.
 Nanosilica addition, even at low amounts such as 5 %, was
found to improve properties, and pre-mixing was more effec-
tive than let-down addition.
 In the test varnishes, both AFM and SEM show that nano-
silica is present in the film along with well-distributed agglom-
erates on the surface, contributing to nano roughness, which
improves properties such as hardness and staining resistance.
Their popcorn-like shape and sub-micrometre size is different
from clusters of spheres previously observed by others.
 Although previous SEM images have shown that nanosilica
additives were well distributed from a 2D view, EDX scans of
fractured paint films show an abundance of nanosilica in the
upper layer and titanium dioxide in the lower layer, instead of a
homogeneous distribution.
Figure 1: Stain resistance of the varnishes and paints
isocyanate in good faith, but primer, additive and formulation differ-
ences, the chemistry of the components, the hydrophilic-hydrophobic
character of the isocyanates, all influence the final properties.But as
determined previously by other researchers [1, 2], when 25 first com-
ponents were polymerised with seven second components (all com-
mercially available products), the most important factors were found
to be the NCO/OH ratio and relative humidity (RH). It was also found
that high humidity, especially in combination with high NCO/OH ra-
tios (contrary to expectations) impeded allophanate formation and in-
creased urea and biuret crosslinks at the surface, impairing hardness
and other properties significantly.
For example, for some crosslinking pairs a reduction in König hard-
ness of up to 50 % was observed. The results of this investigation
will be presented elsewhere. Since most wood industry manufacture
is carried out under ambient conditions and an increase of 20 % in
humidity can stop the production line in a factory, reinforcement by
nano-additives was considered to be a good choice.
ISSUES IN THE USE OF NANOSILICA
From the end of the last century, research on the effects of nano fillers
such as nanosilica, nano alumina, nano zinc oxide and nanoclays be-
came quite popular. Nanosilica became the favourite among these [3-
5] for improving the main coating properties such as scratch, abrasion
and chemical resistance, due partly to its commercial availability and
moderate price. Since the degree of dispersion and accompanying
property improvements depend largely on the stability of the nano-
particles, most of the papers published in recent years are concerned
with preparation of silica-polyurethane hybrids, where attachment to
the hydroxyl groups of the first component containing polyurethane
or acrylate [6, 7] or second component polyisocyanate [8] was sought.
Where chemical bonding was not achieved, hydrogen bonding in-
teractions between the silanol groups of silica and soft and/or hard
groups of the polyurethane were considered to contribute to stabili-
sation and good properties [9, 10].
HOW THE TEST COATINGS WERE PREPARED
A WB 2K polyurethane coating with a low response to RH changes was
chosen, based on an acrylic dispersion and hydrophilic isocyanate,
and improvement of its varnish and paint surface properties by nano-
on a veneered surface of medium density fibreboard (MDF), will pro-
vide optimal properties with minimal cost. Another aim was to study
the compatibility and effect of nanosilica addition at various levels, as
well as whether a micro-roughness can be obtained to improve resist-
ance to staining. Naturally each manufacturer of urethane or acrylic
based first components recommends a second component based on

NANOTECHNOLOGY14
Figure 2: Topographic (30 µm x 30 µm) and phase contrast AFM images of (a) varnish; (b) varnish containing 5 % nanosilica;
(c) oven cured varnish; (d) oven cured varnish containing 5 % nanosilica
silica addition/distribution were studied and are reported here. “Ne-
oCryl XK 540” styrene-acrylic dispersion was used in both varnishes
and paints. It has 4.2 % hydroxyl group content and a Tg of 35 °C. The
nanosilica was “Bindzil CC 301” with 7 nm particle size, 29 % silica and
0.45 mol/ kg reactive hydroxyl content. Crosslinking was achieved with
“Easaqua XD 803”, a hexamethylene diisocyanate and isophorone diiso-
cyanate hybrid water-dispersible aliphatic polyisocyanate with 14.3 %
NCO content. The NCO/OH ratio for the coatings was approximately
1.2, disregarding the hydroxyl content of the nanosilica. Dispersion
of the first component was in a 1 l standard disperser cup with high
speed laboratory disperser. For varnishes, in the pre-mixing method,
nanosilica was added to the acrylic dispersion and dispersed, then the
other components such as non-ionic dispersing agent, fluorosurfactant,
silicone surfactant, polyurethane dispersant, glycol ether solvents and
water were added in that order under mixing. A mixture of non-ionic
polyethy-lene emulsion, silicone surface additive and water was added
later.For paints, a titanium dioxide paste was added after the silicone
surfactant, to provide a PVC of 20 %. In the let-down (post-addition)
method, nanosilica was added at the final stage of mixing. The two com-
ponents were mixed at the predetermined ratio and the varnishes and
paints were applied with applicators on glass plates or sprayed on MDF
boards to give 60 µm dry films and dried under ambient conditions.

15NANOTECHNOLOGY

Figure 3: Topographic (5 µm x 5 µm) and phase contrast AFM images of (a) oven cured varnish;
(b) oven cured varnish containing 5 % nanosilica
Experiment Nanosilica [%] Gloss [60°] Abrasion loss [%] [cycles] Haze Hardness Hardness [Konig.s] [days]
250 500 100
[pencil]
[7 days]
1 7
Varnish 1 0 88 4,1 10,3 16,3 13,2 HB 20 59
Varnish 2 3* 85 3,7 10,0 16,0 16,2 H 22 65
Varnish 3 5* 82 3,6 9,6 15,5 18,2 H 29 81
Varnish 4 8* 76 3,6 9,7 15,5 19,7 H 25 72
Varnish 5 3** 85 3,9 10,0 15,8 19,2 HB 19 58
Varnish 6 5** 80 3,8 9,9 15,7 20,9 B 22 59
Varnish 7 8** 73 3,7 9,9 15,7 26,3 B 21 57
Paint 1 0 79 3,0 9,1 15,1 ND HB 32 68
Paint 2 3* 77 2,8 8,9 14,9 ND H 35 70
Paint 3 5* 69 2,7 8,7 14,7 ND H 41 81
Paint 4 8* 65 2,7 8,6 14,5 ND HB 38 72
Paint 5 3** 59 2,8 8,9 14,9 ND HB 31 67
Paint 6 5** 53 2,9 9,0 15,0 ND HB 29 67
Paint 7 8** 51 3,0 9,0 14,9 ND HB 30 64
* : pre-mix addition, **: let down addition, ND: not determined
Table 1: Summary of initial test results on varnishes and paints
TEST PROCEDURES SUMMARISED
The properties were determined after one or seven days. The stain re-
sistance of films was determined according to DIN 68861-1 for some
common household stainers. 60° gloss was determined using a “Novo
Gloss Statistical Glossmeter”, abrasion loss by “Taber 5135” rotary plat-
form abraser, König hardness by König pendulum with “SimEx” coun-
ter, haze by Byk “Micro Haze Plus”, pencil hardness by a unit from TQC.
An oven curing of 100 minutes at 70 °C was applied to some of the
varnish films. Atomic Force Microscopy (AFM) images of films on mica
plates were obtained using a Digital Instruments “Nanoscope III” AFM
in tapping mode. The same plates of the varnishes and MDF plates of

NANOTECHNOLOGY16
Figure 5: SEM image of the paint containing 5 % nanosilica
Figure 6: SEM-EDAX analysis of the paint containing 5 %
nanosilica
Figure 4: SEM images of (a) oven cured varnish; (b) oven cured
varnish containing 5 % nanosilica

