Development and Testing of a Machine-Coatable Chitosan Coating Applied to a Flexible Packaging Sealant. (Paperback)

Chitosan is a naturally derived material that has anti-microbial properties. Studies have shown that chitosan is effective when it is in contact with the surface of the product upon which the antimicrobial effect is desired. This suggests that chitosan should be on the inside surface of the package. In this work, a machine coatable chitosan coating was developed for application to the sealable (LDPE) side of a PET/LDPE lamination. The viscosities and percent solids of the coating were evaluated over 12 days. The coating was tested using manual drawdowns (Mayer rods) and also on a gravure coating line. Adhesion properties and sealability were tested. Chitosan was dissolved in an acetic acid/water mixture. Wettability against treated LDPE was not achieved with this blend, so ethanol was added. Good gravure coating qualities were noted with solutions that had 5% chitosan dissolved in water with 8% acetic acid and 30-35% ethanol. Viscosity of the chitosan coatings were initially high and decreased over time. Most of the change occurred over the first 4 days, then incremental changes were noted. Viscosity was also found to be dependent on the relative quantities of chitosan, acetic acid and ethanol. Coating qualities were measured using a newly developed percent coverage test using iodine staining of the chitosan. To get sufficient wetting, the treatment level of the LDPE had to be a minimum of 52 dyne/cm. Percent coverages of the surfaces coated by hand using Mayer rods were found to be dependent on chitosan percentage in the formula (must be greater than 1.5%), and on the relative quantities of chitosan, ethanol and acetic acid. The highest percent coverage of the surfaces found using Mayer rod coating was 97 percent. It is believed that the time lost between coating and drying in the manual Mayer rod process explains the lower percent coverage. Percent coverages of gravure coated materials ranged between 95 and 100 percent depending on line speed and drying conditions. The highest line speed for which a good percent coverage was achieved was 150 fpm. Adhesion of the chitosan film to the treated LDPE passed the tape test (ASTM F2252). The chitosan coated film exhibited no sealability for any of the seal conditions.