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In the present paper, we describe how a robust and fundamental methodology was developed for extraction and determination of a principal natural toxin compound, simplexin, from a series of bulk biocomposites. These complex matrices were fabricated by direct encapsulating either ground plant particles or an ethanolic crude extract of the Australian toxic pasture plant Pimelea trichostachya in the biodegradable polymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate). Proton nuclear magnetic resonance spectroscopy was initially employed to examine the chemical compositions of these complicated systems. Then, a more sensitive strategy was developed and validated by combining solid-phase extraction and ultrahigh-performance liquid chromatography hyphenated with a quadrupole Orbitrap mass spectrometer for the quantification of simplexin embedded in different biocomposites. Satisfactory linearity (R2 > 0.99) and recovery ranges (86.8–116%) with precision (relative standard deviations) of between 0.2 and 13% (n = 3) were achieved from seven biocomposites. The established protocol was further shown to be accurate and reliable in confirming the homogeneous distribution of the simplexin in different biocomposite formulations. A limited mass transfer of simplexin (< 3.5%) from one of the biocomposites into a simulated but sterilized in vitro rumen environment after a 10-day incubation was also revealed by utilizing the method. This quantitative analysis of targeted natural product within plant material-integrated polymeric platforms has potential application when controlled release is required in the bovine rumen and other biological systems.

High-resolution micro-computed tomography (μ-CT) provides new insights into the release of water-soluble crystalline materials from hydrophobic polymer matrices. This technique was applied to investigate the complex pathways underpinning the release of the agrichemical dicyandiamide (DCD), a common crystalline, water-soluble nitrification inhibitor, following its encapsulation in a biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) matrix at a loading of 250 g kg−1. Such a material allows controlled DCD delivery and improves its stability in tropical cropping systems. The insights gained from the use of this advanced 3-D imaging technique has led to a new understanding of the processes driving release of active agents and will aid the modelling and design of such tailored delivery formulations. These insights are broadly applicable and relevant to various soluble crystalline agrichemicals, drugs and medical implants. The release rate from DCD-PHBV pellets, fabricated through industrially relevant extrusion processing, was initially rapid, exponentially decaying over the first eight weeks. This was followed by a very gradual, linear release over the next 18 weeks. High-resolution μ-CT (0.5 μm) led to two important conclusions: i) the DCD that was rapidly mobilized existed within channels connected to the surface of the pellet, and ii) fine cracks present before and after release may explain the very slow mobilisation from the eighth week onward. Revealing the microstructure of this type of composite improves our current understanding of the mechanisms controlling the release of soluble crystalline materials encapsulated in a hydrophobic biodegradable polymer matrix.

Polycyclic hydrocarbons are known to be efficient hydrogen carriers capable of yielding high purity H2 upon dehydrogenation. Due to their high hydrogen density, high boiling point, and stability, these compounds demonstrate the potential to be used as hydrogen donors under catalytic transfer hydrogenation (CTH) conditions. In this work, the potential of a suite of hydrogen carriers to donate hydrogen, as well as the mechanisms affecting their hydrogen transfer, are assessed through the CTH of guaiacol, on Pd/Al2O3, as a model system. The results indicated the following descending order of transfer hydrogenation rate: bicyclohexyl > tetralin » hydrogenated terphenyl (HTP) > cyclohexylbenzene. Among the products, cyclohexanone and phenol are the most abundant, directly resulting from CTH. Detailed analysis of the hydrogen carrier conversion and selectivity clearly shows that the potential for CTH is highly linked to the molecular structure of the donor, rather than the amount of hydrogen available for transfer. A density functional theory (DFT) study, supported by experimental data, reveals that when unsaturated hydrocarbons are utilized, such as tetralin, cyclohexylbenzene, and HTP, the effective CTH rate to guaiacol is limited, despite dehydrogenation being more favorable for those molecules than from fully saturated donors, such as bicyclohexyl.

