P. G. Mukunda

Thermal degradation studies of electron beam cured ethylene-vinyl acetate copolymer

The thermal degradation of pure ethylene-vinyl acetate copolymer (EVA, 12% vinyl acetate) and electron beam radiation-cured EVA, cured in the presence of a small amount of sensitizer, has been studied by non-isothermal thermogravimetry and infrared spectroscopy. These studies suggest that radiation-cured EVA is more thermally stable than pure EVA.

Thermogravimetric analysis of compatibilized blends of low density polyethylene and poly(dimethyl siloxane) rubber

The thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis of compatibilized blends of low density polyethylene (LDPE) and poly(dimethyl siloxane) rubber (PDMS) in the proportion of 50:50 containing different proportions of ethylene methyl acrylate co-polymer (EMA) as compatibilizer have been studied. EMA acts as a chemical polymeric compatibilizer for the binary blend system of LDPE and PDMS, the proportion of which varied from 0 to 15 wt.%. The TG and DTG of the blends show that the thermal degradation takes place in two stages, where as neat LDPE shows a three stage degradation and neat EMA and PDMS show only single stage degradations respectively. The activation energies at 10% degradation have been determined using Freeman and Carrolls method and found to be maximum (171 kJ/mol) for the blend containing 6 wt.% of EMA. Half life periods at 200 °C have been evaluated by the Flynn and Wall method and found to be maximum for the blend containing 6 wt.% of EMA.

Thermal degradation and ageing of segmented polyamides

The degradation behaviour and kinetics of degradation of segmented polyamides with varying block lengths have been studied by non-isothermal thermogravimetry in air and nitrogen and by infrared spectroscopy. In air, all the polymers show two stage decomposition, whereas in nitrogen, the decomposition occurs in a single stage. In both atmospheres the degradation, however, follows first order kinetics. The infrared spectroscopic analysis of the degraded products reveals that the decomposition occurs in the polyether linkage followed by polyamide hard block. The mechanism of degradation is of course a complex one. In the case of thermooxidative degradation, a decrease in hard block molecular weight has a great influence on the activation energy values. The effect of ageing on the mechanical properties of these polymers has also been studied. On ageing, it is observed that both tensile strength and elongation at break drop sharply in the initial stage. After this initial drop, both properties show a marginal change with time and temperature of ageing. Retention of physical properties is better with high hard block molecular weight polymers.

Degradation of Hydrogenated Styrene—Butadiene Rubber at High Temperature

Abstract Degradation of hydrogenated styrene—butadiene rubber (HSBR) having different levels of unsaturation has been studied over a wide range of temperatures under anaerobic and aerobic conditions using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), IR and NMR spectroscopy. TGA data indicate higher thermal stability of hydrogenated rubber as compared to SBR in nitrogen, although an anomalous behavior is observed in air due to crosslinking and oxidation of styrene—butadiene rubber (SBR). Isothermal data confirm the above observations. IR and NMR results reveal thermal isomerization, cyclization, oxidation, depolymerization, and chain scission processes. The nature and amount of products formed depend on the time and temperature of degradation and also on the level of hydrogenation of SBR.

Formation of SiC whiskers from compacts of raw rice husks

The formation of SiC whiskers from compacts of raw rice husks without coking and catalyst has been studied. A pyrolysis temperature of 1600°C has yielded a considerable quantity of SiC whiskers. The formation of spherical particles of silica is observed. Whisker formation occurs by reaction between SiO(g) and CO(g).

