Effect of surfactants used for binder synthesis on the properties of latex paints

Transcription

1 Progress in Organic Coatings 53 (2005) Effect of surfactants used for binder synthesis on the properties of latex paints Lauren N. Butler 1, Christopher M. Fellows, 2, Robert G. Gilbert Key Centre for Polymer Colloids, School of Chemistry F11, University of Sydney, Sydney, NSW 2006, Australia Abstract Surfactants are commonly used during emulsion polymerization to produce stable dispersions of polymer particles for applications such as paints, adhesives and other coating applications. Surfactants can improve properties such as shelf-life, freeze thaw stability and mechanical stability. However, the addition of surfactants can also have a negative effect on end-use properties, such as the water resistance of the coating. The type and amount of surfactant used is an important determinant of system behaviour during polymerization, film formation, and throughout the lifetime of the formed coating. The molecular architecture of binder particles is of crucial importance to latex paint properties. The type of surfactant used to stabilize binder particles had an effect on the adhesion of the paint to both alkyd-coated and Zincalume TM panels. The binders containing the polymeric surfactant showed better adhesion to these substrates, as they were better able to wet the surface of the substrates. However, polymeric surfactants also gave a greater amount of blistering when exposed to water and longer recovery times after exposure. The more hydrophobic the stabilization system, the greater the abrasion resistance observed, presumably due to the reduced extent of film plasticization by water. Accelerated weathering tests showed that these systems, designed to have low water sensitivity, gave good protection properties in regards to corrosion and blistering. UV exposure resulted in severe degradation of all films except where the binder contained acrylic acid, which is proposed to act as a photo-stabilizer Elsevier B.V. All rights reserved. Keywords: Paint properties; Latex paints; Binder; Surfactants 1. Introduction Surfactants are commonly used during emulsion polymerization to produce latexes, stable dispersions of polymer particles in an aqueous environment [1]. The latexes produced from this process are used in applications such as adhesives, paints, and other coating applications. In these applications, the prevention of sedimentation and phase separation during the manufacture and storage of the particles is desirable. The use of surfactants improves latex properties such as shelflife stability, freeze thaw stability and mechanical stability. Corresponding author. address: fellows@chem.usyd.edu.au (C.M. Fellows). 1 Present address: Advanced Nano Technologies, 112 Radium St., Welshpool, WA 6106, Australia. 2 Present address: School of Biological, Biomedical, and Molecular Sciences, University of New England, NSW 2351, Australia. However, the addition of surfactants can have a negative effect on film properties such as the water resistance of the coating [2,3]. Thousands of different commercial surfactants are available for use in emulsion polymerization. The type used will determine the behaviour of the system during polymerization, during film formation, and under end-use conditions. There are three main categories of surfactants ionic, polymeric and electrosteric. Ionic surfactants are low-molecular weight molecules that contain a charged hydrophilic end group. They impart particle stability by electrostatic repulsion and due to their small size are readily adsorbed and desorbed from the particle surface. Polymeric surfactants consist of a long hydrocarbon chain as the hydrophobic group and a polar polymer chain as the hydrophilic end group. This type of surfactant stabilizes particles by means of steric repulsion between polymeric chains. Electrosteric stabilizers can be best described as a polymeric surfactant with ionizable groups in /$ see front matter 2005 Elsevier B.V. All rights reserved. doi: /j.porgcoat

