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Study on Mechanical andDielectric Properties ofJute Fiber Reinforced Low-Density Polyethylene (LDPE)CompositesM.J. Miah a , Farid Ahmed a , A. Hossain a , A.H.Khan a & Mubarak A. Khan ba Department of Physics , Jahangirnagar University ,Dhaka, Bangladeshb Radiation and Polymer Chemistry Laboratory ,Institute of Nuclear Science and Technology,Bangladesh Atomic Energy Commission , Dhaka,BangladeshPublished online: 14 Feb 2007.

To cite this article: M.J. Miah , Farid Ahmed , A. Hossain , A.H. Khan & Mubarak A.Khan (2005) Study on Mechanical and Dielectric Properties of Jute Fiber ReinforcedLow-Density Polyethylene (LDPE) Composites, Polymer-Plastics Technology andEngineering, 44:8-9, 1443-1456

To link to this article: http://dx.doi.org/10.1081/200048718

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Study on Mechanical and Dielectric Properties ofJute Fiber Reinforced Low-Density Polyethylene

(LDPE) Composites

M.J. Miah, Farid Ahmed, A. Hossain and A.H. KhanDepartment of Physics, Jahangirnagar University,

Dhaka, Bangladesh

Mubarak A. KhanRadiation and Polymer Chemistry Laboratory, Institute of Nuclear Science and

Technology, Bangladesh Atomic Energy Commission, Dhaka, Bangladesh

Abstract: Jute fiber (Hessian cloth) reinforced low-density polyethylene (LDPE)composites were prepared by heat press molding techniques. The mechanicalproperties such as tensile strength (TS), bending strength (BS), and elongationat break of the composites were studied. The enhancement of TS (33%) andBS (50%) were obtained as a result of reinforcment jute fabrics in LDPE. In orderto improve the mechanical properties and adhesion between jute and LDPE, hess-ian cloth were each treated with 2-hydroxyl ethyl methacrylate (HEMA). TheHEMA-treated jute composite showed higher tensile and bending strength com-pared to untreated jute composite and LDPE. Dielectric properties like dielectricconstant and loss tangent (tan d) of jute, LDPE and composites were studied.Ferro to paraelectric phase transition occurred in both treated and untreated jutecomposites containing more than 20% jute. Water uptake behaviors of the com-posite were monitored and HEMA-treated composite showed lower waterabsorption behavior. The adhesion nature of jute and LDPE also characterizedby scanning electronic microscopy (SEM), better adhesion was observed betweenHEMA-treated jute and LDPE over untreated ones.

Keywords: Low-density polyethylene, tensile stregth, bending strength, hessiancloth

Address correspondence to M.A. Khan, Radiation and Polymer ChemistryLaboratory, Institute of Nuclear Science and Technology, Bangladesh AtomicEnergy Commission, P.O. Box 3787, Dhaka, Bangladesh. E-mail: makhan@bangla.net

Polymer-Plastics Technology and Engineering, 44: 1443–1456, 2005

Copyright Q Taylor & Francis, Inc.

ISSN: 0360-2559 print/1525-6111 online

DOI: 10.1081/200048718

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INTRODUCTION

All fibers, natural or synthetic, are dirived from high polymercompounds; various types of polymers are progressively being used inmodern technology to replace conventional engineering materials likesteel, rock, and wood, etc. Both natural and synthetic polymers areimprotant for mankind and, hence, the demand for polymers is increasingeveryday. Most of the synthetic polymers are not biodegradable, which isvery harmful for the environment. To keep the environment free frompollution, the use of biodegradable and environmental friendly polymeris important. The natural polymers (jute, flax, wood, etc.) are biodegrad-able and easily decomposable in the environment and are, thus, environ-mentally friendly compared to the synthetic polymers (e.g., polystyrene,polypropylene, polyvinyl chloride, etc.). On the other hand, syntheticpolymers have higher tensile strength, sustainability, and durabilitycompared to the natural polymers but cause pollution of the environ-ment. Since the natural polymers do not possess the necessary thermaland mechanical properties desirable for engineering plastics, they aretreated with different materials in different modes to increase theirstrength, durability, and sustainability while possessing their inherentdegradable character to maintain the environment free from pollution.With this aim in mind many researchers developed different compositesby the combination of natural and synthetic polymers and have porvedthat the composites so produced are degradable and decomposable inthe environment. Recently Khan et al.[1] has produced degradable jute-reinforced polymer composites using vinyl and silicon monomers ascoupling agents. Also several reports have documented where the jutefibers are used as a reinforcement in thermoplastics like polyethylene(PE) and polypropylene (PP) and thermosets like unsaturated polyesterand epoxy resin[2]. In all the cases the machanical properties increaseddue to the reinforcement with jute fibers.

