Thermal Stabilizers For Rigid Poly Research Articles

Efficiency and mechanism for the stabilizing action of thiouracil derivatives as novel thermal stabilizers for poly(vinyl chloride) and the synergistic effect with calcium stearate

Novel thiouracil thermal stabilizers for rigid poly(vinyl chloride) (PVC), 6-methyl-2-thiouraci (6M2TU), 5-methyl-2-thiouraci (5M2TU), and 6-propyl-2-thiouraci (6P2TU) were synthesized successfully via a precipitation method, and characterized with 1H NMR spectra. Investigation of these thiouracil derivatives as thermal stabilizers for poly(vinyl chloride) (PVC) was measured by thermogravimetric analysis (TGA), congo red test, fourier transform infrared (FTIR), and discoloration test. The results show that the thiouracil derivatives have strong ability to replace the labile chlorine atoms in PVC chains, but weak ability to absorb hydrogen chloride. Moreover, PVC stabilized with these thiouracil derivatives and calcium stearate (CaSt2) exhibit greater stabilizing efficiency compared with traditional Ca/Zn stabilizers with the same concentration.

Thermally Stable Antimicrobial PVC/Maleimido Phenyl Thiourea Composites

ABSTRACTFour novel antimicrobial maleimido phenyl thiourea derivatives were synthesized from N‐[4‐(chlorocarbonyl) phenyl] maleimide with phenyl thiourea and its derivatives (p‐methyl, o‐chloro, and p‐carboxy). Their structures were characterized by FTIR, 1H NMR, mass spectra, and elemental analyses. Their antimicrobial activities against three types of bacteria (Bacillus subtilis, Streptococcus pneumoniae, and Escherichia coli) and against three crop‐threatening pathogenic fungi (Aspergillus fumigatus, Geotricum candidum, and Syncephalastrum racemosum) were investigated. The results revealed that these derivatives are effective in inhibiting the growth of the tested bacteria and fungi as indicated from the inhibition zone diameter and minimum inhibitory concentration. The antibacterial activities of these derivatives were more effective against Gram‐positive bacteria than Gram‐negative bacteria. These derivatives were investigated as thermal stabilizers for rigid poly(vinyl chloride) at 180°C in air by measuring the rate of dehydrochlorination and the extent of discoloration. The results reveal the greater stabilizing efficiency of the investigated derivatives as shown by their longer thermal stability periods (Ts) and lower dehydrochlorination rates in relation to dibasic lead carbonate, cadmium–barium–zinc stearate, and n‐octyltin mercaptide industrial stabilizers. The stabilizing efficiency increases with the introduction of electron‐donating substituent groups in the aromatic ring of the stabilizer molecules. Moreover, the investigated stabilizers impart better color stability for the degraded samples as compared with the reference stabilizers.

Insights into the use of zinc–mannitol alkoxide as a novel thermal stabilizer for rigid poly(vinyl chloride)

ABSTRACTZinc–mannitol alkoxide (Zn–Man) was synthesized through alcohol exchange reaction, and investigated by means of Fourier transform infrared spectroscopy and elemental analysis. The thermal stability of Zn–Man for rigid poly(vinyl chloride) (PVC) was evaluated by Congo red testing, conductivity measurements, thermal aging testing, thermogravimetric analysis (TGA), and ultraviolet–visible (UV–vis) spectroscopy test. The experimental results demonstrate that the addition of Zn–Man not only apparently prolonged the static thermal stability time to approximately 96.5 min but also evidently improved the initial color of PVC. More importantly, the color of the PVC sheets stabilized with Zn–Man did not change to black within 180 min; this showed that no zinc‐burning phenomenon occurred. In addition, the results of TGA reveal that Zn–Man raised the initial degradation temperature of PVC to about 273.4°C. UV–vis testing indicated that the presence of Zn–Man decreased the content and shortened the length of the conjugated double bonds of PVC. The possible thermal stability mechanism is discussed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42038.

