Advanced and Conventional Processing Aids

Energy savings, carbon footprint, pollution, quality, waste reduction and cost savings are essential requirements concerning the plastics industry. Energy savings decrease pollution and fuel consumption, thus saving money and taking care of the environment. Specially molding and extrusion need a high energy for heating, mechanical work, plasticization, pressure increase, and cooling. Energy consumption depends on rheology, temperatures, pressures, outputs of injected or extruded polymers, and wastes. Wastes are the result of molding and extrusion defects such as melt fracture, 'sharkskin', 'flashes', die build up, machine cleanings.

Lowering of raw material viscosities reduces energy consumption due to a lower processing work, and reductions of pressure and & ⁄ or temperature. One way toward these goals is the use of innovative or conventional processing Aids (See Figure 1: 'Processing-Aids') improving the flow behavior, the energy efficiency, the end product quality, the productivity and all parameters contributing to cost savings.

Technical and economical goals aimed by processing aids depend on the used processing methods, for example:

Easier flows
Higher outputs
Energy savings
Melt fracture removal, shark skin reduction or suppression
Surface defect elimination
Better mold filling
Reduction or elimination of gels and optical defects
Lower die build up
Lower processing pressure
Lower processing temperature
Delaying of machine cleanings and reduction of changeover times

Polymer Processing Aids - PPA

Polymer Processing Additives are multipurpose extrusion additives that can be used in a variety of thermoplastic resins including LLDPE, mLLDPE, HDPE, LDPE, EVA, polypropylene, PVC, acrylic, nylon, thermoplastic polyester, polystyrene. Benefits include improved output and energy saving, die build-up reduction, reduced backpressure, melt fracture elimination, gel reduction.

FluoroPolymer Processing Aids

Fluoropolymer Processing Aids such as Daikin DAI-EL, Viton Free Flow and Fluoroguard (DuPont), Dynamar (Dyneon), Kynar Flex® (Arkema), Tecnoflon® NM and Solef® (Solvay Solexis), Cordulen (Nemitz) are added to incompatible polymer matrices at low levels to form a microscopically thin, non-stick film inside the die. This slippery coating reduces friction at the interface between the compound and the die allowing the extrusion to flow freely and more rapidly through the die opening. It also prevents the accumulation of compound particles at the die exit, eliminating the major cause of die build-up. The film deposit isn't immediate but require some minutes and then, the PPA continuously renews it.

Fluoropolymers as Polymer Processing Aid (PPA) Center

DAI-EL™ PPA DA-910

Daikin, has developed a more efficient PPA (DAI-EL™ PPA DA-910), based on a new fluoro-elastomer chemistry. Thanks to its higher efficiency, similar level of performances can now be achieved at lower concentrations (up to 50% lower than a traditional PPA) - without compromising on gels formation and die build up.

DAI-EL™ PPA DA-910 has been specifically designed to reduce the overall system cost of polyolefin conversion, even LLDPE lamination.

It:

Reduces PPA additives cost as lower PPA additive concentrations are needed (up to 50% less). In average, a concentration of 300 ppm is required to reach an optimal set of performance.
Is suitable for highly demanding blown film applications such as lamination and surface protection with no compromise on gel formation and die build-up.
Eliminates melt fracture, die build-up, and then, angel hair and fines in pellets. Therefore, the production of lamination grades and films with much lower risk of optical and surface defects is possible.

Cost-efficiency can be achieved either by providing more flexibility regarding the polyolefin resin selected or through productivity improvements while maintaining high quality of the PE pellets as well as high quality of the film produced through:

Using linear PE resins that are cheaper
Reducing PE resins amount by producing thinner wall films while maintaining equal or better performance
Reducing preventive cleaning maintenance shutdowns
Increasing the production output

Blown film & cast film products: Packaging film, agricultural film, tapes
Wire and cable insulation ⁄ jacketing: Telecommunication, low voltage
Extrusion blow molding: Bottles, drums, tanks
Pipes & tubing: Water and gas high pressure pipe, sewer and drainage pipe, irrigation tubing, conduits
Extruded fibers: Mono-filament for bailing twine, agricultural net sacks, fishing nets and ropes, multifilament

Siloxane or Silicone Masterbatches and Powders

Dow Corning and Multibase commercialize siloxane or silicone masterbatches and powders as PPA. The level of silicone varies from 10 up to 50 % for the masterbatches and powders are 100% active. Used as polymer process aids they increase melt flow for better mold filling, reduced cycle times, and lower extruder torques. They can also ease mold release, modify the surface of finished plastic parts for friction management and improve mar resistance and wear resistance.

