Grease-proof, biodegradable polymer coating

A great deal of RandD work is underway to find replacments for the perfluoro compounds used to impregnate paper and cardboard packaging materials for the retail of grease and oil containing products.

Such packaging systems are mostly used for dry animal feeds, baked products and chocolate.

In a project funded by the Fachagentur fur Nachwachsende Rohstoffe e.V., the Fraunhofer Institute for Process Engineering and Packaging has now developed a grease barrier based on starch.

Starch coating - an alternative to perfluorinated compounds Cardboard packaging systems are made grease-proof for "cosmetic" reasons.

For some products, a packaging with adequate grease-proof properties can be manufactured by coating the reverse side of the cardboard with polyethylene, preferably HDPE.

If, however, a product requires a very high barrier to grease, several layers of cardboard are impregnated with perfluorinated compounds.

These perfluorinated compounds are problematic.

They can, for example, enter the environment when the cardboard is recycled and concentrate there due to their inert character.

Relevant fluorine compounds have already been detected in human serum.

Studies of Butenhoff et al.

have shown that the half-life in human serum is 4.4 years.

Which starch is suitable? In collaboration with the Fraunhofer Institute for Applied Polymer Research (IAP), the Fraunhofer IVV evaluated the suitability of hydroxypropylated (HP) starches to act as grease barriers.

HP starches possess very good film formation properties and are hence ideal for use as coatings.

The Fraunhofer scientists coated two commercially available types of cardboard which were made available by two of our industrial project partners, VG Nicolaus and Moritz J.

Weig and Co KG.

The studies showed that in principle grease barriers can be achieved using hydroxypropylated starches from tubers, cereals and leguminous plants.

The starches with higher amylose content, e.g amylomaize starch and wrinkled pea starch gave the best results.

Most of the starches were modified by Emsland-Starke .

Environmentally and economically attractive The weight of starch that is applied has a key influence on the effectiveness of the grease barrier and the cost.

The starch derivatives that were developed provide a very effective grease barrier when applied in amounts upwards of ca.

20 g/m 2.

This barrier remained fully intact when the packaging was subjected to extreme climatic conditions (60C and 60% relative humidity) for a period of 5 days.

The best results were obtained using a starch with a high amylose content.

The resulting grease barriers had the highest resistance to mechanical loads, a key prerequisite for the packing process.

The processing of this material has already been demonstrated using a pilot plant.

A coating plant with a slot die was selected for this trial.

A practical test using an original filling demonstrated that corrugated and folded samples possessed as good quality a barrier as commercially available impregnated products.

The new, alternative polymer coating is biodegradable and compatible with paper recycling technology.

From a cost point of view, it is as favorable as a polyethylene coating.

Focus on maximizing the grease barrier The Fraunhofer IVV is now focusing its efforts on developing cardboard packaging systems for dry pet foods that contain high levels of surface grease.

Packaging for pet foods requires a maximum grease barrier.

Another attractive aspect is that the market for pet foods is growing at a very high rate.

The use of starch as a grease barrier has been patented by the Fraunhofer IVV.

The next phase: the application technology In order to commercial the results as quickly as possible, the next development phase will involve further optimization of the starch application technology.

Industrial partners wishing to participate in this work are welcome to contact the Fraunhofer IVV.

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