The flame-retardant material - 1. Studies on thermal characteristics and flame retardance behavior of phosphorus-containing copolymer of methyl methacrylate with 2-methacryloxyethyl phenyl phosphate

2-Methacryloxyethyl phenyl phosphate/methyl methacrylate (MEPP/MMA) copolymers were synthesized by the bulk polymerization of MMA in the presence of various amounts of MEPP. MEPP was prepared by the esterification of phenyl dichlorophosphate with 2-hydroxyethyl methacrylate, followed by hydrolysis. Structural and compositional details of MEPP were obtained by Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance, ¹³C nuclear magnetic resonance, ³¹P nuclear magnetic resonance, and mass spectrometer, as well as by elemental analysis. The monomer reactivity ratios of MEPP/MMA system were calculated by the methods of Fineman-Ross, Kelen-Tüdös, and Joshi-Joshi. The thermal degradation temperature of the MEPP/MMA copolymers was considerably enhanced by only a slight decrease in T_g, as determined by differential scanning calorimetry and thermogravimetric analysis experiments. The fire-retardant properties of MEPP/MMA copolymers were also studied by LOI and UL-94 tests, indicating that an MEPP/MMA copolymer with only 2.17 wt% phosphorus can effectively inhibit burning.     

Thermal and thermo-oxidative degradation of poly(hydroxy ether of bisphenol-A) studied by TGA/FTIR and TGA/MS

The nature and the extent of degradation of poly(hydroxy ether of bisphenol-A) phenoxy resin were analysed by thermogravimetry (TGA/DTGA) under nitrogen and air atmosphere. Decomposition kinetics were elucidated according to Flynn-Wall-Ozawa, Friedman and Kissinger methods. The evolved gases during degradation were inspected by a thermogravimetry analyser coupled with Fourier Transform Infrared Spectrometer (TGA/FTIR) and also with a TGA coupled to a Mass Spectrometer (TGA/MS). Mass spectra showed that chemical species evolved in phenoxy decomposition in air were very similar to those assigned from degradation in nitrogen (water, methane, CO, CO₂, phenol, acetone, etc.). However, these species appear in different amount and at different temperatures in both atmospheres. FTIR analysis of the evolved products showed that water and methane were the beginning decomposition products, indicating that decomposition is initiated by dehydration and cleavage of C-CH₃ bond in the bisphenol-A unit of phenoxy resin. After this initial stage, random chain scission is the main degradation pathway. Nevertheless, in air atmosphere, previously the complete decomposition of the phenoxy obtaining fundamentally CO₂, and water, the formation of an insulated surface layer of crosslinked structures has been proposed.     

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.     

Confirming the Designed Thermal Degradation of a Polycarbonate by Tga/Ft-Ir

Abstract

Integrated thermogravimetric analysis/Fourier transform infrared spectroscopy (TGA/FT-IR) was applied to study the thermal degradation of an aliphatic polycarbonate based on 2,5-dimethyl-2,5-hexanediol and 1,4-cyclohexanediol. A single experiment confirms that the polymer decomposes as designed to the expected products. Carbon dioxide, 1,4-cyclohexanediol, and isomeric hexadienes were thus detected and identified by comparison of their vibrational spectra with those of pure compounds in the spectral library. Some mechanistic implications are discussed.     

CP-MAS C NMR and FT-IR investigation of the degradation reactions of polymer constituents in wood welding

The essential chemical modifications involving the polymeric constituents of wood in friction welding occur in the first 5-6 s slowing down or even stopping afterwards. FT-IR and CP-MAS ¹³C NMR of the welded area of wood have shown dehydration and an apparent increase in the crystallinity of cellulose. A certain level of hemicelluloses degradation occurs, accompanied by the generation of some furfural. Cellulose degradation is instead very slight. Both analytical techniques show an increase in the proportion of lignin in the welding interphase. A proportion of methoxy groups of lignin is de-etherified to phenolic hydroxy groups. Self-condensation of lignin occurs by internal rearrangement with the formation of Ar-Ar and Ar-CH₂-Ar bridges. This progresses throughout the whole process of welding. The formation of C-O-C bridges, although stopping after 6 s welding, at the start of wood carbonisation, also appears to contribute to the increase in cross-linking of the lignin network.     

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.     

Development and characterisation of flame-retardant fibres from isotactic polypropylene melt-compounded with melamine-formaldehyde microcapsules

Intumescent flame-retardant textiles have been developed from flame-retardant microcapsules. The work is based on the synthesis of different melamine-formaldehyde microcapsules containing di-ammonium hydrogen phosphate and/or poly(1,6-hexamethylene adipate) by in-situ polymerisation. Two types of shell have been produced, composed of melamine formaldehyde or melamine formaldehyde-poly(hexamethylene adipate glycol). The microcapsules obtained were melt-compounded at 5%-wt with an isotactic polypropylene matrix using a twin-screw extruder, and multi-filaments have afterwards been spun from the various extrudates. The manufactured fibres were mechanically characterized by measuring their tensile properties, and their thermal properties were investigated by DSC and TGA. Finally, knitted fabrics were processed from the multi-filaments: their flame-retardant properties were evaluated by performing a fire test with a cone calorimeter, and their thermal conductivity measured with a Hot Disk. The different thermal behaviours are discussed in terms of the influence of system formulation on the overall thermal degradation, due to interactions between the different components of the flame-retardant microcapsules. The results showed that for one of the structures, an intrinsic intumescent flame-retardant system has been achieved.     

Physico-mechanical, thermal and morphological behaviour of polyurethane/poly(methyl methacrylate) semi-interpenetrating polymer networks

Semi-interpenetrating polymer networks (SIPNs) of polyurethane (PU) and poly(methyl methacrylate) (PMMA) in different weight ratios viz., 90/10, 70/30, 60/40 and 50/50 were prepared. The SIPNs were characterized for physico-mechanical properties like density, tensile strength and elongation at break. Thermal stability of IPNs was measured using thermogravimetric analysis (TGA). From the TGA thermograms it was noticed that all IPNs are stable up to 325 °C and undergo three-step thermal degradation in the temperature ranges 251-400, 378-508 and 445-645 °C for first, second and third steps, respectively. Thermal degradation kinetic parameters like activation energy (E_a) were calculated using Broido, Coats-Redfern and Horowitz-Metzger models. The values obtained by Broido and Horowitz-Metzger methods showed concurrency, whereas Coats-Redfern method showed relatively lower values. Surface morphology measured using scanning electron microscope (SEM) showed two-phase morphology for all the IPNs.     

Thermal degradation behavior of polymethacrylates containing amine side groups

The thermal degradation behavior of polymethacrylates containing amine groups such as poly(N,N-diethyl aminoethyl methacrylate), PDEAEM, and poly(N-ethyl-m-tolyl-aminoethyl methacrylate), PMEET, has been studied using thermogravimetry coupled with infrared spectroscopy (TGA/FTIR). PDEAEM showed two degradation stages whereas PMEET displayed only one. The thermal degradation of PDEAEM initially takes place through ester cleavage of the polymethacrylate, generating volatile tertiary amines and alcohols and polymethacrylic anhydride in the remaining solid material. This is followed by further fragmentation of the modified polymeric chain formed. It was also observed that storage of the original polymer affected the thermal decomposition behavior of PDEAEM. The main thermal degradation pathway for PMEET is an immediate backbone chain scission to yield oligomers.     

Thermal behavior and degradation mechanism of poly(bisphenyl acryloxyethyl phosphate) as a UV curable flame-retardant oligomer

Poly(bisphenyl acryloxyethyl phosphate) (BPAEP) was blended in different ratios with urethane acrylate EB220 to obtain a series of UV curable flame-retardant resins. The thermal degradation mechanisms of their cured films in air were studied by thermogravimetric analysis, in situ FTIR and direct pyrolysis/mass spectrometry measurements. The results showed that BPAEP/EB220 blends have lower initial decomposition temperatures (T_di) and higher char residues than pure EB220, while BPAEP has the lowest T_di and the highest char residue. The degradation process of BPAEP was divided into three characteristic temperature regions, attributed to the decomposition of phosphate, ester group and alkyl chain, and aromatic structure in the film.     

Unconventional cellulose products by fluorination of tosyl cellulose

The synthesis of novel deoxy-fluoro cellulose derivatives obtained by nucleophilic displacement reactions (SN) of p-toluenesulfonyl (tosyl) cellulose with tetrabutylammonium fluoride (TBAF) is described. Detailed studies concerning the influence of the reaction time and temperature as well as the water content of the TBAF on the composition of the products were carried out. The SN reaction occurs even at room temperature. The degree of substitution of deoxy-fluoro moieties (DSF) is in the range from 0.22 to 0.47. The polymers contain remaining tosyl groups. Preliminary 19F NMR measurements reveal the presence of the CH2F group. The degradation temperature of the deoxy-fluoro cellulose derivatives is increased compared to the starting tosyl cellulose, however, a distinct influence of the remaining tosyl groups appears.     

