Effect Of Pretreatment On Wheat Straw Biomechanical Pulping Performance

With the implementation of the ban on solid waste imports in China and the increasing demand for domestic packaging paper,the domestic paper industry has a shortage of raw materials.It is urgently to be resolved that finding a packaging paper raw material to replace waste pulp.Among papermaking raw materials,non-wood plant fiber raw materials have the advantages of rich reserves,wide distribution,and low price in China.Moreover,pulp and papermaking which non-wood plant fiber is used to be raw material has a long history and has accumulated rich production experience.In order to effectively increase the supply of raw materials and alleviate the pressure brought by the shortage of raw materials,the related research on the exploit and development of non-wood plant fiber raw materials for pulp and papermaking has caused widespread concern.Therefore,in this paper,wheat straw one of the non-wood fiber raw material is used to be raw material to produce pulp for packaging paper.Based on the biomechanical pulping technology,the alkaline hot water impregnation and the pretreatment of enzyme to be performed before mechanical refining.In addition,the microstructure changes of wheat straw before and after pretreatment are observed and analyzed.After mechanical grinding and pulping,the biomechanical pulp mixed with waste pulp is used to produce packaging paper in order to meet the physical strength requirements for the production of primary color packaging paper.The method provide theoretical basis and technical support for the new process of wheat straw biomechanical pulping.First,the wheat straw was refined to be pulp after being impregnated by hot water-alkali.Then the influence of amount of alkali and impregnated time on the strength of pulp was analyzed.Besides,the pulp yield and the amount of lignin and sugars in wheat straw were measured.Studies have shown that with the increase in the amount of alkali and the impregnated time,the strength of the paper increased,while the pulp yield gradually decreased.When the alkali content was 4%and the impregnated time was 20minutes,the extractive part was extracted,the sugar dissolution amount was 2.98 mg/g and the lignin dissolution amount was 58.24 mg/g during the process of wheat straw impregnated.The stratum corneum on the surface of wheat straw was damaged.Therefore,the accessibility of enzymes was improved,and the pulp yield was greater than 80%.The tensile index of the paper was 25.82 N·m/g,and the ring pressure index of the paper was9.59 N·m/g.Secondly,the wheat straw was refined to be pulp after being impregnated by hot water-alkali and being pretreatment by enzymes.Then the effects of the types and amounts of enzymes,the pretreated time,the pretreated temperature,and the p H value of the pretreatment solution on the strength of pulp into paper were analyzed.Furthermore,the dissolution of lignin and sugars after being pretreated by enzymes was detected.Studies have shown that pectinase,lipase,xylanase,and cellulase could remove stratum corneum on the surface of wheat straw and softened fibers.Besides,the compound enzymes had better pretreatment effects than single enzyme.The pretreatment of compound pectinase,lipase and xylanase was the best.Wheat straw was treated with 30U/g pectinase,20 U/g lipase,and 15 U/g xylanase at 55°C for 4 h,8 h and 8 h in the pretreatment solution that p H value of was 7 had better performance.Under this condition,the dissolution amount of sugar was 11.84 mg/g,the dissolution amount of lignin was11.42 mg/g,the tensile index of the paper was 36.85 N·m/g,and the ring pressure index of the paper was 11.41 N·m/g.High-resolution scanning electron microscopy,laser confocal Raman spectrometer,laser confocal microscope,atomic force microscope,and micro-CT were used to observe the microstructure of wheat straw before and after being impregnated by hot water-alkali and being pretreatment by enzymes.Then the cell wall structure and composition,three-dimensional organization structure and fiber morphology were analyzed.The results showed that impregnation of alkaline hot water and pretreatment of enzyme could remove the stratum corneum on the surface of wheat straw,softened the fibers,swelled and dissolved the fibrous cell wall.Both the lignin and carbohydrate in the cytokeratin（CCML）,intercellular layer（CML）,and secondary wall S₂ layer of wheat straw fibroblast wall were degraded to different degrees.The surface and internal organization structure of wheat straw were damaged to varying degrees,and the fiber skeleton became loose.Wheat straw impregnated with alkaline hot water and pretreated by enzyme was refined to be pulp by high-density continuous disc mill was used for atmospheric.Next,the influences of the number of refining stages,the distance between the grinding teeth and the beating degree on the strength of paper and the energy consumption of refining were analyzed.The results showed that the two stages of refining with a clearance of 0.5mm and 0.15 mm,the physical strength of the paper was higher,and the energy consumption of the refining was lower.Wheat straw biomechanical pulp mixed with waste pulp could improve the physical strength of the paper so that could meet the requirements for producing primary color packaging paper.