ORIGINAL PAPER

Synthesis of polyols and polyurethanes from vegetableoils–kinetic and characterization

Roseany de Vasconcelos Vieira Lopes &

Nuno Pedro D. Loureiro & Ana Paula T. Pezzin &

Ana Cristina M. Gomes & Inês S. Resck & Maria José A. Sales

Received: 31 March 2013 /Accepted: 4 August 2013 /Published online: 18 August 2013# Springer Science+Business Media Dordrecht 2013

Abstract The demand of vegetable oils by several sectors ofthe chemical industry is growing at a fast pace fueled by thefossil oil scarcity, its unpredictable price fluctuations and theever increasing environmental concerns. The present workreports for the first time the synthesis of polyols and polyure-thanes (PUs) from linseed seed (Linum usitatissimun L.) andpassion fruit (Passiflora edulis Sims f. flavicarpa Degener)oils. The in situ epoxidation and hydroxylation of vegetableoils in a single step was successfully accomplished using amixture of hydrogen peroxide (H2O2) and formic acid. Kineticstudies were performed on this system. The oils and the corre-sponding polyols were characterized by Fourier transform in-frared (FT-IR), gel permeation chromatography (GPC) andthermogravimetry (TG)/derivative termogravimetry (DTG).The PUs were characterized by FT-IR, TG/DTG, dynamicmechanical analysis (DMA) and scanning electron microscopy(SEM). The study revealed a marked deviation on the properties

between the starting materials and the end products. The PUsproduced showed similar dynamic mechanical properties.

Keywords Linseed oil . Passion fruit oil . Polyols .

Polyurethanes

Introduction

The industry has come under increasing pressure to makechemical production more eco-friendly and efforts to shiftthe prime resource base of industry from fossil (non-renew-able) to renewable feed stocks have recently gained momen-tum due to the rapid rise in the costs of mineral oil and theincreasing concerns about the depletion of these resources inthe near future. Polysaccharides (cellulose, hemicellullosesand starch), sugars, proteins, wood and plant oils are just afew examples of renewable raw materials to which academicand industrial researchers have been devoting increasing at-tention [1–4]. Amongst them, vegetable oils are the mostwidely used for the chemical and polymer industries and still,they are considered to be amid the most promising raw mate-rials for other purposes, owing to their excellent environmen-tal credentials, which include their ready availability, lowprice, inherent biodegradability, low toxicity and their manyversatile applications [5–7].

In the chemical industry plant oils are used as an ingredientor component in many manufactured products, such as sur-factants (soaps), lubricants, plasticizers, cosmetic products,monomers (e.g. dimer acids and polyols) and agrochemicals.In addition, they have been used for decades in paint formu-lations, as flooring materials and for coatings and resin appli-cations [8, 9].

R. de Vasconcelos Vieira Lopes (*)Faculdade do Gama, Universidade de Brasília, Gama, Brasile-mail: roseanyvieira@yahoo.com.br

N. P. D. LoureiroDepartamento de Química, Universidade de Aveiro, Aveiro, Portugal

I. S. Resck :M. J. A. SalesLaboratório de Pesquisa em Polímeros (LabPol) - Instituto deQuímica, Universidade de Brasília, Brasília, Brasil

A. P. T. PezzinDepartamento de Engenharia, Universidade da Região de Joinville,Joinville, Brasil

A. C. M. GomesLaboratório de Microscopia Eletrônica-Centro Nacional de Pesquisade Recursos Genéticos e Biotecnologia (CENARGEN) - EmpresaBrasileira de Pesquisa Agropecuária (EMBRAPA), Brasília, Brasil

