Chitosan-hybridized acrylic resins prepared in emulsion polymerizations and their application as interior finishing coatings.

Chitosan was used to introduce formaldehyde adsorption abilities into an emulsion binder for interior finishing coatings. Chitosan-hybridized acrylic emulsions were prepared by two methods. To produce stable chitosan-hybridized acrylic emulsions, the pre-emulsion dropping method is superior

to the monomer dropping method. The adsorption performances for formaldehyde in chitosan-hybridized acrylic resin films increased with increasing chitosan contents; the films also had adsorption abilities for hydrogen sulfide and ammonia. Tensile strengths and elongation at breaking points decreased with increasing chitosan contents. Interior finishing coatings made from chitosan-hybridized acrylic resin emulsions have the qualities necessary for an interior finishing coating and showed excellent adsorption abilities for formaldehyde.

Keywords: Acrylics, latexes, colloids, emulsions, waterborne, mechanical properties, architectural, water-based, air quality, emissions, VOC control

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In the living environment, sick-building syndrome is a social health problem which occurs when the quality of indoor air diminishes due to harmful substances contained in it. (1) Volatile organic compounds (VOCs) such as formaldehyde cause sick-building syndrome because VOCs are contained in furniture and building materials. (2) To combat this problem, a considerable number of studies have been done to improve indoor air quality. (3,4) In interior materials, both the decomposition of formaldehyde using photocatalysts such as titanium oxide, and decomposition using chemical means or the physical adsorption of formaldehyde, have been studied. (5-10) Although the means for decomposing formaldehyde are effective, if sufficient ultraviolet radiation cannot be supplied throughout the indoor environment, undecomposed formaldehyde remains. In the case of physical adsorption with porous raw materials such as zeolite, diatomite, and charcoal, there is a problem in that adsorbed formaldehyde is emitted. On the other hand, chemical adsorption by reactions with formaldehyde can be efficiently removed and not re-emitted. Chemical adsorbents, however, are not sufficiently safe.

Recently, investigations using natural raw materials as adsorbents were carried out. Among the natural raw materials, chitosan is an environmentally friendly material with many superior properties. Chitosan powder was used to inhibit the emission of formaldehyde from plywood. (11-12) Ishimaru also reported that chitosan is effective in adsorbing formaldehyde. (13) Chitosan is a polysaccharide consisting of 2-amino-2-deoxy-D-glucopyranose as a repeating unit and is obtained by deacetylation of chitin, as shown in Figure 1. Chitin exists in crustacean shells, such as crabs and shrimps; in insects, such as beetles and grasshoppers; in cuttlefish bone; and in the cell walls of fungi, such as mushrooms. Compared to synthetic polymers, chitosan has several important advantages, including biocompatibility, biodegradability, and no toxicity. In addition, chitosan has reactive amino groups on pyranose rings and becomes a cationic polymer upon the protonation of its amino groups. However, chitosan simply added to waterborne coatings cannot uniformly disperse. Furthermore, when chitosan-acid solution is added to waterborne coatings using acrylic emulsions, precipitates are formed because chitosan is a cationic polymer. To resolve this problem, chitosan-hybridized acrylic resins were investigated in emulsion polymerizations between chitosan-acrylic acid ion complexes and acrylic monomers. In this study, the preparation of chitosan-hybridized acrylic resins in emulsion polymerization and their application to interior finishing coatings are discussed.