Degradation study on the thermally stable nickel phthalocyanine sheet polymer

Poly (nickel phthalocyanine) which has exceptional thermal stability is synthesized. Knowledge of modes of degradation of this polymer is found to be necessary for its high temperature applications. This polymer showed very high thermal stability with maximum polymer decomposition temperatures (PDT_max) of 500 °C in air and 890 °C in N₂, with char yield 93% at 800 °C. Because of its excellent thermal stability, degradation study with MS as well as GC–MS techniques were found to be very difficult. The present publication deals with MS and GC–MS studies of nickel phthalocyanine sheet polymer at high temperatures ranging from 700 to 1000 °C. Tentative mechanisms are proposed for its modes of fragmentations and based on GC–MS studies, the most probable degradation products are identified.     

Thermal stability of the silica-aminopropylsilane-polyimide interface

Thermal degradation of the silica–aminopropylsilane–amic acid/imide interface was studied by modifying a high-surface-area, neutral silica gel with a number of substituted aminopropylsilanes (APS). These substrates were reacted further with phthalic anhydride or aromatic amic acid monomers and the thermal decomposition of the adsorbed/reacted materials was monitored by thermogravimetric analysis (TGA) and infrared (IR) spectroscopy. The 3-aminopropyltriethoxysilane/poly[N,N′-(p,p′-oxydiphenylene)pyromellitimide] interface was also evaluated by this method. Comparison clearly distinguishes the thermal decomposition of surface-bound APS from surface-bound alkylphthalimides, the adhesion product of alkylamines and aromatic amic acids. Alkylamine imidization with the elimination of aromatic amine (analogous to polymer scission) and the decomposition of the surface-bound imide are shown in the amic acid TGA profiles. This imidization and the accompanying aniline elimination begin at about 130°C, under nitrogen, to form the surface alkyl imide which slowly decomposes at 400°C. TGA analysis indicates that the surface-bound imide undergoes minimal degradation under nitrogen at 370 ± 10°C; temperatures above this threshold range produce changes in the APS–imide interface.     

The thermal decomposition of metal formates. II. Solid state thermal decomposition studies on magnesium formate dihydrate

Magnesium formate dihydrate has been synthesized by the action of formic acid on anhydrous magnesium oxide. This product analysed as Mg(COOH)₂ · 2H₂O. Its mode of thermal decomposition has been studied by thermal methods of analysis including simultaneous DTA/mass spectrometry. Nitrogen adsorption surface area of the solid products at various stages of its decomposition have been obtained. X-Ray diffraction and scanning electron micrographs have also been used to interpret the results. The decomposition of magnesium formate took place in three stages, which includes a phase change, at 265°C. The endotherm at 430°C changed to an exotherm in the presence of air; it corresponded to the decomposition of a new anhydrous phase of magnesium formate. The effect of the sample holder and changing atmospheres on the DSC analysis has been investigated. A scheme is presented for the thermal decomposition.     

Primary thermal degradation processes occurring in poly(phenylenesulfide) investigated by direct pyrolysis–mass spectrometry

The thermal degradation Processes which occur in poly(phenylenesulfide) (PPS) have been studied by direct pyrolysis-mass spectrometry (DPMS). The structure of the compounds evolved in the overall temperature range of PPS decomposition (400–700°C) suggests the occurrence of several thermal decomposition steps. At the onset of the thermal degradation (430–450°C) this polymer decomposes with the formation of cyclic oligomers, generated by a simple cylization mechanism either initiated at the—SH end groups or by the exchange between the inner sulfur atoms along the polymer chain. At higher temperature (> 500°C) another decomposition reaction takes over with the formation of aromatic linear thiols. The formation of thiodibenzofuran units by a subsequent dehydrogenation reaction occurs in the temperature range of 550–650°C; in fact, pyrolysis products with a quasi-ladder structure have also been detected. Ultimately, above 600°C, extrusion of sulfur from the pyrolysis residue occurs with the maximum evolution at the end of decomposition (about 700°C). It appears, therefore, that the residue obtained at high temperature tends to have a crosslinked graphite-like structure from which the bonded sulfur is extruded. © 1994 John Wiley & Sons, Inc.     

