nanocomposite materials based on polyurethane

8/10/2019 Nanocomposite Materials Based on Polyurethane

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Materials Science and Engineering A 399 (2005) 368376

Nanocomposite materials based on polyurethane intercalated intomontmorillonite clay

Ahmed Rehab , Nehal Salahuddin

Chemistry Department, Faculty of Science, University of Tanta, 31527 Tanta, Egypt

Received in revised form 31 March 2005; accepted 7 April 2005

Abstract

Polyurethane organoclay nanocomposites have been synthesized via in situ polymerization method. The organoclay has been preparedby intercalation of diethanolamine or triethanolamine into montmorillonite clay (MMT) through ion exchange process. The syntheses of

polyurethaneorganoclay hybrids werecarriedout by swelling the organoclay into different kindsof diols followed by addition of diisocyanate.

The nanocomposites with dispersed structure of MMT was obtained as evidence by scanning electron microscope and X-ray diffraction

(XRD). The results shows broaden with low intense and shift of the peak characteristic to d0 0 1spacing to smaller 2and the MMT is dispersed

homogeneously in the polymer matrix. Also, the TGA showed that the nanocomposites have higher decomposition temperature in comparison

with the pristine polyurethane.

2005 Elsevier B.V. All rights reserved.

Keywords: Polyurethane nanocomposites; Nanocomposites; Polyurethane organoclay; Intercalated polymers; Layered silicate; Polymerclay nanocomposite

1. Introduction

Polymer composites were widely used in electronic and

information products, consumer commodities and the con-

struction industry. In these polymer composites, inorganic

materials were used to reinforce polymers with the idea of

taking advantage of the high heat durability and the high

mechanical strength of inorganic and the ease of processing

polymers. Clays have been extensively used in the polymers

industry either as reinforcing agent to improve the physico-

mechanical properties of the final polymer or as a filler to

reduce the amount of polymer used in the shaped structures,

i.e., to act as a diluent for the polymer, thereby lowering

the economic high cost of the polymer systems. The effi-ciency of the clay to modify the properties of the polymer is

primarily determined by the degree of its dispersion in the

polymer matrix, which in turn depends on the clays parti-

cle size. However, the hydrophilic nature of the clay surfaces

impedes their homogeneous dispersion in the organic poly-

Corresponding author. Tel.: +20 40 350804; fax: +20 40 350804.

E-mail addresses:[email protected],

[email protected] (A. Rehab).

mer phase. The interfacial incompatibility between inorganic

and organic polymers existed owing to the difference in thenature of their individual intermolecular interaction forces

and often caused failures in these inorganicorganic compos-

ites. One approach to alleviate the interfacial and the tenacity

problem in these polymer composites is to chemically bond

the inorganic and polymers through the solgel method[1].

The composite materials prepared by solgel method suf-

fered the drawback of large shrinkage during the removal of

the solvent. The other approach is to uniformly disperse the

inorganic in the polymer matrix in the nanometer scale to

form inorganicpolymer nanocomposites[2].

Nanocomposites are a class of composites in which the

reinforcing phase dimensions are in the order of nanome-ters [3]. Layered materials are potentially well suited for

the design of hybrid nanocomposites, because their lamel-

lar elements have high in-plane strength, stiffness and a high

aspect ratio [4]. The smectic clays (e.g., montmorillonite)

and related layered silicates are the materials of choice for

polymer nanocomposite design for two principal reasons:

first, they exhibit a very rich intercalation chemistry, which

allows them to be chemically modified and made compatible

with organic polymers for dispersal on a nanometer length

0921-5093/$ see front matter 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.msea.2005.04.019


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A. Rehab, N. Salahu ddin / Materials Science and Engineering A 399 (2005) 368 376 369

scale. Second, they occur ubiquitously in nature and can

be obtained in mineralogically pure form at low cost. The

layered claypolymer nanocomposites can be prepared by

replacing the hydrophilic Na+ and Ca+ exchange cations of

the native clay with more hydrophobic onium ion to form a

polymer-clay hybrid through two ways. The first is the inter-

calation of a monomer into the clay interlayer and subsequentheat treatment for polymerization [5]. Thesecond is thedirect

intercalation of a preformedpolymer into thelayered clay [6].

