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Chemistry

Without smell and less toxic

USP researchers develop a method for the production of paints almost without smell

MIGUEL BOYAYANTo manufacture a wall paint without smell for rooms that can be made use of shortly after the second coat is applied is an objective sought after by the chemical industry for more than two decades. The product would be useful in hospitals, schools and restaurants, locations where the presence of fumes responsible for the odor characteristic of paints is undesirable. The solution has come one step closer with the studies carried out at the Chemical Systems Engineering Center of the Polytechnic School of the University of Sao Paulo (Poli/USP). The research, coordinated by the chemical engineer Reinaldo Giudici, has presented satisfactory results and has managed to reduce the concentration of the residual monomers – toxic substances responsible for the major part of paint smells – to less than 100 parts per million (ppm), or that is, 0.01% or 0.01 grams of monomer for every 100 grams of polymer emulsion, the resin that is the main component of paint. Although the smell has not been totally removed, it remains almost imperceptible.

“The most efficient processes for the removal of the odor today in commercial use don’t manage concentrations less than 1,000 ppm, ten times greater than that which we had obtained” the researcher says. “In order to achieve this result, we prolonged and intensified the chemical reaction of polymerization, in such a manner that more monomers react and are transformed into polymers.” In order to understand what this  means, before one must understand how the manufacturing process for water soluble (without solvents) latex paints comes about, the paint most widely used for internal and external walls. The main component of the product is an aqueous emulsion made up of polymers, macromolecules formed starting with smaller structural units, the monomers. The monomers most widely used in latex paints are the vinyl acetates (which originate vinyl paints) and the butyl acrylates (the raw material of acrylic paints).

Usually the two type of monomer are polymerized together in such a manner as to obtain determined properties in the polymer. The styrene and butadiene monomers, for their part, are used in the manufacture of a latex used in the covering of glossy paper – the same used in this magazine – a product that will also be benefited with the new technology.

So that the polymerization takes place, substances chemically known as initiators are mixed in with the monomers, and, in a chemical chain reaction, these small molecules join together, transforming themselves into macromolecules, which are the polymers. The problem is that during this process, carried out in a reactor vessel at an average temperature of 60 to 80 Celsius, the monomers do not react completely, a small quantity of these compounds remain intact in the polymeric emulsion at the end of polymerization and, afterwards, in the paint. When it is applied to a wall, the water present in the emulsion evaporates and the polymer particles come together forming a film that covers the surface. “The monomers, since they are volatile substances, also evaporate bringing about the characteristic smell of fresh paints, in general disagreeable. Depending upon the nature and concentration in the air, there can be different levels of toxicity” explains  Giudici. “As well as irritating the mucous membranes of the respiratory system, the residual monomers can cause nausea, allergies and other disagreeable sensations.”

In order to reduce the concentration of the monomers in the final product, the alternative found by the researchers was to intensify the reaction. They altered the conditions of the process’s operation with the objective of consuming more residual monomers. Thus, among other things, the team modified the reaction temperature, altered the component concentrations and varied the presence of initiating reagents. “We took great care not to undermine  the process’s productivity and, at the same time, not to alter the final properties of the latex. On the contrary, we improved the quality because we reduced the levels of residual monomers” explains chemist Giudici.

Currently the process most widely used to reduce paint odors is the so called de-volatilization, which, in spite of being efficient, presents disadvantages in comparison to the method developed at the Polytechnic School. This process consists in bubbling a gas, generally steam, into the polymer emulsion so that the monomers present volatilize, or that is, will be expelled from the product. “The inconvenience of de-volatilization is that this process generates residues that can’t be launched into the environment, since they are pollutants” points out Giudici. For this reason, the effluent needs to be treated, which adds on a stage to the productivity process, turning it longer and more costly.

The technology developed by the USP team took some seven years to be ready and was financed through FAPESP within the Technological Innovation Partnership (PITE) program. Initially the project was signed up with Rhodia, the French multinational company in the chemical sector. However, during the work, the company sold off its units that manufacture styrene and butadiene latex to the Finish company Raisio Chemicals, which made the investment in accordance with that established in the PITE program. Then the Raisio Chemicals company was acquired by the Swiss multinational Ciba Especialidades Químicas (Ciba Specialty Chemicals) , the project’s current partner. With the conclusion of the USP research, the process now finds itself in the phase of laboratory testing by the company in Brazil and France. As yet there is no forecast date of when the new technology will be implanted by the company, which, as a first step, is going to test it on a semi-industrial scale.

“As the industrial tests have not yet begun, we don’t know if it might be more interesting, from the economic point of view, to make use of our process in isolation or to combine it with de-volatilization. As de-volatilization is carried out last and, as the presence of residual monomers will be fewer, there will be little production of effluent, thus reducing the treatment cost” says  Giudici.
“The project carried out at USP was very important for Ciba Especialidades Químicas. The contact and the exchange of information with the researchers involved in the project was excellent, as they always demonstrated concern in the applicability of their results in industrial processes” says Odair Araujo, from Ciba’s polymerization laboratory and the company’s project coordinator. “Another aspect was the quality of the results obtained, which made it possible for us to obtain an important vision of the potential for application in the pilot plant and, in the future, in an industrial plant. We can state that the Ciba Especialidades Químicas and the University of Sao Paulo project was a success and we pretend, in the future, to continue to make use of this type of agreement.”

As well as the creation of a process capable of producing paint practically without smell, the USP group also developed methods for the on-line monitoring of the polymerization reactions in emulsion manufacture. The process is based on spectroscopy systems, which use the absorption and reflection of electromagnetic radiation in the product by way of a laser, permitting the detection of the presence and the quantity of determined substances. Thus, these methods permit remote monitoring and, in real time, of various properties and variables during the polymerization. “Every fifteen seconds, we know what is the quantity of residual monomer, the concentration and composition of the polymer and the average size of the polymer chain molecules. This data is fundamental so that we can have rigid control of the process and we can implement the conditions of operation in a precise manner” advised chemist Giudici.

The Project
Development of polymerization processes for the production of polymers with a low level of residual monomer (nº 98/03194-9); Modality Technological Innovation Partnership (PITE) Program; Coordinator
Reinaldo Giudici – USP; Investment R$ 55,000.00 + US$ 259,000.00 (FAPESP) and R$ 135,000.00 (Ciba Especialidades Químicas)