The most current thermoplastic matrices are polyethylene (HDPE, LDPE, LLDPE), polypropylene, high impact polystyrene, ABS, SAN, polyacetal, nylon 6, EVA, Hytrel, TPU allowing to enhance processing of PP, Styrenics, Acetals, Styrenics ⁄ PVC, Polyesters, Polyamides, TPU, HDPE, PC, PC Alloys, EVA ⁄ PVC, PP ⁄ TPE, PE ⁄ TPE. The silicone masterbatches are often approved for food contact. In USA, some specific grades are agreed FDA. The silicone dispersed in the raw polymer lubricates it and allows to choose between several possible strategies: reduce the powering energy consumption or lower the plasticization temperature, which reduces the thermal energy consumption.

V.B. JOHN & H. RUBROEDER ( IPST, 28, 3, 2001, p. T ⁄ 1) experiment some extrusion and injection scenarios (see Table 1).

The injection molding experiments show that the length of the spiral injected in a spiral mold increases from 30 to 35 % by addition of 0.3 % of silicone in polypropylene. In addition to improved throughput, extruder torque and pressure reduction, siloxane can have beneficial collateral effects such as improved mold release, lower coefficient of friction, durable scratch and mar resistance, improved wear resistance, improved surface feel, smoother surface.

GENIOPLAST® PELLET S by Wacker is a pelletized silicone gum formulation with a high loading of ultrahigh molecular weight (UHMW) siloxane polymer. It does not contain any thermoplastic resin as a carrier but some quantity of fumed silica instead. It provides general compatibility with thermoplastic resins when used as an additive in thermoplastic systems to impart benefits such as processing improvements and modification of surface characteristics.

When added to thermoplastic resin systems at 0.1% to 1%, improved processing and flow of the resin is expected, including less extruder torque, less extruder die pressure, faster throughput, reduction of melt viscosity and better mold filling. At higher addition levels, 1% to 5%, also improved surface properties are expected, including release, lubrication, slip, improved surface gloss, lower coefficient of friction, and greater mar and abrasion resistance. GENIOPLAST® PELLET S can also improve burning characteristics of thermoplastic resins, especially when applied in combination with halogen-free-flame retardant fillers.

More Conventional PPA

A huge variety of polymers, from conventional waxes up to sophisticated or exotic functionalized polymers can be added to recipes based on another polymer to ease its processing.

Without claiming to be exhaustive, let us quote for example:

Natural or synthetic waxes such as polyolefin Licocene by Clariant that have been used for a long time.
Homopolymers and copolymers of polyolefins, polyethylene or polypropylene, possibly oxidized or functionalized with maleic anhydride and others.
Low molecular weight Polyolefin Plastomers (POPs) can be added to other plastics, thermoplastic olefins (TPOs) or thermoplastic vulcanizates (TPVs) or styrene ethylene butylene styrene (SEBS), to improve their flow properties without reducing impact resistance. In trials concerning TPOs, the addition of 5 to 7% of POP (AFFINITY by Dow) can improve the output by 15%.
EXCEREX by Mitsui Chemicals are polyolefin processing aids based on metallocene catalysis technology. They significantly improve productivity in a number of different areas allowing up to 30% faster processing speeds, temperature decreases up to 30°C and related energy and cost savings.
FUSABOND® AEB-560D by DUPONT is a chemically modified ethylene acrylate copolymer, proposed for cost-effective polyamide modification and improvement of the mold flow.
Liquid rubbers such as polybutadiene, EP(D)M, depolymerized natural rubber (DPNR), butyl rubber
Transpolyoctenamer is used (up to 20phr) in natural rubber, reducing the ML(1+4) at 100°C up to 40% according to the mixing time.
Methyl styrenes are standard processing aids for PVC and also act as impact modifiers.
High molecular weight acrylic copolymers can improve processability of PVC compounds reducing adherence of melt to the processing equipment. They are expected suitable for interior and exterior applications and are applied in several markets such as Packaging and Building and Construction: Exterior trim, PVC pipes, Siding, Window frames and profiles, Fence, deck, rail.

