Morphology and ageing behaviour of silicone-EPDM blends

The silicone-EPDM system has been studied with blend ratios (silicons:EPDM) of 5050, 4060 and 3070. The first set of blends was prepared by roll-mixing of the elastomers and curative whereas in the second set, DCP-cured powder of EPDM, prepared in a Brabender plasticorder, was mixed with silicone rubber and DCP in a roll mill. A comparison of blends show that the second set exhibits inferior properties as compared to the first set. Specimens were also aged at 150 and 175 °C for various periods. The physical properties of the aged specimens show a reversal in trend, i.e. the second set of specimens shows better physical properties on ageing. The strengthening of the silicone phase by use of a different curative (Perkadox 14/40) in the 5050 blend of the second set shows a beneficial action on ageing. Morphology studies with SEM confirm the two-phase structure for both sets of blends. In both cases phase separation occurs with ageing, but the continuous phase for the second set of blends maintains its continuity for a higher period than the corresponding specimens of the first set.     

Fracture behaviour of rubber-toughened polymer blends

The fracture toughness of a core-shell rubber modified polycarbonate-copolyester blend was determined by using theJ-integral approach. Single-edge notch bend specimens were tested at room temperature using a crosshead speed of 1 mm min^–1. The resistance curve for the blend was not affected by specimen width, direction of crack growth with respect to mould-flow direction, and sidegrooving. Fractographic analysis suggested that the matrix debonded from the rubber particles thus relieving the triaxial stresses and enabling the matrix to yield more easily. The initiation of crack growth in theJ-tests was observed to occur shortly after the onset of non-linearity in the load-deflection curve. Consequently, an attempt was made to describe fracture in this blend by using linear elastic fracture mechanics.     

Crystallization behaviour and mechanical properties of polypropylene-based composites

The influence of glass fibres on the primary nucleation process, isothermal radial growth rate of spherulites and overall kinetic rate constant of isotactic polypropylene (iPP) has been examined. The polypropylene was also modified by means of acrylic acid (iPP^*) in order to improve the adhesion between the matrix and the fibres, and the relative properties were compared with those concerning the composites having as matrix plain MR Moreover the mechanical properties of injection-moulded composites containing iPP and iPP^* have been studied. These properties improved on increasing the fibre content. It was found that for the same glass-fibre content better values of the elongation at break and creep are observed in the case of reinforced polypropylenes having as matrix acrylic acid modified polypropylene.     

Long-term soft tissue reaction to various polylactides and their in vivo degradation

Cylindrical pins made from poly(L-lactide), poly(L/D-lactide) 95/5% and poly(L/DL-lactide) 95/5% were implanted in the subcutaneous tissue of sheep. The tissue reaction to the implanted materials and their in vivo degradation was investigated at 1,3,6 and 12 months. The capsule formed around the polylactide implants consisted of fibroblasts, fibrocytes, phagocytes, a few foreign body giant cells and polymorphonuclear cells. For all three polylactides used, the cellular response was most intensive during the first 6 months of implantation and significantly subsided at 1 year. The thickness of the capsule was 200 m at 1 month, increased to 200–600 m at 6 months, and decreased to 100 to 200 m at 1 year, depending on the material used. The tissue reaction was more intense for poly(L/D-lactide) than for poly(L/DL-lactide) and poly(L-lactide). The drop in molecular weight of the implants was highest after 1 month of implantation (70 to 95%). Irrespective of the extensive reduction of the molecular weight at 1 month, none of the polymers used was completely resorbed at 1 year. The most advanced resorption was observed for poly(L/D-lactide). Despite molecular weight reduction, the poly(L-lactide) implants had maintained 70% of their initial bending strength and 95% of their shear strength at 3 months. The poly (L/D-lactide) and poly(L/DL-lactide) had maintained only 26 to 27% of their initial bending strength and 26 to 31% of the initial shear strength, respectively. The crystallinity of all the materials increased after implantation as compared with nonimplanted materials. The overall crystallinity increase and the final crystallinity reached by the materials at 1 year was, however, lowest for poly(L/DL-lactide) as compared with the other two polylactides.     

