CHAPTER 3 RESULTS AND DISCUSSION

Size: px

Start display at page:

Download "CHAPTER 3 RESULTS AND DISCUSSION"

Grace Sutton
5 years ago
Views:

1 95 CHAPTER 3 RESULTS AND DISCUSSION This chapter explains the preparation and characterization of nano jute fiber and fabrication of nano jute fiber reinforced epoxy polymer composites with various percentages (1%, 2%, 3%, 4%, 5%, 6%, 7% and 8%). These composite samples were characterized by mechanical (tensile, flexural, impact and hardness), thermal (TGA and HDT), water absorption and surface morphological studies (SEM and AFM). 3.1 CHARACTERIZATION OF NANO JUTE FIBER The preparation of nano jute fiber was confirmed by the following analysis such as chemical analysis, FT-IR, XRD, FE-SEM,TEM and AFM Estimation of Cellulose, Lignin and Hemicellulose Raw and nano jute fiber were analyzed for hemicellulose, lignin, and cellulose contents and it was observed that cellulose content in the nano jute fiber was 89% as compared to the raw jute fiber 71% (Table 3.1). The Figure 3.1 showed the decline in hemicellulose and lignin content and increase of cellulose (Lu et al 2009 and Maiti 2012). Higher content of cellulose leads to a better stiffness and strength of the fibers.

2 96 Table 3.1 Estimation of Cellulose, Hemicellulose and Lignin System Cellulose Hemicellulose Lignin Others Raw jute fiber (untreated) 71(±3) 14(±2) 6(±1) ±9 Nano jute fiber 89(±6) 2(±2) 3(±1) ±6 Figure 3.1 Chemical Analysis of Raw and Nano Jute Fibers

3 FTIR Characterization This topic deals with the structural elucidation of raw jute and nano jute fibers. FTIR of Raw and Nano Jute Fibers is shown in Table FTIR Analysis of the Raw Jute Fiber The peak arising at 3374 cm -1 corresponds to the OH stretching vibration of the water and alcohol group. The peaks at 2900 cm -1 and 2708 cm -1 indicate the existence of the CH 2 vibration and aromatic CH stretching vibration respectively. The peaks around 1731 cm -1, 1603 cm -1 and 1506 cm -1 can be attributed to the stretching of the carbonyl group of lignin and aromatic ring skeleton vibration respectively. The peaks appearing at 1459 cm -1 and 1355 cm -1 correspond to the bending of the CH 2 group (Choi et al 2006). The peaks at 1239 cm -1 and 1067 cm -1 illustrate the presence of phenolic CO of lignin and C-O-C stretching vibration, respectively (Figure 3.2a) FTIR Analysis of the Nano Jute Fiber Infrared measurements were performed on chemically treated nano jute fiber to find out the removal of lignin, hemicellulose and waxy substances. The increase in the cellulose, as confirmed by the FTIR analysis, is shown in Figure 3.2b. The strong O-H stretching absorption value and C-H stretching absorption value are 3400 cm -1 and 2900 cm -1.The characteristic peaks of cellulose and lignin are around cm -1 (C-O stretching vibration of cellulose) and cm -1 (aromatic skeleton vibration of lignin), respectively (Chen etal 2009). The ratio of cm -1 to cm -1 increased, which confirmed that the content of cellulose increased and the content of lignin decreased (Choi et al 2006). The strong peak around

4 cm -1 indicates that the lignin was removed by chemical and physical treatments. This result is consistent with the treated fibers structure that the lignin content decreased and the cellulose content increased (Geethamma et al 2005). Table 3.2 FTIR of Raw and Nano Jute Fibers Peak range[cm -1 ] Raw Jute fiber Peak range [cm -1 ] Nano Jute fiber OH stretching vibration of the water, and alcoholic group CH 2 vibration aromatic CH stretching vibration C=O stretching of the carbonyl group of lignin aromatic ring skeletal vibration , CH 2 bending 1459, , 1154 phenolic CO of the lignin C-O-C stretching vibration

