Polyethylene, polypropylene, polystyrene and polybutadiene samples were chosen as model impurities, and each impurity was added to a polyvinyl chloride (PVC) solid sample together with a NaOH solid sample. The mixture of PVC with an impurity sample was ground with the NaOH sample in air by means of a planetary ball mill to investigate the mechanochemical dechlorination reaction between PVC and NaOH. The presence of any impurity inhibits the mechanochemical reaction of PVC and the degree of inhibition caused by the impurity is correlated with its hardness. The dechlorination yield increases with an increase in the amount of NaOH, reaching almost the same value as in the case without any impurity.