Wypych Handbook of Solvents

Table 14.18.1. Reported solvent releases from the organic chemical industry in 1995 [Data from Ref. 2]

REFERENCES

1EPA Office of Compliance Sector Notebook Project. Profile of the Motor Vehicle Assembly Industry.

US Environmental Protection Agency, 1995.

2EPA Office of Compliance Sector Notebook Project. Sector Notebook Data Refresh - 1997. US Environmental Protection Agency, 1998.

3G. Wypych, Ed., Weathering of Plastics. Testing to Mirror Real Life Performance, Plastics Design Library, Society of Plastics Engineers, New York, 1999.

4 M Harsch, M Finkbeiner, D Piwowarczyk, K Saur, P Eyerer, Automotive Eng., 107, No.2, 211-4 (1999). 5 C A Kondos, C F Kahle, Automotive Eng., 107, No.1, 99-101 (1999).

6D C Shepard, J. Coat. Technol., 68, No.857, 99-102 (1996).

7T Hosomi, T Umemura, T Takata, Y Mori, US Patent 5,717,055, Mitsubishi Gas Chemical Company, Ltd., 1998.

Table 14.18.2. Reported solvent transfers from the organic chemical industry in 1995 [Data from Ref. 2]

14.18 ORGANIC CHEMICAL INDUSTRY

George Wypych

ChemTec Laboratories, Inc., Toronto, Canada

The chemical industry operates about 1000 plants in the USA with 53 companies producing 50% of the total output of $65 billion in sales and employing 125,000 people. There are point source solvent emissions (e.g., laboratory hoods, distillation units, reactors, storage tanks, vents, etc.), fugitive emissions (e.g., pump valves, flanges, sample collectors, seals, relief devices, tanks), and secondary emissions (waste water treatment units, cooling towers, spills). Organic liquid wastes containing solvent are generated from processes such as equipment washing, surplus chemicals, product purification, product reaction, housekeeping, etc.

Tables 14.18.1 and 14.18.2 give the reported solvent releases and transfers from the organic chemical industry. Large quantities of solvents are involved. The organic chemical industry produced the second largest quantity of VOC and the second largest releases and transfers. The industry is actively working to reduce solvent use because of the high costs (waste treatment, fines, liabilities, etc). There are many efforts under way to reduce environmental emissions and improve safe practices. The initiatives include process modifications such as a reduction in non-reactive materials (e.g., solvents) to improve process efficiency, a reduction in the concentration of chemicals in aqueous solution, and improved R&D and process engineering. Equipment modifications are planned to reduce leaks, prevent equipment breakdown, and improve the efficiency of emission control devices.

REFERENCES

1EPA Office of Compliance Sector Notebook Project. Profile of the Organic Chemical Industry. US Environmental Protection Agency, 1995.

2EPA Office of Compliance Sector Notebook Project. Sector Notebook Data Refresh - 1997. US Environmental Protection Agency, 1998.

14.19 PAINTS AND COATINGS

14.19.1 ARCHITECTURAL SURFACE COATINGS AND SOLVENTS

Tilman Hahn, Konrad Botzenhart, Fritz Schweinsberg

Institut fòr Allgemeine Hygiene und Umwelthygiene

Universit¬t Tòbingen, Tòbingen, Germany

Gerhard Volland

Otto-Graf-Institut, Universit¬t Stuttgart, Stuttgart, Germany

14.19.1.1 General aspects

Coating materials and coating techniques can be distinguished and systematized in various ways.

The fundamental principles of common coating systems are:1

•Physical drying. A solid surface film is formed after the evaporation of water or organic solvents.

•Physico-chemical drying/curing. Polycondensation or polyaddition are combined with evaporation of organic solvents.

•Chemical curing. Solvents, e.g., styrene or acrylic monomers, react with the curing system.

The actual effects depend on the surrounding conditions and the ingredients of the coating system, e.g., solvents.

Solvents contribute many essential properties to coating systems. Solvents can improve technical factors such as application or surface properties. Solvents also bring negative qualities to coating materials, especially with respect to environmental conditions (e.g., toxic effects of emitted organic solvents).

14.19.1.2 Technical aspects and properties of coating materials

Application techniques for coatings can be considered in various ways. The stability and durability of coating is essential. Coatings that have normal wear and tear requirements are

The following are examples of architectural surface coatings.

14.19.1.2.1 Concrete coating materials

According to DIN 1045 concrete must be protected against aggressive substances if the chemical attack is severe and long-term. These are the requirements:

•Good adhesion

•Waterproof and resistant to aggressive substances and resistant to the alkalinity of the concrete

•Deformable

To realize these requirements, the following technical solutions can be applied:

•The use of paint coatings based on duroplast or thermoplastic substances

•Surface treatment - impregnation

Protective coatings based on polymers are used in construction with and without fillers and with or without reinforcing materials (fibers).

The following techniques are generally used:

•Film forming paint coatings (brushing, rolling, spraying).

•Coating (filling, pouring).

During application, the coating materials are normally liquid and subsequently harden by evaporation of solvents or as a result of chemical reactions.

The common coating systems for concrete are listed in Table 14.19.1.2. Synthetic resins (e.g., chlorinated rubber, styrene resins, acrylic resins) contain normally 40-60% solvents and form a thin film. Several coats must be applied. Reactive resins may require little or no solvent.

Table 14.19.1.2. Survey of often used coating systems for concrete

14.19.1.2.2 Coating materials for metals

Wet coating processes are detailed in Table 14.19.1.3.

