Photo taken at University of Maine during a research collaboration, courtesy of Surface Science Institute U Maine, 1997
Polymers, Monomers, and Acrylics
Acrylics undergo a dramatic transformation during drying; this is called polymerisation. Tiny acrylic globules, or monomers float individually in a watery emulsion and then link together as the water evaporates. This process can also be aided by the application of gentle heat – for instance by using a hairdryer during initial application.
Industry wants us to believe that acrylics are completely inert and similar to say watercolors drying, and at first glance the method seems very similar. Behind the scenes of an acrylic paint application, incredibly complex and energetic chemistry is at work, which is not entirely understood by science in all its facets and interactions.
- image: Acrylic Paint Review
What is Acrylic Paint ?
The action of ‘initiator compounds’ on the bulk monomer-globules sets off the multiplication and chain formation. What looks like the gentle formation of a paint film through evaporation of water is, on closer inspection, a very powerful chemical reaction that begins when the acrylic paint has left the can, and water evaporates, effectively cooling the near invisible, high-energy process. The actual reaction is heat-generating, or ‘exothermic’. (and off-gassing).
“The heat comes from the energy stored in the chemical bonds of the reactant molecules–which is greater than the energy stored in the chemical bonds of product molecules” (Scientific American). Any such reaction is likely to produce unwanted byproducts, ‘SVOCs’, contained in the mix or airborne and acrylic polymer paints and mediums are no exception to this rule, and in fact the reactivity of free monomeric radicals entering the working atmosphere, entering the body through skin contact, or by inhalation is of increasing medical interest. There evidence that active acrylic monomers can impair the ability for self-repair in human tissue, due to suspected interactions with DNA mechanisms.
image: Zhejiang University
Polymerisation is complete when the monomers for instance methyl methacrylates remain firmly linked in long chains, thus turning them into polymers chains, often thousands of molecules long. Once dry, a very tough, plastic-like substance has formed on the canvas surface or metal plate or other painting substrate that is both hardwearing, as well as perfectly mordant resistant, in etching. Industry already has a history of exploiting these properties; cars are painted with waterbased paints, and acrylic photo resists – are used for making printed circuit boards in the electronics industry.
Good polymerization typically yields monomer conversion into long, hard polymer chains of 70% to 95%, but any number of factors, temperature, humidity, undeclared chemical additions, or separation of ingredients, can produce incomplete reactions and unwanted – often toxic – byproducts that may affect users health. It is known that the suspension/emulsion polymerization techniques employed in water-based paints is intrinsically less efficient than the ‘bulk polymerization’ found in high-end manufacturing or dentistry, so by-products and how to avoid them, should always be of concern.
Acrylics and other Polymers, and Safety
Acrid smelling nerve gas...
Green paints, resins and plastics. In the 90s water-based paint products were generally hailed as being THE safe alternative to the then dominant VOC and oil-based systems. Some of the claims of improved safety may hold true, but the idea of ‘intrinsic’ safety of water based products and polymers is quite exaggerated, and may even be misleading.
Some manufacturers make acrylic paint and printmaking products with fairly ‘pure’, often more expensive ingredients, (lab grade), full MSDS documentation and certified lab testing, and have a better safety record – such products can be deemed a little closer to ‘more controlled’ and ‘less toxic’. But the large majority of water-based products may carry significant toxicity. Especially cheaper products may contain powerful toxins such as glycol ether, plastic softeners (phthalates), formaldehyde, styrene, unreacted or concentrated volatile monomers, or trace amounts of benzene, a recognized carcinogen.
Surprisingly to the artist and consumer, some of the recent safety scares in paints and printing materials are connected to products that were actually marketed as being ‘safe’ and even ‘green’. Users are advised to familiarize themselves with safety facts and recommendations beyond manufacturer’s claims and advertisements; even MSDS information may be misleading, incomplete, or incorrect. Polymer chemistry is highly complex, and chemical firms are known to hide some key facts behind brand names, scientific language and impenetrable patents.
