effect of clay reinforcement on properties of epoxy clay nanocomposites

ISSN 2320-2424 International Journal of Mechanical Science and Civil Engineering IJMSCE Special issue on “Emerging Trends in Engineering & Management” ICETE 2013

PTU Sponsored ICETE-2013 Paper Id: ICETE-17

www.ijmsce.org 6

Effect of Clay Reinforcement on the Properties of Epoxy

based Polymer Matrix Nanocomposites Karanbir Singh

1, Tarun Nanda

2, Rajeev Mehta

3

1, 2 Department of Mechanical Engineering, Thapar University, Patiala, Punjab, India

3 Department of Chemical Engineering, Thapar University, Patiala, Punjab, India

[email protected],

[email protected],

[email protected]

Abstract—Organic/inorganic nano-scaled composites

comprise one of the most important class of synthetic

engineering materials. Their makeup is such that they can

be transformed into new materials possessing advantages

of both organic materials, such as light-weight, flexibility,

and good mould ability, and inorganic materials, such as

high strength, heat stability, and chemical resistance. This

paper is concerned with the properties of epoxy/layered

silicate nanocomposites. The nano-particles used in

nanocomposites, due to their extremely high aspect ratios

(about 100-15000), and high surface area (in excess of

750-800 m/g) promise to improve structural, mechanical,

flame retardant, thermal and barrier properties without

substantially increasing the density or reducing the light

transmission properties of the base polymer. The main

objective of the paper is to review the existing literature to

study the effect of clay addition, different curing

agents/hardeners and different degassing time periods on

the structure and the mechanical properties of

nanocomposites.

Keywords— Epoxy, Clay, Nanocomposites, Curing,

Hardener

I. INTRODUCTION

A. General

Recent advances in producing nano-structured materials with

novel properties have stimulated research to create

multifunctional engineering materials by designing structures

at nanometer scale. Motivated by the recent enthusiasm in

nanotechnology, development of nanocomposites is one of

the rapidly evolving areas of composite research.

Nanotechnology can be broadly defined as, “the creation,

processing, characterization, and utilization of materials,

devices, and systems with dimensions on the order of 0.1-

100nm, exhibiting novel and significantly enhanced physical,

chemical and biological properties; functions, phenomena,

and processes due to their nanoscale size. Current interests in

nanotechnology encompass nano-biotechnology,

nanosystems, nano-electronics, and nano-structured materials

of which nanocomposites are a significant part. Through

nanotechnology, it is envisioned that nano-structured

materials will be developed using bottom-up approach. More

materials and products will be made from the bottom-up, that

is, by building them from atoms, molecules and nanoscale

powders, fibres and other small structural components made

from them. This differs from all previous manufacturing, in

which raw materials get pressed, cut, moulded, and otherwise

coerced into parts and products [1].

B. Nanocomposites New technologies require materials showing novel properties

and/or improved performance compared to conventionally

processed components. In this context, nanocomposites are

suitable materials to meet emerging demands arising from

scientific and technological advances. Nanocomposites are

reported to be materials of the 21st century in view of

possessing design uniqueness and property combinations that

are not found in conventional composites. The general

understanding of these properties is yet to be reached, even

though the first inference on them was reported as early as

1992 [2]. The term ‘nanocomposites’ was used to emphasise

the fact that the polymeric product consisted of two or more

phases each in the nanometer size range. The term is now

universally accepted as describing a very large family of

materials involving structures in the nanometer size range (1-

100nm), where the properties are of interest due to the size of

the structures, and are typically different from those of the

bulk matrix [3]. Nanocomposites are composites in which at

least one of the phases shows dimensions in the nanometer

range (1nm = 109m) [2]. In recent years, usage of nanoscale

fillers in polymers and fibre reinforced composites has

attracted considerable interest. Such nanoscale fillers

frequently exhibit larger surface area per unit volume and

thus enhance the performance of the fabricated composite [4].

