Xiaowen Yuan

Improving the mechanical properties of natural fibre fabric reinforced epoxy composites by alkali treatment

In this article, three bio-composites, i.e. flax, linen and bamboo fabric reinforced epoxy resin, were manufactured using a vacuum bagging technique. The influence of alkali treatment (with 5 wt% NaOH solution for 30 min) on tensile properties of flax, linen and bamboo single-strand yarns, surface morphology and mechanical properties (with respect to tensile and flexural properties) of the composites were investigated. It was found that the failure mechanism of single-strand fibres under tension consists of fibre breakage and slippage simultaneously. The alkali treatment had a negative effect on the tensile strength and modulus of the flax, linen and bamboo single-strand yarns. However, after the treatment, the tensile and flexural properties of all the composites increased, e.g. the tensile and flexural strength of the treated flax/epoxy composite increased 21.9% and 16.1%, compared to the untreated one. After the treatment in all the composites, the tensile fractured surfaces exhibited an improvement of fibre/epoxy interfacial adhesion.

Plasma treatment of sisal fibres and its effects on tensile strength and interfacial bonding

Argon- and air-plasma treatments have been used to modify the surface of sisal fibres. The Taguchi method of experimental design with three factors and three levels is used to optimise the treatment parameters in relation to fibre strength. The effects of plasma treatment on interfacial bonding between sisal fibres and polypropylene are evaluated by means of a single fibre pull-out test. The optimum treatment parameters have been found to be the shortest plasma treatment time, medium power level and medium chamber pressure. Under optimal treatment, the interfacial shear strength of air-plasma treated fibres is higher than that of the argon-plasma treated fibres. Scanning electron microscopy analyses show that the overall roughness of the plasma treated fibre surface increases with treatment time. The Ar-plasma treated fibre surface reveals obvious corrugations whereas cracking is apparent on the air-plasma treated fibre surface.

Mechanical properties of plasma-treated sisal fibre-reinforced polypropylene composites

In recent years, sisal fibres have become a promising reinforcement for composites because of their low cost, low density, high specific strength, high specific modulus, easy availability and renewability. However, the poor adhesion between the hydrophilic sisal fibre and the hydrophobic thermoplastic matrices has adversely affected the widespread use of these composites. In this study, argon and air-plasma treatments have been used to modify the fibre surfaces under suitable treatment parameters to improve the compatibility between sisal fibres and polypropylene (PP). Sisal fibres and PP fibres are blended together to form a random mat which is then vacuum hot-pressed into a preimpregnated composite sheet. Mechanical properties such as tensile strength and modulus, flexural strength and modulus, and the storage modulus of the composite sheets improve after the incorporation of plasma-treated fibres. Furthermore, scanning electron microscopy analyses reveal the increased surface roughness of sisal fibre. Surface characterisation has been performed by X-ray photoelectron spectroscopy, showing an increase in oxygen/carbon ratio of sisal fibres after plasma treatment.

Evaluation of jute/glass hybrid composite sandwich: Water resistance, impact properties and life cycle assessment

The mechanical properties and the life cycle assessment (LCA) of jute woven fabric composites and their hybrids are investigated. Jute woven fabric composites were sandwiched with glass woven composites with the epoxy matrix. The sandwiched composites were prepared using the resin infusion under flexible tooling method. The water absorption test was performed on jute woven composites and composite sandwiches. It shows that thin layers of glass woven composites in the composites sandwich decelerate water penetration to jute woven composites, which are the core materials. The water absorption process applied to jute woven composites and their sandwich was modeled using Fick’s second law. The glass woven composites at the outer surface of the sandwich can act as strong skins. The bending and impact (drop weight) properties of jute–glass woven composites are higher than those of jute woven composites. A commercial LCA software product was employed to evaluate the environmental impacts of manufacturing the jute woven composites and their hybrids. The manufacturing of jute–glass woven composites had more negative environmental impacts (global warming, ozone depletion, etc.) than that of jute fabric composites, because glass fibres are less environmental friendly than natural fibres.

Fiber-matrix interfacial adhesion in natural fiber composites

The interface between natural fibers and thermoplastic matrices is studied, in which fiber-matrix wetting analysis and interfacial adhesion are investigated to obtain a systematic understanding of the interface. In wetting analysis, the surface energies of the fibers and the matrices are estimated using their contact angles in test liquids. Work of adhesion is calculated for each composite system. For the interface tests, transverse three point bending tests (3PBT) on unidirectional (UD) composites are performed to measure interfacial strength. X-ray photoelectron spectroscopy (XPS) characterization on the fibers is also carried out to obtain more information about the surface chemistry of the fibers. UD composites are examined to explore the correlation between the fiber-matrix interface and the final properties of the composites. The results suggest that the higher interfacial adhesion of the treated fiber composites compared to untreated fiber composites can be attributed to higher fiber-matrix physico–chemical interaction corresponding with the work of adhesion.

