Effect of stabilizers in the thermal treatment of PVC—XIII: Study of the stabilization efficiency of combinations of BA and ZN stearates in PVC

The effects of Ba and Zn stearates in PVC mixtures during static heat treatment have been studied. In addition to the course of the dehydrochlorination and the consumption of stabilizer, the spectral changes in the visible and infrared regions have been investigated. The limiting concentration of Zn stearate in the mixture (with respect to the synergistic effect) and complex formation between Ba and Zn stearates are discussed.     

Investigations on poly(vinyl chloride). III. Effects of metal oxides upon thermal decomposition of poly(vinyl chloride)

Thermal decomposition mechanisms of poly(vinyl chloride) (PVC) and the effects of a few metal oxides on the pyrolysis of PVC were previously reported. In the present work, 33 metal oxides were investigated to determine their effects on the thermal decomposition of PVC, by using a pyrolysis gas chromatograph. Most acidic oxides accelerate the recombination of chlorine atoms with double bonds, since PVC containing these metal oxides easily release lower aliphatics, toluene, ethylbenzene, o-xylene, and chlorobenzenes. On the other hand, most basic metal oxides, such as oxides of alkaline earths or silver, inhibit the recombination. These tendencies observed in the thermal decomposition of PVC agree with the contributions of corresponding metal salts to the dehydrochlorination of PVC proposed by other workers. This means that thermal decomposition or dehydrochlorination of PVC is affected by irregularities in head-to-tail linkages formed by the recombination of chlorine atoms during heat treatment of PVC.     

稀土PVC稳定剂的作用机制研究

稀土化合物可以作为聚氯乙烯稳定剂，硬脂酸稀土是稀土复合稳定剂的重要成分。本文通过研究PVC与硬脂酸镧及其它硬脂酸盐作用前后的红外光谱，探讨了硬脂酸盐对PVC的热稳定作用机制，发现了稀土化合物对PVC的特殊稳定机制，即改变PVC的构象和抑制脱氯化氢的作用，并对稀土稳定剂独特的协同作用做出了解释。     

Effect of stabilizers in the thermal treatment of PVC—VIII. An investigation of double bonds in PVC in the presence of Ba and Cd stearates

Thermal degradation of PVC at 180° in air in the presence of Ba and Cd sterarates and of their combination has been studied. In the presence of Cd stearate, dehydrochlorination proceeds at many sites giving rise to relatively short polyenes. In the presence of Ba stearate, the number of degradation sites is smaller, but long polyene sequences are formed, causing the colouration of the polymer. In synergistic combinations of Ba/Cd stearates, both these mechanisms may operate.     

Mechanism of action of some stabilizers in the thermal degradation of poly(vinyl chloride)

The dehydrochlorination of PVC under vaccum has been studied at 170–200°C by a volumetric method. The accelerating effect of HCl is related to its interaction with the forming polyene units of macromolecules. A mechanism is proposed. The effects of various stabilizers, such as organic salts of Ca, Ba, Cd, trialkyl- and dialkyltin, trialkyl phosphites, and mixtures of phosphites with metal salts upon the rate of dehydrochlorination, polymer crosslinking, and electron absorption spectra of PVC during degradation in evacuated ampoules were investigated. The stabilizing activity of these compounds depends primarily on the effectivity of absorption of HCl and destruction of polyene units by these compounds.     

氯化天然橡胶的等速升温热降解动力学

天然胶乳;氯化天然橡胶的等速升温热降解动力学     

Kinetics of the dehydrochlorination of poly(vinyl chloride) in the presence of NaOH and various diols as solvents

The dehydrochlorination of PVC in the presence of NaOH was investigated in different diols. Diethylene glycol (DEG), triethylene glycol (TEG), and propylene glycol (PG) were found to be effective in accelerating the dechlorination of PVC. The dehydrochlorination was promoted in the order TEG > DEG > PG, which was in agreement with the compatibility between PET and the diol. Compatibility resulted in an improved penetration of the PVC particle by the solvent, leading to the acceleration of the dehydrochlorination. The dehydrochlorination of PVC in NaOH/diol followed first-order kinetics, confirming the progress of the reaction under chemical reaction control. The apparent activation energies were 82 kJ mol⁻¹, 109 kJ mol⁻¹, and 151 kJ mol⁻¹ for TEG, DEG, and PG, respectively. The lower the activation energy became the faster the dehydrochlorination of PVC proceeded.     