Invariably, marketing plays on the ‘water-based’ (equals safe?) nature of formulations, while any monomer emulsion is bound to contain solvent additions that are referred to as co-polymers, inhibitors, and catalysts. Most of these are quite toxic, especially to the regular and long term user. Also, most acrylics admixtures contain such small amounts of actual de-ionized water that calling them ‘water-based’ would seem inaccurate; it just sounds better and assures artists and users. ‘Hydrophilic’ might be a better description for these complex mixes of semi-liquid plastic globules, solvents, and co-polymer solvents, as it indicates that the paint or medium can readily be diluted further for layers and wash work through the addition of water.
… read on for more detail on the mixed and compelling history of acrylics, and their underlying chemistry.
impression of an industrial resin reactor (Smedunia, In)
Acrolein, Green Marketing, and Resin Reactors
Acrylics owe their name to the discovery of ‘acrylic acid’ around 1840. Chemists were aghast at the ‘acrid’ stench emanating from a new fluid they had made, realized it was highly toxic, and decided there weren’t any practical applications for it. Over 60 years went past until, in 1901, an ambitious German chemist, Otto RhÃ¶m, did doctoral research in TÃ¼bingen, and saw the potential of acrylic acid and its derivatives to be polymerized and made into useful compounds, such as hard plastics.
During the first world war, ‘Acrolein’, a compound found in burnt fat near identical to acrylic acid was employed as a weapon of war (nerve gas). During the 1920s and 30s the German chemist RhÃ¶m set up in business, (embedded in Nazi Germany, but also operating in New York), secured dozens of patents for plastics, and helped create what would become one of the largest multi-national chemical operations in the world.
Acrolein, acrylic acid, is also prevalent in cigarette smoke, and remains the essential base ingredient in industrial production processes for acrylics and plastics. Here, acrylic acid is ‘reacted’ in multiple iterations into more complex compounds, and then into the acrylates/monomers that are found in most acrylic paint products; these easily form polymers and long polymer chains during a paint application,
because inherent double bonds in the carbon structure are very reactive.
Setting up safe Reactions
In ‘good’ and more expensive acrylic products this reactivity may be controlled and made ‘relatively safe’, but cases are known when a strong ‘acrid and nauseating smell’ from an unidentified source, was present in acrylics, paints, varnishes, or polymer plates, possibly resulting in serious sickness in some users; this may well be attributable to the presence of residual ‘Acrolein’. If a variety of polymer paint, film, or plate product has this kind of strong and acrid smell, (this is quite rare), extra caution would be advised.
Through clever marketing, acrylics generally have a more positive perception in the general public, while medical science takes a different view, and recognizes significant toxicity (e.g. dental, respiratory, reproductive, dermatological; also: nail varnish/beauty). As opposed to traditional solvent based paints, the toxicity of acrylics seems to manifest itself more strongly through long-term and regular use, but not so much in casual or occasional use. (It is thought that the body has a degree of ability to metabolize/hydrolize some of the compounds present).
Some professional artists and house-painters become strongly sensitized, become quite ill, and need to move away from acrylic products.
Industrial ‘Acrylates’ manufacturing in resin reactors is highly skilled, technical, and complex, and is also one of the most difficult to control, reactive, and potentially accident-prone, chemical industrial manufacturing processes.
Internally, industry acknowledges inherent problems in producing acrylic monomers of high purity and low toxicity, and without doubt some toxic impurities are virtually always present in any finished acrylic paint, medium, or end product.
Industrial workers use ventilation and respiratory protection when handling the various monomeric solutions, and artists and consumers of acrylic admixtures are well advised to do the same.
The various fumes that may be emitted by drying acrylics are not fully understood, and scientists refer to these as ‘SVOCs’ (semi-volatile compounds). For safety, we’d recommend using good ventilation and some form of respiratory protection, especially when exposed to large areas of drying paint or varnish.
