Effect of metal stearate stabilizers on the thermal degradation of PVC in solution: The reversible blocking mechanism of stabilization

Systematic thermal degradation studies of PVC solutions have been carried out in the presence of different metal carboxylates (Pb-, Cd-, Ba-, Ca- and Zn- stearates). ZnSt₂ markedly accelerates degradation of the polymer. Significant induction periods (t_i) for the appearance of free HCI are obtained in the presence of the other salts. CaSt₂ acts mainly as an HCI-scavenger and has no direct influence on the elimination process. Mainly short polyenes are formed during the induction period when PbSt₂, CdSt₂, and BaSt₂ are used. After consumption of stabilizers rapid HCI loss occurs, and suddenly longer polyenes are formed, i.e., the amount of double bonds and the average length of polyenes sharply increases. At the same time, the rate of initiation (i.e., the rate of the polyene sequence formation) does not change at all around t_i. None of the investigated stabilizers retard effectively the random initiation of HCI loss. In the presence of PbSt₂, BaSt₂, and CaSt₂, and CaSt₂, the initiation rate is nearly identical to that of the unstabilized PVC. The concentration of labile sites (h₀) in PVC at the end of the induction period has been estimated by kinetic analysis. It has been found that in some cases h₀ is higher than the concentration of labile structures in the virgin PVC. These results indicate that the main role of metal soap stabilizers is the blocking of the fast zip-elimination of HCI from the PVC chain. It is likely that blocking occurs by attachment of a carboxylate group at the end of a propagating zip. This is a reversible process: the blocked structures become active again mainly after the consumption of stabilizers presumably by HCI-catalyzed hydrolysis. In contrast to other stabilization mechanisms by Frye and Horst, Minsker and coworkers, and Michell the reversible blocking mechanism of PVC stabilization is able to explain the experimental findings presented in this study. It also explains such facts of practical importance as color stability of the resin during the induction period and fast blackening after the consumption of stabilizers.     

Thermal degradation of PVC in the presence of polystyrene

The thermal degradation of poly(vinyl chloride) (PVC) and blends of PVC with polystyrene has been studied using thermogravimetric analysis coupled to Fourier transform infrared spectroscopy. The degradation of PVC commences at weak links by an ionic pathway, but there is evidence to suggest the presence of a radical pathway at high temperatures. While there is some chemical interaction between PVC and polystyrene, the principal mode of stabilization is a physical process.     

复合金属皂热稳定剂对聚氯乙烯热稳定性的影响

用X射线(XRD)、差示扫描量热法(DSC)、红外光谱法(IR)、紫外光谱法和热重量分析法(TGA)分析了金属皂复合稳定剂4180,研究了在加工过程中稳定剂的组成结构变化,发现了金属皂的螯合型结构的存在,讨论了金属皂的稳定机理,提出了金属皂热稳定剂的复配原则。     

Adsorbed metal ions as stabilizers for the thermal degradation of polyacrylamide

The thermal degradation of polyacrylamide has been studied in the presence of various metal ions using thermogravimetry. The thermal decomposition of the polymer in general occurs at higher temperatures in the presence of metal ions than with the pure polymer. Empirical measures of the stabilizing effect of the metal ions have been made by determining the temperatures of 12% and 50% decomposition, and the integral procedural decomposition temperature (IPDT). For main group metal ions, the stabilizing effect, as measured by the difference in ipdt between polymer-metal complex and copolymer, was inversely proportional to the radius of the metal ion, suggesting that the strength of the complex between the ion and polymer is important in determining stability. Transition metal ions, in contrast, showed no simple dependence of stabilizing effect on ionic radius, but showed, instead, a dependence upon the ligand field stabilization energy.     

硬脂酸盐热稳定剂对CPE脱氯化氢热降解性的影响

采用刚果红法研究硬脂酸盐热稳定剂对氯化聚乙烯(CPE)脱氯化氢热降解性的影响。结果表明，随着硬脂酸盐用量增大，CPE的脱氯化氢温度呈升高趋势，脱氯化氢初始时间呈延长趋势；采用硬脂酸铅和硬脂酸钡的CPE脱氯化氛温度较高，脱氯化氢初始时间较长；硬脂酸铅／硬脂酸钡、硬脂酸铅／硬脂酸钙和硬脂酸钙／硬脂酸钡并用比分别为1：1，2：1和1：3时，CPE的脱氯化氢温度较高，并用比分别为3：1，2：1和1：1时，CPE的脱氯化氢初始时间较长。     

