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CHAPTER 3

EXPERIMENTAL DETAILS

3.1 INTRODUCTION

The natural fibre composites are to be prepared in view of

achieving the desired properties. In general, the factors that affect the

properties of natural fibre composites are listed below.

1. Type of matrix and fibre

2. Method of fabrication

3. Length, orientation and quantity of fibre

4. Interfacial adhesion between fibre and matrix

5. Stress transfer at the fibre-matrix interface

In this chapter, the matrix material used for the preparation of

composites is discussed in detail. The physical, chemical and mechanical

properties of liquid and cured state of resin are reported in the section 3.2.

The fibre extraction from the Sansevieria cylindrica leaves is described in the

section 3.3. Experiments related to the microstructural, physico-chemical and

mechanical characterisation of raw SCFs are described in the section 3.4. The

chemical treatments performed on SCFs and the experiments related to

characterisation of treated SCFs are separately discussed in the sections 3.5

and 3.6, respectively.

27

The composites fabrication using untreated and chemically treated

SCFs is discussed in section 3.7. The experiments related to characterisation

of untreated and treated SCFP composites are presented in section 3.8 and

3.9, respectively. The above process sequences are illustrated in the

Figure 3.1.

Figure 3.1 Scheme of the present investigation

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3.2 MATERIALS

The matrix used in this research was unsaturated polyester resin.

Methyl Ethyl Ketone Peroxide [MEKP] and cobalt naphthenate were used as

curing catalyst and accelerator. The molecular structures of the polyester

matrix, catalyst and accelerator are illustrated in Figures 3.2 (a), (b) and (c),

respectively.

HO C R C

O O

O CH

CH3

CH2 OC

O

CH CH C

O

O CH

CH3

CH2 OH

(a)

HO O C O OH

CH3

C2H5

(b)

O-

O

-O

O

Co++

(c)

Figure 3.2 Molecular structures of (a) polyester matrix, (b) catalyst and

(c) accelerator

Pure resin mixed with accelerator and catalyst was cast in the

mould of size 300 mm × 150 mm × 3 mm. The cast plate as shown in Figure

3.3, was used to prepare test specimens as per ASTM standards for

29

conducting tensile, flexural, Impact and hardness tests. The tensile and

flexural tests were performed using INSTRON universal testing machine

4301, Impact testing was performed using KARL FRANK GMPH 53568 and

hardness test using Rockwell hardness tester. The above tests were performed

at Composites Technology Centre, Indian Institute of Technology-Madras,

Chennai. The properties of liquid resin and the plate fabricated out of pure

resin are illustrated in the Table 3.1. The tensile fractograph of cured pure

polyester resin is shown in the Figure 3.4.

Figure 3.3 Fabricated cured pure resin

Table 3.1 Typical properties of the unsaturated polyester resin

Liquid resinAppearance Yellow viscous liquidViscosity@25 ºC 200 – 300 cpsSpecific gravity@25 ºC 1.11±0.02Volatile content 40±2 wt%Acid value 25±5 mg of KOH/g

Cured resinTensile strength 33±1.5 MPaTensile modulus 2.2±0.3 GPaElongation at break 1.5±0.14 %Flexural strength 40.6±3.21 MPaFlexural modulus 1.53±0.28 GPaShear strength 4.1±0.64 MPaImpact strength 0.4±0.05 J/cm2

Barcol hardness 40±3

30

Figure 3.4 Tensile fractograph of cured pure polyester resin

The reinforcement used in this investigation was SCFs. It is

extracted from Sansevieria cylindrica leaves by “mechanical decortication”

method that is described in section 3.3. The chemicals used for the treatment

of SCFs are sodium hydroxide, potassium permanganate, benzoyl peroxide,

acetone, stearic acid and ethyl alcohol. The matrix, catalyst, accelerator and

chemicals used for the modification of SCFs were supplied by Raja Traders,

Tirunelveli, Tamil Nadu, India.

