Development of Polymer/Inorganic Nanocomposites Processing Based on an in situ Non-Aqueous Sol-Gel Technology
Final Report Abstract
In this project, a new route for preparing polymer nanocomposites based on in-situ formation of silica nano-sized particles in the polymer matrix during processing was applied. Non-volatile, hydrophobic hyper-branched polyalkoxysiloxanes PAOS are employed as silica precursors. Our investigations were aimed to get a deeper insight into the in-situ process, to understand the correlations between structure and properties and, based on this knowledge, to generate the optimum conditions for silica-nanocomposite preparation using a continuous twin-screw extruder process, resulting in optimal composite properties. Our approach of in-situ nanoparticle formation within a polymer matrix is able to overcome all of the problems resulting from powder mixing. Using the silica precursor PAOS which has a high content of silica inside and shows a good solubility within the polymer melt, we open the possibility to influence the particle sizes formed. So we were able to generate in-situ ultra-small silica particles of 3 to 6 nm in size within iPP. According to Mackay, such small particles are fine dispersed within the matrix increasing the free volume of the polymer by acting as a good solvent and swelling the polymer chains. As a result, melt viscosity should decrease strongly which were found in our system with a reduction of about 70% at shear rate of 12 s -1 in comparison to the neat iPP. To yield high thermal and mechanical properties, a strong interaction of particles and matrix is required. This results from an effective interphase between particles and matrix. In our work we could find a high effective volume fraction phi epsilon of composites prepared on the base of very small amounts (0.5 wt.-%) of C 0-PAOS as well as C 8-PAOS which correlates with a big interfacial region. These composites contain ultra-small silica particles. As a consequence thermo mechanical properties determined by DTMA are found to be improved by an enhanced load transfer from the matrix to the nanoparticles. In contrast, mechanical properties estimated by tensile tests do not improve. As the reason, we established that a broader particle size distribution as aspired as well as a partially heterogeneous particle distribution within the matrix is present. In the case of long alkyl chain modified PAOS used, we do not find such a big increase of mechanical properties, but an enhancement of thermal properties. We evaluated the optimum processing parameters and related the results to the lab scale products. The continuous process mostly suffers from an incomplete conversion caused by the short residence time during processing. As a consequence in contrast to the lab scale composites, residual PAOS acts as a lubricant and softens the material. The interactions between particles and matrix are only weak resulting in decreasing mechanical and thermal properties. After aging the samples over time, an increase of mechanical properties is detected. The aim of the developments was an increase of both, stiffness and toughness of resulting materials. In comparison to neat both iPP, Moplen HF501N and HP501M, an enhancement of stiffness was detected. The results of this project confirm the potential of our approach in creating a PP/silica composite based on in-situ reaction with fine dispersed ultra-small silica particles inside. Especially the yield of ultra-small particles by this approach proofs this. The most advantage of the approach is the application of the precursor polymer PAOS which is able to tailor the solubility in the polymer melt. Based on this fact a completely homogeneous distribution of the precursor in the polymer matrix is possible as a requirement of in-situ formation of well dispersed ultra-small silica particles. For application the processing conditions have to be optimized regarding a faster and complete conversion of PAOS to silica. Another challenge is to obtain a very small size distribution.
Publications
- "Preparation and Application of Poly (alkoxytitanate) as a TiO2 Precursor with High Storage Stability", Journal of Sol-Gel Science and Technology
Q. Dou, K. Peter, D. E. Demco, J. Wang, A. Mourran, M. Jaumann, M. Möller
(See online at https://doi.org/10.1007/s10971-013-3253-9) - “Morphology of Injection-Molded Isotactic Polypropylene / Silica Composites Prepared via In-Situ Sol-Gel Technology”, Macromolecules 2010, 43, 6067–6074
X. Zhu, C. Melian, Q. Dou, K. Peter, D. E. Demco, M. Möller, D. V. Anokhin, J.-M. Le Meins, D. A. Ivanov
- “Structure and Dynamics of Drawn Gel-Spun Ultrahigh-Molecular-Weight Polyethylene Fibers by 1H, 13C and 129Xe NMR”, Macromol. Chem. Phys. 2010, 211, 2611– 2623
D. E. Demco, C. Melian, J. Simmelink, V. M. Litvinov, M. Möller
- “Development of Polymer/Inorganic Nanocomposites Processing based on an in-situ Nonaqueous Sol-Gel Technology”, 27th World Congress of the Polymer Processing Society, Marrakesh, 2011
E. Kluenker, C. Kremer, K. Peter, M. Möller, Ch. Hopmann, W. Michaeli
- “Morphology, Chain Dynamics, and Domain Sizes in Highly Drawn Gel-Spun Ultrahigh Molecular Weight Polyethylene Fibers at the Final Stages of Drawing by SAXS, WAXS, and 1H Solid-State NMR”, Macromolecules 2011, 44, 9254-9266
V. M. Litvinov, J. Xu, C. Melian, D. E. Demco, M. Möller, J. Simmelink
- “Tailor-made inorganic additives for in situ formed nanocomposite fiber materials”, 7th Aachen-Dresden International Textile Conference, Aachen, 28.-29.11.2013
K. Peter, J. Faymonville, X. Zhu, M. Moeller
- „In-Situ Formed Nanocomposites by Application of a Hyper Branched Polyalkoxysiloxane Silica Precursor“, Talk, Third International Conference on Multifunctional Hybrid and Nanomaterials, (Hybrid Materials 2013), 3-7 March 2013, Sorrento, Italy
K. Peter, J. Faymonville, E. Kluenker, X. Zhu, C. Hopmann, M. Moeller
- “Reactive Extrusion Processing of Polypropylene/SiO2 Nanocomposites by In Situ Synthesis of the Nanofillers: Experiments and Properties”, Polymer, Volume 55, Issue 21, 9 October 2014, Pages 5370-5380
E. Kluenker, J. Faymonville , K. Peter, M. Möller, Ch. Hopmann
(See online at https://doi.org/10.1016/j.polymer.2014.08.059)
