Methanol In Poly Research Articles

Sorption and transport of methanol in poly(ethylene terephthalate)

This paper reports the sorption and diffusion characteristics of methanol vapor in polyethylene terephthalate (PET). Amorphous PET, semicrystalline, biaxially oriented annealed and non-annealed samples have been studied for equilibrium sorption and kinetics of methanol. At activities of methanol less than 0.30, uptake shows Fickian kinetics and isotherm follows the Dual Mode model. Diffusion coefficients increase with penetrant concentration and are of the order of 10−10cm2/s. Hysteresis during desorption and increase in solubility during resorption suggest methanol induced conditioning effects which may have detrimental effects on the barrier efficacy of PET. At activities greater than 0.30, swelling and relaxation effects occur and the isotherms show Flory–Huggins behavior for all three samples. Uptake follows two-stage kinetics fit by the Berens–Hopfenberg model. Greater polymer chain stability due to annealing reduces the extent of relaxation and improves the barrier efficacy over amorphous and non-annealed, oriented PET. For amorphous PET, at 80% activity and above, an induction time is observed which is absent in the semicrystalline films, suggesting strong relaxation effects in the amorphous phase of PET.

Effect of sample size on Case II diffusion of methanol in poly(methyl methacrylate) beads

The effect of sample size on the characteristic Case II solvent front penetration behavior has been investigated in a methanol–PMMA bead system at 25 °C in the particle diameter range of 0.125–1.280 mm. The observed induction time generally increases, whereas the front penetration rate exhibits a weak decreasing trend, with increasing sample diameter. Such dependencies of induction time and front penetration rate on sample size, although not predicted by existing theories of Case II diffusion, can be attributed to the size-dependent nature of several physical processes originated from the Fickian precursor penetrating ahead of the moving solvent front in an inhomogeneous swelling system of finite dimension.

The effect of calcium chloride dihydrate on the optical properties and mass transport of methanol in poly(methyl methacrylate)

The effect of calcium chloride dihydrate on optical properties and the mass transport of methanol in poly(methyl methacrylate) (PMMA) has been investigated. The solvent transport was analyzed based on the Harmon model accounting for Case I, Case II, and anomalous diffusions. Both Case I and Case II transports satisfy the Arrhenius equation. Calcium chloride dihydrate depresses Case I diffusion and enhances Case II diffusion. From the mass transport data, the equilibrium solvent content of methanol with various concentrations of calcium chloride dihydrate in PMMA is obtained and satisfies the van't Hoff plot. A comparison of movement of sharp front and mass transport is made. The increase of UV transmittance of specimens treated with a mixture of methanol and calcium chloride dihydrate is attributed to the reduction of the carbonyl group. The critical solvent content to change transmittance from a slow increase to a fast increase occurs when the sharp fronts meet at mid-plane. The decrease of transmittance in UV range is due to void creation for a large amount of solvent. The visible light transmittance of the specimen with small solvent content is the same as that of the specimen without solvent treatment. The visible wavelength dependence of transmittance of specimens with large solvent content is attributed to the void of which the size is smaller than the wavelength of visible light. The void is enlarged during the mass uptake, then it is fully closed after desorption of a small solvent amount and shrinks to a small size after desorption for a large solvent content.

Growth and healing of a surface crack in poly(methyl methacrylate) under case II diffusion of methanol

The behaviour of a pre-crack inserted in a surface swollen layer formed by case II diffusion of methanol in poly(methyl methacrylate) (PMMA) was investigated with reference to the distribution of internal compressive stress induced under constraint by the inner glassy core. The elastic analyses of internal stress were conducted by a finite element method using the data for the mechanical properties and the swelling strains preliminarily obtained for the sheet specimen overall swollen in methanol. The growth of the inserted crack in the surface swollen layer under static tension in methanol at 20°C was almost arrested for a long period at a position where the internal compressive stress in the tensile direction took the maximum magnitude near the boundary between the swollen layer and the glassy core. After being released from the internal compressive stress, the crack rapidly progressed to lead to a general fracture going across the boundary. A relatively long crack inserted in the thinner surface swollen layer completely disappeared in methanol at 40°C during 3 min under no external load. Crack healing, however, was not observed either in methanol at the lower temperature of 20°C or in the entirely swollen specimen, even at 40°C. These results suggest that both high temperature above the glass transition temperature of swollen PMMA and the significant internal compressive stress are required for crack healing.