Kinetics of the Alkaline Dehydrochlorination of Polyvinyl Chloride)

From previous investigations of the alkaline dehydrochlorination of PVC it is well known that polyene sequences are formed. In this paper the true overall kinetics of the dehydrochlorination reaction between PVC and alcoholic KOH in tetrahydrofuran solution was studied at 9.5°C by measuring the rate of disappearance of KOH. Titrations of the hydroxide ions consumed and the chloride ions evolved showed close agreement. IR spectra of the samples did not show any evidence of substitution by hydroxide ions. Small amounts of DMSO present in the solvent were found to increase the reaction rate markedly. The kinetic scheme was discussed and the first rate constant was determined. Preliminary results of reactions of the polyene sequences with various reagents are presented. These reactions were made in order to introduce new functional groups into the PVC chains.     

Comparative non-isothermal kinetic analysis of thermal degradation of poly(vinyl chloride) prepared by living and conventional free radical polymerization methods

Non-isothermal kinetics of the thermal degradation of poly(vinyl chloride) (PVC) prepared by a living radical polymerization (LRP) method was performed and compared with the results obtained from PVC prepared by the conventional free-radical process (FRP). Both differential and integral isoconversional methods were applied for determining the apparent activation energy of the dehydrochlorination stage. This study made clear noticeable differences in the thermal degradation of the PVC samples under analysis. The newly synthesized LRP-PVC material has a better thermal stability and presents substantial differences in the macroscopic kinetics of the dehydrochlorination process compared with conventional FRP-PVC. These differences were assessed in quantitative terms on the basis of the kinetic triplet [E_a,A,f(α)].     

Effect of calcium and zinc carboxylates on the thermal stabilisation of PVC

Metal carboxylate stabilisers are believed to replace labile chlorines in PVC with more stable ester linkages resulting in an increase in the stability of the polymer. In the present work, effects of combinations of stearates, palmitates and laurates respectively of zinc and calcium, in various proportions, on the thermal stability of PVC were studied. Combinations of palmitates and stearates having more than 75 mol% of calcium salt were found to increase the stability of the polymer. The combinations of the three carboxylates showed the following order of stabilising: palmitate > stearate > laurate. This effect is explained in terms of a critical chain length of the n-alkyl group of the carboxylate anion which is most effective in the stabilising process. Highly crystalline, low molecular weight polyethylenes are used as plasticisers for PVC. They were found to have a stabilising effect explained in terms of a dilution effect by the non-polar polyethylenes on the polar interactions in PVC; compatibility of polyethylenes with PVC is the limiting factor in this stabilisation.     

Ion-selectivity of plasticizers in poly(vinyl chloride) membrane electrodes

Electrode membranes were presented which contained only PVC and a plasticizer. The plasticizers studied were tris(2-ethylhexyl)phosphate, 2-nitrophenyl octyl ether and bis(1-butylpentyl)adipate. The response and selectivity of these ligand-free PVC electrodes towards alkali and alkaline earth cations are reported.     

Dehydrochlorination of Poly(viny1 Chloride) in Pyridine. III. Thermal and Mechanical Properties

The thermal properties of dehydrochlorinated PVC (DHPVC) were evaluated. From thermogravimetric analysis (TGA) and differential thermal analysis (DTA), a larger decrease in thermal stability of dehydrochlorinated PVC than of PVC was observed. Thermal stability of DHPVC increased continuously with an increase in dehydrochlorination temperature and dilution of the reaction solution during dehydrochlorination. However, with an increase in dehydrochlorination time, an increase in thermal stability after an initial drop was obtained. The highly cross-linked product separated from the reaction solution at higher dehydrochlorination temperatures showed a lower thermal stability than that of corresponding soluble DHPVC. The stress-strain behavior of dehydrochlorinated PVC samples was also studied.     