Jute is a lignocellulose bast fiber obtained from the bark of an annualagricultural plant. Chemically it contains cellulose, hemicellulose, lignin,etc. But the main constituent of jute is cellulose, which is a hydrogen-bonded material. In a recent study on jute fiber is was observed that jutefiber is a ferroelectric material[3]. Ferroelectricity was confirmed byobserving a hysteresis loop on the oscilloscope. The synthetic polymerpolyethylene is a nonpolar polymer, which has excellent chemical inert-ness and electrical insulating properties, low cost, low temperature tough-ness and low vapor permeability. During the last several years, thedielectric properties of polymers at very low temperatures have drawnattention because of the possibility of operating alternating current (ac)electrical apparatus at cryogenic temperatures[4–8]. It was found thatpolyethylene, which has been widely utilized as an insulating material

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at normal temperature, exhibits relatively hish dielectric loss at liquidhelium temperatures[9–12]. Okimichi Yano et al.[13] measured the dielectricloss of high-density polyethylene (HDPE), low-density polyethylene(LDPE), and copolymers of ethylene at 1.5 to 4.2K in the frequencyrange from 10Hz to 10KHz. They documented that with increasingtemperature the loss-peak frequency increases but the peak heightdecreases. Usually dielectric properties under the action of direct current(dc) voltage offers very high resistance to the passage of electric currents.The mechanical properties and the dielectric properties, especially thedielectric constant and dielectric loss of jute reinforced low-densitypolyethylene composite, are reported in this paper.

MATERIALS AND METHODOLOGY

Low-density polyethylene (LDPE) and jute fabrics were used in this workto prepare the composites. The jute fabrics (Hessian cloth) were graftedwith HEMA (2-hydroxyl ethyl methacrylate) to reduce the hydrophilicnature. Hessian cloth was soaked in 3% HEMA in 2% benzol peroxidein methanol for 15 minutes. Then the Hessian cloth was dried in an ovenat ambient temperature. Ten different composites were prepared with dif-ferent ratios of polyethylene (PE) and jute fabrics. Among them, fivecomposites were prepared by using untreated jute fabrics and five wereprepared using the jute fabrics treated by the 3% HEMA and 2% benzolperoxide formulation.

The jute fabric–polyethylene composites were prepared by sandwich-ing two layers of fabric between three layers of preweighted polyethylenefilms. The preweighted films of 0.5–1.0mm thickness were prepared byheating the polyethylene at 115�C for 5 min between two steel platesunder a pressure of 3 tons. These films were cooled to room temperature,cut to the desired size, and placed in the mold. Finally the compositeswere prepared by heating the films at 135�C under a pressure of 5 tons.

The mechanical properties of polyethylene and the composites weredetermined by means of a universal testing machine (INSTRON, model1011, UK). The tensile-strength measurements and three-point bendingtests were carried out following DIN 53455 and DIN 53452 standardmethods, respectively. All the results were taken as the average valuesof three samples.

The composites were cut into desired size and then dried and weighed.They were then immersed in water contained in a static water bath at 25�Cfor different periods (up to 80 h). The weight gained by the immersedsamples was used to determine the water uptake of the samples.

The dielectric properties, especially the dielectric constant and thedielectric loss of the composites, were measured by using bridge

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technique (two-electrode method) over the temperature range from 20�Cto 100�C at frequency 10 kHz.

RESULT AND DISCUSSIONS

Mechanical Properties

In order to study the reinforcement effects of the composites with thepercentage of jute content mechanical properties are measured. Mechan-ical properties of the prepared jute–polyethylene composites are mea-sured in terms of tensile strength (TS), bending strength (BS),elongation at the break (EB), and bending elongation (BE).

Tensile Strength

The tensile strength as a function of jute content (both treated anduntreated) is shown in Fig. 1. It is found from Fig. 1 that tensile strength

Figure 1. Effect of jute content on the tensile strength of the composites.

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values of the composites increases with jute content and reaches themaximum value when the percentage of jute content in the compositeis 25%. After that tensile strength of the composite decreases slowly withincreasing jute content. The lowering of tensile strength values at highjute fiber content might be due to the presence of so many fiber endsin the composities, which could cause crack initiation and, hence, poten-tial composite failure. The lower density polyethylene (LDPE-virgin)used here has the tensile strength 15 MPa. Thus, it was observed thatmost of the composites showed higher tensile strength (TS) comparedto virgin PE.