Nanocomposites are generally classified on the basis of type

of matrix used in the material. Accordingly they are

categorized into three main classes as shown below:

i) Ceramic Matrix Nanocomposites

ii) Metal Matrix Nanocomposites

iii) Polymer Matrix Nanocomposites

1) Improved Properties of Nanocomposites over Bulk

Materials:

Nanocomposites offer better properties over their bulk

counterparts. It has been observed that changes in particle

properties can be observed when particle size is less than a

particular level, called the ‘critical size’. Feature size < 5 nm

bring changes in catalytic activity, < 20 nm makes hard

magnetic material soft, < 100 nm produces super magnetism,

strengthening, toughening and modify hardness and plasticity

of steel [2]. Additionally, as dimensions reach the nanometer

level, interactions at phase interfaces become largely

improved, and this is important to enhance material

properties. In this context, the surface area/volume ratio of

reinforcement materials employed in the preparation of

nanocomposites is crucial to understand their structure-

property relationships [2]. One of the major factors which

alter the properties in nanocomposites is the increase in ratio

of surface area to volume. The surface area of particle

http://ijcsce.org/

mailto:[email protected]



www.ijmsce.org 7

increases exponentially, creating more sites for bonding,

catalysis or reaction with surrounding material, resulting in

improved properties such as increased strength or chemical or

heat resistance. Hence due to the high surface to volume ratio

associated with nanometer sized particles, it is possible to

control the fundamental properties of materials through

surface/size effect. Nanocomposites typically contain 2-10%

loadings on weight basis, yet property improvements can

equal and exceed traditional composites containing 20-35%

mineral or glass [5].

C. Polymer Matrix Nanocomposites

Polymer materials are widely used in industry due to their

ease of production, light weight and often ductile nature.

However, they have some disadvantages, such as low

modulus and strength as compared to metals and ceramics. In

this context, a very effective approach to improve their

mechanical properties is to add fibres, whiskers, platelets or

particles as reinforcement to the polymer matrix. For example,

polymers are filled with several inorganic compounds, either

synthetic or natural, in order to increase their heat and impact

resistance, flame retardancy, mechanical strength, and to

decrease electrical conductivity and gas permeability with

respect to oxygen and water vapour. Using this approach,

polymer properties can be improved while retaining their

light weight and ductile nature. Another aspect is that

nanoscale reinforcements have exceptional potential to

generate new phenomena which leads to special properties in

these materials. Polymer Matrix Nanocomposites are

polymers (thermoplastics, thermosets or elastomers) that have

been reinforced with small quantities of nano-sized fillers [2].

1) Types of Polymer Matrix Nanocomposites:

Polymer Matrix Nanocomposites (PMNC) can be

classified on the basis of dimensions of the dispersed

particles. Based on the size of dispersed particles, PMNC

are of three main types.

i) Zero Dimensional Nanocomposites

ii) One Dimensional Nanocomposites

iii) Polymer Layered Nanocomposites

The main characteristics of these types are discussed as

follows:

i) Zero Dimensional Nanocomposites are formed when the

three dimensions are in the order of nano-meters.

Spherical silica, carbon black, metal particles

(aluminium oxide, titanium dioxide, and zinc oxide),

semiconductor nanoclusters (silicon carbide) are

examples of iso-dimensional nanoparticle fillers. The

structure of polymer nanocomposites refined with iso-

dimensional particles is similar to that of ceramic and

metal nanocomposites.

ii) One Dimensional Nanocomposites are formed when two

dimensions of the dispersed phase are in the nanometer

scale and the third is larger, forming an elongated

structure. Examples are carbon nanotubes, carbon

nanofibres, cellulose whiskers.

iii) Polymer Layered Nanocomposites are characterized by

only one dimension in the nanometer range. In this case,

the filler is present in the form of sheets of one to few

nano-meters thick to hundred to thousand nano-meters

long. Examples include clays, layered silicates

(montmorillonite, hectorite, saponite, fluoromica,

fluorohectorite, vermiculite and kaolinite) and layered

double hydroxides [2].

2) Benefits of PMNCs over Conventional Composites:

The reinforcing efficiency of polymer nanocomposites, even

at low volume fractions, is comparable to 40-50% for fibres

in micro-composites [2]. Higher filler loading in micro-

composites however causes an undesirable increase of

density, decreased melt flow, and increased brittleness.