MECHANICAL PERFORMANCE OF ROTOMOULDED WOLLASTONITE-REINFORCED POLYETHYLENE COMPOSITES

This paper describes the development of a new processing technology for rotational moulding of wollastonite microfibre (WE) reinforced polyethylene (PE). Manufacturing wollastonite-polyethylene composites involved blending, compounding by extrusion, and granulating prior to rotational moulding. The properties of the resulting composites were characterised by tensile and impact strength measurements. The results show that tensile strength increases monotonically with the addition of wollastonite fibres, but impact strength is decreased. In addition, the processability is also decreased after adding more than 12 vol% WE because of increased viscosity. The effects of a coupling agent, maleated polyethylene (MAPE), on the mechanical performance and processability were also investigated. SEM analysis reveals good adhesion between the fibre reinforcements and polyethylene matrix at the fracture surface with the addition of MAPE. It is proposed that fillers with small particles with high aspect ratio (such as wollastonite) provide a large interfacial area between the filler and the polymer matrix, and may influence the mobility of the molecular chains.

Hybrid thermoplastic composites using ceramic reinforcements

Abstract Polyethylene-based and polypropylene-based composites, incorporating silica nanoparticles and geopolymers, were prepared by melt compounding. Scanning electron microscope (SEM) images indicate that the silica nanoparticles do not distribute uniformly as fine particles in the matrix, but are unevenly distributed as clusters. As a result, the tensile properties of those composites are inferior to those of the matrix polymer. A novel concept of in situ formation of a reinforcing phase has been investigated as a method of resolving that problem. The reinforcing elements are microcrystalline phases developed during melt processing of mixtures of geopolymer precursors with polyethylene or polypropylene. Preliminary tensile test data on injection moulded specimens show some improvement in mechanical properties of both geopolymer–polyethylene and geopolymer–polypropylene composites relative to the matrix polymers. Scanning electron micrographs clearly show the presence in the composites of a nanoscale acicular crystalline structure that is thought to act as a fibre-like reinforcement.

3D printing of fibre reinforced honeycomb structured composite materials

The paper presents the work on manufacturing and preliminary characterisation of fibre reinforced composite honeycomb structured composites by 3D printing. The capabilities and limitations of the processing are discussed. The work aims to compare the effectiveness of reinforcement using specimens of similar dimensions produced on the same machine and characterise them. Initially, tensile performance of unprinted fibre and printed fibre has been evaluated. Challenges associated with the testing of the printed specimens are addressed. Bend testing will follow to assess the performance as a composite structure to assess the interaction between fibre, matrix and core. Continuing work is planned to compare the effect of other parameters such as fill pattern and fill density to assess their effect on the composite.

Effect of Coupling Agents and Particle Size on Mechanical Performance of Polyethylene Composites Comprising Wollastonite Micro-Fibres

The usefulness of rotational moulding (rotomoulding) as a polymer processing technique is often limited by the selection of polymers, which in most cases happens to be polyethylene (PE). In the present study, PE polyethylene was blended with wollastonite microfibres and maleated polyethylene (as a coupling agent) with the purpose of developing an improved material for rotational moulding. The incorporation of wollastonite fibres without any coupling agent improved the tensile strength, but showed a reduction in impact strength. As expected, the most significant enhancement due to wollastonite was in the tensile modulus.. The addition of a coupling agent improved both the impact strength and the processability, especially when wollastonite was coated with aminosilane. Scanning electron microscopy revealed good adhesion between the coated fibre reinforcement and the polyethylene matrix at the fracture surface.

Highly flexible, foldable and stretchable Ni–Co layered double hydroxide/polyaniline/bacterial cellulose electrodes for high-performance all-solid-state supercapacitors

A novel flexible nickel–cobalt layered double hydroxide/polyaniline/bacterial cellulose (NiCo-LDH/PANI/BC) electrode with both excellent electrochemical and mechanical performances is obtained through successively coating PANI and NiCo-LDH on BC. In addition to making the 3D open network (BC) conductive, the PANI layer also functions as a “nanoglue” to uniformly and robustly immobilize nanostructured NiCo-LDH onto the highly enlarged surface of PANI/BC nanofibers owing to its rough surface and hydrophilicity. Benefitting from the hierarchical structure with a 3D conductive network, unobstructed channels, numerous electroactive sites and induced synergistic effect, the NiCo-LDH/PANI/BC electrode shows excellent electrochemical performance in an aqueous electrolyte, exhibiting a high specific capacitance of 1690 F g−1 (761 C g−1) at 1 A g−1, enhanced rate capability (778 F g−1 or 350 C g−1 at 15 A g−1) and outstanding cycling stability (83.2% capacitance retention after 5000 cycles). Besides, the NiCo-LDH/PANI/BC also shows excellent foldability, high tensile strength (90.8 ± 4.9 MPa), high elongation at break (7.2 ± 0.7%) and outstanding electrochemical stability during bending and stretching. Moreover, a flexible all-solid-state supercapacitor is assembled with NiCo-LDH/PANI/BC as the positive electrode and N-doped carbonized BC/carbon cloth as the negative electrode, delivering a high energy density of 47.3 W h kg−1 at a power density of 828.9 W kg−1, and superior cycling stability (91.4% capacitance retention after 3000 cycles). Therefore, this work provides a new path for high-performance flexible energy storage devices and offers a new vision for uniformly and robustly assembling nanohybrids.