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Polymer composites were manufactured using biocarbon particles as a reinforcing filler to improve the mechanical and thermal properties. However, a detailed examination of dispersion and agglomeration of filler is essential to correlate the filler/matrix and the filler/filler interactions with the mechanical properties of the product. We investigated the variations of mechanical, agglomeration behavior of fillers, and thermal properties of polypropylene (PP)/coconut shell biocarbon (CSB) composites. PP/CSB composites were prepared by melt mixing process varying the CSB content (0 to 20 wt%) using a Brabender mixer. The nanomechanical mapping of the composites studied using Atomic Force Microscopy revealed an increase in Young’s modulus from 1.6 to 2.9 GPa when CSB loading increased from 0 to 20 wt%. The dispersion and agglomeration of CSB filler in the PP matrix were investigated using 3D reconstructed images with the help of X-ray micro-CT, and a dedicated 3D reconstruction software. The thermal stability of the PP/CSB composites also improved with an increase in CSB content in PP.

The demand for stretchable, soft and wearable multifunctional devices based on conductive polymer composites is rapidly growing because of their compelling applications, including physical and physiological measurements on the human body. This paper reports a simple and cost-effective technique to fabricate electrically conductive flexible films with graphite (GRP) flakes and an elastomer, silicone rubber (SR). The mechanical, thermal, electromechanical and electrothermal characterisations of the composites were conducted. While the dynamic electromechanical response of the composites demonstrated their potential applications as wearable sensors, the electrothermal characteristics of the devices showed their suitability to be used as flexible protective circuits and flexible temperature sensors. The synergistic effect of GRP flakes with carbon black (CB) particles was also studied. GRP-SR composites showed a thermal conductivity (TC) of 1.08 W m−1 K−1 and were thermally stable up to up to 300 °C. The good TC and thermal stability along with their deformability, make them suitable to be used as thermal interface devices in arbitrarily shaped surfaces.

To minimize the surface roughness and delamination problems during the end milling of natural fiber reinforced composites (NFRCs), it is essential to understand the effects of the machining paramet...

Metal/metal oxides and conductive polymers are common supercapacitor electrode materials, revealing high power density as well as long cycle life. In composites, graphene and metal oxides displayed the combination of the excellent cycle stability of graphene and the high-capacity properties of metal oxides which remarkably improve the comprehensive properties of nanocomposites. The current developments of metal/metal oxide decorated graphene (MGr) composites in the field of electrochemical capacitors are elucidated here on account of their synergistic properties. It is demonstrated that, in comparison with their individual influences, MGr composites have attained substantial improvement in rate capability, capacity, and cycling stability. Mainly, an overview of the characteristics, preparation approaches, and application of graphene (Gr) is outlined. Mechanism of different types of electrochemical capacitance is described explicitly. Finally, the future prospects and challenges of MGr composites have been discussed for energy storage.

Fabrication of electrically conductive yarns (glass, flax and polypropylene fibers) coated with graphene nanoparticles (GNP) were characterized for their mechanical properties and compared with their electrical properties. The composites were produced with the use of polymeric binders (epoxy resin and thermoplastic starch) and two different dip-coating methodologies were developed to create the coating layers. Technique-1 involved coating of binder and then GNP layer whereas Technique-2 had a mixture of binder and GNP in the predetermined ratio, which was coated on the yarns. The mechanism of adhesion varies or influences on a number of factors such as the nature of the fiber surface, coating method and effective binder. Tensile properties of the yarns were measured by an appropriate standard, and the highest tensile strength was noticed with epoxy-based glass fiber samples as 222 MPa followed by flax fiber samples as 206 MPa. The composites of starch-based showed poor mechanical performance compared to those of epoxy ones. This was due to poor adhesion between the surface and starch layer (interphase) where the Van der Wall’s force was quite low. Electrical conductivity, glass fiber yarns with epoxy binder were identified to have the highest electrical conductivity of 0.1 S.cm−1 among other samples.

The paper focuses on the investigation of the 3D printing of multi-functional composites using graphene nanoplatelets (GNP), polypyrrole (PPY) and linear low-density polyethylene (LLDPE). A holisti...

We have developed a method of converting chicken feather to high-performance flame retardant through a solution-based chemical treatment. The synergistic effect of the chicken feather fiber and loa...

In this research, two nano-clays, halloysite nano-tube (HNT) and layered double hydroxide (LDH), were employed to compare fire and mechanical properties of epoxy composites based on ammonium polyphosphate (APP) and each of the two nano-clays. The results showed that the combination of APP and nano-clay achieved a significant reduction (approx. 87%) in peak heat release rate of epoxy resin. The comparative analysis also demonstrated that the total heat release of the composite including HNT was approx. 18% lower than that of the LDH based composite. Moreover, HNT generated higher tensile properties in the composite. Overall, the HNT (∼1.5 USD/kg) is a more cost-effective nano-clay than LDH (∼180 USD/kg) to effectively improve the fire resistance and maintain the mechanical properties of epoxy composites.

This paper focuses on developing hybrid composites of conductive polymers with graphene which have been shown to form a synergistic relationship between the components by lowering the percolation threshold and therefore achieving significant electrical conductivity at relatively low filler loadings. A variety of analytical techniques have been used to determine the factors contributing towards the electrical conductivity performance in these composites and the results of which have been used to construct a production method based on the solution casting process. The key factors identified have included the polarity of the primary polymer, the level of homogeneity of the dispersion of the conductive filler materials and the crystallinity of the resulting composite which in this case is increased by the addition of sucrose. Optimising for these factors the production method has been able to manufacture samples with an electrical conductivity of up to 14.2 S.cm−1 at a filler loading of 10 wt.% graphene and 10 wt.% conductive polymer in the base polymethyl methacrylate matrix. These have been investigated for application in 3D printing as an alternative to wiring or expensive printable conductive inks, and successful samples have been produced with an electrical conductivity of 11.3 S.cm−1.

Even though casein has an intrinsic potential ability to act as a flame retardant (FR) additive, the research regarding the FR performance of casein filled polymeric composites has not been thoroughly conducted. In the present work, two commercial casein products, such as lactic casein 720 (LAC) and sodium casein 180 (SC), were chosen to investigate their effects on the performances of the polypropylene (PP) composites. The melt compounding and compression moulding processes were employed to fabricate these casein-based composites. Ammonium polyphosphate (APP) was also selected to explore its combined effects in conjunction with casein on the composite&rsquo, s flammability. The cone calorimeter results showed that the addition of casein significantly reduced (66%) the peak heat release rate (PHRR) of the composite compared to that of neat PP. In particular, the combination of LAC and APP led to the formation of more compact and rigid char compared to that for SC based sample, hence, a further reduction (80%) in PHRR and self-extinguishment under a vertical burn test were accomplished. Moreover, the tensile modulus of the composite improved (23%) by the combined effects of LAC and APP. The overall research outcome has established the potential of casein as a natural protein FR reducing a polymer&rsquo, s flammability.

Eco-friendly flame retardants are greatly required to meet the expectations of low-toxicity, environmental compatibility and sustainability. Extracellular polymeric substances (EPS), the biopolymers recovered from excess granular wastewater sludge, have been successfully incorporated into poly(vinyl alcohol) (PVA) by a solution casting method. Self-extinguishment of EPS was observed in a vertical burn test. Positive effects of EPS on the reduction of heat release rate and CO emission of EPS/PVA composites were also demonstrated. The presence of various types of phosphates was detected in the EPS and a possible flame-retardant mechanism has been proposed. The investigation of using granular sludge EPS to reduce the flammability of synthetic polymers may open the possibility of converting wastewater sludge into bio phosphorus-based flame retardants.

Wearable electronics have generated a strong demand for stretchable, skin-mountable and flexible sensors. This paper provides an effective technique for fabricating conductive networks using graphene-based polymer composites. Graphene-carbon black-silicone rubber (G-CB-SR) composites were cast in a mould, and a film was fabricated to make a composite strain sensor. Here we investigate how the remarkably different geometry affects the effective conductivity and piezoresistive properties of the composites. The electromechanical response of the G-CB-SR composites showed highly reversible and durable behaviour. It was stretchable up to 300%, and the gauge factor (GF) depended on the composition of the composites. The large strain sensors made of high-quality G-CB-SR film was achieved by solution intercalation with low-cost production and easy scalability.