Some additional tips for safe use of acrylics:
• stir any acrylic paint, or medium before use; this aids the reaction
• avoid damp environments, to avoid build up of vapor
• work in a dry, warm, and well ventilated environment
• use mask with active carbon filter for intensive work
• only use de-ionized water for thinning;(lack of ions/solids aids polymerization,yields a better paint surface,and makes for a safer process)
• avoid skin contact and possibly wear gloves
from Acrylic Paint Products
SAFETY NOTE: in the USA a number of acrylics now carry a note
warning of a possible cancer hazard.
this may be related to any number factors,
such as formaldehyde content,
or other ingredients such as:
MMA Acrylic, Styrene Acrylic, and Vinyl Acrylic
Low-cost acrylic paint products may also contain styrene, vinyl chloride, or benzene compounds.
(an addition to the cancer risks of all of the above, vinyl chloride is known to cause liver damage, even from small exposures).
Other common, but frequently undeclared, chemicals found in acrylics include glycol ether, ammonia, hydroquinone (see below) or MEHQ, various low-level solvents and copolymers (NMP, NEP, etc.),
or the polymerization catalyst Triethylamine (TEA)
which is known to cause eye damage in long exposures.
Most artist acrylics,
–both as monomers and copolymers–
also contain butyl acrylate (with suspected strong kidney toxicity), and ethyl acrylate.
(Characterization of Artists’ Acrylic Emulsion Paints Oscar Chiantore , Dominique Scalarone & Tom Learner Pages 67-82 | Published online: 27 Oct 2010)
Due to the exothermic, instable, even explosive, nature of base monomers
virtually all acrylic paint products must contain substantial amounts of
quinone-based, single benzene-ring, molecules that are added in the factory as essential polymerization inhibitors of the paint.
It is probable that some of the volatile (often toxic) quinone molecules
evaporate during any acrylic painting session in an artist’s studio,
while others get incorporated in the solidifying carbon lattice.
The two most common polymerization initiators in monomer solutions
are benzoyl peroxide (BPO) and 2,2′-azo-bis-isobutyrylnitrile (AIBN).
Most of the compounds listed here have known adverse effects
on the human DNA system.
Strong Solvents / Strippers
Most acrylic paint formulations contain certain amounts of strong solvents
that are also found in paint stripping products. One example is
NMP or 1-methyl-2-pyrrolidone.
The EPA describes NMP as a developmental toxicant.
In 2017, EPA proposed to ban this chemical?s use in paint stripping.
Some more ‘bio-based’ paint products contain
ethyl lactate as a strong solvent, which in low concentrations
is considered relatively safe, while being very toxic at high
acrylic paint formulations are known to contain
triethylamine as a reaction catalyst:
in a lab, the substance requires respiratory protection to avoid lung or kidney damage.
Phthalates in Acrylic Paints
most acrylic paint formulations are likely to contain substantial amounts of phthalate esters, and especially with cheaper ‘vinyl-based acrylics’, (which heavily rely on these bulk additives/softeners), there could be a significant health risk.
Phthalates are one of the most researched and widely debated health risks related to plastics, and the industry is in the process of finder safer alternatives (for instance citrates) to these common, mass produced plasticizing and softening agents.
Different phthalates occur in forms that range from a more oil-like substance to other formulations that are more like a volatile solvent.
In any case, phthalates cannot become part of the long-chain
polymer molecules of cured acrylic paint, and
can easily migrate out of plastics, especially in the
presence of oils or proteins:
this can easily happen by skin contact during painting.
Suspected Effects: Phthalates are thought to interfere with
infant development through disruption of the hormonal systems,
especially in low dose-exposures, and general liver toxicity is also suspected.
While Europe is in the process of implementing regulations
to limit phthalate exposure from plastics, (along with new labeling requirements),
most consumers of plastics or paints in the US are left oblivious to the
presence of migrating phthalates, and there is currently no labeling requirement.
Phthalates are key volume ingredients in many paint
formulations, yet these are not only undeclared on labels
or in SDS sheets, but often also protected as patented ‘trade secrets’.
