Study On The Aging Of Polyvinyl Butyral

Polyvinyl butyral(PVB)is the acid catalyzed condensation product of polyvinyl alcohol(PVA)and n-butyraldehyde.The PVB has excellent performance and is widely used in safety glass,coatings,adhesives,engineering plastics,electronic materials and other fields.The PVB resin is commonly used to prepare PVB films as the safety glass sandwich.It is widely used in automotive safety glass,aircraft glass,building curtain wall glass,etc.PVB films will inevitably be subject to a certain degree of aging during processing,storage,transportation and use.By studying the aging law and aging mechanism of PVB films,the aging process is fundamentally understood.It helps to develop new anti-aging technology,improve the ability of resistance to aging of PVB materials,extend their service life and expand their use range.In this paper,IH-NMR,FT-IR and UV-Vis were used to studying the UV aging,thermo-oxidative aging(80'C,120°C and 140 C),chemical media aging(acid aging,alkaline aging,salt aging and oxidative liquid aging)and outdoor natural aging of PVB.The aging mechanisms of abovementioned agings were explored through the perspective of chemical structure changes during aging.The aging curves and the aging equations were established.The relationship between natural aging and artificial accelerated aging was established.And the following conclusions were obtained:1.UV agingPVB had good anti-UV aging performance.First 2 d of aging,PVB was mainly degraded;after 2 d of aging,crosslinking began to dominate.In the early stage of aging,some plasticizers in PVB were precipitated by UV radiation.Then,ketones,aldehydes,hydroperoxides,esters and other products were produced,under the action of UV and oxygen.The acetal ring was opened.Free radicals produced in the aging process induced molecular chains rupture.They could capture active hydrogen atoms in PVB and then again produced free radicals.Or they were also possible to collide with each other to cause chain termination reactions,and the aging was dominated by crosslinking at this time.The UV aging curves and the aging equations(equations 2.1 and 2.2)were established under the experimental conditions.2.Thermo-oxidative agingIn this chapter,PVB samples were subjected to thermo-oxidative(TO)aging at 80 C,120? and 140 C,respectively.The chemical structure of PVB did not change significantly after aging at 80 C for 30 d,and it showed that PVB had better anti-TO aging performance.The aging temperature increased from 80 C to 140 C,which obviously accelerated aging.Aging was firstly caused by the precipitation of plasticizers under heating.Then,PVB was oxidized to produce alkenes,ketones,aldehydes,alcohols,esters,etc.The acetal ring was opened under heating.In the later stage of aging,free radicals collided with each other to cause chain termination reactions and the aging reaction of PVB was mainly crosslinking.The aging curves and aging equations(equations 3.1-3.4)of TO 120 C aging and TO 140 C aging were established under the experimental conditions.3.Chemical media agingIn this chapter,the aging process of PVB in the solution of 5%NaCl,5%NaOH,5%HCI,5%H2O2 and 5%KMnO4 were studied respectively.It was concluded that,the ability of PVB to resist the solution of 5%NaCI was strong,to resist the solution of 5%NaOH was a bit poor,to resist the solution of 5%HCI was poor,to resist the solution of 5%H2O2 was poor,and in 5%KMnO4 it showed very poor.In the aging process of the solution of NaOH,partial plasticizers of PVB were precipitated and the ester group was hydrolyzed to form hydroxyl group.In the aging process of the solution of HCl,partial plasticizers were precipitated and the acetal ring was hydrolyzed to produce hydroxyl products such as butanol.The free radicals collided with each other to cause chain termination reactions(ethers formed)and the molecular was crosslinked.In the aging process of the solution of H2O2,partial plasticizers were precipitated and then,the polyvinyl alcohol chain in PVB was oxidized to produce ketones,aldehydes,esters,etc.In the aging process of the solution of KMnO4,partial plasticizers were precipitated and tthe polyvinyl alcohol chain in PVB was oxidized to produce aldehydes,esters,etc.The acetal ring was opened by the action of the solution of KMnO4 and produced hydroxyl products.4.Natural agingPVB was still not fully degraded after natural aging of 420 d.It was concluded that the ability of PVB to resist weather was better.The natural aging mechanism of PVB was similar to that of UV aging:under the influence of UV radiation,heat and oxygen,the plasticizers were partially precipitated and then PVB was aged to produce ketones,aldehydes,alcohols,esters and other products.The acetal ring was opened.At 90 d after aging,crosslinking aging began to dominate.The natural aging curves and the aging equations(equations 5.1 and 5.2)were established under the experimental conditions.Identifing the natural aging days of samples,the results showed that the aging days less than 75 d were suitable for the 'H-NMR method.The FT-IR method and 'H-NMR method had low errors in the identification of aging days above 75 d and it could be selected by comparing the two methods.Under the experimental conditions,artificial UV aging 14 d was equivalent to 120 d for natural aging,and 30 d of artificial UV aging was equivalent to 180 d of natural aging.In this chapter,the relationship between natural aging and artificial accelerated aging was discussed firstly.The correlation curves and equations between them were obtained.The aging property of PVB materials could be evaluated and the service life of PVB materials could be predicted by using equations 5.3 and 5.4.