Investigation on the effect of chemical treatment of hybrid reinforced polymer composites

Fiber matrix adhesion was promoted by hybrid fiber composite surface modifications using an alkaline treatment. However, it was found that the resulting strength and stiffness of the composite. The elastic modulus of the composite did not improve with the fiber surface modification. A notable disadvantage of natural fibers is their polarity which makes it incompatible with hydrophobic matrix. The defect can be remedied by chemical modification of fiber so as to make it less hydrophilic. The present contribution reports effects of fiber content and length on the mechanical properties of the banana and kenaf hybrid reinforced polymer composites. The composites prepared with alkali-treated banana and kenaf fibers were used for comparison of the properties. The fibers were subjected to 20 % of sodium hydroxide (NaOH) solution for 6 h. Besides, the fractured surfaces of composite specimen were investigated using scanning electron microscopic (SEM). An improvement in strength, stiffness and toughness was achieved by treating the fibers using NaOH solution. Morphological and structural changes were investigated using scanning electron Microscopic.


INTRODUCTION
Natural fiber reinforced composites have attracted the attention of research community mainly because they are turning out to be an alternate solution to the ever depleting petroleum sources.The production of 100 % natural fiber based materials has been extended to almost all fields.Nowadays, use of natural, cellulosic fibers as reinforcing fillers for commodity plastics has received much attention because of a number of advantages over traditional, inorganic ones such as good specific strength, high toughness, and good thermal insulation, less abrasion, minimal dermal and respiratory irritation, biodegradability, and natural abundance.Conventional and traditional fiber reinforced composite materials are composed of carbon fibers, glass fibers which are incorporated into polyester resin.These composite materials have excellent mechanical properties but these materials cause environmental pollution due to the non degradability of fibers.Chemical treatment of the fiber can clean the fiber surface .The kenaf core materials, which can be used as absorbents and animal bedding, have ready markets .The use of kenaf fiber as reinforcement has grown substantially in the past decade and they are other products, such as extruded plastic fencing, decking, and furniture padding.
Plant bast fibers, such as kenaf, hemp, and flax, have low density and high specific strength, and are of utmost interest in applications striving for lightweight and high strength.In the past decade, natural fiber composites with thermoplastic and thermoset matrices have been embraced by European car manufacturers and suppliers for door panels, seat backs, headliners, package trays, dashboards, and interior parts of automotives .The bast fibers exhibit a superior flexural strength and modulus of elasticity (MOE), but the leaf fibers show superior impact properties.Compared to glass fibers, the bast fibers tend to show approximately the same flexural strength and a higher MOE 1 .These fibers have many properties which make them an attractive alternative to traditional materials.They have high specific properties such as stiffness 2 , impact resistance 3 , flexibility 4 , and modulus 5 .In addition, they are available in large amounts 6 , and are renewable and biodegradable.Other desirable properties include low cost, low density, less equipment abrasion 4,[7][8][9] , less skin and respiratory irritation 10 , vibration damping 2,3 and enhanced energy recovery 10,11 .The glass and hemp fiber composites had specific tensile strength and tensile modulus in the same range 12 .Many types of naturally-derived cellulosic fibers have been explored as reinforcing fillers in commodity thermoplastics, some of which are fibers from rubber wood 13 , beech wood 14 , sisal 15 hemp 16 jute 17 kenaf 18 and ramie 19 .Uses of these fibers satisfy both economic and ecological interests.Hybrid composites including different types of plant fibers have also been obtained.Mwaikambo et.al 21 studied the chemical analysisand environmental durability of sisal/jute/ banana fiber reinforced polyester composites .The authors observed that .Pothan et al 22 investigated the influence of chemical modification of dynamic mechanical properties of banana fiber-reinforced polymer composites.maximum improvement in properties is observed for composites with 40% fiber loading, which is chosen as the critical fiber loading.Mechanical properties of woven banana fiber reinforced epoxy composites were studied 22 .A number of sialane coupling agents were used to modify the banana fibers.S.M.Sapuan 23 studied the experiments of tensile and flexural (three-point bending) tests .Three samples prepared from woven banana Fiber composites of different geometries were used in this research.The banana fiber-reinforced polyester composites were prepared using hand molding method or hand lay-up method.The effects of fiber content of banana fibers on mechanical properties such as tensile, flexural and impact of the composites were investigated and reported.Kenaf fibers have excellent mechanical proper ties and have potential to be outstanding reinforcing fillers in plastics.Zampaloni et al., 24 reviewed the fabrication of kenaf fiber reinforced polypropylene sheets that could be thermoformed for a wide variety of applications with properties that are comparable to existing synthetic composites.The chemical modification of kenaf fibers was carried out by A.M. Mohd Edeerozey 25 .Different concentrations of NaoH were used and the morphological changes were examined by SEM.Shinji Ochi 26 investigated the influence of fiber composite properties and mechanical properties of the unsaturated polyester based composites reinforced using banana/kenaf.In this paper, we seek to understand the fundamental mechanical properties of banana and kenaf fiber bundles, which is necessary to evaluate the natural fiber and fiber bundle reinforcing and mechanism in the composites.The tensile, flexural and impact behavior was evaluated at three percentage of fiber content

Materials
Banana (Musa sepentium)/Kenaf (Hibiscus cannabinus) was reinforced with unsaturated Polyester, which is used as the matrix material.Banana and Kenaf fibers were traditionally used in ropes, bags, toys, etc., Unsaturated polyesters are extremely versatile in properties and applications and have been a popular thermoset used as the polymer matrix in composites.Composites of three different compositions i.e. 30wt%, 50wt% and 60wt% are made.Specimens of suitable dimension are cut for different tests.The matrix material used in this investigation was based on commercially available polyester.The matrix was mixed with curing catalyst at a concentration of 0.01 w/w of the matrix for curing.

