Electrical insulation properties of silicone rubber under accelerated corona and thermal aging

A contactless method based on energy shift of high-energy cut-off of the x-ray bremsstrahlung, the so-called Duane Hunt Limit and a conventional low voltage electrical technique (three-probes technique) is applied on thermal and corona aged silicone rubber (SiR) to measure, respectively, the surface potential, V_s, and the surface resistivity, ρ_s. The effect of aging on these quantities, representing the dielectric properties, is studied. The results are highly reproducible and highlight a good correlation between V_s and ρ_s. It was observed that thermal aging combined with electrical aging deteriorates more the electrical properties of the polymer than thermal aging alone. Explanations for electrical characteristics (V_s, ρ_s) change with aging are supported by attenuated total reflection Fourier transform infrared spectroscopy spectra analysis and a chemical mechanism of aging in three steps (i.e., oxidation-polycondensation, degradation, and thermal cracking). The surface degradation of the polymer is revealed by images of surface morphology obtained by using scanning electron microscopy (SEM). Roughness is greater for combined thermal and corona aging mode compared to thermal aging alone. In addition, the surface degradation of SiR polymer is confirmed by the loss of its hydrophobicity.     

Particular thermal properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) oligomers

Telechelic hydroxylated poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s (PHBV-diols) were synthesized by transesterification with ethylene glycol, which could be used as the macromonomers for synthesis of block copolymers. PHBV-diols owned particular thermal properties. PHBV-diols had much lower the melting temperatures (T _m s) and better thermal stability than original PHBV. With the decrease of molecular weight, T _m s of PHBV-diols decreased gradually and maximum degradation temperatures (T _max s) increased gradually. T _max -T _m of PHBV-diol could increase by 57.9 °C in comparison with original PHBV. It was meaningful that PHBV block in the block copolymers based on PHBV-diol owned the good thermal stability and low melting temperature of its precursor PHBV-diol, which widened greatly the melt-processing window of PHBV. In addition, thermal degradation kinetics was studied by Ozawa method, the integration method and Kissinger method. The results showed that the thermal degradation of original PHBV and PHBV-diols proceeded by at least two steps including a random degradation process and subsequent thermal degradation process due to the auto-accelerated degradation reaction.     

Thermal Degradation Kinetics of Ethylene-Vinyl Acetate Copolymer Containing Hydrotalcite and Red Phosphorus

The thermal degradation of flame-retarded ethylene-vinyl acetate copolymer (EVA) composites containing hydrotalcite (LDH) and red phosphorus (RP) are studied by thermogravimetric analysis. Four kinetics analysis models, i.e., the Kissinger method, the Flynn-Wall method, the Friedman method, and the Kissinger-Akahira-Sunose (KAS) method, are used to study the thermal degradation kinetics of the EVA/LDH composites. The apparent activation energy (E _a ) data calculated from the four methods are compared. The E _a results indicate that the addition of LDH and RP affects mainly the first thermal degradation stage of EVA.     

A study on thermal behavior of a poly(VDF‐CTFE) copolymers binder for high energy materials

This article describes a study on thermal behavior of poly(vinylidene fluoride‐chlorotrifluoroetheylene) [poly(VDF‐CTFE)] copolymers as polymeric binders of specific interest for high energy materials (HEMs) composites by thermal analytical techniques. The non‐isothermal thermogravimetry (TG) for poly (VDF‐CTFE) copolymers was recorded in air and N₂ atmospheres. The results of TG thermograms show that poly(VDF‐CTFE) copolymers get degrade at lower temperature when in air than in N₂ atmosphere. In the derivative curve, there was single maximum degradation peak (T_max) indicating one‐stage degradation of poly(VDF‐CTFE) copolymers for all the samples. The other thermal properties such as glass transition temperature (T_g) and degradation temperature (T_d) for poly(VDF‐CTFE) copolymers were measured by employing differential scanning calorimeter (DSC) technique. The kinetic parameters related to thermal degradation of poly(VDF‐CTFE) copolymers were investigated through non‐isothermal Kissinger kinetic method using DSC method. The activation energies for thermal degradation of poly(VDF‐CTFE) copolymers were found in a range of 218–278 kJ/mol. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal degradation of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) as studied by TG,TG–FTIR,and Py–GC/MS

