Exploring isolated lignin material from oil palm biomass waste in green composites H.P.S. Abdul Khalil ⇑ , M.M. Marliana, A.M. Issam, I.O. Bakare School of Industrial Technology, Universiti Sains Malaysia, 11800 Penang, Malaysia article info Article history: Received 30 September 2010 Accepted 20 January 2011 Available online 24 January 2011 Keywords: A. Composites polymer matrix E. Mechanical E. Thermal abstract Lignin obtained from oil palm biomass empty fruit bunches (EFB) fibers, has been used as curing agent in green epoxy composites. Epoxy–lignin composites, with varying lignin content (15%, 20%, 25% and 30%), reinforced with EFB fiber were prepared. The effect of EFB-based lignin on the mechanical, thermal and morphology properties of the composites were investigated and compared with the composites cured with isophorone diamine curing agent. The improved thermal stability and the observed microstructure of the fractured surface of the composites were attributed to good fiber–matrix interaction, induced by the curing agent. The epoxy composites cured with 25% lignin content proved to be a better matrix and gave optimum value compared with other formulations which was confirmed by its mechanical, thermal and morphological properties. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Palm oil industry generates vast amount of oil palm biomass mainly from milling and crushing palm kernel. Oil palm (Elaeis guineensis) empty fruit bunch (EFB) was a lignocellulosic waste generated during palm oil extraction process is a good source of cellulose, lignin and hemicelluloses which can be used in many industrial processes. Over 15 million tons of EFB waste residue is generated annually in Malaysia [1,2]. This waste is mostly disposed through combustion or land filling, creating considerable pollution and economical problems [1,2]. Therefore, utilization of this organ- ic waste in any industrial process would be of immense environ- mental and economical benefits to society. The process of producing cellulosic pulp from oil palm biomass and other non-wood fibers requires delignification with sodium hydroxide under pressure. This liberates the cellulosic fiber and produces a large quantity of toxic black liquor which is discharged into water bodies without proper treatment [3,4]. Oil palm bio- mass consists of about 20% lignin. This lignin, obtained from the black liquor produced during pulping, is considered as pollutant and it is known to contain about 50% of lignin [5]. Such ‘‘go waste toxic products’’ can be processed into a viable raw material for sev- eral industrial applications. Epoxy resin is a widely used polymer matrix for advanced com- posites where good stiffness, dimensional stability, excellent mechanical properties and chemical resistance is required [6]. The mechanical properties of this un-reinforced epoxy polymer matrix may not be sufficient for some end-use applications. There- fore, other materials such as filler/reinforcement may be incorpo- rated to enhance the performance characteristics. The use of various form of curing agent/hardener has also been reported to influence the properties of such polymers. Several approaches of incorporating lignin into epoxy resins, aimed at partially replacing petroleum-based materials, have been reported in literatures [7,8]. Lignin is a heterogeneous biopolymer of extreme complexity, whose exact chemical composition is not known, hence recent ef- forts at developing lignin-based polymer blends and composites have lead to conflicting reports regarding the benefits of lignin incorporation into polymers [9]. Also, the extensive cross-linking and strong intermolecular interactions prevent its utilization in so- lid material system. Consequently, lignin is often deficient in areas where homogeneity of chemical functionalities and molecular weight distribution is required. It is therefore essential that rigor- ous intensive research on lignin modification and application would be of utmost importance. Moreover, studies by Simionescu et al. [10] showed that significant lignin loads could be incorpo- rated into the epoxy resin whilst still maintaining good electrical (volume and surface resistivity, dielectric constant, loss in dielec- tric tangent angle and dielectric rigidity) and mechanical proper- ties, and high impact toughness compared to the lignin-free phenol epoxy resins. Tertiary amines, polyfunctional amines and acid anhydrides are widely used as curing agents for epoxy resins. These curing agents are toxic and are capable of causing severe irritation, serious rash or an asthmatic response in sensitive persons. Therefore this study was carried out to develop an environmental-friendly curing agent from bio-resource material. In this study, lignin obtained from the oil palm empty fruit bunch (EFB) fiber was used as curing agent in epoxy resin matrix. The effect of varying the lignin contents to epoxy resin on mechanical and thermal properties of EFB 0261-3069/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2011.01.035 ⇑ Corresponding author. Tel.: +60 4 6532200; fax: +60 4 657367. E-mail addresses: akhalilhps@gmail.com, akhalil@usm.my (H.P.S. Abdul Khalil). Materials and Design 32 (2011) 2604–2610 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes