Volume Cost concept with reference to Filled Polyolefins

Volume Cost & its importance
in Plastic applications:
Part 2

Filled Polyolefins
Mr. Siddhartha Roy
Consultant,
RoyPlasTech, Pune.
royplastech@rediffmail.com

Background
In the Feb/March issue of IPI Journal,
my article on Volume costs was published.
I have received a lot of positive feedback
and appreciation and I thank all the members who responded. One common thread
in the feedback is that though it was a
technical article; commercial implications
were well brought out. Thanks to this
article, the IPI Kolkata chapter invited me to
give a lecture on the subject. I readily
agreed as Volume cost is not well understood and it has been one of my passions
to explain this important concept. The
Kolkata lecture was very well received and
I look forward to delivering the same
lecture at other centers and would welcome the opportunity.
The Article had special emphasis on
PVC and highlighted the pitfalls if Volume
Costs were ignored. The Kolkata Chapter
requested me to include filled PP and
HDPE and I extended the presentation to
include Polyolefins. This is what I would like
to cover in this article.
I must admit that I have a lot more
practical experience with Filled PVC as
compared to filled Polyolefins, so my
article is based on theoretical considerations. I would appreciate feedback as to
whether the conclusions drawn are actually reflected in practice.
For those who have not read the first
article, here are some basic concepts.
What is Volume Cost?
The Volume Cost of a Raw Material
input is the purchase cost of a unit volume
of the material. It is extremely important to
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understand the Volume cost of Polymers
and its additives as it plays a key role in
their selection for a particular application.
Volume cost (`/Litre)= Purchase Cost
(`/Kg.) x Density (Kg./Litre or gm/cc)
Let us examine the Volume costs of the
major commodity Polymer families.
Polymer

Abbr.

Unplasticised PVC
Plsticised PVC
Low Density Polyethylene
High Density Polyethylene
Polypropylene Homopolymer
Polypropylene Copolymer
Polystyrene
High Impact Polystyrene
Acrylonitrile Butadiene Styrene

UPVC
FPVC
LDPE
HDPE
PP
PPCO
PS
HIPS
ABS

Price
` / Kg
48
60
70
67
68
70
80
82
85

Density
Kg / Ltr
1.38
1.25
0.92
0.96
0.90
0.905
1.05
1.05
1.05

While it would look that UPVC is by far
the cheapest Polymer, the natural question
is that why does it have such limited applications in, say moulded products?
Assuming, just for arguments sake that
UPVC was as easy to mould as the other
Commodity Thermoplastics, why is it not
used in such widespread applications like,
say, buckets?
The answer lies in Volume Cost.
Combining price with density the Volume
costs in Rs/Ltr. is

Clearly the Polyelefins are cheaper
than PVC on Volume cost basis, and
bucket moulding started with LDPE, and
then to HDPE and lately PP also. PVC was
never in the picture because of its higher
Volume cost. If its volume cost had been
lower than the Polyolefins, ways and
means would have been devised to mould
PVC into buckets!
Importance of Volume Cost to the
Plastics formulator.
The consideration of volume cost is
even more important when Polymers are
compounded with additives. The density of
the final product can change considerably
especially when mineral fillers are added
primarily to reduce costs.
Volume cost and its implications are not
properly understood by many. It is vital to
understand its implications before
embarking on cost reduction exercises.
Plastic finished products are rarely sold
by weight. They are priced either per piece
(Mouldings) or per unit length (Pipes,
Cables, Tape). Even liquid Plastic products like Paints and Varnishes are sold per
litre. Thus the costing and pricing are for
fixed Volumes. As the Plastic Raw materials are always purchased per unit weight,
the tendency is to do cost calculations on a
Per Kilo basis, and the finished product is
priced accordingly to the weight per piece.
If cost calculations are done on Per Kilo
basis, many times the reduction in cost by
adding fillers/extenders is calculated as a
percentage of original formulation cost.
The savings may be translated into a price
reduction based on this percentage. After
IPI JOURNAL August / September, 10

