Gamma irradiation effects on poly(hydroxybutyrate)

Additive Free Crosslinking of Poly-3-hydroxybutyrate via Electron Beam Irradiation at Elevated Temperatures

When applying electron or gamma irradiation to poly-3-hydroxybutyrate (P3HB), main chain scissions are the dominant material reactions. Though propositions have been made that crosslinking in the amorphous phase of P3HB occurs under irradiation, a conclusive method to achieve controlled additive free irradiation crosslinking has not been shown and no mechanism has been derived to the best of our knowledge. By applying irradiation in a molten state at 195 °C and doses above 200 kGy, we were able to initiate crosslink reactions and achieved gel formation of up to 16%. The gel dose Dgel was determined to be 200 kGy and a range of the G values, the number of scissions and crosslinks for 100 eV energy deposition, is given. Rheology measurements, as well as size exclusion chromatography (SEC), showed indications for branching at doses from 100 to 250 kGy. Thermal analysis showed the development of a bimodal peak with a decrease in the peak melt temperature and an increase in peak width. In combination with an increase in the thermal degradation temperature for a dose of 200 kGy compared to 100 kGy, thermal analysis also showed phenomena attributed to branching and crosslinking.

Gamma radiation effect on the chemical, mechanical and thermal properties of PCL/MCM-48-PVA nanocomposite films

In this work, poly (vinyl alcohol) (PVA) was employed to produce a Mesoporous Composition of Matter-48 Modified (MCM-48-M or MCM-48-PVA). After surface modification, MCM-48-M was used to produce nanocomposite (NC) films with polycaprolactone (PCL) as a matrix at room temperature. PCL and MCM-48 nanoparticles (NPs) were chosen due to their great biocompatibility and low toxicity. However, MCM-48-M is more compatible with PCL than MCM-48. NC films were sterilized by gamma radiation with a dose of 25 kGy and characterized by experimental techniques to investigate their chemical, mechanical (tensile) and thermal properties. Scanning electron microscopy (SEM) and transmission electronic microscopy (TEM) results indicated that MCM-48-M exhibited a random distribution in the PCL matrix. The PCL chemical structure was preserved in NC films as described by Fourier transform infrared (FT-IR) spectroscopy as well as the tensile and thermal properties of NC films. FT-IR and thermogravimetric analysis (TGA) results showed surface modification. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) showed that crystalline symmetries were preserved and the crystallinity of NC films had small variations in all samples before and after irradiation, respectively. But, our results did not indicate major changes showing that this method is successful for the sterilization of PCL/MCM-48-PVA NC films.

Exploiting the Physicochemical and Antimicrobial Properties of PHB/PEG and PHB/PEG/ALG-e Blends Loaded with Ag Nanoparticles

Poly(3-hydroxybutyrate) (PHB)-based films containing Poly(ethylene glycol) (PEG), esterified sodium alginate (ALG-e) and polymeric additives loaded with Ag nanoparticles (AgNPs) were obtained by a conventional casting method. AgNPs were produced in aqueous suspension and added to polymeric gels using a phase exchange technique. Composite formation was confirmed by finding the Ag peak in the XRD pattern of PHB. The morphological analysis showed that the inclusion of PEG polymer caused the occurrence of pores over the film surface, which were overshadowed by the addition of ALG-e polymer. The PHB functional groups were dominating the FTIR spectrum, whose bands associated with the crystalline and amorphous regions increased after the addition of PEG and ALG-e polymers. Thermal analysis of the films revealed a decrease in the degradation temperature of PHB containing PEG/AgNPs and PEG/ALG-e/AgNPs, suggesting a catalytic effect. The PHB/PEG/ALG-e/AgNPs film combined the best properties of water vapor permeability and hydrophilicity of the different polymers used. All samples showed good antimicrobial activity in vitro, with the greater inhibitory halo observed for the PEG/PEG/AgNPs against Gram positive S. aureus microorganisms. Thus, the PHB/PEG/ALG-e/AgNPs composite demonstrated here is a promising candidate for skin wound healing treatment.

Optimization of Production of Polyhydroxyalkanoates (PHAs) from Newly Isolated Ensifer sp. Strain HD34 by Response Surface Methodology

Petroleum-based plastics have become a big problem in many countries because of their non-degradability and that they become microplastics in the environment. This study focused on the optimization of production medium and conditions of polyhydroxyalkanoates (PHAs), which are biodegradable bioplastics and are accumulated in microbial cells. Among 341 isolates from 40 composted soil samples, the best isolate was the HD34 strain, which was identified using morphological, molecular, and biochemical methods. The results showed that the strain was most closely related to Ensifer adhaerens LMG20216T, with 99.6% similarity. For optimization of production medium and conditions using response surface methodology, it exhibited an optimal medium containing 3.99% (w/v) of potato dextrose broth (PDB) and 1.54% (w/v) of D-glucose with an adjusted initial pH of 9.0. The optimum production was achieved under culture conditions of a temperature of 28 °C, inoculum size of 2.5% (v/v), and a shaking speed of 130 rpm for 5 days. The results showed the highest PHA content, total cell dry weight, and PHA yield as 72.96% (w/w) of cell dry weight, 9.30 g/L, and 6.78 g/L, respectively. The extracted PHA characterization was studied using gas chromatography, 1H NMR, FTIR, and XRD. The results found that the polymer was a polyhydroxybutyrate (PHB) with a melting temperature (Tm) and degradation temperature (Td) of 173.5 °C and 260.8 °C, respectively.

