Development and Mechanical Characterization of LLDPE-PP Composites Reinforced with Coconut Shell Powder

Composite materials are characterized by several physical and mechanical properties that make them without rival in some applications requiring low weight and suitable strength. The interest in natural fibers reinforced composite materials is due to their environmental benefits, reduced industrial raw material consumption, and low cost. The objective of the present work entails the preparation of PP-LLDPE - Coconut shell powder composite materials, the determination of their optimal preparation conditions and the characterization of their physical and mechanical properties. Composite material samples were prepared by melt mixing the batch constituents in the internal mixer chamber at 170 ºC and 50-rpm rotation speed and pressing the mixed batch at 170 ºC and 20 tons pressure. The specific weight of PP-LLDPE blends was determined using the Archimedes method, and their mechanical characterization was based on tensile tests on standard specimens.

Measured specific weight values of PP-LLDPE blends fall between those of PP and LLDPE and follow nearly the rule of mixture. Specific weight results for PP-LLDPE blends comply with minor porosity of less than 1%. The optimal conditions for the preparation of PP-LLDPE- Coconut shell powder composite materials were batch mixing at 170 ºC and 50-rpm rotation speed and batch pressing at 170 ºC and 20 tons pressure. Tensile results for PP-LLDPE blends showed improvement of tensile stress and Young modulus and a decrease of elongation at break with the increase of PP content. The addition of Coconut shell powder to PP-LLDPE blends induces a gradual decrease in tensile stress and elongation at break and a gradual increase in Young modulus. Tensile results confirmed also that coconut shell powder content could be increased up to 50 wt. % while preserving a suitable range of mechanical properties where tensile strength varied between 10- 30 MPa. This confirms the possibility of varying these composite constituents according to the requirement of the envisaged application without coconut shell powder treatment, using compatibilizers and interfacial promoting bonding agents (silane compounds) between this powder and PP-LLDPE polymer blends.