Sr

JD

a

ARRA

KLPFTR

1

smgemKanPbwnaaifprrt

r

0h

Industrial Crops and Products 42 (2013) 308– 314

Contents lists available at SciVerse ScienceDirect

Industrial Crops and Products

journa l h o me pag e: www.elsev ier .com/ locate / indcrop

tructural, thermal and rheological behavior of a bio-based phenolic resin inelation to a commercial resol resin

.C. Domínguez ∗, M. Oliet, M.V. Alonso, E. Rojo, F. Rodríguezepartamento de Ingeniería Química, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Avda. Complutense s/n., 28040 Madrid, Spain

r t i c l e i n f o

rticle history:eceived 28 February 2012eceived in revised form 19 May 2012ccepted 3 June 2012

eywords:

a b s t r a c t

A commercial phenolic resin and a bio-based phenolic resin formulated partially substituting phenol by amethylolated softwood ammonium lignosufonate were studied to characterize their structural, thermaland rheological properties. The structures of the resins and the modified and non-modified lignosul-fonates were studied by FTIR, showing a similar structure for both resins and higher reactivity for themodified lignosulfonate than for the non-modified. The curing heats of both resins were obtained by DSC,

ignosulfonatehenolic resinTIRhermal analysisheology

showing a reduced reactivity of the lignin-resol due to the incorporation of lignosulfonates. The thermalstability of lignin-phenolic resin studied by TGA was enhanced with respect to that of the commercialresin due to the high thermal stability of lignosulfonate used in its formulation. The addition of lignosul-fonates modified the rheological behavior of resol resin changing its flow behavior from Newtonian topseudoplastic. Rheological behavior of both resins were modeled by applying the experimental data to

several models.

. Introduction

Nowadays, the development of novel eco-friendly materials,uch as resins partially or fully based on biomass, with highechanical and thermal properties has become one of the main

oals in the field of these materials (Effendi et al., 2008; Guigot al., 2010; Marsh, 2008). One of the most widely employed bio-aterials is lignin and its derivatives. Thereby, lignins, such as

raft lignin and lignosulfonates, have been the subject of studiess a raw material for partial substitution of phenol in resol andovolac resins (Alonso et al., 2004b, 2005; Mahendran et al., 2010;érez et al., 2007). As the result of these studies, several phenolicioresins whose cost is partially decoupled from the oil market andith a lower environmental impact have been developed. Theseew lignin-based resins are designed to replace traditional resolnd novolac phenolic resins that typically are used in applicationss diverse as the manufacture of textile felts for the automotivendustry, adhesives in particleboard and plywood, and in manu-acturing molding compounds (Gardziella et al., 2000). Thus, theroperties of the new bioresins must satisfy the specificationsequired to be used for these traditional applications of phenolicesins, as well as for new applications demanded by the cus-

omers.

The study of the structural differences between a phenolicesin and a lignin-phenolic resin is a key to understand how the

∗ Corresponding author.E-mail address: jucdomin@quim.ucm.es (J.C. Domínguez).

926-6690/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.indcrop.2012.06.004

© 2012 Elsevier B.V. All rights reserved.

properties of the original resin are affected by the substitution ofphenol, a low molecular weight compound, by lignin, a heteroge-neous high molecular weight compound. One of the most commontechniques used for this purpose is the Fourier transform infraredspectroscopy (FTIR). In the present work, this technique was usedto identify the functional groups of resins, and therefore it can beemployed to establish a comparison among the structure of thephenolic and the lignin-phenolic resins studied. In addition, theFTIR analysis of the lignin-based compound used in this work asa phenol substitute to formulate the bioresin, a modified ammo-nium lignosulfonate (Alonso et al., 2004b), is useful to explain thechanges experienced by the structure of the lignin-phenolic resinwith respect to the phenolic resin.

The thermal properties of a resin are some of the most sensitiveproperties to structural changes. An increased thermal stability isdesirable for the new lignin-phenolic resin to enhance the proper-ties of the materials produced from it. The changes found for thethermal stability of the lignin-phenolic resin with respect to thephenolic resin can be related to the thermal properties of the mod-ified ammonium lignosulfonate introduced in the formulation ofthe resin (Alonso et al., 2011).

