vinyl acetate/ethylene emulsions: designing for...

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VINYL ACETATE/ETHYLENE EMULSIONS: DESIGNING FOR PERFORMANCE IN LOW ODOR DECORATIVE PAINTS FOR LATIN

AMERICA

Narayan Raman, Sidnei Lamim, Brad Moncla, Brigitte Cardinal, Ming Tsang, Rajeev Farwaha

Celanese Emulsion Polymers, USA

ABSTRACT Vinyl acetate/ethylene (VAE) emulsions have gained wide acceptance in decorative paints in recent years because they enable paint manufacturers to make low odor, low to zero VOC paint with high performance. Significant improvements in VAE technology and a better understanding of the formulation practices in Latin America have enabled development of VAE emulsions which have been tailored to meet local paint performance targets and quality levels. Innovations in the VAE emulsion chemistry have narrowed the performance gap with hard styrene acrylics and Vinyl acetate-Vinyl versatate-Acrylic terpolymers. In this paper we present results of our benchmarking study that show odor-free, low VOC paints based on VAE emulsions can exceed the performance of paints based on hard Styrene/Acrylic emulsions in properties such as wet scrub resistance, hiding power, and blocking resistance. EcoVAE® 402, an emulsion specifically designed for the Latin American paint market, is the newest VAE offering from Celanese, a world leader in VAE technology. Using locally available paint additives and following local formulation guidelines, we show that odor-free paints can be made with EcoVAE® 402 that provide superior performance across different paint quality levels and are cost competitive with styrene-acrylics. In addition, testing results show that significant cost saving can be achieved with these VAE emulsions as they demonstrate excellent colorant compatibility along with higher brightness and tint strength compared to styrene acrylics and Vinyl acetate-Vinyl versatate-Acrylic terpolymers. 1. INTRODUCTION Health, wellness, and environmental stewardship are some of the many mega-trends that are sweeping the advanced and developing economies of the world [1, 2]. The environmental impact of paints and the health issues related to volatile organic content (VOC) emissions have been well documented [3, 4]. Regulatory requirements continue to reduce VOC emissions in paints and have become the key driver for innovations in binder and coating technology. More recently, an increasing number of consumer and professional coatings are being certified for compliance to emission and/or performance standards by third parties.

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Figure 1: Trajectory of VOC limits set by regulatory requirements globally Rapid industrialization of Latin American economies and globalization are making the Latin American consumer more aware of the impact of coatings on indoor air quality, odor, and durability. Recent trends suggest an increasing number of consumers in Latin America are becoming concerned with the environment and a large segment of those consumers are willing to pay more for eco-friendly products [5]. Paint manufacturers have responsed to this trend by developing low VOC paints without solvents or coalescents, while also meeting the high performance expectations of the consumers. Emulsion suppliers have in turn responded with new binder technologies to enable manufacture of high peformance low/zero VOC and low/no odor paints. VOC emissions are mostly caused by the presence of coalescents and solvents in the paint formulation [6]. The solvent content in coatings varies a great deal depending upon the glass transition temperature (Tg) of the polymer, freeze-thaw stability requirements, etc. On the average, the solvent content can range anywhere 0.05-1 wt% of a paint formulation. Introduction of vinyl acetate/ethylene (VAE) emulsions, has enabled manufacture of low to near zero- VOC paints by dramatically reducing the use of coalescing agents (solvents and plasticizers) without sacrificing performance properties. This unique capability of VAE emulsions is due to the plasticizing effect of water. During film formation, water softens the VAE copolymer allowing the formation of a film at a significantly lower temperature than predicted by the glass transition temperature (Tg). As a result, VAE based paints have become the dominant technology for consumers who prefer superior indoor air quality and low odor, while maintaining excellent performance in terms of scrub resistance, hiding power, workability, block resistance, and color intensity. Innovations in the VAE emulsion chemistry have narrowed the performance gap with hard styrene acrylics and Vinyl acetate (VA) -Vinyl versatate (VEOVA™)-Acrylic terpolymers. More recently, VAE emulsions in decorative paint formulations have been the subject of intensive study in an effort to address the wide performance spectrum of paint systems used in the decorative coatings market. In this paper, we present recent developments in Celanese VAE technology and show results of a study benchmarking Celanese VAE emulsions against styrene acrylics, vinyl acetate-vinyl versatate-acrylic terpolymers using locally available paint additives and following local formulation guidelines. These results demonstrate the superior value proposition of VAE emulsions in the paint quality level-performance continuum. 2. LATIN AMERICAN DECORATIVE PAINTS: FORMULATION PRACTICES AND TESTING PROTOCOLS Even though there has been convergence at the global level in terms of the market trends, regulatory issues, and consumer preferences, decorative paints for the most part have an inherently local flavor and usually reflect consumer perception of in-can feel and appearence, painting practices in terms of frequency and methods, sheen and color preferences, and performance requirements and criteria. The paint formulations in different regions of the globe in turn reflect these differences in perception and performance requirements. Based on surverys of paint manufacturers and testing commercial paint benchmarks, we have established a typical paint formulation that we beleive is representative of paints made in Brazil at the various quality levels (Table 1). Wherever possible, we have used the exact pigment, extenders, and other additives used in Brazil and have substituted equivalent or similar additives whenever we could not acquire those additives. Table 2 provides the key performance requirements for the various quality levels. For each quality level, we chose two widely sold paints in Brazil as

