Thermogravimetry Coupled With Fourier Transform Infrared Spectroscopy Research Articles

Degradation of polyacrylic elastomers: Theoretical and experimental studies

A series of Reactive Force Field (ReaxFF) molecular dynamics simulation was performed on polyacrylicester terpolymer for the first time to understand its thermal decomposition characteristics. The effects of time and temperature on the evolution of various products were analyzed. Alkyl radicals were discovered as dominant products at low temperature along with carbon dioxide. Additionally, alkenes were also detected in the final products at higher temperature. Other small molecular products including alkoxy radicals and carbon monoxide were also noticed in the end products. Evolution mechanisms of dominant products (alkyls and alkenes) were explored in detail based on the simulation approach. The fracture of ester linkage is the typical initiation step for the formation of alkyl radicals. The pathway for yielding alkenes mainly consists of the β-hydrogen elimination from the side chain ester groups. The products during the thermal decomposition processes of polyacrylicester predicted theoretically were in agreement with the experimental results from thermogravimetry coupled with fourier transform infrared spectroscopy (TGA-FTIR) and simultaneous thermal analysis coupled with gas chromatography and mass spectroscopy (STA-GC-MS). The apparent activation energy for thermal decomposition of polyacrylicester obtained from the ReaxFF simulation was also consistent with the experimental results.

Aluminium diethylphosphinate versus ammonium polyphosphate: A comprehensive comparison of the chemical interactions during pyrolysis in flame-retarded polyolefine/poly(phenylene oxide)

A systematic comparison of chemical interactions and fire behaviour is presented for the thermoplastic elastomer (block copolymer styrene-ethylene-butadiene-styrene) (TPE-S)/diethyl- and methylvinyl siloxane (Si)/poly (phenylene oxide) (PPO), flame-retarded with aluminium diethylphosphinate (AlPi) and with ammonium polyphosphate (APP), respectively. TPE-S/APP/Si/PPO performed better in the cone calorimeter test (reduction in peak heat release rate from 2042 to 475kWm−2), but TPE-S/AlPi/Si/PPO in the flammability tests (oxygen index (OI) and UL 94). This difference was caused by the different modes of action of APP (more in the condensed phase) and AlPi (mainly in the gas phase). Thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) was used to analyse the mass loss and the evolved gas products, while a Linkam hot-stage cell to investigate the decomposition in the condensed phase. Moreover, a detailed analysis of the fire residues was done using solid-state NMR. 13C MAS NMR showed that both flame-retarded compositions form graphite-like amorphous carbonaceous char, originating from PPO. 31P MAS NMR and 29Si MAS NMR delivered important information about interaction between phosphorus and the siloxane. For TPE-S/AlPi/Si/PPO aluminium phosphate and silicon dioxide occurred, while also silicophosphate was produced in TPE-S/APP/Si/PPO. The direct comparison of two of the most prominent halogen-free flame retardants containing phosphorus delivered meaningful insights into the modes of action and molecular mechanisms controlling flame retardancy.

Sulphurous additives for polystyrene: Influencing decomposition behavior in the condensed phase

ABSTRACTThe thermal decomposition behaviour of polystyrene (PS) containing sulphur and phosphorus additives was investigated, using thermogravimetry coupled with Fourier transform infrared spectroscopy (TGA‐FTIR). It was found that the additives influence the decomposition process of the polymer in the condensed phase, resulting in a decrease in styrene monomer formation and an increase in styrene oligmer derivatives. Via reference measurements with binary mixtures it was found that the presence of sulphur additives influences the radicalic decomposition process of PS. In combination with quantum chemical calculations it was concluded that this is due to the formation of radicals that abstract hydrogen from the polymer matrix at lower temperatures, disfavouring the radicalic decomposition pathway leading to styrene. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2015,132, 41665.