The comparison between the rheological behavior of the pheno-lic and lignin-phenolic resins reveals additional information abouthow the structure and the properties of the new resin are changedby the adding of the modified lignosulfonate as partial substitute

of phenol. Furthermore, the rheological behavior of phenolic resinsis extremely important due to one of their applications. In previ-ous works, we have developed models to simulate the cure cycle ofresins to optimize the manufacturing process, as well as to enhance

rops a

tP

itntorbtwC

2

2

Moh(l2a(ilB

2

taaataaa(ncs

dcaalistaspom−oado

J.C. Domínguez et al. / Industrial C

heir final properties (Alonso et al., 2004a; Dominguez et al., 2010;érez et al., 2009).

In this work, the structural (FTIR), thermal (TGA), and rheolog-cal properties of a novel bio-based phenolic resin formulated byhe partial substitution of phenol by a modified ammonium lig-osulfonate have been studied in order to compare them withhe same properties of a commercial phenolic resol resin. Thebtained results are discussed comparing the properties of bothesins in order to explain how the partial substitution of phenoly a modified lignosulfonate changes the properties in relation tohe commercial resol resin. The rheological behavior of both resinsere modeled by applying the experimental data to Ellis, Cross,arreau-Yasuda and Maxwell models.

. Materials and methods

.1. Materials

Phenolic commercial resol resin (PF) tested was supplied byomentive Specialty Chemicals Ibérica (Spain). This product is

btained by the polymerization between phenol and formalde-yde in an alkaline medium. Lignin–phenol–formaldehyde resinLPF) was synthesized in our laboratory with a 30 wt.% of methylo-ated softwood ammonium lignosulfonate (MSAL) (Alonso et al.,001). The methylolation of ammonium lignosulfonate leads to

compound more reactive than that obtained by phenolationAlonso et al., 2005). The methylolation conditions were reportedn a previous work (Alonso et al., 2001). The softwood ammoniumignosulfonate (SAL) was supplied by Borregaard Deutschland asorresperse AM 320.

.2. Characterization

FTIR spectra were recorded with a Mattson Satellite spec-rophotometer using the potassium bromide pellet method. Thecquisition conditions were: spectral width of 4000–400 cm−1, 32ccumulations, 1 gain, and 4 cm−1 resolution. The data of FTIRllowed analyzing the structural differences of both resins. In addi-ion, FTIR was employed to analyze the structure of methylolatedmmonium lignosulfonate. The calorimetric measurements of PFnd LPF resins and ammonium lignosulfonate were performed on

Mettler Toledo DSC 821e calorimeter using medium pressure pansME-26929) at a heating rate of 10 ◦C/min from 30 to 230 ◦C underitrogen atmosphere. The thermal stability of lignosulfonate wasarried out at a heating rate of 10 ◦C/min under nitrogen atmo-phere in a TGA apparatus (Mettler Toledo TGA 851e).

The rheological behavior of PF and LPF resins were studied byynamic frequency sweep experiments to obtain their rheologi-al spectra. Rheological runs were performed on both resins usingn ARES Rheometer (TA Instruments) with a 25 mm upper platend a 42 mm lower parallel plate; the gap was fixed at 1 mm. Theower plate was filled for sample immersion in a low viscosity sil-cone (Dow Corning 200® FLUID 100 cSt), selected to protect theurface of the sample of drying. The operating conditions duringhe rheological tests were: a frequency range from 0.5 to 80 Hz,n applied strain of 2%, and a pre-shear of 10 s−1 applied to theamples for 30 s after a delay time of 10 min once the operating tem-erature was reached, in agreement with ASTM D 4440, 2001. Theperating temperature, fixed at −10 ◦C for both resins, was deter-ined through dynamic temperature ramp tests carried out from20 to 0 ◦C applying a heating rate of 0.1 ◦C/min and a frequency

f 1 Hz. The initial strain applied to the resins during the temper-ture sweep tests was 0.1%. The auto-strain option was enableduring the tests to keep the torque within the measurement rangef the equipment. All the tests were performed within the linear

nd Products 42 (2013) 308– 314 309

viscoelastic region of both resins. The calculations of the relaxationspectra of the rheological models were done with TA Orchestrator©

software, which uses a method developed using cubic spline inter-polation when needed (Ferry, 1980).

