Degradability of poly(3-hydroxybutyrate) and its copolymer grafted with styrene by radiation (original) (raw)
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Polymer Degradation and Stability, 2011
The PVP/amylose composite films with different amounts of graphene oxide (GO) were prepared by means of a solution casting method. The solution of PVP/amylose/GO was exposed to ultrasonic irradiation (10, 30, 50, and 70 W) and then prepared for casting. The crystallization behavior, thermal stability and enzymatic degradation of PVP/amylose were investigated with differential scanning calorimetry (DSC), X-Ray diffraction (XRD), scanning electron microscopy (SEM), and FTIR spectroscopy. XRD patterns monitored that the addition of GO induced a layered structure to the PVP/amylose composite films. This result indicated that GO nanosheets were uniformly dispersed into the composite network. The thermal properties measured by DSC showed that the glass transition temperature (Tg) was shifted to a lower temperature with the humidity percent increasing. DSC thermograms for PVP/amylose/GO showed an endothermic reaction and reduction in peak temperature, revealing that GO increased the thermal stability of PVP/amylose composite films. FTIR analysis suggests that PVP/amylose composites become more resilient to enzymatic attacks as the content of GO reaches higher, being related to the reduction of AmyloseeAmylose interactions in the presence of GO nanosheets. These results indicate that this approach is an efficient method to improve the properties of PVP/amylose.
Mechanism and kinetics of the hydrolytic degradation of amorphous poly(3-hydroxybutyrate)
Polymer Degradation and Stability
Amorphous poly(3-hydroxybutyrate) films prepared by compression molding and solvent casting were degraded in aqueous media at different pH values. The time dependence of degradation was monitored by the measurement of weight loss, the extraction of the degradation products from the degrading sample, as well as by UV-Vis spectrophotometry and HPLC analysis of the aqueous solution. The results proved that degradation takes place mainly in the bulk of the samples and not on their surface. The overall rate of degradation depends strongly on pH; it increases with increasing pH values. Metabolite extraction and chromatography proved that degradation does not occur randomly, but with larger frequency at the end of the chains. By assuming that the hydrolysis of PHB is a SN2 type nucleofil substitution reaction, a kinetic model was proposed which describes the formation of various degradation products. The diffusion of metabolites was also accommodated into the model thus the concentration in the aqueous solution could also be predicted well. The correlation between prediction and experimental results is excellent. The model can be extended also for the description of the hydrolytic degradation of other aliphatic polyesters. 1 INTRODUCTION Poly(3-hydroxybutyrate) (PHB) is one of the most important biopolyesters from the family of polyhydroxyalkanoates which are produced by microorganisms from renewable resources [1-7]. Unlike in the synthetic polymerization of PHB, the production of the biopolymer by microbial fermentation excludes the presence of toxic products [8-10] and the hydrolytic degradation of PHB leads mainly to the monomer D-3-hydroxybutyric acid. This acid is a normal component of blood and is one of the three ketones which are
Degradation of Poly(3-hydroxybutyrate) and its Derivatives: Characterization and Kinetic Behavior
Chemistry & Chemical Technology, 2012
We focused on hydrolytic degradation kinetics at 310 and 343 K in phosphate buffer to compare PLA and PHB kinetic profiles. Besides, we revealed the kinetic behavior for copolymer PHBV (20 % of 3-hydroxyvalerate) and the blend PHB-PLA (1:1). The intensity of biopolymer hydrolysis is characterized by total weight lost and the viscosity-averaged molecular weight (MW) decrement. The degradation is enhanced in the series PHBV < PHB < PHB-PLA blend < PLA. Characterization of PHB and PHBV includes MW and crystallinity evolution (X-ray diffraction) as well as AFM analysis of PHB film surfaces before and after aggressive medium exposition. The important impact of MW on the biopolymer hydrolysis is shown.
Biodegradation kinetics of poly(3-hydroxybutyrate)-based biopolymer systems
Biochemistry (Moscow) Supplement Series B: Biomedical Chemistry, 2010
The aim of this study was to evaluate and to compare the long term kinetics curves of biodegrada tion of poly(3 hydroxybutyrate) (PHB), its copolymer poly(3 hydroxybutyrate co 3 hydroxyvalerate), and a PHB/polylactic acid composite. The total weight loss and the change of average viscosity molecular weight were used as the parameters reflecting the biodegradation degree. The rate of biodegradation was analyzed in vitro in the presence of lipase and in vivo after film implantation in animal tissues. The morphology of the PHB film surface was studied by the atomic force microscopy technique. It was shown that PHB biodegra dation involves both polymer hydrolysis and its enzymatic biodegradation. The results obtained in this study can be used for the development of various PHB based medical devices.
International Polymer Science and Technology, 2010
The aim of the present work is to record and compare long-term kinetic curves of the hydrolytic degradation of polymer systems: bacterial poly-3-hydroxybutyrate (POB), its copolymer with hydroxyvalerate, and also a composite mixture of POB and polylactide (PLA). To monitor the degree of hydrolytic degradation, use was made of the total weight loss of the specimen and the change in the viscosity-average molecular weight (MW). Atom force microscopy was used to assess the surface state of POB films. It was shown that the rate of hydrolytic degradation depends on the incubation medium (the nature of the buffer), temperature, the chemical composition of the biopolymer, and its molecular weight. Atom force microscopy confirmed that, along with volumetric processes of POB hydrolysis, surface hydrolysis of the polymer also occurs.
