Novel antimicrobial and antitumor organic thermal stabilizers for rigid Poly (vinyl chloride)

Pyrazolodithiones of expected biological activity were examined as thermal stabilizers and co-stabilizers for rigid poly(vinyl chloride) (PVC) in air at 180?°C. Their high stabilizing efficiency were shown by their high thermal stability values (T _s), which is the time needed for the liberation of HCl gas, if compared with dibasic lead carbonate (DBLC) and calcium?Czinc soap (Ca?CZn soap) reference stabilizers used industrially, with better extent of discoloration. Blending these derivatives with reference stabilizers in different ratios greatly lengthens the thermal stability value and improves the extent of discoloration of the PVC. The structure of the novel organic stabilizers was confirmed by elemental analysis, FTIR, Mass spectra, and ¹H-NMR. Thermogravimetric analyses confirmed the improved stability of PVC in the presence of the investigated organic stabilizers, compared to blank PVC and PVC stabilized with the reference stabilizers. Also, GPC measurements were done to investigate the changes occurred in the molecular masses of the degraded samples of PVC in presence of the newly synthesized stabilizers. The stabilizing efficiency of pyrazolodithiones is attributed to the replacement of the labile chlorine atoms on the PVC chains by a relatively more stable moiety of the organic stabilizer. The investigated stabilizers showed a good antimicrobial activity toward two kinds of bacteria, Escherichia coli and Staphylococcus aureus; and also toward two kinds of fungi, Aspergillus flavus and Candida albicans. They also exhibited antitumor activity against both liver and colon human cell lines.     

Influence of lanthanum stearate as a co-stabilizer on stabilization efficiency of calcium/zinc stabilizers to polyvinyl chloride

Influence of lanthanum stearate (LaSt₃) as a co-stabilizer on stabilization efficiency of calcium stearate (Ca)/zinc glutarate (Zn) stabilizers to polyvinyl chloride (PVC) at 180 °C in air was investigated. The results showed that combination of LaSt₃ with Ca/Zn stabilizers presented an obvious improvement of stabilization efficiency to PVC compared with the Ca/Zn stabilizers. Moreover, addition of LaSt₃ to the Ca/Zn stabilizers could significantly enhance static stability time of PVC. Incorporation of 2 phr LaSt₃ co-stabilizer to PVC containing 3 phr Ca/Zn stabilizers resulted in marked increase of onset degradation temperature and reductions in average degradation rate as well as the dynamic storage modulus (G′) and loss modulus (G″) at 180 °C. Influence of Ca/Zn ratio on tensile strength of PVC in the absence or in the presence of LaSt₃ was discussed in detail. At low Ca/Zn ratios LaSt₃ had an obvious improvement in the tensile strength, while at high Ca/Zn ratios this effect became inconspicuous.     

Improvement of Structural and Thermal Stabilities of PVC and Wood/PVC Composite by Zn and Pb Stearates,and Zeolite

Three different chemical stabilizers were introduced into neat PVC and a wood/PVC composite (containing 50 phr wood flour) to improve their thermal and structural stabilities. The changes in CIE yellowness index, polyene index, %wt loss, and decomposition temperature (T_d) were monitored. The effects of type and content of thermal stabilizers, thermal ageing time, and the presence of wood flour were our main interests. The experimental results suggested that the additions of Zn and Pb stearates into PVC and wood/PVC composite could improve the thermal stability of the PVC. At the test temperature of 177°C, the additions of Zn and Pb stearates could improve the thermal stabilities of PVC by retarding the upzipped reaction and by reducing the conjugated double bonds in PVC, Pb stearate being the most suitable for thermally stabilizing the PVC. Around the T_d range (～264°C), the addition of Zn stearate reduced the T_d value of PVC whereas that of Pb stearate had no effect on the change in T_d value. Zeolite loading could shift the T_d value of the PVC from 264 to 280°C. The addition of wood particles increased the polyene content and decreased the decomposition temperature of the PVC. The effect of wood flour on the thermal and structural changes of PVC overruled that of thermal stabilizer loading.     

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.     

The use of organotin compounds in the thermal stabilization of poly(vinyl chloride). VI. An assessment of the relative importance of HCl-scavenging,exchange, and addition reactions

Reactions of PVC with three representative stabilizers Bu₂SnY₂ (Y = OCOC₁₁H₂₃, SCH₂COOCH₂CH(Et)CH₂CH₂CH₂CH₃, OCOCH=CHCOOMe) in solution and under nitrogen were studied by two principal methods. First, using stabilizers with radioactive labels in the Y groups, the uptake of these groups by virgin and degraded polymer was measured. The UV-visible absorption spectra of the stabilized polymers are discussed. Second, the effect of these three stabilizers on the rate of elimination of hydrogen chloride from heated PVC was studied. It is shown that the effects of HCI-scavenging and of exchange reactions in suppressing the evolution of HCI can be separately evaluated. The thermal decomposition of dibutyltin bis(methyl maleate) to give maleic anhydride is reported. Interpretation of the observations is made in terms of assessing the relative importance of the various polymer–stabilizer reactions in promoting stabilization.     

