Evaluation of the Mechanical Resistance of a Powder‐powder Coating by Modulated Dry Feed Particle Size Analysis

Abstract

Dry powder coating is a powerful method for modifying the surface properties of particles whilst retaining their essential bulk properties. The coating of a host powder by guest particles can be achieved via different means ranging from simple stirring together of the two components, to high energy impact coating in devices such as a Nara Hybridizer or Turbula Mixer. The quality of the powder coating resulting from such methods is an important parameter, which depends both on the force of the mechanical action used, and also the physico‐chemical interactions between the host and guest particles. Here, a method for evaluating the strength of host‐guest interactions based on particle size analysis using a standard Malvern Mastersizer with dry powder feed is presented. Basically, the liberation of small guest particles from host particles can be achieved by increasing the air pressure, and the presence of liberated fine particles mixed with guest particles can be detected from differences in volume and number distributions. Complementary examination is undertaken using an environmental scanning electron microscope (ESEM). This technique has been used to evaluate the interaction strength of a coating of hydrophobic magnesium stearate on a herbal extract (Harpagophytum). It is shown that effective coating can be achieved by three different means: simple stirring, a Turbula Mixer and by using a Nara Hybridizer. The respective strength of the coatings is greater with increasing mechanical force used for the process. The method is proposed as a simple means of evaluating powder‐powder coating processes.

Passivation of High-Surface-Energy Sites of Milled Ibuprofen Crystals via Dry Coating for Reduced Cohesion and Improved Flowability

“…It has also been used successfully as a means to assess the extent and efficacy of fine particle coatings in a dry powder process. 47 In general, the dispersibility of a powder can be derived by comparing the slope of the plot of the particle size with respect to dispersion pressure, where smaller absolute slopes indicate better dispersibility and larger ones indicate worse dispersibility. 48 The pressure titrations of the 5 :m uncoated and dry-coated ibuprofen samples are shown in Figure 3 as an example, because finest powders are expected to be more cohesive and agglomerated.…”

Modeling the mean interaction forces between powder particles. Application to silica gel–magnesium stearate mixtures

“…[1]Yoshihara I., Pieper W., Hybridization -Technology for surface modification of powders without binders, Swiss Pharma, 21,6,1999 [2]Pfeffer R., Dave R. N., Dongguang W., Ramlakhan, M., Synthesis of engineered particulates with tailored properties using dry particle coating, Powder Technology, 117, 40-67, 2001…”

“…[19] Munjumbar [20] or more recently by Vilela and al. [21]. One of the important points that appeared in these works is the characterisation of the coated product in terms of quantity and quality of the coating.…”

Production of composite particles using an innovative continuous dry coating process derived from extrusion

“…The method can be qualitative and comparative concerning the coating strength. Indeed, Vilela et al [32] demonstrated that an increase of dispersion pressure can lead to removal of guest particles on the host particles surface. In this work, two levels of dispersion pressures were used: 0.5 and 3.5 bar.…”