Study On Structure And Property Of Bio-fiber/poly Propylene Composites

Bio-fiber Plastic Composites(BPC) are the green and environment-friendly material made from useless forestry leftovers, agricultural by-products and recycled plastics. In addition cost saving on source materials, environmental pollution caused by industrial wastes can be reduced as well. Regarding the ligneous appearance and performance, this kind of products can be used to replace wood materials under most circumstances, which is good for the forest protection thus beneficial to sustainable development. But some drawbacks still exist, such as product performance fluctuation caused by the biodiversity of fiber, poor compatibility between hydrophilic fiber and hydrophobic plastic, low flowability and weak anti-oxidation properties.Based on the existing problems, corresponding experiments have been carried out.This thesis has compared the difference between wood flour(WF), bamboo flour(BF) and rice husk(RH) on micro-morphology, composition, surface free energy and so on. It's found that the bamboo flour has the highest aspect ratio, the maximum cellulose content and the largest total surface free energy. Among all the PP-based composites reinforced respectively by wood flour, bamboo flour or rich husk, bamboo flour/PP composite shows the highest mechanical property, followed by wood flour/PP composite, and rice husk/PP composite the lowest.According to the research, bio-fiber moisture content takes effect on mechanical composite and processing property. It turns out that proper moisture content has a positive effect on impact strength of composites while over high moisture content go against processing property. Increasing fiber content brings to the decreasing melt flow index(MFI) of composites. The apparent viscosity order of materials is, from big to small, 1# wood flour/PP, bamboo flour/PP, 2# wood flour/PP, rice husk/PP, and neat PP. That means the flowability of composites is lower than that of PP. Study on the size change of 2# wood flour point out that composite has the highest apparent viscosity when the wood flour size is 40 meshes.Maleated polypropylene(MPP) and maleated polyolefin elastomer(MPOE) can be used to improve the compatibility between bio-fiber and PP, and thus strengthen the mechanical properties of composites. After adding of wood flour, the tensile strength, flexural strength and flexural modulus of PP with different brands are all enhanced, among which the enhancement on flexural property is most obvious, but the impact strength decrease to a relative low level. The present of SEBS can bring a significant improvement in impact strength. Differential scanning calorimeter(DSC) analysis shows that additional bio-fiber help PP on expediting heterogeneous crystallinity, and increase crystallization temperature.Bamboo flour/PP has the most excellent anti-thermo-oxidative aging property among 2# wood flour/PP, bamboo/PP, and rice husk/PP composites. After exposing in 120℃thermal air for a period of time, composites'surface color turn into yellow, and the yellowing extent is in accordance with what the mechanical property decreasing to, which shows thermo oxidative aging leads to structural change of composites and produces new yellow substance. Antioxidant 1010 can effectively improve anti-thermo-oxidative ageing property of composites. Powdering and fading occur on neat PP and composites surfaces after several days of ultraviolet(UV) exposure. Fourier Transform infrared spectroscopy(FTIR) indicate that PP is oxidized by UV and carbonyl, aldehyde, and hydroxyl are formed at the same period. Carbonyl absorbance peak also shows up in composites'FTIR spectroscopy after UV exposure, and some other absorbance peaks may be attributed to C=C vibration. Lignin chains are broke by UV and then some free-radicals come up. Alkoxyl and peroxyl free-radicals produced from the reaction of oxygen and lignin free-radicals react with the phenoxy free-radical formed to produce the quinonoid coloured chromophore which is associated with light-induced bio-fiber yellowing. There is no change in either appearance or structure of cellulose nanocrystals, which proves an excellent anti-ultraviolet aging property.