Study On Preparation And Performance Of Continuoussteam-exploded Wheat Straw/PP Composites

As a by-product of agricultural development,Wheat straw can be regenerated and the yield is large,but there are few effective high-value utilization methods.The rich wax and silica-based substances on its cuticular is the most important reason which limits its industrial application in the fields of construction materials,pulp and paper,biomass energy,biomass refining and composites.In this paper,wheat straw was used as the research object,and it was pretreated by laboratory-made continuous-steam-explosion equipment and technology to study its effect on the interfacial compatibility and mechanical properties of wheat straw fiber reinforced PP composites.Furthermore,PP/PE blends were used as a matrix to simulate recyclable waste plastics.The effect of pretreatment on the mechanical properties of composites was studied.The work of this paper has important research and application value for the straw pretreatment,preparation and performance research of straw plastic composites.In view of the characteristics of wheat straw,the effect of steam explosion on wheat straw was effectively enhanced by adding straight teeth to the ring die at the discharge port of the equipment.Effects of pretreatment on morphology,composition,structure and surface property of wheat straw were characteried and analyzed by particle size screening,high multiple optical imaging and aspect ratio statistics,SEM,EDS,benzene-ethanol extraction,ATR,XRD,TGA and contact angle and surface free energy measurement.It was proved that the pretreatment effectively reduced the particle size of wheat straw,reduced the content of waxy layer and silicon content on the surface,improved its thermal stability,and reduced the polar component value in the surface free energy of wheat straw.The wheat straw fiber prepared by the ring die with teeth was better than that pretreated by the smooth ring die.The untreated and steam-exploded wheat straw was prepared with PP.The effects of pretreatment on the mechanical properties and aging properties of the composites were studied.The results showed that after pretreatment,the tensile strength of the composite was 19.9 MPa,the flexural strength was 46.4 MPa,and the impact strength was 5.47 kJ/m~2,which was 30.1%,23.1%and 24.3%higher than that of the untreated wheat straw reinforced PP composite,even some mechanical properties exceeded the wood flour reinforced PP composites.However,the anti-aging properties of wheat straw reinforced PP composites were inferior to wood flour reinforced PP composites.For this reason,it is necessary to appropriately modify the materials to improve the anti-aging property of composites.The PP/PE blends were used as the composite matrix to simulate the recyclable waste plastics reinforced by wheat straw.The flexural strength of pretreated wheat straw fiber reinforced PP/PE composites was 26.6%?23.2%,21.0%and 5.5%higher than that untreated wheat straw fiber reinforced PP/PE composites at a ratio of PP:PE of 100:0,90:10,70:30 and50:50,respectively.The test results showed that the steam-exploded wheat straw fiber was beneficial to improve the interface and mechanical properties of composites.In steam-exploded wheat straw fiber reinforced PP/PE composites,the crystallinity of PP and PE was higher than the composites reinforced by untreated wheat straw.The analysis was due to the softness of PE molecular chain and better fluidity.Then PE preferentially wrapped the fiber and blocked the association of fiber and PP,which weakened the effect of fiber on PP crystallinity.To some extent,the storage modulus and crystallinity of the steam-exploded wheat straw fiber reinforced PP/PE composites have been improved.