In this work, the Flory-Huggins parameters corresponding to the amorphous phase of a polyethylene (PE) and two ethylene-vinyl acetate (EVA) copolymers (with 18 and 33 % vinyl acetate content, respectively) samples, with different solvents have been determined below the melting temperature of the polymers, in order to quantify the bulk interactions of these polymer/solvent systems. The employed solvents were a dispersion solvent (cyclohexane), a polar solvent (vinyl acetate) and an association solvent (methanol). Initially, the inverse gas chromatography measurements allowed obtaining the retention volumes, activity coefficients and overall Flory-Huggins parameters of every polymer/solvent system. According to these parameters, in all cases, the more compatible solvent was cyclohexane, so it was selected as the probe to calculate the percentages of crystallinity at room temperature, whose results were in agreement the literature data (35 % for PE, 29 % for EVA18, and 12 % for EVA33). The percentage of crystallinity allowed determining the amorphous Flory-Huggins parameters which are the ones which take into account just the bulk interactions in a polymer/solvent mixture. The Flory-Huggins parameter results show that, to accurately study the vapor-liquid equilibrium between a polymer and a solvent (bulk interactions), when the range of studied temperatures is below the melting point of the polymer, it is crucial to calculate the amorphous contribution (v amorphous ) on the overall FloryHuggins parameter. In the case of this study, the lower the vinyl acetate content (higher crystallinity), the higher the difference between the overall and amorphous Flory-Huggins parameters is. Analyzing the interactions between the three polymeric materials and the solvents it can be noticed that, for the most compatible & Eduardo Díez solvent (cyclohexane), v amorphous represents the less contribution, or the highest correction, to the overall Flory-Huggins parameter (around 50 % for PE and EVA18, and 79 % for EVA33, the less crystalline polymer).
Adsorption of β-glucosidase from almonds, an enzyme with big molecular size (130 kDa, 6.7 nm molecular diameter), on mesoporous SBA-15 silica in fixed bed column was studied. Previously, zeta potential analysis confirmed that the electrostatic interactions between β-glucosidase and SBA-15 were the driving force of the immobilization process. The maximum difference in the zeta potential was 25 mV at pH 3.5. Adsorption isotherm was classified as an L3 (Langmuir type 3) curve according to the Giles classification and fitted to a double Langmuir equation. The adsorbed amount in a fixed bed column was around 3.5 times higher than the amount reached in the adsorption in batch. In addition, the β-glucosidase was strongly immobilized on SBA-15 with only 7 % of leaching in the washing step with buffer solution. Immobilized β-glucosidase was catalytically active in a continuous process, reaching 100 % substrate conversion and maintaining this activity level for more than 10 h without deactivation of the enzyme. Adsorption-desorption isotherms at 77 K before and after the adsorption were carried out, concluding that the adsorption of β-glucosidase was produced blocking the pore mouth, so that a part of the enzyme penetrates inside and another part stays outside the pore.
The solubility parameter and the Flory-Huggins interaction parameter of two EVA (ethylene-vinyl acetate) copolymers, each one with different vinyl acetate content, are calculated by using inverse gas chromatography technique. The influence of the vinyl acetate percentage is analyzed and indicates that the polymer-solvent interactions are stronger in the case of the copolymer with the highest vinyl acetate percentage. The results also point to the fact that the most favorable solvents for the studied materials are the aromatic-type ones. Finally, from the calculated values of the polymer solubility parameter (16.3 MPa 0.5 for EVA 460 and 15.1 MPa 0.5 for EVA410, at 50 C), it can be noticed that the solubility parameter of the EVA copolymer with the largest vinyl acetate content is the closest to the solubility parameter of pure vinyl acetate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.