Impact on HDPE Mechanical Properties and Morphology due to Processing

Many factors contribute to determining the mechanical properties of polymers: synthesis, processing, storing, and testing conditions. Although some work has been carried to deter-mine and compare the effect of processing on polymers, there is still confusion among the scientific community due to the diversity of processing conditions and variety of polymers. Here, we aim to characterize the mechanical properties of pure high-density polyethylene (HDPE) and to provide a relationship between these properties and the samples morphology obtained from injection and compression molding. Mechanical characterization of HDPE samples was carried by uniaxial tensile testing and the degree of crystallinity was calculated using DSC and XRD. Finally, SEM image analysis was conducted to characterize any anomaly or defect that may affect the microstructure of the samples. The results show that compression molding produces samples with superior mechanical properties over injection molding. For example, the yield strength values obtained were 24.5 MPa and 22.3 MPa, respectively. A higher degree of crystallinity was found in compression molded samples (80.15%); this phenomenon is responsible for a higher strength compared with injection molded samples (74.84%). With respect of plastic deformation, compression molded samples show 1170% failure strain, which is 2.5 times greater than the value obtained for injection molded samples (462%). The defects found, through SEM imaging, in the microstructure of injection molded samples are believed to be responsible for premature break. The information presented can be used in the polymer industry to better determine the specific material processing needed to accommodate diverse mechanical properties.