Kinetic and chemical studies of polymer cross-linking using thermal gravimetry and hyphenated methods. Degradation of polyvinylchloride

The chemistry and kinetics of polyvinylchloride (PVC) degradation have been studied using thermal gravimetry and hyphenated spectroscopic methods to identify condensed phase and vapour phase products. A method of kinetic modelling has been devised to estimate Arrhenius parameters for the sequential and competing processes which comprise the thermal decomposition, and to plot concentrations of decomposition intermediates which make up the TG curve. MS and GC-MS have been used to relate the composition of volatile materials to the TG curve and FTIR has related this to changes in the condensed phase. The chemical studies have highlighted a char forming mechanism based on hydrogen disproportionation which results in carbon enrichment and the formation of aliphatic hydrocarbons.     

PVC／PE交联共混体系的动态力学研究

在ＰＶＣ／ＰＥ共混体系中加入交联剂和引发剂能产生ＰＶＣ－ＣＯ－ＰＥ共聚物，这种共聚物在共混物中可起到增容剂的作用。通过动态力学分析和扫描电镜研究了ＰＶＣ／ＰＥ交联共混体系的相容性。发现引发剂、交联剂、稳定剂和增塑剂等对共混物中的交联反应均有较大的影响。     

Phase separation kinetics in mixtures of polymers and liquid crystals

Light scattering has been used to study phase separation kinetics in mixtures containing liquid crystals and epoxy resins. In the samples studied, phase separation was induced by the polymerization of the resins with an appropriate curing agent. Experiments were carried out at different compositions and at different temperatures. The results show that the kinetic mechanism of phase separation is composition dependent. For high liquid crystal content the data are in qualitative agreement with existing theories describing spinodal decomposition; at lower concentrations the mechanism is different. The physical properties of the resulting materials are independent of the decomposition mechanism. The data have also been analysed considering the scaling behaviour expected for late stages of phase separation in polyinduced meric mixtures. Samples obtained in a narrow concentration range, where the two kinetic mechanisms overlap, exhibit peculiar physical properties.     

The main elementary events of degradation and stabilization of PVC

The fundamental aspects of PVC degradation and stabilization are discussed. The primary process of thermal degradation (initiation, zip-elimination of HCl and simultaneous formation of polyene sequences, and termination of unzipping) is reevaluated in the light of results obtained with PVCs containing increased concentrations of labile chlorines. The effect of these defects on thermooxidative stability of the resin is also discussed. It has been shown that results obtained in recent systematic stabilization studies cannot be explained by the widely accepted Frye-Horst mechanism, i.e., substitution of labile chlorines by stabilizers. A new mechanistic proposition, the reversible blocking mechanism, for the stabilization of PVC is presented, and the effect of stabilizing reactions on the main elementary events of thermal and thermooxidative degradation is described in a unified manner.     

Etude de la compatibilite des systemes binaires constitues par le polychlorure de vinyle et polyacetate de vinyle—IV: L'influence de la masse moleculaire sur la compatibilite du systeme PVC/PV AC

Using kinetic thermogravimetry and phase-contrast microscopy, a study has been made on the influence of molecular weight upon compatibility in the solid state for the system PVC/PVAc. For the extreme mixtures 80 PVC/20 PVAc and 20 PVC/80 PVAc, completely different behaviour is shown; the thermal stability of the former is much greater and that of the latter much less than would be expected on the basis additivity. From the results for the various systems, an attempt is made to classify mixtures of solid polymers.     

A chemiluminescence and fluorescence spectroscopy study: An investigation of photocrosslinking processes in polymer systems

Chemiluminescence emission is shown to be a valuable method for the analysis and monitoring of the photochemical transformation process in BZMA-co-S copolymers. BZMA-co-S copolymer films are synthesized and irradiated at λ > 400 nm, in order to induce the phototransformation of benzyl (BZ) to benzoyl peroxide (BP) pendant groups, resulting in thermal decomposition and crosslinking. The chemiluminescence emission increases with irradiation time, and is shown to be related to the benzoyl peroxide moieties generated during irradiation. The increase in chemiluminescence intensity is interrupted at longer periods of irradiation, when the concentration of these species tends to a nearly constant value. In this case, others factors are considered to influence the chemiluminescence emission, for example the increasing crosslinking on irradiated samples, which would restrict the mobility of radicals to recombine due to crosslinking of the network.A good correlation between fluorescence, FTIR and CL measurements during photochemical formation and thermal decomposition of peroxides is found. In this work, an intramolecular excimer forming fluorescent probe, DiPyM, is also used to analyse the crosslinking process. The results obtained contribute significantly to the development of chemiluminescence as a highly sensitive methodology for assessing the photocrosslinking of a polymeric material in the early stages of the process and is due to its sensitivity in comparison to that of fluorescence analysis.     

