Enhancing Toughness\nof Post-Consumer Recycled Polyolefins\nwith Polybutadiene-Derived Block Copolymers

There is a rapidly expanding need for economically viable\napproaches\nfor ameliorating the wasteful disposal of post-consumer plastics in\nlandfills and the leakage of these materials into the environment.\nHere, we assess the efficacy of poly(ethylene)-<i>block</i>-poly(ethylene-<i>ran</i>-ethyl ethylene)-<i>block</i>-poly(ethylene) (EXE) triblock copolymers as compatibilizers in post-consumer\nrecycled poly(ethylene) (rPE) and <i>isotactic</i> polypropylene\n(rPP) containing ca. 10–15% PP and PE impurities, respectively.\nE<sub>67</sub>X<sub>138</sub>E<sub>67</sub> was prepared by anionic\npolymerization of butadiene followed by catalytic hydrogenation, where\nthe subscripts indicate block molecular weight in kg/mol. This triblock\ncopolymer was mixed with rPE and rPP, along with blends formed from\nvirgin PE and PP, and the recycled and blended materials were characterized\nby differential scanning calorimetry (DSC), atomic force microscopy\n(AFM), and tensile testing. The presence of phase-separated impurities\nin the recycled plastics was confirmed by DSC and AFM, and shown to\ncontribute to inferior mechanical properties, <i>e.g.</i>, strain at break, ε<sub>b</sub> < 20% for melt-molded specimens\ncooled at 38 °C/min, referred to as fast cooling. Addition of\n1 wt % of E<sub>67</sub>X<sub>138</sub>E<sub>67</sub> to rPE and rPP\nled to improvements in ductility, dependent on the rate of cooling\nof melt-molded specimens. Fast cooling produced marginal gains in\nductility, ε<sub>b</sub> ≈ 90 and 30% in rPE and rPP,\nrespectively. However, industrially relevant very fast cooling (380\n°C/min) dramatically improved the ductility, where ε<sub>b</sub> ≥ 500% for both recycled plastics. Similar results\nwere obtained with virgin PE/PP blends containing 1 wt % E<sub>67</sub>X<sub>138</sub>E<sub>67</sub>. These findings are compared with the\nresults described in a previous report, where 1 wt % E<sub>65</sub>X<sub>88</sub>E<sub>65</sub> was added to virgin PE/PP blends, indicating\nthat the X block molecular weight plays an important role in the efficacy\nof compatibilization.