An Investigation of the Influence of Interface Chemical Structure on Fiber/Matrix Adhesion
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An Investigation of the Influence of Interface Chemical Structure on Fiber/Matrix Adhesion Dharmaraj Raghavan Department of Chemistry, Howard, 525 College Street, NW, Washington DC, DC, 20059 ABSTRACT The primary objective of the study is to investigate the impact of chemical structure at the interface on the interface strength of fiber/matrix composite. A solvent based method was used to deposit trichlorosilane on E-glass fiber surfaces followed by in situ modification of the deposited layer to prepare pure and mixed amine undecyl self assembled monolayer (SAM). The extent of fiber/matrix adhesion was determined by performing single fiber fragmentation test (SFFT). The SFFT data indicate that ≈ 85 % of fiber breaks obtained for epoxy composite occurs at a much lower mass fraction of amine coverage for SAM while a similar number of fiber breaks occur at a much higher mass fraction of amine coverage for aqueous solution deposited coupling agent system. INTRODUCTION When composites are designed, a small region (< 1 µm), known as the fibermatrix interphase, forms between the fiber and the matrix. The fiber-matrix interphase region plays a vital role in the transfer of stress between the fiber and matrix, the efficiency of the stress-transfer process at the interphase is critical to a composite’s ultimate performance. In this regard, the factors that control the adhesion at the fiber/matrix interface region become very important. The adhesion in the interface region between the glass fiber and epoxy matrix depends on the organofunctionality of the sizing agent and its concentration. Industrially, a mass fraction of 5 % sizing package is typically applied on glass fiber surface. For example, the sizing package contains γ-aminopropyl trimethoxysilane (APS) as the active compound to promote adhesion between the glass fiber and epoxy matrix, while vinyl terminated trimethoxy silane is chosen as the active compound to promote adhesion between the glass fiber and vinyl ester resin. A study of aqueous solution based deposition of APS on glass fiber surface showed that the fiber-matrix adhesion initially increases with concentration and about 85 % of maximum adhesion is achieved at a mass fraction of ≈ 50 % coverage of the glass surface with amine functional groups of APS [1]. The availability of the amino group of the silane couling agent (SCA) to react with the epoxy matrix is influenced by the concentration of SCA and by orientation of the amino group relative to the glass surface [2]. A portion of the amino groups of APS bend inwards to the glass fiber surface so that they are not accessible for the epoxy resin to react. Figure 1 is an idealized representation of up-side down orientation of APS on glass fiber surface. Also, the APS molecule being short they do not pack well as a result the deposited layer of APS on glass fiber is known to be porous through the research of Ishida and Koenig [3]. Therefore, penetration of epoxy resin to the glass surface is quite likely contributing to the mechanical interlockin
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