Environmental Degradation of Blends of Atactic Poly[(R,S)-3-hydroxybutyrate] with Natural PHBV in Baltic Sea Water and Compost with Activated Sludge

Degradation of atactic poly[(R,S)-3-hydroxybutyrate] (a-PHB) binary blends with natural poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV, 12 mol% of 3HV units), has been investigated and compared with plain PHBV in the compost containing activated sludge and under marine exposure conditions in the dynamic water of the Baltic Sea. Characteristic parameters of compost and the Baltic Sea water were monitored during the incubation period (6 weeks) and their influence on the degree of biodegradation is discussed. After specified degradation times of the experiments the weight loss of the samples, surface changes, changes in molecular weight and polydispersity as well as changes of the composition and thermo-mechanical properties of the blends have been evaluated. Macroscopic observations of the samples were accompanied by investigations using optical microscopy, size-exclusion chromatography (SEC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and tensile testing. The degree of degradation of blends of a-PHB with PHBV depends on the blend composition and environmental conditions. In both environments studied the weight loss of plain PHBV was more significant than changes the molecular weight. In both environments only enzymatic degradation of the blends, which proceeds via surface erosion mechanisms, was observed during the incubation period.     

Poly[(R)-3-hydroxy butyrate] Melt Processing: Strategy for Prevention of Degradation Reactions

Poly[(R)-3-hydroxy butyrate] (PHB) as well as all the components of the poly[(R)-3-hydroxy alkanoate]s (PHAs) family tend to degrade during processing at temperatures above their melting point via a hydrolytic mechanism induced by moisture attack and a concerted reaction mechanism induced by temperature. Therefore, the PHAs stabilization in the molten state is particularly important for production of biodegradable ecocompatible plastic items of commercial value. In order to refrain the indicated negative degradation effects, PHB was melt processed in a torque rheometer in the presence of a polymeric carbodiimide agent. Processed specimens were characterized by using FTIR, GPC, DSC, TGA and tensile properties. GPC analysis showed that the increase of the additive content in the formulation resulted in an increase of PHB molecular weight. However, decreasing in PHB thermal stability, glass transition temperature and mechanical properties, was observed with the increase of the additive amount. This behaviour most likely arises from the formation of new chemical structures promoted by the presence of the additive aimed at preventing the onset of hydrolitic processes.     

Influence of Processing Conditions on Morphological,Thermal and Degradative Behavior of Nanocomposites Based on Plasticized Poly(3-hydroxybutyrate) and Organo-Modified Clay

The effect of processing conditions (casting and extrusion) and plasticization on the disintegrability in compost of organically modified clay poly(3-hydroxybutyrate) nanocomposites was studied. Tributylhexadecylphosphonium bromide (TBHP) was used as organic modifier. As revealed by WAXS and TEM observations, intercalated nanobiocomposites with clay stacks and some individually dispersed platelets were obtained. The melting temperature of the neat PHB diminished with the addition of plasticizer, thus broadening the processing window. Biodegradation test revealed that while the clay slows down the degradation rate, the plasticizer increases the degradation of the samples, reaching a similar final percentage of disintegrability when both plasticizer and clay were added in the formulation.     

The Effect of Chain Extender on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate): Thermal Degradation,Crystallization, and Rheological Behaviours

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a semi-polycrystalline biopolymer from the polyhydroxyalkanonate family has in recent years become a commercial bioplastic with mechanical properties comparable to isotactic polypropylene and enhanced O₂, CO₂ and H₂O barrier properties. However, its brittleness and sensitivity to thermal and hydrolysis degradations restrict its applications. To overcome the problems associated with degradation during processing blending of PHBV and an epoxy-functionalized chain extender (Joncryl^® ADR-4368 S) was conducted in a twin screw extruder. The effect of concentration of the chain extender on thermal, crystallization and rheological behaviours of PHBV was investigated. Thermal gravimetric analysis results indicated improvement in the resistance to thermal decomposition of PHBV by introducing the chain extender. This was accompanied with calculation of thermal degradation activation energy (E_a) using the Flyn–Walls–Ozawa method which confirmed increase of E_a with the increase in content of the chain extender. The rheological behaviour and crystallization of modified PHBV was characterized by rotational rheometry and differential scanning calorimetry techniques, respectively. The results show that addition of chain extender enhanced viscosity of PHBV and also reduce the rate of crystallization.     

