Preparation and Characterization of Jute Fabrics Reinforced Urethane Based Thermoset Composites: Effect of UV Radiation

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1 Fibers and Polymers 2010, Vol.11, No.2, DOI /s Preparation and Characterization of Jute Fabrics Reinforced Urethane Based Thermoset Composites: Effect of UV Radiation Haydar U. Zaman, Avik Khan, Ruhul A. Khan*, Tanzina Huq, Mubarak A. Khan, Md. Shahruzzaman, Md. Mushfequr Rahman, Md. Al-Mamun, and P. Poddar Radiation and Polymer Chemistry Laboratory, Institute of Nuclear Science and Technology, Bangladesh Atomic Energy Commission, G.P.O. Box: 3787, Dhaka, Bangladesh (Received March 31, 2009; Revised October 31, 2009; Accepted December 20, 2009) Abstract: Jute fabrics reinforced thermoset composites were prepared with different formulations using urethane acrylate oligomer, methanol, and benzyl peroxide. Jute fabrics were soaked in the prepared formulations and fiber content in the composites was optimized with the extent of mechanical properties. Among all the resulting composites, 55 wt% jute content at oligomer:methanol:benzyl peroxide=75:24.5:0.5 (w/w/w) ratio showed best mechanical properties. The optimized jute fabrics were cured under UV radiation at different intensities and their mechanical properties were measured. Jute fabrics were treated with potassium permanganate (KMnO 4 ) solution of different concentrations (0.01, 0.02, 0.03, and 0.05 wt%) for different soaking times (1-5 min) before the composite fabrication. Optimized jute fabrics (jute fabrics treated with 0.02 wt% KMnO 4 for 2 min soaking time) were soaked in the optimized formulation and cured under UV radiation at different intensities and measured their mechanical properties. Scanning electron microscopic investigation showed that surface modification improves fiber/matrix adhesion. Water uptake and soil degradation test of the treated and untreated composite samples were also performed. Keywords: Jute fabrics, Composite, Oligomer, Potassium permanganate, Mechanical properties Introduction A rapid growth has occurred in the consumption of fiber reinforced polymer composites, yielding a unique combination of high performance, great versatility, and processing advantages at favorable costs by permutation and combination of various fibers and polymers for last three decades. Composites having unique properties for versatile applications as alternatives to conventional materials like metals, woods, etc. have been prepared [1,2]. Early work on composite focused almost entirely on inorganic materials. The art ofgmaking composites was restricted mainly to synthetic matrix and synthetic reinforcement like glass fiber, carbon fiber and nylon fiber. Glass fiber reinforced thermoplastic materials based on commodity resins have proven to be very successful in high volume markets because of their excellent price performance ratio. Glass fibers have some disadvantages such as abrasive, not recyclable, non renewable, and skin irritating properties [3]. In recent years, there has been substantial growth in research, development and application of bio-composites. A composite containing at least one constituent (e.g. matrix or reinforcement) that is derived readily from renewable resources may be considered a bio-composite. The manufacture, use, and removal of traditional composite structures usually made of glass, carbon, and aramid fibers are considered critically because of growing environmental awareness [4,5]. Cellulose fibers from kenaf, hemp, ramie, flax, sisal, coir, and jute are also being used as reinforcing materials. Since 1980s, the interest in composite made from cellulose fiber *Corresponding author: dr.ruhul_khan@yahoo.com has been growing. The indisputable advantages of cellulose fibers, such as low abrasion, multi functionality, low density, low cost, availability, and no waste disposal problems encourage applications on composite. The available technical studies suggest that natural fiber materials certainly have the potential to compete with glass fibers in composite materials [6-10]. Natural fiber composite is the great demand in the whole world for environmental and ecological concern [11]. Among all the natural fiber reinforcing materials, jute appears to be a promising material because it is relatively inexpensive and commercially available in tropical countries. It has relatively low density and higher strength and modulus than plastic [12] and is a good substitute for conventional fibers in many situations. Among commodities, thermosetting urethane acrylate possesses outstanding properties like good surface hardness, scratch resistance, and excellent electrical properties. As a material of construction, jute urethane