Over the course of the last ten years I have had the opportunity to visit many paper mills throughout Europe, South America and elsewhere. One of the cost effective practices that European mills enjoy over many North American mills is enzyme conversion of their size press starch.
The benefits of using enzyme converted starch at the size press are:
- The mill can tailor the viscosity and solids of the size press starch to their unique needs for grade structure and runnability.
- Starch costs are minimized by using lower cost unmodified starches.
- Additionally, by converting on-site, the mill retains a great deal of flexibility in purchas-ing the most cost-advantaged starch, whether wheat, maize, potato or other.
By comparison, most mills in North America have come to rely on preconverted starches: hydroxyethylated, acetylated, and oxidized, primarily. These have the advantage of simpler cooking preparation, a certain degree of enhanced film flexibility, and less tendency for setback and amylose crystallization… but at the cost of higher starch prices and limitation to maize starch, in most cases.
Especially for large volume mills producing commodity printing grades or brown board mills that produce to strength targets, enzyme conversion of unmodified starch is a logical way to lower pur-chasing costs and retain flexibility on the machine. Internal strength, surface strength, and basis weight can all be flexibly managed as targets and raw material input costs change.
Further, as OCC quality deteriorates and mill water discharge volumes decline, developing strength at the wet end becomes ever more challenging. Cost effective and flexible use of starch at the size press is a tool to optimize in an environment of rising costs and resource limitations.