3.3 EXTRACTION PROCEDURE FOR SCFs

The SCFs were separated from the Sansevieria cylindrica leaves,

which were collected from farms around the city of Tirunelveli in Tamil

Nadu, India, using a mechanical process called decortication. In this process,

the Sansevieria cylindrica leaves were fed into a fibre-extracting machine

called a mechanical decorticator that is schematically shown in Figure 3.5.

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The machine consists of a pair of feed rollers and a beater. The leaves were

fed into the beater through the feed rollers between a squeezing roller and a

scraper roller. The fibres were extracted, after separating the pulps. The

decorticated fibres were dried in the sunlight for 24 h to remove the moisture

content, and machine combed for separation. The separated SCFs are shown

in Figure 3.6.

Figure 3.5 Schematic diagram of a mechanical decorticator

Figure 3.6 Dried SCFs

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3.4 CHARACTERISATION OF SCFs

The leaves and fibre specimens of Sansevieria cylindrica were used

for microstructural analysis. The physical analysis of SCF was carried out to

find the density, fineness and cross sectional area of the fibre. The chemical

analysis of SCF was also made to predict the chemical composition. The

tensile behaviour of the SCFs is also discussed in this section.

3.4.1 Microstructural Studies of Sansevieria cylindrica Leaf and Fibres

The microstructural analysis was performed using SEM and

Polarised light microscope, in order to understand the internal structure of the

Sansevieria cylindrica leaf and fibre.

3.4.1.1 Preparation of specimens and sectioning

Healthy Sansevieria cylindrica leaf was collected for

microstructural analysis. For anatomical studies, the leaf was cut into small

pieces (10 mm x 10 mm) and immersed in FAA (5 ml formaldehyde + 5 ml

acetic acid + 90 ml 70% ethyl alcohol) for 24 h. Then the specimens were

dehydrated through a graded tertiary-butyl alcohol series and embedded in

paraffin (Sass 1940). Sections of 10 – 12 µm were cut on a rotary microtome,

affixed to a glass slide and stained with a mixture of Toluidine blue,

safranine, fast green and Lugo’s iodine solution (O’Brien et al 1964).

Polarised light micrographs were taken with a Nikon Labphoto 2 microscopic

unit. For normal observations, bright field imaging was used. For the crystal

studies (starch grains and lignified cells) polarised light was employed.

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3.4.1.2 Scanning Electron Microscopy

Transverse sections of Sansevieria cylindrica leaf and fibres were

examined using a SEM, HITACHI Model S3000H. The leaf section and

fibres were given uniform gold coating on all sides except their cross sections

to make the surfaces conductive. The cross sections of the Sansevieria

cylindrica leaf and fibres were examined at different magnifications. In

addition, the longitudinal view of the fibre was also observed.

3.4.2 Physical Properties of SCFs

The goal of this section is to describe the methodology for

measuring the fibre cross-section, its microstructural features and the physical

properties of fibre (i.e., its density and fineness). The cross-sectional area of

the fibre is needed for measuring the tensile strength of the fibre. The

microstructural features will be useful to identify the internal structure of the

fibre.

Optical microscopy of the fibre cross-section revealed that it is

irregular. To measure the cross-sectional area of the fibre, an adjacent piece of

tensile tested fibre (the piece close to the broken portion) was examined using

the SEM. In order to get acceptable cross-sectional area of the fibre, a 40-mm-

long fibre was cut into four sections of 10 mm each, and four micrographs

were taken. The images were post-processed using ImageJ software. A

contour line was drawn to delineate the fibre cross-section (Figure 3.7), and

the area was determined.

The porosity fraction (PF) of the natural fibres is defined as the

ratio of the total surface area of the fibre lumens to the raw surface area of the

fibre cross-section (Beakou et al 2008). The actual load bearing area of the

natural fibre will be less than the calculated cross sectional area, as it

34

possesses porosity. The PF of the SCF cross-section was computed using

SEM and ImageJ. The actual load bearing cross sectional area of the SCF can

be arrived using the following equation.

