Effect of zinc stearate and/or epoxidized soybean oil on gelation and thermal stability of PVC-DOP plastigels

Abstract

The effects of zinc stearate (ZnSt 2 ) and/or epoxidized soybean oil (ESO) on mechanical properties and on thermal stability of plastigels obtained from polyvinylchloride (PVC) and dioctylphthalate (DOP) plastisols were studied using calorimetric, spectroscopic, and tensile-testing techniques. Plastigels having 2.5 or 5.0 part ZnSt 2 and/or 5 part ESO and 60 part DOP per 100 part PVC (phr) were gelled by heating at 140°C. The tensile strength of plastigels with no additive and having 5 phr ZnSt 2 , ESO, and both ZnSt 2 and ESO were 0.79, 0.46, 0.98, and 0.58 kN/cm 2 , respectively. The decrease of tensile strength of plastigels with ZnSt 2 could be explained by the existence of ZnSt 2 in the solid phase in plastigels, as shown by differential scanning calorimetry (DSC). ESO helped better fusion of the plastisols without any additive and with ZnSt 2 . Higher tensile strengths of ESO containing plates indicated more complete gelation of the plastisols. The thermal stability of plastigels in terms of color and their yellowness index (YI) were higher for ZnSt 2 containing plastigels. Conjugated polyene concentrations were calculated from UV spectra of the films heated at 140°C. The reaction rate constant of the dehydrochlorination of PVC changed with the additives. Faster dehydrochlorination than control gels occurred in gels having ZnSt 2 at long heating times due to the autoaccelerating effect of ZnCl 2 formed by reaction of eliminated hydrogen chloride and ZnSt 2 . Organic acid formation reaction between ZnSt 2 and HCl formed by dehydrochlorination is investigated from the IR band at 1540 cm Ϫ1 and 3400 cm Ϫ1 during heating of the plastigel films. A synergistic effect of ESO and ZnSt 2 was observed when the mechanical strength and heat stability were considered together. Although ESO increased tensile strength, ZnSt 2 increased thermal stability of the plastigels at early times when they were present simultaneously in plastisols.

Synergistic effect of metal soaps and natural zeolite on poly(vinyl chloride) thermal stability

“…The thermal degradation of poly(vinyl chloride) (PVC) has been studied by many researchers [1][2][3][4]. The wide applicability of PVC is due to its easy modification by various additives, its chemical resistance, and its low production cost [1].…”

“…The compounds used as heat stabilizers for PVC are lead compounds, organotin compounds, organic stabilizers, compounds of other metals (calcium, zinc, barium, aluminum, and their composites), and inorganic stabilizers (zeolite and hydrotalcite) [5,9]. Metal compounds are used to displace the labile chlorine atom in PVC polymer chain by more stable groups and they were considered HCl scavengers until Frye and Horst demonstrated the esterification reaction with polymer, substituting allylic chlorides [4,6,8,10]. Zeolite 5A and hydrotalcite are used as acid absorbers in PVC in order to absorb evolved HCl and other strong acids which catalyzed the dehydrochlorination of PVC [11,12].…”

Effect of zinc soaps of rubber seed oil (RSO) and/or epoxidised rubber seed oil (ERSO) on the thermal stability of PVC plastigels

“…The mechanisms for the thermal stabilization of PVC and its compounds with additives such as metal carboxylates, organo-tin compounds, epoxy compounds, zeolitic materials and metal oxides have been discussed in recent reviews [1,3e8]. There are a number of studies regarding the use of zinc stearate and/or epoxidised oil as heat stabilizer for PVC [1,9,10]. The carboxylates derived from zinc have strong Lewis acidity and are able to scavenge HCl and react with the allylic chlorine atom resulting in the formation of ZnCl 2 which promotes dehydrochlorination of PVC [7,11].…”

“…It is well known that PVC undergoes degradation with increasing temperature in a process called ''zip dehydrochlorination'' involving the elimination of hydrogen chloride and the formation of conjugated double bonds followed by a change in the polymer's colour which goes from yellow to orange, red, brown and finally black [1,2].…”

Stabilizing Effect of Biobased Additives on the Thermal Degradation of PVC

“…However, the presence of barium and cadmium soaps of RSO improved the thermal stability of plasticized PVC. Previous studies on the use of metal soaps/epoxides of vegetable oils, notably soybean oil [4,7,14,16] give evidence that these derivatives when added to rigid or plasticized PVC reduce the initial rate of dehydrochlorination and these corroborate with the findings in this study.…”