2 L.N. Butler et al. / Progress in Organic Coatings 53 (2005) Fig. 1. Entry to particles. Sulfato radicals ( OSO 3 ) formed in aqueous phase by decomposition of persulfate initiator can add either hydrophilic monomer (A), such as acrylic acid, which is common in aqueous phase, or hydrophobic monomer (M), such as butyl acrylate, which is largely localized in polymer particles and monomer droplets. Polymer radicals will not enter a particle until they have become sufficiently hydrophobic by adding a critical number of molecules of hydrophobic monomer. the hydrophilic section, allowing both electrostatic and steric repulsion to stabilize particles. The source of the ionizable group is usually a polymerizable electrolyte with acid or base functionality, such as acrylic acid. The aim of this work is to examine how a range of different surfactant systems affect common emulsion paint properties. For the sake of uniform conditions, binder particles comprising primarily poly(methyl methacrylate-cobutyl acrylate) (MMA-co-BA) were polymerized to the same size and surfactant post-added to eliminate the effect of binder particle size on film formation and resultant film properties. The surfactants used in this study include two polymeric surfactants, nonyl phenyl ethoxylates of ethoxylate lengths of 30 (Igepal CO887) and 50 (Igepal CO977), which were used individually and as a 1:1 mixture by weight. A range of electrosteric stabilizers were formed via the addition of a percentage of water-soluble monomers such as acrylic acid (AA) or methacrylic acid (MAA) to the final polymerization stage. These monomers may be incorporated into the polymeric radicals that initiate polymerization inside the polymer particles, and provide a grafted layer of electrosteric stabilizer on the particle surface, as illustrated in Fig. 1 [1]. 2. Experimental 2.1. Paint formulation Seven latexes were prepared as described previously, of approximate particle radius 55 nm and solid content of approximately 45% [4]. These latexes, plus a standard poly(butyl acrylate-co-methyl methacrylate) latex (BASF, 0.2 m diameter) were formulated for a gloss exterior paint Table 1 Paint formulation Component Amount Letdown Latex (g) Water Anti-foaming agent (g) 1.0 Ammonia aqueous 25% To ph 9 Mill base (g) Water Thickener 10.0 Propylene glycol Fungicide Sodium benzoate 5.0 Anti-foaming agent 10.0 Non-ionic polymeric surfactant 15.0 Titanium dioxide Fungicide Premix (g) Water 15.0 Propylene glycol 10.5 Non-ionic polymeric surfactant 1.0 Rheology controller 0.4 Texanol 9.5 Modified polyurethane thickener 1 (g) 3.8 Modified polyurethane thickener 2 (g) 8.0 Wetting agent (g) 3.0 Ammonia aqueous 25% To ph 9 using the recipe in Table 1. The paints were prepared in four stages, all with the same mill-base. The grind size for this paint system was <10 m (ISO 1524:2000 grind gauge) Testing paint properties Formed films prepared from paint formulation were tested for gloss, hardness, abrasion resistance, adhesion, wet adhesion, blistering, prohesion, and UV degradation, as detailed below. The viscosity of each paint formulation prepared was also measured. For gloss testing, the paints were applied to a glass panel using a in. doctor blade. The specular gloss of the film was measured following AS/NZS :1995 [5] after both 1 day and 1 week of drying at room temperature and humidity. For hardness testing the paints were applied to a glass panel using a in. doctor blade. The hardness of the film was checked by the scratch test (AS/NZS :1996 [6]) and the pendulum dampening method (ISO 1522:1998) after both 1 day and 1 week of drying at room temperature and humidity. To test abrasion resistance the paints were applied to Scrub black test panels (Leneta Co. size 6.5 in. 17 in.) using a in. doctor blade in duplicate. Two panels for each sample were tested with different drying times 24 h and 1 week at room temperature. The panels were placed in a scrub machine (Gardner Straight Line Washability and Abrasion Machine), which uses a scrubbing brush that moves back and

3 114 L.N. Butler et al. / Progress in Organic Coatings 53 (2005) forward at a constant rate and force over a substrate. A scrub paste consisting of water, thickener, sand and detergent (10 g) was added to the brush as well as 5 g of water. The abrasion is measured by how many cycles have been performed before a thin black line covering the entire film can be seen. The paints were applied to Zincalume TM and aged alkydcoated panels using a paintbrush and dried at room temperature for adhesion testing. The adhesion of the film to the substrate was measured using the pull-off test method for adhesion (AS :1993 [7]) after various drying times. For one set of Zincalume TM panels dried at room temperature for 2 h, the adhesion of the film to the substrate was measured before and after the panels were immersed in water for 30 min. The recovery of the film was measured by a third adhesion test 30 min after removal from immersion. To measure the degree of blistering, the paints were applied to Zincalume TM panels using a paintbrush