Effect of environmental conditions on okra fiber: flexural and impact properties of okra fiber reinforced polyester composites.

Srinivasababu, N. ; Rao, K. Murali Mohan ; Kumar, J. Suresh 等

Introduction

Flexural properties of acrylonitrile butadiene styrene (ABS), glass bead (GB) and glass fiber (GF) ternary composites have been studied [1]. Woven jute fiber reinforced composite specimens prepared by hand lay-up technique as per ASTM standard. The first report by any single group of researchers in which flexural strength and impact strength are given [2]. Effect of surface treatments of sisal fibers on the flexural properties of sisal / polyester composites was determined. Flexural properties of sisal / epoxy composites were given by Yan Li [3]. Effect of fiber treatment on the mechanical properties of unidirectional sisal-reinforced epoxy composites was investigated [4]. Jute fibers were subjected to alkali treatment with 5% NaOH solution for 0, 2, 4, 6, 8 h at 30[degrees]C. For 35% composites with 4 h treated fibers, the flexural strength improved from 199.1 to 238.9 MPa by 20%. On plotting different values of slopes obtained from the rates of improvement of flexural strength and modulus, against NaOH treatment time, two different failure modes were apparent before and after 4 h of NaOH treatment [5]. Flexural, impact behaviour of cellulose fibers reinforced polymeric matrices, such as poly methyl methacrylate (PMMA) and poly (styrene-c-acrylonitrile) (SAN) are investigated and special attention is given to the effect of fiber surface treatment on the effective properties. The flexural strength of the composites remains constant when fiber is grafted with PMMA and a brittle interface is formed around cellulose fibers, regardless of fiber content. In the case of impact loading, the presence of an elastomeric type material, in this case poly (butyl acrylate)-grafted cellulose fibers seems to provide an alternative mechanism for energy dissipation in the composite, thus, showing a better impact behaviour than the composites with the other fiber surface treatments. The impact behaviour seems to be improved by the mechanical properties of cellulose fibers [6]. Composites were fabricated using banana fiber and glass fiber with varying fiber length and loading. The analysis of flexural and impact properties of these composites revealed that the optimum length of fiber required for banana fiber and glass fiber are different in phenol formaldehyde resole matrix [7]. The effect of fiber treatments and matrix modifications on mechanical properties of flax fiber bundle / polypropylene composites was investigated [8]. A uniaxial natural fabric of Hildegardia Populifolia was treated with 5% NaOH solution for 1 h, and the resulting changes were analyzed by polarized and SEM techniques [9]. The mechanical properties of flax / polypropylene compounds, manufactured both with a batch kneading and an extrusion process were determined and compared with the properties of Natural fiber mat Thermoplastic (NMT) composites [10]. Biodegradable composites reinforced with bagasse fiber before and after chemical treatments were prepared and mechanical properties were investigated. Approximately 14% flexural strength and 30% impact strength improved [11]. Wood composites after water-cross linking treatment exhibited better mechanical properties than the non-cross linked one because of improved chemical bonding between the wood fiber and polyolefin matrix. As the wood flour content reaches to 30 wt% and after water cross-linking for 4h, flexural strength increased by 137.5% (11.2-26.6 MPa) with respect to that of non cross linked ones [12]. Rice straw fibers have been extracted and incorporated in polyester resin matrix to prepare rice straw reinforced polyester composites and flexural properties of resultant composites have been studied. Composites with a mean flexural strength of s66.3 MPa can be formulated with an optimum fiber volume fraction of about 40% [13]. Arecanut FRP composites at 0.39 volume fraction shown mean flexural strength and modulus of 7.5 and 70% more in comparison to those of plain polyester. The work of fracture in impact is measured to be 45.62 J/m [14]. The work of fracture measured in impact for rice straw FRP composites at volume fraction of 45% is 283 J/m [15]. The effect of sisal fiber surface treatments on the fiber-matrix-interfacial adhesion and mechanical properties of the composites were studied [16]. Flexural and impact properties of banana FRP composites showed maximum value at 30 mm length at 30 vol % [17].

