The Reaction of Plumbonacrite (Basic Lead Carbonate) with Hot DOP, and the Stabilisation of Plasticised PVC

The basic lead carbonate ‘plumbonacrite’, 6PbCO3.3Pb(OH)2.PbO, has been reacted with di‐2‐ethyl hexyl phthalate (dioctyl phthalate, DOP), C6H4(COOC8H17)2 at 180d̀C under nitrogen. Anhydrous monobasic lead orthophthalate, PbO.Pb6H4(COO)2, was the only product detected by X‐ray powder diffraction (X.R.P.D.). These studies are related to previous work on reactions taking place in hot polyvinyl chloride (PVC) blends containing DOP plasticiser and basic lead stabilisers. It is concluded that plasticiser stabiliser interaction can play a significant role in stabilising PVC against thermal decomposition, and that efficient stabilisation takes place largely by a free‐radical exchange mechanism. Characteristic X.R.P.D. data are tabulated for anhydrous monobasic lead orthophthalate, and for monobasic lead orthophthalate monohydrate, PbO. PbC6H4(COO)2‐ H2O, which can be made in aqueous suspension and which converts to the anhydrous salt at 180d̀C. X.R.P.D. data are also given for dibasic lead orthophthalate, 2PbO.PbC6H4(COO)2.1/2H2O, which is well known as a stabiliser for PVC, and which might have been expected to form in these experiments, (but did not in fact do so).