Study on effect of fiber weight fraction on physical and mechanical behaviour of jute-epoxy composite laminates

Md. Hasan Ikbal¹, Ayub Nabi Khan², S.M. Kamrul Hasan³, Mukwaya Vincent⁴

¹Department of Knitwear Manufacturing & Technology, BGMEA University of Fashion & Technology, Dhaka, Bangladesh.

²Department of Textile Engineering, BGMEA University of Fashion & Technology, Dhaka, Bangladesh.

³College of Textiles, Key Laboratory of Technical Textiles, Donghua University, Shanghai, China.

⁴State Key Lab of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai, China.

Corresponding author: Dr. Engr. Md. Hasan Ikbal, Assistant Professor, Department of Knitwear Manufacturing & Technology, BGMEA University of Fashion & Technology, Dhaka, Bangladesh.

Email: ikbal@buft.edu.bd

Abstract:

Recently, there has been a growing interest in using natural fibers as reinforcements in polymer matrix composites. Natural fibers do not only provide strength to materials, they are also light in weight and inexpensive. This paper describes the development and investigates characteristics of natural fiber based polymer composites made of jute fiber mat and epoxy resin fabricated using hand lay-up technique. The physical and mechanical behavior of these composites as a function of fiber weight fraction have been evaluated. Scanning electron microscope has been used to characterize the fiber-matrix adhesion and damage morphology.

Keywords: Fiber reinforced polymer composites, natural fibers; jute fiber; epoxy; hand lay-up; fiber weight fraction

1. Introduction

Demands in fiber reinforced polymer (FRP) composites have been rapidly growing since they offer high performance, great versatility and processing advantages at favorable costs. These materials also offer the possibility of attaining a unique combination of properties by permutation and combination of different fibers and polymers [1]. The properties like high specific strength and stiffness, good fatigue performance and damage tolerances, low thermal expansion, non-magnetic properties, corrosion resistance and low energy consumption during fabrication, etc. [2] make the composite materials as an attractive choice over steels, many metals, and their alloys. In many industries today, composites made of carbon, glass, kevlar fibers have been widely used to design structural and non-structural parts.

Environmental concerns have put tremendous pressure on researchers to find out materials which are biodegradable, renewable and of low cost. Therefore, natural fibers and their composites have been a hot research topic for past few years. While compared to the traditional reinforcing materials such as carbon and glass, natural fibers like jute, abaca, hemp, kenaf, sisal, coir and areca have properties including satisfactory specific strength, low density, good thermal properties, enhanced energy recovery and they cause less skin and respiratory irritation [3, 4]. In a research on energy consumption of glass and natural fibers, the authors concluded that replacing glass fibers with natural fibers could save energy at a rate of 60% per ton of product [5].

Besides, production of natural fibers results in less severe environmental impacts compared to production of glass fibers. Natural fiber cultivation depends mainly on solar energy, and fiber production and extraction use small quantities of fossil fuel energy. On the other hand, glass production and glass fiber production are both energy intensive processes depending mainly on fossil fuels. As a result, the pollutant emissions from glass fiber production are significantly higher than that of from natural fiber production [6].

Natural fiber composites reinforced with jute fiber in particular would be suitable for many primary structural applications, such as indoor elements in housing, temporary outdoor applications like low-cost housing for defense and rehabilitation and transportation. The insulating characteristics of jute make it suitable for applications in automotive door/ceiling panels and panel separating the engine and passenger compartments [7].

Known as the ‘golden fiber’ jute is one of the longest and mostly used natural fiber for various textile applications.  Jute fiber is 100% bio-degradable and recyclable and thus environmentally friendly.

Jute is a product of South Asia and specifically a product of India and Bangladesh. About 95% of world jute is grown in these two south Asian countries. Nepal and Myanmar also produce a small amount of jute. Pakistan, although it does not produce much, imports a substantial amount of raw jute, mainly from Bangladesh, for processing. Bangladesh exports nearly 40% as raw fiber, and about 50% as manufactured items. India exports nearly 200,000 tonnes of jute products, the remainder being consumed domestically. Therefore, the use of jute fiber to reinforce polymer matrix may not only help us in ecological balance but can also provide employment to the rural people in countries like Bangladesh and India where jute is abundantly available.

In this study jute fiber mat has been used for the preparation of the composites with the aim of investigating the potential utilization of jute fiber as reinforcements. Also, the effects of jute fiber loading (fiber weight fraction) on physical and mechanical characteristics of the composites have been investigated. Damage criteria and damage morphology have also been investigated using a scanning electron microscope.

