Composite production of polypropylene polymers was considered in this work as the matrix, filled with the fiber of wheat straw and paper mill sludge; different ratios were evaluated relative to their potential as reinforcement materials. Maleic anhydride polypropylene (MAAP) was used at 3% by weight. The bending modulus of elasticity of the composites significantly increased with both types of filler. The highest bending modulus of the composites was found with 40% of paper mill sludge. Using 40% wheat straw fiber decreased bending strength, but the addition of paper mill sludge increased bending strength. The highest bending strength of the composites related to polypropylene/10% of wheat straw fiber and 30% of paper mill sludge. In terms of impact strength, the use of paper mill sludge had a higher impact on strength than wheat straw fiber composites. The inclusion of MAPP improved the mechanical properties of all composites. Scanning electron micrographs showed that the composite paper mill sludge improved the adhesion and dispersion of the filler (paper mill sludge/fiber paper instead of wheat) in the matrix.
Effects of alkali treatment of rice straw flour on the mechanical properties of rice straw flour-polypropylene composites were investigated. Rice straw flour (40 mesh) was first treated with sodium hydroxide using two concentrations of sodium hydroxide, 5 and 10% (W/W), and two treatment times (45 and 90 min) for a total of four treatments. The composites were then made with the rice straw flour as a filler (30%), polypropylene (65%) as a matrix, and maleic anhydride (5%) as a coupling agent. The polypropylene/rice straw flour mixtures were blended in an internal Haake mixer and made into molds that were later used for mechanical testing. The results showed that the treatment of rice straw flour with 5% alkali (W/W) increased the tensile modulus and impact strength. Longer treatment time also resulted in a higher tensile modulus and impact strength. The fiber/matrix interaction was analyzed from the mechanical data and morphological (SEM) studies. Treatment of rice straw flour with 10% alkali (W/W), however, decreased these properties even under a longer treatment time. Increasing the alkali concentration and treatment time increased the flexural modulus, flexural strength, and tensile strength of the composites. The SEM results showed greater adhesion between the rice straw flour and the polypropylene matrix at higher alkali concentrations and longer treatment times.
In the present study poly lactic acid (PLA) and wheat straw fibers are used to make biocomposites. For a better compatibility between the two phases, wheat straw fibers were treated by silane and acetylation. Twin screw extruder was used to mix the substances, and compression molding was used to produce standard samples.Physical properties testing including water absorption and thickness swelling were studied to analyze the composites produced. Order to analyze changes occurred in samples after their immersion in water for 1,440 hours, pictures were made from the surfaces of the samples, using SEM. Results of water absorption and thickness swelling showed that the use of acetylated fibers in PLA composites resulted in the least water absorption and thickness swelling. SEM pictures showed that composites of PLA/ acetylated wheat straw fibers did not indicate a certain change after 1,440 hours of immersion in water. While composites of PLA/ untreated fibers showed noticeable gaps and cracks on the surfaces of the samples, PLA composites treated with silane showed only minute cracks on the surface of the sample. Analysis of tensile properties indicated that the tensile modulus of composites of PLA/ treated fibers showed a meaningful increase compared to pure PLA. The highest level of tensile properties was recorded for composites of PLA/ fibers treated with silane.
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