Jinu Jacob George

Influence of Matrix Polarity on the Properties of Ethylene Vinyl Acetate-Carbon Nanofiller Nanocomposites

A series of ethylene vinyl acetate (EVA) nanocomposites using four kinds of EVA with 40, 50, 60, and 70 wt% vinyl acetate (VA) contents and three different carbon-based nanofillers—expanded graphite (EG), multi-walled carbon nanotube (MWCNT), and carbon nanofiber (CNF) have been prepared via solution blending. The influence of the matrix polarity and the nature of nanofillers on the morphology and properties of EVA nanocomposites have been investigated. It is observed that the sample with lowest vinyl acetate content exhibits highest mechanical properties. However, the enhancement in mechanical properties with the incorporation of various nanofillers is the highest for EVA with high VA content. This trend has been followed in both dynamic mechanical properties and thermal conductivity of the nanocomposites. EVA copolymer undergoes a transition from partial to complete amorphousness between 40 and 50 wt% VA content, and this changes the dispersion of the nanofillers. The high VA-containing polymers show more affinity toward fillers due to the large free volume available and allow easy dispersion of nanofillers in the amorphous rubbery phase, as confirmed from the morphological studies. The thermal stability of the nanocomposites is also influenced by the type of nanofiller.

Fabrication and Properties of Ethylene Vinyl Acetate-Carbon Nanofiber Nanocomposites

Carbon nanofiber (CNF) is one of the stiffest materials produced commercially, having excellent mechanical, electrical, and thermal properties. The reinforcement of rubbery matrices by CNFs was studied in the case of ethylene vinyl acetate (EVA). The tensile strength was greatly (61%) increased, even for very low fiber content (i.e., 1.0 wt.%). The surface modification of the fiber by high energy electron beam and gamma irradiation led to better dispersion in the rubber matrix. This in turn gave rise to further improvements in mechanical and dynamic mechanical properties of EVA. The thermal conductivity also exhibited improvements from that of the neat elastomer, although thermal stability of the nanocomposites was not significantly altered by the functionalization of CNFs. Various results were well supported by the morphological analysis of the nanocomposites.

Morphology–Property Relationship in Rubber-Based Nanocomposites: Some Recent Developments

Recently, rubber nanocomposites reinforced with a low volume fraction of nanofillers have attracted great interest due to their fascinating properties. Incorporation of nanofillers such as layered and fibrillated silicate clays, carbon nanotubes and nanofibers, calcium carbonate, metal oxides, or silica nanoparticles into elastomers can significantly improve their mechanical, thermal, dynamic mechanical, electrical, aging, barrier, adhesion, and flame retardancy properties. These also significantly alter the rheological behavior of polymers, even at low filler loading. The properties of nanocomposites depend greatly on the structure of the polymer matrices, the nature of nanofillers, and the method by which they are prepared. It has been established that uniform dispersion of nanofillers in rubber matrices is a general prerequisite for achieving desired mechanical, rheological, and physical characteristics. This review paper addresses some recent developments on the morphology–property relationship of rubber-based nanocomposites reinforced with various nanoparticles. New insights into understanding the properties of these nanocomposites and morphology development will be discussed.

A Novel Thermotropic Elastomer based on Highly-filled LDH-SSB Composites

Elastomeric composites are prepared based on solution styrene butadiene elastomer and zinc-aluminium layered double hydroxides (LDH), using a conventional sulphur cure system. Up to 100 parts per hundred rubber of LDH are incorporated into the elastomer matrix. The composites exhibit an interesting phenomenon of thermoreversible transparency, i.e. the transparent sample becomes opaque at warm condition and restores the transparency at room temperature. The transparency is found to be increased as the amount of LDH was increased. The addition of LDH gradually improved the mechanical, dynamic mechanical performance and thermal stability of the base elastomer. These developped elastomers could be utilised as smart materials in different applications.

Influence of functionalization of multi-walled carbon nanotubes on the properties of ethylene vinyl acetate nanocomposites.

