Technical Papers Plastics
Volume Cost and its importance in Plastic applications: Part 3. Filled Polyolefins, Recent scenario

Volume Cost and its importance in Plastic applications: Part 3. Filled Polyolefins, Recent scenario

This is a continuation on the articles on Volume Cost. I must admit that I have a lot more practical experience with Filled PVC as compared to filled Polyolefins, so my article on Polyolefins was based on theoretical considerations. I had requested feedback as to whether the conclusions drawn are actually reflected in practice. I have written this particular article on the basis of these feedbacks. The conclusions I had drawn for fillers in Polyolefin were:
1. Injection Moulding: The use of mineral filled injection moulded polyolefins would primarily be where physicals like stiffness, flexural modulus and HDT need improvement. Cost reduction is not possible as the volume cost increases with filled compounds, and nearly all mouldings are sold by volume. Higher density of fillers and high compounding costs are detrimental to cost reduction by filler addition.
2. Raffia Tape: Raffia tape industry centres around the Denier of the tape and denier is Linear Density. Thus unlike in mouldings, if density goes up, so does denier. Thus reduction of denier by adjusting tapegeometry opens up cost reduction avenues.
3. Pipes & Films: These are also effectively sold by volume (Pipe length of specified thickness, meters of specified guage and width). Filler addition would not lead to lower costs.
However, I find that quite recently, there has been a lot of activity in filler addition in various types of blown film. As this is in variance with the theoretical findings in my studies, it warranted a closer look. My cost workings which show the effect of density vis a vis costs have two other factors which can vary with time, Raw material prices and compounding costs. I have tried to track the recent changes in these parameters and re-examined my findings in the light of:
• Higher Polymer prices
• Lower Filler (GCC) prices
• Lower Compounding costs
Some portions of the previous article are reproduced for first time readers.

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 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.
While it would look that UPVC at ~ `50/kg is by far the cheapest Polymer, the natural question is that why does it have such limited applications in, say moulded products? The answer lies in Volume Cost. Combining price with density the Volume costs in Rs/Ltr. is
Prices v/s Volume Cost
Clearly the Polyelefins are cheaper than PVC on Volume cost basis, and is the preferred materials for many mouldings. The Volume cost advantage of PP can be vitiated when it is compounded with Mineral fillers as explained below.
Polymer prices keep on fluctuating and have been particularly volatile lately. PP for example has soared from Rs 68/Kg shown in Chart 1 to around Rs 90/kg in May 2011. This is driven by a worldwide shortage of Propylene as well as rising crude prices. HDPE prices however have been more stable and has risen by only a few Rs/kg as compared to over Rs 20/Kg for PP. It appears that the demand supply balance for Ethylene is nowhere as adverse as for Propylene. A figure of Rs 90/Kg has been assumed for PP while no change is made for HDPE Prices.
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 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 good quality pipe with 2nd 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�(Strong). Physical properties are seriously compromised in Plastic 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 additional 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:
• If the Polymer is in liquid form, it is fairly 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 (pastes) where large quantities of low quality Ground CaCO3 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.
• If the Polymer is in Powder form, like PVC 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.
• If the Polymer is in granule form, 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.
In my previous study I had assumed that the compounding cost for filled compounds was Rs 15/kg. This is the ballpark figure I got from leading compounders when I was the R&D Chief at VIP Industries. Since 2004, when I retired, Compounding capacity has increased dramatically and so has competition. I was advised that currently a figure of Rs 10/kg was more reflective of the Industry norms for good quality compounding of fillers using modern high efficiency twin screw compounders.

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, Polyolefins are non polar, requiring more energy to encapsulate the polar fillers Compounding costs for filling Polyolefins can be as high as Rs 10-15/ kg., (US$220-330/MT) with the lower figure more prevalent when economics of scale with high capacity compounding equipments are dominant.
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 40%, 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 Polyolefins with Filler masterbatches exceeding these levels. I make this distinction because referring to PHR in PVC compounds as % is a common mistake.