All acrylic emulsions contain a tailored anti-foaming
additive, without which the paint produces inferior results
(crackling / frothy paint).
These additives are in themselves complex, patented,
admixtures of various components.
Some of these are relatively
benign, while others are more toxic.
Some formulations are based on mineral oil or silicone,
while others contain ingredients such as
ethylene hydrogenated castor oil,
triisostearates, polyalkyl vinyl ether (may cause liver damage),
polybutadiene, polybutene or polyisoprene
Acrylics contain numerous other additives, such as fungicides, biocides,
preservatives, and surfactants (an essential aid for emulsification, typically
polyethoxylate (PEO) – based nonionic surfactant, as found in detergents).
Especially in cheaper formulations, preservatives
have been known to be harmful or poisonous substances, such
as quarternary ammonium compounds, phenol, or arsenic disulfide.
Most modern acrylics also contain paraffin,
which helps with water resistance and
gives ‘gloss’ properties to the final paint film, when dry.
Should acrylic paint products be
considered potentially carcinogenic?
In the 1990s much has been made of the fact that many
acrylates can be partially metabolised in the human body,
making them safer, or considerably safer, than solvent based paints;
and immediate health effects being rare.
But for more than a decade there has been increased speculation,
and now increasing evidence, that some, or even many, of the ingredients
of acrylic paint formulations should be considered carcinogenic.
Common base chemicals
used in acrylics, resin, and plastics manufacture, include:
- Vinyl Chloride, Polyvinyl chloride:
both should be considered carcinogenic
- Styrene, the staple ingredient in many plastics, styrofoam,
and many acrylics (styrene-acrylic):
has recently been upgraded from ‘possibly’ carcinogen to
– Formaldhyde, present in many acrylics, is a known carcinogen
– Benzene (may be present in trace amounts), is a known carcinogen
– Methyl Methacrylate, not previously thought of as carcinogenic,
has recently been show to be a potential ‘secondary? carcinogen,
during long term exposure (in rats).
in addition to these bulk ingredients, there are many
additional compounds that may also cause pose a cancer hazard,
or exarcebate hazards posed by other compounds.
From a 2023 perspective on carcinogenic solvents and monomer compounds, even stronger precautions are advised than had been previously thought. Recent large scale studies confirmed a number of staple ingedients in acrylics as ‘known carcinogens’, while these may have been in the ‘suspected’ category not long ago.
The small print on packaging of some acrylic paint products for artists,
(not just cadmiums), does contain notices such as ‘contains an ingredient known in State of California to cause cancer?,
although further and more detailed information
is often hard to come by.
(from: A pilot study to evaluate VOCs outgassed in polymer filaments, Shari Cheves, 2014)
Inherent Instability in Monomers and Polymers
“Plastic polymers are created from monomers almost exclusively derived from crude oil with far-reaching impacts on the health of humans and the environment. These highly reactive monomers form stable bonds in polymers through polymerization, though the chemical reactions are never quite complete. This inherent instability contributes to the release of residual monomers, plasticizers, ame retardants, solvents, and other additives as polymers degrade.
Based on the toxicity of monomers, research has defined the most hazardous polymer families as polyurethanes, polyacrylonitriles, polyvinyl chloride, epoxy resins, and styrenic copolymers. Monomers and other by-products are released through various modes of degradation such as heat. Nitrogen-containing plastics such as nylon and polyurethanes typically release hydrogen cyanide; chlorine-containing materials such as polyvinyl chloride typically release hydrogen chloride; and polystyrene, polyesters such as polycarbonate, nylons, and polyurethanes may be more likely to degrade into their original monomers.”
Always ensure airflow, (use fans and open windows), and wear lightweight organic vapor maskwith active carbon filter / acrylics also cure more fully – and safely – in a dry warm environment.
Acrylics, for instance when damp, may emit vapors of chemically reactive mist
— e.g. SVOCs / free monomer radicals — that may be damaging to health.(respiratory, dermatological, reproductive).
