Influence of Silica Nanofiller on the Isothermal Crystallization and Melting of Polyurethane Elastomer Sanja Luc ˇic ´ Blagojevic ´, 1 Zrinka Buhin, 1 Ivona Igrec 2 1 Faculty of Chemical Engineering and Technology, University of Zagreb, Zagreb 10000, Croatia 2 Croatian Meteorological and Hidrological Service, Air Quality Division, Chemical Laboratory, Zagreb 10000, Croatia Correspondence to: S. L. Blagojevic ´ (E-mail: slucic@fkit.hr) ABSTRACT: In this article, isothermal crystallization kinetic of the linear hydroxyl polyester urethane (PUR), as well as influence of amorphous silica nanofiller, was investigated. With the aim to investigate the influence of filler surface modification on the crystal- lization process of polyurethane matrix, nonmodified silica, as well as silica modified with methacrylsilane and octylsilane, were used as fillers for PUR composite preparation. The crystallization kinetics depending on temperature of the isothermal crystallization and volume fraction of filler by using differential scanning calorimetry (DSC) were investigated. The measurements at temperatures 7, 12, and 17  C for PUR and composites with 0.5, 1, 2, and 4 vol % of filler were done. Kinetic parameters of the isothermal crystallization n and K were determined according to Avrami model. Melting of the isothermally crystallized samples was also investigated. Results of the research indicate that by increasing the isothermal crystallization temperature, the crystalliza- tion rate of the PUR soft phase decreases and that the perfection of the crystallites is improved. By addition of all fillers up to 1 vol %, the crystallization rate increases; however, addition of a higher amount of the filler significantly decreases the crystallization rate. It was found that surface modification can significantly affect crystallization rate and that the nucleation effi- ciency of silica increases in the following order: methacrylsilane-modified silica < nonmodified silica < octylsilane-modified silica. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000–000, 2012 KEYWORDS: polyurethanes; composites; crystallization; differential scanning calorimetry Received 25 July 2012; accepted 19 November 2012; published online DOI: 10.1002/app.38846 INTRODUCTION Polyurethane (PUR) elastomers play an important role in various fields of applications such as adhesives, optoelectronics, biotech- nology, and many others. 1,2 This class of materials exhibits supe- rior properties related to their high hardness for a given modulus, high abrasion resistance, excellent mechanical properties, and bio- compatibility. An important factor that enable such wide spread application is the possibility to tailor the structure and properties by varying the type and ratio of starting components during proc- essing. PUR elastomers are block copolymers, consisting of rigid and flexible segments. Because of the difference in polarity, that is, thermodynamical incompatibility, these segments separate into soft and hard phases. The widespread application of the PUR elas- tomers is the reason for extensive research carried out in the fields of novel type synthesis and structure-properties relationship. 3–5 Theory of block copolymers, one of whose components is crystal- lizable, while other component is noncrystallizable and of whose components are incompatible have been studied extensively. 6,7 Compared with other types of polymers, these block copolymers have a unique equilibrium limited lamellar structure. Theory predicts that in this type block copolymers folding of the crystal- lizable blocks exist at equilibrium due to the thermodynamic forces between the crystalline and amorphous domains. For this reason, they have equilibrium lamellar structure that can be obtained by annealing, usually in the presence of good solvent for the amorphous phase. The equilibrium domain sizes are determined by packing constraints as well as the balance of the total energy of chain folding in the crystalline domains with the associated entropic conformational and stretching free energy of the noncrystallizable blocks in the amorphous domains. In the last years, polymer-based nanocomposites that contain nanometric size fillers have been extensively studied. The addi- tion of nanofillers instead of the microfillers to polymer mate- rial can influence the properties of materials more significantly. The observed phenomena are assigned to the high interfacial polymer/filler area at which the interactions are established. Thus, previous research has shown that by decreasing the particle size of silica fillers a more significant impact on proper- ties of PUR can be achieved. 8–10 V C 2012 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2012, DOI: 10.1002/APP.38846 1