3. materals and fabrication

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CHAPTER 3

MATERIALS AND FABRICATION OF LAMINATES

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3.1 MATERIALS AND METHODS

This chapter describes the details of processing of the composites and

the experimental procedures followed for their characterization. The raw

materials used in this work are

1. E-glass fiber

2. Epoxy (60%)-polyester (40%) Hybrid resin3. MWCNT

3.1.1 Glass fiber:

E glass (electrical) and S glass (high strength), out of which these two

types, due to their superior mechanical properties, are most widely used in

structures, composite roofing’s, pressure vessels, containers, tanks, pipes,

etc. Table 3a and 3b gives the fiber properties.

Fiber

Material

Density

kg/m3

Tensile strength

MPa

Tensile

modulus

GPa

Diameter

mm

Glass 2550 3450-5000 69-84 7-14

Boron 2200-2700 2750-3600 400 50-200

Carbon 1500-2000 2000-5600 180-500 6-8

Kevlar 1390 2750-3000 80-130 10-12

Table3a: Fiber properties

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Fiber Melting

point 0C

Heat

Capacity

kJ/(kg.K)

Thermal

conductivity

W/(mK)

Coefficient of thermal

expansion 10-6m/mK

Glass 840 0.71 13 5

Boron 2000 1.30 38 5

Carbon 3650 0.92 1003 -1.0

Kevlar 49 250 1.05 2.94 -4.0

Table3b: Fiber properties

3.1.2 Reinforcements:

The most commonly used thermosets are epoxy, polyester and

phenolic resins, among which polyester resins are most widely used in

various common engineering goods and composite applications. However,

epoxy resins constitute the major group of thermoset resins used in

composite structures and adhesives, as they are stronger and stiffer. Phenolic

resins are rich in carbon and possess good thermal properties and are

normally used in high temperature applications especially as an ablative

material in thermal protection systems. Silicone, bismaleimide, polyimide,

polybenzimidazol, etc. are in fact, high temperature polymers that can

perform at higher temperature ranging from 200-4500C. The structures of

some thermosetting resins are illustrated in Fig. 2.8.

Epoxy resins in general possess good thermomechanical, electrical

and chemical resistant properties. They are so called, because they contain

two or more epoxide groups in the polymer before cross-linking.

A polyester resin is comprised of an unsaturated backbone polymer

dissolved in a reactive monomer. The polyester backbone polymer is formed

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by condensation of a mixture of diabasic acids (saturated and unsaturated)

and one or more glycols. The process of curing is initiated by adding a

source of free radicals (e.g., benzoyl peroxide or hydroperoxide and catalysts

Curing takes place in two stages: a soft gel is first formed and this is

followed by a rapid polymerization with generation of heat. A higher

proportion of unsaturated acid in the backbone polymer yields a more

reactive resin, while with a higher quantity of saturated acid the reaction

becomes less exothermic. During curing, the styrene monomer reacts with

the unsaturated sites of the backbone polymer to form a three-dimensional

cross-linked network. A small amount of wax is often added to the solution

before curing to facilitate proper curing of the surface of a laminate. Wax,

during curing, exudes to the surface to form a thin protective layer that

reduces loss of styrene from the surface and prevents oxygen which inhibits

reaction to come in contact with the radicals. Several types of polyester

resins are commercially available. Vinyl-ester resins are high performance

polyester resins, which are acrylic esters of epoxy resins dissolved in styrene

monomer. Polyester resins can be reinforced with almost all types of

reinforcements to make polyester composites. Polyester resins are cheaper

and more versatile, but inferior to epoxy resins in some respects. Their use in

advanced structural composites is therefore limited. However, they have

been widely used in boat hulls, civil engineering structures, automobile

industries and various engineering products and appliances. The properties

of Resin are given in table 3c.

