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In this study, we examine the effect of multi-wall carbon nanotubes (MWCNT) morphology on electrical and mechanical properties of MWCNT-filled polyurethane (PU) nanocomposites. The main objective of this study is to understand the role of aspect ratio and length of MWCNTs in determining the performance of nanocomposites. Highly aligned MWCNTs were prepared by aerosol-assisted chemical vapour deposition method and compared to commercially available MWCNTs in PU matrix for ease of dispersibility and performance. We observed opposing influence of the MWCNT on electrical and mechanical behaviour of the nanocomposites. The electrical properties were proportional to length of the MWCNTs whereas the mechanical properties were dependent on the aspect ratio of the MWCNTs. Moreover, thicker nanotubes (approximately 40 nm) with a higher aspect ratio (approximately 225) are less prone to shortening and impart better tensile and storage modulus along with improved electrical and therefore are more suitable for the MWCNT nanocomposites.

The aim of this work was to study the effect of stitch pattern and stitch tension on tension-tension fatigue performance of quasi-unidirectional non-crimp fabric reinforced glass-fibre/epoxy laminates. Internal structure variations of the laminates were characterised using cross-sectional microscopy imaging for the evaluation of fatigue test results. Reinforcements for the study were manufactured with three different stitch patterns and two different stitch tensions. Based on the results, the stitch pattern contributes to in-plane and out-of-plane waviness of fibres, as well as on the size and shape of the axial fibre bundles. The fatigue life and slope parameter of the fitted S-N curve were significantly dependent on the stitch pattern, while they were not dependent on the applied stitch tension.

In quasi-unidirectional (quasi-UD) laminates reinforced with stitched non-crimp fabrics (NCF), axial fibre bundles in neighbouring fabrics can lie on top of each other or they may be overlapped. Also, the stitch phase can vary between the neighbouring fabrics. In this study, the effect of mutual location of axial fibre bundles and stitch phase difference on tension-tension fatigue performance of quasi-UD laminates reinforced by glass-fibres was experimentally investigated. Damage development and accumulation were monitored by photographing and thermal-imaging in the specimens' gauge section during the fatigue tests. Internal structure characterisation of the laminates based on micrographs was performed to find possible reasons that might affect the fatigue life. The study revealed that the stitch phase difference clearly affects the damage progression, fatigue life and the slope parameter of fitted S-N curves, but the effect of the mutual location of axial fibre bundles on these parameters is minor.

Two austenitic stainless steel grades, 316L and 904L, and three duplex stainless steel grades, LDX 2101, 2205, and 2507, were erosion–corrosion tested as impeller blade materials for hydrometallurgical applications. Samples were attached to the pressure and suction sides of an impeller and were tested in 50 g/l H 2 SO 4 and 0.5 g/l Fe 2 (SO 4 ) 3 for 72 h at 80°C and 95 °C in a small-scale reactor using quartz sand slurry. The results showed that under lower erosion intensity the ranking of the grades was similar to that in pure erosion. Under higher erosion intensity the ranking of the grades changed completely: lean alloys LDX 2101 and 316L suffered from the highest mass losses followed by 2205, 2507, and 904L. To clarify this behavior, the ability of the grades to repassivate was investigated with scratch tests. It was found that the ranking could be explained by the repassivation rates. The only exception was that 2507 showed a similar repassivation rate to 904L but its erosion–corrosion mass loss under higher erosion intensity was larger. One contributing factor to this was found to be the selective dissolution of the austenite phase of all the tested duplex grades. The prerequisites for the galvanic coupling between the phases that was responsible for the selective dissolution are discussed.

