PhD Thesis
Novel Rubber Nanocomposites with Adaptable Mechanical Properties
Chih-Cheng Peng (12/2005)
Support: Volker Abetz
PhD thesis with Prof. Dr. Volker Abetz
Summary
This work mainly focuses on the synthesis and characterization of new elastomer nanocomposites by hydrogen bonding interaction between reinforcing agents and the rubber matrix. On one hand it was expected that the filler agglomeration is reduced, and on the other hand this specific interaction further enhances the mechanical properties of these nanocomposites. In order to attach hydrogen bonding interacting moieties, the rubbers used in this study were chemically modified via several pathways. Instead of carbon black and conventional silica particles, the reinforcing agents used here were polymeric fillers and silica nanoparticles whose effectiveness in reducing the Payne effect were also examined.
In Chapter 2 a commercial polybutadiene rubber, CB 10, was quantitatively modified from 1 to 20 mol% by a three-step polymer analogous reaction. The resulting PBs are capable of forming supramolecular hydrogen bonding networks. The reactions were monitored using 1H-NMR and the formation of hydrogen bonding complexes was verified by FTIR analysis. DSC analysis showed that crystallinity of the investigated PB was suppressed with a degree of modification > 2 mol% and the glass transition was shifted from -103 °C to -4.1 °C upon a sample with 20 mol% modification. Dynamic mechanical analysis showed that upon a 5 mol% modification, the crystallization was totally restrained and with higher degree of modification the glass transition was further elevated to higher temperatures. These observations indicate that the introduction of this type of hydrogen bonding complexes lead to the formation of effective supramolecular networks. The proposed modification pathway is a simple, economical and highly effective route for rubber and tire industries to design products of new generation.
In Chapter 3 silica nanoparticles were synthesized without surfactants via two different methods: the modified Stöber method and the original Stöber method. The former method unfortunately gave silica particle with unsatisfactory particle size and size distribution, which did not meet our requirement since it brought about unnecessary parameters in investigating filler-rubber interaction. On the contrary, the latter method gave monodisperse, surface unmodified silica particles of a size of 100 nm. Besides, the modification of such silica particles also gave monodisperse particles with less surface polarity. As well as the specific surface area, the resulting particles had similar size and size distribution, which ameliorated the defects of the polymeric microgels studied in Supplement. We also employed the in-situ DLS technique to monitor the growth of silica particles. The results show that this technique holds good for certain reaction conditions. In-situ DLS is simple, straightforward and economic in terms of time, and this method offers a template for size control in silica nanoparticle synthesis as well.
In Chapter 4 a kind of "smart" silica nanocomposites is presented containing surface unmodified and modified silica nanoparticles from Stöber synthesis, and a thermoreversible crosslinking rubber. Both the influence of hydrogen bonding interaction between silica and rubber on the Payne effect, and the temperature dependent dynamic mechanical properties were systematically investigated. The dynamic mechanical analysis showed that the competition and symbiosis between the filler-filler, filler-rubber and rubber-rubber HB interaction are controllable simply by changing the silica surface functionality, the silica loading, the degree of rubber modification and the temperature. TEM micrographs show that both the modifications of silica nanoparticles and rubber promote better silica dispersion in the rubber matrix. By this strategy it was shown that the Payne effect is reduced and it is possible to modify the mechanical properties of such silica filled composites in order to meet the requirements for different applications.
In Supplement, polymeric microgels of different surface functionalities and modified PB were synthesized to investigate the filler-rubber interaction via non-covalent hydrogen bonding. Dynamic mechanical analysis (both RPA and ARES measurements) was used as the main tool to characterize these microgels filled PBs. Due to the poor-defined characteristics of the microgels (distinct rigidity and cluster size), instead of the contribution of hydrogen bonding interaction the results showed that the Payne effect and the mechanical properties were dominated mainly by microgel rigidity and cluster size. The results also revealed that in order to realize the concept of reinforcing filled rubber materials further by hydrogen bonding interaction, one needs well-defined fillers with similar rigidity, size of primary particle and specific surface area, for instance.