Effect of surface modification on starch biopolymer wettability

• A sharp decrease of water contact angle after plasma treatment was observed.
• The contact angle also reduced vs. time due to the reorientation of polar groups.
• After plasma and/or lysozyme modification starch surface was more hydrophilic.
• The opposite trend of changes was visible after chitosan solution treatment.
• FTIR results and the profilometer images well support the contact angle studies.

The main goal of this paper was to determine wettability properties of native starch and starch modified by antibacterial solution of chitosan or lysozyme as a function of temperature and/or after plasma treatment. Contact angles for polar water (and formamide) and nonpolar diiodomethane on glass plates covered with starch film before and after gelatinization (25 °C, 37 °C and 60 °C) were measured. The surface free energy of solid (gel) was determined from the advancing and receding contact angles of these probe liquids, using the contact angle hysteresis model (CAH). The plasma treatment was immediately followed by a sharp decrease of contact angle. In the course of ageing the contact angle also decreased due to the reorientation of polar groups into the surface layer of polymer. Also a sharp decrease in negative values of WS takes place which indicates more hydrophilic character of starch after plasma treatment. The same was after lysozyme modification but to a smaller extent. The opposite trend of changes was visible after chitosan solution treatment. The surface characterization was observed by FTIR measurements and surface topography from the profilometer images and such measurements well support the contact angle results. The arrangement of temperature, plasma treatment or biological modification can lead to improvement of starch surface wettability and stability. The obtained results open up possibilities of starch application in food, paper and packaging industries as well as in pharmacy.

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