Nonequilibrium Sorption of Water in Polylactide (original) (raw)
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Non-Fickian Diffusion of Water in Polylactide
Industrial & Engineering Chemistry Research, 2013
The diffusion of water in polylactide (PLA) was measured at various external water vapor activities (0−0.85) and temperatures (25, 35, 45°C) using three separate experimental techniques: quartz spring microbalance (QSM), quartz crystal microbalance (QCM), and time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Non-Fickian sorption kinetic behavior was observed with all the experimental techniques used over the observed experimental time scales, which was a result of the nonequilibrium state of the glassy polymer. Two phenomena were observed over two distinct time periods (two-stage sorption kinetics), where early time data revealed diffusion driven by a water concentration gradient and later time data revealed diffusion driven by slow polymer relaxation or swelling due to additional water ingress over time. Diffusion coefficients and relaxation time constants were determined by regressing the early time data to a Fickian model and the data over the entire observed experimental time scale to a diffusion-relaxation model, respectively. Diffusion coefficients increased with temperature, were constant with activity and concentration of water in the polymer, and were similar among all three experimental techniques. The high Deborah numbers (relaxation time/diffusion time) determined from the diffusion-relaxation model confirm the observed two-stage non-Fickian behavior.
Moisture Sorption, Transport, and Hydrolytic Degradation in Polylactide
Applied Biochemistry and Biotechnology, 2006
Management of moisture penetration and hydrolytic degradation of polylactide (PLA) is extremely important during the manufacturing, shipping, storage, and end-use of PLA products. Moisture transport, crystallization, and degradation in PLA have been measured through a variety of experimental techniques including size-exclusion chromatography, differential scanning calorimetry, and X-ray diffraction. Quartz crystal microbalance and dynamic vapor sorption experiments have also been used to measure moisture sorption isotherms in PLA films with varying crystallinity. A surprising result is that, within the accuracy of the experiments, crystalline and amorphous PLA films exhibit identical sorption isotherms.
Sorption of Water Vapor in Poly(L-Lactic Acid): A Time-Resolved FTIR Spectroscopy Investigation
Frontiers in Chemistry
In this contribution the sorption of water vapor in Poly(L-lactic acid) (PLLA) was studied by time-resolved FTIR spectroscopy. The collected FTIR data were analyzed by complementary approaches such as difference spectroscopy, two-dimensional correlation spectroscopy (2D-COS), and least-squares curve-fitting analysis which provided information about the overall diffusivity, the nature of the molecular interactions among the polymer and the penetrant and the dynamics of the various molecular species. The diffusion coefficient were evaluated as a function of vapor activity and were found in good agreement with previously reported values. The system showed a Fickian behavior with diffusivity increasing with penetrant concentration. Two distinct water species (first-shell and second-shell layers) were detected and quantified by coupling FTIR and gravimetric measurements.
Thermodynamics of water sorption in high performance glassy thermoplastic polymers
Frontiers in Chemistry, 2014
Sorption thermodynamics of water in two glassy polymers, polyetherimide (PEI) and polyetheretherketone (PEEK), is investigated by coupling gravimetry and on line FTIR spectroscopy in order to gather information on the total amount of sorbed water as well as on the different species of water molecules absorbed within the polymers, addressing the issue of cross-and self-interactions occurring in the polymer/water systems. Water sorption isotherms have been determined at temperatures ranging from 30 to 70 • C while FTIR spectroscopy has been performed only at 30 • C. The experimental analysis provided information on the groups present on the polymer backbones involved in hydrogen bonding interactions with absorbed water molecules. Moreover, it also supplied qualitative indications about the different "populations" of water molecules present within the PEEK and a quantitative assessment of these "populations" in the case of PEI. The results of the experimental analysis have been interpreted using an equation of state theory based on a compressible lattice fluid model for the Gibbs energy of the polymer-water mixture, developed by extending to the case of out of equilibrium glassy polymers a previous model intended for equilibrium rubbery polymers. The model accounts for the non-equilibrium nature of glassy polymers as well as for mean field and for hydrogen bonding interactions, providing a satisfactory quantitative interpretation of the experimental data.
