Siddhartha Roy explores calcium carbonate’s (CaCO3) role in filler applications, with a look at processes around the world with regard to PVC pipes in India and China.

1. Calcium Carbonate
GCC in PVC: More
than a pipe dream
A
s with anything, the way a
plastic is processed and
formulated varies from country
to country.
Overleaf is a table outlining
the different forms of plastics observed in
various parts of the world. There has been
considerable convergence, especially in the last
two decades of globalisation, but the broad
trends are still discernible.
Pipe colours in India
In PVC pipes details are important. Colour,
pressure and models vary. The uses of colour in
August 2012
Siddhartha Roy explores calcium carbonate’s (CaCO3) role
in filler applications, with a look at processes around the
world with regard to PVC pipes in India and China.
different regions of the world is intriguing.
PVC pipes are mainly installed underground,
and apart from Drain Waste Vent (DWV)
applications, are rarely used exposed.
Even in DWV lines the pipes are often
painted over. So why is the colour of pipe
important when it gets hidden anyway?
Until recently, in India, PVC pipes were
made in white like the US system, or black,
similar to PVC conduits for electrical installation.
Wavin India, the world’s largest manufacturers
of plastic pipe systems, stuck to the German
grey.
White pipes needed 3-4 PHR (parts per
hundred resin) TiO2, a more expensive pigment.
Carbon black is much cheaper, and all
High-density polyethylene (HDPE) pipes were
industrial minerals
45

2. Calcium Carbonate
CaCO3 usage in Indian plastics
Pipes and fitting
73%
Footwear
2%
Others
4%
Wires & Films &
cables sheets
6%
5%
Profiles
Calendering
3%
7%
black until a problem was detected with these
pipes.
It was noticed that the pipes were deforming
in storage during the Indian summer.
Investigations showed that the sun radiation
temperature was the cause. This is the
temperature that a black body attains under
direct exposure to sunlight.
At the height of summer in many parts of
India, temperatures can hit the 45oC mark (115
o
F), which leaves sun radiation temperature to
soar to 79-80 o C.
This is higher than the Vicat Softening point
of UPVC which is 72oC. The black pipes were
deforming under their own weight in the sun
or even in closed metal containers, like railway
wagons. Injection moulded fittings which have
lower Vicats were very badly affected.
It was noticed that under similar conditions,
white pipes were unaffected. The sun radiation
temperatures were a good 10-12oC lower than
black pipes and, thus, below the softening
point.
However the industry was reluctant to adopt
white as the pigment cost was high. A
compromise was reached with about 1 PHR
TiO2 and a pinch of carbon black to give a light
grey colour. The colour lowered the sun
radiation temperatures to a manageable level
and was not too expensive. It was necessary for
the industry to standardise the colour as it
would allow long runs during production
without the need to change colours frequently.
The light grey colour standardised in India
had a remarkable and positive side effect.
HDPE pipe was the main competition, and
it had to be coloured black as carbon black is
the preferred UV Protection agent in polyole46
industrial minerals
fins. Unscrupulous manufacturers started
adding recycle and scrap which went undetected by the customer because of the black colour.
On the other hand, the light grey of PVC did
not allow excessive scrap addition to go
undetected.
HDPE pipe quality plummeted; there were
large scale failures in the field and the HDPE
pipe market imploded. PVC pipes took off in
this phase and have left HDPE pipes far behind
ever since.
For specialist waste recycling (SWR) pipes,
Indian PVC Pipe has opted to use a dark grey
colour. In Europe, and in most parts of the
world, a reddish brown colour is prevalent.
China, for some reason, has stuck to white
pipes. Their colour is not as white as the
American pipes, perhaps because TiO2 levels are
lower. Perhaps in China, the drive to use more
and more fillers has something to do with
enhancing the white colour.
The major highly filled applications in
Thermoplastics are in the fields detailed in the
pie chart above.
These applications alone account for between
80-85% of CaCO3 usage in plastics.
PVC pipes along with wires and cables and
calendering is 85% of the 2 MTA PVC market
in India, CaCO3 in PVC is a significant market,
and of considerable interest to the minerals
community.
The development of filler masterbatches as a
tool to spread out the compounding costs over a
larger quantity of polyolefins has been described
in IM previously (Calcium Carbonates Polymer
Promise, December 2011)
The trends are similar worldwide — Automotive, white goods and custom mouldings use
filled compounds, while the more competitive
moulded furniture market exclusively use filler
masterbatches.
There is not much difference in the pattern of
CaCO3 usage in wires and cables, leathercloth,
calendered films and sheets worldwide.
