Experimental Investigation on Effect of Weight Fraction of Sisal Fiber on Mechanical Properties of Sisal-E-Glass Hybrid Polymer Composites

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Introduction
Nowadays, mixing natural fbers with synthetic fbers is a well-known approach to get more advantages over using only pure synthetic fbers.Tis is due to the fact that natural fbers have low cost, ease of availability, less health impact, and easy biodegradability.However, the mechanical properties of natural fbers are not good as compared with those of synthetic fbers.So, in order to improve the mechanical properties of natural fbers, researchers are always in search of solutions in various directions.Mixing/hybridization of synthetic fbers to natural fbers are taken as the efective and cheaper solution.Te authors in [1] studied the mechanical properties of synthetic-natural fber hybrid composites, in which carbon nanofber (synthetic fber) and rice husk (natural fber) were used as reinforcements and bisphenol was used as a matrix.From the results, it was observed that the mechanical properties (including tensile, compression, and fexural) were improved by 12% for the reason of adding rice husk fber to carbon nanofber.Reference [2] also investigated the hybridization efect of natural fbers on synthetic (glass fbers) fbers for application in the pipe industry by using natural fbers including Kenaf, hemp, and fax.Te tensile and fexural behaviors of hybrid natural fber/glass reinforced epoxy composites in the form of laminates and laminas were the primary features investigated in this study.From the result, it was observed that laminas that were made from glass fber have greater mechanical properties than laminas made with natural fbers.Also, using natural/glass fber results in a 20% and 23% reduction in cost and weight, respectively, as compared to existing plastic and metallic pipes.
Te most common problem of using natural fbers as reinforcements is poor adhesion bond with matrix due to the existence of hydrophilic properties in fber and hydrophobic properties in polymer matrices.In addition, high water absorption capacity and relatively lower durability are other challenges that restrict their industrial application and production of natural fbers in the real world, and this is the root cause which reduces the mechanical properties of natural fbers [3,4].However, in order to change the characteristics of natural fbers for industrial application as reinforcement, many schemes and techniques have been used, including the incorporation of coupling agents and the use of diferent treatment methods.
On the other hand, in the study reported by [5], the mechanical properties (tensile strength, fexural strength, and modulus of elasticity) of hybrid composites of sisal fbers with glass fber in an epoxy polymer matrix were evaluated.From the results, it has been observed that by mixing sisal and glass fbers, the tensile strength increased by 86% than that of pure sisal and the elastic modulus also increased by 64%.In the bending tests, the results showed a performance of 19% for the maximum stress and 38% in the breaking stress for the hybrid composites.Te fbers were treated in a sodium hydroxide solution (10% by weight) and subjected to tensile tests in a universal testing machine.As stated by [6], mixing glass fber to natural fbers improved the mechanical properties of natural fbers.In this study, epoxy was used as matrix and sisal fber was treated by acetylene to increase the interfacial bonding between reinforcement and epoxy matrix.From the results, it has been observed that tensile and fexural strength of hybrid composite increased by 4% and 6%, respectively.In a similar manner, [7] investigated the mechanical properties including tensile, fexural, and impact strengths of natural fbers (sisal and jute) to glass fbers, in which sisal-jute-glass fber reinforced polyester composites were manufactured by manual hand layup.Te interfacial properties, internal cracks, and internal structures of the fractured surfaces were evaluated by using the scanning electron microscope (SEM).From the results, it has been observed that adding sisal and jute to glass fber can improve its properties.
In the research conducted and reported by [8], the tensile, fexural, and impact properties of the composite improved when sisal fber was mixed to glass fber.Te hybridization also reduced the environmental efects.In a similar manner, the authors in [9] reported that hybridization of natural fbers with glass fbers allowed a signifcantly improved heat transport ability of the composite.Furthermore, the authors in [10] stated that hybridization of natural fbers with small amounts of synthetic fbers makes natural fber composites more suitable for technical applications such as automotive interior parts.For this study, injection-molded short hemp fbers and hemp/glass fber hybrid with polypropylene was selected as a matrix material.From the results, it has been observed that both the impact and bending properties of the composites can be improved by adding glass fbers.In a similar manner, the thermal properties and moisture resistance capacity of composites were modifed by adding glass fber into hemp/polypropylene composites.
Moreover, reference [11] studied the efect of hybridization of glass fber with a fax fber reinforced polypropylene matrix on the mechanical properties as well as the efect of treating fax fber by chemicals on mechanical properties.From the study, they reported that the ratio of the fbers (glass/fax) has signifcantly afected both the tensile strength and the elastic modulus of hybrid composites.Te other problem comes with using natural fbers as reinforcement in various applications includes durability and lower aging of natural fbers.Tis hinders the wider use of natural fbers.Reference [12] studied the efect of hybridizing bamboo fbers with glass fbers on the mechanical properties of hybrid composites.From this study, both the elastic modulus and tensile strength of glass/bamboo fber reinforced polypropylene hybrid composites were greatly decreased after long period of time.Similar to [12], the efect of hybridizing natural fber by synthetic fber was also studied by [13] using curaua fbers and glass fbers as reinforcement.Tensile and fexural strengths were the parameters used for mechanical properties characterization.From the result, it has been observed that both the tensile and fexural properties of composites were improved by adding glass fber for a higher volume fraction.
