Indo. J. Chem., 2010, 10 (3), 334 -340 334 THE EFFECT OF ACETIC ACID ON PROPERTIES OF COCONUT SHELL FILLED LOW DENSITY POLYETHYLENE COMPOSITES Z.H. Tengku Faisal 1,* , Faisal Amri 2 , H. Salmah 2 , and Iqmal Tahir 3 1 Faculty of Engineering, Medan Area University, Medan, Indonesia 20233 2 School of Materials Engineering, Division of Polymer Engineering, Universiti Malaysia Perlis, 02600 Jejawi Perlis Malaysia 3 Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Gadjah Mada, Yogyakarta Indonesia 55281 Received September 29, 2010; Accepted October 26, 2010 ABSTRACT Natural lignocellulosics have an outstanding potential as reinforcement in thermoplastics. Coconut shell is one of natural lignocellulosic material. In this study, coconut shell (CS) was use as filler in low density polyethylene (LDPE) composites. The effect of surface treatment of coconut shell (CS) with acetic acid (acetylation) on mechanical properties, thermal properties and morphology were studied. The acetylation treatment has improved the tensile strength, elongation at break and Young’s modulus of LDPE/CS composites. Thermogravimetric analysis (TGA) results show that the acetylated composites has better thermal stability compared to untreated composites at 600 °C. Differential scanning calorimetry (DSC) analysis show ed that the esterification treatment increases the crystallinity of LDPE/CS composites. It was found that coconut shell acts as a nucleation agent in the presence of acrylic acid. The scanning electron microscopy (SEM) study of the tensile fracture surface of acetylated composites indicates that the presence of acetic acid increased the interfacial interaction. Keywords: low density polyethylene, coconut shell, acetic acid, composites INTRODUCTION The use of natural plant fibres as reinforcement in polymer composites for making low cost engineering materials has generated much interest in recent years. The advantages of natural plant fibres over traditional glass fibres are acceptable as good specific strengths and modulus, economical viability, low density, reduced tool wear, enhanced energy recovery, reduced dermal and respiratory irritation and good biodegradability [1]. However, natural plant fibre reinforced polymeric composites, also have some disadvantages such as the incompatibility between the hydrophilic natural fibres and hydrophobic thermoplastic and thermoset matrices requiring appropriate use of physical and chemical treatments to enhance the adhesion between fibre and the matrix [2]. * Corresponding author. Tel/Fax : +62-838-69068235 Email address : tengku_faisalzh@yahoo.co.id Chemical modification will be defined as a chemical reaction between some reactive part of a lignocellulosic cell wall polymer and a simple single chemical reagent, with or without catalyst, to form a covalent bond between the two [3]. The most important chemical modification involves coupling methods. The coupling agent used contains a chemical group, which can react with the fiber and the polymer [4]. Esterification is one of the chemical modifications undergone by the natural fiber. Most of the researches conducted on acetylated natural fiber have focused on improving the mechanical properties polymer composites [5-7]. Esterification by means of acetylation is a chemical modification procedure, which has been studied extensively for lignocellulosic compounds [8- 11]. Chemical modification with acetic and propionic anhydrides, substitutes the cell wall hydroxyl groups with acetyl and propionyl groups, rendering the surface more hydrophobic, and thus, more compatible to the polymer matrix. According to Rowell [8], the hydroxyl groups that react with the reagent, are those of lignin and hemicelluloses (amorphous material), while the hydroxyl groups of cellulose (crystalline material), being closely packed with hydrogen bonds, prevent the diffusion of the reagent and thus result in very low extents of reaction, if any. It has been shown that esterification improves the dispersion [12-14] of lignocellulosic materials in a polymer matrix [12,15-16], as well as the interface of the final composite [12,16]. Coconut shell is one of the most important natural fillers produced in tropical countries like Malaysia, Indonesia, Thailand, and Sri Lanka. Many works have been devoted to use of other natural fillers in composites in the recent past and coconut shell filler is a potential candidate for the development of new composites because of their high strength and modulus properties. Composites of high strength coconut filler can be used in the broad range of applications as, building, materials, marine cordage, fishnets, furniture, and other household appliances [17]. Thermal analysis (TA) means analytical experimental techniques which measure the thermal Z.H. Tengku Faisal et al.