Triboelectrification of pharmaceutical powders by particle impact

Abstract

Pharmaceutical powders are very prone to electrostatic charging by colliding and sliding contacts with walls and other particles. In pharmaceutical formulation processes, particle charging is often a nuisance and can cause problems in the manufacture of products, such as affecting powder flow, and reducing fill and dose uniformity. For a fundamental understanding of the powder triboelectrification, it is essential to study charge transfer due to a single contact of a particle with a target plane under well-defined physical, mechanical and electrical conditions. In this study, charge transfer due to a single impact of a particle against a stainless steel target was measured for alpha-lactose monohydrate, aspirin, sugar granules and ethylcellulose. The amount of transferred charge is expressed as a function of impact velocity and impact angle as well as the initial charge. The maximum contact area during impact between a particle and a target plane is estimated by an elastic-plastic deformation model. It is found that the transferred charge is a linear function of the contact area. For a given material, there is an initial particle charge for which no charge transfer occurs due to impact. This is found to be independent of impact velocity and angle, and is hence viewed as a characteristic property, which is related to the contact potential difference and tribo-electric series of the sample powders.

Contact electrification and charge distribution on elongated particles in a vibrating container

“…These phenomena agree with the experimental observation and theoretical analysis by Matsuyama et al (2003), in which the non-uniform charge distribution on the surfaces of particles can influence the charge accumulation process and lead to different charging coefficients. The values of transferred charges on particles in the current study are in the range of 10 -13 to 10 -11 C, which is comparable to the typical charge on pharmaceutical particles induced by impact charging (Watanabe et al, 2007). Under realistic conditions, the charge should be distributed on the surface of a particle and may be under relaxation and dissipation, especially for conductors.…”

“…where S is the maximum contact area during the collision, k is the charging constant (Matsusaka et al, 2000;Watanabe et al, 2007) and is of the order of 10 -4 C·m -2 ·V -1 . After each collision, the charge on materials i and j will hence become q i -Δq and q j +Δq, respectively.…”

“…The material properties of the primary spheres and the container are given in Table 2. The particles are assumed to be a typical pharmaceutical excipient particles (Watanabe et al, 2007;Nwose et al, 2012) and the container is assumed as stainless steel. The friction coefficients between particles and between the particle and the wall are set to 0.3.…”

“…Watanabe et al (2007) investigated the contact electrification of various pharmaceutical particles impacting a tilted steel surface and found that, assuming the particle is spherical, the transferred charge is generally linearly proportional to the estimated contact area. However, ethlycellulose particles developed a different transferred charge from that calculated by assuming a spherical particle shape.…”

Numerical analysis of contact electrification of non-spherical particles in a rotating drum

“…where S m is the maximum contact area during the collision, k s is the charging constant during contact electrification and is of the order of 10 -4 C·m -2 ·V -1 [32][33][34]. During a collision, the charge will be transferred from material i to material j.…”