Thermally stable antimicrobial PVC/maleimido phenyl urea composites

Four novel antimicro bial maleimido phenyl urea derivatives were synthesized from N-[4-(chlorocarbonyl) phenyl] maleimide with phenyl urea derivatives (p-methyl, o-chloro and p-carboxy). They were characterized by FTIR, 1H-NMR, mass spectra, elemental analyses and antimicrobial activities. These derivatives were investigated as thermal stabilizers for rigid poly(vinyl chloride) at 180 °C in air by measuring the rate of dehydrochlorination and the extent of discoloration. The results reveal the greater stabilizing efficiency of the investigated derivatives as shown by their longer thermal stability periods (Ts) and lower dehydrochlorination rates in relation to dibasic lead carbonate, cadmium-barium-zinc stearate and n-octyltin mercaptide industrial stabilizers. The stabilizing efficiency increases with the introduction of electron donating substituent groups in the aromatic ring of the stabilizer molecules. Moreover, the investigated stabilizers impart better color stability for the degraded samples as compared with the reference stabilizers.

Thermally stable antimicrobial polyvinylchloride/maleimido aromatic hydrazide composites

Antimicrobial novel substituted maleimido aromatic hydrazides were synthesized from N‐[4‐(chlorocarbonyl) phenyl] maleimide with salicylhydrazide, p‐aminobenzohydrazide, or p‐aminosalicylhydrazide. They were characterized by Fourier transform infrared (FTIR), hydrogen‐1 nuclear magnetic resonance (1H‐NMR), mass spectra, elemental analyses, and antimicrobial activities. These derivatives were investigated as thermal stabilizers for rigid poly(vinyl chloride) (PVC) at 180°C in air by measuring the rate of dehydrochlorination, the extent of discoloration, and the changes that occurred in the molecular masses of the degraded PVC samples. The previously reported stabilizing efficiency data of a nonsubstituted derivative, which was synthesized from N‐[4‐(chlorocarbonyl) phenyl] maleimide with benzohydrazide, is also given for comparison. The results reveal the greater stabilizing efficiency of the investigated derivatives as shown by their longer thermal stability (Ts) periods and lower dehydrochlorination rates in relation to dibasic lead carbonate, cadmium‐barium‐zinc stearate, and n‐octyltin mercaptide industrial stabilizers. The stabilizing efficiency increases with the introduction of electron donating substituent groups in the aromatic ring of the stabilizer molecules. Moreover, the investigated stabilizers impart better color stability for the degraded samples as compared with the reference stabilizers. A synergistic effect is achieved when the materials under investigation were mixed in various weight ratios with any of the reference stabilizers, reaching its maximum at equivalent weight ratio of the investigated stabilizer to the reference one. J. VINYL ADDIT. TECHNOL., 22:247–258, 2016. © 2014 Society of Plastics Engineers

Synthesis, characterization, and thermal investigation of some transition metal complexes of benzopyran-4-one Schiff base as thermal stabilizers for rigid poly(vinyl chloride) (PVC)

New metal complexes of Schiff base (PB) prepared from condensation reaction of 2-aminopyridine and 6-formyl-5,7-dihydroxy-2-methylbenzopyran-4-one with metal ions; Mn(II), Co(II), Ni(II), and Cu(II) are prepared. Different analysis tools like elemental analyses, FTIR, thermal analysis, conductivity, electronic spectra, and magnetic susceptibility measurements are all used to elucidate the structures of the newly prepared metal complexes. The free Schiff base (PB) has been examined as thermal stabilizer and co-stabilizer for rigid PVC in air, at 180 °C. Its high stabilizing efficiency is detected by its high induction period value (T s) when compared with some of the common reference stabilizers used industrially, such as dibasic lead carbonate and calcium–zinc stearate (Ca–Zn soap). Blending Schiff base or its metal complexes with Mn(II), Co(II), Ni(II), and Cu(II) ions with the reference stabilizers in different ratios had a synergistic effect on the induction period (thermal stability). The stabilizing efficiency is attributed at least partially to the ability of the stabilizer to be incorporated in the polymeric chains, thus disrupting the chain degradation process.