Stability analysis and thermal motion of optically trapped nanowires

We investigate the stability and thermal motion of optically trapped nanowires, with aspect ratios in the range 10-100. A simple analytical model is used to determine qualitative features of the system, assuming that the nanowire is weakly scattering and the incident beam is paraxial. As expected, the model predicts that the nanowire will align with the beam axis. In this configuration the translational stiffness coefficients of the trap approach their limiting values for long nanowires like O(L(-3)), where L is the nanowire length, the limit for the stiffness parallel to the beam axis being zero. The rotational stiffness coefficients vary more slowly, according to O(L(-1)). Also, it is predicted that defocusing decreases the translational stiffness perpendicular to the beam, while increasing rotational stiffness. These findings are reinforced by comparison with rigorous electromagnetic calculations which additionally reveal the effects of radiation pressure and finite scattering. A strong polarization effect is observed in the numerical simulations and coupled translational and rotational motions arise which influence the trap stability. The use of nanowire traps for force sensing is discusse.     

Crystallization behaviour of calcium aluminate glass fibres

Crystallization behaviour of as-spun and fully-nucleated calcium aluminate (CA) glass fibres produced via inviscid melt spinning (IMS), was studied. Differential thermal analysis (DTA) scans on the as-spun and fully-nucleated CA fibres were performed at different heating rates. By applying the Kissinger method to the DTA scan data the activation energy values for crystallization were determined to be 569 and 546 kJ mol–1, respectively for the as-spun and fully-nucleated CA fibres. The Ozawa analysis on the DTA scan data gave the Avrami parameters at 2.7 and 2.4, respectively, for the as-spun and fully-nucleated CA fibres, which indicates high tendency of bulk crystallization mode. The formation of equilibrium phases of Ca12Al14O33 and CaAl2O4 in the crystallized CA fibres was identified by using X-ray diffraction (XRD).     

Surface physical and chemical changes of pure iron after molybdenum ion implantation and their effects on the tribological behaviour II: Tribological behaviour

The components of tribological systems are all quite sensitive to the surface chemistry and microstructure of the tribological material which may be dramatically changed by ion implantation. This paper is aimed at studying the effect of surface physical and chemical changes caused by molybdenum ion implantation on the friction and wear behaviours of pure iron. For this purpose, the wear tests of unimplanted and implanted specimens were conducted on an SRV fretting wear machine in air, at room temperature and with or without lubrication. The surface morphology, composition and chemical state of the wear tracks were also examined using electron probe microanalysis, Auger electron spectroscopy and X-ray photoelectron spectroscopy. The experimental results indicate that the wear resistance of pure iron is largely improved by molybdenum ion implantation. Under dry friction conditions, the wear resistance of the specimen implanted with a dose of 3 × 10¹⁷ is increased to 2.8 times that of unimplanated pure iron since the anti-adhesion, anti-abrasion and anti-deformation abilities are improved as a result of the increase in microhardness. When liquid paraffin is used as a lubricant, the wear resistance of the implanted specimen is 4.8 times as high as that of the unimplanted one. This further increase in wear resistance compared with that for dry friction is mainly due to the boundary lubricating film provided by liquid paraffin, which reduces the adhesion between the wear counterpart and molybdenum atoms in the implanted specimen. When liquid paraffin plus sulphurized olefin is used as a lubricant, the wear resistance of the implanted specimen is 2.8 times as high as that of the unimplanted one. It can be seen that the increasing value of the wear resistance is lower than that of the sample lubricated with liquid paraffin. The reason is that the compounds FeS and FeSO₄ formed between the element of the wear specimen and the active elements of the lubricant in the wear process play an anti-wear role. However, the presence of a molybdenum element in the implanted specimen decreases the atomic ratio of iron, and thus decreases the amount of FeS and FeSO₄ and the wear resistance.     

The yield and deformation behaviour of some polycarbonate blends

Polycarbonate and its blends with PE and MBS have been tested to investigate the impact modification mechanism. These materials have been tested in tension over the speed range 10^–2 to 10² in. sec^–1 (2.5×10^–2 to 2.5×10² cm sec^–1). The tensile deformation behaviour of these materials is similar except for the magnitude of the yield stresses. The yield stress versus log curves have identical slopes. Based on Eyring's equation for the flow of viscous materials, these materials have identical activation volumes, implying that the mechanical behaviour modification is not due to changes in molecular mechanisms. The modifier particles probably change only the stress state of the matrix material. Three-point bending tests on notched bars of these materials have also been performed over the speed range 10^–2 to 10² in. sec^–1 (2.5×10^–2 to 2.5×10² cm sec^–1). The areas under the load-deflection curves have been measured as the total energy absorbed during the deformation. It was found that both geometric constraint and rate of deformation can bring about ductile-brittle transitions. However, the thickness sensitivity of the blends is less than that of the pure material. Scanning electron micrographs show that the matrix material voids and flows extensively around the modifier particles before the ductilebrittle transition speed is reached. This voiding probably relieves plane strain. However, at higher speeds, the modifier particles cannot relax sufficiently rapidly, and they lose this plane strain relieving capability.     