Mechanistic study of thermal behavior and combustion performance of epoxy resins: I homopolymerized TGDDM

Tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) undergoes homopolymerization on heating. Intramolecular reactions which compete with crosslinking favor the formation of cyclic structures with increasing thermal and fire resistance of the resin, whereas physical mechanical properties tend to decrease. The mechanism of thermal decomposition of TGDDM is studied by thermogravimetry, differential scanning calorimetry and thermal volatilization analysis with characterization of volatiles evolved and residue left. Thermal degradation of poly-(TGDDM) starts at 260°C with elimination of water from secondary alcoholic groups which is a typical pathway for epoxy resin degradation. Resulting unsaturations weaken bonds in the β-position and provoke the first chain breaking at allyl–amine and allyl–either bonds. With increasing temperature, saturated alkyl–ether bonds and alkyl carbon–carbon bonds are broken first, followed by the most stable alkyl–aryl bonds at T>365°C. The combustion performance of TGDDM is discussed on the basis of the thermal degradation behavior.     

Thermal decomposition of zinc carbonate hydroxide

This study is devoted to the thermal decomposition of two zinc carbonate hydroxide samples up to 400 °C. Thermogravimetric analysis (TGA), boat experiments and differential scanning calorimetry (DSC) measurements were used to follow the decomposition reactions. The initial samples and the solid decomposition products were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and laser particle size analyzer. Results showed that zinc carbonate hydroxide decomposition started at about 150 °C and the rate of decomposition became significant at temperatures higher than 200 °C. The apparent activation energies (E_a) in the temperature range 150–240 °C for these two samples were 132 and 153 kJ/mol. The XRD analyses of the intermediately decomposed samples and the DSC results up to 400 °C suggested a single-step decomposition of zinc carbonate hydroxide to zinc oxide with not much change in their overall morphologies.     

Decomposition of silane on solid P4O10

Silane undergoes thermal decomposition on the surface of “phosphorus pentoxide” ( P₄O₁₀) into its elements around 200–400°C. The hydrogen formed partially reduces the P₄O₁₀ forming lower oxides of phosphorus and water. Elemental silicon is precipitated as reddish-brown solid, which is separated by dissolving out the phosphorus oxides. Silica and disiloxane are not formed in the reaction.     

High temperature thermal properties of KH2PO4: Phase transitions and decompositions

Phase transitions and the thermal decomposition of KH₂PO₄ have been examined from room temperature to above 300°C by means of hot-stage microscopy, isothermal gravimetry and differential scanning calorimetry. Phase transitions at 198 and 242°C are confirmed, with corresponding enthalpy changes 4.2 and 2.3 kJ mole⁻¹, but no evidence has been found of a transition reported near 110°C. The thermodynamic and other evidence suggest a structural change at 198°C while the change at 242°C is less profound, perhaps involving only changes in the form of the hydrogen bonding. Thermal decomposition occurs in four stages, under conditions of free vapour escape, with the loss of one-quarter of a mole of water per formula unit of KH₂PO₄ in each stage. The products of each stage of decomposition are tentatively identified.     

New liquid crystalline di- and tetra-acrylates for network formation

New liquid crystalline diacrylates and tetra-acrylates containing four to six aromatic rings were synthesized and characterized, and their mesophase behaviour was investigated. They are designed to be used in combination with chiral molecules to form cholesteric mesophases which can be crosslinked by photopolymerization. The acrylates presented exhibit broad mesophase ranges since mesogenic moieties longer than three are employed. Most diacrylates show no isotropization, due to premature thermal polymerization above 180°C. Additionally, liquid crystalline dipropionates were synthesized as reference compounds which cannot be crosslinked, and selected examples of these exhibit isotropization temperatures as high as 238°C prior to thermal degradation. Substituents at the mesogenic moiety have a great influence on the mesophase characteristics. Bulky substituents such as the tert-butyl group, induce a nematic mesophase, whereas compounds with small substituents (e.g. OCH3) or unsubstituted molecules also exhibit smectic phases. Tetra-acrylates with unsubstituted and substituted mesogenic units feature nematic mesophases only as a result of the additional spacers attached. Here isotropization was observed without polymerization at temperatures around 120-160°C.     

