The "green" trend in paintings is a reality. We will raise a discussion about the challenges that this proposal must face in the future.
by M.Sc. Ph.D. Julián A. Restrepo R.*
The "Green" becomes fashionable: We can affirm that, today, the concepts of green, ecological and eco-design dominate the market, and this is because a large part of consumers have based their purchasing decisions on a label that contains the words green, environmental or sustainable [1].
And this is how every time, and with more force, products that call themselves "green" appear on the market: We see how, with various design strategies, manufacturers bet on the development of eco-friendly products. This implies that they are environmentally friendly and have been produced sustainably. This new trend, which is more than a fad, denotes the importance that environmental considerations have acquired in the field of manufacturing, trade and consumers [2].
This trend is due to the fact that for several years there has been a growing concern on the part of environmental organizations in various countries (mainly in those most technologically advantaged), to enact legislation for the regulation and control of the impact exerted by the different industrial processes and especially the products associated with the chemical industry [3].
The paints and coatings industry is no stranger to this problem, since solvent-based paints have been their main product for several decades, they caused (and still do) a significant imbalance in the environment. This type of coating is characterized by having a significant content of organic solvents (in many cases, between 500-750 gr/L) [3]. As a result, various legislations have emerged aimed at reducing emissions of this type of compound. Unfortunately, the situation of the Latin American paint market, even today, is characterized by a high presence of solvent-based products [4].
This document is a review of various publications on the subject, seeking to raise a discussion and reflection on the future challenges facing the industry for the development of paints and coatings that increasingly involve a lower impact on the environment.
Part of the discussion raised is traced around voCs Volatile Organic Compounds), considering the type of substances used by the paint industry that have caused the most environmental damage, due to their important role in air pollution.
The role of "Green Chemistry"
To tell the truth, it is clear that due attention has not been paid to environmental problems, due to the fact that ecosystems (and this is an important lesson of the science of Ecology), are tolerant to certain levels of stress [5]. This is possible because most of the materials that we consider as contaminants in high concentrations, have low levels in nature [3].
It is then due to an increased understanding of the role of different polluting substances in the environment that the concept of sustainability has gained importance in recent years, motivating a need for change in the manufacturing and formulation schemes of current products. At this point, we must indicate that "sustainable development" is defined as [6]: "Development that meets the needs of the present without compromising the ability of future generations to meet their own needs."
"Green Chemistry", also known as Clean, Benign, Ecological or Sustainable Chemistry, is a branch of chemistry that aims to respond to this need for change. It is considered that "Green Chemistry" emerged in 1962 with the book "Silent Spring", by the American writer Rachel Carson, which contributed to the implementation of the modern environmental awareness of our society. His book had an enormous influence on the public, giving a great impulse to what until then was an incipient and dispersed consciousness, helping the environmental movement to crystallize [7].
"Green Chemistry" is defined in twelve principles that are summarized below:
1. Prevent waste by consciously using products
2. Design safer chemicals and products
3. Design less hazardous chemical synthesis
4. Use renewable raw materials
5. Use safe catalysts and reagents
6. Avoid chemical derivatives
7. Maximizing the atomic economy
8. Use safer solvents and control reaction conditions
9. Increase energy efficiency
10. Design chemicals to be biodegradable
11. Analyze processes in real time, to prevent contamination
12. Minimize the potential for accidents
It is therefore seen that most of these principles are aimed at making our products less bad, but it is necessary to be more ambitious, we must manage to develop, if not ecological products, environmentally friendly products.
Although the new technologies associated with the implementation of "Green Chemistry" are initially focused on chemical reactions and catalysis in industrial processes, a careful analysis of these principles shows that the solvent is present, in a more or less direct way, in most of its principles. Its presence in the eighth point: "Safer solvents and auxiliaries" is evident. However, they also appear in principles such as the prevention of discharges, less dangerous synthesis and with a lower energy cost; use of renewable sources of raw materials and safer chemical processes, for example [8].
Pollutants and sustainability
Unfortunately, society's perception is increasingly negative regarding the role of chemistry [9], and this is due to the contaminants associated with chemical processes and products. In fact, today there is a fairly widespread view that the production and use of chemicals cannot be maintained within the current schemes [8].
