The flame-retardant polyester fiber: Improvement of hydrolysis resistance

As far as the flame‐retardant polyester fibers are concerned, the copolymerization of phosphorus retardants is the most common method. But a serious problem is that the phosphorus‐containing polymer is easily hydrolyzed. We investigated the flame retardancy and the hydrolysis properties of two poly(ethylene terephthalate) (PET) fibers, one with a phosphorus compound as a side chain (side‐chain type: HEIM® Toyobo Co., Ltd.), and one with a phosphorus compound inserted in the polymer backbone (main‐chain type). Both types had almost the same properties of fibers and flame retardancy, but the main‐chain type was hydrolyzed about two times faster than the side‐chain type, and led to a decrease of toughness immediately. This difference of hydrolysis properties between main‐chain type and side‐chain type depends on whether a phosphonate ester bond is placed in the polymer backbone or the pendant site. In the case of the main‐chain type, the scission of the polymer backbone chain occurs by hydrolysis of phosphonate ester bonds; however, in the case of the side‐chain type, this does not occur. These results demonstrate that the flame‐retardant polyester fiber with the side‐chain type modifier gives sufficient flame retardancy and excellent hydrolysis resistance. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1134–1138, 2000