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This study investigates the practical applications of biochar as an innovative and sustainable conductive filler in composite materials. Utilizing the conventional melt-blending method, we prepared conductive pinewood biochar-filled poly(lactic acid)/poly(butylene adipate-co-terephthalate) (PLA/PBAT) composites and systematically examined their electrical, mechanical, rheological and thermal properties. Our results reveal a significant enhancement of electrical and mechanical properties upon the inclusion of conductive pinewood biochar in the PLA/PBAT matrix. With the addition of 10 wt% of conductive pinewood biochar, the average surface resistivity of the composites decreased by three orders of magnitude, measuring [Formula: see text], which meets the antistatic requirements for polymer composites. Additionally, the average tensile strength of the biochar filler composites improved by 53% with an addition of just 1 wt% of biochar.

In composites' secondary/machining process, there is still a requirement for a comparative assessment of microstructure features of tool wear and machined surface mechanisms while machining natural fiber against glass fiber-based composites. This experimental study uniquely investigates the dry-end milling of two polypropylene (PP)-based composites made of 30 wt.% discontinuous reinforcements - kenaf and glass fibers (GF). Surprisingly, though, GF are much harder (GF:5.84 GPa > kenaf:0.15 GPa) and abrasive (silicon content, GF:24.16% > kenaf:0.57%) than kenaf inclusions, cutting GF/PP resulted in relatively lower tool wear (≈0.08 mm) but contrarily showed adverse machined surface finishes (>8 μm) depicting tearing-dragging mechanisms with fuzzy textures. This cautions on the appropriate consideration for the tool's life-determining criterion – i.e., whether it should be based on the tool wear or surface finish. While machining GF/PP material, the tool wear growth on the cutting edges was significantly restricted by the formations of continuous-robust microstructural transfer protective film (TPF) characterized by strong Si + O, Al + O, and Fe + O tribo-chemical reactions through the interesting wear mechanisms associated with tribological phenomena. However, thin-patch type microstructural TPFs consisting of weak Si + C bonds occurred on tool edge regions while machining kenaf/PP. Better mechanical properties and fiber-matrix adhesion of GF/PP influenced by fiber dimensions and their higher aspect ratios (GF:27.60 > kenaf:7.20) decisively seem to have a dominant effect on limiting the tool wear. Chip micrographs clarified the cutting of GF/PP and kenaf/PP occurred by predominant melt-extrusion and shearing respectively.

In the present research, a bio-based flame retardant (FR) was prepared using a biopolymer derived from wastewater sludge to improve the fire performance of polypropylene (PP). Extracellular polymeric substances (EPS), which were extracted from wastewater aerobic granular sludge, were absorbed into cellulose-based fibres, such as flax and toilet papers. Thermogravimetric analysis results indicated that the EPS-cellulose fibres played a significant role in enhancing the char formation of PP composite. Furthermore, the incorporation of the bio-based FR into PP restricted its vertical burning characteristics, and at the same time enhanced the tensile moduli of the composites. The reaction between phosphoric acids from EPS and hydroxyl groups of cellulose fibres improved dehydration and char formation of the composites to enhance the overall fire reaction properties. This study opens up new possibilities for the wastewater-derived biopolymer “EPS” to prepare the bio-inspired FRs for cellulose-based fibres and composites, and enhance sustainability of wastewater sludge treatment.

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.

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.

Sensors as a composite film made from reduced graphene oxide (rGO) structures filled with a silicone elastomer are soft and flexible, making them suitable for wearable applications. The sensors exhibit three distinct conducting regions, denoting different conducting mechanisms when pressure is applied. This article aims to elucidate the conduction mechanisms in these sensors made from this composite film. It was deduced that the conducting mechanisms are dominated by Schottky/thermionic emission and Ohmic conduction.

Biochar-based environment-friendly polymer composites are suitable substitutes for conventional non-biodegradable polymer composites. In this work, we developed polylactic acid (PLA)/polybutylene adipate-co-terephthalate (PBAT)/biochar (BC) composites with improved mechanical and electrical properties for antistatic applications. Coconut shell biochar was obtained through the pyrolysis of coconut shell in an inert atmosphere, and characterised using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), to investigate the morphology and structural properties. The biochar was converted to powder form, sieved to reduce the particle size (≤30 μm diameters), and melt-mixed with PLA and PBAT to form composites. The composites were extruded to produce 3D printing filaments and, eventually, 3D-printed tensile specimens. The tensile strength and tensile modulus of the 3D-printed PLA/PBAT/BC (79/20/1) composite with 1 wt% of biochar improved by 45% and 18%, respectively, compared to those of PLA/PBAT (80/20). The interfacial interaction between the biochar and polymer matrix was strong, and the biochar particles improved the compatibility of the PLA and PBAT in the composites, improving the tensile strength. Additionally, the electrical resistivity of the composite did reduce with the addition of biochar, and PLA/PBAT/BC (70/20/10) showed the surface resistivity of ~1011 Ω/sq, making it a suitable material for antistatic applications.

