The review provides an overview of research findings on microencapsulation for functional textile coatings. Methods for the preparation of microcapsules in textiles include in situ and interfacial polymerization, simple and complex coacervation, molecular inclusion and solvent evaporation from emulsions. Binders play a crucial role in coating formulations. Acrylic and polyurethane binders are commonly used in textile finishing, while organic acids and catalysts can be used for chemical grafting as crosslinkers between microcapsules and cotton fibres. Most of the conventional coating processes can be used for microcapsule-containing coatings, provided that the properties of the microcapsules are appropriate. There are standardised test methods available to evaluate the characteristics and washfastness of coated textiles. Among the functional textiles, the field of environmentally friendly biodegradable textiles with microcapsules is still at an early stage of development. So far, some physicochemical and physical microencapsulation methods using natural polymers or biodegradable synthetic polymers have been applied to produce environmentally friendly antimicrobial, anti-inflammatory or fragranced textiles. Standardised test methods for evaluating the biodegradability of textile materials are available. The stability of biodegradable microcapsules and the durability of coatings during the use and care of textiles still present several challenges that offer many opportunities for further research.

Three higher hydrocarbon phase change materials (PCMs) with melting points of 25, 40 and 50 degrees C were microencapsulated by in situ polymerization of amino-aldehyde resins. Trimethylolmelamine (TMM) and hexamethoxymethylolmelamine (HMMM) were studied as amino-aldehyde pre-polymers for microcapsule wall formation, in combination with emulsifying/modifying agents based on styrene-malein anhydride copolymers (SMA) of different molecular weights and different styrene-maleic acid anhydride ratios. Microcapsule sizes, size distribution and wall permeability were analysed. A mathematical model was developed for comparing the mechanical resistance of different batches of microcapsules, produced at different TMM-SMA ratios. Larger microcapsules with thicker walls and larger pores (M(LAR)) expressed lower resistance to breakage than slightly smaller microcapsules with thinner walls and finer pore structure (M(SMA)). Mathematical data were confirmed by a smudging colouration test. Laboratory microencapsulation process parameters were optimized to obtain impermeable microcapsules with improved mechanical stability. The process was transferred into a 10l pilot reactor for two PCMs with melting points of 25 and 40 degrees C. Dry powder of microencapsulated PCMs was obtained by spray drying of aqueous microcapsule suspensions.

Essential oils are environmentally friendly candidates for antimicrobial smart packaging systems. Encapsulation is needed to reduce their volatility and achieve controlled release. Within this study, the essential oil of Cymbopogon citratus (citronella oil) was microencapsulated and applied in pressure-sensitive antimicrobial functional coatings on papers for secondary packaging. Two microencapsulation methods were used: complex coacervation of gelatine with carboxymethylcellulose or with gum arabic, and in situ polymerization of melamine-formaldehyde prepolymers with a polyacrylic acid modifier. Minimum inhibitory concentrations of citronella oil microcapsules were determined for Bacillus subtilis (B. subtilis), Escherichia coli (B. subtilis), Pseudomonas aeruginosa (P. aeruginosa) and Saccharomyces cerevisiae (S. cerevisiae). Microcapsule suspensions were coated on papers for flexible packaging, 2 and 30 g/m², and mechanically activated in the weight pulling test. A novel method on agar plates in sealed Petri dishes was developed to evaluate the antimicrobial activity of released citronella vapours on E. coli and S. cerevisiae. The results showed that both microencapsulation methods were successful and resulted in a container type single-core microcapsules. In situ microcapsule suspensions had better paper coating properties and were selected for industrial settings. The antimicrobial activity of 2 g/m² coatings was not detected; however, the antimicrobial activity of 30 g/m² partially activated coated papers was confirmed. The product enabled a prolonged use with the gradual release of citronella oil at multiple exposures of functional papers to pressure, e.g., by a human hand during product handling.

Article Microencapsulation technology and applications in added-value functional textiles was published on January 30, 2016 in the journal Physical Sciences Reviews (volume 1, issue 1).

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