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Properties Epoxies Polyesters

Density, kg/m3 1100-1400 1200

Tensile strength, MPa 35-100 50-60

Tensile modulus, GPa 1.5-3.5 2-3

Poisson ratio 0.35 0.35

Coefficient of thermal expansion,

10-6m/mK 50-70 40-60

Service temperature, K 300-370 330-350

Table 3c properties of Resin

3.1.3 Carbon Nano Tubes (Fillers):

Carbon nanotubes are molecular-scale tubes of graphitic carbon with

outstanding properties. They are among the stiffest and strongest fibres

known, with Young’s moduli as high as 1 TPa and tensile strengths of up to

63 GPa. They also have remarkable electronic properties and can be metallicor semiconducting depending on their structure and diameter. There is

currently great interest in exploiting these properties by incorporating carbon

nanotubes into some form of matrix. A wide range of polymer matrices have

been employed, and there is growing interest in nanotube/ceramic and

nanotube/metal composites.

The filler material CNT is provided by NANOSHEL India sieved to

obtain particle size in the range 10-30 μm

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Nanoshel page

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3.2. Processing of the Composites

3.2.1. Specimen preparation

E-glass fibers of 610 roving are reinforced with Epoxy LY 556 resin,

chemically belonging to the ‘epoxide’ family is used as the matrix material.

Its common name is Bisphenol A Diglycidyl Ether. The low temperature

curing epoxy resin (Araldite LY 556) and corresponding hardener (HY951)

are mixed in a ratio of 100:10 by weight as recommended; Also the Iso-

polyester and their corresponding catalyst and accelerator are mixed in the

ratio of 100:1.5:1.5 % by weight. Both the resins are taken in a bowl and

mixed in mechanical stirrer, and their corresponding curing agents are

added. The glass fiber of size 300 x 300 mm is placed within a 4mm thick

spacer plate and applied with the resin and fabricated in compression

molding at a pressure of 30 bar for 4 hours at 90°C. A spacer plate is placed

for the purpose of maintaining a constant thickness of 4mm. For mixing up

of MWCNT the resin is mixed in stirrer and then preheated to 60 degree and

then the carbon nanotubes are added. The resin is then sonicated for 4 hours

at 55 degrees.

Sonication is used in nanotechnology for evenly dispersing of

nanoparticles in resins. Sonication can be used to speed dissolution, by

breaking inter molecular interactions.

SEM testing has been done to check the proper dispersion of carbon

nano tubes with the resin. Scanning electron (SEM) was used to investigate

the surfaces of CNT filled samples that yielded information about the

microstructure and the distribution of nanoparticles within the polymer.

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FIG 3.1 ULTRASONICATOR

It is especially useful when it is not possible to stir the sample. Then the

above steps are followed for the fabrication of nano composites.

Specimens:

Composites composition

1 Epoxy + glass fiber

2 Epoxy(60): polyester (40%) + glass fiber

3 Epoxy(60): polyester (40%) + glass fiber + 0.5% CNT

4 Epoxy(60): polyester (40%) + glass fiber + 1% CNT

Table 3d: List of Specimen Prepared

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(a) (b)

FIG3.2: SEM IMAGE of 0.5% CNT

(c) (d)

FIG3.2: SEM IMAGE OF 0.5% CNT

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(a) (b)

FIG3.3: SEM IMAGE OF 1% CNT

(c) (d)

FIG3.3: SEM IMAGE OF 1% CNT

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3.3 Characterization of the Composites

3.3.1 Density:

The actual density (ρce ), however, can be determined experimentally by

immersion technique as shown in fig 3.4.

FIG 3.4: HYDROMETER

The density of the hybrid resin by ASTM D792 is measured as 1.14@35°C.

3.3.2 Viscosity:

The resin epoxy-polyester in the ratio of (60:40) is taken in a beaker. The

viscosity of the resin is calculated by Brookfield viscometer. The viscosity

of the hybrid resin is measured as 280 cps in RV 2 at 20 rpm.

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3.3.3 Gel Time:

The gelling time of the resin is measured manually by mixing up of

epoxy: polyester in a ratio of (60:40) and there corresponding curing agents

are added. An electronic thermometer is set to note the temperature change.

Once the curing agents are mixed the initial time is noted. There will be

sudden increase in temperature, after that the resin starts to gel. The time of

gelling and maximum temperature is noted and plotted as graphical

representation.

FIG 3.5: GEL TIME CALCULATION

The maximum temperature attained is 68 degrees.3.3.4 Hardness:

The Hardness of the resin is determined by ASTM D 2240 for hard

material testing. SHORE D hardness test gives the hardness value of 75.

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tu

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Density hardness pg28

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Viscosity pg29

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