PRESSURE-SENSITIVE ADHESIVE PROPERTIES OF WHEAT-FLOUR DOUGH AND THE INFLUENCE OF TEMPERATURE, SEPARATION RATE, AND MOISTURE-CONTENT

Using the method of reduced variables, probe tack test data on wheat f lour-water doughs was shifted into a series of master curves. This ill ustrated the equivalent influence of increasing temperature, increasin g moisture content, and decreasing separation rate on adhesive behavio r. An adhesive-cohesive failure transition occurred at 25-30 degrees C (43% moisture content). This transition occurs 50-70 degrees C above the T-g of a pressure-sensitive adhesive and is associated with a shif t in viscoelastic behavior from the rubbery state (entanglement networ k present) to the flow state (entanglement network disappears due to s lippage). Low molecular weight plasticizers (such as water) shift the location of the rubbery-flow state transition to lower temperatures an d faster rates. Thus, as the moisture content of the dough increased, the adhesive-cohesive failure transition shifted to lower temperatures and faster separation rates. Processors could prevent cohesive failur e, and thus a residue-buildup on equipment, by changing either the for mulations or the processing rate-temperature conditions to favor the a dhesive side of the failure transition zone.