Indian Journal of Engineering & Materials Sciences Vol. 25, August 2018, pp. 295-300

Experimental study of tensile and flexural properties of kans grass fiber reinforced polyester composites

Vishal Ahlawat*, Anuradha Parinam & Sanjay Kajalc

Mechanical Engineering Department, University Institute of Engineering and Technology, Kurukshetra University, Kurukshetra 136 119, India

Received 18 November 2016; accepted 28 November 2017

The present paper describes the use of kans grass fiber as a new natural fiber in composite development. The fibers are collected from riped kans grass plants and reinforced in to the polyester resin with 0, 10, 13.35, 18 and 20.08 vol%. The tensile strength, tensile modulus and the density of kans grass fiber are found to be 278-619 MPa, 8.1-11.1 GPa and 441 kg/m3, respectively. The composites tensile strength and modulus increase with increase in the fiber vol% from 10 to 20.08. The flexural strength also increases with increase in fiber vol% but remains lower than that of the neat polyester. It has been further observed that the addition of fibers increases the flexural modulus and made the 20.08 vol% specimen 2.1 times stiffer than the neat specimen. The fiber reinforcement has noticeable improvement in specific tensile strength, and modulus and specific flexural modulus of the composite specimens whereas no significant increment is observed in specific flexural strength. This experimental study shows the potential of kans grass fibers in the development of composites for light weight applications due to its low density and better strength.

Keywords: Natural fibers, Kans grass fiber polyester composites, Tensile strength, Flexural strength

Over the past few years, as the environmental awareness increased all over the world, several programs and inventions involving biodegradable products were introduced into the system of production. Composites made of natural fibers greatly contribute to the care of nature. These types of reinforcements having an effective mechanical performance even in hot and humid environment, low density, infinite availability and easy disposal capability, offer a great alternative to the synthetic fibers used in different composites. Natural fibers offer a great competition to the synthetic fibers in relation to their specific strength and stiffness. Hennery Ford was the first person to start using bio based composites made of soybeans. Plastic components reinforced with natural fibers provide low density, adequate specific strength, better energy recovery, CO2 sequestration, and decomposability at very low cost1-3. Nearly one fourth of a vehicle’s weight is just a waste in the form of plastics, fibers, foams, rubber and glass and bio-composites are the best alternatives to such kind of products. The use of raw renewable fibers helps in reducing the energy consumption and the environmental impacts4.

Dynamic mechanical properties such as glass transition temperature, fiber loading and damping peaks of the short banana fibers were investigated on the basis of volume fraction of the fibers5. Most of the properties improved with increase in volume fraction of fiber up to 40% and then subsequently decreased with further fiber introduction. The study of mechanical properties of polypropylene bio-composites reinforced with coir, sisal, hemp, jute and kenaf showed that properties of these composites were in the better agreement than that of the glass in certain cases6. Therefore, the natural fiber composites can become a possible substitute of glass in light weight applications. The coir fiber composites were analyzed for its structural and mechanical properties on the basis of its weight fraction7. It was reported that maximum weight percentage up to 50% of fibers provide the best mechanical properties. The hardness and stiffness of composition decreased with more fiber loading. The golden cane polyester composites showed a gradual increase in the mean tensile strength at a volume fraction of 0.43, which is 2.13 times greater than that of neat polyester8. The mean flexural strength of composite increased moderately from volume fraction of 0.137 of fiber and impact strength was 22 times higher than that of resin. When jowar

———————— *Corresponding author (E-mail: vahlawat2015@kuk.ac.in)

