Study On Preparation Of Microfibrillated Cellulose By Carboxyethylation

Cellulose is important component of plant biomass materials, which exists widely in the cell wall of higher plants such as cotton,wood,flax and grasses. It is the most abundant natural polymer on earth,whichaccounting for over 50% of the carbon content in plant kingdom.Microfibrillated cellulose(MFC for short) is one new type of nanoscale polymer materials which is treated by mechanical processing. Due to itsexcellent properties such as high transparency, high strength and large specific surface area, microfibrillated cellulose is used widely in the pharmaceutical, paper making, textile, etc. It has become a hot spot in global forest products and materials science research in recent years.This thesis studied the feasibility of preparation of microfibrillated cellulose, the results show that this process is divided into two steps: the carboxyethyl modification of cellulose by Na OH/acrylamidend and high pressure homogeneous mechanical processing. Of which, theconditions of high pressure homogeneous mechanical processing are: pressure 60 MPa, traffic 40 L/h, treatment capacity 500 m L, treatment concentration 1%, pass 20 p; treatment time 15 min. According to the different concentrations of total reaction system,the operation process of carboxyethyl modification is different.This thesis focuson the modification of low concentration(5%),which explored the `acrylamidedosage, sodium hydroxide dosage, reaction temperature and reaction time on the content of carboxyethyl. Single factor experiment showed the optimum preparation conditions are: acrylamide dosage 2.12 g·g-1oven dry pulp, sodium hydroxide dosage 1.70 g·g-1 oven dry pulp, reaction temperature 90℃, reaction time 5 h. By this time, the content of carboxyethyl 1.89 mmol ·g-1.Afterhigh pressure homogeneous mechanical treatment, the performance of MFC with different contentsof carboxyethyl is characterized, which includinglength, diameter, length to diameter ratio, degree of polymerization and the transmittance.The results show that the higher the carboxyethyl content is, the smaller the size and degree of polymerization is, and the higher the transmittance is.When the content of carboxyethyl is 1.89 mmol ·g-1, the diameter of microfibrillated is about 20 nm, the length is about 1.5 μm, the length to diameter ratio is about 80, the transmittance in 800 nm is 83.89%, the degree of polymerization is 265.Explore carboxyethyl modification process of middle concentration(13%)and high concentration(24%) respectively, meanwhile make comparisons the process in low concentration(5%),research shows that: compared the process in middle concentration(13%) with low concentration(5%), when carboxyethyl content changed little(3.7%), the acrylamide consumption reduced by 50%, Na OH dosage reduced by 50%, reaction temperature reduced by 22%, reaction time decreased by 40%; compared the process in high concentration(24%) with low concentration(5%), when the carboxyethyl content changed little(1.1%), the acrylamide consumption reduced by 92%, Na OH dosage reduced by 70%, reaction temperature reduced by 22%, reaction time decreased by 40%; compared the process in high concentration(24%)with middle concentration(13%), when the carboxyethyl content changed little(2.7%), the acrylamide consumption reduced by 85%, Na OH dosage reduced by 40%, reaction temperature reduced by 22%, reaction time decreased by 40%.