In the present research two varieties of okra (botanicaaly called as "Abelmoschus esculentus") fiber is taken for the preparation of composites. It is referred by a synonym "Hibiscus esculentus L".

Hybrid okra variety 2405133, supplied by Syngenta India Limited, Shivaji Nagar, Pune, India. The characteristics of seed are as follows.

Germination (Min.)       65%
Physical purity (Min.)   99%
Inert matter (Max.)       1%
Moisture (Max.)           8%
Genetic purity (Min.)    95%

The chemical used for seed treatment is THIRAM.

Hybrid okra INRA-32, supplied by Prabhkar hybrid seeds, Gandhi nagar, Bangalore, India.

The characteristics of seed are as follows.

Kind                     Bhendi

Germination (Min.)       65%
Physical purity (Min.)   98%
Inert matter (Max.)       2%
Moisture (Max.)           6%
Genetic purity (Min.)    98%

Experimental Work

Materials

Fiber

Hybrid okra variety 2405133 fiber extraction

The removed okra stems are placed in a pit containing stagnant mud water for 6 days (i.e. 30th August, 2008 to 4th September, 2008) at ambient conditions. On 7th day i.e. 5th September, 2008 the stems are washed with sufficient quantity of water till complete pulp is detached from fiber. Then the fiber is dried for 7 days at ambient conditions. The fiber obtained is 5 ft. to 7 ft. long. Up to 2 ft. fiber length okra fiber is in woven form and remaining length of fiber is individual. Now onwards this is called as Okra woven fiber variety 1 (OW FV1) and Okra individual fiber variety 1 (OI FV1).

Hybrid okra Indra-32 fiber extraction

The removed okra stems are dried at atmospheric condition for 14 days (i.e. 2nd December 2008 to 15th December, 2008). The dried okra stems are placed in a pit containing stagnant mud water for 2 days (i.e. 15th December 2008 to 18th December, 2008) at ambient conditions. On 3rd day i.e. 19th December, 2008 the stems are washed with sufficient quantity of water till complete pulp is detached from fiber. Then the fiber is dried for 4 days at ambient conditions. The fiber obtained is 3.6 ft. to 7 ft. long. Up to 1.6 ft. fiber length okra fiber is in woven form and remaining length of fiber is individual. Now onwards this is called as Okra woven fiber variety 2 (OW FV2) and Okra individual fiber variety 2 (OI FV2).

Matrix

Ecmalon 4413 general purpose unsaturated polyester resin of medium reactivity is used in the present investigation. The properties of the liquid resin are tested in accordance with IS 6746-1994 and the values can vary within tolerances mentioned therein.

Appearance                           Clear
Viscosity @ 25[degrees]C             500 (Brookfield viscometer)
Specific gravity (25/25[degrees]C)   1.13
Acid value (mgKOH/g)                 25
Volatiles @ 150[degrees]C (%)        35
Gel time @ 25[degrees]C (minutes)    20

The resin contains a volatile monomer with a flash point at 32[degrees]C and is of moderate fire hazard.

Accelerated environmental conditions on okra fiber: Acid Rain

Increasing the utilization of automobiles, industries, and power plants leads to more and more pollutants emitted into the atmosphere and causing very serious disasters.

Oxides of sulphur and nitrogen originating from industrial operations and fossil fuel combustion are the major sources of acid forming gases. Acid forming gases are oxidized over several days by which time they travel thousands of kilometers. In the atmosphere these gases are converted to sulfuric acid and nitric acid. Hydrogen chloride emissions form hydrochloric acid. These acids cause aid rain. Acid rain is only one component of acidic deposition. Acidic deposition is the total of wet deposition (acid rain) and dry deposition. This is schematically represented in Fig. 1 [18].

