Sliding wear performance of polyamide 6–clay nanocomposites in water

Polyamide 6 (PA6) clay nanocomposites, a new class of specialty polymer, shows improved tribological properties under dry sliding conditions. In food and chemical industry, the polymeric materials are widely used in the machine elements due its excellent chemical inertness. Water, being a widely used solvent, tends to have contact with the machine elements and can either act as a lubricant or as a contaminant. Many factors such as the interaction of polymer with water, surface wettability, etc., play a major role on the friction and wear of polymers in aqueous conditions. This work reports the sliding wear performance of PA6 clay nanocomposites in water. Addition of clay affects the crystallinity of the nanocomposites, which in turn affects the plasticization. Plasticization of the surface by water causes increase in wear and decreases the coefficient of friction.     

Creep behaviour of injection moulded polyamide 6/organoclay nanocomposites by nanoindentation and cantilever-bending

The creep behaviour of injection moulded PA 6/organoclay nanocomposites was studied by depth-sensing nanoindentation and DMA cantilever-bending. The glass transitions of PA 6 and its nanocomposites were decreased below room temperature upon saturation with water so that the materials could be tested in the rubbery regime. For nanoindentation creep on the skin and core regions of injection moulded samples, whilst organoclay improves the creep resistance of PA 6, the enhancement is due to the decrease of the initial compliance at zero time but the time-dependent creep is actually increased. In contrast, for cantilever-bending creep, organoclay reduces the creep compliance and the time-dependent creep in PA 6. It is suggested that the organoclay imparts a constraint effect on the PA 6 molecular chains, restricting their mobility in the bulk compared to the surface and hence improving their resistance to creep. A modified Halpin-Tsai equation was used to model their creep behaviour under these two loading configurations and compared to experimental data.     

Nanostructure and mechanical properties of aromatic polyamide and reactive organoclay nanocomposites

Aromatic polyamide/organoclay nanocomposites were synthesized using the solution blending technique. Treatment of montmorillonite clay with p-phenylenediamine produced reactive organophilic clay for good compatibility with the matrix. Polyamide chains were prepared by condensing a mixture of 1,4-phenylenediamine and 4-4′-oxydianiline with isophthaloyl chloride under anhydrous conditions. These chains were end capped with carbonyl chloride using 1% extra acid chloride near the end of reaction to develop the interactions with organoclay. The dispersion and structure–property relationship were monitored using FTIR, XRD, FE-SEM, TEM, DSC and tensile testing of the thin films. The structural investigations confirmed the formation of delaminated and disordered intercalated morphology with nanoclay loadings. This morphology of the nanocomposites resulted in their enhanced mechanical properties. The tensile behavior and glass transition temperature significantly augmented with increasing organoclay content showing a greater interaction between the two disparate phases.     

Influence of graphite filler on two-body abrasive wear behaviour of carbon fabric reinforced epoxy composites

The influence of graphite filler additions on two-body abrasive wear behaviour of compression moulded carbon–epoxy (C–E) composites have been evaluated using reciprocating wear unit and pin-on-disc wear unit under single pass and multi-pass conditions respectively. The carbon fabric used in the present study is a plain one; each warp fiber pass alternately under and over each weft fiber. The fabric is symmetrical, with good stability and reasonable porosity. Abrasive wear studies were carried out under different loads/abrading distance using different grades of SiC abrasive paper (150 and 320 grit size). Graphite filler in C–E reduced the specific wear rate. Further, the wear volume loss drops significantly with increase in graphite content. Comparative wear performance of all the composites showed higher specific wear rate in two-body wear (single-pass conditions) compared to multi-pass conditions. Further, the tribo-performance of C–E indicated that the graphite filler inclusion resulted in enhancement of wear behaviour significantly. Wear mechanisms were suggested and strongly supported by worn surface morphology using scanning electron microscopy.     

Influence of fillers on abrasive wear of short glass fibre reinforced polyamide composites

Various composites of polyamide 6 filled with short glass fibre, polytetrafluoroethylene and metal powders viz. copper and bronze were formulated in the laboratory and characterised for their various mechanical properties such as tensile strength, tensile elongation, flexural strength, hardness and impact strength. Compositional analysis was done with gravimetry, solvent extraction and differential scanning calorimetry (DSC) techniques followed by tribo-performance evaluation in abrasive wear mode by abrading a sample against silicon carbide (SiC) abrasive paper in a single pass condition under various loads. It was observed that the fibre reinforcement deteriorated the abrasive wear resistance of virgin polymer. Combination of fibre and particulate filler was more detrimental in this respect. Efforts were made to correlate the wear performance with the appropriate mechanical properties. Under selected loading condition, wear as a function of product of hardness, elongation to break (e) and ultimate tensile strength (S) showed better correlation than Ranter-Lancaster plot. Scanning electron microscopy (SEM) was used to analyse the worn surfaces of the samples.     