The superior mechanical properities of HEMA-treated jute may beattributed to the fact that HEMA improves the adhesive characteristicsof the fiber by producing a rough surface topography. Thus, the develop-ment of rough surface topography and the enhancement of the fiberaspect ratio offers a better fiber–matrix interface adhesion and increasesthe mechanical properties.

In addition, the vinyl group of the acrylic moiety of HEMA reactswith OH groups of cellulose backbone of jute fiber through graft-copoly-merization. As a result, the hydrophilic nature of jute is reduced, which

Figure 2. Effect of jute content on the bending strength of the composites.

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increases the effective surface area available for content with the matrixpolymer[14].

It was also found that the tensile strength of the treated composite ismore than that of untreated composite. The higher value of the tensilestrength of the treated composite compared to that of untreatedcomposite may be due to the fact that benzol peroxide produces freeradicals during composite fabrication; and these free radicals initiatethe free reaction and react with HEMA and the cellulose backbone ofjute fiber and, thereby, improve the adhesive between jute fiber and PE.

Bending Strength

The effect of jute content on the bending strength is shown in Fig. 2.Results show that bending strength of the composite increases with jutecontent like tensile strength, but it reaches maximum value at 20% of jutein the composites and remains constant up to 25%. After that its value

Figure 3. Effect of jute content on the % of elongation in the composites.

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decreases with further increase of jute content. From this study it wasfound that the bending strength increases with jute content up to an opti-mum value. Thereafter, with further increase in jute content, the bendingstrength either remains constant or shows a decreasing trend, which maybe attributed to the fact that increasing jute content in the compositedecreases the potentiality of the jute–polyethylene matrix. It was alsofound that treated composites have higher values of bending strengththan do those of untreated samples.

Elongation at Break

The effect of jute content on the elongation of break is shown in Fig. 3.From the figure it was found that the percentage of elongation at break

Figure 4. Water uptake of composites (both treated and untreated) againstsoaking time.

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(EB) values slowly rises up to 15% of jute content and then it increasessharply with increasing jute content for treated samples. But untreatedsamples remain almost constant up to a certain ratio (�25%), and theyshows a decreasing trend with further increasing of jute content.

Water Uptake Properties

Water absorption properties of jute polyethylene composites (bothtreated and untreated) are analyzed in relation with time. The resultsare plotted in Fig. 4. It is shown in the figure that the composites thatare not treated show substantially higher water absorption than do thecomposites that are treated by HEMA (2-hydroxyl ethyl methacrylate).The figure shows that the high ultimate water uptake (8.13%) of the addi-tive free composites (containing 10% jute) drops down to <3.49% when2% HEMA is used. The water uptake value (14%–21.5%) of untreatedcomposites containing 20%, 25%, and 30% jute drops down to<5%–9% for HEMA treatment. These indicated that HEMA playsan important role in repeling water molecules. Hydroxy is one of the

Figure 5. Effect of HEMA (2-hydroxyl ethyl methacrylate) on the composites.

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important functional group in jute fiber, which causes the formation oflarge amounts of hydrogen bonds and induces their swelling. Swellingforces are a severe problem in widely used jute composites. The decreaseof water sorption of the treated composites can be achieved by reducinghydroxy groups and introducing cross-linking between filler and matrix.Water sorption equivalent value is also measured in relation to jute con-tent (%) in the composites. Results are shown in Fig. 5 by bar chartgraph. From the results, it can be concluded that water sorption capacityof untreated samples is greater than that of treated samples and it followsa linear relation with increasing jute content (%). Since jute fibres arehydrophilic and polar, jute sorbs more water molecules than does thatof hydrophobic polyethylene. So, increasing the percentage of jute fibersin composites also enhances absorption of water molecules. Also compo-sites can absorb a large amount of water through the ends of the fibers onsurfaces unblocked with polymer matrix, which are formed during thesample preparation procedure.

Figure 6. (a) SEM microgram of tensile fracture of untreated jute composite. (b)SEM microgram of tensile fracture of HEMA-treated jute composite.

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Scanning Electron Microscopy

Interfacial properties of jute–LDPE composites were investigated byscanning electron microscopy (SEM) of the tensile fracture surface.Figure 6 demonstrated the fracture surface of untreated (6a) andHEMA treated (6b) jute composites. The SEM observations indicatethat there is considerable difference in the fiber-matrix interactionbetween the treated and untreated jute composites. The improvedbonding is observed for surface-modified jute composites comparedto their untreated counterparts. Although, we observed fiberpullout phenomena in both cases, in the case of the surface-modifiedcomposite a considerable amount of matrix-polymer residue remainson the fiber. In cases of untreated jute composite (Fig. 6a) fiberpullout in bundle form is observed where, as in case of HEMA modi-fied samples (Fig. 6b) agglomeration of the fibers into bundle form isrelatively prevented indicating better interaction than in the previoussystem.