[FIGURE 1 OMITTED]

The detailed photo chemical reactions in the atmosphere are [19]

NO + [O.sub.3] [right arrow] N[O.sub.2] + [O.sub.2] N[O.sub.2] + [O.sub.3] [right arrow] N[O.sub.3] + [O.sub.2] N[O.sub.2] + N[O.sub.3] [right arrow] [N.sub.5][O.sub.5] [N.sub.5][O.sub.5] + [H.sub.2]O [right arrow] 2HN[O.sub.3]

HN[O.sub.3] is removed as a particulate nitrates after reaction with bases (N[H.sub.3], particulate lime)

S[O.sub.2] + 1/2 [O.sub.2] + [H.sub.2]O [right arrow] [H.sub.2]S[O.sub.4]

The presence of hydrocarbons and NOx steps up the oxidation rate of the reaction. In the water droplests, ions such as Mn(II), Fe(II) and Cu(II) catalyse the oxidation reaction. Soot particles are also known to be strongly involved in catalyzing the oxidation of S[O.sub.2]. HNO3 and and H2SO4 combine with HCl from HCl emission (both by natural and anthropogenic sources) to generate acid precipitation which is known as acid rain. In Greece and Italy, invaluable stone statues have been partially dissolved by acid rain. The Taj mahal in India faces the same at present.

To evaluate the impact of acidic rain on plants there by fiber, accelerated environmental conditions are created through the reaction of okra fiber with sulfuric acid (H2SO4) i.e. chemical treatment (CT-4). Chemically treated fiber is used for the preparation of flexural and impact testing specimens and the properties of composites were determined and compared with untreated ones.

Chemical treatment (CT)

Extracted hybrid okra fiber is treated with different chemicals to investigate the variation in the properties after treatment.

* Chemical treatment-4 (CT-4): OW FV2 and OI FV2 are treated with 0.25 M NaOH solution for 5 hour 55 minutes. Pre treated sodium hydroxide fiber is treated with 0.01265 M KMnO4 solution in presence of 0.003752 M [H.sub.2]S[O.sub.4] for a period of 2 minutes. Now onwards it is OW FV2 CT-4, OI FV2 CT-4.

* Chemical treatment-7 (CT-7): OW FV1 and OI FV1 are treated with 0.1875 M NaOH solution for 13 hours. Now onwards it is OW FV1 CT-7, OI FV1 CT-7.

Preparation and testing of samples

(i) Moisture removal: The fiber is placed in a NSW-143 Oven Universal (Super deluxe model), supplied by Narang Scientific Works Private Limited, New Delhi, India, at a temperature of 70[degrees]C for 1 hour. Then fiber is allowed to cool to room temperature. The fiber is then taken out for the preparation of composite specimen.

(ii) Flexural testing: The specimens were prepared, conditioned and tested according to ASTM D 790-[07.sup.[euro]1] [19]. PC 2000 Electronic Tensometer, supplied by Kudale Instruments Private Limited, Pune, India is used for flexural testing.

(iii) Impact testing: The specimens were prepared, conditioned and tested according to ASTM D 6110-08 [20]. Specimens were prepared having a width of 10 mm and 12.7 mm. Motorized notch cutter, Computerized Izod / Charpy Impact tester, supplied by International Equipments, Mumbai, India is used for cutting the notch on the specimen and Impact testing respectively.

Results and Discussion

Flexural strength, flexural modulus, specific flexural strength and specific flexural modulus of all the okra fiber reinforced polyester composites considered in the present study increases with increasing percentage volume fraction of fiber.

OW FV2 CT-4 FRP composites showed less flexural strength than OW FV1 FRP composites at all volume fractions considered in the study even though okra woven FV2 is chemically treated with NaOH and KMn[O.sub.4] Fig. 2. The possible reason is okra FV2 is dried in ambient conditions for 14 days; thereby fiber lost its strength and sulfuric acid in CT-4 decreased the strength of fiber.

Flexural strength of OW FV1 fiber reinforced polyester composites is 16.02 %, 43.73 %, 180.33 % more than OW FV2 CT-4 FRP composites, OW FV1 CT-7 FRP composites and plain polyester specimens (i.e. [V.sub.f] = 0 ) respectively.

[FIGURE 2 OMITTED]

OI FV1 FRP composites flexural strength is 31.09 %, 24.66%, 231.68% higher than OI FV2 CT-4, OI FV1 CT-7 FRP composites and plain polyester specimens respectively Fig. 3.

[FIGURE 3 OMITTED]

The basis of the superior structural performance of the composite material lies in the high specific strength and high specific stiffness and in the anisotropic and heterogeneous character of the material [20].

