The effect of natural fillers on the marine biodegradation behaviour of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)

Biodegradation behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) containing phenolic compounds in seawater in laboratory testing conditions

Biodegradation in marine medium of PHBV films with or without 5 % wt. of phenolic compounds (catechin, ferulic acid, and vanillin) was assessed at laboratory scale. Respirometric analyses and film disintegration kinetics were used to monitor the process over a period of 162 days. Structural changes in the films were analyzed throughout the exposure period using FESEM, DSC, Thermogravimetric analyses, XRD, and FTIR spectra. Respirometric tests showed complete biodegradation of all materials during the exposure period (the biodegradation half-time ranged between 63 and 79 days) but at different rates, depending on the phenolic compound incorporated. Ferulic acid and vanillin accelerate the PHBV biodegradation, whereas catechin delayed the process. Disintegration kinetics confirmed these results and showed that degradation occurred from the surface to the interior of the films. This was controlled by the degradation rate of the polymer amorphous phase and the formation of a biomass coating on the film surface. This is the result of the compounds generated by polymer degradation in combination with excretions from microorganisms. This coating has the potential to affect the enzyme diffusion to the polymer substrate. Moreover, the cohesion forces of the amorphous phase (reflected in its glass transition temperature) affected its degradation rate, while the slower degrading crystalline fragments were released, thus contributing to the disintegration process on the film's surface. Ferulic acid, with its hydrolytic effect, enhanced degradation, as did vanillin for its plasticizing and weakening effect in the amorphous phase of polymer matrix. In contrast, catechin with cross-linking effect hindered the progress of the material degradation, considerably slowing down the process rate.

Addition of Coffee Waste-Derived Plasticizer Improves Processability and Barrier Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-Natural Rubber Bioplastic

This study aimed to develop a value-added bio-based polymer product for food packaging. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a promising bioplastic with limitations in processability and brittleness, which our group previously addressed by incorporating high-molecular-weight natural rubber (NR) compatibilized with peroxide and coagent. Yet, processability in an industrial setting proved difficult. Coffee oil epoxide (COE), a waste-derived plasticizer, was incorporated into the PHBV/NR/peroxide/coagent matrix via extrusion, and properties of resulting sheets were evaluated. COE incorporation significantly decreased the oxygen and water permeability of the PHBV/NR sheets. Maximum degradation temperature Tpeak (°C) increased by ~4.6 °C, and degree of crystallinity decreased by ~15.5% relative to pristine PHBV, indicating good thermal stability. Melting (Tm) and glass transition temperatures (Tg) of the PHBV/NR blend remained unchanged with COE incorporation. X-ray diffraction (XRD) revealed ~10.36% decrease in crystal size for the plasticized blend. Energy-dispersive X-ray analysis (EDAX) and scanning electron microscopy (SEM) confirmed good dispersion with no phase separation. The water uptake capacity of the plasticized blend was reduced by 61.02%, while surface contact angle measurements showed improved water resistance. The plasticized PHBV sheet shows promise for environmentally friendly packaging films due to its high thermal stability, effective barrier properties, and industrial scalability.

Novel enhancement of interfacial interaction and properties in biodegradable polymer composites using green chemically treated spent coffee ground microfiller

This study investigates the potential of utilizing green chemically treated spent coffee grounds (SCGs) as micro biofiller reinforcement in Poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) biopolymer composites. The aim is to assess the impact of varying SCG concentrations (1 %, 3 %, 5 %, and 7 %) on the functional, thermal, mechanical properties and biodegradability of the resulting composites with a PHBV matrix. The samples were produced through melt compounding using a twin-screw extruder and compression molding. The findings indicate successful dispersion and distribution of SCGs microfiller into PHBV. Chemical treatment of SCG microfiller enhanced the interfacial bonding between the SCG and PHBV, evidenced by higher water contact angles of the biopolymer composites. Field Emission Scanning Electron Microscopy (FE-SEM) confirmed the successful interaction of treated SCG microfiller, contributing to enhanced mechanical characteristics. A two-way ANOVA was conducted for statistical analysis. Mass losses observed after burying the materials in natural soil indicated that the composites degraded faster than the pure PHBV polymer suggesting that both composites are biodegradable, particularly at high levels of spent coffee grounds (SCG). Despite the possibility of agglomeration at higher concentrations, SCG incorporation resulted in improved functional properties, positioning the green biopolymer composite as a promising material for sustainable packaging and diverse applications.

