Impacts Of Temperature On The Mechanical And Creep Behavior Of Polyolefin Wood-Plastic Composites

In this paper, the temperature dependent dimensional change, mechanical properties and the creep-recovery response of four kinds of polyolefin-based wood-plastic composite (WPC) ie PP, HDPE, PP/HDPE and HDPE/PP based materials were studied. The PP and HDPE based WPCs would spontaneously expand firstly, At80℃, the length change rate of HDPE-based WPC was faster than PP-based WPC, and their peak values located in between12and24hours,0.18%and0.12%, respectively. However, with prolonged treating time, the change ratio values gradually decreased and plateaued after288hours. The final length change ratios descend by about40%and35%, respectively, compared with the maximum values. When the WPCs were transformed to room temperatures surroundings, they forward contracted and became shorter than the originality finally.The FS (flexure strength), TS (tensile strength), MOE (modulus of elasticity) and IS (impact strength) of all four composites stored at-10℃were the highest and they exhibited an initial linear relationship between them and temperature. Compared with at-10℃, the FS, TS, MOE and IS of the four composites at80℃decreased about by (13.7,23.2,43.5,9.2%),(10.5,23.6,44.6,10.8%),(17.8,22.6,33.2,8%),(14.1,27.1,38.2,8.5%), respectively. According to the sensitivity analysis, it could be concluded that the MOE of composites was the most sensitive, followed by TS, FS, and IS. The variation of storage modulus E’and loss modulus E" detected from DMA analysis could explain the phenomena.The WAXD method was employed to analyst the crystallinity of the four WPC materials after treated for48hours at respective ambience temperatures, which showed that the crystal structure of PP or HDPE remain unchanged, the presence of crystallites was important for retention of mechanical properties but not the decisive factor influencing the mechanical properties for WPCs.The creep properties were highly relevant to temperature, time and stress. All the composites were still in the secondary creep region at the end the tests for all temperatures. Short-term creep tests on all four WPC materials were conducted at elevated temperatures for the prediction of long-term creep performance by applying the time-temperature superposition principle (TTSP), and the creep curves were shifted by using shift factors at and reference temperature Tref to form several smooth contiguous curves. As a result, the corresponding Williams-Landel-Ferry (WLF) equations were reached, which have been confirmed in many previous studies. The resulting master curves of the four WPCs were modeled as a Prony series. Prediction of creep response was made up to about a theoretical2.1and4.1years for HDPE and HDPE/PP based WPCs.