Volume 39, Issue 1

This investigation highlights the rationale of epoxy-novolac interpenetrating polymer network (IPN) adhesive bonding of low-pressure plasma treated polyether ether ketone (PEEK) to plasma nitrided titanium for aerospace application. Physico-chemical characterization of surface modified PEEK is carried out by surface energy measurement and X-ray photoelectron spectroscopy (XPS) analysis. Lap shear tensile tests are carried out to measure mechanical properties such as lap-shear tensile strength, Young’s modulus, percentage elongation at break (% EB) and toughness of the adhesive bonded PEEK to titanium joint. XPS analysis reveals the presence of the oxygen (O) functional group into the plasma treated PEEK surface. This polar functional group O increases the surface energy on the plasma treated PEEK surface, and consequently, the adhesive bond strength is enhanced. The values of Young’s modulus, % EB and toughness of epoxy-novolac IPN adhesive bonded plasma treated PEEK to plasma nitrided titanium are increased considerably in respect to epoxy-novolac IPN adhesive bonded untreated PEEK to untreated titanium joint. Therefore, the present investigation concludes that the adhesive bond strength not only depends on the surface characteristics of PEEK and titanium, but also on the cohesive properties of the adhesive.

A new type of material was prepared by modifying epoxy/basalt fiber composites with nanoSiO 2 . Mechanical tests showed that the nanoSiO 2 -modified epoxy/basalt fiber composites displayed significant improvement over the unmodified epoxy/basalt fiber composites in interlaminar shear strength and notch impact strength. Scanning electron microscopy revealed that the nanoSiO 2 was homogeneously dispersed in the epoxy matrix and adsorbed large numbers of epoxy molecules onto the surface. Many of the nanoSiO 2 -epoxy complexes tightly surrounded basalt fibers to form transition layers. Therefore, nanoSiO 2 can act as a nano-mediator to promote epoxy molecules to infiltrate between and bind to basalt fibers, which enhances the synergistic cooperation between epoxy and basalt fibers in resisting external forces. This study indicates that modification with nanoSiO 2 is an effective pathway to improve the performance of epoxy/basalt fiber composites and broaden their application fields.

In this study, PA6-66/γ-aminopropyltriethoxysilane-modified clay nanocomposites were prepared by in situ polymerization. It was found that the γ-aminopropyltriethoxysilane was chemically grafted onto clay successfully, and the covalent bond was formed between the clay and polymer chains. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) results indicated that intercalated and exfoliated nanocomposites were obtained. The PA6-66 nanocomposites exhibited improved mechanical performance compared to that of neat PA6-66. Most importantly, the PA6-66 nanocomposites showed significantly improved toughness. In comparison with neat PA6-66, the rupture stress and elongation at the break of the nanocomposite with only 0.5 wt% clay increased 91.9% and 91.8%, respectively. The excellent toughness of PA6-66 nanocomposites should be mainly ascribed to the combined effects of strong polymer-clay interaction, the intercalated-exfoliated structures of clay, refined crystalline, formation of γ-form crystals, and decreased crystallinity of PA6-66.

This article reports some morphological, tribological, and mechanical data on polyamide-11(PA11)/halloysite nanotube (HNT) nanocomposites prepared by melt-compounding. HNTs extracted from the Djebel Debbagh deposit in Algeria were incorporated into the polymer at 1, 3, and 5 wt%. For comparison, commercial HNTs were also used under the same processing conditions. Scanning electron microscopy showed that both HNTs were homogeneously dispersed in the PA11 matrix, despite the presence of few aggregates, in particular at higher filler contents. The tribological properties were significantly improved, resulting in a decrease in the friction coefficient and the wear rate characteristics due to the lubricating effect of HNTs. This is consistent with optical profilometry data, which evidenced the impact of both types of HNTs on the surface topography of the nanocomposite samples, in which the main wear process was plastic deformation. Furthermore, Young’s modulus and tensile strength were observed to increase with the filler content, but to the detriment of elongation at break and impact strength. Regarding the whole data, the raw Algerian halloysite led to interesting results in PA11 nanocomposites, thus revealing its potential in polymer engineering nanotechnology.

The present study focuses on the fabrication and analyses of polyvinyl alcohol (PVA) based films blended with polymers, such as starch and protein. The aim is to improve the moisture absorption, solubility, mechanical and thermal properties of PVA by blending it with various polymers. The thermal cross-linking of the films has been studied by heating the films at 120°C for 4 h. The result shows that PVA was completely soluble in water, while post-blending solubility and moisture absorption of blended films decreased. The tensile strength of blended films was significantly higher (4%–29%) as compared to neat PVA, while thermally cross-linked films showed much higher strength (8%–174%). Blended films were characterized using Fourier transform infrared spectroscopy (FTIR) to confirm the formation of hydrogen bonds. Thermogravimetric analysis showed the increase in degradation temperature post-blending as compared to neat PVA. The viscoelastic behavior of the material as well as glass transition temperature was studied using dynamic mechanical analysis. Creep and recovery behavior were examined to study the effect of stress and temperature on creep strain. The biodegradability of the blended films was increased post-blending. This study showed that PVA based blend films can replace non-biodegradable plastics and hence are necessary for the development of environmentally friendly materials.

