Investigation of the recycling and reuse of glass fiber reinforced polyamide 6,6 injection molding waste in diesel injector socket production

The objective of this study is to investigate the recycling of injection molding process waste (runners) of 35% short glass fiber reinforced PA66 used in diesel injector production. Injection molding is one of the most widely used techniques for processing polymers, wherein molten polymer is injected into a mold under high pressure. To inject the polymer into the specific region of the mold, the runners also need to be filled with the polymer, resulting in waste material after production. The amount of waste generated varies depending on the design of the manufactured part. Mechanical recycling of thermoplastic materials involves granulating and remolding without separating the reinforcing fibers from the matrix. The material is then reused as a composite. The fiber length distribution and the bond between the glass fiber and the polymer are influenced by the injection molding process. For this study, pre-consumer industrial waste (runners) was obtained and mixed with virgin 35% glass fiber reinforced PA66 at various ratios (2%, 5%, 10%, 15%, etc.) to produce test specimens. The thermal, chemical, mechanical, and viscoelastic properties of the recycled polymeric materials were examined. Appropriate proportions of waste material were mixed with virgin 35% glass fiber reinforced PA66 granules each time, and test specimens were prepared to investigate the effect of the number of recycling cycles on material performance. Samples with 1 to 10 cycles of recycled material were analyzed in this study. The tensile strength of virgin 35% GF-PA66 is 169.231 MPa, while the sample containing 2.5% recycled material (2.5% RP) has a tensile strength of 168.477 MPa. In samples containing 5% and 10% recycled material, the tensile strength decreased as the proportion of recycled material increased, dropping to 168.099 MPa and 164.23 MPa, respectively. The lowest tensile strength was observed in the 10% RP sample, which had a tensile strength 3% lower than that of the virgin polymer, measuring 164.231 MPa. In the TGA curves, all samples exhibited a similar stepwise thermal degradation process. It was observed that as the number of mechanical recycling processes increased, the HDT temperature value of 35% glass fiber reinforced PA66 decreased by 2°C. According to the DSC analysis data, the changes in melting temperatures were negligible. The MFI results showed an increase compared to the virgin polymer, indicating a reduction in molecular weight due to the recycling process.