T. Li et al., BLEND STRUCTURE OF COMMINGLED PLASTIC FROM RECYCLED POLYETHYLENE AND POLYSTYRENE, Journal of applied polymer science, 52(2), 1994, pp. 301-314
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.