| As one of the key components of laminated glass,the poly(vinyl butyral)(PVB)interlayer is widely used in automotive,construction,photovoltaic and other fields due to its excellent impact resistance and adhesive properties.As a kind of product with high-tech barrier,the PVB interlayer has long been monopolized by foreign countries,and there is a huge gap in the performance(such as low-temperature impact resistance)between domestic and foreign products.The structure of the material determines the performance.The molecular structure of PVB is well known,but its submicron mesoscopic structure,especially the structure and structure evolution under service is still unclear.The reason,first of all,is the complexity of the PVB interlayer:PVB is a type of ternary random copolymer from the structural point of view,and PVB chain mainly contains polar vinyl alcohol(VA)units that can form hydrogen bonds and nonpolar vinyl butyral(VB)units.The PVB interlayer is a blend of PVB and plasticizer,and there is a large gap in the compatibility between different units in PVB and plasticizer.When mixed together,local structural heterogeneities will emerge.The second arises from their intrinsic featureless or structural amorphousness,whereas most characterization tools,originally designed for ordered structures,cannot be used to characterize the structure under deformation.With the help of first Ultra-Small-Angle X-ray Scattering(USAXS)beamline in China-BL10U1 in Shanghai Synchrotron Radiation Facility(SSRF),this thesis systematically designs experiments to reveal the deformation mechanism of PVB on the submicron scale.First,the PVB interlayer is stretched under different strain rates,and the stretch-induced phase separation in PVB is proposed for the first time from the butterfly scattering pattern.Then the PVB interlayer is stretched at different temperatures,and the phase diagram of the stretch-induced phase separation was established.Its formation process is further elucidated from the perspective of the molecular mobility;then PVB without plasticizer is stretched,and by changing the degree of acetalization,it is found that pure PVB produces a four-lobed scattering pattern when stretched to a large strain.The four-lobed scattering pattern corresponds to the formation of larger and more periodic structures;finally,PVB with different contents of plasticizers is stretched to study how the four-leaf scattering pattern transforms into a butterfly scattering pattern.The specific research work and results are as follows:(1)Plasticized PVB was stretched at different strain rates and a butterfly scattering pattern along the stretching direction was observed by USAXS,which is attributed to stretch-induced phase separation in plasticized PVB.This butterfly scattering pattern corresponds to a wave-like phase-separated structure of hundreds of nanometers in real space,which is a result of stress-concentration coupling under stretching.The phase size increases almost linearly with strain,suggesting that the elastic deformation of the network,crosslinked by entanglements and hydrogen bonding clusters,governs the phase size.We proposed a tentative model to explain the deformation behavior of plasticized PVB,The energy dissipation mechanism and nonequilibrium features of this process are further demonstrated.(2)A systematic tensile test with in-situ USAXS in a wide temperature range(50～70℃)is conducted.This temperature range is divided into four temperature regions(Ⅰ,Ⅱ,Ⅲ,Ⅳ).Phase separation is found to occur only in region Ⅱ(-20～5℃)and region Ⅲ(5-25℃).The cause of this phenomenon was analyzed from the perspective of dynamics by using solid-state nuclear magnetic resonance(SSNMR),the dynamic asymmetry of polymers and plasticizers is a prerequisite for phase separation,and the stretching and temperature play different roles in different temperature ranges.The formed phase-separated structure can exist stably for a long time at room temperature,and irreversible damage will occur when the temperature exceeds 30℃.The phase separated structure is thought to be related to the fracture behavior in plasticized PVB.(3)A series of PVB films with different degrees of acetalization from 30%to 90%were synthesized and prepared,and thermal analysis and condensed state structure characterization were carried out systematically.Among them,PVB with degree of acetalization of 30%,40%,and 50%is semicrystalline polymer,and with 60%or more degree of acetalization is in amorphous state.It was found that semicrystalline PVB stretched at room temperature or amorphous PVB stretched at Tg will result in a four-lobed USAXS scattering pattern,which corresponds to the formation of a hundred-nanometer-scale layered periodic structure characterized by SEM.It is believed that the formation of this layered structure is a process of stretch(stress)-activated self-organization:under stretch(stress),the motion of polymer chain is activated,then polymer chain flows along the stretching direction.Due to the presence of intermolecular hydrogen bonding interactions between VA,the hard phase self-organizes together to form periodic structures.(4)Stretch-induced phase separation of PVB with different amounts of plasticizer at Tg was studied.The addition of a small amount of plasticizer(5 wt%)can reduce the phase size formed in the stretching direction a lot(from approximately 300 nm to approximately 100 nm),and the periodic structure perpendicular to the stretching direction will be destroyed.The formation of a complete phase-separated structure requires a 15 wt%plasticizer.On the other hand,the increase of plasticizer content will reduce the regularity of the periodic structure,broaden its size distribution and decrease the contrast between different phases.Strain plays a key role in the growth of phase-separated structures... |
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