The thermal degradation kinetics of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [poly(HB–HV)] under nitrogen was studied by thermogravimetry (TG). The results show that the thermal degradation temperatures (T_o, T_p, and T_f) increased with an increasing heating rate (B). Poly(HB–HV) was thermally more stable than PHB because its thermal degradation temperatures, T_o(0), T_p(0), and T_f(0)—determined by extrapolation to B = 0°C/min—increased by 13°C–15°C over those of PHB. The thermal degradation mechanism of PHB and poly(HB–HV) under nitrogen were investigated with TG–FTIR and Py–GC/MS. The results show that the degradation products of PHB are mainly propene, 2‐butenoic acid, propenyl‐2‐butenoate and butyric‐2‐butenoate; whereas, those of poly(HB–HV) are mainly propene, 2‐butenoic acid, 2‐pentenoic acid, propenyl‐2‐butenoate, propenyl‐2‐pentenoate, butyric‐2‐butenoate, pentanoic‐2‐pentenoate, and CO₂. The degradation is probably initiated from the chain scission of the ester linkage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1530–1536, 2003     

Kinetics of thermal degradation of nanometer calcium carbonate/linear low‐density polyethylene nanocomposites

To improve the thermal properties of linear low‐density polyethylene (LLDPE), the CaCO₃/LLDPE nanocomposites were prepared from nanometer calcium carbonate (nano‐CaCO₃) and LLDPE by melt‐blending method. A series of testing methods such as thermogravimetry analysis (TGA), differential thermogravimetry analysis, Kim‐Park method, and Flynn‐Wall‐Ozawa method were used to characterize the thermal property of CaCO₃/LLDPE nanocomposites. The results showed that the CaCO₃/LLDPE nanocomposites have only one‐stage thermal degradation process. The initial thermal degradation temperature T₀ increasing with nano‐CaDO₃ content, and stability of LLDPE change better. The thermal degradation activation energy (E_a) is different for different nano‐CaCO₃ content. When the mass fraction of nano‐CaCO₃ in nanocomposites is up to 10 wt %, the nanocomposite has the highest thermal degradation E_a, which is higher (28 kJ/mol) than pure LLDPE. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal Degradation Behavior and Kinetics of 3D Porous Polycarbonate Monoliths

The thermal degradation behavior and kinetics are important to understand the nature of polymers. In this work, the thermal degradation behavior and kinetics of polycarbonate (PC) monoliths with a three dimension (3D) continuous interconnected porous structure is investigated. Thermogravimetric analysis reveals that the thermal stability of the PC monoliths shows a significant reduction compared to pristine PC due to its 3D porous structure, which drastically increases the heating surface area during the thermal degradation process. An interesting second degradation stage at 480–550 °C is observed for PC monoliths from the barrier effect formed by the collapse and coalescence of the porous structure at high temperature, which is further confirmed by volatile and solid char analyses. The kinetic analysis suggests that the PC monolith shows a low degradation activation energy (E_α ) at the first degradation stage, which increases rapidly and goes beyond the E_α of pristine PC at the second degradation stage.     

Thermogravimetric analysis of chitosan

The thermal degradation of chitosan at different heating rates B in nitrogen was studied by thermogravimetric analysis. The results indicate that the thermal degradation of chitosan in nitrogen is a one‐step reaction. The degradation temperatures increase with B. Experimentally, the initial degradation temperature (T₀) is (1.049B + 326.8)°C; the temperature at the maximum degradation rate, that is, the peak temperature on a differential thermogravimetry curve (T_p), is (1.291B + 355.2)°C; and the final degradation temperature (T_f) is (1.505B + 369.7)°C. The degradation rates at T_p and T_f are not affected by B, and their average values are 50.17% and 72.16%, respectively, the maximum thermal degradation reaction rate, that is, the peak height on a differential thermogravimetry curve (R_p), increases with B. The relationship between B and R_p is R_p = (1.20B + 2.44)% min^?1. The thermal degradation kinetic parameters are calculated with the Ozawa–Flynn–Wall method. The reaction activation energy (E) and frequency factor (A) change with an increasing degree of decomposition, and the variable trends of the two kinetic parameters are similar. The values of E and A increase remarkably during the initial stage of the reaction, then keep relatively steady, and finally reach a peak during the last stage. The velocity constants of the thermal degradation vary with the degree of decomposition and increase with the reaction temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Thermal degradation of a phenolic resin,vegetable fibers,and derived composites