07

some time the entrepreneur realizes that
he is sustaining losses as the reduction in
Volume cost was nowhere near the Per kg.
Cost reduction on which the discounts
were based, especially when mineral fillers
are the main cost reducing input. All
Mineral fillers have a higher density than
most plastics.
This is a most dangerous trend. Many
Polymer applications in India have faced
declining demand due to loss in confidence of the consumers because of
repeated failures of poor quality cheap
products. Examples are too numerous,
and is most saddening to persons and
companies who have worked so hard in
establishing such applications. In the Pipe
field itself one can recall the hammering
HDPE pipes took in the early eighties due
to large scale failure of pipes made from
scrap HDPE and sold to prestigious
Government projects as prime grade
pipes. While HDPE pipe market languished because of the bad name, PVC
Pipes surged ahead. Even major companies like PIL were so badly affected that
they had to close down the manufacture of
their well established Hasti brand. It has
taken two decades for HDPE pipes to claw
back to good volumes, which involved
consistent quality and development of new
application areas like Drip and Sprinkler
Irrigation, Gas piping, Large diameter
sewerage pipes etc. as well as consolidation in the core water supply sector with
nd
good quality pipe with 2 generation HDPE
grades.
A dangerous fallout of mindless filler
loadings is when markets change from
pricing per piece or in the case of pipes,
per unit length of specified thickness to
pricing on a per kilo basis. Such a change
encourages higher filler loadings and
should be resisted by all discerning manufacturers In plastics, heavier does not
mean more “Mazboot”. Physical properties
are seriously compromised in PVC products made heavy by excessive filler additions.
Compounding Costs and its
implications
Mineral fillers are fine particle Inorganic
powders The particles agglomerate due to
Vaan Der Waal forces, and it is essential to
break up these agglomerates to disperse
the filler particles uniformly in the Polymer
Matrix. This requires energy and is addi08


tional to the energy required for melt formation and mixing. The energy requirements
and compounding cost depend on various
factors, like the physical form of the polymer, whether it is polar or non polar, the
type of filler, whether the filler is untreated
or treated and processing behavior.
Physical Form
l Polymer is in liquid form, it is fairly
If the
easy to incorporate fillers Examples are
Paint formulations, Liquid adhesives and
Plastisols. A good quality stirrer is normally
sufficient. However, as in the case of
Leather Cloth Plastisols where large quantities of low quality Ground Calcium
Carbonate is used, additional processes
like triple roll milling are required to ensure
adequate dispersion and homogenization.
Each step increases compounding costs,
but they are still comparatively low.
l Polymer is in Powder form, like PVC
If the
resin, fillers are quite easily incorporated in
the dryblending step and High Speed
mixers are commonly used. All PVC has to
be compounded with Stabilisers, lubricants, Plasticisers if required and a host of
other additives. The filler gets incorporated
in the compounding process and there is
hardly any additional filler dispersion cost.
Many UPVC applications do away with the
intermediate pelletising step (essential with
Plasticised compounds), hence filler
addition cost in UPVC is negligible.
Masterbatch manufacturers sometime
pulverize Polyolefins so that large quantities of fillers can be added much more
easily than granule feed. Of course this is
an expensive step, taken only when filler
loadings are high or the compounding
equipment falls a bit short in dispersion.
l Polymer is in granule form, the
If the
compounding cost is the highest. The
primary compounding of the ex reactor
resin has already been carried out by the
Polymer producer when antioxidants,
stabilizers and other processing additives
are added and the melt converted into
pellets. The Filling of mineral fillers are
done by compounding companies which
have the necessary equipment to melt the
pellets, mix and disperse the fillers,
homogenize the melt and convert them
back again into granules. Intensive batch
mixing processes like Banbury mixing
have largely been replaced by modern
high speed co-rotating multiported twin
screw extruders, Buss Co-Kneaders and