Coiled-coils with defined assembly properties are attractive materials for the manufacture of peptide-based hybrid nanomaterials. In tailoring such peptide assemblies, the incorporation of aromatic residues is increasingly being investigated due to their potential to deliver controllable functionalities, such as interaction with aromatic porphyrins, carbon nanotubes, or graphene. Aromatic residues have the potential to either destabilise or stabilise the α-helical peptide structure, depending on the quantity, type, combination, and position of these residues in the peptide chain. In this work, we used a known synthetic three heptad repeat peptide containing no aromatic residues as an α-helical template. We then substituted the aliphatic residues with two different types of aromatic residues (phenylalanine and tryptophan), varying their number, position, and combination in the peptide chain as a preliminary assessment of the impact on peptide architecture. Circular dichroism (CD) spectroscopy combined with coarse-grained (CG) and all-atom (AA) molecular dynamics (MD) simulation were used to analyse the peptide structure and assembly. Aromatic residues designed to be within the hydrophobic core were had impact on self-assembly than those placed on the outer face of the coil. Tryptophan was seen to destabilise α-helical structure more than phenylalanine, potentially due to steric hindrance and hydrogen-bonding interactions. Using atomic force microscopy (AFM) and supported by CG-MD simulation, substituting all phenylalanine residues with tryptophan appeared to completely destabilise fibril-formation propensity. Subsituting tryptophan into the first heptad repeat was seen to have a greater impact on fibril formation compared to subtitution into the third heptad repeat, suggesting the importance of sequence design. These results add to the body of knowledge used to inform the design of α-helical peptides when incorporating aromatic residues.

Nanocellulose, as a biobased versatile nanomaterial that can be derived with tailorable surface functionalities, dimensions, and morphologies, has considerable implications for modifying the rheology, mechanical reinforcement, and influencing the carbonization efficiency in the production of polyacrylonitrile (PAN)-based carbon fibers. Herein, we report the influence of three different nanocellulose types, varying in the derivatization method, source, and aspect ratio, on the mechanical properties and thermal transformations of solution-spun PAN/nanocellulose nanocomposite fibers into carbon fibers. The incorporation of 0.1 wt % nanocellulose into solution-spun PAN fibers led to a 7-19% increase in tensile modulus and 0-27% increase in tensile strength in the solution-spun fibers, compared to a control PAN fiber. These improvements varied depending on the nanocellulose type. After low-temperature carbonization at 1200 °C, improvements in the mechanical properties of the nanocellulose-reinforced carbon fibers, compared with a PAN fiber, were also observed. In contrast to the precursor fibers, the improvement % in the carbonized fibers was found to be dependent on the nanocellulose morphology and was linearly correlated with increasing aspect ratio of nanocellulose. For example, in carbon fibers with a cotton-derived low-aspect-ratio cellulose nanocrystal and spinifex-derived high-aspect-ratio CNC and nanofiber, up to 4, 87, and 172% improvements in tensile moduli were observed, respectively. Due to the processing methods used, the nanocellulose aspect ratio and crystallinity are inversely related, and as such, the increase in the carbon fiber mechanical properties was also related to a decrease in crystallinity of the nanocellulose reinforcers. Raman spectra and electron microscopy analysis suggest that mechanical improvement after carbonization is due to internal reinforcement by highly ordered regions surrounding the carbonized nanocellulose, within the turbostratic carbon fibers.

The crystallisation of a range of as-produced poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer blends from a mixed culture polyhydroxyalkanoate production process, with low (15%), high (82%) and intermediate (62% and 50%) average 3-hydroxyvalerate (3HV) contents, was studied at different temperatures using polarised optical microscopy, differential scanning calorimetry and X-ray crystallography. The low-3HV content material had narrow compositional distribution and crystallised in the typical highly regular banded spherulite morphology, while the other materials displayed varying degrees of interpenetrating crystallisation of separate crystal phases comprising either the 3HV or 3-hydroxybutyrate (3HB) crystal lattice structure. Because of the differing and competing crystallisation kinetics of these phases coupled with diffusion effects, there was a very strong influence of crystallisation temperature on the resulting morphology. Thus manipulation of the final material properties of such copolymeric materials is dependent on understanding these effects and controlling their processing and crystallisation temperatures and conditions.