5 Figure 3.2 FTIR spectra of (a) Raw Jute; (b) Nano Jute Fiber 99

6 X-RAY Diffraction The X-ray diffractograms of raw jute and nano jute fibers are shown in Figure 3.3a and 3.3b XRD Patterns of Raw Jute Fiber and Nano Jute Fiber The XRD patterns of raw jute fiber and nano jute fiber are shown in Figure3.3 a and b respectively. The raw jute fiber revealed the 2 peaks at and due to lignin and hemicelluloses respectively. Similarly, the peaks for nano jute fiber were observed at 22.5 and 14.8, indicating the cellulose part. A slight increase in the intensity of 69% can be attributed to the increase in the hydrogen bonding and the loss of lignin and hemicellulose. The fibers show increasing orientation along a particular axis indicating that the non-cellulosic polysaccharides are removed, and there is a decrease in amorphous zones. The slight increase in the crystallinity after chemical and physical treatments is due to the partial loss of the disordered regions during the washing process, because of their increased water-solubility. Therefore, the nano jute fiber reinforcement will be effective in providing better composite material.

7 Figure 3.3 X-ray Diffraction of (a) Raw Jute Fiber; (b) Nano Jute Fiber 101

8 Morphological Studies on Nano Jute Fiber After each chemical treatment, scanning electron microscopy was done to verify the removal of pectin, hemicellulose, and lignin, and to visualize the separation of the fibers from the fiber bundles. Figure 3.4 shows the change in the morphology of jute fiber after chemical treatment due to the removal of hemicellulose, lignin, and pectin (Sinha and Rout 2009 and Singleton et al 2003). The morphological development of raw jute fiber and nano jute fiber is shown in Figures 3.5 and 3.6. Original jute fibers are bundles of individual strands held together by binder and the bundles have a diameter of around 40~80 nm (Dong et al 2012 and Thwe et al 2002). The size of the individualized micro-fibrils are around 5~10 m. High pressure steam defibrillation created an efficient reduction in the diameter of jute fibers due to jute fibers splitting along the fiber axis (Teixeira et al 2010 and Takagi and Asano 2009). The FE-SEM images of the jute nano fibers are shown in Figure 3.7a and b. Most of the nano fibers were less than 100 nm in diameter (Menezes et al 2009), whereas some exhibited a size slightly higher than 100 nm (Martin et al 2008). TEM analysis to determined size and shape (Figure 3.8). The AFM images of the JNFs shown in Figure indicate an average diameter of 90 nm.

9 Figure 3.4 SEM Image of Raw Jute Fiber 103

10 Figure 3.5 SEM Image of Jute Fiber after Alkali Treatment 104

11 105 Figure 3.6 SEM Image of Jute Fiber after Chemical and Physical Treatment

12 Figure 3.7a FE-SEM Image of Nano Jute Fiber 106

13 Figure 3.7b FE-SEM Image of Nano Jute Fiber 107

14 Figure 3.8 TEM Image of Nano Jute Fiber 108

15 109 Figure Dimensional AFM Picture of Nano Jute Fiber

16 Figure Dimensional AFM Picture of Nano Jute Fiber 110

17 Figure Dimensional AFM Picture of Nano Jute Fiber 111

18 MECHANICAL PROPERTIES Mechanical properties like tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength and hardness test of raw jute and nano jute fiber reinforced epoxy polymer composites are evaluated by the Universal Testing Machine as per ASTM standards (Table 3.3 and Table 3.4) Effect of Weight % of Raw Jute Fiber Reinforced Epoxy Polymer Composites on Mechanical Properties It has been found that the tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength and hardness of the composite samples increase with an increase in the fiber content, for both raw jute and nano jute fiber reinforced epoxy polymer composites upto 7 wt% and thereafter decrease. The increase in the mechanical properties upto 7 wt% may be due to nature of the fiber, polymer and fiber-matrix interfacial bonding (Chakaborty et al 2005). The decrease in the mechanical properties after 7 wt% can be attributed to the poor fiber matrix adhesion, which might have resulted in the micro-crack formation at the interface, and non-uniform stress transfer due to fiber agglomeration within the matrix (Wei-ming et al 2008 and Xia et al 2009). Similar observations were made by (Mohanty et al 2000). On comparing the raw jute fiber epoxy composite with the nano jute reinforced epoxy composite, the latter was found to be superior in the mechanical properties. This is because, the raw jute fibers possess waxy substances and amorphous cellulose (Paakko et al 2007 and Orts et al 2005). The inferiority of the raw jute fiber reinforced composites in mechanical properties was due

