Polyhydroxyalkanoates: biodegradable polymers with a range of applications

Increased and accelerated global economic activities over the past century have led to interlinked problems that require urgent attention. The current patterns of production and consumption have raised serious concerns. In this context, greater emphasis has been put on the concept of sustainable economic systems that rely on technologies based on and supporting renewable sources of energy and materials. Average UK households produce around 3.2 million tonnes of packaging waste annually whereas 150 million tonnes of packaging waste is generated annually by industries in the UK. Hence, the development of biologically derived biodegradable polymers is one important element of the new economic development. Key among the biodegradable biopolymers is a class known as polyhydroxyalkanoates. Polyhydroxyalkanoates (PHAs) are a family of polyhydroxyesters of 3‐, 4‐, 5‐ and 6‐hydroxyalkanoic acids, produced by a variety of bacterial species under nutrient‐limiting conditions with excess carbon. These water‐insoluble storage polymers are biodegradable, exhibit thermoplastic properties and can be produced from renewable carbon sources. Thus, there has been considerable interest in the commercial exploitation of these biodegradable polyesters. In this review various applications of polyhydroxyalkanoates are discussed, covering areas such as medicine, agriculture, tissue engineering, nanocomposites, polymer blends and chiral synthesis. Overall this review shows that polyhydroxyalkanoates are a promising class of new emerging biopolymers. Copyright © 2007 Society of Chemical Industry     

Polyhydroxyalkanoates,a family of natural polymers,and their applications in drug delivery

Polyhydroxyalkanoates (PHAs) are natural biopolymers produced by various microorganisms as a reserve of carbon and energy. PHA synthesis generally occurs during fermentation under nutrient limiting conditions with excess carbon. There are two main types of PHAs, short chain length PHAs (scl‐PHAs) and medium chain length PHAs (mcl‐PHAs). The mechanical and thermal properties of PHAs depend mainly on the number of carbons in the monomer unit and its molecular weight. PHAs are promising materials for biomedical applications because they are biodegradable, non‐toxic and biocompatible. The large range of PHAs, along with their varying physical properties and high biocompatibility, make them highly attractive biomaterials for use in drug delivery. They can be used to produce tablets, micro‐ and nanoparticles as well as drug eluting scaffolds. A large range of different PHAs have been explored and the results obtained suggest that PHAs are excellent candidates for controlled and targeted drug delivery systems. © 2015 Society of Chemical Industry     

Polyhydroxyalkanoates: Recent Advances in Their Synthesis and Applications

Polyhydroxyalkanoates (PHAs) are microbial biopolymers (polyesters) that have a wide range of functions and applications. They serve in nature mainly as carbon and energy storage materials for a variety of microorganisms. In past decades, their utilization has attracted much attention, from commodities and degradable plastics to specialty performance materials in medicine. PHA biosynthesis has been well understood, and it is now possible to design bacterial strands to produce PHAs with desired properties. The substrates for the fermentative production of PHAs are very manifold: some are derived from food‐based carbon sources (e.g., fats and oils (triglycerids)), thus raising concerns with regard to the sustainability of their productions in terms of crop area and food. In addition, hemicellulose hydrolysates, crude glycerol, and methanol are very promising carbon sources for the sustainable production of PHAs. The integration of PHA production within a modern biorefinery is an important issue and can result in a simultaneous production of biofuels and bioplastics. Furthermore, many chemical‐synthetic procedures by means of efficient catalysts can give access to a variety of PHAs. This article summarizes recent developments in these fields and emphasizes the importance of a sustainable PHA‐based industry. Practical Applications: Practical applications of the microbial polyesters PHAs are, for example, a variety of sustainably produced commodities as well as special applications in (bio)medicine, for example, tissue engineering.     