acrylate composite can play a vital role all over the world. Jute urethane acrylate composite can be used as particle board, ceiling, blocks for building construction, and furniture. By the commercial production of jute urethane acrylate composite, it is possible to reduce the use of particle board and cement. Moreover, jute is cheaper than most of other nature fibers like sisal, flax, hemp, etc. In order to compete with the synthetic fiber reinforced composite, the mechanical properties of jute urethane acrylate composite should be improved. Some workers prepared jute urethane acrylate composite with the improved mechanical properties by coating the synthetic urethane acrylate polymers over the natural fiber, jute. To enhance the use of jute fibers, a broader systematic investigation is necessary to search for chemical modifiers 258

2 Jute Fabrics Reinforced Urethane Based Thermoset Composites Fibers and Polymers 2010, Vol.11, No and physical treatments. Several processes such as chemical treatments [13] and photochemical treatments [14-18] have been developed to modify fiber surfaces. Potassium permanganate is a strong oxidizing agent. It was reported that pineapple leaf fiber reinforced polyethylene composites were treated with potassium permanganate (KMnO 4 ) and found better mechanical properties [19]. Improved physicomechanical properties of natural fibers with different impregnating solutions under UV radiation [15-17] have been reported. Another surface treatment was done by Khan et al. [20] where jute fabrics were pre-irradiated with UV radiation before preparing the jute-plastic composite using different formulation of 2-hydroxy ethyl methacrylate (HEMA) and aliphatic urethane diacrylate oligomer (EB-204). Composite was prepared by curing under γ-radiation and the composite prepared by pretreated jute fabrics showed minimum water uptake as well as increased mechanical properties as compared to the composite made by untreated jute fabrics. Ali et al. [21] studied on the effect of additives on reinforcement of radiation-induced jute-urethane polymer composites. Thick polymer film was prepared under γ- irradiation using urethane acrylate in the presence of N- vinylpyrrolidone, ethyl hexyl acrylate, and trimethylol propane triacrylate. The physical and mechanical properties of both jute dust and jute fabric were studied. Some additives such as acetic acid, acrylamide, urea, talc, and titanium oxide were incorporated into the formulation to investigate their effect on the physical and mechanical properties. Water absorption and weathering resistance of the resin and composites were also investigated. The present study deals with the modification of jute fabrics by pulling it through special formulated solutions and curing under UV radiation. Physico-mechanical properties of potassium permanganates pretreatment of hessian cloth reinforced polymer matrix composite were investigated and subjected to water uptake, degradation studies such as soil degradation and simulating weathering of the untreated and treated composites for diversified industrial applications. Experimental Materials Bleached jute fabrics (Tossa jute) were collected from Bangladesh Jute Research Institute Dhaka, Bangladesh. Urethane acrylate (M-1200) of Laromer Company was used as the oligomer without further purification. The thermal initiator benzyl peroxide and solvent methanol were used as received from E. Merck, Germany. KMnO 4 (Reagent grade) was procured from British Drug House (BDH) and was used as surface modifier to improve the adhesion between fiber and matrix. Surface Treatment Jute fabrics were cut into small pieces (12 15 cm 2 ) and Table 1. Composition of formulations (% w/w) Formulations Chemicals (w/w %) Oligomer MeOH Benzyl peroxide F F F F F Table 2. Jute content (wt%) in the oligomer composites Formulations Jute content (wt%) F F F F F dried in an oven at 120 o C for 6 h to remove moisture. A number of solutions (formulations) were prepared with different proportions of oligomer (55-95 wt%) in methanols with 0.5 % benzyl peroxide as shown in Table 1. The solution was mixed in a glass beaker and heated at 100 o C for 15 min. The dried jute samples were soaked in the prepared solutions by hand lay up technique. Percentages of jute content in the oligomer composites are shown in Table 2. Soaked jute fabrics were then cured under UV radiation using UV minicure machine (1ST Technik, Germany, Conveyor type) at different intensities (counted by the number of UV pass). The intensity of the UV lamp was 2 kw at 9.5 amp current and the conveyor speed was 3 m/min. The wave length of UV was nm. After 24 h of radiation, the irradiated samples were subjected to various characterization