Layered silicate nano-fillers have proved to trigger

tremendous property improvements of polymers in which

they are dispersed. Improvements can include, for example,

increased moduli, strength and heat resistance, decreased gas

permeability and flammability [6].

3) Limitations of Polymer Matrix Nanocomposites:

The downside of polymeric composites is their inherent

sensitivity to environmental factors such as temperature,

exposure to liquids & gases, electrical fields and radiation.

Static and dynamic mechanical loads can interact with

environmental parameters and accelerate the degradation

process. It is well known that polymers and polymeric

composites absorb fluids when exposed to ambient liquid

environments, and fluid absorption is accompanied by

expansion strains which may degrade material properties.

The mismatch in moisture induced volumetric expansion

between the matrix and the fibres leads to evolution of

localized stress and strain fields in composites which may

degrade the fibre-matrix interface as a result of either a

reduction of chemical bonding between the fibre and matrix

or a reduction in residual thermal shrinkage stresses at the

fibre-matrix interface due to moisture absorbed-induced

swelling [7].

D. Polymer Layered Silicate Nanocomposites

Amongst all the potential nano-fillers, layered silicates have

been more widely investigated because the starting clay

materials are easily available at low price and also because

their intercalation chemistry has been studied for a long time.

Layered silicate nano-fillers have proved to trigger

tremendous property improvements of polymers in which

they are dispersed [6]. Polymer layered silicate (PLS)

nanocomposites have attracted great interest due to their

improved properties compared with the pure polymer and

conventional micro and macro composites. Some of these

improvements include high moduli, increased strength and

heat resistance, decreased flammability and gas permeability

and increased biodegradability [8], [2]. Two particular

characteristics of layered silicates are generally considered

for PLS nanocomposites. The first is ability of silicate

particles to disperse into individual layers (totally

http://ijcsce.org/



www.ijmsce.org 8

delaminated or exfoliated). The second is the ability to fine-

tune their surface chemistry through ion-exchange reactions

with organic and inorganic cations. These two are, of course,

interrelated, since the degree of dispersion of a layered

silicate in a particular polymer matrix depends on interlayer

ionic species [2]. Montmorillonite, hectorite and saponite

are the most commonly used layered silicates. When the

hydrated cations are ion-exchanged with bulkier organic

cations, a larger interlayer spacing is usually obtained. The

main reason for the remarkable improvements observed in

polymer/layered silicate nanocomposites is the stronger

interfacial interaction between the matrix and the silicate,

compared to conventional filler reinforced systems [6], [2].

1) Structure of Polymer-Clay Nanocompoites:

In layered silicate PMNCs, different types of structures can

be observed in the nanocomposite depending on the

interaction of polymer matrix and nanofiller silicate.

Phase separated (Conventional)

When the polymer is unable to intercalate between the

silicate sheets, a phase separated composite is obtained whose

properties stay in same range as traditional micro-composites.

In other words phase separated structure occurs when the

miscibility between the polymer matrix and the filler does not

support favourable interactions to overcome the

thermodynamic considerations leading to silicate layer to

collapse. In these structures the system is totally immiscible.

Intercalated

When a single (and sometimes more than one) extended

polymer chain is intercalated between the silicate layers

resulting in a well ordered multilayer morphology built up

with alternating polymeric and inorganic layers. The single

polymer chains are intercalated between unaltered silicate

layers with their regular alteration of galleries. The space

occupied by the polymer is typically in order of a few nano-

meters. The system displays limited miscibility. Intercalated

structures are formed when one or more polymer chains

intercalate between the layers. Hereby, the interlayer

spacing is increased but the ordered layer structure of the

clay particles is retained.

Exfoliated (Delaminated)

When the silicate layers are completely and uniformly

dispersed in a continuous polymer matrix, an exfoliated or

delaminated structure is obtained. The silicate layers are

totally delaminated and dispersed in the polymer matrix. Its

ordered structure is lost and distance between the layers is

increased substantially. System is totally miscible. In

exfoliated composites, the clay particles are completely

delaminated and the silicate layers do not show any

periodicity in their arrangement [6], [2], [5], [9].

