Melt rheology and elasticity of natural rubber—ethylene–vinyl acetate copolymer blends

Abstract

SYNOPSISThe melt rheology of blends of natural rubber ( N R ) and ethylene-vinyl acetate copolymer (EVA) has been studied with reference to the effects of blend ratio, cross-linking systems, shear stress, and temperature. When EVA formed the dispersed phase, the viscosity of the blends was found to be a nonadditive function of the viscosities of the component polymers at lower shear region, i.e., a positive deviation was observed. This behavior has been explained based on structural buildup of dispersed EVA domains in the continuous NR matrix. The effect of the addition of silica filler on the flow characteristics of the blends has been investigated. The melt elasticity parameters such as die swell, principal normal stress difference, recoverable shear strain, and elastic shear modulus of NR-EVA blends were also evaluated. 0 1993 John Wiley & Sons, Inc. I NTRO DU CTI 0 NIn recent years, blending of two or more polymers to produce the required combination of properties for specific end uses is gaining industrial importance. Knowledge of flow behavior of polymer blends is of paramount importance to optimize processing operations. In polymer blends, the viscosity of individual components plays a critical role in the flow and forming of compounds. Several investigations have been made to understand the complicated rheological behavior of polymers in view of its relevance to processing.'-4 The melt flow behavior of polymer blends and that of polymers containing cross-linked particles have been studied by different research group^.^-" Danesi and Porter l 1 studied the rheological behavior of polypropylene and ethylene propylene rubber. They explained how the state of dispersion is affected by conditions of blend preparation and extrusion. Utracki and Samut l 2 studied the flow properties of various polyethylene blends. Kuriakose and De13 and Thomas et al.14 studied the * To whom all correspondence should be addressed. Recently, Varughese l5 studied the rheological behavior of poly (vinyl chloride) /epoxidized natural rubber (PVC/ENR) blends. All these studies indicated that the dispersed phase in an immiscible blend is deformable and may give rise to wide range of sizes and shapes during processing. This, in turn, determines the morphology of the system. The melt rheology is particularly sensitive to morphology. Blends of ethylene-vinyl acetate copolymer (EVA) and natural rubber ( NR) are now being used in many applications such as in cables and footwear. These materials combine the superior mechanical properties of NR and the excellent aging properties of EVA. Recently, we have examined the miscibility, morphology, mechanical properties, and aging characteristics of these However, the rheological behavior of these blends has not been studied. This paper examines the rheological characteristics of NR-EVA blends by capillary rheometry. The effects of blend ratio, cross-linking system, and silica on the viscosity of the blends have been studied. In addition, the morphology of extrudate has been examined to understand the...

Effect of electron beam irradiation on the properties of ethylene‐(vinyl acetate) copolymer/natural rubber/organoclay nanocomposites

“…The blend ratio of EVA and SMR L was prefixed at 50:50. The presence of EVA and SMR L at a high proportion increases the thermal aging resistance [23] and melt elasticity [24] of the system, respectively. EB irradiation can be utilized to crosslink both the EVA and the NR in order to obtain further improvements in the mechanical properties and thermal stability of the blend [6,7].…”

Melt rheology and morphology of physically compatibilized natural rubber-polystyrene blends by the addition of natural rubber-g-polystyrene

“…Gupta et al 5 have studied the various rheological aspects of blends of polypropylene with acrylonitrile butadiene styrene (ABS) and low-density polyethylene (LDPE) and correlated it with the morphology studies. Melt rheological behavior of natural rubber-ethylene vinyl acetate copolymer blends was studied by Koshy et al 6 The morphologyrheology relationship of miscible and immiscible blends of ABS with poly(methyl methacrylate) (PMMA) was studied using ABS having different acrylonitrile (AN) content and PMMA with different molecular weights. 7 Rheological properties of dynamically cured ethylene-propylene-diene monomer rubber (EPDM)-polypropylene-HDPE ternary blends were analyzed by Ha.…”

Mercapto-modified copolymers in polymer blends. II. The compatibilization of NBR/EVA blends

“…12 Specific other properties, such as crystallinity degree and flexibility, are also achieved by varying the amount of vinyl acetate in the copolymer. Several rubbers have been blended with EVA and include natural rubber, 8,13 polychloroprene rubber, 14 -17 etc. Blends of nitrile rubber (NBR) with EVA also have been reported in literature.…”