Tensile and Bending Properties of Jute Fabric/Mat Reinforced. Unsaturated Polyester Matrix Composites

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1 Tensile and Bending Properties of Jute Fabric/Mat Reinforced Unsaturated Polyester Matrix Composites Elsayed A. Elbadry *, Mohamed S. Aly-Hassan, and Hiroyuki Hamada Depaetment of Advanced Fibro-Science, Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-Ku, Kyoto , Japan. * Corresponding author. Tel.: ; Fax: d @edu.kit.ac.jp. Key words: Jute fabric; Jute mat; Unsaturated polyester; Mechanical properties;notched tensile strength; Characteristic distance; Recycling. Abstract Recycled jute fabric cloths as skin layers and jute mat as a thick core were used as natural fiber reinforcements for unsaturated polyester matrix composites via modifying the hand lay-up technique with resin pre-impregnation into the jute in vacuum. The effect of skin jute fabric on the tensile and bending properties of jute mat composites was investigated for different fiber weight contents. Moreover, the notch sensitivity of these composites was also investigated. The results showed that the tensile and flexural properties increased by increasing the fiber weight contents. As well as adding the jute fabric as skins for the jute mat composites has improved the tensile and bending properties with respect to those of jute mat reinforced unsaturated polyester matrix composites, whereas the notch sensitivity of the jute mat composites is lower than that of jute fabric/mat composites. Moreover, the fracture behavior of above-mentioned composites was clarified by SEM analysis. 1. Introduction Recently, the strict environmental regulations have forced the composite industry to find alternatively eco-friendly reinforcements and resin systems to produce environmentally friendly composite materials. These natural composites could be used in automotive industry as interior parts and in constructions sector as walls and roofs. Natural fibers reinforced composite materials have been subject of many intensive studies due to the considerable characteristics of the natural fibers, such as biodegradability, abundance, renewability, low cost, low specific gravity, and high specific strength, etc. However, certain drawbacks, such as incompatibility with the hydrophobic polymer matrices, the tendency to form aggregates during processing, and poor resistance to moisture absorption, reduce significantly the mechanical properties of the natural fibers reinforced composite materials [1]. Amongst the natural fibers used as composite reinforcements, jute fiber constitutes large area of investigation. This is because the good mechanical properties of jute fibers when compared with other natural fiber, such as sisal, coir, and ramie [1]. Several authors have studied the continuous jute fiber composites from different aspects, e.g., mechanical properties [2-4], the effect of fiber treatments on mechanical properties [4], dynamic mechanical properties [5], physical properties [3], processing and microstructures [6]. As well known, the jute bags at the end of their longevity will be as waste materials, moreover the 1

2 remaining short slivers of jute fibers yielded from the jute cloth fabrication aren t yet reused efficiently. Therefore, in this research the used jute bags were recycled by mincing them and mingled with short jute slivers to produce jute mats. These jute mats ware produced by applying slightly compressive load on short jute fibers to be packed together in form of mat which can be used as a core needle punched with recycled jute fabric cloths as skin layers which can be used later as reinforcement for valuable polymeric composite structures with certain degree of green. In this research, a modified hand lay-up technique was introduced to fabricate jute mat and jute fabric/mat reinforced unsaturated polyester matrix composites. The same fabrication procedure of the conventional hand lay-up technique was used after primary resin impregnation into the jute fabric /mat in vacuum conditions. The aim of the suggested simple modification is to improve the impregnation of resin throughout the jute and the suggested method is called pre-impregnation hand lay-up technique. The effect of skin jute fabric on the tensile and bending properties of jute mat composites was investigated for different fiber weight contents. Moreover, the notch sensitivity of these composites was also investigated by studying the effect of different ratios of the notch size to the specimen width (D/w) (0.34, 0.44, 0.59) on the tensile strength of these composites with 32 wt% fiber weight content. 2. Experimental procedure Preparation of the composites Jute fiber mats consisting of 50% jute slivers and 50% recycled jute as a core with recycled jute fabric cloths as skin layers were prepared by Yano Co.LTD, Japan. Unsaturated polyester, RigoracTM was obtained from Showa Denko K.K., Japan and the curing agent is Methyl ethyl ketone peroxide (PERMEK N) obtained from NOF Corporation, Japan. The jute mats were dried for 6 h at C and were completely submerged in unsaturated polyester resin. The next step which differentiates the modified technique over the conventional technique is that the jute mat fabrics were degassed in a vacuum for 20 minutes at room temperature to remove the entrapped air bubbles. After that, the jute fabric/mat was cured under a pressure of about 55 kg/cm 2 at room temperature for 24 h with the presence of a 6 mm spacer to produce the composite on the same thickness for different fiber contents. The composite was then post-cured at C for 2 h and finally it was allowed to cool naturally to room temperature for about 30 minutes. Composite panels were prepared with different fiber weight contents (26, 36, 46 wt%) and the specimens of required dimensions were cut and used for testing. For comparison the same procedure was applied to fabricate the jute mat composites without skin layers with ( 22, 32 wt%) and the details were mentioned in reference [7]. Mechanical characterization Tensile properties were determined according to ASTM D 3093/ D3039 M standard with sample dimensions of mm using aluminum taps of 1 mm thickness to prevent gripping damage. The measurements were carried out using a universal Instron testing machine (Model 55 R 4206, Japan) at a crosshead speed of 1mm/min. at room temperature. Three-point bending test was also conducted using the same machine according to ASTM D at a crosshead speed of 1mm/min with sample dimensions of and the span to depth ratio was 16:1. The fracture behavior of the composites for the different mechanical tests was studied using Scanning Electron Microscope (SEM) (JEOL-5200). 3. Results and discussions Tensile properties of the composites The effect of fiber weight content on the tensile strength and young s modulus of the different 2