2.3. Rheological models

The Maxwell model was used to describe the rheological behav-ior of the phenolic and lignin-phenolic resins (Barnes, 2000; White,1990). Storage and loss moduli are predicted by this model usingEqs. (1)–(3):

G′ =∑

i

G∗i

· (ω · �i)2

1 + (ω · �i)2

(1)

G′′ =∑

i

G∗i

ω · �i

1 + (ω · �i)2

(2)

�i = �∗i

G∗i

(3)

where �i, �∗i

and G∗i

are the relaxation time, complex viscosity andthe complex modulus, respectively, of each Maxwell element of themodel; G′ and G′′ are the elastic and viscous moduli of the polymer;and ω is the frequency.

The Ellis, Cross and Carreau-Yasuda models were applied to themeasured complex viscosities of the phenolic and lignin-phenolicresins to describe their flow behavior assuming that infinity viscosi-ties are quite lower than the measured viscosities and substitutingthe shear rate by the frequency employed in the oscillatory tests(Barnes et al., 1989; Yasuda et al., 1981):

• Ellis model:

�∗ = �∗0

1 + (�/�1/2)˛−1(4)

• Cross model:

�∗ = �∗0

1 + ((�∗0 · �)/�∗)1−n

(5)

• Carreau-Yasuda model:

�∗ = �∗0 ·

[1 +

(�∗

0 · �

�∗

)a](n−1)/a

(6)

where � is the shear rate, � is the shear stress, �∗0 is the zero-shear-

rate viscosity, �* is the shear stress at the transition betweenNewtonian and power-law behavior, a is the index that con-trols the transition from the Newtonian plateau to the power-lawregion, � is the relaxation time, �1/2 is the value of the shearstress at which the viscosity is half of the zero-shear-rate vis-cosity, is a parameter obtained from the slope of the curve, andn is the power-law index. The calculations of the parameters ofthe rheological models were done with Matlab© software.

3. Results and discussion

3.1. Analysis by FTIR

The spectra obtained by FTIR technique for the formulated PFand LPF resins, the unmodified (SAL) and methylolated ammonium

lignosulfonates (MSAL) are shown in Fig. 1. The bands representingdifferent functional groups of the resol resins and modified ligno-sulfonate tested were identified according to work of El Hage et al.(2009) and Faix (1991).

310 J.C. Domínguez et al. / Industrial Crops and Products 42 (2013) 308– 314

Ff

bcouTladh

fdlrrteobiiwbaaat

wobpptpmc(

3

f

perature for SAL appears at 260 ◦C. This value is inferior with respectto Kraft and organosolv lignins, which exhibit higher decomposi-tion temperatures, ca. 350 ◦C (Dominguez et al., 2008; Mousaviounand Doherty, 2010). Lower values of decomposition temperature

ig. 1. FTIR spectra of non-modified lignosulfonate (SAL), methylolated lignosul-onate (MSAL), lignin-phenolic resin and phenolic resin.

The FTIR spectrum obtained for MSAL is characterized by aroad OH band at 3400 cm−1 and another at 2854 cm−1, typi-al of methoxyl groups (Fig. 1). The aromatic skeletal vibrationccurs at 1600 cm−1 and 1500 cm−1. The band at 1600 cm−1 wassed for normalization and its intensity was always set to 1.00.he C OH deformation band of asymmetric methyl and methy-ene appears at 1470–1460 cm−1, and carbon–oxygen ether bandst 1400–1000 cm−1. The intensity of OH and C H aromatic bandsecreases for the MSAL with respect to those of SAL; therefore, aigher reactivity can be expected for this modified lignosulfonate.

In Fig. 1, importantly spectral two areas for resol resins areound: 4000–2500 cm−1 and 1800–400 cm−1. The first one presentsifficulties for the identification of functional groups by the over-

ap of bands and by the interference of water due to condensationeactions between prepolymers of resins. In the second spectralegion, there are two types of changes: (i) the substitutions of func-ional groups in the aromatic rings and (ii) the deformation andlongation of the CO bond in primary alcohols (1050 cm−1). On thether hand, the region 950–650 cm−1 is characteristic of the CHond deformation outside the plane of the aromatic ring. Depend-

ng on the number and position of substitution hydroxymethyln type ring can be identified from one to seven bands. A 690 cm−1

as identified as phenol mono-substituted rings. Similarly, thoseands that are close to 735 and 757 cm−1 correspond to mono-nd disubstituted-1,2 in the aromatic rings, respectively. The bandsppearing at wavenumbers of 813 and 837 cm−1 are referred to 1,4-nd 1,2,4-substitutions in the aromatic rings, respectively, whilehe band at 890 cm−1 is due to tetra-substitutions.

