Evaluation of the structure-property-relationships of novel halloysite-polymer nanocomposites
Zusammenfassung der Projektergebnisse
The potential of halloysite nanotubes (chemical formula Al2[Si2O5(OH)4] • 2H2O) as a novel class of filler for the mechanical reinforcement of polyamide 6 (PA 6) nanocomposites was elucidated. Since halloysite occurs as a weathering product of volcanic stones in quantitatively large deposits, it is predestinated for the production of inexpensive polymer nanocomposites. Furthermore, the tubular geometry of nanotubes of the mineral halloysite results in a high aspect ratio and a large interfacial area between the polyamide 6 matrix and the fillers. In this research project, polyamide 6 composites based on unmodified and chemically modified halloysite nanotubes with different amount of filler loading were investigated. The morphological, mechanical and rheological properties of these nanocomposites were evaluated and compared with the properties of layered silicate polymer nanocomposites. Two different grades of PA 6 with different molar masses were chosen for the preparation of the composites. The addition of halloysite to PA 6 clearly increases the modulus and the yield stress of PA 6, in particular at low filler fractions for the low molar mass PA 6. At large filler fractions, the Young‘s modulus and the storage modulus linearly increase with halloysite fraction. The mechanical reinforcement of PA 6 using halloysite is very dominant above the glass transition temperature of PA 6. The reinforcement factor is approx. 1.9 for a halloysite fraction of 30 wt%. This value is comparable to other composites with micron-sized fillers such as wollastonite, but smaller than the value of PA 6 / layered silicate composites. The PA 6 / halloysite composites become more brittle with increasing halloysite loading. Furthermore, halloysite nanotubes influence the crystallization behaviour of PA 6 which is expressed by a pronounced formation of the ?-modification for the low molar mass PA 6. This result suggests that the reinforcement effect at low filler fractions is possibly caused by an effective arrangement of the crystalline phase in the PA 6 matrix. The shear viscosity of PA 6 is only moderately increased by the addition of halloysite nanotubes. Even at a filler concentration of 30 wt% no network formation of halloysite fillers was observed. Moreover the increase of viscosity is less pronounced for the halloysite nanotubes than for, e.g., carbon nanotubes and glass fibres. In order to further enhance the mechanical properties of PA 6, the surface of halloysite nanotubes was chemically modified. Different chemical modifications which were based on silane compounds were tested. The modification method of halloysite led to reproducible results and was suitable for scale-up. The investigation of the thermal properties of the PA 6 nanocomposites with the chemically modified halloysite at room temperature led to the conclusion that the organic modification of the halloysite surface suppresses the formation of the ?-modification of halloysite. In comparison to unmodified halloysite, the tensile modulus and stiffness of the composites is improved using halloysite nanotubes which have been modified using octadecyldimethylchlorosilane.
Projektbezogene Publikationen (Auswahl)
- 1. Thüringer Kunststofftag, May 8, 2007: “Der Zoo der Nanopartikel? Perspektiven und Trends für polymere Nanokomposite“
V. Altstädt
- Sampe ‘08, Long Beach (CA), May 21, 2008: “Novel nanocomposites based on silicate nanotubes of the mineral halloysite”
V. Altstädt
- Annual Conference of the German Rheological Society (DRG), Berlin, March 20, 2009: “Morphologische, rheologische und mechanische Eigenschaften polymeren Kompositen auf Basis von Nanoröhrchen”
U.A. Handge
- Annual European Conference on Rheology (AERC 2009), Cardiff, April 16, 2009: “Linear and nonlinear rheology of polyamide 6 composites with silicate nanotubes of the mineral halloysite”
U.A. Handge
- Compos. Sci. Tech. 69 (2009) 330-334
K. Hedicke-Höchstötter, G.T. Lim, V. Altstädt
- Hong Kong University of Science and Technology, August 21, 2009: “Novel polyamide 6 nanocomposites based on halloysite”
V. Altstädt
- Ioffe Physico-Technical Institute, St. Petersburg, April 18, 2009: “Novel nanocomposites based on halloysite“
V. Altstädt
- J. Plast. Technol. 5 (2009) 71-86
K. Hedicke-Höchstötter, V. Altstädt
- Polymermischungen 2009 – Polymerblends und Nanocomposites, March 26, 2009: “Morphologische, rheologische und mechanische Eigenschaften von PA 6-Nanokompositen auf Basis von Silikat-Nanoröhrchen“
U.A. Handge