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benchmarks and the mostly widely used styrene acrylic and vinyl acetate-vinyl versatate-acrylic polymers as emulsion controls. Table 1: Typical decorative formulation and local additives for various paint quality levels used in this study

Raw Material Description Premium Standard Economic

% Wt. of Formula

Water Water Adjust to make 100%

Sodium Nitrite Sodium Nitrite 0.1 0.1 0.1

Hydroxy ethyl cellulose (HEC)

Natrosol Plus 330 0.2 0.2 0.2

Wetting Agent Aerosol OT 0.15 0.15 0.15

pH Modifier Monoethanolamine 0.2 0.2 0.4

Biocide BIT - Acticide BW20 0.18 0.18 0.18

Defoamer Cognis A-38 0.15 0.15 0.15

Dispersant Tamol 731A 0.5 0.5 0.5

Titanium dioxide Tronox CR-826 11 5.5 2

Ground Calcium Carbonate

Brasmite TT slurry 13 13 16

Precipitated Calcium Carbonate

Brasmite Plus slurry 15 22 30

Diatomite EcoFlat 3 3

Clay Kaolin NP slurry 14 15 15

Latex Latex, 55% solids 18 11 7.5

Coalescing Agent Texanol 1.2 1 0.6

Rheology Modifier HASE –Polyphobe TR-116

Defoamer Cognis A-38 0.18 0.18 0.18

Table 2: Performance targets for the paint formulations used in this study

Properties Premium Standard Economic

NVM% (Solids Content) 48 +/-2 44+/-2 39+/-2

PVC 60 70 78

Target KU Viscosity 90-110 90-105 95-110

Target ICI Viscosity 1,2-1,5 1,2-1,4 1,0-1,2

Main Tests

Wet Abrasion Resistance - ABNT Standard #14940, # of cycles

100, abrasive

40, abrasive

100, no abrasive

Dry Hiding Power - ABNT Standard #14942

6 5 4

Wet Hiding Power - ABNT Standard #14943

90% 85% 55%

Odor (comparative) Blind test

Color Acceptance Rub-up E ≤ control and commercial benchmark

Color Development Pthalo blue 888 series, Tint Strength ≥ control and commercial benchmark

Color by Spectro Guide Pthalo blue 888 series E ≤ control and commercial benchmark

Gloss, 20°/60°/85° 1-1.5/2-3/5-6

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Colorant Compatibility Color Float after 48 hours

