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This study shows the improvement of fire and microbe resistance of sustainable (protein) plastics (i.e. wheat gluten, WG), by using triethylene glycol diamine and dialdehyde. In addition, an anti-microbial agent (lanosol) was also used separately and in combination with the diamine/dialdehyde. The network formed by the diamine and dialdehyde, during the production of compression-moulded plates, resulted in high fire performance index, large amount of char and low thermal decomposition rate. The best fire resistance was obtained by the combination of the dialdehyde and lanosol, which also yielded a char with the intact surface. The peak-heat-release-rate of this material was only 38% of that of the pure gluten material. This material also showed anti-bacterial (E. coli) properties. However, the diamine was more effective than the combination of dialdehyde/lanosol. Gluten materials with diamine resisted mould growth during a 22 days test at a relative humidity of 100%. The gluten material with the lanosol applied to the sample surface resisted mould growth during a three-week test at both ambient temperature and 37 °C. Despite the relatively high contents of the difunctional reagents used (15 wt%), leading to an increased stiffness in most cases, only the network formed with glyoxal resulted in a decrease in water uptake as compared to the pure gluten material.

Three different charcoals (gluten char, pine bark char and carbon black) were used to rectify certain property disadvantages of wheat gluten plastic. Pyrolysis process of gluten was investigated by analysing the compounds released at different stages. Nanoindentation tests revealed that the gluten char had the highest hardness (ca. 0.5 GPa) and modulus (7.8 GPa) followed by pine bark char and carbon black. The addition of chars to gluten enhanced the indenter-modulus significantly. Among all the charcoals, gluten char was found to impart the best mechanical and water resistant properties. The addition of only 6 wt% gluten char to the protein caused a substantial reduction in water uptake (by 38%) and increase of indenter-modulus (by 1525%). It was shown that it is possible to obtain protein biocomposites where both the filler and the matrix are naturally sourced from the same material, in this case, yielding an all-gluten derived biocomposite.

In the present study, Cloisite 30B nanoclay was modified to prepare a nanogel composite based on acrylic acid (AA) and acrylamide (AAm) through in-situ copolymerization. The prepared nanogel composites were cross-linked and subsequently embedded within a commercial epoxy resin to develop a self-healing epoxy-based coating. The nanogel composites were assessed using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). FTIR results confirmed a successful nanogel composite synthesis while the XRD results revealed the increase of the interlayer space of modified nanoclay leading to better dispersion in nanogel, which was also corroborated by TEM. The swelling ratio of the nanogel composite was evaluated to investigate the effect of the crosslinking agent on the swelling of the nanogel. The composite incorporation influence on the properties of the epoxy-based coatings was studied through the pull-off adhesion and elongation at break assessments. The results revealed the nanogel composite embedment within the epoxy coatings slightly decreased the mechanical properties. The self-healing performance of the nanogel incorporated epoxy-based coating was evaluated by electrochemical tests. The obtained results confirmed that the epoxy coating containing 0.5 wt% of nanogel composite provided the highest corrosion resistance after damages with the self-healing efficiency of 99.88%.

The effect of pyrolysis reactors on the properties of biochars (with a focus on flammability and mechanical characteristics) were investigated by keeping factors such as feedstock, carbonisation temperature, heating rate and residence time constant. The reactors employed were hydrothermal, fixed-bed batch vertical and fixed-bed batch horizontal-tube reactors. The vertical and tube reactors, at the same temperature, produced biochars having comparable elemental carbon content, surface functionalities, thermal degradation pattern and peak heat release rates. The hydrothermal reactor, although, a low-temperature process, produced biochar with high fire resistance because the formed tarry volatiles sealed water inside the pores, which hindered combustion. However, the biochar from hydrothermal reactor had the lowest nanoindentation properties whereas the tube reactor-produced biochar at 300 °C had the highest nanoindentation-hardness (290 Megapascal) and modulus (ca. 4 Gigapascal) amongst the other tested samples. Based on the inherent flammability and mechanical properties of biochars, polymeric composites’ properties can be predicted that can include them as constituents.

