Study On The Plasticization Of Poly(vinyl Alcohol) Films

Poly（vinyl alcohol）（PVA）is a biodegradable synthetic cheap polymer with excellent characteristics,which has attracted people’s great interest in research and development of PVA.Because PVA melting point（T_m）which is very high is very close to PVA decomposition temperature,and pure PVA is brittle.So it is necessary to add the plasticizer to PVA during the process of preparing PVA materials,plasticizer is used to lower PVA T_m to contribute to the process and soften PVA materials.In general,there are three kinds of traditional plasticizers.One kind is polyols,such as glycerol,ethylene glycol,PEG with low molecular weight.One other kind is amide,for example caprolactam,urea,formamide.Another kind is inorganic salt,including MgCl₂·6H₂O、LiCl.However,PVA films plasticized by traditional plasticizers have disadvantages,such as,some plasticizers are toxic,some plasticizers are easy to crystallize,properties of some PVA films are not desirable.All the factors restricted the application fields of PVA films.To improve the PVA films properties is one of focuses of current research.The influence of plasticizer on the properties of PVA is very important.Inthepaper,fournontoxicplasticizershydroxyalkylformamides（N,N-Bis（2-hydroxyethyl）formamide（BHF）,N-（2-hydroxyethyl）formamide（HF）,N-（2-hydroxyethyl）-N-methylformamide（HMF）,N-（2-hydroxypropyl）formamide（HPF））are synthesized and used as PVA plasticizers,respectively to prepare PVA films by casting method.PVA films plasticized by traditional plasticizer glycerol are prepared for compare.Fourier transform infrared spectra（FTIR）demonstrate that hydrogen bonds occurred between the new plasticizers HAF and PVA are strong.X-ray diffraction（XRD）indicates that the crystallinity of PVA could be destroyed by HAF.The melting point（T_m）of PVA is examined by differential scanning calorimetry（DSC）.DSC shows that HAF could decrease the melting point（T_m）of PVA.T_m of PVA is related to the molecular weight of the plasticizer.For PVA films with the same weight content plasticizer,the lower the molecular weight of plasticizer,the lower the T_m of PVA.The T_m of PVA plasticized by HF is lower than that of PVA plasticized by traditional glycerol.The mechanical properties and water vapor resistance of PVA films are studied.Generally,water vapor resistance of HAF-plasticized PVA film is better than that of glycerol-plasticized PVA film.HAF are effective plasticizers for PVA.Carbohydrates（CH）are nontoxic and edible.Fructose,raffinose-pentahydrate,xylose,ribose are used as poly（vinyl alcohol）（PVA）plasticizers,respectively to prepare PVA films by casting method.The results show that CH could destroy PVA intramolecular and intermolecular hydrogen bonds,strong hydrogen bonds form between CH with PVA.At the presence of CH,PVA crystallinity reduces and the melting point of PVA lows.CH are effective plasticizers for PVA.WVP of PVA is related to the molecular weight of the plasticizer.For PVA films with the same weight content plasticizer,the lower the molecular weight of plasticizer is,the higher the WVP of PVA is.The mechanical properties of CH plasticized-PVA film are measured.PVA is smashed and sieved,PVA powder with different size is obtained.HF and glycerol plasticize-PVA films using PVA powder with different size as raw are prepared by melt pressing and characterized.The results show that the PVA particle size has a great influence on the plasticization effect of PVA.Under the same conditions,the smaller the particle of PVA,the lower the crystallinity of PVA,which contribute to the penetration of plasticizer into PVA.Penetration of plasticizer into PVA contributes to lower the T_m of PVA,PVA is easy to be plasticized.