Thermal decomposition of fire retardant brominated epoxy resins cured with different nitrogen containing hardeners

Epoxy resins frequently have to meet a flame retardancy grade which can be accomplished by incorporating brominated reactive compounds, like tetrabromobisphenol A (TBBA) cured by a number of hardeners. A few brominated epoxy resins (BERs) have been prepared by curing a mixture of diglycidyl ethers of bisphenol A (DGEBA)/diglycidyl ethers of tertabromobisphenol A (DGETBBA) and different hardeners: dicyandiamide (DICY), 4,4′-diaminodiphenyl sulphone (DDS) and polyethylene polyamine (PEPA). The use of different hardeners strongly affects the thermal degradation behaviour of the BER.The main volatile products of pyrolysis, characterized by Pyrolysis-Gas Chromatography-Mass Spectroscopy (PY-GC-MS) at 423 °C were phenol, isopropyl- and isopropenylphenol, mono- and di-brominated phenols, bisphenol A, mono-, di-, tri- and tetra-brominated bisphenol A. No nitrogen containing volatile products or HBr were evolved whereas SO₂ is formed from BER cured with DDS (BER-DDS) and bromoethylene from BER cured with PEPA (BER-PEPA). Differences of 30-60 °C in thermal stability of epoxy network have been found, depending on the hardener. The experimental evidence suggests a cooperative action of bromine and nitrogen in chain scission of epoxy resins. In particular the ability of the hardener in fixing HBr, evolved from TBBA units, seems to depend on the basicity of the N atom of the hardener: the lower the basicity, the lower the scavenging effectiveness and consequently the higher the thermal stability.     

Utilization of thermodesorption coupled to GC-MS to study stability of different wood species to thermodegradation

Thermodesorption coupled to gas chromatography coupled to mass spectroscopy (TD-GC-MS) has been investigated to identify volatile degradation products generated during wood heat treatment by mild pyrolysis. For this purpose, wood samples of different softwood and hardwood species have been heat treated under nitrogen for different temperatures comprised between 180 and 230 °C during 15 min in the glass thermal desorption tube of the thermodesorber and the volatile wood degradation products trapped. The trapped products were then thermodesorbed and analysed by GC-MS. Chromatograms of the different samples indicated the formation of different products resulting from degradation of lignin and hemicelluloses. Hardwoods were shown to be more sensitive to thermodegradation than softwoods, for which degradation products appear at slightly higher temperature. The important formation of acetic acid is concomitant with the formation of most of degradation products and at the origin of the difference of reactivity observed between softwoods and hardwoods.     

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).     

Influence of polycaprolactone-triol addition on thermal stability of soy protein isolate based films

The influence of polycaprolatone-triol (PCL-T) on the thermal degradation properties of soy protein isolate (SPI)-based films was studied by thermogravimetry and infrared spectroscopy under nitrogen atmosphere. The results showed that in the absence of PCL-T the thermal degradation began between 292 °C (pure SPI films) and ca. 264 °C (SPI/SDS films with more than 20% of SDS), and these values decreased further to the range 250-255 °C for SPI/SDS/PCL-T films. At the same time, the temperature of maximum degradation rate (T_max) decreased from 331 °C (pure SPI film) to ca. 280 °C for SPI/SDS/PCL-T films with 39% PCL-T content. This behavior was also confirmed by the activation energy (E) values associated with the thermal degradation process. Apparently, the low thermal stability of PCL-T as compared to other film constituents, along with its plasticizer characteristics, is responsible for the decreased stability of SPI/SDS/PCL-T films. The FTIR spectra of gas products evolved during the thermal degradation indicated the formation of OH, CO₂, NH₃ and other saturated compounds, suggesting that the reaction mechanism involved simultaneous scission of the C(O)-O polyester bonds and C-N, C(O)-NH, C(O)-NH₂ and -NH₂ bonds of the protein.     

Thermal properties and stability of cassava starch films cross-linked with tetraethylene glycol diacrylate

