Properties of Alkali Modified Jute Reinforced Virgin and Recycled PET Composite

Murugesan M.1*, Senthilkumar T.2

1Department of Textile Technology, Anna University, Chennai 600 025, India
2ICAR-Central Institute for Research on Cotton Technology, Mumbai 400 019, India



The present research work aims to study the mechanical properties of jute fabric reinforced recycled PET matrix composites. The reinforcement of Jute fabric was treated with 5% alkali (NaOH) solution with various time duration of 3, 5 and 7 hours at room temperature. The treated jute fabrics were used as pre-peg for fabricating PET-based composites. The virgin polyester resin and recycled polyester resins were used as a matrix material at different reinforcement matrix combination. The reinforcement was characterized by the effect of alkali treatment and the mechanical properties of composite studied by the effect of mixing proportion of recycled and virgin polyester resin on the mechanical properties such as tensile strength, tensile modulus, flexural strength and a flexural modulus of the composites were studied.

Keywords: Jute Fabrics; recycled PET; Alkali modified; Mechanical Property

1. Introduction

Natural fibres are best alternatives to glass fibre in composites due to low cost, environmentally friendly and lightweight. Natural fibre composites are likely to be environmentally superior to glass fibre [1]. The use of natural fibres in composites reduces 5% cost and 10% weight reduction [2]. The strength and modulus of jute fibres are not as high as those for glass fibre, their strength and modulus are close to the values of glass fibre, indicating the possibility that jute fibres can partially replace glass fibre as reinforcement in composites [3]. To improve the adhesion between the matrix and the jute fibres, it is essential to pre-treat the fibres with alkali so that the wettability of the resin is improved [4]. The major problem of natural fibre composites originates from the hydrophilic nature of the fibre and hydrophobic nature of the matrix. The inherent incompatibility between these two phases results weakening bonding at the interface. Chemical treatments on reinforcing fiber can improve interface bonding and thus improve compatibility with the matrix which leads to achieving better mechanical properties of the composites. The alkali treatment improved the fibre-matrix adhesion which has generally resulted in an increased tensile, flexural and impact properties of jute epoxy composite compared to untreated [5].

The surface treatment is to be given to enhancing the surface properties of the fibers in view of obtaining better interfacial reaction between the matrix and the fiber of the composite, which in turn enhances the mechanical properties of the laminate on the whole [6]. Jute fibres were chemically modified and treated with 5% NaOH solution at room temperature for 2 h, 4 h and 8 h. This chemical treatment was also to alter the characteristic of the fibre surface and improving the degree of crystallinity of the fibre. This may be due to the better fibre matrix interface adhesion caused due to the fibre surface treatment by alkali [7]. Poly ethylene terephthalate (PET) is a semi-crystalline, thermoplastic polyester that exhibits very good mechanical properties, good barrier properties and high transparency. Unsaturated polyester resin is synthesis from the glycolzed method of recycled PET in the form of flakes was obtained by crushing PET beverage bottles. All glycolysis products were reacted with maleic anhydride and mixed with styrene monomer to get unsaturated polyester (UP) resins with cross linked [8]. They found that mechanical blending can be used for recycling purposes without sacrificing of the virgin PET and to reduce material cost in bottle fabrication. In this work, an attempt made to produce low weight modified alkali treated Jute reinforced composite using 100% virgin unsaturated polyester resin (V-UPR), 100% recycled unsaturated polyester resin (R-UPR) and combined 50%V-UPR/50%R-UPR. The mechanical properties of the above composites were compared with the composites prepared by using untreated jute fabric.

2. Materials and Methods

2.1 Materials

The jute woven fabric was procured from M/s. Chetty & Co., Chennai, Tamil Nadu, India. Recycled unsaturated polyester resin and Virgin unsaturated polyester resin, methyl ethyl ketone peroxide and Cobalt octate were procured from the company M/s. Aiswarya Polymers, Coimbatore, Tamil Nadu, India. Methyl ethyl ketone peroxide was used as a catalyst for polymerizing the unsaturated polyester resin. And Cobalt octate was used as an accelerator for the polymerization of the unsaturated polyester resin.

2.2 Methods

2.2.1 Pretreatment by alkalis

The required jute fabrics were soaked in a 5% NaOH solution at 30°C maintaining a liquor ratio of 20: 1. The initial weight of fabric piece (W1) was noted. The fabrics were treated separately in an alkali solution for 3h, 5h and 7h duration. After the alkali treatment, the fabrics were washed thoroughly to remove all NaOH components from the fibre surface. And then the fabrics were dried at room temperature for 48 h followed by oven drying at 100°C for 2h. The final weight of the fabric (W2) was measured. Weight loss due to alkali treatment was calculated in % by the following formula given in equation 1.