Individual processors have their preference for
precipitated calcium carbonate (PCC) or ground
calcium carbonate (GCC) and the micron sizes
as per their equipment and processes.
Extruded floor tiles seem to be exclusively on
GCC and cost considerations have forced use of
coarser particle sizes (10-20 microns). Extruded
floor tiles are very well developed in China and
the Far East, while calendared floorings are well
entrenched in West, US and India.
Cushion vinyl floorings has seen amazing
effects being offered and is a major paste grade
PVC resin outlet.
It is in the area of PVC pipes that there has
been a divergence of approach, below is an
example of the path followed in India and
China. PVC piping systems can be broadly
classified under two groups: pressure pipes and
non-pressure pipes.
Pressure pipes
Pressure pipes are designed to convey many
different fluids under pressure. Ratings are
according to the pressures to be withstood and
range from 2.5 bar right up to 16 and even 20
bar. The wall thickness progressively increases as
the pressure ratings increase.
The stringent specifications restrict CaCO3
levels to 8-10 PHR. Good quality, fine particle
size GCC and PCC actually improve impact
strength and processability at these levels.
Top of the line GCCs like the offerings from
Omya, or the ultrafine PCCs offered by firms
like Solvay actually improve the impact strength
at even higher levels (15-20%), but burst
pressures could be affected adversely over 10
PHR.
As pressure pipes are a critical application,
mature producers worldwide self control the
filler levels to 8-10 PHR. Some specifications,
like the Indian BIS 4985 for pressure pipes,
specify a sulphated ash content limits which
CaCO3 usage in plastics
Application Area
Product
Typical Filler Loading
HDPE and PP Raffia Tape
Blow Mouldings
HMHDPE Shopping bags
Filler Masterbatch
Up to 70% CaCo3.
PVC Wires and Cables
Insulation
Inner Sheating
Outer Seathing,
PHR
10
50
100
%
6%
25%
35%
Top coat
Base Coat
PHR
10
150
%
5%
45%
Soft
Hard
PHR
300
400
%
65%
70%
Pressure
DWV
Highly Filled-1
Highly filled 2
8
40
100
200
7%
27%
48%
65%
PVC Leathercloth
Extruded Floor Tiles
PVC Pipes
August 2012

3. Calcium Carbonate
would not permit higher dosages of mineral
fillers.
Worldwide, PVC pressure pipes form
approximately 30% of the total PVC market.
In India it is a bit different. There is a huge
irrigation sector using many thousands of
kilometers of PVC pipes annually. These are
normally the lower pressure rating pipes like 2.5
bar and four bar and some six bar rated pipes.
This skews the pressure pipe market share right
up to about 70% in the Indian market.
In India, it is in the agri pipe area that
competitive pressures have pushed up filler
loadings.
1. Impact Modifiers: These introduce a
rubbery element in the brittle filled PVC
matrix. They act as shock absorbers and
improve the impact strength of PVC,
sometimes dramatically.
a. Acrylic, MBS and ABS types
b. Chlorinated Polyethylene (CPE)
Non pressure pipes:
In India, such impact modifiers and flow
promoters are extensively used in critical PVC
applications like pharmaceutical blister film,
blown bottles, industrial sheeting, and in the
niche market of column pipes.
Impact modifiers like the ones developed by
Rohm & Haas (KM 323B) and flow
promoters like K-120ND & K-175 are very
well known and are manufactured locally.
Products from Kane Ace are also popular.
However these are very costly additives and
their use is restricted to critical applications.
The Indian PVC pipe industry has tended to
steer clear of these additives because costs will
The bulk of PVC pipes are used in construction
related applications like DWV, SWR (sewage,
waste, rainwater) conduits and tube well casings,
rain water harvesting systems.
These represent nearly 70% of the PVC pipe
market and are a major contributor to filler
tonnage consumed in pipes.
These pipes competed with asbestos cement
pipes and have rapidly replaced them, especially
after the awareness of asbestos’s link with cancer
grew worldwide. PVC pipes offered much
lighter and safer systems, which were easy to
install.
PVC pipes need to be protected against UV
degradation as many of them are exposed to
sunlight, unlike pressure pipes which are
normally buried or concealed. However, because
of competitive pressures an unhealthy trend of
getting rid of expensive UV stabilisers seems to
have permeated the Indian SWR industry.
In many buildings the exposed PVC pipes are
painted to match the building exterior. The
paint layer offers some protection from UV
attack.
The success of PVC pipes in the SWR and
related DWV sectors owes a lot to development
of a wide range of injection moulded fittings.
These fittings either have a rubber ring in groove
jointing systems or are threaded (as in the case of
casing pipes and plumbing).
