(76c) Las Acid Bridges in Detergent Granulation:a Comparison of Adhesion Force and Wetting Behaviour of Different Neutralised States

LAS acid is one of the largest used surfactants in industrial detergent granulation processes. Industries are always trying to improve their products by changing the formulations and operating parameters, therefore understanding the importance of each variable and predicting the behaviour of colliding binder-coated primary particles is necessary to model granulation processes satisfactorily. Information about the early stage of granulation, known as ?nucleation?, can be derived from the analysis of the individual strengths of liquid bridges holding two particles together. The challenge is to relate what is observed at the solid-solid and solid-liquid interfaces to multi-particle granules.

A novel micro-manipulator system, called the Micro Force Balance (MFB), has been developed and used to directly observe the interaction behaviour of a partially neutralised Linear Alkylbenzene Sulphonic acid (Las) binder with glass particles. The partially neutralised samples were prepared utilising the principle of acid-base neutralization reactions between LAS and Na2CO3 to form the salt, LAS-Na, along with some water. The aim of the experimental study reported here is to investigate whether LAS acid phase changes influence the adhesive strength of individual liquid bridges.

The MFB consists of a micromanipulation stage fitted with an optical microscope. The electronic controls are run by Lab-view software and an image analyser system is used to acquire and process images taken during the bridge breakage.

The Las reactive binders wettability have been investigated through direct observation and contact angle measurements. The higher the degree of neutralisation, the lower the tendency of the liquid to wet the particle. However, changes in temperature and humidity could also affect the binder's wettability. A comparison of the results for the different neutralized liquids show how the force exerted by a liquid bridge was largely influenced by the wetting behavior of the liquid on the particles. Low Neutralized binders that wetted both particles well produced the highest forces. The effects of changing the surface energy of the particles have been studied using glass particles silanised to different degrees of hydrophobicity.

Further work is now underway to study the effects of temperature and humidity on the binders. In order to do this, an environmental chamber will be fitted to the MFB, the temperature will be changed with a low rate electronically controlled heater and the humidity will be kept constant with salt solutions. This will give us a better idea of how to control the detergent granulation process once the relationship between acid neutralisation and wetting behaviour is known.