The specific flexural strength of OW FV1 FRP composites is 16.88 %, 52.13%, 208.24 % higher than OW FV2 CT-4, OW FV1 CT-7 FRP composites, plain polyester specimens respectively Fig. 4.

[FIGURE 4 OMITTED]

Whereas OI FV1 FRP composites showed a specific flexural strength of 18.95 %, 36.44 %, 263.87 % more than OI FV2 CT-4, OI FV1 CT-7 FRP composite specimens and plain polyester specimens respectively Fig. 5.

Flexural modulus of OW FV2 CT-4 FRP composites is increasing with increasing volume fraction of fiber and it is 1.344 times, 1.134 times higher than OW FV1 and OW FV1 CT-7 FRP composites Fig. 6.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

Flexural modulus of OI FV2 CT-4 is 1.109 times, 1.257 times higher than OI FV2 CT-4 and OI FV1 CT-7 FRP composites respectively Fig. 7.

[FIGURE 7 OMITTED]

Specific flexural modulus of OW FV2 CT-4 FRP composite is 1.334 times, 1.192 times more than OW FV1, OW FV1 CT-7 FRP composite specimens respectively Fig. 8.

[FIGURE 8 OMITTED]

Specific flexural modulus of OI FV1 FRP composite specimens is 1.23 times, 1.375 times more than OI FV2 CT-4, OI FV1 CT-7 FRP composite specimens Fig. 9.

[FIGURE 9 OMITTED]

Flexural strength and flexural modulus of okra fiber reinforced polyester composites at highest volume fraction is shown in Fig. 10 & Fig. 11.

The values obtained are compared with the values in the literature and is given below.

The values indicated with red color in table (i.e. from literature) are having less & the values indicated with blue color are having more flexural strength, flexural modulus, specific flexural strength and specific flexural modulus than the okra fiber (untreated and chemically treated) reinforced polyester composites.

Impact resistance of okra FRP composites increased with increase in volume fraction of fiber. OI FV1-10 reinforced polyester composites showed 45.32 % more impact resistance than OW FV1-10 at a volume fraction of 27.33 % Fig. 12. With increasing width of specimen form 10 mm to 12.7 mm the impact resistance of OW FV1-12.7 and OI FV1-12.7 increases. This is due to increase in width of the specimen there by more fiber is incorporated in the specimen there by enhancing the impact resistance Fig. 13.

[FIGURE 12 OMITTED]

Conclusions

(1) Hand lay-up technique will be used successfully for the preparation of okra fiber reinforced polyester composites.

(2) Fiber is cheap and biodegradable there by more useful to environment by decreasing hazardous waste generated form synthetic fibers like glass, carbon, Kevlar etc.

(3) From the flexural testing comparison table it is very clear that flexural strength, flexural modulus and specific flexural strength and specific flexural modulus is more in most of the FRP composites i.e. jute, sisal, banana, flax, bagasse fiber reinforced composites.

(4) According to ASTM there is a possibility of varying width of impact testing sample. Impact resistance specimen width 12.7 mm is preferable to know the maximum impact resistance.

(5) Present trend of utilizing automobiles, industries, power plants etc. on biotic community like plants is clearly visible from the flexural and impact testing graphs. There is a clear decline in the values.

(6) Effect of acid rain is dangerous to the plants, which has been proved from the present research by testing the Okra fiber (treated with H2SO4) reinforced polyester composites at flexural and impact loadings.

References

[1] Ulku Yilmazer, 1992, "Tensile, Flexural and impact properties of a thermoplastic matrix reinforced by glass fiber and glass bead hybrids", Composites Science and Technology, 44, pp. 119-125.

[2] Munikenche Gowda T, Naidu A C B, Rajput Chhaya, 1999, "Some mechanical properties of untreated jute fabric-reinforced polyester composites", Composites Part A: applied science and manufacturing, 30, pp. 277-284

[3] Yan Li, Yiu-Wing Mai, Lin Ye, 2000, "Sisal Fibre and its composites: a review of recent developments", Composites Science and Technology, 60, pp. 2037-2055.