Two austenitic stainless steel grades, 316L and 904L, and three duplex stainless steel grades, LDX 2101, 2205, and 2507, were erosion tested as impeller blade materials for hydrometallurgical applications. Samples were attached to the pressure and suction sides of an impeller and were tested for 72 h at 80 °C and 95 °C in a small-scale reactor using quartz sand slurry. Based on the mass losses measured, the steel grades could be ranked into two distinct categories; LDX 2101 and 2507 comprising the category with the better erosion resistance. The categories were the same for the pressure and suction side tests even though the erosion mechanism differed. In most cases, erosion was more severe in the suction side samples, which has practical implications for wear protection design. In the pressure side samples, the variation in the erosion mass loss with different experimental parameters was in line with earlier reported findings. In contrast, in the suction side samples, under some experimental conditions, increasing tip speed and increasing particle size were found to reduce erosion mass loss. This emphasizes the fact that the erosivity of particles for the impeller suction side cannot be deduced solely based on particle size. The reasons for the observed behavior are discussed.

The effect of various fillers on the mechanical, barrier, and flammability properties of polypropylene (PP) was studied. PP was filled with 4 wt% of nano-sized calcium carbonate, titanium dioxide, organoclay, and multiwalled carbon nanotube (MWCNT). For comparison, micron-sized calcium carbonate was also studied. Two-step masterbatch dilution approach of the composites suggested no or only minor improvements in Young's modulus and tensile yield strength, whereas their ductility decreased compared to coupling agent-modified PP matrix. The water vapor transmission results of filled films showed increased permeability compared to their coupling agent-modified counterpart. Oxygen permeability, however, decreased for the composites. The MWCNT-filled matrix showed the highest barrier and fire performance, attributed mainly to its higher filler volume content, but also other reasons such as the effect of filler dispersion, composite's thermal stability, and polymer crystallinity were discussed.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers

The morphological, mechanical, thermal, and tribological properties of high-density polyethylene (HDPE) composites reinforced with organo-modified nanoclay (3 and 6 wt%) were studied. A commercial maleic anhydride-based polymeric compatibilizer (PEgMA) was used to improve the adhesion between the polyethylene and clay. Transmission electron microscopy (TEM) characterization of composites revealed that nanoclay exists mainly in a multilayered structure in the HDPE matrix. Mechanical testing of composites showed that Young's modulus and tensile strength increased with nanoclay content. Coefficients of the linear thermal expansion (CLTE) of HDPE–PEgMA–clay composites were slightly lower in the flow direction than those of HDPE–PEgMA. The tribological properties were measured in dry conditions against a steel counterface. The friction coefficient of the matrix was decreased by the addition of clay. Electron microscopic results suggested that the wear mechanism for HDPE and HDPE composites was mainly adhesive. Clay agglomerates were observed on the worn surfaces of the composites, which may partly explain decreased friction. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Slurry erosion wear performance of glass fibre reinforced vinylester composite (FRP) has been studied using a pilot-scale erosion test apparatus. Tests were conducted at elevated temperatures in aqueous and acidic environments. When using fine quartz as an abrasive material, FRP showed higher mass losses in the aqueous environment than in the acidic conditions, especially at higher temperatures. In this case, the FRP degradation was governed by the penetration of the used medium into the FRP structure. According to the absorption studies, the weight gain of the laminate was more pronounced in the water immersion compared to the acidic solution, which can be a prediction of an increased degradation rate and explain the higher wear in the aqueous medium. When the abrasive material was changed from fine to coarse quartz, the removal of the shielding matrix phase was extensive and a direct route for the acidic solution to the fibres was created causing more severe damage. This was also shown in scanning electron microscopy (SEM) studies, where the samples tested in the acidic solution showed extensive fibre flattening along the erosion flux. By increasing the test temperature close to the boiling point of the medium, an increase in the FRP wear could be seen. The increase in the rotation speed, on the other hand, did not automatically mean higher mass losses. This shows that the wear environment in the present test device is highly complicated with several interrelated parameters affecting the results. acceptedVersion

Magnesium hydroxide (MDH) particles are often used as fillers to improve the flame retardancy of polymers. However, achieving the balance between the enhanced fire resistance and reduced mechanical properties, especially toughness, is still a challenge to the composite community. In this study, the effect of the particle size and silane surface modification of MDH particles on the flame retardant, thermal, and mechanical properties of epoxy was studied. Both nano- and micro-sized MDH particles were modified by a silanization reaction with γ-aminopropyltrietoxysilane in an aqueous solution and filled into epoxy matrix by a high-shear mixer and a three-roll mill. Results show that nano-MDH filled epoxy composites yielded better mechanical properties than their micro-MDH filled counterparts. Furthermore, the adhesion between nano-sized MDH and the matrix was improved by the silane surface modification. When comparing the flame retardant properties, enhancements in heat release rates and total heat released were observed for MDH filled epoxy composites.

