This work reports the qualitative and quantitative identification of volatile products from thermal and thermooxidative decompositions of different epoxy resins to allow selection of the particular chemical species most likely to be detectable in situ by infrared and chemical sensors. Thermogravimetry coupled with Fourier transform infrared analysis (TGA-FTIR) has been carried out on three resins at heating rates ranging from 20 to 70 degrees C/min in increments of 10 degrees C/min to understand the effects of the severities of different heating environments. Pyrolysis-FTIR has been conducted to complement the TGA-FTIR study under static atmospheric conditions hence revealing the volatile production under oxidative conditions. While the evolution of water, CO2, phenolic, carbonyl, aliphatic, aromatic and N-containing species could be observed in all resin types, the intensities and times of evolution of different components varied. Higher heating rates resulted in the evolution of volatiles occurring earlier and at greater intensities, but with a lower total amount of each product being evolved. From detection of CO, CO2 and aliphatic hydrocarbons in early stages of resin decomposition, i.e., prior to ignition, it can be inferred that sensors detecting these gases could be deployed in composites to provide a warning of any potential fires.

This study investigates the mechanism of charring of a hydroxypropyl-modified lignin (TcC) and its 50:50 wt% blend with a bio-based polyamide (PA1010). Potential applications are in carbon fibre and activated carbon production. Thermogravimetric analysis (TGA) coupled with Fourier transform infrared (FTIR) spectroscopy revealed that the blend's thermal stability up to 500 degrees C was lower than expected based on the TGA profiles of the individual components. However, above 500 degrees C, the blend exhibited improved thermal stability. Isothermal pyrolysis was conducted at temperatures between 300 degrees C to 800 degrees C in 50 degrees C intervals. Chars were characterized using FTIR, scanning electron microscopy (SEM), and porosity measurements. There is no evidence of covalent bond formation between the two degrading polymers in the blend. However the melting of PA1010, which surrounds the lignin particles, at 180 degrees C and the relatively high thermal stability of the molten PA1010 up to 400 degrees C, leads to delayed but extended initial thermal dehydration and decarboxylation of the lignin. This results in enhanced aromatization and increased thermal stability of the lignin above 500 degrees C, contributing to enhanced char formation (20.8 % compared to a theoretical value of 17.5 %, calculated form the averaged sum of the chars from its components). These findings indicate the suitability of the blend for carbon fibre formation. However, the reduced porosity of the blend's char (0.5 %), compared to that of lignin alone (4.7 %), indicates that the blend is not suitable for producing an activated carbon. This latter aspect will be discussed in a forthcoming publication.

Fire and mechanical performances of a bio-based flax/furan resin composite are evaluated and, in order to assess their commercial potential, compared with those of conventional carbon/glass fiber-reinforced composites. Fire retardant (FR) variants of flax/furan were obtained by adding FRs to the resin and using (i) flax or (ii) FR-treated flax fabrics. With (i), the fire hazard of the composite could be reduced to minimum, without detrimental effect on the mechanical properties. However, use of FR-flax fabric (ii) led to impairment of mechanical properties. This indicated that for optimized fire and mechanical properties, use of a FR in the resin matrix suffices; there is no advantage in using a FR-treated flax fabric. Natural aging of the samples for 10 years followed by water aging indicated that water absorption in flax/furan composites was much higher than in comparable carbon/epoxy composites. While there was evidence of released acidic components such as acetic acid, oxalic acid, and so forth, in flax/furan composites, mainly from oxidative degradation of furan resin, there was no evidence of leaching of FR additives from the matrix. However, FR treatment of flax fabric affected the fiber-matrix interfacial adhesion, leading to considerable water absorption during aging and disintegration of the reinforcement.Highlights Furan resins are naturally fire retardant, burn only under forced combustion. FR flax/furan composites obtained by adding FRs to the resin or the flax fabric. FR treatment of the flax impairs mechanical properties and water tolerance. FRs in the resin neither affect mechanical properties nor leach out in water. Fabrication of fire retardant (FR) flax/furan composites by adding FR to the resin and using FR-treated flax fabric, and their fire safety indices as compared to conventional carbon/glass fibre - reinforced composites. image

