Preparation and characterization of a newly water soluble lignin graft copolymer from oil palm lignocellulosic waste Mohamad Nasir Mohamad Ibrahim a, * , Mohamed Rashid Ahmed-Haras a , Coswald Stephen Sipaut a , Hassan Y. Aboul-Enein b , Abdullahi Ali Mohamed c a School of Chemical Sciences, Universiti Sains Malaysia, 11800 Pulau Pinang, Malaysia b Pharmaceutical and Medicinal Chemistry Department, National Research Centre, Dokki, Cairo 12311, Egypt c School of Civil Engineering, University of Nottingham Malaysia Campus, 43500 Selangor, Malaysia article info Article history: Received 3 December 2009 Received in revised form 11 January 2010 Accepted 14 January 2010 Available online 25 January 2010 Keywords: OPEFB fibre Kraft lignin PTS Lignin graft copolymer Glass transition temperature abstract Water soluble lignin graft copolymer (LGC) was synthesized using oil palm empty fruit bunch (OPEFB) fibre as a renewable biomass source. Initially, Kraft lignin (KL) was extracted by exploiting the OPEFB fibre Kraft pulping residue. KL was grafted with acrylic acid (AA) by using p-toluenesulfonic acid (PTS) as a catalyst in the condensation process via the bulk technique. The resulting copolymer was character- ized by a Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermo- gravimetry-Fourier transform infrared (TG-FTIR) and carbon–hydrogen–nitrogen analyzer (CHN). The FTIR spectrum of the product showed absorption due to the presence of ester bonds as a proof of grafting. The DSC and TG-FTIR results showed significant improvements in the KL thermal properties at least 27.261% as well as a thermal degradation resistance. The elements percentages of KL compositions were changed as shown by the CHN data. SEM micrographs illustrated the grafting reaction homogenizing the KL morphological structure. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, oil palm empty fruit bunch (OPEFB) fibre, which is one of the lignocellulosic materials, showed great potential to be used as raw material in the Kraft pulping process, especially in Malaysia, which is considered a major palm oil producer in the world (Ibrahim et al., 2005). In conformity with that, Kraft black li- quor remained as a waste after the completion of the pulping pro- cess. This aquatic colored and toxic effluent (Gupta, Ali, & Saini, 2007) i.e. black liquor, considered as a serious pollution source and caused costly disposal problems (Malaviya & Rathore, 2007). Nevertheless, Kraft black liquor consist of dissolved biomass mate- rials such as lignin, hemicelluloses and degradation products of cellulose and hemicelluloses (sugar acids) (Wallberg, Linde, & Jöns- son, 2006). Such biomass from industrial waste products could be a feasibly of cheap and commercially available raw material to pro- duce; adsorbent, corrosion inhibitor and chemically modified bio- polymer (Gupta, Ali, Suhas, & Mohan, 2003). Kraft lignin (KL) is obtained from Kraft black liquor via the acid- ification process using sulfuric acid, hydrochloric acid or sulfur dioxide (Wu, Zhang, Guo, & Huang, 2008). Generally, lignin is a highly stable and complex composite with a three-dimensional aromatic polymer structure formed from three phenylpropanoid alcohols units of p-coumaryl alcohol, coniferyl alcohol and sinaplyl alcohol which are connected by ester groups (Amen-Chen, Pakdel, & Roy, 2001). Furthermore, lignin is the most abundant bio-poly- mer on earth after cellulose and it naturally occurs in several types of plants such as hardwood, softwood and grasses (Pouteau, Dole, Cathala, Averous, & Boquillon, 2003). In spite of these large quantities, lignin has not yet been effectively utilized and this pre- sents environmental problems (Ugartondo, Mitjans, & Vinardell, 2008). Various studies have been conducted on lignin in order to over- come biomass environmental problems and produce new products with beneficial properties. One of these studies is graft copolymer- ization of lignin to produce a copolymer used as drilling mud thin- ner and viscosity reducer in high temperature (Wei, Liu, Yu, & Jiang, 2002). Another graft copolymerization reaction of lignin with 1-ethenylbenzene was used efficiently to enhance thermal stability as well as to change the hydrodynamic radius of poly (1-phenyl- ethylene) (Chen et al., 1996). Graft copolymerization reaction of lignin by means of a specific monomers can be conducted either by the addition or condensation copolymerization. Apart from that, the addition copolymerization reaction is normally carried out using either free radicals or the ionic copolymerization process. 0144-8617/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2010.01.030 * Corresponding author. Tel.: +60 46533554; fax: +60 46574854. E-mail addresses: mnm@usm.my, mra_002@hotmail.com (M.N. Mohamad Ibrahim). Carbohydrate Polymers 80 (2010) 1102–1110 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol