OK
The material selection platform
Coatings Ingredients
The material selection platform
Coatings Ingredients
Article

Overcoming Formulation Challenges for Low-VOC Interior Paints with New Binder Solutions

Edward M. Petrie – Oct 5, 2021

TAGS:  Architectural Coatings      Acrylic Coatings       Sustainability / Natural Coatings    

Overcoming Formulation Challenges for Low-VOC Interior Paints with New Binder SolutionsGrowing concern over indoor air quality is motivating coating manufacturers to reduce or eliminate volatile organic components (VOCs) and other harmful ingredients from their formulations. VOCs are organic chemicals that have a high vapor pressure at ordinary room temperature conditions. Many VOCs are irritants that produce odor and can introduce toxic exposure concerns.

The definition of VOC from a regulatory standpoint depends somewhat on the region and application.

  • In the US, VOCs are legally defined in the various laws and codes under which they are regulated, and different regulations exist in each state.
  • In the EU, VOC is any organic compound having an initial boiling point less than or equal to 250°C and that can damage human senses.

VOCs have been necessary components in many types of coating systems primarily to adjust viscosity, provide good coating properties, and achieve the end-use performance requirements demanded from architects and builders. VOCs are generally produced from the coalescing agents and additives used in waterborne paint systems.

Regulations limiting VOCs and other harmful additives, such as formaldehyde, are getting stricter. These are primarily enforced through:

  • The Environmental Protection Agency (EPA) in the US, and
  • The Registration, Evaluation, and Authorization of Chemicals (REACH) in the EU

These regulations are designed to limit the use of organic chemical compounds that are harmful to human health and contribute significantly to carbon emission and atmospheric ozone depletion.

VOCs can be measured either by analyzing the components that are contained in the formulation (“in-can” VOC content) or by emissions that are released into a simulated indoor environment over time. It is important to note that a “low VOC” coating as determined by an in-can analysis and labeling may still produce harmful emissions during and after coating.

Indoor emission limits were originally promoted by paint consumers such as educational institutions and healthcare organizations. One can expect this market trend to pick up steam throughout the entire interior paint market. As a result, an increasing number of paint manufacturers are reformulating their products to bring their indoor emissions down below mandated levels.

Let's address the importance and measurement of interior VOCs and then introduce several new binder resins that have extremely low levels of VOC. When used in the indoor paint formulations, these binders improve indoor air quality without compromising performance properties. In addition to extremely low levels of VOCs, these binders have low odor and are free of plasticizers, alkylphenol ethoxylate (APEO), formaldehyde, and ammonia producing materials.


Indoor Air Quality (IAQ) has Become an Important Obligation


VOC Emissions – Common Sources, Examples & Formula


Interior wall paints are recognized as a significant source of VOCs in spaces where we occupy 85-90% of our time (e.g., schools, workplaces, leisure areas, etc.). They are the origin of what has been called the “sick building syndrome” since VOCs can be related to allergies, asthma, carcinogens, and other health issues. New buildings and freshly renovated areas especially contribute to the highest level of VOC emissions because of the abundant concentration of VOCs generated at the same time.

Common examples of VOCs that can be present are propylene and ethylene glycol, alcohols, aldehydes, butyl propionate, and butoxyethanol among others. In waterborne coatings, the primary source of these VOCs is coalescing agents and additives such as anti-freeze agents, biocides, and amine neutralizers.

The most widely used approach in determining VOC content in paints and for labeling is to calculate pounds (or grams) of VOC per gallon (or liter) of solution minus exempt solvents (including water and VOC-exempt organic compounds).

VOC = pounds of solvent – exempt solvent
           gallon of coating – exempt solvent

However, note that:
  1. No attempt is made to compare the relative ozone-generation potential of one VOC with another, and
  2. This calculation does not express the amount, rate, or type of indoor emissions during and after paint application.
Thus, “low-VOCs” or “no-VOCs” per the manufacturer’s label is no guarantee of low or safe indoor emissions.1


Regulations, public pressure, and general apprehension regarding the environment have led manufacturers to reduce VOC content from 150-350 g/L to as low as 50 g/L. Concerns with interior air quality have also led to new regulations mandating reduced emission levels.

