No abstract

This work describes the processing of SiC fiber-reinforced Si 3 N 4 matrix composites with boron nitride (BN) interphase. The BN interphase was processed by chemical vapor infiltration (CVI) with BF 3 /NH 3 gaseous precursors. The BN interphase modification involved the continuous treatment of Hi-Nicalon SiC fibers. The relations between (i) the processing parameters, (ii) the mechanisms controlling the kinetics of the CVI of the BN, and (iii) the structure of the deposited BN are presented. A single-or multi-layer BN interphase can be produced depending on the CVI conditions imposed on the fibers during the continuous process. A surface reaction mechanism controlling the CVI promotes a smooth, isotropic BN coating. An anisotropic BN coating can be produced when the CVI kinetics are controlled by a mass transport mechanism. With a controlled temperature gradient, the BN interphase is then made by stacking successive isotropic and anisotropic layers.

Cellulose-derived materials are an emergent opportunity for reducing the environmental impact of polymers. Microcrystalline cellulose (MCC) has increasing relevance in many sectors, including pharmacy, food, and reinforcement of polymers, but its application is limited by the low coupling between it and nonpolar polymers and the polar behavior of cellulose derivates. There is not a well-defined model for the isolation of MCC and the factors involved in the length and width, which are elements of high influence on the reinforcement effect of MCC. This study proposes a mechanism for the size reduction of cellulose fibrils isolated through acid hydrolysis and a post-plasma surface modification (PSM) to enhance coupling of the MCC with hydrophobic polymer matrixes. MCC was characterized by FTIR, XRD, and SEM before and after the plasma surface treatment with caprolactone, a biodegradable polymer. There were no changes in the FTIR spectra; however, in XRD the sample exhibited a decrease in intensity. These results suggest that PSM did not change the structure of MCC or chemical composition. However, an increase in the peak temperature of degradation confirmed the surface modification of MCC.