3 composites was indicated in Fig. 1. It can be seen that the tensile strength and young s modulus increase as the fiber weight content increases and these mechanical properties are enhanced slightly in the case of jute fabric/mat composites compared to the jute composites due to the presence of jute fabric skin layers. The tensile strength of jute fabric/ mat was enhanced by 46% at 26 wt% fiber weight content compared to the value of neat resin, while the young s modulus was enhanced by 94% compared to that of the neat resin. By increasing the fiber weight content to 36 wt%, the tensile strength and young s modulus were improved by 102% and 120% compared to those of the neat resin respectively. Increasing the fiber weight content to 46 wt%, an additional upgrading of tensile strength and young s modulus had occurred by 147% and 179%, respectively with respect to those of the neat resin. It can also be observed that by increasing the fiber weight content, the young s modulus enhanced significantly than that of the tensile strength compared to that of neat resin. The fracture surface of the jute fabric/mat composites for different fiber weight contents under tensile loading is emphasized in Fig. 2, fiber pull out is the failure mode during the fracture behavior. The ability of the interfaces to transfer stresses from the matrix to the fiber plays an important role in determining the mechanical properties of fiber-reinforced composites [8]. As the fiber content increases, holes, which result from complete pull out occurring along the fiber, decrease and the retention of the resin with the fiber ends increases as shown in Fig. 2a, b and c, so the stress transfer characteristics from the matrix to the fibers were improved and therefore the tensile strength and modulus increase. Fig. 1. Effect of fiber weight content on the tensile strength and young s modulus of the different composites. (c) Fig. 2. SEM micrographs of tensile fracture surface of the jute fabric/mat composites for different fiber weight contents 26 wt% 36 wt% (c) and 46 wt.%. 3

4 Flexural properties of the composites The effect of fiber weight content on the flexural strength and modulus is displayed in Fig. 3a and b respectively. It can be observed that as the fiber content increases, the flexural strength and modulus increase and these mechanical properties are enhanced better in the case of jute fabric/mat composites compared to the jute composites due to the presence of jute fabric skin layers. The flexural strength of jute fabric/mat composites was improved by 23% at 26 wt% compared to the value of neat resin, whereas the improvement for the flexural modulus is 102% compared to that of the neat resin. By increasing the fiber content to 36 wt%, the improvement of the flexural strength is 30%, while the flexural modulus was improved by 106% regarding to that of neat resin. The flexural strength and modulus was improved by 34% and 124%, respectively by increasing the fiber weight content to 46 wt% with respect to the value of neat resin. The fracture surface of jute fabric/mat composites after three-point bending test for tension side at different fiber weight contents, where the crack always initiates on the tension side of the beam and slowly propagates in an upward direction is shown in Fig. 4. Fiber pullout is the failure mode for different fiber weight contents. It can be seen from the fracture surface of fiber ends that most of the fibers are broken as a result of the good interfacial properties between the fiber and the matrix, which will lead to good stress transfer characteristics between the matrix and the fiber. Moreover, the higher fiber weight content, the fewer holes were found on the fracture surface as shown Fig.4 a, b and c indicating that partial pull out occurring along the fiber due to better stress transfer characteristics between the matrix and the fiber. Moreover, it can also be observed that as the fiber content increases, the retention of the resin with the broken fiber ends increases as shown in Fig.4 a, b and c indicating that the increase of the fiber weight content enhances the load transfer characteristics from the matrix to the fibers, therefore the flexural strength and modulus increase. Fig. 3. Effect of jute fiber weight content on flexural strength and flexural modulus of the different composites. 4

