R. Chandra

Biodegradation of maleated linear low-density polyethylene and starch blends

Environmental threats restrict the use of nondegradable polymers and encourage the development and use of degradable plastics. In order to obtain a cost-effective biodegradable plastic, starch-filled polyethylene (PE) is still the best alternative. Starch and PE blend is incompatible at the molecular level and often leads to poor performance. In order to overcome this drawback, either PE or starch should be modified. The aim of this study was to modified linear low-density polyethylene (LLDPE) and blend it with starch. Maleic anhydride (MA) was grafted onto LLDPE in xylene using dicumyl peroxide (DCP) as an initiator. Corn starch in varying concentrations (between 10 and 60%) was blended with MA-g-LLDPE in a torque rheometer. The same blend compositions of nonfunctional LLDPE with the starch were prepared for comparative studies. The torque and totalized torque generated during blending are reported as a function of starch content. Torque decreased with increasing starch content for the compositions from 10 to 50% and increased for 60% starch content. Work energy decreased for all the compositions of blends except for 60% starch content. Tensile strength and modulus increased and percentage elongation decreased as the starch content increased in the blends. Water absorption of the blends increased with an increase in starch content. The biodegradability of MA-g-LLDPE/starch blends have been studied in two biotic environments: (1) soil environment over a period of 6 months; (2) mixed fungi inoculum (Aspergillus niger, Penicillium funiculosum, Chaetomium globosum, Gliocladium virens and Pullularia pullulans) for 28 days. The samples containing more than 30% starch content supported heavy fungus growth. Blends exposed to a soil environment degraded more than in fungi alone. Any changes in the various properties of the MA-g-LLDPE/starch before and after degradation were monitored using FTIR spectroscopy, weight loss, a scanning electron microscope (SEM) for surface morphology, a differential scanning calorimeter (DSC) for crystallinity and a thermogravimetric analyzer (TGA) for rapid determination of starch content. Percentage crystallinity decreased as the starch content increased and biodegradation resulted in an increase of crystallinity in MA-g-LLDPE/starch blends.

Studies on dynamic and static crosslinking of ethylene vinyl acetate and ethylene propylene diene tercopolymer blends

The effect of blend ratio on the crosslinking characteristics of ethylene vinyl acetate and ethylene propylene diene tercopolymer (EVA-EPDM) blends was studied by differential scanning calorimetry and a torque rheometer (Rheocord-90). The activation energy decreases with an increase in EVA content in the blend. The cure rate increases whereas the optimum cure time and energy consumption for curing decrease with an increase in the EVA/EPDM ratio. The dynamic curing obtained by the torque rheometer is very fast compared to the static curing obtained by differential scanning calorimetry.

The effect of bismaleimide resin on curing kinetics of epoxy-amine thermosets

An analysis of the cure kinetics of several formulations composed of diglycidyl ether of bisphenol-A (DGEBPA) and aromatic diamines, methylenedianiline (MDA) and diaminodiphenyl sulfone (DDS), in the absence and presence of 4,4′-bismaleimidodiphenylmethane (BM) was performed. The dynamic differential scanning calorimetry (DSC) thermograms were analyzed with the help of ASTM kinetic software to determine the kinetic parameters of the curing reactions, including the activation energy, preexponential factor, rate constant, and 60 min ½ life temperature. The effects of substitution of one curing agent for another, their concentration, and the absence and presence of BM resin and its concentration on curing behavior, ethalpy, and kinetic parameters are discussed.

Stabilization of polyurethane films against thermal and photo-oxidative degradation

The stabilization of poly tetramethylene hexamethylene dicarbamate (PMMC) against thermal and photo-oxidative degradation has been studied in the temperature range 273 to 353 K using monochromatic light of 253·7 nm. 4-Methoxy-2, 6-diphenyl phenol (MDPP) and a,a′-diphenyl diethylsulphide (DPDS) were used as stabilizers. The protective influence of stabilizers alone or in combination has been confirmed by the suppression of catalysed degradation due to incorporation of copper stearate (CuSt2) in the matrix of the polymer. Superior results were obtained when MDPP and DPDS were used in combination. The degradation and stabilization were studied by following the variation in weight average molecular weight (Mw), quantum yield (φcs) for the chain scission, stress-strain properties, IR and UV spectroscopy. PP and DPDS were mixed in two ratios and each combination gave synergism.