Significant efforts have recently been invested in assessing the physical and chemical properties of microbial nanowires for their promising role in developing alternative renewable sources of electricity, bioelectronic materials and implantable sensors. One of their outstanding properties, the ever-desirable conductivity has been the focus of numerous studies. However, the lack of a straightforward and reliable method for measuring it seems to be responsible for the broad variability of the reported data. Routinely employed methods tend to underestimate or overestimate conductivity by several orders of magnitude. In this work, synthetic peptide nanowires conductivity is interrogated employing a non-destructive measurement technique developed on a terahertz scanning near-field microscope to test if peptide aromaticity leads to higher electrical conductivity. Our novel peptide conductivity measurement technique, based on triple standards calibration method, shows that in the case of two biopolymer mimicking peptides, the sample incorporating aromatic residues (W6) is about six times more conductive than the negative control (L6). To the best of our knowledge, this is the first report of a quantitative nano-scale terahertz s-SNOM investigation of peptides. These results prove the suitability of the terahertz radiation-based non-destructive approach in tandem with the designer peptides choice as model test subjects. This approach requires only simple sample preparation, avoids many of the pitfalls of typical contact-based conductivity measurement techniques and could help understanding fundamental aspects of nature’s design of electron transfer in biopolymers.

Wood fibre reinforced polyhydroxyalkanoate (PHA) composites have attracted significant interest as promising new sustainable biocomposites. However, their manufacture can be challenging due to PHA's relatively low thermal stability and melt viscosity. There is currently a lack of understanding of the effect of extrusion processing parameters on the molecular weight of the PHA matrix and, ultimately, on the mechanical properties of the composites. In this study, we show that commercially-relevant mechanical properties of a wood-poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) composite can be achieved through extrusion processing, even at temperatures as high as 190 °C, by adjusting screw speed and feeding rate, and consequently the induced shear rate and residence time. Moreover, the mechanical properties of 40 wt% wood-PHBV were found to be superior to properties previously reported in the literature. Relative to neat PHBV, a 73% increase in modulus and 80% retention of tensile strength was achieved. A Taguchi approach to experimental design was adopted to systematically investigate the effect of extrusion parameters (temperature profile, screw speed, feeding rate, and fibre mixing) on the processing of neat PHBV biopolymer and wood-PHBV composites with wood contents of 10, 20, 30, and 40 wt%. Evaluation of the mechanical performance was conducted through testing of tensile strength, tensile modulus and strain at maximum load. Changes in molecular weight were analysed via gel permeation chromatography (GPC). For both neat PHBV and wood-PHBV composites, molecular weight Mw was found to decrease under high shear stress and long residence time from 550-650 kDa to 350–550 kDa. However, Mw reductions were not enough to result in a decrease of mechanical performance. This discovery is significant for industrial-scale production as it shows that the processing window for wood-PHBV composites is not as narrow as expected, because thermal degradation can be limited by optimising a combination of processing parameters.

The photooxidative stability of an aromatic segmented poly(urethane-urea) (PUU) elastomer, stabilised with a range of carbon black fillers, was assessed after very low UVA doses as a means to identify components that are highly susceptible to UV degradation, and suggest better design of such materials. Fourier-transform infrared (FTIR) analysis indicated rapid degradation of the urea bonds in the hard segments, followed by chain scission and photo-Fries reaction of the urethane linkages. In the soft segments, the oxidation of the original ether groups resulted in the formation of large amounts of ester groups, while some crosslinking of the ether groups was also evident. Carbon black provided moderate protection against degradation, with the smallest-sized particles being the most effective. Protection was evidenced by reduced surface cracking as well as an increased resistance to chemical changes in both the soft segments and hard segments. Even so, significant degradation was still evident at low UV doses suggesting that further stabilisation is required to increase the UV durability of these elastomers and improve their long-term performance.\ud \ud