Shear thickening fluids (STF) are stabilized and concentrated colloidal suspensions of hard nano-particles in a liquid medium (polymer) that, under the influence of impact forces, show non-Newtonian fluid behavior (shear thickening) dissipating the energy of impact. The viscosity of the dispersion medium should be optimum to lead to an increase in shear thickening, and at the same time, should also allow proper dispersion of the particles. Herein, an STF based on 20 wt% fractal nano-fumed silica particles of 11 nm suspended in a liquid medium of polyethylene glycol (PEG 200) with different concentrations of silicone oil was prepared. These systems were studied in terms of steady-state and dynamic-state rheological behavior under a wide range of temperature, shear rate, strain rate and frequency. The STF with replacement of up to only 20% of PEG with silicone oil as the liquid medium shows a large increase (about four times) in shear thickening parameters when compared with STF containing only PEG under the same processing conditions. It also shows more elastic behavior at high frequencies which are due to the high cross-linking property of silicone oil, contributing to much-improved properties, which are highly desirable from the view point of many applications.

In this article, the influence of polylactide and pro-oxidant on the thermal stability, degradation kinetics, and lifetime of polypropylene has been investigated using thermogravimetric analysis under nitrogen atmosphere at four different heating rates (i.e. 5, 10, 15, and 20°C/min). The kinetic parameters of degradation were studied over a temperature range of 30–550°C. The derivative thermogravimetric curves have indicated single stage and two stage degradation processes. The activation energy was evaluated by using the Kissinger, Kim-Park, and Flynn-Wall methods under the nitrogen atmosphere. The activation energy value of polypropylene was much higher than that of polylactide. Addition of polylactide and pro-oxidant in polypropylene decreased the activation energy. The lifetime of polypropylene has also decreased with the addition of polylactide and pro-oxidant.

This work investigates the possibility of using polyetherimide (PEI) as an energy saving alternative to glass, polymethylmethacrylate (PMMA) and polycarbonate (PC) by carrying out heat transfer analysis and suggests vaporized solvent bonding as a viable bonding technique for the fabrication of PEI. By heat transfer analysis using building energy simulation, it is observed that less energy is expended for space-conditioning of a building with windows made of PEI when compared to glass, PMMA and PC. The compression moulding technique is used to mould PEI and fabrication is done using a solvent mixture of dimethyl sulfoxide and tetrahydrofuran in 1:1 ratio. The optical properties of the bonded specimen are studied using UV-visible spectrophotometry and it is found that PEI does not allow UV wavelength radiation to pass through while transmitting visible wavelengths. The mechanical strength of the bond is tested using lap shear tensile strength test and the type of failure is observed to be cohesive from the structure. This is indicative of the fact that using this particular solvent to bond PEI results in the maximum possible strength.

In this study, poly(lactic acid) (PLA) matrix bio-composites reinforced with various quantities of sisal fibers (SFs) (from 10% to 50% in weight) were fabricated by using a self-made vane mixer, which can generate continuous elongation flow. The morphology, crystallization, and mechanical properties of PLA/SF bio-composites under continuous elongation flow were investigated. Scanning electron microscopic images showed that SFs were uniformly dispersed in the matrix and oriented along the extrusion direction. Meanwhile, it was found that the diameter of SFs decreased from 250 to 20 μm, which certified that continuous elongation flow remarkably affected the separation of elementary fibers from fiber bundles. Wide-angle X-ray diffraction and differential scanning calorimetry measurements indicated that the addition of SFs promoted the crystallization of PLA as well as increased the crystallinity of PLA. The mechanical tests exhibited that both impact strength and tensile modulus were significantly enhanced (about 64% and 94.63%, respectively) with SFs loading at 40%, which was due to the well dispersion and separation of elementary fibers.

Graphene oxide (GO) was chemically modified in xylene with dodecyl amine and hydrazine monohydrate to obtain reduced functionalized graphene oxide (RFGO). Composites of high-density polyethylene (HDPE) and GO were made via solvent reaction, whereas both melt mixing and solvent reaction were used for HDPE-RFGO composites for comparison purposes. Elemental and thermal analysis showed the success of GO modification in grafting amine functionalities onto its structure and restoring most of the original graphene C=C bonds. A significant increase in mechanical properties, thermal stability, and crystallization behavior was observed for HDPE-RFGO (solvent) compared with HDPE and HDPE-GO, proving that homogeneous dispersion of RFGO in the polymer matrix and strong interactions between them resulted in facilitated stress transfer, delayed thermal degradation, and more efficient nucleating effect in inducing the crystal growth of HDPE. A comparison of HDPE-RFGO properties enhancement between the melt mixing method and the solvent reaction method showed that, apart from mechanical behavior, the RFGO contribution was the same, suggesting that the optimization of the ecofriendlier approach (melt) could eventually lead to its total use for the mass production of high-performance, cost-effective, and more environmentally friendly graphene-based thermoplastic polyolefin nanocomposites suitable for highly demanding industrial applications.

One of the major issues in the wood industry is the durability of clear coatings. The addition of organic ultraviolet absorbers (UVAs) improves coating resistance by the absorption and conversion of UV radiation into harmless heat. Organic UVAs are, however, easily degraded by free radicals produced by photodegradation inside the polymer matrix and are prone to migration in the coating. In this study, commercial UVAs and hindered amine light stabilizers (HALS) entrapped into poly(methyl methacrylate) (PMMA) microspheres and CaCO 3 templates coated with UV-responsive polymers were added into clear acrylic water-based coating formulation. Artificial accelerated weathering experiments were performed on each formulation. Raman spectroscopy mapping was performed to visualize the concentration and distribution of UVAs and HALS. This study also presents a comparison of the mechanical properties of coatings obtained by dynamic mechanical analysis. Results showed that coating mechanical properties were improved when using encapsulated UVAs and HALS inside PMMA microspheres. The color change of the wood and coating system was minimized and the production of photo-oxidation compounds in the binder was also limited.