Several Physical Properties of Stein-Hall Type and No Carrier Type Corrugating Starch Adhesives

Abstract

In this study, it was investigated the properties of Stein-Hall (SH) type and No Carrier (NC) type corrugating adhesives made from corn starch. SH type adhesive is composed from carrier and main starch portions. It had been reported that NC type adhesive was composed from partially swelled homogeneous starch granule suspension. The distribution of starch granule diameter in both types adhesives and simple slurry respectively containing 21.6% corn starch were a little different. In NC type, slightly swelled granule of 29-101 μm diameter increased by 16% compared with the simple slurry. And in SH type, the distribution had two peaks. The first primary peak was similar to the simple slurry and the secondary peak of 10.5% distribution was broad range of 44-101 μm in diameter. However, the gelatinization enthalpy of NC type was not significantly different from SH type during 0.54-0.94% caustic soda concentration, and in both types, they were decreased to 70% as the concentration of caustic soda increased from 0 to 0.94%. These gelatinization complete temperature (Tc) became a little higher in NC type compared with SH type. In various NC type adhesives of containing 14.4-34.4% starch and SH type of 19.2-24.7%, the ratio of Ford cup (FC) viscosity to Brookfield (B.) viscosity of NC type was half as large as SH type at 40°C. Thus, the viscous properties were different in two types. NC type adhesive was seemed to be high fluidity and good application at glue roll as a result of its low FC viscosity and high B. viscosity. In common practical viscosity (540-2500 m Pa·s at 40°C) of various NC type adhesives containing 14.4-34.4% starch, the proportion of soluble starch to the whole starch increased to 19.0 from 1.2% and the swelling ratio (the ratio of swelled starch volume for air dried starch volume) increased to 5.40 from 2.10 with decreasing starch concentration to 14.4 from 34.4%, and conversely the density of their granule decreased to 1.10 from 1.24 g/cm³. In the NC type adhesives with various viscosities at 40°C of 21.6 and 28.7% starch concentration, the proportion of soluble starch increased as its viscosity became higher, but the swelling ratio of starch granule was almost the same. As the result, the viscosity of NC type adhesives was depended on the proportion of soluble starch rather than the swelling ratio. So, it was thought that the viscosity at preparing the NC type was adjusted with the proportion of soluble starch but not with the swelling ratio, according to the treatment time with high concentration (0.79-1.30%) of caustic soda. As the result from the starch granule diameter distribution, the NC type was not homogeneous and contained the partially swelled starch granules as a part. In the several concentration of caustic soda, the gelatinization enthalpies of NC type adhesives were almost same but not small compared with the SH type contrary to the expectation. It was seemed that SH type and NC type adhesives were characterized as similar endothermic gelatinization properties.