Structural impact of hydroxyvalerate in polyhydroxyalkanoates (PHAscl) dense film monitored by XPS and photothermal methods

Abstract

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-...

Low Molecular Weight and Polymeric Modifiers as Toughening Agents in Poly(3-Hydroxybutyrate) Films

“…As expected, an increase in C1 proportion was observed with the increase in PHO content in PHB/PHO due to the Three peaks were detected in all PHB films: the peak at 284.7 eV (C1), attributed to carbon in hydrocarbons (C-C, C-H), the peak at 286.3 eV (C2), associated with the ether bond (C-O), and the peak at higher binding energy, 288.6 eV (C3), corresponding to the carbonyl (C=O) bond. The values of binding energies of these carbon species are in good agreement with the ones found in the literature [44,45]. Based on the proportion of these carbon species, the surface concentration of the different chemical bonds was calculated and the results are given in Table 4.…”

Microstructural Behaviors of Matrices Based on Polylactic Acid and Polyhydroxyalkanoates

“…On the other hand, PHA films exhibited a T g at −4.7 °C, whereas PLA showed a marked transition at 58.1 °C (Figure 1c). Glass-transition temperatures ranging from 2.7 to −4.4 °C for a PHA matrix obtained by casting were reported by da Silva et al 22 The thermograms of all the mixtures exhibited PLArecrystallization peaks at 107 °C; this transition was more evident with higher PLA proportions in the mixture (Figure 1a). These results indicate that the incorporation of PHA contributes to the process of recrystallization of PLA in all the blend formulations.…”

“…On the other hand, PHA films exhibited a T g at −4.7 °C, whereas PLA showed a marked transition at 58.1 °C (Figure c). Glass-transition temperatures ranging from 2.7 to −4.4 °C for a PHA matrix obtained by casting were reported by da Silva et al…”

Poly(lactic acid) (PLA) and polyhydroxyalkanoates (PHAs), green alternatives to petroleum-based plastics: a review

“…Therefore, this results in increasing the processing temperature window and maintaining degradation rates within acceptable limits. 154,188,[193][194][195][196] In their studies, 178,197 the authors reported a drop in the T m for PHB from 176 C to 158 C with 22 wt% HV content. In another study, the same drop in the melting temperature was obtained with only 8 wt% HV content.…”