Stabilization of polyacetals

A brief introduction describes the main differences between homo, and copolymer polyacetals and their main degradation mechanisms. A short overview describes the importance of stabilization and the necessity of using antioxidants and costabilizers during manufacturing, processing and end use of polyoxymethylene(polyacetals). Various stabilizer systems are presented and studies on the interaction of antioxidants with costabilizers added. The criteria for testing the performance of these additives are discussed and demonstrated by many examples. In a second part the increasing importance of light stabilized polyacetal is mentioned and investigations on the performance of light stabilizer systems are highlighted.     

Isotropic Constitutive Model for Sintering Particle Packings

This paper presents an isotropic model for the effective viscosities of sintering particle packings. The relationship between the macroscopic stress and deformation rate is based on the behavior of individual interparticle contacts, represented by contact viscosities, and the statistics of the packing. The contact viscosities depend on the contact area, which is the primary variable used to describe the state of the packing. A direct consequence of this choice of state variable is that the effective viscosities are identically zero for an undeformed and unsintered packing. Specific results are presented for the case of Newtonian viscous materials. The model is compared with existing models for porous Newtonian viscous materials. Experiments conducted with spherical glass powder packings show good agreement with the model. Finite-element simulations using the model have been used to study forging of a pellet.     

Community similarity and the analysis of multispecies environmental data: A unified statistical approach

The number of species or variables in some designed environmental studies is too large for analysis using standard inferential statistics. To analyze the type of data, a two-stage procedure and follow-up methods are described. First, data are reduced using a measure of similarity or distance. Then, a permutation procedure is used to make inferences. Assuming the hypothesis is rejected, several follow-up analyses are presented as tools in understanding the causes of rejection. For example, to further understand treatment effects, a randomization based, multiple comparison procedure may be used; to better understand what differences the similarity or distance measure describes, a method based on removal of a species is given. The methods are illustrated on a study of the effects of zinc on the periphyton community in the New River, Va, U.S.A.     

Computational prediction of PVC degradation during injection molding in a rectangular channel

A computational model has been developed to calculate the degradation of PVC during injection molding. The results in this work are for the flow in a rectangular geometry. The effects of the injection speed, melt temperature, and material properties were examined. It was determined that the principal factor influencing PVC degradation is the injection speed. Very good agreement between computational and experimental results was obtained. Furthermore, it was calculated that the materials are more thermally sensitive during processing, with activation energy of 65 kcal/mol. Finally, it was calculated that the degradation becomes significant when the melt temperature is above 250°C, independent of the material studied. The model could be used to design the process to avoid degradation. Polym. Eng. Sci. 44:1295–1312, 2004. © 2004 Society of Plastics Engineers.     

Rechnerische Beurteilung der Schubtragfähigkeit einer Spannbetonbrücke mit geringem Querkraft bewehrungsgrad

Assessment of the shear strength of an existing post‐tensioned concrete bridge with a low amount of shear reinforcement – First application of the ”Flexural Shear Crack“ model in practice In recent years it was reported several times, that within a static assessment according to current standards the shear strength of post‐tensioned bridges, which were built in Austria before 1989, cannot be fulfilled any more. However, test results prove, that especially prestressed structures have additional load bearing capacities, which cannot be reproduced with current calculation models. In the framework of a pilot project a new developed shear model (Flexural Shear Crack Model) was used. In this paper the approach as well as the main results of a statical reevaluation of an existing post‐tensioned road bridge at the Tauern Autobahn A10 will be presented.     

Synthesis,characterization, and thermal degradation kinetics of the copolymer poly(4‐methoxybenzyl methacrylate‐co‐isobornyl methacrylate)

A copolymer of 4‐methoxybenzyl methacrylate and isobornyl methacrylate was synthesized by atom transfer radical polymerization. The structure of poly(4‐methoxybenzyl methacrylate‐co‐isobornyl methacrylate) was confirmed by means of Fourier transform infrared, ¹H‐NMR, and ¹³C‐NMR techniques. The molecular weight distribution values of the copolymer were determined with gel permeation chromatography. The number‐average molecular weight and polydispersity index values of poly(4‐methoxybenzyl methacrylate‐co‐isobornyl methacrylate) were found to be 12,500 and 1.5, respectively. The kinetics of the thermal degradation of the copolymer was investigated with thermogravimetric analysis at different heating rates. The activation energy values obtained with the Kissinger, Flynn–Wall–Ozawa, and Tang methods were determined to be 166.38, 167.54, and 167.47 kJ/mol, respectively. Different integral and differential methods were used, and the results were compared with these values. Doyle approximation was also used for comparing the experimental results to master plots. An analysis of the experimental results suggested that the reaction mechanism was an R₁ deceleration type in the conversion range studied. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A study on the optical properties of three‐armed polystyrene and poly(styrene‐b‐isobutyl methacrylate)

Atom transfer radical polymerization (ATRP) of three‐armed polystyrene[PS] and poly(styrene‐b‐isobutyl methacrylate)[PS‐b‐PiBμMA] were accomplished using an initiator with tri‐active C‐Br end group function and cuprous (I) bromide/2,2′‐bipyridyne catalytic system. The characterization obtained by FT‐IR, ¹H‐NMR, and GPC techniques. The average molecular weight and polydispersity of PS and PS‐b‐PiBμMA were determined as 19,800, 29,300 and as 1.37 and 1.15, respectively, which indicates that the constant concentration of growing chains are present throughout the polymerization. The refractive index and extinction coefficient of the samples were determined in the visible range as a function of wavelength. The refractive index dispersion curves of the thin films were fitted by the Cauchy‐Sellmeier model. The width of localized states (E_u) values changed inversely with optical band gaps (E_g) of the films. While the calculated E_u values of films for initiator, PS and PS‐b‐PiBμMA were determined as 2.72, 2.98, and 2.94 eV, the E_g values were determined as 3.43; 3.11, and 3.16 eV, respectively. The dispersion parameters of thin films were determined. These parameters changed in the investigated wavelength ranges. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Addressing the information gaps associated with valuing green infrastructure in west Michigan: INtegrated Valuation of Ecosystem Services Tool (INVEST)

Land use change is profoundly influencing the environmental resources of the Great Lakes region. In West Michigan, population growth and rapid land use change have resulted in urbanization and a loss in the diversity of green infrastructure that provides a variety of benefits–ecosystem services–to regional residents and visitors. To address these changes in land use and cover in ways that are objective, transparent, and defensible, local policy makers need tools to help inform local and regional land use decisions. An interdisciplinary team, engaged by a regional policy organization, developed one such online tool, the INtegrated Valuation of Ecosystem Services Tool (INVEST). INVEST utilizes static GIS maps, graphs, and tables, to help educate local and regional decision-makers about the underlying values of ecosystem services associated with green infrastructure, particularly those services that do not pass through traditional commercial markets. In this article we provide a general overview of the development of INVEST and examine its current application as an educational tool, including the specific challenges associated with addressing the information gaps.