17NANOTECHNOLOGY
 nanosilica agglomerates on the surface, at levels far beyond those ex-
pected at its relatively low content of 5 %. The hard regions observed
in phase contrast AFM images are also present in the oven-cured var-
nish without the nanosilica additive.
The images also confirm that the nanosilica additive exists as nano-
sized particles, which appear as small white dots, as well as forming
these small and well distributed agglomerates. Mhatre et al [15] con-
cluded that the high surface energy of nanosilica particles results in
formation of uniform clusters of particles in a well distributed form.
Sow et al [5] determined even larger formations of nanosilica islands
of up to 6 µm size dispersed in a UV-WB polyurethane acrylate matrix.
But this ‘popcorn’ image of the agglomerate is very different from pre-
viously observed formations.
The disappearance of hard regions in the micrograph of the sample
containing nanosilica indicates that they may have served as initiation
points for the formation of agglomerates due to reaction of residual
isocyanate groups of these hard regions with free hydroxyl groups
of nanosilica, as well as acting as anchorage points. The SEM images
of the paint (Figure 5) show a smoother surface, where only a small
amount of nanosilica agglomerates protruding from the surface can
barely be seen at the higher magnification level.
SEM images supplied by previous authors indicated a good disper-
sion of nanosilica, when the image is 2-dimensional, that is, observed
from above [10]. On the other hand, Energy Dispersive X-Ray EDX–
SEM analysis (Figure 6) confirms that for the paint containing nanosilica
applied on wooden surface (MDF), nanosilica is not evenly distributed.
Since no flocculation was observed, the titanium dioxide is assumed
to be well dispersed throughout the paint film.
In this case, the EDX results show that since the Ti/Si ratio changes
from 10.38 to 4.17 for the lower and upper regions of the fractured
film, respectively; thus, nanosilica concentration is definitely high-
er near or on the surface. It appears that high concentrations of
nanosilica on the surface inducing micro- roughness contributed to
property improvements of 2K WB polyurethane varnishes and paints
in this case. 
ACKNOWLEDGEMENTS
The authors are grateful to the Turkish scientific and technological research
council, Tübitak Teydeb, for its support for this work under project number
3050355.
REFERENCES
[1] Otts D. B., Urban M. W., Polymer, 2005, Vol. 46, pp 2699-2709.
[2] Bao L., Lan Y., Zhang S., Iranian Polym. Jnl., 2006, Vol. 15, No. 9,
pp 737-746.
[3] Yang C. H., Liao W. T., Jnl. Coll. Interface Sci., 2006, Vol. 302, p 123.
[4] Kim B. S., Park S. H., Kim B. K., Coll. Polym. Sci., 2006, Vol. 284,
pp 1067-1072.
[5] Sow C., Riedla B., Blanchet P., JCTR, 2011, Vol. 8, pp 211-221.
[6] Athwale V. D., Kulkarni M. A., Pigt. Res. Tech., 2011, Vol. 40,
pp 49-57.
[7] Qiu F. et al, JCTR, 2012, Vol. 9, pp 503-514.
[8] Nennemann A. et al, Europ. Coat. Congress, April 2009, Nuremberg,
Germany.
[9] Goda H., Frank C. W., Chem. Mater., 2001, Vol. 13, pp 2783-2787.
[10] Zhang S. et al,. Prog. Org. Coat., 2011, Vol. 70, pp 1-8.
[11] Peruzzo P. J. et al, Prog. Org. Coat., 2011, Vol. 72, pp 429-437.
[12] Manvi G. N.et al, Prog. Org. Coat., 2012, Vol. 75, pp 139-146.
[13] Tielmans M. et al, Prog. Org. Coat., 2012, Vol. 75, pp 560-568.
[14 Sakamoto Y. et al, Nippon Polyurethane Industry Co. Ltd,
internal publication, 2009.
[15] Mhatre R. A. et al, Pigt. Res.Tech., 2010, Vol. 39, pp 268 -276.
the paints were used for Scanning Electron Microscope (SEM) studies
performed with an FEI “Quanta 450 FEG” ﬁeld-emission SEM.
SOME IMPROVEMENT IN RESISTANCE PROPERTIES OBTAINED
Table 1 shows the effects of nanosilica addition at various levels either
to the first component at the early stage or during the let-down stage.
The results indicate that, for the formulation employed, in all cases
there was an optimal level for nanosilica content, as well as a distinct
advantage of pre-mixing over let-down additions.
In the case of the varnishes, the improvement in hardness and abra-
sion resistance was accompanied by a moderate loss in gloss and
haze at 5 % nanosilica addition for the pre-mixing method. On the
other hand, the let-down addition method yielded no significant im-
provement beyond abrasion resistance. The paints gave a similar pic-
ture, though the advantages obtained were more moderate and the
losses more severe.
The effect of 5 % nanosilica addition on resistance to some common
household stainers is shown in Figure 1. The test was carried out for
the pre-mixing samples, for two minutes, ten minutes and 16 hours of
contact time. None of the samples was affected after two minutes, but
the paints showed staining after ten minutes by tannin contained in
coffee and tea, as well as anthocyanin in red wine. The varnishes were
not affected during the same contact time.
Staining was more severe after 16 hours’ contact time, but for almost
all contaminants, it was reduced by the presence of nanosilica addi-
tive. Certain nanosilica producers recommend high levels of 15 - 20 %
to obtain best results, but Table 1 and Figure 1 indicate that moderate
levels can significantly improve some of properties of WB 2K varnish
and paints.
SILICA CHANGES SURFACE TOPOGRAPHY SIGNIFICANTLY
AFM is a useful tool for inspection of polymer surfaces, especially the
phase separated microstructure of polyurethanes in case of blends
and nano additives [10-13]. Polyurethanes undergo microphase sepa-
ration due to the immiscibility of their hard and soft segments. The
hard segment domain acts as the physical crosslink as well as a filler
for the soft-segment matrix.
Tapping mode AFM is preferred for these types of polymer surfaces
and two kinds of images can be obtained. The topographic image is
obtained in 2-dimensional form and can be converted to a 3-dimen-
sional form, providing a good idea of the appearance of the surface.
The phase contrast image shows the difference in mechanical prop-
erties of the surface, displaying regions of soft (darker coloured) and
hard (lighter coloured) regions.
The topographic and phase contrast AFM images of varnishes are
shown in Figure 2 and Figure 3. Some samples were oven cured at 70 °C
to enhance crosslinking, which increased the spiky appearance of the
surface, while also reducing the height of the protuberances.
Addition of 5 % nanosilica changed the surface appearance and prop-
erties by occupying a significant portion of it, both in normal and oven
cured samples, filling in the spaces between protuberances and shift-
ing the height scale. This can be more clearly observed from the 5 µm
AFM images given in Figure 3.
The change in surface topology due to oven curing has also been ob-
served previously by Sakamoto et.al. [14], who reported a smoother
surface, decreasing the swelling of films in water. One should also
note that the spikes on the polyurethane surface reflect only the mi-
cro-roughness of the film and not a phase change.
NATURE OF THE AGGLOMERATES CONSIDERED IN DETAIL
SEM images (Figure 4) of the varnishes also confirm the abundance of

18
NANOTECHNOLOGY
Source:wichientep-Fotolia.com
TRANSPARENT
TOUGHNESS
Reactive polyurethane nanoparticles create
high-performance adhesives. By Klaus-Uwe Koch,
Westfälische Hochschule Recklinghausen.
The toughness of many materials can be improved by incor-
porating discrete particles of a softer, rubbery material. A
method is described for creating functionalised rubbery na-
noparticles which on final curing become incorporated in the
polymer chains with no loss of transparency. To demonstrate
this technology, adhesives were prepared with properties
varying across a very wide range.
Strength, flexibility and impact behaviour are among the most in-
teresting and challenging properties of a material. These param-
eters strongly influence the range of application. High strength mate-
rials are often brittle upon impact.
Another problem encountered especially in adhesive technology is
the need to bond materials with different strength and elongation
characteristics. This problem can be overcome by the addition of a
separate phase of high toughness into the brittle matrix, yielding sub-
stances with high impact strength [1].
The reason why these kinds of materials withstand high impact ener-
gies is the dissipation of the applied energy within the rubbery parti-
cles dispersed in the brittle phase. The particle size of the dispersed
phase usually covers a range of 500-6000 nm in diameter.
Due to light scattering, these solid dispersions are more or less opal-
escent even when the matrix is brilliantly transparent. Another draw-
back of the method is that the dispersed phase has to be soluble in
the monomer before the polymerisation step otherwise it would not be
distributed uniformly in the solid state [2]. A novel approach to manage
these problems [3, 4, 5] is described below.
SOFT PHASE MATERIAL SYNTHESISED IN REACTIVE DILUENT
A superfine dispersion of a rubber (phase) in a brittle phase (matrix)
can be achieved by its direct synthesis in the precursor monomer
which will later act as the polymer matrix. The formation of the rubber
phase has to follow a different polymer forming mechanism than the
matrix formation itself.
In the example given (Figure 1a), the rubber phase consists of a polyu-
rethane formed by a step growth mechanism of an isocyanate in ex-
cess to a polyol or polyamine in a vinyl monomer for example methyl
methacrylate (MMA). The latter polymer does not react at this stage.
To produce a very small particle size, which is said to give higher im-
pact strength [6], vigorous stirring is applied during the reaction.
As final step, end-capping of the rubber is achieved by the addition of
hydroxy-functional vinyl compounds. The resulting product is a super
finely dispersed rubber (PU) in the still liquid reactive diluent (vinyl
compound).
This dispersion is stable for a couple of months and can later be poly-
merised by a chain growth mechanism to a solid material (PMMA) con-
taining finely dispersed poly-urethanes as part of the polymer chains.
This step can be performed with the neat material containing 40-60 %
rubber or as part of an adhesive formulation or moulding compound
(Figure 1b).
The uniform dispersion of the rubber phase is retained after the poly-
merisation step in the solid state, which results in a fully transparent
material. However, if the stirring speed is lowered during polyure-
thane formation, the resulting viscosities dramatically increase until
the material cannot be used for formulation purposes anymore.
BASIC PROPERTIES OF THE SYNTHESISED COMPOSITE
The most important properties of these dispersions in the liquid stage
are shown in Figure 2. The particle size, determined by Dynamic Laser
Light Scattering, is below 100 nm (Figure 2a), which yields a viscosity below
2 Pa•s even with rubber contents of 40-60 % and molecular weights
ranging from 5,000 to 25,000 g/mole (Figure 2b).

