Thermal and structural studies of polypropylene blended with esterified industrial waste lignin A. V. Maldhure • A. R. Chaudhari • Jayant D. Ekhe Received: 26 May 2010 / Accepted: 9 September 2010 / Published online: 24 September 2010 Ó Akade ´miai Kiado ´, Budapest, Hungary 2010 Abstract Microwave-assisted chemical modification of lignin was achieved through esterification using maleic anhydride. Modified lignin (ML) was blended in different proportions up to 25 mass% with polypropylene (PP) using Brabender electronic Plasticorder at 190 °C. The structural and thermal properties of blends were investigated by thermogravometric analysis (TG), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM). TG analysis showed increased thermal stability of blends due to anti- oxidant property of ML, which opposed oxidative degra- dation of PP. DSC analysis indicted slight depression in a glass transition temperature and melting temperature of blends due to partial miscible blend behavior between PP and ML. All blends showed higher crystallization tem- peratures and continuously reducing percentage crystal- linity with increasing ML proportion in the blends. WAXD analysis indicated that PP crystallized in b polymeric form in addition to a-form in the presence of ML. However, proportion of b-form did not show linear relation with increase in ML proportion, thus ML acts as b nucleating agent in the PP matrix. SEM analysis showed good dis- persion/miscibility in PP matrix indicating modification in lignin is useful. Keywords Modified lignin  Microwave  Polypropylene  Thermal degradation  TG  DSC Introduction Lignin is a complex, amorphous, polyphenolic, less reac- tive, natural organic polymeric material and built up from poly phenyl propane units. It is the second most abundant biopolymer on earth only next to cellulose. It is obtained as a major industrial waste material from pulp and paper industries. The Kraft/Alkaline Pulping process and Sulfide Pulping process are two main pulping processes of com- mercial importance. Current annual global production of lignin is approximately 50 million tones, which is increasing with the growing demand of pulp products [1]. Out of total lignin produced only, 3 MT of lignosulphonate and 0.1 MT alkali lignin are used for purposes other than fuel like [2, 3] for the production of vanillin and sulfur- containing compounds. In the field of polymer study, inorganic fillers are being replaced by newer type of organic fillers [4–6]. Lignin being largely available and modifiable becomes a promis- ing alternative for the purpose. Lignin has been recently used for many new products like resin [3, 7], adhesive [8, 9] for polymer blending [10, 11], and for preparation of low molecular weight fuel additives [12, 13]. Lot of work can be cited on modification of lignin to prepare suitable blends with commercial polymers. Many workers blended polyolefins using Kraft lignin to find increased thermal and photochemical stability of blends [20, 25, 26]. But the mechanical properties deteriorate with lignin proportion because of very low solubility/compat- ibility/miscibility of polar lignin in nonpolar polymer matrix [14–16]. This opens new area to use modified lignin (ML) (less polar) in polymer matrix which may increase solubility/miscibility of lignin in polymer matrix. Very recently Song et al. [17] and Durmus et al. [18] have reported differential scanning calorimetry (DSC) A. V. Maldhure  J. D. Ekhe (&) Department of Chemistry, Visvesvaraya National Institute of Technology, Nagpur 11, India e-mail: j_ekhe@yahoo.com; jdekhe@chm.vnit.ac.in A. R. Chaudhari Department of Chemistry, Smt. Bhagvati Chaturvedi College of Engineering, Nagpur, India 123 J Therm Anal Calorim (2011) 103:625–632 DOI 10.1007/s10973-010-1048-6