Study On Extraction Of Xylan From Bamboo Chips By Chemical Mechanical Method

Xylan is one of the important components of hemicellulose,and its extraction and preparation has always been a research hotspot.China is rich in bamboo resources and has great application potential.However,because of the dense cell structure and the liquid medicine is hard to penetrate,the extraction of bamboo xylan is difficult and the extraction rate is not high.At the same time,the development of the traditional slurry and paper industry also faces many problems such as single product and decline in industy competitiveness.This thesis takes bamboo as the research object,through spiral extrusion pretreatment-lye pre-impregnation-PFI mill treatment-alkali extraction process,to study the xylan yield of each factor in each link,the product was analyzed by FTIR,NMR,and TGA.The primary and secondary order of the main factors affecting the xylan yield was analyzed by orthogonal experiments.Finally,the papermaking performance of residues under different beating degrees was analyzed.The bamboo pieces were pre-treated by screw extrusion-alkali pre-impregnation-PFI mill.The effects of the number of screw extrusion,feed concentration,the amount of alkali used for pre-impregnation of alkaline liquid,liquid ratio,time and the refining number of PFI mill on the yield of bamboo xylan were explored.The product was analyzed by SEM electron microscope.The experimental results showed that the pretreatment can help improve the yield of xylan by increasing the fine fiber ratio in the slurry fiber and the dividing index.In detail,the single-factor process conditions for bamboo chip pretreatment were spiral extrusion 4times,feed concentration of 35%,pre-impregnation alkali amount of 6%,liquid ratio of 1:4,impregnation of the material at normal temperature for 90 min,and 5000 revolutions refining in PFI mill.In this process,the yield of xylan was 55.23%,the yield of slurry was 68.07%,and the removal rate of lignin was 54.85%.SEM analysis showed that through SEM electron microscopy,it was found that spiral extrusion,PFI milling and lye pre-impregnation played a role in dividing and moistening the bamboo chips.The alkali extraction method was used to extract xylan from the pretreated materials,and the effects of the alkali extraction amount,liquid ratio,time and temperature on the xylan yield were investigated.The products and raw materials were analyzed by FTIR,NMR,TGA and SEM electron microscope.The experimental results showed that the single-factor process conditions for the extraction of xylan by the bamboo chip alkaline method were 80%alkali used for alkali extraction,liquid ratio was 1:8 and was kept in an autoclave with a holding temperature of 125?for 45 min.The xylan yield was 85.13%,the slurry yield was 56.32%,and the lignin removal rate was 70.98%.Through the analysis of raw materials,products and slurries,it was found that the products not only contained xylan,but also arabinose,glucuronic acid,lignin and other substances.Finally,a five-factor four-level orthogonal experiment was designed based on the PFI mill revolutions,the amount of alkali used for alkali extraction,the liquid ratio,the holding temperature,and the holding time.The results showed that the order of the five influencing factors on the yield of xylan yield was:Temperature>amount of alkali used>liquid ratio>time>PFI mill revolutions.After repeating under the optimal conditions of the orthogonal experiment,the yield of xylan was 86.85%.After extracting xylan under the best process conditions,the residue was beaten to different beating degrees.The fiber morphology and papermaking performance at different beating degrees were compared and analyzed.The experimental results showed that as the beating degree increases,the paper strength shows a trend of increasing first and then decreasing.According to the commercial paperboard papermaking requirements,It is found that the beating degree is 39°SR and the paper weight is 90 g/m~2,the paper strength performance meets the technical index requirements of boxboard paper strength,and the comprehensive utilization of biomass resources is realized.