The thermal stability of starch cross-linked with tetraethylene glycol diacrylate was studied under nitrogen atmosphere by thermogravimetry (TG) and infrared spectroscopy (FTIR). The cross-linking reaction was confirmed by the increase in intensity of the absorption band at ca. 3330 cm⁻¹ indicating the reinforcement of hydrogen bonds and the appearance of a new band at 1726 cm⁻¹ associated with the carbonyl group of the cross-linking agent. After cross-linking the solubility of starch in water decreased to the range 9%-16%. The thermogravimetric curves of pure and cross-linked starches showed an initial stage of degradation (up to ca. 150 °C) associated with the loss of water. The main stage of degradation occurred in the range 250-400 °C corresponding to ca. 60%-70% mass loss. The activation energy (E) for the degradation process increased from 145 kJ mol⁻¹ (pure starch) to 195 kJ mol⁻¹ and 198 kJ mol⁻¹ for starch treated for 60 min by UV (30 °C) and at 90 °C, suggesting high stability after cross-linking. A higher value (240 kJ mol⁻¹) was obtained for starch treated by UV for 120 min. The main volatile products determined by FTIR which correspond to hydrocarbons and carbonyl groups are apparently associated with the scission of weak bonds in the chain (probably branched groups) and the scission of stronger bonds (glycosidic linkages), respectively.     

Sol-gel synthesis and characterization of LiNO3-Al2O3 composite solid electrolyte

Composite solid electrolytes in the system (1 − x)LiNO₃-xAl₂O₃, with x = 0.0-0.5 were synthesized by sol-gel method. The synthesis carried out at low temperature resulted in voluminous and fluffy products. The obtained materials were characterized by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy/energy dispersive X-ray, Fourier transform infrared spectroscopy and AC impedance spectroscopy. Structural analysis of the samples showed base centred cell type of point lattice of LiNO₃ for the composite samples with x = 0.1-0.2 and body centred cell for the sample with x = 0.3. A trace amount of α-LiAlO₂ crystal phase was also present in these composite samples. The thermal analysis showed that the samples were in a stable phase between 48 °C and 230-260 °C. Morphological analysis indicated the presence of amorphous phase and particles with sizes ranging from micro to nanometre scale for the composite sample with x = 0.1. The conductivities of the composites were in the order of 10⁻³ and 10⁻² S cm⁻¹ at room temperature and 150 °C, respectively.     

Thermal degradation of poly(siloxane-urethane) copolymers

The aim of this study was to investigate the characteristics and mechanism of the degradation of poly(siloxane-urethane) (PSiU) copolymers by thermogravimetric analysis (TGA) and TGA coupled with Fourier-transform infra-red spectroscopy (TG-FTIR). The PSiU copolymers consisted of 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butanediol (1,4-BD), and OH-terminated polydimethylsiloxane (PDMS). In TGA they exhibited a two-stage degradation at 250-650 °C. The two stages of degradation have been found to comprise eight degradation steps and two interchange reactions, as revealed by TG-FTIR analysis. The main decomposition products have been identified as CO₂, tetrahydrofuran, cyclosiloxane, and macrocyclic species. In addition, the effects of hard segment content (HSC) on the degradation and thermal stability of PSiU copolymers have been investigated by means of TG and DTG curves; notably, a stability region at 410-470 °C is caused by the cyclosiloxane, as verified by TG-FTIR.     

Synthesis and characterization of novel polyamides from new aromatic phosphonate diamine monomer

New aliphatic-aromatic and fully aromatic phosphonate polyamides were prepared by polycondensation reaction of our synthesized aromatic diamine: tetraethyl[(2,5-diamino-3,6-dimethylbenzene-1,4-diyl)dimethanediyl]bis(phosphonate) with the specific di-acylchloride (adipoyl chloride, isophthaloyl chloride and terephthaloyl chloride). The chemical structure of all samples were characterized by (¹H and ³¹P) NMR, MALDI-TOF MS, FT-IR tools, whereas their thermal properties were determined by DSC and TGA techniques. The phosponate polyadipamide (referred as PAP) is a semi-crystalline sample with a melting temperature at about 261 °C and glass transition (T_g) of 71 °C. All polymers show two thermal degradation steps in the temperature range 270-550 °C. Each polymer, independently its structure, shows the first maximum rate of thermal decomposition temperature (PDT) around 300-310 °C, which may be due to thermal degradation of phoshonate groups. MALDI-TOF spectra, beside the linear oligomers terminated with the specific groups expected in accord to the synthesis procedure, reveals the presence of cyclic oligomers in the polyadipamide and polyisophthalamide samples.     