Preparation of Composites
The banana and kenaf fiber contents were set at 30%, 50% and 60% weight of the matrix.
The balance of the mixture was made up of the unsaturated polyester, always to give a total weight batch size of 100%.The fiber length maintained as 50 mm.Natural fiber has the tendency to absorb high content of moisture from atmosphere which cause swelling during compounding and hence, a decrease in mechanical properties.This fiber contents and length was chosen to observe the effect of fiber content and length on the mechanical properties.The natural fiber (banana, kenaf) reinforced polymer matrix composites were fabricated using moulding method.Unsaturated Polyester was used as matrix.For a proper chemical reaction cobalt naphthenate and methyl ethyl ketone were used as catalyst and accelerator respectively.Acrylic sheets with 300 mm x 300 mm x 5 mm dimensions and ASTM rubber with thickness of 3 mm were selected for the preparation of mould.

Material Characterization
Tensile test was performed on a 1000 Ton computer controlled universal testing machine according to the guidelines of ASTM D638 with a gauge length of 50.8 mm.The flexural tests were performed on the same machine as tensile tests using the 3-point bending method according to ASTM D790 standard with a gauge length of 50.8 mm with the cross head speed of 2mm/min.For statistical purpose, a total of six samples for each tests were carried out at room temperature.The impact test experiments were conducted according to ISO 180.The specimen is placed horizontally in the test bed.The pendulum is lifted and is made to hit the specimen from a height.All the test samples were notched.The test specimen was supported as a vertical cantilever beam and broken by a single swing of a pendulum.The pendulum strikes the face of the notch.Six specimens were tested to determine each of the following such as tensile strength, flexural strength and impact strength.The fractographic studies were carried out in detail on the tensile, flexural and impact fracture surfaces of hybrid composites using scanning Electron Microscopy (SEM).

RESULTS AND DISCUSSION
The effect of fiber content on the mechanical properties of banana and kenaf fiber composite is shown in Figs 1-3. the Tensile, flexural and impact strength for different compositions.Fig. 1 and 2 shows the variation of tensile and flexural strengths of the composites with the fiber content.A gradual increase in tensile strength as well as flexural strength with the weight fraction of fiber is noticed.It may be mentioned here that both tensile and flexural strengths are important for recommending any composite as a candidate for structural applications.

Fig. 1: Effect of fiber content and alkali treatment of fibers on tensile Strength of composite material with fiber content
It is due to that the impurities on the fibers are removed by alkali-treatment.The tensile strength of the composites at untreated condition having 30wt% was 27MPa.It was 30MPa at treated condition.The percentage of improvement was found to be 9%.The tensile strength of the composites at untreated condition having 50wt% was 36MPa.It was 37 MPa at treated condition.The tensile strength of the composites at untreated condition having 60wt% was 39MPa.It was 40 MPa at treated condition.The percentage of improvement was found to be 13%.
Generally, the impact resistance was not improved by fiber reinforcement for all fibers/matrix composite materials as shown in Figure 2. The low impact strength could be the results of weak interfacial bond strength between the fibers and the polyester material.It is clear that the scatter on the measured values of the impact strength of the composites is quite large and therefore it is difficult to draw conclusions.It is identified from the results that the impact strength of the composites showed higher strength at 30%fiber content as shown in figure 2. 30% fibers content showed better reinforcements than 50% and 60% fibers content.It is due to that the impurities on the fibers are removed by alkali-treatment.The impact strength of the composites at untreated condition having 30wt% was 0.51kJ/m 2 .It was 0.55 kJ/m 2 at treated condition.The impact strength of the composites at untreated condition having 30wt% was 0.50 kJ/ m 2 .It was 0.57 kJ/m 2 at treated condition.The percentage of improvement was found to be 13%.The impact strength of the composites at untreated condition having 50wt% was 0.47 kJ/m 2 .It was 0.53kJ/m 2 at treated condition.The impact strength of the composites at untreated condition having 60wt% was 0.41 kJ/m 2 .It was 0.47kJ/m 2 at treated condition.
It is observed from the results that the flexural strength of the composites showed 60% Fiber content better performance than other fiber content in figure 3. Fiber content 30% showed poor performance leads to reduction in flexural strength.This could be due to the expansion of the fiber is restricted by the surrounding matrix which in turn produce a un-equilibrium condition between fibers.This resulted the week bonding strength between Scanning electron microscopic provides an excellent technique for examining the fractured surface of the treated fiber composites.From SEM images it is identified that a good bonding strength was created between the fiber and matrix.But during applying load on the specimens are started to failure (Debonding of fiber and matrix) (Figs. 4  and 5).Clearly the impurities were removed from the fiber surface as shown in Figs. 4 and 5. specimen Impact tested specimen

CONCLUSIONS
It was observed in banana/kenaf/polyester matrix composites that increasing the fiber content increases the tensile and flexural strength the addition of banana /kenaf to the matrix was found a scatter on the impact strength.It is thought that 20% of NaOH was too strong and might have damaged the fiber, thus results in lower percentage of improvement in the mechanical properties.The morphological changes were examined using scanning electron microscopy.

Fig. 3 :Fig. 2 :
Fig. 3: Effect of fiber content and alkali treatment of fibers on flexural Strength of composite material with fiber content