In Vivo and In Vitro Degradation Studies for Poly(3-hydroxybutyrate-<Emphasis Type="Italic">co</Emphasis>-3-hydroxyhexanoate) Biopolymer

Studies have shown that the copolymer poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(HB-co-HHx)] possesses favorable mechanical properties for use in medical supplies and products (e.g., sutures, scaffolds, bone plates). One of the major under-addressed issues associated with the use of biodegradable, bio-based PHA polymers in resorbable medical products is the correlation between the mechanical properties and the in vivo material degradation over time. In this study, P(HB-co-17 mol% HHx) matrices were mechanically tested after either incubation in cultures of human embryonic kidney cells (HEK) for in vitro degradation studies for up to 4 weeks, or inserted into Danio rerio (zebrafish) tissues for in vivo degradation studies for up to 7 weeks. The mechanical properties and scanning electron microscopy (SEM) images of the degraded materials were examined and later correlated to understand the degradation phenomenon. Our results show that Young’s modulus of P(HB-co-17 mol%HHx) during in vitro studies decreased from 3.26 to 2.42 GPa within 4 weeks, and in vivo breakdown resulted in a significant decrease in Young’s modulus with a decrease from 3.26 to 0.51 GPa and a mass loss of 59 % within 7 weeks. SEM images showed the development of pores and cracks on the surface of the material over time. Plasticization and recrystallization were observed and likely play a role in the alteration of mechanical properties.     

Physical and Thermal Analysis of the Degradation of Poly(3-Hydroxybutyrate-<Emphasis Type="Italic">co</Emphasis>-4-Hydroxybutyrate) Coated Paper in a Constructed Soil Medium

The degradation of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) coated brown Kraft paper and its components in a constructed soil environment was investigated. Soil burial tests were carried out over 8 weeks. Weight loss measurements, photographic analysis, environmental scanning electron microscopy (ESEM), dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) were conducted to assess the physical, structural, mechanical and thermal behavior before and after the soil burial test. Paper showed the highest physical degradation and weight loss. With respect to the control samples, the stiffness of the partially degraded samples decreased. The overall crystallinity of the biopolymer and the coated paper was affected significantly by burial. The pure biopolymer’s weight loss was substantially enhanced when coated on paper. This result reveals a possible increased microbial population in the coated paper relative to the pure biopolymer.     

Biodegradable Blends from Corn Gluten Meal and Poly(butylene adipate-co-terephthalate) (PBAT): Studies on the Influence of Plasticization and Destructurization on Rheology,Tensile Properties and Interfacial Interactions

Melt extrusion was used to obtain thermoplastic corn gluten meal (tCGM) blends from plasticized corn gluten meal (pCGM) and poly(butylene adipate-co-terephthalate) (PBAT). Dynamic rheological tests, morphology and spectroscopy were employed to understand the effect of the plasticization and destructurization of corn gluten meal (CGM) on tCGM blends. Rheological data showed a plateau in the low frequencies for tCGM blends demonstrating network formation which responds elastically over long timescales. Also, complex viscosity data showed the existing of shear thinning for PBAT and PBAT–CGM blend. Furthermore, rheology and morphology showed the synergistic influence of plasticization and destructuralization of CGM on the phase structure development of the blends. In addition, it was found for unmodified CGM–PBAT blend there was significant frequency dependence for G′ indicating it just acted as filler for PBAT matrix. FTIR studies showed that the urea has helped in unfolding the corn protein and facilitated hydrogen bonding interactions with PBAT. Tensile properties showed an improvement in tCGM blends when compared unmodified CGM blend. Tensile strength of tCGM blends was almost same as that of the neat PBAT matrix. Percent elongation, a strong reflection of the state of interface in the blends has showed higher values, indicating strong interactions between the PBAT and pCGM in the blend system.     

Estimation on Biodegradability of Poly (3-hydroxybutyrate-<Emphasis Type="Italic">co</Emphasis>-3-hydroxyvalerate) (PHB/V) and Numbers of Aerobic PHB/V Degrading Microorganisms in Different Natural Environments

To assess the capacity of the natural environment for degrading PHB/V, the film-MPN method proposed previously was modified to estimate the numbers of PHB/V degrading microorganisms (degraders) in various environments. The First-Order Reaction (FOR) model was used to determine the appropriate incubation period for the method. Numbers of aerobic PHB/V degraders were estimated in garden soil, paddy field soil, farm soil, river bank soil, infertile garden soil, river water, activated sludge, and seawater by the film-MPN method. Results were compared with those estimated by the clear-zone technique and showed that the film-MPN method was suitable for estimating the numbers of PHB/V degraders in the environments tested. On the other hand, biodegradability of injection molded PHB/V samples was investigated in several kinds of environments. The changes of weight were studied and results showed that biodegradability of PHB/V related to the numbers of PHB/V degraders in similar ecosystem in different regions. In different environments the biodegradability of PHB/V not only related to the number of PHB/V degraders, but also depended on whether there were conditions for the PHB/V degraders to grow and proliferate easily in the environment.