References [14][15][16][17] investigated the efects of adding glass fber into sisal fber by using a polymer matrix on tensile properties.As stated by [15], the tensile strength of the sisal/glass hybrid composite is greater than the tensile strength of individual fbers.In addition, this study reported that the tensile strength of the sisal/glass hybrid mainly depends on the weight fraction of glass rather than the sisal weight fraction.Reference [14] also stated that the mechanical properties of PALF and sisal fber are improved by adding the glass fber in to it.Furthermore, [18] conducted research on the efect of glass fber hybridization on the physical properties of sisal-polypropylene composites.From the results, it was concluded that mixing glass fber into the sisal fber reinforced by polypropylene matrix composites can improve tensile, fexural, and impact strengths.In addition, adding glass fber improved the thermal properties and water resistance of the composites.
Te efect of chemical treatment on the mechanical properties of natural fbers is also one of the most investigated areas.Tis is because the major problem of natural fber composites originates from the hydrophilic nature of the fber and the hydrophobic nature of the matrix.Te inherent incompatibility between these two phases results in weakening the bonding at the interface.Te hydrophilicity of natural fbers results in high moisture absorption and weak adhesion to hydrophobic matrices.Te natural fbers can be treated to improve the adhesion to matrix materials.In addition, most natural fbers have low degradation temperatures, which make them incompatible with thermosets that have high curing temperatures.Tis also restricts natural fber composites to limit them to relatively low-temperature applications [19].To solve this negative efect of natural fbers, the natural composites 2 Advances in Materials Science and Engineering should be treated.As stated by [20,21], modifying the fber surface by using chemical treatment can enhance bond strength between the fber and the matrix.Chemical treatment is also an efective way to clean the fber surface, chemically modify the surface, stop the moisture absorption process, and increase the surface roughness.In addition, as reported by [22], the overall mechanical properties of natural fber reinforced polymer composites are highly dependent on the morphology, aspect ratio, hydrophilic tendency, and dimensional stability of the fbers used.Te signifcance of chemically-treated natural fbers is seen through the improvement of the mechanical strength and dimensional stability of the resultant composites.
Efect of treating natural fbers and various methods of treating natural fbers have been researched by diferent researchers.As stated by [17], the interfacial adhesion between the matrix and the fbers mainly afects the tensile properties of natural fbers reinforced by either thermoset or thermoplastic matrix.Not only interfacial adhesion between matrix and fbers but also the tensile strength of natural fbers can be greatly afected by the weight fraction of fbers.
Reference [23] presented the efect of alkali treatment on the properties of natural fbers.Other properties including mechanical, physical, thermal, and tribological properties of biocomposites were also studied in this research.From the results, it was conclude that the properties of bio composite were improved by a great extent by alkali treatment.According to the study reported by [24], raw sisal and raw jute fber reinforced epoxy matrix composites are treated by sodium hydroxide, where both jute and sisal fbers were treated with 20% sodium hydroxide for 2 hours.Te aim of the study was to compare and analyze the mechanical properties of both treated and raw (sisal and jute) fbers.Furthermore, mechanical properties (tensile and fexural strength), water absorption, and morphological changes had been investigated on the prepared specimens.As indicated by the results, both treated jute and sisal fber reinforced epoxy composites showed better properties than raw jute and sisal.Reference [25] also investigated the infuence of fber treatment on the mechanical characteristics of unidirectional sisal-reinforced epoxy composites.In this research, alkalization, acetylation, cyanoethylation, the application of a silane coupling agent, and heating were selected as natural fber treating methods for the purpose of improving the its properties.From this study, it has been observed that when the treated fbers were incorporated into an epoxy matrix, it improves the adhesion force between the fbers and matrix.In the same way, treatments can signifcantly lead to the easy entrance of the matrix resin into the fbers, blocking the pullout of the cells.
From previous study, researchers tried to replace metallic materials by other advanced materials.Among their eforts, nowadays, replacing the existing metallic materials by composite materials is one of the widely adopted methods.Not only composite materials, but also light weight metallic materials like aluminums was used as solutions for the purpose of reducing the weight of components in previous times.However, the high cost of lightweight materials results in other problems and obstacles for using those lightweight materials as alternative materials.Furthermore, researchers decided to use synthetic fbers including carbon, glass, and aramid fbers as alternative materials for metallic materials especially for reducing the weight of components.Tis achievement was not with zero disadvantage because of the nonrenewability, health risks, and high costs that accompany the inventions of synthetic fbers.Te above listed problems can be solved by using natural fbers including the jute and hemp fbers.But, high water absorption and low mechanical properties of natural fbers limit their application.
Terefore, this article aims to investigate the efect of the weight fraction of natural fber (sisal) on the mechanical properties of sisal/E-glass reinforced hybrid composites by mixing both synthetic (E-glass), and natural fber (sisal) by collecting the high strength and stifness advantages from Eglass and the low health risk and low-cost advantages from sisal fbers in order to solve the problem of using synthetic and natural fber individually.