J Polym Res (2013) 20:238DOI 10.1007/s10965-013-0238-x

Vegetable oils (VO) are part of a large family of chemicalcompounds known as lipids. Their major constituents are tri-glyceride molecules, which are fatty acid triesters of glycerol.The fatty acids may all different, two may be different, or maybe all alike. Typically, the fatty acid present in common oils varybetween 14 and 22 carbon atoms in chain length and contain 0–3 double bonds. Triglycerides possess multiple reactive siteswhere chemical reactions can take place: C=C double bonds,the ester groups, the allylic positions, and the α-carbonyl posi-tion. However, by the end of the 80’s, more than 90 % oftriglyceride transformations arose predominantly from reactionsat the carboxylic functionality, with less than 10 % referring tochemical modifications of the alkyl chain. Research on this fieldhas recently regained momentum and increasing attention isnow being focused on the functionalization of the unsaturatedalkyl chains with reactive, due to its potential to considerablyextend the range of valuable compounds obtainable from oiland fats, particularly in the polymer field [1, 10, 11].

However, most of the times, the introduction of reactivemoieties in triglyceride’s unsaturated aliphatic chains can notbe carried out directly due to the low reactivity of the C=Cdouble bonds and hence, a suitable platform must be chosenprior to the functionalization reaction. One of themost popularand effective routes to achieve it is through epoxidation: dueto the high reactivity of the oxirane ring, triglyceride epoxidesare useful intermediates and provide abbreviated pathways toseveral functional derivatives that would not be readily acces-sible otherwise: Of all the routes to oxirane [12, 13], the leasthazardous and most cost-effective procedure is the Prilezhaevreaction, i. e., the epoxidation of alkenes with in situ generatedperacids. Epoxidation of vegetable oils is usually carried outwith performic or peracetic acid formed within the reactionmedium from hydrogen peroxide and the corresponding acid,in the presence of acidic catalysts, either strong inorganicacids or acidic ion exchange resins [12–14].

Linseed (Linum usitatissimun L.) seeds oil is composedmainly by three unsaturated fatty acids-linolenic (57.6 %),linoleic (4.7 %) and oleic acids (25.1 %), featuring an averagenumber of double bonds per triglyceride molecule of 6.3 [15,16]. It is one of the oldest commercial oils, used for long timein formulation of paints and coating alkyds [17].

Passion fruit (Passiflora edulis Sims f. flavicarpa Degener)oil is originated from Tropical America and cultivated mainly inBrazil, Peru and Colombia [17]. At the industry plant, duringthe fruit juice extraction, many thousand tons of seeds areproduced as agroindustry waste, which are generally discardedafter being crushed. These seeds have a high content of fiber andunsaturated fatty acids mainly linoleic acid (73 %), and there-fore, their oil is considered a drying oil, chemically appropriateto be used as a component for polymeric materials [15, 17].

Several methodologies have been developed and used forthe preparation of polyols from VO and one of them involvesthe use of organic peracids and proceeds in two steps. Firstly,

the double bonds are epoxidized with performic or peraceticacid, generated in situ from hydrogen peroxide (H2O2) and thecorresponding acid (Prilezhaev reaction), in the presence of anacidic catalyst, either strong inorganic acids or acidic ion ex-change resins [15, 16, 18]. In the second step, epoxide-ringopening reaction takes place and the oxirane rings are opened tohydroxyl groups. The most important approach for the conver-sion of epoxides into hydroxyl groups are reactions with acids(organic or inorganic), hydrolysis and alcoholysis [16, 19].

Polyurethanes (PUs) belong to a class of versatile polymerswith a wide range of applications and are considered one ofthe most important groups of plastics [17] and subclasses ofthermoplastic elastomers. These materials have been used fora long time by chemical industry as flexible and rigid foams,elastomers, fibers, lacquers and adhesives but yet, their potentialis far to be fully exploited. Research on the PUs field is requiredand lately they have been the subject of many industrial andacademic researches [20, 21]. These materials are producedfrom the reaction of polyols with isocyanates by polyaddition.Besides urethane linkages, the main polymeric chain of PUsmay also contain other functional groups, such as ester, ether,urea and amide. The polymeric chains consist of alternatingshort sequences of hard (rigid) isocyanate and soft (flexible)polyol segments [22–24].

