The Emptying Behaviour of Highly Viscous Liquids. Part II: Development of Test Methods and Evaluation of Untreated and Coated Films

Abstract

Liquid food products stick to solid surfaces. This problem occurs in all supply chain steps from production to recycling. Although the basic problem has been known for a long time, the parameters influencing the interfacial adhesion have not been clarified yet. Here, two methods (product depletion test and tack test) to evaluate the adhesion of highly viscous liquids to solid surfaces have been developed. The product depletion test allows the assessment of the residue amounts and covered surface areas during the gravity-driven flow on an inclined plane. The tack test is conducted by filling the gap between two parallelly mounted, horizontally oriented plates with a liquid product and measuring the normal force while separating the plates by pulling off the upper plate under defined conditions. The influence of the experimental parameters on the maximum normal force (F max ) could be shown. While the correlation between the pull off velocity of the upper plate and F max follows a power law, the dependency between the gap size and F max follows an exponential function. Although no significant correlation between F max or the work of adhesion (W a ) and the solid's properties could be identified, a correlation between F max and W a was observed. As shown by product depletion with ketchup, although the surface coverage is only slightly influenced by the packaging material, the opposite is the case for the covered surface area which, therefore, determines the residue amounts. For some coated samples a large residue reduction was observed.

Review on the Processing and Properties of Polymer Nanocomposites and Nanocoatings and Their Applications in the Packaging, Automotive and Solar Energy Fields

“…The technology relies on non-wetting surface containing micro/nanotextures impregnated with lubricating liquids, which have been shown to exhibit superior non-wetting performance compared to superhydrophobic surfaces based on stable air-liquid interfaces [ 28 , 299 ]. For determination and comparison of the emptying behaviour, depletion or tack test methods can be applied for evaluation [ 300 ].…”

Amount of Fill Product Residues in Plastic Packagings for Recycling

“…The insufficient emptying behaviour of packagings is a reason for this occurrence [29][30][31][32][33][34][35]. Food residues adhere to packaging surfaces [29,31,32,[34][35][36][37][38][39]. Cragnell et al reported that "Approximately 5-10% of the fermented milk remains in the packages upon pouring [.…”

“…Several surface modifications and coatings have been developed to improve the emptying behaviour of packaging [29,35,[43][44][45][46][47]. However, Müller et al claimed that "[.…”