Mechanical and Physical Properties of PP and HDPE

Abstract

The properties of these polymers, as in the case of any materials, depending on the molecular weight of the polymer and the structure of the polymer chains. The main objective of this work is to study the mechanical and physical properties of pure PP and HDPE. To obtain a full characterization of pure polymer, samples were produced using a compression molding technique. Polymeric samples successfully filled the cavity of the die. The mechanical properties of PP and HDPE were determined using three-point bending, compression, hardness and impact test. While the physical properties were studied through density and water absorption. Also, the thermal analysis behavior was determined by thermogravimetric analysis, differential scanning calorimetry and thermomechnical analysis. Results showed the structure affects the properties. The PP showed better elastic modulus and strength due to the methyl attached to the carbon that prevents the chain rotation and hence makes the material stronger but inflexible. On the other hand, the absorbed energy of PP is less than that of HDPE. The thermogravimetric analysis results show a single weight-loss event with a degradation temperature of 310°C for HDPE and 255°C for PP. The differential scanning calorimetry shows that the crystallinity of PP (≅51) is less than that for HDPE (≅68) due to the difference in the specific heat. The coefficient of thermal expansion of HDPE is higher than that of PP due to the stronger interatomic forces.