Injection Molding of Low-Density Polyethylene (LDPE) as a Model Polymer: Effect of Molding Parameters on the Microstructure and Crystallinity

Abstract

Due to its relatively simple structure, low-density polyethylene (LDPE) can be considered as a model polymer for the study of its properties. Herein, the effect of processing variables on the microstructure and crystallinity of injection-molded LDPE specimens was quantitatively determined. The polymer was injected at different temperature conditions in the barrel and the mold. The specimens were characterized by scanning electron microscopy and X-ray diffraction. With the data obtained, an analysis of variance (ANOVA) was carried out, and response surface graphs (SRP) were constructed to quantify and to observe the behavior of the processing variables, respectively. Different models were obtained to predict the effect of the experimental factors on the response variables. The results showed that the interaction of the two temperatures has the greatest effect on the size of the spherulite, while the temperature of the mold affects the crystallinity. The SRP showed different behaviors: for the spherulite, the size increases with the mold temperature, while for the crystallinity, higher values were observed at an intermediate mold temperature and a low melt temperature. The results presented herein are valuable for setting empirical relations between the microstructure, crystallinity, and the molding conditions of LDPE.

The Influence of the Processing Conditions on Changes in Physical and Structural Properties of Injection Moulded Parts Made of Polypropylene

“…in the work [3] it was shown that the rheological properties of the material and the processing conditions are of decisive importance for ensuring the complete filling of the mould cavity. the mould temperature was the factor that had the greatest impact on the size and crystallinity of the spherulite in Pe-lD parts [4]. e. Farotti et al [5] showed that the mould temperature and holding pressure are the factors determining the mechanical properties of moulded parts.…”

Crystallinity and mechanical properties of polypropylene products foamed by microcellular injection molding process

“…Liu et al 20 studied the influence of process parameters on crystallinity and tensile strength, finding a decrease with increased melt temperature and injection speed but an increase with mold temperature and injection pressure. Leyva et al 21 determined that the mold temperature had the most significant impact on spherical crystal size and crystallinity, followed by the melt temperature. Meanwhile, Zhao et al 22 studied the effect of process temperature on induced crystallization of iPPF/poly (ethylene terephthalate) blends, noting increased crystallization rate and orientation of blends increased with rising process temperature.…”