超临界甲苯降解聚苯乙烯反应动力学模型

引言 聚苯乙烯是一种性能优良、应用广泛的通用塑料,且可降解回收苯乙烯单体,因此废聚苯乙烯的回收利用受到广泛关注.但聚苯乙烯热降解高温熔融时黏度很大,造成温度分布不均和局部过热,容易发生二次反应并导致结炭,同时降低了苯乙烯单体收率,因此近年来发展了各种热解技术以抑制结炭、提高苯乙烯收率.超临界降解技术利用超临界流体优异的扩散性能和溶解性能,具有加快聚苯乙烯降解速率,提高反应转化率,抑制结炭等优点[1-4].     

Kinetic analysis of the thermal degradation of PVC plastisols

The thermal degradation of plasticized polyvinyl chloride (plastisol) is reported here. Plastisols used in the present work were prepared with the plasticizer diethylhexyl phthalate in different proportions. Thermogravimetric analysis has been applied to study the behavior of plastisols at high temperatures and to evaluate their degradation kinetics. Several tests were carried out at different heating rates and the variation of the degree of reaction with time and temperature was calculated. The influence of the heating rate in dynamic measurements (5–40°C/min) on kinetic parameters, such as activation energies and reaction orders, has also been studied. These parameters were calculated from dynamic thermogravimetric analysis tests using Friedman analysis and a kinetic model for the degradation of poly(vinyl chloride) and plastisols has been then developed. The obtained model was able to simulate the thermal degradation process of plastisols in dynamic conditions and was used to evaluate the effects of additives in the degradation. The results of this study can be used to optimize the concentration of plasticizers and stabilizers in poly(vinyl chloride) formulations. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1069–1079, 1999     

Phase behavior and kinetics of polystyrene degradation in supercritical toluene

The phase behavior of polystyrene (PS) degradation in toluene was investigated in a visual high‐pressure reactor. The system of PS and toluene was heated from room temperature and atmospheric pressure to 350°C and 5.0 MPa. It was observed that during this process, PS dissolved quickly, and then, the system appeared to be a homogeneous phase, and PS degradation occurred in this system. With another high‐pressure batch reactor, PS degradation was studied in the temperature range 275–360°C and the pressure ranges 4.5–10.5 MPa. The drop‐in molecular weights in the temperature ranges and the amount of PS converted into volatile products were observed. Moreover, the effects of the temperature, pressure, and ratio of toluene to PS on the rate of PS degradation are discussed. The kinetic studies showed that the rate of PS degradation in supercritical toluene increased substantially because the degradation occurred in a homogeneous phase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

热降解明胶的研究

报道了明胶热降解反应,并考察了明胶质量分数、降解时间、降解温度、明胶溶液pH值等因素对明胶热降解反应的影响规律。结果表明:热催化是明胶降解的有效方法,较合适的降解条件为明胶质量分数10%,体系pH值7.00,降解温度121℃,降解时间2 h。     

阻燃热塑性聚酯弹性体的热降解动力学研究

采用阻燃剂与单体共聚合成阻燃共聚热塑性聚酯弹性体(FR-TPEE),对FR-TPEE进行热失重分析,并采用Kissinger法,Flynn-Wall-Ozawa法和Coats-Redfern法对FR-TPEE热降解动力学进行研究。结果表明:FR-TPEE热降解过程分3个阶段,Kissinger法计算其活化能偏小,Flynn-Wall-Ozawa法和Coats-Redfern方法不适用于处理FR-TPEE热降解第三阶段。Coats-Redfern方法得知FR-TPEE第一阶段的降解机理是相界面控制反应机理,第二阶段是一维扩散机理。     

Effects of the pH,concentration, and solvents on the ultrasonic degradation of poly(vinyl alcohol)

The ultrasonic degradation of poly(vinyl alcohol) was investigated at different pHs of the solvent, in different water/solvent binary mixtures, and at different polymer concentrations. The samples were analyzed with gel permeation chromatography. The degradation rate coefficients were determined with a continuous distribution model. A higher degradation rate was obtained at pH extremes, in better solvents, and at lower polymer concentrations. The results are explained and discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4888–4892, 2006     