tests. Five layers of UV treated jute fabrics were placed between the plates of the heat press machine and heated at 140 o C for 5 min under a pressure of 4 tons using Carver Laboratory press (Model 2518, USA). Then composites were cooled to room temperature using another press (Carver, USA), then cut to the desired size and kept in the polyethylene bag prior to mechanical characterization. Again in order to measure the mechanical properties, jute fabrics were treated with KMnO 4 solution in acetone of different concentrations (0.02, 0.03, 0.05, and 0.5 wt%) for 2 min soaking time. After 2 min, each layer of jute fabrics was washed with supply water to remove the unreacted KMnO 4. This was then decanted and the fabrics were dried in an air oven. These dried jute fabrics were soaked in optimized formulation (F3) and cured under UV radiation at different intensities. The tensile properties of the composites were determined using a universal testing machine (model H50 KS-0404, Hounsfield Series S, UK). The load capacity was 5000 N; efficiency was within±1 %. The crosshead speed was 10 mm/min and

3 260 Fibers and Polymers 2010, Vol.11, No.2 Haydar U. Zaman et al. gauge length was 20 mm. For bending properties measurement, the crosshead speed was 10 mm/min, and span distance was 40 mm. Tensile strength measurements and three point bending tests were carried out according to DIN and DIN standards methods, respectively. Scanning Electron Microscopic (SEM) Investigation The fracture surfaces of the tensile specimens of both treated and untreated composite samples were examined using a Hitachi S-4000 field emission scanning electron microscope, operated at 5 kv. Samples were mounted with carbon tape on aluminum stubs and then sputter coated with carbon tape on aluminum stubs and then sputter coated with platinum and palladium to make them conductive prior to SEM observation. Water Uptake Composite samples ( mm 3 ) were immersed in the beaker containing 100 ml of deionized water at room temperature (25 o C) for different time periods (up to 200 h). Weight of the samples was determined initially then after certain periods of time, samples were taken out from the beaker and wiped (5 times) using tissue papers, and then weighed again. The weight gained, i.e., water uptake of the samples was determined by subtracting the initial weight from the final weight. Soil Degradation Tests of the Composites Cellulose has a tendency to degrade when buried in soil whose moisture level is at least 25 %. For this purpose, treated and untreated composite samples were buried in garden soil for a period of 6 weeks. After certain periods of time, samples were carefully withdrawn, washed with distilled water, and dried at a temperature of 80 o C for 8 h and then kept at room temperature for 24 h. The change of tensile strength, tensile modulus, and elongation at break caused by these treatments were periodically noted in order to determine the degradable character of the samples in this environment. Result and Discussion Effect of Jute Content on the Mechanical Properties of the Composites The effect of jute content on the mechanical properties of jute oligomer composites was measured. Tensile strength (TS) and bending strength (BS) of the composites were found to increase up to 55 wt%, and then decreased. The results are presented in Figure 1. The highest TS and BS (55 wt% jute) of the composites were found to be and MPa, respectively. The variation of tensile modulus (TM) and bending modulus (BM) with jute content in the composite is shown in Figure 2. It was found that TM values of the composites were increased with increasing jute content up to 55 wt% and after that TM values were Figure 1. Strength of urethane acrylate-based thermoset composites against jute content. Figure 2. Modulus of urethane acrylate-based thermoset composites against jute content. decreased with increasing jute content. The highest TM value of the composite was found to be 1.24 GPa. But the BM was increased with increasing jute content up to 60 % and above 60 %, it decreases with the increase in fiber loading. The maximum BM was observed to be 1.38 GPa. The effect of jute content on the elongation at break (Eb %) of the composites is shown in Figure 3. It was found that Eb % of the composites were increased with increasing jute content up to 55 % and after that Eb % were found to decrease. The highest Eb % value (15.5 %) was observed at 55 % jute content and the lowest (8.45 %) was observed at 45 % jute content. However, most of the mechanical properties of the composites were increased with the increase of jute content up to 55 wt% of fiber loading. So, 55 wt% jute content was termed the optimum composition of the composite.

