Synthesis And Characterization Of Nanocrystalline Cellulose Reinforced Polyvinyl Alcohol Membrane

In this thesis, nanocrystalline cellulose (NCC) and nanofiber cellulose (NFC) was prepared with industrial reed pulp as raw material, respectively, according to the method of alkali pretreatment before sulfuric acid hydrolysis and high-pressure homogenization. Considering the differences of stability between NCC and NFC in polyvinyl alcohol (PVA) solution, NCC was selected as the enhanced component of PVA/NCC blend membrane. The effects of simple blending, freezing treatment and glutaraldehyde crosslinking on the mechanical properties, light transmittance and thermal stability of blend membranes were discussed. Meanwhile, the problem of NCC and NFC agglomeration in PVA basement was proposed to be resolved using the method of layer-by-layer self-assembly based on hydrogen bond driving force. And the PVA/NCC/PVA and PVA/NFC/PVA membranes with hierarchical structure were fabricated. The composite membrane with superparamagnetism was prepared by introducing Fe3O4magnetic nanoparticles into interlayer of NCC in the PVA/NFC/PVA membrane with hierarchical structure using the method of in-situ synthesis.About PVA/NCC blend membrane, a small amount of NCC has a significant improvement to the mechanical properties of PVA membrane. And the tensile strength of PVA/NCC blend membrane reached maximum of49.01MPa when the mass ratio of NCC was0.5%, increased by15%compared with the tensile strength of PVA membrane. There was no obvious change in light transmittance and thermal stability. After freezing pretreatment, the NCC particles dispersed in NCC/PVA blend membrane better. The tensile strength of PVA/NCC blend membrane increased by16%when the mass ratio of NCC was0.5%, while the light transmittance and thermal stability of blend membranes increased slightly. NCC/PVA and PVA membranes with optimum proportion were modified by glutaraldehyde crosslinking, it turns out that the tensile strength, thermal stability and water resistance could be enhanced with the degree of crosslinking. The light transmittance changed a little, but elongation at break decreased significantly. Furthermore, PVA membrane exhibited a higher crosslinking modification activity.With respect to PVA/NFC/PVA composite membrane with hierarchical structure, the single-phase distribution states of NCC and PVA in composite membrane, NCC lattice oriented state and the structure of NCC as interlayer were investigated by the analysis of ATR-IR, SEM and XRD. And the formation process of composite membrane with hierarchical structure was demonstrated by the proposed assumption of mechanism. According to the measurement of tensile strength, light transmittance and thermal stability, the PVA/NFC/PVA blend membranes with hierarchical structure prepared by LBL shows that high tensile strength, high light transmittance and thermal stability. And compared with PVA membrane, the tensile strength, light transmittance and thermal decomposition temperature of blend membrane increased by46.1%,5.44%and13.2℃, respectively.Regarding to PVA/magnetic NCC/PVA composite membrane with hierarchical structure, the results show that Fe3O4nanoparticles distributed evenly in the interlay er of NCC by using XRD, EDS and SEM. With the analysis of performance test, it turns out that the composite membrane possessed superparamagnetism, better UV barrier property, higher thermal stability and special oxidative degradation ability. The tensile strength of this composite membrane increased by17.0%compared with that of PVA membrane when the Fe3O4solid content was1.1%. But compared to PVA membrane, the elongation at break of this composite membrane decreased.For PVA/NFC/PVA composite membrane with hierarchical structure, the results indicate that the thickness of NFC layer could be controlled by adjusting the concentration of NFC according to the analysis of SEM, and this could affect the mechanical property of composite membrane. The effect of NFC on the improvement of mechanical property and light transmittance of composite membrane with hierarchical structure was much more obvious. The young modulus and tensile strength of sample LBL-3was1.97GPa and80.91MPa, respectively, which increased6.58times and0.90times as to those of PVA membrane. And the light transmittance reached up to92%in the visible region for sample LBL-3.