Generation of WO3-ZrO2 catalysts from solid solutions of tungsten in zirconia

WO₃-ZrO₂ samples were obtained by precipitating zirconium oxynitrate in presence of WO₄ species in solution from ammonium metatungstate at pH=10.0. Samples were characterized by atomic absorption spectroscopy, thermal analysis, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and energy filtered-TEM. The ammonia retained in the dried sample produced a reductive atmosphere to generate W⁵⁺ ions coexisting with W⁶⁺ ions to produce a solid solution of tungsten in the zirconia lattice to stabilize the zirconia tetragonal phase when the sample was annealed at 560 °C. When the sample was annealed at 800 °C, the W atoms near crystallite surface were oxidized to W⁶⁺, producing patches of WO₃ on the zirconia crystallite. The HR-TEM analysis confirmed the existence of the solid solution when the sample was annealed at 560 °C, and two types of crystalline regions were identified: One with nearly spherical morphology, an average diameter of 8 nm and the atomic distribution of tetragonal zirconia. The second one had a non-spherical morphology with well-faceted faces and dimensions larger than 30 nm, and the atom distribution of tetragonal zirconia. When samples were annealed at 800 °C two different zirconia crystallites were formed: Those where only part of the dissolved tungsten atoms segregated to crystallite surface producing patches of nanocrystalline WO₃ on the crystallite surface of tetragonal zirconia stabilized with tungsten. The second type corresponded to monoclinic zirconia crystallites with patches of nanocrystalline WO₃ on their surface. The tungsten segregation gave rise to the WO₃-ZrO₂ catalysts.     

Thermal degradation behaviour of aromatic poly(ester-amide) with pendant phosphorus groups investigated by pyrolysis-GC/MS

The thermal stability of a novel phosphorus-containing aromatic poly(ester-amide) ODOP-PEA was investigated by thermogravimetric analysis (TGA). The weight of ODOP-PEA fell slightly at the temperature range of 300-400 °C in the TGA analysis, and the major weight loss occurred at 500 °C. The structural identification of the volatile products resulted from the ODOP-PEA pyrolysis at different temperatures was performed by pyrolysis-gas chromatography/mass spectrometry (pyrolysis-GC/MS). The P-C bond linked between the pendant DOPO group and the polymer chain disconnected first at approximately 275 °C, indicating that it is the weakest bond in the ODOP-PEA. The P-O bond in the pendant DOPO group was stable up to 300 °C. The cleavage of the ester linkage within the polymer main chain initiated at 400 °C, and the amide bond scission occurred at greater than 400 °C. The structures of the decomposition products were used to propose the degradation processes happening during the pyrolysis of the polymer.     

New fluorinated polymers bearing pendant phosphonic groups for fuel cell membranes: Part 1 synthesis and characterizations of the fluorinated polymeric backbone

Radical copolymerizations of chlorotrifluoroethylene (CTFE) with vinyl ethers such as 2-chloroethyl vinyl ether (CEVE) and ethyl vinyl ether (EVE) were performed at 75 °C in the presence of peroxide initiator. Three copolymers were obtained and characterized by means of both NMR and elemental analysis. Then, the chlorine atoms in the side chains were converted into iodine atoms by nucleophilic substitution, which was monitored by ¹H NMR spectroscopy. A series of five copolymers with different amounts of iodine atoms in the side chains were thus obtained. These copolymers exhibited molecular weight values of about 25,000 g mol⁻¹, and the thermal analysis of the copolymers showed a starting degradation from about 220 °C. The T_g values were in the range of 34-41 °C and showed a linear dependence versus the content of iodine atoms.     

Thermal stability of solid and aqueous solutions of humic acid

The effects of temperature on the stability of a soil humic acid were studied in the present work. Solid samples of Gohy-573 humic acid (HA) and dissolved ones in aqueous solution (pH 6.0, 0.1 mol L⁻¹ NaClO₄) were investigated in order to understand the impact of temperature on the chemical properties of the material. The methods applied to solid samples in the present investigation were thermogravimetric analysis (TGA), temperature-programmed desorption coupled with mass spectrometry (TPD-MS), and in situ diffuse reflectance infrared Fourier transformed spectroscopy (in situ DRIFTS). Humic acid samples were studied in the 25-800 °C range, with focus on thermal/chemical processes up to 250 °C. The reversibility of the changes observed was investigated by cyclic changes to specified temperature ranges (40-110 °C). All measurements were conducted under inert-gas atmosphere in order to avoid samples combustion at increased temperatures. Aqueous solutions were analyzed by UV-vis absorption spectroscopy after storage at temperatures up to 95 °C, and storage times up to 1 week. For temperatures below 100 °C experiments on solid and aqueous samples have shown results which were consistent to each other. The amount of water desorbed is temperature dependent and up to 70 °C this process was totally reversible. Above 70 °C an irreversible loss of water was also observed, which according to UV-vis spectroscopy corresponds to water produced by condensation leading to more condensed polyaromatic structures. The water released up to 110 °C was about 7 wt% of the total mass of the dried humic acid, where less than 50% corresponded to reversibly adsorbed water. At higher temperatures (>110 °C), gradual decomposition resulting in the formation of carbon dioxide (110-240 °C), and carbon monoxide (140-240 °C) takes place. Hence, thermal treatment of Gohy-573 humic acid above 70 °C results in irreversible structural changes, that could affect chemical properties (e.g., complex formation) of the material.     

