Morphology of Injection Molded Samples

Lopez et al. [104] observed that the mold temperature produces signiflcant differences in the macroscopic morphology and properties of the injected SPS samples. In particular, samples molded at high temperatures had higher resistance to the organic solvent than samples molded at low temperatures. The core of the molded samples analyzed by TEM appeared spherulitic [104]. However, the spherulites were not fully developed but appeared sheaf structures type with an elliptical profile. The intermediate region presented lamellar crystals oriented perpendicular to the flow direction. 

Evans et al. [105] found similar results through the depth of injection-molded bars. In particular they found that the skin of samples molded with low mold temperatures was completely amorphous. The differences in the structure and morphology between the two groups are probably due to the techniques used for determining the crystallinity (WAXS and FTIR). 

Hsiung and Cakmak developed a structure-oriented model to simulate the crystalline structure developed in the injection molding of SPS [107]. Their model was elaborated by taking a Lagrangian approach and a three-dimensional mold geometry. The morphological structure of the SPS sample molded at a particular condition quantitatively matches the experimental observations. 

A cold compaction of SPS powders at a temperature well below its melting temperature (273 °C) was found possible [108]. In addition, the mechanical properties of the resulting material were comparable to those of the SPS submitted to compression molding after melting. Parallel experiments on poly(ethylene terephthalate) (PET) and linear low-density polyethylene (LLDPE) suggest that the behavior of SPS is a peculiarity of such polymers, which is likely connected to their polymorphic nature. 

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