Low Viscosity Engineering Polymers CBT and LCP

CBT® (Cyclics Corp.) has a low melt viscosity, making it a useful additive for melt flow enhancement and uniform dispersion with minimal effect on mechanical properties. Compatible with amorphous, semi-crystalline and crystalline polymers, CBT resin can deliver improved processing performance for PC, polyester thermoplastics (PET, PBT, PCT, etc.), nylons, acetals (POM), polyolefins, polyphenylene ethers, PVC, ABS, SAN, and PMMA. Similar benefits are expected for many blends and elastomers. PolymersNet Co. Ltd. proposes a CBT® resin modified polycarbonate with improved molding properties due to a melt flow increased by 30-50%, or more, while maintaining good mechanical properties. Targeted applications are, for example, portable digital memory cards, mobile phone interior and exterior components, electronics for automotive. Adding CBT resin can also bring advantages in better dispersion of pigments, additives and reinforcements.
LCP such as Vectra A-950, because of its low viscosity at high shear rates, acts as a processing aid for thermoplastic polymers, bringing some unique collateral effects such as stiffness, chemical resistance, and a low coefficient of thermal expansion. So, G.O. Shonaike, S. Yamaguchi, M. Ohta, H. Hamada, Z. Maekawa, M. Nakamichi, W. Kosaka, K. Toi (Polymer Engineering and Science, Feb 15, 1995) use a LCP to reduce or eliminate flash formations during molding of poly(phenylene sulfide) (PPS) S. Bastida1 , J. I. Eguiazábal1 and J. Nazábal1 (Journal of Materials Science, Volume 35, Number 1 ⁄ January 2000, pages 153-158) use a thermotropic liquid-crystalline copolyester, Rodrun LC-5000, to strongly improve the processability of PEI. The tensile strength is maintained up to a LCP content of 5%.

Polymeric Esters Act Also as Processing Aids

Polymeric plasticizers acting also as processing aids are esters of adipic, sebacic or glutaric acid derived from polymeric multifunctional alcohols. They give long chain molecules whose properties can be determined by the choice of the used alcohols. BASF, Hallstar, Genovic and others sell a number of polymer plasticizers that are often used for tubing and foils, and also for food contact packaging thanks to specific grades. Molecular weights can be, for example, in a range from 800 up to more than 8000 versus 390 for the DOP.

Hyperbranched Processing Aids (HBPA)

Y. HONG and ALL (J. Rheol. 43-3, May-June 1999) study the viscosity and the processability of LLDPE modified with 0 up to 10% of various hyperbranched additives. The complex viscosity evolves as displayed by the following figure 3: 'Viscosity-of-Hyperbranched Polymer-Modified-LLDPE'. For both grades of HBPA, the viscosity fast decreases up to 2% of HBPA but is then steady for amounts superior to 5% of HBPA.

Polyhedral Oligosilsesquioxane (POSS)

Polyhedral oligosilsesquioxane (POSS) based hybrid polymers are completely defined molecules of nanoscale dimensions that may be functionalized with reactive groups suitable for the synthesis of new organic-inorganic hybrids. POSS have been successfully incorporated into common polymers via copolymerization, grafting or blending. The syntheses of POSS cages, monomers containing POSS cages, POSS-dendrimer cores, POSS-containing polymers (nanobuilding blocks) and POSS nanocomposites lead to specific properties including mechanical, thermal, flame-retardant and viscoelastic properties.

POSS by Hybrid Plastics are used commercially as flame retardant aids in phenolics (under the tradename Thermalguard), as well as in PPE and COC. POSS have a cage-like shape with an inorganic central core functionalized by organic groups. A key advantage of POSS is the action both as intumescent synergist and as a dispersion aid for halogen-free flame retardants (HFFR), which may allow higher levels of HFFR by improving flow. For example, a lithiated POSS aids dispersion, provides thick intumescent char and mitigates loss of mechanical properties compared to using phosphate FRs alone in thermosets such as vinyl esters.

Takashi Kashiwagi (Flame Retardant Mechanism of the Nanotubes-based Nanocomposites, Final Report, NIST GCR 07-912) quotes some examples of fire retardant efficiency for three different polymers with a POSS addition of 10 or 20% (see Table 2)

Hc = Mean Heat of Combustion; SEA = Specific extinction area (smoke measurement)

Mineral Processing Aids

The addition of a limited amount of glass beads can reduce the viscosity of an epoxy resin by 20%.
Talcs are highly lamellar minerals, which not only facilitates slippage against solid surfaces but also provides an internal lubrication. For example, in injection molding and extrusion formulations, Imerys talcs (www.imerystalc.com/) are claimed to provide:

Lower compound viscosities improving mold flow
Reduce mixing time by up to 20%
Improve extrusion rates and surface finish
Minimize wear of processing equipment such as extruder screws and dies

Spherical amorphous silicas can reduce cycle time and plate-out, saving time and money.