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.

Herein, electrically conductive natural and synthetic yarns through electrophoretic deposition (EPD) technique were fabricated. A parametric study on the conductivity enhancement of the yarns is carried out by Taguchi method. Using this method, the desirable conditions are determined by studying the effects of important parameters on the electrical conductivity of the yarns in the EPD coating process. Based on the L18 design of experiments table, the preferred combination of factors to obtain the highest electrical conductivity of the yarns is found by Taguchi analysis. In addition, the Pareto ANOVA analysis is conducted to identify the major contributing factors on the electrical conductivity of the yarns. Characterisation techniques, such as scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) in attenuated total reflectance (ATR) mode, and thermogravimetric analysis (TGA) are utilised for better understanding the microstructure and physical properties. When powered by only 3 V, the maximum temperature of a Joule heated conductive sample based on natural fibre yarns reached 102°C in less than 25 s.

The integration of intumescent flame-retardant (IFR) additives in natural fiber-based polymer composites enhances the fire-retardant properties, but it generally has a detrimental effect on the mechanical properties, such as tensile and flexural strengths. In this work, the feasibility of graphene as a reinforcement additive and as an effective synergist for IFR-based flax-polypropylene (PP) composites was investigated. Noticeable improvements in tensile and flexural properties were achieved with the addition of graphene nanoplatelets (GNP) in the composites. Furthermore, better char-forming ability of GNP in combination with IFR was observed, suppressing HRR curves and thus, lowering the total heat release (THR). Thermogravimetric analysis (TGA) detected a reduction in the decomposition rate due to strong interfacial bonding between GNP and PP, whereas the maximum decomposition rate was observed to occur at a higher temperature. The saturation point for the IFR additive along with GNP has also been highlighted in this study. A safe and effective method of graphene encapsulation within PP using the fume-hood set-up was achieved. Finally, the effect of flame retardant on the flax–PP composite has been simulated using Fire Dynamics Simulator.

Detrimental physical and mechanical properties are common problems for composites when their flame retardancy is improved through filler additions. An increased interest of the synergistic nanoparticle addition to improve the flame retardancy of natural fiber composites is the aim of this work. The paper investigates the synergistic effect of two different nanoparticles (halloysite nanotubes (HNTs) and montmorillonite (MMT) nanoclay) on the flame and mechanical properties in an intumescent ammonium polyphosphate (APP)-based polypropylene (PP)/kenaf composite system. First, the nature of nanoparticle dispersion in PP through X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveals that under twin screw compounding process, the partial exfoliation and intercalation have taken place within the nanocomposites. An increase in the decomposition temperature was observed under thermogravimetric analysis (TGA), with the presence of HNT. However, MMT tends to lower the maximum decomposition temperature under inert atmosphere. The flammability analysis in an intumescent flame retardant (IFR) system shows that the suitable amount of high aspect ratio nanoparticles with their exfoliation characteristics effectively helps to reduce the sustained combustion. Even though, improved stiffness properties can be observed with the presence of increased filler content, particle agglomeration tends to reduce the mechanical strengths of these composites due to low compatibilization and crack propagation.

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.

AbstractRoll forming is a rapid operation that employs consecutive roll stations to progressively deform a strip into a desired profile. The continuous nature of the process coupled with its versatility and speed makes it extremely attractive for producing lightweight, structurally efficient components from sheet materials. This paper describes the roll forming of plywood by heated rolls, which is an innovative concept that can increase the range of usage and add value to the end products. Deformation length measurements from static roll bend tests were carried out to determine the roll spacing and the results agree well with the values predicted by a modified theory based on the minimisation of the total deformation energy for a rigid-plastic material. The deformation lengths, such as in metals and composite sheets, depend essentially on the geometric parameters of the profiles produced and are practically independent of the mechanical properties of the work material. Further, the real-time strain measurements by strain gauges bonded on the roll formed specimens show that the strain profiles compare reasonably well with those obtained for metallic and continuous fibre-reinforced thermoplastic sheets. Finally, the macroscopic deformation of veneer sheets due to roll forming has been analysed kinematically by means of grid strain analysis and the geometric conformance of the product has been determined. [ABSTRACT FROM AUTHOR]

The characteristics of poly(butylene terephthalate) (PBT), poly(ethylene naphthalate) (PEN), and blends with 30, 40, 50, 60, and 70 wt % PEN prepared by melt‐blending were analyzed using Fourier transform infrared spectroscopy, Raman spectroscopy, X‐ray diffraction, solid‐state nuclear magnetic resonance (NMR), and X‐ray photoelectron spectroscopy. The spectroscopic analyses provide no direct evidence for the occurrence of transesterification reactions occurring during melt‐processing of the blends under the conditions that were used. The improved mechanical properties of the PBT/PEN blends are attributed to physical interactions occurring over a large interfacial area. X‐ray diffraction and high‐resolution solid‐state carbon‐13 (13C) NMR confirmed the formation of the α‐PEN phase after annealing samples at 200°C for 19 h. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [ABSTRACT FROM AUTHOR]