Since the development of Nylon-6clay nanocomposite

by Toyota researchers [7], extensive studies on polymerclay

nanocomposites have been investigated in order to obtain

new organicinorganic nanocomposites with enhanced

properties. The use of clay or organically modified clay

as precursors for preparation of nanocomposites has been

studied into various types of polymer systems including

polyamide 6[8], polyoligo (oxyethylene) methacrylate[9],

epoxy[10], polyimide [11], polyester [12], polypropylene

[13], polyacrylamide[14], polypyrrol[15], polystyrene[16],

poly(p-phenylene vinylene) [17], polyethylene oxide [18],polycaprolactone[19]and polymethyl methacrylate[20].

Polyurethane (PU) elastomers are a family of segmented

polymers with soft segments derived from polyols and hard

segments from isocyanates and chain extenders [21]. PU

elastomers represent one of the most attractive elastomers

because they have the advantages, such as the best abra-

sion resistance, outstanding oil resistance and excellent low-

temperature flexibility. They also exhibit the widest variety

of hardness and elastic moduli that just fill in the gap between

plastics and rubbers.

The first example of elastomeric polyurethaneclay

nanocomposites with greatly improved performance proper-ties compared to the pristine polymer was reported by Wang

and Pinnavaia [22]. Preparation, characterization and proper-

ties of polyurethaneclay nanocompositeshave beenreported

by a various researchers[2333].

However, there also exist some disadvantages concerning

with thermal stability and barrier properties. To overcome

the disadvantages, the present work will discuss our initial

efforts to synthesis differentstructure of PUMMT nanocom-

posites. Since the physical properties of the resulting mate-

rials are derived from their structures and study the effect

of organoclay percentage on the resulting nanocomposites

(Scheme 1).

2. Experimental

2.1. Materials

Montmorillonite (Na-MMT) minerals were supplied by

ECC America Inc., under the trade name Mineral Colloid-

BP as fine particles with an average particle size of 75 m

and cation exchange capacity (CEC) of 90 m equiv./100 g

and interlayer spacing of 9.6A. Diethanolamine from Riedel-

De Haen AG Seelze-Hannover; triethanolamine from GDR

Co. Germany; 1,3-butylene glycol, diethylene glycol and

triethylene glycol from Aldrich; tolylene-l,4-diisocyanate

(TDI)from Flukawere usedas supplied.Dimethylformamide

(DMF) from Adwic (Egypt) was used after distillation and

drying over molekularSieb.

2.2. Preparation of materials

2.2.1. Preparation of modified clay Ia,bThe MMT (10 g) was swelled in 600 ml of distilled water

followed by addition of 20 g diethanolamine dropwise with

stirring. The suspension was stirred for 24 h at room tem-

perature followed by addition of dilute HCl (1:1) to obtain

slightly acidic medium (pH 5.56) then the stirring was

continued for 24 h at room temperature. The suspension was

allowed to stand for a few hours, filtered off using sintered

glass (G4), washed many times with distilled water, then

dried at 35 C under vacuum to yield 10.85 g of MMT-

diethanolamine intercalate product. The product was retreat-

ment with diethanolamine by swelling in mixture of 300 mlDMF and 300 ml water followed by addition of 20 g of

diethanolamine and the procedure was repeated as previously

to give 11.05 g of MMT-diethanolamine intercalateIa.

The intercalation of MMT (10 g) with triethanolamine

(20 g) was carried out by the same procedure described in

synthesis ofIato give 11.5 g ofIb. The structural properties

were measured directly by infrared (IR), Fig. 1; thermo-

gravimetric analysis (TGA),Fig. 2;calcinations, elemental

microanalysis, swelling data and X-ray diffraction (XRD),

Fig. 3.