Interior wall paints are recognized as a significant source of VOCs in spaces (e.g., schools, workplaces, leisure areas, etc.)


Different Approaches Followed by Countries in Characterizing VOC emissions


To determine indoor paint emissions, volatile components are investigated in emission test chambers under controlled applications and climatic conditions. Europe and the US follow different approaches in characterizing emissions although there are some commonalities (See table below).2 However, ISO 16000-6 attempts to harmonize emission test methods.

Commonalities Differences
Test chamber climate: 23°C and 50% RH
Components studied: VOCs and volatile aldehydes
Paint substrate: Gypsum or other porous substrates (US). Inert surfaces such as glass or metal (Europe)
Time after coating: 14 days (US). 3 and 28 days (Europe)
Chamber ventilation rate: One air change per hour. One-half air change per hour (Europe)
Reference scenario: Multiple situation scenarios (US). One single scenario (Europe)
Targeted VOCs: 35 individual VOCs taken from California list of chronic respiratory exposure test limit values (US). Up to ~200 VOCs depending on region (Europe)

Differences in European (DIN EN16516) and US (ASTM D5116 and ASTM D6670, LEED, etc.) Indoor Paint Emission Testing


Indoor emission test results of a specific VOC per ISO 16000-6 can be compared to various set reference limits.

  • In Europe, emission concentration limits have been established by French, Italian, and German legislation.
  • In the US, the most widely used comparison standard is the Office of Environmental Health Hazard Assessment (OEHHA) reference levels (RELS).

Certification criteria (e.g., Greenguard, LEED) have also been developed by independent organizations, and they may even be stricter than legislation requirements. Examples of such indoor emission limits are shown in the table below.

Classes
FRENCH legislation
(after 28 days)
(µg/m3)
CAM Italian legislation
(after 28 days)
(µg/m3)

GREENGUARD Gold
(after 96 days)
(µg/m3)

Formaldehyde  <10  <60  <9
Acetaldehyde  <200  <300 <70 
Toluene  <300  <450  <150 
Tetrachloroethylene  <250  <350 <17.5 
Xylene  <200   <300 <350 
1,2,4-Trimethylbenzene  <1000  <1500  Not applicable 
1,4-Dichlorobenzene  <60   <90 <400
Ethylbenzene <750  <1000  <1000 
n-Butylacetate <4800 / Not applicable 
2-Butoxyethanol <1000  <1500 Not applicable 
Styrene <250 <1500  <450 
TVOC [from n-C6 to n-C16] <1000  <1500 <220

Indoor Emissions Safe Thresholds – Examples by Country


Formulation Challenges & Performance Issues


Low-VOC paint compositions can have performance issues that challenge formulators in several respects. One of the more promising routes to producing low- or no-VOC paint is to limit volatile coalescing agents and plasticizers by using softer polymer binder compositions. Coalescing agents function by softening the polymer particles in a latex, enabling the formation of a continuous film as the coating cures. Additional functions of a coalescing agent are to improve open time, prevent skinning, and change the rheology of the formulation.

Traditionally acrylic polymers for interior coatings have a relatively high glass transition temperature (Tg) to provide the required performance properties. Elimination of the coalescing agent requires a binder with a lower Tg and minimum film-forming temperature (MFFT) below about 4°C. However, such softer polymers can result in formulations with reduced performance characteristics such as:

  • Higher odor
  • Poor stain resistance
  • Poor dirt pick-up resistance and cleanability
  • Low wet scrub resistance
  • Poor color development and fastness
  • Poor adhesion to old paint
  • Lack of sufficient hiding power

These poor performance factors can result in reduced service life which necessitates repainting and another cycle of indoor emissions.

New proprietary resin binder technologies relieve many of these performance problems. The optimal use of materials and processes produces resins with reduced Tg and MFFT. As a result of these efforts, low-VOC interior paints can be manufactured without coalescent and yet have properties that are equivalent or superior to high-VOC paints.

