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.

Experimental work has been carried out to study the effect of adding marble and Granite dust (MGD) on the mechanical properties of high impact polystyrene (HIPS). The selected wt.% of MGD was 10, 20, 30, 40, 50 and 60. MGD was chemically treated by adding 2 wt.% stearic acid in an attempt to prevent agglomeration of the dust particles. Mechanical tests were conducted according to the ASTM standards to assess the bending strength and impact strength for both treated and untreated MGD-HIPS composites and also, Vickers hardness test was carried out. SEM analysis was also performed to interpret the results achieved throughout different tests. Surface modification of MGD particles using stearic acid caused better dispersion of MGD particles which lead to reduced agglomerations and this was observed through the SEM micrographs. Bending and impact strength of MGD-HIPS composite decreased by the increase of MGD content in the treated and untreated cases. On the other hand the increase of MGD content resulted in the increase of the surface hardness of treated and untreated MGD-HIPS composites. Surface treatment of the MGD particles using stearic acid had a greater effect on the surface hardness of the composite as the treatment allowed the production of a 70 wt.% MGD-HIPS composite plate which lead to an increase in the surface hardness of the composite by 130% compared to pure HIPS.