Lignin, an inexpensive renewable biopolymer that offers both aliphatic and aromatic hydroxyl ( OH) functional groups, is a potential raw material for the polyurethane industry. Contemporary approaches for incorporating lignin in rigid polyurethane foam (RPUF) involve mechanical mixing of microscale lignin powder under ambient conditions or at high loading levels, resulting in the RPUF with inferior compressive mechanical and thermal conductivity properties compared to petrochemical-based controls. Herein, we demonstrate a significant improvement in the dispersion of an industrial grade kraft lignin in a polyol mixture (96% sucrose/glycerine initiated polyether polyol and 4% glycerol) by dispersing at high-temperature (120 °C, 12 h) resulting in RPUF with enhanced performance. Through this methodology, the polyol/lignin dispersion with 5 wt.% lignin has afforded a simultaneous improvement in thermal insulation (by 5%) and compressive strength (by 4%) of RPUF compared to the control and such a property profile, to the best of our knowledge, has not yet been achieved in lignin substituted RPUF systems.

Electron transfer is central to cellular life, from photosynthesis to respiration. In the case of anaerobic respiration, some microbes have extracellular appendages that can be utilised to transport electrons over great distances. Two model organisms heavily studied in this arena are Shewanella oneidensis and Geobacter sulfurreducens. There is some debate over how, in particular, the Geobacter sulfurreducens nanowires (formed from pilin nanofilaments) are capable of achieving the impressive feats of natural conductivity that they display. In this article, we outline the mechanisms of electron transfer through delocalised electron transport, quantum tunnelling, and hopping as they pertain to biomaterials. These are described along with existing examples of the different types of conductivity observed in natural systems such as DNA and proteins in order to provide context for understanding the complexities involved in studying the electron transport properties of these unique nanowires. We then introduce some synthetic analogues, made using peptides, which may assist in resolving this debate. Microbial nanowires and the synthetic analogues thereof are of particular interest, not just for biogeochemistry, but also for the exciting potential bioelectronic and clinical applications as covered in the final section of the review. Statement of Significance Some microbes have extracellular appendages that transport electrons over vast distances in order to respire, such as the dissimilatory metal-reducing bacteria Geobacter sulfurreducens. There is significant debate over how G. sulfurreducens nanowires are capable of achieving the impressive feats of natural conductivity that they display: This mechanism is a fundamental scientific challenge, with important environmental and technological implications. Through outlining the techniques and outcomes of investigations into the mechanisms of such protein-based nanofibrils, we provide a platform for the general study of the electronic properties of biomaterials. The implications are broad-reaching, with fundamental investigations into electron transfer processes in natural and biomimetic materials underway. From these studies, applications in the medical, energy, and IT industries can be developed utilising bioelectronics.

This study aims to understand the material properties and long-term indoor stability of a biocomposite based on pine wood flour and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) modified by a nucleating agent, boron nitride (BN), and an inorganic filler, talc, and to develop knowledge of the linkage between the microscale-structure and mechanical properties. Both BN, at a loading of 1 wt% and talc, at 5 wt%, had a nucleating effect on polymer crystallisation, with BN being more effective as evidenced by Avrami kinetic analysis. The addition of 5 and 10 wt% of talc enhanced the tensile strength of the PHBV/wood flour (50/50 wt%) composite from 22.3 ± 1.3 MPa (mean ± 95% confidence interval) to 24.3 ± 0.6 MPa and 24.7 ± 0.9 MPa respectively. The tensile modulus was also improved from 5.6 ± 0.6 GPa to 6.9 ± 0.4 GPa and 8.1 ± 0.7 GPa respectively. The micron-sized talc may fill voids within the composite matrix and/or act as an alternate filler, altering the deformation mechanism. However, the level of improvement in modulus was reduced after 1 year of conditioned ageing under a controlled environment (20 °C, 50% humidity). It is proposed that the combined effects of the swelling of wood through moisture uptake, the shrinkage of PHBV through secondary crystallisation, and the localised stress around talc particles led to weakened talc-PHBV interfaces.