Mineral Fillers used in Polyolefins:
Many mineral fillers have been tried, but the most common are Talc and CaCO3. I am not including Glass Fibres and other exotic fillers like Carbon Fibers or Nano Clays which are costlier than the polymer and are performance boosters.
Calcium Carbonate: Probably the cheapest Mineral Filler, it is used by the Plastic industry in two forms:
• Ground Calcium Carbonate (GCC)- The mined CaCO3 is pulverized and classified into different particle sizes. Purity is very much dependant on the Limestone source. Marble gives the purest GCC but is costlier. In India prices range from as low as ` 3/kg. and can go up to Rs 12.50/ kg. (US$80-250/MT). GCC can also be coated by stearates and other additives which reduces surface tension between polymer melt and Filler particle, making homogenization easier. These are costlier, with some of the speciality grades from International companies like Omya andSolvay going upto Rs 22.50-27/kg. (US$500-600/MT.)
• Precipitated Calcium Carbonate (PCC) - Calcium oxide is prepared by calcining the mined calcium carbonate. Water is added to give calcium hydroxide (milk of lime). Insolubles can be separated and the milk of lime carbonated with the CO2 obtained during calcinations. The carbon dioxide precipitates the desired calcium carbonate from the milk of lime, is filtered, dried and pulverized. PCC is purer and less abrasive to processing machinery but costlier than GCC of equivalent particle size. Uncoated PCC prices range from Rs 9 � 13.50/kg. (US$250-300/MT) while Coated PCC would be about Re 1/kg more.
A PCC grade of about Rs 10/kg was used for the previous calculations. Nowadays acceptable GCC grades are available and many compounders have switched over to it. For the current exercise a GCC of Rs 8/kg is used
Let us have a closer look at CaCO3 filled PP & HDPE.
Mineral Filled PPCo & HDPE Applications
• The high volume Filled PP applications are:
     o Automotive Bumpers, Dashboards, and Components
     o Talc is the main filler, supported with smaller quantities of Calcium Carbonate. Compatible rubbers are often added to boost impact strength.
• Moulded Furniture
     o Precipitated or Ground Calcium Carbonate is the main filler.
• Raffia Tape
     o Precipitated or Ground Calcium Carbonate is the main filler. Both PP Homopolymer and HDPE are mixed with Filler masterbatches for the convenience and cost benefits.
• Low Cost Films
     o Talc is the preferred filler as it has least effect on translucency. GCC is also widely used for transluscent films. Fillers have been tried with PP, but activities are more in the HDPE sector as the films are translucent/opaque as compared to PP and LLDPE films.
• The rationale for mineral filled PP and HDPE is more for improving physical properties rather than cost reduction (with an important exception which we will discuss later).
• In PP, CaCO3, Talc, and other mineral fillers improve stiffness and improve paintability.
• In HDPE & PP, CaCO3 is extensively used as an antifibrillating agent for Raffia Tapes.
• PP/LDPE/LLDPE are normally not filled as transparency and film blowing performance are badly affected.

