J.M. Saiter

Characterization of recycled celluloses: thermogravimetry/Fourier transform infra-red coupling and thermogravimetry investigations

Abstract Thermogravimetry/Fourier transform infra-red coupling analysis and thermogravimetry were performed on recycled celluloses of different compositions. Four samples were studied: one from ashless filter paper, two from recycled celluloses with 80% of chemical paper pulp and 85% of mechanical paper pulp respectively, and one from recycled cellulose the composition of which is not known. The major volatile products formed during the degradation process were identified by means of thermogravimetry/Fourier transform infra-red coupling analysis. From thermogravimetry we show that the degradation process of such recycled celluloses may be divided into two stages. The activation energies for these degradation processes were obtained using the Kissinger and Broido methods. Our data show that Broidos method allows the identification of each recycled cellulose from a knowledge of the activation energies (Ea) and the critical rate of transformation (αc).

Crystallization of AsxSe1−x from the glassy state (0.005<x<0.03)

Abstract The crystallization of As x Se 1− x from the glassy state (0.005 x x , the apparent activation energy decreases. It is also found that the dependence of the inverse of the apparent activation energy for crystallization falls linearly with the reciprocal of the mean temperature used in the experiment. The latter result unambiguously indicates that the crystallization process for As x Se 1− x , in the composition range investigated, is mainly controlled by the viscosity of the medium. Therefore, the crystallization reaction totally disappears when the amount of As atoms in the alloys reaches such a value capable of connecting enough Se chains to block their movement.

Study of transport of small molecules through ethylene-co-vinyl acetate copolymers films. Part A: Water molecules

Abstract The transport of liquid water through poly(ethylene-co-vinyl acetate) (EVA) films with 4.5%, 19%, 33%, 50% and 70% w/w VA contents, is studied by permeation measurements. A low density polyethylene LDPE, used as reference, is also studied. The diffusion of water is determined from transient permeation. For a better understanding of the role played by the structure and the surface of these copolymers whose crystallinity varies with the presence of VA groups, Differential Scanning Calorimetry and contact angle (surface free energy) measurements are performed. It is found for LDPE and 4.5% w/w VA membranes that the water diffusion coefficient decreases with increasing water concentration, while for 19% VA a constant diffusion coefficient is obtained. For membranes with 33, 50 and 70% w/w VA a diffusion coefficient which increases exponentially with the local water concentration is obtained. These results are explained by the formation at low VA content of small water clusters, clusters evidenced by means of IR spectrometry. On the other hand, the plasticization effect (concentration-dependent diffusion coefficient) is observed for VA content greater than 19% wt. VA is explained by the increase of the amorphous phase ratio, which allows an increase of the number of interactions between polar groups (carboxyl units in the statistical copolymer) and water molecules

Strong-fragile glass forming liquid concept applied to GeTe chalcogenide glasses

The values of the thermal heat-capacity changes at the glass transition temperature Tg (DCp ¼ CplCpg ) andthe values of the apparent activation energy Dhof the sub Tg relaxation process are determined for GexTe1� x (0.154x40.20) vitreous alloys by means of differential scanning calorimetry investigations. The values of Dhare then used to determine the values of the fragility index, m. The comparison of these new data to those already obtained on the GexSe1� x vitreous system leads to conclude that both systems exhibit strong thermodynamic character. The stronger thermodynamic character is reached at the Phillips-Thorpes floppy-to-rigid transition. On the other hand, we findthat Ge xTe1� x exhibits a kinetically fragile character which decreases as the amount of Ge increases in the alloy. # 2001 Elsevier Science B.V. All rights reserved.