Artist paint manufacturers rarely refer to such exposures on paint tubes or in SDS sheets, but acknowledgement can sometimes be found in ‘how-to’
guides on acrylic painting.
Avoid working with styrene or vinyl chloride based products:
use ‘100% pure acrylic’ paints whenever possible,
as these are considered safer.
In poorly designed ‘polymers’ some of the base compounds
will still be present after curing, while ‘well performing’
polymers consume and use up most of the compounds present
in finely tuned successive (internal) chemical reactions,
resulting in a solid hard wearing substance (paint film) that is
then considered inert and ‘nontoxic’.
Protection against low level VOC exposure
Today there are many paint products that are marketed as –safe–, yet there may still be various harmful low-level VOC emissions, such as glycol ether. Examples: many water-based paints, acrylic floor finish, artist acrylics, low odor, low VOC solvents, and printmaking resists. Recent research showed that wet acrylics have vapors that can be detected by smell that concentrate up to 10-20cm above the paint. It is advisable to avoid getting close to wet acrylics. Harmful fume emissions are likely to be much higher in damp, cold and wet conditions.
Although a full organic respirator may be impractical for a day’s work we would recommend at the very least wearing a disposable light weight mask that offers some organic vapor protection. Dispose of the mask after a day’s work (about $ 5 per mask), coupled with use of fans for extraction.
3M– Particulate Respirator 8514, N95, with Nuisance Level Organic Vapor Relief
© saferpainting.com art+science
A new study from Germany outlined key harmful ingredients found in acrylic paint through chemical analysis. The substances found included formaldehyde, benzene derivatives, mineral spirits (Naphtha), styrene, vinyl chloride, glycol ether, acrylic acid, butyl acrylate, MMA, and ammonia. The study also highlights ways in which acrylic paint can make users sick, and strongly suggests a reduction of some of the most harmful ingredients.
NOTE: According to the now commonplace manufacturers’ ‘zero-VOC’ statements, most of the above chemicals should not be present at all in the acrylic paints we buy, or only in negligible quantities.
‘High grade’ acrylics were to an extent found to be safer, and less off-gassing than the cheapest consumer products with their lower grade ingredients. These have a tendency to polymerize incompletely, thus leaving harmful ingredients in the paint film
Here the link to the full study:
Characterization of Odorous and Potentially Harmful Substances in Artists’ Acrylic Paint
published Nov 2018
Patrick Bauer and Andrea Buettner,
Chair of Aroma and Smell Research, Department of Chemistry and Pharmacy, Emil Fischer Center, Friedrich-Alexander-Universitaet Erlangen-Nuernberg, Erlangen, Germany, and Department Sensory Analytics, Fraunhofer Institute for Process Engineering and Packaging IVV, Freising, Germany
Characterization of Odorous and Potentially Harmful Substances in Artists’ Acrylic Paint
(excerpt from the concluding section | P Bauer / A Buettner):
“In this study we identified the substances that are responsible for the odor of fresh acrylic paint for artists.
The turpentine-like, pungent or mushroom-like odor that was described by the panelists in the sensory evaluation could be traced back to a number of benzene derivatives, PAHs and acrylate monomers that either originate from paint thinners, from acrylic polymer dispersions or are added as a plasticizer.
In this context the grade of the used paint thinner is of high importance. The higher the purity of the paint thinner and the lower the content of benzene derivatives and PAHs, the lower are the odor emission and the likely associated health risk. This is especially valid to be considered in view of the fact that these substances are either known to cause hepatic or nervous damage or have been reported as potential carcinogens.
In addition, the choice of plasticizer was shown to be of importance for the odor of the analyzed samples. Whereas, paints with a high content of acrylate monomers, especially butyl acrylate, showed a noticeable mushroom-like and geranium leaf-like odor, the samples that were manufactured using different, odorless plasticizers were rated lower regarding these odor qualities.
To reduce the unpleasant odor in acrylic paint and to minimize the potential risk of negative physiological effects on humans, the reduction of benzene derivatives, PAHs and acrylic monomers is advisable.”