Transport of Water and Gases through EVA/PVC blend films – Permeation and DSC investigations.

The transport of water vapor and gases (oxygen and carbon dioxide) through poly(ethylene-co-vinyl acetate) (EVA) films of different VA content, poly(vinylchloride) (PVC) and EVA/PVC blend films, was analysed from permeation measurements. A plasticization effect of water on the material was observed for EVA films with more than 19% wt. of VA content and for the EVA/PVC blends, while for gas permeation practically all the experimental curves are characterized by a constant diffusion coefficient, whatever the VA content of the copolymer used. The increase in water absorption with the VA content leads to a steady increase in the water permeability of the EVA copolymers. By mixing the glassy PVC polymer with the EVA copolymer (in a rubbery state) reduced water and gas permeability is observed, resulting mainly from the decrease of the diffusivity due to the low segment mobility of the dense PVC material able to create hydrogen bonds between the hydrogen atoms and the Cl-substituted carbon of PVC with VA carbonyls. Compared to EVA copolymers, the EVA/PVC blends with equivalent VA contents are better in terms of selectivity

Effect of chemical treatments of Alfa (Stipa tenacissima) fibres on water-sorption properties

International audienceNatural fibres have prooved to be an excellent reinforcers in composite materials. Since many years, for economic and environmental reasons, there has been an increasing interest in using plant fibres in composite systems. However, the main disadvantage of the natural fibres being used as reinforcers is their hydrophilic nature, therefore, the ageing of composite materials can be pronounced because of the diffusion of water molecules leading to a swelling effect. Moreover, the adhesion between natural fibres and the polymer matrix is insufficient. In this work, various chemical surface treatments have been performed on the Alfa (Stipa tenacissima) fibre. These different treatments involve acetylation (Ac), with the help of chemicals such as styrene (S), acrylic acid (AA) and maleic anhydride (MA). The treatment effects on the fibres have been characterized by means of infrared spectroscopy, surface energy, and microscopy analysis. A detailed investigation on the water sorption characteristics of Alfa fibres has been carried out. It was found that treatments reduced the overall water uptake of Alfa fibres. In particular styrene treatment allows to increase significantly moisture resistance of these fibres

Water vapor sorption properties of cellulose nanocrystals and nanofibers using dynamic vapor sorption apparatus

Abstract Hygroscopic behavior is an inherent characteristic of nanocellulose which strongly affects its applications. In this study, the water vapor sorption behavior of four nanocellulose samples, such as cellulose nanocrystals and nanofibers with cellulose I and II structures (cellulose nanocrystals (CNC) I, CNC II, cellulose nanofibers (CNF) I, and CNF II) were studied by dynamic vapor sorption. The highly reproducible data including the running time, real-time sample mass, target relative humidity (RH), actual RH, and isotherm temperature were recorded during the sorption process. In analyzing these data, significant differences in the total running time, equilibrium moisture content, sorption hysteresis and sorption kinetics between these four nanocellulose samples were confirmed. It was important to note that CNC I, CNC II, CNF I, and CNF II had equilibrium moisture contents of 21.4, 28.6, 33.2, and 38.9%, respectively, at a RH of 95%. Then, the sorption kinetics behavior was accurately described by using the parallel exponential kinetics (PEK) model. Furthermore, the Kelvin-Voigt model was introduced to interpret the PEK behavior and calculate the modulus of these four nanocellulose samples