Ra

Oa

b

a

ARR2A

KPRLLB

1

pctvpplfam

aedptt

0d

Progress in Organic Coatings 70 (2011) 52–58

Contents lists available at ScienceDirect

Progress in Organic Coatings

journa l homepage: www.e lsev ier .com/ locate /porgcoat

heological behaviour of acrylate/montmorillonite nanocomposite latexesnd their application in leather finishing as binders

nur Yılmaza, Catalina N. Cheaburub,∗, Gürbüz Gülümsera, Cornelia Vasileb

Ege University, Faculty of Engineering, Leather Engineering Department, 35100 Bornova, Izmir, TurkeyPetru Poni Institute of Macromolecular Chemistry of the Romanian Academy, 41A Grigore Ghica Voda Alley, 700487 Iasi, Romania

r t i c l e i n f o

rticle history:eceived 9 May 2010eceived in revised form0 September 2010ccepted 4 October 2010

eywords:olymer/clay nanocomposites

a b s t r a c t

The paper describes the rheological behaviour of nanocomposite latexes based on butylacrylate–co-methylmethacrylate–co-acrylamide terpolymers including various commercial nanoclays obtained viain situ emulsion polymerization. Rotational, oscillatory, emulsion stability and thixotropy tests (recovery)were performed to evaluate the influence of clay incorporation, type of clay and also emulsifier content inthe composition of these nanomaterials. It was observed that the viscosities of the nanocomposite latexeswere increased by clay incorporation at low shear rates, while a shear thinning effect was observed athigher shear rates. Oscillatory tests indicated a dominant elastic behaviour and high physical stabilitiesfor all the nanocomposites. The hydrophobic character of the clay and emulsifier content also influenced

heology

atexeather finishinginder

the viscosity and dynamic modulus of the emulsions.The nanocomposite latexes were tested for leather finishing as polymeric binders. Results showed

that the finish performance of the leather surfaces was improved by clay incorporation. It was also con-cluded that for coating applications it is important to find a balance between the compatibility of thenanoclay type with the polymer and the emulsifier amount necessary for emulsion stabilization whichboth influence the rheology and the final performance of the coatings.

. Introduction

Polymer/clay nanocomposites are a new class of reinforcedolymer materials containing low quantities of nanometric-sizedlay particles which impart them better mechanical, thermal, elec-rical, barrier properties, chemical resistance, etc., making themaluable materials in industrial applications such as automotive,ackaging, coating, construction, and electronics. They have greatotential of increasing the fields of use which indicates them as

ikely to be involved in many various aspects of our lives in the nearuture [1,2]. Accordingly, many research and development studiesre being done in nanocomposite field to enable applications inany industrial sectors.Emulsion based polymers are widely used as coating materi-

ls for textiles, automotives, paints, constructive materials, leather,tc. The emulsion polymerization technique brings advantages

ue to environmental and health care concerns and also easierrocedures of application. However, generally the water resis-ance and mechanical properties of the polymer latexes are lowerhan the solvent based polymer systems. On the other hand, the

∗ Corresponding author. Tel.: +40 232 217454; fax: +40 232 211299.E-mail address: duncaty@icmpp.ro (C.N. Cheaburu).

300-9440/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.porgcoat.2010.10.001

© 2010 Elsevier B.V. All rights reserved.

nanocomposites based on polymer/layered silicates may providean alternative way to enhance the desired properties of waterbornecoatings [3].

Emulsion polymerization for preparation of polymer/claynanocomposites is a process requiring the presence various chem-icals/ingredients such as monomers, water, emulsifiers, initiators,fillers (e.g. different clay types) and the presence of other additives.The system involves multi-interactions between these componentswhich affect either the preparation of the latexes and/or the prop-erties of both latex and polymer. The rheological properties ofnanocomposite latexes are of importance for exploiting the per-formance of the material and its behaviour during applicationprocedures being essential for the performance of the coatings afterapplication.

The rheology of emulsions has gained interest from both the-oretical and practical point of view in processing and applicationtechnologies [4,5]. Among the rheological properties, viscosity isimportant because the knowledge of the latex viscosity is the keyparameter of designing and application of the latex. The factors

affecting the latex viscosity are polymer type, concentration, par-ticle size, emulsifier content, temperature and share rate [6]. Therheological behaviour of nanocomposites depends on the degree ofdispersion of clay aggregates, which depends, among other manyfactors, on the degree of attractive interactions between polymer

Organic Coatings 70 (2011) 52–58 53

msnowiro

mrwblpftaau

agasahTpitlp

bdwieosmmnfb

aciwcpa

2

2

lm1LIa

Table 1Nanocomposite latex series used for rheological characterization.

