Effect of cupric ion on thermal degradation of chitosan

The thermal degradation of chitosan and chitosan–cupric ion compounds in nitrogen was studied by thermogravimetry analysis and differential thermal analysis (DTA) in the temperature range 30–600°C. The effect of cupric ion on the thermal degradation behaviors of chitosan was discussed. Fourier transform-infrared (FTIR) and X-ray diffractogram (XRD) analysis were utilized to determine the micro-structure of chitosan–cupric ion compounds. The results show that FTIR absorbance bands of  N H,  C N ,  C O C etc. groups of chitosan are shifted, and XRD peaks of chitosan located at 11.3, 17.8, and 22.8° are gradually absent with increasing weight fraction of cupric ion mixed in chitosan, which show that there are coordinating bonds between chitosan and cupric ion. The results of thermal analysis indicate that the thermal degradation of chitosan and chitosan–cupric ion compounds in nitrogen is a two-stage reaction. The first stage is the deacetylation of the main chain and the cleavage of glycosidic linkages of chitosan, and the second stage is the thermal destruction of pyranose ring of chitosan and the decomposition of residual carbon, in which both are exothermic. The effect of cupric ion on the thermal degradation of chitosan is significant. In the thermal degradation of chitosan–cupric ion compounds, the temperature of initial weight loss (T_st), the temperature of maximal weight loss rate (T_max), that is, the peak temperature on the DTG curve, and the peak temperature (T_p) on the DTA curve decrease, and the reaction activation energy (E_a) varies with increasing weight fraction of cupric ion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

壳聚糖季铵盐铜配合物的热降解行为研究

采用热重分析(TG)研究壳聚糖季铵盐铜配合物在30℃～600℃的温度范围内的热降解行为,探讨壳聚糖季铵盐铜配合物的热稳定性。研究结果表明:壳聚糖季铵盐铜配合物的热降解为一步反应,取代度对壳聚糖季铵盐的热降解有明显的影响,壳聚糖季铵盐铜配合物的特征降解温度都随取代度的增加而降低。     

Synthesis,characterization, and curing behavior of carborane‐containing benzoxazine resins with excellent thermal and thermo‐oxidative stability

Two benzoxazine precursors bearing carborane moiety ( 1 and 2 ) were designed and synthesized successfully by the Mannich reaction of corresponding carborane bisphenol ( 3 and 4 ) with aniline and formaldehyde in 1,4‐dioxane. The obtained precursors were characterized by using multiple spectroscopic techniques including GPC, FTIR, ¹H NMR, ¹³C NMR, and ¹¹B NMR. Nonisothermal DSC studies showed that precursor 1 owned lower apparent activation energies (E_a) than 2 . The optimum curing processes of benzoxazine precursors were also obtained on the basis of DSC data. TGA analyses manifested that the incorporation of carborane moiety endowed the obtained benzoxazine resins (cured 1 and 2 ) with excellent thermal stability and unique thermo‐oxidative stability. The T_d data showed that the initial degradation of both cured 1 and 2 under nitrogen and air was postponed to some extent owing to the shielding effect of carborane moiety on adjacent organic fragments. At higher temperature three‐dimensional polymer networks with B‐O‐B and B–C linkages were formed as chars by the reaction of carborane cage with atmospheric moisture, degradation products such as phenolic hydroxyl, and oxygen (under air). Under nitrogen this network hindered the motion of radicals formed at elevated temperature and thus inhibited further polymer degradation processes. While under air, the formed boron‐rich networks could hardly be further oxidized into carbon dioxide so that the carborane‐containing benzoxazine resins also showed very high char yields. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43488.     

