AbstractThe thermal decomposition behavior of rayon yarn which had been treated with various chlorosilanes and boron–phosphorus compounds was determined at temperatures up to 800°C. It was found that 70 of the available hydroxyl groups in rayon would react with dichlorodiphenylsilane and that the treated yarn had an initial decomposition temperature 125°C higher than that of untreated rayon. The weight loss of the treated yarn at 800°C was dependent on the nature of the chlorosilane and the type of posttreatment used. Alkylchlorosilanes produced higher weight losses than did the arylchlorosilane‐treated rayons. Treatment of rayon yarn with bis(chlorodiphenyl‐phosphine)decaborane (BCDPD) or dimeric chlorophospha(III)‐o‐carborane (DCPC) resulted in an increase in the char yield of the pyrolyzed yarns. In the case of untreated rayon, weight retention at 800°C was 20, whereas the treated yarns yielded boronated residues of 42–53. Carbon yields as high as 28 were obtained with the BCDPD treatment. This treatment also resulted in substantial improvement in the oxidative stability of rayon at temperatu
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