and dried at room temperature for 2 h. The panels were placed onto a 250 ml paint can (with rim removed) containing 100 g of water at 50 C for 30 min. The panels were rated by size and number of blisters following a test method for evaluation of degradation of paint coatings AS/NZS :1998 [8]. The rating of the panel was subjective, as the panels needed to be examined in comparison to the pictures in the standard. The recovery of the film was checked by repeating the rating every 5 min after removal. Prohesion testing was carried out on Zincalume TM panels of dimensions 100 mm 145 mm. These were primed by paintbrush with a water-based red-oxide primer and allowed to dry at room temperature for 2 h. The paints were applied to the primed panels using a paintbrush and dried at room temperature for 2 h, then a second coating of the paint was applied and the panels were dried at room temperature for a further 24 h. The panels were placed into a Salt-Spray cabinet. This cabinet uses a 4-h cycle of moist air provided by spraying a prepared salt solution (10 g of sodium chloride and 80 g of ammonium sulfate in 20 L of water) followed by 4 h of dry air. The panels were rated over time by size and number of blisters following AS/NZS :1998 [8]. These tests were repeated using panels of Zincalume TM and galvanized steel that had not been primed. To measure the sensitivity of the paints to UV degradation, Zincalume TM panels of dimensions 75 mm 150 mm were primed by paintbrush with a water-based red-oxide primer and allowed to dry at room temperature for 2 h. The paints were applied to the primed panels using a paintbrush and dried at room temperature for 2 h, then recoated and dried at room temperature for a further 24 h. The panels were placed into a QUV-condensation cabinet using fluorescent UVA-340 lamps. The QUV test method is designed to simulate the exposure to sunlight responsible for the degradation of paint films. This cabinet uses a 3-h cycle of UV, in which panels reach a temperature of 60 C, followed by 3 h of water vapour condensation on the panels, in which temperatures around 45 C are reached. The panels were rated over time by measuring the gloss following the AS/NZS :1995 [5] test method. The percentage reduction in gloss over time was calculated. The readiness of the formulations to be applied by paintbrush (application of viscosity at a high shear rate of 10 4 s 1 ) was measured using an ICI cone-and-plate viscometer following the AS :1993 [7] test method. The ease of flow and stirring of the paint (viscosity at a medium shear rate of 10 2 s 1 ) was measured using a Rotothinner (Brookfield model VT-1). A 250 ml paint can, with rim removed, was filled with the paint and the spindle was lowered into the paint to the machine s preset level as described in AS/NZS :1996 [9]. 3. Results Gloss is a function of how well dispersed pigment is within the binder, and hence of how the components in the paint system react to the dispersant. On drawing down the paints onto a glass substrate, variations in surface roughness between films were immediately observed (Table 2). During the mill grinding stage, the pigment-particle agglomerates are broken down by the mill and are stabilized by the dispersant, which is the sodium salt of a polymeric carboxylic acid. It can be seen that binders incorporating low percentage AA stabilizers are most effective at achieving even dispersal of the pigment particles, followed by the low percentage MAA stabilizer, the standard formulation, and Igepal CO887, with the least glossy paints those containing Igepal CO977 and 4% MAA. It would be expected that a more viscous paint would give rise to a rougher final surface, and the binders prepared with the more hydrophobic stabilizers do interact with the asso- Table 2 Gloss levels and hardness of paint films Binder Gloss at 20 Gloss at 60 Sward-rocker hardness (no. of cycles) Pencil hardness Standard B 2% MAA % MAA % AA B 4% AA Igepal CO Igepal CO B Igepal mixture