Materials.
In this research, the E-glass (Figure 1(a)) was purchased from World Fiber Glass and Water Proofng Engineering in Addis Ababa, Ethiopia, and the sisal fber (Figure 1(b)) was obtained from the Addis Ababa Science and Technology University campus.Te basic characteristics of E-glass fber [26] and sisal fbers [7,[26][27][28] are given in Tables 1 and 2, respectively.
Epoxy resin AY-105 with a brand name ("SYSTEM # 2000 EPOXY") was used as matrix material in this article.Tis is since epoxy shows superior mechanical properties when compared to polyester.Epoxy is used very efectively as an adhesive and as a laminating resin for many engineering applications.It ofers excellent moisture-barrier qualities when used in polymer composites.It binds extremely well to fbers for making fber reinforced polymer composites [29].It was obtained from Kadisco Paint and adhesive industry share company in Addis Ababa, and its properties are given in Table 3.
To convert the epoxy resin and monomer component from a liquid to a solid form, a hardener was used, which acts as a curing agent and catalyst so that it cures the epoxy into a strong adhesive.For this research, hardener HY-951 (curing agent) with the brand name ("SYSTEM # 2060 HARDENER") was obtained from Kadisco painting and adhesive company.Te volume ratio of resin to hardener was determined as 2 : 1 for better dimensionally stable laminates with free residual internal stresses.In addition, mold releasing agent (brand name HONEY WAX 250), which can prevent materials from sticking, was obtained from the local market (World Glass Fiber and Water Proofng PLC).