Resol resins, in general, among which include those formulatedith lignosulfonate as extender, are characterized by a strong band

f hydroxymethyl group at 1050 cm−1 and a weak band of etheronds to 1120 cm−1 (Carotenuto and Nicolais, 1999). In Fig. 1, theresence of one or more ortho hydroxymethyl groups (991 cm−1)romotes the formation of intermolecular hydrogen bonds. In addi-ion, 13C NMR spectrum for PF and LPF resins confirmed in arevious work the substitution of the hydroxymethyl group oronomers linked through methylene bridges, indicating the typi-

al condensation reactions of this type of thermosetting polymersAlonso et al., 2004b).

.2. Thermal behavior

The thermogram of lignin-phenolic resin (LPF) is given in Fig. 2or comparison with the commercial resin (PF) and lignosulfonate

Fig. 2. DSC thermograms for LPF and PF resins, and ammonium lignosulfonate (SAL).

(SAL). The DSC profile of PF resin is similar to LPF resin, which indi-cates that the methylolated lignosulfonate is incorporated in theformulation of resol resins as extender. Both resol resins exhibittwo peaks in their thermograms (Fig. 2). The first peak is dueto the free formaldehyde in the resins. The second peak in thethermogram for both resins is as a result of the condensation reac-tions. The exothermic heat for curing of PF and LPF resins is 100and 81 J/g, respectively. These values are lower than the curingheats for a Kraft lignin-phenol-formaldehyde resin (205–206 J/g)measured by Mahendran et al. (2010). The heat flow values showthat exothermicity of LPF is reduced around 20% with respect tothe commercial resol resin. This fact indicates that the LPF resinundergoes a reduction of its reactivity due to the incorporation ofmodified lignosulfonate.

Glass transition temperature (Tg) value of ammonium ligno-sulfonate is ∼130 ◦C (Fig. 2), which is an intermediate value withrespect to Kraft and organosolv lignins that present Tg of 90 and180 ◦C, respectively (Brodin et al., 2010; Mousavioun and Doherty,2010).

TG and DTG thermograms for SAL show the weight loss ofsample and the rate of weigh of loss in relation to temperature,respectively (Fig. 3). The maximum thermal decomposition tem-

Fig. 3. TG/DTG thermograms for ammonium lignosulfonate under an inert atmo-sphere.

J.C. Domínguez et al. / Industrial Crops a

a

b

Fp

cllfwt2

3

swtmF

witTfsaibip

ig. 4. Dynamic temperature rheological tests for: (a) phenolic resin and (b) lignin-henolic resin.

an be related to the ease fragmentation of C C linkages in theignosulfonate. Notice that in a previous work, the maximum rateoss for phenolic resin and phenolic resol resin with lignosul-onate added as a filler occurs at 326 ◦C and 498 ◦C, respectively,hich indicates that the lignosulfonate in the formulation improves

he thermal decomposition temperature of resin (Alonso et al.,011).

.3. Rheological characterization

The minimum operating temperature to carry out the frequencyweeps used to obtain the rheological behavior of PF and LPF resinsas fixed at the melting temperature of the resins. Therefore,

emperature sweep tests were performed in order to deter-ine this temperature for both resins. The results are shown in

ig. 4.The melting point of the resins was determined as the point

here the slopes of the storage and loss moduli change dramat-cally. The melting point of the PF and LPF resins occurs at aemperature of −10 ◦C (Fig. 4a) and −12 ◦C (Fig. 4b), respectively.hus, the minimum operating temperature chosen to carry outrequency sweeps is −10 ◦C; for lower temperatures the PF resinolidifies. The lower melting point of the LPF resin is explained by

higher branching of this resin with respect to the PF resin, which

s supported by the lower reactivity found for the LPF resin. A highranching of the resin causes a reduction of the number of react-

ng sites and renders crystallization more difficult than in a linearolymer (Magnusson et al., 2002). The higher thermal degradation

nd Products 42 (2013) 308– 314 311

temperature obtained for the LPF resin with respect of the PF resinalso supports this explanation, since the thermal stability of a resinis increased as the degree of branching and molecular weight of theresin increase.

