Study On Water Resistance Of Complete Alcoholysis Polyvinyl Alcoho Packaging Films

As an environmental polymer compound, polyvinyl alcohol(PVA)has excellent performance on water-solubility, film forming and biodegradability properties. Since there are a large number of hydrophilic groups on the molecular chain, the production, expanding and application of PVA film are largely restricted by its poor water resistance. The study applied complete alcoholysis PVA for preparing water-soluble PVA packaging film. Through boric acid modification and heat treatment, the PVA film is expect to obtain good water resistance and be widely used in the packaging field. The effects of processing conditions on the properties of the films are preliminarily discussed. The main research contents and results were as follows:(1) Focusing on the different effects of different solution temperature,dipping time on the water resistance properties of PVA film, the cross linking modification of PVA film is explored by adding saturated boric acid solution. The results show that the moisture absorption of PVA film decreases with the increase temperature and immersion time of boric acid solution. The moisture absorption of the film for 72 h decreases from 11.2%to 1.4% and water resistance is improved accordingly. The results of Fu Liye Infrared Spectroscopy(FT-IR) show that this change in water resistance is due to the esterification reaction of boric acid and hydroxyl group on the molecular chain of PVA. Furthermore, the results of Differential Scanning Calorimetry(DSC) show that the glass transition temperature(Tg) of the modified PVA film is improved and the maximum use temperature is increased. The results of Mechanical Property Test show that that the tensile strength of the modified PVA film is improved while the breaking elongation is decreased gradually. Considering the productive efficiency, we ascertain the basic optimal temperature of boric acid bath is70°C and the optimum immersion time is 5 minutes.(2) The properties of PVA film was explored after heat treatment crossed in different time and different temperature. By using Scanning Electron Microscopy(SEM), TGA, FT-IR, electronic tensile machine, light transmittance / hazemeter and other test means, the study focus respectivelyon the influence of temperature and time on the mechanical, optical and water resistance of the film. The results show that with the increase of heat treatment temperature and time, the film has generated a new crystalline structure; molecular arrangement grows more closely, the water resistance of the film, tensile strength and tearing strength are increased while the solubility, elongation at break are decreased; and the light transmittance and haze decreased are decreased slightly.(3) After heat treatment is crossed on the PVA film with boric acid modification, different performances of films prepared before were analyzed respectively with this one. The results show that there are chemical cross-linking and crystal structure after heat treatment is crossed on the PVA film with boric acid modification. The number of molecular chain hydroxyl decreases while the molecular chain arrangement grows more closely. Compared with single treatment, tensile strength of the PVA film increases and the elongation at break and tear strength decreases; and the transparency is reduced, while the water resistance is greatly improved.