Preparation And Properties Of Biochar/Ultra-high Molecular Weight Polyethylene Composites

Every year,a large amount of bioresources such as agriculture residues,wood chips and sawdust wastes are directly discarded in the field in China.This not only pollutes the environment but also is a huge waste of biomass resources.An old and well researched renewable material in the field of soil amendment and contaminant adsorption but new to polymer composites is biochar.It has been considered as a carbon negative material which can sequester carbon(C)over a long period of time and mitigate the climate change.Thus this study was aimed at using biochar particles as a new polymer filler to produce a high-strength,high-toughness,and electrical conductive polymer composite.Highly filled(up to 80 wt.%)biochar/ultra-high molecular weight polyethylene composites with excellent electromagnetic interference(EMI)shielding performance were successfully prepared using mass-producing extrusion and hot-compression methods.The surface morphology and crystalline structure,as well as the thermal,mechanical,creep,electrical,and EMI shielding properties of the composites,were characterized.The main contents and conclusions are as follow:(1)Creep resistance of highly filled bamboo charcoal/ultra-high molecular weight polyethylene composites:Influence of particle size and loadingThe addition of BC greatly improved the tensile properties and creep resistance of the composites.The creep strains of the composites with 60,70 and 80 wt.%were reduced by 70.1%,78.3%and 85.2%compared to the neat UHMWPE at 80?,respectively.To understand the mechanism,the Burger's model was employed to illustrate the influence of BC on the creep performance of the polymer composites.When the external loading was applied to the composites,the BC particles could act as blocking sites and inhibited the stretching of chain segments and the slippage and reorientation of polymer chains,and thus improved long-term properties of the polymer composites.The addition of BC also increased the electrical conductivity of the composites:the composite with 80 wt.%BC had a conductivity of 0.53 S/cm.Moreover,the thermal stability of BC/UHMWPE composites improved apparently with the increased charcoal loading.The particle size of BC strongly affected the properties of BC/UHMWPE composites.The BC with lowest particle size exhibited best reinforcement.(2)Development of electrically conductive nano bamboo charcoal/ultra-high molecular weight polyethylene composites with a segregated networkElectrically conductive nano bamboo charcoal(NBC)/ultra-high molecular weight polyethylene(UHMWPE)composites with a segregated structure were prepared by the high-speed mechanical mixing and hot-pressing method.Instead of uniform dispersion in polymer matrix,NBC distributed along specific paths and formed a segregated conductive network,which resulted in a low electrical percolation threshold(2.0 vol%)of the composites.The composite with 7 vol%NBC possessed a conductivity of 1.1×10~-22 S/cm,which is adequate for many electrical applications.With the incorporation of NBC,the tensile strength of the segregated composites first increased by 10%with 3 wt%NBC content as compared with neat UHMWPE and then decreased with increasing filler content.Moreover,the thermal stability of NBC/UHMWPE composites was also improved as the loading of NBC increased.(3)Highly filled biochar/ultra-high molecular weight polyethylene/linear low density polyethylene composites for high-performance electromagnetic interference shieldingHighly filled biochar/ultra-high molecular weight polyethylene(UHMWPE)/linear low density polyethylene(LLDPE)composites were prepared using extrusion and hot-compression methods.Bamboo charcoal(BC1100)carbonized at 1100? had a defective graphitic structure and exhibited good electrical conductivity and high specific surface area.The addition of BC1100 remarkably improved the electrical conductivity and electromagnetic interference(EMI)shielding effectiveness(SE)of the composites.The composite with 80 wt.%BC1100 exhibited a conductivity of 107.6 S/m and a very high EMI SE of 48.7 dB(99.998%attenuation)at 1500MHz.The addition of BC1100 also enhanced the Young's modulus,tensile strength and hardness of the composites.These results suggested a new way of effectively utilizing biochar in conductive polymer composites,especially for EMI shielding application.(4)Effect of carbonization temperature on mechanical properties and biocompatibility of bamboo charcoal/ultra-high molecular weight polyethylene compositesThe addition of bamboo charcoal significantly improved the processibility of UHMWPE and improved the tensile strength,modulus,and hardness of the composites.The carbonization temperature has a significant effect on the crystallization properties,surface chemistry and specific surface area of BC and also has a influence on the properties of the composites:the higher carbonization temperature led to a higher modulus and hardness of the composite,but decreased the tensile strength and toughness of the material.The water absorption and hydrophilicity of the material also reduced as the carbonization temperature increased.What's more,BC/UHMWPE composites have low cytotoxicity and good biocompatibility,demonstrating it could be used in artificial joints applications.