19NANOTECHNOLOGY
RESULTS AT A GLANCE
 High strength materials are often intrinsically brittle, a prob-
lem which can be resolved by incorporating particles of a dis-
crete softer (rubbery) phase. However, this normally has some
drawbacks including a loss of transparency.
 A method is described for preparing a dispersion of func-
tionalised rubbery nanoparticles by carrying out a polyurethane
synthesis under vigorous stirring. The rubber phase material
is then end-capped, for example by a hydroxyl functional vinyl
compound when the liquid phase is itself a vinyl monomer. This
allows for later polymerisation of the vinyl monomer (either as-
is or with other materials) with the rubbery phase becoming
incorporated in the polymer chains.
 Properties can be varied across a very wide range by alter-
ing the level of rubbery phase present. Adhesives formulated
in this way were shown to have high performance in bonding
dissimilar materials.
To demonstrate the even distribution of the functional groups in the
matrix, PMMA with a functionalised polybutadiene based polyurethane
(Figure 2c) can be stained with OsO4
to reveal the butadiene moieties in a4
to reveal the butadiene moieties in a4
TEM photograph.
The novel polymers show two different glass transition temperatures,
as is demonstrated by a composite material based on polytetrahy-
drofurfuryl methacrylate as the matrix and a polyester polyurethane
as the dispersed phase (Figure 2d). Vinyl monomers (methacrylates,
acrylates, styrenes, etc.) can be used as reactive diluents.
The rubber phase polyurethanes can be based on aliphatic or aro-
matic Isocyanates (e.g. isophorone-, hexa-methylene-, toluene-,
diphenylmethane-diisocyanate) and different polyols or amines (e.g.
based on polyethers, polyesters, polycarbonates, polyacrylates, polyb-
utadienes, polysiloxanes, etc.).
NANOPARTICLES DRAMATICALLY CHANGE
POLYMER PROPERTIES
In Figure 3, some important properties of the undiluted polymerised
material are shown. Polytetrahydrofurfuryl methacrylate (PTHFMA)
was chosen as a matrix polymer because it has a very low odour and
can be cured quickly. However, the cured material is very brittle, which
makes it difficult as a matrix material.
The neat PTHFMA has almost no impact strength (Figure 3a), its tensile
strength cannot be determined and it shows almost no elongation at
break (Figure 3b). Test bars break when mounted in the testing machine
(Figure 3c).
Properties can be dramatically changed through the variation of the
amount of rubber incorporated (up to 43 % in Figure 3d). The polymer-
Figure 1: Synthesis principle of the dispersion and its reaction in the application

NANOTECHNOLOGY20
Figure 2: Properties of liquid and polymerised polyurethane nanoparticles dispersed in reactive diluent
Figure 3: (a) Charpy impact strength (DIN EN ISO 179-1); test sample 80 ± 2 mm long, 10 ±0.2 mm wide, 4 ± 0.2 mm thick;
(b) Tensile strength of shouldered test bars (DIN EN ISO 527) and elongation at break of THFMA-based polymers
(different PU content); (c) Shouldered test bar made from pure PTHFMA; (d) Deformed test bar made from PTHFMA with 43 % PU after
impact resistance test

21NANOTECHNOLOGY
ised dispersion with 25 % rubber content re-
sults in an impact strength more than 1600 %
higher than the matrix material alone (0.32 kJ/
m², Figure 3b). Higher amounts of rubber yield
materials with properties which could not be
measured (Figure 3d). Tensile strength was
first increased up to 3 MPa (15 % rubber) and
then dropped to 0.5 MPa as the elongation at
break rises from about 12 % up to a remark-
able 340 % (Figure 3b).
The polyurethane modification thus allows
PTHFMA properties to be varied within a wide
range, which in turn allows for new applica-
tions.


HIGH STRENGTH ADHESIVES
ARE FORMULATED
Figure 4 provides examples of possible applica-
tions for the introduced dispersions in mould-
ing resins, cast films, laminated glass sheets
and as adhesives for different kind of materi-
als. The design of experiments (Figure 5) shows
that the lap shear strength can be raised by
50 % to well above 30 MPa by incorporating a
functionalised MMA-based PU dispersion into
a patented formulation [7].
The components ‘Resin’ and ‘Rubber’ of the
patented formulation could be substituted by
Figure 4: Possible applications of functionalised PU nano-dispersions
Figure 5: Design of experiments; optimised formulation of functionalised
PU-nanoparticles
the nano-dispersion at appreciable amounts.
The triangular diagram in Figure 5 shows that
a structural adhesive for bonding metals can
be modified continuously by adding the liq-
uid dispersion to adapt to the desired load or
material to be bonded.
Another remarkable result was achieved by
formulating the nano-dispersions into reci-
pes of a structural acrylic adhesives based
on the patent DE2916537 [7]. This time the
weathering resistance was examined by
a single cantilever test [8] with a 50 g load
(Figure 6a), submitted to climate test condi-
tions. One climate cycle consisted of seven
days VW P 1200 (cycling between -40 °C and
80 °C/95 %rh) and seven days steam climate
(80 °C/95 %rh).
Crack growth was taken as an indication of
performance. Conventional acrylic adhesives
failed within the first cycle whereas samples
with the nano-dispersions could be formulat-
ed to withstand the very rigorous conditions
even for more than four cycles unchanged
(Figure 6b). Some adhesives even remained
unchanged after raising the load to 100 g
(not shown in the diagram).
Figure 7 shows another example of a pos-
sible application. UV-curing-adhesives for
the joining of glass as well as glass-to-wood
(pine and spruce) were formulated on the
basis of a patent [9]. Average compression
shear strengths of up to 22 MPa could be
achieved according to DIN EN ISO 13445, in
some cases even with tear out of the glass
(substrate failure).
PU nano-dispersions based on isobornyl
acrylate (IBOA) created adhesives with good
transparency and UV resistance as shown
in Figure 7b. The sample in the middle shows
no discoloration even after 1000 hours sun
test. The same adhesives were used to join
wood (pine and spruce) and glass which
yielded with fibre tearing on the wood
surface (Figure 7c).
After exposure to the climate test (under
the climate conditions described above), the
compression shear strength dropped from
8 to 4 MPa. This is presumed to be caused
by the decomposition of the wood, which is
strongly indicated by its discoloration.
AN EVEN BROADER RANGE OF
APPLICATIONS IS POSSIBLE
In summary, a manufacturing technology has
been introduced which provides access to
a new platform technology of polyurethane
nano-dispersions with high solids and low
viscosity in the liquid state and appreciably
toughened and transparent polymers in the
solid state.
The material properties can be designed
through the selection of widely used
common building blocks (acrylates, polyols,

