摘要:

Several series of modified potato starches covering a wide range of fluidities were prepared by treatment with dilute hydrochloric acid at 50 °C. As in the case of previous results obtained with corn starches, it is shown that the viscosity is dependent on the rate of shear and that the data are well expressed by the exponential relationF=KPn, whereFis the flow,Pis the pressure,Kandnare constants. The value ofndecreases rapidly with increasing degree of modification. It is shown thatndepends on the volume occupied by the swollen granules in the paste, and thatnis much greater in potato starch pastes than in corn starch pastes owing to the greater swelling of the granules. This swelling decreases with increased degree of modification. The stability of the granules in alkaline pastes is described for both potato and corn starches, and the fluidities of alkaline potato pastes are shown to be much greater than those of corn pastes of comparable extent of modification. The gelatinization temperature is shown to rise with increasing modification. At the same time, the power of hydration of the granules decreases and they appear to become denser and more compact. The resistance to mechanical injury becomes greater with increasing modification, and the injured granules swell to a lesser extent. The decreased hydration (hydration plus immobilization) leads to different forms of breakage when the granules are crushed. Prolonged heating of starch pastes causes a rapid decrease in the value ofn, owing chiefly to a disruption of the granules with consequent change in the phase-volume ratio.

ISSN:1923-4287    

DOI:10.1139/cjr36b-044

出版商:NRC Research Press    

年代:1936

数据来源: NRC

摘要:

The critical concentration of a starch paste is the limiting concentration above which structural flow is apparent. The inverse of the critical concentration, termed the effective volume, is the minimum volume of solution per gram of starch below which structural flow is apparent. The critical concentrations and effective volumes have been measured for series of pastes of acid-modified corn and potato starches, and the effective volume has been shown to decrease with increasing degree of modification. The specific viscosities per unit concentration of these pastes, at concentrations below the critical, increases linearly with the effective volume, and the proportionality constants found are compared with those derived from the equations of Einstein and of Hatschek. The effects of phase-volume ratio and ease of deformation of the dispersed phase on the viscosity of a system are discussed, and previous relations applied to experimental data obtained in the present instance. Residual structure below the critical concentration is discussed. Above the critical concentration, the viscosity is dependent on the rate of shear, and the equationF=KPnexpresses the experimental data well, whereFis the flow,Pis the pressure,Kandnare constants. For two starches investigated, within the range of concentrations usednhas been found to increase linearly with the concentrationc,dn/dcbeing dependent on the elasticity or deformability of the granules.The form of lyophilic colloids in solution is discussed and agreement is expressed with the conception of Haller that the long-chain molecules, owing primarily to the free rotatability of the valence linkages, are irregularly bent and tangled in solution, as opposed to Staudinger's conception of straight rigid chains. These molecules occupy on the average a form approximating to the spherical, and solvation is due chiefly to immobilization. A dextrin in solution was found to have aratio close to that of a pasted starch, and the forms of the two are probably similar. A lyophilic sol is considered heterogeneous and similar in many respects to an emulsion, with a very highly deformable discontinuous phase. The viscosity of such a system is due to phase-volume relations, modified by the ease of deformation of the dispersed phase, and the particular characteristics of these important sols admit of explanation on this basis.

ISSN:1923-4287    

DOI:10.1139/cjr36b-045

出版商:NRC Research Press    

年代:1936

数据来源: NRC

摘要:

Methylated methanol lignin prepared from fully methylated spruce wood-meal was subjected, at relatively low temperatures and pressures, to the action of hydrogen in the presence of catalysts, and under conditions such that reduction of open-chain ethylenic linkages readily occurs. Entirely negative results were obtained. This pointed to the absence of ethylenic linkages in the lignin building unit.

ISSN:1923-4287    

DOI:10.1139/cjr36b-046

出版商:NRC Research Press    

年代:1936

数据来源: NRC