Alberto Seves

Crystallization and thermal behaviour of poly(D(-) 3-hydroxybutyrate)/poly(epichlorohydrin) blends

Abstract 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.

Dyeing of Cotton in Supercritical Carbon Dioxide

Abstract The dyeing of cellulosic fibers with disperse and natural dyes was attempted using supercritical carbon dioxide (CO2SCF) as solvent system. The dye uptake was strongly increased if cotton was pretreated with polyethylene glycol (PEG), a known plasticizing agent of cellulose, while reasonable wet-washing and light fastness properties were achieved if PEG-treated cotton was dyed in CO2SCF with disperse dyes included in benzamide crystals. This might be a consequence of partial occlusion of cellulose pores by benzamide, forming hydrogen bonds with cotton and PEG.

Small-angle X-ray scattering study of the phase structure of poly(d-(−)-3-hydroxybutyrate) and atactic poly(epichlorohydrin) blends

Abstract Isothermally crystallized and annealed blends of poly( d -(−)-3-hydroxybutyrate) (PHB) and atactic poly(epichlorohydrin) (aPECH) were examined by wide-angle X-ray diffraction and small-angle X-ray scattering (WAXD and SAXS). The lateral crystal dimensions of PHB increased with annealing treatment and with increasing aPECH component in the blends, while the long-period distances of the blends were slightly smaller than for pure PHB. The scattering observed for the blends resulted from the superposition of the scattering arising from the crystalline regions (made up by alternate stacking of lamellae and thin amorphous layers) and from the aPECH inhomogeneity present outside them. The structural information was obtained, from the SAXS curves, on the basis of Glatter and Debye-Bueche approaches. The results suggest that, during melt-crystallization of PHB, segregation of aPECH occurs within the growing spherulite with its dispersion in the interfibrillar zones that are larger than the interlamellar regions but smaller than the overall spherulite. The aPECH molecules are dispersed at the molecular level in the interfibrillar zones where they can assume a random-coil conformation. The detection of a glass transition temperature ( T g ) close to the aPECH T g value indicates low interactions at the segmental level between the two polymers. The annealing treatment produced a general perfectioning and rearrangement of the sample morphology, enhancing the crystallinity and the crystal dimensions of PHB in the pure state and in the blends, and probably favouring the trend of the aPECH molecules to assume a globular conformation.

First results of small and wide angle X-ray scattering of poly(ethylene oxide)/poly(methyl methacrylate) binary blends

Abstract Some preliminary small and wide angle X-ray scattering results are reported from isothermally crystallized samples of poly(ethylene oxide)/(methyl methacrylate) binary blends.

Phase structure and thermal behaviour of polypropylene/hydrogenated polycyclopentadiene blends

Abstract Isothermally crystallized blends of isotactic polypropylene (iPP) with saturated polycyclopentadiene (PCP) were examined by differential scanning calorimetry and wide- and small-angle X-ray scattering. The presence of PCP did not interfere with the apparent crystal size, and a possible correction by paracrystallinity or microstrain did not produce a significant difference. The long period increased as a function of PCP content, which suggests its distribution in the interlamellar regions. The samples were subjected to chloroform extraction. This solvent, able to remove the PCP fraction, produces a rearrangement of the remaining iPP structure. The crystallinity and apparent crystal size did not change, whereas the microstrain correction became more significant. The long period assumed a new value which was the same for all extracted blends. Density measurements showed swelling of the amorphous phase. The specific volumes of the extracted blends depended on the initial PCP content.

Influence of interfacial agents on the physicochemical characteristics of binary polyethylene/polyamide 6 and ternary polyethylene/polypropylene/polyamide 6 blends

Binary low-density polythylene/polyamide 6 and ternary low-density polyethylene/polypropylene/polyamide 6 blends were prepared by melt mixing, without and with the addition of two different commercial products [poly(ethylere-co-buthylacrylate-co-maleic anhydride) and poly(ethylene-co-vinylacetate) grafted with maleic anhydride] used as interfacial modifiers. More precisely, the polypropylene was a propylene/ethylene random copolymer, containg 6% by weight of ethylene. The polyamide 6/interfacial agent and polyethylene/ interfacial agent systems were also considered. Differential scanning calorimetry, microscopic observations—together with chemical etchings—and mechanical tests supported the occurrence of strong interactions at the interface, especially when using the buthyl acrylate-based agent. The compatibilizing effect of the interfacial agents was also analyzed in the light of interfacial tension determinations. Eventually, low-density polyethylene modifications induced by compatibilization were studied carrying out WAXD analysis.

