Applied Polymer E Comparative Study of the Dielectric Properties of Natural- Fiber-Matrix Composites and E-Glass-Matrix Composites A. Triki, M. Guicha, 2 Med Ben Hassen, 2 M. Arous1 2Laboratoire de Recherche Textile, Institut Superieure des Etudes Technologiques Ksar Hellal, Avenue Hadj Ali Soua, BP 68 unisia lAboratoire des Materiaux Composites, Ceramique et Polymeres, Faculte des Sciences de Sfax, Route de Soukra, 3018, Tur sar Hella 5070. Tunisia Correspondence to: A. Triki (E-mail: trikilamacop @yahoo. fr) ABSTRACT: In this work, we undertook a comparative study of the dynamic dielectric analysis of two composites: natural-fiber-rein- forced unsaturated polyester(NFRUP) and E-glass-mat-reinforced unsaturated polyester(EGMRUP) In both composites, two com- mon relaxation processes were identified, the first of which was the a-mode relaxation associated with the glass transition of the ma- trix. The second one was associated with conductivity that occurred because of the carriers' charge diffusion and was observed at temperatures above the glass transition and at low frequencies. However, the interfacial or Maxwell-Wagner-Sillars polarization was noticed only in the NFRUP composite. This dielectric study also revealed that compared to E-glass fibers, natural fibers enhanced the thermal insulation in the composite. Also, the study of the fiber adhesion in the matrix with scanning electron microscopy, differen tial scanning calorimetry, and tensile testing revealed a great compatibility of the fibers with the matrix in both composites. o 2012 Wiley Periodicals, Inc. J. AppL. Polym. Sci. 129: 487-498, 2013 KEYWORDS: composites; microscopy; matrix; reinforcement; relaxation Received 18 February 2012; accepted 21 August 2012: published online 22 November 2012 Do:10.1002/app38499 INTRODUCTION ubstitutes for synthetic-fiber-reinforced composites Nowadays,natural fibers such as hemp, kenaf, flax, and hene- used in the construction industry because the reinforcement is quen have gained growing interest, and their study has created low in cost and derived from renewable resources. fascinating perspectives in several applications. In fact, they The most prominent natural fibers used in structural compo- have been increasingly used as reinforcements with polymers sites are plant fibers because of their specific strength and stiff- because they have benefits compared with conventional syn- ness compared with that of glass fibers and their accessibility. thetic reinforcements, such as glass fibers, that power this grow- Among these fibers, we can cite alfa, which is the Arabic name ing interest. These benefits include not only environmental of the esparto grass or Stipa tenacissima plant. It is widely culti- and health concerns but also the sustainability of material vated in the dry region of North Africa and especially in the resources center of Tunisia, where it covers about 3500 km with an ar Among the industries that have taken advantage of natural-fiber al production of 60,000 tons. A great deal of recent research composites is the automobile industry, which has been leading work has been carried out to promote alfa fibers in reinforced he way in the use of such composites. Actually, the lower mass polymeric systems, -14 which can be applied in automotive density of natural fibers (1.4-1.5 g/cm for flax and hemp fib industry. Unsaturated polyester(UP)is a popular 2.5 g/cm' for glass fibers)leads to a reduction in vehicle polymer resin used in conventional glass-fiber-reinforced poly weight, which, in turn, leads to a reduction in fuel consump- mer composites. It has been widely used because of its excellent tion. The use of natural-fiber composites in automobile inter- processability and fast crosslinking reaction on the one hand rs also brings about many other benefits, including an increase and its good mechanical and chemical properties when fully n safety(the fractures of natural-fiber composites are not as cured on the other. 5 sharp as glass-fiber composites) and improved comfort due to Of course, the growth of natural-fiber composites cannot be the better acoustic and thermal insulation provided by the natu- carried out without any challenge. Indeed, the hydrophilic na- fibers' Moreover, natural-fiber-reinforced composites are ture of natural fibers is a potential cause of poor interfacial o 2012 Wiley Periodicals, Inc M Www. MaterialSviewS. cOm WILEYONLINELIBRARY. COM/APP J APPL POLYM. SCL 2013, DOl: 10.1002/APP. 38499 487Comparative Study of the Dielectric Properties of Natural-Fiber–Matrix Composites and E-Glass–Matrix Composites A. Triki,1 M. Guicha,2 Med Ben Hassen,2 M. Arous1 1Laboratoire des Materiaux Composites, C
