Multiscale Relaxation Behavior of Amorphous Plasticized Poly(vinyl butyral).

As a key component in laminated glass, plasticized polyvinyl butyral (PVB) interlayer is a kind of impact-resistant polymer material with high toughness. Recently, by using ultrasmall angle X-ray scattering (USAXS) technique, Stretch-induced phase-separated structure on the scale of hundreds of nanometers formed in plasticized PVB for the first time is reported. In this work, the multiscale relaxation behavior of plasticized PVB is further investigated. The relaxation behavior of deformed plasticized PVB is studied from macroscopic stress, mesoscopic phase-separated structure, and microscopic chain segment by combining USAXS, and birefringence with in situ stretching device. The contributions of chain segments and hydrogen bonding clusters for the multiscale relaxation behavior are discussed.

Wrinkling and restabilization of a hyperelastic PDMS membrane at finite strain.

Wrinkles are commonly observed in uniaxially stretched hyperelastic membranes and eventually disappear with the increase of stretching. The widely used scheme at present assumes the material parameters to be empirical values and straightforwardly considers some constitutive models to explore the wrinkling and restabilization behavior. However, this simple treatment may cause deviation from experiment by ignoring the applicability of the models and the authenticity of the input parameters, prompting us to report based on realistic material parameters. This paper presents an experimental, theoretical and numerical investigation on the wrinkling and restabilization behavior of hyperelastic materials. By fitting experimental stress-strain curves of PDMS films, we confirm that the 3-term Ogden model bears a closer resemblance to the experimental data than the widely used neo-Hookean, Mooney-Rivlin, and Arruda-Boyce models under certain circumstances. The simulation results indicate that different constitutive models quantitatively affect the critical buckling strain, wrinkling amplitudes, and restabilization points. Furthermore, the isolated central bifurcation point solved by Koiter stability theory agrees well with the simulation and experimental results. A 3D phase diagram of stability boundaries was established to gain a comprehensive insight into the effects of geometric parameters (length, width, and thickness) on wrinkling.

Manipulation of Chain Entanglement and Crystal Networks of Biodegradable Poly(butylene adipate-co-butylene terephthalate) During Film Blowing through the Addition of a Chain Extender: An In Situ Synchrotron Radiation X-ray Scattering Study.

One prerequisite for the large-scale application of biodegradable polymers is the manipulation of macroscopic performances of commercially available biopolymers during processing according to different real service requirements. Herein, the microstructural evolution of poly(butylene adipate-co-butylene terephthalate) (PBAT) modified by chain extender during film blowing was investigated by in situ synchrotron radiation X-ray scattering to unveil the origin of different performances. The chain dynamics difference induced by the chain extender was first characterized by the rheological measurement and 1H Multiple Quantum (MQ) NMR. It shows that the terminal relaxation is significantly slowed down, while the locally segmental dynamics is not apparently changed. With the assistance of the custom-built film blowing apparatus, the microstructure right above the die exit (D = 13-165 mm) was in situ, simultaneously captured by small- and wide-angle scattering (SAXS/WAXS), where four distinct regimes can be defined. Only the PBAT melt signals are found in regime I, whereas the formation of the mesomorphic domains as shown by the SAXS streaks appearing in regime II. The crystal shows up in regime III, where the WAXS signal appears. A dramatic increment of the crystallinity is found in regime III, which contributes to the continuous increasing bubble modulus with the formation of the crystal-based network. Such a crystal-based network is filled with crystals in regime IV, where the diameter of the PBAT bubble remains constant. The addition of the chain extender is found to significantly influence the structural evolution within different regimes. These dynamics and structure information could supply general guidance for bubble stability improvement and modification of macroscopic performances of biodegradable polymer products.