3. RESULTS AND DISCUSSION

3.1 Tg and Minimum Film formation Temperature: Table 3 below shows the typical properties of the styrene acrylic, VA-VEOVA™-acrylic, and vinyl acetate ethylene (VAE) emulsions used in this study. During drying, the emulsion transforms from a colloidal dispersion to a polymer film. The ability of an emulsion to form a homogeneous, crack-free film during drying is measured by its minimal film formation temperature (MFFT). An emulsion and an emulsion based paint will form a crack free film only at temperatures at or above the MFFT. Figure 2 is a picture comparing the MFFT of 7 mil drawdowns of neat emulsions. It is clear from the picture that the neat VAE emulsions form crack free films at much lower temperatures than conventional styrene acrylics and VA-VEOVA™-Acrylics. Moreover, the Tg-MFFT difference for Styrene-Acrylics, VA-VEOVA™-Acrylics is much less than Tg-MFFT difference for VAE. These differences reflect the hydroplasticizng effect of water on VAE emulsions allowing film formation at a significantly lower temperature than their Tg. For low VOC decorative paints, the MFFT of the paint must ideally be below 5°C.

Table 3: Typical properties of the emulsions evaluated in this study

Properties VAM-VEOVA-

Acrylic Styrene Acrylic

Vinyl Acetate Ethylene

(VAE)

Solids, wt.% 50 50 55

Brookfield Viscosity, cps < 500 6.0-10.0 100-650

pH 5-6 8-9 4-6

Tg, °C + 27 + 25 - 27 +13

MFFT, °C +17 +12-18 +1.5

Figure 2: MFFT drawdowns of the neat emulsions evaluated in this study. 3.2 Thickener Demand: Thickener (Polyphobe TR-116) demand as wt% of the total formulation to achieve target KU and ICI increases progressively when going from premium to economy quality level and is consistent with the decreasing level of binder in paint. VAE emulsions in general show lower thickener demand to achieve viscosity targets compared to styrene-acrylics and VA-VEOVA™-acrylics. At the thickener levels required to achieve target ICI viscosity, the competitive styrene acrylics developed very high KU and became paste like. The standard and economy paint formulation used in this study showed much higher ICI than the commercial benchmark paints at similar quality levels.

VAM-VEOVA-Acrylcis

0°C 9°C 18°C

Styrene Acrylics

1.5°C

1°C

17°C

12°C

>18°C

VAE-

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Figure 3: Thickener demand as wt.T of the entire formulation to achieve ICI viscosity targets. 3.3 Wet Abrasion Resistance: In the premium quality paint, EcoVAE® 402 showed significantly higher wet abrasion resistance (ABNT Standard #14940) compared to SA and VA-VEOVA™-acrylic emulsions as well as commercial paint benchmarks. In the standard quality however, 402 scrubs were comparable to styrene-acrylics and somewhat lower than one of the commercial benchmark paints. At the economy quality level, when scrubs were tested using the abrasive, no significant difference was observed between the various emulsions. The economy level scrubs were also significantly lower than one of the economy level commercial benchmarks.

Figure 4: Comparison of wet hiding power (ABNT Standard #14940), of various emulsion chemistries against Brazil commercial paint benchmarks.

3.4 Wet Hiding Power: In the premium and standard quality paints, the formulations tested in this study showed somewhat higher wet hiding power than the commercial

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paint benchmarks whereas in the economy paints, the opposite behavior was observed. The difference in the wet hiding behavior presumably indicates higher TiO2 levels in premium paint and lower TiO2 level in economy paint compared to the benchmarks. Within typical formulations tested, EcoVAE 402 showed slightly higher wet hiding power than competitive emulsions.

Figure 5: Comparison of wet hiding power (ABNT Standard #14943), of various emulsion chemistries against Brazil commercial paint benchmarks. 3.5 Dry Hiding Power: In general, the dry hiding power mimicked the behavior of wet hiding, indicating differences in the TiO2 levels between the typical formulation and the commercial paint benchmarks across the various quality levels. Within the formulations tested at the same TiO2 level, EcoVAE® 402 based paints met the minimum requirements in dry hiding power across all three PVC levels, whereas competitive emulsions had trouble meeting the minimum requirement of ‘4’ in Economy paints.