Synthesis and thermal cure of diphenyl ethers terminated with acetylene and phenylacetylene

Two kinds of novel compounds, diphenylacetylene diphenyl ether (DPADPE) and diacetylene diphenyl ether (DADPE), were prepared and polymerized under heating. Raman, DSC and ¹³C CP/MAS NMR analyses were used for studying the polymerization reaction. DPADPE and DADPE have melting points at 190 and 79 °C, with exothermic peaks of the DSC curves at 375 and 215 °C for curing, respectively. Raman and ¹³C CP/MAS NMR spectra show that DPADPE could be cured at a temperature higher than 300 °C and DADPE at a lower temperature of higher than 150 °C. The kinetic parameters for the thermal crosslinking reactions were obtained by the Ozawa method and the results show that the apparent activation energy is 152 kJ mol^?1 for DPADPE and 109 kJ mol^?1 for DADPE. An ene–yne Straus product appears in the cured DADPE, whereas this product has not been identified in the cured DPADPE. The cured DPADPE and DADPE demonstrate good thermal and thermo‐oxidative stability. Copyright © 2006 Society of Chemical Industry     

Kinetics of isothermal and non‐isothermal degradation of cellulose: model‐based and model‐free methods

BACKGROUND: The kinetics of the thermal decomposition of cellulosic materials is of interest from the viewpoint of flame retardancy for safety, optimization of incineration processes and reducing energy production from fossil sources and associated pollution. One essential step in these processes is the thermal degradation through mass and energy transport, which determines the rate of evolution of various types of products from cellulosic materials. RESULTS: Kinetic parameters have been determined using various model‐based and model‐free methods in the thermal degradation of cellulose up to 700 °C in helium atmosphere. The values of the activation energy obtained in isothermal processes and non‐isothermal processes have been found to be not far from each other. From the integral method, the random nucleation (F₁)‐type mechanism has been found most probable for cellulose degradation having an activation energy, E_a, in the range 156.5–166.5 kJ mol^?1, lnA = 20–23 min^?1, for first‐order reaction during its decomposition process at heating rates of 2, 5 and 10 °C min^?1. Based on the high correlation coefficient, many types of mechanisms seem equally good for non‐isothermal degradation of cellulose. CONCLUSION: The linear correlation coefficient has a limitation for verifying the correctness of a reaction mechanism in the study of degradation kinetics. Therefore, the correctness of a mechanism should be considered on the basis of comparing the kinetic parameters obtained from isothermal as well as non‐isothermal methods. Copyright © 2008 Society of Chemical Industry     

Thermal stability and kinetics analysis of rubber‐modified epoxy resin by high‐resolution thermogravimetric analysis

A dynamic heating rate mode of high‐resolution thermogravimetric analysis was used to study the thermal and thermal‐oxidative stability, as well as kinetics analyses, of a model liquid rubber‐modified epoxy resin, Ep/CTBN, made up of bisphenol A diglycidyl ether‐based epoxy and carboxyl‐terminated butadiene acrylonitrile rubber (CTBN). Results show that the thermal degradation of Ep/CTBN resin in nitrogen and air consists of two and three independent steps, respectively. Moreover, Ep/CTBN has a higher initial degradation temperature and higher activation energy than those of pure epoxy resin in both gases, indicating that the addition of CTBN to epoxy can improve the thermal and thermal‐oxidative stability of pristine epoxy resin. Kinetic parameters such as activation energy, reaction order, and preexponential factor of each degradation step of both Ep/CTBN and pure epoxy resins in air and nitrogen were calculated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3594–3600, 2003     

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     

New fluorescent monomers and polymers displaying an intramolecular proton‐transfer mechanism in the electronically excited state. III. Thermogravimetric stability study of the benzazolylvinylene derivatives

Six fluorescent benzazolylvinylene derivatives were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and related molecular parameters. The thermal stability was determined in terms of the steps of degradation and its fitting parameters, such as maximum degradation rate (R_max), maximum degradation rate temperature (T_Rmax), degradation temperature range, which is related to the half‐width at half‐height values (Γ), and the kinetic parameters: activation energy (E_a), pre‐exponential factor (A), and reaction order (n) obtained by Barrett's method. Different organic substitutes and heteroatoms do not play a fundamental role in the thermal behavior of the studied dyes. The compensation effect between pre‐exponential factor and activation energy was confirmed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 495–500, 2006     

Kinetic studies of the thermal degradation of cellulose acetate/niobium and chitosan/niobium composites

