Thermal and transport properties of some polyhydroxyalkanoates (PHAs), poly-3-hydroxybutyrate and poly-3-hydroxybutyrate-co-3-hydroxyvalerate copolymers at different concentrations (8, 14, and 22%), were studied by using photoacoustic and photothermal techniques. Mass diffusion coefficients were obtained for carbon dioxide and oxygen by using a gas analyzer. Specific heat capacity measurements were performed by monitoring temperature of the samples under white light illumination against time. Thermal diffusivities were determined by using the open photoacoustic cell configuration. The results were discussed considering the incorporation of hydroxyvalerate units in the poly(3-hydroxybutyrate) unit cell and were correlated with atomic force microscopy images of the upper surface of membranes. New information on transport properties of PHAs is provided.

Polyhydroxyalkanoates (PHAs) are polymers produced from renewable resources with biodegradability and biocompatibility, being therefore attractive for medical and pharmaceutical purposes. Poly (3-hydroxybutyrate) (PHB) is the most important polymer of this family by considering the biotechnology process of its synthesis. In the present study, dense films of PHB were prepared by casting from chloroform solutions (1% m/m). Permeability studies with water, methanol, ethanol and n-propanol were performed using the gravimetric method at different temperatures (from 50 °C to 65 °C). Results provide new data on permeability coefficients of PHB membranes.

The present work discuss the applicability of photothermal techniques for determining diffusion coefficients of oxygen and carbon dioxide of commercial low-density polyethylene (LDPE). The methodology involves the monitoring of diffused gas by a photoacoustic analyzer. Diffusion coefficients measured for CO2 and O2 were 2.77 x 10-8 cm²/s and 1.68 x 10-7 cm²/s, respectively. To support the gas diffusion results, thermal properties were studied using photoacoustic spectroscopy and crystallinity was determined using X-ray diffraction. Values obtained for thermal diffusivity and specific heat capacity were 1.65 x 10-3cm²/s and 2.33 J.cm-3K-1, which are in good agreement with values available in the literature for pure LDPE and thus assure reliability of diffusion coefficients values

Filmes densos de poli(3-hidrobutirato) e poli(3-hidroxibutirato-co-3-hidroxivalerato) com espessuras de 90 µm foram obtidos utilizando o método "casting" de deposição e caracterizados por espectroscopia de fotoelétrons, calorimetria diferencial e métodos fotoacústicos. As frações molares de hidroxivalerato utilizadas foram de 8, 14 e 22 % molar. Seguindo uma mesma tendência, a capacidade térmica específica e a temperatura de transição vítrea diminuem com o aumento da concentração de hidroxivalerato.Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) polymer dense films with thickness of 90 µm were obtained by the casting method and characterized using X-ray photoelectron spectroscopy, differential scanning calorimetric and photo-thermal methods. The HV molar fractions in the copolymer structure were 8, 14 and 22 mol %. The measured specific thermal capacity and the glass transition temperature of the P3(HB-co-x%HV) decrease for increasing hydroxyvalerate content following a similar trend. Keywords: polymers, photoacoustics, XPS, thermal properties IntroductionIn the last years, science and industry have given special attention to the development of biodegradable polymer materials as consequence of today ecological problems caused by most of the chemical and petrochemical synthesized polymers disposed in the environment. 1 Chemically and petrochemically synthesized polymers are generally resistant to enzymatic attack. Although some of these synthetic polymers can be microbiologically degraded, the process of degradation is slow in contrast to the biodegradability of the polymers of biological origin. 2 The biodegradability is not the only characteristic that makes the polymers of biological origin attractive, also their biosynthesis from renewable carbon sources, based on agricultural products, allows a sustainable closed process for the production and use of such polymers.One important family of the biologically produced thermoplastic polyesters is formed by the polyhydroxyalkanoaes (PHAs). Important members of this family are the P3HB and P(3HB-co-3HV)copolymers synthesized and intracellularly stored by numerous prokaryotes by well know fermentation process. The stereoregularity of P3HB makes it a highly crystalline material having melting point of 177 o C, close to that of polypropylene among others similarities, although the biopolymer is stiffer and more brittle. 3,4 The P(3HB-co-3HV) chains also show crystalline conformations and the co-monomer distribution is statistically random. The properties of the copolymers of 3HB and 3 HV changes depending on their HV contents. The minimum of the melting point (≅80 o C, pseudoeutectic point) of the copolymers is observed for a 30% mole fraction of HV. 5,6 The accurate determination of the thermal properties of polymers and particularly of PHAs is of fundamental importance in many processes and engineering projects aiming at the expansion of the uses of these biodegradable materials. In the present work, the effect of HV contents in the P(3HB-co-...

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