similar sophisticated equipment.
Therefore for estimating the volume
costs of a formulation, the compounding
cost has to be added to the formulation
costs before arriving at the true Cost per
Kilo. This multiplied by the finished compound density gives the Volume cost
which is so essential in working out the
economics.
Mineral Filled Polyolefins
With Polyolefins, the situation is different from PVC. Here Fillers like Talc and
Calcium carbonate are added to improve
stiffness to PP, or desired properties like
antifibrilation in HDPE or PP Rafia Tape.
Incorporation of Fillers in Polyolefins is an
expensive process as explained above,
Further, unlike PVC which is polar, POs are
non polar, requiring more energy to encapsulate the polar fillers Compounding costs
for filling Polyolefins can be as high as ` 10
-15/ kg., with the higher figure more prevalent when state of the art compounding
equipments are used.
Filled Polyolefins (10 - 40%) are costlier
per kg. than the base polymer because
compounding costs outweigh the lower
filler cost. The volume costs go up sharply
with density increase, but requirements of
better stiffness in Auto Components,
Moulded Furniture and other technical
parts is the driving force for filler addition. It
is only at filler levels of over 50%, as in filler
masterbatches, that the cost per kilo dips
below Polymer cost levels, but the volume
cost will still be adverse. Thus normally
filler addition does not automatically lead
to cost savings with Polyolefins as it does
with PVC.
Another important difference is that
Fillers are loaded in PVC in Parts per
Hundred Resin (PHR). In Polyolefins, Filler
loading is expressed as a percentage of
the total compound weight. When somebody expresses amazement that his
competitor is using 100% filler in his PVC
Pipes, obviously you can't extrude pipes
out of 100% CaCO3!! What he means is 100
parts PVC Resin, 100 parts Filler plus the
usual Stabilisers, Lubricants and pigment.
Thus the actual filler Percentage would be
100/210 (say)= 48%. This is not an unusual
loading, at least in Polyolifins with Filler
masterbatches exceeding these levels. I
make this distinction because referring to
PHR in PVC compounds as % is a common
mistake.

Let us have a closer look at CaCO3 filled
PP & HDPE.
Mineral Filled PPCo Applications
l
The high volume Filled PP applications
are :

Calcium Carbonate filled PP CoPolymer (Compounding Cost ` 15/Kg)

- Automotive Bumpers, Dashboards, and
Components

- Talc is the main filler
l
Moulded Furniture

- Precipitated or Ground
Calcium Carbonate is the
main filler.
l Tape
Raffia
- Precipitated or Ground
Calcium Carbonate is the
main filler.
lCost Films
Low
- Talc is the preferred filler as it has least
effect on translucency.
l rationale for mineral filled PP and
The
HDPE is more for improving physical
properties rather than cost reduction (with
an important exception which we will
discuss later).
l
In PP, CaCO3, Talc, and other mineral
fillers improve stiffness and improve
paintability.
l
In HDPE & PP, CaCO3 is extensively
used as an antifibrillating agent for Rafia
Tapes.
l
LDPE/LLDPE are normally not filled as
film blowing performance is badly
affected.
Effect of Fillers in PP-Copolymer.
(Compounding Costs ` 15/Kg.)
Like in the previous article, calculations
on the effect of Filler loading on Compound
cost and Volume costs are done in Table 1.
This is a theoretical exercise, as filler
loadings of more than 60-70% are difficult
to achieve. The filler loadings have been
stretched to find out what is the effect on
volume costs and draw conclusions.
It is interesting to note that even though
these are theoretical calculations, the
predicted density is quite near the actually
measured density with the difference
being a few points in the third decimal

Table - 1, The graphical representation of the calculations are shown in chart 2.

place. Rarely do we find errors in the
second decimal place. There is some
density increase due to volatile loss, but
this is quite low in Polyolefins, and I assume
the Filler is not wet.
Interpretation
l
Assuming that `15 a Kg is the
Compounding cost, at a level of approx
25%-26% filler does the cost of Compound
dip below the raw PPCO price (` 70/Kg).
When the business margins of the compounder is included, it is only at the 35%40% Filler level that the Purchase price of a
Filled PPCo compound will come below
base polymer price.
l rate of decrease of
The
Volume Cost is a lot slower,
and even at 90% Filler levels,
the Volume cost is higher than PPCO
Cost.
the base polymer.
l means that for all
This
moulded (or Extruded PP
Products which are sold per
piece (i.e. by volume), purchased filled PP Compounds
will not lower costs. They
should only be used for value
addition like better stiffness,
paintability etc.
There is a way to minimize

the effect of the relatively high
Compounding and conversion costs.
Filler Masterbatches
The route to reduce Compounding
costs is with Filler Masterbatches. A filler
masterbatch is PP filled with 60-70% Filler.
These are blended with Unfilled PP just like
Colour Masterbatches and then processed. I have assumed that the per Kg.
Compounding costs remain the same for
Filler Masterbatches as for Filled
Compounds. The Compounding cost gets
distributed by addition of unfilled PPCo.
Mixing takes place in normal Blender and

PPCO
Vol.
Cost.