Reprocessing Possibilities of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-Hemp Fiber Composites Regarding the Material and Product Quality

An important issue addressed in research on the assessment of the quality of polymer products is the quality of the polymer material itself and, in accordance with the idea of waste-free management, the impact of its repeated processing on its properties and the quality of the products. In this work, a biocomposite, based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with short hemp fibers, was obtained and repeatedly processed, which is a continuation of the research undertaken by the team in the field of this type of biocomposites. After subsequent stages of processing, the selected mechanical, processing and functional properties of the products were assessed. For this purpose, microscopic tests were carried out, mechanical properties were tested in static tensile and impact tests, viscosity curves were determined after subsequent processing cycles and changes in plastic pressure in the mold cavity were determined directly during processing. The results of the presented research confirm only a slight decrease in the mechanical properties of the produced type of biocomposite, even after it has been reprocessed five times, which gives extra weight to arguments for its commercialization as a substitute for petrochemical-based plastics. No significant changes were found in the used parameters and processing properties with the stages of processing, which allows for a predictable and stable manufacturing process using, for example, the injection molding process.

Valorization of Agricultural Waste Lignocellulosic Fibers for Poly(3-Hydroxybutyrate-Co-Valerate)-Based Composites in Short Shelf-Life Applications

Biocircularity could play a key role in the circular economy, particularly in applications where organic recycling (composting) has the potential to become a preferred waste management option, such as food packaging. The development of fully biobased and biodegradable composites could help reduce plastic waste and valorize agro-based residues. In this study, extruded films made of composites of polyhydroxybutyrate-co-valerate (PHBV) and lignocellulosic fibers, namely almond shell (AS) and Oryzite® (OR), a polymer hybrid composite precursor, have been investigated. Scanning electron microscopy (SEM) analysis revealed a weak fiber-matrix interfacial interaction, although OR composites present a better distribution of the fiber and a virtually lower presence of "pull-out". Thermogravimetric analysis showed that the presence of fibers reduced the onset and maximum degradation temperatures of PHBV, with a greater reduction observed with higher fiber content. The addition of fibers also affected the melting behavior and crystallinity of PHBV, particularly with OR addition, showing a decrease in crystallinity, melting, and crystallization temperatures as fiber content increased. The mechanical behavior of composites varied with fiber type and concentration. While the incorporation of AS results in a reduction in all mechanical parameters, the addition of OR leads to a slight improvement in elongation at break. The addition of fibers improved the thermoformability of PHBV. In the case of AS, the improvement in the processing window was achieved at lower fiber contents, while in the case of OR, the improvement was observed at a fiber content of 20%. Biodisintegration tests showed that the presence of fibers promoted the degradation of the composites, with higher fiber concentrations leading to faster degradation. Indeed, the time of complete biodisintegration was reduced by approximately 30% in the composites with 20% and 30% AS.

An on-demand bioresorbable neurostimulator

Bioresorbable bioelectronics, with their natural degradation properties, hold significant potential to eliminate the need for surgical removal. Despite notable achievements, two major challenges hinder their practical application in medical settings. First, they necessitate sustainable energy solutions with biodegradable components via biosafe powering mechanisms. More importantly, reliability in their function is undermined by unpredictable device lifetimes due to the complex polymer degradation kinetics. Here, we propose an on-demand bioresorbable neurostimulator to address these issues, thus allowing for clinical operations to be manipulated using biosafe ultrasound sources. Our ultrasound-mediated transient mechanism enables (1) electrical stimulation through transcutaneous ultrasound-driven triboelectricity and (2) rapid device elimination using high-intensity ultrasound without adverse health effects. Furthermore, we perform neurophysiological analyses to show that our neurostimulator provides therapeutic benefits for both compression peripheral nerve injury and hereditary peripheral neuropathy. We anticipate that the on-demand bioresorbable neurostimulator will prove useful in the development of medical implants to treat peripheral neuropathy.

