Sawdust reinforced polypropylene: Effect of plasticizer incorporation method and properties

Polypropylene reinforced sawdust composites containing paraffinic and vegetable plasticizer, at 5 and 10 wt%, were prepared according to two methods. In the first method, PP, sawdust, compatibilizer and plasticizer were pre-mixed, extruded in a co-rotating twin-screw extruder and injection molded. In the second, plasticizer was added to the extruded composite pellets and then injection molded. The addition of plasticizer reduced tensile and flexural strength, as well as elastic modulus of the composite, and increased impact strength, tensile strain at break and toughness. As to plasticizer type, both had similar effects on impact strength, tensile strain at break and flexural modulus. With the paraffin oil, the increase in toughness of the PP sawdust composite was higher and the decrease in tensile and flexural strength was lower compared to the vegetable oil. Except for impact strength and flexural modulus the method of plasticizer incorporation, statistically, showed no difference in the investigated composite properties; however, deviation around the mean was higher when the plasticizer was added prior to injection molding, compared to addition in the pre-mixing stage.