R. Bajpai

Development of hardened PVF : PMMA polyblend: effect of gamma and electron irradiation

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.

Surface modification on PMMA : PVDF polyblend: hardening under chemical environment

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 (Hv) 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.

Microhardness testing to detect radiation-induced crosslinking in polystyrene : poly(methyl methacrylate) polyblends

Abstract 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.

Plasticization in poly (methyl methacrylate) and poly (chlorotrifluoroethylene) blends detected by microhardness measurements

Abstract 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 Vickers microhardness has been studied. It is observed that poly (chloro trifluoroethylene) acts as a plasticizer for poly (methyl methacrylate).

Radiation induced effects on the microhardness measurements of poly(methyl methacrylate): poly(vinylidene fluoride) polyblends

Abstract 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.

Hardening induced by gamma irradiation in poly(methyl methacrylate): Poly(chlorotrifluoroethylene) blends

Abstract 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 Vickers microhardness tester attached to a Carl Zeiss NU 2 Universal research microscope. The value of Vickers 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.

Photoplastic effect in polycarbonate using microhardness measurements

Vickers microhardness indentation technique has been employed to detect the photoplastic effect in the transparent polycarbonate specimens in darkness and under mercury illumination. For low applied loads, the hardening of specimens under illumination confirms the positive photoplastic effect that causes illumination-induced increase of crosslinking (in polymer). For high applied loads the positive photoplastic effect decreases as the level of microhardness decreases.

A study of the microhardness of ethylene glycol dimethacrylate (EGDM)/poly (methyl methacrylate) (PMMA) network polymer

Abstract The application of the network formed from ethylene glycol dimethacrylate and poly (methyl methacrylate) (PMMA) in dentistry and orthopaedics has generated interest among material scientists in the study of its mechanical behaviour. This paper reports the preparation of the network polymer with varying concentrations of PMMA in the network and its effect on the Vickers microhardness (Hv) of the specimens at different loads ranging from 80 to 160 g. The increasing and decreasing trend in values of Hv have been observed with varying concentrations of PMMA in the network. The observed behaviour has been attributed to the effect of localized plastic deformation and cross-linking density. The role of phase separation has also been envisaged.