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CHAPTER 3

PROPERTIES OF ROSELLE FIBER, SISAL FIBER

AND POLYESTER RESIN

3.1 INTRODUCTION

The plant fiber composites have been used by the human race ever

since the onset of civilization as a source of energy, to make shelters, clothes,

construct tools and produce weapons. The best example is the use of straw as

reinforcement for clay to build walls in ancient Egypt, 3000 years ago. Glue

laminated beams were also introduced using a casein adhesive in 1893 in

Basel, Switzerland. Some creative designs were made but limited by the

shape and weight of the structural elements. As early as 1908, the first

composite materials were attempted for the fabrication of large quantities of

sheets, tubes and pipes (paper or cotton to reinforce phenol- or melamine-

formaldehyde resins sheets). In recent years, there has been a renewed interest

in the natural fiber as a substitute for synthetic fibers. Natural fibers as

reinforcements in polymer matrix composites provide positive environmental

benefits with respect to ultimate disposability and raw material utilization.

The properties of the composites depend upon the properties of the

individual components in the composites. Hence it is essential that the

strength of fiber and matrix have to be established. This chapter deals with the

fiber separation process and their properties. Moisture absorption of the

roselle and sisal fibers in distilled water at room temperature is also studied.

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The matrix material used unsaturated polyester resin and its mechanical

properties are studied and presented here.

3.2 FIBER SEPARATION PROCESS

The common word for H. sabdariffa (Roselle) is Mesta which

produces good fiber of commerce. These are major fiber yielding species in

India. Roselle and sisal fibers find traditional, age-old applications in the form

of high strength ropes in India. From lost decade, Roselle and Sisal fibers

were used traditionally in age-old applications in the form of high strength

ropes in India, especially, in Tamilnadu villages. The roselle fibers used as

low weight and high strength ropes to lift the heavy weight from Well etc.

The sisal fibers used to fix together the coconut leaf and wooden stem while

preparing the roof of a house. These fibers have not been really examined

from a composite angle at that time. These fibers have been the main source

of revenue of the people in this area for more than three decades.

In Tamilnadu region, the roselle (Botanical Name: Hibiscus

sabdariffa L, Family: Malvaceae), Local names: Pulichchai kerai (Tamil);

Lal-ambari (Hindi), fiber is cultivated in many villages to protect the food

plants, as a sides for food, medical purposes and specifically for fibers to

produce the high strength rope and gift articles etc. (Figure 3.1). This plant is

an erect, branched, smooth or nearly smooth annual herb 1 to 2 meters in

height. Roselle is used for making tarts, jellies, and wine. The young leaves of

the roselle are used as a substitute for spinach, or they may be cooked with

fish or meat in making ‘sinigang’. Fiber is prepared from the bast of the stem.

Sisal (Botanical name: Agave sisalana, Family: Agavaceae) fibers

are grown naturally in lakes, stream and river sides in Tamilnadu regions

(Figure 3.2a). It is also cultivated like other plants for fiber production

(Figure 3.2b).

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Figure 3.1 Roselle plant (Hibiscus sabdariffa L)

(a) (b)

Figure 3.2 Sisal plants (a) naturally grown, (b) cultivated

They give good economic value to the people involved in the

roselle and sisal related cultivation and other related work. Sisal fibers are

also used for ornamental purposes. Every scrap or part of the roselle and sisal

fibers can be utilized for some purpose. Rich quantities of fibers can be

produced from the roselle and sisal plants. The fibers from the roselle and

sisal plants are separated from roselle stem and sisal leafs by manually and

also by mechanically. Manual separation process of roselle and sisal fibers

from their plants is shown in Figures 3.3 and 3.4.

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3.2.1 Extraction of Sisal Fibers

Figure 3.3 shows the extraction method of sisal fibers. The sisal

leafs are cut from sisal plant and tied into bundles by using bags. Then bags

contain the sisal leafs are retted in tanks or River or Well for 3-4 days. The

retted leafs are washed in running water and the top portion of the leafs are

removed by manually (May by removed mechanicallly) to get the fiber

separatly and cleaned and dried in the sun.

(a) (b)

(c) (d)

(e)

Figure 3.3 Extraction of sisal fibers (a) sisal plant (b) retting in water

for 3-4days (c) removing the top portion of the leafs

(d) dried using sunlight, and (e) final form of sisal fibers

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3.2.2 Extraction of Roselle Fibers

The fully grown plant is used to extract fibers. Figure 3.4 shows the

extraction procedures of Roselle fibers. For the production of fiber the roselle

crops should be harvested at the bud stage. The stalks are tied into bundles

and retted in tanks or well for 3-4 days, as in the case of sisal leafs. The retted

stem of the roselle plant is washed in running water. Then the fibers are

removed from stem and cleaned and dried in the sun.