2. Materials and methods2.1. Experimental materials and composite fabrication:

   Jute fiber mat (bidirectional) procured from China has been used as reinforcing materials. The matrix was a low-curing-temperature resin system comprising epoxy (EPIKOTETM MGS® RIMR135). Epoxy and the corresponding hardener (RIMH 137) were provided by HEXION. Composite laminates were fabricated by hand lay-up technique and compositions were varied into five different proportions. Table 1 presents the five different compositions of reinforcing material and epoxy matrix. Post curing of the laminates were carried out keeping them at room temperature for 24 hours. Figure 1(a) and Fig. 1(b) schematically present the lay-up and hand lay-up technique used for composite fabrication.

   

   2.3. Mechanical properties evaluation:

   Hardness was determined using a Rockwell-hardness tester equipped with a steel ball indenter. Tensile test was performed as per ASTM: D3039-76 test standards using a universal testing machine Instron 550R. The flexural strength and inter-laminar shear strength (ILSS) were determined on the same machine under three-point bend configuration in accordance with the standard ASTM: D790 and ASTM: D5379, respectively. The cross-head speed was kept at 10 mm/min. Impact strength of the composites was evaluated by a low velocity impact tests conducted in an impact tester in accordance with ASTM: D256 test standards. Dimensions of the test specimens are shown in Fig. 2 and Fig. 3. Delamination is an internal mode of failure in which the layers separate, resulting in loss of strength. Inter-delamination test was performed according to the ASTM: D5528 standard. Specimens were loaded until fractures occurred and the breaking load was determined.

   3. Result and Discussion

   3.1. Density and volume of void contents:

   The presence of voids in the final composite part is an inevitable fact. Voids are formed mainly because of mechanical air entrapment during lay-up and moisture absorbed during material storage. A higher void content indicates weaker adhesion between fiber and resin. This poor adhesion results in weaker interfacial strength which in turn reduces the strength and stiffness of composite materials, mutual abrasion of fiber leads to fiber fracture and damage and crack initiation and growth due to void coalescence [8]. Nonetheless, the removal of voids is quite critical in many advanced composite structures [9-11]. Some of the curing parameters e.g. temperature and pressure have been found to affect the void content of composite laminates. Therefore, the temperature and pressure schedules recommended by the resin manufacturers should avoid any modification that might alter the structural performance significantly. If these parameters are selected properly, then the entrapped air, water vapor and excessive resin will be squeezed out from the laminates, and laminates with low porosity and high performance will be achieved [11]. In many composite applications, the void content is quite critical and levels above about 1% are not tolerable, such as in advanced composites for dynamic aerospace structures [12]. In other applications, levels of 5% and higher can be tolerated [13]. Therefore, in designing composite structures, establishing the acceptable level of voids is an unavoidable issue.

   

   Table 1 presents the compositions of five different composite laminates, their density, and volume of void fraction (%). Observation reveals that pure epoxy has the minimum void content, with the addition of jute fiber (10% by weight) the void content increases instantly to 5.3% for specimen JE1. But with the further increase in the fiber content from 10% to 50% the volume of void content of the specimens decreases to 2.7%. The theoretical density of the composites increases as the fiber loading (fiber weight fraction) increases.

   3.2. Mechanical properties:

   Figure 4 presents that the hardness of the composite increases with the increase in the fiber content. The reinforcement fibers increase the modulus of composite which in turn increases the hardness of composites. This is because hardness is a function of relative fiber content and modulus [14]. Surface hardness value of 43 HRB is obtained from pure epoxy specimen. Incorporation of 10% fiber in the matrix increases the surface hardness value by 70% for specimen JE1. The maximum surface hardness value of 91.3 HRB was obtained from the composite reinforced with 50% of jute fiber.

   Figure 5(a) plots the variation in tensile strength and tensile modulus of composite with increase in fiber weight fractions. The effect of fiber weight fraction on tensile strength and tensile modulus is linear. Maximum strength and modulus are obtained when the fiber loading is 50% for specimen JE5. It is due to proper transmission and distribution of the applied load by the epoxy resin matrix. This agrees with the findings made by Bijwe [15] who worked on composites reinforced by aramid fabric in polyethersulfone matrix. Tensile strength of such bidirectional jute fiber composite is even higher than that of neat or unfilled epoxy. The tensile strength varies from 60 MPa to 125 MPa and tensile modulus from 1.15 GPa to 4.65 GPa with the fiber content varies from 0 to 50%.The result obtained from the three-point bend test is shown in Fig. 5(b). Incorporation of jute fiber in the epoxy resin matrix has resulted in some interesting consequences. It is noticed that there is a reduction in flexural properties of specimen JE1 with 10% fiber content. The reduction in the flexural properties of the composites is due to weak interfacial bonding and existence of voids. The flexural strength and modulus of the composites increases with the increase in the fiber loading after 10% and maximum flexural properties are noticed when the fiber weight fraction is 50%. The effect of fiber weight fraction on flexural strength and flexural modulus is clearly erratic.

