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.     

Cyanine-Like Boronic Acid-Derived Salicylidenehydrazone Complexes (Cy-BASHY) for Bioimaging Applications

Boronic acid-derived salicylidenehydrazone complex (BASHY) dyes with a polymethine backbone were designed to yield efficient red-emitting and two-photon absorbing fluorophores that can be used as markers for astrocytes. The dyes are chemically stable in aqueous solution and do not undergo photodecomposition. Their photophysical properties can be electronically fine-tuned and thereby adapted to potentially different imaging situations and requirements.     

A soft collision detection algorithm for simple Brownian dynamics

We describe a collision detection algorithm for spherical bodies that performs a minimal amount of computation consistent with maintaining reasonable steric exclusion. The algorithm was tested using populations of bodies that move randomly without inertia, simulating Brownian-like motion. Simulations were tested using populations of different size, up to 100,000 bodies, at different densities. The algorithm is linear in time and memory with the number of bodies and would be suitable for the simulation of ‘soft’ objects, such as cells.     

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.     

The major product ion of S‐adenosyl‐L‐methionine arises from a neighbouring group reaction

Previous studies have shown that low‐energy collision‐induced dissociation (CID) of the important sulfonium ion metabolite S‐adenosyl‐L‐methionine (AdoMet, m/z 399) yields five main product ions: an ion at m/z 250 arising from methionine loss; ions at m/z 102 and 298, which arise via cleavage of the γ C? S bond of methionine; and ions at m/z 136 and 264, which arise via loss of protonated and neutral adenine, respectively. These metabolomics studies have, however, either totally ignored the mechanisms that govern the formation of the major product ion at m/z 250 (Gellekink H, van Oppenraaij‐Emmerzaal D, van Rooij A, Struys EA, den Heijer M, Blom HJ. Clin. Chem. 2005; 51: 1487), or have proposed an oxonium ion structure that must arise via a rearrangement involving a 1,2 hydride shift (Cataldi TRI, Bianco G, Abate S, Mattia D. Rapid Commun. Mass Spectrom. 2009; 23: 3465). Here DFT calculations on a model system are used to examine potential mechanisms for the formation of the major product ion of AdoMet. These calculations suggest that a neighbouring group mechanism is preferred over a 1,2 hydride shift mechanism. Copyright © 2010 John Wiley & Sons, Ltd.