Production of polyhydroxyalkanoates: the future green materials of choice

Polyhydroxyalkanoates (PHAs) have recently been the focus of attention as a biodegradable and biocompatible substitute for conventional non degradable plastics. The cost of large‐scale production of these polymers has inhibited its widespread use. Thus, economical, large‐scale production of PHAs is currently being studied intensively. Various bacterial strains, either wild‐type or recombinant have been utilized with a wide spectrum of utilizable carbon sources. New fermentation strategies have been developed for the efficient production of PHAs at high concentration and productivity. With the current advances, PHAs can now be produced to a concentration of 80 g L^?1 with productivities greater than 4 g PHA L^?1 h^?1. These advances will further lower the production cost of PHAs and allow this family of polymers to become a leading biodegradable polymer in the near future. This review describes the properties of PHAs, their uses, the various attempts towards the production of PHAs, focusing on the utilization of cheap substrates and the development of different fermentation strategies for the production of these polymers, an essential step forward towards their widespread use. Copyright © 2010 Society of Chemical Industry     

聚羟基烷酸酯的研究进展

微生物发酵合成的聚羟基烷酸酯(PHAs)作为最具有发展潜力的新型生物高分子材料之一,备受关注。本文介绍了近几年来有关PHAs的生物合成、分离纯化、性能改进、生产与应用现状等方面研究的最新进展,探讨了这一领域未来可能的发展热点和动向。     

Development and characterization of multilayer films based on polyhydroxyalkanoates and hydrocolloids

New biodegradable polymeric materials have been developed in order to minimize the environmental impact caused by the traditional packaging found in the market. Polyhydroxyalkanoates (PHAs) are biopolymers with important features such as biodegradability and biocompatibility; however, the costs associated with PHAs production and the limited mechanical properties reduce their application. Whey is a residual product from dairy industry and gelatin is a biopolymer with good processing characteristics. In this context, a filmogenic solution based on these two biopolymers was incorporated into pure PHA films to improve their optical, mechanical, and structural properties. The filmogenic solution was prepared from gelatin, cheese whey and PHAs, using glycerol as plasticizer agent. The multilayers films (gelatin concentrations at 3 and 5%, w/v) showed higher values for all properties when compared with the PHA standard film. In this sense, the addition of this solution was responsible for the improvement of the film properties. The 5% gelatin multilayers films added of cheese whey and PHAs showed better results when compared with the multilayers films with gelatin at 3%. The film composed of gelatin 5% and cheese whey showed a water vapor permeability ranging from 0.45 g mm/m²/d/kPa, elongation of 2.18%, and opacity of 14.5%. However, the results of the morphological analysis showed that both films presented a homogeneous surface without cracks. Moreover, the results of the thermal analysis of both films indicate polymeric miscibility. Thus, the choice of the best film will depend on its applicability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44458.     

A population balance model describing the dynamics of molecular weight distributions and the structure of PHA copolymer chains

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters produced by many bacterial species under growth-limited conditions when the carbon source is present in excess. It has been recently experimentally demonstrated (Nano Letters 1(9) (2001) 481) that alternating between different carbon sources can lead to the formation of different block copolymer types. This experimental work has been guided by the modeling work presented here as the theoretical considerations permitted evaluation and optimization of the synthesis conditions applied experimentally. To better understand and to optimize the biosynthesis process of different copolymers with desirable properties, we have developed a population balance model that can predict the dynamics of active and inactive PHA polymer chain molecular weight distributions in a nongrowing Ralstonia eutropha cell population. The steady-state version of the model in conjunction with available experimental data was used to compute the steady-state active chain molecular weight distribution and the termination rate as a function of polymer molecular weight for two elongation rate models. For both elongation rate models the steady-state active chain distribution was found to be a monotonically decreasing function of the polymer molecular weight, whereas the termination rate exhibited a maximum. The analytical solution of the steady-state problem was shown to be in excellent agreement with the available experimental data. The population balance model was subsequently used to study the transient dynamics of the process and to predict the experimental conditions, which maximize the production of di- and tri-block copolymer final concentrations. In addition, the structure and molecular weight distribution of the obtained block copolymers were analyzed. Due to the fact that the predicted conditions fall into the range of feasible bioprocessing manipulations, it is expected that such block copolymers can be synthesized. In addition, the proposed model reveals important details of the polymerization process that are difficult to obtain experimentally. Thus, the developed population balance framework should be generally useful for the optimization and control of polymerization processes with similar reaction mechanisms.     