A secondary approach to formulating low-VOC paint is to consider the contributions of conventional paint additives which include – anti-freeze agents, mildewcides, rheology modifiers, defoamers, and surfactants. In conventional VOC coatings, these contributions are not significant, but in low-VOC formulations, they can be the largest source of VOCs. Newly developed additives allow further reduction in VOC.

Watch Webinar: How to Lower VOC in Interior Paints without Compromising Performance


New Low-VOC Binders from Vinavil


Vinavil has recently developed three unique polymers (Crilat 4750, Crilat 4816, and Vinavil 04V) that have less VOC content, reduced emission levels, and performance levels at least equivalent to higher VOC paints. Properties of these resin binders are shown in the table below.

Property ↓ / Product Name → Crilat 4750 Vinavil 04V Crilat 4816
Polymer Type Styene acrylic Vinyl Veova copolymer Pure acrylic
VOC Content, % <0.15% <0.1 <0.1
Formaldehyde, ppm <10 <10 <10
Tg, °C 10 20 8
MFFT, °C 5 5 0
Solids Content, % 50±1 52±1 50±1
Viscosity*, mPas 2000±1000 2500±1000 <1000
pH 8.0±0.5 4.5±0.5 8.0±0.5
*Measured at 23°C with RVT, 20 rpm, spindle 2

Property Comparison of Vinavil Low-VOC Resin Binders


With such low VOC levels, the odor of paints made with these resin dispersions is extremely low. The Vinavil products also have the following ideal characteristics for environmentally friendly interior paints:

  • Low MFFT of 0-5 °C
  • VOC content less than 0.15%
  • Low residual monomer
  • No formaldehyde producing components
  • Free of hazardous and toxic substances (CMR, sensitizers)
  • No environmental hazardous substances (e.g., APEO)
  • Low odor
  • Excellent compatibility with pigments, fillers, and other additives

These resin binders offer excellent versatility in formulating many kinds of waterborne coatings at low, medium, and high pigment volume content (PVC) levels for use in indoor applications. These paint systems have stain resistance, low dirt pick-up, and wet-scrub resistance. This results in improved durability allowing greater intervals between repainting and subsequent reintroduction of indoor emissions.


Starting Formulation Developments for Indoor Paints


Several starting formulations for indoor paints have been suggested for the new Vinavil dispersions. These all have safe and low-VOC additives. Performance properties, as described in the next section, are comparable to premium interior paints with higher VOC content and indoor emission levels.

The formulation shown in the table below is for a low-VOC interior paint with a relatively high 80% pigment volume content (PVC) typically used in flat paint. As PVC increases, density and hiding power increase, but performance properties such as durability (e.g., scrub, stain, and dirt pick-up resistance) typically decrease. The Crilat 4750 formulation, however, shows no reduction in these important performance properties. High PVC paints are often less expensive than lower PVC paints when quality is equal.

Component % % Functions Suppliers
Water 24.55 25.30    
Defoamer 0.20 0.20   Various
Natrosol PLUS 330 PA 0.60 0.60 Cellulose Ashland
NaOH (sol. 10%) 0.10 0.10 pH regulator Various
Sodium hexametaphosphate (sol. 10%) 1.70 1.70 Dispersing agent Various
Nuosperse FN265 0.20  0.20 Wetting agent Elementis
Ecodis P90 0.20  0.20  Dispersing agent Coatex
Acticide B20 0.20 0.20 Biocide Thor
TiO2 type RXL 8.00 8.00 Pigment Huntsman
Kaolin Polestar 200P 4.00  4.00 Filler Imerys
CaCO3 5M type Omyacarb 5AV 44.50 44.50 Filler Omya
TYPICAL STYRENE ACRYLIC BINDER 10.00   Binder n.a.
Crilat 4750   10.00 Binder Vinavil
Texanol / Optifilm 400 0.25   Coalescing Agent Eastman
Propylene Glycol 0.50   Co-solvent Various
Water 5.00 5.00    
TOTAL 100.00 100.00    

Starting Formulation: Interior Paint at 80% PVC with Crilat 4750 Compared to a Typical Styrene Acrylic Binder

The table below describes low-VOC starting formulations with Vinavil 04V or Crilat 4816 having a PVC of 37%. This is a typical PVC level for satin and egg-shell finishes. In high traffic areas, such as hallways, low PVC paint may be preferred for better durability.