Sisal Fiber Extraction Process.
To extract the sisal fbers, hand/manual extraction process was used due to the unavailability and high cost of mechanical decortication.Te Advances in Materials Science and Engineering manual sisal extraction process also has advantages over mechanical decortication for extracting natural fbers because the method does not require a special tool, a skilled operator, or a low cost.Moreover, this method can be used in rural areas where there is no electric power.
After cutting the leaves of the sisal plant at their base with the help of a sickle as shown in Figures 2(a) and 2(b), the leaves were trimmed into two or three parts depending on the size of leaves in the longitudinal direction.Tis is done for ease of the fber extraction process.Ten, the peel was clamped between the wood plank and knife and hand-pulled gently in a longitudinal direction in order to remove the resinous material as shown in Figure 2(c).After the extraction process, the extracted sisal fber was washed with pure water in order to remove and separate unwanted dusts from the fber and it was dried in the sun.Eventually, the required fne fbers were obtained as shown in Figure 2(d).

Sisal Fiber Treatment
Process.Several research activities have been conducted to improve fber adhesion properties with the matrix through chemical treatments, because chemical treatments on reinforcing fber can reduce its hydrophilic tendency and thus improve compatibility with the matrix [30].Due to its broad availability, good modifcation characteristics, improved mechanical qualities, strong impact strength, and low cost, NaOH is the most often used chemical for treating natural fbers.When treating the natural fbers, the percentage of NaOH that is mixed with distilled water needs serious attention.Tis is due to the fact that percentages of alkali concentration afect the mechanical properties of natural fbers.When the percentage of NaOH is increased, it afects the fbers properties by reducing the adhesive, and bonding capacity during preparation of the composite samples [31].Te appropriate ratio of sodium hydroxide and distilled water is important parameters and need attention during treatment of natural fbers because treatment of natural fbers has direct efect on mechanical properties of natural fbers.On the other hand, the immersing time of natural fbers in sodium hydroxide and distilled water solution also has direct efect on mechanical properties of natural fbers.Excess of chemical solution (10%) did not only remove part of the boundary layers of the natural fbers but also causes some deterioration to the fber particles themselves that can reduce the overall tensile strength.On the other hand, if the percentages of sodium hydroxide are minimum, (below 4%) boundary layers of the raw fber are not completely removed.Hence, some weakness is observed in the strengths [32].In this article, based on several literature, the average value of 8% NaOH and 92% distilled water (that was obtained from atomic laboratory and teaching material PLC, Kirkos subcity, Addis Ababa) was mixed at room temperature was used.
After agitating the sodium hydroxide in distilled water, the sisal fber was then immersed in the solution (NaOH and distilled water) for three hours, and the bucket was covered with a plastic sheet in order to avoid the interaction of sodium hydroxide with environments.Ten, it was washed several times with distilled water to neutralize it.Lastly, the fbers were allowed to dry in sun   3. Nowadays, the automotive and construction industries are the largest segments for natural fber composite applications [33].In addition, natural fber reinforced composites are also most promising and interesting for decking (furniture application), railing, plyboard, plastic lumber, and window/door applications [34].Moreover, applications of natural fbers including paper products, building materials, absorbents, and animal feeds [20].

Experimental Design.
In this research, the efect of fber weight fraction on mechanical properties such as tensile, compression, and bending (fexural) strengths were considered.Properties of the E-glass/sisal hybrid were calculated by the rule of mixtures approach.Tis was done due to the fact that the rule of mixtures is a method for estimating composite material properties based on the idea that a composite property is the volume-weighed average of the matrix and fber phases.It approximates parameters such as elastic modulus, mass density, and ultimate tensile strength, theoretically.Te mechanical properties of a fber reinforced composite are directly related to the amount of fber and matrix in the composite.Due to manufacturing characteristics, the fber volume ratios for the fabrication of composites lie between 50% and 65%.Tis is because an extremely high fber volume can lead to more delamination between the fbers.Due to a shortage of space for the matrix to properly surround and connect with the fbers, too much fber volume may also reduce the composite's strength.Terefore, 60% fber (E-glass and sisal), and 40% epoxy resins were selected as reinforcement and matrix, respectively, for this study.Te weight fraction selected in this article is shown in Table 4.