5 (c) Fig. 4. SEM micrographs of the fracture surface of the jute fabric/mat composites under bending load at the tension side for different fiber weight contents 26 wt%, 36 wt% and (c) 46 wt%. Notch sensitivity of the composites The tensile strength of notched composites can be determined from the following equation: σ f = P ( w D) * d where P is the maximum load (N), w is the specimen width (mm), D is the notch diameter and d is the specimen thickness (mm) The characteristic distance d 0 is a material property independent of laminate geometry and stress distribution and represents the distance over which the material must be critically stressed in order to find a sufficient flaw size to initiate failure. The characteristic distance d 0 according to the point stress criterion [9] which the failure occurs when the stress over some distance d 0 away from the discontinuity is equal to or greater than the strength of the unnotched material. (1) Fig. 5 The effect of D/w ratio on the characteristic distance of the composites for jute composites and jute fabric/mat composites. The characteristic distance can be used as a measure of the notch sensitivity; the higher d 0 indicates lower notch sensitivity and vice versa. The effect of D/w ratio on d 0 for the different composites is shown 5

6 in Fig. 5 and the calculated values are shown in Fig. 6. It can be observed that the characteristic distance d 0 is lower for jute composites than those of jute fabric/mat composites. As a result of that, the tensile strength of the jute fabric/mat composites is sensitive higher that of jute composites compared to the tensile strength of unnotched composites as shown in Fig. 6. Fig. 6. The effect of the ratio (D/w) on the σ N /σ o and d o of the different composites jute composites and jute fabric/mat composites. Conclusion Jute fabric/mat reinforced unsaturated polyester matrix composites were fabricated successfully by modifying the hand lay-up technique. The tensile and flexural properties were increased by increasing the fiber weight contents. As well as adding the jute fabric as skins for the jute mat composites has improved the tensile and bending properties with respect to those of jute mat reinforced unsaturated polyester matrix composites, whereas the notch sensitivity of the jute mat composites is lower than that of jute fabric/mat composites. Fiber pull out mechanism is the failure mode revealed at the fracture surfaces under tensile load as well as at tension side of jute fabric/mat composites under bending load. References [1] A. K Mohanty, M. Misra, and L.T. Drazal, Natural fibers, biopolymers, and biocomposites, New York, Taylor & Francis, 2005, pp. 6, 44. [2] P.J. Roe, M.P. Ansell, J. Mat. Sci., 20, pp (1985). [3] B.A. Acha, N.E. Marcovich, and M.M Reboredo, J. Appl. Polym. Sci., 98, pp (2005). [4] I.A.T. Razera, E. Frollin, J. Appl. Polym. Sci., 91, pp (2004). [5] A.K. Saha, S. Das, D. Bhatta, B.C. Mitra, J. App. Polym. Sci., 71, pp (1999). [6] B.N. Dash, A.K. Rana, H.K. Mishra, S.K. Nayak, S.C. Mishra, and S.S. Tripathy, Polym. Compos., 20(1), pp (1999). [7] E. A. Elbadry, M.S.Aly-Hassan and H. Hamada, Proceedings Recent Advancement of Interfacial Materials Science on Composite Materials, Kyoto Institute of Technology, Japan O-2, pp. 1-4 (2011). [8] M.M Thwee and K. Liao, Compos. Sci. Technol., 63, pp (2003) [9] J.M. Whitney, and R.J. Nuismer, J. compos. Mat., 8 (253), pp (1974). 6