Carbon molecular sieve membranes derived from pseudo-interpenetrating polymer networks for gas separation and carbon capture

The design of polyimide-based pseudo-interpenetrating polymer networks (IPNs) is proposed to tailor the molecular structure of polymeric precursors for fabricating carbon molecular sieve membranes (CMSMs). To demonstrate the feasibility of this concept, pseudo-IPNs comprising of poly(2,3,5,6-phenylene-2,2′-bis(3,4-carboxylphenyl)hexafluoropropane) diimide (6FDA–TMPDA) and 2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone (azide) are used to fabricate CMSMs. The gas transport properties of CMSMs are dependent on the azide loading and heat treatment temperature. During the pyrolysis, two competing processes of pore evolution from the released gases and molecular transformation are occurring simultaneously. The creation of pores determines the structural morphology of the CMSM at a low pyrolysis temperature of 550 °C while the molecular rearrangement is the governing factor for carbonization at an elevated temperature of 800 °C. The CMSMs prepared at 550 °C display good CO₂/N₂ separation performance. The 6FDA–TMPDA/azide (90–10) CMSM pyrolyzed at 550 °C shows a CO₂ permeability of 9290 ± 170 Barrer and an ideal CO₂/N₂ selectivity of 26.0 ± 0.8. CMSMs with high CO₂/CH₄ selectivity can be fabricated by carbonization at 800 °C. The 6FDA–TMPDA/azide (70–30) CMSM prepared at 800 °C has a CO₂ permeability of 280 ± 7.0 Barrer and CO₂/CH₄ selectivity of 164 ± 6.0. The CMSMs derived from polyimide/azide pseudo-IPNs exhibit potential use in pre- and post-combustion CO₂ capture.     

Spatter-free laser percussion drilling of closely spaced array holes

Spatter is one of the inherent defects commonly associated with holes produced with laser drilling. This work reports on a method of spatter prevention, workable for a wide range of process parameters. The method is based on the application of a specially developed anti-spatter composite coating (ASCC), containing a mixture of ceramic filler particles embedded in a silicone elastomer matrix, on the workpiece surface prior to laser percussion drilling. Experiments were conducted using a fibre-optic delivered 400 W Nd:YAG laser for the drilling of closely spaced through holes (2 mm hole pitch) in Nimonic 263 alloy sheets. The work revealed that the ASCC effectively prevented the deposition of spatter such that laser drilled holes were produced whilst maintaining the as-received surface characteristics of the Nimonic 263 alloy for all the assist gases tested (O₂, air, N₂ and Ar). The process characteristics and spatter prevention mechanism associated with the use of the ASCC have been investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, contact angle analysis and high-speed photographic imaging. Comparative studies were also made with the case of uncoated laser drilling.     

An essential fungal growth factor derived from ergosterol: A new end product of sterol biosynthesis in fungi?

Concentrations of ergosterol as low as 1.2 mM are effective in satisfying the essential high specificity microrequirement for C5,6 unsaturated sterol in yeast. In a sterol auxotroph supplemented with saturated sterol (cholestanol), aqueous extracts of yeast provide a growth factor that eliminates the ergosterol microrequirement. The factor is easily differentiated from ergosterol by solubility, thermostability, and thin layer and liquid chromatography and is functional at levels equivalent to those of vitamins, hormones and pheromones.     

Lipase‐catalyzed production of medium‐chain triacylglycerols from palm kernel oil distillate: Optimization using response surface methodology