This paper describes the hydroxylation procedure of lin-seed and passion fruit oils, promoted by performic acid gen-erated in situ with kinetic monitoring, as well as for the firsttime the synthesis of PUs from linseed seed and passion fruitoils and characterizations of all materials. The materials werecharacterized by Fourier transform infrared (FT-IR), gel per-meation chromatography (GPC), thermogravimetry (TG), de-rivative thermogravimetry (DTG), dynamic mechanical anal-ysis (DMA) and scanning electron microscopy (SEM).

Experimental

Materials

Linseed oil (LO) was obtained from OlvepinTM (Industry ofVegetable Oils Pindorama) and Passion fruit oil (PFO) waspurchased from Naturais da AmazôniaTM, both with 99 %purity. Formic acid (85 %) was supplied by Isofar, hydrogenperoxide (30% solution) by Dinâmica, and sodium bisulphite,ethyl ether, sodium carbonate and anhydrous sodium sulphatewere purchased from Vetec, all of analytical grade.

Polyols synthesis

The synthesis of the polyols from LO and PFO was adaptedfrom a procedure described in the literature [25]. In this work,25 g (9.08mmoL of double bonds) of degummed passion fruitoil were mixed with 17 mL de formic acid (CH2O2). H2O2

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(19 mL) was slowly added to mixture at room temperature for30 min under strong mechanical stirring. After addition ofH2O2, the mixture was heated to 65 °C for 5 h. Then, theheating was removed and 10 % wt/vol sodium bisulphatesolution was added. The organic layer was isolated and washedwith 10 % wt/vol sodium carbonate solution until neutraliza-tion. Sodium sulfate was used to dry and the solvent wereremoved under vacuum. Hydroxyl index was determined byASTM D 1957–86 [26].

Preparation of PUs

The PUs were prepared in appropriate glass vessels, by mixingthe polyolwith the right amount of diphenylmethanediisocyanate(MDI), (molar ratio [NCO]/[OH] = 1.2). The mixtures werestirred under 3,000 rpm for 5 min and then placed poured intoTeflonTM molds and placed in the oven for 24 h at 100 °C. Thefree isocyanate (NCO) content present in the MDI was deter-mined by titration according to ASTMD 5155-96 [27]. The PUsfrom LO (Linseed Oil) were named as PULO, whereas thoseform PFO (Passion Fruit Oil) as PUPFO.

Polyols and PUs characterization

FT-IR spectra

The FT-IR spectra were taken with a Michelson BomemHartmann & Braun, Serial B, MB-100 FT-IR spectrometer, intransmissionmode. The polyol samples were analyzed betweenNaCl pellets and the PUs sample in KBr tablets. FT-IR spectrawere recorded in the 400–4000 cm−1 range.

Gel permeation chromatography (GPC)

The weight average molar mass (Mw) and number averagemolar mass (Mn) were determined using a gel permeationchromatographer from Waters Instruments, equipped with anisocratic pump (model 1515), using tetrahydrofuran HPLCgrade as solvent, flow rate of 1 mL⋅min-1, refractive indexdetector and column Styragel 2414. The injection volume wasof 200 μL.

Thermogravimetric analysis (TG/DTG)

The thermogravimetry (TG) and derivative thermogravimetry(DTG) were performed in a thermobalance Shimadzu TGA-50, using a platinum crucible. The temperature was scannedup to 650 °C, heating rate of 10 °C⋅min−1, under heliumatmosphere (50 mL⋅min−1). Sample mass varied between6.0±0.5 mg. The temperature of decomposition (Td) wasascertained by DTG.

Dynamic mechanical analysis (DMA)

DMA analyses were performed in a DMTA V RheometricScientific, in the traction mode, in the temperature range of−140 to 300 °C, heating rate of 5 °C⋅min−1, frequency of 1 Hzand 0.20mmwide. Sample dimensions were 6.0×4.5×1.4 mm,approximately.

Scanning electron microscopy (SEM)

Morphological analyses of the surface of PUs obtained wereperformed using a scanning electron microscope Zeiss, modelDSM 962, of the Laboratory of ElectronMicroscopy, NationalResearch Center for Genetic Resources and Biotechnology(CENARGEN) from the Brazilian Research and Agriculture(EMBRAPA). Sample preparation consisted on the cryogenicfracture of the material in liquid N2 and subsequent fixing thestubs using super glue and ribbon bonder. The samples weregold coated in a sputter Emitech (model K550) and recordedat 10 kV.

