Epoxy Lab Report

Decent Essays
Various methods are utilized to modify epoxy resins to improve their toughness. Based on the structure-property relationships, the traditional chemistry approaches have been: chemical modification of a given rigid epoxy backbone to a more flexible backbone structure; lowering the crosslink density by increasing the molecular weight of the epoxy monomers and/or decreasing the functionality of the curing agents. The most common approaches are the incorporation of dispersed toughener phase(s) in the cured epoxy matrix. The second phase includes rubbers, thermoplastics, block copolymers and hard inclusions such as silica, glass beads, etc.
1.2.1 Modification by Rubber
A common method employed in improving the fracture resistance of epoxies is
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Carboxyl- or amine-terminated copolymers of butadiene and acrylonitrile (CTBN and ATBN, respectively) are soluble in most liquid epoxies. The end groups react with the epoxy matrix during the curing process and the rubber separates to form discrete particles. Increasing the fracture resistance of epoxies with CBTN or ABTN rubber particles does have deficiencies. Incorporation of a low-Tg component often reduces the glass transition temperature of the composite material [12]. Similarly, incomplete separation of the rubber during cure may plasticize the epoxy network [14, 15]. Both the tensile modulus and yield strength of epoxies may be reduced upon rubber modification [16]. Sultan and McGarry [17] attributed the toughening effect mainly to the crazing of the epoxy matrix. Bascom et al.[12] accredited the high toughness values of CTBN modified epoxy to an increase in the plastic zone size. A rubber stretching and tearing mechanism was proposed by Kunz et al. [18] as the major toughening mechanism for rubber modified plastics (also known as…show more content…
Another reason is the low glass transition temperatures of the rubbers that lower the maximum use temperature and the modulus of the epoxy resins. The high performance engineering thermoplastics such as poly(ether sulfone)s, poly(ether ketone)s and poly(ether imide)s were used as toughener for epoxy resins [34-36]. The major advantage of these thermoplastic modifiers is that their incorporation into epoxy resins does not result in reduction in modulus and glass transition temperature. In comparison with rubber modified systems, the use of tough thermoplastic polymers offers better improvement in fracture toughness for higher crosslink density epoxy systems. The advantages of thermoplastic modified epoxy systems lie in the fact that the modulus and the Tg of the modified epoxy can be maintained, and the fracture toughness can be improved in direct proportion to the amount of thermoplastic added. The use of reactive thermoplastic modifiers provides good adhesion between epoxy and thermoplastic phases. Several toughening mechanisms that have been proposed for the thermoplastic modified epoxies [37]. These mechanisms are illustrated in the Figure
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