2.2.2. Preparation polyurethaneMMT compositesThematerials were prepared by swelling themodified clay

in the diol followed by addition of the diisocyanate as in the

following procedure. 0.52 g ofIaswelled in 4.66 g (50 mmol)

of 1,3-butylene glycol for 5 h with stirring followed by

addition 8.87 g (50 mmol) of tolylene-2,4-diisocyanate with

stirring at room temperature (20 C). The polymerization

was started after a few minutes (the viscosity of the mix-

ture was increased) and completed very fast. After about 2 h,

the formed solid product was suspended in DMF then pre-

cipitated in distilled water. The white powder product was

filtered off and washed several times with water then dried

under reduced pressure at 35 C to give 13.2g (94% yield)

of (IIa). The other samples (IIbh) were prepared by the same

procedure using different amount of modified clay (Ia) with

different diols and another modified clay (Ib) with the same

diisocyanate as illustrated inTable 1.

2.2.3. Preparation of linear polymers

The linear polyurethanes were prepared by polycondensa-

tion technique using a mixture of diol and diisocyanate as in

the following procedure: 2.83 g (30 mmol) of 1,3-butylene

glycol was cooled in ice bath then added 3.6 ml (4.35 g,

30 mmol) of 2,4-tolylenediisocyanate with stirring. Themix-

ture was stirred for a few minutes then the temperature


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370 A. Rehab, N. Salahuddin / Materials Science and Engineering A 399 (2005) 368376

Fig. 1. Infrared spectra of the organoclay Ia,band PUorganoclay nanocom-

positesIIah and linear polyurethanesIIIad.

increased gradually to the room temperature (20 C) for

about 2 h. The formed solid product was dissolved in DMF

then precipitated in distilled water. The white powder was

filtered off, washed several times with water then dried under

reduced pressure at35 C to give5.3g (74% yield) of prod-

uct IIIa.Theothersamples(IIIbd)werepreparedbythesame

procedure using different diols and the same diisocyanate as

illustrated inTable 2.

2.2.4. Analytical procedures

Infraredspectra were carried out on a Perkin-Elmer 1430

Ratio-recording infrared spectrophotometer using the potas-

sium bromide disc technique in the wavenumber range of

4000400 cm1.

Thermogravimetric analysis was obtained by using a TGA

50 Shimadzu (thermal gravimetric analyzer). The heatingrate was 10 C/min in all cases in the temperature range

30800 C in nitrogen atmosphere.

Calcination measurements:A definite weight of the sam-

ple was introduced into a porcelain crucible and dried in an

electric oven at 120 C overnight, then introduced into an

ignition oven and the temperature was increased to 1000 C

and adjusted at this temperature for 15 h. The loading of each

sample expressed as the weight loss by ignition per 100 g of

the dry sample. The data of all prepared samples are listed in

Table 4.

X-ray diffraction measurementswere carried out using a

Phillips powder diffractometer equipped with a Ni-filtered

Cu Kradiation ( = 1.5418A) at scanning rate 0.005 s1,diverget slit 0.3. Measurements were made for the dried

product to examine the interlayer activity in the composite as

prepared.

Morphology of the composite was examined by a Joel

JXA-840 scanning electron microscopy (SEM) equipped

with an energy dispersive X-ray detector to examine the mor-

phology and particle size of MMT in the polymerMMT

composites. Specimen was deposited on double-sided scotch

tape and examined at their fracture surface.

3. Results and discussion

To disperse MMT nanolayers in a polyurethane matrix,

it was necessary to first replace the hydrophilic inor-

ganic exchange cations of the native mineral with more

organophilic diethanolamine or triethanolamine. The ion

exchangewas carried outbetween sodiumcation in MMT and

ammonium groups in diethanolamine or triethanolamine.The

presence of these group in the galleries of MMT renders the

Scheme 1. Synthesis of intercalated polyurethanes.


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MMT organophilic and promote the absorption of diol into

the interlayer of MMT and improve the particlematrix inter-

actions, since diethanolamine and triethanolamine contains

functionalgroupwhichreact with diisocyanate.Polyurethane

nanocompositeswere prepared by solvationof the organoclay

with the diol. It was found that the modified clay was swelled

easily in the diols at room temperature. This solvation was

followed by adding the diisocyanate.