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fiber composite was compared with sisal and bamboo fiber composites, the former gave tensile strength almost equal to the bamboo composite and approximately twice that of sisal composite9. The tensile modulus as well as flexural strength and modulus of jowar composite were also found to be greater than the bamboo and sisal composites. The mechanical properties of banana/kenaf hybrid polyester composite were investigated in comparison with banana fiber and kenaf fiber polyester composites for fiber weaving patterns and orientation10. Hybrid composite with plain pattern resulted in an increase of about 54% and 15% of tensile strength over banana polyester composite and kenaf polyester composite respectively. The flexible epoxy treatment improved the tensile strength of poly lactic acid based bamboo and coconut fiber composites while it decreased the stiffness 11. However, the improvement depend upon the type of natural fiber. Cotton fiber reinforced isophthallic polyester composites were investigated for their tensile and flexural properties12. It was found that the tensile and flexural strength were maximum at 25 vol%. The addition of bamboo fiber in sisal/unsaturated polyester composites up to 50% by weight improved the mechanical properties whereas a decrease in the moisture absorption property was observed13. The leaf fibers and peduncle fiber reinforced polyester composites were prepared and tested for tensile properties14. It was found that the peduncle fiber composites with 4 vol% of fiber gave better tensile properties. Hybrid composites by reinforcing tamarind fruit and glass fiber in to the polyester resin resulted in improvement in the mechanical properties and chemical resistance for all chemicals except toluene15. Natural fiber reinforced polyester composites were also found better in terms of strength and cost as compared with glass fiber polyester composites16.

Saccharum spontaneum is a grass native to the Indian subcontinent and a part of the family of sugarcane. Therefore, it is sometimes called as wild sugarcane. In India, it is called as kans grass. It usually self-fertilizes along the river side area up to three meters in height20. It is generally used in making temporary sheds, chairs and grains and animal feed storages. In this paper, kans grass fiber is introduced as an agricultural waste for composite preparation. The kans grass fibers are extracted manually from kans grass culms and charged into unsaturated polyester matrix to produce composites at different vol% of fibers. These composites were tested to investigate the effect of varying vol% on the tensile and flexural properties.

Materials and Methods

Matrix The polyester was taken as matrix material from

the Revex Plasticizers (Pvt.) Ltd., Faridabad, India. The resin has a density of 1250 kg/m3 with 32% monomer content. Methyl Ethyl Ketone Peroxide (MEKP) was used as a catalyst for curing of matrix material which was purchased from the same firm.

Releasing agent Polyvinyl alcohol was used as the releasing agent

for the preparation of composites. It is soluble in water and forms glue like paste when mixed in standard volume fraction of both hot water and polyvinyl alcohol. It is formed by polymerizing vinyl acetate. It has excellent film forming and adhesive properties. It has a melting point of 180°C to 190°C. The synthetic matrixes like epoxy and polyester do not stick to polyvinyl alcohol.

Extraction of fibers Ample amount of kans grass plants were available at

the river side area. Suitable quantity of kans grass culms was obtained after cutting at their base. The ends of these culms were trimmed and allowed to dry in shade to remove moisture for nine to ten days. The nodes were removed by cutting followed by separation of culms into pieces of required length after proper removal of moisture. These pieces contained a soft part known as lignin at the center which was peeled off from the culms. These deprived strips were softened by retaining them into water for five hours. After that these deprived strips were beaten by a mallet which resulted in loosening and separation of fibers. The loosened fibers were combed until the individual fibers were obtained. Figure 1 shows the extracted fibers arranged in longitudinal direction.

Fig.1 — Extracted fibers

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Composites preparation The specimens were prepared by using hand-lay-up

technique which is a simple and self-labored process. A wooden mould was used for placing of fibers and matrix. Marble plates were used as flat surfaces for better finish of the composite at top and bottom of the mould. Initially, a single layer of releasing agent (polyvinyl alcohol) was applied at every place of the specified mould area. It was placed untouched at room temperature, for approximately one hour, for the purpose of drying. A catalyst of amount 1.5 percent by volume of polyester resin was added for curing purpose. Then, a layer of polyester resin mix was applied at the bottom of the mould. After getting a semi solid layer of resin, the fibers were introduced longitudinally followed by another layer of resin. Movement of fibers and their deformation were kept minimized during fiber loading to obtain unidirectional composites. A pressure of 0.05 MPa in compression was applied on the top plate of the mould at the time of curing. The specimens were allowed to cure for 24 h, then removed from the mould and post cured at 50°C for two hours. Composite specimens were prepared mainly on the basis of fiber arrangements and vol%. In the present work, continuous unidirectional kans grass fibers with length equal to standard specimen: 160 mm for tensile testing and 100 mm for flexural testing were introduced. The composite specimens with 0, 10, 13.35, 18 and 20.08 fiber vol% were prepared and processed for mechanical testing. The inability of the binder to wet and infiltrate the bundles of fibers limit the reinforcement of fibers by 20.08 vol%. Testing of fibers and composites