Fabrication of Hybrid Specimen.
Tere are diferent fabrication methods of composite laminates including, hand lay-up, autoclave molding, flament winding, pultrusion, and resin transfer molding.In some cases, the fabrication methods determine the shape and application of the composite.For instance, flament winding is generally used for making pipes and tanks to handle chemicals, autoclave forming is used to make complex shapes and fat panels for structures in which low void content and high quality are important, and resin transfer molding is extensively used in the automotive industry because short production runs are necessary [35].Among these, the hand lay-up process is selected for this article because it is the simplest and most widely used fabrication process of composite materials, and this method is commonly used when there is no need of special equipments for production of samples.It also requires low costs.Hand lay-up is widely used for thermoset composites, and it involves a manual mixing procedure of the fber and the matrix.In this process, the uniformity of the composite in terms of thickness, fber to matrix ratio, and void content throughout the sample depends on the workmanship skill [22].In addition, manually hand lay-up is mainly used for the fabrication of natural composite samples due to the problem of natural fbers with fow in injection molding machines, and it has lower elongation properties [36].
After deciding the method of composite laminate fabrication, the next task is preparing the mold that is used for the fabrication of laminates.Te mold may be made of wood, plastics, or metals depending on the number of parts, cure temperature, pressure, etc.In this research, the mold was made from wood (Figure 4(a)).After completing the preparation of the mold, Figure 4, the reinforcements (sisal and E-glass fbers) were cut as per the mold size and measured on the digital weighting machine (Figures 4(c) and 4(d)) to mixing appropriate fbers with matrix.Ten epoxy resin AY-105 and hardener HY-951 (curing agent) were mixed thoroughly for at least 5 minutes (Figure 4(e)).
After spraying the releasing agent (wax) (Figure 4(f )), epoxy was placed on the mold surface as shown in Figure 4(g).Ten, the frst layer of the fbers was placed at the surface of the mold (Figure 4(h)).Te main objective of applying the wax on the mold surface is to avoid the sticking of epoxy to the mold surface and to facilitate the removal of the fnished part.Te epoxy is uniformly distributed with the help of the brush.Te second layer of fbers is then placed on the epoxy surface, and a roller was moved with a mild pressure on the fber-epoxy layer to remove any air trapped as well as the excess epoxy present (Figure 4(i)).Te overall process is repeated for each layer of epoxy and fbers, till the required layers were obtained.After all required thickness was obtained, the mold cover was placed on the top of the mold and 5 MPa pressure was applied on it by using hydraulic pressing machine (Figure 4(j)) for the purpose of curing and to increase the bonding force between epoxy and fbers (E-glass and sisal fbers).After curing for a period of 24 hours, the mold was opened, and the fabricated sisal/Eglass hybrid composite specimen was taken out from the mold (Figure 4(k)) and cut into the required dimension based on ASTM standard specifcations and prepared for further tests.

Secting Sample Sample Size.
In order to study any property of a material, including mechanical properties, material should be sized according to the recommended standards (ISO, ASTM, etc.).Tis is since the specimens are cut according to the standards to get the required dimensions.Among the available standards, ASTM (American standard for testing material) is a well-known standard and many researchers use this standard.Tere are various ASTM standards for testing composite materials and for this article ASTM D3039, ASTM D3410, and ASTM D709 were selected.Tis is because these standards are widely selected by various researchers.As reported by [37,38], for tensile test, fexural test, and compression test, ASTM D3039, ASTM D3410, and ASTM D709, respectively, are convenient for testing composite materials.Te size of the sample used for this study, as recommended by ASTM standards, is shown in Table 5.