Composites based on cellulose acetate/niobium and chitosan/niobium have been obtained by a new synthetic hydrothermal route with different amounts of Nb₂O₅ (0.0%; 3.7%; 5.8%; 6.7% and 10.9%, incorporated on cellulose acetate fibers and 0.0%; 3.0%; 9.3% and 13.9%, attached on chitosan surface). Thermodecomposition studies were carried on 30–800 °C range at rate of 10 °C min⁻¹. Kinetic parameters like activation energy, pre-exponential factor, Gibbs energy, enthalpy and entropy of activation were determined by using Coats–Redfern equation. The activation energy (E) of degradation presented a decreasing with the incorporation of niobium on cellulose acetate, whereas all kinetic parameters maintained constant with the incorporation of niobium, for chitosan what resulted in a more stable that hybrid chitosan/Nb₂O₅ composites.     

Thermal degradation kinetics of rigid polyurethane foams blown with water

The thermal decomposition behavior of rigid polyurethane foams blown with water was studied by dynamic thermogravimetric analysis (TGA) in both nitrogen and air atmosphere at several heating rates ranging from room temperature to 800°C. The kinetic parameters, such as activation energy (E), degradation order (n), and pre‐exponential factor (A) were calculated by three single heating rate techniques of Friedman, Chang, and Coats–Redfern, respectively. Compared with the decomposition process in nitrogen, the decomposition of foams in air exhibits two distinct weight loss stages. The decomposition in nitrogen has the same mechanism as the first stage weight loss in air, but the second decomposition stage in air appears to be dominated by the thermo‐oxidative degradation. The heating rates have insignificant effect on the kinetic parameters except that the kinetic parameters at 5°C/min have higher values in nitrogen and lower values in air, indicating different degradation kinetics in nitrogen and air. The kinetic parameters of foam samples blown with different water level in formulation decline firstly and then increase when water level increases from 3.0 to 7.0 pph. According to the prediction for lifetime and half‐life time of foams, water‐blown rigid foams have excellent thermostability, when used as insulation materials below 100°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4149–4156, 2006     

Isoconversional and thermal methods of kinetic analysis of 2,4‐dihydroxybenzophenone copolymer resin

A copolymer (2,4‐DHBPOF) synthesized by the condensation of 2,4‐dihydroxybenzophenone and oxamide with formaldehyde in the presence of acid catalyst with varying the molar proportions of the reacting monomer. Composition of the copolymer has been determined by elemental analysis. The copolymer has been characterized by UV–visible, FTIR, and ¹H NMR spectroscopy. The morphology of synthesized copolymer was studied by scanning electron microscopy (SEM). The activation energy (E_a) and thermal stability calculated by using Sharp‐Wentworth, Freeman–Carroll, and Freidman's method. Thermogravimetric analysis (TGA) data were analyzed to estimate the characteristic thermal parameters. Freeman–Carroll and Sharp Wentworth methods have been used to calculate activation energy and thermal stability. The activation energy (E_a) calculated by using the Sharp‐Wentworth has been found to be in good agreement with that calculated by Freeman–Carroll method. Thermodynamic parameters such as free energy change (ΔF), entropy change (ΔS), apparent entropy change (S*), and frequency factor (Z) have also been evaluated based on the data of Freeman–Carroll method. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal behavior of poly(dimethyl itaconate) and poly(di‐n‐butyl itaconate) copolymerized with methyl methacrylate

The thermal degradation behavior of random copolymers of dimethyl itaconate and di‐n‐butyl itaconate with methyl methacrylate was studied. The thennal stability of copolymers depends on the structure of the di‐n‐alkyl itaconate comonomer, and on the copolymer composition. The relative thermal stability increases with the methyl methacrylate copolymer molar fraction, following a trend similar to the glass transition temperature variation. The activation energy was obtained by using MacCallum and Tanner's approach. In addition, the thermal degradation of homopolymers was evaluated in inert atmosphere as well as in thermo‐oxidative conditions, presenting different behaviors.     

