| Barley straw is a significant raw material used in cellulose production as an energy resource and for use in agriculture as ruminant feed. The advantages of straw particleboard are its rigidity and strength, built-in insulation, and low cost. Barley straw is also used as a biodegradable substance for sorption in oil spill clean-up, for oil removal from soil and for the inhibition of algae and cyanobacteria growth in aquatic reservoirs. In all these cases, the surface properties of barley straw play a crucial role. Faced with the worldwide shortage of forest resources, industry is showing increased interest in the production of particleboard from agricultural residues. Natural fiber reinforced plastics(NFRP) is a kind of new developing compsite developed in the last few years, it has combined the advantages of the plastics and natrual fiber, and there are very important meanings in solving energy shortage and environment pollution. It is a focus studied at present to regard polyolefin as the matrix resin and prepar NFRP. In this study, Polyolefin/straw composites were fabricated by hot pressing, with HDPE as matrix and wheat straw as the reinforcing agent. Microwave treatment combine with coupling technique was introduced. Modern instrumental analysis, including Scanning Electron Microscopy (SEM), Fourier Transform Infrared Absorotion Spectrum (FTIR), Atomic force microscopy(AFM) and X-ray diffraction (XRD) were used to elucidate the effect of straw surface modification. The mechanical properties of materials were assessed by tensile test and impact test.The effect of the interfacial modifiers and the connection menchanism between straw fiber and plastics. The study indicates that:1. Atomic force microscopy(AFM) was used to study the surface structures of straw fibers treated by microwave radiation. The results showed that the surface structures of treated group was rougher, control group had a smooth surface, relatively. Treated group had a higher Rms Rough (and Ave Rough) of 558.9±33.458 nm (445.0±28.14 nm), whereas control group had a lower Rms Rough (and Ave Rough) of 141.1±9.055 nm (86.7±6.335 nm). The AFM images revealed that the surface structures of straw fibers treated by microwave radiation changed and the ultrastructure also became complex.2. Moreover, the X ray diffraction peak 20=22.3°was moved to 21.8°, the results from XRD indicate that straw fibers still contains noncrystalline and crystalline regions after microwave treating, but its crystallinity and crystal face dimension increase. The ultrastructure of straw fiber treated by microwave radiation has not changed.3. These three surface modification all have good modifying effects, the microwave-grafting KH550 have the best modifying ability and the microwave-grafting tetrabutyl orthotita have better modifying ability then microwave radiation. The dynamic contact angle of modified straw fiber increased, the surface energy was even closed to Polyolefin matrix. After treatment, the straw fiber forms a uniform pore structure, roughness of surface becomes lager, the distribution of straw in Polyolefin and interfacial compatibility was markedly improved. The retention rate of mechanical properties is higher than that of the untreated group. The mechanical properties of Polyolefin/straw composites were improved evidently. Compared with other modifiers, microwave-grafting silane could improve the Hydrophily and mechanical properties of Polyolefin/straw composites more effectively.4. FTIR show that there is no effect of microwaves on the chemical structure of straw fibers, there had multi difference in the apices form the characteristic peak of 3300cm-1 because its intermolecular and intramolecular hydrogen bond change subsequently. After the treament, the C-O-C bond increased and the hydroxy groups decreased, probably due to the dehydration between hydroxy groups. This change may good to combine of straw fiber and plastics.5. Raw straw with the smooth surface has a poor combinative ability with Polyolefin. After treatment, the straw fiber forms a uniform pore structure, roughness of surface becomes lager, the distribution of straw in Polyolefin and interfacial compatibility was markedly improved. The retention rate of mechanical properties is higher than that of the untreated group. At the transverse section of straw fiber-Plastics composites, the straw fiber and the plastic united closely, and the surface of the straw fiber covered with plastic. The wire drawing in the transverse section indicates that the formation of binding layer between the fiber and plastic transferred the crack from the interface to the inner of the plastic when the sample was ruptured.6. Compared with the untreated sawdust, the treated sawdust is more easily to be plastieized, and the flow-ability is better. We find that several modifier can all improve composite performance. Atfer KH550 dealing with the straw fiber, the modified effect is best, CPVC/KH550,CPE/KH550 and TAIC/CPE modify the effect takes second place. On the basis of confirming that unites the best use level of modifier, find that two kinds of silane coupling agent and the inerfacial modifier respectively can produce the synergistic effect, improve the performance of composites further. The tensile strength and impact strength of the composites of the treated straw fiber and Polyolefin obviously increased.According to results given in this paper, the interfacial behavior of straw fiber reinforced composite was improved by Microwave-assisted surface modification and coupling agent, Straw-plastic composites are being accepted widely in to the building and construction industry. The composite industry always looks into alternative low cost lignocellulosic sources, which can decrease overall manufacturing costs and increase stiffness of the materials. However, it is believed that the research focused at the use of these materials could follow a developmental market at the same time can lead to a new market opportunity for these surplus inexpensive field crop leftovers.
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