Polyamide and polystyrene particles were coated with titanium dioxide films by atomic layer deposition (ALD) and then melt-compounded to form polymer nanocomposites. The rheological properties of the ALD-created nanocomposite materials were characterized with a melt flow indexer, a melt flow spiral mould, and a rotational rheometer. The results suggest that the melt flow properties of polyamide nanocomposites were markedly better than those of pure polyamide and polystyrene nanocomposites. Such behavior was shown to originate in an uncontrollable decrease in the polyamide molecular weight, likely affected by a high thin-film impurity content, as shown in gel permeation chromatography (GPC) and scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer. Transmission electron microscope image showed that a thin film grew on both studied polymer particles, and that subsequent melt-compounding was successful, producing well dispersed ribbon-like titanium dioxide with the titanium dioxide filler content ranging from 0.06 to 1.12wt%. Even though we used nanofillers with a high aspect ratio, they had only a minor effect on the tensile and flexural properties of the polystyrene nanocomposites. The mechanical behavior of polyamide nanocomposites was more complex because of the molecular weight degradation. Our approach here to form polymeric nanocomposites is one way to tailor ceramic nanofillers and form homogenous polymer nanocomposites with minimal work-related risks in handling powder form nanofillers. However, further research is needed to gauge the commercial potential of ALD-created nanocomposite materials.

The effects of adhesion promoter properties on the structure and mechanical behavior of nanoclay-filled polyolefin nanocomposites are presented. Two different maleic anhydride-modified polypropylenes having varying maleic anhydride content and molecular weight were used. The influence of these parameters on the performance and morphology of the prepared polypropylene and high density polyethylene-based nanocomposites was examined by mechanical testing, X-ray diffraction, and electron microscopy. The low molecular weight adhesion promoter seemed to be effective in both matrices in relation to mechanical property enhancements, whereas its high molecular weight counterpart performed well only in polyethylene matrix. X-ray diffraction results and examination of morphology revealed that the intercalation and the dispersion of the nanoclay were more even in both matrices when the low molecular weight adhesion promoter with a higher maleic anhydride content was used. On the other hand, the use of high molecular weight adhesion promoter led to a less uniform dispersion but also to a greater amount of exfoliated clay particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Mechanical and tribological properties of melt-compounded titanium dioxide nanocomposites of atomic-layer-deposition (ALD)-coated polyamide particles and commercial nanofillers were compared. The nanofiller dispersion in the polyamide matrix was studied using transmission electron microscopy showing very different morphology for the ALD-created and the traditional nanocomposites: former appearing as ribbons in the matrix whereas latter composing from spherical clusters. The effect of such morphology change on the specimen’s mechanical response subjected to tensile and impact loading was investigated. The results demonstrated that ALD-created nanocomposites possess significantly higher Young’s modulus than pure and traditionally filled polyamide matrix. However, transition from ductile to brittle behavior occurs especially for the ALD-created nanocomposites. Notched impact strength experiments supported this, suggesting that the impact strength of ALD-created composites decreased significantly compared to pure polyamide matrix, whereas traditionally melt-compounded nanocomposites showed no significant changes. Furthermore, the tribological properties of the selected specimens were determined and the effect of the nanofiller on the friction and scratching properties of the polyamide matrix is discussed.

