Fiber reinforced plastics (FRPs) have replaced conventional engineering materials in many areas, especially in the field of automobiles and household applications. With the increasing demand, various modifications are being incorporated in the conventional FRPs for specific applications in order to reduce costs and achieve the quality standards. The present research endeavor is an attempt to study the effect of natural fillers on the mechanical characteristics of FRPs. Rice husk, wheat husk, and coconut coir have been used as natural fillers in glass fiber reinforced plastics (GFRPs). In order to study the effect of matrix on the properties of GFRPs, polyester and epoxy resins have been used. It has been found that natural fillers provide better results in polyester-based composites. Amongst the natural fillers, in general, the composites with coconut coir have better mechanical properties as compared to the other fillers in glass/epoxy composites.
The widespread use of the fiber reinforced plastics (FRPs) over the last few years has led to the increased research interest in the area of FRPs. Though the synthetic fiber reinforced plastics possess excellent properties, their cost of processing is quiet high, mainly due to the material cost. On the other hand, the use of natural fibers leads to cost reduction and light weight composites, though the mechanical properties of natural fiber composites are much lower as compared to the synthetic fiber composites [
Composite laminates of 4 mm thickness were prepared using boron-free EC-R glass mats, epoxy resin, and natural fillers. Rice husk, wheat husk, and coconut coir were used as filler materials. Composite laminates were prepared by conventional hand layup technique in chrome plated mild steel mold, 560 mm by 460 mm at room temperature. The mold is specially designed to produce 4 mm thick laminate sheets. All the composites have 6 layers of woven boron-free EC-R glass fiber mats of 610 GSM manufactured by Owens Corning Fiber Glass, USA. The EC-R glass had a young’s modulus of 80 GPa and density of 2.62 g/cm3. Epoxy resin LY556 (density 1.15–1.20 g/cm3 at 25°C) and hardener HY 951 (density 1 g/cm3 at 20°C) were used. The resin and hardener were mixed and stirred mechanically in a ratio of 10 : 1 by weight. In order to follow a standard comparative procedure, it was decided to fabricate laminates with a thickness of 4 mm. The natural fillers were used in a proportion of 5% of the weight of glass fibers. The decision to add only 5% natural fillers was taken after a pilot study. Initially, 10% natural fillers were added and a remarkable decrease in the mechanical properties was observed. The reduction in the properties may be attributed to the nonwetting of the fibers and fillers by the polymer matrix and agglomeration of the fillers. Moreover, the thickness constraint of 4 mm was also not achieved with the addition of 10% fillers. Here, it is worthwhile to mention that natural fibers before use were reduced to a size of one to four cm in length. Initially, the work side of the mold was coated with a thin layer of PVA (Poly Vinyl Alcohol) which acts as a release agent. After the PVA coating has dried, a light layer of the resin is made with the help of a brush and then the first layer of woven glass sheet is placed in the lower part of the mold. The glass sheet is thoroughly coated with the resin with the help of a brush and then one-fifth of the filler is evenly spread over the layer and the second glass layer is placed. Again, the resin is applied thoroughly so that the resin drips down the glass layer and coats the natural fibers also. This process is continued till the final layer of glass mat is coated with the resin. The top plate of the mold is then properly placed over the lower one to complete the assembly. Finally, the complete mold is placed in a press and a compression load of 15 tonnes is applied. The compression ensures that the entrapped air bubbles are completely removed and the excess resin flows out. The mold is left for 10 hours at room temperature to complete the curing process. The same technique was used to fabricate the other laminates. In all, four different types of specimens were fabricated. Three of the GFR-epoxy-based composites consisted of different natural biofillers, that is rice husk, wheat husk, and coconut coir, as fillers and the fourth laminate had glass fiber alone as a reinforcement.