Biocomposites being environmentally-friendly alternative to synthetic composites are gaining increasing demand for various applications. Hence, biocomposite development should be integrated within a circular economy (CE) model to ensure a sustainable production that is simultaneously innocuous towards the environment. This review presents an overview of the state-of-the-art technologies for the adoption of the CE concept in biocomposite development. The study outlined the properties, environmental and economic impacts of biocomposites. A critical review of the life-cycle assessment of biocomposite for evaluating greenhouse gas emissions and carbon footprints was conducted. In addition, the opportunities and challenges pertaining to the implementation of CE have been discussed in detail. Recycling and utilisation of bio-based constituents were identified as the critical factors in embracing CE. Therefore, the development of innovative recycling technologies and an enhanced use of novel biocomposite constituents could lead to a reduction in material waste and environmental footprints. This article is one of the first studies to review the circularity of biocomposites in detail that will stimulate further research in enhancing the sustainability of these polymeric materials.

Resin-based dental composites are promising tooth-resembling materials in restorative dentistry. The limited longevity of dental composite restorations due to the bulk/marginal fracture and secondary caries as well as possible health risks are the critical challenges faced by such materials. Therefore, developments of resin-based dental composites received considerable attention in academic researches for clinical applications. A comprehensive review of the recent developments in the scientific literature on resin-based dental composites is presented in this article. Firstly, in the article, the challenges in dental composites are introduced and then the chemical aspects of the systems are classified through a review of employed resins. Subsequently, the different characteristics related to the fillers employed for the development of the resin-based dental composites are described. Finally, conclusions are drawn and future insights are proposed. This article provides an insight that paves the way for tailoring and designing resin-based dental composites for clinical applications.

Phytic acid (PA) is one of the widely used flame retardants (FRs) to treat a variety of fabrics owing to its high phosphorus content of ca. 28 wt% (with respect to its molecular weight), abundance, non-toxicity, and biocompatibility. The current review discusses the state-of-the-art of PA-based FRs for natural fabrics such as cotton and wool. The possibilities of making PA and FR-based multi-functional cotton fabrics having antimicrobial, conductive, hydrophobic properties are reported by virtue of the synergistic benefits associated with chitosan, silicon, nitrogen, and boron-based molecules. The factors influencing the FR behaviour as well as the durability of PA-based cotton and wool fabrics are discussed with respect to the concentration of PA, pH of the coating solution, temperature, and preparation methods. Holistically, PA has been proved to be a potential alternative to halogenated FRs to confer fire retardant property to cotton and wool fabrics.

Biochar based wood/polypropylene (PP) composites were manufactured with two flame retardants (FRs): ammonium polyphosphate/APP and magnesium hydroxide/Mg(OH)2. The amounts of wood and biochar were alternated for accommodating the FRs in each blend. Flammability and mechanical characterisation for both the batches containing different FRs were done. Having higher proportion of biochar and less wood is beneficial to reduce flammability. The thermally stable biochar contributes to formation of effective char to restrict O2 transfer into PP. The higher weight ratio of biochar than wood in the composites compromised the tensile and flexural strengths to some extent as the APP and Mg(OH)2 particles were trapped inside biochar pores consequently reducing the effectiveness of biochar pore infiltration by PP. In general, addition of biochar with a woody biomass (with FRs) to neat PP significantly impedes its flammability while enhancing certain mechanical properties, such as flexural strength and tensile/flexural moduli and preserving the tensile strength.

Composite materials based on renewable agricultural and biomass feedstocks are increasingly utilized as these products significantly offset the use of fossil fuels and reduce greenhouse gas emissions in comparison with conventional petroleum-based materials. However, the inclusion of natural fibers in polymers introduces several challenges, such as excess water absorption and poor thermal properties, which need to be overcome to produce materials with comparable properties to the conventional composite materials. Instead of using rather expensive chemical and physical modification methods to eliminate these aforementioned challenges, a new trend of utilizing waste, residues, and process by-products in natural fiber-polymer composites (NFPCs) as additives or reinforcements may bring considerable enhancements in the properties of NFPCs in a sustainable and resilient manner. In this paper, the effects of waste materials, residues or process by-products of multiple types on NFPCs are critically reviewed and their potential as NFPC constituents is evaluated.