4 Jute Fabrics Reinforced Urethane Based Thermoset Composites Fibers and Polymers 2010, Vol.11, No Figure 3. Elongation at break of urethane acrylate-based thermoset composites against jute content. Figure 4. Strength of UV treated jute fabrics reinforced urethane acrylate-based composites against number of UV pass. From the above results, it was observed that jute content has the significant influence on the mechanical properties of oligomer-based composite. At lower level of the jute content in the matrix, non-homogeneity of the fiber was found. As a result, the proper load transfer was not possible by the matrix. The mechanical properties of the composites also depend on the optimum fiber matrix adhesion. With further increasing the percentage of jute content in the composites (above 55 wt%), TS, BS, TM, and BM of the composites showed a decreasing trend, which may be attributed to the fact that increasing jute content in the composite decreased the fiber-matrix adhesion. It can be assumed that stress transfer between matrix and fiber is good at 55 % jute content. Above 55 % jute content, mechanical properties were decreased with increasing jute content due to poor fiber matrix adhesion. The criterion of optimum adhesion between matrix and reinforcing fibers is based on maximizing the wetting tension. The maximum wetting tension criterion best fulfils two important requirements for a strong interface. First one is that the physical interactions at the molecular level between the matrix and the fibers must be maximized and the second one is that the liquid matrix must spontaneously wet the fiber surface in order to minimize the flow density at the interface. Above 55 % jute content, poor fiber matrix adhesion was observed, which in turn deceased the mechanical properties of the composites. Effect of UV Radiation on the Mechanical Properties of the Composites The effect of UV radiation as a method of surface treatment on the mechanical properties of urethane acrylatebased composites were investigated by comparing UV treated and untreated composites as shown in Figures 4-6. Mechanical properties of the treated composites were found higher than those of untreated composites. Of all the Figure 5. Modulus of UV treated jute fabrics reinforced urethane acrylate-based composites against number of UV pass. Figure 6. Elongation at break of UV treated jute fabrics reinforced urethane acrylate-based composites against number of UV pass.

5 262 Fibers and Polymers 2010, Vol.11, No.2 Haydar U. Zaman et al. formulations, best mechanical properties were obtained when jute fabrics were coated with the formulation F3 (oligomer:methanol:benzyl peroxide=75:24.5:0.5) and cured under UV radiation at 25 passes. It was found that the TS, BS, TM, BM, and Eb % were found to be 56.2 MPa, MPa, 1.39 GPa, 1.53 GPa, and 9.75 %, respectively. The maximum increment of TS, BS, TM, and BM of the treated composites were found as 17, 18, 12, and 11 %, respectively, as compared to the untreated urethane acrylate-based composite. TS, BS, TM, BM, and Eb % of untreated urethane acrylate-based composite were found to be Mpa, MPa, 1.24 GPa, 1.38 GPa, and 15.5 %, respectively. But the Eb % of the UV treated composite was decreased about 37 % compared to that of the untreated one. These decaying values of elongation usually decrease the strain or deformation of the resulting composites, which was likely to be responsible for its increasing tensile strength. The increase of mechanical properties of the composites with increasing UV radiation dose may be due to the intercross-linking between the neighboring cellulose molecules, which resulted in the strength of natural/synthetic fiber. It was observed that mechanical properties of the composites increase with UV dose (number of passes) up to a certain limit and then decrease due to the two opposing phenomena, namely, photo cross-linking and photo degradation that take place simultaneously under UV radiation [22]. At lower doses, free radicals are stabilized by a combination reaction and, as a result, photo cross-linking occurs. The higher the number of active sites generated on the polymeric substrate, the greater the grafting efficiency. But at higher radiation, the main chain may be broken down and polymer may degrade into fragments and, as a result, mechanical