B. R. Gupta

Mechanical properties, surface morphology and failure mode of γ-ray irradiated blends of polypropylene and ethylene-vinyl acetate rubber

Abstract The effect of 60 Co γ-radiation on the mechanical properties, surface morphology and failure characteristics of blends of polypropylene [PP] and ethylene-vinyl acetate rubber [EVA] has been studied with specific reference to the effect of blend ratio, dynamic crosslinking of the rubber phase and absorbed radiation doses. Samples were subjected to radiation in the dose range of 1 to 100 Mrad in air at room temperature at the rate of 0·321 Mrad/h. Both chain scission and crosslinking occur simultaneously in the blend samples. PP and blends containing higher proportions of PP (≥50%) undergo predominant chain scission at lower doses (≤50 Mrad), which causes a drastic drop in tensile strength, followed by a levelling out at higher doses of 100 Mrad. EVA undergoes crosslinking at lower doses resulting in an increase in tensile strength in the dose range 1 to 10 Mrad followed by a decrease in the range 10–25 Mrad. Further increase in radiation dose has little effect on tensile strength. The effect of radiation on stress-strain behaviour, elongation at break, energy at rupture and hardness was also studied. The morphology of the irradiated surfaces after an absorbed dose of 100 Mrad has been examined by scanning electron microscopy (SEM). In order to understand the effect of γ-radiation on the failure mechanism, tensile failure surfaces of both unirradiated and irradiated samples have also been examined by SEM.

Scanning electron microscopy studies on tensile, tear and abrasion failure of plasticized poly (vinyl chloride) and copolyester thermoplastic elastomers

Scanning electron microscopic observations on the tensile, tear and abrasion failure of plasticized poly (vinyl chloride) (PVC) and copdyester (Hytrel 40D) thermoplastic elastomers showed that the patterns developed on the fracture surfaces could be correlated with the strength and type of failure of these materials. Hytrel was found to undergo ductile failure whereas PVC showed shear fracture under tensile stress. The higher tear and abrasion resistances of Hytrel than those of PVC were also manifested by the difference in fracture patterns on the failure surfaces of these samples.

Tack and Green Strength of Blends of Bromobutyl and EPDM Rubbers. I. Unfilled Gum Blends

Abstract Polymer blends are gaining importance in recent years because they provide a compromise of properties. In this paper, tack and green strength of several blends of EPDM and bromobutyl rubbers (BIIR) have been studied over a wide range of temperaures, contact times and rates. Tack increases with increase in contact time and with increase in contact temperature up to 47°C for a particular blend. At a much higher temperature the tack strength falls gradually. Green strength increases with increase in bromobutyl content and decreases with temperature. Tack index, a ratio of tack strength divided by the cohesive strength under the same geometry, decreases slowly with the test temperature. At a 50:50 ratio of BIIR:EPDM, the two rubbers form an interpenetrating network as observed under the phase contrast microscope.

Studies on adhesion between rubber and fabric and rubber and rubber in heat resistant conveyor belt

Abstract Adhesion strength between topping rubber and fabric (nylon 66 and polyester-nylon 66) and cover rubber and topping rubber of heat resistant conveyor belt based on SBR and chlorobutyl rubbers have been measured over a range of peel rates and temperatures and after ageing of the joints at various temperatures and durations. The adhesion strength between SBR topping compound and nylon 66 was greatest. TMTM-based SBR cover compound registered highest adhesion strength with the SBR topping compound. Decreasing the rate or increasing the temperature of testing reduced the peel strength of the joints. Rubber to fabric adhesion decreased with ageing time and temperature, while rubber to rubber joint strength initially decreased and then increased or remained constant.

Tear and wear of thermoplastic elastomers from blends of poly(propylene) and ethylene vinyl acetate rubber

Tear and wear properties of thermoplastic elastomers from blends of poly(propylene) (PP) and ethylene vinyl acetate rubber have been studied with special reference to the effect of blend ratios and dynamic crosslinking of the rubber phase. Both tear and wear resistance of the composites were found to increase with increasing proportion of the PP phase. Dynamic crosslinking of the blends containing higher proportions of the rubber phase (> 60%) increases the wear and tear properties, but blends containing higher proportions of the plastic phase show a decrease in properties due to the degradation of the PP phase. Attempts have been made to correlate the changes in properties with the morphology of system. In order to understand the mechanism of failure, the tear and wear fracture surfaces have been examined by scanning electron microscopy. The fractographs have been correlated with the strength and type of failure of these blends.

Mill processing behavior of polychloroprene and acrylic rubbers

Abstract Mill processing behavior, with respect to front to back roll (F-B) transition, of polychloroprene and acrylic rubbers has been studied. The critical nip gap at which F-B transition occurs has been determined for these rubbers and their filled compounds (including HAF, MT, silica, and whiting) over a range of friction ratios and temperatures. The nip gap increases with friction ratio and temperature. The theoretical model of Tokita based on dimensional analysis, reveals three conditions corresponding to three types of behavior of various rubbers in drop mill operation. Mill band formation indices corresponding to these behavior types have been defined. These indices can be used to determine the conditions for front roll band formation. The systems investigated satisfy one of the conditions of the model. The mill processing behavior of these systems in a continuous milling operation has also been reported.