The thermal degradation behavior of resol, several vegetable fibers (two types of cotton fibers, sisal and sugar cane bagasse) and derived polymer composites have been investigated using thermogravimetric analysis (TGA). The initial thermal degradation temperature T_ONSET, the temperature at the maximum degradation rate TD_M, and the char left at 500°C corresponding to the crosslinked resol were higher than the values measured for the fibers and their composites. Thus, the addition of the fibers reduced the thermal resistance of the phenolic thermoset. The polymer and the fiber‐composites showed a complex degradation involving different thermal decomposition processes. For that reason, the DTG curves were deconvoluted and a phenomenological kinetic expression was found for each individual peak. The overall thermal decomposition curve was recalculated adding each degradation process weighted according to its contribution to the total weight loss. An increase in the activation energy corresponding to the cellulose degradation was observed in the composites, highlighting the protective action of the resin encapsulating the fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal degradation behavior and kinetics of porous polymer based on high functionality components

Two kinds of porous polymer were prepared based on high functionality components. Thermogravimetric analysis (TGA) is used to compare the thermal degradation behavior and kinetics of these two materials. The thermogravimetric tests of rigid polyurethane foam (H-RPUF) and polyurea aerogel (H-PUA) were carried out in nitrogen atmosphere at different heating rates. The thermal degradation characteristics of the porous polymer were obtained. The apparent activation energy (E_a) of thermal degradation of the porous polymer was investigated by model-free methods. The results showed that the thermal degradation temperature and ash content of H-RPUF were higher than those of H-PUA, and the volatile content was lower. With the rise of heating rate, thermal hysteresis effect of the two porous polymer was relatively high, while the release amount of volatiles was unchanged. For the Kissinger method, E_a of H-PUA and H-RPUF was 212.8 kJ mol⁻¹ and 157.4 kJ mol⁻¹, respectively. According to Starink method, the average activation energy of H-PUA and H-RPUF was 220.2 kJ mol⁻¹ and 107.2 kJ mol⁻¹, respectively. Obtained by Flynn-Wall-Ozawa model, the average activation energy of H-PUA and H-RPUF was 219.0 kJ mol⁻¹ and 111.5 kJ mol⁻¹, respectively. The data obtained from the three models all show that E_a of thermal degradation of H-PUA is higher than that of H-RPUF, and it is less likely to decompose.     

Thermal Stabilities and Thermal Degradation Kinetics of a Styrene-Butadiene-Styrene Star Block Copolymer

The thermal and thermo-oxidative degradation behaviors of styrene-butadiene-styrene (SBS) star block copolymer were reported using thermogravimetric analysis (TGA). TGA coupled with Fourier Transform Infrared spectroscopy was used to characterize the degradation volatile of SBS in air atmosphere. The thermal degradation kinetics of SBS in nitrogen and air atmospheres was studied in three steps: (1) the activation energies E _α were estimated by iterative method; (2) the proper form of f(α) was deduced by Popescu method; (3) the results obtained by above steps were used in determination pre-exponential factor A.     

Hydrogels based on N-isopropylacrylamide and methacrylic acid: thermal stability and glass transition behaviour

Summary The thermal stability and glass transition behaviour of crosslinked poly(N-isopropylacrylamide) [P(N-iPAAm)], poly(methacrylic acid) [P(MAA)], their random copolymers and sequential interpenetrating polymer networks (IPNs) have been investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). P(MAA) shows a two-step process of degradation. P(N-iPAAm) shows an unique process of degradation at higher temperature. Copolymers having higher content in N-iPAAm units have a lower thermal stability than their component homopolymers and show an unique degradation process at high temperature. On the contrary, enriched MAA copolymers show better stability but they exhibit two degradation steps at the main degradation region. Sequential IPN samples exhibit a better stability than their component homopolymers and copolymers. The high temperature backbone degradation occurs in only one step, which indicates the formation of a true interpenetrating network. The T _g of the same series of materials has been also measured. A T _g vs composition plot of P(N-iPAAm-co-MAA) copolymers presents a S-shaped curve indicating that structural units interact among them through strong specific interactions. For interpenetrating polymer networks, it seems that only one T _g occurs indicating a good compatibility and interpenetration. Received: 1 December 2001 /Revised version: 12 February 2002/ Accepted: 12 February 2002     

Thermal stability and compatibility of epoxy/polycarbonate and epoxy/tetramethyl polycarbonate blends

