Study On Preparation Process Of Polylactic Acid/Cellulose Composite Film And Lignin Phenolic Resin

Due to the increasingly severe fossil energy crisis and environmental damage,the biorefinery production mode,which uses renewable biomass resources as raw materials to produce a variety of products,has attracted increasing attention and support from governments around the world.Using polylactic acid and bagasse cellulose as raw materials to prepare composite film applied in food packaging industry can not only alleviate the shortage of petrochemical resources but also solve the environmental problems caused by non-degradable materials.Using lignin instead of phenol to prepare phenolic resin can reduce the dependence on phenol and the release of formaldehyde.In this study,with Guangxi characteristic renewable biomass bagasse as raw material,bagasse cellulose and bagasse lignin were separated by formic acid pretreatment,and poly(lactic acid)/formacylated bagasse cellulose composite film and lignin based phenolic resin were prepared by using the two as raw materials,to explore the influence of formic acid pretreatment conditions on the structure of cellulose and lignin and the preparation process of composite materials.A new way of resource utilization of bagasse was realized.1.Formic acid was used to pretreat bagasse,and the formyl content in bagasse cellulose was used as the index.Response surface method was used to investigate the effects of formic acid concentration,bagasse particle size and reaction temperature on the formylation degree of cellulose during formic acid pretreatment.When formic acid concentration was 85%,particle size was 180-400 μ m and reaction temperature was 100℃,the formylation content of bagasse cellulose was6.51%.The experimental results showed that compared with pure PLA membrane,the elongation at break of PLA/BFC composite membrane increased by 44.90%,the tensile strength increased by 32.54%,and the water absorption decreased by50.62%.2.The modified lignin of formic acid was modified in water-alcohol mixed solvent system to explore the modification process conditions.Under the optimal reaction conditions,the content of phenolic hydroxyl of the modified lignin was3.207mmol/g,which was 91.12% higher than that of the raw lignin of formic acid.Methanol can be used as a nucleophile to provide active hydrogen for the hydrolysis of lignin C-O-C bond,and can also be used as an end-blocking agent to prevent the condensation of lignin molecules during the reaction.Lignin-phenol-glutaral-formaldehyde(DALPF)resin was synthesized using modified lignin as raw material.Under the optimal technological conditions(glutaraldehyde replacement rate was 40%,lignin replacement rate was 30%,reaction temperature was 90℃),the solid content of DALPF-5 resin was 37.16%.The phenolic release was 2.20% and 0.25%,respectively,and the bonding strength was 1.57 MPa,both of which reached the national standard.Compared with PF,the free phenolic content was reduced by 125.45%,and the bonding strength was increased by 28.69%.The thermal analysis of DALPF resin shows that its thermal stability is better than PF resin at low temperature(< 200 ℃),but the thermal stability is relatively poor at high temperature and the setting speed of DALPF resin is relatively slow.