Influence of iron content on thermal stability of magnetic polyurethane foams

Magnetorheological (MR) materials are a group of smart materials which have the controllable magnetic properties with an external magnetic field. Magnetic foams, a specific type of MR solids, were synthesized from flexible polyurethane (PU) foams and carbonyl iron particles. Effects of the carbonyl iron particles on the thermal stability of the magnetic foams have been studied. Thermogravimetric analysis (TGA) was applied to characterize the thermal degradation process of the magnetic foams and then the apparent activation energy of degradation was calculated by using Ozawa's method [Ozawa T. A new method of analyzing thermogravimetric data. Bulletin of the Chemical Society of Japan 1965; 38: 1881-1886.]. The carbonyl iron particles were found to improve the thermal stability of magnetic foams in nitrogen by showing higher 10 wt% loss temperature, slower weight loss rate and higher apparent activation energy than pure PU foams. But the magnetic foams were observed to have slightly worse thermal stability in air than pure PU foams at the earlier degradation stage. At the later degradation stage, the magnetic foams exhibited the higher activation energy than pure PU foams in air.     

The influence of comonomers on the degradation and flammability of polyacrylonitrile: Design input for a new generation of flame retardants

A series of homo- and copolymers of acrylonitrile was prepared under radical initiation in DMF solutions. The thermal and flammability characteristics of these polymers were evaluated through thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), and by limiting oxygen index (LOI) measurements. The thermal degradation behaviours of the polymers were assessed primarily with a view to designing comonomers, for acrylonitrile-based polymers, bearing flame retardant moieties. Broadly speaking, in LOI tests acrylic-based comonomers were found to improve fire performance. For instance, the incorporation of methacrylic acid gave a limiting oxygen index value of 26.4 at 30.9 mol% loading, and an intumescent char was produced upon burning.     

Pyrolysis products and thermal degradation mechanism of intrinsically flame-retardant calcium alginate fibre

Intrinsically flame-retardant calcium alginate fibre was prepared by wet spinning and its pyrolysis products and thermal degradation mechanism studied. Combustion behaviour and flammability were assessed using the limiting oxygen index (LOI) and cone calorimetry. LOI results showed that calcium alginate fibre was intrinsically flame retardant with LOI value of 48.0, as compared to about 20.0 for viscose fibre. Cone calorimetry indicated that heat release rate and total heat release values of intrinsically flame-retardant fibre were significantly less than those of viscose fibre. It also shown that intrinsically flame-retardant fibre combustion produced greater quantities of residues than did viscose fibre combustion. Combustion residues were examined using scanning electron microscopy, indicating that calcium alginate fibre produced consistent, thick residue crusts. Pyrolysis was investigated using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) which showed that cracking products produced from calcium alginate fibres combustion were less than those in viscose fibre combustion, and pyrolysis of the intrinsically flame-retardant fibre was incomplete. Thermogravimetric analysis (TG) indicated that calcium alginate fibre generated more residues containing carbonaceous char and calcium carbonate, as compared with viscose fibre. We propose a condensed phase mechanism for the calcium alginate fibre flame-retardancy effect.     

TGA/FTIR studies of segmented aliphatic polyurethanes and their nanocomposites prepared with commercial montmorillonites

Nanocomposites prepared with segmented polyurethane (SPU) and commercially available nanoclays (Cloisite™ Na⁺, Cloisite™ 15A, Cloisite™ 30B) were studied using thermogravimetric analysis coupled with Fourier Transform Infrared Spectroscopy (TGA/FTIR). The results showed that the thermal degradation of unfilled SPU and the 4, 6 and 10 wt% hand mixed nanocomposites occurred in two stages being the first due to degradation of hard segments and the second due to the degradation of soft segments. It was also found that the thermal stability of these nanocomposites was not improved by increasing nanoclay concentration except for SPU/Cloisite™ 15A nanocomposites were a 40 °C increase was observed. In a similar manner, FTIR spectra of the evolved gases obtained after the thermal degradation of these nanocomposites were qualitatively similar to the unfilled polymer except in those containing Cloisite™ 30B where isocyanate absorptions were detected. In contrast, SPU/Cloisite™ 30B nanocomposites prepared by in-situ polymerization, exhibited higher thermal stability than the corresponding hand mixed nanocomposites. In addition, these nanocomposites exhibited the presence of carbon dioxide in the evolved gases during its second degradation stage which was not observed in the hand mixed nanocomposites. In this case, it can be said that the presence of clays in the nanocomposites has a significant effect on the thermal degradation pathways.     