Weight loss in % = [(W1 – W2) /W1] x 100                      (1)

2.2.2 Fabrication of Composites

Composites were produced by hand lay-up technique for prepreg preparation and a tailor made mold was used to produce the composite of size 25 x 25 x 0.4 cm. The mold used for the composite preparation can be referred in Figure 3.1. The prepared prepreg was placed on the bottom mold along with resin filled in it. Then, the top mold was placed over it and fastened and compressed. Then it is allowed in the compressed state for gelation. The composites are taken out of the mold and allowed for curing for about 48h at room temperature.

3. Results and Discussion

3.1 Fabric Weight Loss

From Table1, it can be observed that the weight loss in percentage at different treatment periods. The difference between weight loss at 3h and 5h treatment periods is 1% only. But at 7h treatment period the weight loss is nearly double compared to the 5h treatment period.

Table 1. Effect of Alkali treatment on Jute Fabric Weight

Treatment Time (hour) Number of plies Initial weight(g) Final Weight (g) Weight loss (%)
0 12 182.296
3 12 240.818 225.31 6.43
5 12 240.631 222.63 7.48
7 13 246.274 209.81 14.8

3.2 Tensile and Flexural Properties of jute- three different Combinations of Unsaturated Polyester Resins (UPR) Composite

In this work, using Instron 3369, 12 type of jute fabric reinforced composites obtained from the design of experiments were tested for their tensile and flexural behaviour and the results were discussed as follows.

3.2.1 Effect of Alkali Treatment on Tensile Properties of Jute/ UPR Composite

The tensile strength of a composite material is mainly dependent on the strength and modulus of fibres, the strength, chemical stability of the matrix and the effectiveness of the bonding strength between reinforcement and polymer in transferring stress across the interface. From Fig. 1 and 2 the tensile properties of reinforced composite prepared by 100% V- UPR. All alkali treated fabric composites compared with the control sample (0h). Composite consist of 5h treated jute reinforcement shows the higher tensile strength and modulus because the contribution of crystalline cellulose is more but the continuity of the crystalline cellulose structure may support by the amorphous cellulose. And also the improved wettability and more surface area for bonding increase the performance of the composites. Composite with 3hrs treated fabrics shows the decreased in the modulus and tensile strength. This is because of the loss of the structural integrity in the amorphous cellulose and contribution to withstand the applied load. Besides the crystalline cellulose also not contribute to withstand the applied load and removal of some amount of amorphous cellulose was improves the wettability and hence more area available for bonding which also increases the performance of the composite. In the case of 7h treated fabric reinforced composite the amorphous cellulose system was collapsed fully and the fabric stiffness level was improved to the maximum. But, the structural integrity of crystalline cellulose is not adequate to distribute the applied load. Hence, the composites could not attain any improvement in mechanical properties. 100% V-UPR composite, modulus and tensile strength of 5h treated fabrics were 6.448Gpa and 65.751MPa was maximum than untreated, 3h and 7h.

From Fig. 1 and 2, it can be observed that the tensile properties of reinforced composite prepared by 100% R-UPR, modulus and tensile strength of 3h treated fabrics were 5.544Gpa and 88.353MPa was maximum than untreated, 5h and 7h. The same observations are evident on the bar chart diagram. From Fig. 1 and 2, the tensile properties of reinforced composite prepared by combined both 50% V-UPR and 50%R-UPR composite, modulus and tensile strength of 3h treated fabrics were 5.817Gpa and 81.976MPa was maximum than untreated, 5h and 7h. An improvement in the tensile strength of the composites consists of untreated fabric and fabric treated with 5% NaOH for 3h has increased from59.576 MPa to 81.976 MPa. The tensile strength value of 5h treated fabric composite was less than 7h treated fabric composite because of may be due to the presence of void were reported by Soma Dalbehera et al (2014)[9].