[4] Min Zhi Rong, Ming Qiu Zhang, Yuan Liu, Gui cheng yang, han Min Zeng, 2001, "The effect of fiber treatment on the mechanical properties of unidirectional sisal-reinforced epoxy composites", Composites Science and Technology, 61, pp. 1437-1447.

[5] Ray D., Sarkar B.K., Rana A.K., Bose N.R, 2001, "The mechanical properties of vinylester resin matrix composites reinforced with alkali-treated jute fibers", Composites Part A: applied science and manufacturing, 32, pp. 119-127.

[6] Canche-Escamilla G., Rodriguez-Laviada J., Cauich-Cupul J.I., Mendizabal E., Puig J.E., Herrera-Francho P.J., 2002, "Flexural, impact and compressive properties of a rigid-thermoplastic matrix/cellulose fiber reinforced composites. Composites Part A: applied science and manufacturing, 33, pp. 539-549.

[7] Seena Joseph, Sreekala M.S., Oommen Z., Koshy P., Sabu Thomas, 2002, "A comparasion of the mechanical properties of phenol formaldehyde composites reinforced with banana fibers and glass fibers", Composites Science and Technology, 62, pp. 1857-1868.

[8] Arbelaiz A, Fernandez B, Cantero G, Llano-Ponte R, Valea A, Mondragon I, 2005 "Mechanical properties of flax fiber/poly propylene composites. Influence of fiber/matrix modification and glass fiber hybridization", Composites Part A: applied science and manufacturing, 36, pp. 1637-1644.

[9] Guduri B.R., Rajulu A.V., Luyt A.S., 2006, "Effect of Alkali treatment on the Flexural Properties of Hildegardia Fabric Composites", Journal of Applied Polymer Science. 102, pp. 1297-1302.

[10] Harriette L. Bos, Jorg Mussig, Martien J A, Van den Oever, 2006, "Mechanical properties of short-flax-fiber reinforced compounds", Composites Part A: applied science and manufacturing, 37, pp. 1591-1604.

[11] Cao Y, Shibata S, Fukumoto I, 2006, "Mechanical properties of biodegradable composites reinforced with bagasse fiber before and after alkali treatments", Composites Part A: applied science and manufacturing, 37, pp. 423-429.

[12] Chen-Feng Kuan, Hsu-Chiang Kuan, Chen-Chi M. Ma, Chien-Ming Huang, 2006, " Mechanical, thermal and morphological properties of water-cross linked wood flour reinforced linear low-density polyethylene composites", 37, pp. 1696-1707.

[13] Ratna Prasad A V, Murali Mohan Rao K, Anil Kumar M, 2006, "Flexural properties of rice straw reinforced polyester composites", Indian journal of fibre and textile research. 31, pp. 335-338.

[14] Ratna Prasad A V, Murali Mohan Rao K, Mohan Rao K, Gupta A V S S K S, 2006, "Effect of fibre loading on mechanical properties of arecanut fibre reinforced polyester composites", National Journal of Technology. 2, pp. 5662.

[15] Ratna Prasad A V, Murali Mohan Rao K, Anil Kumar M, 2006, "Tensile and impact behaviour of rice straw reinforced polyester composites", Indian journal of fibre and textile research, 32, pp. 399-403.

[16] Suchada Tragoonwichian, Nantaya yanumet, hatsuo ishida, 2007, "Effect of fiber surface modification on the mechanical properties of sisal fiber reinforced benzoxazine/epoxy composites based on aliphatic diamine benzoxazine" Journal of Applied polymer science, 106, pp. 925-2935.

[17] Sreekumar P A, Pradesh Albert, Unnikrishnan G, Kuruvilla Joseph, Sabu Thomas, 2008, "Mechanical and water sorption studies of ecofriendly banana fiber reinforced polyester composites fabricated by RTM", Journal of Applied polymer science, 109, pp. 1547-1555.

[18] Kaushik, Anubha, Kaushik, C.P., 2009, "Environmental Studies", New Age International Publications", 3rd Edition.