NANOTECHNOLOGY22
isocyanates) and the concept is applicable to
formulations for adhesives, lacquers, coat-
ings and cast resins with higher elasticity,
impact- and scratch-resistance. 
REFERENCES
[1] (a) Finter J., Vortrag “Grundlagen der Chemie
der Epoxidharzklebstoffe”, Dechema Work-
shop 27/2/2012; (b) Bishopp J. in Packham
D. E. (ed.) Handbook of Adhesion, 2005. J.
Wiley, p 553; (c) Symietz D., Lutz A., Struk-
turkleben im Fahrzeugbau, verlag moderne
industrie, 2006, Landsberg, p 30.
[2] Bishopp J. in Packham D. E. (ed.) Handbook of
Adhesion, 2005. J. Wiley, p 560.
[3] Koch K.-U., Rutz D., EP 1910436 B1,
Non-aqueous dispersion of polyurethane
(meth)acrylate particles in reactive diluent,
14/04/2006, Fachhochschule Gelsen-
kirchen.
[4] Koch K.-U., Rutz D., Jagielski N., Kaufmann A.,
Kogelnik H.-J., Funktionalisierte PU-Nanopar-
tikel für Reaktivverdünner Teil 1: Synthese-
prinzip und Eigenschaften, adhäsion, 2014,
No.10, pp 38-43.
[5] Koch K.-U., Rutz D., Jagielski N., Kaufmann A.,
Kogelnik H.-J., Funktionalisierte PU-Nanopar-
tikel für Reaktivverdünner Teil 2: Wo werden
Sie eingesetzt?, adhäsion, 2014, No. 11, pp
24-29.
[6] Stabenow J., Haaf F., Z. Angew. Makromol. Chem.
29/30 (1973), p. 1;
[7] Zalucha D. J. et al, Primer or adhesive system
and method for its application, DE2916537,
priority 24/4/1978, Lord Corp.
[8] Hahn O., Kötting G., Weiterentwicklung des
Keiltests zur standardisierten Prüfmethode
für die Bewertung der Haftbeständigkeit von
Klebverbindungen, final report AiF-Nr. 12773
N, 2004.
[9] Eckhardt G., Lechner G., Process for prepar-
ing aqueous dispersions of acrylic-urethane
graft copolymers, DE4343246A1, priority
17/12/1993, THERA-Patent GmbH Co. KG.
Figure 6: (a) Test set-up in the climate chamber; (b) Crack propagation over time;
the white areas represent the testing periods following VW P 1200, the grey areas
represent the testing periods in which the samples are exposed to a steamy climate
Figure 7: (a) Test pieces for measuring compression shear strengths of UV-hardened
glass bonding acc. to DIN EN ISO 13445; (b) Bonded glass plates after 1000 h of sun
test, sample of nano-dispersion in the middle; (c) Substrate failure on UV-cured glass/
wood bonding; tested in grain direction


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POLYURETHANES
Polyurethane chemistry has had a significant
impact on the development of efficient and
environmentally friendly coatings, adhesives,
and sealants – nevertheless, its potential for
further development is by no means exhaust-
ed. The book provides a comprehensive over-
view of the chemistry and the various possible
application fields of polyurethanes – and
thereby serves as a valuable knowledge base
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www.european-coatings.com/seminars

24
BIO-BASED RAW MATERIALS
Source:EvonikIndustries
GROWING GREENER
LACQUERS
Polyols for PUDs prepared with various levels of renewable content. By Joel Neale, Perstorp.
Two biodegradable cyclic esters, e-caprolactone and lactide
monomer, were incorporated into co-polyols. Lactide mono-
mer is obtained from renewable resources. Increasing lactide
levels reduced the crystallinity and increased the Tg
of the
polyols. When these polyols were incorporated into PUD dis-
persions, the highest lactide content showed increased film
stiffness, hardness and scratch resistance.
In recent years there has been heavy investment in renewably
sourced raw materials [1]. These materials not only represent a
more sustainable future for the planet but also a reduction in reliance
on petroleum-derived chemicals and the volatility these can bring in
terms of price fluctuations. Inclusion of these raw materials by substi-
tution into conventional formulations for coatings and adhesives has
not been particularly successful for two main reasons, performance
and cost.
In work discussed here, two cyclic esters (shown in Figure 1) have been
used to prepare polyols with varying renewable content, but the focus
has been placed on the modification of the polyol properties and con-
sequent effects on the coatings derived from these polyols. e-caprol-
actone and lactide based polymers have been researched extensively
in the medical field due to their good biodegradability properties
[1, 2, 3].
Lactide monomer is a cyclic di-ester of lactic acid which can be derived
from sugars [1, 4] and is therefore a renewable monomer or in this
case co-monomer. Both of these cyclic monomers can be polymer-
ised using ring-opening polymerisation [3, 5, 6]. The molecular weight
of the products can be controlled and therefore highly designed, func-
tional polyols can be manufactured for specific applications. Inclusion
of both monomers in the reaction allows, but is not restricted to, ran-
dom copolymers.
Lactide is therefore a good way to include renewable content within
polyester-based polyols. The two monomers are also different enough
in terms of properties for there to be some significant effects on the
intrinsic properties of the parent homo-polyols and therefore the final
properties in application testing.

25BIO-BASED RAW MATERIALS
RESULTS AT A GLANCE
űű Two biodegradable cyclic esters, e-caprolactone and lactide
monomer, were incorporated into co-polyols produced by ring-
opening polymerisation with neopentyl glycol (NPG). Lactide
monomer is of particular interest because it is obtained from
renewable resources.
űű Higher lactide levels reduced the crystallinity and increased
the Tg
of the polyols.
űű These polyols were incorporated into PUD dispersions, also
containing Bis-MPA and NMP. Instability at higher lactide con-
tents was resolved by increasing the level of Bis-MPA in the for-
mulation.
űű The material with the highest lactide content showed the
highest film stiffness, hardness and scratch resistance.
űű Trifunctional polyols were also prepared by the same pro-
cess. The production method thus appears to be flexible with
promise for the development of high quality polyols with sig-
nificant renewable content.
RAW MATERIALS AND POLYOL SYNTHESIS
e-caprolactone monomer, neopentyl glycol (NPG) and trimethylol pro-
pane (TMP) were provided by Perstorp AB. Lactide monomer (“Pura-
lact-L”) was provided by Purac Biochem BV (Gorinchem, Netherlands);
this was stored cold and sealed in dry N2
prior to use. Stannous 2-eth-
ylhexanoate (Sn(Oct)2
) catalyst was provided by Air Products (Utrecht,
Netherlands) and was administered in a blend with toluene.
The various co-polyols were produced as described below and used
as prepared. Dimethylolpropionic acid (Bis-MPA) was provided by Per-
storp AB. Isophorone diisocyanate (IPDI) was used as the isocyanate,
N-methyl-2-pyrrolidone (NMP) was used as a solvent, triethylamine
(TEA) as the neutralising agent and ethylene diamine (EDA) as the
chain extender.
Caprolactone, lactide and NPG or TMP were each weighed out indi-
vidually; see Table 1 for details. All reactants were added to a glass
reactor fitted with a PTFE anchor stirrer, a thermocouple and a nitro-
gen line. They were then heated and catalyst added. The reaction was
then carried out for 12 - 18 hours. The co-polyols were then further
Figure 1: Ring-opening reaction scheme for both caprolactone
(top) and lactide (bottom) monomers
Sample 1 2 3 4 5 6 7
NPG    
TMP   
Caprolactone 100 % 88 % 70 % 50 % 100 % 75 % 50 %
Lactide 12 % 30 % 50 % 25 % 50 %
Table 1: Composition of each polyol; each percentage is by
weight of monomer used
Ingredient Weight Weight Analysis Result
Polyol 80 189.2 Theoretical NCO, wt % 3.29
Bis-MPA 8.05 19.0 NCO/OH 1.6
NMP 30 70.9 NH/NCO 0.9
IPDI 35.57 84.1 Actual solids % 31.8
TEA 5.46 12.9 Actual solvent % 7.1
Water 260.55 616.2 Bis-MPA % 6.51 or 8.0
EDA 3.25 7.7
Viscosity 23°C 1/s
mPas
15
Total wt. 422.88 1000.0
Table 2: Typical PUD formulation and analysis
dried with N2
and cooled. The difunctional products based on NPG
had a target molecular weight of 2000 g/mol, while for the trifunctional
polyols based on TMP this was 900 g/mol. The trifunctional materials
were prepared and would be used in a separate application test; they
were included here to show the flexibility of the production method.
Hydroxyl content and molecular weight were calculated using a back
titration method with acetic anhydride and potassium hydroxide with
pyridine. The acid value was determined using a titration with potas-
sium hydroxide with acetone as a solvent for the polyol.
Colour was measured using a Hach “DR 2000” direct readout spec-
trophotometer at a wavelength of 455 nm. The co-polyols were nor-
malised against purified water (18.2 MΩ). Thermal properties were
measured using a Mettler-Toledo DSC and all scan rates for melting
endotherms were run at 10 °C min-1
while Tg
measurements were run
at 3 °C min-1
. Viscosity was measured using a Haake “RS1” rheometer
with a “C35”/ 2 ° cone and plate at a constant frequency of 60 Hz.
PUD PREPARATION AND TESTING
The co-polyols, Bis-MPA and NMP were added to a 700 ml glass re-
actor equipped with a cooler and a stirrer. The mixture was heated
until a clear and transparent solution was achieved. The temperature
of the mixture was lowered to 50 °C and the isocyanate was added
drop-wise. When the addition was completed, the reactor was heated
to 70 °C and held until the desired NCO content was reached, as as-
sessed by titration. The reaction was cooled to 50 °C and TEA was
added drop-wise. Water was then added to the system and stirred