4 L.N. Butler et al. / Progress in Organic Coatings 53 (2005) ciative thickener to give more viscous formulations (Table 7), but the gloss results do not correlate well with the low-shear viscosity. It is possible that the more hydrophobic binder systems may react in a negative manner with the dispersant in the paint formulation, leading to a formulation in which pigment particles are not dispersed as homogeneously. The hardness of the films was measured using both the Sward-rocker and pencil hardness tests (Table 2). The results of the pencil hardness test are that all the films tested will be scratched with either a 2B or 3B pencil. This suggests that the elastic limits of the films are nearly identical. This is reasonable, as the binder in the system (primarily (poly(baco-mma)) is essentially the same for all preparations, and suggests that the opacifier particles are well-dispersed within a matrix of this polymer. However, the tests used are relatively insensitive to the small differences in hardness expected to arise from the variations in composition and in future work more quantitative measurements of film hardness will be obtained using a nano-indenter. The addition of AA and MAA to the binder will increase the glass transition temperature (T g ) and minimum film forming temperature (MFFT) of the binder, as these monomers form glassy polymers at room temperature. The results from the Sward-rocker test imply differences in the MFFT of the binders, with the 4% AA and 4% MAA preparations displaying a significant increase in hardness compared to the other binder systems. No appropriate controlled humidity environment was available for determining reproducible MFFT values of the paint formulations. The abrasion test (Table 3) was performed under wet conditions, so the main factors affecting the results will be the pigment binding ability of the latex and the hydrophilicity of the latex, the particle size and type of polymer in the latex being held constant. Poor pigment-binding ability would be expected to give rise to both low gloss and poor abrasion resistance. However, little correlation was seen between the results of these two tests. A more likely explanation for the differences in the binders that could account for the abrasion results are the varying hydrophilicities of the binder film caused by modifying the particle surface; paints prepared with binders with a high proportion of polymerizable carboxylic acid (2 and 4% AA, 4% MAA) were more easily abraded than the Table 3 Results from abrasion testing Binder Number of scrub cycles 24 h 1 week Standard Igepal CO Igepal CO Igepal mixture % MAA % MAA % AA % AA Error = ±10 scrub cycles. standard paint formulation, while all other paints were more resistant to abrasion than the standard paint. It is most likely that swelling of the more hydrophilic films with water causes a loss of tensile strength and elastic modulus. Abrasion testing was performed using two drying conditions (24 h and 1 week) in order to check the effect of the coalescent agent on abrasion resistance. As the coalescent agent evaporates from the film, the abrasion resistance should increase as the MFFT is lowered and the film becomes more elastic. In most cases, however, the change in abrasion resistance over 1 week was not significant. The number of scrub cycles decreased over time only for the latex containing Igepal CO887. Strong increases in abrasion resistance over time were seen for the Igepal CO977-containing latexes 4% MAA latex and 2% AA latex. It is possible that these carboxylic acid preparations, which can bind a greater amount of water than the latexes with a reduced hydrophilic component, will show a more improved MFFT with loss of bound water over this time. Adhesion is the measure of the degree of wetting of paint to a substrate and the strength of bonds formed between the polymer and substrate. The two substrates, Zincalume TM and Alkyd coated panels, have surfaces consisting of an acrylic coating and a mixture of alcohol and polyester functionalities, respectively. The test method rating scheme is along a scale from 1 to 5, with 0 corresponding to the case where no paint is removed and 5 to complete removal of paint from the substrate. The results of adhesion tests are given in Table 4. Table 4 Adhesion test results Binder Drying time 24 h 2 h 6 h 48 h min immersion Adhesion on alkyd-coated panel Adhesion on Zincalume TM Standard Igepal CO Igepal CO Igepal mixture % MAA % MAA % AA % AA

