Pyrolysis gas-chromatographic studies of homopolymers and copolymers of chlorotrifluoroethylene with vinylidene fluoride and methyl methacrylate (original) (raw)
Journal of Macromolecular Science, Part B, 2019
Commercial fluororubber SKF 32, fluoroplastic F-32L, fluoroelastomer Kel-F, fluoroplastic FK 800 (labeled as SKF 32, F-32L, Kel-F and FK 800) and an in-house prepared poly(vinylidene fluoride-chlorotrifluoroethylene) (FKM) copolymer were investigated in terms of their thermal degradation kinetics, reaction models and corresponding thermodynamic parameters. All samples underwent a single step thermal degradation using thermogravimetric analysis (TGA) at different heating rates under nitrogen atmosphere. The kinetic parameters were determined through the Kissinger method and three isoconversional methods; viz. the Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Starink. The activation energies of the SKF 32, F-32L, Kel-F, FK 800 and FKM obtained using the Kissinger method were 206, 200, 185, 221 and 243 kJ mol-1 , respectively. The activation energy values for the degradation obtained using the KAS method were: 180-225 kJ mol À1 for SKF 32, 192-209 kJ mol À1 for F-32L, 163-185 kJ mol À1 for Kel-F, 213-227 kJ mol À1 for FK 800 and 187-269 kJ mol À1 for FKM with the extents of conversion (a) ¼ 0.1-0.9. These values of the activation energies obtained from the KAS method were in good agreement with those obtained using the FWO and Starink methods. In addition, the appropriate degradation reaction models were determined by means of the Coats-Redfern and Criado methods. The thermodynamic parameters, such as activation Gibb free energy, DG Ã , activation enthalpy, DH Ã , and activation entropy, DS Ã , for formation of the activated complexes during the thermal degradation were also determined and discussed. The positive values of the E a , DG Ã , DH Ã , and DS Ã for SKF 32, F-32L, FK 800 and FKM indicated a non-spontaneous process, while the positive values of the E a , DG Ã and DH Ã , and negative value of DS Ã for Kel-F meant that the formation of the activated complex was accompanied by a smaller decrease of entropy than for the other polymers.
Polymer Degradation and Stability, 2003
Three series of linear aromatic copolyimides containing hexafluoro isopropylidine moieties (i.e., 6F) were synthesized by reacting 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) with various mole percents of (a) 1,3-phenylene diamine (mPDA) and 2,6-diamino toluene (DAT) (b) mPDA and 2,4,6-trimethyl-l,3-phenylene diamine (TMemPDA) and (c) DAT and TMemPDA in N-methyl-2-pyrrolidone (NMP). These copolyimides were characterized by inherent viscosity, GPC, DSC, XRD, and TGA. T g increased with increase in TMemPDA content in [6FDA+TMemPDA+mPDA] and [6FDA+TMemPDA+DAT] copolyimides and increase in DAT content in [6FDA+mPDA+DAT] copolyimide series. All the copolyimides were found to be amorphous. Activation energy was determined for the thermal degradation of these copolyimides using the Coats-Redfern equation and was found to follow first-order kinetics in air and nitrogen. CO 2 was the main decomposition product in air and CHF 3 in nitrogen atmosphere.
Pyrolytic degradation of common polymers present in packaging materials
Journal of Thermal Analysis and Calorimetry, 2019
Pyrolysis of polymers with widespread use, such as PET, HDPE, PVC, LDPE, PP and PS, been utilized extensively as plastic packaging materials, is the subject of this study. Low biodegradability and short life of polymers used in packaging have resulted in enormous waste amounts; thus, polymer recycling is more than imperative for modern, developed municipalities. One of the main problems is the production of either feedstock or valuable secondary materials, without additional environmental burden. In this context, the thermochemical methods lead not only to recycling of plastics but also to the creation of specific petrochemical industrial products, and the profit will be considerable. Pyrolizer accompanied by a GC/MS is a useful instrumental array for the study of the thermal degradation of several types of polymers. It is resulted that the cracking temperature affects the type and number of the segments produced, since higher temperatures strongly parcel the polymer chain to monomers and release smaller molecules, while at lower temperatures it is more likely to detect oligomers. Chromatographic results were sometimes complicated due to the isomers produced during pyrolysis. It is mainly supposed that polyolefins decompose through a radical process, where depolymerization propagates until H-abstraction occurs. PVC behaves differently due to the presence of halogens, fond to chain reactions, while for PS the main fragments eluted are styrene monomer, dimmer and trimmer. From PET analysis, it is concluded that the products of decomposition include CO 2 , PhCOOH, PhCOOCH = H 2 and other aromatic vinyl-substitutes, while PET depolymerization is keen on CaO catalysis for lower decomposition temperatures.
Gas-phase decomposition of 1-trifluoromethoxy-1,1,2,2-tetrafluoro-2-iodoethane
Journal of Analytical and Applied Pyrolysis, 1988
The gas-phase decomposition of l-trifluoromethoxy-l,1,2,2-tetrafluoro-2-iodoethane induced by hot-wall pyrolysis, continuous-wave CO, laser-photosensitized (SF,) pyrolysis and UV photolysis leads to the same variety of products. The pattern of fragmentation suggested for all the processes involved a sequence of C-I and CO bond cleavages and rearrangement of the CF,OCF,CF; radical into a CF,CF; radical and carbonyl fluoride. The rearrangement was confirmed by mass spectral fragmentation.