Cut-growth behaviour of EPDM-bromobutyl rubber blends under repeated stressing

Cut-growth behaviour of ethylene-propylene -diene rubber (EPDM), bromobutyl rubber (BIIR) and their blends under dynamic loading has been studied over a range of temperatures. The crack-growth resistance increases with the increase of BIIR content in the gum and filled blends. The 30: 70 EPDM : BIIR blend, however, gives the best fatigue resistance because of morphology and strain energy density factors. Failure surfaces have been examined both by photography and electron microscopic techniques. The crack always propagates from the precut. The rate of crack propagation is faster for EPDM gum samples. The blends show fracture features intermediate between those of fractured BIIR and EPDM rubbers. Straight flow lines, cracks and fatigue striations (10 to 15μm distance between two consecutive striations) are observed for gum samples. The flow lines are increased and the cracks are reduced for filled samples. The fractography of the crack front at the precut and that away from it are similar. At a higher temperature (100° C), there is a reduction of fatigue life for the blends and pure rubbers. Many cracks are observed on the fracture surface of gum and filled samples.

Tack and green strength of filled blends of bromobutyl and EPDM rubbers

Effect of fillers on tack and green strength of blends of EPDM and bromobutyl rubbers has been studied. The fillers used are carbon black and china clay. Test temperature and mode of mixing are varied. Tack increases with the addition of carbon black and china clay. The highest value of tack strength is achieved when the loading of filler is 50% in each phase or all in EPDM phase. The tack strength of filled blends decreases with an increase of test temperature. Tack index, a ratio of tack strength divided by cohesive strength measured under the same geometry, also decreases with test temperature. It has been found that tack strength (Ga) of filled blends is proportional to the contact time (t) and varies as t1/2 or t1/4. Green strength of carbon black filled mixes is much higher than that of china clay filled mixes. The green strength falls with a rise of temperature in both cases. Green strength of carbon black filled mixes increases with the increase of bromobutyl content in the mix. China clay mixes s...

Abrasion of high temperature conveyor belt compounds based on ethylene propylene diene and bromobutyl rubber blends

Abstract Abrasion of both unfilled and filled ethylene propylene diene rubber (EPDM), bromobutyl rubber (BIIR) and their blends has been studied at different compositions (70:30, 60:40, 58:42, 55:45, 50:50, 42:58, 45:55, 40:60 and 30:70), aging times (12 and 36 h) and aging temperatures (70, 100 and 150°C). Abrasion resistance decreases with increasing BIIR content in the blends for unfilled systems. For filled systems, the abrasion loss shows a minimum at a composition of about 50:50 EPDM-BIIR. For both the systems, the volume loss due to abrasion increases gradually with abrading time. With increasing aging temperature, the abrasion resistance increases owing to post-vulcanization reaction. Examination of the abraded surfaces by scanning electron microscopy indicates that EPDM (both unfilled and filled) generates microridges, the spacing of which is 85 ± 25 μm for unfilled compounds and 80 ± 50 μm for filled compounds. Unfilled BIIR wears by a cutting mechanism. However, the filled blends show wear by fatigue or roll formation. EPDM wears in powder form, whereas BIIR forms agglomerated fibrils.

Studies on mechanical properties and fractography of γ-ray irradiated blends of plasticized poly(vinyl chloride) and thermoplastic copolyester elastomer

The mechanical properties and fracture mode of 60Co γ-ray irradiated blends of plasticized poly(vinyl chloride) [PVC] and thermoplastic copolyester elastomer [Hytrel 40D] have been investigated with specific reference to the effect of blend ratios and absorbed radiation doses. Samples were irradiated in the dose range of 0.1–50 Mrad in air at room temperature (25°C) at the rate of 0.321 Mrad/h. Hytrel and blends containing higher proportion of hytrel (⩾50%) were found to undergo extensive crosslinking in the bulk which in effect caused a maximum in ultimate tensile strength at an absorbed dose of 1 Mrad, but showed a drastic drop in tensile strength at higher radiation doses (10–50 Mrad) due to embrittlement and surface oxidation. In the case of PVC and blends containing a higher proportion of PVC (⩾75%), a slow decline in tensile strength was observed at lower radiation doses up to 10 Mrad, whereas at higher doses (10–50 Mrad), they showed a sharp decrease in tensile strength due to the degradation of the PVC phase. The elongation at break, tear strength and tensile set after failure of all the samples remain unchanged up to an absorbed dose of 1 Mrad but showed considerable reduction at higher radiation doses. The morphology of the irradiated surfaces after an absorbed dose of 50 Mrad has been examined by scanning electron microscope (SEM). SEM studies on the tensile and tear fracture surfaces also have been undertaken in order to gain an insight into the mechanism of failure.