(a)

(b) (c)

(d) (e)

Figure 3.4 Extraction of roselle fibers (a) cultivated roselle plant

(b) stalks in the form of bundles (c) retting in water for

3-4days (d) removing the fibers from the stem, and (e) final

form of roselle fibers

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This method has been traditionally followed for fiber separation.

These fibers are also separated by mechanical crushing between the rollers

and followed by cleaning with motorized combing device. The separated

fibers are then dried under sunlight. During the separation of fibers from the

plants, a large quantity of fibrous waste is produced, in which the roselle

fibrous wastes are used as a fertilizer for other plants during cultivation, but

the sisal fibrous wastes have no value. For the present study the fibers are

separated from the roselle and sisal plants by traditional method. The fibers

thus obtained have lot of impurities and these impurities are cleaned by the

motorized combing device. The fibers and the waste materials are collected

separately. The fibers are subjected to different mechanical test and

environmental condition to study their mechanical properties and the

environmental effect on mechanical properties. The bundle of roselle and sisal

fibers used to fabricate roselle and sisal fiber hybrid polyester composites is

shown in Figures 3.3 and 3.4.

3.3 PROPERTIES OF ROSELLE AND SISAL FIBER

The roselle fibers are and light gold in color. The shape varies from

fiber to fiber, and also non uniform. The length of the fiber varied from 1 m to

2 m. Fiber thickness is measured using an electron (Digital microscope)

microscope for 25 samples and it was found to be varying between 0.13mm to

0.24mm which depends on the age and area of cultivation of the plant. The

density was calculated using Archimedes principle and it was found to be

around 1.45 g/cm3.

The sisal fibers obtained from the leaf of sisal plants are

white/golden white in color. They can be twisted in to yarns and ropes in wet

conditions. Fiber thickness, length and strength depend upon the age and

location of the plant. The length varied from 0.5m to 1m and diameter is

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between 0.21mm to 0.29mm. The density of the fiber was found to be around

1.51 g/cm3.

3.3.1 Tensile Properties of Fibers

The cleaned and dried single fiber was mounted along the

centerline of a slotted paper window as shown in Figure 3.5. The ends of the

paper window were clamped in the grips of the Single Yarn Testing machine

with gauge length of 20 mm and its mid section was cut off during loading.

The load is applied with the crosshead speed of 1mm/min till the fiber break

and the breaking point load values were recorded. 20 samples were tested and

the results are tabulated in Tables 3.1 and 3.2. From the load deflection curve

the strength and modulus values were calculated.

It is observed that the strength of the roselle fibers was not uniform

and it varied from 145.385 to 184.676 MPa. The modulus was also in the

range of 18.423 to 36.395 GPa. The percentage of elongation varies between

0.5 and 0.8. It was observed that the strength of the sisal fibers was also not

uniform and it varied from 80.193MPa to 235.019 MPa. The modulus was

also in the range of 7.460GPa to 18.802GPa. The percentage of elongation

varies between 1.0 to 1.5.

The Strength of the fibers depends mainly on the fibrillar structure,

micro fibrillar angle and the cellulose content. The relation between the

elongation and the fibrillar angle is

є = -2.78+7.28 x 10-2θ+7.7x10-2 θ2 (3.1)

σ = -334.005-2.83 θ+12.22W (3.2)

where θ is microfibrillar angle and W is cellulose content.

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Figure 3.5 Methodology of tensile test of roselle and sisal fibers

Table 3.1 Tensile properties of roselle fibers as received

Fiber specimen

Diameter (mm)

Load (N)

Deflection (mm)

Strength (MPa)

Strain % Elongation

Modulus (GPa)

1 0.13 2.450 0.250 184.676 0.005 0.5 36.935 2 0.16 3.330 0.275 165.705 0.006 0.6 30.128

3 0.18 4.116 0.325 161.831 0.007 0.7 24.897 4 0.23 6.370 0.350 153.396 0.007 0.7 21.914 5 0.20 5.488 0.350 174.777 0.007 0.7 24.968 6 0.21 5.978 0.375 172.682 0.008 0.8 23.024 7 0.14 2.548 0.300 165.605 0.006 0.6 27.601 8 0.17 3.724 0.325 164.150 0.007 0.7 25.254 9 0.24 6.664 0.400 147.381 0.008 0.8 18.423

10 0.19 4.214 0.325 148.702 0.007 0.7 22.877 11 0.18 3.920 0.325 154.124 0.007 0.7 23.711 12 0.16 3.528 0.300 175.557 0.006 0.6 29.260 13 0.15 2.842 0.275 160.906 0.006 0.6 29.256 14 0.14 2.352 0.250 152.866 0.005 0.5 30.573 15 0.17 3.822 0.300 168.470 0.006 0.6 28.078