Actual load bearing area = Total cross sectional area x (1- PF) (3.1)

The dimensions of various microscopic features (i.e., the middle

lamellae, primary wall, secondary wall and fibre lumen) of the SCF were

calculated using the SEM and ImageJ.

Figure 3.7 Area calculation using ImageJ from the polarised light

micrograph showing a transverse section of the structural

fibre (40X)

The density measurement of the SCF was carried out using a

pycnometer for solids with toluene as the immersion liquid following the

procedure of Beakou et al (2008). The fibres were dried for 96 h in a

35

desiccator containing silica. They were then cut into lengths of 5-15 mm and

introduced into the pycnometer and then placed in the desiccator for 24 h. The

temperature in the room was 18.1°C. The hygrometry was 57% in the room

and only 3% in the desiccator. Before carrying out the hydrostatic weighing

with toluene, the fibres were impregnated in toluene for 2 h to evacuate the

micro bubbles in the fibres. The density of toluene ( t) is 0.866 g/cm3.

The density of the SCF was calculated using the following formula:

SCF = (m2 – m1) t (3.2)

(m3 – m1) – (m4 – m2)

where SCF is the density of the SCF (g/cm3), t is the density of the toluene

(g/cm3), m1 is the mass of the empty pycnometer (kg), m2 is the mass of the

pycnometer filled with chopped fibres (kg), m3 is the mass of the pycnometer

filled with toluene (kg) and m4 is the mass of the pycnometer filled with

chopped fibres and toluene (kg).

The fineness of the SCF was determined in terms of linear density

in accordance with ASTM D 1577-92. The linear density was obtained as Tex

and denier from the weight of 100 single fibres that were each 60 mm in

length.

3.4.3 Chemical Properties of the SCFs

This analysis was performed to determine the content of lignin,

cellulose, hemicelluloses, wax and moisture of the SCF using conventional

chemical, XRD and FTIR analyses.

The determination of the lignin content was carried out according

to the Klason method (Pearl 1967). The samples were crushed and extracted

with dichloromethane before being hydrolysed in a 72% solution of sulphuric

36

acid. Lignin was the only insoluble component and separated from the fibre

and quantified. The cellulose content was measured according to Kurshner

and Hoffer’s method (1933). The samples were crushed and extracted with

dichloromethane, and then a mixture of ethanol and 95% nitric acid was

added. The cellulose that corresponds to the insoluble fraction of the samples

was weighed. The determination of hemicelluloses was carried out according

to standard NFT 12-008. The samples were heated in hydrobromic acid. The

hemicelluloses was transformed into furfural, and the latter was extracted by

distillation and measured by spectrophotometry.

The wax content in the SCF was determined following the method

developed by Conrad (1944). The SCF samples were crushed and subjected to

soxlet extraction using ethanol for 6 h. The resulting solution containing

sugar, wax and other alcohol-soluble substances was transferred to a separator

funnel. Chloroform was added to extract the wax from the alcohol solution.

Purified water was then added and separate layers of chloroform and alcohol

were formed. After separation, the chloroform evaporated from the solution

leaving a waxy residue. After extraction, the dried residue and the SCF

samples were weighed, and the wax content was expressed in terms of the

original weight of the SCF samples.

The moisture content in the SCF was determined by drying the

weighed SCF samples in an oven at 104°C for 4 h. The dried samples were

weighed and the moisture content in the SCF was determined using the

following expression:

% of Moisture Sample weight - Sample weightContent in SCF = before drying after drying 100 (3.3)

Sample weight before drying

X-ray spectra (scan range (2 ) = 10 – 80°; = diffraction angle;

scan speed = 5.0 deg/min) of the SCF were obtained with a Rigaku X-ray

37

diffractometer D/Max Ultima III with an X-ray tube producing

monochromatic Cu K radiation. The integrated intensities of the Bragg peaks

in the spectrum of the SCF were identified, and their crystallinity indices were

estimated.