BIO-BASED RAW MATERIALS26
at 300 rpm. Heating was removed and EDA
chain extender was added. The solution was
then filtered if required. The general recipe is
shown in Table 2.
Films were cast onto glass panels at a thick-
ness of 100 µm and dried for 24 hours at
room temperature and then 24 hours at 70
°C. The viscosity of the PUD formulation was
measured at 23 °C at 100 Hz.
Hardness was measured via a König pen-
dulum. Scratch resistance of the coatings
was measured using 385 g pressure on
a “ScotchBrite 07442” abrasive pad with
the gloss being measured at 0, 10, 25 and
50 double rubs. Tensile properties were
also measured using a Zwick “Z010” table-
top machine with a 100 N load cell. E-mo-
dulus was calculated at 0.25 mm/min and
everything else was measured at 50 mm/min.
HOW LACTIDE CONTENT AFFECTS
POLYOL PROPERTIES
All six polyols were synthesised successful-
ly, giving high quality products with differ-
ing properties, as shown in Table 3. Polyols
2, 3, 4, 6 and 7 are all random copolymers
with polyols 1 and 5 being homopolymers
of caprolactone. Acid value and colour lev-
els were kept very low, allowing for crystal
clear resins with no haze or yellowing on
standing.
There was a slight increase in acid value as
the lactide content increased; however this
is acceptable and within the limits of com-
mercially available polyesters, with values
typically 1.0 mg KOH g-1
. The control of acid
value is assisted by the type of polymerisa-
Sample Difunctional Trifunctional
1 2 3 4 5 6 7
Molecular weight 1979 2022 2059 2200 895 938 927
OH value
(mg KOH g-1
) 56.7 55.44 54.0 50.3 188.6 179 181
Acid value
(mg KOH g-1
) 0.08 0.2 0.2 0.26 0.1 0.13 0.13
Colour
(Co/Pt Units) 10 4 10 25 25 26 23
Viscosity, mPas 25 °C
Solid Solid 8720 18000* 1530 2510 8220
Viscosity, mPas 60 °C 285 625 970 2000 480 975 1993
Onset glass transition
temperature (Tg
) °C
-65 -58.3 -53.64 -35.53 -65 -58.00 -41.19
* Upper limits of the cone were reached so data not entirely reliable
Table 3: Basic properties of the experimental polyols
Figure 2: Precipitation of higher lactide content grades and the stable reformulated PUD
tion used, i.e. ring-opening polymerisation.
Differences were observed in the viscosity
and thermal properties of the materials. In
the difunctional polyols 1, 2, 3 and 4 the re-
duction of the crystallinity can clearly be seen
from a semi-crystalline solid with a melting
point of 60 °C to an amorphous liquid as the
lactide content increases.
This effect is not visible in the tri-functional
materials; however in both cases the glass
transition temperature of the polyols can be
seen to rise with increasing lactide content.
Caprolactone homopolymers typically have
a glass transition of around -65 °C and the
reported transition for polylactide homopoly-
mers is around 50 – 60 °C [1].
REFORMULATION RESOLVES
INSTABILITY PROBLEMS
There was a problem with evaluation of the
PUD dispersions with large amounts of lac-
tide present. The PUD solutions made from
polymers 3 and 4 were fine for a time but
then proceeded to drop out of solution pro-
ducing a tough rubbery solid, indicating that
the dispersion was unstable, as shown in
Figure 2. This was countered by a reformula-
tion increasing the amount of Bis-MPA from
6.5 % to 8 % in the overall formulation.
This problem may be caused by the changing
polarity of the polyols with increasing lactide
content. Another possibility is sensitivity to-

27BIO-BASED RAW MATERIALS
wards water, with lactide being more sensi-
tive to hydrolysis than caprolactone. The
modified dispersions were, however, stable
during storage and produced good smooth
coatings.
The viscosity of the polyols seemed to have
little bearing on the overall viscosity of the
PUD formulation, as can be seen in Figure 3.
The results appear to show co-polyols 2, 3
and 4 as being less viscous than co-polyol 1.
This result may be explained by the high lev-
els of crystallinity of the original polyol, but at
present this remains to be proved.
There was also no influence on the reaction
time, with all reactions being completed in
6–7 hours. An issue that can arise with com-
binations of caprolactone and lactide is the
increase in secondary end group functional
hydro-xyls in the co-polyols compared to
the primary OH groups of the caprolactone
homopolymer (co-polyol 1). Fortunately, the
potential effect of a drop in reactivity was not
observed in these formulations.
LACTIDE MONOMER CAN INCREASE
COATING HARDNESS
Co-polyols 1 and 2 were directly compared
with the lower levels of Bis-MPA, co-polyols 3
and 4 were compared at the higher levels of
Bis-MPA. The samples were tested for hard-
ness. Two effects occur as more lactide is
added to the co-polyols. Firstly, in co-polyol 2
(see Figure 4) the inclusion of a small amount
of lactide (12 %) is not enough to dramati-
cally affect the Tg
. However, the inclusion is
enough to interrupt a large portion of the
crystallinity of the polyol (around 60 %), drop-
ping the overall melting endotherm from
-88.7 J g-1
to -37.8 J g-1
, as shown in Figure 5.
When co-polyols 3 and 4 are compared,
the increase in lactide content increas-
es the hardness by 100 %. At this point
both co-polyols are fully amorphous,
which rules out any effects of crystallin-
ity on the hardness. The large change is
most likely due to the stiffness of the mo-
lecules and the Tg
increase due to the in-
creasing influence of lactide monomer.
The scratch resistance of the coatings was
evaluated. The influence of the softening of
the coating in co-polyol 2 can be seen by a
decrease in scratch resistance compared to
polyol 1. The reduction in crystallinity of the
soft segment polyol appears to have had an
effect on both the hardness and scratch re-
sistance in the two examples presented.
Comparing co-polyols 3 and 4, an increase
in the scratch resistance can be seen. When
comparing this to the reference adipate,
the results are excellent for a softer coat-
ing. It can be seen that with correct formu-
lation a good scratch-protective coating
can be achieved with an increasing content
Figure 3: Viscosities of PUD formulations measured at 23 °C at a frequency sweep of
30 - 300 - 30 s-1
; the viscosity of the reference NPG adipate was around 0.014 Pa∙s
-20
-10
0
-30
-40
-50
-60
-80
-100
-90
-70
Polyol thermal properties
5030120
Lactide content
ΔHm (J g-1)
Tg (oC)
Figure 4: Thermal properties measured on each di-functional polyol showing the
increase in Tg
and the reduction in crystallinity (DHm)