新型稀土热稳定剂的制备及其对PVC热降解反应动力学性能的研究

针对PVC加工过程中热稳定性差的问题,成功合成了一种新型稀土热稳定剂N-十六烷基马来酰胺酸根合镧(Ⅲ)。通过傅里叶红外光谱(FTIR)、元素分析、熔点等表征了其结构与性能;同时利用刚果红实验、紫外-可见光谱(UV-Vis)、热重(TGA)对聚氯乙烯(PVC)的热稳定作用进行了研究。     

新型稀土热稳定剂的制备及其对PVC热降解反应动力学性能的研究

针对PVC加工过程中热稳定性差的问题,成功合成了一种新型稀土热稳定剂N-十六烷基马来酰胺酸根合镧(Ⅲ)。通过傅里叶红外光谱(FTIR)、元素分析、熔点等表征了其结构与性能;同时利用刚果红实验、紫外-可见光谱(UV-Vis)、热重(TGA)对聚氯乙烯(PVC)的热稳定作用进行了研究。     

PVC加工用热稳定剂概述

介绍了铅盐类、金属皂类、有机锡类、稀土类、复合类及一些辅助PVC加工用热稳定剂的品种、性能及应用情况。铅盐稳定剂的热稳定作用较强,具有良好的介电性能,且价格低廉,与润滑剂配合使用可使PVC塑料的加工温度变宽,加工及后加工的产品质量稳定,但铅盐有毒,不能用于接触食品的制品,也不能制得透明制品。金属皂类稳定剂配合使用,可显示协同效应,大幅度提高效勇。有机锡类稳定剂是最佳的聚氯乙烯热稳定剂,具有优异的热稳定性和耐光、耐候性,而硫且不吸水,适用于透明制品,但价格较高,无自润滑性,有不适气味。同时还指出多种稳定剂复合使用、采用自然资源和化学改性是PVC稳定剂的发展方向。     

含磷阻燃共聚酯热氧化降解过程分析

研究了一种含磷阻燃共聚酯在空气条件下的热氧化降解过程 ,得出了该种阻燃共聚酯的热氧化降解规律 ,为阻燃共聚酯的后加工工艺条件的选择提供了重要依据     

Thermooxidative degradation of natural rubber/clay composite

The clay is treated with a reducing agent and an acid so as to obtain a clay containing various metal components with a variable‐valence state. Then, the clay is coprecipitated with natural rubber (NR) latex to prepare a vulcanized NR/clay composite. The degradation process of the NR/clay composite under hot air condition was studied dynamically by using a Fourier transform infrared spectrometer attaching an in situ sample cell and was also investigated using the TGA method. The test result obtained from the infrared spectrometry indicated that under low decomposition temperature, the decomposition products of the test samples mainly are ethylene, low molecular olefinic hydrocarbon, and carbonyl compounds. As the decomposition temperature rises, the low molecular olefinic hydrocarbon content decreases, the olefine with longer chain is formed, and a lot of alkane decomposition products are formed at the same time. When the content of the metal components with a variable‐valence state in clay such as Cu, Mn, Co, and Fe increases, the oxidation products containing the carbonyl group, the olefinic hydrocarbon, and CO₂ in the decomposition product of the test sample also increase. The TGA result clearly shows a shoulder peak that appears by the side of the main peak on the DTG curve of NR/clay composite. With the increase in the content of metal components with variable‐valence state in clay, the initial degradation temperature of the test sample (T₀), the degradation peak temperature (T_p1), and the final degradation temperature (T_f1) in first‐stage reaction, as well as the degradation peak temperature (T_p2) and the last final degradation temperature (T_f) in second‐stage reaction of all the test samples more or less shift to the direction of low temperature; besides, the activation energy (E) of the reaction of the test samples more or less decreases. This means that the metal components with variable‐valence state promote the oxidative degradation of the clay–rubber masterbatch. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3809–3815, 2006     

有机锡稳定封在PVC加工中的应用

考察了有机锡稳定剂F-50的用量对试样热稳定性能的影响。结果表明：F-50用量达到0．8份时,稳定效果达到最佳;再增加其用量,稳定效果无明显提高。     

Study on the degradation of low‐density polyethylene in the presence of cobalt stearate and benzil