Thermal stability of an explosive detonator

Mercuric 5-nitrotetrazole is a possible replacement for lead azide. The thermal decomposition peak maximum ranged from 185 to 270°C as the heating rate increased from 0.1 to 100°C min⁻¹. The activation energy and frequency factor for thermal decomposition were determined from dynamic and isothermal DSC and isothermal TG data; the average values were 38.8 kcal mol⁻¹ and 3.56×10¹⁴ s⁻¹. A half-life experiment confirmed the kinetic constants and indicated that the decomposition reaction was first order. The heat of explosion was determined by a pressure DSC test and found to be 2587 J g⁻¹. The linear coefficient of expansion was 37±2×10⁻⁶°C⁻¹ from −60 to 160°C and indicated secondary transitions near −10 and 90°C. The specific heat was 0.0003154T+0.1339 in the region −40–90°C. The critical temperature for a slab with a half-thickness of 0.035 cm was calculated to be 232 °C.     

Thermal degradation characteristics of a novel flame retardant coating using TG-IR technique

A novel phosphate acrylate monomer (TGMAP) has been synthesized by allowing phosphoric acid to react with glycidyl methacrylate. Its structure was characterized by Fourier transformed infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H NMR). The thermal degradation mechanism was characterized using thermogravimetric analysis/infrared spectrometry (TG-IR). The char yield was 36.3% at 600 °C. TG data indicate that the material undergoes degradation in three characteristic temperature stages, which can be attributed to the decomposition of the phosphate, thermal pyrolysis of aliphatic chains, and degradation of an unstable structure in char, respectively. The volatilized products formed on thermal degradation of TGMAP indicated that the volatilized products are CO, CO₂, carboxylic acid, acid anhydride, water, alkane, and aromatic compounds according to the temperature of onset formation.     

Thermogravimetric analysis of aluminised E-glass fibre reinforced unsaturated polyester composites

Novel aluminised E-glass fibre reinforced unsaturated polyester composites, originally formulated for enhanced thermal and electrical shielding properties were evaluated in terms of their thermal performance. The thermal degradation of these specimens was analysed using a thermogravimetric analyser (TGA). The samples were heated from ambient temperature to 500 °C at a heating rate of 20 °C/min. All specimens were decomposed under dry nitrogen (N₂) at a flow rate of 40 ml/min to yield gases and solid char. Aluminised E-glass composites were compared alongside the unmetallised E-glass and unreinforced composite. The major weight loss occurred between 200 and 400 °C. The unreinforced polyester had a maximum weight loss, 1.25%/°C, occurring at 360 °C. For the aluminised and unmetallised E-glass composites, the maximum rate of weight loss was 0.34 and 0.55%/°C, respectively. Experimental results show the degradation of the aluminised E-glass composites obtained from TGA tests is higher compared to those of unmetallised E-glass fibre and unreinforced polyester composite. This improvement is correlated to the aluminium coating.     

Thermal degradation studies of methacrylonitrile polymers and copolymers—3. Polymers capable of chain end-initiated colouration

Polymethacrylonitrile (PMAN) prepared by free-radical polymerisation with the initiator 4,4′-azo-bis(4-cyanovaleric acid) (ACVA) has chain ends from the initiator fragment which incorporate carboxyl groups. These ends are found to act as reactive sites for initiation of colouration in the polymer at temperatures from 140 °C. Several polymers, with different chain-end concentrations, have been made and the thermal degradation behaviour has been studied under programmed heating in the absence of air to 500 °C, with full product characterisation. In contrast with pure PMAN prepared with 2,2′-azo-bis(isobutyronitrile) (AIBN) as initiator, which degrades quantitatively to monomer, these ACVA-initiated polymers give very much reduced monomer yields, an important tar/wax fraction and a substantial amount of residue, amounting to 32–48% of the sample weight, dependent on the initial molecular weight of the polymer. The infrared spectral changes at the onset of the colouration reaction have been examined at 160 °C. Mechanisms are suggested to account for the observed products.     