An intumescent flame retardant working with various combinations of acid source, blowing agent, and char former promises high performance and low toxicity. However, the research for more potent functional constituents and their best combination is still extremely important. Here we report on a novel way to use keratinous fibers as the host material for creating an effective flame retardant. A simple solution-based treatment to implant amine phosphate and phosphoric acid in the fiber through sequential monomer infiltration is found to be significantly effective for applying flame retardancy and reducing the flammability of polymeric materials. After the flame-retardant fiber modification, polypropylene (PP) shows significantly improved flame retardancy to achieve V-0 grade and >70% reduced peak heat release rate in vertical burning and cone-calorimeter tests, respectively. We expect this strategy of converting the low-grade keratinous fiber to valuable flame-retardant material to become a novel and attract...

Several studies have been done on physiochemical properties of thin films of graphene materials, but less on their mechanical properties. The mechanical properties such as tensile and storage modulus of films of graphene oxide (GO), different reduced graphene oxides (rGO), functionalised reduced graphene oxide (frGO) and a few layers graphene (graphene) were analysed in this study. During syntheses processes, a range of variations occurs due to different reducing agents and functionalising components used; this affects or changes the mechanical properties of the materials. In addition, it has become vital to comprehend the mechanical properties of these films as the potential applications such as sensor and electrodes demand extended life cycles or lifetime. It has been found that the ultimate tensile strength (UTS), tensile modulus, and storage modulus vary across all the samples that highly depend on nature/efficiency of reducing agent used, amount of impurities such as oxygen functional groups and defect density such as discrepancies/holes in the aromatic structure. The highest UTS and modulus have been identified with a few layers graphene and with hydroiodic acid reduced GO among the rGOs. The frGO shows almost similar properties to that of graphene.

Susceptibility to damage from heat and flame is one of the major issues for utilisation of natural fibre reinforced polymeric composites in practical applications. Thus, the knowledge of thermal decomposition and flammability of the bio-based fibres, polymers and their composites is highly required for the materials selection and the development of composite products. Moreover, suitable flame retardant treatments on these composites have shown to effectively enhance their thermal stability and fire resistance. This article provides a review of research on thermal behaviour and flammability of natural fibres, such as cellulose and protein based fibres, and polymers along with composites filled with these materials. Furthermore, eco-friendly flame retardant treatments to overcome the environmental impact of conventional flame retardants are introduced with the combined effects of natural fibres on composites' fire performance. In addition, a review of studies on the predictive models regarding thermal response and structural damages of composites in fire is also included with their advantages and limitations.

The effect of crystal orientation and strain rate on the deformation behaviour of high-purity Ni single crystals is investigated using in-situ micro-tensile techniques. Ni foils, 12 μm thick, were fashioned into micro-tensile samples. The samples were pulled in tension along and directions at nominal displacement rates of 5 nm/s and 500 nm/s. These orientations were chosen because of the expectation of multiple slip on different numbers of slip systems. Analysis of stress-strain plots in conjunction with orientation imaging revealed that the oriented samples featured a lower yield stress, higher elongation and more complex deformation behaviour than the oriented sample. In fact, the samples with orientation showed two peaks in the engineering stress-strain curves, a unique behaviour hitherto unobserved. The higher strain rate increased the flow strength for both orientations, the results being in broad agreement with macroscopic tests. These results are analysed using plasticity theory, and it is shown that the results obtained from microscopic tests in single crystal Ni are largely consistent with macro-scale behaviour in polycrystalline samples if the appropriate theoretical adjustments are made for size and orientation effects, using Hall-Petch and Taylor theories.

Influence of wool fibres (WF) in improving the flame retardant and mechanical properties of polypropylene/kenaf fibre/intumescent ammonium polyphosphate (PP/KF/APP) composites is described. Flammability of PP/KF/APP/WF composite was evaluated using cone calorimetry, UL 94-V vertical burning tests and thermo-gravimetric analysis, and compared to results of similar composites which contained an ultraviolet ray stabiliser and colourant combination (PP/KF/APP/UVC). Tensile, bending and impact test analyses were also conducted on both sets of composites. PP/KF/APP/WF system had stable residual char at elevated temperatures, significantly improving fire protection. High degree of cross-linked stable char formation and residual char in PP/KF/APP/WF composite provided sufficient evidence of synergistic effect of wool. WF increased the tensile modulus of the composite by approximately 16%, while UVC (together with APP) improved the composite's flexural stiffness by 21%.