FTIR spectra of the SCF were recorded using a Perkin Elmer

Spectrum RXI FTIR spectrometer in a KBr matrix with a scan rate of 32

scans per minute and a resolution of 2 cm-1 in the wave number region from

400–4000 cm-1. The SCF samples were chopped into small particles using

scissors and ground to a fine powder using a mortar and pestle. This powder

was mixed with KBr and pelletised by pressurisation to record the FTIR

spectra under standard conditions.

3.4.4 Tensile Behaviour of the SCFs

The dried SCFs were tested in dry conditions under tensile loading

at gauge lengths (GL) of 10, 20, 30 and 40 mm in an INSTRON universal

testing machine of type 5500 R (Figure 3.8) according to the ASTM D 3822-

01 standard. The GL was varied to determine its effect on the tensile

properties. Pneumatic grips were used to clamp the fibre with a pressure of

0.4 MPa. The load was measured using 1.0 kN capacity load cell. The

displacement of the fibre was measured by a short-stroke transducer with a

resolution of approximately 0.1 µm. The tensile tests were conducted with a

cross head speed of 0.1 mm/min. The average strain rates were on the order of

0.6 s-1 and 0.15 s-1 for the gauge lengths of 10 mm and 40 mm, respectively.

Due to the variability of the natural fibres, 20 samples were tested at each GL,

and the average value was reported. All testing was conducted at ambient

temperature (~21°C) and a relative humidity of about 65%.

The compliance of the loading and gripping systems was

determined by obtaining the force versus displacement behaviour of the fibre

38

at various GLs following the methodology used by Chawla et al (2005). The

total cross–head displacement during fibre testing, t, is expressed using the

following expression.

t/ F) = (l/EA) + c (3.4)

where F is the applied force, l is the GL, E is the Young’s modulus of the

fibre, A is the cross-sectional area of the fibre and c is the machine

compliance. A plot of t / F versus GL (l) yields a straight line of Slope

1/(EA) and intercept c, which is the compliance of the load train.

Figure 3.8 INSTRON universal testing machine used for tensile testing

3.5 SURFACE TREATMENTS ON SCFs

The wax and hemicelluloses contents present over the surfaces of

SCFs reduce the adhesion between matrix and fibre. The surfaces of SCFs

were chemically treated to improve interfacial bonding with a polyester

39

matrix. The raw SCFs were subjected to different surface treatments using

alkali, benzoyl peroxide, potassium permanganate and stearic acid.

3.5.1 Alkali-treated SCF (ASCF)

The SCFs were soaked in a stainless steel vessel containing 10%

sodium hydroxide solution for 1 h. The fibres were washed thoroughly with

water to remove the excess of sodium hydroxide on the fibres. Final washing

was done with water containing a little acetic acid. Fibres were dried in an air

oven at 70 oC for 3 h (Sherely Annie Paul et al 2008).

3.5.2 Benzoyl-peroxide–treated SCF (BSCF)

The ASCFs were placed in 6% benzoyl peroxide diluted acetone

for half an hour. The fibres were then removed out and dried in air for 24 h

(Augustine Paul et al 1997).

3.5.3 Potassium-permanganate–treated SCF (PSCF)

The ASCFs were soaked in 0.5% potassium permanganate diluted

acetone for half an hour. The fibres were then taken out and dried in air for 24

h (Sherely Annie Paul et al 2008).

3.5.4 Stearic-acid–treated SCF (SSCF)

In all, 1% stearic acid was dissolved in ethyl alcohol. The solution

was then added dropwise to the ASCFs placed in a stainless steel vessel with

continuous stirring. These fibres were then dried in an air oven at 80 oC for 45

min (Augustine Paul et al 1997).

All of the chemical treatments and their reactions are schematised

in Figure 3.9.

