Studies on the Development of BiodegradablePoly(HEMA)/Cloisite Nanocomposites

Rahul Singhal, Monika DattaAnalytical Research Laboratory, Department of Chemistry, University of Delhi, Delhi 110007, India

The structural arrangement of molecules, ions, andother molecular species in the confined spaces of nano-scale pores and mineral interlayer are a key factor inunderstanding transport and reactivity in many techno-logical and biological systems. In this respect, consider-able research efforts have been focused on the designof nanoscale oral sustained- and controlled-releasedrug delivery systems. Biodegradable polymers havelong been of interest in controlled release technologybecause of the ability of these polymers to be reab-sorbed by the body. There are not very many polymerswhich intercalate Cloisite, forming a good nanocompo-site. The present study highlights some preliminaryinvestigations on the synthesis of Cloisite and biode-gradeable poly hydyroxyethyl methacrylate (PHEMA)nanocomposites. The nanocomposite were prepared byin situ intercalative polymerization of PHEMA within theCloisite galleries and were characterized by spectral aswell as morphological studies. POLYM. COMPOS., 30:887–890, 2009. ª 2009 Society of Plastics Engineers

INTRODUCTION

The development of biodegradable materials with con-

trolled properties has been a subject of great research

challenge to the community of materials scientists and

engineers [1]. Most biodegradable polymers have excel-

lent properties comparable to many petroleum-based plas-

tics and readily biodegradable, and may soon be compet-

ing with commodity plastics [2]. Biodegradable polymers

have great commercial potential for bio-plastic, but some

of the properties such as brittleness, low heat distortion

temperature, high gas permeability, low melt viscosity for

further processing etc. restrict their use in a wide-range of

applications. Therefore, modification of the biodegradable

polymers through innovative technology is a formidable

task for materials scientists [3].

Of particular interest are polymer and organically

modified layered silicate (OMLS) nanocomposites

because of their demonstrated significant enhancement,

relative to an unmodified polymer resin, of a large num-

ber of physical properties, including barrier, flammability

resistance, thermal and environmental stability, solvent

uptake, and rate of biodegradability of biodegradable

polymers [4]. Montmorillonite (MMT) and hectorite are

among the most commonly used smectite-type layered sil-

icates for the preparation of nanocomposites. In their pris-

tine form they are hydrophilic in nature, and this property

makes them very difficult to disperse into biodegradable

polymer matrices. The most common strategy to over-

come this difficulty is to replace the interlayer clay cati-

ons with quarternized ammonium or phosphonium cati-

ons, preferably with long alkyl chains intercalation of

polymer chains into the silicate galleries is done by using

one of the following two approaches: insertion of suitable

monomers in the silicate galleries and subsequent poly-

merization [5–7] or direct insertion of polymer chains

into the silicate galleries from either solution [8] or the

melt [9]. Of the wide diversity of materials available, we

chose to work with synthetic hydrogel scaffolds because

they have been used in several biomedical applications

due to their versatile nature [10–12]. Hydrogels are soft

and flexible, exhibiting physical characteristics similar to

those of soft tissue.

Poly(2-hydroxyethyl methacrylate) (pHEMA) is partic-

ularly attractive for biomedical engineering applications

because its physical properties can be easily manipulated

through formulation chemistry [13] and it has been used

extensively in medical applications, such as contact

lenses, keratoprostheses, and as orbital implants [14, 15].

Furthermore, a pHEMA scaffold could be easily incorpo-

rated into the nerve guidance tubes that we have already

developed as a part of our entubulation repair strategy

[16, 17]. We describe herein a new and facile method for

the creation of poly (HEMA)/Cloisite nanocomposites

using in situ intercalative polymerization. The nano-

composites were characterized by FTIR, XRD, and TEM

techniques.

MATERIALS REQUIRED

Cloisite clay was procured from Aldrich (Chemical

Co., USA) and was used as such. Ammonium persulphate

Correspondence to: Prof. Monika Datta; e-mail: monikadatta_chem@

yahoo.co.in

DOI 10.1002/pc.20627

Published online in Wiley InterScience (www.interscience.wiley.com).

VVC 2009 Society of Plastics Engineers

POLYMER COMPOSITES—-2009

(Sigma-Aldrich), hydrohyethylmethacrylate (HEMA)

(Sigma-Aldrich) were used as such without further

purification.

Synthesis of Cloisite/PHEMA Nanocomposites

A measured volume of HEMA (1 mL) was syringed

slowly into a well-stirred suspension containing Cloisite (1

g). Ammonium persulphate (0.2 g) was added and stirred

for 24 h at room temperature. After 24 h the total mass

was centrifuged and washed several times with distilled

water and methanol. The nanocomposite thus obtained was

dried under vacuum at 608C for 48 h, to obtain white pow-

der. Following the same procedure different ratios of Cloi-

site/PHEMA nanocomposites were prepared by varying the

amount of HEMAin the nanocomposite.

