title: Assessment of surface caking of powders using the ball indentation method.
abstract: Powder caking is a ubiquitous problem, which could significantly decrease product quality and lead to economic losses. Hence it is important to know the conditions under which it occurs. The caking behaviour of three powder materials (PVP, HPC and CaHPO4) has been investigated by the ball indentation method (BIM) as affected by relative humidity (RH), temperature and time. The resistance to powder flow, as indicated by the hardness is measured by a ball indenting the powder bed surface. The surface hardness increases with increasing RH and temperature, indicating caking of the powder bed. Moreover, the temperature and RH show a coupled effect on powder caking. Irreversible caking is formed in PVP and HPC at 75% RH; the particles coalesce and the volume of powder bed is significantly reduced with time. However, the caking of CaHPO4is reversible. To examine the caking mechanism of PVP and HPC, the critical glass transition RH is determined at 25°C and 45°C. The values are 63% and 53% RH for PVP and 61% and 50% RH for HPC, respectively. The glass transition moisture content in the ball indentation experiments is comparable with that determined by the dynamic vapor sorption measurement. BIM could be a fast and effective method for the assessment of powder surface caking.
authors.affiliation: Institute of Food Science and Technology, Chinese Academy of Agricultural Science (CAAS)/Key Laboratory of Agro-Products Processing, Ministry of Agriculture, Beijing 100193, China; School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Qinqin
authors.initials: Q
authors.lastname: Chen
authors.affiliation: School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Umair
authors.initials: U
authors.lastname: Zafar
authors.affiliation: School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, UK. Electronic address: m.ghadiri@leeds.ac.uk.
authors.forename: Mojtaba
authors.initials: M
authors.lastname: Ghadiri
authors.affiliation: Institute of Food Science and Technology, Chinese Academy of Agricultural Science (CAAS)/Key Laboratory of Agro-Products Processing, Ministry of Agriculture, Beijing 100193, China.
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Bi
mesh_terms: D002626:Chemistry, Pharmaceutical / Q000379:methods*; D019245:Compressive Strength; D006244:Hardness; D006813:Humidity / Q000009:adverse effects; D010316:Particle Size; D011208:Powders / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D011208:Powders
keywords: Ball indentation; Caking; Glass transition; Hardness; Moisture sorption; Pharmaceutical powders