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Summary: Surface modification induced on poly(ethylene terephthalate) (PET) fibers by cold SF6 plasma treatment has been investigated systematically as a function of plasma device parameters. The observed wettability modifications of fibers plasma-treated under different operating conditions were correlated to their dyeability modifications and to the changes in surface chemical composition, determined by X-ray Photoelectron Spectroscopy (XPS), and topography, investigated by atomic force microscopy (AFM). Optical emission spectra from the SF6 plasma at different pressures gave information on its content of fluorine atoms. A striking transition was observed between the increased hydrophilicity and high dyeability, imparted by plasma treatment at low pressure (

Water molecules retained in native cellulose gels obtained from Acetobacter xylinym (AX) were displaced by poly(ethylene glycol)s (PEG) of different molecular weight. The so obtained native cellulose/PEG material, characterized in film form by differential scanning calorimetry, dynamic mechanical thermal analysis and wide angle X-ray scattering, revealed that strong interactions occur between PEG and cellulose and that the polymer mixture is in the rubbery state at ambient temperature. Moreover, it could be dyed in supercritical carbon dioxide by disperse dyes, thus exhibiting typically lipophilic properties and suitability to be employed as a bio-compatible support for lipophilic active species.

Silk samples, treated in an appositely set-up radio frequency SF6 plasma reactor under different operation conditions, were characterized by XPS, EPR, DSC, XRD, ATR analyses and water contact angle measurements, also as a function of storage time after the treatment. Efficient attachment of fluorine atoms on the polymer surface occurred during the plasma treatment, imparting water repellence to it. Also the percentage of surface oxygen increased after the treatment, partially as a consequence of radical scavenging by molecular oxygen and the formation of peroxides. An increase in silk crystallinity during the treatment seems to contribute to ensuring durable water repellence properties.

The aging of bacterial polyester poly(D(—)3-hydroxybutyrate) has been studied by coloring it with 4-diethylamino-4′-methoxyazobenzene and determining the reduction in isomerization rate of the dye with aging, such a reduction being a measure of the loss in polymer sequential mobility that is responsible for the considered phenomenon. A preliminary test carried out on poly(ethylene terephthalate) colored with 4-diethylaminoazobenzene proved the isomerization of the dispersed dye to be a sound probe for determining the aging process. In the case of the bacterial polyester, the aging process appeared even above the polymer Tg value measured by calorimetric analysis. The kinetics and rate coefficients of aging were determined at 30°C for the examined polymers. Aging in the copolymer poly(hydroxybutyrate-hydroxyvalerate) was also investigated. © 1995 John Wiley & Sons, Inc.

Atactic poly(epichlorohydrin) (PECH) was blended in a wide range of ratios with poly(D(−)3-hydroxybutyrate) (PHB) isolated from Alcaligenes eutrophus cultures. The crystallization and thermal behaviour of PHB/PECH blends were analysed by d.s.c. and microscopy. All blends show a single glass transition temperature, whose value is dependent on composition, in good agreement with the theoretical values calculated by the Fox equation. The influence of blend composition on the overall crystallization rate and on the spherulite growth rate suggests that the two components form a miscible blend in the amorphous phase. The equilibrium melting temperature decreases with blending; the negative value of the χ12 parameter of the PHB/PECH system suggests that the two components can form a miscible mixture which is thermodynamically stable above the equilibrium melting temperature. The reorganization phenomenon of PHB crystals after first melting was also observed.

Oxygen permeation through films of pure poly(propylene) (iPP) and iPP blended with a fully saturated alicyclic hydrocarbon resin (IST), obtained by oligomerization of indonaphthene, α-methylstyrene and vinyltoluene, was studied as a function of temperature and weight fraction of the two components. Increasing IST content lowers oxygen permeability and increases the glass transition temperature of the polymer blends. Annealing for 2 min at 375 K was shown to transform completely the smectic phase in the α crystalline form, while annealing for 10 min at 393 or 403 K induces a marked increase in crystallinity and in effective oxygen permeability per unit of amorphous component, Pa. This experimental behaviour may be explained by the formation of microvoids; the increase in microporosity modifies the mechanism of the permeation process.

Films obtained from native cellulose synthesized by Acetobacter xylinum and from cellulose obtained from cuproammoniacal solutions (cellulose II) were morphologically characterized by studying the cis-trans isomerization of azo dye Chrysophenine dispersed in their amorphous region. The kinetic measurements of the reaction showed that both films behave as glassy polymers in the temperature range explored (36–66°C). In going from native cellulose to cuproammoniacal cellulose, an increase of the isomerization rate was observed, revealing a more homogeneous distribution and likely larger extent of free volume in the amorphous phase of cellulose II.

Two polycaprolactam films were prepared characterized by different crystallinity degrees, the free volume model being prevalent in the former and the pore model in the latter. They were colored with azo dyes XC6H4NNC6H4N(C2H5)2 (where X is H and COOH), the latter of which gives specific interactions with the polymer. The kinetics of the thermal cis–trans isomerization of these dyes has been studied below and above the glass transition temperature of the polymer (Tg) in the range 20–80°C. In every case, the isomerization process was found to be the result of a multiplicity of first-order reactions and the dependence on temperature exhibited a break at the Tg value. Lightfastness of the dyes in the polymer matrices has been also investigated. The isomerization and fading kinetics are discussed in terms of polymer structural features as well as of the nature of the dye.

