The effect of surface chemistry and rugosity on the interfacial adhesion between Bisphenol-A Polycarbonate and a carbon ber surface subjected to surface treatment to add surface oxygen groups was investigated. The surface oxygen content of PAN based intermediate modulus IM7 carbon bers was varied by an oxidative surface treatment. The oxygen content of the carbon ber surface increased from 4 to 22% by changing the degree of surface treatment from 0 to 400% of nominal commercial surface treatment levels. The oxidative surface treatment also causes an increase in surface roughness by creating pores and ssures in the surface by removing carbon from the regions between the graphite crystallites. To decouple the effects of surface roughness and the surface oxides on the interfacial adhesion, the oxidized ber surface was passivated via hydrogenation at elevated temperature. Thermal hydrogenation removes the oxides on the surface without signi cantly altering the surface topography. The results of interfacial adhesion tests indicate that an increase in the oxygen content of the ber does not increase the ber-matrix interfacial adhesion signi cantly. Comparing adhesion results between oxidized and hydrogen passivated bers shows that the effect of the surface roughness on the interfacial adhesion is also insigni cant. Overall, dispersive interactions alone appear to be the primary factor in adhesion of carbon bers to thermoplastic matrices in composites.

The adhesion of bisphenol-A polycarbonate, an amorphous thermoplastic, to carbon fiber was studied by varying both the intrinsic and the extrinsic properties such as the molecular weight, processing conditions, and test temperature. It was seen that processing methods and conditions had a significant effect on adhesion as measured by the interfacial shear strength. Commercial grade Lexan 141 solvent deposited onto carbon fibers showed poor adhesion when processed below the glass transition temperature and reached a limiting value at a higher temperature. Melt consolidated pure polycarbonate specimens showed increases in adhesion both with increasing processing temperature and with time. Pure polycarbonate having a molecular weight above the critical molecular weight exhibited a higher adhesion at different processing conditions, while for polycarbonate below the critical molecular weight adhesion was poor and unaffected by the processing temperature. Increases in temperature lowered the adhesion as a result of the dependence of adhesion on the matrix modulus, which decreases with increasing temperature.

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A structure property study between the interfacial adhesion and the polymer molecular weight, fiber chemistry and processing temperature in thermoplastic composites was undertaken. In the first phase of the study, four different molecular weight grades of pure bisphenol A polycarbonate (BPA-PC) and three different consolidation temperatures were used. Molecular weight and processing temperatures were found to have significant effect on interfacial adhesion, with a major increase in adhesion between the low molecular weight grade, which is below the critical molecular weight and the next higher molecular weight grade and a monotonous increase, but to a lesser degree above the critical limit. Further, the study shows that the interface might affect the segregation of polymer chains by their molecular weight resulting in a higher concentration of low molecular weight chains at the interface and consequent loss in mechanical properties [1]. In the second phase of the study, Hercules IM7 carbon fiber with four different levels of proprietary oxidative surface treatment and subsequent hydrogen passivation were employed to determine the effects of fiber chemistry on the interfacial adhesion. It was observed that, differing amount of surface oxygen functionalities have no effect on the level of adhesion, indicating insignificant polar or hydrogen bonding interactions between the fiber and the matrix. The level of adhesion was also found to be very weakly dependent on mechanical interlocking between the fiber and the matrix. In the third phase of the study, BPA-PC and polymethyl methacrylate (PMMA) were grafted on the surface of carbon fiber to study the effect of grafted chain length and entanglement on improvement in adhesion over ungrafted fiber composites. Grafting polymer chains to the fiber surface produced a penetrable interface, which improved adhesion levels by 25-100% over the ungrafted composites. The improvement in adhesion was independent of molecular weight of the grafted chains.

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