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Figure 6: Comparison of dry hiding power (ABNT Standard #14942), of various emulsion chemistries against Brazil commercial paint benchmarks. 3.6 Tint Strength: Tint strength was calculated from the tristimulus values after tinting with pthalo blue 888 pigment. The tint strength of the paints was compared against the tint strength of control paint 1 at each quality level, which was used as the tint strength standard. In general, the higher TiO2 level in premium and standard quality paints contributed to higher tint strength compared to commercial controls, while the lower TiO2 level in economy paint showed the opposite behavior. Within the formulations tested, EcoVAE® 401 and 402 consistently gave higher tint strength compared to competitive emulsions indicating better TiO2 interaction and higher scattering efficiency. It is quite possible to realize significant cost savings from lower TiO2 usage in these paints by switching to VAE emulsions without significantly altering other performance parameters. In addition to higher tint strength, VAE emulsions in general show better color rub-up resistance compared to styrene acrylics and VA-VEOVA-acrylics in all quality levels. The lower DE values for the VAE emulsions are indicative of good dispersion of TiO2 and the tint without flocculation.

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Figure 7: Comparison of tint strength of various emulsion chemistries against Brazil commercial paint benchmarks. Pthalo Blue 888 series tint was used. 3.7 Color Float: After 48 hours, severe color float was observed in the commercial premium quality paint benchmarks and VA-VEOVA™-acrylics and no color float was observed in premium and standard quality paints made with styrene acrylics and VAE. As the level of binder decreased, all of the emulsion chemistries began to show color float issues. See Figure 9 and data in Table 4. Table 4: Comparison of color float, after 48 hours, of tinted paints with various emulsion chemistries against Brazil commercial paint benchmarks

Paint quality

Control 1 Control 2 EcoVAE

401 EcoVAE

402 Styrene Acrylic

VAM-VEOVA-Acrylic

Premium Severe Severe None None None Severe

Standard None None None None None Severe

Economy Moderate Slight Moderate Moderate Moderate Moderate

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Figure 8: Comparison of color rub-up resistance, DE, of various emulsion chemistries against Brazil commercial paint benchmarks.

Figure 9: Photo of a tinted premium quality paint showing severe color float with VA-VEOVA-Acrylic and no color float with styrene-acrylic and VAE after 48 hours. 3.8 Odor: A blind odor test of the paints at the various quality levels was conducted with the various emulsion chemistries. Careful attention was paid to insure the headspace in all the glass containers with paints were similar. The results from the blind odor test (Table 5) indicated that the commercial and styrene acrylic based premium and standard quality paints showed unpleasant odor while the VAE and VA-VEOVA™-acrylic based paints showed very mild to no odor. VOC contents of two neat emulsions, a Celanese VAE and a commercial styrene-acrylic, were analysed using the headspace gas chromatograph technique to understand the level of emissions and the source of odor. Figure 10 shows that VAE has generated only relatively low levels of organic volatiles as emission, while the styrene-acrylic generated a much higher amount of emission, which include residual monomers such as free styrene which in turn contribute to the much higher level of odor.

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Table 5A: Results of a blind odor test comparing various emulsion chemistries against Brazil commercial paint benchmarks

Paint quality

Control 1 Control 2 EcoVAE

401 EcoVAE

402 Styrene Acrylic

VAM-VEOVA-Acrylic

Premium Unpleasant Unpleasant Very Mild Very Mild Unpleasant None

Standard Strong Strong Very Mild Very Mild Moderate Moderate

Economy Moderate Mild None None None None

Figure 10: Headspace GC/MS - VAE vs. Styrene Acrylic. Please note that (1) the peak at 8.25min is the GC internal standard methyl isobutyrate which was added intentionally to both emulsions prior to the measurement; (2) the peak at 1.2min is the solvent we used to extract VOC from emulsions.

3.9 QUV and Exterior Exposures: Premium quality paints with various emulsion chemistries along with the corresponding commercial paint benchmarks were tinted with pthalo blue 888 series tint and exposed in the QUV as per ASTM G154 cycle 1

for 500 hours. Figure 11 compared the E of the exposure panels after 500 hours.