Enabling electrospinning of medium-chain length polyhydroxyalkanoates (PHAs) by blending with short-chain length PHAs

Polyhydroxyalkanoates (PHAs) have recently attracted significant attention in medical applications. Electrospinning of short chain-length (scl-)PHAs has been extensively investigated, while medium chain length (mcl-)PHAs are not suitable for electrospinning since they are elastomeric at room temperature. We improved the electrospinability of an mcl-PHA poly (3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHHx) by blending with a scl-PHA poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV25, with 25?mol% HV). Morphology of electrospun PHBV25/PHOHHx blends at various ratios was investigated. Effects of various processing parameters on nanofiber morphology were investigated, such as solution concentration, feeding rate and applied voltage. Crystallinity, chemical structure, and mechanical properties of the electrospun mats were also studied.     

A review of biodegradable polymers: uses,current developments in the synthesis and characterization of biodegradable polyesters,blends of biodegradable polymers and recent advances in biodegradation studies

This review considers the uses of biodegradable polymers in terms of their relevance within current plastic waste management of packaging materials, biomedical applications and other uses; research papers and patents are catalogued. The chemical synthesis of polyesters and the microbial production of poly(hydroxyalkanoate)s, including recent publications in these areas, are covered and methods of characterization and structural analysis are outlined. Current research into two- and three-component blends is reviewed as a method of reducing overall costs and modifying both properties and biodegradation rates of materials. Finally, there is a summary of degradation processes. Both abiotic and biotic reactions are discussed, together with the development of biodegradation test methods, particularly with respect to composting. © 1998 Society of Chemical Industry     

Green nanobiocomposite: reinforcement effect of montmorillonite clays on physical and biological advancement of various polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are emerging as the candidate of biodegradable material for the future, which in combination with nanoclay reinforcement can produce nanobiocomposites for a variety of applications. Thus, this project was intended to develop nanobiocomposites using various biodegradable PHAs: poly(3-hydroxybutyrate) [P(3HB)], poly(3-hydroxybutyrate-co-6 %3-hydroxyvalerate) [P(3HB-co-6 %3HV)] copolymer, poly(3-hydroxybutyrate-co-70 %4-hydroxybutyrate) [P(3HB-co-70 %4HB)] copolymer and poly(3-hydroxybutyrate-co-10 %3-hydroxyvalerate-co-10 %4-hydroxybutyrate) [P(3HB-co-10 %3HV-co-10 %4HB)] terpolymer through solvent casting method. Pronounced improvement in the optical transparency, mechanical and thermal properties were achieved through reinforcement of 5 wt% Claytone into P(3HB-co-70 %4HB) having the lowest molecular weight as compared to the other polymers. P(3HB-co-70 %4HB)/5 wt% Claytone composite also exhibited enhancement in the antimicrobial performance which increased with the clay concentrations. P(3HB-co-70 %4HB), a biocompatible and biodegradable nanocomposite which had demonstrated salient features with comparable good performance is believed to create new prospects with special incidence in regenerative medicine and as environmentally friendly materials (green nanocomposites).     

Hyperbranched aromatic polyesters: From synthesis to applications

During the last two decades, hyperbranched polymers have become the focus of interdisciplinary research, and received considerable attention due to their unique chemical and physical properties as well as their potential applications. As an important class of hyperbranched polymers, aromatic hyperbranched polyesters have attracted increased interest and are intensively studied because of their excellent thermal stability, chemical resistance, and mechanical properties. This article reviews the developments in synthesis, modifications, and applications of aromatic hyperbranched polyesters.     

