Study Of PVA/Laponite Nanocomposite Hydrogel Membrane

Hydrogel membrane made from poly(vinyl alcohol)(PVA)holds good gas barrier,transparency,antistatic and organic solvent resistance properties,as well as biocompatibility and biodegradability,so it has wide application prospect in the fields such as biomedicine,packaging,filtration for separation and fuel cell.However,pure PVA hydrogel membrane are generally of poor mechanical property and r water-resistance,which limits its practical applications.Although its mechanical property and water-resistance can be improved by chemical crosslinking method and the physical crosslinking method of many times repeated freezing-thawing,toxic and harmful chemical crosslinking agent or organic solvent is usually used,and the latter method is difficult to be industrialized.In addition,its modification by natural clay suffers from the limited modification effectiveness and the difficulty of removing the impurities of the clay.Therefore,in this thesis,PVA and laponite were used to prepare nanocomposite hydrogel membranes with different laponite contents by solution-intercalation and casting method,based on selecting the type of anti-gelling agent and optimizing its used amount.The mechanical properties and water-resistance of the nanocomposite membranes were further improved by drying treatment.The effect of the used amount of laponite or the drying temperature on the mechanical properties and water-resistance of the nanocomposite membrane was investigated.The relationship between its microstructure and macroscopic properties was also studied.The obtained research results of this thesis are described as the following three aspects:(1)The gelling of the aqueous solution of PVA and laponite was avoided by adding anti-gelling agent.Based on taking anti-gelling effect,volatility,toxicity,cost and other factors into consideration comprehensively,acetone was selected as anti-gelling agent.In order to probe the anti-gelling mechanism of acetone,the apparent viscosity of the aqueous solution of PVA/laponite with different amounts of added acetone was measured at different shearing rates,and then the zero shear viscosity of the solution was calculated by Cross equation.It was found that the zero shear viscosity of the solution decreases with the increase of the amount of acetone,so it can be concluded that the anti-gelling effect is due to the strong interaction between acetoneand laponite.With the increase of the concentration of acetone in the casting solution,the crystallinity of the prepared PVA / laponite nanocomposite membranes shows a tendency of first increase and then decrease,and the same tendency was found for the change of the tensile strength,Young's modulus and water resistance of the membrane with the actone amount.The results indicate that the crystallization of PVA induced by laponite is the main reason for improving the mechanical properties and water-resistance of the nanocomposite membranes.(2)In order to investigate the influence of the laponite content on the structure and properties of the membranes,different amounts of laponite were loaded into PVA/laponite nanocomposite hydrogel membranes by solution-intercalation and casting method.Fourier transform infrared spectroscopy(FTIR)and scanning electron microscopy(SEM)show that there is an interaction between the PVA chains and exfoliated laponite crystal plates within the nanocomposite membranes.The results obtained bydifferential scanning calorimetry(DSC)and X-ray diffraction(XRD)exhibit that the new crystalline phaseinduced by laponite was formed within the membranes.The more the amount of the added laponite,the more ordered the new crystalline phase,and the higher its content.The equilibrium swelling ratio of the nanocomposite membrane in water decreases gradually with the increase of its laponite content,so the water resistance of the membrane is improved.The Young's modulus and tensile strength of the nanocomposite membranes increase with their increasing content of laponite,but their elongations at break increase first and then decreases.The formation of new crystalline phase may be the main reason for the improvement of the water resistance and mechanical properties of the nanocomposite membranes.Compared with pure PVA membrane,the light transmittance of the nanocomposite membrane is slightly lowered.(3)In order to investigate the effect of drying temperature on their structure and properties,a series of PVA/laponite nanocomposite hydrogel membranes were prepared by changing the drying temperature in the range of 40 ? ~ 70 ?.The results obtained by FTIR and XRD show that the crystallinity and crystallite size of the membranes increase with the rise of drying temperature,correspondingly their tensile strength and Young 's modulus increase and their elongation at break decrease.This is because that the increase of the microcrystalline content and the physical crosslink density within the membrane lead to enhancement of the rigidity of the membraneand weakness of its elasticity.With increase of the drying temperature,the water resistance of PVA/laponite nanocomposite hydrogel membrane is improved obviously.This is owing to the fact that water molecules are difficult to enter the t crystal area composed of closely aligned PVA molecular chains,so that the higher crystallinity of the membrane leads to its better water resistance.