A polyvinyl chloride (PVC, [-CH2-CHCl-](n)) sample was ground with one of the following oxide samples, lanthanum oxide (La2O3) and calcium oxide (CaO), as a reference, to investigate its mechanochemical (MC) decomposition. According to the XRD patterns for the ground products, peaks of lanthanum oxy-chloride, LaOCl which is water insoluble, were observed to appear in the patterns of the mixture samples at a molar ratio of (PVC: La2O3 = 1:2) and (1:4), after 20 min grinding, while the patterns of the ground PVC-CaO mixtures show the formation of CaOHCl, which is water soluble, in the products after 2 h grinding. TG patterns taken for the PVC-La2O3 mixtures ground for different periods of time do not indicate significant weight loss in the range from 200 to 300 degrees C, and this suggests that La2O3 is more effective additive than CaO in the MC decomposition for PVC. FT-IR patterns for organic phases in the ground mixture show the reduction of C-Cl bindings in the PVC structure. The MC reaction between PVC and La2O3 is accompanied by the formation of C-O single bonds, to form LaOCl, which is insoluble in water at ambient condition. This is the reason why the yield of Cl extracted by the water leaching reaches only less than 50%, while it reaches almost 100% in the yield of Cl from the PVC-CaO mixture ground for 2 h or more. (c) 2006 Elsevier B.V. All rights reserved.