Rubber-toughened polyamide 6/clay nanocomposites

Toughening of polyamide 6 (PA6) based nanocomposites (PN’s), with 3 wt% organically modified montmorillonite (OMMT), was investigated by blending with up to 40 wt% of maleinized styrene–ethylene/butadiene–styrene copolymer (mSEBS). The nanostructure of the PA6 matrix did not change on blending with mSEBS, nor did the nature of the two polymeric phases on addition of OMMT. The morphology of the rubber particles in the PN’s was homogeneous, with particle sizes larger than those of the corresponding blends, due to limitations imposed by the clay on the compatibilizing effect of the mSEBS. All the PN’s were ductile and, despite the incorporation of rubber, showed higher small strain tensile properties than those of the corresponding blends. Super-tough nanocomposites were obtained with 30 wt% mSEBS. The critical interparticle distance to attain super-toughness (τ_c) was slightly larger in the blends than in the PN’s, indicating that an increased modulus of the matrix on addition of OMMT leads to smaller τ_c values.     

Effect of organic modification of sepiolite for PA 6 polymer/organoclay nanocomposites

Polyamide 6 nanocomposites based on sepiolite needle-like clay were prepared via melt extrusion. Sepiolite was organomodified with trimethyl hydrogenated tallow quaternary ammonium (3MTH) by using different amounts of modifier respect to the sepiolite. The effect of modifier/sepiolite ratio on the final nanocomposite properties and the catalytic effect of the sepiolite on the polymeric matrix were evaluated. The presence of organomodified sepiolite on the polymer matrix favoured the crystallinity of the PA 6. The catalytic effect of the sepiolite was reduced as the modifier amount increased. The elastic modulus and Heat Deflection Temperature (HDT) in PA 6/organosepiolite nanocomposites increased ∼2.5 times respect to the neat PA 6 matrix. The higher the modification grade the better the dispersion and orientation of needle-like sepiolite clay were attained. This effect supported the reinforcement efficiency of organosepiolites with high modifier content.     

Effects of graphite particle addition upon the abrasive wear of polymer surfaces

The abrasive wear performance of vinyl ester resins modified with various volume fractions (5, 10, 15, 20 and 30%) of graphite powder has been measured. Using a conveyor belt driven testing machine developed locally, it has been possible to realistically simulate the effect of three-body abrasive wear upon these graphite modified polymer samples. A comparison of the calculated dimensionless wear rates obtained for these surfaces reveals that the effect of the graphite powder depends strongly upon the volume fraction of particles in the resin matrix. It appears that, for intermediate volume fractions, the presence of graphite powder in the resin matrix reduces the abrasive wear of the polymer surface. Scanning electron microscopy has been used to probe the mechanisms of abrasive wear of the pure resin and graphite modified surfaces. It appears that the embedded graphite particles can act as a lubricant during the abrasion process thus reducing the wear rate. The effect of increasing graphite powder volume fraction upon the abrasive wear mechanism is discussed.     

Investigation of surface properties of plasma-modified polyamide 6 and polyamide 6/layered silicate nanocomposites

Polyamide 6 and polyamide 6/layered silicate nanocomposites were treated by oxygen plasma and the resulting surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared-attenuated total reflection (FTIR-ATR). The surface properties were also analyzed by water contact angle measurements and Taber abrasion test. It is found that plasma treatment had different effects on the surfaces of the homopolymer and the polymer nanocomposites. Furthermore, both plasma duration and nanoclay content affect the contact angle and degree of abrasion resistance. In pure polyamide 6, plasma treatment caused the surface to be highly hydrophilic due to the formation of cyclic cis-amide species. Polymer nanocomposites treated with plasma also became more hydrophilic due to oxidation and enrichment of clay at the surface. The abrasion resistance of pure polyamide 6 was increased after exposure to plasma. This is attributed to cross-linking of polymer chains when exposed to plasma. For the polymer nanocomposites, an improvement in abrasion resistance was obtained in samples with low clay content when exposed to plasma for a short time. This is also due to cross-linking as well as the higher abrasion resistance of clay. However, longer exposure to plasma resulted in poorer abrasion resistance due to self-aggregation of clay particles which can be easily removed from the surface. A model was proposed to explain the effect of oxygen plasma on polymer nanocomposite surface.     