Determination of butyltin and octyltin stabilizers in poly(vinyl chloride) products by headspace solid-phase microextraction and gas chromatography with flame-photometric detection

Headspace solid-phase microextraction (HS-SPME) and gas chromatography with flame photometric detection (GC-FPD) have been investigated for determination of butyltin and octyltin stabilizers in poly(vinyl chloride) (PVC) products. The organotin stabilizers were first released from the plastic matrix by dissolving the PVC sample in tetrahydrofuran (THF). The stabilizers were then hydrolyzed to the chloride forms, by treatment with 6 mol L⁻¹ HCl, then derivatized with sodium tetraethylborate (NaBEt₄) in 0.2 mol L⁻¹ sodium acetate buffer (pH 4.5) at 50 °C. HS-SPME was performed with a fused-silica fiber coated with a 100-μm film of polydimethylsiloxane (PDMS). The collected organotin compounds were then desorbed in the GC injector at 280 °C and analyzed by GC-FPD. Linearity (r≥0.994) over a concentration of approximately two orders of magnitude was usually obtained. Limits of quantitation (LOQ) of the four organotin compounds studied, viz., monobutyltin (MBT), dibutyltin (DBT), monooctyltin (MOT), and dioctyltin (DOT), were in the range 0.3–1.0 ng Sn mL⁻¹. Recovery was >90% for butyltins and >80% for octyltins. The method was validated by analyzing two reference standard PVC sheets with known organotin content. The applicability of the method to analysis of organotin stabilizers in commercial PVC products was also demonstrated.     

Effect of thermal stabilizers composed of zinc barbiturate and calcium stearate for rigid poly(vinyl chloride)

Zinc barbiturate [Zn(H₂L)₂·2H₂O, abbreviated as ZnL₂] was synthesized by a precipitation method in aqueous solution, and investigated as a co-stabilizer with calcium stearate (CaSt₂) for rigid poly(vinyl chloride) (PVC) by the discoloration test and the dehydrochlorination test at 180 °C. ZnL₂ exhibits high stabilizing effect with excellent initial colour of PVC films. In comparison with the synergistic effect of CaSt₂/ZnSt₂ stabilizers, the CaSt₂/ZnL₂ stabilizers in mass ratios ranging from 0.3/1.2 to 0.6/0.9 exhibit better synergistic effect. Moreover, PVC films stabilized by CaSt₂/ZnL₂ show better initial colour with the addition of dibenzoyl methane as an auxiliary stabilizer. The mechanism of stabilizing action of ZnL₂ is also proposed. ZnL₂ may replace the labile chlorine atoms to interrupt the formation of conjugated double bonds in PVC chains, and act as the absorber of hydrogen chloride to restrain the self-catalytic dehydrochlorination.     

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.     

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

Zinc soaps of rubber seed oil (RSO) and epoxidised rubber seed oil (ERSO) were prepared and their use as PVC stabilizers investigated. Characterization of Zn soaps of RSO prepared by different techniques and ERSO gave information on the purity, structure and thermal behaviour of these materials. From the analysis, the production of these materials for use in thermal stabilization of PVC would be optimized as their use greatly enhanced the stability of PVC as obtained from the conductivity measurements using the 763 PVC Thermomat. The minimum amount of HCl release was obtained for the samples with Zn soaps and ERSO indicating a synergistic effect. Zn soaps having Zn(OH)₂ stabilized PVC better than pure Zn soaps.     