A study of the flammability of a biobased furan resin via limiting oxygen index and UL-94 has shown its inherent flame retardant properties. In a cone calorimetric test at 50 kW/m2 external irradiance, however, it ignited within 50s and burnt, producing 489 kW/m2 peak heat release and 24 MJ/m2 total heat release but minimal smoke production. The flame retardance of the furan resin was further improved by the addition of the phosphorus-containing inorganic flame retardants, ammonium polyphosphate (APP) and melamine polyphosphate (MPP), and their well known condensed phase activity was further supported by thermogravimetric analysis (TGA). The organic flame retardants, resorcinol bis(diphenyl phosphate) (RDP) and bisphenol-A bis(diphenyl phosphate) (BAPP) had no effect on flame retardance, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) had only minimal effects in LOI and cone calorimetric tests, which was at variance to the results of TGA tests. This disconnect between the tests involving flaming combustion (LOI and cone calorimetry) and slow controlled heating (TGA) was attributed to the low flash points and high boiling points of the organic flame retardants, respectively.

Thermal and thermo-oxidative decompositions of polyamide 6.6 (PA66) in the presence and absence of zinc (ZnSt), calcium (CaSt) and copper stannates (CuSt), and in the presence of antimony trioxide (ATO), have been studied by TGA-FTIR and pyrolysis GC/MS. It is shown that whilst ATO has a negligible effect on the rate of decomposition and products of pyrolysis under both slow heating on a TGA and rapid heating on a pyrolysis/GC/ MS apparatus, the stannates have a catalytic effect in the order ZnSt approximate to CaSt > CuSt, evident through release of volatiles at a lower temperature and in a different product distribution following rapid high temperature py-rolysis. In particular, rapid pyrolysis at high temperature in the presence of the stannates promotes formation amongst the pyrolysis products of, for example, 6-aminohexanenitrile. 1,6-hexanediamine, 1-methyl-3-formylin-dole and 1,2,3,7-tetramethylindole, whilst yields of others are reduced, e.g., hexanedinitrile, caprolactam, diaminomethylidene(2-hydroxypropyl)azanium, prop-2-enenitrile (acrylonitrile) and azacyclodecan-5-ol. We suggest that these effects arise from complexation of the electropositive metal in the stannate (Zn, Ca or Cu) with the C=O groups of PA66, thus weakening the C(O)-C and C-N bonds adjacent to the C=O groups. The fact that ZnSt has the most pronounced effect on the pyrolysis product distribution and CuSt the least, we explain in terms of the order of electropositivity of the metal (Zn>Ca>Cu).

A novel blend of unsaturated polyester (UP) resin with an inherently flame-retardant and char-forming melamine formaldehyde (MF) resin has been prepared with the aim of reducing the flammability of the former. MF resin, sourced as a spray-dried resin, was dissolved in diethyleneglycol solvent; the dissolved resin and the UP-MF blend were autocured by heating under conditions normally used for curing UP, i.e., room temperature for 24 h and post-curing at 80 °C for 12–24 h. The cured UP-MF blends, although heterogeneous in nature, were rigid materials having fire performances superior to those of the cured UP alone. The blends also burned, but with a much reduced smoke output compared with that from UP. Although the heterogeneity of the blends helped in improving the fire performances of the blends in terms of the MF domains forming a semi-protective char, acting as thermal barriers for the adjoining UP domains, and hence reducing their thermal degradation, the mechanical properties of composites based on them were impaired. Nevertheless, whilst UP/MF blends may not be suitable for use as matrices in glass-reinforced composites in load-bearing applications, they may lend themselves to applications as fire-retardant gel coats, especially in view of their low-smoke, char-forming attributes.

