CHAPTER 4 MECHANICAL PROPERTIES OF PROSOPIS JULIFLORA, JUTE AND GLASS FIBER REINFORCED COMPOSITES

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1 62 CHAPTER 4 MECHANICAL PROPERTIES OF PROSOPIS JULIFLORA, JUTE AND GLASS FIBER REINFORCED COMPOSITES 4.1 INTRODUCTION In the last chapter, the mechanical properties of sandwich composites reinforced with fibers like Prosopis juliflora, Sida rhombifolia, sisal and glass was reported. It was observed from the study that prosopis containing specimens exhibited superior mechanical properties compared to all other specimens. As prosopis proved to be good reinforcement, it is worth to study the mechanical properties of laminates reinforced only with prosopis, reinforced with prosopis sandwiched between jute and glass fiber mats. In this chapter, fabrication and mechanical properties of seven different types of laminates made using prosopis, jute and glass fibers were reported. 4.2 MATERIALS AND METHODOLOGY Materials Used The fibers extracted from the bast of prosopis juliflora and subjected to alkali treatment using NaOH at 5% concentration was used after crushing it in to finer form. Glass fiber bidirectional woven roving mat of 610gsm and jute fiber mat of 367gsm were used. Vinyl ester resin was used as matrix and chemical compounds such as cobalt naphthanate, methyl ethyl ketone peroxide and dimethyl amine were used as acceralator, catalyst and promoter.

2 Specimen Preparation Seven different types of specimens were fabricated using hand layup technique and cold pressing method. The details about the specimens are given in Table 4.1. The representative samples of test specimens are shown in Figure 4.1 (a) to (e). Out of Seven types of laminates, four were of sandwich type with prosopis fibers placed between layers of glass and jute fiber mats, one was prepared using only prosopis fibers and the remaining two were made using alternate layers of jute and glass fiber mats in 0 o, 90 o and 45 o orientations. After fabrication, the laminates were kept in an oven at a temperature of 60 o C for a period of 2hrs. The specimens required for performing tensile, impact, flexural and water absorption tests were cut from the laminate as shown in Figure 4.1 and Figure 4.2, following the appropriate ASTM standards Testing Methods The tensile test was carried out using TUN 400 universal testing machine by adopting the dimensions and standards stipulated in ASTM 638. During the test, the cross head speed was maintained at 5mm/min. The extensometer was mounted at the centre of gauge length of the specimen to observe the change in length experienced by the specimen during the test. The dimension of flexural test specimen and the procedure adopted for the flexural test was carried out as per ASTM 790. The span of the specimen was kept as 120mm. The specimens were subjected to point load at the centre and the corresponding deflection was measured using dial gauge of 0.01mm accuracy. The impact test and water absorption test was performed by adopting the specifications laid out in ASTM 256 and D 570. The test results of all the specimens are given in Table 4.2.

3 64 Table 4.1 Details of the Specimens Specimen Layup Code Glass (wt%) Jute (wt%) Prosopis (wt%) Resin (wt%) GPJG Glass/PJ/Glass JPJJ Jute/PJ/Jute PJ PJ GPJGPJG Glass/PJ/Glass/PJ/Glass JPJJPJJ Jute/PJ/Jute/PJ/Jute GJGJG Glass 0 /Jute 90 /Glass 0 /Jute 90 /Glass [GJGJG] 45 Glass 45 /Jute 45 /Glass 45 /Jute 45 /Glass (a) (b) (c) (d) Figure 4.1 (e) Representative samples of (a) GPJG (b) JPJJ (c) PJ (d) GPJGPJG and (e) JPJJPJJ

4 65 (a) (b) Figure 4.2 Fractured Specimen after tensile, flexural and impact test (a) GJGJG and (b) [GJGJG] RESULTS AND DISCUSSION Tensile Strength From Table 4.2 and Figure 4.3, it is evident that the specimen GJGJG with alternate layers of jute and glass fiber mats in 0 o and 90 o orientations was found to have maximum tensile strength of MPa. The presence of glass and jute fibers along the direction the tensile load has resulted in appreciable increase in tensile resistance. The next highest tensile strength was observed in specimen GPJG where prosopis fibers sandwiched between two layers of glass fiber mats. The uniformity in distribution of prosopis fibers in the core layer held between two layers of glass fiber mats has resulted in better stress transfer compared to specimen GPJGPJG where in prosopis fibers sandwiched between three layers of glass fiber mats. A similar trend was observed in the study wherein chopped banana and sisal fibers were used as sandwich between two and three layers of glass fiber mats. The tensile strength of banana fiber sandwiched and sisal fiber sandwiched two layer

