Isotropic Shrinkage of Injection‐Molded Plates of Polypropylene Containing Calcium Salt of 4‐Methyl‐Cyclohexane‐1,2‐Dicarboxylic Acid

ABSTRACT The effect of a calcium salt of 4‐methyl cyclohexane‐1,2‐dicarboxylic acid (MHPA‐Ca) on the shrinkage behavior of polypropylene (PP) during injection molding was investigated and compared with that of 1,3:2,4‐bis‐O‐(4‐methylbenzylidene)‐D‐sorbitol (MDBS). Both MHPA‐Ca and MDBS are effective nucleating agents. The shrinkage behavior was evaluated as a function of holding pressure with structural characterization at various positions. Shrinkage decreased as the holding pressure increased in all samples. The nucleating agents reduced the gate‐seal time and pressure values after gate sealing, which were more obvious in the sample with MDBS due to the accelerated flow‐induced crystallization. Furthermore, isotropic crystal growth occurred frequently from the MHPA‐Ca particles in the core. Consequently, PP/MHPA‐Ca exhibited isotropic shrinkage at various holding pressures that was similar to that of pure PP, even though the shrinkage values were larger than those of PP.