Fracture behaviour and morphology of PC/ABS blends

The toughness behaviour of polycarbonate (PC)/acrylnitrile-butadiene-styrene (ABS) blends under dynamical loading (1 ms^–1) based on the J-integral concept was studied. For this the multiple specimen R-curve method was used. A special experimental technique of a stop block method was developed. It was shown that the materials exhibit a very different toughness behaviour depending on temperature and ABS content. The reasons for this material behaviour are discussed with the help of scanning and transmission electron microscopical (SEM and TEM) investigation methods. It can be shown that a combination of fracture mechanics and electron microscopy allows a toughness optimization to be made on the basis of quantitative morphology-toughness correlations.     

On cavitation and macroscopic behaviour of amorphous polymer-rubber blends

Abstract

The macroscopic behaviour of rubber-modified polymethyl methacrylate (PMMA) was investigated by taking into account the microdeformation mechanisms of rubber cavitation. The dependence of the macroscopic stress–strain behaviour of matrix deformation on the cavitation of rubber particles was discussed. A phenomenological elastic-viscoplastic model was used to model the behaviour of the matrix material, while the rubber particles were modelled with the hyperelasticity theory. A two-phase composite material with a periodic arrangement of reinforcing particles of a circular unit cell section was considered. Finite-element analysis was used to determine the local stresses and strains in the two-phase composite. In order to describe the cavitation of the rubber particles, a criterion of void nucleation is implemented in the finite-element (FE) code. A comparison of the numerically predicted response with experimental result indicates that the numerical homogenisation analysis gives satisfactory prediction results.     

On cavitation and macroscopic behaviour of amorphous polymer-rubber blends

The macroscopic behaviour of rubber-modified polymethyl methacrylate (PMMA) was investigated by taking into account the microdeformation mechanisms of rubber cavitation. The dependence of the macroscopic stress–strain behaviour of matrix deformation on the cavitation of rubber particles was discussed. A phenomenological elastic-viscoplastic model was used to model the behaviour of the matrix material, while the rubber particles were modelled with the hyperelasticity theory. A two-phase composite material with a periodic arrangement of reinforcing particles of a circular unit cell section was considered. Finite-element analysis was used to determine the local stresses and strains in the two-phase composite. In order to describe the cavitation of the rubber particles, a criterion of void nucleation is implemented in the finite-element (FE) code. A comparison of the numerically predicted response with experimental result indicates that the numerical homogenisation analysis gives satisfactory prediction results.     

Crystallization behaviour of isotactic polypropylene blended withtrans-octenylene rubber

The crystallization behaviour of isotactic polypropylene (iPP) blended withtrans-octenylene rubber (TOR) has been investigated by optical microscopy. It is found that crystallization kinetical parameters like nucleation densities, Avrami exponents and spherulitic growth rates are strongly dependent on the TOR concentration in the blend. While at 10% TOR content the nucleation density passes through a maximum, both the Avrami exponent and the spherulitic growth rate are minimal. Due to an increased dispersion of TOR in iPP at 10% TOR concentration and the subsequent formation of interfaces, the nucleation changes from preferentially homogeneous to preferentially heterogeneous. The concentration oftrans double bonds in the TOR chain has no influence on the crystallization behaviour of the samples.     

Fatigue propagation behaviour of polystyrene/polyethylene blends

Fatigue crack propagation (FCP) of injection-moulded polystyrene (PS) and 95/5, 85/15 and 70/30 PS/high-density polyethylene (HDPE) blends at loading frequencies of 2 and 20 Hz was studied. The FCP results showed that increasing the HDPE content caused a progressive reduction of the fatigue crack growth rates, especially when a styrene/ethylene– butylene/styrene (SEBS) terpolymer was added as a compatibilizer. Increasing the loading frequency also led to a fatigue crack growth rate reduction. Moreover, the fatigue crack growth rates were lower at a given cyclic stress intensity factor range, K, when the crack propagated normal, instead of parallel, to the melt-flow direction during injection moulding. Fractographic observations indicated that discontinuous growth bands (DGBs), associated with the fracture of crazes in the plastic zone, were present through most or all of the fracture surfaces of the PS/HDPE specimens. In the presence of sufficient HDPE, these DGBs were formed by the initiation, growth and coalescence of large dimples initiated at HDPE particles ahead of the microscopic crack front, similar to a multiple crazing effect. The loading frequency effect on the FCP behaviour of these blends is attributed to a time-dependent deformation process. It is concluded that the FCP behaviour of these blends is strongly affected by the loading direction with respect to the matrix and minor phase orientation, by the presence of a compatibilizer, by the composition of the blend and by the testing conditions. © Chapman & Hall.     