Structural Chemistry, 2018
Pyrohydrolysis, oxygen bomb combustion, and alkaline carbonate fusion are the most frequently used methods for decomposition of fluorine containing materials. The efficiency of these methods was proven by the determination of fluorine content in certified reference materials of clay and vegetation. Possible reactions proceeding during decomposition were suggested and accompanying thermochemistry discussed. The Gibbs energies were estimated to establish if suggested reactions are thermodynamically favorable or not. In addition, linear relationships between the enthalpies of formation of metal fluorides and the balanced values of the enthalpies of formation of the plausible reaction products (metal tungstates, metal oxides, or metal carbonates), electronegativity of metals, and number of fluorine atoms in metal fluorides were established. These equations were suggested for the estimation of the enthalpies of formation of metal tungstates, metal oxides, or metal carbonates, for which experimental data are not available.
Korean Journal of Chemical Engineering, 2021
During catalytic pyrolysis of HFC-134a over γ-alumina, the formation of HF and coke causes catalyst deactivation. Catalyst deactivation and product selectivity depend on the contact time during catalytic pyrolysis of HFC-134a as reported in this paper. γ-Alumina calcined at 650 oC was used as the catalyst due to its higher quantity of acidic sites and larger surface area, which are crucial for catalytic pyrolysis. X-ray diffraction (XRD), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS), and thermogravimetric analysis (TGA) of the catalysts were performed to determine the influence of contact time and flow rate of HFC-134a. 2 mL/min of HFC-134a balanced with nitrogen to 25, 50, 100, and 200 mL/min total flow rates was studied at 600 °C. 200 mL/min showed a 9.4 h catalyst lifetime with a small number of by-products. Shorter contact time between HFC-134a and HF with the catalyst was found to be the key to the longer lifetime of the catalyst. The catalyst lif...
…, 2005
Solubilities of N2, CO2, C1-C3 saturated hydrocarbons, C1-C3 saturated fluorocarbons, and normal-and cyclo-C5 and -C6 alkanes at 35°C are reported in an amorphous, rubbery, random copolymer composed of 50.7 mol % tetrafluoroethylene and 49.3 mol % perfluoromethyl vinyl ether, TFE/ PMVE49. Permeabilities of N 2, O2, CO2, and C1-C3 saturated hydrocarbons in this polymer at 35°C are also presented. Solubilities of hydrocarbon vapors in this fluoropolymer are lower than those of their corresponding fluorocarbon analogues due to less favorable interactions of the fluorinated polymer with hydrocarbon vapors than with fluorocarbon penetrants. Polymer density was measured over a wide temperature and pressure range to estimate parameters for equation-of-state modeling of gas sorption. Modeling the sorption isotherms with the Sanchez-Lacombe equation-of-state model requires a reduction of approximately 10% in the cohesive energy density of the gas-polymer mixture from that predicted by the geometric mean mixing rule for all hydrocarbon penetrants other than CH 4. Sorption of CH4 and fluorocarbon penetrants is well described with little or no variation in the geometric mean rule estimate of interaction energy. While linear correlations between the natural logarithm of hydrocarbon gas solubility and penetrant critical temperature in hydrocarbon polymers often have slope values of about 0.019 K -1 at 35°C, this fluoropolymer has a much lower slope value, 0.011 K -1 . Hydrocarbon/nitrogen permeability selectivity is much lower in TFE/PMVE49 than in hydrocarbon-based rubbery polymers such as poly-(dimethylsiloxane). This effect is, to a very large extent, a result of hydrocarbon solubility suppression in the fluoropolymer, due to less favorable hydrocarbon-fluorocarbon interactions. terms of the gas boiling point, modified using the Guldberg-Guye rule 18 relating boiling and critical tem- † University of Texas at Austin.
Mechanistic study of the reaction of CHF3 with CH4
Chemical Engineering Journal, 2011
Gas phase reaction of CHF 3 with CH 4 , and the effect of additives such as CBrF 3 and CH 3 OH on the reaction, have been investigated in the temperature range of 800-1100 K. The major products detected include CH 2 CF 2 and C 2 F 4 under all conditions studied. The presence of small amounts of CBrF 3 and CH 3 OH enhances the conversion of CH 4 and rate of formation of CH 2 CF 2 significantly, while concomitantly the rate of formation of C 2 F4 decreases. The experiments were modeled against a comprehensive reaction mechanism involving 90 species and 790 reactions. Based on the experimental observations and reaction modeling, the crucial steps influencing the conversion of CHF 3 and CH 4 , the formation of major and minor products and the promoting effects of CBrF 3 and CH 3 OH are fully elucidated. For comparative purposes, the reaction of CHClF 2 with CH 4 under similar conditions is also studied and the results are consistent with the reaction mechanism developed and discussed. (E.M. Kennedy).