Synthesis and application of uracil derivatives as novel thermal stabilizers for rigid poly(vinyl chloride)

Novel uracil thermal stabilizers for rigid poly(vinyl chloride) (PVC), N, N-dimethyl-6-amino-uracil (DAU), N-monomethyl-6-amino-uracil (MAU) and N-monomethyl-6-amino-thiouracil (MATU) were synthesized successfully via a precipitation method, and characterized with 1H NMR spectra. Evaluation of these compounds as thermal stabilizer for rigid PVC was measured by discoloration test, and also using Haake torque rheometer and TGA. The results showed that, these novel uracil derivatives exhibited greater stabilizing efficiency compared with traditional Ca/Zn stabilizers (CZ) and diphenylthiourea (DTU) with the same concentration in PVC mixtures. This is attributed to the ability of these compounds to replace the labile chlorine atoms in PVC chains, and absorb of HCl released by the degradation of PVC, which was proved by the FTIR and 1H NMR spectral analysis. Furthermore, an excellent synergistic effect could be obtained when the model compound MATU combined with zinc stearate (ZnSt2) in different mass ratios, and the initial color and long-term stability of PVC products were remarkably improved.

Study on pentaerythritol–zinc as a novel thermal stabilizer for rigid poly(vinyl chloride)

AbstractPentaerythritol–zinc (penzinc) was prepared by a solid‐phase reaction technique. The principal volatile products of the reaction between pentaerythritol and ZnO were analyzed with a coupled thermogravimetry—mass spectrometery system. The results indicated that a large amount of water was formed at the reaction temperature. Scanning electron microscopy (SEM) results showed the appearance of penzinc as flaky particles. Accordingly, the penzinc obtained through the dehydration between pentaerythritol and ZnO is likely to be a monopentaerythritol complex, such as zinc monoglycerolate. The thermal stability of poly(vinyl chloride) (PVC) with penzinc as a thermal stabilizer was investigated by a Congo Red test, Oven aging test and thermal gravimetric analysis (TGA). The Congo Red test showed the thermal stability time of PVC with penzinc was 38 min, longer than those with commercial thermal stabilizers. TGA indicated that the penzinc had little impact on the thermal degradation of PVC, but could increase the mass of residues. Oven aging test showed that the penzinc could significantly retard the discoloration during the long‐term decomposition of PVC. Meanwhile, no “zinc burning” was observed in the PVC with penzinc. These results indicate that the penzinc is an excellent thermal stabilizer for rigid PVC. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis, characterization and application of enrofloxacin complexes as thermal stabilizers for rigid poly(vinyl chloride)

Synthesis and characterization of both binary Co(II)- (1), Ni(II)- (2) complexes with enrofloxacin drug (HL(1)) and ternary Co(II)- (3), Ni(II)- (4) complexes in presence of DL-alanine (H(2)L(2)) are reported using physico-chemical techniques. The antimicrobial activity of these complexes has been screened against two gram-positive and two gram-negative bacteria. Antifungal activity against two different fungi has been evaluated and compared with reference drug. All the binary and ternary complexes showed remarkable potential antimicrobial activity higher than the recommended standard agents. Ni(II)-complexes exhibited higher potency as compared to the parent drug against bacterial and fungal strain. In addition, it was of interest to investigate the reported complexes as thermal stabilizers and co-stabilizers for rigid PVC in air at 180 °C. Their high stabilizing efficiency is detected by their high induction period values (T(s)) compared with some of the common reference stabilizers used industrially, such as dibasic lead carbonate (DBLC) and calcium-zinc soap. Blending these complexes with some of the reference stabilizers in different ratios had a synergistic effect on both induction period as it gave better thermal stability and lower extent of discoloration. The stabilizing efficiency is attributed at least partially to the ability of the metal complex stabilizer to be incorporated in the polymeric chains, thus disrupting the chain degradation and replace the labile chlorine atoms on PVC chains by a relatively more s moiety of the inorganic stabilizer. Their amenability to use as a biomedical additives for PVC, has afforded them great potential for various medical applications.

Metal lanolin fatty acid as novel thermal stabilizers for rigid poly(vinyl chloride)

The synergistic stabilization effect of different metal lanolin fatty acids as natural-based thermal stabilizers for poly(vinyl chloride) (PVC) including calcium lanolin fatty acid (Calan 2), zinc lanolin fatty acid (Znlan 2) and lanthanum lanolin fatty acid (Lalan 3) were studied through Congo red testing, color measurements, FTIR analyses and thermal behavior in this paper. The results showed that Lalan 3/Calan 2/Znlan 2 stabilizers exhibited more excellent thermal stabilization efficiency to PVC than Calan 2/Znlan 2 thermal stabilizers, and the optimal mass ratio of Lalan 3/Calan 2/Znlan 2 was 8:9:3. At last, the effect of degradation mechanism on PVC and synergistic stabilization was also investigated by FTIR analyses and thermal behavior.