BIO-BASED RAW MATERIALS28
of renewable monomer. The mechanical
properties of the coatings were tested. Ba-
sic tensile properties were evaluated and
the results show the general trend of a
stiff base polyol with an increasing E-mod-
ulus across the increase in lactide mo-
nomer. This may be skewed slightly by the in-
fluence of the increased amounts of Bis-MPA
used in the formulation, but even compari-
sons between co-polyols 3 and 4 show this
pattern. The overall extension of the coatings
is reduced by the increasing lactide mono-
mer, this again representing the change in
flexibility of the polyol chains.
RENEWABLE MONOMER PROVIDES
GOOD COATING PROPERTIES
Random co-polyols were successfully syn-
thesised with varying levels of renewable
Figure 5: Scratch resistance (measured as gloss reduction) of coatings on glass
substrates: the percentage amounts are the content of lactide and reference is
an NPG adipate
content. The intrinsic properties of the poly-
ols were studied and there is a clear trend
due to the inclusion of lactide monomer of
an increase in properties such as viscosity
and glass transition temperature. Increasing
amounts of lactide also lead to a highly amor-
phous product with control of crystallinity of
the polyol being possible.
The production chemistry is flexible, with
multiple functionalities and varying molecu-
lar weight ranges made. This can lead to a
polyol that can potentially be highly specified
in terms of the properties described.
The di-functional co-polyols were introduced
into a PUD formulation, although it is appar-
ent that work is needed to fully understand
the formulation requirements. The general
trends of the polyols can be seen in the final
coating. There are two competing effects in
this study which were slightly difficult to dis-
tinguish. The drop in crystallinity of the origi-
nal homopolymer of caprolactone leads to
a softer coating overall with a poor scratch
resistance, but could potentially affect prop-
erties such as clarity and viscosity. Also the
influence of the increasing stiffness and Tg
of the coating is apparent in the hardness,
based on polyol 3 and 4. The rising effects
can be seen across the mechanical proper-
ties with a sharp increase in the E-modulus
and a drop in elongation.
These subtile refinements to coatings prop-
erties can add to the value if they can be
properly refined. Inclusion of renewable
monomers will not be the only potential ben-
efit if real added value can be found. Moreo-
ver, these types of polyol will be similar to
current products on the market in terms of
quality and functionality. 
REFERENCES
[1] Vroman I., Tighzert L. Review: Biodegradable
polymers, Materials, 2009, Vol. 2, pp 307-
344.
[2] Lazdina B. et al, Synthesis and properties
of cross-linked poly(ester urethanes) from
poly(lactide) triols and poly(caprolactone)
diols, Estonian Acad. Sci. Chem.,
2006, Vol. 55, No. 2, pp 85–92.
[3] de Groot J. H. et al, On the role of aminolysis
and transesterification in the synthesis of
e-caprolactone and L-lactide based poly-
urethanes, Polym. Bull., 1998, Vol. 41,
pp 299–306.
[4] Tokiwa Y. et al, Review: biodegradability of
plastics, Int. Jnl. Mol. Sci., 2009, Vol. 10, pp
3722-3742.
[5] Ping P. et al, Poly(e-caprolactone) polyu-
rethane and its shape-memory property,
Biomacromol., 2005, Vol. 6, pp 587-592.
[6] Baimark Y., Malloy R., Synthesis and charac-
terization of poly(L-lactide-co-e-caprolac-
tone) copolymers: effects of stannous octoate
initiator and diethylene glycol coinitiator
concentrations, ScienceAsia, 2004, Vol. 30,
pp 327-334.
ACKNOWLEDGEMENTS
The author extends thanks to Purac Biochem for
their help in the collaboration, to Malin Rex and
Marie Westerblad, Perstorp AB, for their help with
the PUD formulation and application evaluation
and to Graham Carr and Anthony Maher, Perstorp
AB, for their contributions to the polyol formula-
tions.
Table 5: Tensile properties of films cast from the different co-polyols
(all units are n mm-2
; typical number of samples tested was 4-8)
Co-polyol 1 Co-polyol 2 Co-polyol 3 Co-polyol 4 Reference
Lactide content 0 % 11.4 % 28.4 % 47.4 % NPG adipate
Hardness 23 16 18 36 66
Table 4: König hardness of dried films
Tensile Properties Co-polyol 1 Co-polyol 2 Co-polyol 3 Co-polyol 4 NPG adipate
E-Mod 0.05 to 2 % 3.4 6.7 25 40 -
Stress at 100 % strain 2.3 2.95 - 5.1 6.7
Max. stress 7.7 2.6 2.5 5.2 7.5
Strain at break % 900 170 36 140 285

Source:ShanePhoto-Fotolia.com
ANCIENT PAINTS
Popular pigments used for
cave paintings were iron oxi-
de, maganese oxide and char-
coal, mixed with water, spit or
fat. Researchers assume that
other raw materials were ore,
feldspar, blood, limestone, re-
sin, milk and herbal juices.
FROM BRUSHES TO
SPRAY PAINTING
The paint was applied with
branches, stamps or
fingers. In addition to this,
paints were also spray
painted using pipes made
from bone.
29WORLD OF COLOUR

30
BIO-BASED HARDENER
Source:stokkete-Fotolia.com
HIGH PERFORMANCE
ENABLED BY NATURE
New polyurethane crosslinker with significant bio-based content. By Gesa Behnken, Andreas Hecking, Berta Vega Sánchez.
Figure 1: Structural formulas of (a) Pentamethylene diamine
(PDA), (b) Pentamethylene diisocyanate (PDI), (c) PDI trimer and
(d) Hexamethylene diisocyanate (HDI); the carbon atoms from
biomass are shown in green.
a) H2
N - CH2
- CH2
- CH2
- CH2
- CH2
- NH2
b) OCN - CH2
- CH2
- CH2
- CH2
- CH2
- NCO
c) O
OCN N N NCO
O N O
NCO
d) OCN - CH2
- CH2
- CH2
- CH2
- CH2
- CH2
- NCO
Seventy percent of the carbon content of a new hardener for
polyurethane coatings and adhesives is provided by biomass.
The bio-based crosslinking agent matches the high perfor-
mance and quality level of conventional petrochemical-based
isocyanates, even meeting the very high demands of the auto-
motive industry.
The ecological compatibility of products is becoming a critical fac-
tor for businesses that want to defend their position and grow in
the market, because consumers are increasingly deciding in favour of
sustainable goods and making sure they incorporate renewable ma-
terials. Environmental labels help them to identify relevant products
more effectively. Examples include the “Vincotte OK Biobased”, “DIN
CERTCO Biobased” and “USDA Certified Biobased Product” labels.
A number of U.S. states are supporting this trend. For exam-
ple, the “BioPreferred” programme from the U.S. Department of
Agriculture (USDA) compels public institutions to buy the material with
the highest proportion of renewable raw materials for purchases over
10,000 US dollars [1].
COATINGS INDUSTRY COMMITS TO ‘GREEN PRODUCT’ TREND
In striving to fulfil these consumer demands, brand owners are in
search of bio-based sustainable materials. This applies to the auto-
motive industry, but also to others including the Ikea furniture stores
and the Coca-Cola Company, which developed the “plant bottle” made
partially from plants [2].
The coatings and adhesives industry has recognised this trend to-
wards eco-friendly products, too. “Sustainability has become a key

31BIO-BASED HARDENER
RESULTS AT A GLANCE
űű A new bio-based, high-performance hardener for polyure-
thane (PU) coatings and adhesives was developed. It is the first
product of a new platform based on pentamethylene diisocy-
anate (PDI). Five of the seven carbon atoms in the material are
bio-based.
űű Tests have shown that the bio-based hardener can create
coatings that are just as weather-, chemical- and scratch-resist-
ant and easy to apply as conventional coatings made exclusive-
ly with petrochemical inputs. The innovative hardener can offer
greater freedom in formulation and faster drying.
űű Good results have been obtained in tests of automotive
OEM and refinish formulations, anticorrosive and wood coat-
ings. Chemical modification of the hardener allows an even
wider range of PU systems to be crosslinked.
duced environmental footprint.” The right starting materials can make
a key contribution to meeting sustainability demands in the coatings
and adhesives industry. Covestro (formerly Bayer MaterialScience)
has launched a new high-performance hardener made from renew-
able raw materials. It is the perfect reaction partner to the bio-based
polyols already used in polyurethane coatings and adhesives. Now
these coatings can be formulated almost entirely from bio-based
components.
At the 8th International Conference on Bio-based Materials in April
in Cologne, Germany, the new hardener was honoured with the Bio-
based Material of the Year 2015 innovation award [6]. With this new
hardener, users and manufacturers in various industries can position
themselves as pioneers of more sustainable materials.
PRODUCTION SHOWS GREATLY REDUCED CO2
FOOTPRINT
The new hardener “Desmodur eco N 7300” is a trimer of pentameth-
ylene diisocyanate (PDI) (Figures 1b, 1c). PDI is manufactured from
pentamethylene diamine (PDA) using innovative gas-phase technol-
ogy which consumes significantly less energy and solvent than con-
ventional processes.
The PDA suppliers use biotechnology – specifically fermentation – to
manufacture PDA (Figure 1a) from biomass. PDI is therefore synthe-
sised in just two steps, as opposed to the four required for the pet-
rochemical synthesis of the corresponding petrochemical substance
hexamethylene diisocyanate (HDI, Figure 1d), a conventional diisocy-
anate raw material. The internal evaluation showed a significant dou-
ble-digit improvement in percentage of the CO2
footprint of bio-based
PDI in comparison to HDI. The energy efficiency of PDI cradle-to-gate
is significantly better.
PDA is produced from the starch of field corn (maize), which is con-
verted enzymatically by specially developed microorganisms in a
highly efficient process. Field corn comprises varieties of maize which
are not suitable for human consumption, meaning that PDA manu-
facturing does not compete directly with the food chain. Field corn
is already used in the production of bio-fuels and numerous other
products, such as paper, cosmetics, cleaners and textiles.
It has been estimated that only 80 square kilometres of arable land
– an area slightly larger than the city of Leverkusen in Germany – are
Figure 2: Viscosity of the conventional (red curve) and
bio-based hardener (black curve), dissolved in butyl acetate.
Common solvents behave in the same way.
part of the growth and marketing strategies of a number of coating
companies,” reported the Coatings World European correspondent
Sean Milmo in October 2014 [3].
This is backed up by statements such as that by Peter Nieuwenhui-
zen, former Director of Innovation and Partnerships at AkzoNobel [4]:
“Given the challenges the world is facing in terms of resource scarcity,
we are actively looking for bio-based alternatives for our chemicals.”
Henkel has also committed itself to a sustainability strategy and is-
sued a guideline [5]: “Our products deliver greater value with a re-
Figure 3: Property profile of coatings based on the new PDI
hardener (black curve), compared with those containing the
conventional HDI hardener (red curve).