General purpose polyester resin (density 1.1 g/cm3) was used along with Methyl Ethyl Ketone Peroxide (MEKP) and Cobalt Octoate. First, the general purpose resin was mixed with Cobalt Octoate (with 6% Cobalt content) which acts as an accelerator. The accelerator accelerates the decomposition of organic peroxide initiators called catalysts and in turn increases the polymerization. Then just before the application of the resin to glass fiber, MEKP is added to the resin which acts as a catalyst and initiates the polymerization of polyester resins. MEKP also helps in cold setting of polyester-based composites. As the sheets were made in summers with normal temperature being around 40 degree plus in India, just 10 mL of Cobalt Octoate and 10 mL of MEKP were added to the resin. It has to be kept in mind that once MEKP has been added to the resin, the hand layup process has to be completed quickly; otherwise, the resin starts to gel and leads to wastage. The manufacturing of polyester-based glass fiber sheets with natural fillers is done in the same way as the epoxy-based sheets. The natural fibers are again used in the proportion of 5% by weight of the glass fiber weight and initially hand-layup process is used and then the complete mold assembly is subjected to compressive force of 15 tonnes in a press. The polyester-based laminates get ready for use within 3 hours. Similar to the epoxy-based FRP laminates; four polyester-based FRP sheets were prepared. One with woven glass fiber alone and other three laminates are with different natural fillers, that is, wheat husk, rice husk, and coconut coir.
The tensile test was performed in accordance with ASTM D3039. The test specimen size was 250 mm × 25 mm × 4 mm. The test was performed on a universal testing machine (UTM) of 10-tonne capacity. The flat specimens of required size were fixed between the grips of each head of the testing machine in a way that the direction of force applied to the specimen is coincident with the longitudinal axis of the specimen. The strain rate was so selected so as to produce the failure from 1 to 10 min:
The compressive strength of the test specimens was found using UCSB compressive fixture [
The cross breaking test was conducted as per IS: 1998-1962. According to the IS standards, the test specimen needs to be 15 mm ± 0.5 mm in breadth and should have a length of 24 to 30 times the thickness of the laminate measured nearest to 0.03 mm. The test was conducted on the UTM. Two parallel V-shaped supports were used to fix the specimen in the machine. The distance between the supports was kept equal to sixteen times the measured thickness of the test specimen. A load was applied by the third V-block parallel to and between the supporting blocks across the width of the test specimen. The load was steadily increased at such a rate that the test specimen fractures in 15 to 45 seconds from the time of initial application of load:
Izod Impact Strength was found according to IS0 180 : 1993, on an Izod Impact Testing Machine (0–168 Joule capacity). A rectangular piece of length 63.5 ± 2 mm and width 12.7 ± 0.2 mm having thickness of the laminate (4 mm) was prepared as shown in Figure
Specimen for Izod Impact Strength.
Test specimens of size 25 mm by 25 mm were prepared according to ASTM D785-08. A steel ball indenter of 3.175 mm diameter was used to find the hardness on a Rockwell machine. The hardness was measured on Rockwell hardness K-scale with a major load of 150 kg and an average of five hardness tests was taken.
The specific gravity test was done in accordance with Indian Standard IS: 10192-1982. The specimen prepared for the test was a square of 40 ± 1 mm with thickness being that of the laminate (4 mm). The specimen was first weighed in air by suspending it with the help of a thread fixed to the hook of the balance, and the weight
The water absorption test was conducted according to Indian Standard IS: 1998-1962. A square test specimen of
The volume fraction of glass fibers (glass content) was found according to ASTM D2584-08. The test specimens of 20 mm × 20 mm × 4 mm were prepared. Initially, a desiccated ceramic crucible was weighed (
In all, eight different types of GFRP laminates were fabricated. Four of the GFRPs were epoxy resin based and other four were general purpose polyester (orthophthalic resin commonly known as G. P resin) based. In general, with the same resin, one specimen was reinforced with glass fiber alone and three other were reinforced with different natural fillers that is wheat husk, Rice husk, and coconut coir. Various characterization tests were conducted and their results are depicted in Table
Summary of experimental findings.