可反应性纳米二氧化硅填充聚氯乙烯树脂在空气中的热分解行为

利用热重分析和差热重量分析(TG/DTG)技术研究了可反应性纳米二氧化硅填充聚氯乙烯(PVC/n-SiO2)树脂在空气气氛中的热分解行为,利用Ozawa-Flynn-Wall (OFW)方程和Friedman方程对其热分解进行了动力学分析.结果表明,可反应性纳米SiO2对PVC树脂热分解的第一阶段影响比较明显,当纳米S...     

Hydrophilic magnetic polymer latexes. 2. Encapsulation of adsorbed iron oxide nanoparticles

The encapsulation of seed polymer particles coated by anionic iron oxide nanoparticles has been investigated using N-isopropylacrylamide as a main monomer, N,N-methylene bisacrylamide as a crosslinking agent, itaconic acid as a functional monomer and potassium persulfate as an anionic initiator. The magnetic latexes obtained have been characterized with regard to particle size, iron oxide content and electrophoretic mobility. All these properties have been examined by varying several polymerization parameters: reaction medium, monomer(s) and crosslinking agent concentrations, nature of seed latexes and type of polymerization (batch versus shot process). The magnetic content in the polymer microspheres strongly depends on the polymerization procedure (i.e., encapsulation process) and varies between 6 and 23 wt%, and monodisperse magnetic polymer particles were obtained. Received: 28 December 1999 Accepted in revised form: 15 June 1999     

A thermal decomposition study of polymers by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry

The thermal decomposition of polymers (poly(vinyl chloride) (PVC) and polystyrene (PS)) has been studied with synchrotron VUV photoionization mass spectrometry at low pressure. Pyrolysis products formed at different temperatures have been identified by the measurement of photoionization mass spectra at different photon energies. The experimental results demonstrate the variation of the pyrolysis product pool of PVC at different temperatures, dividing the thermal decomposition process into two stages: the low‐temperature stage to form HCl and benzene, and the high‐temperature stage to form numerous large aromatic hydrocarbons. For the thermal decomposition of PS, four reaction categories are determined. This work reports a new application of synchrotron VUV photoionization mass spectrometry in the study of the thermal decomposition of polymers, and demonstrates its good performance in product analysis, which is expected to help understand the thermal decomposition mechanism of PVC, PS and other synthesized polymers. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermogravimetric analysis of PVC/ELNR blends

The thermal behaviour of a series of solution-cast blends of polyvinyl chloride/epoxidised liquid natural rubber (ELNR) of different mole percentage of epoxidation has been examined using thermogravimetric analysis. Thermal degradation is found to occur through a two-step route in which the first step corresponds to the dehydrochlorination of PVC to form a polyene and the second step is attributed to the decomposition of the ELNR and the polyene. Introduction of 20 and 50 mol% of epoxy group into the liquid NR is found to enhance the thermal stability of PVC. Probable mechanisms of degradation have been suggested on the basis of the kinetic analysis of the degradation studies. It is found that the mechanism is influenced by the epoxy content of the blend system. Activation energy for the degradation and the entropy change have also been reported.     

Physico-mechanical properties of GAMMA induced polymer modified mortar

The effect of a radiation initiated polymer on the physico-mechanical properties of polymer incorporated mortar has been investigated. The monomer used was methylmethacrylate with divinylbenzene as a crosslinking agent, used at concentrations ranging from 2 to 10% of methylmethacrylate and polymerization was carried out using γ-radiation from 5 to 25 kGy. The influence on polymer loading, compressive strength, water absorption, apparent porosity and bulk density, in addition to thermal behaviour (as investigated by DTA) of polymer incorporated in mortar, were studied. The results indicate that the polymer loading, compressive strength and bulk density increase with increases in percentage of divinylbenzene as well as with the γ-radiation doses, whereas the water absorption and apparent porosity of the specimens decrease. This behaviour is attributed to the amount of polymer deposited in the pores of the samples.     

Studies of decomposition of a foaming agent in PVC plastisols

The preparation of foamed products from paste PVC is an area of great commercial importance. In this work, the decomposition of a blowing agent, azodicarbonamide (ADA), in PVC plastisols has been studied using primarily differential scanning calorimetry (DSC) and thermomechanical analyses (TMA). Some results obtained by thermogravimetric analyses (TGA) and thermosonimetry (TS) are also reported. The results show that DSC and TMA can give very valuable information about the foaming process in PVC plastisols.     