Degradable polymers are in great demand for a variety of applications such as packaging, agriculture, and medicine. Polyolefins blended with photodegradants/biodegradants are potential candidates for replacing the nondegradable thermoplastics in areas where litter abatement poses problems. In the present article, the effect of metallic photoinitiators like cobalt stearate and a combination of metallic/nonmetallic photoinitiators, i.e., a mixture of cobalt stearate and benzil, on the photooxidative degradation of low‐density polyethylene (LDPE) films have been investigated. Attempts have been made to correlate the results as a function of mixed additives. Films of LDPE containing varying amounts of cobalt stearate and a combination of benzil and cobalt stearate were prepared. The photodegradation of these films has been monitored by various techniques like FTIR spectroscopy, differential thermal analysis, and density and viscosity measurements. Cobalt stearate was highly effective in accelerating the photodegradation of LDPE films at low concentrations. The addition of benzil to cobalt stearate decreased the rate of photodegradation compared to cobalt stearate alone. A retarding effect was observed when benzil alone was added to LDPE. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 236–243, 2006     

水滑石类热稳定剂在PVC型材中的应用

介绍了水滑石类热稳定剂的基本情况,通过对比试验研究了水滑石类热稳定剂与铅盐类热稳定剂的热稳定性能及在PVC型材中的应用效果,并对试验结果进行了思考与讨论,建议改进水滑石类热稳定剂。     

Protection of styrene-butadiene copolymer film with bound synergistic stabilizers against ferric stearate — catalysed photo-oxidative degradation at elevated temperature

The thermal and photo-oxidative stability at 90°C against 365 nm light in air of commercial styrene-butadiene copolymer (SBR) film in the absence and presence of ferric stearate as an oxidation accelerator was compared with that of SBR in which a synergistic mixture of an antioxidant 3,5-di-t-butyl-4-hydroxybenzylmercaptan (BHBM) in combination with a stabilizer, 1,1,5-triphenyl-2-s-(3′,5′-di-t-butyl-4′-hydroxy) benzyl-iso-4-thiobiuret (PBHBT) bounded with the polymer. The chain-scission and crosslinking reactions were followed by measurement of molecular weight, degree of degradation, gel fraction, elongation-to-break, density, hydroperoxide, carbonyl and hydroxyl groups contents. The newly developed metal-deactivator and photostabilizer PBHBT, has been found to possess a very high efficiency in SBR. It is also shown that the bound PBHBT in combination with BHBM results in improved physical, mechanical and chemical properties of SBR even in the presence of ferric stearate.     

Mechanism of action of PVC thermal stabilizers

Based on experimental data, changes of properties of plasticized PVC containing stearates of Ca, Zn, Cd, and Pb stabilizers during thermal degradation are discussed. The mechanism of action of these stabilizers is described in kinetic form.     

有机锡和金属皂类热稳定剂并用对软质PVC脱HCl反应的影响

采用刚果红法研究了有机锡和金属皂类热稳定剂的并用对软质PVC脱HCl反应的影响。在实验过程中,硬脂酸钡(BaSt2)、硬脂酸钙(CaSt2)、硬脂酸锌(ZnSt2)分别单独、两两和三者混合后与双丁基硫醇锡并用。重点讨论了金属皂用量对软质PVC刚果红初始变色时间和完全变色时间以及初始变色温度的影响。实验结果表明,单独使用时,BaSt2与有机锡的并用效果最好,能产生明显的协同效应;在两两混合与有机锡并用的过程中,BaSt2/CaSt2的并用效果最好,它们与有机锡也能产生较明显的协同作用;而在3种金属皂与有机锡并用后,软质PVC的脱HCl过程不但没有被抑制,反而被加速。     

硬脂酸稀土和硬脂酸钙对PVC热稳定特性的比较研究

为有助于加深对稀土热稳定剂的认识,尝试以CaSt2为参照,并以LaSt3为代表,比较研究了硬脂酸稀土对PVC的热稳定特性,并探讨了有关的原理。结果表明:(1)硬脂酸稀土的热稳定特性与CaSt2相似;(2)LaSt3/ZnSt2和环氧大豆油(ESO)的并用效果与CaSt2/ZnSt2相当,但与季戊四醇(PET)和二苯甲酰甲烷(DBM)的并用效果与CaSt2/ZnSt2相比略有逊色;(3)LaSt3/ZnSt2和PET、DBM的并用效果不如CaSt2/ZnSt2的原因可能在于,与Ca2 相比,La3 能更强烈地与Zn2 竞争和PET和DBM形成配合物,从而使后两者的作用更不能得到充分发挥。