THE MECHANICAL-PROPERTIES OF PRESSED PROCESSED WHEAT MATERIAL

Breakfast wheatflake materials, produced by two methods, were milled a nd different sieve fractions reconstituted by hot pressing into bar-sh aped test pieces, to reduce the geometry and structure effects of flak es. The stiffness and fracture properties of these pressed bars of dif ferent particle size in ranges <0.5 mm, 0.5-1 mm, 1-1.4 mm, 1.4-2 mm a nd of different water content were compared. Dynamic mechanical therma l analysis showed that the bending modulus, E', superimposed as a func tion of temperature in the range -40 to 140 degrees C. The value of E' at 20 degrees C decreased with increasing water content corresponding to depression of the glass transition temperature. Microscopy of the test pieces revealed that starch was the continuous phase. The stiffne ss properties were similar in many respects to data published for pres sed starch specimens. However, the energy to break samples at 7% water content (wet weight basis) was greater when a range of particle sizes was used compared to the results of narrow particle size ranges. This is consistent with published results on fracture toughness of particu late compacts. The energy to break samples increased with increasing w ater content.