5 66 glass fiber specimens was found to be higher than three layered glass fiber sandwiched specimens (Arthanarieswaran et al. 2014). The lowest tensile strength was observed in specimens containing only prosopis and prosopis sandwiched between two layer jute fiber specimens. The failure of specimen PJ containing only prosopis fibers was found to be in brittle mode. Table 4.2 Test results of specimens Specimen Layup Code Tensile Strength (N/mm 2 ) Flexural Strength (N/mm 2 ) Energy Absorption (Joules) Percentage of Water absorption GPJG Glass/PJ/Glass JPJJ Jute/PJ/Jute PJ PJ GPJGPJG Glass/PJ/Glass/PJ/Glass JPJJPJJ Jute/PJ/Jute/PJ/Jute GJGJG Glass 0 /Jute 90 /Glass 0 /Jute 90 /Glass 0 [GJGJG] 45 Glass 45 /Jute 45 /Glass 45 /Jute 45 /Glass Flexural Strength From the Figure 4.3, it can be observed that specimens GJGJG and [GJGJG] 45 were found to have maximum flexural strength compared to other specimens. When the specimen is subjected to bending, stress transfer between the layers of fiber mats occur through shear. The presence of glass and jute fibers in mat form enhances the flexural resistance substantially. However, all the sandwich specimens containing prosopis was found to exhibit good flexural resistance. The fiber continuity in the core layer has resulted in better stress transfer from mid region to the supports. The lowest flexural strength was reported for specimen PJ containing only prosopis

6 67 fibers. The absence of fibers of high flexural strength such as glass at the periphery led to premature failure of the specimen PJ in brittle mode. Figure 4.3 Plot of Tensile Strength Figure 4.4 Plot of Flexural Strength

7 68 Figure 4.5 Plot of Impact strength Figure 4.6 Plot of percentage of water absorption

8 Impact Strength From Table 4.2 and Figure 4.4, it is evident that specimen GJGJG and [GJGJG] 45 tend to exhibit maximum energy absorption against impact load. The specimen PJ containing only prosopis fibers was found to possess high impact resistance. The interweaving of prosopis fibers while mixing them intimately with the polymer matrix has abruptly improved its impact strength. Although the tensile and flexural strength of specimen PJ was considerably lower than other specimens, its impact strength was found to be good and comparable with glass fiber reinforced specimens. The specimen JPJJ with prosopis sandwiched between two layer jute fiber specimens was found to exhibit lowest impact resistance compared with other specimens. The absence of fiber mat in the mid region of the specimen has decreased its energy absorption capability and this fact is proven from the result of prosopis sandwiched three layered jute specimen JPJJPJJ for which the impact resistance was found to increase moderately Water Absorption Properties From Figure 4.5, it can be observed that specimens PJ and GPJGPJG reported lowest water absorption compared to other specimens. In specimen PJ, prosopis fibers in mixed sizes enables voids filled up with fibers of next lower size. The other reasons for substantial improvement in the water resistance of PJ could be intimate mixing of fibers with the resin before laying and alkali treatment of fibers at optimum concentration. In specimen GPJGPJG, presence of glass fibers in the periphery as well as at the middle layer has reduced the moisture absorption appreciably. The specimen JPJJ exhibited highest water absorption compared to other specimens. Jute fibers offer least resistance against water absorption and its presence at the periphery of specimen JPJJ has resulted in appreciable increase in water absorption.

9 CONCLUSION The mechanical properties of prosopis sandwiched glass and jute fiber reinforced specimens were studied and compared with specimens reinforced only with prosopis and with glass/jute fibers in alternate layers. From the study, it can be concluded that 1. The tensile strength of specimen reinforced with alternate layers of glass and jute was found to be MPa, highest among all specimens. The orientation of glass and jute fibers along the direction of tensile load has enhanced the tensile resistance appreciably. 2. The tensile strength of two layer glass fiber reinforced prosopis sandwiched specimens was found to be 16.39% more than three layer glass fiber reinforced sandwich specimen. The efficiency of stress transfer between prosopis fibers present in the core layer to the glass fiber at the periphery was found to decrease with increase in sandwich layers. 3. The tensile resistance of specimen containing only prosopis fibers tend to be lowest, only 19.53% of the tensile strength of two layers glass fiber reinforced prosopis sandwiched specimens and the failure was observed to be brittle. 4. The specimens with Glass/Jute combination in 0 0 /90 0 and 45 0 orientation was found to offer high flexural resistance with GJGJG being 16.18% more than [GJGJG] 45 specimen. Out of the specimens containing prosopis fibers, specimen with prosopis sandwiched between three layers of glass fiber mat was found to offer appreciably higher flexural resistance,

10 % of strength offered by GJGJG. The specimen reinforced only with prosopis was found to exhibit the lowest flexural strength, only 45.90% of strength offered by GPJGPJG. 5. The variation of impact resistance showed a different trend with specimen containing only prosopis exhibited higher energy absorption when subjected to impact load. Specimen with prosopis sandwiched between two layers of jute fiber mat was found to offer lowest impact resistance, only 38.57% of strength offered by PJ specimen. The absence of jute fiber mat at the middle layer reduced the energy absorption capacity of the specimen drastically. 6. The water absorption of prosopis sandwiched specimen with jute fibers placed at the periphery was found to be maximum, which proves the greater affinity of jute fibers towards moisture. The water absorption of specimen reinforced only with prosopis fibers was found to be lowest, only 18.69% of the absorption exhibited by JPJJ. The uniform fiber distribution, complete wetting and alkali treatment of prosopis fibers has improved the moisture resistance appreciably. The water absorption of prosopis sandwiched glass fiber reinforced specimens tends to be lower which is mainly due to the presence of glass fibers at the periphery.