19 113 to the presence of waxy substances and amorphous cellulose which lead to the brittle nature of the jute fiber (Oksman et al 2006 and Nishino et al 2004). In a nano jute fiber reinforced composite, the waxy substances are eliminated and the cellulose is associated with the matrix by hydrogen bonding. This bond is flexible and compact, and so increases the mechanical properties. In addition to this, wetting of the nano jute fibers in the resin takes place during curing, thereby increasing the mechanical properties. The comparative mechanical properties of neat resin, 7% wt of raw jute and nano jute fiber reinforced epoxy polymer composites are shown in Figures Table 3.3 Mechanical Properties of Raw Jute Fiber Reinforced Epoxy Polymer Composites Systems Pure epoxy Tensile strength (MPa) Tensile modulus (MPa) Flexural strength (MPa) Flexural modulus (MPa) Impact Strength KJ/m 2 Hardness % % % % % % % %

20 114 Table 3.4 Mechanical Properties of Nano Jute Fiber Reinforced Epoxy Polymer Composites Systems Pure epoxy Tensile strength (MPa) Tensile modulus (MPa) Flexural strength (MPa) Flexural modulus (MPa) Impact Strength KJ/m 2 Hardness % % % % % % % %

21 115 Figure 3.12 Tensile Strength of 7 wt% Raw and Nano Jute Fiber Reinforced Epoxy Polymer Composites

22 116 Figure 3.13 Tensile Modulus of 7 wt% Raw and Nano Jute Fiber Reinforced Epoxy Polymer Composites

23 117 Figure 3.14 Flexural Strength of 7 wt% Raw and Nano Jute Fiber Reinforced Epoxy Polymer Composites

24 118 Figure 3.15 Flexural Modulus of 7 wt% Raw and Nano Jute Fiber Reinforced Epoxy Polymer Composites

25 119 Figure 3.16 Impact Strength of 7 wt% Raw and Nano Jute Fiber Reinforced Epoxy Polymer Composites

26 120 Figure 3.17 Hardness of 7 wt% Raw and Nano Jute Fiber Reinforced Epoxy Polymer Composites

27 THERMAL ANALYSIS Thermo Gravimetric Analysis (TGA) TGA of Raw Jute and Nano Jute Fibers Reinforced Epoxy Polymer Composites In the raw jute fiber reinforced composite, initially a sharp weight loss starts around 280 C and extends upto 360 C (Fig 3.18a). This weight loss may be due to the loss of the absorbed water. After 360 C there is a decrease, perhaps due to the elimination of hemicellulose and lignin (Plackett and Va zquez 2004). Figure 3.18b shows the nano jute fiber reinforced epoxy composite; the steep decrease in the curve from 200 C to 300 C reveals the loss of absorbed water. After 300 C, there is a shallow curve, indicating that less water was absorbed due to the non-availability of hemicellulose and lignin, and also due to a cellulose chain split ( C) ( Fukuzumi et al 2009 and Park et al 2003). The bonds of C-C and C-O in the cellulose chain were broken (Capadona et al 2009). This can also be attributed to the decrease in crystalline cellulose chains caused by the thermally unstable anhydroglucuronate units present in the nano jute fiber (Fukuzumi et al 2010).