Testing of fibers The prepared fibers were tested for tensile strength

on UTM according to the test standard ASTM D 3379-8917. An arrangement for testing was made by gluing each fiber of gauge length 50 mm on a soft cardboard with the help of resin. This arrangement was tested at a cross head speed of 0.5 mm/min. The

test was conducted on 15 fiber specimens. Figure 2 shows the fiber specimen during tensile testing. The fiber specimens were assumed cylindrical in cross-section to measure the average cross-sectional area. An optical microscope was used to measure the diameters of the fibers at five different locations along the gauge length. The tensile strength and modulus of kans grass fibers were evaluated by force-stroke data and cross-sectional areas. Tensile and flexural testing of composites

Five composite specimens of dimension 160×12.5×3.5 mm were prepared and tested for the tensile properties as per test standards ASTM D 638-8918. In case of flexural testing, the composite specimens of dimension 100×25×3.5 mm were prepared and tested as per test standards ASTM D 790 M-8619. In flexural testing, the points for support were kept 64 mm apart. A strain rate of 0.5 mm/min was used for tensile and flexural testing of composite specimens on universal testing machine (UTM). Results and Discussion

Tensile properties Table 1 summarizes the physical and tensile

properties of different natural fibers along with kans grass fibers. The measured diameter of kans grass

Fig. 2 — Fiber specimen during tensile testing

Table 1 — Comparison of physical and mechanical properties of kans grass fiber with other natural fibers9

Fiber Density (kg/m3) Diameter (µm) Tensile strength (MPa) Tensile modulus (GPa) % Elongation

Sisal 1450 80-300 227-700 9-20 3-14 Coir 1150 100-460 131-175 2.5-6 15-40 Banana 1350 80-250 529-759 8-20 1-3.5 Bamboo 910 88-330 440-600 35-46 1.4 Jowar 922 80-500 302 6.99 4.32 Kans grass 441 250-780 278-619 8.1-11.1 1.7-2.8

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fiber ranges from 250 µm to 780 µm. The density of kans grass fiber is 441 kg/m3 which is lower than all other natural fibers. The tensile strength is greater than the coir fiber and comparable to other natural fibers. Therefore, low density and good strength make kans grass fiber a better choice for manufacturing of light weight and high strength products. The tensile modulus was also observed to be better than the jowar and coir fiber whereas the percentage elongation is less than coir, sisal and jowar fiber.

Figure 3 shows the force versus stroke curve for composite specimen at (0, 10, 13.35, 18 and 20.08) vol% of fibers during tensile testing. The stroke indicates the composite displacement in mm. It can be seen from Fig. 3 that increase in fiber vol% increases the force bearing capacity. The neat polyester has more force bearing capacity than 10 vol% of composite specimen. The percentage elongation of neat polyester specimen is more than other fiber composite specimens. However, it is found that it slightly increases with increase in fiber vol% from 10 to 20.08.

Table 2 shows the tensile properties of composites at different vol% of fiber. The tensile strength of fiber composite at 20.08 vol% is found to be 2.7 times more than the neat polyester. It has maximum ultimate tensile strength of 39.72 MPa, load carrying capacity 2003.20 N and tensile modulus of 1.588 GPa. The tensile modulus increases with increase in fiber vol% from 0 to 20.08.

Figure 4 shows the effect of vol% of fiber on the specific tensile strength and modulus of fiber composites. The specific tensile strength remains almost the same up to 10 vol% then rapidly increasing

up to 13.35 vol%. Further increase in fiber up to 18 vol% does not affect the specific tensile strength. It again increases rapidly up to 20.08 fiber vol. %. The rapid increase in specific tensile strength was observed due to significant increase in tensile strength from 10 to 13.35 vol% and 18 to 20.08 vol%. The composite density also decreases with increase in fiber vol%. The specific tensile modulus increases linearly up to 13.35 fiber vol% then follow the similar trend as that of the specific tensile strength and approaches the same value at 20.08 vol%.

