Study On Several Kinds Of Polyols As Thermal Stabilizers For Poly (Vinyl Chloride)

The thermal stability of tris（hydroxymethyl）aminomethane （TRIS）,bis-（2-hydroxyethyl）iminotris（hydroxyethyl） methane （Bis-TRIS） and other polyols,which have structures similar to that of pentaerythritol （PER） as pure organic thermalstabilizers and costabilizers of poly（vinyl chloride）（PVC） in calcium stearate/zincstearate （CaSt₂/ZnSt₂） system were studied. The thermal stability was investigated bythe discoloration test and dehydrochlorination test. The thermal stabilizationmechanism of PER and TRIS were researched by extraction procedure, FT-IR,absorption HCl. The influence on processing rheology from PER and TRIS wereexamined by torquer.These results indicate that TRIS is a kind of new and environmental pure organicthermal stabilizer. When it is used alone in PVC system, the samples perform excellentinitial thermal stability effect and long-term stability. The stabilizing mechanism ofTRIS is suggested as follows: a nucleophile for attacking unstable chloride atoms; ascavenger for trapping HCl. Stearic acid is not only a lubricant, but also a organic acid.It may have neutralization reaction with TRIS, which can consume part of TRIS.Samples containing TRIS have better processability than samples containing PER.In the system of CaSt₂/ZnSt₂, PER is an excellent costabilizer, samples includingit have both fine initial whiteness and long-term stability; TRIS can remarkablyimprove the initial color, and prolong degradation time; Bis-TRIS can greatly prolongthe “zinc burning” time, and there is also a perceptible improvement in initial color.PER and Bis-TRIS have not good thermal stability when they are used alone. Thethermal stabilization mechanism maybe: PER form complex compound with ZnSt₂andZnCl₂, it also can substitute unstable Cl. TRIS may have similar complex compound,furthermore, amino-group in TRIS may have nucleophilic substitution with unstable Cland neutralization reaction with HCl. The results may be that the complex compoundand neutralizing product are untable, and they release HCl and ZnCl₂at a relativelyhigher reation rate, leading to the degradation of PVC. Because of the obstruction fromalcoholic hydroxyl group, Bis-TRIS can only prolong the “zinc burning” time.