The knowledge of impact behaviour of heat exposed composites is very limited, even though this could be one of the critical issues for many practical applications. Therefore, the current study was conducted to investigate the effect of preheating on the impact performance of glass and flax fibre reinforced composite laminates by a comprehensive set of experiments. The composite laminates were partially damaged by heat convection (using a fan assisted furnace) and their impact properties, such as force and energy absorption, were measured under a low velocity (1.85 m/s) impact loading situation. The impact test results showed that the heat exposure at 300 °C increased the energy absorption of the glass fibre composites but reduced those of the flax fibre composites. Furthermore, an addition of ammonium polyphosphate, as a flame retardant, also incremented the absorbed energy of the heat exposed composites and significantly reduced the heat release rate, resulting in an acceptable vertical burning behaviour, that meets the aviation standard requirements.

Although the effectiveness of organic–inorganic combination on the flammability reduction in polymeric materials has been proved by the multi-layer coating method on fabric and foam, the technique has not been intensively investigated for bulk polymers. In order to impart the excellence of the combination to bulk polymers, the thermal barrier resulted from the hybrid has to be triggered in the entire region of the polymer during combustion. In this work, phosphate loaded chicken feather fibers (CFF) with layered silicate outer coatings are developed into an efficient intumescent flame retardant (IFR) material system for polypropylene (PP). The organic–inorganic hybrid material, designed for silicate reinforced composite char formation during combustion, allows the modified PP composite to achieve significantly improved flame retardancy compared to that of the composite modified by the only phosphate. A small silicate content (0.4 wt%) leads to 27 wt% reduction in phosphate to achieve the same level of flame retardancy for PP. Furthermore, the efficiency of loaded phosphate, measured by a cone calorimeter, is 14% higher than that of a commercial IFR, ammonium polyphosphate (APP). Thermal gravimetric analysis and cone calorimeter tests demonstrate a suppressed decomposition of phosphorus and CFF at a higher temperature due to robust char formation. The characterization of the char residue using SEM-assisted elemental analysis confirms the silicate reinforced char. Flame retardant mechanism and mechanical performance have also been investigated to aid a better understanding and furthering its performance improvement.

This article focuses on the optimisation of electrical and mechanical properties of hybrid blends of polyoxymethylene (POM) as primary thermoplastic matrix, polypyrrole (PPY) as secondary conducting polymer and graphene (G) as reinforcement. An initial Taguchi analysis was performed with a focus on improving electrical conductivity (σ) and tensile strength. A mixture analysis using ‘simplex’ statistical design was applied to develop an experimental subset that identified an optimal combination in weight-percentage. Both electrical and mechanical properties were improved by the addition of PPY and graphene particles due to hybridisation mechanism as well as double percolation threshold. The maximum electrical conductivity of 0.95 S cm−1 was achieved with POM reinforced with 3 wt.% of G and 2.5 wt.% of PPY loading. The mechanical properties were found to be increased with increase in addition of both G and PPY.

A titanium aluminide (TiAl) alloy 45XD has been irradiated by a He ion beam with an energy of 5 MeV on a tandem accelerator at the Australian Nuclear Science and Technology Organization (ANSTO). The total fluence of He ions was 5 × 1017 ion cm−2. A 17 μm uniform damage region from the material surface with a helium concentration of about 5000 appm was achieved by using an energy degrading wheel in front of the TiAl target. The micro-size test specimens from the damage layer were fabricated using a focused ion beam & scanning electron microscope (FIB-SEM) system. The in situ SEM micromechanical compressive testing was carried out inside an SEM and the results indicated irradiation embrittlement in the helium affected region. Electron back scatter diffraction (EBSD) analysis has been applied to reveal the orientation of the lamellae in the TiAl specimens, and used to understand the deformation processes in the sample. The irradiation damage of gallium ion beam from FIB on the surface of TiAl sample was also investigated.

Pre-impregnated flax and thermoplastic poly(amide) composite tapes have been produced using a novel process. The manufacturing method uses an impregnation unit with a siphon system to impregnate continuous flax yarns with the polymer in the form of a slurry. After water evaporation, the powder is sintered and the coated yarns are compressed by passing them through a pair of heated rollers. Using a parametric study of the process, tape quality has been assured using the key outcome criteria of tensile strength/stiffness, surface roughness, fibre weight fraction, width and thickness. The temperature of the air heater placed before the roller has the biggest influence on tape quality. A heating model was developed using finite element software LS-DYNA. The research novelty comes from producing composite tapes with good tensile properties and surface finish using aligned natural fibres; the feasibility of automated tape placement and winding has also been demonstrated.

