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Polyamide 6 can be produced by anionic ring-opening polymerization of ε-caprolactam using e. g. sodium-caprolactamate as a catalyst. One of the best known anionically polymerized polyamide 6 is so called cast polyamide 6, used for particularly stressed parts. The reason for its good mechanical properties is the comparably high molecular weight. When using cast polyamide 6 for extrusion or injection molding, its high molecular weight can be a disadvantage due to its very high viscosity. To enhance processability, the flow behavior of these materials has to be adjusted. Besides the use of a lubricant, shorter chains would be another way to achieve better processability. In this work, the latter is performed by compounding anionically polymerized cast polyamide 6 using a chain scissorer, e. g. terephthalic acid. Compounding of dry-blends made of cast polyamide 6 and said terephthalic acid is done on a twin-screw extruder type ZSK 26MC of Coperion, Stuttgart. Mechanical properties and flow behavior were investigated afterwards. Surprisingly, it could be shown, that adding very small amounts of terephthalic acid did not reduce but raise viscosity significantly. However, higher amounts of terephthalic acid reduce these viscosities, as expected. Additionally, a reduction of viscosity can be seen over time, because remaining ingredients seem to still be active. Mechanical properties such as Young’s modulus or tensile strength are not affected by adding terephthalic acid and are comparable to those of injection molding polyamide 6. Solely impact strength was slightly reduced, when a larger amount of terephthalic acid was added. [ABSTRACT FROM AUTHOR]

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]