Study On The Application Of Thermostable Xylanase In Pulp Bleaching

As one kind of environmental friendly additives,enzyme is widely used in pulp and paper industry,especially applied in pulp bleaching.The environment of pulp bleaching is mostly high temperature and alkali,common enzyme is difficult to survive.In recent years,many researchers regard the development of temperature resistant and alkali resistant enzyme preparation as one of the research focuses.thermostable xylanase is a new kind of enzyme with high temperature resistance,enzyme activity,stability and adaptability.In this paper,poplar pulp and abaca pulp were used as the main experimental materials,the effect of thermostable xylanase on pulp bleaching was discussed.The process conditions of the two types of pulp were optimized,and the effect of enzyme treatment on the fiber morphology and properties was analyzed,which provided some references for its application in actual production.The influencing factors of enzyme activity were first studied by testing the pH,temperature resistance and stability of the thermostable xylanase.The results showed that the thermostable xylanase has a high activity at the conditions of neutral pH and the temperature of 85?.Enzyme activity changes smaller in the storage time at 12 months,the stability of thermostable xylanase activity is good.Thermostable xylanase was used to pretreat poplar unbleached pulp with the conditions of different dosage,temperature,pH and time.Then take the experiment of H₂O₂ bleaching and optimized the process conditions of enzyme pretreatment.The results showed that the optimal conditions of pretreatment were:the dosage of enzyme at 150 g/t?dry pulp?,pH at neutral and slightly alkaline,treating temperature at above 85?,treating time at about120min;Under this condition,the whiteness of pulp increased by more than 2.5%ISO,and the kappa number decreased by about 1.Thermostable xylanase and neutral cellulase were used to pretreat abaca pulp before hydrogen peroxide bleaching.The effects of enzyme treatment on hydrogen peroxide bleaching of abaca pulp were investigated and optimized.The optimal conditions of pretreatment were:the enzyme dosage at about 200 g/t,pH neutral,the temperature at about 85?or above,pretreatment at about 100 min,under this condition of the pulp whiteness increased by 3%ISO,kappa number decreased by about 1.5.At the same time,this paper lists the application effect of thermostable xylanase as the main raw material in the actual large-scale production.Scanning electron microscopy?SEM?was used to observe the abaca pulp fiber which pretreated by compound enzyme,and then beating the pulp.Analyzing the influence of enzyme pretreatment on fiber surface structure and pulp beating features.The experimental results show that the surface of the pulp treated by enzyme becomes rough and the fiber splitting is increased and the area of fiber bonding is increased,which is beneficial to improve the physical strength of the pulp.The beating features of abaca pulp were changed before and after enzyme treatment.The enzyme treated abaca pulp is easier to beat.Thermostable xylanase was used to pretreat softwood pulp,hardwood pulp,abaca pulp and bamboo pulp,the effect of the pretreatment was discussed:The effect of xylanase on this four pulps from high to low is.abaca pulp,bamboo pulp,hardwood pulp,softwood pulp.The effects of thermostable xylanase on the content of Xylan in different fiber materials were studied.It was found that the reducing sugar content of softwood changed least,the other three kind of pulps were similar and more than softwood.So,the effect of thermostable xylanase on hardwood pulp and hemp pulp and bamboo pulp was more obvious than that of softwood pulp.