AbstractThermoforming of wood veneers into profiles is a novel idea and the focus of this paper is to study the formability characteristics of thin radiata pine (Pinus radiataD. Don) veneers, which are generally used as surface coverings. Radiata pine is well suited as a raw material for furniture, joinery, and interior architectural products. This is because it has excellent turning, shaping, and laminating properties and readily achieves brilliant stain and paint finishes. In this study, radiata pine veneers were softened by immersion in a hot water bath and then thermoformed by means of heated dies/moulds. The formability characteristics were investigated by conducting single-curvature V-bending tests. The influence of the forming method on the shape conformance of softened veneers under single- and multiple-bend conditions was examined. The paper also discusses the influences of manufacturing parameters that include the softening method, the die temperature, the duration of forming, the ratio of bend radius to veneer thickness, and the veneer architecture. The study clearly establishes the feasibility of forming veneers into multi-bend products in a semi-continuous manner using matched dies. [ABSTRACT FROM AUTHOR]

To understand the mechanism of bulk wood forming, compressive stress relaxation experiments were performed on radiata pine (Pinus radiata D. Don) specimens with various moisture contents at a temperature of 200°C. The results aided in understanding the time-dependent viscoelastic behaviour with respect to springback and microstructural changes. This study clearly demonstrates the commercial feasibility of value-adding applications such as pattern forming on wood panels using a relatively simple, quick and inexpensive procedure. The experimental data were characterised by a three-component model with a spring and a Maxwell element in parallel, which showed very good agreement under different forming conditions. [ABSTRACT FROM AUTHOR]

For many applications, the perceived quality of a medium-density fibreboard (MDF) is influenced by the appearance of its machined surface. The behaviour of MDF has been studied by passing a cutting tool through it at a relatively low speed. A digital camera was used that travels synchronously with the tool and the deformation occurring in front of the tool tip was recorded. The magnification of approximately 30× also allows the individual fibres or bundles to be clearly observed. Photographic images have also been taken of the same machining process at a much higher speed, producing similar results and thus establishing the slow-speed study as a viable option. The machining of different MDF samples has been recorded using a cutting speed of 1.6 mm s−1 and varying depths of cut (0.5, 0.75 and 1.0 mm). The video recordings of various panels permit the identification of their peculiar machining characteristics. Unrefined particles play a major role during machining. The trends of results have also been confirmed by scanning electron micrographs. The board densities were found to have a major influence on the machinability characteristics of the boards. [ABSTRACT FROM AUTHOR]

Melt blends of poly (butylene terephthalate) (PBT) and poly (ethylene naphthalate) (PEN) with 30, 40, 50, 60 and 70 wt% PEN were prepared using a single screw extruder and injection moulding machine. 13C and 1H nuclear magnetic resonance (NMR) spectra were obtained with a Bruker DRX-400 instrument, on solutions prepared by dissolving samples of the homopolymers and each blend in deuterated trifluoroacetic acid + chloroform mixtures (1:1 by volume). The absence of new signals in 1H and 13C spectra, that would be expected to result from transesterification reactions in the PBT + PEN blend system, provides convincing evidence that such reactions do not occur in these blends under the melt processing conditions that were used. In the light of published work on solid-state NMR studies of these and related blend systems, and our observations of partial miscibility with a very small domain size, together with substantial enhancement of the mechanical properties of PBT by blending with PEN, we conclude that the improvement in mechanical properties arises from molecular scale mixing of the homopolymers and strong but non-covalent bonding interactions over the very large interfacial area between the PBT-rich and PEN-rich phases. [ABSTRACT FROM AUTHOR]

Straining of PVA/PE and PVA/PP blends (70:30) is monitored by small-angle x-ray scattering (SAXS). Sheet-extruded films with different predraw ratio are investigated. The discrete SAXS of predrawn samples originates from polyolefin nanofibrils inside of polyolefin microfibrils immersed in a PVA matrix. PE nanofibrils deform less than the macroscopic strain without volume change. PP nanofibrils experience macroscopic strain. They lengthen but their diameter does not decrease. This is explained by strain-induced crystallization of PP from an amorphous depletion shell around the core of the nanofibril. The undrawn PVA/PE film exhibits isotropic semicrystalline nanostructure. Undrawn PVA/PP holds PP droplets containing oriented stacks of semicrystalline PP like neat precursors of hard-elastic thermoplasts. Respective predrawn films are softer than the undrawn material, indicating conversion into the hard-elastic state. Embedding of the polyolefin significantly retards neck formation. The polyolefin microfibrils can easily be extracted from the water-soluble matrix.