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.

Graphene has received significant attention in recent years due to its outstanding electronic, mechanical, chemical and physical properties. Graphene materials can potentially be used in a variety of applications, such as functional nanocomposites, electrodes, flexible transparent devices and thin conductive films. This article focuses on the analysis of structural evolution and development of different of reduced graphene oxides (rGOs), and the results are compared with structural features of functionalised reduced graphene oxide and graphene. The aromatic disorder and irregularity of these materials influence their own properties; particularly, their electrical conductivity aspects were studied indirectly through Raman spectroscopy. The quantification of their Raman spectra and microstructural analysis were examined to assess the relationship between aromatic structures and electrical conduction mechanism. The results showed that aromaticity of GO changes under different chemical reduction treatments and hydroiodic acid reduction gave an electrical conductivity of 103.3 S cm−1 as highest amongst a number of rGOs produced. Moreover, the integrity of aromatic structure through different reduced graphene oxides changed quite significantly and the Raman results were able to correlate the electrical conductivity with their structural regularity.

Novel sandwiched structures of cellulose nanowhiskers (CNWs) were found for the first time at the cross section of fractured starch/CNWs composite films. CNWs were obtained by hydrolysing bleached flax yarns through heating in a concentrated sulfuric acid (60 wt. %) aqueous solution at 55 °C for 60 min. Starch and starch/CNWs composite films were prepared by casting starch and mixtures of starch/CNWs homogenous aqueous suspensions, which was followed by drying at atmosphere. The CNWs’ layers are sandwiched within starch matrices in a parallel direction to nanocomposite film surfaces. The layer thickness increases with an increase in the content of CNWs. The discovery of novel sandwiched structures demonstrates that both the interaction and evaporation rate of the solvent can affect the dispersion and thus play important roles in the nanoparticle dispersion. Such nanocomposite films in the presence of self-assembled multi-layer structures may further improve mechanical and gas barrier properties as a promising material candidate for food packaging applications.

The combined effects of ammonium polyphosphate and talc on the fire and mechanical behaviour of epoxy/glass fabric composite systems and neat epoxy resin were investigated. Recorded data from cone calorimeter and UL-94 vertical burning experiments reveal that the incorporation of additives can enhance the flame retardancy of both epoxy resin and glass fabric reinforced composites. TGA results demonstrate that the introduction of additives improve the thermal stability of epoxy resin at high temperatures. Moreover, the addition of flame retardants to epoxy resin increases the tensile and flexural moduli. However, due to the incompatibility of the additives with epoxy, the strengths are compromised. Then again, the epoxy/glass fabric composites with flame retardant additives have improved the fire properties without significantly affecting the mechanical performance.

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.

Keeping sustainability in mind, polymer composites are usually fabricated with biobased materials instead of synthetics. However, these “biocomposites” often lack the required strength and are extremely susceptible to fire. This necessitates the application of fire-retardant treatment, which could render the composite fire resistant. This chapter gives an overview of the types of fire retardants that are generally applied, and a review of studies done to impart fire retardancy in composites. Several instruments and standards used for determining fire behaviors of composites are also described in detail. Biochar (especially made at high pyrolysis temperatures) is very resistant to ignition and thermally stable, owing to its extensive network of cross-linking between adjacent aromatic carbon sheets. Its inclusion in polymeric composites is advantageous for both fire and mechanical properties. The inherent fire-resistant and char-forming ability of wool (a natural protein fiber) has been exploited to develop composites that exhibit the highest degree of flame resistance (V0 rating in UL94 tests). Finally, wheat gluten, a by-product of the cereal industry, has shown potential regarding fire retardancy and thermal stability. Gluten's flame-resistant properties can be made even more potent by applying other additives (e.g., silica).

