Utilization of Wallostonite/ Quasi Isotropic S2 Glass Fiber Doped in to Epoxy on Mechanical and Thermal Properties

Study focused on the performance of injection moulded short Wallostonite filler and chopped glass fiber reinforced hybrid epoxy composites. Results showed that hybridization of glass fiber and Wallostonite was found to be comparable to that of epoxy glass fiber composites. Analysis of fiber length distribution in the composite and fracture surface was performed to study fiber breakage fracture mechanism. The simultaneous compounding of epoxy with two fillers was done to obtain a hybrid composite. The mechanical properties of hybrid, injection molded, chopped glass fiber/ Wallostonite/epoxy composites have been investigated by considering the effect of hybridization by these two fillers. This system is expected to have considerable mechanical properties. It has been found that the tensile, flexural, and impact properties of the filled epoxy were higher than those of unfilled epoxy. The hybrid effects of the tensile strength and modulus were studied by the rule of hybrid mixtures (RoHM) using the values of single fiber composites.


INTRODUCTION
The need of development of new materials to meet the challenges for innovative applications in the scientific and technological fields has become a very much essential in the recent days. The present conventional materials are unable to fulfill all the conditions and the requirements such as higher strength, heat distortion temperature and light weight with low cost. In order to achieve the above requirements an attempt has been made in the technology to find a novel material called 'Composite' whose constituents will act synergistically to solve the need of the applications. As we cross the threshold into the 'Composite material age', it becomes increasingly important to understand the properties, performance, cost and potential of the composites. Composite is one such material, which has revolutionized the concept of high strength. A wide range of particulate materials are used in the composites. These new

International Letters of Chemistry, Physics and Astronomy
Online: 2014- 10-23 ISSN: 2299-3843, Vol. 40, pp 24-35 doi:10.56431/p-24av6e CC BY 4.0. Published by Academic Open Access LTD, 2015 advanced materials with specific properties have led to the development of better cheaper polymer composites. The natural fibers like coconut fiber, banana fiber, sisal fiber, sansevaeria cylindrica fiber, sugarcane fiber etc. which is having low density with good strength can be used as reinforcing agent to strengthen the composite [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Not only the natural fiber but also sometimes synthetic fibers like various types of Glass fiber, Almond fiber, Carbon fibers which is having high strength with low density can also be used as reinforcing agents. Any powdered material can also be used as fillers. The most commonly used fillers are various grades of CaCO 3 , talc, various types of silica, talc, Graphite, Montmorillonite clay (nano size) etc now recently Wallostonite powder is used as filler and S2 Glass fiber as reinforcing agent.
S2-Glass fiber (alumino silicate glass without CaO, whereas high MgO content with high tensile strength) with is a light weight (density 2.43g/cm 3 ), extremely strong and robust material. The Tensile strength of S2 glass material is 4890 MPa, compressive strength is 1600 MPa. Although the strength properties are somewhat lower than carbon fiber, it is less expensive. Its bulk strength and weight properties are also very favorable when compared to metals, and it can be easily formed during molding process. The plastic matrix may be epoxy, a thermosetting plastic (most often polyester or vinylester) or thermoplastic [21][22][23][24][25][26][27][28][29][30].
Wallostonite is calcium in silicate mineral (CaSiO 3 ) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. It forms when impure lime stone or dolostone is subjected to high temperature and pressure some times in the presence of silica-bearing fluid as skarns or contact metamorphic rocks. Associated minerals include garnets, vesuvianite, diopside, tremolite, epidote, plagioclase feld spar, pyroxene and calcite. Some of the properties that make Wallostonite so useful are its high brightness and whiteness, low moisture and oil absorption, and low volatile content. Wallostonite is used primarily in ceramics, friction products (brakes and clutches), metal making, paint filler and plastics. In our current work Wallostonite is chosen as natural filler in the second composition [31][32][33][34][35][36][37][38][39][40][41][42].
In the present work, epoxy polymer matrix was filled with Wallostonite mineral filler and same was reinforced with quasi-isotropic S2 glass fiber used for preparing the epoxy hybrid composites. After the composite been prepared, its performance was evaluated by means of mechanical and thermal properties. Tensile, flexural, impact and DSC and TGA properties are tested and optimized.

MATERIALS
In the present work commercially available Epoxy (Thermosetting plastic), S2 glass fiber and Wallostonite powder is used.
S2-Glass fiber ( alumino silicate glass without CaO but high MgO content with high tensile strength) with is a light weight (density 2.43g/cm 3 ), extremely strong and robust material. The Tensile strength of S2 glass material is 4890 MPa, compressive strength is 1600 MPa. Although the strength properties are somewhat lower than carbon fiber, it is less expensive. Its bulk strength and weight properties are also very favorable when compared to metals, and it can be easily formed during molding process. The plastic matrix may be epoxy, a thermosetting plastic (most often polyester or vinylester) or thermoplastic.
Wallostonite is calcium in silicate mineral (CaSiO 3 ) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. It forms when impure lime stone or dolostone is subjected to high temperature and pressure some times in International Letters of Chemistry, Physics and Astronomy Vol. 40 the presence of silica-bearing fluid as skarns or contact metamorphic rocks. Associated minerals include garnets, vesuvianite, diopside, tremolite, epidote, plagioclase feld spar, pyroxene and calcite.

1. Preparation of Composites
The Wallostonite powder in the ratio of (1gm, 2gm, 3gm, 4gm & 5gm) is mixed separately in the epoxy resin of 50 gm weight. The 2gm wt of S2 glass fiber is placed randomly in the mould (300 x 300x 3 mm 3 ) and the mixture of epoxy with different weight ratios of Wallostonite along with the hardener (catalyst) is injected into the mould using Injection moulding apparatus. The mixture of epoxy, Wallostonite and hardener is stirred well using ultra sonic sonicator. The composites are cured at room temperature for 24 hours.

