The influence of boehmite crystallite sizes, varied between 10 and 60 nm, was studied with respect to the morphology development, crystallization behavior and mechanical properties of the boehmite‐based iPP nanocomposites. The nanometer‐scaled boehmites were formed during twin‐screw melt extrusion of iPP at 200 °C. Even in the absence of polymer compatibilizers, the boehmites, obtained from Sasol's process, enabled very effective deagglomeration and in‐situ dispersion of nanoboehmites. With increase in boehmite crystallite size it was possible to improve simultaneously stiffness and impact strength of iPP. As evidenced by means of DSC, POM and WAXS measurements, the deagglomerated nanoboehmites nucleated crystallization of poly(propylene)'s α‐modification.

IntroductionAmong commodity thermoplastics, isotactic poly(propylene) (iPP) is outstanding with respect to its very attractive combination of low cost, low weight, tailor-made property profiles, wide application range, and recycling capabilities including recovery of oil and gas resources by means of pyrolysis. [1,2] In order to qualify iPP for engineering applications it is important to improve stiffness without sacrificing toughness. In conventional iPP compounds fillers and fibers are dispersed in the iPP in order to reinforce iPP. Traditional reinforcing agents for poly(propylene) include calcium carbonate, talc, glass fibers, wollastonite, mica, glass beads, and wood flour. [3,4] When the same volume fraction of micrometer-scaled fillers is substituted by nanometer-sized fillers, the number of particles increases by nine orders of magnitude. As a result most iPP is located at the nanofiller interface in iPP nanocomposites. Moreover, small amounts of a few percent nanofillers are needed to convert bulk iPP into interfacial iPP exhibiting new property profiles. Incorporation of nanofillers can promote higher stiffness, strength, and dimensional stability combined with improved barrier resistance and flame retardancy. [5,6] In state-of-the-art technology, considerable amounts of expensive compatibilizers like maleic-anhydride-grafted poly(propylene) are added to improve nanofiller dispersion and interfacial adhesion. [7] During the last decade nanocomposite research has been iPP/organoboehmite nanocomposites were prepared to examine the influence of both boehmite crystallite size and organophilic boehmite modification on morphology development, thermal, and mechanical properties. Effective deagglomeration of the micrometer-scaled organoboehmites was achieved, producing uniform dispersions of nanometer-scaled boehmite crystallite assemblies within the iPP matrix. CSmodified organoboehmites gave improved stiffness at the expense of elongation at break and impact strength. In contrast to CS, boehmites modified with OS2 lowered iPP crystallization (''anti-nucleation effect'') without affecting crystal modification, affording iPP nanocomposites with significantly larger elongation at break and strain induced crystallization.focused on organophilic layered silicates, modified by means of cation exchange. [8] Much less is known about organoboehmite nanofillers produced by means of acid modification of nanoboehmites.The boehmite mineral AlO(OH) has a layered structure illustrated in Figure 1. In Sasol's process for producing synthetic boehmites (cf. Scheme 1) aluminum alcoholates are formed by reacting aluminum metal with alcohol, followed by hydrolysis. [9][10][11] Highly pure nanoboehmites free of alien transition metal impurities are formed and very effective control of the boehmite crystallite sizes (10, 40, and 60 nm) is achieved. Treatment with organic carboxylic and sulfonic acids renders boehmites organophilic. During drying, the boehmite crystallites assemble to afford micrometer-scaled agglomerates of crystal...