Thermal degradation of graft copolymers of PVC prepared by mastication with styrene and methyl methacrylate,and of further PVC mixtures and vinyl chloride copolymers

Graft copolymers prepared by mastication of PVC in the presence of styrene or of a styrene/ methyl methacrylate mixture, have been studied by thermogravimetry, estimation of hydrogen chloride, thermal volatilization analysis, and flash pyrolysis/g.l.c. The degradation behaviour of PVC/ polystyrene mixtures, vinyl chloride/styrene random copolymers, a random copolymer of methyl methacrylate and styrene, and PVC/poly-α-methylstyrene mixtures has also been studied. The graft copolymers resemble the PVC/methacrylate graft copolymers previously studied in showing retardation of the dehydrochlorination reaction, but contrast with them in yielding chain fragments but no monomer during HCl production. Some stabilization of the second component at higher temperatures is also found. PVC/polystyrene mixtures behave in the same way as the corresponding graft copolymers, but vinyl chloride/styrene copolymers show reduced stability towards both dehydrochlorination and monomer production compared with the homopolymers. PVC/poly-α-methylstyrene mixtures yield some monomer concurrently with HCl loss, and display marked retardation of the latter reaction. Stabilization of the second polymer at higher temperatures is again observed. Many of these results add further strong support to the view that chlorine atoms are involved as chain carriers in the thermal dehydrochlorination of PVC.     

Investigating poly-(vinyl-chloride)-polyethylene blends by thermal methods

Poly-vinyl-chloride (PVC)-polyethylene (PE) alloys were prepared by melt blending using both low- and high-density polyethylene without applying a compatibilizer. The PVC and the PE are incompatible polymers; in spite of this fact stable microheterogeneous materials were obtained. Mechanical methods e.g. tensile tests generally (measured in the usual concentration range) do not support any compatibility. At higher concentrations, the incompatible parts mask the effect of molecular mixing, easily detected at low PE contents. Dynamic mechanical (DMA), differential scanning calorimetric tests were carried out. Glass transition temperatures were determined by both methods. DMA tests were made at four frequencies, and the energy of activation of PVC main transition was also calculated. The decrease of glass-transition temperatures and energy of activation show that there is a slight mixing of the polymers. Specimens were also investigated by infrared method. From the results of IR spectra, grafting reaction of PE can be assumed onto the PVC because of its dehydrochlorination.     

稀土PVC热稳定剂作用模式及协同效应研究

稀土化合物对ＰＶＣ良好的稳定作用，并存在广泛的协同效应。探索了一种计算机辅助研究稀土ＰＶＣ热稳定剂作用模式及效应的方法，可以预测稳定剂的稳定效能。结果表明，在稀土硬脂酸盐及同类稳定剂中，曲线回归方程参数有效地反映了热稳定剂类型的差别；引入协同效应函数，不仅提高了回归方程的可信度，而且能反映协同效应的形成规律。     

硫化对聚乙炔结构和性能的影响

本文利用DSC, FT-IR光谱对聚乙炔硫化产物进行了表征, 研究了聚乙炔硫化前后结构和性能的变化。采用量子化学CNDO/2晶体轨道方法, 首次对硫化聚乙炔的分子结构及电子性质进行理论计算, 探讨了硫化对聚乙炔结构和性能的影响。     

Tripodal compound 1,1,1-tris(N-ethyl-N-phenylamino-carboxylmethoxymethyl) propane as an ionophore for alkali and alkaline earth metal cations-selective electrode

A new tripodal compound, 1,1,1-tris(N-ethyl-N-phenylamino-carboxylmethoxymethyl) propane, has been synthesized and evaluated as an ionophore in PVC membrane electrode for the analysis of alkali and alkaline earth metal cations. The influence of the nature of the plasticizers (o-NPOE, DBP and DOP) and of the amount of incorporated ionophore on the characteristics of the electrode was discussed. Selectivity coefficients against alkali and alkaline earth metal cations were calculated. The electrodes based on the tripodal compound with o-NPOE and DBP as plasticizer gave good performance (slope, limits of detection) to lithium and sodium ions. The electrode plasticized with o-NPOE also exhibited near-Nernstian response to divalent ions: Ca(2+), Sr(2+) and Ba(2+). The electrode prepared with 3.9 mg ionophore, 185 mg o-NPOE, 92 mg PVC and 0.46 mg KTpClPB can be used as a Ca(2+) electrode. The influence of pH has also been studied. The electrodes exhibited better potential stability and operational lifetime of more than 3 months.     