Owing to their high versatility from chemical and processing perspectives and hence their capability of being tailored for required properties, epoxy resins are used in a wide range of applications ranging from general use to high performing materials. Most of the applications though also require conformation to certain specified fire safety regulations. The flammability (and other properties) of cured epoxy resins depend on the type of resin, curing agent and curing process used, which have been highlighted in this article. The focus of the review though is on the type of flame retardants required to achieve certain levels of flame retardancy. There are numerous research articles and reviews dealing with flame retardancy of epoxy resins in the open literature and it is beyond the scope of this review to cover them all, hence only selected representative papers are discussed here, while references to previous reviews are provided that cover additional work. Different flame retardants and their chemically modified/synthesized variants developed by various researchers have been critically reviewed in terms of their flame retardant efficiency relative to their commonly used/ commercially available counterparts. The issues related to their suitability in terms of processability and performance in certain applications have also been discussed.

The kinetics of pyrolysis of organosolv (TcA) and hydroxypropyl-modified (TcC) lignins have been investigated using thermogravimetric analysis (TGA). Three isothermal models (single first order, Guggenheim and Avrami-Erofeev) and one non-isothermal model (Kissinger) were used to analyse the mass-loss data. Sensible derived kinetic parameters, i.e., activation energy and pre-exponential factor, were obtained only for the initial stages of pyrolysis where the kinetics were approximately first order. Models that analysed TGA data beyond the initial stage gave inconsistent results, indicating the complexity of subsequent decomposition steps occurring at higher temperatures and/or longer times. The kinetics of the initial stage are important for designing routes to lignin's valorisation into useful products, such as carbon fibres, activated carbons, polymer additives, etc. TcC had a higher activation energy (41.5 kJ/mol) for initial decomposition than TcA (39 kJ/mol), consistent with its greater thermal stability observed previously during conversion of lignin-based fibres into carbon fibres.

This study investigated the effects of phosphorus fire retardants (FRs) in matrices from co-cured blends of an unsaturated polyester (UP) with inherently fire-retardant phenolic resoles (PH) on the mechanical and flammability properties of resultant glass fibre-reinforced composites. Three different phenolic resoles with UP have been used: (i) an ethanol soluble (PH-S), (ii) an epoxy-functionalised (PH-Ep), and (iii) an allyl-functionalised resin (PH-Al) with two different phosphorus FRs: resorcinol bis (diphenyl phosphate) (RDP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The flammabilities of the resultant composites were evaluated using cone calorimetry and the UL-94 test. Cone calorimetric results showed reductions in peak heat release rate (PHRR) and total heat released (THR) as expected compared to those of UP and respective UP/PH composite laminates without FRs. UL-94 tests results showed that while all composites had HB rating, FR containing samples self-extinguished after removal of the flame. The mechanical properties of the composites were evaluated using flexural, tensile and impact tests. All FRs reduced the mechanical properties, and the reduction in mechanical properties was more severe in UP/PH-S (least compatible blends) composites with FRs than in UP/PH-Al (most compatible blends) composites with FRs. Amongst the different composites, those from UP/PH-Al with DOPO showed the best fire retardancy with little deterioration of mechanical performance.

The purpose of this work is to functionalize and characterize the surface of nylon 6.6 fabrics by exposure to a novel atmospheric cold plasma coupled with ultraviolet (UV) excimer laser treatment. It was found that plasma/ UV treatment does not significantly physically degrade or ablate fibre surfaces, but creates changes to surface chemistry in the form of additional functional groups (principally NH2 and COOH). These chemical surface changes are not easily analyzed with techniques such as FTIR-ATR, which was found to be too insensitive; therefore, a new low-temperature surface diagnostic dyeing method was developed, and the results of this compared with those from X-ray photoelectron spectroscopy (XPS). Mechanisms for surface changes are proposed, in which surface free radicals are created by the plasma in the presence or absence of the laser, the characteristics of which depend on the atmosphere type and plasma power used. Radical production was observed through the use of a radical scavenger in combination with UV-vis spectroscopic analysis and by electron paramagnetic resonance (EPR).

