MATERIALS | POLYOLEFIN ADDITIVES
Figure 1: Total gel count in PE film containing 30% PCR and PIR recyclate streams showing the impact of Doverphos LGP-12 Source: Dover Chemical Corporation
thinking about specific additives used further downstream from the resin manufacturers. Dover highlights two current problems in
antioxidant technology (both regulatory driven) that require solutions — the emphasis on increasing recycled content in all polymer streams and finding suitable replacements for fluoropolymers (PFAS). “For recycled streams, the technical challenge is to produce an article that has high recyclate content but with the same performance as when using 100% virgin materials,” said Cook.
Recycling challenge “In some cases, the answer is just to use more polymer overall. That is certainly counter to the spirit of using recycled content. No company wants to use more material to make the same articles, but that is the current means to address the issue. I believe the solution lies in engagement throughout the entire system, with collaboration between resin manufacturers, additive suppliers, article producers and recycling companies,” he said. “For PFAS replacements, it is currently a bit of a
‘Wild West’ situation. There is an industry-wide standard that is soon to be banned with no real viable alternative. Existing solutions are temporary at best, or they would already be used, and new solutions will have to undergo considerable scrutiny. After all, no company wants to commer- cialise a product and go through lengthy and expensive approvals only to have to repeat the process in a few years. Any solution has to work and be future-proofed,” Cook said. Dover claims it has solutions for these problems, most based on its Doverphos LGP-12 phosphite antioxidant. The company says LGP-12 was designed to be high-performance while minimising
14 FILM & SHEET EXTRUSION | December 2023
current and predicted future regulatory concerns. As an antioxidant, it can help to stabilise recycling streams in-situ to make a higher quality recycled resin, it says. The use of post-consumer resin (PCR) and post-industrial resin (PIR) in film production often means that recycled streams are of a lower quality than virgin resin, it says. Gels — visual or structural defects in the film — can have a detrimental impact on elongation strength, leading to premature tearing. They can arise from contamination caused by water and debris, as well as cross-linked resins, typically arising from inadequate stabilisation and/ or excessive heat. During re-granulation, PCR and PIR exhibit insufficient stabilisation, leading to excessive gel formation that reduces tear and elongation strength of the film. Doverphos LGP-12, which has an alkylphenol-
free composition and is produced from bio- sourced raw materials, can ease gel problems (Figure 1). It is compatible with thermoplastic resins, reduces additive migration and eliminates plate-out and blooming of the phosphite. Intro- duced during PCR re-granulation, the company says LGP-12 scavenges free radicals generated during the thermal degradation of polymers, preventing gel formation and other degradation byproducts. It can also help preserve the melt flow index of the resin, leading to comprehensive stabilisation and smoother processing. A secondary property of LGP-12 is its metal
affinity and fast film formation as a polymeric liquid. Dover says it has been able to enhance this inherent property into a suitable replacement for fluoropolymers used as processing aids in the polymeric film industry, under the tradename of DoverClear.
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