| The problem of poor water resistance of poly(vinyl alcohol)(PVA) film is quite prominent during the using process, celluloses offer advantages to overcome this problem. Cellulose-based composites are biodegradable, low cost and multifunctional materials that is attractive in the field of materials science. In this work, photo-crosslinked PVA/CNC and PVA/(M/NFC)/polyHEMA composite materials which exhibite improved water resistance as well mechanical strength and other properties were designed in simple and convenient methods, combining of UV light cross-linking technology. The main research work as follows:1. In the first system, cellulose nanocrystals(CNC) were obtained by optimized hydrolysis time, and the products were used to blend with PVA. Firstly, the different morphology of CNC were extracted from cotton fiber using sulfuric acid. The morphology of CNC were observed by TEM. The changes in the structure of cellulose were characterized with FT-IR. Polymorphs and crystallinity of CNC were characterized with XRD. Combined with the degree of crystallinity of CNC products, the thermal stability was investigated by TGA. The surface charge of the CNC and rheological behavior of their suspension were analysised with Zeta-potential measurements and Rheological measurements, respectively. Finally, the relationship between the morphology of CNC and the reinforcing effect of CNC in PVA matrix were discussed. The conclusions are as follows: CNC obtained by hydrolysis time of 45 min were chosed to blend with PVA. Compared to PVA film, PVA/15% CNC composites exhibited lower value of water absorption(31.79%) and higher tensile strength(83 MPa), which indicated improved water resistance and mechanical strength.2. As the agglomeration of CNC in PVA was notable in the previous system, the modified CNC were obtained for the purpose of the better dispersion. Firstly, the chemical modification of CNC was carried out with methacrylic anhydride(MA) to obtain CNC-g-MA, which were characterized by FT-IR, UV-vis, 13C-NMR and TGA. Then CNC-g-MA were added into PVA to prepare PVA/CNC-g-MA nanocomposite films. For the purpose of improved water resistance and more functional properties of PVA, the ring-opening reaction between PVA and glycidyl methacrylate(GMA) was carried out under acidic conditions to obtain PVA-g-GMA. The photo-initiator was added into the mixtures of PVA-g-GMA and CNC-g-MA to prepare PVA-g-GMA/CNC-g-MA nanocomposite films, and the photo-crosslinked films were obtained after cross-linking upon exposure to UV. The effects of the content of CNC-g-MA and the degree of photo-crosslinking on the water resistance, mechanical properties, optical transparency, barrier and thermal properties of the composites were investigated. The results showed that the dispersion of CNC in PVA would be improved after modification. With the addition of CNC-g-MA, PVA/CNC-g-MA nanocomposite films exhibited improved tensile strength but poor water resistance. Compared to the case of PVA/CNC-g-MA and PVA, the photo-crosslinked PVA-g-GMA/CNC-g-MA systems exhibited the improved tensile strength and the water resistance. When the content of CNC-g-MA is 10 wt%, the photo-crosslinked PVA-g-GMA/CNC-g-MA composite exhibits good mechanical properties, with a tensile strength of 74 MPa, which is about 137% higher than that of neat PVA. And it also exhibits the best water resistance, with the value of water absorption of 15.18%, which is 65.45% lower than that of neat PVA.3. In the third system, microfibrillated cellulose(M/NFC) which has a higher aspect ratio were blended with the photo-initiator and hydroxyethyl methacrylate(HEMA) to obtain PVA/(M/NFC)/polyHEMA composite films after cross-linking upon exposure to UV. The effects of the content of HEMA and the degree of photo-crosslinking on the water resistance, mechanical properties, optical transparency, barrier and thermal properties of the composites were investigated. The results showed that HEMA increased the interaction between PVA and(M/NFC) and improved the(M/NFC) distribution in PVA/(M/NFC)/polyHEMA composite films. With the addition of(M/NFC), PVA/(M/NFC) nanocomposite films exhibited the improved tensile strength and the water resistance. In the optimal PVA/(M/NFC) ratio of 1/0.25(w/w), PVA/(M/NFC) composite exhibits the better mechanical properties, with a tensile strength of 54 MPa, which is 73% higher than that of neat PVA. And it also exhibits the better water resistance, with the value of water absorption of 32.70%, which is lower than that of neat PVA. Compared to PVA/(M/NFC) films, the photo-crosslinked PVA/(M/NFC)/polyHEMA systems exhibited improved water resistance as well thermal and barrier properties. The photo-crosslinked PVA/(M/NFC)/polyHEMA5 composite exhibits the good mechanical properties, with a tensile strength of 41 MPa, which is 30% higher than that of neat PVA. And it also exhibits the best water resistance, with the value of water absorption of 20.7%, which is 52.48% lower than that of neat PVA. |
PDF Full Text Request