[19] DE A.K., 2007, "Environmental Chemistry", New Age International Publications, 6th Edition.pp, pp. 128-129.

[20] ASTM D 790-[07.sup.[euro]1]: Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials

[21] ASTM D 6110-08: Standard Test Method for Determining the Charpy Impact Resistance of Notched Specimens of Plastics

[22] Daniel Isaac M., Ori Ishai: Engineering Mechanics of composite materials. Oxford University Press. pp. 7 (1994)

N. Srinivasababu (1) *, K. Murali Mohan Rao (2) and J. Suresh Kumar (3)

(1) Assistant professor, Department of Mechanical Engineering, PVP Siddhartha Institute of Technology, Vijayawada, India

(1) * Corresponding author E-mail: cnjlms22@yahoo.co.in

(2) Principal, Sri Viveka Institute of Technology, Madalavarigudem, India

(3) Associate Professor, Mechanical Engineering Department, JNT University, Hyderabad, India

Composites
                                Flexural
                                strength                Flexural
                                   (MPa)           modulus (GPa)

                                Values obtained the presresearch

OW FV1 FRPC                       101.93                    4.53

OW FV2 CT-4                        87.85                    6.09

OW FV1 CT-7                        70.92                    5.37
FRPC

OI FV1 FRPC                        120.6                    9.97

OI FV2 CT-4                           92                    8.99

OI FV1 CT-7                        96.74                    7.93

                           Values according to in the literature

Jute reinforced                     92.5                     5.1
polyester
composites [2]

Untreated sisal/                   59.57                   11.94
polyester
composites [3]

N--substituted                     76.35                   15.35
methacrylamide
treated sisal/
polyester [3]

Silane treated sisal               96.88                   19.42
/polyester [3]

Titanate treated                   75.59                   15.13
sisal/polyester
[3]

Zirconate treated                  72.15                   14.46
sisal/polyester
[3]

Untreated jute/                    106.3                    4.22
vinyl ester
composite 8 vol%
[5]

Banana/PF                             50                   2.481
composites at 40
mm fiber length
[7]

Glass/PF                              55                   3.781

composites at 50
mm fiber length
[7]

Banana/PF                             50                     2.4
composites at 45
wt % fiber loading
[7]

Glass/PF                              73                   6.454
composites at
40 wt % fiber
loading [7]

Glass/unmodified       84.0 [+ or -] 2.2    5.119 [+ or -] 0.181
PP composites [8]

Flax/MAPP PP           58.3 [+ or -] 0.8     3.985 [+ or -] 0.12
composites [8]

Flax/MA +              76.0 [+ or -] 1.9    5.495 [+ or -] 0.311
Peroxide PP
composites [8]

Flax/VTMO +            72.3 [+ or -] 2.4     5.374 [+ or -] 0.22
peroxide PP
composites [8]

20 wt % untreated                  31.19                 1.13687
bagasse fiber
composite [11]

20 wt % alkali                     34.71                 1.32172
treated bagasse
fiber composite
[11]

35 wt % untreated                  38.37                 1.45181
bagasse fiber
composite [11]

35 wt % alkali                     43.96                 1.62236
treated bagasse
fiber composite
[11]

50 wt % untreated                  40.16                 1.84134
bagasse fiber
composite [11]

50 wt % alkali                     46.05                 2.03137
treated bagasse
fiber composite
[11]

65 wt % untreated                  43.87                 2.29202
bagasse fiber
composite [11]

65 wt % alkali                     50.86                 2.67373
treated bagasse
fiber composite
[11]

Rice straw FRP                      66.3                    2.63
composites [13]

Arecanut FRP                       59.17                   2.896
composites [13]

Banana polyester         57 [+ or -] 2.2   2.329 [+ or -] 0.0052
composites at 30
vol % with 10 mm
fiber length [17]

Banana polyester         66 [+ or -] 0.9   2.601 [+ or -] 0.0046
composites at 30
vol % with 20 mm
fiber length [17]

Banana polyester         78 [+ or -] 3.2   2.997 [+ or -] 0.0038
composites at 30
vol % with 30 mm
fiber length [17]