The rheological spectra of the phenolic and lignin-phenolicresins, storage and loss moduli and complex viscosities were deter-mined by frequency sweep tests as shown in Fig. 5a–c, respectively.

The profiles of the storage and loss moduli of both resins are inagreement with the typical shape of the profiles of these param-eters for polymer solutions (Ferry, 1980). This is due to the highwater content of both resins, more than 50 wt%. The rheologicalspectra obtained for PF and LPF resins are included within the latterregion of the five regions of the rheological spectrum of a polymerproposed by Sperling (2006), named the fluid flow region. The val-ues of storage modulus of the PF and LPF resins vary from 10 to103 and 5 to 104 Pa, respectively (Fig. 5a); and their loss modulus isbetween 102–104 and 50–104 Pa, respectively (Fig. 5b). These val-ues are in the same range obtained for a commercial copolyamideresin by Incarnato et al. (2004).

In Fig. 5a and b, the storage and loss moduli of the phenolicresin are lower than those obtained for lignin-phenolic resin. Themodified lignosulfonate added in the formulation of the LPF resincould cause interferences with the polymer that could explain thedifferent rheological spectra obtained for both resins. These inter-ferences have been reported in the literature for a copolyamideresin when clay particles were added to the resin (Incarnato et al.,2004). Moreover, the reduction of the moduli can be explainedby the differences found for the storage modulus of both resins,which is more sensitive to morphological state than the loss mod-ulus. The different behaviors of the storage modulus of the PF andLPF resins, suggesting a different structural network, is due to anincreased condensation of the lignin-phenolic resin, higher molec-ular weight and higher degree of branching, with respect to thephenolic resin (Gardziella et al., 2000; Li et al., 2001), which is inagreement with the respective melting points of the resins foundpreviously.

The flow behavior of both resins is markedly different, as shownin Fig. 5c. The complex viscosity of the phenolic resin exhibits abehavior close to a Newtonian flow, which is in agreement withthe behavior of a neat prepolymer (Ganguli et al., 2003). The lignin-phenolic resin shows a pseudoplastic behavior, which is typical ofgels and pastes, and was found for polymers in the literature foruncured cyanate esters and for a commercial copolyamine resinwith clay particles added as filler (Ganguli et al., 2003; Incarnatoet al., 2004).

Relaxation spectra of the PF and LPF resins, calculated fromtheir storage and loss moduli are shown in Fig. 6. This parame-ter is defined as the contribution to the rigidity of the mechanismsassociated with viscoelastic relaxation times. The relaxation spec-tra of the resins indicate how a material is closer to the solidor fluid ideal behavior after applying a strain (Riande et al.,2000).

Relaxation spectra of PF and LPF resins are very similar andclose to the behavior of a polymer in solution, as expected giventhat the two resins containing more than 50% water in their for-mulations. This rheological parameter was the closest match inrheological characterization of the two resins under study. How-ever, the relaxation time for the peak found for both resins, whichis associated to the relaxation of the entangled chains in the net-work (Deiber et al., 2002), is lower for the PF resin than forthe LPF resin. This shorter relaxation time is in this case relatedto an easier mobility of the chains of the PF resin compared to

the LPF resin, and therefore points to a lower branching of thePF resin, which is in agreement with the curing heats, meltingpoints and storage moduli found previously for these resins in thiswork.

312 J.C. Domínguez et al. / Industrial Crops and Products 42 (2013) 308– 314

a

b

c

Fig. 5. Rheological properties of phenolic (PF) and lignin-phenolic (LPF) resins: (a)storage modulus, (b) loss modulus, (c) complex viscosity.

Fig. 6. Relaxation spectra for phenolic (PF) and lignin-phenolic (LPF) resins.

3.4. Rheological modeling

The Maxwell model was employed in the modeling of the rhe-ological behavior obtained for the PF and LPF resins. Furthermore,the measured complex viscosities were fitted to Ellis, Cross andCarreau-Yasuda models.

