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ADDITIVES | PROCESSING AIDS


in the reduction of migration. When plasticising lubrication is sought, POSS additives bearing long groups like i-octyl or i-butyl are desirable. These POSS are highly thermally stable and not subject to depolymerisation and volatilisation.” Lichtenhan says a number of mechanisms have been put forward to explain the effect of the POSS additives on flow, based on Einstein sub-rheology and the effect of weak forces – Van der Waals or London forces - between the POSS cages and polymer chain “Perhaps a simpler explanation is that POSS cages melt during compounding. In the molten state the cages act as low viscosity liquids and thus provide a reduction in extrusion torque and viscosity during processing. Upon cooling the POSS cages and the polymer re-solidify. The solidification of POSS is highly advantageous as it does not result in post processing plasticisation,” he says. Future POSS developments will exploit the


effects from combining chemical compatibility with


surface area and volume control, resulting in significant viscosity reductions and enhanced dispersion effects for particle loaded polymer formulations, according to Lichtenhan.


Alternative approach Meanwhile, Dover Chemical Corporation has developed a new approach for polymer processing improvement with the introduction of its new polymeric liquid phosphite stabiliser, Doverphos LGP-11. The company says that it offers a variety of advantages compared to other phosphites, such as trisnonylphenyl phosphite (TNPP). [Within the EU, TNPP is under consideration for addition to the REACH SVHC list over concerns that it may display endocrine disrupting properties.] Doverphos LGP-11 is claimed to improve colour stability during processing and NOx


gas fading. It


also offers a reduction of plate-out on processing equipment and elimination of surface bloom or exudation in the final product, does not contain any alkylphenols and is said to greatly reduce migration into food from plastic containers. Dover says fluoroelastomers are commonly used as polymeric process aids (PPAs) in polyolefin applications. “They offer several benefits, such as the reduction of melt fracture during blown film processing. Many of the common commercially available PPAs also include an interfacial agent or synergist that improves the general performance. These are often low molecular weight polymers, such as polyethylene glycol [PEG],” according to Trisha McNutt, Product Manager at the company. “Due to the polymeric nature of Doverphos


Figure 7: Improvement in time to clear melt fracture for LLDPE containing TNPP compared with Doverphos LGP-11 stabiliser and processing aid Source: Dover Chemical


LGP-11, it can also replace PEG as a synergist in PPAs and offers enhanced benefits such as reduced pressure during melt extrusion. In various LLDPE studies, Doverphos LGP-11 has shown the potential to reduce melt fracture using lower levels of PPA, improve processing throughput, allow lower processing temperature and improve overall thermal stability. These benefits can be realised by simply replacing commonly used solid or liquid phosphites with Doverphos LGP-11. In addition, Doverphos LGP-11 can also be added separately to the formulation through the use of an antioxidant or PPA solid masterbatch,” McNutt says. Doverphos LGP-11 also has FDA clearance for use in indirect food contact applications such as LLDPE, HDPE, PP, HIPS and adhesives.


Figure 8: Pressure reduction effect of Doverphos LGP-11 compared to solid phosphite stabiliser in metallocene LLDPE Source: Dover Chemical


70 COMPOUNDING WORLD | April 2019


Targeting friction Recent developments from Axel Plastics Research Laboratories include a process aid additive with reduced coefficient of friction. TD INT-33LSER is a


www.compoundingworld.com


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