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Specimens of poly(vinyl formal) (PVF) : poly(methyl methacrylate) (PMMA) polyblends with different weight percentage ratios were subjected to gamma irradiation (1 to 50 Mrad) and electron irradiation (1 to 20 Mrad). The effect of irradiation on the strength of the blend specimens was studied by measuring the surface microhardness using a Vickers microhardness tester attached to a Carl Zeiss NU 2 Universal research microscope. Significant changes were observed in the Vickers microhardness number, Hv. The Hv values of gamma irradiated specimens are found to be higher than the unirradiated specimens indicating an occurrence of radiational crosslinking. The maximum value of Hv is obtained at the gamma radiation dose of 15 Mrad. In case of electron irradiation the radiational crosslinking is found to take place for the blend specimens having lower wt% content of PMMA (0 and 1 wt%) in PVF matrix. On the other hand degradation of polymeric system is observed for the blends having PMMA content more than 1 wt‰ The maximum value of Hv is obtained for all the blend specimens at the electron irradiation dose of 8 Mrad. The degree of crosslinking in polyblends due to gamma irradiation is found to be more than electron irradiation. The scissioning mechanism is found to predominate in the polyblend system in case of electron irradiation.

Plaques of blends of Eurdragit RL 100 and poly(methyl methacrylate) (PMMA) with different weight percentage ratios were obtained by compression moulding at 150°C. The mechanical strength of these blends was studied by a microindentation technique. The results show a decrease in brittleness and increase in hardness, toughness and yield strength by addition of PMMA to Eudragit.

Specimens of poly(methyl methacrylate) (PMMA) and poly(chloro trifluoroethylene) (PCTFE) polyblends with different weight percentage ratios were irradiated with various doses of gamma irradiation (1–100 Mrad). The effect of irradiation on the strength of blend specimens was studied by measuring the surface microhardness using the Vicker's microhardness tester attached to a Carl Zeiss NU 2 Universal research microscope. The value of Vicker's hardness number, H v , was found to increase up to 5 wt% of PCTFE, beyond which decrease in hardness level was observed. Thus the maximum value of H v was observed in the blends having 5 wt% of PCTFE. Also, a general increase in the microhardness level was observed in the irradiated specimens as compared to the untreated blends. The blends became brittle after the irradiation dose of 100 Mrad and indentation testing resulted in the cracking of the specimens.

The method of preparation of polymer blends of poly (methyl methacrylate) and poly (chlorotrifluoroethylene) with different ratios of the two polymers is described. The effect of load and ratio of the two polymers in the polyblend on the Vicker's microhardness has been studied. It is observed that poly (chloro trifluoroethylene) acts as a plasticizer for poly (methyl methacrylate).

The effect of annealing and quenching temperatures on the morphology of glass-fibre reinforced polymer (GFRP) has been studied utilizing the Vickers microhardness H v tests as an analytical tool. Increase in annealing temperature results in two peak values of H v at 60 and 180°C. The quenching temperature in different mediums, viz. air, water and ice-water, first increases H v up to 60°C, and then decreases it up to 140°C. Thereafter, H v goes on increasing ut to its melting point of 260°C. The value of H v of ice-water quenched specimens is higher than those of air and water quenched specimens. The quenching behaviour has been explained on the basis of an empirical relationship between quenching temperature and microhardness.

Specimens of PS:PMMA polyblends with different weight percentage ratios were irradiated with various doses of gamma irradiation (1 to 75 Mrad) and electron irradiation (1 to 30 Mrad). The effect of these irradiations on the strength of blend specimens has been studied by measuring the surface microhardness using a Vickers microhardness tester attached to a Carl Zeiss NU-2 Universal research microscope. The irradiation was found to produce crosslinking behaviour in the specimens and the crosslinking degree is related to the type and dose of irradiation and to the miscibility of PS and PMMA in the blend.

Solution-mixed poly(methyl methacrylate) (PMMA): poly(vinylidene fluoride) (PVDF) polyblends with different weight percentage ratios were irradiated with various doses of gamma irradiation (1–100 Mrad). The effect of irradiation on the strength of blend specimens was studied by measuring the surface microhardness using a Vickers microhardness tester attached to a Carl Zeiss NU-2 Universal research microscope. The irradiation was found to produce hardening in the blend specimens; however, the degree of hardening depends upon the dose level, testing conditions and also on the miscibility of PMMA and PVDF in the blend specimens. The increase and decrease in microhardness has been explained on the basis of crosslinking and scissioning. The two limits of irradiation dose were 1 and 75 Mrad where significant changes in mechanical strength were observed.

