The Influence of Hexamethylenetetramine and Formaldehyde on the Rheological Behavior of Casein Base Coating Colors

The experimental work presented in this thesis shows the effects of formaldehyde and hexamethylenetetramine on the flow characteristics of coating colors formulated with casein as an adhesive. All experiments were performed at room temperature. In general, the pH has marked effect upon viscosity of the coating colors: the higher the pH value, the more viscous the coating color. Furthermore, formaldehyde reacted faster with proteinaceous coating colors than hexamine. Specifically, coating colors containing four per cent hexamine showed little change in viscosity and flow behavior while coating colors at the neutral pH value of seven containing eight per cent hexamine showed significant changes in viscosity and rheological behavior in storage over a period of several weeks. The coating colors at alkaline pH values in the eight per cent hexamine series showed little change in viscosity and flow behavior after six weeks. Finally, coating colors containing formaldehyde were very reactive showing viscosity increases for all pH values. After a period of two weeks, the flow behavior changed from practically Newtonian to thixotropic-pseudoplastic at pH values of seven and eight while coating colors at pH value of nine were initially thixotropic-pseudoplastic and became increasingly thixotropic in storage. The colors at pH value of ten were initially thixotropic-plastic and became increasingly thixotropic in storage