Temina Mary Robert

Alkylated phenolic resole resins are of special interest in the adhesive industry due to their attractive features such as tackiness, compatibility with a variety of substrates, and low cost. 4‐ tert ‐Butylphenol –formaldehyde resole (PTBF) and its etherified derivatives using isopropyl alcohol (PTBF‐IPA), n ‐Propanol (PTBF‐NPA), n ‐Butanol (PTBF‐NBA) and tert ‐Butanol (PTBF‐TBA) were synthesized and characterized. Glass transition temperature and adhesive property (lap shear strength) retention were found to be superior by 43% and 75%, respectively, for PTBF‐NBA‐based contact adhesive upon repeated testing. This inspired us to investigate the observation through molecular simulations and experimental measurements. This paper unveils an unexplored potential of these resins viz., self‐assembly in solid state, which is an intriguing phenomenon in molecular dynamics since the mechanism cannot be explained by a single category of molecular interaction. The mechanisms and impact of this self‐assembling phenomenon on practical application in an adhesive system have been thoroughly examined and correlated. The studies revealed that the chain motif (chain length and branching) influenced the type and extent of supramolecular interactions including hydrogen bonding and hydrophobic interactions, leading to self‐assembly and consequent physical, thermo‐physical, mechanical, and interface properties. Among the different alkyl homologues used for end‐capping, n‐ Butyl modified 4 ‐tert ‐Butylphenolic resin (PTBF‐NBA) exhibited the strongest hydrogen bonding, mediated through crystallization and van der Waals interactions, which resulted in widely differing physical and mechanical properties. It is unequivocally proven that the adhesive processed using PTBF‐NBA bears commendable capability. Also, it is evident that as branching of the end‐capped alkyl chain increased, the effect of hydrogen bonding with phenolic hydroxyl groups became less prominent. Thus, this work opens up new avenues for supramolecular interaction‐facilitated applications in interfacial chemistry.

Poly(ether ether ketone) s with terminal propargyl groups (PEEK‐PR) were synthesized from hydroxyl terminated PEEK (PEEKTOH) and characterized. The heat‐triggered polymerization of PEEK‐PR to poly bischromenes having PEEK backbone was confirmed by Fourier transform infrared spectroscopy and differential scanning calorimetric studies. PEEK‐PR was blended with a bisphenol based epoxy resin‐diamino diphenylsulphone system in different proportions and cured to form PEEK‐bischromene‐interpenetrated‐epoxy‐amine networks. Tensile strength and elongation of the cured blends increased up to 10‐phr loading of PEEK‐PR and then declined. Tensile moduli of all formulations were comparable. Fracture toughness increased by a maximum of 33%, and the fractured surface morphology showed a ductile fracture. The blends exhibited slightly lower glass transition temperature to that of the neat epoxy‐amine system. A reference sample of epoxy‐amine was processed with the optimum loading of the precursor polymer, PEEKTOH, and compared its properties with the PEEK‐PR incorporated epoxy systems. In this way, it is found that the incorporation of addition curable propargylated PEEK increases the strength characteristics with adequate thermal stability and fracture toughness for high‐performance structural applications.

Syntactic foams based on oxazolidone‐modified epoxy resin using glass microballoons as reinforcing filler with varying densities were processed. The influence of various grades of microballoons and their concentration on the mechanical, thermal, thermomechanical, and flammability characteristics were investigated. The effect of temperature on the compressive strength with density was monitored in detail. By incorporating the microballoons, T_g of the syntactic foam increased from 90 °C to 115 °C. Thermal conductivity was found to decrease from (0.064 to 0.056 W/(m·K)) in conjunction with decreasing resin to filler ratio. In the case of composites filled with K25 alone, the creation of large voids due to less effective packing between the microballoons led to lower thermal conductivity. The specific heat of the different composites was in the range of 0.32 to 0.44 cal/g/°C, and the coefficient of thermal expansion was in the range of 13.2 to 17.4 × 10⁻⁶/°C with limiting oxygen index of 28% to 33%.

Graphene oxide (GO) possessing hydroxyl and epoxy groups was synthesized by a modified Hummer's process and was found to conform to the empirical formula C_0.801[epoxy]_0.190[OH]_0.009. GO was examined as a curative for amino novolac phthalonitrile (APN). It was found to facilitate the crosslinking reaction by acting as a reactant for the amino group. Additionally, epoxy and OH groups in GO react with the nitrile groups of APN providing another pathway for facilitating the curing of APN. Epoxy groups in GO react with the nitrile groups of APN in the presence of OH groups (generated by the epoxy–amine reaction), facilitating the crosslinking at a lower curing temperature. Blending with GO decreases the overall curing temperature of APN. The co-reaction of the two systems led to a single phase matrix whose failure mode changed from brittle to ductile with no penalty in the thermal stability.

Ablative nanocomposites based on nanoclay‐dispersed addition curable propargylated phenolic novolac (ACPR) resin, reinforced with chopped silica fiber, were investigated for their thermal response behavior under simulated heat flux conditions corresponding to typical atmospheric re‐entry conditions. Organically modified nanoclay (Cloisite 30B) was incorporated to different extents (1–10%) in the ACPR resin matrix containing silica fiber to form the composite. The composites displayed optimum mechanical properties at around 3 wt% of nanoclay loading. The resultant composites were evaluated for their ablative characteristics as well as mechanical, thermal and thermo‐physical properties. The reinforcing effect of nanoclay was established and correlated to the composition. The mechanical properties of the composites and its pyrolysed product improved at moderate nanoclay incorporation. Plasma arc jet studies revealed that front wall temperature is lowered by 20°C and that at backwall by 10–13°C for the 3 wt% nanoclay‐incorporated composites due to impedance by nanoclay for the heat conduction. Nanoclay diminished the coefficient of thermal expansion by almost 50% and also reduced the flammability of the composites. The trend in mechanical properties was correlated to the microstructural morphology of the composites. The nanomodification conferred better strength to the pyrolysed composites. Copyright © 2014 John Wiley & Sons, Ltd.