The chemical properties of binders are not affected by the drying process if coatings are of physically drying type. After solvent has evaporated, the polymer molecules become intermeshed, thus producing the desired coating properties.

In contrast to physical drying, binders based on reactive resins such as epoxy resins, polyurethanes or polyesters consist of two components (liquid resin and curing agent) which are either mixed shortly before the coat is applied, or, in the case of a one component system, one which is applied as slow reacting mixture. The setting reaction occurs at the surface of the coated material. The final products are normally more resistant and more compact than products based on physically drying binders. Pretreatment of substrate is more critical for applications where chemically hardening products are applied. Coatings can be more or less permeable to water vapor and oxygen. Damage to the metal substrate can occur if water and oxygen reach the reactive surface simultaneously. This is normally impossible if the coatings adhere well and the coated surface is continuous. The adhesion of the coating also prevents the penetration by harmful substances via diffusion processes. Adhesion is enhanced by adsorption and chemical bonds.

14.19.1.2.3 Other coating materials

Other aspects of solvents contained in paint coatings and varnishes are given in Chapter 18.3.

The market offers a wide spectrum of coating systems. Examples of common industrial coating materials are listed in Table 14.19.1.4 and relevant aspects concerning application and environmental or health risks are also included.

Table 14.19.1.4. Examples of coating materials containing hazardous ingredients, especially solvents3

References

1 Ullmann´s Encyclopedia of Industrial Chemistry,1998.

2DIN 1045 (Deutsches Institut für Normung), Concrete and Reinforced Concrete. Beton und Stahlbeton, Beuth Verlag, Berlin (1988), part 1 (1997), part 2 (1999).

3Sika TechnoBauCD, Sika Chemie GmbH, Stuttgart (2000).

14.19.2RECENT ADVANCES IN COALESCING SOLVENTS FOR WATERBORNE COATINGS

David Randall

Chemoxy International pcl, Cleveland, United Kingdom

14.19.2.1 Introduction

The role of coalescing solvents in coating formulations, the factors which affect the choice of coalescing solvents, and the recent developments in esters of low volatility, low odor and rapid biodegradability for use in coating formulations are discussed.

The term “paint” is widely used to describe a coating applied to a variety of substrates for protective or decorative purposes. “Paint” also implies a pigmented species, whereas “surface coatings” is a broader term for coating systems with or without pigments used for any coating purpose.

All paint systems may be considered as a combination of a small number of constituents. These are: continuous phase or vehicle (polymer and diluent), discontinuous phase or pigment and extender, and additives.

This paper is not concerned with the detail of paint formulation, but the polymer types most widely encountered are alkyds, polyurethanes and nitrocellulose in solvent based systems, and acrylics, styrene-acrylics, and copolymers of vinyl acetate in water-based coatings.

14.19.2.2 Water based coatings

Until recent times, most paints were solvent based. Since many polymers were produced in solution, it was natural that the coating system, derived from these polymers, would use the solvent of reaction as the diluent for the polymer. These were almost invariably organic species. The objections to the use of organic solvents in paint formulations were at first confined to those with strong views regarding the loss of significant quantities of organic species to the environment. Latterly, these opinions have been reinforced by the role of some organic species in damage to the ozone layer, or to the production of smog in the lower atmosphere. This is as a result of the reaction between organic species present catalyzed by sunlight and exacerbated by the presence of other pollutants associated with motor vehicles, etc. Flammability of paints also poses a significant problem in storage and use.

All this tended to reinforce the need to develop aqueous based systems, for which these problems would be eliminated.

14.19.2.3 Emulsion polymers

Of course, the manufacture of polymers need not be carried out in solution; emulsion polymerization has a long and honorable tradition in the field of macromolecular chemistry. This polymerization technique is performed using water-insoluble monomers, which are caused to form an emulsion with the aqueous phase by the addition of a surfactant. Polymerization may be effected by the use of a variety of radical generating initiating species, and the molecular weight of the polymer is controlled by the use of chain transfer agents and the concentration of initiator employed. The final polymer dispersion is often described as a latex, named after natural rubber, which is also an emulsion polymer!

This polymerization technique allows for the formation of copolymers in which the addition of relatively small quantities of comonomer may have a significant effect on the final properties of the polymer. This is particularly the case with the glass transition temperature, Tg, of the polymer. This is a physical transition, which occurs in the polymer when the amorphous structure of that polymer begins to change from a glassy to a rubbery state. At temperatures below a polymer’s Tg, it will be relatively brittle, and will be unlikely to form a coherent film.

This effect has a major impact on the use of polymers in aqueous systems. In the case of a polymer in solution, the presence of the solvent plasticizes the polymer during film formation. A polymer with a high Tg, i.e., one greater than ambient temperature, can, when in solution be applied at temperatures below its Tg. In the case of an emulsion polymer, water is a non-solvent in the system and film formation below the polymer Tg is unlikely. The temperature at which a coherent film may be formed from a solution or emulsion based system is known as the Minimum Film Forming Temperature (MFFT or MFT).

Figures 14.19.2.1-14.19.2.4 describe the formation of a discrete film from an emulsion system.

When the film is applied onto the substrate, discrete polymer particles are dispersed in the aqueous phase. The system is stabilized by the presence of the surfactant at the wa- ter-particle interface. The particles are spherical, with an average diameter of 0.1-0.2 m.

As water is lost from the system, the mutual repulsive forces associated with the surfactants present inhibit the close packing of the particles and a cubic arrangement of the particles is formed.