Deformation Mechanism of Amorphous Plasticized Poly(vinyl butyral)

Abstract

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.

Multiscale Relaxation Behavior of Amorphous Plasticized Poly(vinyl butyral)

“…Recently, we used ultrasmall-angle X-ray scattering (USAXS) [16,17] to study the deformation process of plasticized PVB. [18] We observed a stretch-induced butterfly scattering in USAXS, which is attributed to as a hundred-nanometerscale wave-like structure with normal direction along stretch (Figure 1b), which is different from the two-phase model proposed for static condition. The structural entity of this phase separation induced by stretch was characterized by atomic force microscope (AFM), which is composed of a rigid phase and a soft phase.…”

“…Before stretching, plasticized PVB exhibits weak and isotropic scattering signal. This scattering signal has been compared with background scattering (air scattering) in our published work, [18] the similar scattering signal illustrates limited structural heterogeneity in hundreds of nanometers. For loading stage, it can be seen that the deformed plasticized PVB exhibits a butterfly scattering pattern along the stretching direction.…”

“…Although a large difference appears in stress, the plasticized PVB exhibits almost the same stretchinduced phase separation behavior under different strain rates, as demonstrated in our previous study. [18] In the following, we choose the strain rate of 0.1 s −1 to study how chain segment and phase structure relax during strain holding.…”

“…In plasticized PVB, the existence of hydrogen bonding clusters has been demonstrated. [10,11,18] The hydrogen bonding clusters should exist in both soft and hard phases when stretch-induced phase separation occurs. In the soft phase, the concentration of hydrogen bonding cluster is low, while the situation is inverse in the hard phase.…”

“…This phenomenon was reported in our recent study for the first time. [18] The butterfly scattering pattern has been characterized by AFM, which corresponds to the formation of a wave-like phase separated structure with the normal direction along stretching in real space. [18] The spatial size of this phase separated structure is about 100-300 nm.…”