Processing and Properties of Natural Fiber-Reinforced Polymer Composite

A novel low cost polymer composite using brown grass �ower broom reinforcement is prepared.e prepared polymer composite has the lowest porosity, homogeneous surface structure, and the greatest interface bonding. From the physico-mechanical characterization such as: hardness measurement, density measurement, void fraction or porosity measurement, and �exural strengthmeasurement, it is found that the prepared composite is of light weight and high strength. Again, from dielectric behaviour of this polymer composite, it is found that this material has an efficiency that is considered as a high valued marketable product. As the composite is made using bio-materials from local resources, its cost is less compared to other polymer composites available today.


Introduction
Natural �ber-reinforced polymer composites have raised great attention and interest among materials scientists and engineers in recent years due to that the composites give a combination of superior mechanical property, dielectric property, and environmental advantages such as renewability and biodegradability.Due to various disadvantages such as: high progressing technologies, rising prices of �nite resources, and ecounfriendly, the conventional petroleumbased plastic, glass or carbon �ber materials are compensated by natural/bi-based �bers.ese �ber composites are well suited as wood substitutes in the housing and construction sector.�sing such natural/bio�bers with polymers based on renewable resources will allow many environmental issues to be solved.e various natural �bers such as jute, coir, sisal, pineapple, ramie, bamboo, and banana are used as reinforcement of polymer composite, nowadays [1][2][3][4][5][6][7][8][9][10][11][12].In recent years, a number of investigations have been made which prove that the worth of natural �bers against their synthetic counterparts such as glass and/or carbon �berreinforced polymer composites [13][14][15][16].e potential of �ber-reinforced polymer composites was recognized more than 50 years ago, now they can �nd their applications in almost every industry including construction, aerospace, automotive, and electronics.Composite materials are increasingly used for dielectric applications, that is, applications that make use of electrically insulating or nearly insulating behaviour.is is because of the need of the electronic industry for dielectric materials in electrical insulation, encapsulation, multilayer ceramic chip, and capacitors and for piezoelectric, ferroelectric, and pyroelectric devices that provide sensing, actuation, and so forth.Development of dielectric material with low dielectric constant  and low dielectric loss is considered to be one of the main issues in high-speed microelectronics.e dielectric constant of any material depends upon the polarizability of its molecules and is determined by different contributions: interfacial, dipole, atomic, and electronic polarizations.Interfacial polarization in the composite in�uences the dielectric properties at very low frequencies and usually decreases with increasing frequency [17][18][19].
Developing an efficient and light weight dielectric material with high strength from sustainable resources, such as brown grasses broom �bre, is quite attractive from both application and environmental point of view.is paper aims at development of a bio�bre-reinforced polymer composite using natural �bre, that is, brown grass �ower broom which is lightweight, commonly available, biodegradable, and low cost.e raw material is commonly available in agricultural sector.

Materials and Methods
2.1.Materials Used.Epoxy LY 556 (common name: bisphenol A diglycidyl ether) is used as matrix material in the composite fabrication.e hardener used here is HY-951(IUPAC name: NN ′ -bis (2-aminoethylethane-1, 2-diamin).Epoxy Resin and hardeners are mixed in a ratio of 10 : 1 by weight.Brown grass �ower broom (shown in Figure 1) is commonly used in house.Short �ber of the broom that is nearly 10 mm length was prepared and used as the reinforcing agent in the composite preparation.

Preparation of Test
Samples.e bio�ber (brown grasses �ber) was mixed with the epoxy by stirring at room temperature, in a glass beaker with the help of suitable glass rod.Hardener was added into the beaker containing mixture at the time of stirring.With proper stirring for 10 minutes, uniform mixing of the reinforcing agent and the polymer matrix were possible.Proper stirring was required for uniform mixing of the reinforcing agent and the polymer matrix and they were poured into suitable moulds to obtain discshaped samples of 12 mm diameter and 2.5 mm thickness.ree different broom �ber-reinforced epoxy composites were fabricated varying the amount of reinforcement.Test specimens of suitable dimensions are cut from the composite (shown in Figure 2).e different composites prepared are described in Table 1.
e surface morphology of the sample (Epoxy + 10% brown grass �ower broom) was examined with JEOL T-330 Scanning Electron Microscope.Samples were coated with 60 Å thick platinum in JEOL sputter ion coater for surface conductivity and then observed under SEM, operated at an acceleration voltage of 20.0 kV.Hardness test was conducted in a Vickers hardness tester, Leitz, Germany.e Vickers hardness numbers (VHN) of the hybrid composite were measured under a load of    Kgf and Vickers hardness number was calculated by using the formula: where  is the applied load,  is the diagonal of square impression (mm),  is the horizontal length (mm), and  is the vertical length (mm).e density of neat epoxy and the composites were measured by measuring its mass and volume.e bulk density and void fraction of the composite materials will be obtained from following equations by using Archimedes' principle: where dry weight is the weight of the sample at completely dried condition, soaked weight is the weight of the sample that soaked in kerosene oil, and suspended weight is the weight of the sample suspended in the oil through a string.
To evaluate the value of �exural strength (FS), the short-beam shear (SBS) tests (3-point bend test) were performed on the samples at room temperature.e SBS test was conducted as per ASTM D2344-84 using the Instron 1195 UTM.e span length was 40 mm, and the cross head speed was 5 mm/min.e FS of any composite can be calculated by using the following formula: where  is the applied load,  is span length, and  and  are the thickness and width of the specimen, respectively.Dielectric measurements were carried out with the help of a Solartron 1296 Impedance Analyser.For that, the samples of the composites had to be cut into thin circular shape, and their surfaces were polished.en graphite coating was given on their surfaces to make surface conducting and for allowing measurements over frequency interval from 100 Hz to 1 MHz.e dielectric constant and dielectric loss were determined as follows.
Dielectric constant where  ′ (pF) is the measured capacitance, and  (pF) is calculated using the equation where  is area of the electrode (mm 2 ) and  is the thickness of the sample (mm).e dielectric loss is given by where  = 2,  is the measuring frequency, and  =  0 (   0 ) [20].