This paper is an overview of current understanding in the areas of composites made from biodegradable thermoplastics and wood fillers. The review finds that the composite properties depend on the type of wood filler, the choice of polymer matrix, the wood filler content, the compatibilization technique used and the processing parameters. The extent of interfacial adhesion and the filler morphology are identified as the underlying factors that control the composite properties. Future research needs are identified, including establishment of fundamental relationships between quantified interfacial adhesion and end-use properties and advanced modelling of biodegradation processes.

The service lifetime of polymer films is controlled by the chemical reactions leading to chain scission and the mediating environmental factors. For application as agricultural cropping film, controlled accelerated degradation is required. For a photo-sensitive linear low density polyethylene (LLDPE) + 1% nano-titania (as the anatase/rutile mixed phase P25), the environmental factors are not only UV dose and temperature but also soil parameters such as moisture and organic material content. This provides a challenge in predicting the useful lifetime from laboratory accelerated ageing studies. To enhance degradation when the (LLDPE + 1% P25) is buried, UV-C pre-irradiation has been shown to accelerate strength loss but the rate of embrittlement is not sufficient for the application as crop propagation film. Biodegradable poly(butylene adipate-co-terephthalate) or PBAT has a higher rate of degradation when buried outdoors in soil than when buried under laboratory conditions: The elongation at break fell from 900% to 70% in one month in the field while similar changes required 6 months in the laboratory. The small changes in M n ¯ for embrittlement in the field suggests that the loss of mechanical properties was not linked to bulk property changes but rather to surface morphology (cracks and holes) as seen by SEM. This suggests that even in thin films, enzyme-mediated hydrolysis of PBAT is surface controlled. DNA analysis of the soil around the buried films after 35 days ageing outdoors showed fungi play a more dominant role in PBAT biodegradation compared to bacteria. UV degradation of PBAT film is controlled by the photochemistry of the terephthalate moiety in the polymer and the development of fluorescence is a useful indicator of the extent of photo-degradation.

The partial oxidation of dodecane and paraffin wax with bromine at relatively low temperatures (≤120 °C) and the dehydrobromination of the subsequent alkyl bromide intermediates at higher temperatures (>175 °C) to form higher alkenes were investigated. Products were analyzed using nuclear magnetic resonance spectroscopy, gas chromatography, and mass spectrometry. Bromination favored the formation of alkyl bromides on internal carbons of the model long chain alkanes over terminal sites. At lower temperatures (∼90 °C), ultraviolet photochemical initiation of bromination was necessary, while above 105 °C, thermally initiated bromination was observed. Photochemical bromination was found to be inhibited by water and oxygen. The formation of alkenes by the dehydrobromination of the alkyl bromides was observed by temperature-programmed reaction to occur at higher temperatures for n-dodecane (∼190 °C) than for the mixed alkanes in paraffin wax (∼175 °C).

The determination of the safe working life of polymer materials is important for their successful use in engineering, medicine and consumer-goods applications. An understanding of the physical and chemical changes to the structure of widely-used polymers such as the polyolefins, when exposed to aggressive environments, has provided a framework for controlling their ultimate service lifetime by either stabilising the polymer or chemically accelerating the degradation reactions. The recent focus on biodegradable polymers as replacements for more bio-inert materials such as the polyolefins in areas as diverse as packaging and as scaffolds for tissue engineering has highlighted the need for a review of the approaches to being able to predict the lifetime of these materials. In many studies the focus has not been on the embrittlement and fracture of the material (as it would be for a polyolefin) but rather the products of degradation, their toxicity and ultimate fate when in the environment, which may be the human body. These differences are primarily due to time-scale. Different approaches to the problem have arisen in biomedicine, such as the kinetic control of drug delivery by the bio-erosion of polymers, but the similarities in mechanism provide real prospects for the prediction of the safe service lifetime of a biodegradable polymer as a structural material. Common mechanistic themes that emerge include the diffusion-controlled process of water sorption and conditions for surface versus bulk degradation, the role of hydrolysis versus oxidative degradation in controlling the rate of polymer chain scission and strength loss and the specificity of enzyme-mediated reactions.