Synthesis,characterization, and properties of silylene–acetylene preceramic polymers

A series of silylene–acetylene preceramic polymers 3a–e were synthesized by polycondensation reaction of dilithioacetylene with dichlorosilane (H₂SiCl₂) or/and methyldichlorosilane (MeSiHCl₂). Their structures were confirmed by infrared spectra (IR), and ¹H and ²⁹Si NMR spectroscopies. Differential scanning calorimetry (DSC) diagrams show exotherms centered at 200 to 233°C temperature range, attributed to crosslinking reaction of the acetylene and Si? H groups. After thermal treatment, the obtained thermosets 4a–e possess excellent thermal stability. Thermogravimetric analysis (TGA) under nitrogen show the T_d5s (temperature of 5% weight loss) for all the thermosets are above 600°C, and the overall char yields are between 95.62% and 89.67% at 900°C. After pyrolysis at 1200°C, the obtained ceramic residues 5a–e exhibit good thermo‐oxidative stability with final weight retention between 98.76% and 91.66% at 900°C under air. In particular, perhydroploy(silylene)ethynylene 3a , which has the highest Si/C ratio in silylene–acetylene polymers, has the highest char yield, and the derived ceramic material 5a displays the best thermo‐oxidative stability. Based on Scanning electron microscopy and its associated energy‐dispersive X‐ray microanalysis (SEM EDX) and ¹³C magic angle spinning nuclear magnetic resonance (MAS NMR) analysis, ceramic 5a contains the highest SiC content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

MnSt2–kaolin–polyethylene film: An eco‐friendly polyethylene composite film and its thermo‐ and biodegradable research

A novel thermo‐ and biodegradable MnSt₂–kaolin–polyethylene (signed as MKPE) composite film was prepared through a melt blending technique. Manganese stearate and common kaolin were employed as thermo‐degradable additives and biodegradable promoter to improve the degradable efficiency of the waste PE. Thermo‐oxidative testing was carried out in an air oven maintained at 70°C simulating a compost temperature. The biodegradation of the aging films was also investigated by analysis of evolved carbon dioxide of films in aquatic test systems according to the International Standards ISO 14852 (1999). The composite film was characterized by electronic universal testing machine, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, attenuated total reflection‐flourier transformed infrared spectroscopy and thermo gravimetric analysis. These results showed that the MKPE film exhibited a high degree of susceptibility to thermo‐oxidation and biodegradation. After thermal aging for 30 days, the mechanical properties of MKPE films reduced quickly and oxygen groups were introduced into the polymer chains. The kaolin particles wrapped in polymers were exposed gradually because of the rupture of polymer chains by thermal aging. The biodegradation degree reached 24.26% after incubation in an aqueous medium for 60 days. A possible mechanism for thermal oxidative degradation and biodegradation was also discussed. POLYM. COMPOS., 36:939–945, 2015. © 2014 Society of Plastics Engineers     

Kinetic analysis of thermo‐oxidative degradation of PEEK/thermotropic liquid crystalline polymer blends

The thermal degradation behavior of blends of poly(aryl ether ether ketone), PEEK, with a thermotropic liquid crystalline polymer (TLCP), Vectra®, were investigated in an oxidative atmosphere, using thermogravimetric analysis under dynamic conditions. The theoretical weight loss curves of the blends were compared with the experimental curves in order to explain the effect of blending on the thermal stability of the pure polymers. The thermo‐oxidative degradation of PEEK/Vectra® blends of different compositions takes place in various steps and the characteristic degradation temperatures and the kinetic parameters such as activation energy are strongly influenced by blending. Polymer blends based on this TLCP polymer had not been previously studied from kinetic viewpoint. POLYM. ENG. SCI. 46:129–138, 2006. © 2005 Society of Plastics Engineers     

Chitosan from Muga silkworms (Antheraea assamensis) and its influence on thermal degradation behavior of poly(lactic acid) based biocomposite films

