Having demonstrated the viscosity stabilizing effect of Exilva in starch adhesives, for this third blog post in the corrugated boards application series, I will focus on the effect on glue ability and production speed.
You can find the previous posts in this series here; A way to reach prolonged stability of starch adhesives and Bring your corrugated starch adhesive robustness to a new level with Exilva MFC.
In the production of corrugated boards, a typical bottleneck can be the ability to glue efficiently on complex and heavy paper qualities, typically at the double backer station. In several factory trials, the effect of Exilva, as an additive to current adhesive solutions, on gluing of these complex qualities was evaluated. These trials were done by firstly optimizing the corrugator settings at existing recipes, secondly by increasing to maximum possible speed, and finally, change to the same recipe with Exilva added. Three different corrugators participated with a combination of Stein-Hall, Minocar, native wheat and corn starch. For these quality reference cases where the glue was the bottleneck, speed improvements of 21 to 45% were achieved with Exilva (Table 1).
Table 1. Increased productivity from improved glue characteristics.
|Quality reference cases||Paper combinations||Increase in speed with Exilva (%)|
|Quality BC I||250K/110SC/180EK/110SC/250K||+ 33%|
|Quality BC II||300K/115HP/90R/125HP/300K||+ 45%|
|Quality BC III||115R/115R/90R/90R/115R||+ 21%|
|Quality Heavy White C||170 full white/150SC/180EK||+ 30%|
The Stein-Hall native wheat glues used in the trials for qualities BC-flutes I and Heavy white C-flute (Table 1), are given in Table 2. The new glue with Exilva, is made by adding 0.8% w/w Exilva 01-V relative to the overall weight of the formulation (corresponding to 0.08% w/w microfibrillated cellulose), to the primary portion (carrier) of the reference glue recipe, after the dosing of caustic soda (Table 2).
Table 2. Example of an Exilva recipe for productivity enhancement.
|Ingredients||Weight||Reference glue||New glue with Exilva||% of total|
|Primary water 37°C||kg||520||520||39.5|
|Primary starch wheat kg||kg||40||40||3.0|
|Caustic soda (31%)||kg||12||12||0.91|
|Reaction time (stirring)||sec||500||500|
|Exilva 01-V (10%)||kg||0||10||0.76|
|Reaction time (stirring)||sec||500||500|
|Boron Fullbor 6364||kg||1||1||0.08|
|Secondary starch wheat||kg||320||320||24.3|
|Boron Fullbor 6364||kg||2||2||0.15|
|End reaction time (stirring) +/- 450||sec||650||650|
|End viscosity||lory sec.||37||40|
|Dry solids CB||%||27.6||27.4|
|Dry solids abs||%||24.7||24.6|
Both glues have the same gel point of 58°C, since Exilva does not affect the caustic soda concentration of the glue. The addition of Exilva increases somewhat the viscosity of the glue, demonstrating the fibrils network formation which improves the glue stability. Moreover, upon increasing shear rate, the glue comprising Exilva is more shear-thinning, providing the similar viscosity during application (Figure 1). Thus, the reference and new Exilva glues were used for both Single Facer and Double Backer, and were run with the same corrugator settings on a combined BHS and Fosber corrugator of 2.8 meters width.
Figure 1.Flow curves, showing viscosity as function of shear rate, for the Stein-Hall wheat starch reference glue (blue), and the similar glue with 0.8% Exilva 01-V (green).
Exilva can be used in all glue processes and with different kinds of starches, including one bag mixes (OBM). However, any potential improvement must be documented by running Exilva trials measured against its benchmark, as every corrugator is quite different. Until now, the Exilva glue has allowed users to increase speed until another bottleneck came up, for example take off from the stacker or the order length.
The Stein-Hall native wheat Exilva glue given in Table 2 has currently been used in continuous production for more than one year, at the trial factory. The productivity, both at the corrugator as well as through converting, has increased due to reduced warp, better gluing and increased corrugator speed on the complex qualities.
The strength of the bonding and the impact of the Exilva cellulose fibrils network on the boards quality, I will demonstrate in the following blog post; and I can’t wait to share those numbers.
Are you eager to try as well? Get your free sample of Exilva here:
Synnøve Holtan has worked with microfibrillated cellulose MFC since 2005 and has developed an in-depth understanding of the product characteristics, as well as production processes and application innovation. As a senior scientist at Borregaard she focuses on the analyses and performance of Exilva in industrial applications, such as coatings and adhesives. Synnøve has a PhD in biopolymer chemistry from the Norwegian University of Science and Technology.
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