Preparation And Application Of Wheat Straw Microfibrillated Cellulose

Bleached chemi-thermomechanical pulp(BCTMP)is widely used in paper making,with its good optical properties and bulk.Meanwhile,the BCTMP fiber retained a large proportion of lignin during pulping process,leading to the weak bonding strength of fiber-fiber,which results in a weak paper strength,low proportion of blending and low utilization rate of wood resource.The main objective of this study was to isolate the MFC from the straw material of low cost to improve the strength properties of BCTMP handsheets,and further broaden the application scope of MFC.Firstly,the microfibrillated cellulose(MFC),as a novel fiber-based reinforcing agent,was isolated from treated wheat straw pulp to improve strength properities of BCTMP sheet.The wheat straw pulp was subjected to high presure homogenization to obtain MFC with water retention value(WRV)559%,absolute viscosity 158mPa s(1 wt%).The MFC was of nanoscale filaments with much high length to diameter ratio,width in dozens nanometers and length in dozens micrometers,in the observation of SEM and TEM.Secondly,the addition of prepared MFC was used to compared with PFI refining inimproving the BCTMP physical properties of handsheets.The results showed that tensile index and burst index of handsheets were enhanced by adding MFC.When 20%was added,43.58 N m/g and 2.83 kPa m2/g were obtained respectively for tensile index and burst index,increased by 110.27%and 130.08%,whereas the bulk decreased by 22.33%.Thirdly,the enhancement effects of MFC with different degree of homogenization was discussed.The results showed that,tensile index and burst index increase by 78.24%and 125%with MFC of homogenization 40 times in 10%addition,whereas bulk and air permeability decreased by 11.74%and 81.38%.As 8%MFC(homogenization 20 times)was added to BCTMP(22°SR),the tensile index increased by 29.15%.The enhancement effects became weaker with the increase of beating degree of BCTMP.At last,the effects of residual lignin content on MFC properities was investigated.The effect of residual lignin content on MFC properities were investigated by thermogravimetric analysis,XPS,SEM,TEM and the enhancement effects of MFC with differen lignin content on BCTMP sheet were also investigated.The results showed that the presence of lignin in cellulosic fiber was adverse to fibrallating and microfibril released.The surface lignin concentration,temperature of maximum decomposition rate and crystallinitys of MFC decreased with the decrease of residual lignin content in wheat straw pulp fiber.Reactive brilliant red dyeing and EDS annlysis showed that the content of surface hydroxy groups of MFC increased with the increase of alkali dosage in cooking,meanwhile,tensile index,burst index were increased more dramatically with MFC of addition.