Functionalized Materials Based on the Clay Mineral Kaolinite
Creators: name: Fafard, Jonathan
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2018
Subjects: Kaolinite
Clay mineral
Intercalation
Nanocomposite
Solid state NMR
XRD
FTIR
TGA
Polymer
Poly(lactide)
Poly(ethylene glycol)
Block copolymer
Melt intercalation
Solid state 1H NMR
Solid state 27Al NMR
Covalent grafting

description: The use of kaolinite for preparing functionalized materials for specialized applications is still a relatively niche research subject. This is in spite of its low cost, high availability, and the potential for covalently grafting organic functional groups to its inner and outer surfaces. These grafted compounds have been shown to be highly resistant to heat and solvents, making them very useful for certain applications, for example in polymer nanocomposite materials that require high thermal resistance during polymer processing. Solid state NMR has been shown to play an essential role in solving the structure of functionalized kaolinite materials, however the current knowledge base for these functionalized kaolinites is notably lacking for some nuclei such as 1H, 27Al and 17O. Research was undertaken to address these concerns by developing new synthetic strategies for preparing kaolinite based materials for use as nanocomposites and to examine commonly prepared modified kaolinite precursors materials by 1H and 27Al MAS NMR in an attempt to demonstrate their utility for characterizing kaolinite intercalated and grafted complexes. Solid state 1H NMR of a natural kaolinite, kGa-1b, identified two main proton signals attributed to inner and inner surface hydroxyl protons. The different affinity of these two types of hydroxyl groups towards exchange with deuterium was used to differentiate between the two. The 1H NMR spectra of a DMSO intercalated kaolinite, kDMSO, and a methanol grafted kaolinite, kmethoxy, were fitted with high accuracy using models consistent with the known structures of these materials. The 27Al MAS NMR spectra of a natural kaolinite, kGa-1b, a DMSO intercalated kaolinite, kDMSO, and a methanol grafted kaolinite, kmethoxy measured at 21.1T showed little difference between one another, while noticeable differences could be seen at 4.7T. 27Al MQMAS experiments found almost no difference between these materials in the multiple quantum dimension, suggesting the differences that were observed are a result of differences in quadrupolar parameters rather than chemical shifts. The 27Al NMR spectra of kGa-1b, kDMSO and kmethoxy were fitted with good accuracy using models consistent with known structures of these materials. Different Al(III) sites with CQ values varying by up to 0.6MHz were found. The 27Al NMR spectra of two different methanol grafted kaolinites were also compared and it was found that the intensities of the sites with lower values of CQ were dependent on the quantity of grafted aluminum sites. The interlayer space of kaolinite was functionalized with a block copolymer: poly(ethylene)-block-poly(ethylene glycol) using a kaolinite pre-intercalated with DMSO, kDMSO, and with a biodegradable polymer: poly(lactide) using a kaolinite pre-intercalated with urea, kurea, both by using melts of the polymer. The polymers were found to completely displace their precursors from the interlayer space giving a monolayer type arrangement of the polymer. Attempts were made to graft compounds containing polymerizable functional groups: 3-allyloxy-1,2-propanediol and ethylene glycol vinyl ether to kaolinite’s inner surfaces using a kaolinite pre-intercalated and grafted with methanol, kmethoxy, and a kaolinite pre-intercalated with DMSO, kDMSO, respectively. Both compounds were found to displace their precursors from the interlayer space, adopting a monolayer type arrangement. 13C and 29Si NMR results suggest 3-allyloxy-1,2-propanediol’s allyl group remains intact and partially keys into the clay mineral’s siloxane rings. Ethylene glycol vinyl ether was found to undergo intramolecular cyclization to form an acetal product, consuming its vinyl group in the process. This reaction was observed using an unmodified kaolinite, kGa-1b, suggesting that the clay mineral’s surfaces, both inner and outer, act as an acid catalyst.