Structure and physical properties of bacterially synthesized polyesters

Sustainable Materials with Enhanced Mechanical Properties Based on Industrial Polyhydroxyalkanoates Reinforced with Organomodified Sepiolite and Montmorillonite

Microplastics have become one of the greatest environmental challenges worldwide. To turn this dramatic damage around, EU regulators now want to ensure that plastic itself is fully recyclable or biodegradable. The aim of the present work is to develop a biobased and biodegradable biocomposite based on commercial polyhydroxyalkanoates (PHAs) and nanoclays, with the objective of achieving a reduction of rancid odour while avoiding any loss in thermomechanical properties, thus tackling two key disadvantages of PHAs. This research aims at completely characterising the structural, thermal and mechanical behaviour of the formulations developed, understanding the compatibility mechanisms in order to be able to assess the best commercial combinations for industrial applications in the packaging and automotive sectors. We report the development of nine nanobiocomposite materials based on three types of commercial PHA matrices: a linear poly(3-hydroxybutyrate) (P3HB); two copolymers based on poly(3-hydroxybutyrate)-co-poly(4-hydroxybutyrate) (P3HB-co-P4HB); and nanoclays, which represent a different polar behaviour. Dispersion achieved is highly relevant compared with literature results. Our findings show impressive mechanical enhancements, in particular for P3HB reinforced with sepiolite modified via aminosilanes.

Synthesis and Characterization of Electroconductive PHA- graft-Graphene Nanocomposites

With increasing demand of environmentally friendly materials, development on biobased polymers such as polyhydroxyalkanoate (PHA) is indispensable. An unsaturated PHA, namely, poly(3-hydroxydodecanoate- co-3-hydroxy-9-decenoate), short as P(3HDD- co-3H9D), provides possibilities for functionalization. Two different strategies are explored for synthesis of PHA- graft-graphene nanocomposites with graphene content ranging from 0.2 to 1.5 wt %. Chemical structures of intermediates and products were confirmed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Uniform dispersion of graphene was observed in formed PHA nanocomposites under scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). PHA- graft-graphene nanocomposites exhibited higher thermal degradation temperature and enhanced electricity conductivity compared with that of neat PHA. Moreover, lower critical filling content and lower electrical resistivity at same graphene content demonstrated enhanced electrical conductivity of PHA- graft-graphene nanocomposites compared with previously reported blends. The lowest electrical resistivity was 2 Ω·m in sample PHA- graft-graphene nanocomposites with approximately 1.5 wt % graphene content.

Scale-Up Fabrication of Biodegradable Poly(butylene adipate-co-terephthalate)/Organophilic-Clay Nanocomposite Films for Potential Packaging Applications

The development of biodegradable packing materials is a global priority due to the huge volumes of plastic refuse entering landfills and the environment. In this study, a series of biodegradable nanocomposite films based on poly(butylene adipate-co-terephthalate) (PBAT) and reinforced with an organophilic layered double hydroxide (OLDH) were scale-up fabricated. The OLDH nanosheets with a basal spacing of 4.07 nm were presynthesized on a large-scale by solvent-free high-energy ball milling. All of the PBAT/OLDH nanocomposite films (0.5-4 wt % OLDH) showed a uniform dispersion of OLDH nanosheets in the PBAT matrix. A PBAT/OLDH film containing 1 wt % OLDH (denoted herein as OLDH-1) demonstrated outstanding thermal, optical, mechanical, and water vapor barrier properties compared with a pure PBAT film (OLDH-0), including a 37% reduction in haze and a 41.9% increase in nominal tensile strain at break dramatically. Furthermore, the food packaging measurement revealed that the OLDH-1 film showed a better packaging effect than the pure PBAT film and commercial polyethylene packing materials. The feasibility of scale-up manufacture and the excellent processability, manufacturing scalability, mechanical performance, optical transparency, water vapor barrier properties, and food packaging performance of the PBAT/OLDH nanocomposite films encourage their future application as biodegradable packaging films.

Methanotrophic production of polyhydroxybutyrate-co-hydroxyvalerate with high hydroxyvalerate content

Type II methanotrophic bacteria are a promising production platform for PHA biopolymers. These bacteria are known to produce pure poly-3-hydroxybutyrate homopolymer (PHB). We isolated a strain, Methylocystis sp. WRRC1, that was capable of producing a wide range of polyhydroxybutyrate-co-hydroxyvalerate copolymers (PHB-co-HV) when co-fed methane and valerate or n-pentanol. The ratio of HB to HV monomer was directly related to the concentration of valeric acid in the PHA accumulation media. We observed increased incorporation of HV and total polymer under copper-free growth conditions. The PHB-co-HV copolymers produced had decreased melting temperatures and crystallinity compared with methanotroph-produced PHB.

