1、tall, d,band Mathematics, 1a Parades st., Daugavpils, Latviaarticle infoammability, polyurethanes form carbon monoxide, hydrogen cy-anide, and other toxic products on thermal decomposition andcombustion 1. Studies on the rigid PU-PIR foam thermal decom-position usually investigates the data obtained
2、 from anaerobicpyrolysis or combustion in air/aming, yet neither method canthose in real res.between thefoam form a directheat and oxygenknow asfoam excretes apyrolytic and lowy dependent oningredients used in the foam production.In general, the foams are prepared primarily by the reaction ofpolyiso
3、cyanates (NCO) with polyol compounds. Additionally, theisocyanates can also react in the presence of water to produce acarbamic acid (step 1) which decomposes to produce an amine andcarbon dioxide (CO2) (step 2). (see Fig. 1)The CO2performs as a blowing agent and the amines may reactfurther with the
4、 isocyanates to form disubstituted ureas (step 3).Further reactions occur with amines, water, ureas, urethanes and* Corresponding author. Latvian State Institute of Wood Chemistry, 27 DzC22erbenesst, Riga, LatviaContents lists available at ScienceDirectPolymer DegradationPolymer Degradation and Stab
5、ility 180 (2020) 109313E-mail address: sanita.reinerteinbox.lv (S. Reinerte).1. IntroductionWithintheheatinsulationindustry, rigidpolyurethane(PU)andpolyisocyanurate (PIR) foams have long established their place asone of the best commercial insulation materials, possessing anextremely low thermal co
6、nductivity and lightness in mass. Thesecharacteristics are due to their cellular structure, which, unfortu-nately, also renders the material highly ammable. In addition toyield results that would be fully comparable toThe compact placement of the rigid PU-PIR foambuilding external and internal walls
7、 shields theame, thus it is the combination of transferredthat initiates and sustains the thermal decompositionsmouldering. Under smouldering, the rigid PU-PIRcombination of gaseous compounds released inoxygen conditions, the chemical compounds highl 2020 Elsevier Ltd. All rights reserved.Article hi
8、story:Received 6 March 2020Received in revised form29 April 2020Accepted 20 July 2020Available online 24 July 2020Keywords:Thermal stabilityRigid PU-PIR foamTall oil fatty acidsTGADTAFTIRhttps:/doi.org/10.1016/j.polymdegradstab.2020.109310141-3910/ 2020 Elsevier Ltd. All rights reserved.abstractThis
9、 study is an investigation of the suitability of the thermogravimetry and differential thermal analysismethod coupled with Fourier Transform Infrared spectrometry (TG/DTA-FTIR) for a thermal degradationgaseous product analysis of a rigid polyurethane-polyisocyanurate (PU-PIR) foam synthesised from h
10、ighfunctionality tall oil fatty acids (TOFA) based polyols. The FTIR spectra of the TG-generated gaseousthermal degradation products of three PU-PIR formulations with varied high functionality TO basedpolyol content (45, 75 and 95 pbw) and a different tier of isocyanate (NCO) indexes (110, 150, 200,
11、 300and 400) for each formulation were compared to the spectra of a formulation developed using con-ventional raw materials. The chemical bands of known chemical compounds and unknown compoundscontaining specic groups for the foams were evaluated; the focus was on the maximum release rate forspecic
12、chemical compounds (CO2; eNCO; H2O; CO) to determine the temperature zone values of themain thermal degradation phases. The experiments were carried out at a low oxygen environment,providing valuable data on the trends for the excretion of specic gaseous substances from the rigid PU-PUR foam that co
13、uld be released in a real re, where organic building materials that possess a porousmatrix might be present and the nature of the combustion process is predominantly heterogeneousoxidation.dDaugavpils University, Faculty of Natural SciencesUniversity of Latvia, Faculty of Chemistry, 1 Jelgavas st.,
14、Riga, LatviacUniversity of Latvia, Institute of Chemical Physics, 1 Jelgavas st., Riga, LatviaTG/DTA-FTIR as a method for analysis ofpolyurethane foam decomposition gaseousenvironmentSanita Reinertea, b, *, Liga Avotinac, Arturs ZarinscaLatvian State Institute of Wood Chemistry, 27 DzC22erbenes st.,
15、 Riga, Latviajournal homepage: based rigidproducts in a low oxygenUgis Cabulisa, Arturs Viksnaband Stabilityocate/polydegstabformationeven other NCO to produce a diverse range of functional groupsincluding urethanes, ureas, isocyanurates, carbodiimides and ure-tdiones 1. In the presence of excess NC
16、O, the above productsundergo additional reactions, yielding allophanate and biuretstructures that may produce further cross-linking, forming poly-isocyanurates (PUR). Due to the acute toxicity of NCO and its effectson human health and the environment, NCO alternatives for a saferPU production are se
17、arched for, with a method involving the step-growth polyaddition of 5-membered cyclic carbonates with di-amines, possibly representing the most promising route for a large-scale production of non-isocyanate polyurethane (NIPU) products3.The polyols containing ether or ester linkages are the source o