The photo-oxidative degradation of two complementary linear low density polyethylene (LLDPE) films has been studied: a Ziegler-Natta catalysed 1-octene copolymer (ZN-LLDPE) and a 1-octene copolymer produced by a single site constrained catalyst (m-LLDPE). The degradation processes were followed using a range of characterisation techniques including tensile testing, GPC, MAS-NMR, FTIR, WAXS and SAXS. The chemical species formed on degradation were similar for both polymers. Both also showed an increase in crystallinity and modulus with UV ageing time and a decrease in the long spacing of the lamella. However, the m-LLDPE showed a significantly shorter time to embrittlement than the ZN-LLDPE, which correlated in both polymers with the disappearance of the second yield point. The major observed difference in crystalline structure was a significantly higher interfacial thickness between the crystalline lamellae and the amorphous regions for the ZN-LLDPE, which decreased rapidly on UV ageing. This difference in behaviour was attributed to the nature of the branching in the ZN-LLDPE, which was presumed to sit in blocks along the chain and thus to reside in the interfacial regions. Cleavage of the tertiary carbons in these interfacial regions was less damaging to the mechanical properties than for the m-LLDPE, where chain scission broke more of the tie molecules, thus limiting the ability of the polymer to draw. . This work advances our understanding of polymer microstructural evolution during degradation and the implications of initial polymerisation route and molecular structure on the degradation mechanisms.

The energy requirements for the production of high quality carbon fiber and other carbon-based materials made by carbonization is a key factor limiting the commercial application of these materials. With the aim of enhancing the carbonization efficiency, we have prepared polyacrylonitrile (PAN) based precursor materials doped with high aspect-ratio cellulose nanofibers (CNF) derived from Australian spinifex grass (T. pungens). This was achieved by systematically investigating the rheology and electrospinning properties of composite fibers of PAN and CNF prepared at various CNF concentration levels and subsequently stabilized and carbonized. The carbon properties were characterized by X-ray diffraction and Raman spectroscopy. Upon carbonization, the incorporation of CNF into the PAN precursor led to changes in the crystallite and graphitic structure of the carbon materials, and these changes found to be closely related to the CNF concentration. CNF loadings of 0.5–2 wt % resulted in spinnable solutions wit...

The limiting features of existing ammonium-recovery technologies, such as pH-dependency, inefficient manufacturing, and low removal capacity of ammonium sorbents, limit their commercial application potential. To overcome these technical limitations, we employed reactive extrusion (REx) as a sustainable alternative synthesis method to prepare cost-effective ammonium sorbents based on starch-copolymers. This paper describes the graft copolymerization of starch with acrylamide and 2-acrylamido-2-methylpropane-sulfoacid monomers using twin-screw extrusion technology and evaluates the resulting products’ structural features and ammonium uptake capacity. The relationship between the starch molecular structure and effectiveness of the REx process was studied by monitoring the specific mechanical energy, die pressure and torque during the extrusion process. The impact of the starch features on the product’s chemical structure, thermal resistance, and swelling capacity was also determined. The ATR-FTIR, 1H NMR, and TG-DSC and elemental analysis confirmed the success of the proposed REx method for producing starch-copolymers, with an average graft efficiency of ∼65% across all samples. The starch structure and chemical composition controlled the grafting reaction efficiency, but had limited influence on monomer conversion. Cationic starch produced amphoteric copolymers that behaved similarly to acrylamide-based polyampholytes in electrolyte solutions. The starch- copolymer’s adsorption capacity increased proportionally with the initial ammonium concentration and remained constant within the pH range of ∼5.5–8.5. A monolayer adsorption capacity of ∼23 mg/g was recorded for the as-prepared starch-copolymer at 25 °C, comparable with those of the hydrogel sorbents at ambient temperature. This study highlights the potential of the as-prepared starch-copolymers as a cost-effective material solution for achieving sustainable ammonium removal.