This article focuses on the influence of surface topography (roughness), surface chemistry (carbon and oxygen functional groups) and physical (film thickness) parameters on the electrical conductivity of graphene oxide (GO) and reduced graphene oxide (rGO) films. This study was carried out to understand how changes in chemistry, roughness and film thickness, arising from the reduction process, alter the electrical properties of the films. Improved understanding is needed to control and optimise these parameters in graphene/rGO films for future applications where targeted property performance is needed. Films with smooth surfaces, measured using confocal imaging, and lower thicknesses have been shown to possess higher electrical conductivity. X-ray diffraction patterns shows minor changes in d-spacing, though improvements in crystal perfection, orientation and crystallinity could be concluded. X-ray photoelectron spectroscopy shows a significant decrease in the oxygen present at the surface as the films are exfoliated to reduce their thickness. Conductivity improves as the materials become increasingly defect-free, achieved by careful control of reduction and post-processing techniques. Ideal practical conductivity is achieved for films of 4 μm thickness: beyond this point, no practical gains are made (about 25 exfoliation trials from the bulk cast film).

Wool, as a naturally fire resistant fibre, has been incorporated with other additives, such as ammonium polyphosphate (APP), talc and maleic anhydride grafted polypropylene (MAPP), to manufacture polypropylene (PP) based composites. A single-screw extruder, attached with a flat die, has been used to successfully produce continuous wool-PP composite sheets. Furthermore, the significant roles of nitrogen content of APP and the talc in forming the effective char to increase the composites' fire retardancy have been identified through cone calorimeter tests. In particular, it is highly interesting to note that a reduction of APP content from 20 to 15 wt% was possible to achieve a direct self-extinguishment (V-0 rating) of the composite. The decrease in APP amount has also led to the reduction of material cost due to APP's relatively high price (USD 13–14/kg) and limit the possibility of deteriorating mechanical properties due to APP addition. The MAPP has enhanced thermal stability and mechanical properties compared to those without the additive, which could be attributed to the improved interfacial adhesion between wool and PP. A computational fluid dynamics model has also been developed by Fire Dynamics Simulator to mimic the cone calorimeter tests, which agreed reasonably well with the experiments. Keywords: Wool, Ammonium polyphosphate, Flammability, Mechanical properties, Fire Dynamics Simulator

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.

This article focuses on the hybridization of thermoplastic polymer matrices with conducting polymers and graphene derivatives. Polypropylene (PP), polymethylmethacrylate (PMMA) and polyoxymethylene (POM) were used as primary polymer matrices and polypyrrole (PPY) and polyaniline (PANI) as secondary conducting polymers. Highly conductive-reduced graphene oxide (rGO) and graphene (G) have been used as reinforcements. A Taguchi analysis has been performed for the blends to find the optimal combination of the blends with respect to electrical conductivity (σ) and mechanical properties. Both electrical and mechanical properties were improved by the hybridization process. The maximum electrical conductivity of 0.85 S.cm−1 has been acquired with POM/PPY/G blend with 3 wt.% and 5 wt.% of PPY and graphene loading, respectively. The mechanical properties have been found to improve with all the blends but, PP/PPY/G blend with 3 wt.% and 6 wt.% of PPY and graphene loading displays overall better properties in comparison with other blends.

Functional particles or fibres when incorporated into polymeric matrices produce composites of greater density, improved electrical conductivity, and, consequently, improved mechanical behaviour at demanding operating conditions, such as high temperature and pressure. Adhesion behaviour in particulate composites and fibre-reinforced composites, together with comparison between theoretical and experimental outcomes are reviewed here. Current research outcomes with respect to electrical conductivity and in relation to the preparation of conductive wires using glass fibres and thermoplastic yarns, and surface-coated with graphene (G) using a binder (epoxy or starch) are also included. Additionally, electrical and mechanical characteristics of hybrid particulate composites involving a primary polymer, a secondary polymer, and reinforcements have been discussed. Comments have been made on the influence of adhesion phenomena in these cases.

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.

