Fabrication And Properties Of Cellulose Nanofiber/Polymethylmethacrylate Nanocomposites

In this research, absorbent cotton and poplar wood powder was used as raw materials toprepare cotton cellulose nanofiber and wood cellulose nanofiber (CNF) which was successfullyfabricated using the combined method of chemical treatment and mechanical treatment. Thechemical treatment included three parts which were sodium chlorite (NaClO2), potassiumhydroxide (KOH) and hydrochloric acid (HCl) treating, and three different mechanical treatmentswere used here which were grinding, ultrasonication and high pressure homogenizing.Furthermore, the CNF suspension was made into CNF sheet by vacuum filtration, and theCNF/polymethylmethacrylate (PMMA) nanocomposites sheet was successfully fabricated byimmersing the CNF sheet into PMMA solution. Another way which was called hot pressingmethod to paepare CNF/PMMA nanocomposites sheet was also tried as a kind of exploratoryresearch. Fourier infrared analysis, optical microscope analysis, field emission scanning electronmicroscopy analysis, thermal mechanical analysis, tensile test and light transmittance test wasused in this research, and the following conclusions are drawn:1) The NaClO2treating and KOH treating can remove lignin and hemicelluloses,respectively, but they have little influence on absorbent cotton. The HCl treating has noeffectiveness on absorbent cotton's and wood powder's chemical composition, but it can weakenor even wipe off the binding force of hydrogen bond between fibers.2) The wood CNF has made by3times grinding was thinner than the cotton CNF made by7times grinding, and the former has more narrow diameter distribution. It means that it is easier tofabricate CNF using wood powder than using cotton as raw material.3) The properties of CNF sheet and CNF/PMMA nanocomposites sheet have direct relationwith the morphology of CNF. And the relationship can be summarized as: If the CNF was thinnerand has greater aspect ratio, the CNF sheet and CNF/PMMA nanocomposites sheet has bettertensile property and transparency, and has lower coefficient of thermal expansion (CTE) at thesame time.4) The morphology of CNF has intimate connection with the mechanical treatment duringthe fabrication procedure. This research proves that when the grinding time is less than7, thediameter of CNF can be much thinner by increasing the grinding times, and the properties of itscorresponding CNF sheet and nanocomposites sheet become much better. But when the grindingtime is more than7, keeping increasing the grinding times can't lead obvious change to thediameter of CNF.5) The diameter of CNF can be obviously reduced by ultrasonication or high pressurehomogenizing after7times grinding, and the properties of CNF sheet and CNF/PMMAnanocomposites sheet are obviously improved. For example, the average diameter of CNF made by7times grinding and high pressure homogenizing is less than100nm. And the tensilemodulus, tensile strength, CTE and light transmittance of its corresponding CNF sheet is6058MPa,148.8MPa,16.72×10-6/k and82.1%, respectively. And the tensile modulus, tensile strength,CTE and light transmittance of its corresponding CNF/PMMA nanocomposites sheet is3606MPa,92MPa,21.58×10-6/k and86.3%, respectively.6) The tensile property and thermal expansion property of CNF/PMMA nanocompositessheet can be improved by increasing the content of CNF, but it can lead to the reduction ofnanocomposites sheet's transparency. For example, the tensile modulus, tensile strength, CTEand light transmittance of CNF/PMMA nanocomposites sheet (67.9%CNF content) is1866MPa,57.8MPa,23.73×10-6/K and89.2%, respectively. And the tensile modulus, tensile strength, CTEand light transmittance of CNF/PMMA nanocomposites sheet (88.3%CNF content) is3545MPa,102.7MPa,20.26×10-6/K and84.4%, respectively.7) The properties of CNF/PMMA nanocomposites sheet fabricated by hot pressing are muchworse than the properties of CNF/PMMA nanocomposites sheet fabricated by immersingmethod.