Many industrial
processes involve powders in some form when making products, and the behavior
of the powders processed is impacted by the adhesion of the individual particles
which comprise it. This adhesion behavior, in turn, is critically influenced by
the complementarity between the topography of a surface and the shape and
roughness of the particles that adhere to that surface. Problems such as poor
flowability, dust hazards, and equipment wear arise due to uncontrolled
particle adhesion and can lead to production challenges. Computational models
have been developed to predict the behavior of highly idealized powders (i.e.,
powders comprised of simple geometries such as spheres) under various processes
but are limited in their ability to model and optimize the manufacturing and
handling of powders comprised of many complex particles. This work focuses on
further developing an experimental and modeling framework, called the Enhanced
Centrifuge Method (ECM), that maps particle-scale and surface properties onto
experimentally-validated ‘effective’ adhesion distributions that describe the
adhesion between particles in powders. These distributions represent an
engineering approach that allows powders comprised of particles of complex
shape and roughness, which are challenging to model, to be described as if they
were perfect, smooth spheres, which are comparatively simple to model. The
complexity associated with the shape and size distributions of the individual
particles is captured by the ‘effective’ adhesion parameters. These ‘effective’
adhesion parameter distributions provide a quantitative guide as to how the
specific particle properties are interacting with the surface topography which
directly impacts the overall powder adhesion. The initial framework of the ECM
is constructed around characterizing the van der Waals adhesion of silica and
polystyrene powders. The impact of the surface topography and the particle
properties of each of the powders is captured in ‘effective’ Hamaker constant
distributions. These distributions provide a quantitative guide for
specifically how the particles interact with the surface topography based on
the respective scales of the particle and surface features. The ECM framework
is further adapted here to investigate the effects of topographical changes of
stainless steel due to polishing on the adhesion properties of three different
pharmaceutical powders to the stainless steel. In this adaptation of the ECM
framework, the force of adhesion was described by modifying the Johnson,
Kendall, and Roberts (JKR) model describing elastic-like particle contact to a
flat plate. Within the modified JKR adhesion description, the work of adhesion
is tuned to be an ‘effective’ work of adhesion parameter. These size-dependent
‘effective’ work of adhesion distributions provide a quantifiable measure of
the change in the powder and surface adhesion that reflects the size, shape,
and topographical features on the powder and surface with which the powder
interacts. To investigate environmental effects on the adhesion properties, the
ECM framework is also extended to characterize the effect humidity has on
altering surface and particle interactions of the three pharmaceutical powders
to stainless steel. In addition to the work with the pharmaceutical powders,
the investigation of the effect of humidity on the powder’s adhesion includes a
study of the influence of water on the interactions between silica particles and
a silica substrate. In all cases, the ‘effective’ adhesion force distributions
developed through the ECM provide the ability to quickly determine
quantitatively how environmental and process conditions alter particle and
surface properties, and overall powder behavior.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/17118860 |
| Date | 03 December 2021 |
| Creators | Caralyn A Stevenson (11786483) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/BRINGING_PARTICLE_SCALE_PROPERTIES_INTO_DESCRIPTIONS_OF_POWDER_BEHAVIOR_VIA_THE_ENHANCED_CENTRIFUGE_METHOD/17118860 |
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