Comparative study on thermal decomposition and combustion behavior of glass‐fiber reinforced poly(1,4‐butylene terephthalate) composites containing trivalent metal (Al, La, Ce) hypophosphite

High fire hazards of glass‐fiber reinforced polymer composites have greatly limited their development and application. To reduce their flammability, the composites have to be treated with flame retardants. This work examines the use of three trivalent metal (Al, La, Ce) hypophosphites as halogen‐free flame retardants for glass‐fiber reinforced poly(1,4‐butylene terephthalate) (GRPBT) composites. The aim of this study is to quantitatively investigate the effect of metal hypophosphites on the thermal decomposition and combustion behavior of GRPBT composites by means of cone calorimeter and thermogravimetry coupled with Fourier transform infrared spectroscopy (TG‐FTIR) techniques. The peak heat release rate and total smoke production of GRPBT/cerium hypophosphite (CHP) composite evaluated by cone calorimeter are reduced, respectively, by around 76 and 44% compared to the results of GRPBT. The volatilized esters measured by TG‐FTIR in the decomposition of GRPBT/CHP are decreased by about 69%. The results showed that rare earth hypophosphites can effectively inhibit the thermal decomposition and combustion behaviors of GRPBT in comparison with aluminum hypophosphite. POLYM. COMPOS., 34:1832–1839, 2013. © 2013 Society of Plastics Engineers

Thermal degradation of organic matter in the interlayer clay–organic complex: A TG-FTIR study on a montmorillonite/12-aminolauric acid system

The storage of natural organic matter within the interlayer space of layered silicate is an important type of clay–organic association in sediment. However, the role of the interlayer space of clay minerals in the thermal degradation of organics and the generation of hydrocarbons has not been well understood. In this study, an interlayer clay–organic complex was synthesized using montmorillonite (Mt) and 12-aminolauric acid (ALA). An Mt–ALA complex in which Mt and ALA were simply mixed was also prepared for comparison. Thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) was applied to monitor the thermal events and the corresponding products during the thermal degradation of the Mt–ALA complexes. In the absence of Mt, ALA decomposed at 467°C via the cleavage of CC bonds, producing aliphatic hydrocarbon, N-containing compounds, and carboxylic acid. The decomposition temperatures of organic matter in the mixed Mt–ALA complex and the interlayer Mt–ALA complex decreased to 402 and 342°C, respectively. The most characteristic products of the interlayer Mt–ALA complex were NH3 and saturated hydrocarbons. The Brønsted acid sites in the interlayer space of Mt, arising from the dissociated interlayer water, initiated the deamination of ALA via the Hoffmann elimination pathway and significantly promoted the cracking of hydrocarbons via a carbonation mechanism. Lewis acid sites had little effect on the thermal degradation of ALA. This work indicated that the interlayer space of clay minerals provided the storage space for organic matter. Moreover, the active sites within the interlayer space strongly promoted the thermal degradation of organics.

Comparison of the effect of montmorillonite, magnesium hydroxide and a mixture of both on the flammability properties and mechanism of char formation of HDPE composites

The effects of pristine (MMT), organo-modified montmorillonite (OMMT), magnesium hydroxide (MDH) and combination of montmorillonites and magnesium hydroxide on the fire retardancy of high density polyethylene were assessed using TGA-FTIR analysis, limiting oxygen index (LOI), UL-94 test and the cone calorimeter. The results indicated that the addition of organo-modified montmorillonite to high density polyethylene HDPE/MDH composites allowed achievement of higher limiting oxygen index values at lower total flame retardants content while fulfilling the fire retardancy requirements. High density polyethylene composites with pristine (MMT) or organo-modified (OMMT) montmorillonite were prepared by melt-blending in a twin-screw co-rotating extruder introducing two methods. In the first method montmorillonites or magnesium hydroxide was directly provided to high density polyethylene matrix to obtain HDPE/MMT, HDPE/OMMT and HDPE/MDH composites. The second method consists of two stages. The extrusion of master batches of ethylene-vinyl acetate copolymer (EVA) with pristine or organo-modified montmorillonite (ratio 1:1) in first stage and dilution of obtained premix in high density polyethylene matrix in second stage. The thermogravimetry coupled with Fourier transform infrared spectroscopy (TGA-FTIR) results indicate that pristine MMT, OMMT, MDH and their combination have an effect on the thermal degradation of HDPE in oxidative atmosphere. Cone calorimetry showed that, montmorillonites shorten times of ignition and reduce peak heat release rates (peak HRRs). Magnesium hydroxide, however delayed ignition owing to loss of water at lower temperatures, reduced the peak HRR. The reduced peak HRRs for OMMT and MDH together can be attributed to the formation of a surface layer which acts as mass and heat barrier to protect the underlying material from further burning. The flame retardant efficiency of magnesium hydroxide in high density polyethylene matrix was improved by application of MMT or OMMT introduced in ethylene-vinyl acetate copolymer.