Results and Discussion
e surface morphology of the prepared test sample with 10% broom �ber is shown in Figure 3. e interface bonding of the broom �ber with epoxy resin is clearly visible.is composite has lowest porosity and homogeneous surface structure.Hardness values of the samples are given in Figure 4. From the �gure, it can be seen that the hardness of broom �ber-reinforced polymer composite is more than that of the pure epoxy and also increases with the increase in amount of reinforcement.e increase in hardness of the composite may be due to stronger interface bonding of the broom �ber with epoxy resin.e actual density of the composite is determined experimentally by simple water immersion technique by using Archimedes principle.e densities of the samples are given in Table 2. �t is observed that the presence of broom �bres as �llers in epoxy matrix reduces the density of polymer composite and hence makes it lightweight.is may be due to presence of the high air content.�ith addition of �ower broom �ber in epoxy resin, the volume fraction of voids is increased as shown in Figure 5. e voids signi�cantly a�ect some of the mechanical properties and even the performance of the composites in the place of use.
Figure 6 shows the comparison of �exural strengths of the �ower broom-reinforced epoxy composites.ere is an increase in the �exural strength that is associated with an increase in wt% of short �ber �ower broom in composites.is may be due to the presence of stronger interfacial bonds (as shown in SEM �gure).�mpregnations of natural �bre help in the interface bonding which improve the structural properties of the composite.e micromechanical events that occur for a long �ber-reinforced composite are not the same as those observed for a short �ber reinforced composites.�n a short �ber, there are variations in stress distribution along the �ber matrix interface, and end e�ects can be neglected in the case of long �bers, but they can be very important in the case of short �ber-reinforced composites.Weight percent of flower broom fiber F 6: Variation of �exural strength of composites with weight percent of �ower broom �ber-reinforced epoxy composites.
It is observed from Figure 7 that the dielectric constant (at 100 Hz frequency) increases with the volume fraction reinforcement.However, from Figures 8 and 9, it is inferred that the dielectric constant and the dielectric loss initially reduce and attain a steady state with an increase in frequency.is may be due to the fact that (i) dielectric behavior is dependent on porosity, (ii) on material properties, and also on (iii) interface bonding in case of composite materials.So in this study the materials used are having many diverse physico-mechanical properties.However, it is found that making a composite with these wastes, using a polymer binder, is best suited for providing good mechanical strength without sacri�cing its dielectric property.Impregnation of natural �bre helps in the interface bonding and distribution of absorbed moisture in the material which may be one of the reasons for change in dielectric properties.With increase in frequency, the dielectric constant of the composites decreases due to dielectric relaxation.From structural point of view, the dielectric relaxation involves oriental polarization which in turn depends on molecular arrangement of the dielectric material.At high frequency, the rotational motion of polar molecule is not sufficiently rapid for attainment of equilibrium with applied �eld, hence dielectric constant decreases.
As the reinforcement content increases, the dielectric constant also increases.Dielectric loss of the composite shows a stabilizing trend with an increase in frequency which appears to be a bene�cial from application point of view.

Conclusions
�rown grass �ower broom �ber-reinforced epoxy composites can be prepared easily with different weight percentage of reinforcement.e polymer composite cost will be low as the raw material is plant �bre based, and the processing technique is simple.is composite has the lowest porosity and homogeneous surface structure, and a strong interface bonding of the broom �ber with epoxy resin is present.e void fraction of the composites increases slightly with the increase in the reinforcement content.It might be due to the presence of pores/cavities in the �bre.ere is an increase in the �exural strength along with the increase in weight percent of short �ber �ower broom in composites.Moreover the material is of light weight and possesses high strength.With the increase in reinforcement content, the density of the composite decreases, and the hardness of the composite increases, and hence make it of light weight and high of strength.Dielectric properties (relative permittivity and loss factor) of pure epoxy resin and composites with different amount of broom �ber-reinforced polymer composite have been studied in the frequency range from 100 Hz to 1 MHz.e experimental results indicate that the dielectric constant and dielectric loss factor decrease with the increasing frequency.It may/can be due to the orientation polarization, which has increased with increasing temperature, due to greater movement of polar molecular dipoles appears to be bene�cial in electronic industry and can be processed by village artisans also.As the composite is made using bio-materials from local resources, its cost is less, compared to other polymer composites available today.is can further open up a new frontier for the industrialization at rural sectors.

F 2 :
Polymer composites of brown grass �ower broom and epoxy.
density  dry weight soaked weight − suspended weight , void fraction or porocity  soaked weight − dry weight soaked weight − suspended weight × 1,

T 1 :
Test samples prepared.brown grass �ower broom Sample CEpoxy + 20% brown grass �ower broom T 2: Variation of density with di�erent weight percent of �ber reinforced in epoxy matrix.

F 3 :F 4 :
Surface morphology of the composite with 10% of broom �ber reinforcement.Variation of hardness (HV) of composites with weight percent of �ower broom �ber-reinforced epoxy composites.

F 5 :
Variation of void fraction of composite with weight % of broom �ber-reinforced epoxy composites.

F 7 :F 8 :
Variation of dielectric constant with amount of �bre reinforcement.Variation of dielectric constant with frequency.

F 9 :
Variation of dielectric loss with frequency.