Runs Monomers Clay type wt.% Clay

A0 BA/MMA/AAm Without 0

Group A (2 wt.% SDS)A93A BA/MMA/AAm Cloisite 93A 3A30B BA/MMA/AAm Cloisite 30B 3ACNa BA/MMA/AAm Cloisite Na+ 3AI31 BA/MMA/AAm Nanomer I.31 PS 3

B0 BA/MMA/AAm Without 0B15A BA/MMA/AAm Cloisite 15A 3

The rheological investigations were performed at 25 C bymeans of an Anton Paar 301 Rheometer (USA) device using acone/plate geometry measuring system with an angle of 1.003◦.

The rheological tests performed on the nanocomposite latexesare as follows:

Table 2The clay types and their modifiers used for nanocomposite preparation.

Group Clay type Modifier

A

Cloisite 93A Methyl, dehydrogenated tallowquaternary ammonium

Cloisite 30B Methyl, tallow, bis-2-hydroxyethyl,quaternary ammonium

Nanomer I.31 PS 15–35 wt.% octadecylamine, 0.5–5 wt.%aminopropyltriethoxysilane

Cloisite Na+ Unmodified montmorillonite

Cloisite 15A Dimethyl, dehydrogenated tallow,quaternary ammonium

O. Yılmaz et al. / Progress in

atrix and clay [7]. For this reason, the degree of clay disper-ion (intercalation and/or exfoliation) in polymer matrix affectsot only the mechanical properties of the film but also the rhe-logical behaviour of the latex. It is generally established thathen nanocomposites are formed, the viscosity at low shear rates

ncreases with filler concentration [8]. On the other hand, manyesearchers reported that a shear thinning behaviour was usuallybserved at higher shear rates [9–12].

The term of leather finishing is used to describe the processainly for enhancing some physical and fastness properties like

esistance to abrasion, resistance to light and heat, resistance toater etc. of the surface of leather products (such as jackets, shoes,

ags, and upholstery leathers) as well as improving the aspect ofeather by surface coloring and adding fashionable effects. In thisrocess some polymeric binders are used as pigment carriers toorm a homogenous film on the surface of leather. Due to resis-ance to hydrolysis, high block resistance, hardness–softness, gooddhesiveness, good film forming properties and inexpensiveness ofcrylates, they are the most common commercial leather binderssed in the leather industry [13–15].

These acrylic emulsion binders are mostly thermoplastic, havelow Tg value to possess a good flexibility during usage and a

ood pigment binding capacity. They also fulfill some criteria suchs abrasion, chemical, water and heat resistance. Acrylic emul-ions used for these purposes have the advantages as mentionedbove but unfortunately they may present sticking problems, pooreat and water resistance and moderate mechanical properties.o overcome some of these problems we had synthesized in ourrevious study [16] a set of water based acrylate/clay nanocompos-

tes composed of butylacrylate–methyl methacrylate–acrylamideerpolymer with eight different types of commercial montmoril-onites. The results had showed improved mechanical and thermalroperties for the nanocomposite films.

The rheological behaviour of the finishing fluid plays a key roleefore and after application. The finishing mixtures are formulatedifferently to be proper to the application technique being usedhich each one requires certain characteristics of the fluid. For

nstance, during a spraying application, the viscosity must be lownough to flow from the nozzle, but not so low or high to promoteptimal contact with the substrate for the leveling of the film byurface tension. Thus, the rheological behaviour of a coating for-ulation influences not only application performance, but also theixing process and film uniformity. The water based acrylate/clay

anocomposites are the major components in leather finishingormulations proposed in this study, therefore their rheologicalehaviour must be known and understood.

Present study deals with the rheological characterization of thecrylate based nanocomposite latexes including eight differentlay types and the application of the latexes as polymer bindersn leather finishing. The importance of the rheological properties

as evaluated in the view of application technique. The affects oflay loading, clay type and emulsifier amount on the rheologicalroperties of the latexes and the coating performance were alsossessed.