Optimization of lipase‐catalyzed esterification for the production of medium‐chain triacylglycerols (MCT) from palm kernel oil distillate and glycerol was carried out in order to determine the factors that have significant effects on the reaction system and MCT yield. Novozyme 435 from Candida antarctica lipase was found to have the highest activity at 52.87 ± 0.03 U/g. This lipase also produced the highest MCT yield, which is 56.67%. The effect of different variables on MCT synthesis was studied with a two‐level five‐factor fractional factorial design. The various variables include (1) reaction temperature, (2) enzyme load, (3) molecular sieves concentration, (4) reaction time and (5) molar substrate ratio. Reaction temperature, reaction time and molar substrate ratio strongly affect MCT synthesis (p <0.05). However, enzyme load and molecular sieve concentration did not have a significant (p >0.05) influence on MCT yield. Therefore, the significant variables such as reaction temperature, reaction time and molar substrate ratio were further optimized through central composite rotatable design (CCRD). Comparisons between predicted and experimental values from the CCRD optimization procedures revealed good correlation, implying that the quadric response model satisfactorily expressed the percentage yield of MCT in the lipase‐catalyzed esterification. The optimum MCT yield is 73.3% by using 2 wt‐% enzyme dosage, a molecular sieves concentration of 1 wt‐%, a reaction temperature of 90 °C, a reaction time of 10 h and a molar substrate ratio of 4 : 1 (medium‐chain fatty acid/glycerol). Experiments to confirm the predicted results using the optimal parameters were conducted and an MCT yield of 70.21 ± 0.18% (n = 3) was obtained.     

Facile Synthesis and Characterization of Palm CNF-ZnO Nanocomposites with Antibacterial and Reinforcing Properties

Cellulose nanofibers (CNF) isolated from plant biomass have attracted considerable interests in polymer engineering. The limitations associated with CNF-based nanocomposites are often linked to the time-consuming preparation methods and lack of desired surface functionalities. Herein, we demonstrate the feasibility of preparing a multifunctional CNF-zinc oxide (CNF-ZnO) nanocomposite with dual antibacterial and reinforcing properties via a facile and efficient ultrasound route. We characterized and examined the antibacterial and mechanical reinforcement performances of our ultrasonically induced nanocomposite. Based on our electron microscopy analyses, the ZnO deposited onto the nanofibrous network had a flake-like morphology with particle sizes ranging between 21 to 34 nm. pH levels between 8–10 led to the formation of ultrafine ZnO particles with a uniform size distribution. The resultant CNF-ZnO composite showed improved thermal stability compared to pure CNF. The composite showed potent inhibitory activities against Gram-positive (methicillin-resistant Staphylococcus aureus (MRSA)) and Gram-negative Salmonella typhi (S. typhi) bacteria. A CNF-ZnO-reinforced natural rubber (NR/CNF-ZnO) composite film, which was produced via latex mixing and casting methods, exhibited up to 42% improvement in tensile strength compared with the neat NR. The findings of this study suggest that ultrasonically-synthesized palm CNF-ZnO nanocomposites could find potential applications in the biomedical field and in the development of high strength rubber composites.     

Effect of prolonged water absorption on mechanical properties in cellulose fiber reinforced vinyl‐ester composites

With the increasing of worldwide societal awareness about environmental impact, sustainability, and renewable energy sources, the polymer natural fiber composites recently have attracted the attention of researchers due to the fact that they are recyclable and biodegradable. This study conducted a new infiltration method that involved very thin sheets of recycled cellulose fibers (RCF) being fully soaked in vinyl‐ester resin for the development of natural fiber reinforced polymer composites. The effect of prolonged water absorption on the mechanical behavior of cellulose fiber (0–50 wt%) reinforced vinyl‐ester composites was investigated. The elastic modulus of these composites was measured and the data were validated with various mathematical models. The modeling results revealed that the experimental data matched the prediction data obtained by the Cox–Krenchel model. Prolonged exposure of these composites to water absorption caused a reduction in elastic modulus, strength, and toughness. POLYM. ENG. SCI., 55:2685–2697, 2015. © 2015 Society of Plastics Engineers     

Dilemmas of Representation in Post-apartheid Durban

This paper aims to provide a sketch of the ways in which ‘formal’ institutions of democratic representation worked in practice in Durban/eThekwini in the 2000-2004 period. In so doing, it assesses how the representation of eThekwini’s citizens functioned at both the ward and metropolitan levels. After outlining the formation of the new metropolitan political arena, we consider the relationships amongst political parties at Metro and Ward levels, and, in particular, explore some contextually specific forms of democratic practice which emerged through the interaction of proportional representation and ward representation over time. The election of councillors as such does not resolve a series of dilemmas concerning how to institutionalise democratic representation within a racially diverse, spatially divided, and rapidly changing metropolitan area. Electoral-representative aspects of a urban democratisation are not a straightforward ‘formal’ framework alongside which other processes of democratic discussion, mobilisation and contestation can be easily situated.