| Poly(vinyl alcohol)(PVA)is a water-soluble polymer with excellent comprehensive properties.Due to superior solvent resistance and gas barrier property of PVA,it has a unique advantage in the packaging of organic solvents,food,drug and so on.However,there are so many hydroxyl groups in PVA,which contribute to forming a large number of hydrogen bonds,resulting in thermal-decomposition temperature approaching to melting temperature of neat PVA.Therefore,melt processing of PVA is very difficult.In this study,a graft reaction took place between silane coupling agent and PVA to investigate impacts on melting points of PVA.Tannic acid,Gelatin and Phosphoric ester of poly(ethylene oxide)were blended with PVA to study on effects on thermal stability and melting points of PVA respectively.According to results,it was successful to prepare PVA blends with wide melting processing window.Silane coupling agents,KH602 and KH560,were used to modify PVA to prepare graft copolymers PVA-g-KH602 and PVA-g-KH560.The results showed that melting points of PVAg-KH602 and PVA-g-KH560 were decreased from 230 ? to 193 ? and 218 ? respectively.The contact angle of modified PVA was enhanced.Compared with neat PVA,the tensile strength of PVA-g-KH602 and PVA-g-KH560 was declined from 87.5 MPa to 59.6 MPa and 64.5 MPa,and the elongation at break was raised from 156% to 486% and 338%,respectively.Tannic acid(TA)and Gelatin(GEL)were blended with PVA to prepare PVA/TA and PVA/GEL blends with high thermal stability.The results suggested that the decomposed temperatures of PVA were enhanced by 103 ? and 87 ? in nitrogen when the amount of TA and GEL were 7 wt% and 15 wt% respectively.DSC curves indicated that the melt temperatures of PVA blends decreased slightly.Morever,PVA/TA and PVA/GEL blends kept high mechanical properties and light transmittance.Phosphoric ester of poly(ethylene oxide)with different length of carbon-carbon chains(NP-4P,NP-10 P,NP-15P)were used to enhance the thermal decomposed temperatures of PVA.TGA results demonstrated that the thermal decomposed temperature of PVA with NP-10 P was improved much higher than these with NP-4P and NP-15 P.Three models were used to calculate the activation energies of PVA and PVA/NP-10P(5 wt%)blends.The results indicated that thermal degradation of PVA/NP-10 P blends was most probably a one-step process while pure PVA was multistep process.Mechanical properties results implied that the tensile strength decreased and elongation at break increased,with increasing the content of NP-10 P.When the amount of NP-10 P was 5 wt%,the tensile strength was 72.2 MPa,and the elongation at break was 473 %.The light transmittance of PVA/NP-10P(5 wt%)blend was 85 %.PVA with wide melting processing window was obtained by incorporation of NP-10P(5 wt%)into the PVA-g-KH602.The results showed that melting points(Tm)of PVA-gKH602(7%)/NP-10 P was decreased to 185 ?,and its thermal decomposed temperature(Td)was enhanced to 286 ?.Td-Tm reached up to 101 ?,which was beneficial for melting processing.What was more,the blending material had a good comprehensive property with the strength of 64.3 MPa and elongation at break of 492 %.Besides,a small amount of NP-10 P had a little effect on the light transmittance of PVA-g-KH602. |
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