16 0.22 6.080 0.400 160.025 0.008 0.8 20.003 17 0.19 4.905 0.275 173.086 0.006 0.6 31.470 18 0.19 4.120 0.350 145.385 0.007 0.7 20.769 19 0.18 3.924 0.300 154.282 0.006 0.6 25.714 20 0.15 2.648 0.250 149.922 0.005 0.5 29.984

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Table 3.2 Tensile properties of sisal fibers as received

Fiber specimen

Diameter (mm)

Load (N)

Deflection (mm)

Strength (MPa)

Strain % Elongation

Modulus (GPa)

1 0.29 10.791 0.7 50 163.454 0.015 1.5 10.897 2 0.29 10.594 0.700 160.470 0.014 1.4 11.468 3 0.23 3.727 0.550 89.750 0.011 1.1 8.159 4 0.26 8.730 0.750 164.512 0.015 1.5 10.967 5 0.22 3.330 0.525 87.645 0.011 1.1 8.347 6 0.24 4.020 0.600 88.907 0.012 1.2 7.409 7 0.26 5.984 0.525 112.765 0.011 1.1 10.740

8 0.28 9.711 0.575 157.790 0.012 1.2 13.721 9 0.21 8.136 0.625 235.019 0.013 1.3 18.802 10 0.23 4.116 0.575 99.117 0.012 1.2 8.619 11 0.27 9.212 0.500 160.974 0.010 1.0 16.097 12 0.25 5.782 0.550 117.850 0.011 1.1 10.714 13 0.29 10.780 0.575 163.288 0.012 1.2 14.199 14 0.24 3.626 0.525 80.193 0.011 1.1 7.637 15 0.21 3.136 0.550 90.587 0.011 1.1 8.235 16 0.28 10.202 0.625 165.768 0.013 1.3 13.261 17 0.26 8.436 0.750 158.972 0.015 1.5 10.598 18 0.25 5.490 0.750 111.898 0.015 1.5 7.460 19 0.25 4.136 0.625 84.301 0.013 1.3 6.744 20 0.22 3.531 0.500 92.936 0.010 1.0 9.294

3.4 WATER ABSORPTION CHARACTERISTICS OF FIBERS

3.4.1 Water Absorption Kinetics of Roselle and Sisal Fibers

Water or moisture uptake in natural fiber reinforced polymer matrix

composites has a deleterious effect on their mechanical properties. The

growth of natural fiber composites is not without challenges. The hydrophilic

nature of natural fibers is a potential cause of poor interfacial adhesion

46

between fibers and matrix. Understanding the moisture diffusion mechanisms

in natural fiber composite materials is essential for the improvement of their

durability. As a raw material for polymer composites, the water-absorption

behavior of roselle and sisal fibers has to be comprehensively investigated.

Water-diffusion characteristics of roselle and sisal fibers in water have been

investigated and the results are discussed.

About 10g of dried fibers having an approximate length of 50mm is

taken for the water absorption examination. The samples were immersed in

raw water at room temperature. Increase in weight of the samples was noted

at specific time intervals. This process was continued until equilibrium is

reached. The molar percentage uptake Qt for water for 100g of polymer was

plotted against the square root of time.

2 1

118tW WQ

W

(3.3)

where 18 is the relative molecular mass of water. When equilibrium is

reached Qt is taken as the molar percentage uptake at infinite time, Q∞

(Bhagavan et al 2003). The water absorption of fibers was calculated as the

number of moles of water absorbed by 100g of the fiber. The major factors

that control the interaction between fibers and water are diffusion,

permeability and sorption. Roselle and sisal fibers are lingo cellulose, they

contains hemi-cellulose, lignin, pectin, waxy material and water-soluble

substances. The swelling behavior of natural fibers is greatly affected by its

morphology as well as physical and chemical structures. The water

penetration through the microspores of the fiber surface by capillary action

was explained (Sreekala 2001). The fibers have a porous internal structure.

The penetrating water enters into the fiber structure and stay in the pores

medium. Roselle fiber contains less waxy (0.5) materials when compared to

sisal fibers. The waxes present on the fiber surface reduce the moisture

47

absorption. Due to porous and less waxy material, the roselle fibers have the

large initial uptake due to capillary action.

The diffusion of water in water – cellulose system is reported to be

non-Fickian or anomalous and two-stage absorption behavior is reported in

natural fibers (Sreekala 2001). During the present investigation it was

observed that both roselle and sisal fibers exhibited single stage behavior is

observed in water, which is shown in Figure 3.6. The initial stage of water

penetration is by capillary action, which is shown by the linear portion of the

curve, and the second linear portion of the moisture absorption is up to

360 minute. It is due to the late filling of micro pores. The equilibrium

sorption is higher for roselle fibers, which due to pores and less waxy

materials.