E. Epoxy Resin Nanocomposites

Epoxy resin is one of the most important thermosets that have

been widely used as a matrix for polymer composites and

structural materials. Epoxy resin based PMNCs show high

modulus and strength, excellent chemical resistance and are

simple in processing. Due to low density (of around 1.3

g/cm3) and good adhesive and mechanical properties, epoxy

resin has become a promising material for many high

performance applications usually in the form of composite

materials such as fibre composite or in honeycomb structures

[10], [3]. Epoxies are defined as cross-linked polymers in

which the cross-linking is derived from reactions of the

epoxy group. Epoxy resins can be cross-linked through a

polymerization reaction with a hardener at room

temperature or at elevated temperature (latent reaction).

Curing agents are used for room temperature cure and these

are usually aliphatic amines, whilst commonly used higher

temperature, higher performance hardener are aromatic

amines and acid anhydrides. An increasing number of

specialized curing agents, such as poly-functional amines,

polybasic carboxylic acids and inorganic hardener are also

used. All of these result in different, tailored properties of the

final polymer matrix. In general, the higher temperature cured

resin systems have improved properties, such as higher glass

transition temperatures, strength and stiffness, compared to

those cured at room temperature [9].

II. LITERARTURE REVIEW

Improvement in mechanical properties of epoxy/polymer

matrix based nanocomposites results from changes in nano-

filler content in the PMNCs. The tensile modulus,

compressive modulus, tensile and compressive strengths

show significant changes with different clay loadings

(1 wt. % - 10 wt. %) can provide an optimum combination of

properties. At higher clay concentrations, the improvement in

properties starts decreasing due to agglomeration/ formation

of clay aggregates. Increase in degassing time led to

improvement of properties due to removal of voids. Storage

modulus increases with increase in clay content because of

enhancement effect from addition of clay particles. The Tg of

the nanocomposite decrease with increasing clay

concentration up to 4 wt % due to the plasticization effect

from the small molecular organic modifier (surfactant) within

the interlayers of the organically modified clay used in this

study [11], [12], [13], [14], [15], [16], [17], [18]. Clays are

organophobic in nature, modification of clay to make it

organophillic also lead to improvement in properties of the

composites [19]. Mechanical mixing produces better

exfoliation as compared to, shear mixing and showed better

impact strength and tensile modulus as clay hindered the

movement of epoxy in its vicinity [15]. Premixing methods

with high shear and temperature show positive effect on

dispersion exfoliation of the nanocomposites [20]. Elastic

forces are the primary forces behind clay layer exfoliation in

epoxy-nanoclay systems. The elastic force exerted by the

cross-linking epoxy molecules inside the clay galleries

pushed out the outermost clay layers from the tactoids against

the opposing forces arising from electrostatic and van der

Waals attraction. Exfoliation continues till the extra-gallery

epoxy turns into a gel (got highly viscous); on the other hand,

the formation of gel advances by higher curing temperatures

http://ijcsce.org/



www.ijmsce.org 9

and presence of clay particles. It was found in this study that

complete exfoliation of clay structures can be produced till

elastic forces inside the galleries were prevailed by viscous

forces offered by the extra-gallery epoxy as reported by [21].

Different curing agents used also affect on the properties of

the composites. Nanocomposite prepared with clay treated

with aliphatic diamine (Jeffamine D-230) shows better

exfoliation and hence better properties that the

nanocomposites with clay treated with two cycloaliphatic

polyamine amines (3 DCM and PACM) due to lower

reactivity of D-230 as lower is reactivity, higher is the degree

of exfoliation achieved as reported by [22]. Curing agent

Elastomeric System: Polypox H205 cause an increase in both

tensile modulus (14.2% for 5 wt. % clay loading and 28.6%

for 10 wt. %) and ultimate stress (12.2% increase for 5 wt. %

and 4.4% for 10 wt. %) and both compressive modulus and

ultimate compressive stress with increase in clay loading. For

10 wt. % clay loading, percent increase achieved in these

properties (compared to neat epoxy) was 25.9% and 5.3%

respectively. Glassy System curing agent (Ethacure 100)