Fig. 3 — Force versus stroke for composites at different vol% of fibers in tensile testing

Table 2 — Tensile properties of composites at different vol% of fiber

Fiber vol. %

Max. force (N)

Ultimate tensile strength (MPa)

Tensile Modulus (GPa)

% Elongation

0 819.594 14.6048 0.199 7.3

10 581.406 14.3827 0.921 1.6

13.35 1042.34 25.6280 1.139 2.2

18 1140.39 26.7748 1.162 2.3

20.08 2003.20 39.7225 1.588 2.5

Fig. 4 — Variation of composites specific tensile strength and modulus at different fiber vol%

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Table 3 — Flexural properties of composites at different vol% of fiber

Fiber vol%

Max. force (N)

Max. disp. (mm)

Max. Stress (MPa)

Max. Strain (%)

Flexural modulus

(GPa)

0 93.44 14.26 16.43 9.61 0.479 10 30.09 8.77 11.06 4.11 0.520

13.35 51.34 7.91 14.91 4.17 0.703

18 66.75 5.32 15.90 3.15 0.988

20.08 73.13 5.24 16.04 3.31 1.053

Flexural properties

The prepared composites at varying vol% of fibers were tested on universal testing machine (UTM) for flexural strength as per ASTM standard. Figure 5 illustrates the behavior of the composite specimens in term of force versus stroke.

It is clearly seen that the neat polyester has maximum flexural load bearing capacity as well as strain. Reinforcement of fibers in to polyester resin from 10 to 20.08 vol% increases the load bearing capacity while decreasing the displacement.

Table 3 shows the flexural properties of fiber composites at different vol% of fiber. It can be seen that increase in fiber vol% increases the flexural strength and modulus and found to be 16.04 MPa and 1.053 GPa, respectively. It can be attributed to the fact that decrease in polyester vol% decrease the percentage strain and the fiber increment contributes to the flexural strength. It indicates that the flexural strength may be further improved by addition of more vol% of fibers. Figure 6 shows the effect of vol % of fiber on the specific flexural strength and modulus of fiber composites.

The neat polyester composite has higher specific flexural strength than the fiber composite having 10 vol% of fiber. It increases with increase in fiber vol% from 10 to 20.08. A sharp linear increase in the specific flexural modulus is observed when fiber vol% increases from 10 to 20.08 whereas for increase from 0 to 10 vol% of fiber the effect is insignificant. Conclusions

Kans grass is a wasteland weed easily available in India. Extraction of these fibers is a very easy process. It provides lengthened fibers of good quality which is useful for the production of large sized products. The tensile strength of kans grass fiber is also in better agreement with other natural fibers such as coir, jowar and sisal. The density of kans grass fiber is very much lower than other natural fibers which become an interesting parameter in the designing and fabrication of light weight products. On the basis of experiments performed on the composite specimens, the following conclusions are drawn:

Fig. 5 — Force versus stroke for composites at different vol% of fibers in flexural testing

Fig. 6 — Variation of composites specific flexural strength and modulus at different fiber vol%

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(a) The tensile strength of composite specimen at 10 vol% of fiber is in the close approximation with neat specimen. It increases with increase in fiber vol% from 10 to 20.08.

(b) The neat polyester has greater percentage elongation than the composite specimens. It slightly increases with increase in fiber vol% from 10 to 20.08.

(c) The tensile modulus significantly increases with increase in fiber vol% and found 7.97 times greater than that of the neat polyester at 20.08 vol%.

(d) The flexural strength and modulus of fiber composites increases with the increase in fiber vol% from 10 to 20.08.

(e) The fiber reinforcement has noticeable improvement in specific tensile strength and modulus and specific flexural modulus of the composite specimens while no significant increment was observed in specific flexural strength.

Acknowledgements The authors would like to thank the CIPET,

Murthal, Sonepat (India) for providing the testing facilities for the research work.

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