Photoacoustic Monitoring of Internal Plastification in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Copolymers: Measurements of Thermal Parameters

Journal of the Brazilian Chemical Society

Sanchez, Ruben R.¹  Universidade Estadual do Norte Fluminense, Campos dos Goytacazes, Brazil¹  Gatts, Carlos N.¹  Rieumont, Jacques B.¹  Cardoso, Sergio L.¹  Massunaga, Marcelo S. O.¹  Silva, Marcelo G. da¹  Sthel, Marcelo S.¹  Vargas, Helion¹ 

关键词: photoacoustic spectroscopy;    thermopysical parameters;    poly(hydroxyalkanoates);    poly(3-hydroxybutyrate-co-3-hydroxyvalerate);   

DOI  :  10.1590/S0103-50531999000200004

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

of 3HV units in the copolymer. It was observed that copolymer thermal conductivity increased approximately linearly with the 3HV content. On the other hand, thermal diffusivity was very sensitive to the change in the copolymer composition showing a sudden rise that attained a saturation plateau. Amplitude-frequency plots indicate that a thermoelastic bending mechanism is operating. In this paper a new photoacoustic arrangement for the measurement of thermal effusivity is presented. Keywords: photoacoustic spectroscopy, thermopysical parameters, poly(hydroxyalkanoates), poly(3-hydroxybutyrate-co-3-hydroxyvalerate)    IntroductionPhotoacoustic (PA) spectroscopy and related photothermal techniques1-3 are well-established spectroscopic techniques. The PA technique, apart from providing direct optical absorption spectra4,5, can also be used to perform depth profile analysis4,6, and characterization of thermal properties7,8. In addition, there has been a substantial development of new, versatile and competitive instrumentation and experimental methodologies suitable for use in daily practice. For a comprehensive review of the photothermal wave phenomenon and its applications the reader is referred to the books by Rosencwaig1 and Almond3 and to some of many published reviews on the subject2,9,10. This paper is concerned with the use of PA methodologies to study the thermophysical properties of poly(hydroxyalkanoates) which are biodegradable and bio-compatible polyesters produced from various carbon substrates by microorganisms such as prokaryotic organisms, including gram-positive and gram-negative bacteria11. In particular, research on microbial polyesters is expanding in both the biological and polymer sciences. Furthermore these materials have attracted industrial attention as large-scale biotechnological products12. One of these interesting polyesters is the poly(3-hydroxybutyrate) poly(3HB), which can be obtained as homopolymer or, its copolymer with 3-hydroxyvalerate, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) poly(3HB-co-3HV)10. Despite the large body of literature that already exists on poly(3HB-co-3HV), so far there have been no reports on the thermophysical properties of these important materials. To our knowledge diffusivity and thermal conductivity measurements are lacking in the literature for these materials. Thermal properties should contribute to the using of these materials as membranes and envelopes for complex biomaterials in medicine and also for agrotechnical and daily life purposes. Our objective is to determine the potential of the photoacoustic technique for measuring the thermophysical properties of poly(3HB) and poly(3HB-co-3HV) polymers. The thermophysical properties of polyesters are important when predicting heat transfer rates during processing and for process control.   Materials and MethodsSample preparation Poly(3HB) and poly(3HB-co-3HV) copolymers (8, 14, and 22% 3HV) were obtained from Aldrich. These copolymers are produced in a fed batch fermentation process by Alcaligenes eutrophus when grown on glucose and propionic acid as the sole carbon source. This bacterium accumulates poly(3HB-co-3HV) up to 80% of the entire dry weight of the biomass by limiting a nutrient such as nitrogen while maintaining an excess of carbon source. Polymer solutions were prepared by boiling weighed sample in chloroform until dissolution. Films were prepared by spin coating from chloroform polymer solutions (1 g/10 mL) at 160 rpm. Films were separated in water and dried at room temperature overnight. The films had a thickness of roughly 20 mm.Thermal diffusivity PA measurementThe room temperature characterization of the samples thermal properties was based upon the measurements of the thermal diffusivity, a, and the thermal effusivity, e. The thermal diffusivity, defined as alpha a = k/rc, measures essentially the thermalization time within the sample, whereas, the thermal effusivity, given by e = (krc)1/2 measures the sample thermal impedance for the heat transfer. Here, k denotes the sample thermal conductivity, r the material density, and c the specific heat at constant pressure. The measurements of a and e determine the thermal properties of the samples. The significance of a as a physical parameter to be monitored is due to the fact that like the optical absorption coefficient, it is unique for each material. Furthermore, the thermal diffusivity is extremely dependent upon the effects of composition and micro-structural variables, as well as processing conditions as in the

【 授权许可】

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