Study on the Thermal Stability and Stabilization Mechanism of a Novel Thermal Stabilizer for Rigid Poly (Vinyl Chloride)

A novel thermal stabilizer for rigid poly (vinyl chloride) has been examined. Its high stabilizing efficiency is detected by the extent of discoloration and the mass loss rate of the degraded samples when compared with some of reference stabilizers. A higher stabilizing efficiency is produced as the novel thermal stabilizer is mixed with different co-stabilizers. The study results for thermo oxidative stability of the degraded samples with novel thermal stabilizer have shown that the novel thermal stabilizer can prevent or delay the thermal oxidative degradation of PVC. A probable stabilization mechanism for the novel thermal stabilizer has been proposed.

Effect of cyanoguanidine‐metal and urea‐metal complexes on the thermal degradation of poly(vinyl chloride)

AbstractTin, nickel, cobalt, zinc, and copper complexes of cyanoguanidine and urea were synthesized and investigated as thermal stabilizers for rigid poly(vinyl chloride) at 180°C in air. Their stabilizing efficiencies were evaluated by measuring the induction period (the period during which no evolved hydrogen chloride could be detected) and the rate of dehydrochlorination as determined by continuous potentiometric measurements, in addition to the extent of discoloration. The results clearly revealed the greater efficiency of all of the investigated metal complexes as compared to those of well‐recognized reference stabilizers. The tin complex always exhibited the highest efficiency irrespective of the type of ligand used. The nickel and cobalt complexes also possessed high stabilizing efficiencies. The order of the stabilizing potency of the various metal complexes was Sn ⋙ Co, Ni ≫ Zn, Cu. Combining the ligand itself with dimethyltin‐s,s′‐bis (isooctyl thioglycolate), as a reference stabilizer containing a tin atom, led to a true synergism. This synergistic effect might be attributed to the formation in situ of a complex between the ligand and the tin atom. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers

N′‐acryloyl benzhydrazide as a thermal stabilizer for rigid poly(vinyl chloride)

AbstractN′‐Acryloyl benzhydrazide (ABH) was examined as a thermal stabilizer and costabilizer for rigid poly(vinyl chloride) (PVC) in air at 180°C. Its high stabilizing efficiency was shown by its high thermal stability value (Ts) when compared with those of two common reference stabilizers used industrially, dibasic lead carbonate (DBLC) and a calcium–zinc soap. Blending this organic stabilizer with the reference stabilizers in different ratios had synergistic effects on both the thermal stability and the extent of discoloration of the PVC. The Ni2+ complex of ABH gave better thermal stability and lesser discoloration than the parent organic stabilizer. Also, blending that complex with DBLC in different ratios gave better stability and lower discoloration. Thermogravimetric analysis confirmed the improved stability of PVC in the presence of the ABH stabilizer. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.

Hydroxylbenzylthioethers as novel organic thermal stabilizers for rigid PVC

An investigation was carried out on the performances of hydroxylbenzylthioethers employed as organic thermal stabilizers for rigid poly(vinyl chloride). The efficiency of these compounds as thermal stabilizers was evaluated by using Haake polydrive mixer and TGA. The stabilizing efficiency was compared with Ca–Zn soap and methyltin stabilizer. Hydroxylbenzylthioethers exhibit greater efficiency than both of these stabilizers. This is attributed to the ability of these compounds to prevent the formation of polyene sequences. The hydroxylbenzylthioethers-stabilized PVC showed a slightly lower glass transition temperature ( T g) in comparison with the original PVC. Hydroxylbenzylthioethers and epoxidized soybean oil (ESBO) exhibit synergistic effect on the stabilizing effect, when the mass ratios of ESBO to hydroxylbenzylthioethers are less than 0.5.

