Wet end starch: its importance and measurement.

Alkaline papermaking uses starch as one of several wet end specialty chemical additives. Starch has three critical purposes in the wet end: 1) dry strength enhancement, 2) internal size retention, and 3) first pass retention. Starch's importance to dry strength and size retention is generally accepted, but there is debate about its importance to first pass retention. This author's experience shows starch as a major contributor to first pass retention through charge neutralization, through polymer flocculation, and as a component of micro particulate retention systems.

One problem that many mills face today is that they do not pay adequate attention to this important wet end additive. It is not made down consistently, not fed/metered with state of the art technology, and its effectiveness is rarely measured once added. Starch should not be exposed to high shear pumps, agitators and re-circulation loops in the make down and storage process. Starch should then be fed through low shear pumps with properly sized flow meters and adequate filtration. At a minimum, slurried and cooked starch solids, viscosity, and pH should be measured and controlled.

Mills should run a simple in-mill starch residual test to measure its effectiveness. This test will quantitatively measure free (non-adsorbed) wet end starch, including starch from the broke. This free starch should be minimized since it can lead to biological activity, foam, deposits, poor specialty chemical efficiency, etc. This test leads to an understanding of where non-adsorbed starch is coming from and to a reduction in process variability and upsets.--Kasy King, TAPP1 Editorial Board, email: [e-mail]