Challenges associated with cellulose composite material: Facet engineering and prospective

Cellulose is the most abundant polysaccharide on earth. It has a large number of desirable properties. Its low toxicity makes it more useful for a variety of applications. Nowadays, its composites are used in most engineering fields. Composite consists of a polymer matrix and use as a reinforcing material. By reducing the cost of traditional fibers, it has an increasing demand for environment-friendly purposes. The use of these types of composites is inherent in moisture absorption with hindered natural fibers. This determines the reduction of polymer composite material. By appropriate chemical surface treatment of cellulose composite materials, the effect could be diminished. The most modern and advanced techniques and methods for the preparation of cellulose and polymer composites are discussed here. Cellulosic composites show a reinforcing effect on the polymer matrix as pointed out by mechanical characterization. Researchers tried their hard work to study different ways of converting various agricultural by-products into useful eco-friendly polymer composites for sustainable production. Cellulose plays building blocks, that are critical for polymer products and their engineering applications. The most common method used to prepare composites is in-situ polymerization. This help to increase the yields of cellulosic composites with a significant enhancement in thermal stability and mechanical properties. Recently, cellulose composites used as enhancing the incorporation of inorganic materials in multi-functional properties. Furthermore, we have summarized in this review the potential applications of cellulose composites in different fields like packaging, aerogels, hydrogels, and fibers.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Electrospun Nanofibers Containing Natural Deep Eutectic Solvents Exhibiting a 3D Rugose Morphology and Charge Retention Properties

In the present study, electrospun nanofibers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a biodegradable polyester, containing natural deep eutectic solvents (NADES) were obtained and reported for the first time, exhibiting an unreported 3D morphology and enhanced charge retention properties. Choline chloride (ChCl)/urea/water in a molar ratio of 1:2:1 was used as the NADES model system. Electrospun nanofibers were produced from a 10 wt % solution of PHBV containing 26 wt % NADES with respect to the polymer and were deposited on different substrates, that is, aluminum foil and non-woven spunbond polypropylene (PP). The morphology and charge retention ability were characterized under different conditions and on different substrates. The attained fiber morphology for the NADES-containing mats showed an average fiber diameter of around 300 nm, whereas the pure PHBV polymer under the same conditions produced electrospun fibers of around 880 nm. However, the deposition of PHBV/ChCl/urea/water fibers resulted in a surprising macroscopic rugose 3D surface morphology made of aligned nanofibers when processed at 50% relative humidity (RH). The nanofiber grammages above which this 3D morphology, associated with NADES-induced charge retention, formed was found to be dependent on the substrate used and RH. This morphology was not seen at 20% RH nor when pure PHBV was produced. Charge stability studies revealed that PHBV/ChCl/urea/water nanofibers exhibited lasting charge retention, especially when sandwiched between spunbond polypropylene textiles. Finally, such multilayer structures containing a very thin double layer of PHBV/ChCl/urea/water fibers after corona treatment exhibited improved paraffin aerosol penetration, which was ascribed to the combination of thinner fibers and their charge retention capacity. The here-developed electrospun PHBV fibers containing NADES demonstrated for the first time a new potential application as electret filter media.