TGA/FTIR study on thermal degradation of polymethacrylates containing carboxylic groups

In this work, the thermal degradation of polymethacrylates containing carboxylic groups namely poly(methacryloyloxy butanoic acid), PMBA; poly(methacryloyloxy hexanoic acid), PMHA; and poly(p-methacryloyloxy benzoic acid), PMBeA was investigated by TGA/FTIR. Moreover, in order to shed more light on the reaction pathways during the thermal decomposition of these polymers, an FTIR spectroscopic study of structural changes in the degrading material was performed. By TGA it was observed that PMBA exhibited two well-defined degradation stages at 327 and 450 °C; PMHA presents only one main weight loss at ca. 402 °C although from DTG curve it was noted that the single step degradation was composed by two overlapped peaks located at 414 and 449 °C and a small shoulder at 317 °C; finally PMBeA showed three weight loss regions at 265, 353 and 468 °C. From FTIR analysis of the partially degraded samples it was found that the thermal degradation of these polymers resembled that of polymethacrylic acid, i.e. anhydrides were initially formed and then the modified structure is broken to yield an aromatic structure with phenolic groups. In contrast, the analysis by FTIR of the volatile products from the studied polymers differs notably than those obtained for polymethacrylic acid: β-lactones and γ-lactones were released from PMBA and PMHA, respectively, during its thermal degradation, whereas an ester derivative from benzoic acid evolves from PMBeA probably through depolymerization.     

Synergistic effects of layered double hydroxide with hyperfine magnesium hydroxide in halogen-free flame retardant EVA/HFMH/LDH nanocomposites

The synergistic effects of layered double hydroxide (LDH) with hyperfine magnesium hydroxide (HFMH) in halogen-free flame retardant ethylene-vinyl acetate (EVA)/HFMH/LDH nanocomposites have been studied by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), thermogravimetric analysis (TGA), limiting oxygen index (LOI), mechanical properties' tests, and dynamic mechanical thermal analysis (DMTA). The XRD results show that the exfoliated EVA/HFMH/LDH can be obtained by controlling the LDH loading. The TEM images give the evidence that the organic-modified LDH (OM-LDH) can act as a disperser and help HFMH particles to disperse homogeneously in the EVA matrix. The TGA data demonstrate that the addition of LDH can raise 5-18 °C thermal degradation temperatures of EVA/HFMH/LDH nanocomposite samples with 5-15 phr OM-LDH compared with that of the control EVA/HFMH sample when 50% weight loss is selected as a point of comparison. The LOI and mechanical tests show that the LDH can act as flame retardant synergist and compatilizer to apparently increase the LOI and elongation at break values of EVA/HFMH/LDH nanocomposites. The DMTA data verify that the T_g value (−10 °C) of the EVA/HFMH/LDH nanocomposite sample with 15 phr LDH is much lower than that (T_g = −2 °C) of the control EVA/HFMH sample without LDH and approximates to the T_g value (−12 °C) of pure EVA, which indicates that the nanocomposites with LDH have more flexibility than that of the EVA/HFMH composites.     

Thermal degradation of aliphatic hyperbranched polyesters and their derivatives

In this study results of thermal degradation of aliphatic hyperbranched polyesters, AHBP, and their derivatives, determined by non-isothermal thermogravimetric analysis in inert atmosphere (N₂) are presented. The thermal stability of linear polyester PHPA (polyhydroxypivalic acid), additionally synthesized from hydroxypivalic acid, was also studied. AHBP samples, from second to tenth pseudo-generation, were synthesized starting from 2,2-bis(hydroxymethyl)propionic acid and di-trimethylolpropane. Modification of some selected AHBP samples was accomplished with the propionyl and benzoyl chloride, as well as with stearic acid. Thermal degradation of AHBP samples starts in the region between 250 °C and 275 °C and it ends around 430 °C. The thermal stability of AHBP samples increases with the number of end groups in the macromolecule, as well as with the modification of end groups with stearic acid and propionyl chloride. An AHBP sample of the fourth pseudo-generation, where all -OH end groups are modified with benzoyl chloride, shows lower thermal stability than the corresponding unmodified sample. The thermal stability of the linear polyester PHPA is lower than the thermal stability of the AHBP samples of the similar molar mass. The activation energies of thermal degradation for all synthesized AHBP samples were also calculated.     