Tensile Test Results
. Te tensile test is the fundamental material characterization method for engineering applications in which the samples prepared as per ASTM standards were subjected to controlled tension force.In this research, the tensile test was performed by preparing three specimens of a hybrid E-glass/sisal hybrid of fve diferent weight fractions of (0%, 20%, 30%, 40%, and 60%) of E-glass fbers with (60%, 40%, 30%, 20%, and 0%) of sisal fbers, while the weight fraction of the epoxy matrix was kept constant at 40%.

Stress versus Elongation of Hybrid Composites.
Te stress-elongation (strain) is the basic parameters that are recorded during longitudinal tensile test on a universal testing machine.But, due to many factors including testing conditions, temperature efects, manufacturing errors since the specimens were fabricated by manual hand layup, and personal errors, the values of all specimens were not exactly   5(a)), while the highest weight fraction of sisal fber, i.e., lowest (zero) weight fraction of E-glass fber, has the lowest tensile strength (Figure 5(e)).In other words, the tensile strength decreases with an increasing weight fraction of sisal fber.Te tensile strength results of the fve diferent weight fractions of the composites are shown in Figure 6.From the bar graphs of the tensile strength results, the weight fraction of sisal fber mixed to E-glass fber did afect the longitudinal tensile strength of the E-glass/sisal hybrid samples.Te tensile strength improved with decreasing sisal fber weight fraction and an increasing weight fraction of the E-glass fber.Te results reported in this work agree with the result reported by [39] , which stated that the hybrid composites with a higher weight fraction of glass fber layers achieve higher values of tensile strength.In the article reported by [40] , it is also reported that by incorporating 20% of glass fber by weight improves the tensile strength of bamboo/ glass fber reinforced hybrid composites by 7%.Teir conclusion indicates that the tensile strength properties of the fabricated hybrid composite increased as the weight fraction glass fber content increased and decreased as the weight fraction of sisal increased.Tis is due to the fact that natural fbers have lower mechanical properties than synthetic fbers.Generally, this report agrees with the results reported by [41], which stated that natural fber composites are not having sufcient strength to replace the conventional materials and that the hybrid combinations of natural fbers are preferred for applications like automotive interior parts.
Te maximum longitudinal tensile strength was 464 MPa which occurred for the composites of 0% sisal and 60% Eglass with a 40% epoxy matrix.Te minimum longitudinal     Advances in Materials Science and Engineering tensile strength was 86 MPa which occurred for the composites of 60% sisal, and 0% E-glass with 40% epoxy.From the tensile test results, it is easily observed that the longitudinal tensile strength of 60% sisal and 0% E-glass fber reinforced composites tensile strength was decreased by about 81% when compared to the tensile strength of 0% sisal and 60% E-glass fber reinforced epoxy matrix composites.
In addition, the longitudinal tensile strength of 20S/40G, 30S/30G, and 40S/20S were decreased by 23%, 36%, and 59%, respectively, from longitudinal tensile strength of 0S/ 60G composites.As seen from the results, the longitudinal tensile strength of E-glass/sisal hybrid reinforced epoxy matrix composites decreases in a linear manner with an increasing weight fraction of sisal fber.Tis decrement in longitudinal tensile strength results from the lower bonding between sisal and E-glass fber.Moreover, the tensile strength of natural fbers (in this case, sisal) has lower tensile strength than synthetic (E-glass) fber.Te weight fraction of the matrix (epoxy) was kept constant at 40% throughout the test.

