In this study, the effect of the high-energy mechanical milling of a mixture of poly(vinyl chloride) (PVC) with zinc borate (ZB) or ZB-aluminum trihydrate (ATH), a mixture of ZB and ATH, on the flame-retardant and mechanical properties of ZB and ZB-ATH filled PVC was examined. The high-energy mechanical milling of PVC/ZB and the PVC/ZB-ATH mixture produced chemical bonding between PVC and ZB or ZB-ATH, increasing the interfacial interaction of PVC/ZB and PVC/ZB-ATH blends, which resulted in a great increase in the limiting oxygen index, the impact and yield strengths, and the elongation at break of PVC/ZB and PVC/ZB-ATH blends. The results from ultraviolet spectroscopy and gas chromatography-mass spectroscopy show that mechanochemical modification of ZB and ZB-ATH much more effectively suppressed the release of aromatic compounds in PVC/ZB and PVC/ZB-ATH blends during burning. Mechanochemical modification provided an excellent route for the improvement of the flame-retardant and mechanical properties of flame-retardant-additive-filled PVC. (C) 2003 Wiley Periodicals, Inc. Inc.