Components w. % Function Suppliers
Water 12.8  
Tego Antifoam2-89 0.2 Defoamer Evonik
Natrosol Plus 330 PA 0.2 Cellulose Ashland
Sodium hydroxide (10% sol.) 0.2 pH regulator Various
Sodium hexametaphosphate (10% sol.) 2.5 Dispersant  Various
Ecodis P90
0.6 Dispersant Arkema
Metolat 388 0.3 Wetting agent Munzing
Acticide B20 0.2 Biocide Thor
Vinavil 04V or Crilat 4816 6.0 Binder Vinavil
Titanium dioxide type RXL 24.0 Pigment Huntsman
Calcium carbonate 5m type Omyacarb 5 AV 16.0 Filler Omya
Vinavil 04V or Crilat 4816
35.0 Binder Vinavil
Tafigel PUR 80 0.2 PU-thickener Munzing
Sodium hydroxide (10% sol.) 0.2 pH regulator Various
Tego Antifoam 2-89 0.2 Defoamer Evonik
Total 100.0    

Starting Formulation: Interior Paint at 37% PVC with Vinavil 04V or Crilat 4816


Comparisons with Conventional Coatings


Characteristics of Crilat 4750 vs Styrene Acrylic Copolymers


Crilat 4750 is a styrene acrylic copolymer waterborne dispersion. It is free of APEO, coalescent, plasticizers, formaldehyde, and ammonia. Styrene acrylic copolymers are used as binders for medium and high PVC paints due to their outstanding pigment binding properties.

Crilat 4750 dispersion has lower in-can VOC content and emission levels when compared to conventional styrene acrylic binders. The low indoor emission levels meet Classification A+ according to the Grenelle de l'environnement French legislation (See table below). In comparison to conventional styrene-acrylic copolymers, Crilat 4750 has good flexibility. It is suitable for interior and exterior waterborne paint formulations.

  Units Crilat 4750 Typical Styrene Acrylic Binder
In-can VOC  g/l 1 3.5
Emission VOC after 24h µg/m3 520 21200
Emission VOC after 48h µg/m3
170 9190

Crilat 4750 Emission VOC Compared to a Typical Styrene Acrylic Binder

In addition to its exceptional environmental profile, the main features of Crilat 4750 paint formulations are:

  • Water resistance and wet scrub resistance even in high PVC paints
  • High binding power with fillers and pigments, even at high PVC paints
  • Good stain resistance
  • Excellent alkali resistance that allows the formulation of both exterior paint and textured coating
  • Low dirt pick-up and good cleanability
  • Odorless

The properties of Crilat 4750 satin paint with 37% PVC are provided in the table below. Its versatility and excellent compatibility with cement and mineral binders make it a good solution for medium to high VOC interior paints and wall texture coatings.

Analysis Method Unit 35% PVC Satin Paint Crilat 4750 Market Reference Paint
Brookfield viscosity, 23°C (20 rpm) UNI 8490/3  mPas 7000 26000
pH UNI 8490/4 1-14 9.21 8.27
Web scrub resistance UNI 10560 N° cycles >5000 >5000
Web scrub resistance (200 cycles) ISO 11998 µm 2.5 n.d.
Dirt pick-up UNI 10792 ΔL 0.12 0.17
Cleanability (Carbon black) UNI 11021 ΔE
2.34 4.28
Gloss (85°) MV AT 034bis - 13 6
VOC ISO 11890 g/l 1 40

Performance Characteristics of Crilat 4750 in Satin Paints


Characteristics & Emission Results of Vinavil 04V vs Vinyl Acetate Copolymers


Vinavil 04V is a new generation waterborne dispersion of vinyl acetate – Veova copolymer. The copolymer has a unique, highly branched aliphatic structure which contributes to key polymer performance properties. It shows a lower VOC content than conventional vinyl acetate copolymers, and it is free of APEO, coalescent, plasticizers, and formaldehyde.