Abrasive wear of epoxy composites filled by abrasive particles and reinforced by polyamide fibres

Abrasive wear caused by sandy soil of steel coated by epoxy resin was investigated. Experiments were carried out using an abrasive wear tester developed to simulate the wear of the tillage tools under controlled testing conditions. Epoxy coatings were filled by abrasive particles such as aluminium oxide, silicon carbide and silicon oxide of different particle size. Also, epoxy coatings were reinforced by polyamide fibres of different diameters. The test results showed that, relatively lower wear values were displayed by epoxy coatings filled by silicon oxide particles of 5 wt% content. The wear values performed by silicon oxide of (10–20) μm particle size were lower than that displayed by uncoated steel surface. Solid lubricant such as graphite and molybdenum disulphide as filling material caused significant increase in wear due to the weak adhesion between epoxy/solid lubricant layers. Wear of epoxy reinforced by polyamide fibres showed the minimum wear values. Orientation of fibres much affected wear. Parallel fibres represented higher wear than perpendicular ones. The minimum wear was observed for cross plied coatings where shorter wear tracks and higher tensile strength in both perpendicular and parallel directions were existed. The minimum wear values which were lower than that displayed by uncoated steel test specimens were displayed by 0.1 and 0.3 mm polyamide fibre diameters. This observation confirmed the application of the polyamide fibres as reinforcement in epoxy coatings.     

Effect of hygrothermal ageing on morphology and indentation modulus of injection moulded nylon 6/organoclay nanocomposites

The effect of water immersion on the morphology and indentation modulus of injection moulded nylon 6 and its organoclay nanocomposites was investigated. XRD analysis showed that at 70 °C water promoted further crystallization in the nylon matrix and aided the γ- to α-crystal phase transition in the skin region. However, the presence of organoclay deterred this transformation. The combined actions of water and heat (70 °C) did not further degrade nylon 6 and its nanocomposites compared to water ageing at room temperature (25 °C). In fact, there was relative enhancement of the indentation moduli owing to the beneficial morphological changes induced in the nylon matrix. The largest improvements were found in the skin region of the injection moulded bars.     

Polymorphism in polyamide 6 and polyamide 6/clay nanocomposites molded via water-assisted injection molding

Differing from the conventional injection molding, being featured by a monotonous decrease of cooling rate from the outer layer to the core layer, the water-assisted injection molding (WAIM) is characterized by a unique distribution of cooling rate across the part wall, which would be expected to result in the formation of unique hierarchical structures in WAIM parts. So the crystal structures of the WAIM parts of two grades of polyamide 6 (PA6s) with different molecular weights (MWs) and PA6 (with higher MW)/clay nanocomposite were investigated. It is found that the α-form is predominant at low cooling rates, whereas the γ-form is predominant when the cooling rate is high or in the presence of the clay combining with an appropriate cooling rate, which may be confined by both upper and lower critical values. The MW of the PA6 exhibits more effect on the formation of the γ-form as the cooling rate decreases. Moreover, the shear is found to hinder the formation of the γ-form for the PA6 with higher MW. This work help further understand the crystal formation mechanism in the PA6 and its nanocomposites upon processing.     

Effect of fracture toughness on abrasive wear resistance of steels

Various abrasive wear mechanisms were reviewed and an abrasive wear modeling experiment is assessed. Abrasive wear resistance of non-heat treated and heat treated steels has been determined by using a pin-abrasion machine with five abrasive papers, which grinds on a small pin of test materials. The mass loss of test material during abrasive wear was determined gravimetrically. A correlation between abrasive wear resistance and Mode II fracture toughness of materials was established. The effect of fracture toughness on abrasive wear resistance of steels was outlined.     

Influence of morphology on the dynamic mechanical characteristics of PP-EP/EVA/organoclay nanocomposites

A study on the dynamic mechanical properties of polypropylene copolymer/ethylene–vinyl acetate/organoclay (PP-EP/EVA/C20A) nanocomposites is presented. Nanocomposites were obtained by melt blending. Morphology consisting of intercalated–exfoliated clay nanolayers preferentially located within the EVA phase was observed by transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD). Polar groups of vinyl acetate in the EVA facilitated the polymer–clay interactions. Changes in the glass transition temperature (T_g) were correlated with changes in the clay intercalation–exfoliation levels. The highly reinforced with intercalated–exfoliated clay layers EVA phase was considered as the origin of the improvement on mechanical properties of the ternary nanocomposites and is associated with the increase on viscosity, heat deflection temperature (HDT), and storage modulus.     