Results and discussion

Because of the diversity of applications, the recognition of itschemical composition and its functional properties, the VOand fats should be evaluated. Research information aboutthese materials can be used to develop new products.

In a previous paper it was reported that LO and PFO presentsa high content of unsaturated fatty acids, mainly linolenic(57.6 %) and linoleic (72.8 %) acids [15]. In this work, theseoils were used for preparation of polyols. The conversion of theunsaturated triglyceride molecules to polyols using the one-stephydroxylation procedure described above was confirmed by 1HNMR and reported in previous paper [15].

The conversion of triglyceride double bonds to epoxiderings followed by their conversion to the hydroxyl groups(Fig. 1) occurs in a single step and involves multiple reactions[22, 28]. The epoxidation is a heterogeneous reaction systemand happens when the peroxyacids are produced from formicacid or acetic acid with H2O2 (reversible reaction that takesplace in the aqueous phase), to an oxygen atom to each doublebond of unsaturated chains, forming the organic phase [29–33].

The reaction progress was monitored by determining thehydroxyl index throughout time. The hydroxyl index (% OH)is a way of expressing the concentration of hydroxyl groups inany polyol. It is defined as the amount of hydroxyl groupsavailable to react with isocyanates in the sample [25, 30–33].Hydroxyl index determination is accomplished by reaction ofthe sample of polyol with an organic anhydride. The terminalhydroxyl groups are converted to ester function by reactionwith an organic anhydride. Upon the esterification reactionacid molecules are released, which are then neutralized with a

J Polym Res (2013) 20:238 Page 3 of 9, 238

potassium hydroxide solution. By indirect titration, the aver-age hydroxyl number can be determined. The (IOH) averageobtained for the LO polyols was found to be between 55.00

and 125.45 mg KOH⋅g−1, whereas. For the PFO it rangedfrom 11.50 to 122.60 mg KOH⋅g−1. The wide range of valuesobtained for OH index was due the wide range of time during

Fig. 1 Mechanistic proposal forthe hydroxylation reaction of atriglyceride by means of organicperacid

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the reaction kinetics which evidenced that it grows during 5 hof reaction.

Figure 2 shows that the hydroxylation reaction of the LO(dotted line) is faster in the initial stage and is complete afterabout 150 min, indicating that, after this time, all the doublebonds were converted to hydroxyl groups. The dotted linerepresents a power law that describes the points in the range:IOH = IOH

∞ (t/t∞)1/5with IOH∞ = 125.40 mg KOH⋅g−1 and

t∞=300 min. The solid line shows that the hydroxyl numberfor PFO increases as a function of time because the number ofunsaturated sites in the oils is different. The solid line curve isa power law to describe the points in the interval studied:IOH = IOH

∞ (t/t∞)3/4 with IOH∞ = 122.40 mg KOH⋅g−1 and

t∞ = 300 min. This indicates that a larger time is required at thebeginning of the reaction to initiate PFO hydroxylation. This iscorroborated by the OH indexes after 10 min of reaction, i.e.,55.00 and 11.50mgKOH⋅g−1 for the LO and PFO, respectively.

In the present work, the NCO index was 30.82%, similar tothe values found in literature [34, 35].

The different behavior of both oils at the early stages of thehydroxylation reaction suggests that the LO is more reactivethan PFO, most likely, due to steric hindrance and electroniceffects. In general, double bonds closer to the glycerol moietyare less reactive than those farther located. In LO, the doublebonds located closer to the extremity of the carbon chain, i.e.,carbon-15 are less prone to be affected and therefore they areepoxidized faster [30].