Kinetic study of the decompositions involved in the thermal degradation of commercial azodicarbonamide

The transitions and reactions involved in the thermal treatment of several commercial azodicarbonamides (ADC) in an inert atmosphere have been studied by dynamic thermogravimetry analysis (TGA), mass spectrometry and Fourier transform infrared (FTIR) spectroscopy. A pseudo‐mechanistic model, involving several competitive and non‐competitive reactions, has been suggested and applied to the correlation of the weight loss data. The model applied is capable of accurately representing the different processes involved, and can be of great interest in the understanding and quantification of such phenomena, including the simulation of the instantaneous amount of gases evolved in a foaming process. In addition, a brief discussion on the methodology related to the mathematical modeling of TGA data is presented, taking into account the complex thermal behaviour of the ADC. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

间规聚苯乙烯热性能研究

对间规聚苯乙烯（sPS）的热性能（包括熔点、晶型及热稳定性等）进行了差示扫描量热、热重分析和动态力学性能等的测量和分析，发现sPS中存在着不同的晶型，它理想晶体的热力学临界分子量熔点为270．13℃，sPS在静态和动态时间的使用温度可达250℃，说明sPS具有良好的热性能。研究结果有助于sPS的进一步加工和应用。     

高性能超高分子量聚乙烯的热降解及抗氧剂的应用

综述了在干法纺丝工艺中,高性能超高分子量聚乙烯热降解的原理、影响因素以及防止高性能超高分子量聚乙烯发生热降解的方法。主要介绍了应用于高性能超高分子量聚乙烯热降解的抗氧剂种类及作用原理。     

The influence of carbon nanotubes, organically modified montmorillonites and layered double hydroxides on the thermal degradation and fire retardancy of polyethylene, ethylene-vinyl acetate copolymer and polystyrene

Nanocomposites of polyethylene, ethylene-vinyl acetate copolymer and polystyrene with single- and multi-wall carbon nanotubes, organically modified montmorillonites and layered double hydroxides were prepared by melt blending. Their morphologies were assessed by X-ray diffraction and transmission electron microscopy, while the flammability properties were evaluated by thermogravimetric analysis and cone calorimetry. The relative amounts and the identity of the degradation products are changed when both well-dispersed cationic and anionic clays are used, but there is no difference in the degradation products when carbon nanotubes were utilized. When the nano-dimensional material is not well-dispersed, the degradation products are not changed. Unlike their smectite counterparts, polymer/layered double hydroxide nanocomposites give reasonably good reductions in peak heat release even when good nano-dispersion has not been obtained. These data suggest that the enhancement in the fire behavior must be, at least in part, due to different mechanisms for montmorillonite, layered double hydroxides and carbon nanotube-based nanocomposites.     

Modeling of poly(L‐lactide) thermal degradation: Theoretical prediction of molecular weight and polydispersity index

A mathematical model to describe the molecular weight and polydispersity index (Q) in poly(L ‐lactide) (PLLA) thermal degradation has been developed. Based on the random chain scission mechanism, effects of temperature and time on the molecular weight and polydispersity index are included in this model. It incorporates the degradation and recombination reaction of PLLA thermal degradation, while taking into account the equal probability assumption. The developments of molecular weight and polydispersity index of PLLA polymer in the thermal degradation process were investigated at temperature ranging from 180–220°C, the experimental data show PLLA reaches its thermal degradation equilibrium in 2 h. The simulated results of this model are compared with the measured molecular weight and polydispersity index of the PLLA polymer. The changes of the molecular weight and polydispersity index in the PLLA thermal degradation can be predicted by this model. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2557–2562, 2003     

两性纤维素接枝共聚物CGAD热降解行为的研究

本文用热失重分析法研究了两性纤维素接枝共聚物CGAD的热分解特征，用三种不同方法进行实验得到了热降解反应的动力学参数，取得了比较—致的结果，时对接枝共聚物的热降解机理进行了初步探讨。     

Kinetic modeling of polypropylene thermal oxidation during its processing by rotational molding