Vanillin–Schiff’s bases as organic thermal stabilizers and co-stabilizers for rigid poly(vinyl chloride)

Vanillin–Schiff’s bases (VSB) were examined as thermal stabilizers and co-stabilizers for rigid poly(vinyl chloride) (PVC) in air at 180 °C. Their high stabilizing efficiency were shown by their high thermal stability value (Ts), which is the time elapsed for the detection of HCl gas, if compared with dibasic lead carbonate and cadmium–zinc soap reference stabilizers used industrially, with better extent of discoloration. Blending these derivatives with reference stabilizers in different ratios greatly lengthens the thermal stability and the extent of discoloration of the PVC.Condensation products of Vanillin with amines are very active biologically, besides having good complexation ability with metal ions. The Ni²⁺ and Co²⁺ complexes of VSB derivatives gave better thermal stability and less discoloration than the parent organic stabilizer. Also, blending these complexes with either of the used reference stabilizers in different ratios gave better thermal stability and lower extent of discoloration. Thermogravimetric analysis confirmed the improved stability of PVC in the presence of the VSB derivatives, compared to blank PVC, PVC stabilized with reference stabilizers and PVC stabilized with binary mixture of VSB derivatives with reference stabilizer.The stabilizing efficiency of Vanillin–Schiff’s base (VSB) derivatives is attributed to the replacement of the labile chlorine atoms on the PVC chains by a relatively more stable moiety of the organic stabilizer.     

Determination of Dialkyltin Compounds in Poly(Vinyl Chloride) by High-Performance Liquid Chromatography

A high-performance liquid chromatography (HPLC) method has been developed for the analysis of dialkyltin compounds in polyvinyl chloride (PVC) materials. The PVC sample was first dissolved in tetrahydrofuran. Concentrated hydrochloric acid was then added to convert the dissolved dialkyltin stabilizers into the chloride forms, followed by extraction with hexane. The extracted dialkyltin chlorides were preconcentrated and were finally separated by HPLC. Separation was performed using a C₁₈ column and an eluent of aqueous methanol containing 8-hydroxyquinoline (oxine) as the completing agent. Photometric detection of the dialkyltin-oxine complexes was carried out at 380 mm. Under optimum experimental conditions, the detection limits for dimethyltin, dibutyltin and dioctyltin are 1.7 ng, 2.1 ng and 2.9 ng (all as tin), respectively. Residual dialkyltin stabilizers in several commercially available PVC products were successfully analyzed via this method.     

Studies of the degradation of organotin stabilizers in poly(vinyl chloride) during gamma irradiation

Organotin stabilizers of the type Bu₂SnX₂ (X = SCH₂CO₂C₈H₁₇ or O₂CCH?CHCO₂C₈H₁₇) present in poly(vinyl chloride) (PVC) and subjected to varying doses of gamma irradiation in the range 1–200 kGy (0.1–20 Mrad) are shown to suffer degradation with dealkylation to form monobutyltin trichloride and tin(IV) chloride, which have been characterized by a subsequent alkylation procedure followed by gas chromatographic analysis. The extent of degradation of the stabilizers on prolonged gamma irradiation is much more severe than during thermal degradation leading to comparable blackening of the polymer.     

Influence of lanthanum stearate and calcium/zinc stabilizers on stabilization efficiency of dibutyltin dilaurate to polyvinyl chloride

<正>Influences of lanthanum stearate(LaSt_3) and calcium stearate/zinc stearate(Ca/Zn) stabilizers on stabilization efficiency of dibutyltin dilaurate(DBTDL) to polyvinyl chloride(PVC) in air were investigated.The results revealed that the stabilization effect of DBTDL could be achieved by the La/Sn stabilizers with a ratio of 8/2.Addition of DBTDL could enhance thermal property and reduce dynamic storage modulus(G′) at 180℃for PVC containing LaSt_3 or Ca/Zn stabilizers. On the other hand,incorporation of LaSt_3 did not influence the stabilization efficiency of DBTDL markedly;while addition of Ca/Zn stabilizers could significantly decrease thermal property for the DBTDL stabilized PVC.Furthermore,the effects of LaSt_3 and Ca/Zn stabilizers on the stabilization efficiency of DBTDL were explained in the framework of ionization potential.     

Photo-oxidation of poly(vinyl chloride)

The photo-oxidation of PVC has been studied over the temperature range 30–150°C. Initiation with ultraviolet (2537A) radiation has been correlated with the presence of minute amounts of ozone. The contribution of atomic oxygen and singlet oxygen (¹Δ_g) molecules to the initiation mechanism is discussed. The β-chloroketones probably formed in the photo-oxidation of PVC, decomposed according to a Norrish type I reaction without loss of chlorine atoms. The gaseous products of the photo-oxidation of PVC at 30°C were carbon dioxide, carbon monoxide, hydrogen, and methane. Hydrogen chloride was obtained only when PVC was heated at high temperatures. When PVC was photo-oxidized and then heated at high temperature, benzene was obtained in addition to hydrogen chloride. The gaseous products from the photo-oxidations of model compounds, such as 4-chloro-2-butanone and 2,4-dichloropentane, were also compared with those from PVC. Hydrogen chloride was detected only after photo-oxidation at temperatures of 25°C or higher. Therefore, it was concluded that hydrogen chloride is mainly a product of thermal decomposition. Since unsaturation was not observed in photo-oxidized PVC films, the cause of discoloration is unclear. When PVC was modified by stabilizers or additives, the oxidative degradation was further complicated by side reactions with the additives.     