5 116 L.N. Butler et al. / Progress in Organic Coatings 53 (2005) For adhesion to the alkyd panel, the results suggest that those latexes that contain the polymeric surfactant have better adhesion than those that contain electrosteric stabilizers. Since adhesion is a function of the degree to which the adhering latex can wet the surface, insufficient surface wetting due to the higher surface tension of the latexes that contain electrosteric stabilizers may explain these results. The standard latex formulation, containing conventional surfactant, clearly shows the best adhesion. The poor performance of the NPE mixture may also be related to poor surface wetting. Longer NPEs inhibit coalescence [10] while the mixture would be expected to stabilize w/o emulsions to a greater extent than the NPE50 alone, leading to inclusions localizing the surfactant to a greater extent within the forming film than on the film-substrate interface. The adhesion of the paints on Zincalume TM improves over time for all systems. After 2 h of drying, the paints that contain AA take a considerable amount of time to develop strong adhesion with the Zincalume TM, as does the paint formulated with a mixture of NPE30 and NPE50. This poor adhesion could be a function of poor wetting of the substrate by these latexes, or be related to a lack of favourable adhesive interactions between the carboxylic acid groups on the surface of the particles and the poly(acrylate) binder of the primer. The latexes containing polymeric surfactants gave reasonable initial adhesion to the Zincalume TM panels, as they did to the alkyd panels. The wet adhesion was poor for all systems except the standard. The standard latex is likely to contain a wet-adhesion promoter, as is the case for most commercial latexes, but no wet-adhesion promoter was added to the test formulations. A common method of wet-adhesion promotion is addition of dimethylaminoethyl methacrylate [11] during the final stages of binder production. The wet-adhesion promoter is able to form either strong hydrogen bonds with the surface through the amino functionality in the wet-adhesion promoter or chemical bonds with any acidic functionality in the substrate surface. Both the alkyd coatings and Zincalume TM have primarily carboxyl or hydroxyl polar surface groups Chemical properties of paint films The prohesion test is used to examine how a paint film reacts to a salty environment in terms of corrosion, blistering, chalking and discoloration of films. Normally this test is performed with a more concentrated salt solution (0.5 M NaCl). However, it has been found that the less concentrated solution of NaCl and (NH 4 ) 2 SO 4 used in this study gives results that correlate more readily to exterior exposure [12,13]. Primed Zincalume TM and galvanized steel both initially give white deposits of zinc oxide that were difficult to distinguish from the paint films. All the latexes formulated into paints had latex films that give an approximately 10% gain in weight when immersed in water. This test should not therefore be able to distinguish the latexes on the basis of water uptake but on the interac- Table 5 Blistering test results Latex Size/density of blisters Recovery time (min) Standard 3/1 15 2% MAA 0/0 N/A 4% MAA 2/3 5 2% AA 2/2 5 4% AA 2/4 5 Igepal CO887 2/5 17 Igepal CO977 2/5 10 Igepal mixture 2/4 15 tion that the binder has during the formulation of the paint that promotes water uptake. The results are shown in Table 5. The rating scheme for this test is AS/NZS :1998 [8], where 0 = no blisters and 5 = dense, large blisters. The rating of the panel was subjective, as the panels needed to be examined in comparison to the pictures in the standard. Most of the panels began to blister at the edges, making it difficult to give a rating for density as the density refers to the entire area of the film. A duplicate of each paint system was tested to account for any differences in film thickness. On the primed Zincalume TM and galvanized steel, all the latexes that contained the polymeric surfactants showed signs of blistering. The samples containing the lower amounts of acid showed no signs of blistering on the Zincalume TM after 8 weeks exposure. However, the level of blistering in all samples was minimal. The worst blistering is seen for the standard formulation and the formulations using polymeric surfactants, suggesting that these latexes are effective at binding and trapping water in the film and are slow in releasing that water. The blistering observed with latexes containing carboxylic acid followed the order of hydrophilicity, that is, as the latex became more hydrophilic, more water was apparently trapped at the film/substrate surface Accelerated weathering The conditions experienced by the paint films under the QUV test are much harsher than that in the natural environment. During the condensation cycle, the water droplets on the surface of the film can act as lenses, magnifying the effects of the UV light. Water may also be absorbed into the film and wash away small chain fragments. This test method is used as a guide to indicate which paints would be more likely to fail under UV light. The results from the QUV test are shown in Table 6, displayed as the percentage of loss in 60 gloss. Fairly rapid degeneration is seen for the standard formulation, for formulations prepared with polymeric surfactant, and for formulations prepared with MAA (after an initial period of relative stability). The latexes containing polymeric surfactants started blistering after one month of exposure. The latexes containing MAA also degraded on a macroscopic scale much

