Novel Analysis Techniques for Particulate ProductsG

Lead Research Organisation: De Montfort University
Department Name: School of Pharmacy

Abstract

Many materials in common use come in particulate form, including food, pharmaceuticals, coatings, pigments and fertilizers. A frequent quality control problem with such materials is their tendency to form unwanted, lumpy agglomerates from a phenomenon known as CAKING. Over the years this has been combated by using chemicals, known as anti-caking agents. However, new materials on the market are now being produced to higher customer specifications that regard such additional ingredients as contamination. This issue, combined with the storage and transportation at more extreme conditions and the trend towards powders being more concentrated, means that a more systematic study into combatting caking is required. Previous studies looked at caking on a bulk scale, but this study will examine what happens on the particle scale by using Atomic Force Microscopy (AFM). AFM can map out surfaces on the nanoscale and can also be used to measure the mechanical hardness of particles. The strength of bonds between caked particles can also be measured using AFM and this value can be used to estimate the strength of lumps formed during the caking process. By gaining a greater understanding of the mechanisms of caking, companies will be able to to produce better powdered products that should be more resistant to caking, as well as formulations that would normally be incompatible with anti-caking agents.
 
Description This project aimed to examine particle caking by examining how changes in temperature and humidity could affect the hardness and stickiness of particle surfaces and how they might form bridges. This was done using an Atomic Force Microscope (AFM), which can measure surface features non-destructively. This meant that images of areas of particle surfaces could be measured again and again under different conditions. Several types of complex powdered materials were examined, including powdered milk formulations and washing powder formulations. The following findings were obtained:
1. The amount of moisture absorbed or desorbed at the surface of the particle under a range of relative humidities at 20-40?C was measured. This was done using an IGAsorp based at Unilever Research Port Sunlight and measured the change in mass of a known amount of powder in a controlled chamber that very precisely changed the temperature and relative humidity. As expected the solids absorbed most moisture at high relative humidities and temperatures.
2. The effect of temperature and humidity on the surface properties of particles was studied intensively using AFM. Many of these particles were made up of complex mixtures, such as spray dried milk powder and washing powder. Humidity had a considerable effect, causing actual flow of material and the swelling of large particles to absorb smaller ones. "Wrinkly" particles also showed a greater tendency to cake than smooth spherical ones, presumably as there was a greater surface area for the mechanisms to take place.
3. The stickiness and hardness of these particles was also examined using the AFM, by indenting the particle surface and also using various modes of AFM to measure visco-elastic properties and friction. Again high humidity and temperature also softened the surface of the particles, but the relationship with ingredients was complex. Migration of different components on the surface of the particle was observed, as well as crystallisation. Grant proposals are being prepared to ensure this is studied further.
4. AFM was also used to measure the formation of solid bridges between particles and assess their properties. With multi-component particles, the bridges had very different properties from the particles, presumably because of increased crystallinity and different proportions of ingredients. Amorphous spray-dried particles were also connected by crystalline bridges.
5. Uniaxial compression tests were also performed on a number of powders to analyse the mechanisms of compaction and compare them with AFM data. This analysis is still ongoing and will be the subject of publications in the near future.
Exploitation Route The findings can be transferred to other sectors, for instance pharmaceutical formulation. The issue of stability and powder handling is significant in this sector.
Sectors Agriculture, Food and Drink,Chemicals,Construction,Education,Healthcare,Pharmaceuticals and Medical Biotechnology

 
Description East Midlands Development Agency
Amount £55,000 (GBP)
Funding ID FDINET008 
Organisation East Midlands Development Agency 
Sector Public
Country United Kingdom
Start 01/2009 
End 12/2009