Flexural Test Results
. Flexural strength is the ability of the material to withstand bending forces applied perpendicular to its longitudinal axis.For the three-point bending test, three specimens for fve diferent weight fractions of Eglass and sisal fber with a constant weight fraction of matrix (epoxy) were prepared by manual hand layup as per ASTM D790 standard with the dimension of 150 mm × 20 mm × 4 mm.
Te fexural properties of sisal/E-glass hybrid reinforced composites of diferent weight fraction of sisal and E-glass fbers are shown in Figure 7.It is observed from the plots that the fexural characteristics of the composites are afected by the weight fraction of sisal fber.Tis result agrees with the result reported in [31].Te glass hybrid laminates have better fexural properties than the pure natural laminates, and the properties seem to be increasing with the addition of the weight fraction of glass fbers.Furthermore, as reported in [28], the hybrid composites with a higher weight fraction of glass fber have higher fexural properties than pure sisal composites.
Te plots in Figure 7 also show that the maximum fexural strength of 60G/0S is maximum, and its value is about 239 MPa, while the fexural strength of hybrid composites with 0G/60S is found to be about 98 MPa.From the fexural test results, it is easily observed that the fexural (bending) strength of 60% sisal and 0% E-glass fber reinforced composites strength decreased by 59% when compared to the bending strength of 0% sisal and 60% E-glass fber reinforced epoxy matrix composites.In addition, the fexural strength of 20S/40G, 30S/30G, and 40S/20S are decreased by 18%, 29%, and 50%, respectively, when the results compared with the fexural strength of 0S/60G composites.Tis decrement in fexural strength properties results from the lower fexural properties natural (sisal) and the lower bonding between natural (sisal) and synthetic (E-glass) fbers.Also, as seen from the results, the fexural strength of E-glass/sisal hybrid reinforced epoxy matrix composites decreases in a linear manner with an increasing weight fraction of sisal fber.From these results, we conclude that fexural (bending) stress decreases as the weight fraction of sisal fber increases.

Longitudinal Compression Test Results
. Te stresselongation (strain) is the basic parameter that is recorded during the longitudinal compression test on the universal testing machine.Te longitudinal compressive strengthelongation of E-glass/sisal hybrid laminates for each weight fraction of fbers is shown in Figure 8 below.Due to the same reason for the tensile test, however, the values of maximum longitudinal compressive stress for all specimens are not exactly the same, so the average value of the longitudinal compressive stress of those specimens is used in this article.
For the compression test, three specimens with fve diferent weight fractions of E-glass and sisal fber were prepared as per ASTM 3410D.Te dimension of the specimens was 50 mm long × 50 mm wide × 4 mm thickness.Te results of the average compressive strength of the three composites types are shown in Figure 8.As depicted, the composite 0G/60S has the lowest compressive strength, which is 17.1 MPa, whereas the composites of 60G/0S has the highest compressive strength which is equal to 40.1 MPa.From the compression test results, it is easily observed that the compressive strength of 60% sisal and 0% E-glass fber reinforced composites compressive strength was decreased by 57.4% when compared to the tensile strength of 0% sisal and 60% E-glass fber reinforced epoxy matrix composites.In addition, the compressive strength of 20S/40G, 30S/30G, and 40S/20S were decreased by 12.7%, 19%, and 40%,  Advances in Materials Science and Engineering respectively, when the results are compared with the compressive strength of 0S/60G composites.As seen from the results, the compressive strength of E-glass/sisal hybrid reinforced epoxy matrix composites decrease in linear manner with an increased weight fraction of sisal fber.Tis agrees with the study reported by [42] on the mechanical property of E-glass/sisal hybrid reinforced composites has the higher compressive strength than pure sisal composites.In addition, as stated by [43], the incorporation of natural fbers such as sisal/jute with glass fber composites has gained increasing applications both in many areas of engineering and technology.
For the sake of validation of the results of this study, the tensile strength and fexural strength results are summarized in Table 6 and compared with published work on the same topic.Tough the proportions of sisal fbers are diferent, the comparison shows that a higher weight fraction of sisal fber infuences (lowers) both the tensile and fexural strengths.

