Physical and Mechanical Properties of Thermoplastic Composites Filled with Wood Flour of Underutilized Chaste Tree

Abstract

The potential use of a lignocellulosic filler, Vitex agnus-castus plant (Chaste tree), which is a deciduous invasive shrub, in thermoplastic composites was investigated. The stems of chaste trees with a diameter of 5-10 cm from Mugla city, Western Turkey, were used for the study. The different amounts (0 to 50 wt%, by 10 % increments) of the wood flour passing through the screen openings of 0.237 mm were added to the polypropylene matrix. Premixed raw materials were put into the volumetric feeder of the twin-screw extruder. The extruder barrel temperature was gradually increased from 170 °C (feeding zone) to the die zone (190 °C) at a constant screw speed (40 rpm). Then, the dried granules were hot-pressed into the 4 mm thick WPC panels at 2 MPa and 190 °C for 5 min. 3 wt% of maleic anhydride grafted polypropylene (MAPP) was added as compatibilizer into the formulation. The WPCs showed an increase in the thickness swelling (0.58 to 5.68 %) as the amount of the filler increased from 10 to 50 wt% in the polypropylene. The bending strength of the polypropylene composites increased from 33.9 to 44.8 MPa as the amount of the chaste wood flour was increased to 30 wt%, but further increase caused the decrease in the tensile strength (25.7 MPa). As for the bending modulus, it increased from 815 to 3250 MPa when the wood content reached 50 wt%. The tensile modulus increased from 1690 to 2253 MPa when the wood content arised from 10 to 50 wt%. The tensile strength, tensile modulus, flexural strength and flexural modulus of the unfilled polypropylene were found to be 19.6 MPa, 1505 MPa, 30.2 MPa and 664 MPa, respectively. According to the test results, it was concluded that the 30-40 wt% of Vitex agnus-castus wood could be efficiently used in the polypropylene composites for the semi-building applications such as decking or siding. The evaluation of underused invasive chaste wood in the production of tWPC production may result in an effective way to utilize this resource.