Dielectric relaxation analysis of biopolymer poly(3‐hydroxybutyrate)

Abstract

Poly(3-hydroxybutyrate), PHB, is a widely distributed carbon storage polymer among prokaryotes including Rhizobium. Capacities of Rhizobium etli R13 to produce the bioplastic during growth on media with different carbon sources appeared to be specific carbonsource. In fed batch fermentation, R. etli R13 resulted in cell dry weight 6.2 g/L and PHB 51.4%. Gas chromatography-mass spectrometry and gel permeation chromatography analysis revealed that PHB produced from R. etli R13 was solely composed of 3-hydroxybutyric acid and the molecular mass of the purified PHB was 3.4 Â 10 5 Da with polydispersity 1.47. Dielectric relaxation of PHB has been studied in the temperature and frequency ranges 300-440 K and 10 kHz-4 MHz, respectively. A clear dielectric a and q-relaxation processes are observed in these studied ranges of temperature and frequency. The first process is due to the dipole relaxation in the crystalline phase of PHB. The second one is due to the space-charge formation or Maxwell-Wagner-polarization. The a-relaxation process has been investigated by semiempirical Havriliak-Negami relaxation function. The activation energy (E a ) and the relaxation time (s 0 ) are calculated using the Arrhenius equation. The dielectric relaxation strength (De) is strongly temperature dependent. The calculated values of E a for ac conductivity, ln(r), of PHB provide information about the presence of electronic conduction.

Miscibility Behavior of Poly Ethylene Glycol or Poly Ethylene Succinate/Chlorinated Poly Vinyl Chloride Blends Studied by Dielectric Relaxation Spectroscopy

“…The values of Ea are higher than that reported [31][32][33]. This may refer to the existence of micro-homogeneities within the polymeric materials [1]. Figure 7 shows the normalized dielectric relaxation peaks, ε"/ε" max versus f/f max , of the α-relaxation process for pure CPVC and CPVC-PEG blend and CPVC-PES blend.…”

“…Biodegradable polymers can usually be classified into two categories. One is the biosynthetic polymers, such as bacterial Poly(3-hydroxybutyrate) (PHB) [1]. The other is the chemosynthetic polymers such as poly ethylene glycol (PEG) and the poly ethylene succinate (PES) as aliphatic biodegradable polyester.…”

Estudo da miscibilidade das misturas de PHB e PLA, com um PHB de alta polidispersividade

“…Este comportamento inesperado pode ser justificado pela característica bimodal do PHB [8][9][10][11] , onde a partir de 40°C, as relaxações da fração oligomérica se distinguem da fração de maior massa molar. Na Figura 7 é apresentado o gráfico de F max vs. o inverso da temperatura, em frequência constante.…”

“…Na Figura 7 é apresentado o gráfico de F max vs. o inverso da temperatura, em frequência constante. Percebe-se claramente que as duas relaxações não pertencem ao mesmo processo, possuindo comportamentos distintos, com a relaxação denominada α 1 apresentando um comportamento de Vogel-Fulcher, característico deste tipo de relaxação [8][9][10][11] . As Figuras 8 e 9 apresentam a representação gráfica e a representação gráfica isocrônica de relaxação dielétrica do PLA, respectivamente.…”

“…Pode ser produzido a partir de fontes renováveis, como a cana-de-açúcar, através de um processo de fermentação bacterial [3,4] . Suas propriedades físicas já foram amplamente estudadas através de técnicas como a difração de raios-x de alto ângulo [5][6][7] e espectroscopia dielétrica [8][9][10][11] . O poli (ácido lático) -PLA, assim como o PHB, é um poliéster biodegradável, produzido por síntese química a partir de fontes renováveis como o milho [12][13][14] .…”