STRETCH & SHRINK FILM | MATERIALS
Added benefit Meanwhile,Wells Performance Materials has developed PFAS-free polymer processing aids for use in stretch and shrink film production. The additives help eliminate melt fracture and die build-up, for a smoother, higher-gloss surface finish – allowing higher production speed and output, and lower energy consumption. Fluoropolymers have an affinity for metal
surfaces, incompatibility with other polymers, high melting point and thermal resistance – so finding a replacement is difficult. However, Wells says it has created a range of PFAS-free process aid master- batches with similar melt fracture elimination as traditional fluoropolymer equivalents. Its latest generation, PA96965, was developed for metallocene polymers and blends with conven- tional polyethylene and has proved effective at removing melt fracture. At standard addition rates, melt fracture from metallocene and metallocene blends can be efficiently removed, said Wells.
Stable performance At the earlier North American version of the
conference, Shawn Cook – sales manager for plastics additives at Dover Chemical – explained how stabilisers can improve sustainability. While stretch and shrink films are using more
recyclate, it can come with problems: a need to upgauge (meaning more virgin resin); more die build-up; and higher wear – plus the possibility of more gels,
“Gels can be caused by contamination,” he said. “Good filtration and production practices can prevent these types. Others are cross-linked resin – typically created due to under-stabilisation or excessive heat. Once a gel is created, nothing can undo it.” In response, Dover has developed LGP-12 liquid
green phosphite as a liquid alternative to other phosphites that have toxicity or environmental concerns. It is not derived from alkylphenols, has a high phosphorus content (7.3%) and is highly soluble in polyolefin systems (up to 10%). Other properties include lubricity, metal chelating and low-temperature peroxide scavenging. LGP-12 is typically introduced before regranula-
tion. Adding it during or after extrusion is too late – because gel formation will already have happened. �
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