Paper Technology International 2024 - Journal - Page 77
PAPERTECHNOLOGYINTERNATIONAL
U
Unlocking the bene昀椀ts of low
cationic starches in surface sizing
Andreas Voigt, Technical Account Manager for Cargill Paper & Board
INTRODUCTION:
In the ever-evolving paper manufacturing industry, the quest for improved ef昀椀ciency and sustainability continues to drive innovation.
One such development is the use of low cationic starches for surface sizing applications. Unlike their wet-end counterparts, cationic
starches designed for surface sizing have fewer cationic moieties in their molecular structure. This adjustment allows for optimal af昀椀nity with
cellulose 昀椀bres and 昀椀llers, ensuring great self-retention of starch. Originally developed to address the challenge of starch load in 昀椀ne paper
manufacturer ef昀氀uents, these cationic starches may offer a multitude of bene昀椀ts for modern mills.
Surface sizing of 昀椀ne paper is primarily used to increase
the strength of the paper surface; it improves wet resistance and
enhances printability by binding particles, such as 昀椀bres and
pigments, to the paper surface.
CFlex™ and CSize™ are our standard starch solutions
for surface sizing. They are traditionally hydrolysed via an enzymatic
conversion process at the paper mill. Our new low cationic grades
CiSize™ are modi昀椀ed starches that do not require enzymatic
conversion. They bring additional value, such as a reduction of the
ef昀氀uent load, and improved surface strength at smooth runnability of
the machine.
There are several bene昀椀ts to using cationic starches for
surface sizing applications:
1. Reduction of Ef昀氀uent Load
When comparing the chemical oxygen demand (COD)
of a 昀椀ltrate from repulped, surface-sized paper, from our trials is
evident that the COD value linearly increases with the add-on of
non-ionic starches, such as enzymatically converted native starches.
However, when cationic starches are utilized, the COD load of the
昀椀ltrate remains signi昀椀cantly lower (Graph 1). With an industrial
trial we also proved that the Biochemical Oxygen Demand (BOD)
measured during 5 days followed a similar trend as COD. BOD
was signi昀椀cantly reduced when using low cationic starch instead
of native starch (Graph 2). The strong interaction between the
cationic moieties of the starch and the anionic moieties on 昀椀bre
and 昀椀ller surfaces leads to more substantial ionic bonds, which are
better maintained upon repulping. Consequently, the use of cationic
starches results in a remarkable reduction in ef昀氀uent load, making it
a potential valuable solution for 昀椀ne paper manufacturers seeking to
comply with certain environmental regulations.
2. Improved Self-Retention and Runnability
Surface sizing with low cationic starches offers substantial
advantages in terms of self-retention. It has been observed that low
cationic starch tends to achieve a self-retention rate of 90% when
paper is manufactured from 100% surface sized broke, while nonionic native starches only achieve a retention rate of 30% (Graph
3 overleaf). This increased self-retention ensures that a sizeable
portion of starch is retained within the paper, reducing losses,
contributing to strength and minimizing the need for additional 昀椀bre
replacement to maintain consistent grammage.
Furthermore, the enhanced binding power of low cationic
starches, derived from their strong ionic interactions, contributes to
improved runnability, allowing for higher molecular weights without
compromising machine performance.
Graph 1: In昀氀uence of starch content on COD after re-pulping.
Graph 2: Lowering of ef昀氀uent BOD by a cationic starch in
surface sizing.
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