Pyrolysis of medium density fiberboard impregnated with phenol-formaldehyde resin

Woodceramics (WCS) are new porous carbon materials that have been shown to possess many excellent properties, but the chemical mechanism during pyrolysis has not been reported yet. In order to investigate this process, pyrolysis of medium density fiberboard (MDF) was analyzed by thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) in this study. The results showed that the pyrolysis consisted of three stages up to 700°C. The first stage of the pyrolysis occurred below 240.0°C and was mainly due to moisture evaporation. The second stage between 240.0° and 390.2°C accompanied the main mass loss. The maximum pyrolysis speed (mass loss) was about 3.79% per minute at 313.2°C. This was believed to coincide with the cleavage of ether bridges between the wood material and phenol-formaldehyde (PF) resin, and pyrolysis of carbohydrate. At higher temperature, the pyrolysis of PF resin and lignin was the main reason for the mass loss in the third stage. The microcosmic environments of both the MDF and PF resin in the MDF treated with PF resin were different from the untreated MDF and PF resin, so that the temperatures at which their pyrolysis occurred and the quantities of evolved gases were different. During the process of WCS preparation, the rate of temperature increase should be very slow before it reaches 700°C, especially at around 313.2°C, at which point violent pyrolysis occurs. Such temperature control should allow uniform sintering of the sample and should reduce flaws in the product.

Thermal degradation studies of alkyl-imidazolium salts and their application in nanocomposites

Increasing the thermal stability of organically-modified layered silicates is one of the key points in the successful technical application of polymer-layered silicate nanocomposites on the industrial scale. To circumvent the detrimental effect of the lower thermal stability of alkyl ammonium-treated montmorillonite, a series of alkyl-imidazolium molten salts were prepared and characterized by elemental analysis, thermogravimetry (TGA) and thermal desorption mass spectroscopy (TDMS). The effect of counter ion, alkyl chain length and structural isomerism on the thermal stability of the imidazolium salts was investigated. Alkyl-imidazolium-treated montmorillonite clays were prepared by ion exchange of the imidazolium salts with Na-montmorillonite. These organically-modified clays were characterized by X-ray diffraction (XRD), TDMS and thermogravimetry coupled with Fourier transform infrared spectroscopy (TGA-FTIR), and compared to the conventional quaternary alkyl ammonium montmorillonite. Results indicate that the counter ion has an effect on the thermal stability of the imidazolium salts, and that imidazolium salts with PF 6 −, N(SO 2CF 3) 2 − and BF 4 − anions are thermally more stable than the halide salts. A relationship was observed between the chain length of the alkyl group and the thermo-oxidative stability; as the chain length increased from propyl, butyl, decyl, hexadecyl, octadecyl to eicosyl, the stability decreased. The results also show that the imidazolium-treated montmorillonite has greater thermal stability compared to the imidazolium halide. Analysis of the decomposition products by FTIR provides an insight about the decomposition products which are water, carbon dioxide and hydrocarbons.

TG-MS and TG-FTIR applied for an unambiguous thermal analysis of intumescent coatings

Thermogravimetry (TG), thermogravimetry coupled with mass spectroscopy (TG-MS) and thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) were used to characterise the thermo-oxidative behaviour of two intumescent coating materials. The temperature dependence, the corresponding volatile products and the amount of residue of the different processes were determined. Using both TG-MS and TG-FTIR results in an unambiguous interpretation of the volatile products. Characteristics such as the influence of endothermic reactions, the release of non-flammable gases, the dehydrogenation enhancing the char formation and the stability of the cellular char were discussed in detail. It was demonstrated, that TG, TG-MS and TG-FTIR are powerful methods to investigate mechanisms in intumescent coatings and that they are suitable methods in respect to quality assurance and unambiguous identification of such materials.

TG/FT-IR studies of poly(vinyl chloride) blends

Thermogravimetry coupled with Fourier transform infrared spectroscopy (TG/FT-IR) was used to investigate the stabilizing action of 3-(2,4-dibromophenylazo)-9-(2,3-epoxypropane)carbazole on the degradation of poly(vinyl chloride) (PVC). It was found that this secondary stabilizer increases the initial temperature of hydrogen chloride evolution (the main process responsible for PVC decomposition), thereby allowing its application for novel PVC systems with enhanced thermal stability. The application of TG/FT-IR technique for study of the thermal properties of polymeric materials offers additional characterization options in comparison with thermogravimetry, if used alone.