. Materials and methods

.1. Materials

The nanocomposite emulsions composed of butyl acry-ate (BA), methyl methacrylate (MMA), acrylamide (AAm)

onomers (Aldrich products) and different types of clays (Cloisite5A/20A/93A/C30B/Na+: Southern Clay Products Co., Dellite 67G:aviosa Chimica Mineraria S.P.A., Nanomer I.31 PS and Nanomer.44 P: Nanomer Products—Aldrich) were used for rheological char-cterization and finishing applications.

Group B (3.5 wt.% SDS)B20A BA/MMA/AAm Cloisite 20A 3B67G BA/MMA/AAm Dellite 67G 3BI44 BA/MMA/AAm Nanomer I.44 P 3

The synthesis of the nanocomposites was reported in detailin our previous study [16]. Briefly, the clay was mixed with themonomers overnight, ultrasonicated for 30 min and they werepolymerized at 75 ◦C for 3 h using potassium persulfate (KPS) asinitiator, sodium bicarbonate as buffer, sodium dodecyl sulfate(SDS) as emulsifier and a water soluble polymer (Mw = 3000) ascolloidal stabilizer (CS). The clay amount was 3 wt.% in respectto total monomer quantity and solid content of the latexes wasaround 20%. The nanocomposite latex series are given in Table 1.The nanocomposite samples are divided into 2 groups: group A hasa lower emulsifier content and group B has higher emulsifier con-tent. The classification of the samples was done by the emulsifieramount used to obtain stable latexes which is determined by thehydrophobicity of the clays. Therefore, the group A nanocompos-ites includes more hydrophobic clays which was stabilized with3.5 wt.% of emulsifier, while the group B comprises relatively lowerhydrophobic clays stabilized with 2 wt.% of emulsifier. The claysand their modifiers are also shown in Table 2.

Black dyed crust leathers proper for garment production weresupplied from a regional tannery company Tezcan Deri Co. (Aydın-Turkey) and were used for leather finishing applications. All theleathers had the same origin and same processing conditions tillfinishing stage. Other necessary commercial chemicals for finishingsuch as pigment, wax, aqueous nitrocellulose lacquer, surface mod-ifiers were supplied from Verbo Co. Inc. (Izmir-Turkey) and used inthe formulations together with the nanocomposite emulsions.

2.2. Methods

2.2.1. Rheological measurements◦

B Cloisite 20A Dimethyl, dehydrogenated tallow,quaternary ammonium

Dellite 67G Ditallowdimethylammonium ionNanomer I.44 P 35–45 wt. % dimethyl dialkyl

(C14–C18) amine

5 rganic Coatings 70 (2011) 52–58

(

2

slcc

amo(pb4lcIip4s8udr

3

3

F

4 O. Yılmaz et al. / Progress in O

(i) Flow behaviour (Newtonian or non-Newtonian): The flowbehaviour was tested by rotational controlled shear ratecondition (CSR) where the viscosity (�) of the sampleswere measured as a function of increasing shear rate(� = 0.1–1000 s−1).

(ii) Viscoelastic behaviour: Dynamic modulus, storage modulus(G′) and loss modulus (G′′) of the nanocomposite latexes weremeasured as a function of angular frequency (ω = 0.1–1000 s−1)using oscillatory tests. To perform the frequency sweep tests,the linear viscoelastic range of the samples (LVE) was obtainedfrom amplitude sweep tests (with a strain amplitude between0.01 and 500%) using a constant angular frequency ω = 10 s−1.

iii) Stability and recovery tests: The stability test was carriedout after 6 months of storage of the latexes. The tests wereperformed at very low shear load (ω = 5 rad/s) under givennumbers of cycles of rapid heating-cooling between 5 ◦C and50 ◦C. After each cycle of heating-cooling, the storage modu-lus (G′′) was compared with the initial storage modulus (G′

i)

and the changes were recorded. The recovery test named asthixotropy is done stepwise and consists of three intervals:oscillation/rotation/oscillation. In the first interval of oscilla-tion, the test was performed at a constant angular frequencyω = 10 rad/s and � = 0.01% which has a value in the LVE-rangedetermined previously by the amplitude sweep tests. In thesecond interval, a deformation was applied to the sampleunder rotational regime with a shear rate of 3000 s−1. The thirdinterval is similar with the first one. Between the second andthird interval, there is a resting period (60 s) where the noshare rate was applied. The comparison of the complex viscos-ity obtained from the first interval and third interval indicates ifthe structural recovery of the material took place that meaningthe thixotropic behaviour of the material.

