Fibers and Polymers 2014, Vol.15, No.4, 800-808 800 Chitosan-filled Polypropylene Composites: The Effect of Filler Loading and Organosolv Lignin on Mechanical, Morphological and Thermal Properties Faisal Amri Tanjung*, Salmah Husseinsyah, and Kamarudin Hussin Division of Polymer Engineering, School of Materials Engineering, University Malaysia Perlis, 02600, Jejawi, Perlis, Malaysia (Received January 30, 2013; Revised August 27, 2013; Accepted September 6, 2013) Abstract: In this work, the effect of organosolv lignin on properties of polypropylene (PP)/chitosan composites was investigated. Mechanical and thermal properties of the composites were analyzed by means of ASTM D 638-91, ASTM D 256, thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Tensile strength and elongation at break of the PP composites decreased upon the presence of chitosan filler, but Young’s modulus improved. Impact strength was found to increase with the maximum value at 30 php of filler loading. At a similar loading, treated PP/chitosan composites were found to have higher tensile strength, elongation at break, Young’s modulus as well as impact strength than untreated composites. Furthermore, the presence of organosolv lignin imparted a plasticizing effect. Thermal properties of the treated PP/chitosan composites were better as compared with the untreated PP/chitosan composites; although the chemical treatment did not alter the thermal degradation mechanism. In addition, the obtained results were comparable to results from previous studies. This finding implied that the organosolv lignin could be a potential reagent to replace its synthetic counterpart. Keywords: Polypropylene, Chitosan, Chemical modification, Organosolv lignin, Properties Introduction Currently, the use of natural fibers in emerging environ- mentally friendly materials has become an important issue, besides energy generation [1]. Consequently, natural fibers such as sisal [2], banana fiber [3], wood [4], bagasse [5], chitosan [6], etc. have attracted more and more interest to be used as reinforcements for both thermoplastic and thermo- setting polymer composites, as they are promising alternatives to replace synthetic fibers [7,8]. Additionally, their use could minimize environmental pollution, reducing environmental problems in future [9]. The main advantages of using natural fibers in polymer composites include a high strength per unit weight, ease of processing, a lower specific weight (density), and desirable thermal properties [10]. However, some disadvantages such as high moisture absorption, low maximum processing temperatures, poor fire resistance and incom- patibility with hydrophobic polymer matrices, can limit their potential use as reinforcements in polymer composites for industrial applications [11]. Among the existing natural fibers, chitosan is known to possess excellent mechanical and thermal properties. Chitosan is the second most abundant natural fiber after cellulose; it is extracted from crustaceous shells such as crabs, shrimp and prawns [12]. In solid form, chitosan is a crystalline polymer; it is also non-toxic, biodegradable and biocompatible [13]. Recently, chitosan fiber has been used as reinforcement in thermoplastic composite materials; however, it is not as widespread as synthetic fibers. Research is still required to determine several unknown factors, e.g. the ideal matrices for reinforcements. This factor has limited the application of chitosan as reinforcement, mainly because hydrophobic polymeric matrices repel the polar sites of the chitosan fiber [14]. The problem of filler-matrix incompatibility arises due to different polarity character between hydrophilic natural fibers and hydrophobic polymer matrices, resulting poor interaction on interface. Filler-matrix interfacial adhesion plays a major role on properties of composite systems, because only a well formed interface allows good stress transfer from matrix to filler [15]. Thereby, in case of using natural fibers as reinforcements, an enhancement of fiber- matrix adhesion is an important issue and usually achieved by the chemical or physical treatment of the fiber, by means of a surface treatment or a coupling agent, which is usually a functionalized polymer or using other techniques [16,17]. In previous works, chitosan fiber was chemically treated with acrylic acid and 3-aminopropyltriethoxysilane to reduce the hydrophilic character of chitosan enhancing its adhesion with a hydrophobic polypropylene matrix [18,19]. It was obtained that the hydrophilic character of chitosan fiber significantly decreased led to improved mechanical and thermal properties of the PP composites. Nowadays, chemical modification is extensively used for enhancing the interfacial interaction between filler and matrix in polymer composite systems, because it is an effective method to reduce the hydrophilic character of natural fibers [20]. However, chemical modifications add another step in the preparation of composites, hence increasing the production cost. Ideally, the reagents used in the chemical modifications are inexpensive and involve compounds obtained from renewable sources. Alternatively, the use of reagents obtained from non-renewable sources reduces the benefits of using natural fibers [21-23]. *Corresponding author: icalamri@gmail.com DOI 10.1007/s12221-014-0800-0