Eu_2(p-ClC_6H_4COO)_6(C_(12)H_8N_2)_2配合物热分解机理及非等温动力学

0 IntroductionThe complexes formed by rare earth and aromatic carboxylic acid have many special structuresand interesting luminous properties, thus arouse people's interest to study them. They can be used.in many areas such as extraction and separation, germicide, catalyst, luminous materials andfunctional materials and so on.The crystal structure and luminescence spectra of the europium p-chlorobenzoate complex withl, 10-phenanthroline has been reported"], but the study for its non-isothermal…     

Prediction of thermal stability of fresh and aged parchment

The hyphenated thermal analysis-mass spectrometry technique (TA-MS) was applied for the investigation of the thermal behavior of reference and aged parchment samples. The kinetic parameters of the process were calculated independently from all recorded TA and MS signals. The kinetic analysis showed the distinct dependence of the activation energy on the reaction progress. Such behavior is characteristic for the multistage mechanism of the reaction. The comparison of the kinetic parameters calculated from the different signals i.e. TG, DSC, MS for H₂O, NO and CO₂, however, indicated that they were differently dependent on the aging of the sample. For the parchment samples, the aging almost does not change the kinetics of the decomposition calculated from the DSC data: the influence of aging seems to be too negligible to be detected by these techniques. On the other hand, the much more sensitive mass spectrometric technique applied to the kinetic analysis allowed monitoring of visible changes in the thermal behavior of the parchment samples due to the aging process. The influence of aging was especially visible when the MS signals of water and nitric oxide were applied for the determination of the kinetic parameters. The applied method of the kinetic analysis allowed also the prediction of the thermal behaviour of reference and aged parchment samples under isothermal and modulated temperature conditions. Presented results have confirmed the usefulness of thermoanalytical methods for investigating behaviour of such complicated systems as leather or parchment.     

Study of the early deactivation in pyrolysis of polymers in the presence of catalysts

In this work, the early degradation step of the pyrolysis of some polymers in the presence of certain catalysts has been studied using thermogravimetric analysis (TGA). Three commercial polymers (PE, PP and EVA) and three catalysts were studied (ZSM-5, MCM-41a, and MCM-41b), and the MCM-41a catalyst has been selected for the analysis of the earlier steps of the pyrolysis process carried out in the presence of catalysts. Several cycles of heating–cooling were performed using a thermobalance, in order to analyze the influence of the first stages of decomposition on the activity of the more accessible active sites involved. In this way, the behaviour of the polymer–catalyst mixtures (20% (w/w) of catalyst) was studied and compared with that observed in the corresponding thermal degradation as well as in the pyrolysis in the presence of catalysts, in a single heating cycle.The results obtained clearly show the existence of an early degradation step. For a polymer–catalyst system with low steric hindrances such as PE-MCM-41, this early degradation step causes a noticeable decrease of the catalyst activity for the main decomposition step (i.e., cracking of the chain). The decrease of the catalytic activity is lower for a polymer–catalyst system with higher steric restrictions, as occurs in the EVA-MCM-41 degradation process. However, in this case, the catalyst activity in the first decomposition step (i.e., the loss of the acetoxi groups) is noticeable decreased after one pyrolysis run, thus reflecting that the active sites involved are mainly the most accessible ones.     

Phase behaviour of poly(vinyl methyl ether)-cross-polystyrene semi-interpenetrating networks

Semi-interpenetrating polymer networks of varying composition are prepared by crosslinking polystyrene containing a small number of maleic anhydride groups (4.8 mol% of MA units) with hexamethylene-diamine (HMDA) in the presence of linear poly(vinyl methyl ether) (PVME). Lightly crosslinked samples are homogeneous at room temperature and show a phase behaviour similar to uncrosslinked blends, i.e. lower critical solution temperature (LCST) behaviour. The influence of crosslinking on the phase behaviour has been studied by small angle light scattering (SALS) and turbidity measurements. The cloud point strongly depends on the heating rate. The presence of the network reduces the stable single phase region in agreement to theory. In systems showing spinodal decomposition, it is expected that some concentration fluctuations will grow more rapidly than others resulting in a separated phase system which shows high degree of connectivity with characteristic dimensions. Using temperature jump experiments, SALS can be used to estimate parameters of the phase separation kinetics and the characteristic dimensions of the phases. In temperature jump experiments into the spinodal region a maximum in the scattered light intensity is observed with time at a certain scattering vector. However, the semi-IPN's develop no scattering maximum. This is explained by a damping of the thermodynamical dominant wavelength in spinodal decomposition in the network.     