The weight average molecular masses obtained for LO andPFO by GPC were 863.75 Da and 869.00 Da, respectively,were found to be in good agreement with the values available inthe literature [36]. As VO triglyceride molecules result from thecombination of three fatty acids with a glycerol residue, chem-ical heterogeneity among them is expected and deviations from

the molar mass values reported in the literature can be antici-pated, if you bear in mind that vegetable oils fatty acid compo-sition depend on the climate, soil and cultivation conditions.

We found that the molar masses for the VOs used on thiswork differ very little from each other. Their similarityconcerning their molecular weight is justified by both havingmainly C-18 fatty acid chains [30]. The molar mass of PFO isslightly higher than LOs, given that the latter has a higheriodine number and therefore, more double bonds less hydro-gen atoms.

The molar masses obtained by GPC for the LO and PFO-based polyols were 1777 Da and 1746 Da, respectively. Thesevalues were twice the molecular weight of the respective oils,which suggest oligomerization had occurred. It was also foundthat the average molar mass for the PFO-based polyols wasslightly lower than for the LO-based ones, most likely to thefact that PFO has fewer reactive sites, i.e., double bonds, thanLO, and therefore less hydroxyl groups in the carbon chain. It’sworth mentioning that despite of the (hydroxyl content) IOH ofpolyols of LO and PFO have been next, they did not haveoxirane rings hydroxylated, a fact that contributes to vary themolecular weight of polyols, depending on the percentage ofoxirane rings present in the carbon chains.

The functionality of the polyols was determined by GPCand was found to be approximately 4.0 for LO and 3.8 forPFO. These results were smaller than the expected, as theaverage numbers of double bonds per triglyceride moleculeestimated by 1H NMR spectroscopy and reported in a previ-ous paper were found to be 6.33 for LO and 4.8 for PFO [16].

FT-IR spectra of the VOs and of the respective polyols areshown in Figs. 3 and 4. FT-IR analyses corroborate the occur-rence of oligomerization. The main differences between the FT-IR spectra of the oils and from their respective polyols are:absence of band at 3009 cm−1, assigned to the =CH stretchingand the presence of a broad and intense band at 3380 cm−1,related to OH group stretching vibration, which indicates intro-duction of hydroxyl moieties [28, 30, 33]. The presence of theepoxy ring characteristic absorption bands at 1250 cm−1, related

Fig. 2 Comparison OH variation index: (black square) LO and (blackcircle) PFO as function of time Fig. 3 FT-IR spectra of the LO and LO-based polyol

J Polym Res (2013) 20:238 Page 5 of 9, 238

to the CO symmetric stretching, at 950 and 810 cm−1, corre-sponding to the C–C asymmetric stretching and at840 and750 cm−1, assigned to the C–O vibration, suggests that not alloxirane rings were converted to hydroxyl groups. It is worthpointing out that the absorption of the OH (3380 cm−1) andC=O (1740 cm−1) groups confirm that the hydroxylated polyolsare polyester type.

The curing reaction of the PUs was monitored through FT-IR, by the disappearance of the band at about 3380 cm−1,assigned to –OH stretching, and the emergence of new bandsat approximately 3300 cm−1 and 1530 cm−1, arising from thereaction between the −OHgroups of the polyols and the -NCOof the MDI [34, 35] and assigned to the N–H stretching anddeformation, respectively. The progress of the curing reactionof the LO and PFO-based PUs was monitored by FT-IR(Fig. 5a and b, respectively).

As one can see, after 24 h of reaction, the curing of bothPUs was complete: the band assigned to unreacted NCOgroups was no longer perceptible, indicating that the MDIreacted completely. The band at about 3340 cm−1, assigned toNH, was present in the spectra of both materials, inferring thepresence of hydrogen bonds in the chain of the PUs [35].

The FT-IR spectra of the samples after 24 h of curing showedthe presence of a band between 1084 cm−1 and 1064 cm−1,assigned to the N–CO–O urethane bond. The band at 900–675 cm−1 corresponds to the vibrations of axial deformationcharacteristic of the angular deformation outside the plane ofthe C–H bond of the aromatic ring [37].

The thermal profiles of LO and PFO and of their respectivepolyols is shown in Figs. 6 and 7.

