P. Sasidharan Achary

Reactive compatibilization of a nitrile rubber/phenolic resin blend: Effect on adhesive and composite properties

Resole phenolic resins containing various p-cresol (PC) to phenol (P) mol ratios were prepared and characterized. These phenolic resins were blended with nitrile rubber (NBR) and the measurements of adhesive joint strength, stress–strain properties, DSC, TGA, DMA, TEM, and SEM were performed using a 50 : 50 NBR/phenolic resin blend. It was observed that the adhesive joint strength and the mechanical properties of the blend enhanced significantly on incorporation of p-cresol into the phenolic resin, and the optimum p-cresol/phenol mol ratio was in the vicinity of 2 : 1. Observation of a more continuous phase and the increase in Tg of the rubber region in the blend indicated increased reactivity and compatibilization of NBR with phenolic resin as p-cresol was incorporated. The effect of silica filler on the properties of the nitrile rubber/phenolic resin blend was also studied without and with p-cresol modification and the results suggest that silica filler take not only the role of a reinforcing filler in the nitrile–phenolic–silica composite, but also a role as surface compatibilizer of the blend components.

Adhesion Development in a Polysulphide Sealant

Abstract The necessity for good adhesion in sealants and the mechanism of adhesion development in polysulphide sealants are discussed. The studies reported give the effect of co-reacting polysulphide resin with epoxy resin on the adhesion of a polysulphide sealant composition to an aluminium substrate and also on selected mechanical properties. The sealant was formulated from a mercaptan-terminated liquid polysulphide polymer. The liquid polymer was co-reacted with epoxy resin before formulating the sealant. Modification with epoxy resin improved the adhesion of the sealant. Adhesion is improved because of the presence of hydroxyl groups in the chain after co-reaction. The hydroxyl groups increase the ability of the polymer to remove the loosely adsorbed water layer present on the surface and establish strong interfacial forces with the surface.

Effect of a Phenol Formaldehyde Resin of the Adhesion of a Polysulfide Sealant

The results obtained in a study to evaluate the effect of a phenol formaldehyde resin on the adhesion of a polysulphide sealant is presented. The adhesion of the sealant is improved significantly by the incorporation of phenol formaldehyde resin. This is explained on the basis of increased boundary layer strength and the results obtained are compared with the ‘theory of attachment site’. Addition of phenol formaldehyde resin to the sealant caused an increase in cross-link density, ultimate tensile strength, stress at 100% elongation, hardness and a decrease in ultimate elongation and water absorption. The observed property changes are explained on the basis of polymer-filler interactions. Higher concentrations of phenol formaldehyde resin in the sealant caused a decrease in bond strength, cross-link density and mechanical properties. This is attributed to the lesser extent of cure of polysulphide resin.

Study on a Vinyl Ester/Methyl Methacrylate Based Reactive Acrylic Adhesive Toughened by Hydroxyl Terminated Polybutadiene

Abstract The effect of addition of a hydroxyl-terminated liquid polybutadiene (HTPB) rubber on the morphology, adhesive, thermal and mechanical properties of a vinyl ester (VE)/methyl methacrylate (MMA) based reactive acrylic adhesive has been investigated. Phase separation was observed in the cured HTPB-modified acrylic adhesive. Low levels of HTPB enhanced the adhesive properties and the optimum adhesive strength was observed at about 10wt% HTPB. HTPB modification had no significant effect on the thermal properties, but decreased the mechanical strength, which was attributed to the inadequate bonding of the rubber particles. Introduction of a chemical link between HTPB and VE by toluene diisocyanate coupling showed significant improvement in adhesive and mechanical strength.

Effect of a reactive interfacial agent on the properties of a nitrile-rubber-modified epoxy film adhesive

Reactive interfacial agents are often used to homogenise the morphology of immiscible polymer blends and to improve the level of adhesion between the phases to achieve enhanced properties. This paper demonstrates the ability of hydroxyl methyl bisphenol A (HMBPA) to function as a reactive interfacial agent (compartibilizer) in a nitrile-epoxy film adhesive made from nitrile rubber (NBR) and solid epoxy resin blend. The curing of the adhesive film was achieved at 170° C by adding dicyandiamide, a latent curing agent for epoxy resin, and rubber vulcanising agents. Hydroxyl methyl bisphenol A resins with different hydroxyl methyl content, synthesised by the base-catalysed reaction of bisphenol A and formaldehyde in various mole ratios, were used to compatibilize a blend of nitrile rubber (NBR) and epoxy resin 50/50wt/wt. The effect of addition of HMBPA on the morphology, adhesive, thermal, and mechanical properties of the adhesive film was investigated. The nitrile-epoxy adhesive films were characterised by measurements of adhesive joint strength, stress-strain properties, DSC, TGA, TMA, DMA, and SEM. Results revealed that significant improvement in joint strength occurred at low levels of HMBPA, and the optimum strength was obtained at about 15 wt% of HMBPA in the blend. The hydroxyl methyl content in HMBPA was found to influence the properties of the adhesive film. The concept of strengthening the interphase between NBR and epoxy through the coupling reactions of HMBPA was used for interpreting the results. The effect of addition of silica, alumina, and aluminium fillers on the properties of the nitrile-epoxy adhesive film was also studied, and a comparison of properties with and without HMBPA is presented.

Modification of a nitrile-phenolic bonding agent by addition of an interfacial agent : effect on the practical adhesion between nitrile rubber and metal

—The mechanism of vulcanization bonding of a nitrile rubber (NBR) elastomer to metal with a single-coat nitrile-phenolic bonding agent is discussed. A nitrile-phenolic bonding agent consisting of NBR, phenol formaldehyde (PF) resin, and vulcanizing agents was modified with an interfacial agent (p-cresol formaldehyde resin) and the effect of interfacial agent addition on the practical adhesion between metal and the NBR elastomer after vulcanization was investigated. The adhesion strength was measured in terms of the metal-to-NBR elastomer peel strength using the bonding agent. The addition of p-cresol formaldehyde (PCF) resin to the bonding agent with a proportionate reduction of PF resin initially improved the peel strength; a maximum was reached at about 20% PCF content and then decreased with a further increase in the PCF content. The improvement in peel strength produced by the addition of PCF resin is attributed to the increased chemical bonding between NBR and the phenolic resin. The drop in peel str...