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Keywords:

  • fine powders;
  • cohesion;
  • fluidization;
  • agglomeration;
  • van der Waals force;
  • powder compaction;
  • contact plasticity

Abstract

The adhesion force between previously consolidated polymer particles is affected by the use of additives that modify relevant surface parameters, such as the contact hardness and size of asperities at contact. Both the size of silica nanoparticles uniformly coating the particle surfaces, and their surface coverage have been investigated. The effects of the presence of other additives, such as wax and cross-linking polymer were tested. The experimental results are compared with predictions from theoretical models. Our measurements are shown to be in semi-quantitative agreement with the theoretical expectations built on the hypothesis of plastic flow of interparticle contacts. Moreover, the results indicate that the aggregation of individual particles in the fluidlike regime must play a relevant role in how bulk stresses distribute among interparticle contacts when the powder transits to the solid state. This work highlights the need of considering particle aggregation and contact plasticity as central features, mostly obviated so far, to deal with real problems on cohesive powders. © 2006 American Institute of Chemical Engineers AIChE J, 2006