showed only a modest improvement in tensile modulus and a

decrease in ultimate tensile stress with increased clay

loadings. Increase in both compressive modulus and stress,

the extent of improvement is comparatively less (4.5% and

3.5% respectively) [23]. [24] study the interface boundary

characteristics of epoxy/clay nanocomposite (with surfactant

NH C18H37, Epoxy DGEBA, hardener DETDA and clay

MMT) via fracture mechanics (crack opening mode) and

quantified the key parameters such as peak strength (for

damage initiation criterion), fracture energy and final failure

separation distance (for post damage evolution) from the

traction-separation curves. The traction stress (τ) initially

increases rapidly to a maximum value of 99.87 MPa and 131

MPa for gallery interface and matrix interface respectively

due to the adjustment of equilibration positions of atoms by

the van der Waal’s and electrostatic interactions. Beyond the

peak stress, the traction stress decrease gradually to zero (at d

= 2.3 nm for gallery interface and at d = 2.25 nm for matrix

interface) due to the debonding between surfactant and epoxy

molecules. During the debonding process, the ammonium

head groups of surfactants remained adhere to the silicate

surface due to the opposite charges and the alkyl chains were

stretched by the epoxy molecules as the interaction (between

alkyl chain and epoxy) was mainly governed by van der Waal

forces. III. CONCLUSIONS

Nanoclay is an easily available and a cheap filler, which is

added to epoxy resin in PMNCs to improve their properties

viz. storage modulus, impact strength, heat resistance,

flammability, gas permeability and biodegradability etc.

Degassing, as the name suggests, is done to remove trapped

gases, voids etc. from the nanocomposites. Proper degassing

is necessary for improvement in properties as it remove any

trapped gasses. Dispersion of clay takes place during

premixing (before curing). Higher temperature and shear

premixing conditions help in improvement of properties

Curing refers to the chemical reactions that solidify the resin.

Curing is accomplished by heat, pressure and by addition of

curing agents. Authors have synthesized nanocomposites

with different curing agents with different curing time periods

and temperature. The reasons for improvement in a few

properties (elastic modulus, permeability etc) have been well

explained but there has been lack of studies focusing on

calculating optimum degassing periods for specific clay

loadings. Optimum curing time and temperature and the best

combination of curing agent/epoxy also need to be studied.

