A study of the mechanical properties of short natural-ﬁber

A study of the mechanical properties of short natural-fiber reinforced composites P.J. Herrera-Franco * , A. Valad ez-Go nza ´ lez Centro de Investigac io ´ n Cientı ´ fica, de Yucata ´ n A.C., Division de Materiales, Calle 43 # 130, Col. Chuburna ´ de Hidalgo, C.P. 97200 Me ´ rida, Yucata ´ n, Me ´ xico Received 10 January 2005; accepted 10 April 2005 Available online 22 June 2005 Abstract The degree of fiber–matrix adhesion and its effect on the mechanical reinforce ment of short henequen fibers and a polyethylene matrix was studied. The surface treatments were: an alkali treatment, a silane coupling agent and the pre-impregnation process of the HDPE/xylene solution. The presence of Si–O– cellu lose and Si–O–Si bonds on the lignocellu losic surface confirmed that the silane coupling agent was effic iently held on the fibres surface through both condensation with cellulose hydroxyl groups and self-condensation between silanol groups. The fiber–matrix interface shear strength (IFSS) was used as an indicator of the fiber–matrix adhesion improvement, and also to determine a suitable value of fiber length in order to process the composite with relative ease. It was noticed that the IFSS observed for the different fiber surface treatments increased and such interface strength almost doubled only by changing the mechanical interaction and the chemical interactions between fiber and matrix. HDPE-henequen fiber composite materials were prepared with a 20% v/v fiber content and the tensile, flexural and shear properties were studied. The comparison of tensile properties of the composites showed that the silane treatment and the matrix-resin pre-impregnation process of the fiber produced a significant increase in tensile strength, while the tensile modulus remained relatively unaffected. The increase in tensile strength was only possible when the henequen fibers were treated first with an alkaline solution. It was also shown that the silane treatment produced a significant increase in flexural strength while the flexural modulus also remained relatively unaffected. The shear prope rties of the composite s also increase d signifi cantl y, but, only when the hene quen fibers were trea ted with the silane coupling agent. Scanning electron microscopy (SEM) studies of the composites failure surfaces also indicated that there is an improved adhesion between fiber and matrix. Examination of the failure surfaces also indicated differences in the interfacial failure mode. With increasing fiber–matrix adhesion the failure mode changed from interfacial failure and considerable fiber pull-out from the matrix for the untreated fiber to matrix yielding and fiber and matrix tearing for the alkaline, matrix-resin pre-impregnation and silane treated fibers. q 2005 Elsevier Ltd. All rights reserved. Keywords: (C)Resin; Fiber–matrix 1. Introduction Cel lul osic fibe rs, like hen equen, sisa l, coc onut fibe r (co ir), jut e, pal m, bamboo , woo d, pap er in the ir natural condition, as well as, several waste cellulosic products such as shel l flour, wood flour and pulp have be en used as reinforcement agents of different thermosetting and thermo- plastic resins [1–8]. During the decortication of the henequen leaves, and also during the transformation of the raw fibers into cordage, approximately a 10% of waste is produced. These waste fibers could be profitably used in the manufacture of short- fiber polymer reinforced composites because they posses attract ive physic al and mecha nical proper ties [9]. These was te fibe rs are compos ed of w60% of cel lulose pul ps wh ic h are ea si ly obtained and could also be used to reinforce polymeric materials. Unlike the traditional engineering fibers, e.g. glass and carbon fibers, and mineral fillers, these lignocellulosic fibers are able to impart the composite certain benefits such as low density , les s mac hine wear dur ing processing tha n tha t produced by mineral reinforcements, no health hazards, and a high deg ree of flexibil ity. The later is especially true because these fibers, unlike glass fibers, will bend rather than fracture dur ing proces sing. Who le natur al fibers Composites: Part B 36 (2005) 597–608 www.elsevier.com/locate/compositesb 1359-8368/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesb.2005.04.001 * Corresponding author. E-mail address : [email protected] (P.J. Herrera-Franco).

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A study of the mechanical properties of short natural-ﬁber