Thesis (DSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / Aqueous polyurethane (PU) dispersions were synthesized for use in paper coatings. These
PUs contained a polyester polyol soft segment (content of between 65 to 75%) and a
urethane hard segment (content of between 30 to 35%). Triethylamine (TEA) was used as
the neutralizing agent. The polyester polyol segment consisted of neopentyl glycol (NPG),
adipic acid, 1,4-cyclohexane dicarboxylic acid (1,4-CHDCA) and 2-phosphonobutane-
1,2,4-tricarboxylic acid (PBTCA), while the urethane hard segment consisted of toluene
diisocyanate (TDI), dimethylolproponic acid (DMPA) and ethylene glycol (EG) as a chain
extender for increasing the hard segment content.
Waxes and fillers were incorporated into the PU coating mixtures to investigate their effect on
the barrier properties of the PU. Two types of fillers were used: nano-fillers and micro-fillers.
The nano-fillers used included the Cloisite nano-clays NC15A, NC93A and NC30B, and the
micro-fillers used included talc, kaolin clay and barium sulfate.
Two different polyester polyols were synthesized: one containing a phosphate and the other
containing no phosphate. The polyols were characterized in terms of their acid value,
hydroxyl value and molecular mass. The PUs synthesized from the polyol containing no
phosphate showed unfavourable barrier properties compared to results achieved with the
phosphate-containing PU.
The PU dispersions were applied to paperboard, and then dried at a maximum temperature
of 130oC for 15 to 60 seconds, depending on the coating volume. The PU-coated paperboard
was characterized primarily by determining the moisture vapour transmission rate (MVTR),
and by scanning electron microscopy (SEM).
PU films (stand alone, not supported by paper) were prepared by heating the concurrent PU
dispersion in Teflon holders over three different temperature stages (60, 90 and 120oC) for
about 2 days. The dried films were then characterized by thermogravimetric analysis (TGA),
differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier
transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy.
The PU coatings showed self-assembly properties, which were affected primarily by the ionic
content (comprising of DMPA, PBTCA and excess TEA) and emulsion viscosity. These
self-assembly properties were analyzed by static contact angle (SCA) and MVTR measurements. It was found that the final coating properties were affected by the
self-assembly mechanism of the PU.
Generally, the phosphated PU coatings had lower MVTR values than the non-phosphated
PU coatings. SEM analysis showed that the phosphated PU coatings had no pinholes, while
the non-phosphated PU coatings had pinholes. DMA analysis showed that the phosphated
PUs had higher Tg values than the non-phosphated PUs. Further, the inclusion of the
phosphate monomer increased the emulsion stability and the compatibility between the hard
and soft segments of the PU.
Also, the exfoliated PU nanocomposites at 1% filler loading gave much better MVTR results
compared to the PU microcomposites. It also rendered the coating to be non-blocking, with
minimal change in MVTR.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1198 |
| Date | 12 1900 |
| Creators | Seboa, Sharrief |
| Contributors | Sanderson, R. D., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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