Commercially available multiwalled carbon nanotubes (MWNT) were chemically modified by amine, acid and silane and their ethylene vinyl acetate (EVA) based nanocomposites were prepared. Unmodified and modified nanotubes were characterized by thermogravimetry, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. Early degradation of modified nanotubes from the thermogravimetry study proved the presence of functional groups on nanotube surface. Increase in D-band to G-band ratio and a shift in radial breathing mode peaks from the Raman spectra indicated the generation of surface defects due to functionalization and variation in van der Waals force of attraction between nanotube aggregates on modification. The unmodified nanotubes improved the tensile strength by 30% with 4 weight% of filler. Amine modification imparted further increase in strength due to the presence of functional groups on the nanotube surface and the subsequent better dispersion of the nanotubes in the polymer matrix. The silane treatment imparted maximum improvement in various properties of the nanocomposites. The nanotubes provided better thermal degradation stability and also higher thermal conductivity to virgin EVA. The results were well supported by the morphological as well as swelling study of the various samples.

Fire-safe and environmentally friendly nanocomposites based on layered double hydroxides and ethylene propylene diene elastomer

In this work we describe layered double hydroxide (LDH), known as naturally occurring hydrotalcite, based rubber composites that can serve as outstanding fire retardant elastomeric materials. The preparation and detailed characterization of these composites are presented in this study. The inherent slow sulfur cure nature of EPDM rubber is considerably improved by the addition of LDH as realised by the observation of a shortening of the vulcanization time and an improvement of ultimate rheometric torque. This behavior of LDH signifies not only the filler-like character of itself, but also offers vulcanization active surface properties of layered double hydroxide particles. A good rubber–filler interaction was also realised by observing a positive shift of the glass transition temperature of ethylene propylene diene rubber (EPDM) in dynamic mechanical analysis (DMA). The flame retardant property was studied by the cone calorimeter test. The cone calorimeter investigation with sulfur cured gum rubber compounds found a peak heat release rate (PHRR) value of 654 kW m−2. However, at a higher phr loading of Zn–Al LDH i.e., at 40 phr and 100 phr, the PHRR is diminished to 311 kW m−2 and 161 kW m−2, respectively. Thus, this present work can pave the way to fabricate environmentally friendly fire retardant elastomeric composites for various applications.

An Investigation of the Electromagnetic Shielding Effectiveness of Ethylene Vinyl Acetate Elastomer Reinforced With Carbon Nanofillers

Electrically conducting polymeric composites are gaining popularity not only due to their light weight, corrosion resistance, flexibility and low cost, but also due to their electromagnetic interference (EMI) shielding ability. A novel ethylene vinyl acetate (EVA)-carbon nanofibre (CNF) nanocomposite has been successfully developed, and its electromagnetic interference shielding effectiveness (SE) was measured in the frequency range of 8–12 GHz. The dependence of SE on the applied electromagnetic frequency and the amount of filler loading has been evaluated. The SE of the composites was found to be directly proportional to the applied electromagnetic frequency and the amount of filler. Incorporation of 16 wt.% of CNF produced the optimum SE. The AC conductivity of the CNF reinforced EVA composites has also been measured in order to correlate the conductivity values with the SE of the respective composites. The level of filler loading governed the conductive network formation and hence the SE and conductivity. In order to do a comparative study of SE, three other carbon based nanofillers such as multiwalled carbon nanotube (MWCNT), expanded graphite (EG) and conductive carbon black (CB) have been used in this study. Morphological studies using transmission electron microscopy (TEM) supports various findings. These results indicate that CNF is an effective filler for the development of composites with excellent EMI shielding capability.

HIGH STRENGTH -LOW HARDNESS THERMOPLASTIC ELASTOMERS FROM ETHYLENE-BUTENE COPOLYMERS AND LOW DENSITY POLYETHYLENE

Abstract A thermoplastic elastomer (TPE) is a rubbery material with final properties and functional performance similar to those of a conventional vulcanized rubber at ambient temperature, yet it can be processed as a thermoplastic at elevated temperature. The main objective of the present investigation was to prepare novel olefinic thermoplastic elastomers based on blends of a thermoplastic i.e. low density polyethylene (PE) and new ethylene-butene copolymers (PEB), which would have higher strength and lower hardness compared to the existing TPEs. The 70:30 PEB: PE blend exhibited the best properties. Ethylene vinyl acetate was found to work as compatibilizer at lower loadings in these blends. The resultant blends were of low hardness (60–80 Shore A) and high strength (26–33 MPa). The interaction parameter and the morphology of the blends were the key parameters, which governed the final properties of blends.