The synthesis of new organicinorganic nanocomposite

materials was achieved by the intercalation of polyurethane

onto functionalized montmorillonite clay through in situ

polycondensation polymerization technique. The nanocom-

Fig. 2. TGA thermogram of PUorganoclaynanocomposites (a) IIadwith differentratios of organoclay Iaand linear polyurethanes IIIa, (b) IIehwithdifferent

diols, (c) TGA thermogram of linear polyurethanes IIIad.


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Table 1

Polymerization data of intercalated samples IIah

Run Modified clayb Diol Diisocyanatea Product

g wt%c Typed g mmol g mmol g Yield (%)

IIa 0.52 3.83 1,3-Bu-G 4.66 50 8.87 50 13.2 93.9

IIb 1.17 7.98 1,3-Bu-G 4.62 50 8.87 50 11.3 77.1

IIc 1.65 10.91 1,3-Bu-G 4.63 50 8.87 50 14.0 92.4IId 2.80 17.21 1,3-Bu-G 4.60 50 8.87 50 14.0 92.5

IIe 0.594 3.749 TEG 7.12 47 8.18 47 10.65 67.21

IIf 0.591 3.703 DEAm 5.80 55 9.57 55 10.79 67.61

IIg 0.595 3.717 DEG 5.84 55 9.57 55 11.85 74.03

IIh 0.256 3.641 1,3-Bu-G 2.43 25 4.35 25 5.51 78.37

a Diisocyanate is 2,4-tolylene diisocyanate.b Modified clay in all cases isIaexcept in the sampleIIhthe modified clay isIb.c wt% = (weight of dry modified clay/total weight of all components introduce the polymerization process).d 1,3-Bu-G, butane diol; DEAm, diethanolamine; DEG, diethylene glycol; TEG, triethylene glycol.

Table 2

Polymerization data of linear polymer samplesIIIad

Run Diol Diisocyanateb Product

Typea g mmol g mmol g Yield (%)

IIIa 1,3-Bu-G 2.83 30 4.35 30 5.311 73.97

IIIb DEG 3.25 30 4.35 30 1.233 16.22

IIIc TEG 4.556 30 4.35 30 5.083 57.07

IIId DEAm 4.4 40 4.35 30 5.366 61.33

a 1,3-Bu-G,butane diol; DEAm, diethanolamine; DEG,diethylene glycol;

TEG, triethylene glycol.b Diisocyanate is 2,4-tolylene diisocyanate.

posites were synthesized through the intercalation of diols

into organoclayIa,binterlayers followed by addition of TDI

to produce the intercalated polyurethanes IIah. The yields

of the products were ranging from 67% to 94%, as shown

inTable 1. It was found that the 1,3-butylene glycol giveshigh yields than the other diols in the polymerization into

organoclay. The different ratios of organoclay used during

the polymerization do not appear as an important factor to

affect the yield percent of the product. It was found that the

percentages of yield in the nanocomposites is higher than

the yield percentage of linear polyurethane (Table 2), which

may be attributed to catalytic effect for the clay. The struc-

tural composition and properties of the product materials was

determined by several analytical techniques.

The data in Table 3 illustrate that a high intercalation

yields for Ia,boccurred. Also, the swelling data indicated that

the organoclayIa,baccount for higher swelling in the organicsolvents and lower swelling in water. While, the affinity to

water still present due to the presence of OH group (Ib> Ia).

Moreover, the swelling behavior increased in the polar and

aprotic solvents than the non-polar solvent (the swelling

followed the order DMF > 1,4-dioxane > water > acetone >

benzene.

The IR spectra of all the prepared samples were illustratedinFig. 1andTable 3. The spectra of modified clayIa,bshows