CHARACTERIZATION

FT-IR spectra of the powdered polymer(PHEMA) and

nanocomposites of Cloisite/PHEMA nanocomposites were

taken in the form of KBr pellets on FT-IR spectrometer

model IMPACT 410, NICOLET U.S.A. X-ray diffracto-

grams were also recorded in form of powder on X-ray

diffractometer model Philips PW3710 using copper Karadiations. Transmission electron micrographs were taken

on Morgagni 268-D TEM, FEI, USA. The samples were

prepared by depositing a drop of well-diluted nanocompo-

site suspension onto a carbon (100)-coated copper grid

and dried in an oven at 558C for 2 h.

RESULTS AND DISCUSSION

FTIR Analysis

Cloisite 30B having a surfactant (MT2EtOH) with the

chemical structure methylbis-2-hydroxyethytallow alkyl

quaternary ammonium chloride is shown in Scheme 1. In

the chemical structure of MT2EtOH, Nþ denotes quater-

nary ammonium chloride and T denotes tallow consisting

of about 65% C18, about 30% C16, and about 5% C14,

and in the chemical structure of 2M2HT, Nþ denotes

quaternary ammonium chloride and HT denotes hydrogen-

ated tallow consisting of about 65% C18, about 30% C16,

and about 5% C14. Note that 100% of Naþ ions in natu-

ral clay (montmorillonite, MMT) have been exchanged.

The FTIR spectra of pristine Cloisite 30B reveals a

band at 3,430 cm21 indicated in Fig. 1a is assigned to the

OH stretching of surface hydroxyl group. The hydroxyl

groups in the surfactant residing at the surface of Cloisite

30B have an absorption peak at a wave number of 3,400

cm21.The bands of CH2 asymmetric and symmetric

stretching appear at 2,926 cm21 and 2,853 cm21 respec-

tively. The peak at 1,637 cm21 can be correlated to the

HOH bending of lattice water vibrations [18, 19].The

peak at 1,470 cm21 corresponds to the deformation vibra-

tion of the tertiary amine group .The Si��O bending

vibrations appear at 1,048 cm21, respectively. The

Al��OH stretching peak appears at 918 cm21 while the

Al(Mg)O stretching vibration peak is noticed at 884

cm21, 798 cm21, 724 cm21.

As compared to pristine Cloisite 30B the spectra of

Cloisite/PHEMA:1:0.5, Fig. 1c, nanocomposite exhibits a

the presence of carbonyl of HEMA at 1719 cm21. A

broad band at 1,056 cm21 can be correlated to the intense

hydrogen bonding between Si��O of Cloisite and car-

bonyl group of PHEMA. The peaks show a shifting of

8 cm21. Interestingly none of the other peaks appear to

be shifted .The spectra of Cloisite/PHEMA: 1:1, Fig. 1d,

shows similar broadening of the Si��O peak at 1,051

cm21 while the spectra of Cloisite/HEMA 1:2, Fig. 1e,

reveals a major shift of 11 cm21 .The increasing in the

broadening as well as shifting of the Si��O peaks in Cloi-

site confirms the intercalation of PHEMA in Cloisite 30B

via intense specific interaction of Cloisite 30B with car-

bonyl of PHEMA through hydrogen bonding. The interac-

tion appears to increase with the increase in the concen-

tration of PHEMA in Cloisite 30B thus confirming theSCHEME 1. Structure of Cloisite.

FIG. 1. FT-IR spectra of (a) Cloisite and (b) Cloisite 30B (c) Cloisite/

PHEMA:1:0.5 (d) Cloisite/PHEMA 1:1 (e) Cloisite/PHEMA 1:2.

TABLE 1. Recipe for the synthesis of Cloisite/PHEMA composites.

Sample code Clay (g) Monomer (g)

Cloisite/PHEMA (1:0.5) 1 0.5

Cloisite/PHEMA (1:1) 1 1

Cloisite/PHEMA (1:2) 1 2

888 POLYMER COMPOSITES—-2009 DOI 10.1002/pc

polymerization of HEMA within the organically modified

galleries of Cloisite, Scheme 2 .

The presence of the characteristic peaks of PHEMA in

the spectra of the nanocomposites confirms the polymer-

ization of the former within Cloisite layers [18]. It is

observed that the structure of the peaks around 1,637

cm21 and 1,041 cm21 appears to be different in these

nanocomposites, which indicates the difference on the

conformation of PHEMA chains in them. On the basis of

the shifting of characteristics Cloisite peaks, it can be

inferred that intercalation of PHEMA has taken place

within clay layers [19, 20].

