The Case for Polylactic Acid as a Commodity Packaging Plastic

Abstract

Polylactide, sometimes called polylactic acid (PLA), meets many requirements as a packaging thermoplastic and is suggested as a commodity resin for general packaging applications. Its general physical properties and melt processing ease are similar to conventional packaging resins. PLA slowly degrades by hydrolysis in even a slightly moist environment over a period of several months to a year to environmentally-friendly products, which, in turn, biodegrade to carbon dioxide, methane, and water. PLA is a clear, colorless thermoplastic when quenched from the melt and is similar in many respects to polystyrene. When plasticized with its own monomers, PLA becomes increasingly flexible so that a continuous series of products can be prepared that can mimic PVC, LDPE, LLDPE, PP, and PS. Degradation is increased with increasing plasticizer, and shelf life is favored by decreasing plasticizer content and/or orientation. Orientation also substantially improves tensile strength, modulus, and heat stability. A general rationale for the commercial development of PLA is presented.     

Development of a Fourier-transform waveguide spectrometer for space applications

We describe the development of a waveguide Fourier-transform spectrometer for space-borne high-resolution sensing. A prototype device is designed to monitor the water vapor absorption band near 1,364?nm with a resolution of 0.05?nm. It has no moving parts and is based on a unique concept of arrayed interferometers implemented in silicon-on-insulator planar waveguide chip. The optical input is formed by many independent waveguides, providing a significantly increased light gathering capability (étendue) compared to single-waveguide input configurations. Enhancements of the spectrometer capabilities are achieved by stacking planar waveguide layers and by using surface gratings to couple light into the waveguides.     

On the pressure and stress singularities induced by steady flows of a pair of nonmiscible, incompressible, viscous fluids in contact with a wall

Design for structural integrity requires an appreciation of where stress singularities can occur in structural configurations. While there is a rich literature devoted to the identification of such singular behavior in solid mechanics, only of late has there been much in the way of corresponding identifications of flow-induced stress singularities in fluid mechanics. These recent asymptotic identifications are for a single incompressible viscous fluid： Here the asymptotic approach is extended to apply to a configuration entailing two such fluids, For this configuration, various specifications leading to power or log singularities are determined. These results demonstrate that flow-induced stress singularities can occur in a structural container at a location where no singularities are identified within solid mechanics alone.     

Virtual encounters: the murky and furtive world of mathematical inventiveness

Based on Châtelet’s insights into the nature of mathematical inventiveness, drawn from historical analyses, we propose a new way of framing creativity in the mathematics classroom. The approach we develop emphasizes the social and material nature of creative acts. Our analysis of creative acts in two case studies involving primary school classrooms also reveals the characteristic ways in which digital technologies can occasion such acts.