Degradation mechanism of diethylene glycol units in a terephthalate polymer

Diethylene glycol (DEG) is incorporated into poly(ethylene terephthalate) (PET) during industrial synthesis in order to control crystallisation kinetics. DEG is known to be a weak point in the thermal degradation of PET, which is problematic during the recycling of the polymer.Studies on the thermal decomposition of the model polymer poly(diethylene glycol terephthalate) (PDEGT) have been performed using TG, DSC, TVA and spectroscopic techniques. They revealed a degradation behaviour with two distinct steps, where the first step initiates some 100 K below the degradation temperature of PET. The second step is similar to the behaviour of PET.Based on our observations, a new degradation mechanism specific to DEG units is proposed, where random ether groups along the backbone can back-bite and form cyclic oligomers. These cyclic species, containing ether moieties, are evolved at 245 °C and constitute the first of the two steps of degradation observed for PDEGT.     

Studies on structure property relationship in a polymer–clay nanocomposite film based on (PAN)8LiClO4

A new combination of ionically conducting polymer–clay nanocomposites based on (PAN)₈LiClO₄ + x wt % montmorillonite (unmodified) clay has been prepared using the standard solution cast process. X-Ray diffraction (XRD) analysis reveals strong interaction of polymer salt complex (PS) with the montmorillonite matrix evidenced by changes in d₀₀₁ spacing of the clay and enhancement in the clay gallery width on composite formation possibly due to intercalation of polymer–salt complex into nanometric clay galleries. Evidences of such an interaction among polymer–ion–clay components of the composite matrix has also been observed in the Fourier transform infrared (FTIR) spectrum results. FTIR results clearly indicated cation (Li⁺) coordination at nitrile (CN) site of the polymer backbone along with appearance of a shoulder suggesting strong evidence of polymer–ion interaction. Addition of clay into the PS matrix has been observed to affect ion–ion interaction resulting from ion dissociation effect at low clay loading in the PNC films. Complex impedance spectroscopy (CIS) analysis has provided a response comprising of a semicircular arc followed by a spike attributed respectively, to the bulk conduction and electrode polarization at the interfaces. Electrical transport appears to be predominantly ionic (t_ion = 0.99) with significant improvement in the electrical conductivity and thermal stability properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2577–2592, 2008     

Thermal oxidative degradation kinetics of flame-retarded polypropylene with intumescent flame-retardant master batches in situ prepared in twin-screw extruder

The thermal oxidative degradation kinetics of pure PP and the flame-retarded (FR) PP materials with intumescent flame-retardant (IFR) master batches in situ prepared in twin-screw extruder were investigated using Kissinger method, Flynn-Wall-Ozawa method and Coats-Redfern method. The results showed that the activation energy order of PP and FR PP samples with different blowing agent/char former ratios obtained by Kissinger method agrees well with that obtained by Coats-Redfern one, which well illustrates the relationship between the composition of IFRs and their flame-retardancy, i.e. FR material with richer carbonization agent has higher activation energy for thermal oxidative degradation, hence leading to a better flame-retardancy. For Flynn-Wall-Ozawa method, due to its adoption of Doyle approximation, the obtained activation energy and its order of samples are very different from those of both Kissinger and Coats-Redfern methods. Criado method was finally used to determine the degradation reaction mechanism of various samples.     

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.     

TGA/FT-IR: Thermogravimetric analysis with fourier transform infrared detection of evolved gases

Thermogravimetric analysis (TGA) is a widely employed technique for measuring the change in weight of a sample as a function of temperature or time in a controlled atmosphere. FT-IR has been utilized with success in the identification of gases [1]. The combination of these two techniques permits a complete characterization of materials in terms of thermal stability and decomposition mechanisms [2]. A complete integrated system for TGA/FT-IR analysis is described.