Chart 2

09

Injection Moulding machine.
As an illustration let us assume that the
cost of a Filler Masterbatch is as in Table 1
70% loading or around ` 40/Kg.:
Benefits of Filler Masterbatch
l
At 20% Filler level, blend is ~ ` 11/kg.
cheaper (14.7% reduction)
l
At 30% Filler Level, blend is ~ ` 9/kg.
cheaper (12.8% reduction)
l
Though Density remains the same,
Volume cost reduction vis a vis bought in
Compound is higher, ` 11.30 and ` 9.73
respectively, but is still higher than Unfilled
PPCo (63 `/Ltr).
l
By blending, it is much easier to adjust
the Filler level for the desired properties.
Recommendations for Moulded
Furniture (And other products Sold by
Volume).
l Filler Masterbatches is a good
While
way to reduce costs, the volume costs
stayhigher than unfilled PP.
l at 90% Filler, Compound Volume
Even
cost does not go below Unfilled PPCo (`
63.5/Ltr.)
l
In Moulded Furniture, Cost per chair is
unlikely to reduce by increasing Filler
Loadings.
l
Resistance to deflection (Stiffness)
improves with Filler Loading.
l
Reduction in Impact strength has to be
balanced with required stiffness to arrive at
optimum filler loading for a
particular Moulded
Furniture Model.
l
Rigorous evaluation
with blends of PPCo,
PPHomo, and Filled
Masterbatches with
impact resistance,
Stiffness and Weight
tested for each blend
should be done. Analysis of the results and
trends will help establish the most cost
effective solution for each mould
Mineral Filled HDPE applications:
Raffia Tape.

10


Cost Reduction with Filler Masterbatch. (70% Filled with CaCO3)

o in Filled PPCo
Cost of Bought

o PPCo/ Filler M.B.
Cost of Blended

Rs. 40.00

This is one area of the Polyolefin processing scene that use of filler is widespread. In order to understand why it is so,
it is important to understand Volume costs
and the way Raffia products are specified
and sold.
Antifibrilating Masterbatch
Use of Filler by the Raffia Tape Industry
started as an Antifibrilating agent. This was
started with HDPE tapes and then later with
PP. The Industry soon realised that good
cost savings could be achieved with filler
loadings higher than that required for
antifibrilation.
Volume cost considerations can
explain why Raffia manufacturers get cost
savings by filler addition and not moulders
or for that matter the large HDPE Pipe and
other extruded products.
What are the basic differences? In the
moulding Industry, products are sold per
unit volume. The volume is the mould
volume. To reduce volume a new mould is
required. This is an expensive proposition,
but is the only way to reduce costs. Most
moulded furniture manufacturers have built
up a large stock of different moulds yielding similar design chairs but of different
weights. These cater to different market
segments. The mindless Filler loadings that
have happened in the PVC Pipe industry
has been mirrored by a mindless wall
thickness reduction (Mr. M.P. Taparia's

words, not mine) in the moulded furniture
industry. The results are as disastrous as
outlined in my earlier paper. I give this as
an illustration of the power of Volume cost.
If Volume cost does not decrease on
adding fillers even though the purchase
cost of the filled compound goes down,
other methods are required to reduce cost,
which may run into several crores in capital
costs.
In the Raffia tape industry, however the
Tape denier is the primary specification.
Rafia tape is not sold by volume The
Extrusion process allows easy modifications in tape dimensions without any
added capital costs. We will now explore
how Volume cost has made filler addition
lucrative in the Raffia Tape Industry
Woven Sack Specifications
The woven sacks or other end product
woven from HDPE / PP Rafia are normally
specified by:
l Denier. These are around 1000Tape
1200 and is much higher than synthetic
Yarn Deniers
l & Weft: No. of tapes per inch/cm.
Warp
used in the ends and picks.
l of the bag.
Weight
Denier and dtex-Definitions from
Wikipedia.
l is a unit of measure for the linear
Denier
mass density of fibers. It is defined as the


