Crystals in protein films: What are they good for?
Abstract Biopolymers were developed comprising 100% renewable resources. The protein-based films were produced by the casting method involving enzymatically mediated cross-linking of the protein network as well as incorporation of KNO 3 . This additive provides a fertilizing effect for biopolymer films in agricultural purposes and is one tool for the modification of physico-chemical properties of protein films. The variation of the parameters, temperature and air humidity, during the drying process of films revealed the opportunity to enhance the film's mechanical performance and to control the crystal morphology of the inner-film crystallized additive, respectively. Drying at room temperature led to small crystals with regular shapes which have been identified to be trigonal phase-III KNO 3 . With higher temperature, the supersaturation level of KNO 3 increased, provoking dendritic shapes. A rise of air humidity consolidated that trend and resulted mainly in the increase of the crystal number. Indeed, further investigation on the stability of the obtained crystal structures within the protein-based has to be performed, as a polymorph transition to orthorhombic phase-II KNO 3 was observed after 48 h that led to an unfavored acicular network.