Efficiency and mechanism for the stabilizing action of N,N'-bis(phenylcarbamoyl)alkyldiamines as thermal stabilizers and co-stabilizers for poly(vinyl chloride)

A series of novel ureido organic stabilizers for poly(vinyl chloride) (PVC) with different length of alkyl chains, including N,N' -bis(phenylcarbamoyl)ethylenediamine (NA2), N,N' -bis(phenylcarbamoyl)butylenediamine (NA4) and N,N' -bis(phenylcar- bamoyl)hexamethylenediamine (NA6) were designed and synthesized, which have greater stabilizing efficiency compared with Ca/Zn stabilizers and phenylurea at the same concentration in PVC mixtures. The results of Congo red test, discoloration test, thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectra showed that the ureido moieties of NAn ( n  = 2, 4, 6) have stronger ability to replace the labile chlorine atoms in PVC chains, but weaker ability to absorb hydrogen chloride (HCl) than those in phenylurea . On the other hand, longer alkyl chains in the synthesized organic stabilizers had positive effect in stabilizing efficiency for PVC, which was proved by the results that NA6 was the most efficient stabilizer among the present study, followed by NA4 and NA2. Furthermore, mixing the model compound NA6 with zinc stearate in different mass ratios led to a true synergistic effect, the “zinc burning” of PVC products was remarkably postponed.