The research work is focused on extraction of chitin from Muga silkworms (MS) and its conversion into chitosan by chemical treatment process. The extracted amount of chitin and chitosan from MS were obtained ～8 wt % and ～7 wt %, respectively. Potentiometric titrations, conductometric titrations, elemental analysis, ¹H‐NMR and FTIR analyses were employed to calculate the degree of deacetylation of chitosan (extracted at 80 ºC after 10 h) and found as 77% ± 2, 81% ± 1.8, 82% ± 2.4, 97.77% ± 0.3, and 82% ± 1.8, respectively. The deacetylation process of chitin showed pseudo‐first order reaction kinetics and activation energy was estimated as ～15.5 kJ/mole. The extracted chitosan (at 80 ºC after 10 h) showed higher crystallinity and improved thermal stability with respect to chitosan extracted from other marine sources. Subsequently, poly(lactic acid) (PLA) and extracted chitosan dispersed biocomposite films were prepared by solution casting method. Significant dispersion of chitosan (extracted at 80 ºC after 10 h) micro‐particles were observed in biocomposite films using FESEM analysis. Due to chitosan interaction with PLA, significant reduction in thermal degradation and activation energy was observed during nonisothermal degradation scan of such films using Flynn‐Wall‐Ozawa and Kissinger‐Akahira‐Sunose models. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43710.     

Kinetics and mechanism of the K2CrO4?NaAsO2 redox‐initiated aqueous polymerization of acrylonitrile

The kinetics and mechanism of acrylonitrile polymerization initiated by a redox pair [potassium chromate (K₂CrO₄) and sodium arsenite (NaAsO₂)] were studied. The overall rate of polymerization was proportional to √[K₂CrO₄] × [NaAsO₂], and the energy of activation was approximately 10.5 kJ/mol. Polyacrylonitrile was recovered as a coagulum in the medium. The formation of polyacrylonitrile was confirmed with Fourier transform infrared and ¹H‐NMR analyses. Scanning electron microscopy analysis of the polymer revealed the formation of aggregates of polymer particles (3–67 nm). Thermogravimetric studies indicated 50% weight loss at 400°C, and dynamic thermal analysis scan studies revealed an exothermic peak at 507°C due to massive oxidative thermal degradation of the polyacrylonitrile backbone. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 276–280, 2005     

A new Schiff base epoxy oligomer resin: Synthesis,characterization, and thermal decomposition kinetics

Oligo{2,2′‐{1,4‐phenylenebis[nitrilomethylylidene]}bis(6‐methoxyphenol)} (OPNMMP) was synthesized from o‐vanillin and p‐phenylene diamine by oxidative polycondensation with NaOCl in an aqueous alkaline. Then, a new Schiff Base epoxy oligomer resin, OPNMMP–epichlorohydrine (EPC), was produced with EPC. The structures of the resulting compounds were confirmed by Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, ¹H‐NMR, and ¹³C‐NMR. Further characterization processes were preformed by thermogravimetry (TG)–differential thermal analysis, gel permeation chromatography, and solubility testing. Also, the kinetics of the thermal decomposition of OPNMMP–EPC were investigated by thermogravimetric analysis. The TG curves showed that the thermal decomposition of OPNMMP–EPC occurred in one stage. The kinetic parameters related to the decomposition kinetics of OPNMMP–EPC were obtained from TG curves with the following methods: Friedman, Flynn–Wall–Ozawa, Kissinger, invariant kinetic parameter, and Coats–Redfern (CR), under an N₂ dynamic atmosphere and different heating rates (5, 10, 15, and 20°C/min). The mechanism function and pre‐exponential factor were also determined by a master plots method. The apparent activation energies of the thermal decomposition were calculated from these methods for OPNMMP–EPC. The analysis of the results obtained by the CR and master plots methods showed that the decomposition mechanism of OPNMMP–EPC in N₂ was a deceleration‐type mechanism. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

气氛对壳聚糖及其铜离子混合物热降解的影响

利用热重分析(TGA)和差热分析(DTA)研究了壳聚糖及其铜离子混合物在氮气气氛和空气气氛中的热降解行为,探讨了气氛对壳聚糖及其铜离子混合物热降解的影响,并采用FTIR、X-射线衍射对壳聚糖铜离子混合物进行了表征.结果显示,壳聚糖及其铜离子混合物的热降解和热氧降解分三个阶段进行:第一阶段为材料失水,为吸热反应;第二阶段为主链脱乙酰和糖苷键的裂解,为放热反应;第三阶段为吡喃环的裂解和炭化残渣的分解,为放热反应.气氛对壳聚糖第一、第二阶段的降解影响较小,对第三阶段的降解影响较大.