N: Nanoscale Food Science JFS N: Nanoscale Food Science, Engineering, and Technology Rheological and Thermal Properties of Polylactide/Silicate Nanocomposites Films JASIM AHMED,SUNIL K. VARSHNEY, AND RAFEAL AURAS ABSTRACT: Polylactide (DL)/polyethylene glycol/silicate nanocomposite blended biodegradable films have been prepared by solvent casting method. Rheological and thermal properties were investigated for both neat amorphous polylactide (PLA-DL form) and blend of montmorillonite (clay) and poly (ethylene glycol) (PEG). Melt rheology of the PLA individually and blends (PLA/clay; PLA/PEG; PLA/PEG/clay) were performed by small amplitude oscillation shear (SAOS) measurement. Individually, PLA showed an improvement in the viscoelastic properties in the temper- ature range from 180 to 190 ◦ C. Incorporation of nanoclay (3% to 9% wt) was attributed by significant improvements in the elastic modulus (G ′ ) of PLA/clay blend due to intercalation at higher temperature. Both dynamic modulii of PLA/PEG blend were significantly reduced with addition of 10% PEG. Rheometric measurement could not be con- ducted while PLA/PEG blends containing 25% PEG. A blend of PLA/PEG/clay (68/23/9) showed liquid-like properties with excellent flexibility. Thermal analysis of different clay loading films indicated that the glass transition tempera- tures (T g ) remained unaffected irrespective of clay concentration due to immobilization of polymer chain in the clay nanocomposite. PEG incorporation reduced the T g of the blend (PLA/PEG and PLA/PEG/clay) significantly. Both rheological and thermal analysis data supported plasticization and flexibility of the blended films. It is also inter- esting to study competition between PLA and PEG for the intercalation into the interlayer spacing of the clay. This study indicates that PLA/montmorillonite blend could serve as effective nano-composite for packaging and other applications. Keywords: amorphous, complex viscosity, elastic modulas, glass transition temperature, intercalation, melt rheology, viscoelasticity Introduction P olylactide (PLA) has been intensively studied and used for biomedical materials because of its high biocompatibility and good biodegradability in the human body as well as in the nature. (Fetters and others 1994; Tullo 2000; Ragauskas and others 2006). PLA has a high mechanical strength, and excellent shaping and molding properties. The development of biodegradable packaging alternatives has been the subject of research and development in recent times, particularly with regard to renewable alternatives to traditional oil derived plastics (Ahmed and Varshney 2010). PLA is the front runner among alternatives to petroleum based plastics for disposable items because of its close similarity with poly (ethylene terephthalate) (PET) (Auras and others 2004; Ahmed and others 2009). The use of PLA has been further extended to other food pack- aging applications due to its high film and packaging performance characteristics. However, an understanding of the stability of PLA under realistic food packaging conditions is essential to match the shelf life of the foods with the shelf life of the packaging material (Holm and others 2006). PLA has already been approved as gen- erally regarded as safe (GRAS) status for food packaging (Jin and Zhang 2008). Currently, PLA containers have been used for pack- aging bottled water, bottled juices, sandwich containers, and yo- gurts. However, PLA falls short of the required properties for poten- tial applications. Major limitations of PLA are its inherent brittle- ness and low toughness. The flexibility and toughness of PLA can be enhanced by modifying its physical properties through several MS 20091007 Submitted 10/12/2009, Accepted 11/30/2009. Authors Ahmed and Varshney are with Polymer Source, Inc., 124 Avro Street, Dorval, Mon- treal, Quebec, Canada H9P 2X8. Author Auras is with The School of Pack- aging, Michigan State Univ., East Lansing, MI 48824-1223, U.S.A. Direct inquiries to author Ahmed (E-mail: jahmed2k@yahoo.com). approaches including copolymerization, blending and incorpora- tion of filler materials. Blending (in solution or melt) is a simpler and more economic way compared with copolymer synthesis and much attention has been focused on the blends of PLA with low molecular weight poly- mers, which acts as plasticizer and drastically reduced the glass transition temperature (T g ). For PLA to be able to compete with more flexible and ductile commodity polymer such as polyethy- lene or polypropylene, there is a need to plasticize PLA matrix (Paul and others 2003). Such plasticizers further produce homogeneous and flexible materials. The plasticizers used for the purpose are poly (ethylene glycol; abbreviated as PEG), poly (propylene glycol), and poly (hydroxy butyrate). However, the low T g of produced blends may affect the processing and molding of final products. The incorporation of particulate fillers into polymer matrices is an eminent technique to improve or modify some properties of neat polymers (Swain and Isayev 2007). Polymer nano-composites become a promising class of hybrid materials by the incorpora- tion of particulate nanofillers into polymer matrices to enhance the properties of neat polymers. Polymer nanocomposites are made by dispersing inorganic or organic nanoparticles into either a ther- moplastic or thermoset polymer. Such nanoparticles offer enor- mous advantages over traditional macro- or micro-particles due to their higher surface area and aspect ratio, improved adhesion be- tween nanoparticle and polymer, and lower amount of loading to achieve equivalent properties. It has been reported that layer sili- cate based polymer nano-composites have improved thermal, rhe- ological, mechanical, optical and physical properties of polymers (Sinha Ray and others 2003). The excellent barrier properties of clay-based polymer nanocomposites would result in considerable enhancement of shelf life for many types of packaged food. Meanwhile, the C  2010 Institute of Food Technologists R  Vol. 75, Nr. 2, 2010—JOURNAL OF FOOD SCIENCE N17 doi: 10.1111/j.1750-3841.2009.01496.x Further reproduction without permission is prohibited