The E of VAE emulsions was comparable to one of the controls and were slightly higher than both the styrene acrylics and VA-VEOVA™-acrylics. Six month Florida exposure data (South 45°) of the premium paints and commercial paint controls on

primer wood is shown in Table 6. The paint boards were rated by Marshall Labs, an independent testing lab, from 1-10 with 1 being worse and 10 being the best. It is clear from Table 6, that the UV durability of VAE emulsions based paints were comparable to other emulsion chemistries and even slightly better with respect to color fading after six months.

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Figure 11: Comparison of E values after 500 hrs of QUV exposures, of tinted premium paints made with various emulsion chemistries against Brazil commercial paint benchmarks. Table 6: Six month South 45° Florida exposure data of premium paints

Rating Criteria

Brazil Commercial

Premium Paint-1

Brazil Commercial

Premium Paint-2

VAE Styrene Acrylic-

1

Styrene Acrylic-

2

VAM-VEOVA-Acrylic

General Appearance

7.5 7.5 6 5.5 6.5 7.5

Severe Wrinkling

No No No No No No

Dirt Pickup Minimal difference among panels

Cracking 10 7.5 6 5.5 5.5 8.5

Mildew Minimal difference among panels

ΔE* 19.13 11.4 11.88 12.61 13.27 11.01

4.0 SUMMARY VAE emulsions appear to show significant performance advantages compared to conventional styrene-acrylics and VA-VEOVA™-acrylics in premium and standard Brazil paint formulations. Their superior value proposition includes, lower thickener demand, higher tint strength and better rub-up resistance, good wet abrasion resistance by ABNT method, and low odor. Additionally, VAE emulsions showed

somewhat comparable E to commercial benchmarks and other emulsion chemistries after 500 hrs in QUV and similar durability to other conventional styrene acrylic emulsions after six months of Florida exposures. The performance advantage of VAE compared to conventional styrene-acrylic emulsions moderated as the paint quality level went down, primarily due to the reduced amount of binder usage in the lower quality paints. EcoVAE® 401 and 402 showed consistently higher wet abrasion resistance by ABNT method compared to Styrene-acrylics and VA-VEOVA™-acrylic and were comparable to Brazil commercial paint benchmarks. 5.0 CONCLUSIONS Our benchmarking studies have shown that emission-free, low odor paints based on VAE emulsions achieve the same high performance as conventional paints based on hard emulsions (i.e. hard Styrene/Acrylics) and coalescing agents in terms of scrub resistance (i.e. scrubbability) while improving the quality of indoor air for the end-user. In addition, testing results show that significant cost saving can be achieved with these VAE emulsions as they demonstrate lower thickener demand and

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excellent colorant compatibility along with higher brightness and tint strength compared to styrene acrylics and Vinyl acetate-Vinyl versatate-acrylic terpolymers. These attributes give the paint formulator sufficient latitude to lower the overall cost of paint without losing the performance characteristics.

6.0 ACKNOWLEDGMENTS: The authors would like to acknowledge the diligent and timely work done by Dempsey Schleuter, Ryan Brashear, and Irena Bernat for this project. 7.0 REFERENCES 1. TOP 12 MEGATRENDS TOWARD 2020, Edited Form developed by Klaus E.

Mogensen and Troels Theill Erikesen, From Copenhagen Institute for Futures Studies, Additional Editing by – Joel Johnson

2. Frost and Sulliven, Top 20 global megatrends and their impact on business,

cultures, and society. 3. EPA's Integrated Risk Information System (IRIS) (a compilation of electronic

reports on specific substances found in the environment and their potential to cause human health effects)

4. What are the Health Concerns of Volatile Organic Compounds, Thurston County

Public Health and Social Services, Washington, USA, 1 May 2013.

5. According to a study by TNS, Global Shades of Green (May 2008), 82% of respondents in Latin America agreed that they are more concerned with the environment than 5 years ago. In addition, 79% say they are willing to pay more for eco-friendly products.

6. EPA's Office of Research and Development's "Total Exposure Assessment

Methodology (TEAM) Study" (Volumes I through IV, completed in 1985), Indoor Air Quality

vinyl acetate/ethylene emulsions: designing for...

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