Effect of Fillers in PP-Copolymer (Compounding Costs Rs 10/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 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.
Calcium Carbonate filled PP CoPolymer May 2011(PP: Rs. 90/kg, Filler Rs. 8/kg. Compounding Cost Rs.10/Kg)
    10% Filled 20% Filled 30% Filled
Ingredient Price Rs. /Kg Density Kg/Ltr. Kgs. Cost Rs. Volume Ltr PHR Kgs. Cost Rs. Volume Ltr. PHR Kgs. Cost Rs. Volume Ltr.
PP Copolymer 90 0.905 90.0 Rs.8,100 99.45 80 Rs.7,200 88.40 70 Rs.6,300 77.35
Filler 8 2.7 90.0 Rs.80 3.70 20 Rs.160 7.41 30 Rs.240 11.11
Additives 150 0.95 0.3 Rs.45 0.32 0.3 Rs.45 0.32 0.4 Rs.60 0.42
Compounding costs 10 Per Kg   Rs.1,003     Rs.1,003     Rs.1,004  
Totals     100.3 Rs.9,228 103.47 100.3 Rs.8,408 96.12 100.4 Rs.7,604 88.88
Compound Cost       Rs.92.00 Density   Rs.83.83 Density   Rs.75.74 Density
Volume Costs       Rs.89.19 0.969   Rs.87.47 1.043   Rs.85.55 1.130
    40% Filled 50% Filled 60% Filled
Ingredient Price Rs. /Kg Density Kg/Ltr. Kgs. Cost Rs. Volume Ltr. PHR Kgs. Cost Rs. Volume Ltr. PHR Kgs. Cost Rs. Volume Ltr.
PP Copolymer 90 0.905 60.0 Rs.5,400 66.30 50 Rs.4,500 55.25 40 Rs.3,600 44.20
Filler 8 2.7 40.0 Rs.320 14.81 50 Rs.400 18.52 60 Rs.480 22.22
Additives 150 0.95 0.4 Rs.60 0.42 0.6 Rs.90 0.63 0.6 Rs.90 0.63
Compounding costs 10 Per Kg   Rs.1,004     Rs.1,006     Rs.1,006  
Totals     100.4 Rs.6,784 81.53 100.6 Rs.5,996 74.40 100.6 Rs.5,176 67.05
Compound Cost       Rs.67.57 Density   Rs.59.60 Density   Rs.51.45 Density
Volume Costs       Rs.83.20 1.231   Rs.80.59 1.352   Rs.77.19 1.500
    70% Filled 80% Filled 90% Filled
Ingredient Price Rs. /Kg Density Kg/Ltr. Kgs. Cost Rs. Volume Ltr. PHR Kgs. Cost Rs. Volume Ltr. PHR Kgs. Cost Rs. Volume Ltr.
PP Copolymer 90 0.905 30.0 Rs.2,700 33.15 20 Rs.1,800 22.10 10 Rs.900 11.05
Filler 8 2.7 70.0 Rs.560 25.93 80 Rs.640 29.63 90 Rs.720 33.33
Additives 150 0.95 0.7 Rs.105 0.74 0.8 Rs.120 0.84 1 Rs.150 1.05
Compounding costs 10 Per Kg   Rs.1,007     Rs.1,008     Rs.1,010  
Totals     100.7 Rs.4,372 59.81 100.8 Rs.3,568 52.57 101 Rs.2,780 45.44
Compound Cost       Rs.43.42 Density   Rs.35.40 Density   Rs.27.52 Density
Volume Costs       Rs.73.10 1.684   Rs.67.87 1.917   Rs.61.19 2.223

The graphical representation of the calculations are shown in Chart 2,

• Assuming that Rs 10 a Kg is the Compounding cost, at a level of approx 15% filler does the cost of Compound dip below the raw PPCO price (Rs 90/Kg). When the business margins of the compounder is included, it is only at the 20-25% Filler level that the Purchase price of a Filled PPCo compound will come below base polymer price.
• The rate of decrease of Volume Cost is a lot slower, and only at 50% Filler levels, the Volume cost reduces to the base polymer level.
• This means that for all moulded (or Extruded PP Products which are sold per piece (i.e. by volume), purchased filled PP Compounds (normally 10-40% filler) will not lower costs. They should only be used for value addition like better stiffness, paintability etc. This is a very sweeping statement and seems to be borne out in practice.
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 Injection Moulding machine/Extruder.
As an illustration let us assume that the cost of a Filler Masterbatch is as in Table 1, 80% loading or around Rs 36/Kg. 80% is a very high loading but I have used it to illustrate the maximum cost reduction potential:

Cost Reduction with Filler Masterbatch. (70% Filled with CaCO3)
Cost of Bought in Filled PPCo
(see Table 1)

• Though Density remains the same, Volume cost improvement vis a vis bought in Compound is higher, Rs 7.87 and Rs 6.99 respectively, but Filler masterbatch addition does not bring down the Volume cost to below Unfilled PPCo (81.45 Rs/Ltr).
• 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).
• While Filler Masterbatches is a good way to reduce costs, the volume costs stay higher than unfilled PP.
• Even at 50% Filler, Compound Volume cost does not go below Unfilled PPCo (81.45 Rs/Ltr)
• In Moulded Furniture, Cost per chair is unlikely to reduce by increasing Filler Loadings.
• Resistance to deflection (Stiffness) improves with Filler Loading.
• Reduction in Impact strength has to be balanced with required stiffness to arrive at optimum filler loading for a particular Moulded Furniture Model.
    o Rigorous evaluation with blends of PP Co, PP Homo, 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.
• These observations should hold true for all moulded products in PP and HDPE. The use of Mineral Filled injection moulded polyolefins would primarily be where physicals like Stiffness, Flexural Modulus and HDT need improvement.

