Recycling of Cast Polyamide 6 Using a Lubricant.

Cast polyamide 6 is a high-quality material due to its long polymer chains. Because of sprues and post-processing, a comparably large amount of the produced material, up to 30 %, becomes waste. Until today, this high-quality waste is burned or added into standard virgin polyamide 6 raising its molecular weight. Instead of using cast polyamide waste as an additive or combustion material, it would be beneficial to process high-molecular weight recyclates made of this cast polyamide 6. To enhance its processability, using a lubricant as a processing additive is a reasonable approach. Our previous findings within this field revealed an unusual behavior of a lubricant consisting of a polyester modified wax, which is already used for standard polyamide 6 without known problems. In this work, milled cast polyamide 6 chips obtained from machining are washed and dried and then used for producing high-molecular weight recyclates. In literature the deposition of such waste is recommended because of pollution and contaminations. It is hence possible to get clean material for recycling. The recycling step itself is performed on a twin-screw extruder type ZSK 26MC of Coperion, Stuttgart, by processing a dry-blend of cast polyamide and said lubricant. Rheological measurements show increasing complex viscosities of recyclates depending on the lubricant’s content. It is possible to achieve viscosities higher than those of the solely processed polyamide recyclate. Even the viscosity of unprocessed cast polyamide 6 can be reached. Compared to virgin extrusion polyamide 6, the processed recyclates achieve higher tensile strengths, while an increasing amount of lubricant does neither affect Young’s modulus nor tensile strength. It is also shown that the lubricant raises impact strength significantly. [ABSTRACT FROM AUTHOR]