40

41

3.6 CHARACTERISATION OF CHEMICALLY TREATED SCFs

In view of predicting the enhancement in the surface morphology,

physico-chemical and mechanical characteristics of the chemically treated

fibres, it becomes necessary to analyse the fibres after chemical treatment and

compare the same with the properties of raw fibres. In this section the studies

on experiments related to treated SCFs are present.

3.6.1 Surface Morphology of the Chemically Treated SCFs

The effects of modification upon the fibre surface were examined

using a SEM, JEOL model 6390 for the untreated SCFs (USCFs), ASCFs,

BSCFs, PSCFs and SSCFs samples. Prior to the analysis, the samples were

coated with platinum (layer thickness ~ 30 nm) to avoid sample charging

under the electron beam. The secondary electrons were used for imaging. The

surface morphology of untreated and treated SCFs was examined at different

magnifications. In addition, the transverse sections of ASCFs, BSCFs, PSCFs

and SSCFs were also observed in order to calculate their cross-sectional areas.

3.6.2 Physical, Chemical and Mechanical Characterisation of the

Chemically Treated SCFs

The physical, chemical and mechanical characterisations of the

chemically treated SCFs were performed by following the experiments

explained in the sections 3.4.2, 3.4.3 and 3.4.4 for raw SCFs. In addition

under physical analysis of the chemically treated SCFs, the percentage weight

loss of treated SCFs due to chemical treatments was evaluated using the

following expression.

% weight loss of treated SCFs = ((Wx – Wy)/Wx) x 100 (3.5)

where Wx is the weight of a dry USCF sample (g) and Wy is the weight of a

dry SCF sample after chemical treatment (g).

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3.7 PREPARATION OF SCFP COMPOSITES

The compression moulding method was adopted for the fabrication

of composites. The cleaned and dried SCFs were chopped into different

lengths of 10 mm, 20 mm, 30 mm, 40 mm and 50 mm. A known weight of

SCFs of definite length was randomly spread between two mild steel plates.

Extreme care was taken to obtain a uniform distribution of fibres. A load of

40 metric tons was applied on the mild steel plates by hydraulic compression

to form a single sheet. This compressed sheet was placed in a mould with a

size of 300 mm x 150 mm x 3 mm. Then, 97.5% of unsaturated polyester

resin was mixed with 2% MEKP (catalyst) and 0.5% cobalt naphthenate

(accelerator). The prepared matrix solution was degassed before pouring. The

degassed matrix solution was applied on the compressed sheet by using a

brush, and air bubbles were removed carefully with a grooved roller. The

mould was closed, and hydraulic pressure was applied until complete closure.

The closed mould was kept under pressure for 24 h. The composites were

fabricated in the form of a flat plate with a size of 300 mm x 150 mm x 3 mm.

Composite plates were prepared by varying fibre weights of 10%, 20%, 30%,

40% and 50%, in each fibre length mentioned above. A short SCFP composite

plate is shown in Figure 3.10.

3.8 CHARACTERISATION OF SCFP COMPOSITES

The raw SCFP composite plates were used to prepare the test

samples as per ASTM standards. Then the samples were used to evaluate

mechanical properties like tensile, flexural, impact and hardness. The

fractured surfaces of composites were analysed using SEM. XRD analysis

was performed to identify the chemical functional group existing in SCFP

composites. Water absorption characteristics of raw SCFP composites were

also studied.