Study of the effect of stabilizer on the degradation of poly(vinyl chloride) by pyrolysis–gas chromatography

The effect of stabilizer on the thermal degradation of poly(vinyl chloride) was studied by means of pyrolysis–gas chromatography. The stabilizers used in this study were dibutyltin dilaurate, dibutyltin bis(n-dodecyl mercaptide), barium stearate, and zinc stearate. PVC containing these stabilizers was degraded in a stream of nitrogen at temperatures ranging from 350 to 570°C. It was found that observed drastic reduction of benzene yield from the PVC containing zinc stearate had a close correlation with the formation of crosslinking structures.     

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XI: Anthraquinone derivatives

Anthraquinone and 1-aminoanthraquinone derivatives have been examined as thermal stabilizers or co-stabilizers for rigid PVC in air, at 180 °C. Their high stabilizing efficiency is detected by their high induction period values (Ts) when compared with some of the common reference stabilizers used industrially such as dibasic lead carbonate, calcium-zinc soap and octyl tin mercaptide. Blending these organic stabilizers with some of the reference stabilizers in different ratios had synergistic effect on both the induction period and the dehydrochlorination rate.A probable mechanism for the stabilizing mode of these derivatives has been proposed. The stabilizing efficiency is attributed partially to the stabilizers' ability to intervene in the radical chain degradation process of PVC and to the replacement of the labile chlorine atoms on PVC chains by a relatively more stable moiety of the organic stabilizer.     

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XII: N-phenyl-3-substituted-5-pyrazolone derivatives

N-phenyl-3-substituted-5-pyrazolone derivatives have been examined as thermal stabilizers or co-stabilizers for rigid PVC in air, at 180 °C. Their high stabilizing efficiency is detected by their high induction period values (T_s) when compared with some of the common reference stabilizers used industrially, such as dibasic lead carbonate, calcium-zinc soap and n-octyl tin mercaptide. Blending these derivatives with some of the reference stabilizers in different ratios had a synergistic effect on both the induction period and the dehydrochlorination rate.A probable mechanism for the stabilizing mode of N-phenyl-3-substituted-5-pyrazolone derivatives has been proposed. The stabilizing efficiency is attributed at least partially to the ability of the organic stabilizer to be incorporated in the polymeric chains, thus disrupting the chain degradation.     

Application problems of PVC materials irradiated with high doses

Radiation crosslinking of PVC in the presence of triallyl cyanurate as a sensitizer, dioctyl phthalate as a plasticizer and lead and tin stabilizers was examined. Standard methods of testing PVC materials were used. Direct relations between crosslinking extent, elongation, and Vicat softening temperature changes were found. Lead stabilizers proved to be more efficient than tin stabilizers. The influence of radiation dcse on immediate and long-term changes of PVC was investigated.     

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XIII: Eugenol (4-allyl-2-methoxy-phenol)

Eugenol (4-allyl-2-methoxy-phenol) has been examined as a thermal stabilizer and co-stabilizer for rigid PVC in air, at 180 °C. Its high stabilizing efficiency is detected by its high thermal stability value (Ts) when compared with some of the common reference stabilizers used industrially such as dibasic lead carbonate, calcium-zinc soap and octyl tin mercaptide.Blending this organic stabilizer with some of the reference stabilizers in different ratios had synergistic effect on both the induction period and the dehydrochlorination rate together with the longer extent of discolouration of PVC stabilized by eugenol as compared with the blank and the samples stabilized with reference commercial stabilizers.A probable mechanism for the stabilizing action of eugenol has been proposed. The stabilizing efficiency is attributed partially to the stabilizer's ability to intervene in the radical chain degradation process of PVC and to the replacement of the labile chlorine atoms on PVC chains by a relatively more stable moiety of the organic stabilizer.     

Synthetic aspects of tetraorganotins and organotin(IV) halides

Organotin(IV) compounds are being used for many applications, e.g., as stabilizers in PVC, in anti-fouling paints and coatings for the protection of ship hulls and as precursors for SnO₂-coatings on glass. Tetraorganotins and especially organotin(IV) halides often serve as synthetic precursors. A wide range of methods for the synthetic preparation of these compounds has been developed since the 1940s. This review gives an overview of the available routes for the preparation of organotin(IV) compounds and discusses their selectivity and yield. In particular, monoorganotin trihalides are often not accessible in high yield.