A microscopy study of the transition from yielding to crazing in polypropylene

The deformation mechanisms in polypropylene as a function of strain rate have been studied by scanning electron microscopy. Injection molded, dogbone specimens were tested in tension at a temperature of 50°C and strain rates from 10^?4 to 90 s^?1. With increasing strain rate a gradual transition from cold drawing and necking to nearly homogeneous deformation was observed. The transition is characterized by a strong elastic recoil after fracture. At $ {\rm \dot \varepsilon } $ = 90 s^?1, the elastic recovery has its maximum value of 70% of the strain at break (ε = 0.3). The morphology was studied post mortem at small strains outside the neck using permanganically etched samples. The transition in the macroscopic behavior was found to coincide with a change in the deformation mechanism. Whereas yielding is the dominant mechanism at low strain rates, homogeneous voiding is found at $ {\rm \dot \varepsilon } $ = 90 s^?1. A correlation is suggested between the failure of chain slip within the lamellae and the occurrence of voiding, leading to distinct voiding patterns in the spherulites.     

Poly(ethylene glycol)‐based poly(urethane isocyanurate) hydrogels for contact lens applications

Over the past few decades, the global use and market of contact lenses have expanded steadily. Due to the many demands on material properties (e.g. mechanical, optical and biological), the development of novel contact lens materials is challenging. Specifically, the ideal combination of high equilibrium water content, high toughness in the hydrated state and low protein adsorption is difficult to realize. In this work, poly(ethylene glycol)‐based poly(urethane isocyanurate) (PEG PUI) type hydrogels that combine the above important properties are presented as a new class of materials for contact lens applications. It is shown that these PEG PUI hydrogels demonstrate high toughness values in the hydrated state ranging from 98 to 226 kJ m^?3 and elastic moduli ranging from 0.8 to 17.2 MPa for networks with equilibrium water contents ranging from 76.3 to 16.1 wt%. These hydrogels also demonstrate transmittance values >90% across the visible spectrum, clarities close to 100% in most cases and refractive indices ranging from 1.48 to 1.36. Importantly, these hydrogels are non‐cytotoxic and demonstrate lower bovine serum albumin adsorption values than several commercial contact lenses of 0.24 to 0.65 mg g^?1 compared to 0.55 to 1.38 mg g^?1 after 24 h, respectively. This combination of high equilibrium water content, high toughness in the hydrated state and low protein adsorption is exceptional. These properties can be attributed to the PEG PUI network structure: the use of a PEG polymeric backbone provides hydrophilicity and chemical inertness while the PUI‐type crosslinking units provide high toughness in the hydrated state. © 2019 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

The Total Degumming Process – Theory and Industrial Application in Refining and Hydrogenation

The degumming of vegetable oils prior to physical refining is a crucial preliminary step. The degumming process is not only largely responsible for the quality of the final product, but it also determines the amount of bleaching earth to be used, which has a substantial effect on the yield improvement which can be attained by this route. Investigations show clearly that iron, as a pro-oxidant, strongly influences the stability of refined oils, and that oil, degummed before bleaching and physical refining, may contain a maximum of 0.2 ppm Fe, if it is to yield a stable product. The Total Degumming Process has been developed on the basis of these findings, to make it possible to degum oil to a residual Fe-level below 0.2 ppm and a residual phosphorus content below 10 ppm. The principles and industrial application of the process have been considered. The results of industrial production using different raw materials of various qualities have been used to make a comparison between the conventional refining process (neutralization – bleaching – deodorization) and the Total Degumming Process in combination with physical refining. The combination of the Total Degumming Process and a simplified caustic refining process, and the use of Totally Degummed Oil for hydrogenation have also been considered.     

Specificity of practice: Interaction between concurrent sensory information and terminal feedback.

In 2 experiments, the authors investigated a potential interaction involving the processing of concurrent feedback using design features from the specificity of practice literature and the processing of terminal feedback using a manipulation from the guidance hypothesis literature. In Experiment 1, participants produced (198 trials) flexion-extension movements to reproduce a specific pattern of displacement over time with or without vision of the limb position and with 100% or 33% knowledge of results (KR) frequency. The transfer test was performed without vision and KR. In Experiment 2, the authors assessed whether sensory information processing was modulated by the amount of practice. Participants performed 54 or 396 trials under a 100% or a 33% KR frequency with vision before being transferred to a no-vision condition without KR. Results of both experiments indicated that the Vision-33% condition suffered a larger detrimental effect of withdrawing visual information than the Vision-100% condition. Experiment 2 indicated that this detrimental effect increased with practice. These results indicated the reduction in terminal feedback prompted participants to more deeply process the concurrent visual information thus reinforcing their dependency on the visual information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of high-sugar grasses on methane emissions simulated using a dynamic model

