Studies On The Structure And Properties Of Polyvinyl Alcohol Modified With Natural Polyphenol

Tea polyphenol(TP)is one kind the polyphenolic compounds with good biocompatibility and biodegradation ability. The comprehensive utilization of tea and to develop tea-based novel products with desired aspects is a considerable way and to be importantly taken as research project.In general,TP is known of abundant,renewable and having many bio-properties,e.g.as a natural antioxidant to eliminate free radicals in body,to protect ultraviolet effect and as the resisting agent in treatment of cancer, tumor,antiviral,anti-inflammatory and deodorization properties. Because the polyhydric phenol structure is capable to cause condensation reaction with the aldehyde,and its hydrogen bond to be interacted with other polymer groups,the application of the polyphenol in polymer is thus available to provide a possibility for modification of latter with new function. In this paper,TP was characterized by FTIR and contact angle measurement initially.Then its dissolution behavior was studied by applying dynamic conductivity measurement, meanwhile a mathematical model was deduced based on recorded dynamic curves.The polyvinyl alcohol,PVA,and tea polyphenol,TP,blends were prepared by casting from H₂O.FTIR spectra indicated that the intermolecular interactions are occurred between PVA and TP due to the presence of hydrogen bonds.All PVA/TP blends presented a single T_g peak over the entire blending ratios prepared suggesting these two polymers blends having good compatibility. This was also evidently in recorded SEM photographs for PVA/TP blends.Based on the Beer-Lambert law and Nonlinear Least Squares Fitter,the FTIR stretching vibration of the C-O group of PVA can be quantitatively analyzed.On the basis of the T_g observed in DSC curves and estimated from the Kwei and Couchman equations,it was found the T_g of PVA/TP blends was increased with the increase of TP centent, while the melting point is however decreased.Obviously,such blending behavior are beneficial for PVA thermoplastic processing. A good linear relationship between the T_g of blends and the weight ratio has been found to be as:T_g=111.17-13.46 ln(W_PVA/W_TP),R=0.998.XRD results indicated that main peak related 2θto be at 11.3°,19.7°,23.1°,28.0°,31.8°and 40.8°,respectively in relation to the crystal structure of(100),(101),(200),(201),(002)and (111),respectively.The peak strength was observed to reduce with the increase of the TP content.The Ozawa,Jeziorny and Mo equations are used to describe the non-isothermal crystallization kinetics and results show that the Ozawa equation is unable to fit this case and the Jeziorny and Mo equations exhibited great possibility.The parameters of the non-isothermal crystallization kinetics were therefore estimated using the Jeziorny and Mo equations.The water absorption capacity and the surface hydrophilicity of PVA/TP blends are measured by contact angle measurement. We found that the water contact angle on the surface of PVA/TP was increased with the increase of the TP%indicating the surface hydrophilicity decreased.It was also observed that the water absorption capacity of the blends tends to decrease with the increasing of TP%.Additionally,the water absorption capacity for blends has been found to be lower in acidic solution and higher in alkaline solution comparing with the distilled water.To modify PVA using TP,the biodegradability,antibacterial properties and ultraviolet protection of m-PVA are found significantly improved.For example,after 60 days of a soil burial test,the original PVA lost of 5.20 wt%while the weight loss for PVA/TP blend in 100/5 and 100/40 W/W were 6.94%and 38.53%, respectively.The antibacterial activity of PVA and PVA/TP blends was tested in accordance with AATCC90-1982 by plate medium and three types of bacteria,e.g.Staphylcoccus aures,Escherichia coli,and Proteus valgaris,were used.The results indicated that the PVA/TP blends have the antibacterial activity visible for all these used three bacteria but PVA on the contrary.The inhibition levels for PVA/TP blends corresponding to three bacteria to be as in Staphylcoccus aures the best,the followed is in Escherichia coli then the Proteus valgaris.Moreover,the antibacterial activity has been found also increased gradually with the TP content increase.According to the Australia/New Zealand standard, AS/NZS 4399:1996,the ultraviolet protective properties of the PVA/TP blends were evaluated and the result show that the capacity of the ultraviolet protection for blends was extremely increased by adding TP to PVA even after immersion blends in water for about 72 h.A comparison of PVA and PVA/TP blends indicated the blends could be classified to have excellent UV-protection possibility.