COMPATIBILISERS | ADDITIVES
Helping plastics come together
Whether to manage mixed waste streams or to develop innovative polymer blends, compatibilisation is set to be a key future technology. Peter Mapleston reports
As the circular economy takes form, the need to increase the value of recycled plastics will intensify. Ideally, of course, materials will be separated into perfect streams of single polymer types; reality is likely to be quite different – mixed streams will be the norm. Compatibilisers could help extract the full potential of these streams, making it possible to obtain good performance from engineering plastics contaminated with commodities, and from mixtures of polar and non-polar polymers. They can also play an important role in the creation of blends of virgin polymers, helping compounders create blends that are tailor-made for specific applications. This article reviews some of the latest developments in the field.
Copolyolefins score Block and graft copolymers that have polar and non-polar sections are well-established as compati- bilising agents for otherwise immiscible polymer blends. The advantage of such “amphiphilic” copolymers compared to low molar mass additives is the achievement of entanglements of the compatibiliser with the blend components on both sides of the interface. This results in improved mechanical strength, says Dr Rudolf Pfaendner,
www.plasticsrecyclingworld.com
Director of the Plastics Division at Fraunhofer LBF (Structural Durability and System Reliability). Pfaendner says Fraunhofer LBF continues to develop its versatile toolbox for the compatibilisa- tion of polymer blends based on amphiphilic block and graft copolymers to address new compatibilis- ing issues. “LBF is specialised in the synthesis of block copolymers where a direct access to block copolymers via typical processes such as living ionic or controlled radical polymerisations is impossible,” he says. An example is the preparation of polyolefin block copolymers to improve the compatibility of various polyolefins to other blend partners. Since polyolefins cannot be prepared by living and controlled techniques, LBF uses a two-step strategy. Polybutadiene block copolymers are prepared and then hydrogenated to create compatibility to the respective polyolefin. “Chang- ing the reaction conditions during anionic butadi- ene polymerisation, a compatibility to all common polyolefins (PE-HD, -LD ,-LLD, PP, POE) can be achieved,” he says. Combining different polymeri- sation and coupling techniques enables the compatibilisation of unusual blend compositions and recyclates.
Main image: Realising the circular
economy will likely mean dealing with mixed polymer streams. Compatibilisa- tion could help manage that challenge
� May/June 2018 | PLASTICS RECYCLING WORLD 47
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