Thermochimica Acta 479 (2008) 45–52 Contents lists available at ScienceDirect Thermochimica Acta journal homepage: www.elsevier.com/locate/tca Non-isothermal crystallization kinetics and activity of filler in polypropylene/Mg–Al layered double hydroxide nanocomposites M. Ardanuy ∗ , J.I. Velasco, V. Realinho, D. Arencón, A.B. Martínez Centre Català del Plàstic, Universitat Politècnica de Catalunya, C/Colom 114, E-08222 Terrassa, Spain article info Article history: Received 11 July 2008 Received in revised form 22 September 2008 Accepted 23 September 2008 Available online 30 September 2008 Keywords: Layered double hydroxide Polypropylene Nanocomposites Non-isothermal crystallization Nucleation activity abstract The non-isothermal crystallization behaviour of Mg–Al layered double hydroxide (LDH)/polypropylene (PP) nanocomposites prepared by melt-dispersion was investigated through differential scanning calorimetry and discussed in comparison with that of montmorillonite (MMT)/PP ones. Combined effects of the LDH interlamellar modification and blending the PP with maleic anhydride-grafted PP (PP-g- MAH) and maleic anhydride-grafted poly(styrene-co-ethylenebutylene-co-styrene) (SEBS-g-MAH) were analysed. Different approaches were applied to determinate the crystallization kinetic parameters. The nucleation activity parameter indicated that LDH particle resulted active for heterogeneous nucleation of PP. Overall; the crystallization rate constant of the PP increased in presence of LDH in a similar extension that in presence of MMT nanoparticles. By applying an isoconversional method to the calorimetric data it was found that the effective activation energy decreased because of the effect of the nanoparticles and its value displayed different growing trends with the crystallization degree depending of the nanocomposite composition. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Polypropylene (PP) is widely used in industry due to its well- balanced physical and mechanical properties, as well as to easy processing at a relatively low cost. The application of PP, however, has been limited by its high flammability, tendency to brittleness at temperatures below its glass transition temperature and low stiffness particularly at elevated temperatures. Traditionally, com- pounding PP with different inorganic particles has been of wide interest and it has been an effective way to improve thermal and mechanical properties of this polymer. Nanocomposites consisting of PP matrix and natural or synthetic layered minerals like clays have been attracted much interest of researchers on the last decade. Mostly focused on cationic clays [1,2], and particularly on smectite-type layered silicates, clay-based fillers have recently been extended to the family of layered dou- ble hydroxides (LDH) [3] and different approaches to prepare LDH nanocomposites have been described in previous papers [4–10]. LDHs are a family of lamellar compounds containing exchangeable anions in the interlayer space (anionic clays). The structure con- sists of brucite-like sheets of typical thickness 0.5 nm, in which partial substitution of trivalent for divalent metallic ions results in a positive charge compensated by anions within interlayer gal- ∗ Corresponding author. Tel.: +34 937398158; fax: +34 937398101. E-mail address: monica.ardanuy@upc.edu (M. Ardanuy). leries. The general formula is: [M 1-x 2+ M x 3+ (OH) 2 ][A x/n n- ·mH 2 O], where M 2+ and M 3+ are di- and trivalent metal cations, respectively, that occupy octahedral positions in the hydroxide layers, and A n- is an interlayer anion [11]. The nature of the layer metal ions can be changed among a wide possible selection and the interlayer anion can be also chosen among inorganic or organic species. The melt-mixing preparation procedure of polymer/LDH nanocomposites include the LDH particle organophillization, con- sisting in swelling via ion exchange process with an anionic surfactant, followed by dispersion into a polymer matrix by apply- ing high local shear stresses in a melt-mixer dispositive. These organophillized particles display an expanded crystalline structure because of the higher free volume of the interlamellar organic ion [8–10]. Owing to the low polarity of PP, it is usually necessary to use polar compatibilizer agents to promote strong interactions between the polymer melt and the particles, which ideally cause effective platelet dispersion within the melt matrix by shear and/or elongational mixing forces. Graft copolymers combining an iden- tically or miscible part with functional groups capable to interact with the inorganic particle surface are usually used as compatibi- lizer [12–14]. Different studies have been focused on the effect of montmo- rillonite (MMT) and other smectite clays on the crystallization behaviour of PP nanocomposites. Most of them reported like sil- icate layers are active substrates for the heterogeneous nucleation of PP and PP-g-MAH. As a consequence, the polymer crystallization 0040-6031/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2008.09.016