The influence of chemical environment on polymers include the surface alteration as well as other deep modifications in surface layers. The surface hardening, as an effect of organic liquids on poly(methyl methacrylate): poly(vinylidene fluoride) (PMMA: PVDF), which is one of the few known miscible blends, has been detected using microhardness testing. Organic liquids like acetone, toluene, xylene and benzene were introduced on the surface of blend specimens for different durations. Vickers microhardness (H v) was measured for treated and untreated specimens. The study reveals both hardening and plasticization of specimens at different exposure times. The degree of surface hardening is maximum under acetone treatment. All the specimens exhibit surface hardening at an exposure time of 1 h with all the four liquids. This feature is prominent with longer exposures for specimens with increasing content of PVDF. However, the degree of hardening decreases with the time of exposure in the respective environments. In general, acetone and toluene impart surface hardening, whereas, xylene and benzene soften the specimen. PMMA: PVDF (83 : 17) blend exhibits surface hardening under all the four treatments when compared with the respective untreated specimens.

The dark current in commercial polypropylene (PP) is measured at temperatures ranging from 333 to 413 K and fields ranging from 70 to 125 kV/cm. The specimens are metallized on both sides by evaporated layers of silver and aluminium. An attempt is made to identify the nature of the current by comparing its observed dependence on electric fields, electrode material, and temperature with the respective characteristic features of the existing theories of electrical conduction. The observed results suggest that the electrical conduction in PP is governed by a Jonscher-Ansari modified Poole-Frenkel mechanism.

The Vickers microhardness test is found to be a suitable analytical method for studying thermal change in thin films of polymers. It is utilised to analyse the effect of thermal pretreatment (annealing and quenching) on the surface microhardness of guargum (GG); a natural polymer), polyacrylonitrile (PAN; a synthetic polymer) and their cast blends, guargum-grafted-polyacrylonitrile (GG-g-PAN) and polyacrylonitrile-guargum (PAN-GG). Annealing at various temperatures reveals the change in configuration and crystallinity of thin films of polymers. Peak values of hardness are found to occur in GG, PAN and PAN-GG but not in GG-g-PAN. The quenched hardness for GG is found to be nonlinear with temperature. However, for other polymers quenched hardness decreases, initially, up to a certain temperature and then starts increasing; such temperatures for PAN, PAN-GG and GG-g-PAN are 86, 66 and 86°C, respectively. The behaviour of polymer blends on quenching can be represented by a calculated value of the exponent which is 0·62 and 0·75 for GG-g-PAN and PAN-GG, respectively.

Thin films of polystyrene-ferrocene (PSFe) composite were irradiated with various doses of gamma irradiation ranging from 4·1 to 25·3 Mrad. The Vickers hardness number (Hv) was calculated for pure and irradiated specimens. It was used to analyse mechanical strength at a saturation load of 100 g. The mechanical strength was found to increase with irradiation dose up to 12 Mrad. Brittleness of the composite PS-Fe was found to occur at a higher dose of 25 Mrad as compared to 15 Mrad for polystyrene. Further, fracture toughness, brittleness index and yield strength were calculated for various irradiated specimens consequent to crack propagation in the specimens.

Thin films of guar gum (GG)—a natural polymer, polyacrylonitrile (PAN)—a synthetic polymer, GG grafted with PAN, and a composite of GG and PAN were made by the usual solvent evaporation method. All the four films were subjected to Vickers microhardness tests in order to explain surface morphology, crystallinity and composition. The breaking strength of all the films was also determined. The load dependence of Vickers microhardness, Hv, has been explained by a logarithmic index, n. The small stress behaviour of Hv was found to be related to the Newtonian resistance pressure of the specimen itself.

The Vickers microhardness test has been carried out on GFRP specimens at different loads ranging from 5 to 160 g. The Vickers hardness number (H v )-load behaviour has been explained on the basis of strain hardening phenomena. This reveals that the value of H v is greater at small stresses and it becomes independent of load beyond 110 g. In this range the value of the logarithmic index, n, is 2. The non-linear behaviour of microhardness with load has three different values of logarithmic index. Further, the dependence of load on H v in GFRP specimens has been explained on the basis of Newtonian resistance pressure as proposed by Hays and Kendall.

