ORIGINAL PAPER Rheological and mechanical characterization of poly (lactic acid)/polypropylene polymer blends Kotiba Hamad & Mosab Kaseem & Fawaz Deri Received: 31 October 2010 / Accepted: 17 February 2011 / Published online: 4 March 2011 # Springer Science+Business Media B.V. 2011 Abstract Poly(lactic acid) (PLA) was melt blended with polypropylene (PP) with the aim of replacing commodity polymers in future applications. Since cost of PLA is quite high, it is not economically feasible to use it alone for day to day use as a packaging material without blending. This paper reports the preparation of poly (lactic acid)/polypropylene polymer blends (PLA/PP) using a laboratory scale single screw extruder. Rheolog- ical and mechanical properties of the prepared blends were determined. The rheological experiments were carried out on a capillary rheometer, the effect of shear rate, temperature and PLA content on the flow activation energy and true viscosity of the blends were described. Mechanical properties of the blends were investigated on dog bone-shaped samples obtained by injection molding; tensile tests were performed using Testometric M350- 10KN. The effect of PLA content on Young’s modulus, strain at break and stress at break of the blends were described. The rheological results showed that the true viscosity of the blends is between that of the pure polymers, whereas the flow activation energy of the blends is less than that of the pure polymers. The mechanical results showed incompatibility between PLA and PP in the blend. Keywords PLA . PP . Polymer blends . Rheology . Mechanical properties Introduction Poly(lactic acid) (PLA) is well-known biodegradable polyes- ter that has been studied extensively for tissue engineering and drug delivery system and has been widely used in human medicine. Many of the PLA properties are compared to those polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) (such as stiffness, tensile strength, and gas permeability), turning PLA into a potential substitutes to petroleum-based products such as trash bags, table utensils, films, paper coating, fiber, and cloth [1]. PLA is made from lactic acid produced via fermentation of carbohydrate crops such as corn, wheat, barley, cassava, and sugar cane [2]. It is made from L- or D-lactic acid through two procedures: (a) ring-opening polymerization, a solvent free process where lactic acid is first transferred to a low-molecular weight poly(lactic acid), followed by depoly- merization to lactide (fluctuating dimer), and then polymer- ized continuously to a controlled high-molecular weight polymer through a catalytic ring-opening process [3]; (b) direct condensation polymerization, a catalyzed process where the water generated during the polymerization is removed by an azeotropic dehydration process, producing a high-molecular weight polymer [4]. The products from both procedures present similar properties. PLA-based polymer is completely degraded under compost conditions. Although it has a hydrophobic characteristic (non-water soluble), microbes in marine environments can degrade it into water and carbon dioxide [5], and hydrolyzes more promptly than polyhydroxyalkanoates in anaerobic condition [6]. The first step of PLA degradation does not require microbial action and is characterized by the cleavage of the ester linkages to lactic acid by a temperature and humidity-enhanced process. Then lactic acid is biodegraded by microbes into carbon dioxide, methane, and water. The complete degradation of PLA K. Hamad (*) : M. Kaseem : F. Deri Department of Chemistry, Faculty of Science, Laboratory of Materials Rheology (LMR), University of Damascus, P. O. Box 31513, Damascus, Syria e-mail: kotibahamad@yahoo.com J Polym Res (2011) 18:1799–1806 DOI 10.1007/s10965-011-9586-6