Mechanism of poly(vinyl chloride) stabilization by mixtures of zinc and calcium carboxylates with various complexing agents

Investigations were made on the effects of zinc and calcium carboxylates, polyols and other oxygen-containing compounds, nitrogen- and sulphur-containing compounds and of mixtures of zinc calcium carboxylates, zinc carboxylates-complexing agent, calcium carboxylate-complexing agent and of zinc carboxylate-calcium carboxylate-complexing agent upon the rate of dehydrochlorination and crosslinking and on the absorption spectrum of PVC during degradation in vacuum at 180°. The interaction of the stabilizers with 2-chlorobutane (a model for normal units of PVC) was studied at 180°. It was shown that, in the thermal degradation of PVC, zinc carboxylates give synergistic mixtures with compounds having -OH, -SH or -NH groups. In the thermal degradation of PVC in the presence of mixtures of zinc carboxylates with polyols, there are exchanges between chloro-containing groups of PVC and carboxylic groups of salt and alcohol residue. Zinc salts also catalyze the interaction of polyols with double (particularly conjugated double) bonds of degraded PVC. The investigated compounds do not form synergistic mixtures with calcium carboxylates. The triple mixtures of zinc and calcium carboxylates with complexing agents are more effective stabilizers of PVC than the binary mixtures zinc carboxylate-calcium carboxylate and zinc carboxylate-complexing agent. The mechanism of synergistic interaction in PVC stabilization by these mixtures are discussed.     

Polycarbonate Resins: Synthesis and Thermogravimetric Analysis

Resins from diphenols with an aromatic ring as side group, phosgene, and a triphenol as crosslinking agent were synthesized under phase transfer conditions. The resins obtained with a phase transfer catalyst showed higher thermal stability than those obtained without catalyst. The function of the catalyst is to transport triphenol from the aqueous phase to the organic phase. The thermal stability of the resins was related to the structure and the content of triphenol. It was found that resins derived from diphenol I exhibited higher thermal stability as the content of triphenol increased. On the other hand, when diphenol II was used, the thermal stability decreased as the content of triphenol increased, due to steric hindrance of the methyl group on the side ring. Also, a resin from the triphenol alone was synthesized in the same conditions. The kinetic parameters of the decomposition process were determined for all resins.     

Mechanisms and kinetics of thermal decomposition of plastics from isothermal and dynamic measurements

The kinetics of decomposition of plastics are of interest from different points of view, i.e. evolution of harmful substances during fires or waste incineration, recovering of chemical raw materials from plastic refuses and designing of recycling procedures. To measure the formal kinetic parameters of the degradation of polymers isothermal and dynamic methods are applied in this work. Dynamic measurements are performed by combined thermogravimetry mass spectrometry (TG-MS), the isothermal measurements are carried out with a new closed loop-type reactor. To evaluate consistent kinetic data from isothermal and dynamic measurements, the energy balance for the sample in dynamic measurements has to be considered to obtain the true sample temperature and heating rate. Subject of this investigation is the exploitation of dynamic and isothermal methods for measuring and interpreting the kinetics of thermal decomposition of plastics. Results for commodity plastics polyethylene and poly(vinyl chloride) (PVC) are presented. The combined application of TG–MS, isothermal experiments in the closed loop-type reactor and DSC leads to new results for the decomposition kinetics of PVC. The dehydrochlorination mechanism at moderate temperature can be distinguished in an endothermal and exothermal part. The benzene formation is identified as a second order reaction. A great advantage of the isothermal method is, that changes in the mechanisms are detectable, i.e. changes in the apparent order of the reaction and the apparent activation energy. From that, new mechanistic aspects of the decomposition kinetics of polyethylene were obtained.     

Study on thermal behavior of thermooxidized poly(vinyl formal)

The thermal behavior of thermooxidized poly(vinyl formal) has been investigated by means of thermogravimetry, derivative thermogravimetry, and differential thermal analysis. As a result, it has been clarified (1) that thermal decomposition is composed of three weight loss processes, (2) that, when investigating the ratic of percentage of weight remaining in each process, the behavior differs for each both before and after the thermooxidizing time of 2–4 h; the second weight loss process caused by formation of crosslinking structure prevails in the initial stage of thermooxidation while the first weight loss process caused by decomposition of various types of thermooxidation products such as unsaturated bonds and crosslinking prevails as the thermooxidation proceeds, and (3) that the volume of carbonaceous residue produced as the thermooxidation advances increases about 4 times. When kinetic parameters have been evaluated by applying the Coasts and Redfern method to each weight loss process, on the other hand, it is concluded (1) that each order of reaction is first and (2) that the value of activation energy in the third process of carbonization and burning reaction is substantially lowered as the process of the thermooxidation advances.