Study On Thermoplastic Modification Of Wood Powder In Different Dissolving Systems

Modification of wood fiber can prepare polymer materials,which can also relieve resource constraints and reduce environmental pollution.Mulberry branches are typical wood fiber’s raw materials and usually used as fuel wood as a kind of agricultural and forestry wastes which have caused waste of resources.The preparation of bio-based plastics from the mulberry branches can conducive to the sustainable development of the ecological environment and achieve the resource utilization of agricultural and forestry waste to some extent too.In this research,the DMSO/TEAC and DMSO/LiCl binary solvents were used as modifying agents to modify the mulberry branches powder,and the feasibility of preparing injection grade bio-based plastics was studied.The main contents and achievements of the paper are as follows:1.The wood powder of mulberry branches was modified by DMSO/LiCl solvent through a simple dissolution and precipitation process after ball milling.Li⁺combines with the oxygen atoms on the hydroxyl group to form a coordination bond,Cl^-combines with the hydrogen atoms of hydroxyl groups to form a hydrogen bond,which destroy the original hydrogen bond network structure of cellulose,the modified products possess thermoplasticity,which proved that DMSO/LiCl solvent modified ball-milled wood powder was feasible.The effects of disposal time,disposal temperature,the amount of LiCl on the weight gain rate（WPG）and the mechanical properties of the modified products were discussed.The results showed that when the disposal time was 2 h,the disposal temperature was 50°C,the amount of wood powder was 6g and the amount of LiCl was 8g,the prepared bio-based plastics had the highest flexural and tensile strengths of 18.43 MPa and 8.29 MPa respectively.FTIR spectrum analysis confirm that no new functional groups are produced during the process of modifying the wood powder.Thermogravimetric analysis and XRD analysis show that the thermal stability and crystallinity of the modified products is significantly lower than that of the ball-milled wood powder.2.Ball-milled wood powder was modified by DMSO/TEAC solvent through a simple dissolution and precipitation process.TEAC gradually penetrate into the molecular chain of cellulose during the modification process,（C₂H₅）₄N⁺and Cl^-combine with the hydroxyl groups of cellulose to form coordination bonds and stable hydrogen bonds respectively,hinder the formation of hydrogen bonds between the molecular chains,make the modified products thermoplastic,and injection grade bio-based plastics have been successfully prepared.This method is simple and environmentally friendly.The effects of disposal time,disposal temperature and the amount of TEAC on WPG and the mechanical properties of modified products were investigated.Ethanol,water and isopropyl alcohol were used to filter the precipitated products and in this way it was explored whether it could improve the properties of the material.The results showed that the mechanical properties were the best when the disposal time was 2h,the disposal temperature was 60°C,the amount of wood powder was 6g and the amount of TEAC was 15g,the flexural and tensile strengths were 26.28 MPa and 9.63 MPa respectively when the WPG was 99.5%.The thermoplasticity of the products obtained after suction filtration of the three washing reagents was poor and the method of improving products performance by changing the washing reagents is not feasible.3.Based on the modification of ball-milled wood powder by DMSO/TEACsolvent,dioctyl phthalate（DOP）,triacetin（GT）,tributyl citrate（TBC）,and glycerin（GI）were selected as plasticizers to study the effects of different plasticizers on the mechanical properties.The plasticizing ability of the four plasticizers was as follows:GT>GI>TBC>DOP,so GT was determined as the best plasticizer.The following experiments took GT as the research object and the effect of the amount of GT and its addition method,the amount of TEAC and extrusion conditions on the mechanical properties of bio-based plastics were discussed.The results showed that the experimental method of blending the modified product with GT was the best and the maximum flexural strengths（34.71MPa）and tensile strengths（16.34MPa）appeared at the condition of 12.5g TEAC,6g wood powder,5%GT,60 r/min screw speed,and 140°C extrusion temperature.Blending the modified products with GT for extrusion further destroyed the cellulose and hemicellulose of the modified products and the thermal stability and crystallinity of the GT extruded products were reduced through XRD、FTIR and TG/DTA analysis.Observation of the SEM photographs revealed that the bent section of the GT extruded product was dense and compact.