The Maxwell model was applied to the rheological propertiesof the PF and LPF resins using two and three Maxwell elements.The parameters of each Maxwell element, relaxation time (�i) ofthe piston and Young modulus (G∗

i) of the spring were calculated

by fitting the measured data to the model. The obtained values forthe parameters of the model for the storage and loss moduli ofthe resins together with the correlation coefficient (R2) and thestandard deviation (�) are shown in Tables 1 and 2, respectively.

The fits obtained for the storage modulus of the PF resin providecorrelation coefficients (R2) higher than 0.999 and an acceptablestandard deviation for three Maxwell elements. For the LPF resin,the use of only two Maxwell elements is enough to obtain a

Table 1�i and G∗

icalculated values for the storage moduli of phenolic and lignin-phenolic

resins.

�i (s) G∗i

(Pa)

n 2 3 n 2 3

PF3767 4193

PF0.01171 0.0103

326.3 312 0.2003 0.107490.39 0.6339

R2 0.998 0.999 � 18.82 11.55

LPF1.574 × 104 1.684 × 104

LPF0.0164 0.0128

2436 3381 0.1366 0.0648623.2 0.4238

R2 0.999 0.999 � 106 51.03

n, number of Maxwell elements.

Table 2�i and G∗

icalculated values for loss moduli of phenolic and lignin-phenolic resins.

�i (s) G∗i

(Pa)

n 2 3 n 2 3

PF1.742 × 104 1.754 × 104

PF0.0068 0.0068

335.2 279.6 0.1605 0.109895.66 0.4264

R2 0.999 0.999 � 20.25 18.76

LPF3.721 × 104 3.739 × 104

LPF0.0099 0.00095

2835 2901 0.1013 0.0694573.2 0.3767

R2 0.999 0.999 � 94.70 64.54

n, number of Maxwell elements.

J.C. Domínguez et al. / Industrial Crops a

Table 3Parameters of the viscosity models for the lignin-phenolic resin.

Parameters LPF

Ellis Cross Carreau-Yasuda

1.533n 0.465 0.518�1/2 (Pa) 19.96�0 (Pa s) 144 144 143�* (Pa) 2882� (s) 0.074a 0.565

2

cMoobpmtikcmrncAmta

ceboCt

NisoLmaeesi

cwlboficscoeP

ester-organically layered silicate nanocomposites. Polymer 44, 6901–6911.

R 0.999 0.999 0.999� 5.56 5.57 5.14

orrelation as good as for the storage modulus. Two and threeaxwell elements ensure a reliable prediction of the behavior

f loss modulus for PF and LPF resins. An important reductionf the standard deviation is found when increasing the num-er of Maxwell elements from two to three and therefore theredicted spectra are more accurate when a greater number ofodel elements are employed. Rheological models for thermoset-

ing polymers are highly linked to their use as flow sub-modelsncluded in a manufacturing cycle model, which also includesinetic, chemorheological, shrinkage, voids growth and microme-hanical sub-models (Kenny, 1994). Therefore, these sub-modelsust reduce the time required for a simulation to be performed,

emaining the accuracy of the global model, i.e. reducing theumber of the parameters of the model keeping its accuracy. Aompromise between accuracy and computing time must be found.ccording to this criterion, the Maxwell model using three ele-ents, in the case of the studied phenolic resins, is recommended

o predict with a good accuracy the rheological behavior of the PFnd LPF resins.

The complex viscosity of the PF resin (Fig. 5c) shows an almostonstant value and therefore a Newtonian behavior is consid-red (ca. 30 Pa s). However, the LPF resin exhibits a pseudoplasticehavior. Thus, the modeling of the complex viscosity profilesbtained for the LPF resin was carried out by the Ellis, Cross, andarreau-Yasuda models. The calculated parameters obtained forhese models are shown in Table 3.

The parameters “n” and “˛” indicate the degree of deviation fromewtonian behavior. The LPF resin shows a pseudoplastic rheolog-

cal behavior, as exhibited in Fig. 5c. All the models employed areuitable to predict the complex viscosity dependence on frequencyf the resin, as the high achieved correlation coefficients for thePF resin confirmed (R2 = 0.999). The Carreau-Yasuda model is theore complex model, four parameters instead of three, and the

ccuracy attained was the same than for the rest of the modelsmployed, as proved the calculated R2 values (Table 3). Therefore,ither Ellis or Cross models, whose common parameters have theame value when the models are applied to the data, can be usedn the prediction of the viscous behavior of the LPF resin.