Structural and thermal properties of PVDF/PVA blends

Thermal properties such as thermal diffusivity and thermal conductivity are measured by photoacoustics at room temperature for various particle sizes, thicknesses and the percentage of mixing of poly (vinyl alcohol) (PVA) in Poly (vinylidene fluoride) (PVDF)/PVA blends. The results are compared with other experimental reports, which is by laser flash technique for various temperatures. The agreement is very good at room temperature; in our study, it is 0.20 Wm⁻¹ K⁻¹, whereas by laser flash technique it is 0.18 Wm⁻¹ K⁻¹ for thermal conductivity. The importance of dislocation density and strain is discussed.     

Phase behaviour, mechanical properties and thermal stability of thermosetting polymer blends of unsaturated polyester resin and poly(ethylene oxide)

The results of dynamic mechanical analysis reveal that crosslinked polyester resin (PER)/poly(ethylene oxide) (PEO) blends show a composition dependent glass transition temperature, Tg, which suggests that the blends studied are homogeneous in the amorphous state. The initial dynamic storage modulus, E', decreases with increasing PEO content up to 30 wt% in the blends, whereas E for both the 60/40 and 40/60 PER/PEO blends is close to that for the 80/20 PER/PEO blend and much larger than that for the 70/30 PER/PEO blend. The addition of crystalline PEO has a remarkable effect on the mechanical properties of crosslinked PER. Tensile testing shows that the elongation at break first increases greatly and then decreases slightly, whereas the Young's modulus and the tensile strength first decrease and then increase slightly with increasing PEO content in the blends. The variation of tensile properties was considered to be due to both the plasticization effect and the crystallization effect of PEO in the blends. The impact strength remains almost unchanged with increasing PEO content in the blends studied. No dramatic decrease of thermal stability for PER/PEO blends was observed for the blends with PEO content up to 30 wt%.     

Thermodilatometric behaviour of pure and doped ZrTiO4-SnO2

Thermodilatometric tests have been performed to investigate the shrinkage of green compacts of pure and ZnO-doped 4ZrO₂-5TiO₂-SnO₂ prepared by dry ball milling, flo-deflocculation and coprecipitation. Experiments have shown that the powder preparation procedure has a significant influence on the sintering process. Optimizing the homogeneity composition, which is enhanced from dry ball milling to coprecipitation, raises the starting sintering temperature. The reduction of the dimension of the starting particles increases the sintering rate and the addition of ZnO favours the shrinkage of the green bodies. Coprecipitated products lead to the highest final density because the evaporation of tin oxide on firing is reduced.     

Synthesis and thermal behaviour of sodium monoimidocyclotriphosphate

Trisodium monoimidocyclotriphosphate dihydrate, Na₃P₃O₈NH·2H₂O, was made by hydrolysing triimidocyclotriphosphate in an aqueous acetic acid solution at 70 °C. The monoimidocyclotriphosphate was converted to cyclotriphosphate by heating in air according to the reaction Na₃P₃O₈NH + H₂O (NaPO₃)₃ + NH₃     

The constant stress behaviour of polystyrene-low density polyethylene blends

The constant-stress behaviour of low-density polyethylene toughened polystyrene has been analysed. It was found that the initial strain-time behaviour during constant-stress tensile tests is well described by a simple model that predicts a proportionality between strain and the square of time, provided a correction for craze formation during the application of stress is made. By analysing strain-time curves at different stresses it has been determined that the product of the rates of craze initiation and of craze growth is exponentially dependent on stress. The attainment of a constant strain rate during constant-stress experiments and the attainment of a constant-stress level during constant strain-rate experiments result from a strong decrease in the rate of craze initiation. This effect allowed the determination of the stress and temperature dependences of the rate of craze growth. This rate was found to be well described by the Eyring equation, which is in agreement with earlier results obtained from constant stress- and strain-rate experiments.