A series of the blends of tetrafunctional epoxy resins with polycarbonate (PC) or tetramethyl polycarbonate (TMPC) was prepared to investigate thermal stability and compatibility. The T_g behavior as a function of isothermal curing time was observed. The thermal stability of epoxy and epoxy/thermoplastics blends was estimated using thermogravimetric analysis (TGA). Fourier transform infrared (FTIR) investigation demonstrated the occurrence of thermal degradation and hydrolysis in epoxy and epoxy/PC blends during the curing process. The thermal degradation of cured epoxy was induced with etherification, a sort of side reaction, and resulted in the chain scission of networks leading to the decrease of T_g. The variance of thermal stability with a combination of two components in these blends resulted from the difference of the compatibility due to chemical structure similarity. The compatibility was corroborated with the morphology by scanning electron microscopy (SEM). © 1996 John Wiley & Sons, Inc.     

Thermal degradation of epoxy/silica composites monitored via dynamic mechanical thermal analysis

A dynamic mechanical thermal analyzer (DMTA) was used to monitor changes of dynamic mechanical properties during thermal degradation of two types of epoxy/silica composites, both of which are used as electrical insulation in power apparatus. It was found that the peak value of the dynamic loss factor (tan δ), glass transition temperature (T_g), and dynamic storage modulus (E′) above T_g changed considerably with increasing thermal degradation, while E′ at the glassy state only underwent a moderate change with increased thermal degradation. It is concluded that the DMTA technique is very sensitive to the structural changes in the investigated epoxy composites due to the thermal degradation. It is also confirmed by DMTA tests that further cross-linking and loss of dangling chains are occurring slowly during the stage prior to the onset of the severe degradation. © 1992 John Wiley & Sons, Inc.     

Study on the thermal degradation of epoxidized natural rubber

The thermal degradation and thermooxidative degradation of epoxidized natural rubber (ENR) were studied by thermogravimetry (TG). In the thermal degradation of ENR, the initial temperature of weight loss T₀ = 1.20B + 348, the temperature of maximum weight loss rate T_p = 1.07B + 392, and the final temperature of weight loss T_f = 0.77B + 445. The C_p, which corresponds to the degradation rate at temperature T_p, increases along with the heating rate B and its mean value is 43%, but C_f, which corresponds to the degradation rate at temperature T_f, is not affected by the heating rate, and its average value is close to 100%. As in the thermooxidative degradation, T₀ = 1.84B + 246, T_p = 0.30B + 378, and T_f = 2.27B + 584. The value of C_p increases along with the heating rate B and its mean value is 36%, but C_f is not affected by the heating rate and the average value approximately equals 100%. The thermal degradation in nitrogen could be a one-step reaction, whereas the thermooxidative degradation has a multiple-step reaction. The reactive environment has a great effect on the thermal degradation of ENR and the difference of the mechanisms of the two reaction systems is obvious. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2207–2211, 1998     

On the thermal degradation of poly(styrene sulfones). VII. Evaluations of poly(styrene sulfone) thermal stability using invariant kinetic parameters

The thermal degradation behavior of poly(styrene sulfone) was investigated by thermogravimetric analysis (TGA) measurement. This study described its thermal stability by applying the invariant kinetic parameter (IKP) method. The thermogravimetric and differential thermogravimetric analyses of different compositions of poly(styrene sulfones) were carried out over the temperature range 100–500°C under nitrogen. The kinetic parameters (preexponential factor and activation energy) of thermal decomposition of poly(styrene sulfone) can be obtained by dynamic measurement of TGA. The IKP method assumes that the kinetic parameters are independent of the experimental conditions. These parameters are computed without any hypothesis on the form of the kinetic degradation function. Invariant activation energies of the degradation of poly(styrene sulfone) show that the thermal stability decreases as the SO₂ content of poly(styrene sulfone) increases due to the thermal instability of the C? S bond. The relation equation, Ea_inv = 237.0 ? 290.5X_SO2, where X_SO2 is the molecular fraction of SO₂, was obtained to describe the effect of sulfur dioxide on the thermal stability of poly(styrene sulfone). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1698–1705, 2002     

Preparation and characterization of the copolymer containing N‐pyridyl bi(methacryl)imide unit