eramiques et Polyme
`res, Faculte des Sciences de Sfax, Route de Soukra, 3018, Tunisia
2Laboratoire de Recherche Textile, Institut Superieure des Etudes Technologiques Ksar Hellal, Avenue Hadj Ali Soua, BP 68,
Ksar Hellal 5070, Tunisia Correspondence to: A. Triki (E-mail: trikilamacop@yahoo.fr) ABSTRACT: In this work, we undertook a comparative study of the dynamic dielectric analysis of two composites: natural-fiber-rein￾forced unsaturated polyester (NFRUP) and E-glass-mat-reinforced unsaturated polyester (EGMRUP). In both composites, two com￾mon relaxation processes were identified, the first of which was the a-mode relaxation associated with the glass transition of the ma￾trix. The second one was associated with conductivity that occurred because of the carriers’ charge diffusion and was observed at temperatures above the glass transition and at low frequencies. However, the interfacial or Maxwell–Wagner–Sillars polarization was noticed only in the NFRUP composite. This dielectric study also revealed that compared to E-glass fibers, natural fibers enhanced the thermal insulation in the composite. Also, the study of the fiber adhesion in the matrix with scanning electron microscopy, differen￾tial scanning calorimetry, and tensile testing revealed a great compatibility of the fibers with the matrix in both composites. VC 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 129: 487–498, 2013 KEYWORDS: composites; microscopy; matrix; reinforcement; relaxation Received 18 February 2012; accepted 21 August 2012; published online 22 November 2012 DOI: 10.1002/app.38499 INTRODUCTION Nowadays, natural fibers such as hemp, kenaf, flax, and hene￾quen have gained growing interest, and their study has created fascinating perspectives in several applications. In fact, they have been increasingly used as reinforcements with polymers because they have benefits compared with conventional syn￾thetic reinforcements, such as glass fibers, that power this grow￾ing interest.1,2 These benefits include not only environmental and health concerns but also the sustainability of material resources. Among the industries that have taken advantage of natural-fiber composites is the automobile industry, which has been leading the way in the use of such composites. Actually, the lower mass density of natural fibers (1.4–1.5 g/cm3 for flax and hemp fibers vs 2.5 g/cm3 for glass fibers) leads to a reduction in vehicle weight, which, in turn, leads to a reduction in fuel consump￾tion. The use of natural-fiber composites in automobile interi￾ors also brings about many other benefits, including an increase in safety (the fractures of natural-fiber composites are not as sharp as glass-fiber composites) and improved comfort due to the better acoustic and thermal insulation provided by the natu￾ral fibers.3 Moreover, natural-fiber-reinforced composites are used as substitutes for synthetic-fiber-reinforced composites used in the construction industry because the reinforcement is low in cost and derived from renewable resources.4 The most prominent natural fibers used in structural compo￾sites are plant fibers because of their specific strength and stiff￾ness compared with that of glass fibers and their accessibility.5–7 Among these fibers, we can cite alfa, which is the Arabic name of the esparto grass or Stipa tenacissima plant. It is widely culti￾vated in the dry region of North Africa and especially in the center of Tunisia, where it covers about 3500 km2 with an an￾nual production of 60,000 tons.8 A great deal of recent research work has been carried out to promote alfa fibers in reinforced polymeric systems,9–14 which can be applied in automotive industry. Unsaturated polyester (UP) is a popular thermosetting polymer resin used in conventional glass-fiber-reinforced poly￾mer composites. It has been widely used because of its excellent processability and fast crosslinking reaction on the one hand and its good mechanical and chemical properties when fully cured on the other.15 Of course, the growth of natural-fiber composites cannot be carried out without any challenge. Indeed, the hydrophilic na￾ture of natural fibers is a potential cause of poor interfacial VC 2012 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2013, DOI: 10.1002/APP.38499 487