Comparison of fiber‐reinforced recycled polyamide in single stage and two stage injection molding

Climate change and a growing energy demand drive the development of lightweight construction in the automotive industry. The recent focus of interest is on glass and carbon fiber‐reinforced plastics. A resulting increase of production waste and scrap parts requires an efficient recycling. Although thermoplastics are generally suitable for reprocessing, recycled polyamides like PA6 show differing mechanical properties in comparison to virgin material due to molecular degradation processes. To achieve a high recycling rate and to compensate for the reduced mechanical properties, the parts of the test series of this study are filled with glass fibers (20 and 30 wt%). To increase the mechanical properties even further, a single‐stage injection molding compounder is used. A comparison with the standard, two‐stage production process provides further understanding of the complex interactions. The study is carried out with various blends of recycled and virgin PA6 with a recycling rate of 0, 25, 50, and 75%. Both single and double recycled PA6 are used. For the evaluation of the mechanical properties, tensile tests, bending tests and impact bending tests are conducted and assessed by fibers length, fiber–matrix adhesion, and fiber content. The results of all tested recycling ratios show no direct influence of the recycling‐related impairment of the plastic on tensile strength, tensile modulus, bending strength, and impact resistance. Rather, the investigations indicate an expected direct relationship to the fiber content, whereby an increase in fiber content relates to a significant improvement of the mechanical properties. Furthermore, the investigated fiber length distributions show a correlation with the mechanical properties. Therefore, the more gentle material processing of the injection‐molding compounder and an associated reduction in fiber shortening, result in a superiority to the two‐stage production process. POLYM. COMPOS., 40:1731–1739, 2019. © 2018 Society of Plastics Engineers