The copolymer of methacrylic acid anhydride and N‐2‐pyridyl bi(methacryl)imide was prepared based on the reaction of polymethacrylic acid with 2‐pyridylamine. The molecular structure was characterized by ¹H‐NMR, FTIR, UV–Vis, and circular dichroism techniques. The physical properties of polymethacrylic acid change significantly after an introduction of 6 mol % N‐2‐pyridyl bi(methacryl)imide unit. In particular, the thermal degradation of the polymer was systematically studied in flowing nitrogen and air from room temperature to 800°C by thermogravimetry at a constant heating rate of 10°C/min. In both atmospheres, a four‐stage degradation process of the copolymer of methacrylic acid anhydride and N‐2‐pyridyl bi(methacryl)imide was revealed. The initial thermal degradation temperature T_d, and the first, second, and third temperatures at the maximum weight‐loss rate T_dm1, T_dm2, and T_dm3 all decrease with decreasing sample size or changing testing atmosphere from nitrogen to air, but the fourth temperature at the maximum weight‐loss rate T_dm4 increases. The maximum weight‐loss rate, char yield at elevated temperature, four‐stage decomposition process, and three kinetic parameters of the thermal degradation were discussed in detail. It is suggested that the copolymer of methacrylic acid anhydride and N‐2‐pyridyl bi(methacryl)imide exhibits low thermal stability and multistage degradation characteristics. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1673–1678, 2002     

The effect of preparation methods on the thermal properties of poly(acrylic acid) / alumina composites

Poly(acrylic acid) - alumina composites have been prepared by two different methods and thermally characterized. The glass transition temperatures (T_g) of the PAA/Al₂O₃ systems prepared by mixture and polymerization method were found to be 126°C and 130°C, respectively, irrespective of the alumina amounts involved in this work. The composites prepared by mixture and polymerization method have been investigated by using thermogravimetry (TGA) to follow the kinetics of anhyride formation and thermal degradation reactions. The activation energy of thermal anhydride formation and thermal degradation reaction was not found to change very much with the ratio of PAA/Al₂O₃ when the composites were prepared by simple mixing. For the composites prepared by the polymerization method, the activation energy of anhyride formation and thermal degradation reaction were observed to change with percentage conversion.     

Chitosan and N‐carboxymethylchitosan: I. The role of N‐carboxymethylation of chitosan in the thermal stability and dynamic mechanical properties of its films

Chitosan (degree of deacetylation of 90.2%) and N‐carboxymethylchitosan (N‐CMCh) (degree of substitution of 18.5%) were analyzed using thermogravimetric analysis in order to determine their thermal stability. Also, their films were evaluated using scanning electron microscopy (SEM) and mechanical and dynamic mechanical analysis (DMA). Both polymers showed a thermal degradation peak at T_m ～ 250 °C, with T_onset and weight loss of 175 °C and 62% and 190 °C and 35% for chitosan and N‐CMCh, respectively. N‐CMCh showed a second thermal degradation peak at T_m = 600 °C, with an additional weight loss of 25%. Kinetic thermal analysis showed a slower process of degradation at 100 °C for N‐CMCh compared with chitosan, and an activation energy 13 times higher for the former, confirming the higher stability of N‐CMCh. Analysis of chitosan and N‐CMCh films showed that the latter support a high tension, with lower elasticity, and, as revealed by DMA, N‐CMCh has a more compact film structure, with a crossing arrangement of N‐CMCh fibers, as compared with the chitosan films which were determined from SEM analysis to have fibers in one direction only. Copyright © 2006 Society of Chemical Industry     

Kinetic analysis and modelling of thermal degradation of perspex (PMMA) and perspex blend plastic waste

The thermal decomposition of pure perspex and a mixture of 50% perspex and 50% poly(ethylene terephthalate; PET) was carried out between 295 and 325°C using a thermogravimetric analyser (TGA) in air and nitrogen (N₂) atmosphere. The weight losses of decomposition products were measured during these experiments. The thermal degradation process is slower in inert atmosphere than air, where oxidation reaction expedites the decomposition process. Kinetic rate constants (k), pre‐exponential factor (A) and activation energy (E) for both pure prespex and a blend of perspex/PET were calculated for both air and N₂ conditions. The thermal degradation process followed a third‐order reaction in air and second‐order in N₂. A second‐order (n = 2) model for the pyrolytic process based on simultaneous reactions was developed using experimental data for pure and blend. The pyrolytic products are gases, liquids, waxes, aromatics and char, which can be ultimately used as raw material and fuel in various applications. It is important to note that the addition of PET to perspex was found to suppress/inhibit the decomposition of perspex compared with pure perspex. Pre‐exponential factor (A) and activation energy (E) values support such an observation. © 2012 Canadian Society for Chemical Engineering