Polyethylene as a polymeric precursor for carbon fibre production has attracted much attention over recent years. Not only is it a low-cost commodity polymer, it has a higher theoretical carbon yield (at 100%) than polyacrylonitrile (at 67%) and is very readily melt processed into fibres. The challenge is to efficiently dehydrogenate and graphitize polyethylene fibres. This paper explores the use of bromine as a novel oxidant to functionalise polyethylene prior to carbonisation, leading to efficient cyclisation and carbonisation on heating. Through a process of low-temperature photo-induced liquid-phase bromination followed by dehydrobromination at moderate temperature and subsequent carbonisation to 800 °C, a carbonaceous product was obtained in high carbon yield (>90%). The effects of a range of process conditions, as well as the use of different types of polyethylene and polyethylene blends, were explored.

Polyhydroxyalkanoate (PHA) biopolymers are emerging as attractive new sustainable polymers due to their true biodegradability and highly tuneable mechanical properties. However, despite significant investments, commercialisation barriers are hindering the capacity growth of PHA. In this work, we investigated the market potential for wood plastic composites (WPCs) based on PHAs. We considered the latest global production capacity of PHAs, estimated at 66,000 tonnes/year, and examined the implications of using PHAs for WPC production on the WPC market. Results indicate that a hypothetical usage of the current global PHA production for WPC manufacture would only represent the equivalent of 4.4% of the global WPC market, which is currently experiencing a 10.5% compounded annual growth rate. An economic assessment revealed that a wood-PHA composite as a drop-in alternative WPC product could cost as little as 37% of the cost of its neat PHA counterpart. Thus, WPCs with PHA offer a means to access benefits of PHA in engineering applications at reduced costs, however, further developments are required to improve strain at failure. The successful adoption of wood-PHA composites into the market is furthermore reliant on support from public sector to encourage biodegradable products where recycling is not a ready solution.

To promote the large-scale production of starch-based biomaterials, we developed a method of synthesis based on reactive extrusion that combines the benefits of continuous manufacturing with the use of green chemistry principles. This paper describes the grafting of four different types of starches with acrylamide monomers via free radical copolymerization using twin-screw extrusion technology. The elemental analysis confirmed the success of this method, with an average monomer conversion of 80% and grafting efficiency of ˜74% across all samples. The 13C-NMR/1H-NMR and ATR-FTIR analysis revealed that the type of starch substrate used strongly influenced the mechanism of the grafting reaction. Thermal analysis (TG/DTG-DSC) indicated that the graft-copolymers thermal stability was influenced by the amylose-amylopectin content ratio. Swelling tests suggested that cationic modification of the substrate is a promising approach to produce stimuli-responsive graft-copolymers via reactive extrusion. The proposed method has proved to be a viable alternative for the production of starch-copolymers.

The present study investigates the effects of copolymer composition on the mechanical properties of extruded mixed culture poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB) copolymers and their composites with 50 wt% wood flour. The use of copolymers with a higher strain at break (i.e. 24 mol% 3-HV and 15 mol% 4-HB copolymers) for composite production resulted in a slight but promising improvement in strain at break at the cost of lower strength and modulus. The inclusion of 4-HB comonomer was more effective at improving the strain at break of the composites than for the 3-HV comonomer due to the inability of the 4-HB monomer unit to co-crystallise. However, unlike for the tensile properties, the matrix properties did not affect the composite impact strength. It is interpreted that the mechanical properties of the PHA-based WPCs with 50 wt% wood content are dominated by the rigid and brittle wood flour, with the matrix properties having limited influence on the bulk composite properties.