Organic thermal stabilizers for rigid poly(vinyl chloride) VII. Effect of mixing 2-benzimidazolyl- ω-phenylpropenylidineacetonitrile with some commercial stabilizers

The effect of mixing 2-benzimidazolyl- ω-phenylpropenylidineacetonitrile (BPAN) with each of the reference stabilizers: dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), barium–cadmium–zinc stearate (Ba–Cd–Zn stearate), or dibutyltin maleate (DBTM) on the stabilizing efficiency in thermal degradation of rigid PVC at 180 °C, in air, has been investigated. Mixing was effected in the range of 0–100 wt.% of BPAN relative to each of the reference stabilizers. The stabilizing efficiency was evaluated by measuring the length of the induction period ( T s), the period during which no detectable amounts of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric determination on the one hand, and the extent of discoloration of the degraded polymer samples on the other. The results show a true synergistic effect from the combination of BPAN with any of the reference stabilizers. Mixing of the stabilizers improves the T s values, decreases the rate of dehydrochlorination, and lowers the extent of discoloration of the polymer. The synergism reaches its maximum when the BPAN is mixed with either DBLS or Ba–Cd–Zn stearate in weight ratio of 25/75%, respectively. In case of DBLC or DBTM, the maximum synergism was attained when the stabilizers mixtures were in equivalent weight ratio (50/50%). The observed synergism may be attributed to the different mechanisms by which the investigated and the reference stabilizers work.

Organic thermal stabilizers for rigid poly(vinyl chloride) VI. Effect of mixing p-chloro- N-phenylphthalimide with some commercial stabilizers

The effect of mixing p-chloro- N-phenylphthalimide ( p-Cl- NØPI) with the reference stabilizers: dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), barium–cadmium–zinc stearate (Ba–Cd–Zn stearate), n-octyltin mercaptide ( n-OTM) or dibutyltin maleate (DBTM) on the stabilizing efficiency in thermally degradation of rigid PVC at 180 °C, in air, has been investigated. Mixing was effected in the range of 0–100 wt.% of p-Cl- NØPI relative to the reference stabilizers. The stabilizing efficiency is evaluated by measuring the length of the induction period ( T s), the period during which no detectable amounts of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric determination on one hand, and the extent of discoloration of the degraded polymer samples on the other. The results reveal that mixing of the stabilizers improves the Ts values, decreases the rate of dehydrochlorination and lowers the extent of discoloration of the polymer. This improvement attains its maximum when the p-Cl- NØPI is mixed with any of DBLC, DBLS, Ba–Cd–Zn stearate or DBTM reference stabilizers in weight ratio of 25/75%, respectively. Mixing of p-Cl- NØPI with n-OTM is an exception, as maximum synergism was attained at equivalent weight ratio (50/50%).

Organic thermal stabilizers for rigid poly(vinyl chloride) IV. N-Arylphthalimides

N-Arylphthalimide derivatives have been investigated as thermal stabilizers for rigid poly(vinyl chloride) (PVC). Their stabilizing efficiencies compared with some conventional thermal stabilizers have been measured by the continuous potentiometric determination of the evolved hydrogen chloride gas from the degradation, and by the extent of discoloration of the degraded samples. The results reveal the greater stabilizing efficiencies of most of the investigated derivatives as compared with reference stabilizers. A mechanism for the stabilizing action of the investigated stabilizers is proposed.

Organic thermal stabilizers for rigid poly(vinyl chloride) V. Benzimidazolylacetonitrile and some of its derivatives

2-Benzimidazolylacetonitrile (BAN) and some of its conjugated unsaturated derivatives namely: 2-benzimidazolylbenzylidineacetonitrile (BBeAN), 2-benzimidazolyl-ω-phenylpropenylidineacetonitrile (BPAN) and 2-benzimidazolylbut-2-enylidineacetonitrile (BBuAN) have been investigated as organic thermal stabilizers for rigid PVC at 180 °C in air. Their stabilizing efficiencies are based on measuring the length of the induction period ( T s), the period during which no detectable amounts of HCl gas could be observed, and also from the rate of dehydrochlorination as measured by the continuous potentiometric titration on the one hand, and the extent of discoloration of the degraded polymer samples on the other. The stabilizing efficiencies of the investigated stabilizers were compared with that of dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), barium–cadmium–zinc stearate (Ba–Cd–Zn stearate) and dibutyltin maleate (DBTM) which are commonly used industrial stabilizers. The results reveal the higher stabilizing efficiency of the investigated materials relative to the reference stabilizers concerning the T s values. However, the rate of dehydrochlorination at the later stages of degradation for PVC stabilized with the investigated stabilizers is found to be relatively higher than that in the presence of reference stabilizers. These experimental findings indicate that almost all the stabilizers actions are exhausted during the induction period. The stabilizing efficiencies of the investigated stabilizers can be attributed to the replacement of the labile chlorine atoms on the polymer chains by a relatively more thermally stable groups derived from the stabilizer. This substitution reaction proceeds most probably through a radical mechanism. Moreover, the results also reveal the effect of the extent of conjugated unsaturates in the organic stabilizer molecule. The stabilizing potency of the investigated materials increases with the extent of their conjugated unsaturation sites. On the other hand, the results also reveal that while the extent of discoloration of thermally degraded PVC in the presence of BPAN stabilizer is comparable with most of the investigated reference stabilizers, the other derivatives showed a relatively higher extent of discoloration.

