1. SNIPPETSAn ISO 9001:2008 Company
Forming Fabrics Dryer Screens
Metal Wire Cloth C h e m i c a l s
Vol.14 / Issue-10 OCTOBER 2010 www.wirefabrik.com/snippets/Oct10.pdf
PLAYING WITH WET END CHEMISTRY
The production of paper is essentially the dewatering of a
paper making slurry, which takes place on a moving wire
(Forming Fabric). This process of uniform drainage and sheet
formation can be greatly assisted by a variety of chemical
additives.
The different varieties of paper and board and the desired
quality parameters, together with composition of the furnish
and the equipments used would dictate the choice of
chemicals whether process or functional.
Process chemicals are additives which help to optimize the
papermaking process. Examples are retention aids,
defoamers, fixatives and biocides.
Functional chemicals are products which are required to
impart the basic properties to the paper such as sizing,
strength and printability. Examples are AKD resin, Dry
Strength Resin and coating binders.
The boundary between process and functional chemicals is
very fine, as sometimes one can do the job of the other. For
instance, a retention aid can greatly influence the performance
of a sizing chemical.
UNDERSTANDING THE WET – END
Wet-end chemistry deals with the surface chemistries of
fibers, fines, fillers water and other additives. Phenomena such
as adsorption, desorption, flocculation, surface modification,
wet and dry strength, dye retention, foaming control, pitch and
sticky control, etc. are the subjects of study.
The ultimate purpose of wet-end chemistry is to use the
principles of colloid and surface chemistry, together with
polymer chemistry to control both machine runnability and
paper quality.
WHAT HAS CHANGED
The past 50 years have seen increased use of recovered
paper and white natural pigments as fillers ; by an ongoing
improvement of the paper machine productivity ; and an
emphasis on economics, ecology and quality, all this
supported by chemical additives and their creative application.
The modern paper machine requires excellent fibre web
strength, good retention of fines and fillers, and fast drainage.
Many problems related to wet-end chemical applications
continue to get high research attention allowing new chemicals
to join the race like microparticle retention systems.
GLOBAL CHEMICAL CONSUMPTION
Paper and pulp processing and additive chemicals represent a
USD 25 billion a year global industry. These chemicals are an integral
part of the total papermaking process : from pulp slurry, through sheet
formation, to effluent disposal.
Nearly 40% of these are Basic and Bleaching Chemicals, 40 % are
functional chemicals including starch and coating binders and the
balance 20% are ‘Specialty Chemicals’. However these chemicals
constitute only 1.1 per cent of the total raw material used in paper
production.
SPECIALTY CHEMICALS FOR PAPER & BOARD PRODUCTION
WHATS NEW :
Conversion to alkaline papermaking in the 1990s was the last
‘major’ change in paper making chemistry with the last several
years being a period of optimization of major wet end technologies
in terms of cost, impact on product quality and machine efficiency.
However developments have taken place in the following areas:-
1. Improved water chemistry management: Realizing the
detrimental effect of impurities on the process and final sheet
qualities, effective cationic charge neutralizer chemicals were
introduced to combat Anionic trash. Apart from polyamines,
polydadmacs, and polyvinylamines, research is directed
towards starches modified with polymer adducts.
2. Drainage and Retention: Achieving good retention as well as
drainage without affecting formation is an on-going challenge.
Various combinations of microparticles and flocculants are a
subject of intense research.
3. Strength Additives: Natural polysaccharides such as
gallactomannans are being constantly modified to provide
novel products.
ITC-PSPD and BILT have occupied the 90
th
and 95
th
positions respectively in the just published
PPIs list of top 100 global paper industries.
INDUSTRY
NEWS

2. Website: http : // www.wirefabrik.com
4. Sizing: Modification in the hydrophobic backbone of ASA and
introduction of an unsaturated hydrocarbon chain in AKD
(changing from wax to liquid) have reduced size fugitiveness and
slipperiness.
5. Enzymes: An interesting application is the use of esterase
for sticky control. Other enzymatic treatments are for
increased delignification; increase of freeness; improving
beatability of fibres and pitch control. In certain cases, use
of the enzyme ‘pectinase’ helped reduce cationic demand by
about 50%.
USING THEM RIGHT : SYNERGIES AND INCOMPATIBILITIES
Running a lean and efficient wet-end has huge beneficial
effects on paper making system operation. Reducing unneeded
additives can dramatically impact paper quality and machine
efficiency.