Surface Modification of Polyhydroxyalkanoates toward Enhancing Cell Compatibility and Antibacterial Activity

Biomaterials for in vivo application should induce positive interaction with various histocytes and inhibit bacteria inflection as well. Cells and/or bacteria response to the extracellular environment is therefore the basic principle to design the biomaterials surface in order to induce the specific biomaterial–biological interaction. Polyhydroxyalkanoate (PHAs) are of growing interests because of their natural origin, biodegradability, biocompatibility, and thermoplasticity; however, quite inert and intrinsic hydrophobic characteristics have hindered their extensive usage in medical applications. Surface modification of PHAs tailors the chemistry, wettability, and topography without altering the bulk properties, and introduces specific proteins/peptides and/or antibacterial agents to mediate cell–matrix interactions. This review describes the recent developments on the surface modification of PHAs to construct cell compatible and antibacterial surfaces.     

聚酯生物降解及评价方法研究

塑料“白色污染”越来越引起人们的广泛关注,在自然界微生物的作用下能降解成为二氧化碳、水和无机物的生物降解材料是解决问题的一种有效途径。新型生物降解聚酯的开发离不开对材料生物降解性能的研究和评价方法的开发,为此,本文评述了生物降解聚酯的类型及其生物降解性能、聚酯降解微生物与酶的研究进展,介绍了土壤、堆肥和水体环境中的材料生物降解性评价方法。可以看到低成本、高性能是生物降解聚酯的发展方向;现有聚酯降解微生物和酶尚不能满足聚酯工业回收应用要求,需开发更高效、更稳定的酶;目前生物降解评价方法受接种环境影响大、评价周期长且难完全模拟材料在自然环境中生物降解行为,新型生物降解聚酯的开发也亟需可靠、快速的降解评价方法。     

Lignocellulosic and marine biomass as resource for production of polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are considered as sustainable ‘green/bio plastics’ because they have potential to replace their depleting petroleum-based competitors in the recent future. To reach this goal, PHAs must be able to compete with the established petroleum-based plastics in both technical and economic aspects. The current PHA production is based on high-priced substrates of high nutritional value and simple carbon sources such as glucose, sucrose, starch, or vegetable oils. Non-food based carbon-rich complex polysaccharides of lignocellulosic and marine biomass can be used as alternative and suitable feedstock through consolidated bioprocessing (CBP). CBP is a promising strategy that involves the production of lytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products in a single process step. CBP offers very large cost reductions if microorganisms possessing the abilities are found or microbial processes are developed to utilize substrate and simultaneously produce products. This review focuses on possible available complex polysaccharides of lignocellulosic and marine biomass that can be used as resources to produce PHAs in biorefineries, including CBP.     

Selected Applications of Chitosan Composites

Chitosan is one of the emerging materials for various applications. The most intensive studies have focused on its use as a biomaterial and for biomedical, cosmetic, and packaging systems. The research on biodegradable food packaging systems over conventional non-biodegradable packaging systems has gained much importance in the last decade. The deacetylation of chitin, a polysaccharide mainly obtained from crustaceans and shrimp shells, yields chitosan. The deacetylation process of chitin leads to the generation of primary amino groups. The functional activity of chitosan is generally owed to this amino group, which imparts inherent antioxidant and antimicrobial activity to the chitosan. Further, since chitosan is a naturally derived polymer, it is biodegradable and safe for human consumption. Food-focused researchers are exploiting the properties of chitosan to develop biodegradable food packaging systems. However, the properties of packaging systems using chitosan can be improved by adding different additives or blending chitosan with other polymers. In this review, we report on the different properties of chitosan that make it suitable for food packaging applications, various methods to develop chitosan-based packaging films, and finally, the applications of chitosan in developing multifunctional food packaging materials. Here we present a short overview of the chitosan-based nanocomposites, beginning with principal properties, selected preparation techniques, and finally, selected current research.     

