Structure development and crystallization behaviour of PP/nanoparticulate composite C. Saujanya, S. Radhakrishnan * Polymer Science and Engineering, National Chemical Laboratory, Council of Science and Industrial Research, Pune 411008, India Received 20 November 2000; received in revised form 9 January 2001; accepted 31 January 2001 Abstract The structure development and crystallization behaviour of polypropylene PP) containing nanoparticles of calcium phosphate prepared by a new route based on matrix mediated control of growth and morphology was investigated by X-ray diffraction XRD), optical microscopy and DSC techniques. The results obtained were compared with that of PP containing conventionally prepared calcium phosphate CaP0). Both nanoparticle ®lled PP as well as CaP0 ®lled PP crystallized in monoclinic a crystalline phase. However, considerable changes were observed in the relative intensities of the XRD peaks, especially the peak II 040 re¯ection), in the case of PP ®lled with nanosize calcium phosphate. The isothermal crystallization curves showed dramatic increase of crystallization rate and decrease in t 1/2 value for PP/nano- particulate composites resulting in a rapid decrease in the ultimate spherulite size as compared to PP/CaP0 samples. The nucleating ef®ciency was found to be dependent on the particle size as inverse exponential power law. These results were further con®rmed by DSC analysis. The optical transparency of the PP/nanoparticle composites was found to be much higher than that containing conventional CaP0 for the same concentrations and this could be associated with the reduction in the PP crystallite size. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Nanoparticles; Calcium phosphate; Nanocomposite 1. Introduction Polymernanocompositescompriseanewclassofmaterials where nanoscale particulates inorganic such as clay or any other mineral) are ®nely dispersed within a matrix. These have been reported to exhibit markedly improved properties as compared to the pure polymers or conventional particu- late composites [1±5]. These include increase of modulus and strength, improved barrier properties, increase in solvent and heat resistance, good optical transparency, etc. Further, these improvements are achieved at very low load- ings of the inorganic component 1±10 wt%) as compared to conventional ®lled polymers, which require a high load- ing of the order of 25±40 wt%. Many routes have been attempted in recent years for the synthesis of inorganic/organic nanocomposites. These include mainly a) sol±gel processing [6,7], b) in situ intercalative polymerization [8,9], and c) in situ polymerization [10,11], etc. Polymer/clay nanocompo- sites have been extensively studied by using both in situ intercalative and polymerization methods. These were investigated by dispersing the mineral clays in various polymer matrices such as nylon-6 [12], polypro- pylene [13] PP), polyethylene terephthalate [14], poly- styrene [15], epoxy [16], polyacrylates [17,18], etc. A large improvement in the properties of the polymers was observed for such materials. However, the above routes employed by the various researchers showed a major disadvantage of dif®culty in handling and proces- sing of nanoparticles. Further, in the case of semicrys- talline polymers, it is known that the crystallization behaviour and morphology get affected by the presence of particulate additives especially at low concentrations. These structural features can affect the overall proper- ties of the material but such detailed investigations have not been reported earlier. Matrix mediated control of growth and morphology has received considerable attention in the recent years since it offers a novel route to material synthesis [19±21]. This novel route was earlier investigated by us in different types of materials such as CaCO 3 ,K 2 CO 3 , CdS, CaSO 4 , etc. which were prepared in situ within a polymer matrix such as polyethylene oxide PEO) giving rise to modi®ca- tion of morphology, crystalline phase, orientation and growth habits of these compounds [22±24]. This method Polymer 42 2001) 6723±6731 0032-3861/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S0032-386101)00140-9 www.elsevier.nl/locate/polymer * Corresponding author. Tel.: 191-212-331-453; fax: 191-020-589- 3041. E-mail address: srr@ems.ncl.res.in S. Radhakrishnan).