Sintering studies on submicrometre-sized Y-Ba-Cu-oxide powder

The isothermal sintering behaviour of submicrometre-sized (<50 nm) powders of single-phase YBa2Cu3Ox (123) and unreacted stoichiometric mixture of submicrometre-sized (<50 nm) powders of BaCO3, Y2O3 and CuO (which on calcination at 1173 K gives YBa2Cu3Ox) was investigated through dilatometry under different sintering atmospheres. The sintering rate of the powder compacts was impeded by the presence of oxygen. The activation energies,Q, of sintering were determined to be 1218 kJ mol−1 in argon, 1593 kJ mor−1 in air and 2142 kJ mol−1 in oxygen. A decrease in the apparent sintered density with increasing oxygen partial pressure was also observed. X-ray diffraction and thermal analyses (thermogravimetry and differential thermal analysis) showed no reaction during sintering of the single-phase product. Pellets fabricated from uncalcined powder exhibit two stages of sintering, one between 1073 and 1173 K having an activation energyQ=627kJ mol−1, and a second one above 1173 K withQ=383.7 kJ mol−1. A.c. susceptibility, resistivity and critical current density were determined as a function of the temperature of the sintered samples.

Sintering mechanisms of attrition milled titanium nano powder

Detailed sintering studies have been carried out on attrition milled nanocrystalline titanium powder through isothermal dilatometry over a temperature range of 300–1250 °C along with microstructural and x-ray diffraction studies. The sintering behavior of attrition milled nanocrystalline titanium appears to be characterized by: (i) very low activation energies, (ii) high shrinkage anisotropy, (iii) very rapid grain growth in the beta range, and (iv) two kinds of densification processes, namely, intra-agglomerate and inter-agglomerate. Analysis of the kinetic data through sintering diagram approach indicates the operation of particle sliding and grain boundary rotation, type of mechanism in addition to the grain-boundary diffusion, and lattice diffusion as the dominant mass transport mechanisms.

Thermal analysis of blends of poly(ethylene co-acrylic acid) (PEA) and epoxidised natural rubber (ENR)

Abstract The decomposition behavior of blends of poly(ethylene co-acrylic acid) (PEA) and epoxidised natural rubber (ENR) have been studied by thermogravimetric (TG) and (first) derivative thermogravimetric analysis. The thermograms of ENR show a clear two-stage degradation, whereas that of PEA exhibits three-stage degradation. Surprisingly, in the blends containing 70 and 50% of ENR, multistage degradation is observed, whereas blends containing 30, 20 and 10% ENR exhibit two-stage decomposition with a T 1max (first maximum decomposition temperature) at 430 °C. This higher T 1max in the latter blends indicates the existence of a single phase, owing to strong chemical interactions during melt processing. Activation energy at 10% degradation and half life at 200 °C of the blends have been reported.

Machinability Investigations on High Chrome White Cast Iron Using Multi Coated Hard Carbide Tools

This study investigated the performance of multilayer hard coated carbide tool and multi-response optimization of the turning process for an optimal parametric combination to yield the minimum cutting forces and machining power with a maximum material removal rate (MRR) using Taguchi and artificial neural network (ANN) methods. In recent times, high chrome white cast iron finds increasing applications in aerospace, mining, mineral process industries. Its machinability using carbide insert (TiC/TiCN/Al2O3) cutting tool has been studied. The influences of cutting parameters on the cutting forces, MRR and machining power of the process have been analyzed using analysis of variance and the results are correlated using ANN. Linear regression method was used to establish the relation between the cutting parameters and the process responses. The confirmation test reveals that, the accuracy of prediction of ANN is better than that of the regression analysis. In view of the good performance of the carbide tools (at optimum conditions), it can replace the cosly CBN, with improved economic benefits.

Kinetics of thermal degradation and related changes in the structure of blends of poly(ethylene-co-acrylic acid) (PEA) and epoxidized natural rubber (ENR)

Abstract The thermal degradation of blends of poly(ethylene-co-acrylic acid) (PEA) and epoxidized natural rubber (ENR) has been studied in nitrogen at heating rates of 5, 10, 15 and 20 °C/min from room temperature to 600 °C. The kinetic parameters have been calculated at various conversions and their accuracy tested at different rates of heating. IR spectroscopy was used to study the chemical and structural changes which occur during degradation at 375 and 430 °C.