Purifying Mechanism Of Paper Grade Chemical Pulp By Using ?-valerolactone/H₂O System

Dissolving pulp is an important raw material for viscose fiber production.In recent years,the market demand was increased rapidly.Simplifying the production process and established new production technology of dissolving pulp have become an important field.For this reason,paper grade chemical pulp was a kind of potential source for dissolving pulp with high cellulose content and large output.In this study,the bleached kraft pulp from softwood and hardwood was selected as raw material.The?-valerolactone(GVL)/H₂O system was used to purify the pulp,as well as integrated with PFI refining and xylanase treatment.The properties of treated pulps were determined based on standard method,such as viscosity,Fock reactivity,SEM(Scanning electron microscopy)analysis,FT-IR(Fourier transform infrared spectroscopy)analysis and XRD(X-ray spectroscopy)analysis.Paper grade chemical pulp upgrading using GVL/H₂O system.The treatment condition including GVL concentration,temperature and time was carried out.The optimized condition was GVL concentration 60%,temperature 120°C,time 2 h,sulfuric acid concentration 0.005 N,liquid ratio 1:15.Under such conditions,the?-cellulose and hemicellulose contents of softwood and hardwood pulp were Increased from 84.3%,85.0%and 11.0%,12.9%to 92.0%,93.2%and 4.35%,4.54%,and the hemicellulose removal were 60.5%and 64.8%,respectively.In addition,the Fock reactivity was increased by 35%and 36.5%,the viscosity was decreased by 10.6%,13.2%,and the alkali solubility(S₁₀ and S₁₈)reached(8.7%and 5.2%)and(8.9%and5.7%),respectively.Finally,the XRD analysis showed that the typical cellulose crystalline structure was maintained while the crystallinity was reduced slightly.The FT-IR verified the reduced absorption strength of hemicellulose.SEM observed the slightly split and much more pores present on the treated sample.PFI refining enhancing paper grade chemical pulp upgrading using GVL/H₂O system.Results showed that PFI refining positive enhancing the GVL upgrading effect.Results showed that the beating revolution of 15000 r could produce pulp with?-cellulose of 6.2%(softwood pulp)and 7.1%(hardwood pulp)at a much lower GVL treatment temperature(80°C),which could decrease hemicellulose content by 46.5%(softwood pulp)and 51.7%,respectively.Meanwhile,Fock reactivity and viscosity was improved by 34%,39.3%(softwood pulp)and 12%,7%(hardwood pulp),and alkaline solubility(S₁₀ and S₁₈)reached(8.13%and 5.18%)and(9.82%and 5.92%),respectively.XRD analysis showed the cellulose crystalline structure was well preserved while the crystalline index was slightly decreased.SEM observed the enhanced fibrillation effect by PFI refining.Xylanase treatment improving the GVL purifying process of paper grade chemical pulp.Results showed that the?-cellulose contents of softwood and hardwood pulp could reached to 92.7%and 93.3%,while the hemicellulose content was decreased to4.25%and 3.83%,respectively.At the same time,the Fock reactivity was improved by83.4%and 100.8%,and viscosity was improved by 15.2%and 14.4%,respectively.The alkaline solubility(S₁₀ and S₁₈)was decreased to(6.7%and 4.2%)and(7.23%and3.54%),respectively.XRD analysis showed the cellulose crystalline structure was not destroyed and the crystalline index was decreased.SEM showed the fiber surface showed less changes.