Conclusion
Research progress on the mechanical behavior and performance of composite materials reinforced with natural fbers has been a topic of interest in the past decades.Tis article investigates the efect of the weight fraction of the sisal fber on mechanical properties (tensile, compression, and fexural) of E-glass/sisal hybrid reinforced epoxy matrix composites.Te ultimate tensile strength, tensile modulus, and ultimate compressive strength of samples prepared as per ASTM standards were obtained experimentally.In order to improve the surface roughness and increase the adhesive bond capacity with matrix, the sisal fber was treated by 8% percentages of sodium hydroxide (NaOH) for three hours.
Based on the experiments conducted (tensile, compression, and fexural), the following conclusions can be drawn: (1) Weight fraction of the sisal fber added to the E-glass fber afects the mechanical properties in tensile, compression, and fexural tests.
(2) From tensile test results, adding the sisal fber to the E-glass fber decreases the tensile strength of hybrid laminates.But if the weight fraction of sisal mixed to E-glass fber increases, the tensile strength of the hybrid composite decreases.
(3) From the fexural test, adding the sisal fber to the E-glass fber afects the fexural properties of hybrid samples.But the efect of the weight fraction of the sisal fber has not shown a signifcant change in fexural properties.
(4) From the compression test, mixing the sisal fber to the E-glass fber reduces the compression properties of hybrid composites.Terefore, the longitudinal compressive stress of the E-glass/sisal hybrid sample greatly afects the compression properties of the hybrid composites.
(5) Generally, all samples consisting of 60% E-glass and 0% sisal fbers with a 40% epoxy matrix showed better mechanical properties than other hybrid samples.Te longitudinal tensile strength, longitudinal compressive strength, and the fexural strength of 60% E-glass, 0% sisal, and 40% epoxy matrix were observed to be 464 MPa, 40 MPa, and 239 MPa, respectively.
(6) Also, the lower mechanical properties were obtained in the samples that are made from 0% E-glass and 60% sisal fber with a 40% epoxy matrix.Teir tensile, fexural, and compression values are 86.4MPa, 98.4 MPa, and 17.1 MPa, respectively.Tis is due to the fact that natural fbers have lower mechanical properties when compared to synthetic fbers.

Figure 3 :
Figure 3: Sisal alkali treatment process, (a) apparatus required for treatment, (b) adding the distilled water to bucket, (c) adding the NaOH to distilled water, (d) preparing solution of NaOH and distilled water, (e) immersing the sisal fber in to solution, (f ) covering the bucket with plastic sheet, (g) washing the sisal fber by distilled water, and (h) drying the treated sisal fber in sun.

Figure 4 :
Figure 4: Laminates preparing procedure: (a) mold preparation process, (b) cutting the fbers in required dimension,(c and d) measuring the fbers and epoxy, (e) mixing the hardener and epoxy, (f ) spraying the wax to the mold surface, (g) placing the epoxy resin on mold surface, (h) placing the fbers in the mold, (i) applying pressure to provide good contact of fber and epoxy by roller, (j) curing the laminates under HPM, (k) removing the laminates from mold, and (l) cutting the laminates under pressing machine, in to ASTM standard dimension by hack saw.

Figure 5 :Figure 6 :
Figure 5: Stress versus elongation for various weight fraction of E-glass/sisal hybrid composites.

Figure 8 :
Figure 8: Longitudinal compressive stress of various weight fraction of fbers.
4Advances in Materials Science and Engineering light for 3 days.Te whole treatment process is shown in Figure

Table 4 :
Fibers versus matrix weight fraction.

Table 5 :
ASTM standard size of samples.

Table 6 :
Mechanical properties of sisal/glass hybrid composite.Tis article is only limited to the mechanical properties including the tensile, compression, and fexural strength of sisal-E-glass hybrid reinforced composites and epoxy matrix composites.Possible future works in this research include conducting microstructure studies using scanning electron microscopy (SEM).