Fabrication And Interface Improvement Of Wheat Straw(WS)/Polactic Acid (PLA) Green Composite

Composite materials have great advantages in the area of materials because of its high performance, modulus and energy saving properties. However, the recycle of used-composites brings a lot of problems. Therefore, how to solve the regeneration and recycling of composites attracts more and more attention among all the researchers in this area.As to the nature fiber composite, the nature fiber can be decomposed into water and carbon dioxide by the microorganism in the soil after disposal, therefore it does not cause the problem of regeneration and recycling. China is a vast agricultural country, and wheat is one of the main crops in our country, therefore China has rich wheat straw resources (almost100million tons per year). However, most of these resources haven’t been reused reasonably. In the past, the most used method to dispose WS was pulping and paper-making or directly burning, which not only wastes precious renewable resources, but also brings serious environment pollution. So, how to develop and utilize WS resources has already caused attention, and thus becomes an important research project. This subject focused on making WS/PLA green composite, which meets the requirement of sustainable development and provides a new way to deal with the WS resources.This project selected long WS and PLA as the reinforcement and matrix materials respectively, utilized the hot-press method to fabricate WS/PLA green composite, made researches on how to optimize the fabrication parameters, then fabricated WS/PLA composites with different WS volume fraction. At last, it tested the tensile and bending properties of all these composites and analyzed the results of all tests. The research details are as follows:1. To better utilize the WS, this project tested and featured the physical properties of WS systematically, such as the length, density and external diameter. Meanwhile, in order to obtain suitable fabrication parameters, studied the tensile properties of WS under at different form and temperature. The results are as follows:the density of WS is0.33g.cm-3, and the external diameter and thickness are respectively0.019cm and0.238cm. The tensile strength, modulus and strain of WS at formal form are respectively92.18MPa,2.88GPa and1.81%, when it is pressed, the results respectively raise to96.86MPa,3.04GPa and1.96%, which indicates that the tensile properties varies with different temperature. 2. To fabricate WS/PLA composites with super performance, this research focused on optimizing the fabrication parameters of PLA film and WS/PLA composite. The tensile strength, modulus and strain of PLA are respectively25.09MPa,742.32MPa and3.43%. The crosswise tensile strength, modulus of WS/PLA composite with20%WS volume fraction are21.61MPa and0.92GPa; when WS volume fraction raises to30%, the results are23.59MPa and1.04GPa. The lengthways tensile strength and modulus of20%volume fraction composite are26.53MPa and1.35GPa, when the WS volume fraction is up to30%, the results changes to30.14MPa and1.61GPa. As for the bending properties, the strengths are respectively64.13MPa and74.26MPa for composites with20%and30%WS volume fraction, and the modulus are1.81GPa and1.95GPa. Therefore, the properties of composite with20%WS volume fraction are much better than the30%one.3. As WS is a kind of hydrophilic material, while PLA is a kind of hydrophobic material, thus it is hard for them to combine with each other. For the sake of improving the properties of the interface between the two materials, this project modified WS with alkali treatment, and tested the contact angle, SEM and tensile properties of modified WS. Using the WS treated with2%and4%NaOH solution to make modified WS/PLA composites with20%WS volume fraction, and then tested their tensile and bending properties. The results shows that after modified with2%and4%NaOH solution, the crosswise tensile strength rises24.20%and34.29%respectively; the longitudinal tensile strength increases22.16%and12.63%separately; and the bending strength enhances22.44%and16.095respectively. All these results indicate that the composites represent a much better performance after alkali modification, and different concentration of NaOH solution have different effects on the composites.