   Similar interesting consequences have been noticed for inter-laminar shear strength, Fig. 6(a). The ILSS value decreases drastically for the composites with fiber content from 0 to 10%, however, it increases on further increase in fiber loading from 10% to 50%. The maximum ILSS of 71.8 MPa is obtained at 50% fiber weight fraction of specimen JE5.

   The maximum impact strength is of 6.301 J was exhibited by the specimen JE5 designed with 50% fiber loading, Fig. 6(b). The impact strength increased linearly with increasing the fiber weight fraction. In principle, more energy was required to break the coupling between the interlaced fiber bundles. It may also be due to the fact that good adhesion between the fiber and matrix acted as a resistance to crack propagation during impact load. In general, the contact area between the fiber and matrix increased with increasing in fiber content and hence, there was good impregnation of fibers in the resin. According to some literatures, the impact transfer should be more efficient when fiber loading is substantial [1].

   Delamination in laminated composites is a common problem caused due to cyclic stresses. The break load and maximum displacement obtained from the inter-delamination test are shown in Fig. 7.  It can be observed that in each category, specimen designed with 50% jute fiber exhibited the highest results. This indicates that composite with higher jute fiber content has superior delamination properties. Specimen with the incorporation of 50% fibers resulted in delamination load of 1.227 KN which is 33% higher than that of designed with 10% fiber, Fig. 7(a). In terms of maximum displacement, specimen with 50% fiber content exhibited displacement of 2.91mm which is 37% higher than that of specimen containing 10% fiber, Fig. 7(b). This is maybe because of proper transmission and distribution of the applied load by the epoxy resin matrix to the fibers.

   In all loading conditions, maximum result has been noticed when the percentage of fiber weight fraction was optimum. Besides, higher jute fiber loading means the reduction of volume and weight fraction of the epoxy resin matrix used in the composite. The life cycle energy use and emissions from the production of most base polymers used in composites are significantly higher than those associated with natural fiber production [6]. Hence substitution of epoxy polymer by higher jute fiber fraction will improve the environmental performance of jute fiber reinforced composites.

   3.3. Damage morphology:

   Damage criteria and damage morphology have also been investigated using a scanning electron microscope (Hitachi TM3000 microscope). Each sample was dried and sputtered with a layer of gold of thickness of 15 -20 nm using an ion-sputter device. Figure 8(a) clearly identifies the presence of void in the composites. Figure 8(b) proves the poor adhesion between the fiber and the matrix. Figure 8(c) presents the fracture surface of specimen after impact loading and Fig. 8(d) is a closer view of breakage of fibers. Both these micrographs illustrate that the load was not uniformly distributed. Fig. 8(d) also shows the complete breakage of fibers which means that composites failed not only because of resin matrix failure but also due to fiber breakage.

   

   4. Conclusion

   Composite laminates have been fabricated using jute fiber as reinforcement mat and epoxy as resin matrix by the hand lay-up technique. Void contents, tensile properties, flexural properties, inter-laminar shear strength and impact strength have been evaluated as a function of percentage fiber content. Tensile, hardness and impact strength increase almost linearly with increasing in fiber content percentage. In case of inter-laminar shear strength and flexural properties, however, incorporation of fiber in the resin matrix has resulted in some interesting consequences. It has been noticed that these properties reduced from 0% to 10% fiber content and with the reduction in the void content from 10% to 50% the properties improved. Incorporation of 50% jute fiber in the epoxy matrix resulted in superior delamination properties. In all cases, maximum result has been noticed when the fiber loading was optimum. Besides, higher jute fiber content means the reduction of volume and weight fraction of the epoxy resin matrix used in the composite. The life cycle energy use and emissions from the production of most base polymers used in composites are significantly higher than those associated with natural fiber production. Hence substitution of epoxy polymer by higher jute fiber content will improve the environmental performance of jute fiber reinforced composites. 

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