Figure 6. Continued.

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Dielectric Properties

In the present study dielectric constant along with loss tangents of bothchemically (HEMA) treated and untreated jute–polyethylene compositeswere examined with the variation of jute content at a fixed frequency of10 KHz. The variation of dielectric constant is recorded for differenttemperature gradients and these values together with temperature areshown in Fig. 7. and Fig. 8. (Fig. 7 for untreated composites and Fig. 8for treated composites) for different jute composition in the composites.The variation of loss tangent with respect to temperature has beendepicted in Fig. 9. and Fig. 10.

Figures 7 and 8 shows that the degree of variation of dielectric con-stant with temperature is similar for both the treated and untreated com-posites containing 10% jute fabrics. The dielectric constant for untreatedcomposites is higher than that of treated ones. It is evident from thesefigure that all the measurements (except 10% jute composite) showed asharp initial increase of dielectric constant up to transition temperature,and above the transition temperature it decrease rapidly to almost roomtemperature and with further increase of temperature it reduces to aconstant value. These figures reveal that 20% and 30% jute composites(both treated and untreated) undergo a definite phase transition, 20%

Figure 7. Dielectric constant vs. temperature curve (for untreated composites).

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Figure 8. Dielectric constant vs. temperature curve (for treated composities).

Figure 9. Dielectric loss vs. temperature curve (for untreated composites).

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jute composites (both treated and untreated) show the transition ataround 36�C whereas 30% jute composites show at 47�C for untreatedand at 42�C for treated samples. From the foregoing discussions it wasobserved that an increase of jute content in the composite leads to a tran-sition, which may be associated with ferro-paraelectric transition. Fora more elaborate conclusion about the nature of such transitiona hysteresis loop study is needed.

In Fig. 9 and Fig. 10 the variation of loss tangent (tan d) with tem-perature has been shown for both treated and untreated composites of10%, 20%, and 30% jute content, respectively. These figures show thatthe loss tangent for 10% jute composites (both the treated anduntreated), initially remains constant and then decreases with tempera-ture. It was also observed that the transition of jute composite for 20%and 30%, both treated and untreated, is around of 36� � 43�C.

Jute is composed of cellulose whose skeletal backbone is linked byintramolecular hydrogen bonding. With increasing temperature thesebonds break up to split the chain into smaller unit of dipoles. The dipoles

Figure 10. Dielectric loss vs. temperature curve (for untreated composites).

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so formed tend to align themselves with the applied electric field and thusincreases the dielectric constant. At the transition temperature the align-ment of dipoles towards the field is maximum giving rise to maximumdielectric values, whereas above the transition temperature the dipolestend to be oriented randomly and, hence, lower the dielectric values.At an optimum temperature the dielectric values them become constant.

CONCLUSIONS

The jute fiber polyethylene composites were prepared by the variation ofjute content. The jute fabrics were treated by 3% HEMA (2-hydroxylethyl methacrylate) and 2% benzol peroxide. The mechanical and dielec-tric properties of the composite were studied. Mechanical properties suchas tensile strength, bending strength, longitudinal elongation, and bend-ing elongation at the break of the treated jute polyethylene compositesare more than that of untreated composite. The water resistance ofuntreated composite is improved when the jute fiber is treated by HEMA.The dielectric constant and loss tangent are dependent on temperature.Phase transition, likely ferro to paraelectric transition, takes place inthe composites (both treated and untreated) containing more than 20%jute fabrics in the temperature range 36�C to 46�C.

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Polym-Plast Technol. Eng. 1995, 34 (5), 729.3. M. Sci. Thesis submitted from the Polymer Science Lab. Dhaka University,

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Chap. 5, 1975.5. Chant, M.J. Cryogenics 1967, 7, 351.6. Allan, R.N.; Kuffel, E. Proc. IEE 1968, 115, 432.7. Allan, R.N.; Buxton, P.H. Proc. IEE 1968, 115, 1846.8. Muller, F.H.; Heybey, O.; Knispel, G. Z.Z. Kolloid Polym. 1973, 251, 932.9. Fallou, B.; Bobo, J.C. Electrical Insulation Conf. British Electrical and Allied

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