The mechanical properties of poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) copolymers with 3HV unit content ranging from 12 mol% to 72 mol% were evaluated. Samples were produced using a naturally enriched mixed culture fed with acetic and propionic acids. A range of feeding strategies was used to explore the manipulation of comonomer composition and sequence distribution of the monomeric units in order to influence mechanical properties. GC/MS, 13C NMR and DSC analysis of the resulting solvent cast films revealed that the as-produced PHAs were a mixture of copolymers distinct in microstructure and/or composition. Atomic force microscopy demonstrated the formation of varying phase structures as well as surface morphologies. In spite of the range of microstructure or compositional variation that was achieved through feeding strategies, all samples but one exhibited mechanical properties similar to the homopolymer P(3HB). The one distinct copolymer, with 43 mol% 3HV content, showed significantly increased elongation to break, as assessed after 2 weeks of ageing. These results were attributed to the formation of different phase structures arising from the competition between cocrystallisation and phase segregation in blends of semicrystalline copolymers.

This work investigates the use of polyhydroxyalkanoate (PHA) films as moisture barriers for thermoplastic starch (TPS) films, to produce biodegradable, multi-layer materials with high gas barrier properties. This is a necessary extension to the limited work available on this topic and confirms that PHAs are suitable coating materials for TPS films intended for use in food packaging. Under storage conditions of up to 75% relative humidity (RH) for 2 weeks, a PHA coating maintained the moisture content (MC) of the TPS below the point at which its barrier properties were detrimentally affected. Furthermore, for PHBV coating thicknesses of 91–115 μm, the MC of the TPS remains significantly lower than uncoated TPS for the duration of the experiment (>25 days). The flux of water into the coated TPS fit to a model based on Fick's law. However, when the multi-layered films were stored at 95% RH delamination occurred within 24 h. Preliminary investigation into possible material design improvements showed that the addition of a small amount of PHA to the TPS layer prolonged the time to delamination.

This study represents the first detailed analysis of the thermal, morphological, and crystallization properties of the blend components within a range of mixed-culture polyhydroxyalkanoates (PHAs), with 3-hydroxyvalerate content in the as-produced materials and in the fractions ranging from low (12 mol %) to high (91 mol %). Both coarse and fine fractionation of the as-produced copolymers confirmed that they were blends of nominally blocky and/or random copolymers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), with very broad compositional distributions as governed by the PHA accumulation strategy. The crystallization kinetics and thermal properties of the fractions were found to be very significantly different from each other, consistent with the hypothesis that the overall mechanical properties were primarily controlled by the more rapidly crystallizing components. Two materials produced using an alternating feeding strategy demonstrated unique crystallization and thermal properties in their fractions, which are considered to have contributed to distinctly more elastic mechanical properties in these particular samples.

The filamentous peptide-based nanowires produced by some dissimilatory metal-reducing bacteria, such as Geobacter sulfurreducens, display excellent natural conductivity. Their mechanism of conduction is assumed to be a combination of delocalized electrons through closely aligned aromatic amino acids and hopping/charge transfer. The proteins that form these microbial nanowires are structured from a coiled-coil, for which the design rules have been reported in the literature. Furthermore, at least one biomimetic system using related synthetic peptides has shown that the incorporation of aromatic residues can be used to enhance conductivity of peptide fibers. Herein, the de novo design of peptide sequences is used to enhance the conductivity of peptide gels, as inspired by microbial nanowires. A critical factor hampering investigations in both microbiology and materials development is inconsistent reporting of biomaterial conductivity measurements, with consistent methodologies needed for such investigations. We have reported a method herein to analyze non-Ohmic behavior using existing parameters, which is a statistically insightful approach for detecting small changes in biologically based samples. Aromatic residues were found to contribute to peptide gel conductivity, with the importance of the peptide confirmation and fibril assembly demonstrated both experimentally and computationally. This is a small step (in combination with parallel research under way by other researchers) toward developing effective peptide-based conducting nanowires, opening the door to the use of electronics in water and physiological environments for bioelectronic and bioenergy applications.