Five polypropylene films were prepared having different crystallinity and morphology, the latter having been modified by stretching. They were colored with azo dyes XC6H4NNC6H4N(C2H5)2 (where XH, OCH3, CN, and NO2). The kinetics of the thermal cis-trans isomerization of these dyes has been studied in the range 21–41°C, much above the glass transition temperature of the polymer. The isomerization process was found to be strictly first-order; the kinetic parameter values have been correlated with the free volume extent in the amorphous regions of the matrix. Lightfastness of the dyes in the polymer matrices has been also investigated: It appeared to be more important for the unoriented samples with respect to the stretched ones and substantially independent on the crystalinity degree.

A model has been applied to release of plasticizers from polymer films through vapor phase, for which the overall rate of release may be generally determined by evaporation of the plasticizer from the surface of the film, and/or by migration to the surface at below saturation in the polymer. The experimental system employed made use of n-butyl formate, diethyl-phthalate, di-n-butylphthalate, and N,n-butylbenzenesulfonamide as model molecules in polycaprolactam films, both with the aims of studying undesirable loss of plasticizers, and of simulating a model able to envisage releasing, at a constant rate, of any desired additive, with relatively high solubility and vapor pressure, to the content of packaging films. Experimental measurements were made (at 298–333 K) by investigating in a suitable cell the permeation of plasticizers both at concentrations below and above the saturation limit. Rate of evaporation of plasticizers from the membrane surface above the saturation limit, measured in this cell, were found to coincide satisfactorily with those calculated by application of the mass transfer theory to evaporation from a stationary liquid into a stirred gas, at a known velocity of gas flowing past the surface. From these latter rates and solubilities, the mass transfer coefficients H for evaporation could be obtained, as well as from experimental time lags the diffusivities Dp through the polymer membrane. In the light of the theoretical model a correlation was found between activation energies of H and evaporation enthalpies of the model molecules.

Photoinitiated grafting and graft polymerization of liquid mixtures, adsorbed onto polypropylene, polycaprolactam, and poly(ethylene terephthalate) films, containing one of four acryloxy-substituted aromatic diazenes and one of four diacrylate comonomers, in the presence of 1,2-diphenyl-2,2-dimethoxyethanone as photoinitiator, were investigated kinetically at 30 ± 2°C. Irradiation was carried out polychromatically, with impinging photoenergy from 2.1 × 10−8 to 20.5 × 10−8 einstein s−1 cm−2; in some of the runs the ultraviolet radiation was filtered. The ratio R between the molar concentration of photoinitiator and the sum of concentrations of dye and diacrylate varied between 0.005 and 0.095; the ratio M between the molar concentration of dye and diacrylate varied between 0.005 and 0.046. The moles of dye and diacrylate n initially deposited per unit apparent polymeric surface S varied between 2 and 74 μmol cm−2. No selective effect was shown by the presence of dyes in the comonomer mixture. The surface density of grafted molecules at the end of the grafting process was not affected by the photoinitiator concentration (for 0.030 < R < 0.095), by diacrylate or dye concentrations, or by the kind of polymer substrate. This parameter, on the contrary, clearly depended on n/S, and linearly up to n/S ≅ 30 μmol cm−2. Quantum efficiencies for the two consecutive kinetic processes of grafting and graft polymerization (Φ1 and Φ2, respectively) were evaluated. The dependency of Φ1 on R, as well as of Φ2 on n/S, are critically discussed on the basis of the proposed mechanism involving grafting of an oligomeric chain (Φ1 values up to the order of 102) followed by a step-by-step graft polymerization (Φ2 limiting values of the order of unity). The sensitizing effect of acryloxy-substituted aromatic diazenes on both Φ1 and Φ2 is evidenced.

Three poly(ethylene terephthalate) films were prepared having the same crystallinity but different morphology. They were colored with azo dyes XC6H4N = NC6H4N(C2H5)2 (where X is H, OCH3, CN, and COOC2H5). The kinetics of the thermal cis-trans isomerization of these dyes has been studied below the glass transition temperature in the range 25–56°C. The isomerization process was found to be the result of a multiplicity of first-order reactions. The kinetic parameters have been correlated with the order degree at molecular level of the polymer. Lightfastness of the dyes in the polymer matrices has been also investigated: it appeared to be in relation with the supermolecular structure of the film.

The thermal cis-trans isomerization of azo dyes XC6H4N=NC6H4N(C2H5)2 (where X is H, OCH3, CN, and NO2) in poly(ethylene terephthalate) matrices, below the glass transition temperature, and in dibutylphthalate solutions has been studied kinetically in the temperature range 20–60°C. Kinetic behavior in the polymer is characterized by two or three simultaneous first-order processes with similar activation enthalpies. These processes reflect an unequal distribution of “tie-molecules,” “folds,” and “cilia” in the amorphous region of the polymer. Lightfastness of the dyes in poly(ethylene terephthalate) films has been investigated. Polymer morphology strongly affected the photofading, but no significant influence was observed in the kinetic experiments.