.2.2. Finishing applicationFor finishing application the leather specimens were cut in the

quares to ensure a homogenous uptake of emulsions. The formu-ation mixture used for finishing consisted of a base coat and a topoat. In the finishing formulation all chemicals and their ratios wereonstant except the nanocomposite type used as binder.

The leathers to be tested by physical methods were conditionedccording to the standard of EN ISO 2419 and the sampling wasade according to EN ISO 2418. The efficiency of finishing applied

n leathers was evaluated by the physical tests as Flexing enduranceBally flexes-EN ISO 5402) which simulates the bending of leatherroduct during daily use and evaluates the cracking of the film atending region; Color fastness of leather to To and Fro rubbing (SLF50), measures the resistance of the film to a moving felt on the

eather surface and evaluates both the damage on finish layer andolor transfer to felt; Change in color with accelerated ageing (ENSO 17228), to evaluate the change of surface color and the leathertself due to ageing by creating an environment at selected tem-erature, humidity and time; Color fastness of leather to ironing (SLF58), a test which a metal finger moves on leather surface underpecified pressure and speed at a temperature selected in the range0–240 ◦C and the resistance of the color of leather to heat is eval-ated. The evaluation of all the tests related to color change wasone according to grey scale standard (IUF 131-132) which gives aating between 1 and 5 (5: no color change, and 1: failure).

. Results and discussion

.1. Flow behaviour

Flow behaviour of the nanocomposite emulsions is shown inig. 1a–c where the viscosity changes as a function on shear rate

Fig. 1. Viscosity changes of the nanocomposite emulsions in a function of shear rate:(a) group A nanocomposite latexes, (b) group B nanocomposite latexes, (c) influenceof emulsifier content.

are given. All the nanocomposites showed higher viscosity valuesthan the neat polymer emulsions except the nanocomposite B15A

showing lower viscosity (Fig. 1b). The unexpected lower viscos-ity of the sample B15A is difficult to explain, however, it might bebecause of the lowest average particle size among all samples as itwas shown in the previous paper [16].

Organic Coatings 70 (2011) 52–58 55

swTmcHsohcttiterhtwtgbrtbto

AoedtaTssa

tassBeuflitprvs(Osctceattir

O. Yılmaz et al. / Progress in

As it can be observed from Fig. 1a–c, viscosity of the emul-ions without clay (A0, B0) showed an increase at lower shear rateshich can be considered as a slight shear-thickening behaviour.

his behaviour can be observed when shearing emulsions and thisay be due to a reduction of the medium droplet size which is

aused by droplet subdivision resulting from shear forces [17].owever, by further increase of shear rate, the neat latexes (A0, B0)

howed a plateau exhibiting a Newtonian behaviour. The viscositiesf the nanocomposite emulsions at low shear rates showed muchigher values than the polymer emulsions without clays which areharacteristic for nanocomposites. The corresponding increase ofhe volume specific surface (the ratio between droplet surface andhe droplet volume) and, as a consequence, the resulting increasen the interactions between the droplets leads to higher values ofhe flow resistance (viscosity). Besides, almost all nanocompositemulsions showed a decrease of viscosity with increasing shearates exhibiting a shear-thinning behaviour. Usually the polymersaving higher molecular weights have a tendency to entangle withheir neighboring macromolecules in their three dimensional net-ork at “rest” state (low shear rates). But during the shear process,

he molecules are usually oriented in the shear direction by entan-ling to a certain extend which lower their flow resistance. Thisehaviour is attributed to the physical jamming or percolation ofandomly distributed silicate layers [18]. The clay layers, especiallyhe intercalated or exfoliated ones could support this orientationy alignment of their rigid crystalline lamellar structure towardshe direction of flow at higher shear rates as similarly reported byther authors [11,19].

In Fig. 1c the viscosity of some selected samples from groupsand B are compared. The viscosity curves of the samples with-

ut clay (A0, B0) indicated similar trend lines which show that themulsifier amount did not show a significant effect on viscosityependence on shear rate but the type of clay affect the viscosi-ies. Accordingly, the shear thinning behaviour was more obvioust the nanocomposites having more hydrophobic clays (group B).his is rather an expected result since more organophilic clays couldhow better compatibility with the polymer chains which leads totronger intermolecular interactions resulting in higher viscositiesnd stronger shear thinning effects.