Due to the realisation of the reinforcement potential of waste based biochar and wool in polymeric composites, in the recent past, their individual flammability, thermal and mechanical properties were determined. Composites were manufactured with biochar and with both biochar and wool in conjunction with the halogen free flame retardant, which was followed by their characterisation through cone calorimeter, limiting oxygen index (LOI), thermogravimetry, tension/flexural tests, and scanning electron microscopy (SEM). Biochar exhibited a high resistance to heat without being ignited and possessed very low heat release and smoke production rates. Wool, although, had relatively high peak heat release rate (PHRR), its advantageous charring ability enabled a gradual reduction in heat release until flameout. The hardness and modulus of biochar were 4.3 GPa and 26 GPa, respectively. The tensile strength and modulus of wool were 160 MPa and 4.8 GPa, respectively. Composites containing biochar and wool significantly reduced the PHRR, smoke production, and elevated the mass loss rate (compared to neat polypropylene/PP). Hybridisation with wool proved to be beneficial for enhancing the LOI. Certain mechanical properties, such as flexural strength and tensile/flexural moduli, were preserved and enhanced, respectively, due to biochar pore infiltration by PP as seen in SEM.

Biocomposites were manufactured with biochar and polypropylene at five loading levels (0, 15, 25, 30, and 35 wt%) by compounding and injection moulding. Biocomposites were tested by tension, bending, cone calorimeter, thermogravimetry, differential scanning calorimetry, X–ray diffraction, and infrared spectroscopy. Incorporation of increasing amount of biochar to neat polypropylene continuously improved its tensile modulus and flexural strength/modulus. The peak heat release rate and smoke production of the biocomposites were significantly reduced as a result of biochar addition. The high surface area of biochar allowed polypropylene to flow in creating a mechanical interlocking and improving the mechanical properties. The thermally stable biochar provided a compact char structure during combustion which prevented the heat and mass transfer between the polypropylene and the ambient O2. Thermal stability of polypropylene was increased as a result of biochar inclusion, as observed in thermogravimetry.

A parametric study of biochar/wood/polypropylene (PP) composites has been conducted in order to evaluate the significant material factors that could affect the mechanical and flammability properties of the resulting composites. The presence/absence of coupling agent and wood, particle size of biochar and melt flow index of PP are the four factors investigated employing the Taguchi’s design of experiment technique. Eight composite samples were manufactured by extrusion and injection moulding to be tested for their mechanical and flammability properties. Experimental results indicate that the presence of coupling agent and wood (in conjunction with biochar) play a critical role in achieving improved tensile and flexural properties. It is interesting to note that in terms of flammability properties, there does not appear to be much difference in the values of peak heat release rate amongst the composites, thus allowing the selection of the composition that would essentially be best suited for mechanical properties.

Polymer-based materials are increasingly produced through fused deposition modelling (FDM) – an additive manufacturing process, due to its intrinsic advantages in manufacturing complex shapes and structures at low overhead costs. The versatility of this technology has attracted several industries to print complex geometrical structures. This underlines the importance of studying the mechanical strength of FDM printed polymeric materials, especially their fatigue behaviour in cyclic loading conditions. Conventionally manufactured polymeric materials (e.g. injection moulding) have superior fatigue performance than FDM printed materials. Unlike conventionally manufactured polymers, FDM-made polymers have layer by layer adhesion and the influence of printing parameters make fatigue analysis complex and critical. The influences of printing parameters and printing material characteristics have a significant impact on the fatigue behaviour of these materials. The underlying mechanism behind the fatigue of FDM printed polymers is crucial for the assessment of these materials in structural applications. However, the fatigue behaviour of FDM printed polymeric materials has not been reviewed in detail. Therefore, this article aims to evaluate 3D printed polymeric materials’ fatigue properties. The importance of fatigue in the FDM printed biomedical materials is also reviewed, and more importantly, the novel FDM printed architected cellular material fatigue properties are also introduced.