properties will decrease after certain UV doses. An intense UV radiation results in a decrease of mechanical properties caused by photo cross-linking and photo-degradation as described elsewhere [22,23]. Effect of Surface Treatment of Jute Using Potassium Permanganate Jute fabrics were subjected to surface treatment with KMnO 4 solutions. Jute fabrics were soaked in KMnO 4 solution in acetone of different concentrations (0.01, 0.02, 0.03, and 0.05 %) for different soaking time (1, 2, 3, and 5 min). After that jute fabrics were coated with the formulation F3 (oligomer:methanol:benzyl peroxide=75:24.5:0.5) and their mechanical properties were measured. It was found that 0.02 % KMnO 4 solution for 2 min soaking time showed better results as compared to the control composite sample. The results are shown in Table 3. Optimized jute fabrics (jute fabrics treated with 0.02 % KMnO 4 solution and coated with F3 formulation) were then cured under UV radiation at different number of UV passes. The mechanical properties such as TS, BS, TM, and BM of the resulting composites were plotted against the number of UV passes. The graphical representations are given in the Figures 7 and 8. The highest TS, BS, TM, and BM values of the resulting composites were found to be MPa, MPa, 1.34 GPa, and 1.45 GPa, respectively for 0.02 % KMnO 4 treated urethane acrylate-based composite at 30th UV pass. The maximum increment of TS, BS, TM, and BM of the treated composites were found as 11, 13, 8, and 5 %, respectively as compared Figure 7. Strength of 0.02 % KMnO 4 treated jute fabrics reinforced urethane acrylate-based composites against number of UV pass. Table 3. Optimization of KMnO 4 concentrations and soaking time Mechanical properties TS (MPa) TM (GPa) Soaking time (min) Concentration of KMnO 4 (%) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.006

6 Jute Fabrics Reinforced Urethane Based Thermoset Composites Fibers and Polymers 2010, Vol.11, No Figure 9. SEM images of tensile fracture surface of (a) untreated composite and (b) 0.02 % KMnO 4 +UV treated jute fabrics reinforced urethane acrylate-based composite. Figure 8. Modulus of 0.02 % KMnO 4 treated jute fabrics reinforced urethane acrylate-based composites against number of UV pass. to the non-irradiated urethane acrylate-based composite (TS, BS, TM, and BM of untreated composites were found as MPa, MPa, 1.24 GPa, and 1.38 GPa, respectively). The improved interaction can be explained in terms of permanganate induced grafting of oligomer on to jute. The highly reactive MnO 3 ions are responsible for initiating graft copolymerization as shown below [23]. Surface and morphological effects also contribute to the improvement in properties. But at higher concentrations of KMnO 4, there is the possibility of degradation of cellulosic fibers to forms polar groups. After treatment with high concentration of KMnO 4 the fibers became thin and a color change was observed. SEM Analysis Interfacial properties of jute fabrics reinforced oligomerbased composites were investigated by SEM (Figure 9). SEM observations indicated that there is a considerable difference in the fiber-matrix interaction between the untreated (Figure 9(a)) and 0.02 % KMnO 4 +UV treated (Figure 9(b)) composites. Some gaps between jute fiber and matrix are clearly found for untreated samples which are responsible for the low mechanical properties. Jute is a natural biodegradable fiber and strongly hydrophilic [20,21]. But urethane based oligomer is strongly hydrophobic. Thus it was expected poor fiber matrix adhesion for jute/oligomer composites and SEM image reflected it. To reduce hydrophilic nature of jute, surface modifications were carried out using KMnO 4 +UV radiation. Because of surface treatment of jute fibers, the hydrophilic nature was reduced, which contributed to the improvement of the mechanical properties of the composites as described above sections. So, increased mechanical properties of the treated composites were supported from this SEM image by enhancing fiber-matrix adhesion. For the treated SEM image, gaps between fiber and matrix were not observed. But fiber pull out was evident for both types of composites but intensity is lower for treated composites than for untreated one. During KMnO 4 treatment, organic constituents of jute (lignin, pectin, impurities, traces