Viscosity is a very important parameter for finishing applica-ions, in every case whether the formulation is sprayed, paddednd curtain-coated or printed. When the viscosity is not proper,erious problems like flowing on the surface, coating thickness,treaks and application marks may occur during application [20].esides, the application technique requires a specific viscosity ofmulsion to be applied. A spray coating technique which is widelysed in leather industry requires low viscosity fluids to facilitateow through the nozzle. Furthermore, the high shear rates found

n a spray finishing process may make it desirable to have a shearhinning fluid, i.e., a fluid whose viscosity decreases with shear, toromote an optimal fluid flow and spray application. Similarly, foroll coating application the viscosity should be controlled to pre-ent the fluid from sagging on the roll [21,22]. Spray applicationubjects the water based coating to the greatest range of shear rates106 s−1) compared to pumping or curtain coating (103–104 s−1).n the other hand, mixing procedures before application subjects

hear rates of 100 s−1 to the finishing solution [22,23]. In all theseases the coating performance is affected by shear rates accordingo the behaviour of the fluid before or during mixing and appli-ation. Moreover, the viscosity of coating emulsion must be lownough to exit the relatively small spray-tip orifice but not so low

s to exhibit running and sagging after it contacts the surface ofhe substrate. The control of the formulation rheology profile ishe key to achieve optimum coating application performance. Tak-ng into account these aspects, the nanocomposite emulsions withelatively higher viscosities than blank polymer samples and show-

Fig. 2. Viscoelastic behaviour of acrylate/clay based nanocomposite emulsions atvariable frequencies: (a) group A nanocomposite latexes, (b) group B nanocompositelatexes, (c) influence of emulsifier content.

ing shear thinning effect, present improved properties for sprayapplication which is the most common coating method in leatherfinishing.

3.2. Oscillatory tests

Oscillatory tests are presented in Fig. 2a–c where storage modu-lus (G′) and loss modulus (G′′) are plotted as function of the angularfrequency (ω) under a constant amplitude strain (LVE range). All

the samples showed similar shapes of G′, as well as for G′′. As it canbe observed from the curves of Fig. 2, for all frequency ranges, G′ hashigher values in comparison to G′′ (G′ > G′′) which indicates that theelastic behaviour dominates the viscous one. In general, within the

5 rganic Coatings 70 (2011) 52–58

sfsiswaiib

cButnvpaiimmshwb

stcitbepryesasti

3

ciotovcs

tmspaB

at

6 O. Yılmaz et al. / Progress in O

table dispersions, emulsions and gels, intermolecular interactionorces are forming three-dimensional networks and thus they arehowing G′ > G′′ in whole frequency ranges with a slight increasen the slope at higher frequencies [24]. Usually emulsions, disper-ions or unlinked polymers show a low structural strength “at rest”hich refers to decreased G′ values at lower frequencies, however

s it can be seen from Fig. 2, all the samples showed high stabil-ties even at low frequencies possibly due to high intermolecularnteractions between polymer chains. Therefore the samples cane evaluated as highly stable emulsions.

The Fig. 2a and b presents the influence of clay type on vis-oelastic behaviour of the nanocomposites. In both groups (A and), the clay incorporation led to significant increase in storage mod-lus of the emulsions for the entire frequency range in respect tohe polymer emulsions without clay (A0 and B0). In group A ofanocomposites the sample AI31 seemed to have the highest G′

alues among the others in this group while in group B the sam-le B20A had the highest storage modulus (Fig. 2c). This result islso in accordance with the shear viscosities of the nanocompos-tes since the samples AI31 and B20A had the highest viscositiesn their groups showing a good compatibility with the copolymer

atrix by increased intermolecular interactions resulted in higheroduli values. In addition, the comparison of two blank polymer

amples showed that the storage modulus of B0 which includeigher emulsifier content (3.5 wt.%) was slightly higher than A0ith lower emulsifier content indicating that modulus also could

e affected by total emulsifier content of emulsions.In the application of emulsion based polymers in industry, emul-

ion stability is another key factor which determines the duration ofhe product without being deformed from production until appli-ation. This period may even be longer when the product standsn shelf. The definition of “emulsion stability” can be made by bothhermodynamic and kinetic point of view. The thermodynamic sta-ility is explained by the electrostatic force interactions within anmulsion while rheology enables us to predict compositions whichrovide physically stable emulsions. In accordance with the resultseported in our previous paper [16] obtained by zeta potential anal-sis showing good electrostatic stabilities for the nanocompositemulsions, the oscillatory tests also verified physically stable emul-ions. These stable emulsions can be obtained if the system formsn elastic gel network [25,26]. All the nanocomposite emulsionshowed elastic network for all frequency range and clay addi-ion seemed to enhance the network strength and hence, led toncreased stability of emulsions.

