Ruel asks,
My question is regarding the types of starch. Between corn and tapioca, will one provide better bonding in the corrugator or are they both so similar that it makes no difference?
We are planning to experiment with tapioca starch because it is cheaper per ton/kilo, but I want to make sure we are not sacrificing quality for cost. Also relevant to this, do you know of a generic adhesive formulation of tapioca? We are more familiar with cornstarch and we have no experience with tapioca. Do they have different reaction to caustic soda, etc.
The best I can do to process your question is pass you along to one of the excellent associates my network of technical contacts. Roman Skuratowicz, Lead Industrial Application Specialist at Ingredion Inc. was happy to help out. See his comments below.
– Ralph
“We have experience with both tapioca and corn starch, in the US we are using corn starch almost exclusively but tapioca starch is being used extensively in Asia. There are no significant bonding differences between the two starches. Both starches have similar granule structure, gel temp, and similar amylose/amylopectin ratios, although tapioca has larger amylose molecular weight on average. The largest differences in corrugating adhesives are the critical caustic values and alkali sensitivity of tapioca starch, and this will vary by region, growing condition, or age of the root before it is processed.
Tapioca starch has a lower critical caustic level, meaning less caustic is required to swell the granule compared to corn starch. The simple adjustment here is to lower the amount of caustic in the formula, and that needs to realistically be done in the field with the tapioca starch being employed. I would recommend lowering caustic 10% relative to a corn starch formulation as a start, then adjusting caustic further based on the gel temp of the adhesive.
The bigger issue by far is the alkali sensitivity of tapioca starch, which as I indicated varies day to day, root to root, and by process conditions. We ran an audit of unmodified tapioca starch from our Thailand facility and saw variations of 400% daily over a two week period. As a result, many corrugators will use very low viscosity formulations so they can absorb potential swelling from the starch. Many in Asia and Australia have moved to hybrid systems like the Rapidbond mixer or more accurately no-carrier formulations. In No-carrier adhesives, all of the starch slurry is partially swollen to a fixed viscosity (caustic addition is varied), and then quenched with boric acid solution (rather than borax). These formulas are more tolerant to swings in alkali sensitivity. Another option to use existing high shear mixing equipment is to test the alkali sensitivity of incoming batches and adjust caustic level based on these values. For this I recommend an alkali sensitivity viscosity test rather than a settling test, as a settling test will take 24 hours to run. If you decide to follow this route I can assist with test methods, however the bulk of formulation work you will need to do yourself based on adhesive performance.”
– Roman
askralph 