The role of rubber and label disruptors in the re-processing of polyester from PET-rich textile Wastes

From a global perspective, the share of post-consumer textile waste subjected to recycling amounts to a mere 0.5 %, whereas most textile waste ends up in landfills or incineration. Often this is the consequence of apparel being composed of fiber blends, e.g. cotton/polyester. Recycling of such mixed textile waste at their end-of-life is challenging because of elementary differences in the structure and chemical properties of the constituents. Moreover, small fractions of impurities and contaminants as well as residues from the other fiber type(s), have commonly to be accepted to some extent. In particular, minor elements of apparel, for instance labels or rubber bands, can usually not be completely removed with reasonable effort because of chemical similarities with the main textile fibers. Consequently, during re-processing and compounding of recovered polymers, such elements and disruptors are inevitably present and are hypothesized to play a major role in the mechanical performance of recycled polymers. In this study the impact of potential disruptors commonly present in mixed fiber waste, in particular labels and rubber bands, on the mechanical performance of recovered polymers was investigated. Model formulations of polyester obtained from PET-rich waste streams with known fractions of disruptors were thermo-mechanically re-processed on a conical, co-rotating laboratory scale twin screw extruder and their mechanical properties characterized. Whereas labels had only a small impact on the mechanical performance of recovered polyester, rubber present during extrusion caused a decrease in tensile strength by more than 40 % from 63 to 36 MPa. This was assigned to degradation processes taking place in-situ at processing temperatures, resulting in chain scission and influencing the crystallization behavior.