.3. Emulsion stability and recovery tests

Emulsions stability tests at very low shear load (ω = 5 rad/s) andycles of rapid heating-cooling between 5 and 50 ◦C are presentedn Fig. 3a for some representative samples (B0, B67G and B15A). Thebtained data were analyzed by means of the ratio between the ini-ial storage modulus (G′

i) and the storage modulus after each cycle

f heating-cooling. The emulsions containing clay showed smallerariations of the Gı in comparison to the reference sample withoutlay (B0) during the loop of temperature indicating the increase oftability for nanocomposite latexes by clay incorporation.

The characteristic thixotropic behaviour refers to the reduc-ion of the structural strength during a shear load phase and a

ore or less rapid and complete structural regeneration during aubsequent “rest” period. It is a time-dependent property. As com-ared with the reference sample (A0) without clay, which recovers

round 70% of the structure, the nanocomposites latexes (A93A,I31) showed recovery over 90% of their structure after resting.

Both the rheological properties of stability and recovery maylso be important for application depending on the applicationechnique and procedure. Before, during or after application, when

Fig. 3. (a) Stability of some of the nanocomposite latexes during the repeated cyclesof heating–cooling (5–50 ◦C), and (b) thixotropic behaviour of some of the nanocom-posite latexes.

a heating process is applied to the finishing mixtures, a minimumstructural change of latex is usually required. This can also be animportant issue during drying of the substrate after applicationwhere in some cases drying can be done in cycles. The recoveryproperty of latexes after a shear load gives us information if thestructural strength changes during application by the shear forcesof spraying, roll coating, etc. The results showed that clay incor-poration may help to increase also the structural recovery of thepolymer after shear loading applied during finishing process, sothat the performance of the final coating can be improved.

3.4. Leather finishing application

The finish formulation applied on the leathers is given in Table 3.The formulation includes a base coat in which the nanocompositeemulsions were used as binders together with pigment and waxand also a topcoat layer was applied containing a nitrocelluloselacquer emulsion for general purpose. The coatings were appliedby a hand spraying gun with a lower air pressure of 2 atm to ensure

the surface to be coated lightly and to prevent from excess loss ofthe finishing solution. The formulation was prepared as simple aspossible for an easier evaluation of the effect of the nanocompositebinders on finish properties. The leathers used for application werefull grain black dyed crust leathers for garment production. After

O. Yılmaz et al. / Progress in Organ

Table 3The finishing formulation applied on the leathers including nanocomposites asbinder.

Components Application steps Descriptions

Basecoat (A) Topcoat (B)

Water 350 g 200 g Spray A × 2 timesBlack pigment 100 g Hot plate 70 ◦C/40 barWax 75 gBindera (20%) 250 g Spray A × 4 timesAqueous NC lacquer 100 gSilicone modifier 15 g Spray B × 1 time

◦

tsbfigmpaFcws

fti

a

Table 4 shows the results of ironing resistance of the leathers

F

Hot plate 70 C/60 barSpray B × 1 time

a Binder refers to each nanocomposite applied on leathers.

he application the leathers resulted in glossy appearance for allamples and it was not observed any impairment on the appearancey clay usage since silicates are normally used as matting agents innishing formulations when a dull leather surface is desired. Thislossy appearance could be due to the fine particle size and a nano-etric scale dispersion of silicate layers in polymer matrix. The

hotographs of some representative leathers before and after thepplication taken by a digital camera (Nikon D3000) are shown inig. 4. From the images it can be seen that the leathers were suc-essfully finished, they had good surface coverage, all the surfacesere glossy and smooth and the natural grain pattern of the leather

urfaces was kept.The flexing endurance of the leathers (Bally flexes-EN ISO 5402)

or all samples was perfect after 50,000 times of flexing showing

hat the flexibility of the finishing layer was not impaired by clayncorporation.