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Figure 3.10 Short SCFP composite plate

3.8.1 Mechanical Tests

Test specimens were cut from the composite plates as per the

ASTM standard. Tensile testing was carried out in a FIE universal testing

machine UTE–40 with a 400-kN capacity with a gauge length of 100 mm and

a cross head speed of 1 mm/min, as per ASTM D 638-01 (2002). The three-

point flexural properties were determined by an INSTRON universal testing

machine 4301 with a 5-metric ton capacity, a test span of 50 mm and a cross

head speed of 1 mm/min, according to ASTM D 790–00 (2002). The Izod

impact test was done on unnotched specimens with a KARL FRANK GMBH

53568 impact testing machine with a pendellange of 390 mm. The impact test

was carried out with an impact speed of 3.46 m/s and an incident energy of

2.75 J according to ASTM D 6110-97 (2002). The hardness of the composites

was measured using a Rockwell hardness testing machine, according to

ASTM D 785-98 (2002). A minimum of six samples were tested in each case,

and the average value is reported. All testing was conducted at ambient

temperature (~ 21 C) and a relative humidity of about 65%.

3.8.2 Scanning Electron Microscopy (SEM)

Fractography of the failure surface of composite samples were

examined using a SEM, JEOL model 6390. The fractured portions of the

44

samples were cut, and the SEM micrographs were taken. A uniform coating

of platinum was given to the samples in order to make the surface conducting,

and then they were examined under the above microscope. The secondary

electrons were used for imaging. The surface of the fractured specimens under

tensile and impact tests were examined at different magnifications.

3.8.3 X-ray Diffraction (XRD) Analysis

XRD analysis was performed on the short SCFP composite

possessing the critical fibre length and optimum fibre weight percent. X-ray

spectra (scan range ( ) = 10-80 ; = diffraction angle; scan speed = 5.0

deg/min) of the short SCFP composites were obtained with a Rigaku X-ray

diffractometer D/Max Ultima III with an X-ray tube producing

monochromatic Cu K radiation. The integrated intensities of the Bragg peaks

in the spectrum of the short SCFP composites were identified, and their

crystallinity indices were estimated.

3.8.4 Water Absorption Test

In order to measure the water absorption characteristics of the

composites, rectangular specimens were prepared with dimensions of 39 mm

x 10 mm x 3 mm. The specimens were dried in an oven at 105 °C, cooled in a

desiccator using silica gel and immediately weighed. A Denver Instron

balance was used for weight measurement. The dried and weighed specimens

were immersed in distilled water according to ASTM D 570-99 (2002). The

water absorption tests were carried out by immersing the specimens for 2 h

and 24 h in hot and cold water, respectively. After immersion, the excess

water on the surface of the specimens was wiped up using a piece of soft cloth

and the final weights of the specimens were taken. The water absorption in

percentage was calculated using the following equation (3.6).

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Water absorption (%) = Final weight – Original weight x 100 (3.6)

Original weight

3.9 CHARCTERISATION OF CHEMICALLY TREATED SCFP

COMPOSITES

Separate composite plates were prepared using each type of

chemically treated SCFs such as ASCFs, BSCFs, PSCFs and SSCFs, with

critical fibre length and optimum fibre weight percent. The composites were

fabricated by compression moulding method, which was explained in section

3.7. The experiments related to tensile, flexural, impact, hardness and water

absorption characteristics of chemically treated SCFP composites were

explained in section 3.8. The tensile, flexural, impact, hardness and water

absorption characteristics of these composites were analysed and compared

with untreated SCFP (USCFP) composites. Based on the mechanical

properties, the optimum chemical treatment for short SCFP composite was

identified and reported. SEM micrographs were utilised to describe the failure

modes of composites.

3.10 SUMMARY

SCFs were extracted from Sansevieria cylindrica leaves using

mechanical decortication method. The fibres were subjected to chemical

treatments in order to improve the interfacial bonding between fibre and

matrix. The experimental procedures related to microstructural, physico-

chemical and mechanical characterisation of raw and chemically treated SCFs

were studied. Raw SCFP composites were prepared by compression moulding

method by varying the fibre length and fibre weight percentage. Treated

SCFP composites were prepared from each type of chemically treated SCFs

separately at critical fibre length and optimum fibre weight percentage. The

experiments relevant to mechanical properties of raw and chemically treated

SCFP composites were also studied in this chapter.