Study On Preparation And Properties Of Wheat Straw Fiber And Its Composites

Wheat straw is one of the most important agricultural residues, and it is an annuallyrenewable fiber resource available in abundant quantity in many regions of the world. Today,coal, oil and natural gas reserves is shrinking. Development and utilization of crop productionas the new energy is on the strategic position of national energy development. Due to the richresource, low price, and its outstanding advantages are biodegradable and renewable, wheatstraw are important in energy, resource and environment. Taking reasonable and efficientadvantage of these large amounts of renewable, biodegradable and low prices wheat strawresources has become a top research project.In this paper, the study focused on preparation and properties of wheat straw fibers andPLA/wheat straw fiber composites. A large number of studies have been done on thefollowing aspects in the research.Firstly, this paper investigated the pretreatment method with the dilute alkali to wheatstraw for application in composites. The effects of the quality concentration of sodiumhydroxide solution，liquid-solid ratio, processing temperature and time on the weight loss rateof wheat straw were studied. Then, the mechanical properties, the surface structures and thecontact angles of the treated wheat straws were tested. The results showed that the optimizedprocessing parameters with dilute alkali were30of liquid-solid ratio,4%of qualityconcentration of sodium hydroxide solution，100℃of processingtemperature and60min ofprocessing time. The mechanical properties of the wheat straw fibers prepared by the aboveprocessing parameters weren’t remarkably damaged. Compared with untreated wheat straw,the inner and outer surface structures of the treated wheat straws were looser, their specificsurface area increased and contact angle decreased. The above structure changes wouldimprove the infiltration property of polylactic acid to the wheat straw fibers and theinterfacial bondability. The investigation was helpful to the further research on neweco-friendly composites based on wheat straw fibers and polylactic acid.Secondly, Study the hot-pressing process of the PLA/wheat straw fiber composites．Atfirst，we do single-factor and orthogonal testhas with hot-pressing stress, temperature, timeand wheat straw fiber concentration. Then by using mechanical property in composites as ameasure of evaluation index，we can get the best thermal processing conditions:10MPa,175℃，5min and60%．At the best thermal processing conditions，tensile strength is13.57MPa, tensile modulus is3746.21MPa, flexural strength is39.55MPa, flexural modulusis4989.78MPa, impact resistance is183.44J/m.Thirdly, The water absorption rate, mass loss rate, the tensile properties of the preparedcomposites after being treated in buffer solution with different pH values5.8-7.0for different times5-50days were measured, and their surface morphology were observed by scanningelectron microscopy. The results showed that the water absorption rate and mass loss rate ofthe composites increased with the increasing degradation time in the buffer solution withvarious pH value and increased slowly after degradation for30days. The degradation of thecomposites was fastest in weak alkali solution, and slowest in neutral solution. The tensilestrength and Young’s Modulus of composites decreased obviously with the increasingdegradation time, and the surface changed from smooth to rough and uneven.Finally, the study has been done on the preparation of wheat straw fibers with the dilutealkali at high temperature. The results showed that the mechanical properties of PLA/wheatstraw fiber composites are optimal when the sodium hydroxide concentration is2.5%and thealkali treatment temperature is125℃. The contact angles after alkali treatment decreasesignificantly, indicating that the surface wettability of the treated wheat straw is improved.