Effect of polymer modifier chain length on thermal conductive property of polyamide 6/graphene nanocomposites

The influence of polymer modifier chain length on the thermal conductivity of polyamide 6/graphene (GA) nanocomposites, including through-plane (λ_z) and in-plane (λ_x) directions were investigated. Here, three chain lengths of double amino-terminated polyethylene glycol (NH₂–PEG–NH₂) were used to covalently functionalize graphene with graphene content of 5.0 wt%. Results showed that λ_z was enhanced with the chain length of NH₂–PEG–NH₂ increased, but λ_x reached a maximum value at a certain chain length of NH₂–PEG–NH₂. The maximum λ_z and λ_x of GA are 0.406 W m⁻¹ K⁻¹ and 9.710 W m⁻¹ K⁻¹, respectively. This study serves as a foundation for further research on the thermal conductive property of graphene nanocomposites using different chain lengths of polymer modifier to improve the λ_z and λ_x of the thermal conductive materials.     

Effect of abrasive wear on the tensile strength of steel wire rope

Known amounts of external abrasive wear were introduced into a new 6-strand steel wire rope and the effects of this wear on the tensile strength of the rope examined against the rope discard criteria for wear stated in ISO 4309: 1990 and other selected international standards. The variations of strength with degree of wear in the test rope were compared with continuous observations on two haulage ropes which were in service under abrasive wear conditions up to the stage of failure. The results point to a need for greater caution in applying available discard criteria for wear. The results also indicate the existence of two different rapid strength deterioration regimes in strand wire rope under increasing amounts of external abrasive wear and they direct towards test parameter levels which signal the onset of these regimes.     

Effect of aging on the abrasive wear properties of AlMgSi1 alloy

In this paper, the wear performance of the aged AlMgSi1 alloy was investigated. Great improvements in mechanical properties of Al alloys can be achieved by suitable solution treatment and aging operations. A pin-on-disk wear machine was designed and developed for abrasive wear tests. The wear resistance was evaluated using a pin-on-disk wear testing method with a SiC abrasive paper counterface. The variation of wear volume is presented as a function of applied normal load, abrasive grit size and sliding distance for running speed. Mass losses were measured within a load range of 6.45–11 N, a sliding velocity range of 0.078–0.338 m/s and abrasive grit size of 5–30 μm. The effects of different sliding speeds and loads on wear resistance and surface roughness were also examined. It was measured amounts of mass loss and examined worn surfaces. Metal microscope was used to study the microstructures of the wear scars. Natural aged specimen observed maximum wear resistance.     

尼龙6/埃洛石纳米管纳米复合材料的制备与性能

通过熔融共混制备了尼龙-6(PA6)/埃洛石纳米管(HNTs)纳米复合材料.研究了HNTs含量对PA6/HNTs纳米复合材料微观形态、力学性能、结晶行为的影响.结果表明,在熔融共混条件下,HNTs不经过任何表面处理即可以纳米尺度均匀地分散于PA6基体中.随着HNTs含量的增加,纳米复合材料的弯曲强度和弯曲模量显著提高.DSC结果显示HNTs的存在起到了成核剂的作用,提高了PA6的结晶温度.HNTs份数少时能提高PA6/HNTs纳米复合材料的结晶度,份数多时会使其结晶度下降和生成不稳定的晶体.     

Polyolefin-based nanocomposites: the effect of organosilane on organoclay dispersion

This work dealt with the morphology and properties of polypropylene/organoclay (PP/OMMt) nanocomposites prepared using maleic anhydride-grafted polypropylene (PP-g-MA) or organosilane (OTMS) as a compatibilizing agent. The content of OMMt was 2 wt%, and different concentrations of OTMS were used to obtain OTMS/OMMt mass ratios of 0/1, 1/1, 0.5/1 or 0.25/1. The results of wide-angle X-ray scattering and transmission electron microscopy investigations showed that the OTMS promoted the total exfoliation of OMMt in the PP matrix, while the OMMt yielded a micrometer-scale dispersion when PP-g-MA was used. In general, the OTMS satisfactorily compatibilized the PP/OMMt nanocomposites, increasing the modulus of the PP matrix. When a hybrid compatibilizer of OTMS/PP-g-MA was used, better thermal and mechanical properties were achieved.