Thermal and hydrolytic degradation of electrospun fish gelatin membranes

The thermal and hydrolytic degradation of electrospun gelatin membranes cross-linked with glutaraldehyde in vapor phase has been studied. In vitro degradation of gelatin membranes was evaluated in phosphate buffer saline solution at 37 °C. After 15 days under these conditions, a weight loss of 68% was observed, attributed to solvation and depolymerization of the main polymeric chains. Thermal degradation kinetics of the gelatin raw material and as-spun electrospun membranes showed that the electrospinning processing conditions do not influence polymer degradation. However, for cross-linked samples a decrease in the activation energy was observed, associated with the effect of glutaraldehyde cross-linking reaction in the inter- and intra-molecular hydrogen bonds of the protein. It is also shown that the electrospinning process does not affect the formation of the helical structure of gelatin chains.     

Thermal degradation mechanism of dodecylbenzene sulfonic acid- hydrochloric acid co-doped polyaniline

Co-doped polyaniline (PANI) was synthesized in microemulsion by hydrochloric acid (HCl) and dodecylbenzene sulfonate (SDBS) then thermal treated in air at 160 and 200 °C for 0.5 h, respectively. The changes of structure, thermal stability, micromorphology and electrical conductivity after thermal treatment were studied by Fourier transformed infrared (FT-IR), Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM) and four-probe technique. It was found that the conductivity of PANI decreased about 50% after thermal treated at 160 °C, and droped by 2 orders of magnitude at 200 °C. This may be explained by that only a fraction of total mass of HCl losses during thermal treatment at 160 °C, but after heating at 200 °C, the dedoping of dodecylbenzene sulfonic acid (DBSA) along with cross-linking, chain scission and oxygen incorporation in a form of carbonyl groups take place, resulting in destruction of crystal structure, decrease of the emeraldine sequence, lower thermal stability and heterogeneous micromorphology.     

Thermal degradation of polymethacrylic acid

The thermal degradation of polymethacrylic acid was found to have two separate decomposition regions. The first decomposition region, due to anhydride formation primarily, was caused by the conversion of polymethacrylic acid to polymethacrylic anhydride. This reaction followed first-order kinetics and had an activation energy of 40.5 kcal/mol. The second decomposition region was the thermal degradation for the corresponding polymethacrylic anhydride. In this region, the fragmentation of anhydride rings structure in polymethacrylic anhydride constitutes the major decomposition reaction with an activation energy of 37.4 kcal/mol. © 1992 John Wiley & Sons, Inc.     

Morphological behaviour of poly(lactic acid) during hydrolytic degradation

The hydrolytic degradation and the morphological behaviour of a packaging grade of poly(lactic acid) (PLA) were characterized by a series of techniques. During the initial degradation process (stage 1) at a temperature near the glass transition temperature (T_g), the molecular weight of PLA decreased as degradation time increased following a bulk erosion mechanism while the crystallinity increased simultaneously, but no observable weight loss occurred at stage 1. Mainly α-form PLA crystal structure was formed for the crystalline PLA with a low content of d stereo-isomers, but the material displayed a lower regularity, smaller domain size, lower melting temperatures T_m and different motional dynamics as compared to the original PLA with a similar level of crystallinity achieved by annealing. The amorphous PLA with a higher amount of d stereo-isomers also yielded the α crystalline phase as well as stereo-complex crystals at stage 1. When the molecular weight and the crystallinity reached a stable level, PLA started erosion into the degrading aqueous medium. During this stage of degradation (stage 2), the crystalline structure in PLA residues was further modified and both pH and temperature influenced the modification. The degradation at stage 2 was likely to follow a surface erosion mechanism with lactic acid as the major product of the weight loss. Besides the crystallinity effect on the degradation, temperature also played a key role in determining the rate of PLA degradation in both stages. The process was very slow at temperatures below the T_g of PLA but the rate was greatly enhanced at temperatures above the T_g.     

Comparison of fuel cell performance of selected fluoropolymer and hydrocarbon based grafted copolymers incorporating acrylic acid and styrene sulfonic acid

Fuel cell tests have been carried out on ion exchange membranes produced by the radiation grafting of either acrylic acid or styrene monomers (followed by a sulphonation reaction) onto selected hydrocarbon and fluoropolymer films. Relationships between the membranes' intrinsic properties, composition, ion exchange capacity and equilibrium water content and their respective fuel cell performance have been established. Copyright © 2002 John Wiley & Sons, Ltd.     