Green composites made of polyhydroxybutyrate and long-chain fatty acid esterified microcrystalline cellulose from pineapple leaf

Pineapple leaf fibres are an abundant agricultural waste product that contains 26.9% cellulose. The objective of this study was to prepare fully degradable green biocomposites made of polyhydroxybutyrate (PHB) and microcrystalline cellulose from pineapple leaf fibres (PALF-MCC). To improve compatibility with PHB, the PALF-MCC was surface modified using lauroyl chloride as an esterifying agent. The influence of the esterified PALF-MCC laurate content and changes in the film surface morphology on biocomposite properties was studied. The thermal properties obtained by differential scanning calorimetry revealed a decrease in crystallinity for all biocomposites, with 100 wt% PHB displaying the highest values, whereas 100 wt% esterified PALF-MCC laurate showed no crystallinity. The addition of esterified PALF-MCC laurate increased the degradation temperature. The maximum tensile strength and elongation at break were exhibited when adding 5% of PALF-MCC. The results demonstrated that adding esterified PALF-MCC laurate as a filler in the biocomposite film could retain a pleasant value of tensile strength and elastic modulus whereas a slight increase in elongation can help to enhance flexibility. For soil burial testing, PHB/ esterified PALF-MCC laurate films with 5-20% (w/w) PALF-MCC laurate ester had higher degradation than films consisting of 100% PHB or 100% esterified PALF-MCC laurate. PHB and esterified PALF-MCC laurate derived from pineapple agricultural wastes are particularly suitable for the production of relatively low-cost biocomposite films that are 100% compostable in soil.

Biodegradation of Biodegradable Polymers in Mesophilic Aerobic Environments

Finding alternatives to diminish plastic pollution has become one of the main challenges of modern life. A few alternatives have gained potential for a shift toward a more circular and sustainable relationship with plastics. Biodegradable polymers derived from bio- and fossil-based sources have emerged as one feasible alternative to overcome inconveniences associated with the use and disposal of non-biodegradable polymers. The biodegradation process depends on the environment's factors, microorganisms and associated enzymes, and the polymer properties, resulting in a plethora of parameters that create a complex process whereby biodegradation times and rates can vary immensely. This review aims to provide a background and a comprehensive, systematic, and critical overview of this complex process with a special focus on the mesophilic range. Activity toward depolymerization by extracellular enzymes, biofilm effect on the dynamic of the degradation process, CO2 evolution evaluating the extent of biodegradation, and metabolic pathways are discussed. Remarks and perspectives for potential future research are provided with a focus on the current knowledge gaps if the goal is to minimize the persistence of plastics across environments. Innovative approaches such as the addition of specific compounds to trigger depolymerization under particular conditions, biostimulation, bioaugmentation, and the addition of natural and/or modified enzymes are state-of-the-art methods that need faster development. Furthermore, methods must be connected to standards and techniques that fully track the biodegradation process. More transdisciplinary research within areas of polymer chemistry/processing and microbiology/biochemistry is needed.

Development and Characterization of Fully Renewable and Biodegradable Polyhydroxyalkanoate Blends with Improved Thermoformability

Poly(3-hydroxybutyrate-co-3-valerate) (PHBV), being one of the most studied and commercially available polyhydroxyalkanoates (PHAs), presents an intrinsic brittleness and narrow processing window that currently hinders its use in several plastic applications. The aim of this study was to develop a biodegradable PHA-based blend by combining PHBV with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), another copolyester of the PHA family that shows a more ductile behavior. Blends of PHBV with 20% wt., 30% wt., and 40% wt. of PHBH were obtained by melt mixing, processed by cast extrusion in the form of films, and characterized in terms of their morphology, crystallization behavior, thermal stability, mechanical properties, and thermoformability. Full miscibility of both biopolymers was observed in the amorphous phase due to the presence of a single delta peak, ranging from 4.5 °C to 13.7 °C. Moreover, the incorporation of PHBH hindered the crystallization process of PHBV by decreasing the spherulite growth rate from 1.0 µm/min to 0.3 µm/min. However, for the entire composition range studied, the high brittleness of the resulting materials remained since the presence of PHBH did not prevent the PHBV crystalline phase from governing the mechanical behavior of the blend. Interestingly, the addition of PHBH greatly improved the thermoformability by widening the processing window of PHBV by 7 s, as a result of the increase in the melt strength of the blends even for the lowest PHBH content.

