POLY(HYDROXYBUTYRATE-CO-HYDROXYVALERATE) MICRONIZATION BY SOLUTION ENHANCED DISPERSION BY SUPERCRITICAL FLUIDS TECHNIQUE

Influence of Electrospinning Parameters on the Morphology of Electrospun Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Fibrous Membranes and Their Application as Potential Air Filtration Materials

A large number of non-degradable materials have severely damaged the ecological environment. Now, people are increasingly pursuing the use of environmentally friendly materials to replace traditional chemical materials. Polyhydroxyalkonates (PHAs) are receiving increasing attention because of the unique biodegradability and biocompatibility they offer. However, the applications of PHAs are still limited due to high production costs and insufficient study. This project examines the optimal electrospinning parameters for the production of PHA-based fibrous membranes for air filtration. A common biodegradable polyester, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), was electrospun into a nanofibrous membrane with a well-controlled surface microstructure. In order to produce smooth, bead-free fibers with micron-scale diameters, the effect of the process parameters (applied electric field, solution flow rate, inner diameter of hollow needle, and polymer concentration) on the electrospun fiber microstructure was optimized. The well-defined fibrous structure was optimized at an applied electric field of 20 kV, flow rate of 0.5 mL/h, solution concentration of 12 wt.%, and needle inner diameter of 0.21 mm. The morphology of the electrospun PHBV fibrous membrane was observed by scanning electron microscopy (SEM). Fourier transform infrared (FTIR) and Raman spectroscopy were used to explore the chemical signatures and phases of the electrospun PHBV nanofiber. The ball burst strength (BBS) was measured to assess the mechanical strength of the membrane. The small pore size of the nanofiber membranes ensured they had good application prospects in the field of air filtration. The particle filtration efficiency (PFE) of the optimized electrospun PHBV fibrous membrane was above 98% at standard atmospheric pressure.

Effect of 3-Hydroxyvalerate Content on Thermal, Mechanical, and Rheological Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Biopolymers Produced from Fermented Dairy Manure

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with various 3-hydroxyvalerate (3HV) contents biosynthesized by mixed microbial consortia (MMC) fed fermented dairy manure at the large-scale level was assessed over a 3-month period. The thermal, mechanical, and rheological behavior and the chemical structure of the extracted PHBV biopolymers were studied. The recovery of crude PHBV extracted in a large Soxhlet extractor with CHCl₃ for 24 h ranged between 20.6% to 31.8% and purified to yield between 8.9% to 26.9% all based on original biomass. ¹³C-NMR spectroscopy revealed that the extracted PHBVs have a random distribution of 3HV and 3-hydroxybutyrate (3HB) units and with 3HV content between 16% and 24%. The glass transition temperature (T_g) of the extracted PHBVs varied between −0.7 and −7.4 °C. Some of the extracted PHBVs showed two melting temperatures (T_m) which the lower T_m1 ranged between 126.1 °C and 159.7 °C and the higher T_m2 varied between 152.1 °C and 170.1 °C. The weight average molar mass of extracted PHBVs was wide ranging from 6.49 × 10⁵ g·mol⁻¹ to 28.0 × 10⁵ g·mol⁻¹. The flexural and tensile properties were also determined. The extracted polymers showed a reverse relationship between the 3HV content and Young’s modulus, tensile strength, flexural modulus, and flexural strength properties.

Formation of Polymer-Carbon Nanotube Composites by Two-Step Supercritical Fluid Treatment

An approach for polymer-carbon nanotube (CNT) composite preparation is proposed based on a two-step supercritical fluid treatment. The first step, rapid expansion of a suspension (RESS) of CNTs in supercritical carbon dioxide, is used to de-bundle CNTs in order to simplify their mixing with polymer in solution. The ability of RESS pre-treatment to de-bundle CNTs and to cause significant bulk volume expansion is demonstrated. The second step is the formation of polymer-CNT composite from solution via supercritical antisolvent (SAS) precipitation. SAS treatment allows avoiding CNT agglomeration during transition from a solution into solid state due to the high speed of phase transition. The combination of these two supercritical fluid methods allowed obtaining a polycarbonate-multiwalled carbon nanotube composite with tensile strength two times higher compared to the initial polymer and enhanced elasticity.

Co-precipitation of anthocyanin in PHBV by the SEDS technique

Anthocyanins are pigments of plant origin responsible for most blue, purple and all shades of red found in flowers, fruits and some stems and roots of plants, besides comprising a class of potent antioxidant phenolic compounds. Due to the relevance of anthocyanins this work aims to encapsulate anthocyanin extracted from the wine lees through the Solution Enhanced Dispersion by Supercritical Fluids (SEDS) technique and to evaluate the thermal stability of encapsulated versus non-encapsulated anthocyanin. The highest encapsulation efficiency obtained was approximately 66%. Submicron size particles ranging from 0.22 to 0.30 μm were obtained and they were free of residual organic solvent. In relation to the thermal stability, it was verified that the particles degraded about six times less than the non-encapsulated sample, which allows numerous applications since one of the barriers of anthocyanin use is its sensitivity to high temperatures.

Green Composites from a Bioplastic Blend of Poly(3-hyroxybutyrate-co-3-hydroxyvalerate) and Carbon Dioxide-Derived Poly(propylene carbonate) and Filled with a Corn Ethanol-Industry Co-product

Sustainable green composites were engineered from distillers' dried grains with solubles (DDGS), a co-product from the corn ethanol industry as a sustainable filler in bioplastic matrices made from a carbon dioxide-derived poly(propylene carbonate) (PPC) and poly(3-hyroxybutyrate-co-3-hydroxyvalerate) (PHBV) blend. The effect of water-washed DDGS (15 and 25 wt %) on the properties of injection-molded green composites from PHBV/PPC blends (60/40) and (40/60) and DDGS without and with peroxide (0.5 phr) has been investigated. From the results, it was noticed that the glass transition temperature (T _g) of the PHBV/PPC (60/40) bioplastic matrix increased by ∼9.6 °C by adding a peroxide cross-linking agent, indicating significant interaction (linkage) between PHBV and PPC polymers in this particular composition ratio, which was supported by SEM analysis as no phase separation was observed between PHBV and PPC. The tensile modulus of PHBV/PPC (60/40) and PHBV/PPC (40/60) blends with peroxide was improved by ∼40.7 and 1.5% after the addition of 25 wt % DDGS, respectively, due to its fibrous flaky structure. The % elongation values at break of the PHBV/PPC (60/40) blend matrices with and without peroxide were drastically improved by 18.5 and 90.7 folds, respectively, as compared to that of brittle pristine PHBV.