28 122 Figure 3.18 TGA Analysis of (a) Raw Jute Fibers and (b) Nano Jute Fiber Epoxy Polymer Composites

29 Heat Deflection Temperature (HDT) Effect of Weight % of Raw Jute and Nano Jute Fibers Reinforced Epoxy Polymer Composites on HDT Heat deflection temperature (HDT) is a property which would provide the basis for the selection of the material to be used at higher temperature. Table 3.5 shows the HDT values of raw and nano jute fiber reinforced epoxy polymer composites with wt % (1% to 8%). The HDT value increases with increasing fiber weight percentages upto 7% for both raw and nano jute fiber reinforced epoxy polymer composites, and decreases after 7%. due to poor wettability of the fiber with the matrix resin. The nano jute fiber reinforced epoxy polymer gave better HDT value (82 C) than raw jute fiber reinforced epoxy polymer composites, because of poor interfacial bonding between the fiber and the matrix (Maries Idicula et al 2005 and 2006). These results of the HDT of fiber based composites have demonstrated that the samples having lower jute fiber weight fraction or higher matrix content would be useful for higher temperature applications. The comparative HDT properties of neat resin, 7% wt of raw jute, and nano jute fiber reinforced epoxy polymer composites are shown in Figure 3.19.

30 124 Table 3.5 Heat Deflection Temperature of Raw Jute and Nano Jute Fibers Reinforced Epoxy Polymer Composites Systems HDT of Raw Jute Fiber Composites ( C) HDT of Nano Jute Fiber Composites ( C) Pure Epoxy % % % % % % % % 70 76

31 125 Figure 3.19 HDT of 7 wt% Raw and Nano Jute Fiber Reinforced Epoxy Polymer Composites

32 WATER ABSORPTION STUDIES The water absorption studies of raw jute and nano jute fibers reinforced polymer composites were analyzed as per ASTM standard D Effect of Weight % of Raw and Nano Jute Fibers Reinforced Epoxy Polymer Composites on Water Absorption Table 3.6 shows the dry weight, immersed weight and water uptake percentage of the raw and nano jute fiber reinforced epoxy polymer composites. It shows a decrease in the water uptake capability of the 7wt% nano jute fiber reinforced composite. This may be due to the effect of the alkaline solubilization of hemicelluloses, which is usually ascribed to the destruction and breaking of the hydrogen bonds. In particular, all the esterlinked substances of the hemicelluloses can be cleaved by an alkali except for the cleavage of -ether bonds between lignin and hemicelluloses. This tends to increase the hydrophobicity, and hence, the solubility of the polymer. One can see that the unloaded sample showed a negligibly small increase in weight after 24 h, followed by a loss in weight, which might be due to its dissolution in water. In contrast, the incorporation of JNFs provided a stabililization effect to the matrix (Premlal et al 2002 and Rana et al 2003). This phenomenon can be ascribed to the presence of a three dimensional cellulosic network, that strongly restricts the dissolution of the polymeric matrix in water (Ray et al 2001 and Potluri et al 2012). The comparative water absorption properties of neat resin, 7 wt% of raw jute and nano jute fiber reinforced epoxy polymer composites, are shown in Figure 3.20.

33 127 Table 3.6 Water Absorption Behaviour of Raw Jute and Nano Jute Fibers Reinforced Epoxy Polymer Composites System % of moisture absorption (mg) Raw Jute fiber epoxy composites Nano jute fiber epoxy composites Pure epoxy % % % % % % % %

34 128 Figure 3.20 Water Absorption of 7 wt % Raw and Nano Jute Fiber Reinforced Epoxy Polymer Composites