The differences that direct melt compounding and masterbatch dilution cause in the properties of melt compounded polypropylene (PP) and high density polyethylene-based (PE-HD) nanocomposites are presented. The results include comparison of properties and morphology of directly melt processed organoclay nanocomposites with similar compounds diluted from commercial and in-house-made masterbatches to clay concentrations of 1, 3, 6, and 8 wt%. The compounds were prepared with a co-rotating Brabender twin-screw extruder. The degree of exfoliation and the dispersion of the nanoclay were verified with transmission electron microscopy and X-ray diffraction. Thermal stability of the materials was examined with thermogravimetric analysis and the mechanical properties of the compounded materials were also determined. The most promising results regarding mechanical behavior were achieved with the in-house-made masterbatch in the form of a notable increase in Young's modulus in both matrices. There was also a distinct increase in impact strength when masterbatch was used. Changes were more pronounced in case of PP. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Polycarbonate nanocomposites were prepared by melt processing from two surface-modified montmorillonite organoclays. The intercalation spacing and degree of the dispersion were characterized with wide-angle X-ray diffraction and transmission electron microscopy, respectively. The polycarbonate nancomposites showed rather good dispersion of nanoclay, with a mixture of exfoliated, intercalated, and confined morphology. The effect of nanoclay on the mechanical response of specimens subjected to tensile and impact loading was investigated. Results demonstrated that nanocomposites based on nanoclay possess increased Young's modulus and yield strength. However, their ductility upon tensile loading is significantly affected. A transition from ductile to brittle deformation occurs at studied clay loadings. Notched impact strength experiments supported this, showing that impact strength decreases significantly as nanoclay content increases from 1 to 5 wt%, regardless how the nanoclay surface was modified. Thermal analysis demonstrated that addition of nanoclay leads to decreased thermal stability of polycarbonate suggesting, enhanced dynamics of polymer chains. Finally, the tribological properties of selected specimens were evaluated using a pin-on-disc, and the effect of nanoclay fillers on tribological properties is discussed.

Glass fibre (GF) reinforced vinylester composites (VE-FRP) are commonly used materials in hydrometallurgical reactors, the pulp and paper industry and waste water treatment plants, due to their excellent chemical resistance combined with good mechanical performance. In these applications, materials can be subjected to erosion, elevated temperatures (as high as 95 °C) and various chemical environments. However, studies on the slurry erosion of vinylester-based composites at high temperatures have not yet been reported. In this study, the erosion resistance of GF reinforced VE-FRP was investigated with a pilot-scale reactor. The effect of slurry concentration, erodent particle kinetic energy and slurry temperature was studied. The dominating wear mechanism was found to be abrasive wear. The VE-FRP structure was found to be prone to erosive turbulent flow and cavitation. Moreover, an increase in the erodent concentration of the slurry (10-20. wt%) or in the total kinetic energy of the erodent particles (30-770. kJ) increased the wear rate of the material markedly (up to 6 times higher weight loss). However, the total effect of different interrelated parameters was found to be complex. Consequently, it is recommended that predictions of the erosion rate of VE-FRP components are based on tests carried out in conditions that simulate the actual service environment. acceptedVersion

This study evaluates the slurry-erosion wear of glass fibre reinforced vinyl ester composites (VE-FRP) using a high speed slurry-pot type wear tester. The wear rates of VE-FRP were compared using different abrasives, namely quartz, chromite, copper ore, zinc concentrate, and tailings. Furthermore, the effect of abrasive particle size and slurry concentration on the VE-FRP wear was studied. The erosion wear results of VE-FRP were compared to natural rubber (NR) and bromobutyl rubber (BIIR) as well as to few common thermoplastics, such as polypropylene (PP) and polyvinyl chloride (PVC). Moreover, the failure characteristics of VE-FRP were analyzed. The results demonstrated that coarse quartz produced the largest wear rates on VE-FRP samples, while the zinc concentrate showed the lowest wear. Minor changes in the abrasive particle size had no effect on the wear results, only when the particle size was markedly raised, the wear started to increase. When comparing the wear rates of different materials, it was concluded that with all abrasive types, tested rubbers and thermoplastics had lower wear rates than VE-FRP. acceptedVersion