18、fhydroxyl groups. The most common polyols are based on pro-poxylated sucrose, aromatic polyamines, pentaerythritol, and sor-bitol. Depending on the desired properties for the end material, theformulations of rigid polyurethane foam may also include surfac-tants, re retardants, llers, and catalysts,
19、such as tertiary amines2. Historically, organotin compounds (stannanes) have been alsoemployed as chemical catalysts, but due totheir intrinsic toxicity tothe health and the environment, those have been largely phasedout of the PU-PIR production processes 4,5.Because the NIPU production processes ar
20、e still optimised forlarge-scale production, the conversion plan from a purely conven-tional PU and a fully environmentally friendly NIPU is temporarilylled with an ecological production of the polyol moiety, madefrom renewable resources. One such resource, deemed a wastefrom the Kraft process of wo
21、od pulp manufacturing, is tall oil (TO).Also called “liquid rosin” or tallol, it is a viscous yellow-blackodorous liquid obtained as a by-product when pulping mainlyconiferous trees. In the raw or crude state, TO contains rosin acids,mainly abietic acid and its isomers, fatty acids (mainly palmitica
22、cid, oleic acid and linoleic acid) and fatty alcohols, unsaponiablesterols (5e10%), and some sterol and other alkyl hydrocarbon der-ivates 6. Through fractional distillation, TO rosin can be obtained,with the rosin content of 10e35%. Further reduction can lead to1e10% rosin content, the product now
23、called tall oil fatty acid(TOFA). TOFA consists mostly of oleic acid and is an economicalsourceofvolatilefattyacids,thereasonitisstudiedasaprospectiveFig. 1. Generalised urethane bondS. Reinerte et al. / Polymer Degradation2material for polyol synthesis. Therefore, it was chosen as the rawmaterial f
24、or the polyol component in the rigid PU-PIR foam for-mulations in this study.The thermal degradation type of rigid PU-PIR foam is solid fuelcombustion degradation. The chemical pathways of solid fuelcombustion can be simplied to the following equations (Eqs.(1)e(3): smouldering (Eq. (2) and aming (E
25、q. (3) res of solidfuel. (see Fig. 2)Flaming is characteristically different from smouldering;smouldering is the heterogeneous reaction of solid fuel with anoxidiser involving heterogeneous chemical reactions and thetransport of heat, mass and momentum in the gas and solid phases,whereas aming is th
26、e homogeneous reaction of gaseous fuel withan oxidiser, which releases more heat. The two res have theirgenesis from the same process, namely, pyrolysis (Eq. (1) 7. Thefundamental difference between smouldering and aming com-bustion is that, in the former, the oxidation reaction and the heatrelease
27、occur on the solid surface of the fuel or porous matrix and,in the latter, these occur in the gas phase surrounding the fuel.Typical values in smouldering at ambient conditions are around500e700C14Cfor thepeaktemperatureand6e12kJ/gfortheaverageheat of combustion; typical values during aming are arou
28、nd1500e1800C14C and 16e30 kJ/g, respectively 8. Smouldering, dueto its lowtemperature,is characteristicallyan incompleteoxidationreaction and thus emits a mixture of toxic, asphyxiant and irritantgases and particulates at a higher yield thanamingres.It favoursCO2to CO ratios around unity (as opposed
29、 to ratios around 10 inaming combustion), so CO is an important toxic factor in smoul-dering res 9.Smouldering fuels are characterised by having a signicantlygreatercharacteristic thermal time thanne fuels but allowoxygentransport to the surface. These characteristics lead to the slow butpersistent
30、burning typical of smouldering combustion. In generalterms, the fuel consists of an aggregate and permeable mediumformed by particulates, grains, bres or a porous matrix, includingcellulosic insulation, coal, cotton, tobacco, dust, paper, peat, duffand humus, wood, board of organic bres, synthetic f
31、oams andcharring polymers like polyurethane foam 10, making smoul-dering a serious hazard in both residential and wildland areas. Theaggregate fuel elements facilitate the surface reaction with oxygenby providing a large surface area per unit volume, also acting asthermal insulation that reduces hea
32、t loss but, at the same time,permittingoxygen transport to the reaction sites byconvection anddiffusion 10.As stated in the previous paragraph, synthetic foams, likepolyurethane foam, are highly susceptible to smouldering com-bustion. The porous nature of the foam allows air to feed theexothermic re
33、action while protecting the reaction zone from heatlosses to the surroundings. PU foam, because it is easy to ignite, hasa high propensity to smoulder, and also because its compositionand physical properties are very homogeneousean advantage notpresent in most natural fuelseit is the material of cho
