Low-temperature processing of ‘baroplastics’ by pressure-induced flow

Abstract

The manufacturing of plastics traditionally involves melt processing at temperatures typically greater than 200 °C—to enable extrusion or moulding under pressure into desired forms—followed by solidification. This process consumes energy and can cause substantial degradation of polymers and additives (such as flame retardants and ultraviolet stabilizers), limiting plastics performance and recyclability¹. It was recently reported that the application of pressure could induce melt-like behaviour in the block copolymer polystyrene-block-poly(n-butyl methacrylate) (PS-b-PBMA)², and this behaviour has now been demonstrated in a range of other block copolymer systems^3,4,5,6,7,8. These polymers have been termed baroplastics^2,3,4,5. However, in each case, the order-to-disorder transition, which gives rise to the accompanying change in rheology from soft solid to melt^9,10, was observed at temperatures far exceeding the glass transition temperatures (T_g) of both components. Here we show that baroplastic systems containing nanophase domains of one high-T_g and one low-T_g component can exhibit melt-like flow under pressure at ambient temperature through an apparent semi-solid partial mixing mechanism that substantially preserves the high-T_g phase. These systems were shredded and remoulded ten times with no evident property degradation. Baroplastics with low-temperature formability promise lower energy consumption in manufacture and processing, reduced use of additives, faster production and improved recyclability, and also provide potential alternatives to current thermoplastic elastomers, rubber-modified plastics, and semi-crystalline polymers^11,12.