Improving CMP Properties From Fast-grown Woodchips With Ultrasonic Aidance And Its Mechanism

Since the 1980 s,chemimechanical pulp has developed rapidly in China due to the advantages of wide adaptability of raw materials,low investment,high yield of pulp and so on.Due to the shortage of high-quality pulp raw materials in China,most enterprises use commercial wood chips for production.The quality of wood chips cannot be controlled,and the variety of wood and the differences of wood property,which leads to the production of high chemical consumption and high power consumption.The main reason is that it is difficult to achieve homogeneous impregnation and softening of commercial wood chips.This study is aimed at the problem that it is difficult to homogenize impregnation of commercial eucalyptus and poplar tablets,and utilizes the unique cavitation effect of ultrasonic to improve the penetration of liquid in wood chips.In order to solve the problem that the commercial eucalyptus and poplar tablets are difficult to be homogeneously impregnated,the effects of ultrasonic pretreatment on the bleaching of the machine pulp impregnation section and the eucalyptus mechanical pulp(TMP)bleaching were optimized,and the effect of the two-stage ultrasonic synergy was optimized.The optimum process for ultrasonic assisted bleaching impregnation was determined.The mechanism of ultrasonic assisted impregnation bleaching was clarified by means of infrared analysis,crystallinity analysis and scanning electron microscopy.The ultrasound assisted impregnation has been studied with eucalyptus and poplar as raw materials and chemical thermomechanical pulp(CTMP)as the process in this paper.By continuously monitoring the change of amount of liquid absorbed and residual sodium hydroxide in impregnation system,it was found that ultrasonic-assisted technique can significantly improves impregnation efficiency of wood.The experimental results show that:the optimum conditions for ultrasound assisted impregnation were the ultrasonic strength of585 W,the temperature of 75℃,the time of 30 min,the alkali content of 6%for eucalyptus,thealkali content of 5% for poplar and 10% pretreatment slurry.In this case,The alkali absorption of eucalyptus increased by 3.31%,and thealkali absorption of poplar increased by 6.15%.In addition,the brightness increased by 2.11% ISOand the residual hydrogen peroxide content increased by 4.4% for eucalyptus,the residual hydrogen peroxide content increased by 2.73%and the brightnessunchanged for poplar.The effects of ultrasonic pretreatment on the bleaching of eucalyptus mechanical pulp(TMP)were explored,by analyzing the physical properties such as whiteness and residual hydrogen peroxide content of eucalyptus mechanical pulp before and after ultrasonic treatment.And the optimum technological conditions for ultrasonic pretreatment were further explored.The experimental results show that: the optimum technological conditions for ultrasonic pretreatment was as follows: 585 W ultrasonic strength,30 min pretreatment time,2%pretreatment slurry,80 ℃ temperature and the treatment process was ultrasonic-assisted bleaching liquid treatment,22.5Hzfrequency,witch with the brightness increased by 1.97%ISOand the residual hydrogen peroxide content increased by 8.5%.The physical strength was improved,and the tensile strength was the most obvious.The tensile index was increased by1.11 N?m/gunder the optimal process.The process conditions of the two-stage ultrasonic pretreatment were optimized by measuring the brightness and residual hydrogen peroxide content after two-stage ultrasonic treatment impregnation.The optimal ultrasonic pretreatment conditions were determined by comparing the brightness and residual hydrogen peroxide content of the bleached pulp after single-stage ultrasonic treatment and two-stage ultrasonic treatment.The experimental results show that the whiteness of eucalyptus is 3.9% higher than that of a section of ultrasonic impregnation,and the whiteness of poplar is 3.58% ISO.Compared with the single-stage ultrasonic pretreatment bleaching stage,the whiteness of eucalyptus is reduced by 1.19% ISO,and the whiteness of poplar is reduced by 2.1.%ISO,but the amount of Na OH used in the two-stage sonication was 4% higher than that of the single-stage single-stage ultrasonic pretreatment bleaching,and the amount of poplar alkali was 3% higher.The fracture index,tear index and tensile index of the eucalyptus after two-stage ultrasonic treatment were increased by30.23%,12.5% and 20.92%,respectively,compared with the single-segment ultrasonic treatment;Yangmu increased by 15.58 respectively.%,34.11% and 22.37%.Scanning electron microscopy,confocal Raman microscope and material composition analysis show that the ultrasonic wave can break the pits,and then open the flow channel of the liquid inside the wood,improve the impregnation rate of the liquid,and thus improve the removal rate of lignin.Infrared,X-RD and fiber quality analysis showed that ultrasonic-assisted bleaching liquid treatment of pulp fiber can improve the softness of the fiber and the water filtration performance of the pulp fiber,and improve the fibrillation and filamentization of the pulp fiber.