The TG/DTG curves for LO exhibited only one stage ofthermal decomposition, ranging from 280 °C to 490 °C. Thisthermal event is associated to fatty acid decomposition, withTd around 394 °C and a mass loss of 98 %. On the other hand,the TG/DTG curves for PFO showed two stages of thermaldecomposition. The first stage, less pronounced, between150 °C and 280 °C, with Td close to 230 °C and a mass loss

around 8 %. The second stage occurred more rapidly be-tween 363 °C and 436 °C, with Td close to 406 °C. This step isprobably associated with the oxidation of fatty acids (saturatedand unsaturated) present in the oil.

The LO and PFO TG/DTG curves obtained under inertatmosphere, suggest that the decomposition of the saturatedand unsaturated fatty acids occurs in a single step. The DTG

Fig. 4 FT-IR spectra of the PFO and PFO-based polyol

Fig. 5 FT-IR monitoring of the cure reaction for a PULO and b PUPFO

Fig. 6 TG/DTG curves of LO and LO-based polyol

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curve for the LO-based polyol showed two thermal decompo-sition stages: the first andmain one, between 229 °C and 443 °C,with Td at 389 °C and 90 % mass loss; and a very discreetsecondary stage, between 443 °C and 497 °C (Td=450 °C),corresponding to a mass loss of 7 %. This second step could berelated to a secondary thermal decomposition superimposed onthe main reaction. One can infer that the first major event isassigned to the decomposition of the functionalized fatty acidchains and the Td of LO is higher than the Td of polyol from LObecause the unsaturated chains functionalized of the fatty acidsof LO have formiate/hydroxyl and epoxy groups in their struc-ture, after hydroxylation reactions that are less thermally stablethan unsaturated chains [38]. This fact is probably related to thebinding energy. As LO has many unsaturated bonds (C=C)and CH bonds with binding energies 614.2 kJ⋅mol−1 and413.4 kJ⋅mol−1, respectively, that enables it to bemore thermallystable than their polyol which has several hydroxyl groupslinked CO, which have lower binding energy (353.5 kJ⋅mol−1)[39]. Nevertheless, DTG data suggests that the thermal degra-dation mechanisms are distinct.

The TG/DTG curves for the PFO-based polyol showed thatthe second and main stage of thermal decomposition occursbetween 304 °C and 520 °C, with Td around 410 °C and amass loss of 83 %. This second stage is related to presence offormiate/hydroxyl and epoxy groups. It is worth pointing out,that PFO’s and PFO-based polyol’s second stage of decom-position takes place at similar temperature range. This sug-gests that PFO and the PFO-based polyol have similar thermalstabilities and that the mean thermal decomposition of unsat-urated chains and chains of PFO of their respective function-alized polyol occurred at the same temperature range [38].Figure 8a and b show the TG/DTG curves for the LO-basedPU (PULO) and the PFO-based PU (PUPFO). The profile ofthese curves suggests that the thermal decomposition of PUsoccurs in three stages.

The first stage, related to the thermal decomposition of ure-thane bonds is more pronounced than the second and occurred atthe same temperature range for both PUs (198 °C–445 °C and

195 °C −448 °C, respectively), with similar Td values (383 °Cand 387 °C, respectively). These features suggest that the thermalstabilities of both PUs are similar. This case involves the decom-position of the urethane bonds and the regeneration of theisocyanate and alcohol functions. Then, there is the formationof primary and secondary amines [25, 40–42].

The DTG curves suggest that the first stage of thermaldecomposition is similar for both PUs. DTG curve of PUPFOexhibits a peak slightly more acute than PULO, probablybecause after the polyaddition reaction to PUPFO, the materialpresented in the largest group of urethane linkages than thePULO that suggesting a higher rate of decomposition of theurethane linkages and with their larger mass loss. The secondstep of thermal decomposition, related to the flexible segmentsfor the temperature range considered, was similar for both PUs.The Td values of the PUs for both stages of thermal decompo-sition were analogous, indicating that the maximum degrada-tion rate of these PUs occurs at similar temperatures. Thisinformation was summarized on Table 1.