GFRP specimens were irradiated with various doses of gamma and electron radiations ranging from 60 to 200 Mrad. Tensile tests using an Instron Model-1185 have been utilized to study the effect of these radiations on the mechanical strength of GFRP. A typical load-elongation curve of this composite consists of two stages. The first stage is linear, and the deformation produced is elastic. Beyond the first linear stage, the change of slope of the curve is attributed to the initiation and extension of cracks at fibre ends. Evidence of decrease as well as increase in the strength of specimens has been observed at different doses of radiation. The electron irradiation increases the strength of GFRP at all doses of irradiation except 200 Mrad. However, gamma irradiation decrease the strength of GFRP. The ductile and brittle character of GFRP has been explained.

Vickers microhardness testing has been utilized to study plasticization effects in environmentally-affected commercial polypropylene. The paper provides experimental evidence on the effect of some organic liquids and acids on the surface microhardness of polypropylene at different loads and different pouring times of liquids.

GFRP specimens were irradiated with various doses of gamma irradiation ranging from 40 to 250 MRad. The Vickers microhardness test has been utilized to study the effect of irradiation on the mechanical behaviour of GFRP at different loads. Evidence of both the decrease and increase in the strength of specimens has been observed at different doses of irradiation.

The preparation of polymer blends of polystyrene and poly(methyl methacrylate) in different weight percentages is described. The strengths of these blends have been studied by measuring their surface microhardness making use of a Vickers microhardness tester.

Specimens of poly(methyl methacrylate) (PMMA): poly(chlorotrifluoroethylene) (PCTFE) polyblends with different weight percentage ratios were subjected to electron beam irradiation (1–10 Mrad). The effect of irradiation on the strength of the blend specimens was studied by measuring the surface microhardness using a Vicker's microhardness tester attached to a Carl Zeiss NU 2 Universal research microscope. Significant changes were observed in the Vicker's hardness number, Hv. An irradiation dose of 3 Mrad was found to enhance greatly the microhardness level of the specimens. An increase of approximately 78% in microhardness was observed as the radiation dose was increased from 1 to 3 Mrad. Electron irradiation was also found to induce crosslinking and degradation in the material. The degree of crosslinking was found to be maximum at a dose of 3 Mrad. Specimens incorporating 10 wt% PCTFE were found to exhibit the highest level of microhardness at all radiation doses.

The dielectric ac bridge measurements have been carried out to understand molecular motion and their relaxation behaviour in PMMA:PVDF polyblends of different wt% composition. The dielectric constant (/spl epsiv/') and dielectric loss (/spl epsiv/") factors of 100 /spl mu/m thick films of these polyblends were measured as a function of temperature in the range of 40 to 140/spl deg/C and at different frequencies from 100 Hz to 10 MHz. The dielectric constant decreased with frequency and increased with temperature in the entire frequency range. The dielectric loss also increased with temperature in the studied frequency range. The observed characteristic behaviour has been consistently explained in terms of dipolar motions and the plasticization effect brought about by blending PMMA with PVDF.

Mechanisms of charge production and its persistence in one and both side vacuum-aluminized EC:PMMA blend foil thermoelectrets, prepared under different field and temperature conditions, have been analyzed using the short- and open-circuit thermally stimulated current (TSC) techniques. The results indicate the existence of heterocharge due to dipole orientation and ionic charge drift together with the injection of charge carriers from electrodes with their subsequent localization in surface and bulk traps. Various characteristics of both types of thermograms indicated the injection of charge carriers from electrodes during short-circuit TSC under high electric field created at the interface by the strong heterocharge. >

Irradiation gamma a des doses entre 2 et 75 Mrad; calcul du nombre de durete de Vickers Hv. Diminution de Hv en augmentant la dose jusqu'a 50 Mrad, puis accroissement brusque. Interpretation par des ruptures de chaine et la reticulation du polymere

Etude de l'effet de la charge sur le nombre de Vickers. Discussion de la nature des polymeres selon la loi de Meyer et en fonction de leur comportement aux contraintes faibles a l'aide de la pression de resistance newtonnienne

Mesure des courants thermostimules en circuit court et ouvert, de la diminution de charge isotherme et des courants d'absorption d'electrets de polypropene