BIO-BASED HARDENER32
required to produce 20,000 tonnes of the new hardener, enough to
apply three coats of paint to 30 million cars. To make production even
more sustainable, PDA suppliers are working intensively on ways to
use bio-waste or cellulose instead of field corn. The development of
this second generation feedstock is expected to take several years to
be fully integrated into PDA production.
RADIOCARBON TESTING CONFIRMS BIO-BASED CONTENT
Field corn is the carbon source for all five of the non-functionalised
carbon atoms in PDI. In other words, of the total of seven carbon
atoms in the monomer, five - or 71% - are plant-based, as confirmed
by 14
C radiocarbon testing in accordance with the ASTM D8666
standard [7].
The method is based on the following phenomenon: the dead organ-
isms from which petroleum and natural gas deposits have formed
contain only low percentages of 14
C isotopes of carbon due to radioac-
tive decay. In contrast, living organisms constantly acquire new carbon
from the environment, which translates into a higher percentage of
14
C isotopes. Despite the slow continuous decay, this higher percent-
age remains virtually constant because 14
C is constantly being created
in the upper atmosphere.
PERFORMANCE MATCHES PETROCHEMICAL STANDARDS
The new hardener can be used for the same applications as the HDI-
based hardener “Desmodur N 3300”. This is a long-established prod-
uct for automotive OEM coatings, automotive refinish, industrial coat-
ings including anti-corrosive and wood coatings, as well as adhesives
for flexible packaging.
The viscosity of the solvent-free, bio-based hardener is 9,200mPa•s,
meaning it is higher than that of the conventional hardener
(3,000mPa•s). This, however, is of no significance in practice, as illus-
trated in Figure 2, because the viscosities of the conventional hard-
ener and the new bio-based alternative equalise for formulations con-
taining common solvents and at solids content below 75%.
The reason for this behaviour is that in the solvent-free state, the
stacked PDI trimers attract one another more strongly than the HDI
trimers because the PDI-based materials have higher polarity. How-
ever, just a small amount of solvent is sufficient to break down the
stacking. As soon as this happens, the inter-molecular forces of PDI
and HDI trimers do not differ significantly.
Figure 3 gives an overview of the bio-based hardener’s properties.
Coatings formulated with this component are not inferior to those with
a conventional hardener in terms of weathering, scratch and chemi-
cal resistance, hardness or processing (pot-life). They even dry slightly
faster. The bio-based hardener offers major advantages when it comes
to compatibility, particularly with highly functionalised polyols.
Figure 4 illustrates this, using the example of coatings formulated with
highly branched polyesters “Desmophen 650 MPA”: because of the
lack of compatibility between the hardener and the polyester, the gloss
of the HDI-based coating is measurably and visibly lower than that of
the bio-based coating. For coatings manufacturers, the better compat-
Figure 5: Gloss and yellowing levels after weathering:
comparison of automotive coatings with the new PDI hardener
(black curves) and conventional HDI hardener (red curves).
Figure 4: Gloss levels of coatings in which the bio-based hard-
ener (left) and the conventional hardener (right) were combined
with a branched polyester.
Figure 6: Chemical resistance of automotive coatings with the
new PDI hardener (black) and the conventional HDI hardener
(red) expressed as failure temperature in a gradient oven.

33BIO-BASED HARDENER
ibility of the new hardener means greater freedom in formulation.
HIGH PERFORMANCE IN AUTOMOTIVE OEM FORMULATION
In automotive OEM coatings, the new hardener allows auto manufac-
turers in particular to further increase their percentage of bio-based
materials. The current Mercedes C class, for instance, incorporates 76
components made from renewable raw materials with a total weight of
26.3 kilograms, an increase of 55% over the previous model range [8].
However, until now car manufacturers have used renewable raw ma-
terials primarily in the automotive interior. But now these raw materi-
als can start taking over a vehicle’s exterior as well, which carries very
high emotional value. Tests with sample formulations have confirmed
that coatings with the new hardener meet the high demands of au-
Figure 7: Dry scratch resistance and self-healing effect of
automotive coatings with the new PDI hardener (left) and the
conventional HDI hardener
Figure 8: Drying time of automotive refinish coatings
with the new PDI hardener (black) and the conventional
HDI hardener (red).
Figure 9: Pot-life and drying time of anti-corrosive coatings
with the new PDI hardener (black) and the conventional
HDI hardener (red).
tomotive manufactures just as well as those made from established
petro-based hardeners.
Figure 5 shows that both coatings deliver virtually identical results in
weathering tests: Even after 6,000hours of weather exposure, the
gloss does not deteriorate and only slight yellowing is detectable.
GOOD CHEMICAL AND PHYSICAL RESISTANCE
Chemical resistance was tested in a gradient oven at temperatures
between 36 and 68°C. The sample substances – resin, pancreatin,
demineralised water, 1% sodium hydroxide solution and 1% sulfuric
acid solution – were applied to the coatings and the samples exposed
to heat for 30minutes. The results were assessed after 1 hour and
24hours in storage under standard climate conditions.
The temperature at which each sample substance displays the first
signs of damage was recorded to obtain the test results (Figure 6). No
significant differences were determined between the coatings made
from petrochemical products and those containing the bio-based
hardener.
Dry scratch resistance was determined using the hammer test: The
flat side of a hammer was wrapped in a layer of steel wool or sandpa-
per. The hammer is placed at right angles to the coating and pulled
evenly in a line over it, without using the edge or applying any addi-
tional physical force.
The residual gloss was then measured on the damaged areas. After
storing the coated sheets for 2 hours at 60 °C in a laboratory drying
cabinet, gloss levels were measured again to test self-healing (reflow).
The results are shown in Figure 7. The coating based on the new hard-
ener also compared very favourably in this category.
A WIDE RANGE OF LOWER CURE TEMPERATURE APPLICATIONS
Automotive refinish coatings are applied at lower temperatures (40-
70 °C) than automotive OEM coatings, and are therefore formulated
differently. In this application too, coatings made with the bio-based
hardener are comparable with the properties of conventional PU
coatings, for example in terms of dry and wet scratch resistance,
weathering resistance and processing.
Figure 8 shows that coatings incorporating the bio-based hardener