For example:

Sidistar by Elkem gives remarkable advantages in WPC compounds. Due to its particle shape and size, the additive functions as a viscosity modifier "ball bearing effect". This improves the processing behavior of the WPC and considerable gains in extrusion speed can be obtained. By using SIDISTAR® the aesthetic quality of WPC extrudate can be improved. Nanosil ASD (http://nanosilasd.com/) is claimed reducing the injection molding cycle time by 30 % to 40 % for most plastics resins like PP, PE, nylons, PBT, PC, LCP, PEEK, and Rigid PVC. It reduces the flow lines and weld lines and improves the overall dimensional stability of the molded parts.

For example, ChipCoolers uses a small percentage of boron nitride to improve the flow characteristics of its heat dissipative compound based on silicone and silver.

Conclusion

Processing Aids improve the flow behavior, the energy efficiency, the end product quality, and the productivity contributing to solve the main technical, economical and environmental requirements concerning the plastics industry: cost savings, carbon footprint, pollution, energy savings, and waste reduction. Innovative PPAs are new and developing ways using Fluoropolymers, Siloxane or silicone masterbatches or powders, low viscosity polymers such as CBT or LCP and others, Hyperbranched processing aids (HBPAs), POSS, polymeric esters. Conventional PPAs have been used for a very long time, including among others Polyethylene waxes, Modified polyethylenes, Polypropylenes, Metallocene polyolefins, Liquid polymers.

Mineral Processing Aids facilitate slippage against solid surfaces and provide an internal lubrication, improved mold flows, reduced mixing times, enhanced extrusion rates and surface finish, lower wear of processing equipment such as extruder screws and dies. Targeted goals depend on the used processing methods, for example easier flows, higher outputs, energy savings, melt fracture removal, shark skin reduction or suppression, surface defect elimination, better mold filling, reduction or elimination of gels and optical defects, lower die build up, lower processing pressure, lower processing temperature, delaying of machine cleanings and reduction of changeover times. Polymer and Mineral Processing Aids are not easily removable and, very often have interesting collateral effects among ease of release, lower friction coefficients, plasticizing effects or impact enhancement.

Technical books and guides, papers, websites: 3M, Akrochem, Akzo, Arkema, Axel Plastics, Baerlocher, BASF, Bayer, BP, BYK, Chemax, Chemplast, Chemtura, Ciba, Clariant, COMAIP, Crompton, Cyclics Corp., Daikin, Degussa, Dow, Dow Corning, DSM, DuPont, DuPont Performance Elastomers, Dyneon, Elkem, Evonik, Ferro Corp, Flow Polymers, GE, Genovic, Hallstar, Honeywell, Hybrid Plastics, Imerys Talc, Lanxess, Mitsui Chemicals, Multibase, Nan-O-Sil, Nemitz, Phoenix Plastics, PolymersNet, PolyOne, Repol, Röhm GmbH, Saint Gobain Advanced Ceramics, Sartomer, Solvay Solexis, SpecialChem, Struktol Co, Ticona, Wacker Chemie, Additives & Compounding J. STANSFIELD (ANTEC 2006, Charlotte, p 428) NAGAMATSU T. and ALL (ANTEC 2006, Charlotte, 2006, p. 1062) MALTBY (Additives & Compounding, Vol 7, n°6, 2005, p.28) SUMITOMO (Model Change of Main Hydraulic Type Molding Machines "FN Series" March 2005). LEWAN M. and ALL (Plastics, Rubbers and Composites, Vol 33, n°4, 2004, p. 177) DAWSON A.J. and ALL (Antec 2002, p. 576) V.B. JOHN & H. RUBROEDER ( IPST, 28, 3, 2001, p. T/1) S. BASTIDA1 , J. I. EGUIAZ?BAL1 AND J. NAZÁBAL1 (Journal of Materials Science, Volume 35, Number 1 ⁄ January 2000, pages 153-158) N.DHARMARAJAN and ALL. (ACS Rubber Division, October 2000, paper 33) BEAM Services (ICE '99, Cincinnati, May 1999) Y. HONG and ALL (J. Rheol. 43-3, May-June 1999) TED JOHNSON (ACS, Rubber Division, Sept 1998, paper 12) YAMAGUCHI, M. OHTA, H. HAMADA, Z. MAEKAWA, M. NAKAMICHI, W. KOSAKA, K. TOI (Polymer Engineering and Science, Feb 15, 1995)