Waterborne formulations manufactured with Vinavil 04V dispersion have an in-can VOC content of less than 0.1% and emission levels significantly below strictly set environmental limits. The table below shows the results of chamber tests according to ISO 16000-6. As a result, Vinavil 04V can be classified Class A+ according to the Grenelle de l'environnement French legislation, and it also passes the Italian minimum environmental criteria (CAM).

Classes
Results after 10 days
(µg/m3)
FRENCH legislation
(limit at 28 days)
(µg/m3)

CAM
Italian legislation

(µg/m3)

Formaldehyde  <5 <10 <60
Acetaldehyde  <5  <200 <300 
Toluene  <5  <300  <450 
Tetrachloroethylene  <5  <250 <350 
Xylene  <5   <200 <300 
1,2,4-Trimethylbenzene  <5 <1000  <1500
1,4-Dichlorobenzene  <5   <60 <90
Ethylbenzene <5  <750 <1000 
n-Butylacetate <5 <4800 /
2-Butoxyethanol <5 <1000 <1500
Styrene <5 <250  <1500
TVOC [from n-C6 to n-C16] 193  <1000 <1500

ISO 16000-6 Emission Results for Vinavil 04V 37% PVC Interior Paint Compared to Local Environmental Limits


In addition to being low-odor and low-VOC, Vinavil 04V paint is characterized by a combination of features that rival interior paint systems with high VOC levels:

  • Good color development and hiding power
  • Good wet / dry scrub resistance and adhesion
  • Low odor
  • Good rheological behavior
  • Low water resistance
  • Good stain and alkali resistance
  • Very good compatibility with fillers, pigments, and other additives

The excellent performance properties of Vinavil 04V 37% PVC interior paint are shown in the table below. Vinavil 04V offers great versatility in the preparation of any kind of water-based paints with medium and high PVC.

Property Values
Brookfield RVT viscosity - 20 rpm (mPas) 7.250
pH 7.41
Density (g/ml) 1.40
Gloss at 60°/85° - 24 hours 2.7 / 7.3
Gloss at 60°/85° - 7 days
2.6 / 7.3
Matt
Persoz hardness - 24 hours / 7 days 87 / 87
Contrast ratio (hiding powder) UNI EN ISO 6504-3 (%) 98.41 Class 2 (*)
Wet scrub resistance DIN 53778 (N° cycles) >5000
Wet scrub resistance ASTM D2486 (N° cycles) 1200
Wet scrub resistance ISO 11998 (at 200 cycles) (µm) 3.1 class 1 (*)
(*) Classification according to UNI EN 13300

Performance Characteristics of Vinavil 04V 37% PVC Paint


Characteristics & Emission Results of Crilat 4816


Crilat 4816 is a pure acrylic water dispersion, free from coalescing agents, plasticizers, and APEO. It has a low in-can VOC level of less than 0.1% and emission levels significantly below strictly set environmental limits. The table below shows the results of chamber tests according to ISO 16000-6. As a result, Crilat 4816 can be classified Class A+ according to the Grenelle de l'environnement French legislation, and it also passes the Italian minimum environmental criteria (CAM).

Classes
Results after 10 days
(µg/m3)
FRENCH legislation
(limit at 28 days)
(µg/m3)

CAM
Italian legislation

(µg/m3)

Formaldehyde  <5 <10 <60
Acetaldehyde  <5  <200 <300 
Toluene  <5  <300  <450 
Tetrachloroethylene  <5  <250 <350 
Xylene  <5   <200 <300 
1,2,4-Trimethylbenzene  <5 <1000  <1500
1,4-Dichlorobenzene  <5   <60 <90
Ethylbenzene <5  <750 <1000 
n-Butylacetate <5 <4800 /
2-Butoxyethanol <5 <1000 <1500
Styrene <5 <250  <1500
TVOC [from n-C6 to n-C16] 275 <1000 <1500