that the reported NH stretch band near 3425 cm1 and NH

bend band near 1630 cm1 are shifted quite substantially to

regions associated with +NH3 vibration which facilitate the

ion exchange with MMT. A characteristic band at 464 cm1

for SiO and at 3626 cm1 for OH group are shown. This

free OH band at 3626 cm1 in organoclay was disappeared

in nanocomposite indicating the strong interaction are occur-

ring between OH group in organoclay and the isocyanate

forming the isocyanate linkage. Comparing the +NH3 band

near 1630 cm1 in organoclay with nanocomposite, it is clear

that this band is shifted to higher wavelength near 1710 cm1

indicating that an interaction occur between organoclay and

the polymer. The spectra of polyurethane IIIa shows the

absorbance appeared at 1724 cm1 that was assigned to

hydrogen-bonded urethane carbonyl (C O), 1413 cm1 to

a secondary urethane amide (CNH). The spectra of the syn-

thesized PUmodified clay shows IIa, peaks at 1712 was

caused by the stretching of urethane carbonyl group (C O)

and the 2927 and 2864cm1 were due to the asymmetric and

symmetric CH stretching vibration. The 3317 cm1 peak

resulted from the NH group in hydrogen bonding; the main

features of various bond vibration and hydrogen bonding of

these PUmodified clay nanocomposites remained the same

as that of neat PU. These results deduce that there were nomajor chemical structural changes in PU, owing to the pres-

ence of organoclay.

Table 3

Characterization of modified montmorillonite clay

Run no. Microanalysis Loading Swelling (%) IR (, cm1)

C% H% N% wt% mmol/100 ga Acetone H2O Bz DMF Dioxane Free OH CH aliphatic N+ Si 0

Ia 3.2 1.9 1.4 13.6 111.4 37 142 30 168 95 3434 2930, 2852 1520 1046, 523, 464

Ib 6.3 2.9 1.35 17 104.6 133 203 19 328 181 3358 2934, 2899 1489 1045, 523, 465

a Number of mmol of nitrogen per 100 g of clay, from calcination; (loss of weight/molecular weight)1000.


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Fig. 3. XRD pattern of the organoclayIaand PUorganoclay nanocomposites (a)IIad, (b)IIa and IIegand (c)IIh.

Table 4

X-ray diffraction and thermal analysis data for the intercalated samples

Sample X-ray dataa Calcination TGA datab

2 d-Spacing Polymer (%) Clay (%) Weight loss (%) in first stage Weight loss (%) in second stage Residue

Ia 6.2 14.26 11.7 88.3 16.5 83.5

Ib 6.35 13.94 15.6 84.4 20.3 79.7

IIa 5.9 14.98 96.96 3.04 55.1 41.5 3.4

IIb 6.0 14.73 97.2 2.8 59.5 33.8 6.7

IIc 6.0 14.73 89.54 10.46 58.4 32.5 10.1

IId 5.7 15.50 90.68 9.32 57.4 28.1 14.5

IIe Shoulder >49 50.8 40.9 8.3

IIf 4.5 19.64 96.4 3.6 54.4 42.8 2.8

IIg 4.5 19.64 98.1 1.9 62.2 34.4 3.4

IIh 4.0 22.09 51.5 41.7 1.8

a 2();d-spacing (A).b First stage 30350 C, second stage 350800C and residue at 800 C.


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Thermal analysis of polyurethane and intercalated mate-

rials were determined by both calcination and TGA data

listed inTable 4andFig. 2ac. The data and the figure shows

the weight loss encountered during heating the PUmodified

clay materials were ranging from 85% to 98% as determined

by both TGA and calcination. The associated weight loss evi-

dent in TGA curves is nearly compatible with the calcinationmeasurements. The TGA curves for all samples indicate that

there are two stages of decomposition. The first stage is the

major and sharp, which involve the thermal decomposition of

the intercalated polymers, specially the polymers present on

the surfaces of the layers of the clay. The decomposition tem-

perature in this stage was started at 200 C and take place

to350 C, which corresponds the weight loss ranging from

54%to 62%. In this stage,there is no clear difference between

the samples. Also, it was found that the composites degrade

slightly fasterthan thepure polymer. This maybe attributed to

the degradation of the small molecules between the interlay-

ers. The second stage is broad, in which the weight loss rang-

ing from 32% to 42% in the temperature range300700 C.

In this stage, the composites displayed higher thermal resis-

tance than pure polymers. This stage was attributed to furtherdecomposition of the rest intercalated polymers, specially

the polymers present in the interlayers of the clay or some

salts in the interlayer of the clay or interval the clay mineral

loses OH groups and the crystallographic structure collapsed

[9].

