Deformation Mechanism of Amorphous Plasticized Poly(vinyl butyral)

Understanding the deformation mechanism of amorphous polymeric materials is indispensable for their applications but is quite challenging. Here, with amorphous plasticized poly(vinyl butyral) (PVB) as a model system, we studied its structural change in situ during uniaxial deformation with ultrasmall-angle X-ray scattering (USAXS). We observed a stretch-induced phase separation behavior characterized by a butterfly scattering pattern in plasticized PVB for the first time. This phase separation, featured by a concentration fluctuation along the stretch direction, is a result of stress–concentration coupling under stretch. The phase size at its formation is around 100 nm, which increases almost linearly with strain. The strain rate has a weak effect on the phase size. This suggests that the elastic deformation of the network, cross-linked by entanglements and hydrogen-bonding clusters, governs the phase size. We proposed a tentative model to explain the deformation behavior of plasticized PVB, where the breaking and reforming of hydrogen bonds, the formation and growth of phase separation against osmotic pressure, and the plastic deformation and rupture of phase structure dissipate a large amount of energy and endow the plasticized PVB with excellent mechanical performance. We believe our findings are general and should be applicable to other amorphous polymers with solvents or plasticizers.