Thermal degradation of microbial copolyesters: poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Abstract

Thermal degradation processes of microbial copolyesters were studied in the temperature range 100-200 °C by monitoring the time-dependent changes in molecular weights of melt samples. Two types of copolyesters, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV); 3HV = 0-71 mol %) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB); 4HB = 0-82 mol %), were used in this study. All copolyester samples used were thermally unstable at temperatures above 170 °C, and their molecular weights decreased rapidly with time. The time-dependent changes in molecular weights during the thermal degradation followed the kinetic model of random chain scission at ester groups. The rates of random chain scission were independent of the compositions of the copolyesters but dependent strongly on temperature. These copolyester samples were thermally stable at temperatures below 160 °C. It has been suggested that the microbial copolyesters with melting temperatures below 160 °C are applicable to conventional plastics processing methods.

Crystallization kinetical and morphological peculiarities in binary crystalline/crystalline polymer blends

“…A complication may arise from the disposition of PHB to degrade at elevated temperature. 102 All essential crystallization schemes as described in Table 1-S-co-S, IPC, and ILC-can be observed and realized in that blend system. 12,[14][15][16] In case of ILC and IPC, the components form individual lamellar stacks, 13,15 and the interlamellar regions contain an amorphous mixture of the blend components.…”

The influence of the industrial processing on the degradation of poly(hidroxybutyrate) - PHB

“…These results show a huge drop of PHB molar mass after each processing step, and it also observes a reduction in the polydispersity, proportional to the reduction of the molar mass, which indicates a systematic and preferential rupture of the high length chains. According to Kunioka et al 4 , this chain rupture occurs by a random scission of an ester group of the structure, generating low molar mass products and forming carboxylic and crotonate vinyl groups in a rate calculated by Equation 2:…”

“…Using the residence time of PHB at extrusion and injection (0.5 minutes for each step) and the average molar mass of the polymer before processing (245,790 g.mol -1 ) as P N,0 , the average molar mass of the polymer after each processing step can be estimated, considering that there are losses only due to the thermal degradation at 175 °C (k d = 2.2.10 -8 min -1 ) [4] . Results calculated by using Equation 1 are also showed in Table 4.…”

“…PHB has high crystallinity, hydrophobicity, is a 100% biodegradable 2 and, like most thermoplastics, can be processed by extrusion, injection, and melt press molding 3 . However, PHB has a limited stability at high temperatures required for melting processes 4,5 and undergoes thermal degradation, which affects its physical and mechanical properties, impairing industrial application 6 .…”

Precise Depolymerization of Poly(3-hydoxybutyrate) by Pyrolysis

“…Several thermoanalytical procedures have been used to investigate the thermal degradation behavior of PHB, including thermogravimetry (TG) for the analysis of weight loss behavior (Kopinke et al, 1999;Galego & Rozsa, 1999;Li et al, 2001;He et al, 2001;Lee et al, 2001;Aoyagi et al, 2002;Carrasco et al, 2006;Kim et al, 2006;Kawalec et al, 2007;Liu et al, 2009;Ariffin et al, 2008Ariffin et al, , 2010, differential scanning calorimetry (DSC) for monitoring the heat of reaction (Kopinke et al, 1996), fast atom bombardment mass spectrometry (FAB-MS) (Ballistreri et al, 1989), electrospray ionization mass spectrometry (ESI-MS) (Kawalec et al, 2007), pyrolysis-mass spectrometry (Py-MS) (Abate, 1994;Kopinke et al, 1996), pyrolysisgas chromatography (Py-GC) (Lehrle, 1994), pyrolysis-GC/mass spectrometry (Py-GC/MS) (Kopinke et al, 1996(Kopinke et al, , 1997Aoyagi et al, 2002;Ariffin et al, 2008Ariffin et al, , 2010, TG/Fourier transform infrared spectroscopy (TG/FTIR) (Li et al, 2003), NMR (Melchiors et al, 1996;Kopinke et al, 1996;Ariffin et al, 2009), and pyrolysis-GC/FTIR (Li et al, 2003;Gonzalez et al, 2005), for the analysis of volatile products, and size exclusion chromatography (SEC) (Grassie et al, 1984;Kunioka & Doi, 1990;Nguyen et al, 2002;Kim et al, 2006) for the analysis of changes in molecular weight of residual PHB. (Kopinke et al, 1996;Galego & Rozsa, 1999;Li et al, 2001;…”