The DMA curves for the PULO and PUPFO are represent-ed in Fig. 9a and b, respectively.

In the Log E′ versus temperature curves of PUs (Fig. 9a), itwas observed a decreased of E′ with increasing temperature.

Fig. 7 TG/DTG curves of PFO and PFO-based polyol

Fig. 8 a TG curves of PULO and PUPFO b DTG curves of PULO andPUPFO

J Polym Res (2013) 20:238 Page 7 of 9, 238

For PULO, the decline occurred gradually to −1.3 °C and thenthe modulus decreased rapidly to near 100 °C, also presentedelastic plateau region up to 200 °C, indicating typical behav-ior of a crosslinked material. PUPFO featured a gradual de-crease of Log E′ to −37 °C, being most pronounced betweenthis temperature and 90 °C, approximately, with an elasticplateau region to 200 °C.

The Log E′ versus temperature curves (Fig. 9a) show thatthe region of fastest decrease of module corresponds to thetemperature range where the glass transition takes place. Tg

values were determined by plotting tan δ versus temperature(Fig. 9b). PULO and PUPFO shown a Tg at about 42 °C and31 °C, respectively, suggesting that PULO is more crosslinkedthan PUPFO. Evaluating the degree of mechanical damping in

Fig. 9b, the values of 0.5 for both PUs suggest that they havesimilar flexibility.

The difference in Tg values, as well as the peak shape,position and intensity in the tan δ versus temperature plot shownto be dependent on several parameters, namely the crosslinkdensity, distribution and orientation of these bonds in the mo-lecular structure [36, 43–46].

PUs foams were also analyzed by SEM. The micrographs(Fig. 10a and b) revealed the existence of closed cell porosity.

PUs surface showed uneven texture, caused, probably,by the disorderly cryogenic fracture. Slots are perceived insome samples and the appearance seems brittle. This wasverified in whole micrographs, even for microcells in smallproportions with spherical shape. However, studies are beingcarried out by our group to improve the porosity of thesematerials.

The fact that PUs has shown uneven porosity may be attrib-uted to the amount of remainingwater present in the polyol aftersynthesis. Studies have shown that the presence of water in thepolyol increases the number of cells, and therefore the disorderof the system [46].

Table 1 Td values and mass loss for the VO-derived PUs

PUs Td1 (°C) Mass loss (%) Td2 (°C) Mass loss (%)

PULO 383 60 476 22

PUPFO 387 67 472 21

Fig. 9 a Variation of storage modulus (Log E′) versus temperature forPULO and PUPFO; b variation of tan δ versus temperature for PULO andPUPFO Fig. 10 SEM micrographs of a PULO and b PUPFO

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Conclusions

The LO and PFO-based polyols synthesized from LO andPFO presented an average IOH of 125.45 mg KOH⋅g−1 and122.60 mg KOH⋅g−1, respectively. FT-IR analysis showed thepresence of free OH groups, confirming the partial conversionof the epoxy groups to hydroxyl moieties. It was also provedthat the synthesized polyols are polyester-type. The molecularweight of the synthesized polyols was found to be twice themolecular weight of the original oil tryglyceride, suggestingthat in situ hydroxylation and oligomerization occurred. TheTG/DTG curves of the studied oils showed a major stage ofthermal decomposition which is associated with the fatty aciddecomposition of the triglyceride molecules. TG/DTG curvesof the polyols showed two steps of thermal decomposition,attributed to decomposition of hydroxyls and epoxy groups.The TG/DTG curves for PULO and PUPFO suggest theyhave similar thermal stabilities as the degradation rate reachesits maximum at the same temperature range. DMA resultssuggest that PULO is more crosslinked than PUPFO, despitepresenting similar flexibilities. The SEM analysis of the PUsshowed the existence of closed cell porosity of the materials.

Acknowledgments The authors thank the National Council of Tech-nological and Scientific Development (CNPq), the Institute of Chemistryat the University of Brasilia (IQ/UnB) and Coordination of Improvementof Higher Education Personnel (CAPES) for financial support.

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