To understand the behaviour change of the leather finish aftergeing, the leathers were exposed to an accelerated aging pro-

ig. 4. The photographic images showing the leather surfaces after application of the fini

ic Coatings 70 (2011) 52–58 57

cedure at 60 ◦C for 72 h. After this period the surface colors ofthe leathers were evaluated (grey scale) and the flexing test (DIN53340) was repeated to check any flexibility change in the finishlayer. It was observed that either the color fastness or the flexingendurance of leathers did not show any impairment.

The rub fastness results of the leathers are given is Table 4. After150 times of rubbing it was not observed a failure for nanocompos-ite samples, therefore the test was kept till 500 rubs. As it can beclearly seen the leathers finished with pure latexes as binders (A0and B0) showed lower rub fastness values as 1/2 after 500 rubs.However, with clay incorporation rub fastness values increasedremarkably and the best results were obtained by A93A and ACNawith a level of 3/4. From rheological point of view it is not easyto make interpretation for rub fastness test results because thefinish performance depends on multi factors such as leather struc-ture, application procedures and performance of the chemicals.However, viscosity of the finish formulation affects the contact effi-ciency of the liquid and the leather. Usually an acceptable highviscosity is more preferred to prevent the formulation from run-ning into the lower parts of the grain and flows away from thesurface [20]. Although finishing formulations consist of many com-ponents such as binder, pigment, and wax, the binder is the keyelement affecting the rheological behaviour and performance offinishing formulations. Taking into consideration of these, all thenanocomposites having relatively higher viscosities gave better rubfastness than the reference polymer samples. Moreover, the groupA nanocomposites seemed to give better results possibly due tolower emulsifier content.

coated with the nanocomposites. The ironing resistance test letsus to assess the behaviour of leather color on exposure to a hotiron, as for instance in crease removal in shoe manufacture orironing in garment manufacture. The failure temperature of the

shing formulations containing acrylate/clay based nanocomposites as binders.

58 O. Yılmaz et al. / Progress in Organic Coatings 70 (2011) 52–58

Table 4The psychical test results of the leather finishes.

Sample Flexing endurance 50,000× Fastness level—dry, 500 rubs Ironing temperature (◦C)

Leather Felt

A0 Excellent 1/2 4 80–100A93A Excellent 3/4 5 100–120A30B Excellent 2/3 3 80–100ACNa Excellent 3/4 4/5 120–140AI31 Excellent 3 4/5 100–120B0 Excellent 1/2 4 80–100

2/3332/3

fifcltrccb

4

pwmrisispsltnt

ibencctacsrFpaemf

[[

[[

[[[

[

[[

[[

[[

B15A ExcellentB20A ExcellentB67G ExcellentBI44 Excellent

nish layer against ironing was found to be between 80 and 100 ◦Cor the leathers coated with neat latexes. However the usage oflay increased the maximum ironing temperature by 20 ◦C for theeathers coated with A90A, AI31, B67G and BI44, moreover for ACNahe improvement was higher by around 40 ◦C. The higher thermalesistance of ACNa including natural montmorillonite (Cloisite Na+)an be due to its higher inorganic content since an important per-entage of hydrophobic clays are organic compounds (15–45 wt.%)ecause of their modifiers.

. Conclusions

The obtained water based acrylate/clay nanocomposites com-osed of BA-co-MMA-co-AAm terpolymers with various clay typesere rheologically tested in respect with flow behaviour, dynamicoduli measurements in oscillatory mode and also stability and

ecovery tests (thixotropic behaviour). Almost all nanocompos-te latexes showed higher viscosity values than their referenceamples with a shear thinning effect. Oscillatory measurementsndicated that all nanocomposite emulsions showed more elastictructure (G′ > G′′) having higher storage modulus (G′) in com-arison to reference samples which refers to increased physicaltabilities. Additionally it seemed that the group B nanocompositeatexes including hydrophobic clays and higher emulsifier con-ent had higher viscosity and storage moduli values than group Aanocomposite latexes possibly due to better interactions betweenhe polymer and clay layers.

