Dynamic mechanical analysis of banana fiber reinforced polyester composites

Telechelic liquid natural rubber: A review

Dynamic mechanical analysis (DMA) was used to study the miscibility and various transitions (α, β, and γ) in binary blends of ethylene vinyl acetate copolymer (EVA) with low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Addition of a rubbery phase, such as EVA, reduced all the transition temperatures. A peak broadening of tan δ was observed with increasing EVA content in the blends. This can be explained by the observed reduction of the crystallinity of the systems. The presence of a single transition peak in the region of glass transition temperature (Tg) has indicated that the blends were miscible. However, morphological investigation by scanning electron microscopy (SEM) revealed the features of a two phase system in which the EVA domains would be dispersed in the polyethylene (PE) phase. The results have demonstrated that DMA is not sensitive enough to study the miscibility of polymeric blends with a similar backbone structures (such as PE and EVA) in view of the small difference in their Tg. For such blends, therefore, the use of direct observations, such as microscopic examinations is necessary. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 307–315, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20019

Dynamic mechanical properties and morphology of polyethylene/ethylene vinyl acetate copolymer blends

Thermoplastic elastomers from blends of polystyrene and natural rubber: morphology and mechanical properties

Ethylene vinyl acetate (EVA) co-polymers can potentially provide novel materials for inclusion into extruded high voltage cable systems, providing a degree of electrical conductivity whilst avoiding the dispersion problems associated with conventional particulate fillers or conducting polymers. Although a degree of conductivity can decrease the electrical breakdown performance, it can help to suppress the development of space charge and increase the tree initiation voltage leading to enhanced dielectric properties. In addition, novel two phase morphologies can be formulated leading to the ability to control key thermal and mechanical properties and the ability to tailor these to suit the application. In addition, one of the problems with conventional cross-linked polyethylene (XLPE) is that it cannot easily be recycled; therefore, in this time of increasing environmental awareness, it is prudent to begin investigations into alternative recyclable materials to replace XLPE in extruded cables for the medium to long term. The current article focuses on the crystallisation behaviour, morphology, mechanical and dielectric properties of a range of polymeric insulation systems based on an EVA co-polymer together with a high density polyethylene (HDPE) component. The morphology was controlled by choosing co-polymers containing different vinyl acetate contents together with appropriate crystallisation routes. The relationships between the morphology and the mechanical and dielectric properties were explored. Blends containing a low vinyl acetate content co-polymer combined with HDPE have significant potential to replace XLPE in cable systems and have the advantage of being easily recycled at the end of their service life.

An investigation of the potential of ethylene vinyl acetate/polyethylene blends for use in recyclable high voltage cable insulation systems

Morphology, mechanical and viscoelastic behaviour of blends of nitrile rubber and ethylene-vinyl acetate copolymer

The morphology and mechanical and viscoelastic properties of a series of blends of natural rubber (NR) and styrene butadiene rubber (SBR) latex blends were studied in the uncrosslinked and crosslinked state. The morphology of the NR/SBR blends was analyzed using a scanning electron microscope. The morphology of the blends indicated a two phase structure in which SBR is dispersed as domains in the continuous NR matrix when its content is less than 50%. A cocontinuous morphology was obtained at a 50/50 NR/SBR ratio and phase inversion was seen beyond 50% SBR when NR formed the dispersed phase. The mechanical properties of the blends were studied with special reference to the effect of the blend ratio, surface active agents, vulcanizing system, and time for prevulcanization. As the NR content and time of prevulcanization increased, the mechanical properties such as the tensile strength, modulus, elongation at break, and hardness increased. This was due to the increased degree of crosslinking that leads to the strengthening of the 3-dimensional network. In most cases the tear strength values increased as the prevulcanization time increased. The mechanical data were compared with theoretical predictions. The effects of the blend ratio and prevulcanization on the dynamic mechanical properties of the blends were investigated at different temperatures and frequencies. All the blends showed two distinct glass-transition temperatures, indicating that the system is immiscible. It was also found that the glass-transition temperatures of vulcanized blends are higher than those of unvulcanized blends. The time-temperature superposition and Cole-Cole analysis were made to understand the phase behavior of the blends. The tensile and tear fracture surfaces were examined by a scanning electron microscope to gain an insight into the failure mechanism.

Morphology and mechanical and viscoelastic properties of natural rubber and styrene butadiene rubber latex blends

The rheological behavior of blends of natural rubber (NR) and styrene–butadiene rubber (SBR) latices has been studied with reference to the effects of blend ratio, shear rate, surface-active agents (casein and sodium carboxymethyl cellulose), and temperature. When the SBR content was less than 50%, the viscosities of the blends appeared to be a nonadditive function of the viscosities of the constituent homopolymers; i.e., a positive deviation was observed. This was due to the structural buildup of the SBR domains. The SBR domains underwent agglomeration and consequently so-called microflocculation took place. The viscosities of all the blends were found to decrease with increase of temperature and shear rate. The increase in temperature and shear rate marginally weakened the structural buildup as evidenced by the lowering of viscosity. As the SBR content in the system increased, the pseudoplasticity of the blend increased. Even in the presence of surface-active agents the blends showed composition-dependent positive deviation. However, surface-active agents marginally reduced the extent of structural buildup by reducing the microflocculation behavior of SBR domains. © 1995 John Wiley & Sons, Inc.

Rheological behavior of blends of natural rubber and styrene–butadiene rubber latices

The effect of prevulcanization on the rheological behavior of natural rubber (NR), styrene butadiene rubber (SBR) latices, and their blends was studied with special reference to shear rate, blend ratio, vulcanizing systems, prevulcanization time, and accelerator systems. The NR latex showed a sharp increase in viscosity with increase in prevulcanization time due to high extent of crosslinking. However, SBR latex showed marginal effect on viscosity with prevulcanization time due to its low dry rubber content and low degree of unsaturation. Blends showed variations in viscosity according to the change in composition. The use of a single accelerator was found to have marked influence on the viscosity of the blends compared with a combination of accelerators. Swelling experiments were carried out in order to determine the crosslink density of the blends. The viscosity changes have been correlated with the crosslinking density of the latices and their blends. © 1996 John Wiley & Sons, Inc.

Effect of prevulcanization on the rheological behavior of natural rubber/styrene butadiene rubber latex blends

A study on the flow behavior of blends of natural rubber (NR) and epoxidized natural rubber (ENR) latices was carried out using a Contraves viscometer. The effects of blend ratio, shear rate, and temperature on the flow properties were determined. The viscosities of the blends showed negative deviation from additivity. Unlike the homopolymer latices, the viscosities of the blends increased with increase of temperature. Blends are found to be less pseudoplastic than homopolymers.

S. Someswara Rao

Papers

Morphology, mechanical and viscoelastic behaviour of blends of nitrile rubber and ethylene-vinyl acetate copolymer

Morphology and mechanical and viscoelastic properties of natural rubber and styrene butadiene rubber latex blends

Rheological behavior of blends of natural rubber and styrene–butadiene rubber latices

Effect of prevulcanization on the rheological behavior of natural rubber/styrene butadiene rubber latex blends

Flow Behavior Of Natural Rubber/Epoxidized Natural Rubber Latex Blends