Development of Sansevieria trifasciata - Carbon Fiber Reinforced Polymer Hybrid nanocomposites

This paper presents studies on experimental values of tensile strength properties of hybrid nanocomposites were studied and compared with theoretical values. It was observed that, experimental strengths were fallen shorter than the theoretical values. Nanocomposites were fabricated by filling MMT nanoclay by weight ratio and reinforced with short sansevieria trifasciata (STF) and short carbon fibre (CF) by randomly orientation. Organically modified montmorillonite clay filled with different proportions viz.0, 1, 3 and 5 wt.% dispersed into the vinyester matrix modified system by hand lay-up technique. Natural fiber was treated by NaOH solution was brought significant performance. Tensile strength was found maximum when clay content was Clay 3wt%. In the fracture surfaces of samples were analysed by SEM analysis, in which it was observed that, increased clay viscosity played vital role in bringing the performance as the viscosity of the mixture made difficult to flow the resin. Thermal stability was significantly improved for the 5wt% sample due to the high content of silicate particles and carbon fibre content.


INTRODUCTION
Hybrid composites are those composites which have a combination of two or more reinforcement fibres/filler in a predetermined geometry and scale, optimally serving a specific engineering purpose. The most common type of hybrid composites are carbon-aramid reinforced epoxy (which combines strength and impact resistance) and glass-carbon reinforced epoxy (which gives a strong materials at a reasonable price). Hybrid composites are usually used when a combination of properties of different types of fibres need to be achieved, or when the longitudinal as well as the lateral mechanical performance are required. The reinforcing phase material may be in the form of fibers, particles, or flakes. The matrix phase materials are generally continuous. Examples of composite systems include concrete reinforced with steel and epoxy reinforced with graphite fibers, etc. The composite material however, generally possesses characteristic properties, such as stiffness, strength, weight, high-temperature performance, corrosion resistance, hardness, and conductivity that are not possible with the individual components by themselves. Analysis of these properties shows that they depend on (1) the properties of the individual components; (2) the relative amount of components; (3) the size, shape, and distribution of the discontinuous components; (4) the degree of bonding between components; and (5) the orientation of the various components. Vinylester, is a resin produced by the esterification of an epoxy resin with an unsaturated monocarboxylic acid. The reaction product is then dissolved in a reactive solvent, such as styrene, to 35 -45% content by weight. It can be used as an alternative to polyester and epoxy materials in matrix or composite materials, where its characteristics, strengths, and bulk cost intermediate between polyester and epoxy. Vinyl-ester resin, as a structural polymer, was chosen as a polymer matrix in current study due to the fact that the cured resins are thermosetting with a network structure possessing high resistance to the moisture and chemicals, and good mechanical properties. Thus the resultant composites have the potential applications in fabrication and building materials such as electrodeposition tanks, automotive parts and marine vessels which require superior mechanical properties and/or high resistance to harsh environments such as strong acid or base. Furthermore, the functional groups of the polymer surrounding the nanoparticles enable these nanocomposites as good candidates for various applications such as site-specific molecule targeting in biomedical areas.
The properties of carbon fibers, such as high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion, make them very popular in aerospace, civil engineering, military, and motorsports, along with other competition sports. It is commonly called the snake plant (not to be confused with the very similarly named "Snake plant",Nassauvia serpens), because of the shape of its leaves, or mother-in-law's tongue because of their sharpness. Like some other members of its genus, S. trifasciata yields bowstring hemp, a strong plant fiber once used to make bow strings. It is now used predominantly as an ornamental plant, outdoors in warmer climates, and indoors as a house plant in cooler climates. It is popular as a houseplant as it is tolerant of low light levels and irregular watering; during winter it needs only one watering every couple of months. It will rot easily if overwatered. A study by NASA found that it is one of the best plants for improving indoor air quality by passively absorbing toxins such as nitrogen oxides and formaldehyde. Natural fibers such as banana, cotton, coir, sisal and jute have attracted the attention of scientists and technologists for application in consumer goods, low cost housing and other civil structures. It has been found that these natural fiber composites possess better electrical resistance, good thermal and acoustic insulating properties and higher resistance to fracture. Natural fibers have many advantages compared to synthetic fibers, for example low weight, low density; low cost, acceptable specific properties and they are recyclable and biodegradable. They are also renewable and have relatively high strength and stiffness. .The main aim of this research is to check suitability of STF/CF hybrid nanocomposites for specific applications in aerospace and automotive applications.
In the present research paper hybrid nanocomposites were prepared which are reinforced with STF and CF using rule of hybrid mixture. Nanoclay was dispersed into the vinyester matrix with different weight proportions to see where strength was optimised. Experimental values of tensile strengths were correlated with theoretical values with experimental values. SEM was also evaluated by comparing the different samples of their cross sections.

Materials
In the present work, a commercially available vinylester, and methyl ethyl ketone peroxide (catalyst), Cobalt napthenate (accelerator) were purchased from the V.G.R. Enterprises, Madhurai, Tamialnadu, India. Vinyl-ester monomers with two reactive vinyl end groups enable the crosslinking for network formation. The liquid resin has a density of 1.045 g/cm 3 and a viscosity of 350 centipoises (cps) at room temperature. A JEOL JSM-6400 JAPAN scanning electron microscope at 15 kV accelerating voltage was equipped with energy dispersive spectroscopy (EDS) to ascertain the fiber/filler interfaces with the main modified matrix. Fractured specimen surfaces were goldcoated and the fractures surface was observed using a scanning electron microscope. The fractured surfaces were gold-coated with a thin film to increase the conductance. The thermal characteristics TGA, DSC measured on laminated polymer nanocomposites using SDT Q600 TGA/DSC (TA Instruments) at a rate of 10ºC/min under nitrogen flow measurements were carried out at 20ºC In each case, five identical specimens were tested and their average load at first deformation was noted and the average value tabulated. All the tests were accomplished at a room temperature of 20 °C. At least, 5 samples were tested for each composition and results were averaged.

