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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).

In this article, the thermodynamic behavior of polyvinylacetate (PVAc)–solvent, and polyethylene (PE)–solvent mixtures have been studied by determining the thermodynamic sorption parameters (enthalpy, entropy, and free energy), the mass‐based solvent activity coefficients (Ω) and the Flory Huggins parameters (χ), by means of inverse gas chromatography (IGC) measurements. According to the Flory Huggins parameters of the PE–solvent mixtures, determined between 40 and 60°C the compatibility (the ability to interact with each other) of this polymer with the different types of solvents follows this order: dispersion solvents > polar solvents > association solvents. In the case of PVAc mixtures, the thermodynamic parameters were determined between 60 and 80°C, only for polar‐type and association‐type solvents due to, in the studied temperature range, the retention diagrams of dispersion solvents show that there are not bulk interactions. The Hildebrand solubility parameters of both polymers were also determined, according to Guillet procedure. The higher values of PVAc material (14.1 MPa0.5 for PE and 19.8 MPa0.5 for PVAc, at 60°C) are related to the strong interactions of vinyl acetate monomer. POLYM. ENG. SCI., 56:36–43, 2016. © 2015 Society of Plastics Engineers

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The Hansen solubility parameters (HSPs) of two ethylene–vinyl acetate (EVA) copolymers (with 18 and 33 wt% of vinyl acetate) and their corresponding homopolymers (polyethylene, PE, and poly(vinyl acetate), PVAc) have been studied at various temperatures, employing the previously obtained Flory–Huggins parameters. From these latter values, a procedure based on the Hansen solubility spheres theory was employed to determine the HSPs, as well as the radius of interaction. The procedure was validated with literature data, with deviations of around 3%. The HSP values (dispersion, polar and association terms, respectively, all in MPa1/2) at 333.15 K are 14.84, −3.88 and 1.78 for PE, 17.65, −1.24 and 2.76 for EVA410 (with 18 wt% of vinyl acetate), 17.52, 0.15 and 3.61 for EVA460 (with 33 wt% of vinyl acetate) and 19.45, 10.59 and 5.76 for PVAc. The main characteristic of the obtained HSP values is that the high polar term of PVAc tends to increase the solubility character of the pure PE, and thus the EVA copolymers, allowing them to solubilize dispersion and polar compounds. Finally, it was also demonstrated that it is possible to predict the HSPs of EVA copolymers using the vinyl acetate content and the HSPs of pure PE and PVAc as input data. © 2017 Society of Chemical Industry

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.