It is self evident that it is unwise to use more
that 10 PHR filler for pressure pipes. In
non-pressure pipes a balance has to be made
between the reduction in cost and the deterioration in impact properties which directly
translates to losses due to pipe breakage during
transportation and installation.
In order to to improve the performance of
highly filled PVC pipes, the impact properties
need to be modified. It is in this area that the
practices followed in India are widely different
from China.
Unplasticised PVC
There are two important additives which
enhance unplasticised PVC (UPVC) processing and performance. These need to be studied
in some detail.
August 2012
2. Flow Promoters: They smoothen the flow
of the UPVC melt allowing it to encapsulate
and homogenise the filler particles. The
extrusion of the filled PVC melt improves
and the pipe surface finish is enhanced.
a. Predominantly Acrylic (ACR)
increase. In fact many producers take pride in
the fact that they are able to produce saleable
pipe without the use of these expensive
additives.
It should be noted that smaller producers
who employ single screw extruders for PVC
are forced to use at least the flow promoter to
make acceptable pipes. They were forced to use
single screw extruders as they could not afford
the costlier twin screw technology. Hence they
compromise with a costlier formulation.
Column pipes which have to support heavy
submersible pumps in deep tubewells, is about
the only application where impact modification is resorted to, with nominal filler levels <
10PHR.
The starting torque of the submersible
pumps has to be resisted by a tough pipe,
especially as they are attached by threading,
which weakens the joint as PVC is inherently
notch sensitive.
Highly filled PVC pipes are processed in
India without any impact modifiers and flow
promoters. Even the agri pipe, which is a low
pressure application, has seen high filler
loadings. However it becomes increasingly
difficult to make acceptable pipe at filler
loadings higher than 40PHR, which seems to
be the norm in non branded SWR pipes.
Examples of PVC pipe technology
Technology
Style
Approach
Examples in PVC Pipe technology
Countries following
German
High precision
Automation
High cost
Rugged and robust
machinery
Pioneered twin screw extrusion
Automation
Precision in extrusion
Long life machinery
Switching from lead stabilisation to
lead free systems
Grey is the preferred colour
European countries,
UK
Australia
South Africa
India
Gulf Countries
US
Strong in
manufacturing,
Lags Germany in
technology but
catches up when
newer innovations are
accepted
Persisted with single screw extruders
well into the 1980s while the world
had embraced twin screws
Tin stabilised white pipe is the norm
Conservative with filler loading
Most countries in
North and South
America
Japanese
Precision
instrumentation
and control systems
compensate for
technological
gap with German
technology
Strong in Automation.
Embraced twin screw technology
early.
Parallel screw systems with excellent
controls competed with German
conical screw technology
Comparable capital costs and
machinery life
Lead based stabilisation, but shifting
to non lead
Grey preferred colour
Conservative with filler loading
Japan
Taiwan
South Korea
Chinese
Low cost
Manufacturing
Machinery derived
from German and
Japanese technology,
but of lower cost and
shorter life.
Conical twin screw extrusion seems
to be the norm, though parallel
screws also used
Lead based systems
Very high filler loading in non
pressure pipes
White is the preferred colour
Most aggressive in filler loadings
China
Vietnam
Thailand
Malaysia
Sri Lanka
industrial minerals
47

4. Calcium Carbonate
Main effects on PVC pipe properties as CaCO3 loadings increase
Property
0- 8 PHR
10-50 PHR
50-100 PHR
Density Gms/cc
1.38-1.44
1.45-1.66
1.66-1.84
Formulation Cost, Rs/Kg
`50.08 to `47.19
`46.53 to `37.39
`37.39 to `30.67
Volume Cost Rs/Kg
`69.99 to `68.33
`67.94 to `62.05
`62.05 to `56.21













Impact Strength, Falling Dart.
Breakage in Transportation/
Unaffected
Installation
Tensile Modulus.
Unaffected
Burst Pressure (Hoop Stress_
Unaffected
Rigidity (Flexural Modulus)
Unaffected
Processing Ease
Unaffected
(The dangers of such “mindless filler
loadings” were explained in ‘Volume Cost in
Plastics Applications’ July 2011).
In China, the approach has been quite
different and has spawned its own industrial
sector.
PVC processors in China realised the
problems of using expensive impact modifiers
and flow promoters which were the norm in
Western and Japanese Industries. They started
investigating CPE and results were good. At
3-4 PHR CPE levels, filler loadings could be
boosted substantially and still yield a workable
pipe.