Composite Manufacturing
A glass mould was prepared based on the ASTM standards and mould was coated with PVA solution as it facilitates easy removal off the composite after curing completes. The resin, catalyst and accelerator were taken in the ratio of 100: 2:2 parts by weight, respectively. Then, a precalculated amount of catalyst/accelerator was mixed with the vinylester resin and stirred for 10 min before pouring into the mould. The hand lay-up technique was used to impregnate the composite structures [12,18]. A predetermined amount of clay was mixed with vinylester and stirred with mechanical stirrer and ultra sonicator subsequently. In this technique, the CF and the STF were wetted by a thin layer of vinylester suspension in a mould. A stack of hybrid fibers were carefully arranged in a unidirectional manner after pouring some amount of resin against the mould to avoid the poor impregnation. The remaining mixture was poured over the hybrid fiber. Brush and roller were used to impregnate fibre. The closed mould was kept under pressure for 12hours at room temperature. Then the post cured sheets were cut on par with ASTM standards.

Fiber Treatment
Sansevieria trifasciata was taken in a glass tray and a 5 % NaOH solution was added in to the tray and the fibers were allowed to soak in the solution for 1 hr separately. The fibers were then washed thoroughly with water to remove the excess of NaOH sticking to the fibers. Final washing was carried out with distilled water and the fibers were then dried in hot air oven at 70 °C for 4 hrs. The fibers were chopped into short fiber length of 3 cm for molding the composites.

TENSILE STRENGTH
A tensile test is a fundamental mechanical test where a carefully prepared sample is loaded in a very controlled manner while measuring the applied load and the elongation of the sample over some distance. Tensile strength or ultimate strength is defined as the maximum load that results during the tensile test, divided by the cross-sectional area of the test sample. Therefore, tensile strength, like yield strength, is expressed in MPa. Tensile tests are used to determine the modulus of elasticity, elastic limit, elongation, proportional limit, reduction in area, tensile strength, yield point, yield strength and other tensile properties. Tensile strength can be obtain from the following formula: ; where σ = tensile strength (N/m 2 ); P = test load (N) ; A=Area of cross section(m 2 ).

RESULTS AND DISCUSSIONS
The primary goal of the hybrid composites as a product is to withstand the applied mechanical forces. This is achieved by load transfer between the matrix and the nanoparticle induced by the shear deformation of the matrix around the filler. This shear deformation is produced because of the high young's modulus of the nanoparticles and the larger differences between the mechanical of the International Letters of Chemistry, Physics and Astronomy Vol. 50 composite constituents.Tab.1 and Fig.1 shows the experimental and theoretical values of the tensile strength of the hybrid composites. It was observed that tensile strength of the pure vinylester matrix is 15.1 MPa for experimental values. It was also noticed that experimental values are unable to meet the theoretical strengths due to constraints. The tensile strength of composites increased up to 3wt% clay loaded into vinylester matrix. The increase in strength was due to good filler matrix interactions, which was largely due to the needle shaped structure might have enhanced ability of the filler. Needle type fillers have higher aspect ratio and this increases the wet ability of the fillers by the matrix, thus creating fewer micro voids between the filler and matrix. The filler has higher surface area due to its small particle size, tends to agglomerate and these results in the reduction of surface interactions between the matrix and the filler. This may be the substantial reason for reduction of tensile strength after 3wt% clay. Similar observations were observed from the literature [10,14,15].  Fig. 2 (a &b) shows the morphological analyses of various samples of 3 and 5 wt.% clay loaded reinforced with STF and CF fiber hybrid composites. From the fig.2 (a) the fracture sample cross sections were clearly indicates that filler distribution was homogeneous and there was only no voids, and pullouts and also it is slightly looks like ductile nature of cross section. This is the genuine reason for improved performance at 3wt%. It indicates the bright whitish matrix indicates feature from nanoclay of microstructure indicates well cross linking between the fiber and matrix, on other hand in fig.2 (b) cross section was slightly somewhat different as it looks like more ductile nature but due to increased viscosity of the modified composites it was unable to flow all over the mold in a given time as result of that it led to poor strength as stuff can left unfilled and consequently suffered with voids. When viscosity increases generally there will be a tendency of formation of voids and also from the same image we can also observe the random orientation of the fiber [23,24]. After comparing the two images we come to conclusion that adding more clay leads to agglomeration as a result which causes microvoids which at as a stress concentration factors which facilitates shear yielding in the system and therefore ultimately strength would be going down [16,17]. Fig.3 shows the TGA analysis of the two different clay loaded samples such as 3wt.% and 5wt.%, and also it was noticed that for 5wt.% clay loading thermal stability was increase from 352°C-356°C. it was found that 5wt.% clay loaded sample is more thermal stability than the 3wt.%., clay contains the more silicate particulates, that makes when addition of clay and fiber makes the composite highly viscous and also same contains the more unburnt stuff which led to high thermal stability [14,18].

CONCLUSION
Vinyl ester glass fibre reinforced composites filled individually with OC at room temperature has been successfully fabricated using hand layup technique. Improved tensile and impact strengths were factor are observed in OC filled hybrids over vinyl ester Sansevieria trifasciata fibre and carbon fibre reinforced composites.