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Processing low density poly(urethane-isocyanurate) rigid foam boards still remains challenging, especially for high thickness panels. In particular, subsequent shrinkage of the foam panel during cooling and cross-linking of the matrix creates in-plane compressive stresses in the facing that can be relieved by buckling with a relatively uniform wavelength of a few millimeters. An extensive study in the scientific literature documents the variety of wrinkling morphologies obtained when a thin film bonded on top of a soft substrate is compressed, and we proposed to apply this model in order to explain experimental observations of wrinkling in the case of a flexible facing bonded to a poly(urethane-isocyanurate) rigid foam. The wavelength, amplitude, and pattern of the waves were found to give information about the mismatch in Young's modulus as well as the level of compressive strain in the foam panel at the moment of wrinkling formation. A shore durometer (type 00) was systematically used to quickly probe the mechanical properties of the foam surface at various locations along the width of the insulation panel (after removal of the facing) and was found to be a valuable tool to explain the location of surface wrinkling and its evolution with time. Variations in mechanical properties of the foam surface were explained in terms of differences in cell orientation near the surface. [ABSTRACT FROM AUTHOR]

Microcellular polystyrene foam sheets prepared by extrusion foaming with CO2 as the blowing agent were found to exhibit a significant anisotropy in mechanical behavior which could not be explained solely by the shape anisotropy of the cells and/or the preferential orientation of polystyrene molecules in the machine direction. Surprisingly, samples allowed to fully relax were still found to maintain part of their mechanical anisotropy, which was attributed to the weakness of the cell walls perpendicular to machine direction. [ABSTRACT FROM AUTHOR]

A semicrystalline poly(lactic acid) (PLA) was modified with the help of an epoxy-based chain extender (CE) during reactive extrusion. Different amounts of CE were used resulting in samples with increased and broadened molar mass distributions as revealed by size exclusion chromatography. Thermal properties were then investigated using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). On one hand, the thermal ramps performed with DSC revealed that the glass transition was not modified by the chain extension process. On the other hand, thecrystallization behavior was found to be highly impacted by this molecular modification. Decreases in the cold crystallization temperatures Tcc and in the melting temperatures Tm occurred when the CE content was raised. Isothermal crystallizations from the melt were performed using both DSC and POM. It revealed that the overall crystallization process was significantly faster for the chain-extended PLAs while crystalline ratios were lowered. An improvement of the nucleation process coupled with a reduced crystal growth was assumed to be responsible for this change. POLYM. ENG. SCI., 54:616-625, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract: This study has been dedicated to the foaming of modified poly (lactic acid) with supercritical CO2. The first part of this work consisted in a rheological modification of neat PLA through chain extension. Improvement of the melt viscosity and elasticity has been achieved by the use of an epoxy additive during a reactive extrusion process. Rheological characterizations confirmed an increase of the melt strength due to this chain extension process. Foaming was then performed on the neat and modified PLAs using a batch process with supercritical CO2 as blowing agent. The investigation of the foaming temperature revealed an enlarged processing window for modified PLAs compared to neat PLA. Depending on the foaming parameters, foams with a cellular structure ranging from macro scale to micro scale have been obtained. A concomitant effect of the CO2-plasticization and the crystallisation on the melt rheology could explain this wide range of cellular morphologies. [Copyright &y& Elsevier]