Rubber Nanodomains Reinforced Epoxy Resin
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Rubber Nanodomains Reinforced Epoxy Resin JA. Arcos Casarrubias1, A. Reyes-Mayer2,3, R. Guardian-Tapia3 P. Castillo-Ocampo4 and A. Romo-Uribe2,† 1 División de Ingeniería Química y Bioquímica, Tecnológico de Estudios Superiores de Ecatepec, Edo. de Mex. 55210, MEXICO. 2 Laboratorio de Nanopolimeros y Coloides, UNAM, 62210. MEXICO. 3 Centro de Investigación en Ingeniería y Ciencias Aplicadas, UAEM, 62209. MEXICO. 4 Laboratorio de Microscopia Electronica, Universidad Autonoma Metropolitana- Iztapalapa †To whom all correspondence should be addressed: [email protected] ABSTRACT It has been reported that the addition of liquid rubbers, like poly(dimethylsiloxane) (PDMS), to epoxy resins alter the final morphology, increase the toughness and influence the curing kinetics. Due to immiscibility, there is phase separation of the elastomeric phase during curing giving rise to microdomains embedded in the epoxic matrix. The resultant heterogeneous morphology obtained after the reaction controls to an important extent the properties of the epoxy composite. Here we report a method to obtain well-dispersed rubber nanodomains of silyldiglycidyl ether terminated polydimethyl siloxane (PDMS-DGE) in diglycidyl ether of bisphenol-A (DGEBA) epoxy by using a prepolymerization step. Light scattering and optical microscopy showed that initial mixing of pre-polymerized rubber produced phase separation with micron-scale droplet formation. However, as the curing reaction proceeded, the rubber domains decreased below optical resolution, light scattering intensity reached a maximum and then decreased. Finally, rubber nanodomains of about 100 nm size were formed at the end of curing reaction, as revealed by transmission electron microscopy (TEM). The pre-polymerization step induced a two-fold increase in gel time, tgel, due to lesser active groups available for reaction. Strikingly, tensile modulus and toughness increased, suggesting rubber-epoxy interaction. The final nanocomposite also exhibited higher thermal stability and char formation. INTRODUCTION Epoxy resins are used in industry as protective coatings and for structural applications, such as laminates and composites, tooling, molding, casting, bonding and adhesives [1]. Epoxy resins have high chemical and corrosion resistance, exhibit good mechanical and thermal properties, outstanding adhesion to various substrates, low shrinkage upon cure, good electrical insulating properties, and the ability to be processed under a variety of conditions. However, in terms of structural applications, epoxy resins are usually brittle and notch sensitive. As a result, efforts have been focused on toughness improvement [2]. Thus, addition of elastomers to epoxy resins has been used to induce higher impact strength [3]. The search for epoxy formulations with improved toughness has led to the investigation of functional silanes, polysiloxanes, sislesquioxanes, and nanosilicas as possible reinforcers of epoxy resins [4]. However, polysiloxanes have solubility parameters different from epoxy giving rise
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