Han Min Zeng

The effect of fiber treatment on the mechanical properties of unidirectional sisal-reinforced epoxy composites

The present paper investigates the effect of fiber treatment on the mechanical properties of unidirectional sisal-reinforced epoxy composites. Treatments including alkalization, acetylation, cyanoethylation, the use of silane coupling agent, and heating were carried out to modify the fiber surface and its internal structure. As indicated by infrared spectroscopy, X-ray diffraction and tensile tests, variations in composition, structure, dimensions, morphology and mechanical properties of the sisal fibers can be induced by means of different modification methods. When the treated fibers were incorporated into an epoxy matrix, mechanical characterization of the laminates revealed the importance of two types of interface: one between fiber bundles and the matrix and the other between the ultimate cells. In general, fiber treatments can significantly improve adhesion at the former interface and also lead to ingress of the matrix resin into the fibers, obstructing pull-out of the cells. As a result, the dependence of laminate mechanical properties on treatment methods becomes complicated. On the basis of a detailed analysis, the relationship between optimized fiber treatment and performance improvement of sisal composites was proposed.

Improvement of tensile properties of nano-SiO2/PP composites in relation to percolation mechanism

Abstract Low nano-silica loaded polypropylene composites are produced by conventional compounding technique in which the nanoparticles are grafted by polystyrene using irradiation beforehand. A high interfacial stress transfer efficiency is demonstrated by both strengthening and toughening effects perceived in tensile tests. The role of the modified nanoparticles in improvement of tensile properties of the nanocomposites is discussed in terms of percolation concept. A double percolation of yielded zones is presented to explain the specific influence generated by the nano-SiO 2 particles at low-filler loading regime.

Carbon-black-filled polyolefine as a positive temperature coefficient material : Effect of composition, processing, and filler treatment

Polymer-based positive temperature coefficient (PTC) composites are of special interest because they have great potential in temperature-sensitive devices. To obtain a reproducible PTC composite with acceptable PTC intensity, effect of conductive filler content, processing conditions and filler treatment with nitric acid, and titanate coupling agents on room temperature resistivity and PTC intensity of carbon-black-filled low-density polyethylene composites have been described and discussed herein. The results showed that filler arrangement is a key factor influencing the ultimate material performance, which can be tailored in various ways.

Laser ablation of polymer-based silver nanocomposites

Abstract Polymer films (polystyrene and acrylonitrile–styrene copolymer) filled with silver nanoparticles were analyzed by optical absorption spectrometry, X-ray photoelectron spectrometry and laser ablation/time-of-flight mass spectrometry. The results indicated that optical absorption of polymer films was affected by Ag nanoparticles and the interfacial interactions between Ag and the polymer matrices, and the latter was highly dependent on the chemical structure of the polymers. The mass spectral data further demonstrated that the incorporation of Ag nanoparticles into polymers significantly changed the laser ablation mechanism and the products of the polymers. As a result, nano-Ag/polymer films showed a Ag-induced laser-decomposition behavior accompanied by a series of carbon cluster negative ions.

Fractal approach to the critical filler volume fraction of an electrically conductive polymer composite

It has been known for quite a long time that polymers filled with electrically conductive particles, foils or fibres exhibit a distinctive dependence of conductivity on filler volume fraction. With a rise in filler content, there is always a drastic increase in composite conductivity by the order of ten magnitudes at a certain threshold, namely, the critical volume fraction. Such a transition-like change in conductivity is usually interpreted as percolation. Many models have been proposed for explaining the conduction mechanism involved, but often they possess evident drawbacks mainly due to the negligence of relative filler arrangements or the Euclidean geometric description of the arrays. The present work focused on the prediction of the critical volume fraction by a new electrical conductive model, based on the fractal technique and the generalized unit-cell method proposed by Pitchumani and Yao for modelling the thermal conductivity of fibrous composites. It was found that the electrical conduction behaviour of a polymer composite is governed by both a filler geometry factor and a material factor of the components. The critical volume fractions estimated by the model are in good agreement with experimental results taken from the literature. In addition, possible improvements of the present approach are discussed.

Surface modification of magnetic metal nanoparticles through irradiation graft polymerization

To tailor the interfacial interaction in magnetic metal nanoparticles filled polymer composites, the surfaces of iron, cobalt and nickel nanoparticles were grafted by irradiation polymerization. In the current report, effects of grafting conditions, including irradiation atmosphere, irradiation dose and monomer concentration, on the grafting reaction are presented. The interaction between the nanoparticles and the grafted polymer was studied by thermal analysis and X-ray photoelectron spectrometry. It was found that there is a strong interfacial interaction in the form of electrostatic bonding in the polymer-grafted nanoparticles. The dispersibility of the modified nanoparticles in chloroform was significantly improved due to the increased hydrophobicity.