Analysis of Selected Properties of Microporous PLA as a Result of Abiotic Degradation

In the study, an investigation was made into the hydrolytic degradation behavior of the microporous polylactide (PLA) in the initial stage in three biological buffer solutions with various pH-simulating body fluids in comparison with pure PLA. Studies also include the analysis of selected mechanical properties and physical structures. A microporous PLA was obtained by melt extrusion using a chemical blowing agent. The rate of Mw decrease induced by hydrolysis over 35 days of microporous PLA was roughly comparable to the pure material. The rate of depolymerization was slightly accelerated at an acid pH due to acid-catalyzed hydrolysis at the end of the observed period. The mechanical analysis showed the influence of various pH on the obtained results.

The Influence of Additives and Environment on Biodegradation of PHBV Biocomposites

The biodegradation of polyhydroxybutyrate-co-hydroxyvalerate (PHBV) ternary biocomposites containing nature-based plasticizer acetyl tributyl citrate (ATBC), heterogeneous nucleation agents-calcium carbonate (CaCO₃) and spray-dried lignin-coated cellulose nanocrystals (L-CNC)-in vermicomposting, freshwater biotope, and thermophilic composting have been studied. The degree of disintegration, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and the evaluation of surface images taken by scanning electron microscopy (SEM) were conducted for the determination influence of different environments and additives on the biodegradation of PHBV. Furthermore, the method adapted from ISO 14855-1 standard was used for thermophilic composting. It is a method based on the measurement of the amount of carbon dioxide evolved during microbial degradation. The highest biodegradation rate was observed in the thermophilic condition of composting. The biodegradation level of all PHBV-based samples was, after 90 days, higher than 90%. Different mechanisms of degradation and consequently different degradation rate were evaluated in vermicomposting and freshwater biotope. The surface enzymatic degradation, observed during the vermicomposting process, showed slightly higher biodegradation potential than the hydrolytic attack of freshwater biotope. The application of ATBC plasticizers in the PHBV matrix caused an increase in biodegradation rate in all environments. However, the highest biodegradation rate was achieved for ternary PHBV biocomposites containing 10 wt. % of ATBC and 10 wt. % of CaCO₃. A considerable increase in the degree of disintegration was evaluated, even in freshwater biotope. Furthermore, the slight inhibition effect of L-CNC on the biodegradation process of ternary PHBV/ATBC/L-CNC could be stated.

A New Wave of Industrialization of PHA Biopolyesters

The ever-increasing use of plastics, their fossil origin, and especially their persistence in nature have started a wave of new innovations in materials that are renewable, offer the functionalities of plastics, and are biodegradable. One such class of biopolymers, polyhydroxyalkanoates (PHAs), are biosynthesized by numerous microorganisms through the conversion of carbon-rich renewable resources. PHA homo- and heteropolyesters are intracellular products of secondary microbial metabolism. When isolated from microbial biomass, PHA biopolymers mimic the functionalities of many of the top-selling plastics of petrochemical origin, but biodegrade in soil, freshwater, and marine environments, and are both industrial- and home-compostable. Only a handful of PHA biopolymers have been studied in-depth, and five of these reliably match the desired material properties of established fossil plastics. Realizing the positive attributes of PHA biopolymers, several established chemical companies and numerous start-ups, brand owners, and converters have begun to produce and use PHA in a variety of industrial and consumer applications, in what can be described as the emergence of the “PHA industry”. While this positive industrial and commercial relevance of PHA can hardly be described as the first wave in its commercial development, it is nonetheless a very serious one with over 25 companies and start-ups and 30+ brand owners announcing partnerships in PHA production and use. The combined product portfolio of the producing companies is restricted to five types of PHA, namely poly(3-hydroxybutyrate), poly(4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), even though PHAs as a class of polymers offer the potential to generate almost limitless combinations of polymers beneficial to humankind. To date, by varying the co-monomer type and content in these PHA biopolymers, their properties emulate those of the seven top-selling fossil plastics, representing 230 million t of annual plastics production. Capacity expansions of 1.5 million t over the next 5 years have been announced. Policymakers worldwide have taken notice and are encouraging industry to adopt biodegradable and compostable material solutions. This wave of commercialization of PHAs in single-use and in durable applications holds the potential to make the decisive quantum leap in reducing plastic pollution, the depletion of fossil resources, and the emission of greenhouse gases and thus fighting climate change. This review presents setbacks and success stories of the past 40 years and the current commercialization wave of PHA biopolymers, their properties, and their fields of application.