mass in grams per 9,000 meters. The
denier has its standard based in nature, a
single strand of silk is one denier.
Therefore, a sampled 9,000 meters length
of silk will weigh one gram. The term denier
is a literal combination of the words linear
and density.
l In the International System of Units
dtex:
the tex is used instead Tex is a unit of
measure for the linear mass density of
fibers and is defined as the mass in grams
per 1000 meters Tex is more likely to be
used in Canada and Continental Europe,
while denier remains more common in the
United States and United Kingdom. The
unit code is "tex".
l
The most commonly used unit is actually
the decitex, abbreviated dtex, which is the
mass in grams per 10,000 meters This
comes fairly close to the denier definition.
How Filler addition Tape Denier

Let us start with unfilled HDPE Tape of
1000 Denier. At a Density of 0.96 gms/cc
(Kg/Ltr.), 9000 mtrs of tape should weigh
1000 grams. When Mineral Filled HDPE is
use, Density is higher, and Denier
increases in proportion.
Denier can be brought down to the
specified 1000 by Downsizing:
l
Reducing Tape Thickness
l
Reducing Tape Width
l
Reducing both
To maintain Denier, the volume per unit
length of tape can be reduced. If the filled
Compound has a density 15% higher,
volume can be reduced by 15%.
How Filler affects Woven products.
l ends and picks are kept the same
If the
after downguaging Rafia Tape, the bag
weight should remain unaffected. However
strength will go down due to lesser amount
of polymer and the reduction in
mechanicals due to the filler. Drop tests
have to be carried out to assess suitability /
failures.
l Width is reduced too much to
If the
maintain Denier, the weave will become
more open, and may not be acceptable in
some applications.
l downsizing the tape, extra orienWhile
tation can be applied to partially offset loss


in strength. The stretch applied should be
within the processing limit to avoid excessive tabe breakage.
Limitations to Filler Addition in
Raffia Tape.
l
Physical properties like Tensile
Strength, Elongation at Break, Tensile
Modulus etc. reduce with filler. Loss in
strength is dramatic at higher filler levels
(above 15% Filler)
l
Stiffness increase is not much of an
issue in Raffia Tape as thickness is much
lower than mouldings.
l
For Woven Raffia products where high
performance is demanded, like Jumbo
bags, Filler loadings should not increase
over 6-8%.
l
For less demanding applications like 25
Kg. Bags or lightweight Tarpaulins, higher
filler levels can be tolerated.

Filler Masterbatch addition
In this example we will consider what
happens when Filler Masterbatch is added
to HDPE. The Filler Masterbatch should
have a suitable Carrier. This is important as
HDPE and PP are not very compatible, thus
a PP based Filler Masterbatch should not
be used with HDPE and Vice Versa
High MFI LLDPE Masterbatches are
compatible with both HDPE & PP. High MFI
LLDPE allows large filler levels. However,
high dosages of High MFI based Filler
masterbatches can adversely affect the
resultant MFI an reduce physical properties further. In Pigment Masterbatches, this
is not an issue as addition levels are 1-4 %
unlike 20% to as much as 50% and more
resorted to with Filler Masterbatches.
Assumptions: A 60% Filler loading is
selected for this study. Compounding
costs are the same as the PP example.
l Volume costs are still higher than
While
unfilled HDPE (64 `/Kg.), costs are saved
as less Volume of material per bag is
needed.
l costs keep on decreasing with
As
addition of filler, caution is advised not to
overdo the loading.
What is the Optimum Filler Loading in
Raffia.

Unlike
l

in many other PP/HDPE applications, costs can be reduced by filler loading in Raffia Tape. There is a temptation to
go on increasing filler loadings as markets
become more and more competitive.
l should be taken not to disturb the
Care
MFI chosen by high levels of Filler
Masterbatch.
l addition levels for a particular
Filler
application should be self regulatory.
Self Regulatory considerations.
l performance requirements of the
The
end use should be clearly understood.
Tests like Loaded Drop Test, Bursts
strength, Stitch ability should be set up to
reflect the performance requirements.
l Masterbatch levels should be
Filler
carefully experimented with to find the
optimum %.
l tests similar to BIS-4985 could be
Ash
formulated for critical applications like Bulk
Sacks/ Jumbo Bags.
Summary for Raffia
lprevious calculations and findings
The
are equally true for PP Raffia. Similar
considerations are valid when Talc or
combinations of Talc & CaCO3 are used.
l studies are theoretical and follow
These
the reasoning of Volume Costs. It would be
interesting to know how close these findings compare to actual Raffia industry
experience.
Some words of caution

