The injected specimens of recycled poly(ethy1ene terephthalate) (R-PET) and its blends with engineering PET (E-PET) are studied with differential scanning calorimetry (DSC).
Specimens are dissected into three segments of (1) outer skin, ( 2 ) middle, and (3) the core for the topographic study of their separate crystallinities, which are induced by different crystallization rates in the injection mode. DSC thermograms reveal the different crystallinity states among these three segments with decreasing crystallinity from core to middle to the skin segments and the times and contact of injection-molded specimens with the mold during the cooling cycle after the injection of the specimens. With the same procedures of injection molding, comparisons of crystallinity among various specimens of virgin blow molding grade P E T (B-PET), E-PET, and R-PET are made. There are little differences in crystallinity among three segments of Bor E-PET specimens. In contrast, a higher degree of crystallinity in the core segment than either middle or skin segments is observed for the R-PET. This may contribute to the faster crystallization rate of the R-PET in the mold. Specimens of R-/E-PET blends follow the R-PET pattern, even in 20% of R-PET in the blend. This faster crystallization rate of R-PET is confirmed with the lowering crystallization temperatures (T,) of the R-PET and R-/E-PET blended specimens in the DSC heating process. Dynamic DSC cooling analysis reveals a high order of crystallinity in R-PET and R-/E-PET blends. Gel permeation chromatography (GPC) measurements of molecular weights and distributions support the orderly structure for R-PET. Terminal group analysis and intrinsic viscosity measurements of the R-PET support the chain modification of R-PET during the thermal treatments in accordance with the evidences of smaller M u and narrower molecular weight distribution from the GPC findings for the recycled PET.