Mineral Filled HDPE applications: Raffia Tape
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 a Raffia Tape manufacturer 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 Raw Material 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 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:
• Tape Denier. These are around 1000-1200 and is much higher than synthetic Yarn Deniers
• Warp & Weft: No. of tapes per inch/cm. used in the ends and picks.
• Weight of the bag.
Denier & dtex- Definitions from Wikipedia.
• Denier is a unit of measure for the linear 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.
• dtex: In the International System of Units 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".
• The most commonly used unit is actually the decatex, abbreviated dtex, which is the mass in grams per 10,000 meters This comes fairly close to the denier definition.
How Filler addition affects Tape Denier
How Filler addition affects 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:
• Reducing Tape Thickness
• Reducing Tape Width
• 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%.

Filler Masterbatch addition
Filler Masterbatches are extensively used by the Raffia Industry with bought in filled compound being a rarity. 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, ` 10/Kg. HDPE prices have not increased as dramatically as PP and a price of Rs 70/kg is assumed. A GCC costing ` 8/Kg is used.

Calcium Carbonate filled PP CoPolymer May 2011(PP: Rs. 90/kg, Filler Rs. 8/kg. Compounding Cost Rs.10/Kg)
      25% Filler Masterbatch 40% Filler Masterbatch 50% Filler Masterbatch
Ingredient Price
Density Kg/Ltr. Kgs. Cost Rs Volume Ltr. PHR Kgs. Cost Rs. Volume Ltr. PHR Kgs. Cost Rs Volume Ltr.
HDPE 70 0.96 75.0 .5,250 78.13 60 .4,200 62.50 50 3,500 52.08
Filler Masterbatch Rs. 44.008 1.559 25.0 1,100 16.03 40 1,760 25.66 50 2,200 32.07
Effective Filler Level     100.0 15.00%     24.00%     30.00%  
Totals     100.7 6.350.00 94.16 100 5,960.24 88.16 100 5,700.30 84.15
Blended Cost Rs/kg       63.50 Density   59.60 Density   .57.00 Density
Volume Costs Rs/ltr       67.44 1.062   67.35 1.130   67.74 1.118
Increase in Density 10.63% 17.71% 23.78%

• While Volume costs are still higher than unfilled HDPE (67.2 Rs/Ltr.), costs are saved as less Volume of material per bag is needed.
• As costs keep on decreasing with addition of filler, caution is advised not to overdo the loading.

What is the Optimum Filler Loading in Raffia.
• Unlike 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.
• Care should be taken not to disturb the MFI chosen by high levels of Filler Masterbatch.
• Filler addition levels for a particular application should be self regulatory.

Self Regulatory considerations.
• The performance requirements of 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.
• Filler Masterbatch levels should be carefully experimented with to find the optimum %.
• Ash tests similar to BIS-4985 could be formulated for critical applications like Bulk Sacks/ Jumbo Bags.

Summary for Raffia
• The previous calculations and findings are equally true for PP Raffia. Similar considerations are valid when Talc or combinations of Talc & CaCO3 are used.
• These studies are theoretical and follow 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. Only if Compounding costs come down drastically and cheaper GCC is used is there any chance of Volume costs of Filled PP/HDPE to be lower than the base Polymer
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 Rs/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 Plasticised PVC, the filler is already well dispersed in the High 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 Ko-Kneaders.
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 Rs 6-7/kg (US$130-150/MT). 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 stabilizers to compensate for degradation. With Compounding costs on modern twin Screw lines dipping to Rs 10/kg, it does not seem worthwhile to base a filler masterbatch unit on single screw extruders just for another Rs.3-4 /kg reduction. Perhaps the driving force with smaller entrepreneurs is the lower capital costs of Single screw lines.
Even with higher Polymer prices, lower Filler and Compounding costs, according to the calculations in Table -5 the volume cost are still not favorable as compared to unfilled polymer. There is an increasing trend for using Talc filled filler masterbatches for HDPE and even LLDPE Blown film and it is difficult to understand why this is happening.
I am convinced that if the Film or the bags made thereof are sold by Volume, filler addition would not reduce costs, even at higher Polymer and lower Filler prices. 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 fact that the filled compound he is extruding is of a lower cost in Rs/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.
(Source Courtsey: Siddhartha Roy, Consultant, RoyPlasTech)
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Complete film converting lamination unit

Complete film converting lamination unit