High-sugar grass varieties have received considerable attention for their potential ability to decrease N excretion in cattle. However, feeding high-sugar grasses alters the pattern of rumen fermentation, and no in vivo studies to date have examined this strategy with respect to another environmental pollutant: methane (CH(4)). Modeling allows us to examine potential outcomes of feeding strategies under controlled conditions, and can provide a useful framework for the development of future experiments. The purpose of the present study was to use a modeling approach to evaluate the effect of high-sugar grasses on simulated CH(4) emissions in dairy cattle. An extant dynamic, mechanistic model of enteric fermentation and intestinal digestion was used for this evaluation. A simulation database was constructed and analysis of model behavior was undertaken to simulate the effect of (1) level of water-soluble carbohydrate (WSC) increase in dietary dry matter, (2) change in crude protein (CP) and neutral detergent fiber (NDF) content of the plant with an increased WSC content, (3) level of N fertilization, and (4) presence or absence of grain feeding. Simulated CH(4) emissions tended to increase with increased WSC content when CH(4) was expressed as megajoules per day or percent of gross energy intake, but when CH(4) was expressed in terms of grams per kilogram of milk, results were much more variable due to the potential increase in milk yield. As a result, under certain conditions, CH(4) (g/kg of milk) decreased. The largest increases in CH(4) emissions (MJ/d or % gross energy intake) were generally seen when WSC increased at the expense of CP in the diet and this can largely be explained by the representation in the model of the type of volatile fatty acid produced. Effects were lower when WSC increased at the expense of NDF, and intermediary when WSC increased at the expense of a mixture of CP and NDF. When WSC increased at the expense of NDF, simulated milk yield increased and, therefore, CH(4) (g/kg of milk) tended to decrease. Diminished increases of CH(4) (% gross energy intake or g/kg of milk) were simulated when DMI was increased with elevated WSC content. Simulation results suggest that high WSC grass, as a strategy to mitigate N emission, may increase CH(4) emissions, but that results depend on the grass composition, DMI, and the units chosen to express CH(4). Overall, this project demonstrates the usefulness of modeling for hypothesis testing in the absence of observed experimental results.     

Influence of molar mass and temperature on the dynamics of network formation in polycarbonate/carbon nanotubes composites in oscillatory shear flows

The influence of molar mass and temperature on the formation of networks of multiwalled carbon nanotubes (MWCNT) in oscillatory shear flows was investigated. Combined rheological and electrical investigations were performed using composites with 0.5-5.0 wt% MWCNT in a low- and a high-viscosity polycarbonate (PC) at 190 °C and 250 °C. The objective of this work was to study the dynamics of the simultaneous formation of electrical and rheological networks by taking into account the superposition of (i) network breakup by the applied shear field and (ii) the diffusion-controlled clustering of carbon nanotubes. The formation (i.e. the buildup) of electrical and rheological networks proceeds more rapidly for a lower-viscosity matrix and at higher temperatures, whereas breakup of the electrical network is more pronounced at lower temperatures because of a larger stress-transfer between polymer matrix and MWCNT network. Sinusoidal shear deformation results in an oscillatory electrical conductivity with decreasing average value at large shear amplitudes, indicating that the electrical nanotubes network consists of weakly bonded carbon nanotube clusters which can be easily released and reformed. These data also show that MWCNT-MWCNT bonds can be reversibly deformed up to a maximum deformation. The latter experimental result precises the current understanding of electrical carbon nanotubes networks.     

Alternative feedstocks: a continuing trend in the polymer industry?

Polymers as we know them today have been developed from the feedstock available at the time of their formulation, i.e. crude oil in particular. Fossil feedstocks are used primarily for heating, cooling and fuelling engines in automobiles and power plants. Due to environmental awareness, increasing oil prices and strong progress in biotechnology in recent decades, new feedstocks will become available for fuels. Bio‐refineries will emerge in parallel with the existing oil refineries, and the feedstocks produced by these bio‐refineries will in part also be used to make polymers. This paper elucidates the historical developments and the possibilities for protecting our planet from pollution and global warming. Copyright © 2011 Society of Chemical Industry     

The structure-function relationship of the lipases from Pseudomonas aeruginosa and Bacillus subtilis

Within the BRIDGE T-project on lipases we investigate the structure-functionrelationships of the lipases from Bacillus subtilis and Pseudomonasaeruginosa. Construction of an overproducing Bacillus. strainallowed the purification of > 100 mg lipase from 30 l culturesupernatant. After testing a large variety of crystallizationconditions, the Bacillus lipase gave crystals of reasonablequality in PEG-4000 (38-45%), Na₂SO₄ and octyl-ß-glucosideat 22°C, pH 9.0. A 2.5 Å; dataset has been obtainedwhich is complete from 15 to 2.5 A resolution. P.aeruginosawild-type strain PAC1R was fermented using conditions of maximumlipase production. More than 90% of the lipase was cell boundand could be solubilized by treatment of the cells with TritonX-100. This permitted the purification of 50 mg lipase. So far,no crystals of sufficient quality were obtained. Comparisonof the model we built for the Pseudomonas lipase, on the basisof sequences and structures of various hydrolases which werefound to possess a common folding pattern (/ß hydrolasefold), with the X-ray structure of the P.glumae lipase revealedthat it is possible to correctly build the structure of thecore of a protein even in the absence of obvious sequence homologywith a protein of known 3-D structure.