The CPE grades available from DuPont and
Dow were found to be too expensive, and CPE
from local technology gradually found good
acceptance with the pipe manufacturers in
China. Concurrently, flow modifiers were
developed to replace the more expensive
Western counterparts. The locally developed
acrylic flow modifiers were generically known
as ACR. It was quite effective at 1-1.5 PHR
Level.
The Chinese PVC pipe industry has
progressively increased the filler levels from
40PHR to 75 PHR using 3-4 PHR of CPE
and 1-1.5PHR of ACR. The results were
acceptable to the non pressure pipe consumers,
and filler levels were boosted to 100PHR, and
there are reports of even 200PHR being used.
What is lesser known is that it is CPE and
ACR which are making such staggeringly high
filler loadings possible. A lot of research has
gone into this activity and, while this is not in
the public domain yet, use of impact modifiers
and flow promoters seem to be the cornerstone
of the success.
The Chinese PVC pipe industry is huge.
Added to this is the profile and ceiling tile
markets, meaning the CPE and ACR
consumption must be impressive.
Many PVC resin manufacturers now state
that they produce CPE and sometimes ACR
also. Chlorinated PVC uses chlorine as a
feedstock — a major raw material in PVC
48
industrial minerals
plants. So it makes sense for such plants to put
up an auxiliary polyethylene chlorination plant
to support PVC sales.
Non pressure PVC pipes are not only solid
wall — corrugated, two layer corrugated, foam
core PVC pipes and other variants have been
developed where the pipe is lighter than the
equivalent solid walled pipes.
The key feature in the design of such
lightweight pipes is resistance to crushing from
external loads rather than any internal pressure
resistance. Filler levels are not very high in
such applications.
PVC resin
Suspension grade PVC resin can be manufactured from the petrochemicals or non
petrochemical route.
Ethylene obtained by cracking of petroleum
fractions like naphtha, heavy ends and light
ends like c4 gases is the key input. The process
is:
PVC made by this route is termed ePVC
(Ethylene or Petrobased PVC).
PVC is a major plastic which can be and is
manufactured from non petrochemical
sources. Key inputs are two minerals — coal
and limestone — and cheap electricity.
The carbon in coal is reacted with the
calcium carbonate in limestone in an electric
furnace. The calcium carbide then formed is
treated with water to release acetylene, which is
then converted to vinyl chloride by combining
with HCl and polymerised to PVC.
PVC made by this route is known as carbide
based PVC.
The availability of cheap electricity and
abundant coal and limestone is crucial to the
economic viability of carbide based PVC.
China has these inputs in abundance
— about 80% of the PVC capacity in China is
carbide based. This translates to about 9m tpa
of the 11m tpa of China’s installed PVC
capacity. Thus huge quantities of coal and
limestone are consumed.
There are many such producers which are
located close to major chlor-alkali projects and
also near coal, limestone and hydel power
units in the interior of China. Many such units
have their captive coal fed power units if hydel
power is not conveniently available.
The electricity generated is used for the
carbide furnaces as well as the chlor-alkali
plants which produce caustic soda and the
hydrochloric acid gas needed for converting
acetylene to vinyl chloride.
India V China on carbide process
In India, out of the six PVC plants in
operation, only one is based on the carbide
process.
Here also there is a major difference. The
Chinese carbide passed PVC is considered
inferior in quality to ePVC and fetches lower
prices. ePVC is found suitable for all PVC
applications including stringent applications
like clear film, medical tubing and highly
plasticised applications.
The Chinese carbide route PVC is deficient
for such applications. Fortunately carbide
based PVC works for opaque low plasticiser
applications, like PVC pipes and profiles,
which accounts for 70-80% of the PVC
market.
In India, the scene is quite different. The
carbide based plant produces a quality of PVC
resin universally accepted in India as the best
quality PVC, and in many cases fetches a
premium.
The contradiction is puzzling. Perhaps the
Indian plant uses superior technology in
purifying the vinyl chloride and world-class
polymerisation technology to convert it to
PVC?
Perhaps, then, the Chinese carbide PVC
plants could follow the technologies implemented by the Indian unit to upgrade their
quality.
Even with their huge PVC capacity, China is
a net importer of ePVC for critical applications. With the slowing down of construction
and infrastructure projects in China, which
were huge consumers of PVC products, there
is a currently a severe PVC overcapacity in
China.
If China was able to upgrade its carbidebased PVC quality, not only can ePVC
imports stop, but also they would be able to
export to wider PVC markets overseas to tide
over the — hopefully temporary — overcapacity situation.
There is no reason why this cannot be done.
If an Indian plant can produce PVC from
carbide which is superior to ePVC, the
Chinese PVC plants should be able to do the
same if they employ similar technologies.
August 2012