A Critical Review on the Economically Feasible and Sustainable Poly(3-Hydroxybutyrate-co-3-hydroxyvalerate) Production from Alkyl Alcohols

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) is the most studied short-chain-length polyhydroxyalkanoates (PHA) with high application importance in various fields. The domination of high-cost propionate and valerate over other 3-hydroxyvalerate (3HV) precursors owing to their wide preference among PHA-producing bacteria has hindered the development of diverse production processes. As alkyl alcohols are mainly produced from inexpensive starting materials through oxo synthesis, they contribute a cost-effective advantage over propionate and valerate. Moreover, alkyl alcohols can be biosynthesized from natural substrates and organic wastes. Despite their great potential, their toxicity to most PHA-producing bacteria has been the major drawback for their wide implementation as 3HV precursors for decades. Although the standard PHA-producing bacteria Cupriavidus necator showed promising alcohol tolerance, the 3HV yield was discouraging. Continuous discovery of alkyl alcohols-utilizing PHA-producing bacteria has enabled broader choices in 3HV precursor selection for diverse P(3HB-co-3HV) production processes with higher economic feasibility. Besides continuous effort in searching for promising wild-type strains, genetic engineering to construct promising recombinant strains based on the understanding of the mechanisms involved in alkyl alcohols toxicity and tolerance is an alternative approach. However, more studies are required for techno-economic assessment to analyze the economic performance of alkyl alcohol-based production compared to that of organic acids.

Physical-Chemical and Structural Stability of Poly(3HB-co-3HV)/(ligno-)cellulosic Fibre-Based Biocomposites over Successive Dishwashing Cycles

In order to lengthen the life cycle of packaging materials, it is essential to study their potential for reuse. This has been never carried out for emerging bio-based and biodegradable materials such as PHBV/(ligno-)cellulosic fibre-based biocomposite materials. This work therefore highlights the impact of successive dishwashing cycles on the physical-chemical and structural stability of such materials. Several parameters were considered to assess this stability, such as the visual aspect and colour, the microstructure, the thermal and tensile properties, and the overall migration in food liquid simulants. The effect of fibre composition, morphology, and content was investigated by selecting three types of commercial (ligno-)cellulosic fibres and two filler contents (20 and 40 wt%). A great potential for reuse of PHBV films was highlighted by their high stability after up to at least 50 dishwashing cycles. However, the addition of (ligno-)cellulosic fillers negatively impacts the stability of PHBV-based materials, especially due to the hygroscopic behaviour of (ligno-)cellulosic fillers and the heterogenous microstructure of biocomposites, with at best up to 10 possible dishwashing cycles for ultra-pure cellulose. In conclusion, reuse including dishwashing steps can be considered for neat PHBV materials, while this should be prohibited for PHBV/(ligno-)cellulosic fibre-based biocomposite materials.