Detailed kinetic modeling of pyrolysis of tetrabromobisphenol A

The thermal degradation of 4,4′-isopropylidenebis(2,6-dibromophenol), commonly known as tetrabromobisphenol A (TBBA), was studied by means of a semi-detailed kinetic model. TBBA is a widely adopted flame retardant. It decomposes in a temperature range between 200 °C and 500 °C, forming gaseous mixtures of HBr and harmful compounds such as bromine-containing phenols, the precursors of brominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs). These thermochemical characteristics constitute a significant risk of environmental contamination right throughout TBBA's whole life cycle. A kinetic model based on about 60 components (real and lumped species and radicals) and about 900 reactions satisfactorily reproduces the main aspects of TBBA degradation and volatilization. The model was validated by comparison with several thermogravimetric analyses, both isothermal and dynamic at 10 °C/min. The vaporization of pure TBBA, the formation of hydrogen bromide and of carbonaceous residue were all correctly predicted in quantitative terms right across the entire temperature range. Compared to conventional one-step global apparent degradation models, the proposed model spans much larger operating ranges, especially in predicting the gas phase products distribution. The results are encouraging and confirm the validity of the detailed kinetic model.     

Study of the thermal degradation of poly(furfuryl methacrylate) by thermogravimetry

The thermal degradation of poly(furfuryl methacrylate) (PFM) has been studied by means of dynamic thermogravimetric analysis (TGA) in the temperature range 100–600°C under nitrogen and oxygen atmospheres at various heating rates, and the apparent activation energy for the interval 230–340°C corresponding to the first degradation step was determined. Isothermal TGA at 250°C, 275°C and 300°C was carried out and the apparent activation energy values obtained were compared with those determined in dynamic experiments. The residues from isothermal degradation experiments were analysed by infrared spectroscopy and the results seem to indicate that in the thermal degradation of PFM the formation of cyclic structures of 2,4-dimethylglutaric anhydride occurs in the macromolecular chains, together with partial depolymerization of polymer segments, as well as intermolecular crosslinking through oxidation of the C---H bond in position 5 of some furfuryl rings.     

Thermal and spectroscopic studies of scandium complex of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone

The scandium complexes of Sc(PMBP)₃·H₂O (non-crystal) and Sc(PMBP)₃ (crystal) with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) were prepared and characterized by thermal analysis, IR, NMR and MS spectroscopies. The crystal structure of the complex, obtained by X-ray analysis, indicates that PMBP is a bidentate ligand in the complex and that the Sc atom is six-coordinate and is in a meridional octahedral environment. The order of the ring current effect on the pyrazolone ring is Sc(PMBP)₃ >PMBP(enol)> PMBP(keto).

The metal to ligand stoichiometry was found to be 1:3. The crystalline complex melts at 209 °C, followed by degradation at about 310 °C, with the beginning of decomposition. The enthalpy of melting was found to be 61 kJ/mol. On the other hand, the non-crystalline complex was found to change into a crystalline complex at 176 °C with an exothermic reaction before melting at 217 °C. The IR band observed at approximately, 450 cm⁻¹ is possibly due to the stretching of the Sc–O bond.     