In general, the viscoelastic behavior found for the phenolic resinhanged from Newtonian to pseudoplastic when lignosulfonateas added as a partial substitute of phenol to formulate a new

ignin-phenolic resin. This change is a consequence of the increasedranching obtained for the lignin-phenolic resin. The viscoelasticityf the LPF resin is either desirable or undesirable depending on itsnal application. For instance, if the LPF resin is used for coating oromposite manufacturing – where bleeding during some processesuch as vacuum infusion could be an important drawback – the vis-oelasticity of the LPF resin can be an advantage. However, for some

ther processes including extrusion, resin transfer molding (RTM),tc., the increased resistance to flow of the LPF with respect to theF resin could be an inconvenience.

nd Products 42 (2013) 308– 314 313

4. Conclusions

In this work the study of the structure, reactivity, thermal sta-bility and rheological properties of a commercial resol resin anda bioresin formulated partially substituting phenol by a modifiedammonium lignosulfonate (more reactive than the commercialammonium lignosulfonate) has been performed. The PF resin hasa higher reactivity than the LPF; however, the LPF resin has ahigher thermal stability. The addition of MSAL increases the flowresistance of the LPF resin with respect to the PF resin. The rheo-logical behaviors of both resins were successfully predicted by theMaxwell (three elements), Ellis and Cross models.

The viscoelasticity found for the LPF resins as a consequenceof the increase of their branching encourages further studies that,according to the present results, suggests that a better mechanicalperformance can be obtained for the LPF resins than for PF resins.Furthermore, this study can also be employed as a base for futureworks that could help to determine the optimal amount of ligno-sulfonate used in the manufacturing of new lignin-phenolic resinswith enhanced thermal and rheological properties calculated adhoc for different applications.

Acknowledgment

The authors are grateful to the “Ministerio de Economía y Com-petitividad” for financial support (project CTQ2010-15742).

References

Alonso, M., Oliet, M., Dominguez, J., Rojo, E., Rodriguez, F., 2011. Thermal degradationof lignin–phenol–formaldehyde and phenol–formaldehyde resol resins. Journalof Thermal Analysis and Calorimetry 105, 349–356.

Alonso, M.V., Oliet, M., Pérez, J.M., Rodriguez, F., Echeverría, J., 2004a. Determina-tion of curing kinetic parameters of lignin–phenol–formaldehyde resol resinsby several dynamic differential scanning calorimetry methods. ThermochimicaActa 419, 161–167.

Alonso, M.V., Oliet, M., Rodriguez, F., Astarloa, G., Echeverría, J.M., 2004b. Use of amethylolated softwood ammonium lignosulfonate as partial substitute of phe-nol in resol resins manufacture. Journal of Applied Polymer Science 94, 643–650.

Alonso, M.V., Oliet, M., Rodriguez, F., Garcia, J., Gilarranz, M.A., Rodriguez, J.J., 2005.Modification of ammonium lignosulfonate by phenolation for use in phenolicresins. Bioresource Technology 96, 1013–1018.

Alonso, M.V., Rodriguez, J.J., Oliet, M., Rodriguez, F., Garcia, J., Gilarranz, M.A., 2001.Characterization and structural modification of ammonic lignosulfonate bymethylolation. Journal of Applied Polymer Science 82, 2661–2668.

Barnes, H.A., 2000. A Handbook of Elementary Rheology. Aberystwyth.Barnes, H.A., Hutton, J.F., Walters, K., 1989. An Introduction to Rheology. Elsevier,

Amsterdam, Netherlands.Brodin, I., Sjöholm, E., Gellerstedt, G., 2010. The behavior of Kraft lignin during

thermal treatment. Journal of Analytical and Applied Pyrolysis 87, 70–77.Carotenuto, G., Nicolais, L., 1999. Kinetic study of phenolic resin cure by IR spec-

troscopy. Journal of Applied Polymer Science 74, 2703–27015.Deiber, J.A., Peirotti, M.B., Villar, M.A., Ressia, J.A., Vallés, E.M., 2002. Linear viscoelas-

tic relaxation modulus of polydisperse poly(dimethylsiloxane) melts containingunentangled chains. Polymer 43, 3035–3045.