Understanding the purpose of each additive is easy; figuring
out what they are actually doing to the sheet and each other is
the complex but important part. Hence different additives used
at the wet-end can either lead to a synergistic effect or found to
be incompatible with each other.
Some of these effects which have been noted are :-
Coagulants: Normally used in contaminated stock streams to
neutralize charge and improve performance of retention aids, a
negative synergy is possible if the coagulant overcharges the
system causing a desorption and loss of efficiency of short loop
additives.
Starches: Wet-end starch is a good source for cationic
charge and has a positive effect on retention and drainage.
Highly charged starches can overcharge the wet-end and
decrease efficiency.
Dispersants and retention: Bio-dispersants used to assist
the function of biocides can react negatively during interaction
with retention aids, hence these need to be pre-tested.
Microparticulates: These are derived from silica, bentonite
or other inorganic particles which when combined with retention
aids almost always positively help to increase drainage while
holding formation at an acceptable level.
Deaerators: As these remove microbubbles adhering to fibres,
deaerators enhance the action of almost all chemical additives due
to improved fibre-chemical interactions.
Sizing Chemicals: Sizing can be positively affected with
adequate use of coagulants and scavengers like microparticles.
Alum has a positive synergistic effect in ASA sizing by stabilizing
the ASA emulsion and providing a more uniform particle size
distribution. However overdosing may form deposits at the
alkaline pH. Excessive surfactants in the system in form of
defoamers, bio-dispersants and deinking soap carry-overs can
also lead to poor sizing.
Talc filler : Predominantly used as a filler, it was soon found to
be beneficial as a deposit control additive too.
Colourants: Dyes need to be used keeping in mind their ionic
character (anionic or cationic) as otherwise, it can form precipitates
with oppositely charged chemicals.
It is always wise to discuss in detail the entire process with
existing chemical suppliers before commencing a new chemical
treatment program.
DOSING IT RIGHT
Wet end chemistry measurement and control is today a norm.
The ability to precisely control the flow of additives is essential for
producing a high quality paper product. On-line charge
measurements by automatic titration is standard in all modern
machines.
Dosing pumps have achieved sufficient sophistication to
provide precise, repeatable and pulseless flow for smooth
dispensing of chemical additives.
CONCLUSION
The papermachine wet-end is one of the most complex and
influential areas in the papermaking process and hence assumes
the greatest importance for costs and quality. In a well balanced
wet end, additives impart sheet functional properties, improve
machine performance, and increase operational flexibility while
reducing costs. A chemically unbalanced wet end often typified
by overuse of additives, competing ions and performance
variability, can severely limit quality and productivity.
QUOTABLE
QUOTE It is not the language but the speaker that we want to understand - The Upanishads
SCRABBLE What does S F I stand for ? ( Hint : A forest certification programme )
First correct answer will win a Parker Vector Roller Pen (Maximum two prizes for one person in a year).
Post / Fax / Email your answers to EDITOR-W&F SNIPPETS by 20th
October, 2010.
WINNER
SEPT’10
Mr. Atul Kaul, Director (Pulp & Paper), Arab Paper Manufacturing Co., Damman (Saudi Arabia).
Correct Answer: H A C C P : HAZARD ANALYSIS AND CRITICAL CONTROL POINT
?QUIZ
Choose the right option :-
Retention of fibres and fillers in a papermaking slurry improves when the zeta potential figure is :
(a) near zero (b) highly negative (c) highly positive
Post / Fax / Email your answers to EDITOR-W&F SNIPPETS by 20th October, 2010.
WINNER
SEPT’10
No correct answer received.
Quiz : Choose the right option from the bracket :-
Printing ink gloss is ( directly / inversely ) proportional to particle size of the coating pigment.
Answer : Printing ink gloss is inversely proportional to particle size of coating pigments (Higher gloss from smaller/finer pigments).
Prizes
1. Best / first correct answer received will win one-year subscription to IPPTA Journal (Maximum one prize for one person in a year).
2. Best of the 12 monthly winners in a year, will win one-year subscription to Paper 3600
Magazine, USA.
☺ “Oh God,” sighed the wife one morning” I think my mind is almost completely gone”.
The husband looking up from his newspaper “I am not surprised. You’ve been giving me a piece of it everyday for the
last twenty years”.Mindboggling
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Wires & Fabriks (S.A) Ltd,
JAIPUR-302012, India.
Phone: 0141-2341722 Fax: +91-141-2340078
Email: snippets @ wirefabrik.com
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