35 DYNAMIC MECHANICAL ANALYSIS Dynamic storage modulus (E ) is the most important property to assess the load-bearing capability of a composite material. The ratio of the loss modulus (E ) to the storage modulus (E ) is known as a mechanical loss factor (tan ), which quantifies the measure of balance between the elastic phase and the viscous phase in a polymeric structure. This can relate to the impact properties of a material. Generally, the tan peak (at low frequency) is at a temperature C above the Tg, as measured by the dilatometer or differential thermal analysis (DTA). The temperature of the maximum loss moduluse is very close to that oftg Effect of the Weight Ratio of Raw Jute and Nano Jute Fiber Epoxy Composites on the Storage Modulus (E ) with Temperature Figures3.21 and 3.22 shows that the E value of the nano jute fiber reinforced composites is higher than that of the raw jute fiber reinforced composites. Initially the storage modulus (E ) decreases slightly with increasing temperature and a sharp falling trend was observed for both raw jute fiber and the nano jute fiber reinforced epoxy polymer composites at 65 C and 79 C respectively, indicating a glass transition temperature (Ray et al 2002 and Pothan et al 2001). The higher value of E for the natural fiber reinforced composites is due to the inter and intra molecular hydrogen bonding, resulting from the increased number of hydroxyl groups and regeneration of the hydrogen bonds (MariesIdicula et al 2005).

36 130 This leads to the closer packing of the cellulose chain that increases the stiffness of the fibers, which is reflected in the storage modulus (Laly et al 2006). The decrease in E with respect to temperature may be due to the molecular movement of the polymeric material (Laly and Thomas 2003) Effect of the Weight Ratio of Raw Jute and Nano Jute Fiber Epoxy Composites on Loss Modulus (E ) with Temperature The loss modulus values of raw jute and nano jute fibers reinforced epoxy polymer composites samples are tabulated in Table It is observed that loss modulus value is higher for raw jute fiber reinforced epoxy polymer composites sample than for the nano jute fiber reinforced epoxy polymer composites sample. This may be due to the rigidity and stiffness of the fiber into the matrix resulting from the chemical treatment (Li et al 2009 and Pothan et al 2003) Effect of Weight Ratio on Mechanical Loss Factor (tan ) with Temperature Figures 3.23 and 3.24 show that the damping parameter (tan ), which is the ratio of the loss modulus to the storage modulus, is the maximum for the raw jute fiber reinforced epoxy polymer composites sample. It has been reported that the incorporation of stiff fibers in a composite (Li x tabil et al 2007). Structure reduces the tan peak height, because of the restricted movement of the molecules. As a result, the amount of matrix (volume) has become inadequate to dissipate the vibrational energy of the molecules properly, and hence, the tan value decreases.

37 131 Figure 3.21 Storage Modulus Curve for 7wt% of Raw Jute Fiber Reinforced Epoxy Polymer Composites

38 132 Figure 3.22 Storage Modulus Curve for 7wt% of Nano Jute Fiber Reinforced Epoxy Polymer Composites

39 133 Table 3.7 Storage Modulus, Loss Modulus and Mechanical Loss Factor Value of Raw and Nano Fiber Reinforced Epoxy Polymer Composites Weight ratio (%) of Jute fiber Storage modulus (E ) (Pa) Loss modulus (E ) (Pa) Mechanical loss factor (tan ) 7% raw jute fiber Epoxy composites 7% nano jute fiber Epoxy composites

40 134 Figure 3.23 Tan Curve for 7wt% of Raw Jute Fiber Reinforced Epoxy Polymer Composites

41 135 Figure 3.24 Tan Curves for 7wt% of Nano Jute Fiber Reinforced Epoxy Polymer Composites

42 SCANNING ELECTRON MICROSCOPE (SEM) Scanning Electron Microscopy Analysis of 7 wt % Raw Jute and Nano Jute Fiber Reinforced Epoxy Polymer Composites The scanning electron microscopic analysis of 7% wt raw jute fiber reinforced epoxy polymer composites is shown in Figures The microscopic images of the fracture surfaces of 7wt% raw jute fiber reinforced epoxy polymer composites indicate that the phenomenon of pull-out occurred to a greater extent causing the failure of materials. The image analysis also shows the formation of voids due to fiber pull-out. Further, due to the absence of the fiber-matrix interaction (Li et al2005 and Lin et al 2006), the fibers tend to agglomerate into bundles, and become unevenly distributed throughout the matrix (Liu et al 2009 and Liu et al 2008). The lack of fibermatrix interfacial bonding shown in Figure 3.28 resulting in low mechanical properties has been discussed in sections The scanning electron microscopy analysis of 7% wt nano jute fiber reinforced epoxy polymer composites is shown in Figures The microscopic images of the fracture surfaces of 7wt% nano jute fiber reinforced epoxy polymer composites show the formation of smooth surfaces and no voids due to fiber pull-out (Rong et al 2001 and revol et al 2007). This may be due to the treatment of fiber, better wettability of the fiber with the matrix, and better bonding between the fiber and the matrices(ray et al 2001and Rong et al 2002).