Mass spectrometry for the elucidation of the subtle molecular structure of biodegradable polymers and their degradation products

Contemporary reports by Polish authors on the application of mass spectrometric methods for the elucidation of the subtle molecular structure of biodegradable polymers and their degradation products will be presented. Special emphasis will be given to natural aliphatic (co)polyesters (PHA) and their synthetic analogues, formed through anionic ring-opening polymerization (ROP) of β-substituted β-lactones. Moreover, the application of MS techniques for the evaluation of the structure of biodegradable polymers obtained in ionic and coordination polymerization of cyclic ethers and esters as well as products of step-growth polymerization, in which bifunctional or multifunctional monomers react to form oligomers and eventually long chain polymers, will be discussed. Furthermore, the application of modern MS techniques for the assessment of polymer degradation products, frequently bearing characteristic end groups that can be revealed and differentiated by MS, will be discussed within the context of specific degradation pathways. Finally, recent Polish accomplishments in the area of mass spectrometry will be outlined.

Fabrication of magnetite nanoparticle doped reduced graphene oxide grafted polyhydroxyalkanoate nanocomposites for tissue engineering application

In tissue engineering, the magnetic nanocomposites are more attractive due to some superior properties that promote in the monitoring of cell proliferation, differentiation and activation of cell construction in tissue regeneration phase.

Advances and needs for endotoxin-free production strains

The choice of an appropriate microbial host cell and suitable production conditions is crucial for the downstream processing of pharmaceutical- and food-grade products. Although Escherichia coli serves as a highly valuable leading platform for the production of value-added products, like most Gram-negative bacteria, this bacterium contains a potent immunostimulatory lipopolysaccharide (LPS), referred to as an endotoxin. In contrast, Gram-positive bacteria, notably Bacillus, lactic acid bacteria (LAB), Corynebacterium, and yeasts have been extensively used as generally recognized as safe (GRAS) endotoxin-free platforms for the production of a variety of products. This review summarizes the currently available knowledge on the utilization of these representative Gram-positive bacteria for the production of eco- and bio-friendly products, particularly natural polyesters, polyhydroxyalkanoates, bacteriocins, and membrane proteins. The successful case studies presented here serve to inspire the use of these microorganisms as a main-player or by-player depending on their individual properties for the industrial production of these desirable targets.

Effect of graphene content on the properties of poly(lactic acid) nanocomposites

Preparation of graphene reinforced poly(lactic acid) nanocompositesviasolution casting approach for packaging applications.

Phase morphology, physical properties, and biodegradation behavior of novel PLA/PHBHHx blends

In this study, two biodegradable polyesters [i.e., polylactic acid (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx)] with complementarity in terms of mechanical performance have been combined, and a series of blends with a broad range of compositions has been prepared by thermal compounding. The evolution of phase morphologies with the variation of compositions has been characterized by using Fourier transform infrared spectroscopic imaging together with scanning electron microscope analyses. Thermal, mechanical, and biodegradation properties of the PLA/PHBHHx blends were systematically investigated. Mechanical properties were further analyzed by using theoretical models and correlated with the results of the morphology/structure and compatibility of the blends. Results indicate that PLA/PHBHHx blends are immiscible but can be compatible to some extent at certain compositions (e.g., PLA/PHBHHx (w/w) = 80/20 and 20/80). The physical properties of the blend could be fine tuned by adjusting the blend composition.

Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in recombinant Corynebacterium glutamicum using propionate as a precursor

Lipopolysaccharides free P[3-hydroxybutyrate (3HB)-co-3-hydroxyvalerate (3HV)] production was achieved using recombinant Corynebacterium glutamicum harboring polyhydroxyalkanoate (PHA) biosynthetic genes from Ralstonia eutropha. Cells grown on glucose with feeding of propionate as a precursor of 3HV unit accumulated 8-47wt% of P(3HB-co-3HV). The 3HV fraction in the copolymer was varied from 0 to 28mol% depending on the propionate concentrations.

Bacterial polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyalkanoates (HAs) synthesized by numerous bacteria as intracellular carbon and energy storage compounds and accumulated as granules in the cytoplasm of cells. More than 80 HAs have been detected as constituents of PHAs, which allows these thermoplastic materials to have various mechanical properties resembling hard crystalline polymer or elastic rubber depending on the incorporated monomer units. Even though PHAs have been recognized as good candidates for biodegradable plastics, their high price compared with conventional plastics has limited their use in a wide range of applications. A number of bacteria including Alcaligenes eutrophus, Alcaligenes latus, Azotobacter vinelandii, methylotrophs, pseudomonads, and recombinant Escherichia coli have been employed for the production of PHAs, and the productivity of greater than 2 g PHA/L/h has been achieved. Recent advances in understanding metabolism, molecular biology, and genetics of the PHA-synthesizing bacteria and cloning of more than 20 different PHA biosynthesis genes allowed construction of various recombinant strains that were able to synthesize polyesters having different monomer units and/or to accumulate much more polymers. Also, genetically engineered plants harboring the bacterial PHA biosynthesis genes are being developed for the economical production of PHAs. Improvements in fermentation/separation technology and the development of bacterial strains or plants that more efficiently synthesize PHAs will bring the costs down to make PHAs competitive with the conventional plastics.