Among the different polluting chemicals it is worth mentioning some of the most notable in the paint industry [9]:
VOCs are generated by the emission of vapors when using organic solvents or products that use them: VOCs have an inherent toxicity and an adverse effect on the health of living beings and the environment, due to their role in the formation of the so-called "tropospheric ozone" ("bad ozone") and "photochemical smog" [3]. But in addition, they are flammable and have a risk of explosion, so they have a risk of fire both in their transport, storage, and in the manufacture of paints and their use. Therefore, there is increasing pressure to reduce the use of this type of compound [4] [10].
Toxic and hazardous substances and others reported in the so-called "dirty list" (or "black list" of chemical substances [11]), among which are carcinogenic and mutagenic substances, neurotoxic and sensitizing, toxic to reproduction, endocrine disruptors, POPs (persistent organic pollutants) and substances harmful to the environment, type TPB (toxic, persistent and bioaccumulative), as well as so-called "heavy metals" (or "toxic metals", such as mercury, lead, cobalt, etc.) [12].
CFCs (carbonated chlorofluoro) and COHs (halogenated organic compounds), for their demonstrated effect on the destruction of the ozone layer (stratospheric ozone or "good ozone"). As well as the so-called HAPs (or Hazardous Air Pollutants, CPAs, for its acronym in Spanish), of which the US EPA has a list of about 189 compounds. CPAs are carcinogenic and non-carcinogenic compounds, which can cause serious and irreversible effects on human health. Most of them are VOCs [13].
But we must say that among the different pollutants mentioned, the most significant factor by which conventional paints contribute to environmental pollution is the emission of VOCs [14]. Although at this point, it is important to comment that there is a relative great confusion around the environmental impact associated with VOCs, since environmental problems such as "Global Warming", "Climate Change" and "ozone depletion", are not, in fact, directly related to the effect caused by VOCs [15].
Additionally, the fact that a varied number of definitions are presented for VOCs in different parts of the world, reflects that there is no clear environmental legislation of global utility for this type of compounds, which can generate conflicts between international markets. Although it is clear that, in the definition of VOCs it is only possible to exclude water and non-volatile compounds.
The following table, taken from the literature [15], summarizes the environmental problems in which the VOC-related paint industry is mainly involved:
Environmental problem | Global Warming | Climate change | Ozone depletion | Photochemical smog |
Contribution of the Paints and Coatings Industry | Casualty | Casualty | Low 1 | Loud |
Consequently, it is clear that the solvents used in the formulation of paints only have an important effect on the environmental problem of the generation of "photochemical smog", while their participation in phenomena such as "Global Warming", "Climate Change" or "Depletion of the ozone layer" is much more moderate [15].
In detail: VOCs and the environmental problem of paints: A solvent-based paint is composed of a vehicle (resins + organic solvents), pigments and additives. Of these components of the formulation, the solvent is the one that becomes VOC during the drying process of the paint, and it is precisely this component that has led to the development of alternative technologies, which seek to reduce its content in conventional coatings [16].
Among the main alternative technologies are: water-based paints, high solids paints, UV curing paints, powder coatings and the use of solvents less harmful to the environment ("green solvents" or "neoteric solvents"). There are even cases of the use of reactive solvents: Reactive diluents in epoxy solvent-based systems and reactive coalescing in water-based paints [3] [4], to mention a few examples. But, it must be said that, when thinking about new systems to replace conventional solvent-based, the main doubt remains the performance of the products [1].
Thus, despite the existence of various alternative technologies for some years, even today the paints and coatings industry formulates products with solvents and VOC contents higher than those recommended by international standards2. The reasons are multiple: from the lack of regulation in the Latin American market in relation to VOCs, ignoring the benefits of other alternative systems (water-based and high solids, for example), to the lack of own research and developments, among others. The architectural segment (of water-based paints), which presents greater informality among the applicators, curiously is the one that has the lowest share of solvents within the total of products available on the market [1].
In the case of solvent-based paints, we have that current formulations involve the loss of a component during film formation. This is necessary to dissolve the resin and other components of the formulation, and facilitate the manufacturing process and application of it, and generally has the lowest cost of the different components used. So we have that, after the evaporation of the solvent (generation of VOCs), the paint suffers a "decrease in volume" and the loss of a low-cost component. But the main problem is that the component that "is lost from the paint", becomes an air pollutant, is toxic and also flammable [16].