Effect of filler treatment on temperature dependence of resistivity of carbon‐black‐filled polymer blends

Polyblends prove to be able to provide more possibilities for tailoring conductive polymer composites in comparison with individual polymer systems. Accordingly, ethylene–vinyl acetate—low-density polyethylene (EVA–LDPE) filled with carbon black (CB) was prepared in this study as a candidate for positive temperature coefficient (PTC) material. In consideration of the fact that CB distribution plays the leading role in controlling a composites conduction behavior, chemical treatment of CB was applied to reveal its influence on percolation and the PTC effect. It was found that titanate coupling agent treatment facilitated sufficient distribution of CB in LDPE phase, leading to lower resistivity and a squarer PTC curve. Composites filled with nitric-acid-treated CB exhibited specific temperature dependence of resistivity as a result of the heterogeneous dispersion of CB at the interface of EVA–LDPE, which might provide the materials with a new function.

Interfacial interaction in Ag/polymer nanocomposite films

Metallic nanoparticles possess a wide range of novel physical properties, such as electrical, optical, magnetic properties, etc. due to their intermediate structures between atomic state and the bulk [1–3]. For example, strong third-order nonlinear optical susceptibility and ultrafast time response of noble metal (i.e. gold, silver, copper, etc.) nanoparticles have been observed around the surface plasma resonance peaks in the visible region as a result of local-field enhancement [4, 5]. From the practical point of view, these particles have to be dispersed in a solid-state matrix, made of polymers or glasses, to form nanocomposites for the purposes of gaining the necessary stability and processability for making devices [6, 7]. Noble metal nanoparticle/organic polymer composite films are of particular interest because of their potential applications for photonics and electro-optics. Polymer matrices can prevent oxidation and coalescence of the particles and provide them with a long-time stability. As a result, the specific optical and electrical properties of the nanoparticles can be brought into full play, while the typical advantages of organic polymers (e.g., elasticity, transparency, relatively simple ways of synthesis, etc.) are retained in the composite films [8– 10]. Up to now, several methods have been developed for the fabrication of nanocomposite films containing noble metal nanoparticles dispersed in polymer matrix, including in-situ formation of nanoparticles in the matrix of a polymer film, simultaneous plasma polymerization associated with metal evaporation, thermal relaxation technique, etc. [11–16]. However, performance tailoring and optimization of the nanocomposite films are limited, because the factors that affect their performance, including size, shape, microstructure, aggregated structure and concentration of nanoparticles, structure and properties of polymer matrices, and interfacial structure of composites [3, 17, 18], are difficult to be controlled simultaneously by the above approaches. In an earlier report of the authors, a simple fabrication process was developed to obtain 0–3 polymer-based silver nanocomposite films through direct mixing of polymer solution with microemlusionsynthesized silver nanoparticles [19]. It was found that nanoparticles with different geometries (e.g. sphere

Surface modification and particles size distribution control in nano-CdS/polystyrene composite film☆

Preparation of nano-CdS particles with surface thiol modification by microemulsion method and their influences on the particle size distribution in highly filled polystyrene-based composites were studied. The modified nano-CdS was characterized by X-ray photoelectron spectroscopy (XPS), light absorption and emission measurements to reveal the morphologies of the surface modifier, which are consistent with the surface molecules packing calculation. The morphologies of the surface modifier exerted a great influence not only on the optical performance of the particles themselves, but also on the size distribution of the particle in polystyrene matrix. A monolayer coverage with tightly packed thiol molecules was believed to be most effective in promoting a uniform particle size distribution and eliminating the surface defects that cause radiationless recombination. Control of the particles size distribution in polystyrene can be attained by adjusting surface coverage status of the thiol molecules based on the strong interaction between the surface modifier and the matrix.

Friction induced mechanochemical and mechanophysical changes in high performance semicrystalline polymer

By using X-ray photoelectron spectroscopy (XPS) and Fourier transform Raman (FT-Raman) spectroscopy, the worn specimens of polyetheretherketone (PEEK) tested under unlubricated sliding friction and wear conditions at a constant sliding speed were investigated in order to reveal mechanochemically and mechanophysically induced structural changes of polymer as well as wear mechanisms on a molecular scale. Chain scission was found on the worn surface layer. The results suggest that oxidation was the major mechanochemical reaction that followed the chain scission on the top surface. Evidence for chain branching or even crosslinking in bulk materials was also presented. Moreover, two-stage loading dependencies were found for both surface and subsurface in the bulk as revealed through wear rate measurement and wear debris analysis. It was proved that a thermo-activation of polymer segments may be responsible for the transition in the dependence of structure on load. The results of the present work also provide a method (based on spectral analyses) that can be used for studying micromechanisms accounting for shear deformation and failure.