Analysis of thermal degradation of diacetylene-containing polyurethane copolymers

This work investigates the thermal degradation of diacetylene-containing polyurethane (PUDA) copolymers that consist of 2,4-hexadiyene-1,6-diol (DA), 4,4′-diphenylmethane diisocyanate (MDI) and polytetramethylene glycol (PTMG), by thermogravimetric analysis (TGA) and TGA coupled with Fourier transform infra-red spectroscopy (TG-FTIR). The results of TGA at different heating rates and under various annealing conditions demonstrated that the PUBD and PUDA copolymers underwent three stages of degradation. These stages of degradation of PUBD copolymers differed from those in earlier works, in which two stages of degradation were proposed. The three stages of degradation of PUBD and PUDA copolymers involved four and five steps of degradation, respectively, as revealed by TG-FTIR, which identified the main decomposition products, CO₂, tetrahydrofuran and ether-containing olefin. The effect of the cross-linked network of diacetylene-containing hard segments on the degradation of PUDA copolymers was investigated under various annealed conditions. Annealing at a high temperature for a long time promote the PUDA TG and DTG curves shifting to a higher temperature region, but the effect on the temperature does not obviously increase as the annealing further performed at 80-160 °C for a long time. This event is caused by the cross-linked networks inhibiting further cross-polymerization in the diacetylene-containing hard-segmented domains.     

Purge efficiency in the determination of trihalomethanes in water by purge-and-trap gas chromatography

Purge-and-trap gas chromatography-mass spectrometry (PT-GC-MS) has become an accepted method for the analysis of trihalomethanes (THMs) in water. The purge-and-trap technique is based on an efficient transfer of volatile organic compounds from the liquid (contained in the purge chamber) to the gaseous phase by bubbling with an inert gas. The aim of this work was to study the purge system's efficiency by means of several consecutive purge cycles lasting 11 min each of the same liquid sample. The concentration range chosen of THMs was very wide [5-200 μg L⁻¹]. The inert gas flow rate was 40 mL min⁻¹, and experiments were performed at temperatures of 25, 35 and 50 °C. Bromoform (CHBr₃), the least volatile compound, needed 19 cycles to be purged quantitatively at a concentration of 200 μg L⁻¹ and only 7 cycles at 5 μg L⁻¹ for a 25 mL sample at 25 °C. Chloroform (CHCl₃), the most volatile compound, required 4 cycles to be fully extracted at 200 μg L⁻¹ and 2 at 5 μg L⁻¹. Finally, Novak's theoretical model, based on the distribution constant between gas and liquid phases, was used to correlate the THMs purging extraction data.     

Synthesis, characterization and thermal degradation of 8-hydroxyquinoline-guanidine-formaldehyde terpolymer

Terpolymer (8-HQGF) has been synthesized using the monomers 8-hydroxyquinoline, guanidine, formaldehyde in 1:1:2 molar proportions. The structure of 8-HQGF terpolymer has been elucidated on the basis of elemental analysis and various physicochemical techniques, i.e. UV-Visible, FTIR-ATR and ¹H NMR spectroscopy. Detailed thermal degradation study of the new terpolymer has been carried out to ascertain its thermal stability. Thermal degradation curve is discussed which shows two decomposition steps (265-475 °C and 540-715 °C). Sharp-Wentworth and Freeman-Carroll methods have been used to calculate activation energies and thermal stability. The activation energy (E_a) calculated by using the Sharp-Wentworth (21.98 kJ/mol) has been found to be in good agreement with that calculated by Freeman-Carroll (23.57 kJ/mol) method. Thermodynamic parameters such as free energy change (ΔF), entropy change (ΔS), apparent entropy change (S^∗) and frequency factor (Z) have also been evaluated on the basis of the data of Freeman-Carroll method. The order of reaction (n) is found out to be 0.9979.     

New structures from the thermal rearrangement of polybutadiene revealed by 2D HSQC NMR

The thermal reactions of polybutadiene (PB) at 260 °C in inert atmosphere were followed by ¹H and ¹³C NMR spectroscopy. Within 24 h of heating, the change in the intensities of some peaks and the appearance of new peaks of NMR spectra permits to follow the reactions occurring in polybutadiene. The sample, after heating for 6 h, was then characterized by a two dimensional HSQC NMR spectrum, showing the appearance of CH₃CH moiety, and the migration of double bond in polybutadiene. From these results the new mechanism of intra/intermolecular reactions was proposed.