BIO-BASED HARDENER34
reach drying stage 4 (DIN 53150) even faster than the conventional
ones. This improved drying also comes into play in protective coatings
such as anti-corrosive formulations: Figure 9 illustrates an improve-
ment in drying behaviour with only a slight influence in shortening of
the processing time (pot-life).
The new bio-based hardener is also suitable for 2K PU wood clear-
coats in both matt and gloss formulations. With regard to chemical re-
sistance, scratch resistance and gloss, it demonstrates the same high
performance as conventional hardeners, but shows slight advantages
when it comes to the drying time of the coatings.
The new hardener is just as reactive in adhesive formulations (for ex-
ample, in flexible packaging applications) as the established product.
BUILDUNG BLOCK FOR A BROAD TECHNOLOGY PLATFORM
It is not planned to commercialise the PDI monomer itself but instead
wants to use it as the foundation for a new technology platform.
Blocked, hydrophilic, silanised and water-borne polyurethane disper-
sions (PUDs) have already been produced and tested during develop-
ment of the new hardener.
As with the bio-based hardener, the properties of the modified systems
are very similar to those of the established HDI products. Unexpected
and advantageous properties have also been found in these systems.
Examples here include coatings where the bio-based hardener has
been modified with silane groups. They have a higher residual gloss
after mechanical loading and thus scratch less easily than coatings
based on similarly structured silanised HDI polyisocyanates. Coating
films manufactured with PDI polyisocyanate show much better solvent
and chemical resistance with the same proportion of silane groups.
Systems hydrophilised using internal and external emulsifiers and based
on the PDI product have been crosslinked with standard waterborne hy-
droxy-functional polyacrylate dispersions. In terms of their coating prop-
erties, these products are at least comparable to the similarly structured
hydrophilic HDI polyisocyanates and exhibit much faster drying.
In tests with standard blocking agents, the new hardener blocked with
diethyl malonate showed a much lower tendency to crystallise than
a product similarly based on HDI polyisocyanate. For the first time, a
purely diethyl malonate blocked, linear aliphatic polyisocyanate thus
seems possible.
The other blocked versions of the new hardener behaved in testing in
a way that is at least comparable to similarly manufactured HDI poly-
isocyanates.
Substituting conventional hardeners with bio-based crosslinking
agents in various water-borne systems showed that the conventional
hardeners in water-reducible, lightfast single-component polyurethane
baking coatings and in waterborne urethane acrylate dispersions, for
example, can be replaced without compromising performance. 
REFERENCES
[1] www.biopreferred.gov
[2] http://www.plantbottle.info/index.shtml
[3] www.coatingsworld.com/issues/1014/view_europe-reports/
concept-of-sustainability-used-as-key-marketing-strategy/
[4] https://www.akzonobel.com/news_center/news/news_and_press_
releases/2014/akzonobel_and_photanol_developing_chemical_
compounds_of_the_future.aspx
[5] www.henkel.de/nachhaltigkeit/nachhaltigkeitsstrategie/
strategische-prinzipien
[6] www.biowerkstoff-kongress.de/award
[7] www.astm.org/Standards/D6866.htm
[8] www.daimler.com/Projects/c2c/channel/documents/
2453638_UZ_C_Class_en.pdf
“Faster curing
and greater
compatibility.“
Dr Gesa Behnken
Covestro
gesa.
behnken@
covestro.com
Three questions to Gesa Behnken
Is the hardener already on the market? Has there been
any initial feedback? “Desmodur eco N 7300” was launched on
the market at the European Coatings Show in April 2015. Sam-
ples have been sent out on a wide scale since 1 August 2015,
while the commercial rollout will be taking place next year with
an annual capacity of up to 20,000 metric tons. We worked with
selected partners to develop this new hardener in the run-up to
the market launch. The positive feedback from these customers
was a key factor in deciding to commercialise it.
You’re only taking into account the CO2
footprint from
manufacturing the new PDI. What about the full environ-
mental assessment? The new hardener was also superior to
standard products in other categories, such as the overall energy
balance. Yet there are also challenges, as with the vast majority of
bio-based products, since agricultural land is needed to produce
biomass.
What weaknesses does the hardener have that can/must
still be optimised? Compared to standard HDI trimers, the
hardener has even better properties, such as faster curing and
greater compatibility with high hydroxyl containing polyols. How-
ever, there are areas of application that we cannot cover with it.
We’re looking to establish a new technology platform based on
PDI that enables applications to be used on a widespread basis.
For instance, we’re working with selected partners on further
potential products in the area of water-borne polyurethane
coatings.

Source:platongkoh55-Fotolia.com
COLOURED TREES
50,000 litres of protecti-
ve coatings were used on
Singapore‘s Gardens by the
Bay. This attraction consists
of the world‘s largest clima-
te-controlled glass houses
as well as 18 of the pictured
supertrees.
MIMICKING NATURE
Not only the consevatories
of Gardens by the Bay but
also the trees are home to
many tropical plants. They
provide air intake and mimic
the ecological functions of
real trees.
35WORLD OF COLOUR

36
RADIATION CURING
REFLECTIONS ON
RADIATION CURING
Novel waterbased UV-PUD for robust single-coat mirror effect. By Michel Tielemans, Claire-Sophie Bernet and Patrice Roose, Allnex.
Waterbased energy curable polymers can create high perfor-
mance coatings with good productivity. A new low viscosity
and regulatory compliant tin-free waterborne resin provides
mirror-like coatings with good hiding power and resistance to
application defects from a single-coat spray application.
High gloss coatings showing a good mirror effect are usually obtained
with solventbased polymers and are often associated with a labour-
intensive polishing step during application. There is a growing market de-
mand for low VOC substitutes, such as waterbased polymers. In general,
these are built from high molecular weight polymers, including vinyl and
acrylic emulsions and their reduced polymer flow after film formation usu-
ally prevents the formation of high gloss coatings with a mirror effect.
However, ethylenically unsaturated polyurethane dispersions used in UV
curing, and so abbreviated as UV-PUDs offer the interesting possibility of
delivering a much higher polymer flow resulting in a high gloss coating
with a good mirror effect, referred to as Distinctness-Of-Image (DOI), and a
good substrate coverage, referred to as ‘body’ or ‘levelling’ in relation to the
coating’s ability to minimise ‘telegraphing’ of the original surface roughness
[1]. These concepts are depicted in Figure 1.
The antagonism between the good oligomer flow required during the ap-
plication process and the chemical and mechanical resistance required
afterwards can be advantageously resolved by energy-curing of the oli-
gomer, since the film formation and the hardening take place in two dis-
tinct application steps.
The high level of performance of these energy-cured coating compositions
is achieved through high crosslinking density – including superior mechani-
cal and chemical resistance with excellent adhesion on various substrates.
Despite the major advantages offered by the technology [2], it is also nec-
Property Value
20 ° gloss in GU 83.3
DOI gloss in % 98.8
Log Haze 1.6
R Spec in GU 79.3
Table 1: Optical properties of the new product
Source:imaginando/Fotolia

37RADIATION CURING
RESULTS AT A GLANCE
 Very high gloss finishes are usually obtained with solvent-
based systems and may require a final polishing step. UV-cur-
able polyurethane dispersions are, however, capable of deliv-
ering much higher polymer flow than most other waterborne
systems even with very low VOC contents.
 Potential problems with UV-PUDs are that uncured coating
can accumulate then drip off the application equipment, while
the uncured coating remains tacky and so can pick up contami-
nation. A novel UV-PUD combines low creep with low tack to
minimise application defects.
 This low viscosity and regulatory compliant (tin-free) proto-
type offers single-coat spray usage for wood coating applica-
tions, creating mirror-like coatings with a good hiding power. It
also delivers the very good mechanical and chemical resistance
required to match the challenging opportunities in today´s
coating industry.
essary to control the oligomer flow after film formation in order to avoid
defects appearing during the application. It can happen, for instance, that
the oligomer accumulates in a relatively thick layer around the sprayguns
and other machine parts in the coating line.
This resulting oligomer bed, which can still be swollen with some residual
water, can easily drip onto the substrates or into the machine parts. This
creates defects and cleaning problems and affects the robustness and the
productivity of the overall coating process. On top of that, the dry coating
before cure is often still tacky, which makes it sensitive to dust pick-up and
fingerprints and imposes severe constraints for the manipulation of the
coated objects (sticky edges).
These coated materials cannot be handled without careful precautions.
There is a market need for an upgraded product with a more suitable oli-
gomer flow to overcome some or all of these problems.
CREEP VISCOSITY MEASUREMENT PROCEDURE
The dry oligomer flow was assessed using a specifically developed protocol
relevant to the application process. This creep measurement relates to the
viscoelastic response of a material to a constant stress where the deforma-
tion is monitored over time upon loading. The steady-state creep viscosity
is measured according to the method described below.
In order to mimic the flow behaviour of a droplet of resin subjected to grav-
itational stress, the creep of the dry oligomer is determined after evapora-
tion of water and before UV curing using a rotational rheometer.
An estimate of the magnitude of the stress acting on a droplet with a
nominal diameter d ≈ 5 mm under normal gravity is provided by
g(ρresin
-ρair
)d ≈ 50 Pa where g ≈ 9.81 m/s2
is the gravitational acceleration
and where ρresin
≈ 1 g/cm3
and ρair ≈ 1 mg/cm3
are the specific gravity for
the resin and air, respectively. The dry oligomer is obtained by casting the
liquid dispersion in an aluminium cup and by evaporation of the water at
Telegraphing
Coating
Substrate λ of substrate
A of substrate
Average height
of coating
Figure 1: Distinctness of image and body of a coated substrate
(A and γ represent the amplitude and wavelength of the surface
roughness respectively)
Figure 2: Creep measurement of the new product versus a
benchmark
room temperature for 72 hours, followed by a heat treatment at 50 °C for
24 hours in a convection oven. After this thorough drying procedure, the
oligomer layer has a thickness between 500 and 800 µm. The bottom of
the aluminium cup is covered with a release paper for easy removal of the
dry oligomer which is subsequently cut as a circular sample with a diam-
eter of 25 mm.
The creep properties are measured using an “MCR300” rheometer (Anton
Paar) fitted with a parallel plate system with a diameter Ø = 25 mm and
a Peltier temperature control. After loading the circular polymer sample
between the plates, the gap is fixed at ≈500 µm using a normal force not
Figure 3: Visual comparison of the dry oligomer flow behaviour
from a glass rod for the new product and the internal reference
(Glass rod diameter Ø = 10 mm; approx. 5 g of polymer; picture
after 1 hour at 22 °C)

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