2022 Volume 48 Issue 5 Pages 191-200
Short fiber-reinforced thermoplastics (SFRTPs) have a strength and elastic modulus superior to those of other materials. In injection molding, these thermoplastics continually transition between the solid and liquid phases. The temperatures at which these phase transition behaviors occur are called the crystallization temperature (Tc) and glass transition temperature (Tg). In previous research, we proposed a short beam method for determining the interfacial shear strength (IFSS) of SFRTP injection-molded products. By analysis of the IFSS and weld strength, the solidification temperature (Tsolid) could be quantified. However, the relationship between Tsolid, Tc, and Tg has not been specified. In this study, Tsolid was calculated for three kinds of glass fiber-reinforced thermoplastics in a matrix of polypropylene (PP), polystyrene (PS), and polylactic acid (PLA). Heat flow analysis by differential scanning calorimetry (DSC) was then performed and the heat flow curve in the cooling process was compared with the Tsolid value. It was shown that when crystalline plastic was used as the matrix, Tsolid equated to Tc, but when amorphous plastic and semi-crystalline plastic were used, Tsolid corresponded to Tg.