A critical review on microbial degradation of petroleum-based plastics: quantitatively effects of chemical addition in cultivation media on biodegradation efficiency

Petroleum-based plastics (PBP) with different properties have been developed to suit various needs of modern lives. Nevertheless, these well-developed properties also present the double-edged sword effect that significantly threatens the sustainability of the environment. This work focuses on the impact of microbial cultivating conditions (the elementary compositions and temperature) to provide insightful information for the process optimization of microbial degradation. The major elementary compositions in cultivation media and temperature from the literature were radically reviewed and assessed using the constructed supervised machine learning algorithm. Fifty-two literatures were collected as a training dataset to investigate the impact of major chemical elements and cultivation temperature upon PBP biodegradation. Among six singular parameters (NH₄⁺, K⁺, PO₄^3-, Mg²⁺, Ca²⁺, and temperature) and thirty corresponding binary parameters, four singular (NH₄⁺, K⁺, PO₄^3-, and Mg²⁺) and six binary parameters (NH₄⁺/K⁺, NH₄⁺/PO₄^3-, NH₄⁺/Ca²⁺, K⁺/PO₄^3-, PO₄^3-/Mg²⁺, Mg²⁺/Temp) were identified as statistically significant towards microbial degradation through analysis of variance (ANOVA). The binary effect (PO₄^3-/Mg²⁺) is found to be the most statistically significant towards the microbial degradation of PBP. The concentration range, which locates at 0.1-0.6 g/L for Mg²⁺ and 0-2.8 g/L for PO₄^3-, was identified to contribute to the maximum PBP biodegradation. Among all the investigated elements, Mg²⁺ is the only element that is statistically and significantly associated with the variations of cultivation temperature. The optimal preparation conditions within ± 20% uncertainties based upon the range of collected literature reports are recommended. Five representative cultivation elementary compositions (NH₄⁺, K⁺, PO₄^3-, Mg²⁺, and Ca²⁺) and temperature were reviewed from fifty two different literature reports to investigate their impacts on the microbial degradation of PBP using supervised machine learning algorithm. The optimal cultivation conditions based upon collected literature reports to achieve biodegradation over 80% were identified.

High natural PHA production from acetate in Cobetia sp. MC34 and Cobetia marina DSM 4741T and in silico analyses of the genus specific PhaC2 polymerase variant

BACKGROUND

Several members of the bacterial Halomonadacea family are natural producers of polyhydroxyalkanoates (PHA), which are promising materials for use as biodegradable bioplastics. Type-strain species of Cobetia are designated PHA positive, and recent studies have demonstrated relatively high PHA production for a few strains within this genus. Industrially relevant PHA producers may therefore be present among uncharacterized or less explored members. In this study, we characterized PHA production in two marine Cobetia strains. We further analyzed their genomes to elucidate pha genes and metabolic pathways which may facilitate future optimization of PHA production in these strains.

RESULTS

Cobetia sp. MC34 and Cobetia marina DSM 4741T were mesophilic, halotolerant, and produced PHA from four pure substrates. Sodium acetate with- and without co-supplementation of sodium valerate resulted in high PHA production titers, with production of up to 2.5 g poly(3-hydroxybutyrate) (PHB)/L and 2.1 g poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/L in Cobetia sp. MC34, while C. marina DSM 4741T produced 2.4 g PHB/L and 3.7 g PHBV/L. Cobetia marina DSM 4741T also showed production of 2.5 g PHB/L from glycerol. The genome of Cobetia sp. MC34 was sequenced and phylogenetic analyses revealed closest relationship to Cobetia amphilecti. PHA biosynthesis genes were located at separate loci similar to the arrangement in other Halomonadacea. Further genome analyses revealed some differences in acetate- and propanoate metabolism genes between the two strains. Interestingly, only a single PHA polymerase gene (phaC2) was found in Cobetia sp. MC34, in contrast to two copies (phaC1 and phaC2) in C. marina DSM 4741T. In silico analyses based on phaC genes show that the PhaC2 variant is conserved in Cobetia and contains an extended C-terminus with a high isoelectric point and putative DNA-binding domains.

CONCLUSIONS

Cobetia sp. MC34 and C. marina DSM 4741T are natural producers of PHB and PHBV from industrially relevant pure substrates including acetate. However, further scale up, optimization of growth conditions, or use of metabolic engineering is required to obtain industrially relevant PHA production titers. The putative role of the Cobetia PhaC2 variant in DNA-binding and the potential implications remains to be addressed by in vitro- or in vivo methods.

