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Engineered Interfaces in Fiber Reinforced Composites Part 2

Tham khảo tài liệu 'engineered interfaces in fiber reinforced composites part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 14 Engineered interfaces in fiber reinforced composites reinforcements like glass silica and alumina but are less effective with alkaline surfaces like magnesium asbestos and calcium carbonate Plueddemann 1974 . 2.2.4. Chemical bonding Chemical bonding is the oldest and best known of all bonding theories. Physical adsorption mechanisms discussed in Section 2.2.2 depend on van der Waal forces or the acid-based interaction while chemical bonding mechanism is based on the primary bond at the interface. A chemical reaction at the interface is of particular interest in the study of polymer matrix composites because it offers a major explanation for the use of silane coupling agents on glass fibers embedded in thermoset and amorphous thermoplastic matrices. Surface oxidative treatments of carbon fibers have been known for many years to promote chemical bonding with many different polymer resins. Recent work Buxton and Baillie 1995 has shown that the adhesion is a two-part process the first part is the removal of a weak layer of a graphitic-like structure from the fiber surface particularly at low levels of treatment and the second part is chemical bonding at the acidic sites. However much further work is still needed to verify this hypothesis. In this mechanism of adhesion a bond is formed between a chemical group on the fiber surface and another compatible chemical group in the matrix the formation of which results from usual thermally activated chemical reactions. For example a silane group in an aqueous solution of a silane coupling agent reacts with a hydroxyl group of the glass fiber surface while a group like vinyl on the other end will react with the epoxide group in the matrix. The chemical compositions of the bulk fiber and of the surface for several widely used fiber systems are given in Table 2.2. It is interesting to note that except for glass fibers the chemical composition of the surface does not resemble that of the bulk fiber and oxygen is common to all .