John Ebdon

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°C was lower than expected based on the TGA profiles of the individual components. However, above 500°C, the blend exhibited improved thermal stability. Isothermal pyrolysis was conducted at temperatures between 300°C to 800°C in 50°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°C and the relatively high thermal stability of the molten PA1010 up to 400°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°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.
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•Lignin/PA1010 blend less stable than lignin, but produces more char than expected.•No chemical, only physical interactions between lignin and PA1010 during pyrolysis.•Molten PA1010 encapsulates lignin, promoting aromatisation and char formation.•Blend a suitable precursor for carbon fibre, but for high-porosity activated carbon.

This work reports the qualitative and quantitative identification of volatile products from thermal and thermo-oxidative 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 °C/min in increments of 10 °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.

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

•Furan resin has low ignitibility, but burns readily only under forced combustion.•Inorganic P-containing FRs reduce flammability of resin by catalysing charring.•Organic P-containing FRs, RDP, BAPP and DOPO, are only minimally effective in resin.•Organic FRs show unexpected behaviours in TGA vs. LOI and cone calorimetric tests.•Differences in behaviour attributed to high boiling and flash points of organic FRs.
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 50 s 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 ≈ CaSt > CuSt, evident through release of volatiles at a lower temperature and in a different product distribution following rapid high temperature pyrolysis. 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-formylindole 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).

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.

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 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 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.