of metals, etc) might be dissolved and the surface of the cellulose in jute became smooth which enhanced fiber matrix adhesion. Moreover, UV radiation may generate some active sites and can reduce more moisture which might be responsible for better fiber-matrix bond in the composite. As a result of the surface treatment of jute with KMnO 4 +UV radiation improved all the mechanical properties of the composites compared to that of the untreated jute based composites. Water Uptake of Untreated and Treated Composites Water uptake values of the untreated (C-0), UV treated jute oligomer composite (C-1), 0.02 % KMnO 4 treated composite (C-2), and 0.02 % KMnO 4 +UV treated composite (C-3) samples were calculated by immersing the samples in deionized water contained in a static glass beaker at room temperature. The samples were taken out of water after constant time interval and their mass gain were calculated. The results of water uptake values of the treated and untreated composite samples are shown in Figure 10. All the samples gained water up to 200 h but treated sample took up less water after 150 h of soaking, and then the values were almost constant. But the untreated sample continued to take up water throughout the period of monitoring. The minimum amount of water was taken up by the UV treated sample

7 264 Fibers and Polymers 2010, Vol.11, No.2 Haydar U. Zaman et al. Figure 10. Water uptake values of treated and untreated jute fabrics urethane acrylate-based composites against the soaking time in water. Figure 11. Degradation of tensile strength of the composites during soil degradation tests. (23 %) and the maximum amount of water was counted by untreated sample (45 %) at the maximum period of observation (200 h). Jute is mainly built up with cellulose which is the hydrophilic glucan polymer. The elementary unit of jute is anhydro-d-glucose which contains three hydroxyl (-OH) groups. This hydroxyl groups in the cellulose structure account for the strong hydrophilic nature of jute and as a result, within some days jute absorbs such a huge amount of water [24]. The hydroxyl groups of the cellulose molecules were filled up by the monomer molecules. So the water uptake value of that system was lowest. Soil Degradation Tests of the Composites Both untreated (C-0), UV treated jute oligomer composite (C-1), 0.02 % KMnO 4 treated composite (C-2), and 0.02 % KMnO 4 +UV treated composite (C-3) samples were buried in soil (at least 25 % water) for up to 6 weeks in order to study the effect of such an environmental condition on the degradability of the samples. TS and TM values are plotted against degradation time and are shown in Figures 11 and 12. It was found that for untreated and treated composites, both TS and TM were decreased slowly with degradation time. After 6 weeks of soil degradation, C-1, C-2, and C-3 composites decreased almost 39, 43, and 41 % of TS and 19, 21, and 20 % of TM, respectively, whereas untreated composite lost about 51 and 28 % of TS and TM, respectively. This is clear that treated composite retained its tensile properties more than untreated composite during soil degradation. Jute is a natural biodegradable fiber and a cellulose-based fiber, which absorbs water within a couple of minutes due to strong hydrophilic character. Cellulose has a strong tendency to degrade when buried in soil [20]. During soil degradation tests, water penetrates from the cutting edges of the composites in jute based samples and Figure 12. Degradation of tensile modulus of the composites during soil degradation tests. degradation of cellulose occurred in jute and as a result, the mechanical properties of the composites decreased significantly. Conclusion Jute fabrics reinforced urethane acrylate-based thermoset composites were prepared by compression molding. Jute content in the composites was optimized with the extent of mechanical properties and 55 wt% jute content in the composite showed higher mechanical properties. Irradiated jute-urethane acrylate thermoset composite at 25th pass of UV radiation performed the best mechanical properties compared to the control composite. Again, jute fabrics were treated with KMnO 4 solution and cured under UV radiation, and then their mechanical properties were measured. But

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