The primary aim of this paper is to analyze the fiber length retention capacity of extrusion and injection molding processes for short and long kenaf fiber reinforced polypropylene composites. The composites were manufactured by adding maleic anhydride grafted polypropylene (MAPP) and an antioxidant (Irganox) using twin-screw extrusion and injection molding processes. A higher level of fiber attrition rate was observed during the twin-screw compounding compared to that in the injection molding. During high-temperature shear mixing, both processes caused a reduction in fiber length below the calculated critical fiber length along with considerable fiber damage. The mechanical and thermal properties of the resultant composites were subsequently characterized. Cone calorimeter tests demonstrated that the peak heat release rate for the kenaf fiber composites (30 wt.%) was reduced by 37% compared to pure polypropylene (PP). In the UL-94V tests, the presence of lignin in kenaf reduced the dripping time considerably, which further led to the formation of char residue after burning. Although the fiber length obtained was below the critical fiber length under high shear processing (twin-screw compounding and injection molding), effective fiber dispersion, orientation and opening led to significantly improved mechanical performance of the PP/kenaf composites, irrespective of the initial fiber length. Keywords: Kenaf fiber, Degradation, Twin-screw extrusion, Injection molding, Fiber dispersion

Graphene has obtained a great interest both in research and industries due to its potential and promising physical, electrical and mechanical properties. While it has been widely researched for advanced applications, its fundamental properties are still being explored and have to be well understood. The physical properties such as specific surface area (SSA), inter-sheet distance (d-spacing) and Raman spectroscopy data for graphene derivatives are closely related to each other, and this work focused on establishing the correlation between these critical factors with respect to their electrical conductivities. Different graphitic materials f(graphene oxide (GO), reduced graphene oxides (rGO), functionalised graphene oxide (frGO) and graphene nanoplatelets (GNP)) were taken in to account to elaborate the underlying mechanisms between extrinsic SSA and other physical parameters, such as intrinsic electrical conductivity. It has been analytically observed that SSA has a direct relationship with d-spacing and defect density of the graphene materials and thus their electrical conductivity highly depends on how large their SSA is the largest the SSA, the highest the electrical conductivity. Materials that poorly reduced were identified to be having low SSA and a higher level of discrepancies. Among different reducing agents used, hydroiodic reduced graphene oxide found to be having larger SSA as 670.98 m2 g−1 and higher electrical conductivity up to 103.3 S cm−1.

Flexible strain sensors attained significant attraction due to their numerous applications, such as personal healthcare, robotics, human entertainment technology and sports performance monitoring. However, there still exist challenges to find out a strain sensing mechanism with a facile and cost-effective method. Polypyrrole (PPy)/SR composites were prepared by a simple, low-cost solution casting method. Carbonaceous fillers, graphene nano platelets (GNP), and carbon black (CB) were introduced along with PPy and the sensor performances including stretchability, flexibility, gauge factor (GF), linearity and durability were studied. PPy/SR composites showed a GF between 1.2 and 1.7 and exhibited reversible and stable electromechanical characteristics with an average response time of 150 milliseconds. The conductive mechanism, which causes piezoresistivity and the temperature-dependent resistance characteristics and mechanical properties, were studied. The excellent composite properties, such as super-stretchability, flexibility, biocompatibility, durability along with facile production and environmental stability, make them an ideal candidate for the fabrication of large strain wearable sensors which can be integrated to clothes or directly attached to the human body for real-time human body deformation measurements.

Due to the high flammability of polymeric materials, the development of a flame retardant with high-performance, low-toxicity and cost-effectiveness has been one of the most important issues in the polymer industry. To address these requirements, keratinous fibres have been employed for a novel intumescent flame-retardant fabrication. Phosphate loaded keratinous fibres through the sequential infiltration of phosphoric acid and reactive amines have shown a successful demonstration of the self-extinguishment (V0 grade) and ~80% reduced peak heat release rate in the vertical burn test (UL94) and cone calorimeter test, respectively. Owing to the unique char formation behaviour of the fibres with the combined effects of phosphorus compounds, the composites have achieved the improvement of flame retardancy compared to the commercial ammonium polyphosphate/polypropylene composite. Furthermore, the fibre addition has contributed to enhance the mechanical properties of the composites. For the practical application of the new FR, cost reduction capability depending on the type of reactive amine used for the phosphate production in the fibre, has also been investigated.

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.

