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ABSTRACT A fundamental understanding of the expansion kinetics of expandable polystyrene (EPS) is crucial for the design and optimization of processes for EPS-filled syntactic foams. In this study, a general formulation was developed to model EPS expansion. A semi-analytical solution was obtained on the basis of the case of a single bubble expansion in an infinite matrix. The dimensionless bubble radius and pressure were defined and found to be exponential functions of the dimensionless expansion time. The characteristic bubble expansion time was able to characterize the timescale of the expansion process. The semi-analytical solution could qualitatively predict the radial expansion of the EPS microsphere observed in a real-time experiment. To obtain an accurate prediction, a numerical solution was obtained to the model that coupled the nucleation and expansion of multiple bubbles in a finite matrix at various temperatures. The results show that the numerical solution was able to quantitatively predict the radial expansion of EPS. A parameter sensitivity study was performed to examine the effect of each parameter over the expansion process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43886. [ABSTRACT FROM AUTHOR]

Gel spinning of UHMWPE fibers using low molecular weight polybutene (PB) as a new spin solvent was investigated. A 98/2 wt% PB/UHMWPE gel exhibits a melting temperature around 115°C and shows large-scale phase separation upon cooling the solution to room temperature. The resulting precursor fiber from this gel was hot-drawn to a ratio of 120, yielding a fiber with tensile strength of 4 GPa and Young's modulus of over 150 GPa. Wide-angle X-ray diffraction indicates good molecular orientation along the fiber axis. The results also demonstrate the potential to further improve the mechanical properties. With respect to the gel spinning industry, this new solvent has a number of advantages over paraffin oil and decahydronaphthalene, and holds a promise of greatly improving the process efficiency. POLYM. ENG. SCI., 56:697-706, 2016. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

In this work, a microwave expansion process to produce thermoset-matrix syntactic foam containing thermoplastic foam beads was designed and developed. Expandable polystyrene (EPS) microspheres and epoxy resin were chosen as a model material system. This process is featured with a capability to effectively expand EPS microspheres in syntactic foam with high EPS loading. The resin viscosity and specific microwave energy are found to be the two primary control parameters determining the process window. Mechanical characterization showed that the specific flexural strength and modulus of the syntactic foam are similar to those of the neat epoxy. By comparison, the flexural moduli over density squared or cubed of the foam are much higher, especially at high EPS loadings, than those of the neat resin. The foamed EPS microspheres can also effectively toughen the syntactic foam, preventing propagation of cracks. Furthermore, the microwave expansion process was found to be capable of molding syntactic foam parts of relatively sophisticated geometry with smooth surfaces. POLYM. ENG. SCI., 55:1818-1828, 2015. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Composite polystyrene foam with a honeycomb-like barrier structure was processed from an expandable aqueous suspension. Optical observations confirmed the formation of such a unique structure that encapsulates each expanded polystyrene microsphere in the resulting foam. The suspension viscosity was found to highly influence the foam morphology. Results from mechanical tests showed that the existence of the barrier structure can considerably improve the mechanical performance of the composite foam. Fire retardation tests demonstrated that the barrier structure can effectively stop the fire path into the foam, suppress toxic smoke generation, and maintain structural integrity, leading to improved fire resistance in comparison with the neat polystyrene foam. POLYM. ENG. SCI., 55:1494-1503, 2015. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

A microsphere templating process was recently developed for fabrication of open-cell porous elastomer. The material contained a unique cocontinuous structure having micropores interconnected by microchannels. In this work, a follow-up study was conducted to investigate the mechanical behavior of such porous materials. Polysiloxane was chosen as a model material. The deformation characteristics and mechanical properties of the porous elastomer under tension and compression were then studied. For both tensile and compressive tests, the mechanical properties measured were found to largely deviate from those calculated by the additive rule assuming affine deformation. This nonaffine mechanics was further verified by microscopic observations. Cyclic loading and unloading tests were also performed to study the hysteresis of the material. In comparison with the solid elastomer, the hysteresis of the porous elastomer was considerably higher and more sensitive to the strain rate. An attempt was further made to fit the stress-strain curve using existing hyperelastic models, and the results showed that the Arruda-Boyce model, in general, fit both the solid and porous polysiloxane very well. POLYM. ENG. SCI., 54:1512-1522, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]