The main drawback of rotational molding is a long stay (several dozens of minutes) of polymer in melt state at high temperature in atmospheric air. To prevent any significant polymer thermal degradation, it is necessary to define, preliminary, a processing window in a temperature‐molar mass map. The objective of this article is to elaborate and check the validity of a general thermal degradation model devoted to determine, in a near future, some important boundaries of this processing window. This model is composed of two distinct levels: (i) The first level is derived from the thermal transfer mechanisms occurring during a processing operation, polymer phase changes (i.e., melting and crystallization) being simulated by the enthalpy method; and (ii) The second level is derived from the oxidation mechanistic scheme of free additive polymer in melt state established in a previous study, but completed, here, by adding the main stabilization reactions of a common synergistic blend of antioxidants, widely used for rotational molding polymer grades. By juxtaposing such “thermal” and “chemical” levels, it is possible to predict the polymer thermal degradation during a whole processing operation. The validity of both levels is successfully checked in real rotational molding conditions for polypropylene (PP). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci 000: 000–000, 2010     

Mechanism studies on the catalytic degradation of waste polystyrene into styrene in the presence of metal powders

In the present article, the effects of Al, Zn, Fe, Ni, and Cu powders on the thermal degradation of waste polystyrene were studied. The results show that the catalytic effects of metal powders have a relationship with their activities. The catalytic effects increase with the increasing activities of metals. It is suggested that polystyrene degrades through a transient intermediate in the presence of metal powders, and the degradation of the transient intermediate is the rate-determining step. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1139–1143, 1999     

Effect of melamine polyphosphate on thermal degradation of polyamides: a combined X-ray diffraction and solid-state NMR study

The effect of melamine polyphosphate (MpolyP) on the thermal degradation of both polyamide 66 (PA66) and polyamide 6 (PA6) was studied using a combination of solid-state techniques. The mixtures of MpolyP with polyamides were heated for different times at 350 and 450 °C. The residues were then analyzed by X-ray diffraction and both solid-state ¹³C NMR and ³¹P NMR. The chemical structures formed in these oven experiments were used to study the chemical changes that take place during a standard flammability test. The mixtures of MpolyP with polyamides were also characterized by frequency-dependent rheological experiments. It was shown that MpolyP could induce significant cross-linking in PA66 and leads to dramatic depolymerization of PA6. These results were used to explain the performance of MpolyP as a flame retardant in these polyamides.     

Kinetic parameters of thermal degradation of polyethylene glycol‐toughened novolac‐type phenolic resin

The miscibility and thermal degradation of poly(ethylene glycol) (PEG)‐toughened novolac‐type phenolic resin were investigated. Differential scanning calorimetry (DSC) results confirmed that the phenolic resin/PEG blend was blended completely. Infrared spectra show that hydrogen bonding existed in the blends. Thermal degradation of PEG blended with novolac‐type phenolic resin was studied utilizing a dynamic thermogravimetric technique in a flowing nitrogen atmosphere at several heating rates (i.e., 5, 10, 20, 40°C/min). Thermal degradation of phenolic resin/PEG blends takes place in multiple steps. The thermal behavior and the thermal stability affected the thermal degradation, which coincided with the data from the thermal degradation of novolac‐type phenolic resin/PEG blends by thermogravimetric analysis (TGA). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 188–196, 2001     

Effects of different molecular weights of polystyrene on the acylation reaction and on the reaction kinetics

In this study, chemical modification reactions of polystyrenes with different molecular weights with maleic and acetic anhydrides in the presence of a catalyst [BF₃ · O(C₂H₅)₂] were examined. The number of polyfunctional groups bound to the polymer structure changed according to the molecular weight of the polymer, and more functional groups were bound to lower molecular weight polystyrenes. The bound functional groups and their amounts were determined with spectral and chemical analysis methods. The effects of the molecular weights of the polystyrenes on the chemical modification kinetics with maleic and acetic anhydrides in the presence of BF₃ · O(C₂H₅)₂ were examined. The kinetic parameters of the reaction and its activation energy were calculated. The higher the molecular weight of polystyrene was, the lower its rate of modification was and the greater its activation energy was; the lower the molecular weight of polystyrene was, the higher its rate of modification was and the lower its activation energy was. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 253–259, 2005