How to Measure Cohesiveness
COHESIVENESS is the tendency of a product to cohere or stick together. The intermolecular attraction by which the elements of a body or mass of material are held together determine its cohesiveness. It is related to the internal stickiness of a product and is usually determined by measurement of the amount of force to remove an item from the product mass.
High cohesiveness may be favourable for products such as paint where easy removal of a brush from the main mass of paint needs to be a clean separation and without the tendency to extend from the surface of the mass to the brush for a considerable distance. However, low cohesiveness may be a favourable property of a product such as honey or syrup where considerable extension of the product from its main body of material is accepted.
Cohesive materials, such as ceramics, rocks and cementitious materials are important due to their wide applications in various fields of engineering. Accurate measurement of their physical behaviour is necessary for correctly forecasting the damage and failure response of these materials for their chosen application.
Cohesion of soil is an important factor of soil consistency and is the force that holds together molecules or like particles within a soil. A healthy soil has complex strength requirements. It wants to be a stable structure to support vegetation and a certain level of traffic, and protect the vast array of pores and fissures but at the same time it wants to support cultivation by the farmer, earthworks by soil fauna and the exploration of roots, water and gasses. In other words, it wants robust friability and does not want to mimic concrete. Cohesion of soil is usually measured using an Unconfined Compressive Strength Test.
Whilst Adhesion describes the bonding power to a surface, cohesion is the inner strength of a material that has to withstand external forces without breaking. So, for a pressure-sensitive adhesive, cohesion is an imperative characteristic as it is the inner bond or the degree to which it holds strongly together by itself. High cohesion means that the adhesion is especially strong, tough and stable in itself and it is therefore very resistant to tearing. That is important, for example, if adhesive tape should hold a large amount of weight stably, since the adhesive may not rip apart. The molecules must bond strongly and “hold” firmly to each other. When you consider honey, for example, whilst it might be extremely sticky its cohesion is very low.
Cohesion may be an important or undesirable property of dry powdered or granulated materials. This characteristic can be measured using a Powder Flow Analyser.
Typical properties that can be obtained from a texture analysis graph:
Consistency, Firmness, Cohesiveness, Index of Viscosity, Tailing, Stringiness, Shortness
Typical Texture Analyser graph with annotated properties of cream back extrusion test
Typical Powder Flow Analyser graphs showing region where cohesion properties are measured
Typical Probe/Fixture used for Measurement:
Cylinder Probes and Platens >>
Moderate/Large Cylinder Probe >>
Back Extrusion Rig >>
Powder Flow Analyser >>
Unconfined Yield Stress Rig >>
The above are only typical examples of cohesiveness measurement. We can, of course, design and manufacture probes or fixtures that are bespoke to your sample and its specific measurement.
Once your measurement is performed, our expertise in its graphical interpretation is unparalleled – no-one understands texture analysis like we do. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.
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