The application of the nanocomposite emulsions in a basic fin-shing formulation showed that they were successful as base coatinders for leather finishing by offering a good film forming prop-rties, elasticity and pigment binding efficiency besides glossy andatural appearance of leathers. The physical tests showed that thelay incorporation increased the performance of the coatings. Theomparison of both rheological and application results indicatedhat the clay type and/or the emulsifier content had significantffects on the final use of the polymers. While more hydrophobiclays show better compatibility with the polymer, the higher emul-ifier content necessary for stabilization affects negatively wateresistance and mechanical properties of the polymer in final use.or this reason, it is important to find a balance between the com-

atibility of the clay type with the polymer and the emulsifiermount which is necessary for stabilization. We claim that mod-rate hydrophobic clays (i.e. Nanomer I.31PS, Cloisite 93A) seemore proper for preparation of emulsion based nanocomposites

or coating applications. In this way, the mechanical and thermal

[

[[

4/5 80–1004/5 80–1004/5 100–1204/5 100–120

properties of coated surface can be increased as in our case whichgives a way for producing a new class of “nano binders” for leatherindustry.

Acknowledgements

The research leading to these results has received partial supportfrom the European Community’s Seventh Framework Programme[FP7/2007-2013] under grant agreement no. 218331 NaPolyNet.The authors are grateful to the CNCSIS and ANCS for financialsupport by the IDEI 17/2007 (Romania) and Directorate of Admin-istrative and Financial Affairs of Ege University (Turkey), grant no.07MUH006.

References

[1] F. Wypych, K. Satyanarayana, J. Colloid Interface 285 (2005) 532–543.[2] S.J. Ahmadi, Y.D. Huang, W. Li, J. Mater. Sci. 39 (2004) 1919–1925.[3] M.L. Nobel, E. Mendes, S.J. Picken, J. Appl. Polym. Sci. 104 (2007) 2146–2156.[4] H.A. Barnes, Colloids Surf. A 91 (1994) 89–95.[5] Th.F. Tadros, Colloids Surf. A 91 (1994) 39.[6] J.U. Park, J.L. Kim, D.H. Kim, K.H. Ahn, S.J. Lee, Macromol. Res. 14 (2006) 318–

323.[7] C.D. Han, Cpt 2 in Rheology and Processing of Polymeric Materials, Oxford

University Press, USA, 2007, pp. 569–603.[8] J.W. Cho, D.R. Paul, Polymer 42 (2001) 1083–1094.[9] B.J. Park, T.H. Kim, H.J. Choi, J.H. Lee, J. Macromol. Sci. B: Phys. 46 (2007)

341–354.10] H. Li, Y. Yu, Y. Yang, Eur. Polym. J. 41 (2005) 2016–2022.11] T.H. Kim, L.W. Jang, D.C. Lee, H.J. Choi, M.S. Jhon, Macromol. Rapid Commun. 23

(2002) 191–195.12] R. Wagener, T.J.G. Reisinger, Polymer 44 (2003) 7513–7518.13] E. Heidemann, Cpt 18 in Fundamentals of Leather Manufacturing, 1st ed., E.

Roether KG, Darmstadt, 1993, pp. 570–612.14] F. Schindler, J. Am. Leather Chem. Assoc. 98 (2003) 570–611.15] M. Greif, J. Am. Leather Chem. Assoc. 72 (1977) 162–165.16] O. Yilmaz, C.N. Cheaburu, D. Durraccio, G. Gulumser, C. Vasile, Appl. Clay Sci.

49 (2010) 288–297.17] T.G. Mezger, The Rheology Handbook, 2nd ed., Vincentz Network GmbH & Co.

KG, Hannover, 2006.18] S. Pavlidou, C.D. Papaspyrides, Prog. Polym. Sci. 33 (2008) 1119–1198.19] R. Krishnamoorti, R.A. Vaia, E.P. Giannelis, Chem. Mater. 8 (1996) 1728–

1734.20] W. Wenzel, World Leather (August/September) (1996) 64–66.21] S. Alonso, L. Medina-Torres, E. Brito De-La-Fuente, Chem. Eng. Commun. 192

(2005) 839–854.22] J. Biles, J. Am. Leather Chem. Assoc. 85 (1990) 163–178.23] J. Biles, N. DiCandilo, P. Gehlhaus, W. Prentiss, J. Am. Leather Chem. Assoc. 80

(1985) 284.24] R. Brummer, in: H.G. Barth, H. Pasch (Eds.), Rheology Essentials of Cosmetic and

Food Emulsions, Springer-Verlag, Berlin/Heidelberg, Germany, 2006.25] T. Tadros, Adv. Colloid Interface Sci. 108–109 (2004) 227–258.26] L.G. Torres, R. Iturbe, M.J. Snowden, B.Z. Chowdhry, S.A. Leharne, Colloids Surf.

A: Physicochem. Eng. Aspects 302 (2007) 439–448.