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Bridging the gap between usually incompatible ingredients, mineral oils hold the key to new and more flexible formulations for hot melt adhesives.
"We have shown that it is possible to use mineral oil as a compatibilizer between new metallocene-based polyolefins and resins derived from natural resources,” says Nynas’ polymer specialist Dr Peter Kaali.
Normally incompatible in formulations, both these ingredients can offer significant cost-advantages to producers of hot melt adhesives. Naturally derived resins are typically less expensive to use as a tackifier than alternative hydrocarbon resins, partly because their production is based on renewable feedstock and offers a higher supply security.
Unfortunately, for incompatibility reasons it is currently not possible to combine the use of such resins with metallocene polyolefins (mPOs), which are much easier to manufacture than traditional polymers, with the catalyst metallocene being hailed as revolutionary for the polymer industry.
Together with his Nynas colleagues, Peter Kaali set up a comparative study to explore the potential of using naphthenic oil to enable compatible mixtures, paving the way for more flexible hot melt formulations that are not exposed to feed stock shortages.
“We found that the most polar oil performed best. This makes sense as naturally based resins are polar materials and in hot melts, usually the resin is dissolved in the oil. The theory of ‘like dissolves like’ is very much applicable here.” explains Kaali.
However, for final formulations including polymers, results were slightly different. Peel performance testing of hot melt formulations revealed that the polarity of the oil is not the only determining factor for compatibility between natural resins and mPOs.
“We need to investigate this further, but our initial results are very promising. I think there is a huge potential for making new, more flexible and cost-effective hot melt formulations with mineral oils, natural resins and mPOs.”
Dr Peter Kaali
Technical Advisor, Chemical Industry, Nynas Naphthenics, is a materials engineer holding a PhD in Polymer Technology. He joined Nynas in 2012.
Proving a point
Rheology as well as cloud point studies were used to examine the oil/resin and resin/polymer compatibility for a variety of tackifiers and oils with different characteristics. In Figure 1, rheological data show how the oil is able to make normally incompatible blends compatible.
Figure 2 illustrates how although formulations with hydrocarbon resin showed better overall peel strength, the results are comparable, and some of the alternative resin formulations displayed an improved peel strength on glass and polyethylene surfaces.
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