Study of transport of small molecules through ethylene-co-vinyl acetate copolymers films. Part B: CO2 and O2 gases

Abstract The transport of gases (pure oxygen and carbon dioxide) through poly(ethylene-co-vinyl acetate) (EVA) of different VA contents, was studied by permeation measurements. Permeabilities, diffusivities, and solubilities were determined for EVA films containing 19, 33, 50 and 70% (w/w) VA. A low density polyethylene LDPE (used as reference with 0% VA) was also studied. The diffusion of oxygen was determined from transient permeation fluxes and the diffusion of carbon dioxide from time-lag permeation. In the case of gas permeation, whatever the VA content of the polymer used, the experimental transient fluxes are characterized by a constant diffusion coefficient for both O2 and CO2. In terms of gas permeability, compared with water permeability (Part A), these copolymers are characterized by very low coefficients, especially for oxygen. Assuming that D is constant, the O2 and CO2 solubility coefficient was then deduced and its value is shown to increase proportionally with the VA content in these rubbery copolymers (whose quantity of crystalline phases decreases and become nil for 70% VA). The H2O/CO2 and H2O/O2 ideal selectivity α increases with the VA content, in agreement with the increase in average polarity of the copolymer.

Enthalpy relaxation in GexSe1−x chalcogenide glasses

Abstract Enthalpy relaxation in selenium samples and Ge x Se 1− x alloys with x =0.08 and 0.12 has been investigated by differential scanning calorimetry. All the samples have been submitted to comparable aging temperatures 10°C below the glass transition temperature for a period from 0.5 to 800 h. The apparent activation energy and the Narayanaswamy parameter, X , were calculated and the non-exponentiality parameter, β , was estimated for the samples. The introduction of the germanium atoms in the selenium chain changes the distribution of relaxation times, increases the relaxation rate per decade and decreases the apparent activation energy. No differences were observed in the Ge x Se 1− x alloys in the evaluation of these parameters.

Surface modification by low-pressure glow discharge plasma of an unsaturated polyester resin: effect on water diffusivity and permeability

Abstract Unsaturated polyester resin (UPR) films have been modified by a tetrafluoromethane microwave plasma. The treated surface morphologies investigated by contact angle, atomic force microscopy and permeation measurements show that the CF 4 plasma treatment decreases drastically the surface energy by increasing the hydrophobic character. The surface modification due to plasma fluorination decreases the water content diffusing through the UPR film and the time lag diffusion coefficient and thus, the sorption kinetic. From these results, it is clearly shown that the CF 4 plasma treated layer improves drastically the barrier effects.

Fragility index of drawn or annealed poly(ethylene terephthalate) films studied by thermally stimulated depolarisation currents

Abstract According to the ‘strong-fragile’ glass forming liquid concept, amorphous poly(ethylene terephthalate) (PET) must be classified as a ‘fragile’ supercooled liquid. In this work we show that the value of the fragility index of the glassy material (mg) can be obtained by means of Thermally Stimulated Depolarisation Currents measurements. Experiments were carried out on different PET for which the molecular mobility of the vitreous domain was constrained by the existence of a crystalline phase. This crystalline phase was obtained in two different ways, i.e. by thermal cold crystallisation or by a uniaxial hot-drawing method. Depending on the degree of crystallinity, but whatever the nature of the crystalline morphology (spherulitic or oriented crystallites), it is found that the initial fragile character becomes stronger as the degree of crystallinity increases.

Permeametric and microgravimetric studies of sorption and diffusion of water vapor in an unsaturated polyester

Abstract A detailed analysis of the sorption equilibrium and the diffusion of water vapor under different activities through an unsaturated polyester resin (UPR) has been undertaken by differential permeation and microgravimetry techniques. The BET-type III sorption isotherm obtained by microgravimetry was analyzed with the Zimm–Lundberg approach to determine the mean cluster size in the UPR film: the latter increases drastically with the water content in the film. The transient permeation flux can be well fitted when a concentration-dependent diffusivity of exponential type is used. From the water content at sorption equilibrium and the steady-state permeability, a mean diffusion coefficient for the steady state can be determined; its decrease with increasing water activity is consistent with the increase in the mean cluster size.

Fragility and non-linearity in polymethyl(α-n-alkyl)acrylates

Abstract In this work, the fragility indices, m, of some new polymers from the polymethyl(α-n-alkyl)acrylate family, with 3, 5, or 8 carbons in the side chain, were determined with the method proposed by Bohmer. We have found that the value of the fragility index decreases as the length of the lateral chain increases. We also confirm a previous work in which we found a critical length of the alkyl chain which separates two types of dependence, identified by different relaxation parameters. The correlations between the ms and the Narayanaswamy parameter are also investigated.