This study is based on previously reported reaction to fire properties of flax fibre-reinforced polymeric (polypropylene, PP and polylactic acid, PLA) composites, prepared by pre-treating the fabrics with different fire retardants (FRs) prior to composite preparation. It was observed that while all of these treatments were very effective in flax/PLA in terms of achieving a V-0 rating in a UL-94 test, only an organophosphonate FR was capable of achieving a V-0 rating for flax/PP. However, all fire-retardant treatments impaired the mechanical properties of the composites; the reduction was more in flax/PLA compared to flax/PP composites. To understand these effects further, here thermal analysis and pyrolysis combustion flow calorimetry of the composites and each component separately treated with FRs have been conducted and the results analysed in terms of the effect on each component so as to observe any interaction between the different components. The results indicated that in flax/PLA composites, the water released during FR catalysed dehydration-decomposition of flax may hydrolyse PLA, changing decomposition pathway of PLA to produce less flammable volatile, hence resulting in reduced flammability.

Thin coatings of crosslinked poly(vinylphosphonic acid), PVPA, display good adhesion and excellent intumescent, fire-retardant barrier properties when applied to the surfaces of a typical thermoplastic, such as poly(methyl methacrylate), but perform relatively poorly in water-soak tests. To strengthen and further improve the barrier properties of the intumescent char and to make the coating more hydrophobic, PVPA has been complexed with various inorganic and organic species. The chars formed from coatings of some of these hybrid materials are less friable than chars from coatings synthesized from crosslinked PVPA alone, and show higher levels of water tolerance with no significant reduction in dry adhesion to the substrate.

ABSTRACT Coatings based on the in situ photopolymerization of vinyl phosphonic acid (VPA) with triallyl cyanurate as a crosslinking agent are shown to be effective not only for fire‐protecting glass fiber‐reinforced epoxy resin (GRE) composites but also poly(methyl methacrylate) (PMMA), a typical meltable and flammable thermoplastic. Dry adhesion of polyVPA coatings to PMMA surfaces is excellent but, as with coatings on GRE, adhesion following water‐soak tests is poor. Copolymerizing VPA with more hydrophobic monomers improves wet adhesion, albeit with some impairment of fire performance, with copolymers of VPA and acrylonitrile giving the best results. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137 , 47601.

Fabrics from commingled natural (flax), thermoplastic (polypropylene (PP)/polylactic acid (PLA)) polymeric fibres were fire retarded with an oragnophosphonate flame retardant (FR). The fire-retarded flax/PP and flax/PLA fabrics were melt pressed to prepare respective thermoplastic composites. The effect of FR concentration on the fire and mechanical properties of composites was studied and the results analysed in terms of concentration of FR elements in the composites. While the UL-94 test was used as a benchmark to achieve a V-0 rating, cone calorimetric parameters were used for in-depth analysis of fire performance. The results show that flax/PP and flax/PLA composites require a minimum 0.9 and 0.6% phosphorus, respectively, to achieve a V-0 rating in the UL-94 test. Mechanical properties, evaluated in tensile and flexural modes, are however slightly impaired, most probably due to the acidity of the FR solution (pH = 3.2). In order to improve the mechanical properties, a buffer solution was used to change the pH to 6.0, which while having a minimal effect on mechanical properties of flax/PP, significantly reduced those of flax/PLA and increased flammability of both composites and hence overall showed no benefit.

New PCL-HBPG/SiHBPG triblock copolymers composed of a polycaprolactone (PCL) core with two outer blocks of trimethoxysilyl end-capped hyperbranched polyglycidol (HBPG/SiHBPG), of varying molecular weight, have been successfully synthesised and characterised. The effect of copolymer composition and structure upon the crystallization, melting, thermal degradation and aqueous solution behaviour were investigated at various temperatures. In aqueous solution, at concentrations above their corresponding critical aggregation concentration the PCL-HBPG/SiHBPG copolymers readily self-assemble into large multicore structures composed of PCL domains and corona consisting of HBPG/SiHBPG branches. The multicore structures were stabilized by numerous hydrogen-bonds from the HBPG moieties as well as via formation of siloxane crosslinks (i.e. Si-O-Si bonds). As the formation of the siloxane linkages is irreversible the PCL-HBPG/SiHBPG-based particles will be covalently crosslinked at higher concentrations in vivo and form injectable gels scaffolds that will be biocompatible and capable of invoking cell attachment and differentiation without the need for exogenous biological stimuli.