I understand that in the last few years,
there have been concerted steps taken to
reduce the Filler addition costs in
Polyolefins. It is quite clear that as compared to the PVC Industry, the high compounding costs is a major barrier to filled
Polyolefins from finding wider applications
and market share.
The route taken is quite worrying. It is
well known that Plasticised PVC
Compounding is successfully done on
single screw extruders, some of which are
quite unsophisticated, and therefore very
cheap. The capital costs are a fraction of
co-rotating Twin Screw extruders and
compounding `/kg cost for Plasticised
PVC is in the low single digits. It seems a
similar route is now being used for filling
Polyolefins, mainly HDPE for the Raffia
tape and Blown film industry.
One must understand that in SPVC, the
filler is already well dispersed in the High

11

ers to compensate for degradation.
There is also a trend for using Talc filled
filler masterbatches for HDPE and Even
LLDPE Blown film. I am convinced that if
the Film or the bags made thereof are sold
by Volume, filler addition would not reduce
costs. Assuming that the film rolls are sold
in meters of a specified gauge, it is being
sold by Volume. Bags sold per piece of a
fixed gauge (thickness), again it is sold by
Volume. We have seen that in Polyolefins,
Volume cost does not go below the unfilled
Polymer levels even at high filler loadings.
Thus the processor may be lulled by the

Speed Mixer/Cooler Mixer before being
fed to the Single Screw extruder. The
extruder is essentially for melting and
pumping the PVC through the die for
pelletising. The induced mixing action of
the single screw is enough to complete the
homogenization.
With HDPE and relatively high filler
loadings as required in a filler
masterbatch, a single screw extruder,
even with mixing zones can never come
even close to the intensive mixing capabilities of Co- rotating multi-segmented Twin
Screw Compounders or Buss KoKneaders.
As the single screw extruder is so much
cheaper, quite a few have been pressed
into service to compound Polyolefins with

high filler levels, while still keeping the
compounding costs down to ` 6- ` 7/kg. If
dispersion is not proper, multiple passes
are resorted to compensate for the
improper mixing. This is self defeating as
repeated heat history eats into the
Stabiliser and Antioxidant levels incorporated by the polymer producer. There is
every chance that the filler masterbatch will
reduce the life of the finished product it is
used for. Filler masterbatches are used at
much higher levels than Colour
Masterbatches, and presence of degraded
polymer in the masterbatch will adversely
affect product quality. I would urge those
who are compounding HDPE with filler on
single screw extruders in multiple passes
to add additional Antioxidants and stabiliz-

fact that the filled compound he is extruding is of a lower cost in `/kg. terms, his
product weight will go up for the fixed
volume units he sells. The additional
material cost will outweigh whatever
savings he was expecting over unfilled
product.
If the film is being sold by weight basis,
it is another matter. Here the customer
suffers. He gets less meters for the same
gauge film as density goes up with filler.
The meterage reduction % will be more
than the price discount offered with Talc
filled films. I would request the industry
leaders to nip this trend in the bud and
educate their customers on the Volume
Cost concept so that they are not exploited
by unscrupulous competition.

About the Author
Mr. Siddhartha Roy is a Chemical Engineer from IIT Kharagpur (1968). He has worked with plastics all throughout his
career. He was actively involved in development of PVC markets and applications, especially Pipes and Fittings. He worked
with Shriram Vinyls, PRC (now DCW) and Chemplast, manufacturers of PVC Resin & Compounds. He has managed a PVC
Pipes & Fittings factory in Kuwait and helped Jain Pipes (now Jain Irrigation) set up their Pipe production facilities.
He headed R&D at VIP Industries, Nasik, and is well versed in the processing of Polyolefins, Styrenics, Polyamides and PC.
He has been active in IPI activities and has delivered several Endowment lectures. He was recently awarded the Fellowship
by the Governing council of IPI for his contribution to the Plastic Industry.
He is currently a consultant and can be contacted at royplastech@rediffmail.com (Mobile 9890366632

12



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