Atomic force and scanning electron microscopic studies of effect of crosslinking system on properties of maleated ethylene–propylene–diene monomer rubber composites filled with short melamine fibers

Abstract

This article reports the development of new composites based on maleated ethylene-propylene-diene monomer (EPDM) rubber and melamine fiber. The compositions are cured using three different types of curing systems: conventional covalent crosslinking based on sulfur and an accelerator, fully ionic crosslinking based on zinc oxide/zinc stearate, and mixed crosslinking involving both covalent and ionic bonds. A dry bonding system comprising resorcinol, hexamethylene tetramine, and hydrated silica, popularly known as HRH, is found to increase the mechanical properties of the composites cured using both the sulfur/accelerator and mixed crosslinking systems. However, incorporation of the dry bonding system and/or melamine fiber adversely affects the strength of the composites if the linkages are fully ionic. Among the three crosslinking systems employed, composites prepared by using the mixed crosslinking system give higher tensile strength and modulus. Aging at 150°C for 48 h causes improvement in the strength and modulus of the composites cured by using the sulfur/accelerator system, particularly at higher fiber loading. However, in the case of an ionic system, both the modulus and strength drop with aging; in the case of the mixed crosslinking system, the modulus increases, but there is a drop in strength on aging. Rheological studies of the uncured compounds show that the presence of zinc stearate in the formulations of mixed and ionic crosslinking systems results in reduced viscosity and a smoother extrudate as compared to the sulfur crosslinking system. An atomic force microscopy analysis of the roughness reveals that the fiber surface roughness is reduced because of aging for the ionic crosslinking system. This is attributable to the formation of a zinc stearate layer on the fiber surface, which also reduces the adhesion between the fiber and the matrix, thereby reducing the hysteresis after aging. However, for the sulfur and mixed crosslinking system, the roughness of the fiber surface is increased and there is a concomitant increase in hysteresis.

Effect of electron‐beam irradiation on the thermal vulcanization of a natural rubber compound

“…So, the lower Δ G ′/ T v obtained for the pre‐irradiated systems could have been mainly affected by the plasticizing effect of zinc stearate around the interphase between assembled sheets that were used for the rheometer test; this is in agreement with some published cases where the modulus decreased with D −1 …”

“…The migration of low‐molecular‐weight zinc stearate from the bulk to the surface could be enhanced by electron‐beam irradiation during the pre‐irradiation treatment. Thereby, a thinner layer over the irradiated surface may be formed by zinc stearate moieties; this reduces the mechanical behavior (Scheme ) …”

“…Even though different kinetics model have been proposed, the complete characterization of the rubber curing reaction is complex to achieve. Although a recently published mathematical kinetic model has attracted great attention because it is a simplified, reliable, and optimized approach, the two general kinetic models frequently used to describe the curing mechanisms of rubber compounds are n th‐reaction order and autocatalytic kinetics . The reaction rate of n th‐order kinetics is expressed as follows: where ∂θ/∂ t is the rate of the reaction and n is the reaction order.…”

Atomic Force Microscopic Studies on the Silicone Rubber-Fluororubber Blend Containing Ground Rubber Vulcanizate Powder

“…The mechanical properties also follow the same order, leading one to believe that surface roughness may be related to the reinforcement of the rubber. On the basis of AFM studies on short melanine fiber-filled rubber composites, Rajeev et al [14,15] have reported that changes in surface roughness of the composites due to aging could be related to changes in hysteresis and mechanical properties of the composites. CONCLUSIONS 1.…”

Nylon 66 short fiber reinforcement in EPDM power transmission belting: A path to enhanced mechanical performance

“…The increase of storage modulus (E 0 ) indicates the existence of finest dispersion of short fiber in the rubber matrix and thereby confirms the fiber reinforcement effect. 42,46 The tan δ attains its maximum value within the temperature range of À40 to À42 C Figure 7B. It is attributed to the fact that EPDM exhibits a glass transition temperature within this range, and no peak shift is observed.…”