Waste based activated biochar was used to manufacture wood/polypropylene biocomposites. The biochar used had no surface functional groups, however, possessed high surface area (335 m2/g). Therefore, it was hypothesised that less than usual amount (3–5 wt%) of compatibiliser (maleic anhydride) could be used, to reduce production costs, while maintaining similar mechanical and flammability properties of the biocomposite. The biocomposites were characterised mechanically through tension, flexural, impact, and micro–hardness tests. The flammability and thermal behaviours were determined using cone calorimetry and thermogravimetry, respectively. Infrared spectroscopy and X–ray diffraction were also employed to comprehend the chemical changes occurring in the biocomposites. It was found that the amount of compatibiliser could be reduced to 1 wt% (from 3 wt%) without compromising on the mechanical performance (especially, tensile strength/modulus, impact strength, and micro–hardness) and flammability properties of the biocomposites. Electron microscopy revealed that the lack of compatibiliser in the biocomposites was compensated by well–dispersed biochar particles whose pores were infiltrated by the polymer causing a mechanical interlocking. In general, addition of biochar improved the mechanical and fire performance of the biocomposites compared to the neat polymer. Reduction of compatibiliser to 1 wt% from 3 wt% in conjunction with biochar saves ∼18% of the biocomposite production costs.

Biochar produced from the pyrolysis of waste pine wood was employed to manufacture wood/polypropylene biocomposites. Mechanical properties of micron–sized biochar particles were investigated and compared with those of waste pine wood and neat polypropylene particles by nanoindentation technique. An attempt was made for nanoindentation–assisted prediction of comprehensive mechanical properties of the resulting biocomposites. Theoretical models (i.e. rule of mixtures, Halpin–Tsai–Nielsen, and Verbeek) were applied using the nanoindentation properties of individual constituent particles to calculate the bulk properties of biocomposites. Good agreement was observed between the predicted and experimental moduli values. The hardness prediction through rule of mixtures correlated well with the Vicker's hardness test values. The nanoindentation hardness values of individual components follow an order: biochar (0.43 GPa) > wood (0.3 GPa)> polypropylene (0.1 GPa), whereas the moduli values are 1.5, 5.6, and 4.9 GPa for polypropylene, wood, and biochar, respectively.

To identify a route for organic wastes utilisation, biochar made from various feedstocks (landfill pine saw dust, sewage sludge, and poultry litter) and at diverse pyrolysis conditions, were collected. These biochars were used to fabricate wood and polypropylene biocomposites with a loading level of 24 mass%. The composites were tested for their mechanical, chemical, thermal, morphological, and fire properties. The poultry litter biochar biocomposite, with highest ash content, was found to have high values of tensile/flexural strength, tensile/flexural modulus, and impact strength, compared to other composites. In general, addition of all the biochars enhanced the tensile/flexural moduli of the composites. The crystal structure of polypropylene in the composite was intact after the incorporation of all the biochars. The final chemical and crystal structure of the composite were an additive function of the individual components. The biochar particles along with wood acted as nucleating agents for the recrystallization of polypropylene in composite. Each component in the composites was found to decompose individually under thermal regime. The electron microscopy revealed the infiltration of polypropylene into the biochar pores and a general good dispersion in most composites. The poultry litter composite was found to have lower heat release rate under combustion regime.

To impart usability in waste based biomass through thermo-chemical reactions, several physical and chemical pre-treatments were conducted to gain an insight on their mode of action, effect on the chemistry and the change in thermal degradation profiles. Two different waste biomasses (Douglas fir, a softwood and hybrid poplar, a hardwood) were subjected to four different pre-treatments, namely, hot water pre-treatment, torrefaction, acid (sulphuric acid) and salt (ammonium phosphate) doping. Post pre-treatments, the changes in the biomass structure, chemistry, and thermal makeup were studied through electron microscopy, atomic absorption/ultra violet spectroscopy, ion exchange chromatography, and thermogravimetry. The pre-treatments significantly reduced the amounts of inorganic ash, extractives, metals, and hemicellulose from both the biomass samples. Furthermore, hot water and torrefaction pre-treatment caused mechanical disruption in biomass fibres leading to smaller particle sizes. Torrefaction of Douglas fir wood yielded more solid product than hybrid poplar. Finally, the salt pre-treatment increased the activation energies of the biomass samples (especially Douglas fir) to a great extent. Thus, salt pre-treatment was found to bestow thermal stability in the biomass.