The crystal structure of MMT consists of two-dimensional

layers formed by fusing two silica tetrahedral sheets to an

edge-shared octahedral sheet of aluminum hydroxide. Stack-

Fig. 4. (a) Scanning electron micrograph of PUorganoclay nanocompositesIId, (b) Elemental mapping for Si of PUorganoclay nanocompositesIId.


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A. Rehab, N. Salahuddin / Materials Science and Engineering A 399 (2005) 368376 375

ing of layers of clay particles are held by weak dipolar or van

der Waals forces[34].XRD is powerful technique to observe

the extent of silicate dispersion, ordered or disordered struc-

ture in the polyurethane nanocomposites.Fig. 3aand c show

typical XRD for the organoclayIa,b. The 0 0 1 reflection has

sharp intense peak at 2 = 6.2, 6.35 for Ia and Ib, respec-

tively. Thed0 0 1spacing was calculated and listed inTable 4from peak positions using Braggs law d= /2 sin . It is clear

that thed-spacing for Na-MMT (9.6A) increased to (14.26,

13.94A) since the small inorganic Na+ cation is exchanged

by onium group in ethanolamineand diethanolaminethrough

an ion exchange process.Fig. 3ac presents three series of

XRD corresponding to polyurethane clay nanocomposites:

(a) with different ratios of organoclay, (b) with different

types of diols and (c) with different types of organoclay. In

polyurethane clay nanocomposites IIad, the position of the

peak corresponding to intercalated organoclay show some

change to smaller 2= 6.05.7 as inTable 4andFig. 3a. It

is note worthy that the sharp peak obtained in organoclayIadue to a more narrow distribution of the interlamellar spac-ing become broad and have small intensity. The intensity

decrease (i.e., broadness increase) with decreasing the per-

centage of organoclay. This suggests that the stacking of the

silicate layers become disordered. In one earlier work[35],

the sameresults obtained for polymethylmethacrylateMMT

composites. On the contrary, it is interesting to find that at

constant ratio of organoclay, the peak characteristic to 0 0 1

plane in IIf,g is shifted to higher d-spacing = 19.64A. This

confirmed that the polyurethane is intercalated between the

layers. However inIIe, XRD is featureless of ordered struc-

ture and there is no apparent peak of the clay that can be

detected as in Table 4andFig. 3b. It is clear that the typeof diol affect on the structure of the resulting nanocompos-

ites. This diol is used to swell the organoclay before addition

toluene diisocyanateFig. 3c. In IIh, the peak characteristic

to 0 0 1 is shifted to smaller 2= 4 and the intensity of the

peak is small. The broadness of the peak may suggest that

clay show some mixture of intercalated and exfoliated struc-

ture. However, the exfoliated structure of the silicate layers is

not judged from only this diffractograms. These results con-

firm that modified MMT with different chemical structure,

different percentage of clay lead to various degree of the

dispersion in the polymer matrix. These results similar to the

one described usinganother structures in PU nanocomposites

[36].

SEM examination of the fracture surface of the

compression-molded samples did not reveal the inorganic

domains at the maximum possible magnification. Fig. 4a

shows a micrograph of the fracture surface at 9000 magnifica-

tions. It is observed that there is no mineral domains could be

seen. The search for any aggregation was aided by an energy

dispersion X-ray probe. An image for element mapping for

Si was shown in Fig. 4b. The uniformity of the white dots

representative of Si, indicates that the mineral domain are

submicron and are homogenously dispersed in the polymer

matrix.

4. Conclusion

A series of polyurethane organoclay nanocomposites were

synthesized by in situ polymerization using different kinds of

diols and toluene diisocyanate in the presence of montmoril-

lonite clay modified with diethanolamine or triethanolamine.

The infrared spectroscopy confirms the interaction betweenthe polymer and silicate layers. X-ray analysis showed that

the d-spacing increased to about 22A or more with some dis-

order for low MMT content, whereas for higher content, the

intercalated clay rearranged to a minor extent. SEM results

confirm the dispersion of nanometer silicate layers in the

polyurethane matrix.

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