34、ice for mostlaboratory-controlled tests of smouldering combustion 11. Theand decomposition 2.and Stability 180 (2020) 109313studies on the thermal degradation products originated from PUfoammaterialsrevealsimilaritiesbetweenthethermaldegradationgaseous product content obtained from rigid andexible P
35、U foams.For example, in a study by Frana de SC19a et al., the thermal degra-dation of exible PU foam revealed a decrease and a shift of thebidentate urea band (ca. 1640 cmC01) to monodentate urea (ca.1660e1680 cmC01), followed by the large increase of its relativeintensityat ca.1640cmC01,wasdetected
36、inbothagedreferencesandPUR historical objects 12. Frana de SC19a et al., based on their ob-servations, have proposed the CO band at ca. 1640 cmC01to beconsidered as an infrared marker for evaluating the ether-basedPUR foams condition 12. A study by Jiao et al. on rigid PU foamunder a non-oxidizing g
37、aseous environment 13 is one of the mostinsightful rigid PU foam thermal degradation observationretardant systems. Their results have conrmed that results fromlaboratory based degradation studies must be used with cautions of solidS. Reinerte et al. / Polymer Degradationpublished to date. The result
38、s of this study reveal that the urethanebond groups of PUR break up into isocyanates and polyols fromabout 200C14C; meanwhile, the polyols segments decompose tosome kinds of aliphatic ether alcohols and the products becomemore complex as the evolved products interact with each other,whereas in the r
39、ange of 350e500C14C, primary amines, secondaryamines, vinyl ethers and CO2become the dominant products ofPUR, and at temperatures above 500C14C, the aliphatic alcohol withbranched chains and benzene alkyls are generated 13. Otherstudies have observed similar results: Huo et al. concluded that themaj
40、or compounds released from the foams included H2O, CO2, CO,carboxylic acids, aldehydes, ketones, phenols, alcohols and ethers14; Aguirresarobe et al. have observed the formulations thatevolved isocyanate volatile moieties in the rst degradation step(150e275C14C) 15. Interestingly, Delgado-SC19anchez
41、 et al. witnessedthat the rst degradation stage, until 350C14C, is independent of theatmosphere since the results in air mirrored those in a nitrogenatmosphere 16. However, the point of the fastest degradationshifted to higher temperatures under oxidative conditions, asevident by the results obtaine
42、d at a temperature range of350e550C14C, where the second stage of decomposition occurredonly in air, which indicated the predominance of oxidativedecomposition. The maxima of weight loss rate were reached forboth samples at around 300C14C under pyrolytic conditions, and ataround 450C14C under oxidat
43、ive conditions 16. Lorenzetti et al.found similar results, because in the rst degradation step, absor-bance peaks of urethane and urea groups (1540, 1650 and1740 cmC01), NCO group (2277 cmC01), CeOeC (1128 and 1075 cmC01)and CeH aliphatic (2940 and 2880 cmC01) groups deriving fromFig. 2. Chemical pa
44、thwaypolyol fragments could be found. In this thermal degradation step,as well as in the second one, aromatic absorbance bands (3086,3046 and 1500 cmC01) were observed, in addition to the absorbanceof NeH group (3550 and 3570 cmC01) in the second step due toaniline and its substituted compounds, con
45、rming the presence ofthe NCO group 17. Finally, Allan et al. have determined that thedegradation mechanisms of PU are dependent on the experimentalconditions of the degradation or the degradation technique beingemployed, because the degradation studies under air have revealedthat the degradation of
46、PU occurs at a lower temperature thanundernon-oxidativeconditionsandthatthechemistryoccurringinthe condensed-phase is different. The degradation in a low oxygenenvironment was shown to be a complex process, with thedegradation behaviour lying between that of thermal and thermo-oxidative degradation.
47、 The foam begun to degrade and becamemorecharredatlowertemperaturesthanundernitrogen;however,it was not as extreme as when the foam was degraded under air.These ndings have led to a proposal that both thermal andand may not necessarily be representative of a re situation,because in most cases, degra
48、dation studies will deal simply withthe degradation under air and/or nitrogen, not in a low oxygenenvironment 18.In the present study, the suitability of the thermogravimetry/differential thermal analysis method coupled with Fourier trans-form infrared spectrometry (TG/DTA-FTIR) for analysis of the
49、rigidPU-PIR foam synthesised from high functionality TOFA based pol-yols was investigated. The FTIR spectra of gaseous thermal degra-dation products of three PU-PIR formulations with varied highfunctionality TO based polyol content (45, 75 and 95 pbw) and adifferent tier of isocyanate (NCO) indexes (110, 150, 200, 300 and400) for each formulation were compared to the spectra of aformulation developed using conventional raw materials. Thechemical bands of known chemical compounds and unknowncompounds containing specic groups for the foams were evalu-ated, with attention to the maximum release