Douglas fir wood, a forestry waste, was attempted to be converted into value added products by pretreatments followed by pyrolysis. Four different types of pretreatments were employed, namely, hot water treatment, torrefaction, sulphuric acid and ammonium phosphate doping. Subsequently, pyrolysis was done at 500°C and the resulting bio-oils were analysed for their chemical composition using Karl Fischer titration, thermogravimetry, ion exchange, and gas chromatography. Pretreatment with acid resulted in the highest yield of bio-oil (~60%). The acid and salt pretreatments were responsible for drastic reduction in the lignin oligomers and enhancement of water content in the pyrolytic liquid. The quantity of xylose/mannose reduced as a result of pretreatments. Although, the content of fermentable sugars remained similar across all the pretreatments, the yield of levoglucosan increased. Pretreatment of the biomass with acid yielded the highest amount of levoglucosan in the bio-oil (13.21%). The acid and salt pretreatments also elevated the amount of acetic acid in the bio-oils. Addition of acid and salt to the biomass altered the interaction of cellulose-lignin in the pyrolysis regime. Application of pretreatments should be based on the intended end use of the liquid product having a desired chemical composition.

The widespread applications of biochar in agriculture and environmental remediation made the scientific community ignore its mechanical properties. Hence, to examine the scope of biochar's structural applications, its mechanical properties have been investigated in this paper through nanoindentation technique. Seven waste derived biochars, made under different pyrolysis conditions and from diverse feedstocks, were studied via nanoindentation, infrared spectroscopy, X-ray crystallography, thermogravimetry, and electron microscopy. Following this, an attempt was made to correlate the biochars' hardness/modulus with reaction conditions and their chemical properties. The pine wood biochar made at 900°C and 60min residence time was found to have the highest hardness and elastic modulus of 4.29 and 25.01GPa, respectively. It was shown that a combination of higher heat treatment (≥500°C) temperature and longer residence time (~60min) increases the values of hardness and modulus. It was further realized that pyrolysis temperature was a more dominant factor than residence time in determining the final mechanical properties of biochar particles. The degree of aromaticity and crystallinity of the biochar were also correlated with higher values of hardness and modulus.

The onset of coronavirus pandemic has sparked a shortage of facemasks in almost all nations. Without this personal protective equipment, healthcare providers, essential workers, and the general public are exposed to the risk of infection. In light of the aforementioned, it is critical to balance the supply and demand for masks. COVID-19 will also ensure that masks are always considered as an essential commodity in future pandemic preparedness. Moreover, billions of facemasks are produced from petrochemicals derived raw materials, which are non-degradable upon disposal after their single use, thus causing environmental pollution and damage. The sustainable way forward is to utilise raw materials that are side-stream products of local industries to develop facemasks having equal or better efficiency than the conventional ones. In this regard, wheat gluten biopolymer, which is a by-product or co-product of cereal industries, can be electrospun into nanofibre membranes and subsequently carbonised at over 700 °C to form a network structure, which can simultaneously act as the filter media and reinforcement for gluten-based masks. In parallel, the same gluten material can be processed into cohesive thin films using plasticiser and hot press. Additionally, lanosol, a naturally-occurring substance, imparts fire (V-0 rating in vertical burn test), and microbe resistance in gluten plastics. Thus, thin films of flexible gluten with very low amounts of lanosol (, Graphical abstract The possible pathway to develop fully bio-based facemasks.Unlabelled Image, Highlights • Coronavirus pandemic have made facemasks worldwide healthcare essentials • Shortage of masks exposes medical personnel and the public to the risk of infection • Utilisation of sustainable raw materials to develop bio-based masks is needed • Electrospun and compression moulded gluten can be used to develop bio-based masks • Gluten masks can be made flame retardant by adding

The aim of the present work was to comprehend the fire retardant and mechanical properties of protein based natural fibre and biopolymer composites. Wool fibre and wheat gluten as environmentally sustainable materials were selected as fibre reinforcement and polymer matrix, respectively. With the use of the Taguchi design-of-experiment tool, it was possible to identify the desired combinations of the selective factors: wool/plasticiser (glycerol) contents and processing temperature, to improve the composites properties. Pareto ANOVA indicated that the wool content was the most important factor (ca. 78%) to influence the peak heat release rate due to its charring competency. On the other hand, the content of plasticiser significantly affected the tensile strength of the composites. Of particular importance was that the addition of 30 wt% wool to the gluten polymer, having no flame retardant, was sufficient to achieve a self-extinguishing flame during the vertical burn test (V-1) and improve the composite's strength.