Banana polyester         69 [+ or -] 2.4   2.684 [+ or -] 0.0064
composites at 30
vol % with 40 mm
fiber length [17]

                                Specific             flexural
Composites                      flexural             Specific
                                strength              modulus
                       (Mpa/[kgm.sup.-3]   (Mpa/[kgm.sup.-3])
                           * [10.sup.-3]        * [10.sup.-3]

                             Values obtained the presresearch

OW FV1 FRPC                        90.87                 4.04

OW FV2 CT-4                        77.74                 5.39

OW FV1 CT-7                        59.73                 4.52
FRPC

OI FV1 FRPC                       107.27                 8.87

OI FV2 CT-4                        90.18                 7.21

OI FV1 CT-7                        78.62                 6.45

                        Values according to in the literature

Jute reinforced                       --                   --
polyester
composites [2]

Untreated sisal/                      --                   --
polyester
composites [3]

N--substituted                        --                   --
methacrylamide
treated sisal/
polyester [3]

Silane treated sisal                  --                   --
/polyester [3]

Titanate treated                      --                   --
sisal/polyester
[3]

Zirconate treated                     --                   --
sisal/polyester
[3]

Untreated jute/                       --                   --
vinyl ester
composite 8 vol%
[5]

Banana/PF                             --                   --
composites at 40
mm fiber length
[7]

Glass/PF                              --                   --

composites at 50
mm fiber length
[7]

Banana/PF                             49                 2.33
composites at 45
wt % fiber loading
[7]

Glass/PF                              46                4.059
composites at
40 wt % fiber
loading [7]

Glass/unmodified                      --                   --
PP composites [8]

Flax/MAPP PP                          --                   --
composites [8]

Flax/MA +                             --                   --
Peroxide PP
composites [8]

Flax/VTMO +                           --                   --
peroxide PP
composites [8]

20 wt % untreated                     --                   --
bagasse fiber
composite [11]

20 wt % alkali                        --                   --
treated bagasse
fiber composite
[11]

35 wt % untreated                     --                   --
bagasse fiber
composite [11]

35 wt % alkali                        --                   --
treated bagasse
fiber composite
[11]

50 wt % untreated                     --                   --
bagasse fiber
composite [11]

50 wt % alkali                        --                   --
treated bagasse
fiber composite
[11]

65 wt % untreated                     --                   --
bagasse fiber
composite [11]

65 wt % alkali                        --                   --
treated bagasse
fiber composite
[11]

Rice straw FRP                      43.7                1.358
composites [13]

Arecanut FRP                        57.2                2.799
composites [13]

Banana polyester                      --                   --
composites at 30
vol % with 10 mm
fiber length [17]

Banana polyester                      --                   --
composites at 30
vol % with 20 mm
fiber length [17]

Banana polyester                      --                   --
composites at 30
vol % with 30 mm
fiber length [17]

Banana polyester                      --                   --
composites at 30
vol % with 40 mm
fiber length [17]

Figure 10: Flexural strenght of okra fiber (before and after chemical
treatment reinforced polyester composites at highest percentage volume
of okra fiber.

Flexural      % Volume
strength      fraction of
(Mpa)         fiber

OW FV1CT-7   24.05
OW FV2CT-4   26.72
OW FV1       26.86
OI FV2CT-4   27.86
OI FV1CT-7   28.3
OI FV1       35.07

Figure 11: Flexural modulus of okra fiber (before and after chemical
treatment reinforced polyester composites at highest percentage volume
fraction of okra fiber.

Flexural     % Volume
modulus      fraction of
(Gpa)        fiber

OW FV1CT-    24.05
OW FV2CT-4   26.72
OW FV1       26.86
OI FV2CT-4   27.86
OI FV1CT-7   28.3
OI           35.07

Figure 13: Impact resistance of okra fiber reinforced polyester
composites at highest percentage volume fraction of okra fiber.

Flexural     % Volume
resistance   fraction of
(J/m)        fiber

OW FV1-10          23.19
OI FV1CT-4-10      25.51
OI FV1-10          27.33
OW FV1-12.7        27.87
OI FV1-12.7        33.34
OI FV1-CT-4-12.7   38.52