Studies of composition and crystallinity of bacterial poly(β-hydroxybutyrate-co-β-hydroxyvalerate)

Abstract

Samples of bacterial poly(d-hydroxybutyrate-co-fl-hydroxyvalerate) (P(HB-co-HV)) were analyzed by 250-MHz 1H nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. The compositions of 40 copolyester samples, as determined by NMR, ranged from 0 to 47 mol % ß-hydroxyvalerate (HV). The shapes and intensities of numerous IR bands, particularly those at 1279,1228, and 1185 cm"1, were found to be sensitive to the degree of crystallinity. FTIR bands sensitive to composition include the C-H bands around 2900 cm'1 and the C-C band at 977 cm"1. By use of the 2900-cm"1 bands, methods were developed for composition analysis of as-received samples of equal degree of crystallinity in the solid state and in solution. Relative areas, in which the C-H area was normalized to the compositioninsensitive C=0 area, were calibrated to the copolymer compositions determined by 250-MHz 1H NMR. The experimental uncertainties of composition analysis of P(HB-co-HV) by NMR and FTIR were estimated to be ±1 and ±2-3 mol % HV, respectively. FTIR and wide-angle X-ray diffraction (WAXS) studies on solution-cast and melt-quenched samples showed a dramatic trend in that the rate of crystallization of these copolyesters decreases with increasing HV content. A two-stage crystallization process was identified for P(HB-co-HV) cast from solution and was attributed to changes in both nucleation rate and rate of crystal growth, whereas crystallization from the melt is largely nucleation rate limited. The crystallinity index (Cl) determined by FTIR for as-received samples of P(HB-co-HV) was nearly independent of HV content, indicating that the copolyesters are as highly crystalline as PHB homopolymer. The degree of crystallinity (Xc) derived from X-ray diffraction was used to follow crystallization from the melt. The final value of Xc ranged from 62 to 69% for equilibrated copolyesters quenched from the melt. Crystallization of these copolyesters from the melt is faster than for solution-cast samples. However, both processes are slow when compared to the rate of crystallization of solution-precipitated samples.

Properties of melt-processed poly(hydroxybutyrate-co-hydroxyvalerate)/starch 1:1 blend nanocomposites

“…Similarly to the data reported by other authors [43] , highintensity reflections at 13º and 17º (2θ) were visualized in the diffractogram for the crystalline PHBV (trace II). For TPS (trace I), the presence of V H -type crystals, related to processing-induced aggregation of amylose single helices, was evidenced by the reflection at ~20º (2θ).…”

Biodegradação de filmes de polipropileno (PP), poli(3-hidroxibutirato) (PHB) e blenda de PP/PHB por microrganismos das águas do Rio Atibaia

“…Os espectros de PHB (Figura 1 e 2) e blenda (Figura 3) foram normalizados pela intensidade de absorbância de uma banda considerada como padrão interno em 1380 cm -1 , atribuída à deformação simétrica de grupos CH 3 [14,15,16] , e desconvoluídos pela função Lorentziana para obter melhor resolução das bandas (separação em picos) [17] .…”

“…Na Tabela 4 estão apresentados os índices de fase amorfa e cristalina do PHB, obtidos, respectivamente, dos valores de absorbância da banda em 1186 cm -1 atribuída ao estiramento simétrico de grupo C-O-C e da banda em 1230 cm -1 atribuída à conformação helicoidal de cadeia, em relação à banda de referência em 1380 cm -1 , mantida como padrão interno [14,16] .…”

Biodegradation of films of low density polyethylene (LDPE), poly(hydroxibutyrate-co-valerate) (PHBV), and LDPE/PHBV (70/30) blend with Paecilomyces variotii

“…These changes suggest the presence of 2-butenoic acid, formed by enzymatic hydrolysis reaction [31] . The bands at 1280 cm -1 (CH 3 deformation), 1228 cm -1 and 1055 cm -1 (C-O-C stretching) (all of these bands are sensitive to the polymer crystallization [32] suffered a decrease in intensity, indicating a decrease in the film crystallinity and in the C-O-C ester group.…”