Roof Coatings
October 2014 www.coatingsworld.com Coatings World | 71
stable suspensions unlike latexes which will settle out over time. 10
A study of effect of molecular weight variation on CUP formation
and stability has shown that CUP particle size tracked the molecular weight except at very low molecular weight. From MW 13k up,
the theoretical and experimental particle size data were in very good
agreement. The CUP of 153K MW also went well and was of zero
VOC. For conventional water reducible resins, as the molecular
weight goes up so does the VOC. For example, water reducible resin
with 20K MW, the VOC is about 1lb/gal and at 40K it is about 3.2
lbs/gal making it impossible to use higher molecular weight resins
with the VOC restrictions we have today. 11
The viscosity of CUP systems are dependent upon concentration
and the amount of charge on the particle. As the CUP concentration
increases the distance between particles decreases and the charges on
the particles repel each other which increases the viscosity. The higher
the charge density the higher the viscosity. Thus, keeping the charge
to the minimum needed to stabilize the particle in solution should be
targeted to give the lowest viscosity. As the particle size increases, the
point at which the viscosity rises, decreases in terms of percent solids. 12
As shown in Figure 2, the particles with surface water and charge
can randomly pack or form a close pack configuration. In the end, the
resin must conform to the Kepler conjecture which limits the volume
solids before gelation. The thickness of the bound water layer (λ) as
indicated in Figure 2, is approximately 0.56 nm. This layer is approximately the same for the three resins depicted in Figure 3 which represents a 100nm latex, a 25nm urethane dispersion and a CUP particle.
Solvent reduction can be achieved by using various methodologies and is an active field of research. With unique modifications to the existing water-reduction technique we have
developed novel aqueous polymer systems (CUPs) with zero
VOC to address the solvent issues and paved the way for future
developments in resin technology. CW
References
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4P. C. Painter, M. M. Coleman, Fundamentals of Polymer
Science, 2nd Edition, Technomic Publishing Co. Inc., 1997.
5 P. C. Hiemenz, Polymer Chemistry: The Basic Concepts, CRC
Press, 1984.
6 K. Jindal, D. Bhattacharya, L. F. Francis, A. V. McCormick, L.
T. Germinario, C. Williams, Progress in Organic Coatings, 67,
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7 A. R. Marrion, The Chemistry and Physics of Coatigs, 2nd
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C. J. Riddles, W. Z hoa, H, Hu, M. Chen, M. R. Van De Mark,
8 Polymer, 55, 2014, 48-57.
9 J. K. Mistry, A. M. Natu and M. R. Van De Mark, J. Appl. Poly.
Sci., 2014 DOI: 10.1002/APP.40916.
10 M. Chen, C. J. Riddles, M. R. Van De Mark, Langmuir, 29,
2013, 14034-14043.
11 M. R. Van De Mark, A. M. Natu, S. V. Gade, M. Chen, C.
Hancock, C. J. Riddles, J. Coat. Technol. Res., 11, 2013,
111-122.
12 M. Chen, C. J. Riddles, M. R. Van De Mark, Colloid Polym.
Sci., 291, 2013, 2893-2901.
Figure 1. General water reduction process. I. Random coil configuration in THF.
II Random coil intimate ion pair. III. Extended coil solvent separated ion pair. IV.
Collapsed coil. V. Hard sphere. M. R. Van De Mark, A. M. Natu, S. V. Gade, M.
Chen, C. Hancock, C. J. Riddles, J. Coat. Technol. Res., 11, 2013, 111-122
Figure 2. Random close packing of CUP with surface water (left); Kepler Conjecture with CUP and its surface water (right). M. Chen, C. J. Riddles, M. R. Van
De Mark, Colloid Polym. Sci., 291, 2013, 2893-2901
Figure 3. Relative viscosity against volume fraction. M. Chen, C. J. Riddles, M.
R. Van De Mark, Colloid Polym. Sci., 291, 2013, 2893-2901