The effects of matrices from co-cured blends of an unsaturated polyester (UP) with inherently fire-retardant and char-forming phenolic resoles (PH) on the mechanical and fire performances of resultant glass fibre-reinforced composites have been investigated. Three different phenolic resoles with increasing order of compatibility with UP have been used. These are: (i) an ethanol soluble resin, (PH–S), (ii) an epoxy-functionalised resin (PH-Ep), and (iii) an allyl-functionalised resin (PH–Al). The mechanical properties of the composites increased with increasing compatibility with two resin types as might be expected, but not previously demonstrated. However, even with the least compatible resin (PH–S), the impact properties were unaffected and the flexural/tensile properties while reduced, were still acceptable for certain applications. Fire properties were however, in reverse order as previously observed in cast resin samples from these composites. Moreover, the reduction in flammability was less compared to those of the cast resin samples, reported previously, explained here based on the insulating effect of glass fibre reinforcement.

Thermoplastic composites were prepared by melt pressing fabrics from commingled natural (flax) -thermoplastic (polypropylene (PP) and polylactic acid (PLA)) polymeric fibres. Fabrics were treated with a number of commercial flame retardants (FRs) used for textiles prior to composite preparation. Their flammabilities and mechanical performances have been evaluated in terms of FR types effective on each fibre type. The fire performances of the composite laminates evaluated using UL-94 showed that flax/PP control and all flame retarded composite samples failed the UL-94 test, except for one treated with organophosphonate FR. On the other hand all flame retarded flax/PLA samples achieved V0 rating. Cone calorimetric results obtained at 35 kW/m(2) also showed that all FRs significantly reduced the flammability of the composites and that their efficiencies were more pronounced in flax/PLA than in flax/PP composites. The mechanical performances of composites evaluated in tensile, flexural and impact modes indicated that all flame retardants reduced the mechanical properties of the composites, with the extent of reduction dependent on the pH of the flame retardant solution used. The reduction in mechanical properties was more severe in flax/PLA composites than in flax/PP composites. (C) 2018 Elsevier Ltd. All rights reserved.

Radical emulsion polymerization of 1,1-bis(ethoxycarbonyl)-2-vinylcyclopropane (ECVCP) was examined in the presence of potassium persulfate (KPS) as an initiator. ECVCP underwent both emulsifier-in emulsion and emulsifier-free emulsion polymerizations to afford the ring-opened polymer in good yields. The copolymerization efficiency of this monomer was also evaluated with methyl methacrylate (MMA) and butyl methacrylate (BMA) as comonomers under the same reaction conditions. The emulsion copolymerization of ECVCP with a relatively hydrophobic monomer, lauryl methacrylate (LMA) was also investigated in presence of ?-cyclodextrin hydrate (?-CD) as a phase transfer agent. Polymerization/copolymerization kinetics, change in particle size and olefin contents were followed during the reaction.

A phenolic novolac resin has been chemically reacted with 4-vinylbenzyl chloride to introduce polymerizable vinyl benzyl groups. The modified novolac spontaneously polymerizes like styrene, is physically and chemically compatible with a typical unsaturated polyester (UP) resin, and can be free-radically cured (crosslinked) alone and in mixtures with UP using styrene as a reactive diluent. The cured vinylbenzylated novolac and co-cured blends of it with UP show superior flame retardance to cured UP alone and have potential applications as matrix resins in glass-reinforced composite laminates especially for marine structures.

Novel blends of two furan resins with an unsaturated polyester have been prepared and cured by parallel free radical (for the unsaturated polyester) and acid-catalysed crosslinking (for the furan resin) to give co-cured composite materials. Although these materials have inferior physical properties, such as low Tg and low storage modulus compared with those of unsaturated polyester and furan resins alone, they show markedly improved flame retardance compared with that of the normally highly flammable unsaturated polyester. This increased flame retardance arises from a condensed phase mechanism in which the furanic component forms a semi-protective char, reducing rates of thermal degradation and total heat release and heat of combustion. The blends also burn with reduced smoke output compared with that from unsaturated polyester alone.