BLEND STRUCTURE OF COMMINGLED PLASTIC FROM RECYCLED POLYETHYLENE AND POLYSTYRENE

The hierarchical morphology of commingled plastic waste in the form of thick beams prepared by the ET-1 process has been examined. Blends of recycled high-density polyethylene (RHDPE, New Jersey Curbside Tailin gs) with 25 and 35 wt % expanded polystyrene (EPS) were compared with blends of a virgin high-density polyethylene resin (VHDPE). At the mac roscale, observed with the optical microscope, the beams consisted of a solid skin that extended about one-third of the distance to the cent er of the beam and a voided core with about half the density of the sk in. The phase morphology of the skin at the microscale was characteriz ed by examining etched cryogenic fracture surfaces in a scanning elect ron microscope. The blends of RHDPE and VHDPE exhibited a gradient mor phology with highly elongated EPS domains near the edge and spherical or co-continuous EPS domains closer to the core. The morphology gradie nt was created by the competition between the relaxation rate of the m elt-flow morphology and the cooling rate in the mold. In addition to h igh-density polyethylene, a variety of other components were identifie d in RHDPE by photoacoustic infrared and thermal analysis. These inclu ded polypropylene, polystyrene, poly(ethylene terephthalate), and chun ks of nonpolymeric material. As a result of the heterogeneous composit ion, the crystallinity of RHDPE was significantly lower than that of V HDPE. (C) 1994 John Wiley & Sons, Inc.