XRD Analysis

The intercalation has been characterized by XRD,

which is the most frequently used methods to study the

structure of nanocomposites. Because of the hydrophilic

nature of poly(HEMA), this biopolymer has good misci-

bility with Cloisite and can easily intercalate into the

interlayers by means of hydrogen bonding [18]. Figure 2

illustrates the XRD patterns of Cloisite and Cloisite/

PHEMA nanocomposites. The XRD pattern of the Cloi-

site, Fig. 2a, shows a reflection peak at about 4.7708(001) corresponding to a basal spacing of 1.85 nm. The

XRD pattern of Cloisite/PHEMA: 1:0.5, Fig. 2b, shows a

shift of 1 nm in the reflection peak (001) observed at

4.7758.A small shift is observed in this case owing to the

presence of lower concentration of PHEMA in Cloisite.

As the loading of PHEMA is increased to equimolar ratio

of Cloisite, Cloisite/PHEMA 1:1, Fig. 2c, the reflection

peak shows the characteristic shift of 10 nm. The move-

ment of the basal reflection of Cloisite to lower angle

indicates the formation of an intercalated nanostructure,

whereas the no peak broadening and intensity decrease is

observed indicating the formation of an ordered interca-

lated nanocomposite structure. Incase of Cloisite/PHEMA

1:2, Fig. 2d higher intercalation of the PHEMA takes

place due to higher loading .The peak broadening as well

as the decrease in the intensity of the peak is noted. The

broadening of the peak is due to partial disruption of par-

allel stacking or layer registry of the pristine organoclay,

which reveals the existence of some exfoliated clay plate-

lets. Thus we observe that at optimum amount of polymer

loading, we obtain a well-ordered nanocomposite struc-

ture. Since one HEMA unit possesses two hydroxyl func-

tional groups, these functional groups can form hydrogen

bonds (see Scheme 2) with the silicate hydroxylated edge

groups, which lead to the strong interaction between

matrix and silicate layers. This strong interaction is believed

to be the main driving force for the assembly of Cloisite/

PHEMA ordered structure. Excessive hydrogen bonding

disrupts the well-ordered morphology of the nanocompo-

site leading to exfoliation upon higher loading of HEMA

in Cloisite.

TEM Analysis

The TEM micrograph of Cloisite shows the presence

of nearly spherical globular particles Fig. 3a that appear

to be randomly dispersed. The morphology reveals a non-

distribution of Cloisite particles. The average diameter of

the clay particles was found to be in the range of 50 nm

as reported in our earlier studies [18]. The TEM image of

Cloisite/PHEMA: 1:0.5 nanocomposite Fig. 3b shows

extremely uniform distribution of nanometer-range inter-

calated clay particles of 70–80 nm have an as well as par-

ticle size. The TEM micrograph of Cloisite/PHEMA: 1:1

Fig. 3c reveals a nearly granular morphology and the par-

ticle sizes are found to be in the range 50–80 nm. No

aggregation or clustering is observed in any case. TEM

observations reveal the homogeneous dispersion of spheri-

cal clay platelets in nanometer range throughout the nano-

composite without aggregation, distortion or tactoid for-

mation. The concentration of the clay nanoplatelets

seemed to be low and the excellent homogeneous disper-

sion of clay nanoplatelets was achieved due to the clay

modification with PHEMA.SCHEME 2. Structure of Cloisite/PHEMA.

FIG. 2. XRD of (a) Cloisite (b) Cloisite/PHEMA 1:0.5 (c) Cloisite/

PHEMA 1:1 (d) Cloisite/PHEMA 1:2.

DOI 10.1002/pc POLYMER COMPOSITES—-2009 889

Hence it can be concluded that the internal structure of

the nanocomposites is strongly influenced by the clay

structure and the intercalated polymer. In our case uni-

form morphology as well as uniform particles size distri-

bution is obtained incase of all the Cloisite/PHEMA nano-

composites exhibiting a well-intercalated polymer/clay

structure. According to the XRD and TEM studies an

increase in the gallery spacing of Cloisite favors intercala-

tion of PHEMA by interaction between hydroxyl func-

tional groups present in the PHEMA backbone as shown

in scheme 0.2.

CONCLUSION

Intercalated nanocomposites of Cloisite/PHEMA were

successfully synthesized. The nanocomposites were found

to exhibit intercalation and hydrogen bonding between

Si��O of Cloisite and CþO of HEMA. Well ordered uni-

form particle size morphologies of the nanocomposites

was analyzed using transmission electron microscopy.

The control drug release studies by these nanocomposites

are in progress in our laboratory and will be published

soon.

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FIG. 3. (a) TEM micrographs of (a) Cloisite, (b) Cloisite/PHEMA ¼1:0.5, (c) Cloisite/PHEMA ¼ 1:1. [Color figure can be viewed in the

online issue, which is available at www.interscience.wiley.com.]

890 POLYMER COMPOSITES—-2009 DOI 10.1002/pc