Antioxidant action of organic sulfites—II. Esters of sulfurous acid as primary antioxidants

The effect of esters of sulfurous acid as primary antioxidants was examined. Different aliphatic, aromatic, open-chain and cyclic sulfites were synthesized. The reactions of organic sulfites with RO₂ and RO radicals, the chain carriers of the autoxidation of hydrocarbons and polymers, were simulated by means of the thermal decomposition of azobisisobutyronitrile (AIBN) in the presence of oxygen and of di-tert-butylperoxalate (DTBPO). The reactivity of organic sulfites with 2-cyanoisopropylperoxyl radicals is low. Only aromatic sulfites are able to trap peroxyl radicals; however, they are not very effective primary antioxidants. The reactions of the organic sulfites with tert-butoxyl radicals generally lead to an increase in the rate of decomposition of DTBPO, as determined from rate constants measured at 50 °C. A decomposition of DTBPO induced by liberated tert-butyl radicals in the presence of alkyl sulfites is very probable. Alkyl sulfites and aromatic sulfites with aliphatic groups act mainly as hydrogen donors in reactions with alkoxyl and peroxyl radicals.     

The effect of humidity on thermal process of zinc acetate

The thermal decomposition of zinc acetate dihydrate Zn(CH₃CO₂)₂·2H₂O in some humidity-controlled atmospheres has been successfully investigated by novel thermal analyses, which are sample-controlled thermogravimetry (SCTG), thermogravimety combined with evolved gas analysis using mass spectrometry (TG–MS) and simultaneous measurement of differential scanning calorimetry and X-ray diffractometry (XRD–DSC). The thermal processes of anhydrous zinc acetate in dry gas atmosphere by conventional linear heating experiment initiated with the sublimation around 180 °C, followed by the fusion and the decomposition over 250 °C. SCTG was useful to interpret clearly the successive reaction because the high-temperature parallel decompositions were effectively inhibited. The thermal behavior changed dramatically by introducing water vapor in the atmosphere and the thermal process was quite different from that in dry gas atmosphere. Zinc oxide (ZnO) was formed only in a humidity-controlled atmosphere, and could be easily synthesized at temperatures below 300 °C. XRD–DSC equipped with a humidity generator revealed directly the crystalline change from Zn(CH₃CO₂)₂ to ZnO. A detailed thermal process of Zn(CH₃CO₂)₂·2H₂O and the effect of water vapor are discussed.     

Kinetics and hazards of thermal decomposition of methyl ethyl ketone peroxide by DSC

Differential scanning calorimetry (DSC) was applied to analyze thermal decomposition of methyl ethyl ketone peroxide (MEKPO). Thermokinetic parameters and thermal stability were evaluated. MEKPO decomposes in at least three exothermic decomposition reactions and begins to decompose at 30–32 °C. The total heat of decomposition is 1.26 ± 0.03 kJ g⁻¹. Thermal decomposition of MEKPO can be described by a model of two independent reactions: the first is decomposition of a less stable isomer of MEKPO, followed by decomposition of the main isomer, after which an exothermic reaction of the reaction products with the solvent, dimethyl phthalate. The results can be applied for emergency relief system design and for emergency rescue strategies during an upset or accident.     

Synthesis and characteristics of cellulose peroxides of the peracid type having a temperature-responsive function

The synthesis of cellulose peroxides of the peracid type having a temperature-responsive function was studied by using carboxymethyl cellulose (CMC) and acrylic acid (AA)-grafted cellulose, into which the temperature-responsive component, poly(N-isopropylacrylamide) [poly(NIPAAm)], was introduced by a photografting method (λ > 300 nm). Dissolving pulp from softwoods was used as cellulose sample. NIPAAm-grafted CMC samples prepared by photografting with CMC peroxide exhibited a slightly larger temperature-responsive character than the samples prepared by photografting with xanthone photoinitiator, where the grafted CMC samples swelled and shrank in water at 5 °C and 60 °C, respectively. Ungrafted and NIPAAm-grafted CMC samples were subjected to peroxidation with hydrogen peroxide in the presence of methanesulfonic acid. About 90% of the initial amount of peroxide on the ungrafted CMC sample disappeared after thermal decomposition at 50 °C for 60 min. On the other hand, about 50% of the peroxide on the NIPAAm-grafted CMC sample remained stable under the same conditions. Peroxides on AA/NIPAAm-grafted samples, which were prepared by photografting of AA/NIPAAm binary monomers followed by peroxidation with hydrogen peroxide, were more stable towards thermal decomposition than those on NIPAAm-grafted samples.