Mechanical tests
Tests for determining tensile and flexural properties were conducted on computer controlled Instron 4301 type universal testing machine. For tensile test, standard dumbbell specimen were maintained from cast sheet and tested according to ASTM D 638. The cross head speed was 50 mm/min. Flexural properties were determined by three point bending method as per ASTM D 790. The test speed was maintained between 1.3 to 1.5 mm/min. Izod impact strength was determined using Izod Charpy digital impact tester, as per ASTM D 256. Shore D hardness test was conducted according to ASTM D 2240. A minimum of five specimens were tested in each case to obtain average value.

3. Thermal Properties
Thermogravimetric analysis (TGA) of the samples was done using Netzsch Model STA 409 PC with heating rate of 10 °C/min in nitrogen atmosphere. Dynamic mechanical analysis (DMA) was performed using Netzsch (DMA 242C) dynamic mechanical analyzer in the three-point bending mode at a frequency of 10 Hz and amplitude of 120 μm over the temperature range of 20-180 °C at a heating rate of 2°C/min.

1. Flexural properties
Results of the variation of flexural strength and flexural modulus of composites with filler content are shown in Figure 1. The flexural strength of epoxy filled Wallostonite and S2 glass fiber composites increased up to 3gm of Wallostonite powder (145.78-3.53 MPa). The increase in strength is mainly due to good filler matrix interaction, which is due to platy nature of the fillers. Platy filler have high aspect ratio and this increase the wet ability of the fillers by the matrix, thus creating fewer micro voids between the filler and the matrix. The Wallostonite powder, which has a higher surface area due to its small particle size, tends to agglomerate and this result in the reduction of surface interaction between the epoxy and Wallostonite. This explains the reduction in the flexural strength of Wallostonite powder filled epoxy composites (> 3gm of Wallostonite) at higher filler loading [7,10,12,18].

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ILCPA Volume 40   Flexural modulus of all types of the composite studied are found to increase linearly with increasing filler content in the matrix, indicating the positive toughening effect. The increased modulus is due to the presence of dispersed rigid particles.
The presence of Wallostonite particles might have stiffened the matrix inducing the increase observed in the modulus. It was assumed, that the space between the Wallostonite particles was filled with the matrix minimizing the presence of voids and bubbles consequently leading to increase in modulus [19,25].

2. Tensile Properties
The tensile strength and tensile modulus of the different composites investigated are shown in the Figure 2. Pure Epoxy shows the tensile strength of 22 MPa. The tensile strength of Wallostonite powder filled epoxy was shown in the Table 2.
The tensile strength of Epoxy composites increase with the Wallostonite content up to 4 gm and on further addition of Wallostonite powder (> 4gm) the tensile strength decreases. The improvement in tensile strength is caused due to limited mechanical restraint and the filler particle size. The decrease in the ultimate tensile strength is due to improper wetting of Wallostonite powder at higher filler content [28,39].   Filler may enhance or deteriorate the impact properties of composites. Impact strength is an indication of tolerability for a sudden impact. When a composite is subjected to an impact, rapid crack propagation is initiated through the material. Improvement in impact strength is due to the limited cross linked network structure of the cured resin.
The Wallostonite powder particle is tracer to move within the matrix and correspondingly, the matrix is free to stretch around particles. The stress transfer rate becomes very low, which leads to a lowest impact strength. In the filled composites, as filler loading increases the tendency of agglomerates also increase, interfacial adhesion becomes weaker leading to the weaker interfacial region. These agglomerates then acts as strength concentration points or crack initiation sites. Therefore reduction in the impact strength with increasing filler content is expected.

1. Differential Scanning Calorimetric (DSC)
The DSC test is carried out to find the glass transition temperature of different composites. Glass Transition temperature (T g ) of composites increase with increase in Wallostonite powder in the Epoxy matrix. The glass transition temperature is more for 5gm Wallostonite filled composite. The variation of glass transition temperature for different composites is shown in the

2. Thermo Gravimetric Analysis (TGA)
Thermo gravimetric analysis (TGA) of the samples was done using Netzsch Model STA 409 PC with heating rate of 10 °C/min in nitrogen atmosphere. Dynamic mechanical analysis (DMA) was performed using Netzsch (DMA 242C) dynamic mechanical analyzer in the three-point bending mode at a frequency of 10 Hz and amplitude of 120 μm over the temperature range of 20-180 °C at a heating rate of 2 °C/min [12,18].

CONCLUSION
Quasi-isotropic glass fiber reinforced and Wallostonite filled epoxy hybrid composites were developed and tested for mechanical and thermal properties. Wallostonite was dispersed in to the matrix with various proportion such as 1, 2, 3, 4, 5 gm by keeping glass fiber as a constant. Due to less moisture content and more metallic nature particle was attributed the improved thermal stability for 5gms Wallostonite filled epoxy hybrid composites. Thermal stability as increased for the same sample up to 50 ºC when compared with the 1gm Wallostonite filled composites. It was observed in the DSC analysis that due to increased viscosity of the specimen at 5gm as a result of that decreased glass transition temperature was observed when compared with 4gm Wallostonite filled composites. Tensile and flexural modulus was increased linearly due increased ductility. Impact strength was increased up to 3gm after that it was started getting down. On other hand flexural strength was optimized at 3gm whereas at 4gm tensile strength was optimized. These types of composites can be used fuel tanks, automobile and airplane bodies for fuel economy.