Composites of Poly(vinyl chloride) with Residual Hops after Supercritical Extraction in CO₂

The common applications of poly(vinyl chloride) (PVC) in many industries mean that the topic of recycling and disposal of post-consumer waste is still very important. One of the methods of reducing the negative impact of PVC waste on the natural environment is to use technological or post-consumer waste of this polymer to produce new composite materials with favorable utility properties, with the addition of natural fillers, among which agro-waste, including hop residue, is deserving of special attention. In this study, the effect of the addition of residual hops (H) on the mechanical and physicochemical properties of poly(vinyl chloride) was investigated. PVC blends containing 10, 20 and 30 wt % of hop residue were mixed in an extruder, while the specimens were obtained by the injection molding method. It was observed that the addition of H increased their thermostability, as shown by a Congo red test. Furthermore, thermogravimetric analysis showed that the degradation rate of PVC/H composites in the first and second stages of decomposition was lower in comparison with unmodified PVC. In turn, composite density, impact strength and tensile strength decreased significantly with an increasing concentration of filler in the PVC matrix. At the same time, their Young's modulus, flexural modulus and Rockwell hardness increased. Flame resistance tests showed that with an increasing residual hop content, the limiting oxygen index (LOI) decreased by 9.0; 11.8 and 13.6%, respectively, compared to unfilled PVC (LOI = 37.4%). In addition, the maximum heat release rate (pHRR) decreased with an increasing filler content by about 16, 24 and 31%, respectively. Overall, these composites were characterized by a good burning resistance and had a flammability rating of V0 according to the UL94 test.