Dominguez, J.C., Alonso, M.V., Oliet, M., Rojo, E., Rodriguez, F., 2010. Kinetic studyof a phenolic-novolac resin curing process by rheological and DSC analysis.Thermochimica Acta 498, 39–44.

Dominguez, J.C., Oliet, M., Alonso, M.V., Gilarranz, M.A., Rodriguez, F., 2008. Thermalstability and pyrolysis kinetics of organosolv lignins obtained from Eucalyptusglobulus. Industrial Crops and Products 27, 150–156.

Effendi, A., Gerhauser, H., Bridgwater, A.V., 2008. Production of renewable pheno-lic resins by thermochemical conversion of biomass: a review. Renewable andSustainable Energy Reviews 12, 2092–2116.

El Hage, R., Brosse, N., Chrusciel, L., Sanchez, C., Sannigrahi, P., Ragauskas, A., 2009.Characterization of milled wood lignin and ethanol organosolv lignin from mis-canthus. Polymer Degradation and Stability 94, 1632–1638.

Faix, O., 1991. Classification of lignins from different botanical origins by FT-IR spec-troscopy. Holzforschung 45, 21–28.

Ferry, J.D., 1980. Viscoelastic Properties of Polymers. John Wiley & Sons, New York.Ganguli, S., Dean, D., Jordan, K., Price, G., Vaia, R., 2003. Chemorheology of cyanate

Gardziella, A., Pilato, L., Knop, A., 2000. Phenolic Resins. Springer, Berlin.Guigo, N., Mija, A., Vincent, L., Sbirrazzuoli, N., 2010. Eco-friendly composite resins

based on renewable biomass resources: polyfurfuryl alcohol/lignin thermosets.European Polymer Journal 46, 1016–1023.

3 rops a

I

K

L

M

M

M

14 J.C. Domínguez et al. / Industrial C

ncarnato, L., Scarfato, P., Scatteia, L., Acierno, D., 2004. Rheological behavior of newmelt compounded copolyamide nanocomposites. Polymer 45, 3487–3496.

enny, J.M., 1994. Application of modeling to the control and optimization of com-posites processing. Composite Structures 27, 129–139.

i, P., Coleman, D.W., Spaulding, K.M., McClennen, W.H., Stafford, P.R., Fife, D.J.,2001. Fractionation and characterization of phenolic resins by high-performanceliquid chromatography and gel-permeation chromatography combined withultraviolet, refractive index, mass spectrometry and light-scattering detection.Journal of Chromatography A 914, 147–159.

agnusson, H., Malmström, E., Hult, A., Johansson, M., 2002. The effect of degree ofbranching on the rheological and thermal properties of hyperbranched aliphatic

polyethers. Polymer 43, 301–306.

ahendran, A.R., Wuzella, G., Kandelbauer, A., 2010. Thermal characterization ofKraft lignin phenol–formaldehyde resin for paper impregnation. Journal ofAdhesion Science and Technology 24, 1553–1565.

arsh, G., 2008. Composites that grow in fields. Reinforced Plastics 52, 16–22.

nd Products 42 (2013) 308– 314

Mousavioun, P., Doherty, W.O.S., 2010. Chemical and thermal properties of fraction-ated bagasse soda lignin. Industrial Crops and Products 31, 52–58.

Pérez, J.M., Oliet, M., Alonso, M.V., Rodriguez, F., 2009. Cure kinetics of lignin-novolacresins studied by isoconversional methods. Thermochimica Acta 487, 39–42.

Pérez, J.M., Rodriguez, F., Alonso, M.V., Oliet, M., Echeverría, J.M., 2007. Character-ization of a novolac resin substituting phenol by ammonium lignosulfonate asfiller or extender. BioResources 2, 270–283.

Riande, E., Díaz-Calleja, R., Prolongo, M.G., Masegosa, R.M., Salom, C., 2000. PolymerViscoelasticity. Marcel Dekker, New York.

Sperling, L.H., 2006. Introduction to Physical Polymer Science. John Wiley & Sons,New Jersey.

White, J., 1990. Principles of Polymer Engineering Rheology. John Wiley & Sons,Chichester.

Yasuda, K., Armstrong, R., Cohen, R., 1981. Shear flow properties of concen-trated solutions of linear and star branched polystyrenes. Rheologica Acta 20,163–178.