Thermal degradation of silane crosslinked unplasticized PVC

The thermal decomposition behaviour of rigid PVC, crosslinked using bis(γ-trimethoxysilylpropyl)amine as crosslinking agent has been studied. Different thermal stabilizers (tin and lead based) have been used with different crosslinking agent concentrations, and the influence of these factors on the decomposition behaviour in inert atmosphere studied. Results obtained have shown that the main effect of aminosilane is an advance of the first stage of the PVC degradation (i.e. the dehydrochlorination process). Moreover, samples with different concentrations of silane, and at different stages of their processing (i.e. after milling, pressing, crosslinking) have also been used in order to elucidate the influence of these factors on their thermal behaviour. A quantitative kinetic model has been developed and the corresponding kinetic constants have been obtained by modelling the experimental thermogravimetric data. The kinetic parameters obtained have revealed a reduction in the apparent activation energy of the hydrogen chloride loss process, which has shown to be markedly dependent on the thermal stabilizer used.     

M/C3N4/AC (M=Au,Pt,Ru)催化乙炔与二氯乙烷耦合反应:双功能催化剂性能如何?

聚氯乙烯是世界上产量最大的通用塑料,在日常生活的诸多领域具有广泛应用.按照原料来源划分,聚氯乙烯的工业生产方法主要有基于煤炭的电石法和基于石油的“平衡法”.我国有丰富的煤炭资源,因此,电石乙炔法是合成聚氯乙烯的主要途径.该方法采用乙炔与氯化氢在活性炭担载氯化汞催化剂上进行氢氯化反应得到聚氯乙烯的单体氯乙烯.然而,由于汞催化剂的挥发性以及毒性,开发汞替代催化剂迫在眉睫.乙炔与二氯乙烷耦合反应是将煤炭与石油资源共同利用来制备聚氯乙烯的一条极具吸引力的途径.相对于研究相对成熟的氢氯化反应,目前耦合反应的研究较少,所开发的催化剂活性与氢氯化体系相比仍有数量级的差距,反应机制仍存在较大争议.争议的焦点在于:二氯乙烷是通过先裂解产生氯化氢,后者再与乙炔发生氢氯化反应,还是二氯乙烷活化后直接与乙炔进行耦合反应.本文报道了一种通过结合预氧化-热裂解的新方法用于制备高活性、高稳定性氮化碳基催化剂,并且将其应用到二氯乙烷裂解反应中,获得较好的活性.表征结果表明,通过改变预氧化温度能够调控不同氮物种缺陷的分布,并发现较高的吡啶氮含量更有利于提高催化剂催化催化裂解反应的活性.进一步添加金属组分(金、铂和钌)修饰上述氮化碳催化剂构建了一系列M/C₃N₄/AC(M=Au,Pt,Ru)双金属催化剂.结合多种表征技术、稳态反应性能测试以及动力学研究发现,金属组分主要以氯化物的形式单原子分散在载体上,且金属的存在造成两种反应物分子在金属位点上的竞争吸附,因此催化剂在强化氢氯化反应的同时,也减弱了脱氯化氢反应性能,其催化耦合反应总体性能呈现如下趋势:Au/C₃N₄/AC>Pt/C₃N₄/AC>Ru/C₃N₄/AC.基于上述结论,通过装填C₃N₄/AC和单原子催化剂Au/C3N4/AC的串联反应器,实现了耦合反应的过程强化.综上可见,二氯乙烷脱氯化氢反应是乙炔与二氯乙烷耦合反应的必要步骤,未来催化剂的设计需要考虑到乙炔与二氯乙烷的活化需要不同的活性位点.     

Polymerization products of p-benzoquinone as thermal stabilizers for rigid poly(vinyl chloride). Part II—Evaluation of the stabilizing efficiency

Quinone-tin polymers prepared by the cationic polymerization of p-benzoquinone with tin(II)chloride in the absence of solvent have been investigated as thermal stabilizers for rigid PVC at 180°C in air by measuring the rate of dehydrochlorination. The results reveal the higher stabilizing efficiency of these products relative to dibutyltin maleate, basic lead carbonate and barium-cadmium stearate stabilizers commonly used in industry. The induction period in the early stages of the dehydrochlorination process increases as a function of the metal content in the stabilizer molecule. The evidence indicates that the quinone and the metal part (

) of the stabilizer participate in the stabilization process by trapping the radical intermediates, as well as blocking the odd electron sites formed on the PVC chains. The mechanism of stabilization suggested to account for the results obtained supports a radical mechanism for the dehydrochlorination reaction.