Thermal degradation behaviour of resins in aluminium composite under isothermal condition

As a member of the aluminium composite, GLARE (GLAss fibre/epoxy REinforced aluminium laminates) was used in the upper fuselage of Airbus A380 because of its superior mechanical properties over monolithic aluminium alloys. Thermal processing is a potential method for materials recycling and reuse from GLARE scrap with the aim of environmental protection and economic benefits. Thermal delamination is a crucial pre-treatment step for GLARE recycling. Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA) tests have been used to identify the decomposition temperature range of epoxy resins under non-isothermal condition in our previous work [1]. To obtain an appropriate solution for GLARE thermal delamination, the thermal degradation behaviour of epoxy resins in GLARE under isothermal conditions were investigated and isothermal decomposition kinetic models were built up based on DSC and thermogravimetric analysis TGA. The thermal delamination process of GLARE is determined based on thermal analysis results and experimental optimization.     

Radiation grafted poly(vinylidene fluoride)-graft-polystyrene sulfonic acid membranes for fuel cells: Structure-property relationships

<正>Structure-property relationships for poly(vinylidene fluoride)-graft-polystyrene sulfonic acid(PVDF-g-PSSA) fuel cell membranes prepared by a single step method involving radiation-induced grafting of sodium styrene sulfonate(SSS) onto electron beam(EB) irradiated poly(vinylidene fluoride)(PVDF) films were established.The physico-chemical properties of the membranes such as ion exchange capacity,water swelling and proton conductivity were correlated with the degree of grafting(G,%) and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity and the thermal stability of membranes was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis(TGA),respectively.The membranes were found to undergo substantial structural changes in forms of ionic sites increase,hydrophilicity enhancement,hydrophobicity reduction and crystallinity decrease with the variation in G(%) and the preparation method.The structural and thermal properties of the obtained membranes were also compared with their counterparts prepared by a conventional two-steps method i.e.radiation induced grafting of styrene onto EB irradiated PVDF films followed by sulfonation.The PVDF-g-PSSA membranes obtained by a single-step method were found to have superior properties compared to those obtained by the conventional two-steps method.     

Thermal and rheological behaviour of some random aromatic polyethersulfone/polyetherethersulfone copolymers

The thermal and rheological behaviour of seven random Cl-ended aromatic PES/PEES copolymers (M_n ≈ 9500 g mol⁻¹), at various PES/PEES repeating unit ratios, was studied. The glass transition temperatures (T_g), determined by DSC experiments, showed a dependence on copolymer composition significantly different from the ideal linear behaviour expected on the basis of Fox equation. Degradations were carried out in the scanning mode, under flowing nitrogen, in the temperature range 35-650 °C and a single degradation stage was observed for all copolymers. The initial decomposition temperatures (T_i) and the half decomposition temperatures (T_1/2) were directly determined by TG curves, while the apparent activation energies of degradation (E_a) were obtained by the Kissinger method. In addition, the complex viscosity (η^∗) of molten copolymers was determined in experimental conditions of linear viscoelasticity. T_i, T_1/2, E_a, and η^∗ values were depending on copolymer composition, showing a trend similar to that of T_g values. The results obtained were discussed and interpreted.     

Thermostable poly(p-phenylene sulfide sulfonic acid) as ion exchangers

Poly(p-phenylene sulfide sulfonic acid) was thermally crosslinked for use as a cation exchange polymer with high thermal stability. The decomposition temperature (T_d) of the polymer increases with an increase in the crosslinking temperature. The crosslinking reaction at 300°C in air resulted in the formation of a strongly acidic cation exchange polymer with a T = 467°C and having an SO₂ bond, whose crosslinked structure was investigated using IR spectroscopy.     

Thermal degradation of copolymers of styrene with dicarboxylic acids - II: Copolymers obtained by radical copolymerisation of styrene with maleic acid or fumaric acid

Thermal degradation processes in copolymers of styrene with two stereoisomers of 1,2-ethylenedicarboxylic acids (i.e. maleic acid (the cis-isomer) and fumaric acid (the trans-isomer)) have been studied by mass spectrometry, FTIR and TG measurements. The influence of the chemical composition on thermal degradation of copolymers with acid by non-isothermal thermogravimetric analysis (TG) was also studied. The stereo-configuration of carboxyl groups in copolymers was analysed by potentiometric titration. It was found that copolymers degrade in two main complex stages. The initial step in the decomposition involves the formation of cyclic five-membered anhydrides. The presence of trans configuration of carboxyl groups hinders the formation of cyclic anhydrides and shifts the decomposition to higher temperatures, making decarboxylation competitive. At higher temperatures anhydride decomposition takes place and finally the degradation of main chains occurs.     