Morphological changes and dye uptake of poly(ethylene terephthalate) and 2,5-cellulose diacetate immersed in supercritical carbon dioxide

Abstract The dyeing process of poly(ethylene terephthalate) (PET) and 2,5-cellulose diacetate (CA) fibers at 40–100°C using supercritical carbon dioxide (CO2SCF) as solvent system has been kinetically investigated in relation to the morphological modifications induced by the CO2SCF treatment in these fibers, determined through DSC, X-ray diffraction, SEM analysis and shrinkage measurements. A comparison between the effects of annealing both polymer fibers in CO2SCF and in hot air evidenced that CO2SCF has a plastifying action towards PET by lowering its Tg value to 0–5°C and thus favoring the dyeing process at low temperature. Such effect was not observed with CA.

Blending polypropylene with hydrogenated oligocyclopentadiene: A new method for the production of dyeable fibers

Abstract Conventional direct dyeing techniques have limited use for the coloration of polypropylene fibers. In this paper, blends of isotactic polypropylene (iPP) with hydrogenated oligocyclopentadiene (HOCP), a glassy amorphous resin, have been used for the preparation of fibers dyeable in an aqueous dyebath. These fibers show better light, wet-washing and cleaning fastness properties than iPP while retaining similar statical mechanical properties.

Characterization of a poly(3-hydroxybutyrate) depolymerase fromaureobacterium saperdae: Active site and kinetics of hydrolysis studies

An extracellular poly(3-hydroxybutyrate) (PHB) depolymerase was purified fromAureobacterium saperdae cultural medium by using hydrophobic interaction chromatography. The isolated enzyme was composed of a single polypeptide chain with a molecular mass of 42.7 kDa as determined by SDS-PAGE and by native gel filtration on TSK-HW-55S. The enzyme was not a glycoprotein. Its optimum activity occurred at pH 8.0 and it showed a broad pH stability, ranging from pH 3 to pH 11.N-Bromosuccinamide and 2-hydroxy-5-nitrobenzyl bromide completely inactivated the enzyme, suggesting the involvement of tryptophan residues at the active site of the protein. The enzyme was very sensitive to diisopropyl fluorophosphate and diazo-dl-norleucine methyl ester, showing the importance of serine and carboxyl groups. The modification of cysteine residues byp-hydroxy mercuricbenzoate did not cause a loss of activity, whereas dithiothreitol rapidly inactivated the enzyme, revealing the presence of disulfide bonds.A saperdae depolymerase acted on the surface layer of PHB films and the degradation proceeded by surface erosion releasing monomers and dimers of 3-hydroxybutric acid. The degradation of PHB films byA. saperdae depolymerase was partially inhibited in the presence of excess amounts of enzyme. This phenomenon, already observed by Mukaiet al. with poly(hydroxyalkanoates) depolymerases fromAlcaligenes faecalis, Pseudomonas pickettii, andComamonas testosteroni, was analyzed according to the kinetic model proposed by these authors. The experimental data evidenced a general agreement with the kinetic model, although higher initial degradation rates were found withA. saperdae depolymerase.

Inducing water bath dyeability in polypropylenic fibers by their blending with polyamide 6

Melted blends of polypropylene and polyamide 6 compatibilized with a poly(propylene)/maleic anhydride copolymer were extruded and stretched to give filaments. The polypropylenic fibers obtained by this method were found to be easily dyeable in an aqueous dyebath. The wet-washing at 40, 60, and 90°C and the light and dry-cleaning fastnesses of the new material appeared quite satisfactory.