Chitin Nanocomposite Based on Plasticized Poly(lactic acid)/Poly(3-hydroxybutyrate) (PLA/PHB) Blends as Fully Biodegradable Packaging Materials

Fully bio-based poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) blends plasticized with tributyrin (TB), and their nanocomposite based on chitin nanoparticles (ChNPs) was developed using melt mixing followed by a compression molding process. The combination of PHB and ChNPs had an impact on the crystallinity of the plasticized PLA matrix, thus improving its oxygen and carbon dioxide barrier properties as well as displaying a UV light-blocking effect. The addition of 2 wt% of ChNP induced an improvement on the initial thermal degradation temperature and the overall migration behavior of blends, which had been compromised by the presence of TB. All processed materials were fully disintegrated under composting conditions, suggesting their potential application as fully biodegradable packaging materials.

Effect of Radiation Crosslinking and Surface Modification of Cellulose Fibers on Properties and Characterization of Biopolymer Composites

Recently, polymers have become the fastest growing and most widely used material in a huge number of applications in almost all areas of industry. In addition to standard polymer composites with synthetic matrices, biopolymer composites based on PLA and PHB matrices filled with fibers of plant origin are now increasingly being used in selected advanced industrial applications. The article deals with the evaluation of the influence and effect of the type of surface modification of cellulose fibers using physical methods (low-temperature plasma and ozone application) and chemical methods (acetylation) on the final properties of biopolymer composites. In addition to the surface modification of natural fibers, an additional modification of biocomposite structural systems by radiation crosslinking using gamma radiation was also used. The components of the biopolymer composite were a matrix of PLA and PHBV and the filler was natural cellulose fibers in a constant percentage volume of 20%. Test specimens were made from compounds of prepared biopolymer structures, on which selected tests had been performed to evaluate the properties and mechanical characterization of biopolymer composites. Electron microscopy was used to evaluate the failure and characterization of fracture surfaces of biocomposites.

Carriers based on poly-3-hydroxyalkanoates containing nanomagnetite to trigger hormone release

Poly-3-hydroxybutyrate (P(3HB)) and poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (P(3HB-co-3HHx)) are biocompatible and bioabsorbable biopolymers produced by different bacteria with potential for drug delivery in thermo-responsive magnetic microcarriers. Microparticles of P(3HB) and P(3HB-co-3HHx), with 5.85% mol of 3HHx, produced by Burkholderia sacchari, containing nanomagnetite (nM) and lipophilic hormone were prepared by simple emulsion (oil/water) technique leading to progesterone (Pg) encapsulation efficiency higher than 70% and magnetite loads of 3.1 and 2.3% (w/w) for P(3HB)/nM/Pg and P(3HB-co-3HHx)/nM/Pg, respectively. These formulations were characterized by Infrared spectroscopy, X-ray diffraction, Thermal gravimetric analysis and Electron microscopy (TEM, SEM) techniques. The P(3HB)/nM/Pg and P(3HB-co-3HHx)/nM/Pg microparticles presented spherical geometry with wrinkled surfaces and average size between 2 and 40 μm for 90% of the microparticles. The release profiles of the P(3HB)/nM/Pg and P(3HB-co-3HHx)/nM/Pg formulations showed a hormone release trigger (6.9 and 11.1%, respectively) effect induced by oscillating external magnetic field (0.2 T), after 72 h. Progesterone release in non-magnetic tests with P(3HB-co-3HHx)/nM/Pg revealed a slight increment (5.6%) in relation to P(3HB)/nM/Pg. The experimental release of the P(3HB)/nM/Pg and P(3HB-co-3HHx)/nM/Pg samples presented a good agreement with Higuchi model. The 3HHx comonomer content improves the hormone release of the P(3HB-co-3HHx)/nM/Pg formulation with potential for application to synchronize the estrous cycle.

Utilization of Sugarcane Bagasse by Halogeometricum borinquense Strain E3 for Biosynthesis of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Sugarcane bagasse (SCB), one of the major lignocellulosic agro-industrial waste products, was used as a substrate for biosynthesis of polyhydroxyalkanoates (PHA) by halophilic archaea. Among the various wild-type halophilic archaeal strains screened, Halogeometricum borinquense strain E3 showed better growth and PHA accumulation as compared to Haloferaxvolcanii strain BBK2, Haloarcula japonica strain BS2, and Halococcus salifodinae strain BK6. Growth kinetics and bioprocess parameters revealed the maximum PHA accumulated by strain E3 to be 50.4 ± 0.1 and 45.7 ± 0.19 (%) with specific productivity (qp) of 3.0 and 2.7 (mg/g/h) using NaCl synthetic medium supplemented with 25% and 50% SCB hydrolysate, respectively. PHAs synthesized by strain E3 were recovered in chloroform using a Soxhlet apparatus. Characterization of the polymer using crotonic acid assay, X-ray diffraction (XRD), differential scanning calorimeter (DSC), Fourier transform infrared (FT-IR), and proton nuclear magnetic resonance (¹H-NMR) spectroscopy analysis revealed the polymer obtained from SCB hydrolysate to be a co-polymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] comprising of 13.29 mol % 3HV units.

Complex study of the physical properties of a poly(lactic acid)/poly(3-hydroxybutyrate) blend and its carbon black composite during various outdoor and laboratory ageing conditions

Carbon black improved retention of mechanical properties of compostable PLA/PHB – based foil during ageing making it suitable as mulching material.

Encapsulation of gold nanoparticles with PHB based on coffee ring effect

The hydrodynamic process of ring formation has been utilized to encapsulate gold nanoparticles in the matrix of PHB using an ink jet printing technique.