Property | FRP | |||||||
---|---|---|---|---|---|---|---|---|
Glass fiber reinforced epoxy | Glass fiber reinforced polyester | |||||||
No filler | Wheat husk filler | Coconut coir filler | Rice filler | No filler | Wheat husk filler | Coconut coir filler | Rice filler | |
Tensile strength (N/mm2) | 398.73 | 353.05 | 372 | 307.65 | 352.5 | 283 | 315 | 324.9 |
Compressive strength (N/mm2) | 351.3 | 222.24 | 289 | 280.43 | 212.9 | 173.69 | 224.14 | 199.47 |
Cross breaking strength (N/mm2) | 896.07 | 698.03 | 827.45 | 733.33 | 614 | 522 | 702 | 548 |
Impact strength (N/mm2) | 263.84 | 206.47 | 214.84 | 234.37 | 234.37 | 245.53 | 278.93 | 256.69 |
Hardness (K-scale) | 56.1 | 30.33 | 42.83 | 40.33 | 41 | 33.25 | 35.9 | 41.375 |
Specific gravity | 1.6727 | 1.6152 | 1.6629 | 1.6166 | 2.082 | 1.6723 | 1.707 | 1.7272 |
Water absorption | 0.0343 | 0.6541 | 0.205 | 0.2316 | 0.47395 | 1.824 | 0.7522 | 0.685 |
Glass content | 52.14 | 54.77 | 52.83 | 55.55 | 52.39 | 54.02 | 51.41 | 53.19 |
In general, it has been found that the tensile strength of epoxy-based GFRPs is more than polyester-based composites. The tensile strength values of the eight different composites under consideration are shown in Figure
Tensile strength of composites with/without filler.
The compressive strength was found using UCSB fixture on Universal Testing Machine. The compressive strength of epoxy-based composites is more than that of polyester-based composites as shown in Figure
Compressive strength of composites with/without filler.
The three-point bending test conducted on UTM shows that among the GFR-Polyester composites, the composites with coconut coir fillers show better strength than the plain GFR-polyester composites. Even in GFR-Epoxy composites, the specimens with coconut coir fillers show comparable strength to the plain GFR-Epoxy specimens. As shown in Figure
Results of three-point bending test.
Figure
Izod Impact Strength of composites with/without filler.
The hardness of plain GFR-Epoxy composites was found to be maximum with a value of HRK 56.1. The hardness of GFR-Epoxy composites reduced with the addition of fillers. The hardness of GFR-Polyester with rice fillers was more than simple GFR-Polyester composites. The hardness of composites with wheat husk as fillers was found to be the lowest with both epoxy and polyester as resin as shown in Figure
Hardness of composites with/without filler.
The specific gravity of GFR-Polyester-based composites is more than GFR-Epoxy-based composites. As is clear from Figure
Specific gravity of composites with/without fillers.
Water absorption in case of GFR-Polyester composites was found to be much greater than the GFR-Epoxy composites. Water absorption, even in GFR-Epoxy composites with fillers, is less than the plain GFR-Polyester specimen. The test results of water absorption test are shown in Figure
Results of Water Absorption Test.
The water uptake may affect the mechanical behavior of the developed composites. It has already been established by the authors that the water uptake affects the tensile behavior of the polymer matrix composites [
The glass content for all the specimens is found to lie in the range of 51.4%–55.55%. The variation is due to the variation in weight of glass fiber mats used.
In the present research endeavor, various characterization tests were conducted over GFR-Polyester- and GFR-Epoxy-based composites. In general, the addition of fillers leads to cost and weight reduction of the regular glass fiber reinforced composites. The effect of the addition of natural fillers has been studied and the following conclusions can be drawn. The tensile strength of epoxy-based composites is better than that of polyester-based. The tensile strength of GFR-Epoxy composites with coconut coir as fillers is comparable to that of plain GFR-Epoxy composite and in case of polyester composites GFR-polyester with rice husk filler is comparable to that of plain GFR-Polyester laminate. The compressive strength of GFR-Epoxy-based composites is better than that of GFR-Polyester-based composites. The compressive strength of GFR-Polyester specimens with coconut coir as fillers results in better compressive strength than plain GFR-Polyester composites. The impact strength of polyester-based filler composites is better than that of epoxy-based composites. The impact strength of GFR-Polyester composites with coconut coir fillers is even more than the GFR-Epoxy composites with no fillers. The cross breaking strength of GFR-Epoxy composites is better than that of GFR-Polyester composites. Addition of coconut coir shows good results in both epoxy and polyester composites. The hardness of epoxy-based composites is more with respect to polyester-based composites. The specific gravity of polyester-based composites is more than epoxy-based composites. The addition of fillers leads to reduction of specific gravity in all types of composites investigated in the present research endeavor. Water absorption is more in polyester-based composites. Overall, coconut coir fillers should be used instead of wheat husk and rice husk in general to improve the properties of the developed glass fiber reinforced composite laminates.