Establishment of a repeatable test procedure for measuring adhesion strength of particulates in contact with surfaces

Ermis, Ertan (2011) Establishment of a repeatable test procedure for measuring adhesion strength of particulates in contact with surfaces. PhD thesis, University of Greenwich.

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Abstract

The firm adhesion of flavouring particles onto snack surfaces during coating processes is a major concern in the snack production industry. Detachment of flavouring powders from products during handling and production stages can lead to poor appearance and reduced taste of the product as well as substantial financial losses for the industry, in terms of variable flavour performance and extended cleaning down time of fugitive particle build-up on process equipment. Understanding the adhesion strength of applied bulk particulates used for flavouring formulations will help analysts to evaluate the efficiency of coating processes and potentially enable them to assess the adhesion strength of newly formulated flavouring powder prior to commitment to full scale plant trials.

Meeting this object has required the development of an over-arching review of the adhesion mechanisms as a primary step. Based on this overview to the work of previous researchers, technological gaps and promising techniques have been identified for further research and development. A prototype of a novel adhesion tester called an Impact Adhesion Tester (IAT) has been designed and constructed. The development of the overall tester design is presented, and details of its parts and the resulting tester are discussed.

The IAT and its experimental procedure were primarily designed and implemented for use in the snack industry, in particular, for the measurement and evaluation of the key factors affecting the adhesion behaviour of flavour powder onto snack surfaces qualitatively and quantitatively. This measurement can indicate the percent flavour powder loss within production stages (from coating to packing) and in package.

The instrument has been evaluated using different materials and substrates subjected to different coating conditions such as rotational speed of the drum, retention time in drum, the amount of surface oil and the amount of powder applied. By plotting the detachment versus impact force, the difference has been obtained between adhesion strength of different flavouring powders (which is a strong function of particle size, particle shape, particle density and surface oil content of the snack). In addition to the above work, ultra-centrifuge method was used as a reference for comparison.

The research work conducted using IAT on flavouring powders has proved the importance of particle adhesion strength and that the particle adhesion strength can reflect the changes in particle loss, based on particle characteristics as well as process conditions during snack production. It proved that bench size IAT would be a useful tester to measure adhesion strength of particles. The results obtained from experiments have confirmed that the tester may be able to usefully determine the variations between different powder materials. However the tester needs to be further evaluated by industrialists and researchers before possible use or commercialisation.

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