Properties of Oil Shale Ash Filled Polypropylene Composite Material: Mechanical and Physical Characterization

The outcome of oil shale ash (OSA) filler addition on the mechanical, morphological, thermal and water uptake properties of the polypropylene (PP) matrix was investigated. The test specimens were prepared with various ratios of the mixtures that contain OSA and polypropylene in the following weight percentages: 0%, 10%, 20%, 30% and 40% OSA in polymer matrix. Composites specimens were produced by using a co-rotating twin screw extruder and a thermal press machine. The properties of the polymer composite specimens were characterized by using a universal testing machine (WDW-5) and izod impact testing machine (FI-68). The morphology of the composite samples was also characterized by using the scanning electron microscopy (SEM). Impact strength and Young’s modulus of the OSA/PP composite formulations were consistently improved on OSA inclusion. On the other hand, addition of OSA to pure polypropylene had consistently reduced the tensile stress at yield, tensile stress at rupture, tensile strain at yield and tensile strain at break. Adding OSA to polypropylene decreased the maximum flexural stress and flexural strain of maximum force. The observed SEM confirmed that the addition of OSA to pure polypropylene resulted in a significant increase in its agglomerates and filler pullout. Differential scanning calorimetry (DSC) results confirmed the addition of the OSA to pure polypropylene resulted in a significant decrease in normalized heat of crystallization, normalized enthalpy of melting. Where the degree of the crystallinity (Xc) of polymer composite decreased from 59% to 34% for 0% and 40% OSA addition, respectively. While melting temperature (Tm) of the composite did not change (167 °C) the crystallization temperature (Tc) increased from 116.6 °C to 127.1 ºC for 0% to 40% OSA addition, respectively. Water uptake, however, demonstrated different behaviour. The initial addition of OSA to polypropylene increased the water uptake property up to 4% for the 40% filler addition. The results of this study demonstrated that the OSA could be used as reinforcement material for polypropylene, as long as good mechanical properties and homogeneous morphology obtained.