Figure 1.  Effect of Alkali Treatment on Tensile Strength of Jute/ UPR Composite
Figure 1. Effect of Alkali Treatment on Tensile Strength of Jute/ UPR Composite
Figure 2.  Effect of Alkali Treatment on Tensile Modulus of Jute/ UPR Composite
Figure 2. Effect of Alkali Treatment on Tensile Modulus of Jute/ UPR Composite

3.2.2 Effect of Alkali Treatment on Flexural Properties of Jute/UPR Composite

Flexural behaviour of the 12 types of jute fibre reinforced composites were tested with Instron. From Fig. 3 and 4, the flexural properties of reinforced composite prepared by 100%V- UPR. Heavy fibre pull-out and breakage was observed in untreated fabric composite. These were found to be decreased in case of alkali treated fibre composites, imperative of a better bonding at the interface between the fibre and the matrix. The mechanical properties of composite reinforced with 3h and 5h alkali-treated fabric were found to be superior in comparison to the untreated fabric reinforced composite and 5h treated fabric reinforced composite having an increase in the flexural strength of 56.29Mpa and 59.60Mpa. This shows that the wettability and adhesion of matrix improved gradually in the composites made up of alkali treated jute reinforcement. The maximum improvement in strength was observed for composite prepared with 5h alkali treated fabric although 7h treated fabric had superior fabric characteristics. Alkali treatment makes the fabric rigid and somewhat brittle afterwards owing to the development of crystallinity causing high strength and low extensibility. On the application of stress, this fabric suffered breakage due to increased brittleness and could not take part in effective stress transfer at the interface, thus lowering the strength of the composite were reported by Rout et al (1999) [10]. Also, From Fig. 3 and 4 the shows flexural strength and flexural modulus for untreated jute fabrics laminates and various alkali treated jute fabrics laminates with recycled unsaturated polyester resin (100%R-UPR) are shown in Fig. 3 & 4 Flexural strength and flexural modulus are increased in various alkali treated jute fabrics laminates such as 3h, 5h and 7h were compared to untreated jute fabrics laminates. So that values of flexural strength of treated jute fabrics laminates are to 71.799Mpa, 57.842 MPa and 62.603 MPa. The value of flexural modulus of alkali treated jute fabrics laminates is found to be higher, compared to the untreated jute fabrics laminates. From Fig. 3 and 4 the flexural strength and modulus of jute/ combined both 50%V-UPR and 50% R-UPR composites for untreated and the alkali treated. The trend of flexural strength is similar to the trend of tensile strength. When compared to control fabric the treated fabric showed higher flexural strength and modulus. It is evident that alkali treated jute fabric laminates consistently improved the flexural strength compared to the untreated jute fabric laminates. The flexural strength and modulus were consistently better for 3h, 5h and 7h alkali treated jute fabric laminates compared to untreated jute fabric laminates. Maximum flexural strength and modulus values were consistently obtained from 3h alkali treated jute fabrics laminates composite in comparison to the 5h and 7h alkali treated jute fabrics laminates. The condition above indicates that 3h alkali treated jute fabrics reinforced composite is stiffer and stronger than 5h and 7h. Because the increased time of treatment which helps the jute fibres to achieve higher stiffness. But due to lack of structural integrity between the stiffer fibres, the expected performance was reduced. Average values for the ultimate flexural strength and flexural modulus for the composites are 70.033 MPa and 3.479 GPa respectively, and the corresponding values for the untreated jute fabrics laminates are 43.894 MPa and 2.323GPa.

Figure 3.  Effect of Alkali Treatment on Flexural Strength of Jute/ UPR Composite
Figure 3. Effect of Alkali Treatment on Flexural Strength of Jute/ UPR Composite
Figure 3.  Effect of Alkali Treatment on Flexural Strength of Jute/ UPR Composite
Figure 3. Effect of Alkali Treatment on Flexural Strength of Jute/ UPR Composite


The effect of alkali treatment of jute fabric on the mechanical properties of jute/unsaturated polyester resin composites was studied. Treatment of jute fabrics by 5% NaOH at room temperature for varying times showed an overall improvement in properties of jute fabric reinforced composites. The treated fabric composite showed better tensile properties than untreated composite due to enhancement in bonding between fabric and matrix. The improved properties of the fabric with alkali treatment were also as the result of the dissolution of hemicellulose and development of crystallinity and fibrillation, thus created superior bonding with unsaturated polyester resin. The control fabric showed a higher tensile strength values compared to the alkali treated material. The fibres were finer after treatment of fabrics, having less hemicellulose content, increased crystallinity, a reduced amount of defects resulting in superior bonding with the unsaturated polyester resin. The mechanical properties were maximum when reinforced around 3–5 h treated jute fabric. The results showed that the mechanical properties are varied indicating the possibility of two different failure modes before 2h and after 5h treatment. Improper bonding between fibres and matrix so fibre pulls out was predominant up to 2h and after 5h the fracture occurred with minimum fibre pull out due to the superior bonding and improved tenacity and low extensibility of the fibres. A treatment time between 3-5h was therefore optimal to get maximum strength of the unsaturated polyester resin reinforced with jute fabrics treated with 5% NaOH solution at 30°C.


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