REFERENCES

[1] Thostenson, E.T., Li, C. and Chou, T.W., 2005,

Nanocomposites in context, Composites Science and

Technology, 65, 491–516

[2] Camargo, P.H.C., Satyanarayana, K.G. and Wypych, F.,

2009, Nanocomposites: Synthesis, Structure, Properties

and New Application Opportunities, Materials Research,

12, 1-39

[3] Kotsilkova, R., Pissis, P., Silvestre, C., Cimmino, S. and

Duraccio, D., 2007, Thermoset Nanocomposites for

Engineering Applications, Smithers Rapra Technology

Limited,1-11

[4] Hamidi, Y.K., Aktas, L. and Altan, M.C., 2008, Effect of

Nanoclay Content on Void Morphology in Resin

Transfer Molded Composites, Journal of Thermoplastic

Composite Materials, 21, 141-163

[5] Karabulut, M., 2003, Production and Characterization of

Nanocomposite Materials from Recycled

Thermoplastics, Master of Science Dissertation, The

Middle East Technical University, Turkey,2-15

[6] Alexandre, M. and Dubois, P., 2000, Polymer-layered

silicate nanocomposites: preparation, properties and uses

of a new class of materials, Materials Science and

Engineering, 28, 1-63

[7] Ramirez, F.A., Carlsson, L.A. and Acha, B.A., 2008,

Evaluation of water degradation of vinylester and epoxy

matrix composites by single fiber and composite tests,

Journal of Materials Science, 43, 5230–5242

[8] Lee, J. H., Advani, S. G., Lin, L. Y., and Yoo, G. H.,

2004, The Preparation of Clay/Glass Fiber/Epoxy

Hybrid Nanocomposites using VARTM , 7th

International Conference on Flow Process in Composite

Materials, Newark, Delaware, USA, 551-556

[9] Mahajan, S., 2011, Epoxy layered silicate

nanocomposites as matrix in fibre reinforced composites,

ME Dissertation, Thapar University, Patiala,6-10

[10] Chow, W.S., 2007, Water absorption of epoxy/glass

fiber/organo-montmorillonite nanocomposites eXPRESS

Polymer Letters, 1, 104–108

[11] Lu, H., Roy, S., Sampathkumar, P. and Ma, J., 2002,

Characterization of the Fracture Behavior of Epoxy

Nanocomposites, 17th Annual Technical Conference of

the American Society for Composites, Purdue

University, West Lafayette, Indiana

http://ijcsce.org/



www.ijmsce.org

10

[12] Isik, I., Yilmazer, U. and Bayram, G., 2003, Impact

modified epoxy/montmorillonite nanocomposites:

synthesis and characterization, Polymer, 44, 6371–

6377

[13] Yasmin, A., Abot, J.L. and Daniel, I.M., 2003,

Processing of clay/epoxy nanocomposites by shear

mixing, Scripta Materialia, 49, 81–86 [14] Avila, A., Duarte, H.V. and Soares, M.I., 2006, The

nanoclay influence on impact response of laminated

plates, Latin American Journal of Solids and Structures,

3, 3-20

[15] Gupta, N., Lin, T.C. and Shapiro, M., 2007, Clay/Epoxy

Nanocomposites: Processing and Mechanical Properties,

The Journal of the Minerals, Metals & Materials Society,

59, 61-65

[16] Chakradhar, K.V.P., Subbaiah, K.V., Kumar, M.A. and

Reddy, G.R., 2011, Epoxy/polyester blend

nanocomposites: Effect of nanoclay on mechanical,

thermal and morphological properties, Malaysian

Polymer Journal, 6, 109-118

[17] Liu, T., Tjiu, W.C., Tong, y., He, C., Goh, S.S. and

Chung. T.S., 2004, Morphology and Fracture Behavior

of Intercalated Epoxy/Clay Nanocomposites, Journal of

Applied Polymer Science, 94, 1236–1244

[18] Somwangthanaroj, A., Tantiviwattanawongsa, M. and

Tanthapanichakoon, W., 2012, Mechanical and Gas

Barrier Properties of Nylon 6/Clay Nanocomposite

Blown Films, Engineering Journal, 16, 93-105.

[19] Satapathy, S., Mohanty, G.C. and Nayak, P.L., 2012,

Synthesis and characterization of layered silicate/epoxy

nanocomposite, Advances in Applied Science Research,

3, 3981-3986

[20] Ngo, T.D., That, M.T.T., Hoa, S.V. and Cole, K.C.,

2009, Preparation and Properties of Epoxy

Nanocomposites. I. The Effect of Premixing on

Dispersion of Organoclay, Polymer Engineering and

Science, 49, 666-672

[21] Park, J.H. and Jana, S.C., 2003, Mechanism of

exfoliation of nanoclay particles in epoxy-clay

nanocomposites, Macromolecules, 36, 2758-2768

[22] Kornmann, X., Lindberg, H. and Berglund, L.A., 2001,

Synthesis of epoxy-clay nanocomposites: influence of

the nature of the curing agent on structure, Polymer, 42,

4493-4499

[23] Hackman, I. and Hollaway, L., 2005, Durability and

mechanical properties of polymer-layered silicate

nanocomposites, International Symposium on Bond

Behaviour of FRP in Structures, Hongkong, China, 525-

530

[24] Chen, Y., Chia, J.Y.H., Su, Z.C., Tay, T.E. and Tan,

V.B.C., 2013, Mechanical characterization of interfaces

in epoxy-clay nanocomposites by molecular simulations,

Polymer, 54, 766-773

http://ijcsce.org/

effect of clay reinforcement on properties of epoxy clay nanocomposites

Documents