6 L.N. Butler et al. / Progress in Organic Coatings 53 (2005) Table 6 Percentage gloss change at 60 from QUV test for duplicate panels Latex Time (day) Standard 14/ 18 18/ 18 18/ 18 20/ 27 27/ 26 27/ 29 2% MAA 3/ 1 5/ 3 18/ 15 28/ 23 34/ 28 55/ 40 4% MAA 9/ 1 17/ 15 35/ 40 54/ 56 55/ 65 78/ 76 2% AA 5/ 8 7/ 1 6/ 4 14/ 13 8/ 11 14/ 14 4% AA 4/6 2/0 4/7 3/ 2 6/ 7 16/ 6 Igepal CO887 7/ 3 9/ 9 20/ 17 23/ 21 57/ 59 a 53/ 58 a Igepal CO977 9/ 15 15/ 20 27/ 27 35/ 26 66/ 50 a 57/ 53 a Igepal mixture 7/ 9 11/ 13 30/ 21 37/ 24 49/ 48 a 47/ 53 a a Indicates that blisters were present on the panels. more quickly than the other panels while samples containing AA show small gloss losses over time. Poly(butyl acrylate-co-methyl methacrylate) undergoes photo-degradation either through oxidation of the tertiary carbon to give stable hydroperoxides or through oxidation of methylene groups adjacent to ester functionalities to give less stable hydroperoxides, with the latter reaction predominating when the amount of butyl acrylate is higher [14]. Co-monomers such as styrene and dialkyl acrylamides have been reported to act as photo-stabilizers, as they sacrificially undergo photo-oxidation reducing the amount occurring in the system [15]. Titanium dioxide has been known to increase the amount of photo-degradation that occurs in paint films [16]. The titania used in these paints has an alumina and tri-methylol propanol layer on the surface to increase photo-stability and dispersibility. The low percentage gloss loss in the paints containing AA suggests that this monomer may act as a photo-stabilizer in the system, although the mechanism of this is unclear. While carboxylic acid functionality on the surface of the particles could complex transition metals, which could act as radical scavengers, there is no obvious source for such transition metal ions in these systems. Further experiments on photodegradation are required to validate this effect of poly(aa) and test possible mechanisms Viscosity During formulation, it was noticed that different latices responded differently towards the rheology modifiers, as shown in Table 7. Product quality specifications for a water-based Table 7 High and mid-shear viscosities of the paints formulated (P) Latex ICI cone and plate Rotothinner Standard % MAA % MAA % AA % AA Igepal CO Igepal CO Igepal mixture gloss white exterior paint are an ICI cone and plate viscosity of P and Rotothinner viscosity of 5 7 P [17]. The implications of having the high- and mid-range viscosities out of this range is that the paint will drip and splatter on application if viscosity is too low, or give poor levelling if it is too high. Having high viscosities will also result in the appearance of pinholes in the film caused by micro air bubbles in the paint, as the system will be too viscous for bubbles to rise to the surface and the defoamer can only effectively remove large bubbles. The differing high- and mid-range viscosities of the various paints give an indication of how the surface charge of the binder affects the response of the rheology modifiers. The rheology modifiers consist of modified polyurethane chains with hydrophobic domains on a hydrophilic backbone that have an associative thickening action. When placed into paint, thickening occurs by the rheology modifiers forming a complex network structure that increases the viscosity. The hydrophobic domains connect with the binder particles to create this network [18]. The results appear to indicate that the systems with the more hydrophobic surfaces have higher viscosities. For example, latices containing Igepal CO887 are more viscous then those containing Igepal CO977 and latices containing 2% MAA more viscous than those with 4% MAA. The greater hydrophobicity of the binder particle surfaces probably improves the ability of the associative thickeners to establish a network between binder particles. The results for the latices containing AA are opposite to this trend, suggesting that AAcontaining polyelectrolytes in the aqueous phase are formed during the polymerization of the binder, which can act themselves as rheology modifiers. As the amount of AA is increased, these polyelectrolytes will have a greater average molecular weight and have a more pronounced affect on the viscosity of the system. 4. Conclusions The molecular architecture of binder particles specifically, the type of stabilizer used has been shown to be of crucial importance to paint properties. Frequently, there