Use of Magnetic Resonance Imaging To Study Transport of Methanol in Poly(methyl methacrylate) at Variable Temperature

The transport kinetics of methanol in PMMA have been studied over the temperature range 25−60 °C, using magnetic resonance imaging. It is shown that transport behavior changes from being relaxation controlled (Case II) at the lowest temperature to approaching Fickian behavior at the higher temperatures. It is also shown that the change of the exponent of time, n, describing the methanol uptake, with the swelling temperature can be compared with a change of the mechanical behavior of the polymer matrix in the presence of the penetrant. From DSC and DMA measurements, it can be concluded that the transition from Case II toward Fickian diffusion takes place at a temperature around the effective Tg of the imbibed material.

In-Situ Analysis and Quantification of Swelling Kinetics in Glassy and Rubbery Networks Using 1H and 19F Magnetic Resonance Microscopies

[sup 1]H and [sup 19]F magnetic resonance microscopies are used to determine the characteristics of diffusion in four different network-solvent systems. Transport of methanol in poly(ethyl methacrylate) (PEMA) and pyridine in coal is explored and compared with Fickian transport of toluene in polybutadiene rubber (PBD) and hexafluorobenzene in poly(methyl silicone) (PMS). These former two systems are characterized by sharp solvent fronts which propagate into the cores of the samples at a constant velocity. The swelling kinetics are quantified by applying a simple model which couples the kinetics of solvent diffusion to a second-order phase transition which induces network relaxation. Parameterization is accomplished with two kinetic terms and one thermodynamic parameter. These are a mass-fixed glassy diffusion coefficient, a network relaxation constant, and a critical concentration corresponding to the concentration of solvent necessary to induce a glass to rubber transition. Solvent from velocities, obtained through magnetic resonance microscopy, are used with independently derived critical concentrations to calculate the glassy diffusion coefficient and network relaxation rate constant. Kinetic swelling data are then fit with theoretical uptake curves computed using these parameters. A high-quality fit demonstrates that the proposed model successfully quantifies non-Fickian transport using a small number of physical based dynamic parameters.

Strain effects in the mass flux of methanol in poly(methyl methacrylate)

AbstractDiffusion of organic solvents into glassy polymers often results in a phase transformation of the hard, solid polymer into a swollen, rubbery material. During the sorption, internal stresses exist in the swollen and glassy parts of the polymer and are thought to contribute significantly to the “anomalous” diffusion observed in many penetrant–polymer systems. In this investigation, isothermal sorption data for the methanol–poly(methyl methacrylate) system have been obtained on plates ranging in thickness from 1/32 to ¼ in. The results show features characteristic of both a strain‐dependent diffusion coefficient and of a stress gradient contribution to the mass flux. An attempt to reproduce these results by combining a strain‐dependent diffusion coefficient model with a stress‐induced contribution to the flux is presented.

Diffusion and relaxation in glassy polymer powders: 2. Separation of diffusion and relaxation parameters

Gravimetric sorption measurements for organic vapours in monodisperse glassy polymer powders have shown widely varied non-Fickian kinetic behaviour. These varied kinetics are interpreted by a single mathematical model involving a linear superposition of one or two phenomenologically independent first order relaxation terms upon the ideal Fickian diffusion equation. Analysis of experimental data for submicron powders through this model yields kinetic and equilibrium parameters describing the individual contributions of the diffusion and relaxation processes. This analysis has been applied to both integral and incremental sorption data for vinyl chloride, acetone, and methanol in poly(vinyl chloride) and for n-hexane in polystyrene. Sorption by initially penetrant-free polymer samples is dominated by a rapid Fickian diffusion process, while incremental sorptions show larger relative contributions from slow relaxation processes. The relaxation processes appear to be related to slow redistribution of available free volume through relatively large scale segmental motions in the relaxing polymer. The diffusion—relaxation model seems to provide a meaningful analysis of several non-Fickian ‘anomalies’, including a very slow approach to apparent equilibrium, two-stage and sigmoidal sorption curves, and sorption curves involving an initial maximum followed by temporary desorption and subsequent resorption.

Transport of methanol in poly(methyl methacrylate)

The transport kinetics of liquid methanol in PMMA sheet (Perspex) have been studied over the temperature range 23° to 63°C. At the lower temperatures the transport is typical Case II; the methanol penetrating the polymer behind a sharp front which moves at constant velocity. For higher temperatures the concentration of methanol at the front and the front velocity both decrease with increasing penetration. These factors, which are no doubt related, combine to give mass absorption kinetics in which the exponent of time is no longer unity (Case II) but approaches 0.5, the value typical of Fickian diffusion. Iodine has been added to the methanol to make the positions of the penetration fronts readily visible. The iodine does not affect either the rate of penetration or the equilibrium absorption. Measurements of colour density profiles on thin cross-sections using a microdensitometer give a reliable indication of the true methanol profile. The rate at which the methanol penetrates the glassy polymer is proportional to its concentration at the advancing fronts. The apparent activation energy for methanol penetration for constant concentration at the fronts is 25 kcal/mol.