Production of Polyhydroxyalkanoates (PHAs) by Vibrio alginolyticus Strains Isolated from Salt Fields

Vibrio alginolyticus is a halophilic organism usually found in marine environments. It has attracted attention as an opportunistic pathogen of aquatic animals and humans, but there are very few reports on polyhydroxyalkanoate (PHA) production using V. alginolyticus as the host. In this study, two V. alginolyticus strains, LHF01 and LHF02, isolated from water samples collected from salt fields were found to produce poly(3-hydroxybutyrate) (PHB) from a variety of sugars and organic acids. Glycerol was the best carbon source and yielded the highest PHB titer in both strains. Further optimization of the NaCl concentration and culture temperature improved the PHB titer from 1.87 to 5.08 g/L in V. alginolyticus LHF01. In addition, the use of propionate as a secondary carbon source resulted in the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). V. alginolyticus LHF01 may be a promising host for PHA production using cheap waste glycerol from biodiesel refining.

Recent developments in short- and medium-chain- length Polyhydroxyalkanoates: Production, properties, and applications

Developing renewable resource-based plastics with complete biodegradability and a minimal carbon footprint can open new opportunities to effectively manage the end-of-life plastics waste and achieve a low carbon society. Polyhydroxyalkanoates (PHAs) are biobased and biodegradable thermoplastic polyesters that accumulate in microorganisms (e.g., bacterial, microalgal, and fungal species) as insoluble and inert intracellular inclusion. The PHAs recovery from microorganisms, which typically involves cell lysis, extraction, and purification, provides high molecular weight and purified polyesters that can be compounded and processed using conventional plastics converting equipment. The physio-chemical, thermal, and mechanical properties of the PHAs are comparable to traditional synthetic polymers such as polypropylene and polyethylene. As a result, it has attracted substantial applications interest in packaging, personal care, coatings, agricultural and biomedical uses. However, PHAs have certain performance limitations (e.g. slow crystallization), and substantially more expensive than many other polymers. As such, more research and development is required to enable them for extensive use. This review provides a critical review of the recent progress achieved in PHAs production using different microorganisms, downstream processing, material properties, processing avenues, recycling, aerobic and anaerobic biodegradation, and applications.

Development of Toughened Flax Fiber Reinforced Composites. Modification of Poly(lactic acid)/Poly(butylene adipate-co-terephthalate) Blends by Reactive Extrusion Process

The presented study focuses on the development of flax fiber (FF) reinforced composites prepared with the use of poly(lactic acid)/poly(butylene adipate-co-terephthalate)-PLA/PBAT blend system. This type of modification was aimed to increase impact properties of PLA-based composites, which are usually characterized by high brittleness. The PLA/PBAT blends preparation was carried out using melt blending technique, while part of the samples was prepared by reactive extrusion process with the addition of chain extender (CE) in the form of epoxy-functionalized oligomer. The properties of unreinforced blends was evaluated using injection molded samples. The composite samples were prepared by compression molding technique, while flax fibers reinforcement was in the form of plain fabric. The properties of the laminated sheets were investigated during mechanical test measurements (tensile, flexural, impact). Differential scanning calorimetry (DSC) analysis was used to determine the thermal properties, while dynamic mechanical thermal analysis (DMTA) and heat deflection temperature (HDT) measurements were conducted in order to measure the thermomechanical properties. Research procedure was supplemented with structure evaluation using scanning electron microscopy (SEM) analysis. The comparative study reveals that the properties of PLA/PBAT-based composites were more favorable, especially in the context of impact resistance improvement. However, for CE modified samples also the modulus and strength was improved. Structural observations after the impact tests confirmed the presence of the plastic deformation of PLA/PBAT matrix, which confirmed the favorable properties of the developed materials. The use of PBAT phase as the impact modifier strongly reduced the PLA brittleness, while the reactive extrusion process improves the fiber-matrix interactions leading to higher stiffness and strength.