N-(Substituted phenyl)itaconimides as organic stabilizers for rigid poly(vinyl chloride) against thermal degradation

Several N-(substituted phenyl)itaconimide derivatives, N-(RPh)II, (R:-NO 2, –COOH, –H, –OH, –OMe, –Me, –Cl or –Br) have been investigated as organic thermal stabilizers for rigid poly(vinyl chloride) (PVC) at 180 °C in air. Their stabilizing efficiencies are evaluated by measuring the length of the induction period ( T s), the period during which no detectable amounts of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric determination on one hand, and the extent of discoloration as well as the change in the mechanical properties of the degraded polymer on the other. Their stabilizing efficiencies were compared with that of dibasic lead carbonate (DBLC), barium–cadmium–zinc stearate (Ba–Cd–Zn stearate) and n-octyltin mercaptide ( n-OTM), which are commonly used industrial stabilizers. The results clearly reveal the greater stabilizing efficiency of almost all the N-(RPh)II derivatives except those of the nitro-derivatives as compared with industrially used thermal stabilizers. This is well illustrated by the longer T s values, and by the lower rates both of dehydrochlorination and discoloration as well as mechanical properties loss of the polymer during degradation relative to those of the reference stabilizers. The results also demonstrate how the stabilizing efficiency is affected both by the nature and position of the substituents in the phenyl ring of the itaconimide stabilizers. Thus, while N-(RPh)II derivatives with groups of positive resonance effect (+R) show higher values of T s and lower rates of dehydrochlorination relative to those having groups of negative resonance effect (−R), the unsubstituted N-PhII lies between these two extremes. The stabilizing efficiency of N-(RPh)II derivatives is attributed to the replacement of the labile chlorines on the PVC chains by relatively more thermally stable stabilizer moieties. A radical mechanism for the stabilizing action of the investigated stabilizers is suggested. A synergistic effect is achieved when the materials under investigation were blended in various molar ratios with either of the reference stabilizers. This synergism attains its maximum when both the investigated and the reference stabilizers are taken in equivalent molar ratios.

Organic thermal stabilizers for rigid poly(vinyl chloride) III. Crotonal and cinnamal thiobarbituric acids

Crotonal thiobarbituric acid (CTBA) and cinnamal thiobarbituric acid (CiTBA) have been investigated as thermal stabilizers for rigid poly (vinyl chloride) (PVC) at 180°C in air. Their stabilizing efficiency is evaluated by measuring the length of the induction period ( T s), the period during which no detectable amounts of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric titration on one hand and the extent of discoloration of the degraded polymer on the other. The results reveal the higher stabilizing efficiency of the investigated materials as compared with industrially used thermal stabilizers such as dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), n-octyl tin mercaptide ( n-OTM), dibutyl tin maleate (DBTM) and barium–cadmium–zinc stearate (Ba–Cd–Zn stearate). This is well illustrated by the longer T s values, and by the lower rates both of dehydrochlorination and discoloration of the polymer during degradation relative to those of the reference stabilizers. A radical mechanism for the stabilizing effect of the investigated materials is suggested. The results indicate the important role played by the extent of conjugation in thiobarbituric acid derivatives on the stabilizing efficiency of the stabilizers. The stabilizing potency of the stabilizer increases with the extent of conjugation. The effect of blending CiTBA with either of the reference stabilizers on the stabilizing efficiency of the thermally degraded rigid PVC has been also investigated. The results reveal that mixing of the stabilizers improve both the T s values, the rate of dehydrochlorination and the extent of discoloration. This improvement attains its maximum when both the investigated and the reference stabilizers are taken in equivalent weight ratios.