It is urgent to develop new photocatalytic materials that could optimize H2 generation and efficiently degrade environmentally persistent pollutants. Herein, Sr-ZnO/g-C3N4 spherical flowers composed of hierarchical nano-rods composites have been successfully synthesized via facile single step method and utilized in photocatalysis for efficient degradation of Methylene green (MG) and H2 production under UV–vis irradiation. The resultant Sr-ZnO/g-C3N4 showed enhanced activities for MG degradation (i.e. 96 % in 20 min), and H2 evolution (31.2 μmolh−1 g-1) which is much obvious compared to the bare g-C3N4, ZnO and Sr-ZnO. It is investigated that Sr ion doping has extended the light absorption toward visible light region. The g-C3N4 grafted Sr-ZnO provided an extra boost up absorption spectra in the visible light region compared to bare ZnO. The photoluminescence spectroscopy and photo-electrochemical measurement confirmed excellent photo-generated charge carrier’s separation in the hierarchical structure of spherical flowers. The improved activities are attributed to the combined impact of in-situ doping, hierarchical morphology, and heterojunction formation.

Up until now, no standard procedure to analyze and quantify the dispersion of particles in the polymer matrix exists. From the conductive hybrid polymer–polymer–graphene nanoplatelets composites we developed, this article attempts to showcase methodologies to analyze and quantify particle with the use of scanning electron microscopy images and collection of the elemental maps of carbon, oxygen, and nitrogen by energy dispersive spectroscopy (EDS) analysis. Image analysis was performed on the resulting map to extract the area and location data of graphene particles by subtracting elemental maps. Shadowing or charging problem in the images acquired from EDS was overcome by the polished surface and analyzing a sample twice using a novel approach of 180° opposed. Merging the data from the two elemental maps, taken 180° opposed, can be an alternative to the use of polished samples. From these different dispersion analysis approaches, it was possible to quantify different particles and their effects on the properties of the composites.

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.

With the high amount of flame retardant content required to produce acceptable levels of fire retardancy for natural fibre composites, it is a challenge to achieve a balance between the mechanical and the flammability properties of these composites because often the fire retardants adversely affect the mechanical performance. In this research, we have used the Taguchi design of experiments approach using standard L9(34) orthogonal array to develop the favourable flame retardant combination for polypropylene/kenaf composites. The parametric responses have been analysed to maximise the fire performance index (FPI) obtained under the cone calorimeter testing. Furthermore, Underwriters Laboratory Vertical burning (UL-94 V) tests have also been conducted to take into the account the flame extinguishing ability under sustained combustion for evaluating the desired parametric combination. The results indicate that the maximum levels of intumescent flame retardant ammonium polyphosphate (APP) content and synergistic natural flame retardant additive (wool) content are the most significant influencing factors in the development of desired flame retardant combination. The compatibiliser and antioxidant contents have been observed to be relatively less influential in FPI evaluation and an increased level of maleic anhydride-grafted polypropylene compatibiliser is found to be adversely affecting to the sustained combustion under UL 94 V tests.

In spite of inherent low flammability, wool fibres have not been thoroughly investigated in fire retardant performance of natural fibre polymer composites. In the present work, polypropylene (PP)-short wool fibre composites were produced by compounding in a twin screw extruder and compression moulding. The enhancement of fire retardancy of the composites by adding wool and ammonium polyphosphate (APP) was confirmed by flammability tests. The cone calorimeter and vertical burn tests showed a significant decrease in heat release rate and a direct flame self-extinguishment of composites, respectively. Furthermore, the cone calorimeter experiments and char morphology have revealed that different polymer viscosities in the composites can influence the APP dispersion, leading to different flammability characteristics. The charring tendency of wool contributed to the formation of a rigid char layer and an increase in the amount of residues in the compact micro-structure of PP-wool-APP composites. The effects of wool and APP on mechanical properties have also been reported with improved tensile moduli of PP-wool-APP composites over those of neat PPs.

Polyethylene terephthalate microfibril-reinforced composites with linear low-density polyethylene (LLDPE) matrix were manufactured by four industrial processing methods: compression moulding, slit-die extrusion with calendering, extrusion blow moulding and injection moulding. The microfibrils were generated in situ by blending the two polymers together and thermomechanically processing the blend. Thin sheets were manufactured in all the processes, except injection moulding, which was employed for making containers. The oxygen permeability of the films was determined using a commercial machine. The greatest improvement in oxygen barrier property (compared to neat LLDPE films), was found in the compression-moulded microfibrillar composite (MFC) films. Two existing theoretical models were modified to reasonably forecast the oxygen permeability of compression-moulded MFC films. The parallel filler model provides a very good fit to the experimental data for the full mass ratio range. The Lewis and Nielsen model was also trialled for various polymer combinations, producing reasonable results with minor modifications.