Sorption and transport of water vapor in glassy poly(acrylonitrile)
Polymer Engineering & Science, 1980
Sorption data for H2O in glassy poly(acrylonitrile)(PAN) are presented for a range of relative vapor pressures at temperatures from 20 to 50°C. Simple dual mode sorption, involving “hole‐filling” and molecular solution appears to dominate the low activity region of sorption. Based on the clustering analysis suggested by Zimm and Lundberg, pronounced clustering of penetrant appears to occur above a relative pressure of 0.6. The form of the effective concentration‐dependent diffusion coefficient for H2O in PAN, determined by analysis of steady state permeation data, suggests that water in the microvoids and clusters has a lower mobility than the molecularly dissolved water in the polymer matrix. Time lag measurements at high upstream relative water vapor pressures suggest that the transient state permeation has a non‐Fickian character due to relaxations which occur slowly to accommodate the clustering process.
Sorption Thermodynamics of CO2, H2O, and CH3OH in a Glassy Polyetherimide: A Molecular Perspective
Membranes, 2019
In this paper, the sorption thermodynamics of low-molecular-weight penetrants in a glassy polyetherimide, endowed with specific interactions, is addressed by combining an experimental approach based on vibrational spectroscopy with thermodynamics modeling. This modeling approach is based on the extension of equilibrium theories to the out-of-equilibrium glassy state. Specific interactions are accounted for in the framework of a compressible lattice fluid theory. In particular, the sorption of carbon dioxide, water, and methanol is illustrated, exploiting the wealth of information gathered at a molecular level from Fourier-transform infrared (FTIR) spectroscopy to tailor thermodynamics modeling. The investigated penetrants display a different interacting characteristic with respect to the polymer substrate, which reflects itself in the sorption thermodynamics. For the specific case of water, the outcomes from molecular dynamics simulations are compared with the results of the present...
STUDY OF ISOTHERMS OF WATER VAPOR SORPTION FOR HYDROPHILIC POLYMERS
Chemistry of Plant Materials, 2022
Various models and equations of water vapor (WV) sorption for hydrophilic polymers were considered. However, these models often do not correspond to the sorption mechanism. This study is based on the thermodynamics in binary systems and the Van Krevelen method of polar group contributions in the sorption of WV. Moreover, it was shown that the mechanism of WV sorption by various hydrophilic polymers is the absorption of water molecules in the volume of amorphous domains of these polymers. As a result, a universal physicochemical equation was proposed allowing adequately to describe the sorption isotherms of WV by amorphous hydrophilic polymers knowing only the chemical formulas of repeating units of these polymers. To calculate the sorption isotherms for semicrystalline polymer samples, it is necessary to use an additional parameter, namely the degree of amorphicity (Y). The adequacy of the derived equation was verified for samples of cellulose and other natural polysaccharides, as well as for samples of synthetic hydrophilic polymers such as polyvinyl alcohol, polyamide-6, and polycaprolactone having various Y-values. The verification showed that the experimental isotherms are almost identical to the isotherms calculated by the universal equation.
Chemical Engineering Science, 2004
We have conducted di erential water vapour sorption experiments on Kevlar TM 49 at 30 • C over a series of water vapour pressures from 0 to 90% of saturation, and on the as-polymerised form of the material at 30 • C, 45 • C and 60 • C over a series of water vapour pressures of 0-60%, 0-25% and 0-15%, respectively. The equilibrium isotherms obtained for both samples show a distinct hysteresis-type behaviour. For Kevlar TM 49, the hysteresis loop can be divided into two regions, namely above 30%, which is indicative of the presence of microvoids, and below 30%, which suggests inclusion of water into the intimate structure of the surface layer of the polymer crystallites, in a process known as intercalation.