By Jaakko Ekman, Sr. Research Scientist, Kemira Oyj, Matti Hietaniemi, Sr. Research Scientist, Kemira Oyj, Marko Kolari, Sr. Principal Scientist, Kemira Oyj, Mark Nelson, Marketing Manager, Kemira Chemicals, Inc., Ken Keegan, Sr. Product Line Manager, Kemira Chemicals, Inc. ABSTRACT The fibre stream raw materials utilised to manufacture recycled paper and board contain a significant amount of starch. Due to microbial activity, process waters in paper mills utilising recycled fibre usually contain high amounts of starch-degrading amylase enzymes. This usually results in degradation of most of the starch before recycled fibre enters the paper machine, thus potentially increasing COD in waste waters, pH reductions, and higher conductivity due to calcium carbonate dissolution. In this paper we present a new concept for improving starch reuse and the strength properties of packaging board. It consists of preventing starch degradation in recycled fibre and broke by utilising a specific amylase enzyme inhibitor, coupled with a novel retention system that ultimately improves starch retention into the end product. Amylase enzyme inhibitor, as such or combined with biocides, was efficient in prevention of starch degradation. This was shown both in lab studies and in mill scale trials. Additionally, retention and strength experiments showed that a combination of coagulant, micro-particle and a new high molecular weight polymer IMPROVING STARCH REUSE WORLD PULP&PAPER 62 Novel Starch Saving Program Improves Sustainability in Board Manufacturing through the Reuse of Recycled Fibre Starch improved starch retention and drainage. INTRODUCTION Recycled paper and board contains a significant amount of starch. Process waters in mills utilising recycled fibre (RCF) usually contain high amounts of bacteria and other microbes which can produce starch degrading amylase enzymes. This enzyme is capable of breaking down starch molecular chains into glucose units. After this process, bacteria can utilise free sugars and produce organic acids (such as acetic and propionic acid) and gases (CO2, H2) in the fermentation process. This can lead to pH drop, calcium dissolution and even production of dangerous concentrations of gases. Amylase activity usually leads to the degradation of most of the starch before recycled fibre enters a paper machine. Altogether, yield loss is about 4% of the recycled fibre raw material because starch cannot be reused (REF). This increases chemical oxygen demand (COD) in the process and waste water. Starch degradation can be prevented by using abnormal amounts of biocides, but this approach is not cost efficient, because low microbial numbers are required to be maintained continuously throughout the process. In addition, good strength properties are generally difficult to achieve using recycled fibre material because of the high ash content of the raw material. Research was divided into two parts: prevention of starch degradation and improved retention and strength. Prevention of starch degradation was studied in authentic paper making process water, and amylase enzyme inhibitor products were also trialed in board machines using recycled fibre. The full-scale trials were followed by measuring soluble starch from the RCF towers and by analysing mill production data. It was shown that this novel approach, where amylase enzyme inhibitors were used against free amylase enzymes, was efficient in starch protection. Retention and strength properties were studied using dynamic drainage analyser (DDA) and handsheet tests. It was shown that a novel polymer developed by Kemira allows recycled starch retention, strength, and drainage increase – all simultaneously. In this paper we present a unique and innovative chemical concept. Starch degradation can be prevented by using abnormal amounts of biocides, but this approach is not cost efficient