Jyotishkumar Parameswaranpillai

Structure and thermo-mechanical properties of CTBN-grafted-GO modified epoxy/DDS composites

Carboxyl terminated poly(acrylonitrile-co-butadiene) (CTBN) is grafted on to graphite oxide (GO) to prepare GCTBN in order to improve the dispersion and interfacial bonding between GO and epoxy resin in an epoxy/DDS system. GCTBN was characterized by FTIR, XPS, Raman spectroscopy, XRD, TEM, TOM (morphology) and TGA. All these studies reveal the grafting of CTBN with GO. The thermal stability of GCTBN was found to improve considerably. The TEM micrograph of epoxy/GCTBN reveals an excellent dispersion of GCTBN in the epoxy matrix. Tensile strength (ca. 25%), tensile modulus (ca. 34%), tensile elongation (ca. 10%), and fracture toughness (ca. 128%) improved remarkably for GCTBN modified epoxy matrix. SEM micrographs reveal no sheet pull out for GCTBN modified epoxy, due to the complete wetting of GCTBN by the epoxy matrix. This confirms effective sheet/matrix interfacial bonding for the GCTBN modified epoxy matrix. Moreover, the viscoelastic properties reveal a very high modulus and improved Tg for the epoxy/GCTBN when compared with the neat crosslinked epoxy.

Development of hybrid composites for automotive applications: effect of addition of SEBS on the morphology, mechanical, viscoelastic, crystallization and thermal degradation properties of PP/PS–xGnP composites

In this article, we report on a simple and cost effective approach for the development of light-weight, super-tough and stiff material for automotive applications. Nanocomposites based on PP/PS blend and exfoliated graphene nanoplatelets (xGnP) were prepared with and without SEBS. Mechanical, crystallization and thermal degradation properties were determined and correlated with phase morphology. The addition of xGnP to PP/PS blend increased the tensile modulus at the expense of toughness. The presence of xGnP increased the enthalpy of crystallization and enthalpy of fusion of PP in the blends, without affecting segmental mobility and thermal stability. Addition of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) improved the toughness of PP/PS blends, but decreased the stiffness. The incorporation of xGnP into this ternary blend generated a super-tough material with improved stiffness and tensile elongation, suitable for automotive applications. It is observed that the presence of SEBS diminished the tendency of agglomeration of xGnP and their unfavorable interactions with thermoplastics, which in turn reduced the internal friction in the matrix.

Mechanical Properties and Failure Topography of Banana Fiber PF Macrocomposites Fabricated by RTM and CM Techniques

Banana fiber reinforced phenol formaldehyde composites with different fiber lengths and fiber loadings were prepared by compression molding (CM) and resin transfer molding (RTM) techniques. The mechanical properties such as tensile, flexural, and impact behavior were studied. RTM composites showed improved tensile and flexural properties as compared to CM composites. On the other hand, impact strength of RTM composites is slightly lower than that of CM composites. From the studies, it was found that mechanical properties increased with the increase in fiber loading, reached a plateau at 30–40 wt%, and then subsequently decreased with an increase in fiber loading in both techniques. At high fiber weight fractions, the strength decreased due to poor wetting and very poor stress transfer. The stress value increased up to 30 mm fiber lengths and then decreased. In order to examine the fracture surface morphology of the composites, scanning electron microscopy (SEM) was performed on the composite samples. A good relationship between morphological and mechanical properties has been observed. Finally, tensile strength of the composites fabricated by RTM and CM was compared with theoretical predictions.

Graphene based room temperature flexible nanocomposites from permanently cross-linked networks

Graphene based room temperature flexible nanocomposites were prepared using epoxy thermosets for the first time. Flexible behavior was induced into the epoxy thermosets by introducing charge transfer complexes between functional groups within cross linked epoxy and room temperature ionic liquid ions. The graphene nanoplatelets were found to be highly dispersed in the epoxy matrix due to ionic liquid cation–π interactions. It was observed that incorporation of small amounts of graphene into the epoxy matrix significantly enhanced the mechanical properties of the epoxy. In particular, a 0.6 wt% addition increased the tensile strength and Young’s modulus by 125% and 21% respectively. The electrical resistance of nanocomposites was found to be increased with graphene loading indicating the level of self-organization between the ILs and the graphene sheets in the matrix of the composite. The graphene nanocomposites were flexible and behave like ductile thermoplastics at room temperature. This study demonstrates the use of ionic liquid as a compatible agent to induce flexibility in inherently brittle thermoset materials and improve the dispersion of graphene to create high performance nanocomposite materials.

Thermally flexible epoxy/cellulose blends mediated by an ionic liquid

Blends between the widely used thermoset resin, epoxy, and the most abundant organic material, natural cellulose are demonstrated for the first time. The blending modification induced by charge transfer complexes using a room temperature ionic liquid, leads to the formation of thermally flexible thermoset materials. The blend materials containing low concentrations of cellulose were optically transparent which indicates the miscibility at these compositions. We observed the existence of intermolecular hydrogen bonding between epoxy and cellulose in the presence of the ionic liquid, leading to partial miscibility between these two polymers. The addition of cellulose improves the tensile mechanical properties of epoxy. This study reveals the use of ionic liquids as a compatible processing medium to prepare epoxy thermosets modified with natural polymers.

Phase morphology, mechanical, dynamic mechanical, crystallization, and thermal degradation properties of PP and PP/PS blends modified with SEBS elastomer

Binary and ternary blends comprised of polypropylene (PP), polystyrene (PS) and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) were prepared. The effect of phase composition of minor components on the morphology, mechanical, viscoelastic, crystallization, and thermal degradation properties was studied. Binary blends exhibited inferior properties, typical of immiscible and incompatible multi-phase systems and showed matrix-droplet phase morphologies. Ternary blends, especially those with greater concentration of SEBS minor phase, exhibited interesting properties. Scanning electron micrographs of SEBS compatibilized PP/PS blends, did not show any PS particle pulling out of the PP matrix, indicating good compatibility of SEBS with PP/PS blends. Dynamic mechanical analysis also supported the heterogeneous phase structure of the blends. Thermogravimetry and differential scanning calorimetry showed that addition of PS and SEBS decreased the thermal stability of PP marginally, but shows slight variations in melting and crystallization behavior.

Thermal properties of epoxy/block copolymer blends

New ways to improve the thermal properties of epoxy systems have been interesting topic for polymer researchers for several years. The block copolymer-modified epoxy matrix has received a great deal of attention and is still being intensely studied. Differential scanning calorimetry (DSC) is the most commonly used technique to investigate the thermal properties of epoxy/block copolymer systems. It can generally provide information such as phase behavior, miscibility, glass transition temperature, melting temperature, etc. between the block copolymer blocks and the epoxy matrix. In this chapter, we have mainly focused on the changes in the glass transition properties of the thermosets modified with block copolymers. The influence of the type of block copolymers and curing agents used and the effects of cure time and temperature on the phase behavior and microphase separation of epoxy thermosets are also discussed.