A review on the processing–morphology–property relationship in biodegradable polymer composites containing carbon nanotubes and nanofibers

Carbon nanofillers containing biodegradable polymer composites have become an emerging frontier in materials science and engineering because of their potential as environmentally friendly materials in multiple applications, from load-bearing to advanced packaging to biomedical applications. Herein, we present the effect of processing parameters on the final morphology and the resulting properties of the biodegradable polymer composites containing carbon nanotubes (CNTs) or carbon nanofibers (CNFs). Various strategies can be employed to develop such composites; however, the type of morphology, which results during processing, significantly affects the final properties of the obtained composites. Therefore, various processing strategies such as melt-blending, additive manufacturing, and electrospinning are critically reviewed, together with the potential applications in load-bearing, tissue engineering, electromagnetic shielding, gas sensing, and packaging. Finally, we discuss the existing challenges and future directions in designing CNTs/CNFs containing biodegradable polymer composites with desired properties.     

Influence of recycling of poly(lactic acid) on packaging relevant properties

The most promising representative of biodegradable plastics in packaging applications is polylactide (PLA). Despite this, there is only a small market of PLA in Europe. Reasons for that are the high price of PLA raw material and the lack of knowledge of the behavior in packaging applications. It has a number of peculiarities so producers of plastics packaging hesitate to use it. Like other polyesters, it can degrade at increased temperatures in the presence of moisture by hydrolysis whereby it loses its physical and chemical properties. In all production processes, production waste is generated (i.e., stamping grids or edge trim). In most cases, this waste is used. It is not known in detail, how an internal recycling process will influence the final product properties. One problem is hydrolysis by which the production waste is partially degraded. Target of this study is to analyze the recycling process of PLA within the context of necessary process adaptions and the effects upon ecological efficiency. Films for packaging containing multiple types and amounts of production waste will be produced by extrusion and tested concerning their mechanical properties. The analysis of the recycling behavior showed that internal PLA production waste is well suitable for recycling. The influence of the recycling on the molecular weight is negligible. The effect on the viscosity and thus on the extrusion process is higher. Packaging relevant properties like mechanical or optical properties are hardly influenced. Especially recycling with a recycling quota of up to 50% has an insignificant effect on the film properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41532.     

Extraction and purification of Polyhydroxyalkanoates (PHAs): application of Thermoseparating aqueous two-phase extraction

Being biodegradable, non-toxic and renewable as well as having similar or better properties than commercial plastics, polyhydroxyalkanoates (PHAs) can be a potential game changer in the polymer industry. Although viewed as a sustainable alternative to petrochemicals due to its biodegradability, PHAs are plagued with low commercial value due to their high production and recovery costs. Having the benefits of providing a mild environment for bioseparation, being environment-friendly and scalable, together with it its distinctive thermoseparating properties and ease of recyclability, thermoseparating-based aqueous two-phase extraction (ATPE) has provided the eco-friendly and economical solution to the PHA dilemma. ATPE-influencing factors such as types of thermoseparating polymer, concentration of phase-forming components, pH, and effect of centrifugation were investigated. Under the condition of 14 wt/wt% of EOPO 3900 concentration, 14 wt/wt% of ammonium sulfate concentration and pH 6 without the needs for extra centrifugation steps, a recovery yield and a purification factor of up to 72.2% and 1.61 fold can be achieved with the copolymers which can be recycled and reused twice. Thermoseparating ATPE has thus been proven to be a powerful primary purification tool for PHAs.     

Nanocellulose-Polymer Composites for Applications in Food Packaging: Current Status,Future Prospects and Challenges

Nanocellulose has potential applications across the several industrial sectors and addresses a lot of issues related to environmental concern. As biodegradable filler in composite manufacturing, coating, and self-standing thin films, it offers novel and promising properties. Very few available reviews report on nanocellulose-impregnated composite materials for food packaging. Nanocellulose reinforcement is found to be promising for mechanical and barrier properties of composite for biopolymer and synthetic polymer. In this paper, we provide a thorough review of recent advances of nanocellulose synthesis and its application as a filler material for production of nanocomposites to be used for food packaging.