In the case of the industrial, marine and aerospace paints sector, the growth of high solid systems has had excellent results, where products of recognized quality and performance are currently on the market [17]. For its part, for this same sector, but in the case of the new aqueous systems, the change has been gradual and slower, because higher performances are required, in certain aspects, than the solvent-based systems, such as resistance to chemical attacks or caused by the environment, durability, adhesion and anticorrosive capacity.
In this sense, technically we can affirm that "the use of solvents distinguishes a technological society", since in the case of paints, organic solvents are not part of the coating formed, and therefore go to the atmosphere causing an environmental problem: Not only is money lost by the deliberate dumping of a material for which the consumer is paying and that will not be part of the paint that applies, rather, it is a material that has associated various risks of toxicity, flammability and for the environment. This is how, from the point of view of the so-called "Green Chemistry", the best solvent is the one that does not exist! [8] [15]. A good alternative is that if a solvent is required, it is water, which is non-toxic and still economical [18].
Footnote:
1. Because much of the paint industry has already largely replaced the use of CFCs.
2. 250 g/b is the internationally recommended color content.
Note: In the next edition we continue with the second part of this article developing the role that the green paint industry plays in this topic.
References
[1] Restrepo, V., "Solvents still do not disappear", Inpralatina, Vol. 15, No. 5, Sept/Oct 2010, pp. 9-11.
[2] http://www.elespectador.com/tomalapalabra/pacific-rubiales/que-tan-verdes-son-los-productos-verdes-205-articulo
[3] Restrepo, J.A., "Ecology and VOC: Developing Environmentally Friendly Products." Inpralatina, Vol. 11, No. 4, July/August 2006, pp. 34-36
[4] Restrepo, J.A., "An Analysis of Some Definitions of These Substances: Volatile Organic Compounds (VOCs)." Vol. 12, No. 6, Nov./Dec. 2007, pp. 24-26
[5] a) Hazel, N. J. "Using LCA to select coatings for optimum environmental and cost performance". JCT, Vol. 68, No. 861. Oct, 1996; b) Hofland, A. "Ecology at any price?: Ecological balance of some water-based paints". Conference presented at the EUROCOAT 94 congress in Sitges, Barcelona.
[6] Report of the World Commission on Environment and Development (Brundtland Commission): Our Common Future, UN, 1987.
[7] (a) http://www.thomasnet.com/articles/chemicals/green-chemistry-history; b) https://en.wikipedia.org/wiki/Rachel_Carson
[8] Mayoral, J.A., "Use of alternative solvents", Internet publication: www.unia.es/nuevo_inf_academica/visualizar_file_adjunto.asp?ID=1606
[9] Restrepo, J.A., "Green Chemistry in Paintings". Inpralatina, Vol. 13, No. 4, July/August 2008, pp. 28-31
[10] - Restrepo, J.A., "Renewable Solvents", Inpralatina, Vol. 13, No. 6, Nov/Dec. 2008, pp. 16-20
[11] http://www.istas.net/web/index.asp?idpagina=3447
[12] http://www.lineaysalud.com/que-es/metales-pesados-o-metales-toxicos
[13] http://www.inecc.gob.mx/calaire-informacion-basica/524-calaire-cont-peligrosos-aire
[14] Pulgarín, D.F. and Restrepo, J.A. "Reduction of volatile organic compounds (VOCs) through water-based technology in wood coatings". Thesis National University, Headquarters Medellín, 2002.
[15] a) Restrepo, J.A., "Oil and its adaptation to paintings, part I". Inpralatina, Vol. 18, No. 2, March/April 2013, pp. 16-20; b) Restrepo, J.A., "El petróleo y su adaptación a las pinturas, parte II". Inpralatina, Vol. 18, No. 3, May/June 2013, pp. 14-17
[16] http://es.ppgrefinish.com/es/acerca-de-ppg/ppg-industries/
[17] You can also visit PPG Industries' corporate website: www.ppg.com, "Bringing innovation to the surface".
[18] Restrepo, J.A., "Alternative Solvents". Inpralatina, Vol. 13, No. 5, sept./oct. 2008, pp. 16-19.
* M.Sc. Ph.D. Julián A. Restrepo R. PMC Technical Manager of PPG Industries Colombia. [email protected]
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