Adhesion of powders to metal surfaces during compaction

Publication Reference: 
Author Last Name: 
Csaba Sinka, Ahmad Ramahi and Vishal Shinde
Report Type: 
ARR - Annual Report
Research Area: 
Particle Formation
Publication Year: 
United Kingdom

The original aim and objectives of the project remained unchanged: to design a diagnostic tool to determine if a powder formulation will stick to the punch-face during tablet production.
 To establish a test methodology
 To identify the key factors
 To establish a predictive criteria

Timeline. Work on the project started effectively in August 2021 with the arrival of PhD student Ahmad Ramahi. In February 2022 PhD student Vishal Shinde joined the project. The first two objectives have been completed and work on the third objective is ongoing aiming to complete by the AGM in June 2023.

Approximately 20 characterisation techniques were employed or explored at different levels of detail as described in this report. Measurement of the % area of the punch covered by the sticking powder was selected as the main method to quantify sticking. Following regular monthly project meeting with the IFPRI advisory group, given the complexity involved in the sticking phenomena (summarised in Section 1), the focus was maintained on empirical studies to identify the relevant mechanisms for the materials of interest and on creating a database of approximately 20 powder materials (including sticking and non-sticking APIs, sticking and non-sticking excipients, powder formulations and lubricated formulations), and delve into the science of each mechanism in the follow-on proposal.

The database contains material properties including chemical information (formula, structure, molecular weight), physical characteristics (particle size distribution, density, shape, morphology of the particles, bulk density of powders), mechanical properties of particles (Young’s modulus, Poisson’s ration, yield strength), interaction properties between particles (friction coefficient between particles, surface energy), thermal properties (conductivity, heat capacity, thermal expansion coefficient) and humidity related properties (water adsorption isotherms, water activity).

The sticking behaviour of powders during single compression events is characterised considering 4 processing parameters: compaction pressure, temperature, humidity, and compaction rate. Work is ongoing, only 4 materials were characterised so far. The compression tooling used was provided by iHolland (B tooling). Long term sticking (multiple compaction events) are planned.

The deliverable the end of the 3 years is a predictive toolkit comprising of the database analysed using Principal Component Analysis to extract functional relationships between material properties, process parameters (compaction pressure and rate) and environmental conditions (temperature and RH) and finally assign a risk for sticking.

A proposal is being developed for a follow-on project to extend the database for new materials to further validate the predictive capability, establish the science base to understand the underlying mechanisms, link molecular level information to sticking behaviour and develop mitigating strategies for sticking at early stage product development. A collaboration with Professor Jerry Heng at Imperial College is proposed to cover the Chemistry/Chemical Engineering aspects.