Differential scanning calorimetry and thermogravimetric analysis investigation of the thermal properties and degradation of some radiation‐grafted films and membranes

The influence of irradiation and grafting on the crystallinity of three base polymers has been investigated with differential scanning calorimetry. Grafting has the largest effect on the base polymer crystallinity and results in a reduction of the crystallinity. The thermal degradation of the base polymers and grafted films has been investigated with thermogravimetric analysis. The extent of the fluorination of the base polymer, the irradiation method, and the graft level all influence the thermal degradation and its activation energy. It is proposed that the variation of the chain lengths of the grafted polystyrene chains is actually a primary underlying factor responsible for the influence of these various parameters on the degradation process. The first results of a comparative thermal analysis of some fuel‐cell membranes are also presented, and the promise and shortcomings of this method are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2612–2624, 2004     

Thermal oxidative degradation of poly-lactic acid

The study of molecular weight and rate of change of molecular weight during thermal degradation of PLA suggests the random nature of chain scission with activation energy of 28 kcal/mol. The rate of weight loss indicates the formation of the volatiles by chain end initiation. The melting temperature of the polymer initially decreases and afterwards increases with increase in time of heating due to chain stiffening.     

Chemoselective trimethylsilylation of alcohols catalyzed by saccharin sulfonic acid

Abstract  Saccharin sulfonic acid was easily prepared by the reaction of saccharin with neat chlorosulfonic acid at room temperature. This reagent is efficiently able to catalyze the chemoselective trimethylsilylation of alcohols with hexamethyldisilazane in the presence of amines and thiols. Graphical abstract        

An investigation about the solid state thermal degradation of acetylsalicylic acid: polymer formation

An investigation about the thermal degradation of acetylsalicylic acid (ASA) is performed. It is verified that the thermal degradation of ASA produces not only salicylic acid (SA) and acetic acid (AA) as products but also an ASA polymer, which is transparent and solid. And also verified that the temperature in which the polymer is obtained influences its physical consistence (solid or semi-solid). Furthermore, the ASA polymer is very stable from a thermic point of view, as verified by TG and DSC analysis. X-ray diffraction patterns obtained for the ASA polymer show that it exhibits a low crystallinity.     

Dynamic and equilibrium swelling of a sulfonic acid superabsorbent copolymer in salt solutions

Superabsorbent copolymers were synthesized by free radical reverse emulsion from the monomers acrylamide and 2‐acrylamido‐2‐methyl‐propanosulfonic acid with a divinyl crosslinker (methylene‐bisacrylamide). The copolymer synthesized was then identified by Fourier transform infrared spectroscopy, its porosity was examined by electronic microscopy, and its specific gravity was determined by the conventional procedure. The dynamic and equilibrium swelling behavior of the copolymer was studied, in water and in salt solutions, at 25 °C (chlorides and sulfates of sodium and magnesium). As to the equilibrium swelling, the influence of the pH as well as of the salt type and its concentration was observed. As to the dynamic swelling, it was interpreted in terms of both a simple power of time equation, and a more detailed model based on a coupled diffusion‐relaxation mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 505–514, 2004     

Thermal degradation behavior of poly(4-hydroxybutyric acid)