43 137 Voids due to Fiber pull -out Figure 3.25 SEM Micrograph of Fractured Surface of 7wt% Raw Jute Fiber Epoxy Composite after Tensile Test

44 138 Figure 3.26 SEM Micrograph of Fractured Surface of 7wt% Raw Jute Fiber Epoxy Composite after Flexural Test

45 139 Figure 3.27 SEM Micrograph of Fractured Surface of 7% Raw Jute Fiber Epoxy Composite after Impact Test

46 140 Poor interfacial bonding Figure 3.28 SEM Micrograph of Fractured Surface of 7wt% Raw Jute Fiber Epoxy Composite with Weak Interface

47 141 Figure 3.29 SEM Micrograph of Fractured Surface of 7wt% Nano Jute Fiber Epoxy Composite after Tensile Test

48 142 Figure 3.30 SEM Micrograph of Fractured Surface of 7wt% Nano Jute Fiber Epoxy Composite after Flexural Test

49 143 Figure 3.31 SEM Micrograph of Fractured Surface of 7wt% Nano Jute Fiber Epoxy Composite after Impact Test

50 144 Figure 3.32 SEM Micrograph of Fractured Surface of 7wt% Nano Jute Fiber Epoxy Composite with Strong Interface

145 3.7 ATOMIC FORCE MICROSCOPY (AFM) 3.7.1 AFM of Raw Jute and Nano Jute Fibers Reinforced Polymer Composites The AFM images of the raw jute and nano jute fibers reinforced epoxy polymer composites are shown in Figures 3.

51 ATOMIC FORCE MICROSCOPY (AFM) AFM of Raw Jute and Nano Jute Fibers Reinforced Polymer Composites The AFM images of the raw jute and nano jute fibers reinforced epoxy polymer composites are shown in Figures Figure 3.33 and 3.34 show more voids after the fiber pull out tests, due to poor interfacial bonding between the fiber and the matrices in the case of raw jute fiber reinforced epoxy polymer composites (Sheltamia et al 2012). Figure 3.35 shows rough surface because of poor wet ability between fiber and matrices (Seena Joseph et al 2002 and Samir et al 2005). In the case of nano jute fiber reinforced epoxy polymer composites the figures( ) show smooth surfaces and better bonding between the fiber and the matrix. Figure D AFM Picture of Raw Jute Fiber Reinforced Epoxy Polymer Composites

52 146 Figure D AFM Picture of Raw Jute Fiber Reinforced Epoxy Polymer Composites after Pull it out Test

53 147 Figure 3.35 AFM 3D Image Raw Jute Fiber Reinforced Epoxy Polymer Composites Rough Surface

54 148 Figure 3.36 FM 2D Image Nano Jute Fiber Reinforced Epoxy Polymer Composites

55 149 Figure 3.37 AFM 2D image Nano Jute Fiber Reinforced Epoxy Polymer Composites after Pull it out Test

56 150 Figure 3.38 AFM 3D Image Nano Jute Fiber Reinforced Epoxy Polymer Composites Smooth Surfaces

Surface Modification to Improve the Impact Performance of Natural Fibre Composites

Surface Modification to Improve the Impact Performance of Natural Fibre Composites J. George, J. Ivens and I. Verpoest Department MTM, Katholieke Universiteit Leuven De Croylaan 2, B-3001 Heverlee, Leuven,