Study of the Mechanical Recycling on the Properties of Glass Fiber-Reinforced Aliphatic Polyketone Composites

This study aims to evaluate the effects of repeated mechanical recycling on the properties of a novel aliphatic polyketone composite reinforced with 15 wt% and 30 wt% glass fibers (PK15GF and PK30GF), providing insights into its potential for sustainable engineering applications. The investigation focuses on three main aspects: changes in melt flow index (MFI) and viscosity, the influence of glass fiber content on thermal and mechanical stability, and the retention of structural integrity and crystallinity under multiple processing cycles. Composites, commercially available since 2019, were subjected to single- and five-cycle recycling with 100% reprocessed content. Comprehensive characterization-including tensile testing, Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), Fourier Transform Infrared Spectroscopy (FT-IR), Melt-Flow Index (MFI), Differential Thermal Analysis (DTA), and mechanical tensile testing-revealed filler-dependent alterations in morphology, thermal stability, and crystallinity. MFI decreased from 100.56 to 42.63 g/10 min for PK15GF, indicating pronounced chain scission, recombination, and crosslinking, whereas PK30GF decreased only from 89.00 to 59.76 g/10 min. FT-IR spectra confirmed greater crosslinking in PK15GF, while DSC and DMA demonstrated smaller T_g and ΔHm variations in PK30GF (T_g +0.45 °C, ΔHm -13.93 J·g^-1) versus PK15GF (T_g +1.13 °C, ΔHm -69.24 J·g^-1). These findings reveal that higher glass fiber content mitigates degradation, preserves structural integrity, and maintains thermal and viscoelastic stability, establishing clear correlations between filler content, mechanical performance, and recyclability. Overall, this work provides mechanistic insights into degradation pathways and demonstrates the potential of glass fiber-reinforced aliphatic polyketones for sustainable, high-performance engineering and automotive applications.