Flexibility improvement of short glass fiber reinforced epoxy by using a liquid elastomer

In certain applications of fiber reinforced polymer composites flexibility is required. The aim of this study was to improve flexibility of short glass fiber reinforced epoxy composites by using a liquid elastomer. For this purpose, diglycidyl ether of bisphenol-A (DGEBA) based epoxy matrix was modified with hydroxyl terminated polybutadiene (HTPB). A silane coupling agent (SCA) was also used to improve the interfacial adhesion between glass fibers and epoxy matrix. During specimen preparation, hardener and HTPB were premixed and left at room temperature for an hour before mixing with epoxy resin to allow possible reactions to occur. In order to compare flexibility of the specimens flexural tests were conducted and the data were evaluated numerically by using a derived relation. Test data and scanning electron microscope analysis indicated that surface treatment of glass fibers with SCA, and HTPB modification of epoxy matrix improved flexural properties especially due to the strong interaction between fibers, epoxy, and rubber. It was also observed that HTPB modification resulted in formation of relatively round rubber domains in the epoxy matrix leading to increased flexibility of the specimens.     

Preconcentration of Pb(II), Cr(III), Cu(II), Ni(II) and Cd(II) ions in environmental samples by membrane filtration prior to their flame atomic absorption spectrometric determinations

A method for separation-preconcentration of Pb(II), Cr(III), Cu(II), Ni(II) and Cd(II) ions by membrane filtration has been described. The method based on the collection of analyte metal ions on a cellulose nitrate membrane filter and determination of analytes by flame atomic absorption spectrometry (FAAS). The method was optimized for several parameters including of pH, matrix effects and sample volume. The recoveries of analytes were generally in the range of 93-100%. The detection limits by 3 sigma for analyte ions were 0.02microgL(-1) for Pb(II), 0.3microgL(-1) for Cr(III), 3.1microgL(-1) for Cu(II), 7.8microgL(-1) for Ni(II) and 0.9microgL(-1) for Cd(II). The proposed method was applied to the determination of lead, chromium, copper, nickel and cadmium in tap waters and RM 8704 Buffalo River Sediment standard reference material with satisfactory results. The relative standard deviations of the determinations were below 10%.     

What determines farmers’ adaptive capacity? Empirical evidence from Malawi

This paper assesses farmers’ incentives and conditioning factors that hinder or promote adaptation strategies and evaluates their impact on crop productivity by using data from nationally representative sample households in Malawi. We employed multivariate probit (MVP) and multinomial treatment effect (MTE) techniques to model adoption decisions and their yield impact. Exposure to delayed onset of rainfall and greater climate variability was positively associated with the choice of risk-reducing agricultural practices such as tree planting, legume intercropping, and soil and water conservation (SWC) but reduced the use of inputs (such as inorganic fertilizer) whose risk reduction benefits are uncertain. Concerning household adaptive capacity, wealthier households were more likely to adopt both modern and sustainable land management (SLM) inputs and were more likely to adopt SLM inputs on plots that were under greater security of tenure. In terms of system-level adaptive capacity, rural institutions, social capital and supply-side constraints were key in governing selection decisions for all practices considered, but particularly for tree planting and both organic and inorganic fertilizer applications. A combination of practices gave rise to higher yields suggesting that this might be a course of action that would sustain growth of yield in Malawi in the future.