The aim of the study was to impart fire retardancy in wheat gluten polymer through naturally-occurring additives such as lanosol. The fire properties of lanosol were compared with two other conventional brominated fire retardants (Tetrabromobisphenol A and Hexabromocyclododecane). Samples containing fire retardants and gluten were prepared through compression moulding process and then characterised for their fire and mechanical properties. All fire retardants enhanced the reaction-to-fire and thermal properties of gluten while generating V-0 (i.e. vertical position and self-extinguished) ratings in the UL-94 test. The presence of all the fire retardants increased the modulus of the gluten polymer but the fire retardant particles were detrimental for the tensile strength. Nevertheless, lanosol addition delayed ignition and lowered peak heat release rate of gluten by the maximum amount, thereby leading to relatively higher fire performance index (compared to the other fire retardants). Lanosol also allowed the gluten to create a dense char barrier layer during burning that impeded the transfer of heat and flammable volatiles. The fact that only 4 wt% lanosol was able to cause self-extinguishment under direct flame and reduce peak heat release rate by a significant 50% coupled with its inherent occurrence in nature, raises the question if lanosol can be a potential fire retardant in polymeric systems, although it is a bromophenol.

Biochar is being considered for environmental sustainability by the scientific community and as a result is extensively investigated for various applications in agriculture, remediation and construction. Hence, a sound knowledge of biochar's physical and chemical properties is critical. However, the dynamics of biochar-water interaction remain ambiguous. We hypothesize that the hydrophobicity of a biochar made at low pyrolysis temperature is not permanent under water-rich conditions. Our results suggest that the aliphatic functional groups responsible for biochar's hydrophobicity are displaced when subjected to water which eventually increases the affinity of the biochar towards water. We envisage that commentary would stimulate researchers to investigate the biochar-water interaction in a new light and eventually help design a biochar which would be apt for their intended end use.

In an attempt to concurrently address the issues related to landfill gas emission and utilization of organic wastes, a relatively novel idea is introduced to develop biocomposites where biochar made from pyrolysis of waste wood (Pinus radiata) is added with the same wood, plastic/polymer (polypropylene) and maleated anhydride polypropylene (MAPP). Experiments were conducted by manufacturing wood and polypropylene composites (WPCs) mixed with 6 wt%, 12 wt%, 18 wt%, 24 wt%, and 30 wt% biochar. Though 6 wt% addition had similar properties to that of the control (composite without biochar), increasing biochar content to 24 wt% improved the composite’s tensile/flexural strengths and moduli. The biochar, having high surface area due to fine particles and being highly carbonised, acted as reinforcing filler in the biocomposite. Composites having 12 wt% and 18 wt% of biochar were found to be the most ductile and thermally stable, respectively. This study demonstrates that, WPCs added with biochar has good potential to mitigate wastes while simultaneously producing biocomposites having properties that might be suited for various end applications.

Five different rice husks (RHs) having different geographical origins were characterised for their mechanical and fire reaction properties using nanoindentation and cone calorimetry, respectively. Analyses relating to ash and extractives contents, density and morphologies were also performed. The RHs had statistically similar extractives content, nanoindentation properties and peak heat release rates (PHRRs). The polypropylene-based composites made from these RHs also had insignificant differences in their tensile moduli, elongation and PHRR values. The RH inclusion conserved the tensile/flexural strengths while enhancing the moduli of the composites, as compared to the neat polypropylene. The material characteristics being ubiquitous amongst the different RH types enable the creation of biocomposites with foreseeable performance properties. Moreover, the individual nanoindentation and fire reaction properties of the RHs allowed the presaging of the bulk biocomposites’ properties using theoretical models. Good agreements between predicted and experimental moduli/PHRRs were achieved using rule of mixtures and Halpi-Pegano models.