Thermal stability of ethylene–vinyl acetate and ethylene–propylene–diene (EVA–EPDM) blends

The thermal behavior of ethylene–vinyl acetate (EVA) and ethylene propylene–diene (EPDM) blends have been studied by thermogravimetry in nitrogen. The activation energy, preexponential factor, and lifetime have been calculated using software-based on the Flynn and Wall isoconversional procedure. The maximum thermal stability in nitrogen atmosphere was observed for the EV80–EP20 blend.

Mechanistic study of fatigue behavior of vinyltriethoxysilane‐coupled carbon black/styrene‐butadiene rubber vulcanizate

The increase in fatigue to failure (FTF) cycles by three times was observed for styrene-butadiene rubber (SBR) vulcanizate containing carbon black treated with 2.73 phr vinyltriethoxysilane (VTEOS) over the untreated furnace carbon black (UFCB) vulcanizate at an extension ratio of 1.80. There could be several factors responsible for such a phenomenal increases in FTF; however, specifically the chemical reactions associated with this are investigated. The UFCB contains carboxylic and lactone groups on its surface besides other groups. On treatment with VTEOS, the ethoxy or silanol group(s) of it reacts with the carboxylic and lactone groups of UFCB. This provides an interface between the particulate UFCB and the flexible rubber matrix unlike UFCB, which adsorbs polymer in absence of VTEOS. Furthermore, the vinyl group thus attached to the UFCB takes part in vulcanization reaction and increase in the degree of cross-linking. In addition, the VTEOS substantially reduces the formations of weak polysulphidic linkages. The added flexible interface increased cross-linking and reduced polysulphidic linkages seem to be mainly responsible to the significant improvement of FTF behavior.

Thermal and photo-stabilization of poly(methyl methacrylate) film by 1-(2-phenothiazinyl)-3-(p-anisyl)-2-propen-1-one

Abstract Copolymers of methyl methacrylate (MMA) and 1-(phenothiazinyl)-3-( p -anisyl)-2-propen-1-one (PAP), containing up to 5 mol % of the latter have been studied. The reactivity ratios for MMA and PAP were determined by IR and NMR analysis. Increasing contents of PAP bring about increased light and thermal stability in the copolymer. Thermogravimetry, derivative thermogravimetry and differential scanning calorimetry have been used to study the effect of copolymer composition on thermal stability. Poly(methyl methacrylate) (PMMA) and MMA-PAP copolymer films have been irradiated with 253·7 nm light (in air) in the temperature range 303–333 K to determine the change in the weight-average molecular weight, degree of degradation and quantum yield for chain scission. The changes in carbonyl, hydroxyl and hydroperoxide contents on photo-irradiation have also been determined. The data so obtained have been used to obtain heats of activation of the system.

Photostabilization of poly-(2,6-dimethyl-1,4-phenylene oxide) films by metal dialkyl dithio-phosphate

Abstract The photostabilization of poly-(2,6-dimethyl-1,4-phenylene oxide) film in air, using Cd(II) O , O ′-diisopropyl dithiophosphate as a stabilizer, in the temperature range 313–363 K with a light intensity flux of 8·7 × 10 −9 einstein s −1 cm −2 , was investigated. The course of stabilization has been determined by means of light scattering, potassium ferrioxalate actinometry and gel formation. The extent of stabilization was also followed by IR and UV spectroscopy and by monitoring the formation of carbonyl and hydroxyl groups. These results have been used to support the proposed mechanism of photostabilization.