Page 189 - Engineered Interfaces in Fiber Reinforced Composites

Chapter 5

SURFACE TREATMENTS OF FIBERS AND EFFECTS
ON COMPOSITE PROPERTIES

5.1. Introduction

The interaction of a fiber with a matrix material depends strongly on the
chemical/molecular features and atomic composition of the fiber surface layers as
well as its topographical nature. The chemical composition of the fiber surface
consists of weakly adsorbed materials that are removable by heat treatments as well
as strongly adsorbed materials that are chemically attached with strong covalent
bonds. Both types of adsorbed material influence significantly the interaction at the
fiber-matrix interface. In addition, the fiber surface topography or morphology is
vital not only to constituting the mechanical bonding with matrix resins or molten
metals, but also to adsorption behavior of the fiber (Kim and Mai, 1993). It is well
known that surfaces of many fibers, e.g. carbon, silicon carbide and boron fibers in
particular, are neither smooth nor regular.
Although the techniques of bonding organic polymers to inorganic surfaces have
long been applied to protective coatings on metal surfaces, the majority of new
bonding techniques developed in recent years is a result of the use of fibers as
reinforcement of polymer resins, metals and ceramic matrices materials. Since the
advent of organofunctional silane as a coupling agent for glass fibers, there have
been a number of attempts to promote the bond quality at the interface between the
fiber (or rigid filler, broadly speaking) and organic resins. For polymer matrix
composites (PMCs), fiber surfaces are treated to enhance the interface bonding and
preserve it in a service environment, particularly in the presence of moisture and at
modcratc temperatures. For many metal and ceramic matrix composite systems,
chemical incompatibility is a severe problem due to inadequate or excessive
reactivity at the interphase region at very high temperatures required during the
fabrication processes. Therefore, fibers are usually treated with a diffusion barrier
coating to protect them from damages by excessive reaction. Further, stability of the
interface is an important requirement that is made critical by the high temperature
service desired for these composites.
This chapter is concerned primarily with the surface treatments of high
performance fibers, including glass, carbon (or graphite), aramid, polyethylene

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