Plasticized and Unplasticized PLA/Organoclay Nanocomposites: Short- and Long-Term Thermal Properties, Morphology, and Nonisothermal Crystallization Behavior Serap Gumus, 1 Guralp Ozkoc, 1,2 Ayse Aytac 1 1 Department of Chemical Engineering, Kocaeli University, Izmit, 41380, Kocaeli/Turkey 2 Department of Polymer Science and Technology, Kocaeli University, Izmit, 41380, Kocaeli/Turkey Received 26 October 2010; accepted 29 April 2011 DOI 10.1002/app.34841 Published online 1 September 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: The short- and long-term thermal proper- ties, organoclay dispersion state, and the nonisothermal crystallization kinetics of organoclay based nanocompo- sites of poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) plasticized PLA were investigated. Differential scan- ning calorimetry analyses showed that plasticization of PLA/PEG blend was diminished due to physical aging by the time. The change in thermal properties such as glass transition temperature, cold crystallization temperature, and melting temperature was monitored. It was revealed from X-ray diffraction analyses that in long term, the exfo- liated and/or intercalated organoclay structure of nano- composites observed in short term (just after processing) was differentiated to a tactoidal form (i.e., nonseparated clays). The nonisothermal crystallization behavior and kinetics were examined by using Avrami, Ozawa, and com- bined Avrami–Ozawa models. Moreover, the nucleating effect of clays was investigated in terms of Gutzow and Dobrewa approaches. It was found out that clays did not act as nucleating agents in plasticized PLA nanocomposites, which was also in good agreement with activation energy values obtained from Kissinger and Takhor models. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2837–2848, 2012 Key words: PLA; nanocomposite; plasticization; physical aging; nonisothermal crystallization INTRODUCTION In recent years, researches in biodegradable poly- mers have attracted attention from packaging indus- try. A great quantity of petroleum based plastics is used for packaging purposes. As biodegradable polymers are produced from renewable sources, and easily composted into water and carbon dioxide, they are good alternatives to petroleum-based poly- mers. 1 The most popular biodegradable polymers are aliphatic polyesters, such as poly(lactic acid) (PLA), polycaprolactone (PCL), poly(butylene adi- pate terephthalate) (PBAT), and poly(hydroxy butyr- ate) (PHB). 2,3 Among them, PLA has a special place due to its high strength, high modulus, transpar- ency, processability, and its commercially avail- ability. An important requirement for packaging materials is high flexibility at room temperature. 3 However, the brittleness of PLA is a disadvantage to produce flexible films. Therefore, the flexibility of the PLA needs to be chemically or physically modi- fied. Blending with plasticizers is a cost-effective physical modification method to improve flexibility. 4 Plasticizers are used to decrease the glass transi- tion temperature (T g ), increase the elongation at break and processability of polymers. A plasticizer should be compatible and miscible with the polymer matrix. Citrate ester, oligomeric lactic acid, poly(eth- ylene glycol) (PEG), and poly(propylene glycol) were reported to be compatible with PLA and used as effective plasticizers. 5 Miscibility of PLA/PEG blends has been extensively studied. It was found that blends up to 30 wt % PEG were miscible when they were quenched form the melt. They exhibited a single T g and had no detectable crystallinity of either constituents. 6 However, the PLA plasticized with more than 30 wt % PEG was found to be unstable over the time and also an increase in modulus accompanied by a decrease in elongation at break was observed. 7,8 This was attributed to the migration and crystallization of PEG which results in phase separation in the blend. As a result, T g increased due to the enriching of amorphous phase in PLA. 7 For several years now, the field of polymer nano- composites, especially layered silicates (clays), have received significant interest due to good physical per- formance of nano-scaled filler at a low loading level Correspondence to: G. Ozkoc (guralp.ozkoc@kocaeli.edu.tr). Journal of Applied Polymer Science, Vol. 123, 2837–2848 (2012) V C 2011 Wiley Periodicals, Inc.