ISO 16000-6 Emission Results for Crilat 4816 37% PVC Interior Paint Compared to Local Environmental Limits


In addition to being environmentally friendly, Crilat 4816 paints are characterized by a combination of features that rival interior paint systems with high VOC levels:

  • Good color development and hiding power
  • Good wet scrub resistance
  • Low odor
  • Low dirt pick-up
  • Low sensitivity to water and weathering
  • Good stain resistance
  • Very good compatibility with fillers, pigments, and other additives

The excellent performance properties of Crilat 4816 37% PVC interior paint are shown in the table below. Paints formulated with Crilat 4816 are also noted for their excellent weathering resistance and durability. They can be used in interior and exterior applications.

Property Values
Brookfield RVT viscosity - 20 rpm (mPas) 6.200
pH 8.24
Density (g/ml) 1.40
Gloss at 60°/85° - 24 hours 2.7 / 4.7
Gloss at 60°/85° - 7 days
2.7 / 4.5
very matt
Persoz hardness - 24 hours / 7 days 47 / 50
Wet scrub resistance DIN 53778 (N° cycles) >5000
Wet scrub resistance ASTM D2486 (N° cycles) 1600
Wet scrub resistance ISO 11998 (at 200 cycles) (µm) 3.7 class 1 (*)
(*) Classification according to UNI EN 13300

Performance Characteristics of Crilat 4816 37% PVC Paint


Conclusion


Architects and builders view indoor air quality as one of the most important attributes when considering interior paint. Indoor air quality is assessed by international certifications, regulatory standards, and third-party agencies. Paint manufacturers are responding to this challenge by formulating products that have low VOC content and provide safe, low levels of emissions when tested according to ISO 16000-6.

The major source of indoor emissions are coalescents or co-solvents and certain formulation additives. To eliminate these environmentally harmful elements, one must use binder resins with a low Tg and MFFT. This can be done with softer resins so that they self-coalesce. However, these softer resins can adversely affect drying times, dirt pickup, scrub ability, and other durability and appearance factors.

Vinavil has developed three unique binder resins (Crilat 4750, Crilat 4816, and Vinavil 04V) that provide ultra-low levels of VOCs and indoor air emissions without compromising the performance of the paint. These resins have the requisite low Tg and MFFT to reduce VOC content to less than 0.15% and still provide excellent film formation without the need for coalescing agents or plasticizers. These resins also have low odor, no APEO, no formaldehyde producing elements, and both Crilat 4750 and Vinavil 04V are free of ammonia.

A series of starting formulations have been provided for formulators to take advantage of these eco-friendly resins and to provide indoor emission levels that are within the limits mandated by legislation. In addition to being environmentally responsible, these paint systems also provide fast drying times, low dirt pick-up, stain resistance, and good wet scrubability. Their performance and durability are comparable to or surpass conventional indoor paint systems having high VOC content and emission levels.

SEE ALL VINAVIL PRODUCTS HERE:


View the full range of resin grades from Vinavil, analyze technical data of each product, get technical assistance or request samples.



References

  1. Schiewreck, A. and Bock, M-C., “Emissions for Low-VOC and Zero-VOC Paints – Valuable Alternatives to Conventional Formulations Also for Use in Sensitive Environments?”, Building and Environment, Vol. 85, 2015, pp. 243-252.
  2. Oppi, R., “Clearing the Air Indoors”, European Coatings Journal, April 2013, pp. 114-117.
  3. Geurts, J., et. al., “New Waterborne Acrylic Binders for Zero VOC Paints”, J. Coating Technology Research, Vol. 8, No. 1, 2008, pp. 57-63.

1 Comments on "Overcoming Formulation Challenges for Low-VOC Interior Paints with New Binder Solutions"
Alberto N Oct 12, 2021
Very useful and instructive.

Leave a comment





Your email address and name will not be published submitting a comment or rating implies your acceptance to SpecialChem Terms & Conditions
Back to Top