Thermal degradation behavior of poly(4-hydroxybutyric acid) (P(4HB)) was investigated by thermogravimetric and pyrolysis-gas chromatography mass spectrometric analyses under both isothermal and non-isothermal conditions. Based on the thermogravimetric analysis, it was found that two distinct processes occurred at temperatures below and above 350 °C during the non-isothermal degradation of P(4HB) samples depending on both the molecular weight and the heating rate. From ¹H NMR analysis of the residual P(4HB) molecules after isothermal degradations at different temperatures, it was confirmed that the ω-hydroxyl chain-end was remained unchanged in the residual P(4HB) molecules at temperatures below 300 °C, while the ω-chain-end of P(4HB) molecules was converted to 3-butenoyl units at temperatures above 300 °C. In contrast, the majority of the volatile products evolved during thermal degradation of P(4HB) was γ-butyrolactone regardless of the degradation temperature. From these results, it is concluded that during the thermal degradation of P(4HB), the selective formation of γ-butyrolactone via unzipping reaction from the ω-hydroxyl chain-end predominantly occurs at temperatures below 300 °C. At temperatures above 300 °C, both the cis-elimination reaction of 4HB unit and the formation of cyclic macromolecules of P(4HB) via intramolecular transesterification take place in addition to unzipping reaction from the ω-hydroxyl chain-end. Finally, the primary reaction of thermal degradation of P(4HB) at temperatures above 350 °C progresses by the cyclic rupture via intramolecular transesterification of P(4HB) molecules with a release of γ-butyrolactone as volatile product. Moreover, we carried out the thermal degradation tests for copolymer of 93 mol% of 4HB with 7 mol% of 3-hydroxybutyric acid (3HB) to examine the effect of 3HB units on thermal stability of P(4HB).     

Thermal degradation behaviour of a nearly alternating copolymer of vinylidene cyanide with 2,2,2-trifluoroethyl methacrylate

The thermal decomposition under non-oxidative conditions of a copolymer of vinylidene cyanide (VCN) and 2,2,2-trifluoroethyl methacrylate (MATRIF) was investigated by thermogravimetry (TG) and Pyrolysis-GC-MS. The type and composition of the pyrolytic products and the shape of the TG curve indicate that both the main thermal degradation process, with onset at 368 °C, and a minor weight loss at around 222 °C are mainly associated with random main-chain scission. The kinetic parameters were determined by means of dynamic and, in the case of the main degradation stage, also isothermal methods. The results obtained from the dynamic methods (Friedman, Flynn-Wall-Ozawa, and Kissinger, respectively) are in good agreement with those obtained from isothermal TG data. The activation energy was in the 177-213 kJ/mol range for the first stage, and 224-295 kJ/mol for the second stage, the highest respective values being determined from the kinetic analysis according to the Kissinger method.     

Phospho sulfonic acid as an efficient and recyclable solid acid catalyst for the solvent-free preparation of acylals

Phospho sulfonic acid (PSA) acts as a highly effective and reusable catalyst for the chemo-selective protection of aldehydes with acetic anhydride under solvent-free conditions. The desirable features of this new catalytic methodology include its sustainability, effectiveness in the absence of solvent, a facile work-up procedure, and economic viability. PSA is fully characterized by Fourier transform infrared spectroscopy, wide-angle X-ray scattering analysis, and scanning electron microscopy with energy dispersive X-ray spectroscopy. The catalyst can be reused several times without significant loss of activity. In addition, no chromatographic separations are needed to obtain the desired products.     

Thermal degradation study of gadolinium and lutetium methanesulfonates

The synthesis, characterization and thermal degradation study of gadolinium and lutetium methanesulfonates is reported. The prepared salts were characterized by elemental analysis and infrared spectroscopy. The thermal degradation study was performed by using thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). By using thermogravimetric data, a kinetic study of the dehydration of Gd and Lu methanesulfonates is performed employing the Coats-Redfern and Zsakó methods. It is verified that under heating, the gadolinium and lutetium methanesulfonates suffer three main processes: dehydration, thermal degradation and oxide formation. The thermal degradation products were characterized by infrared spectroscopy and X-diffractometry. Furthermore, depending on the atmosphere nature, i.e. inert or oxidant, the thermal degradation process could be endothermic (N₂) or exothermic (air).     

Imidazolium ionic liquid-supported sulfonic acids: efficient and recyclable catalysts for esterification of benzoic acid

Several imidazolium ionic liquid（IL）-supported sulfonic acids with different anions,[C₃SO₃Hmim]HSO₄,[C₃SO₃Hmim]BF₄, [C₃SO₃ Hmim]PF₆,and[C₃SO₃Hmim]CF₃SO₃,were synthesized and applied as catalysts for esterification reaction of benzoic acid. The experimental results indicate that imidazolium IL-supported sulfonic acid containing anion of HSO₄^- shows the best catalytic activity.Only when less[C₃SO₃Hmim]HSO₄（0.3 equiv.） applied,was the product obtained with high yield of 97%.Furthermore, the produced esters could be separated by decantation,and the catalyst could be reused after the removal of water.