Biomaterials, 1990
The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in the form of blends with the polysaccharides amylose, dextran, dextrin and sodium alginate, has been studied under a range of conditions (pH 2.3,7.4and 10.6 and at 37°C and 70°C). The hydrolytic degradation of the PHB-PHV copolymers was found to be dramatically affected by the presence of polysaccharides. Its progress was characterized by an initial increase in the wet weight, with concurrent decrease in the dry weight as the polysaccharides eroded from the matrix. Surface energy measurements and goniophotometry proved to be particularly useful in monitoring this stage of the degradation process. The concurrent increase in internal porosity leads to the eventual collapse of the matrix, a process which occurs, but less rapidly, in the degradation of the unblended PHB-PHV copolymers. Information obtained from molecular weight and crystallinity studies enabled a comprehensive profile of the overall degradation process to be built up. Poly( hydroxybutyrate)-poly( hydroxyvalerate) copolymers represent a useful range of potential biodegradable polymers which offer advantage in the field of biomaterials. They are produced by a bacterial synthesis process', and are now available in a wide range of molecular weights and copolymer compositions. Although a substantial body of information exists relating to the thermal degradation and processability of the poly(hydroxybutyrate) homopolymer, published information relating to the behaviour of the copolymers and in particular their hydrolytic degradation is relatively limited. In the first part of this series2, we reviewed published information on the biodegradation and hydrolysis of esterbased polymers. It was clear from this that the hydroxybutyrate-hydroxyvalerate (H B-HV) copolymers provided a considerable extension to available materials of this type. I na subsequent paper3 we reported the results of an experimental study of the hydrolytic degradation of the hydroxybutyrate homopolymer together with a series of HB-HV copolymers.
Biomaterials, 1987
The hydrolytic degradation of poly(hydro~butyrate) together with a series of hydro~butyrate-hydro~valerate copolymers has been studied. The effects of copolymer composition and molecular weight are presented together with the results of varying pH and temperature on the degradation rate. ~eg~dation has been monitored by weight loss and water uptake measurements together with goniophotometric, surface energy and scanning electron microscopic studies. Some comparisons with the more widely used so-called 'biodegradable' polymers, poly(glycolic acid), poly(dioxanone) and the glycolic-lactic acid (90: 10) copolymers are presented together with the effect of blood plasma on the degradation process.
Determination of multiple thermal degradation mechanisms of poly(3-hydroxybutyrate
Polymer Degradation and Stability, 2008
The thermal degradation of poly(3-hydroxybutyrate) (PHB) was investigated by kinetic analyses in detail to clarify its complex degradation behavior, resulting in a finding of mixed mechanisms comprising at least a thermal random degradation with subsequent auto-accelerated transesterification, and a kinetically favored chain reaction from crotonate chain ends. The thermal degradation behavior of PHB varied with changes in time and/or temperature. From the kinetic analysis of changes in molecular weight, it was found that a non-auto-catalytic random degradation proceeding in the initial period was followed by an auto-accelerated reaction in the middle period. From the kinetic analysis of weight loss behavior, it is proposed that there are some kinetically favored scissions occurring at the chain ends, where the degradation proceeded by a 0th-order weight loss process in the middle stage. The observed 0th-order weight loss process was assumed to be an unzipping reaction occurring at ester groups neighboring the crotonate end groups.
Thermal Properties and Biodegradability Studies of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)
Journal of Polymers and the Environment, 2012
For investigating the relationship between thermal properties and biodegradability of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), several films of PHBV containing different polyhydroxyvalerate (HV) fractions were subjected to degradation in different conditions for up to 49 days. Differential scanning calorimetry (DSC), thermogravimetry (TG), specimen weight loss and scanning electron microscopy (SEM) were performed to characterize the thermal properties and enzymatic biodegradability of PHBV. The experimental results suggest that the degradation rates of PHBV films increase with decreasing crystallinity; the degradability of PHBV occurring from the surface is very significant under enzymatic hydrolysis; the crystallinity of PHBV decreased with the increase of HV fraction in PHBV; and no decrease in molecular weight was observed in the partially-degraded polymer.
Thermal and thermo-mechanical degradation of poly(3-hydroxybutyrate)-based multiphase systems
Polymer Degradation and Stability, 2008
The influence of fermentation residues and quaternary ammonium salts on the thermal and thermo-mechanical degradation of a biodegradable bacterial poly(3-hydroxybutyrate), PHB, was studied. The results obtained from DSC, SEC and TG analyses performed on blends reveal that ammonium cations greatly enhance the degradation leading to a dramatic decrease in PHB molecular weight. These results are confirmed by the thermo-mechanical study. Besides, we show that the presence of fermentation residues does not affect significantly the PHB thermal stability in comparison to the ammonium cations. A kinetic analysis based on the Coats and Redfern model was applied to the non-isothermal TGA data. This method completed by NMR characterizations led us to determine the most probable mechanism for PHB degradation in the presence of the ammonium salts. The results demonstrate that ammonium surfactants commonly found in commercial nanoclays (for nanocomposites' production) effectively have a catalytic effect on the PHB degradation.