7 118 L.N. Butler et al. / Progress in Organic Coatings 53 (2005) is a trade-off between desirable properties, with a particular stabilizer providing improvements in some properties and impairing others (e.g., acrylic acid in this study gave reduced blistering and increased UV resistance, but also reduced adhesion). The following trends have been observed: (1) The more hydrophobic the stabilization system, the greater the abrasion resistance as the incorporation of water into the film can soften the paint film. (2) The most hydrophobic stabilization systems also gave poor gloss, for reasons that are as yet unclear. (3) The binders containing the polymeric surfactant showed better adhesion to both alkyd-coated panels and Zincalume TM, possibly due to better wetting of the surface of the substrates. However, polymeric surfactants gave more blistering and longer recovery times after exposure than electrosteric surfactants. (4) UV exposure resulted in severe degradation of all films, except for those with binders that contained acrylic acid, which is proposed to act as a photo-stabilizer. The accelerated weathering tests performed showed that all these binder systems, designed to have low water sensitivity [4], gave adequate protection from corrosion and blistering when formulated into paints. Surfactants in current binder systems affect all of particle size, freeze thaw stability, paint rheology and water sensitivity. A surfactant which adversely affects one of these properties may be beneficial for another. A possible way around this nexus of problems is through the advent of new latex synthesis methods [19,20], which obviate the need for surfactant during particle formation, and thus enable formulators to choose surfactants for optimizing desirable properties, by decoupling particle size from the other properties. Acknowledgement The Key Centre for Polymer Colloids is established and supported by the Australian Research Council s Key Centres Program. Dr. Butler s Ph.D. studies were supported by the Australian Research Council s Australian Postgraduate Award Industry program and Wattyl Australia Pty. Ltd. References [1] R.G. Gilbert, Emulsion Polymerization: A Mechanistic Approach, Academic Press, London, [2] S. Paul, Prog. Org. Coat. 5 (1977) 79. [3] J. Snuparek, A. Bidman, J. Hanus, B. Hajkova, J. Appl. Polym. Sci. 28 (1983) [4] L.N. Butler, C.M. Fellows, R.G. Gilbert, J. Appl. Polym. Sci. 92 (2004) [5] Australian Standard/New Zealand Standard :1995, Paints and related materials methods of test measurement of specular gloss of non-metallic paint films at 20 degrees, 60 degrees and 85 degrees, [6] Australian Standard/New Zealand Standard :1996, Paints and related materials methods of test determination of pencil hardness of paint film, [7] Australian Standard :1993, Paints and related materials methods of test adhesion (cross-cut), [8] Australian Standard/New Zealand Standard :1998, Paints and related materials methods of test coatings exposed to weathering degree of blistering, [9] Australian Standard/New Zealand Standard :1996, Paints and related materials methods of test consistency rotothinner, [10] L.A. Cannon, R.A. Pethrick, Polymer 43 (2002) [11] Surface Coatings Association of Australia, Surface Coatings, Chapman & Hall, London, [12] B.S. Skerry, C.H. Simpson, Corrosion 49 (1993) 663. [13] S.K. Boocock, J. Protect. Coat. Linings 11 (1994) 51. [14] N.S. Allen, C.J. Regan, R. McIntyre, B.W. Johnson, W.A.E. Dunk, Macromol. Symp. 115 (1997) 1. [15] N.S. Allen, C.J. Regan, R. McIntyre, B.W. Johnson, W.A.E. Dunk, Prog. Org. Coat. 32 (1997) 9. [16] H. Cao, R.W. Zhang, C.S. Sundar, J.P. Yuan, Y. He, T.C. Sandreczki, Y.C. Jean, B. Nielsen, Macromolecules 31 (1998) [17] Wattyl Australia Pty. Ltd., Quality control specifications of waterbased gloss exterior white paint, private communication, [18] E. Sprong, Ph.D. Thesis, The University of Stellenbosch, [19] C.J. Ferguson, R.J. Hughes, B.T.T. Pham, B.S. Hawkett, R.G. Gilbert, A.K. Serelis, C.H. Such, Macromolecules 35 (2002) [20] A. Guyot, K. Tauer, J.M. Asua, S. Van Es, C. Gauthier, A.C. Hellgren, D.C. Sherrington, A. Montoya-Goni, M. Sjoberg, O. Sindt, F. Vidal, M. Unzue, H. Schoonbrood, E. Shipper, P. Lacroix-Desmazes, Acta Polym. 50 (1999) 57.