Figure 3.6 Comparison of moisture absorption curves of roselle and

sisal fibers

3.4.2 Properties of the Matrix

Thermoset resins are usually liquids or low melting point solids in

their initial form. By its three dimensional cross linked structure, they have

high thermal stability, chemical resistance, good dimensional stability and

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also high creep properties. The most common thermosetting resins used for

composite manufacturing are unsaturated polyesters, epoxies, vinyl esters and

phenolics. Unsaturated polyester is economical as is used due to its excellent

process ability and good cross linking tendency as well as mechanical

properties when cured (Regnier and Mortaigne 1995; Mortaigne et al 1999)

and due to these reasons unsaturated polyester has been chosen. The typical

properties of the unsaturated polyester are listed in Table 3.3. Unsaturated

polyester as matrix for the current investigation was tested at Saint-Gobain

Vetrotex India Ltd.

Table 3.3 Typical properties of unsaturated polyester resin matrix

Appearance Yellow viscous liquid

Specific Gravity @ 25°C 1.1

Viscosity

(a) FC-4 (Seconds) @ 30°C 110

(b) Brookfield (CPS) @ 25°C RVT model 480

Volatile content (%) @150°C 42.5

Acid value (Mg.KOH/G) 6.97

To find the mechanical properties a plate was cast with neat resin

mixed with accelerator and catalyst in mould of 150 mm × 20 mm × 3 mm.

Figure 3.7 shows the fabricated neat resin sample. Tensile test was carried out

using computerized FIE universal testing machine. Six samples were tested

and the average strength was estimated as 24 MPa and the tensile modulus to

be 997.89 MPa. For the flexural strength, the samples were tested by three

point loading and flexural strength of 28 MPa was observed. The flexural

modulus of the samples was observed as 1.07 GPa. Impact test was carried

out on Izod impact testing machine. The impact strength was observed as

0.49 KJ/m2.

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Figure 3.7 Fabricated neat resin sample

3.5 ALKALI TREATMENT OF ROSELLE AND SISAL FIBERS

The quality of a fiber reinforced composite depends considerably

on the fiber-matrix interface because the interface acts as a binder and

transfers stress between the matrix and the reinforcing fibers. Strong

interfacial bonding can be developed as result of good wetting of the fibers by

the matrix and the formation of a chemical bond between the fiber surface and

the matrix. In order to develop composites with good mechanical properties

and good environmental performance, it is necessary to impart hydrophobicity

to the fibers by mechanical treatments, surface treatments and chemical

treatments. This results in increase of the strength of the composite specimen.

Many studies were carried out to improve the properties of the composites.

Mwaikambo et al (2002) studied the alkalisation or acetylation of plant fibers

resulting in the changes of the surface topography of the fibers and their

crystallographic structure. Dewaxing method has been used to remove waxy

substances from sisal fiber surfaces. Soxhlet extraction is one technique

adopted. It was found that the properties of the fiber are not enhanced but the

fiber matrix bond is improved.

The fiber was washed with sodium hydroxide prior to any

treatment. The sodium hydroxide opens up the cellulose structure allowing

the hydroxyl groups to get ready for the reactions. During washing with

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sodium hydroxide, the wax, cuticle layer and part of lignin and hemicellulose

were removed. The major reaction takes place between the hydroxyl groups

of cellulose and the chemical used for the surface treatment. The fiber

treatment resulted in the decrease of the properties of the fiber, but increase in

the strength of the specimen as a whole. As per the literature reviews about

the alkali treatment of natural fibers reinforced composites, it was confirmed

that the treatment of the fibers with NaOH solution is the most suited one.

The alkali treatment process has some critical parameters like:

1. Alkali used

2. Concentration of the solution

3. Treatment duration

Here any two of the parameters need to be fixed such that the

variation in the properties of the composite can be studied carefully. The

concentration of solution and treatment duration plays major role. There is a

positive effect cited when the concentration increases up to certain limit,

beyond that the value drops suddenly. In this case, the roselle and sisal fibers

are treated in 10% of alkali solution (NaOH) for 2 h, 4 h, 6 h and 8 h.

Figure 3.8 shows the treated roselle and sisal fibers.

(a) Roselle (b) Sisal

Figure 3.8 Alkali treated roselle and sisal fibers

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3.6 SUMMARY

The fiber separation process and its physical and mechanical

properties were studied. From the test it was observed that the fiber size and

the strength are not uniform. The moisture absorption characteristic of the

fibers was also studied. From the study it was observed that the equilibrium

sorption is higher for roselle fibers when compared with sisal fibers. The

mechanical properties of the matrix material were studied. The roselle and

sisal fibers are treated with alkali solution for different duration and then used

to fabrication of the composites.