Experimental study on single droplet drying of hydroxypropylated pea starch: Drying kinetics and particle morphology Imen Gouaou #1 , Samira Shamaei *2 , Koutchoukali Mohamed Salah #3 , Bouhelassa Mohamed #4 , Evangelos Tsotsas +5 , Abdolreza Kharaghani +6 # Department of Process Engineering UniversityConstantine3, Ali Mendjeli, Constantine, Algeria 1 imen.gaou@hotmail.fr 3 saloh_k@hotmail.fr 4 mbouhela@hotmail.com * Department of Food Science and Technology, University of Tabriz, Tabriz, Iran 2 samira.shamaei@gmail.com + Thermal Process Engineering, Otto von Guericke University, P.O. 4120, 39106 Magdeburg, Germany 5 evangelos.tsotsas@ovgu.de 6 abdolreza.kharaghani@ovgu.de Abstract— Spray drying is widely used nowadays in the pharmaceutical and food industries to produce fine dry powders from a liquid solution by rapidly drying with a hot gas. The produced powders can be directly attached to larger particles by cohesive forces in order to improve the surface properties and/or alter the functionality of these larger particles, such as in the dry powder coating technology. For the efficient production of spray-dried fine powders it is crucial to find a suitable operating condition and an appropriate initial composition of the solution. In this paper, a single droplet drying suspension device is employed to investigate the drying process of hydroxypropylated pea starch particles. Using this device the influence of the drying air temperature (80-160°C) and of the initial solid content of the agent (15-30 %w/w) on the drying kinetics, shrinkage and locking point of a single liquid droplet are systematically investigated. Then, a lab-scale X-ray microtomograph is employed to acquire three-dimensional images of dried particles, which are then used to analyze their surface structure and internal morphology. This contribution provides guidelines for the production of powder suitable for the dry powder coatings by using spray dryers, and thus it may serve as a basis for product design. Keywords— Hydroxypropylated pea starch, Single droplet drying, Particle size, Microstructure I. INTRODUCTION There is an increasing interest in scientific and engineering communities to develop and implement an efficient particle coating technology which can be readily used in food, pharmaceutical, or chemical industries. The conventional method for particle coating process is wet coating. It involves the application of a liquid precursor on particles that is then converted to the desired coating material by subsequent post-treatment steps. The main disadvantage of the wet coating is a high concentration of volatile solvent in the final product. In the case of coating of medicines or other biologically active products, humidity may cause product destruction or its inactivation. It is hence necessary to dry gently the product for a long time, which increases the costs and lengthens the time of the entire process. Dry powder coating is a promising alternative to the traditional coating powder process with organic or aqueous solutions [1]. This technology is simpler, cheaper, safer and more environmentally friendly compared to solvent-based coatings [2]. In this technology, one or more polymers as ―guest‖ dry powders together with a small amount of liquid plasticizer feed directly into a drum coater or a fluidized bed chamber [3]. Then, these powders are attached to ―host‖ large particles by cohesive forces. Thereby, the properties and the functionalities of the host particles can be changed in order to create particles with desirable end-user properties. For instance, the flowability of silicon carbide powder was improved by using fine silica particles as coating and blending material [4]. It was found that the cohesive forces between two primary host particles in the presence of fine coating is directly proportional to the size ratio of the coating particles to the host particle. The kind of selected polymers and physico-chemical, microstructural and dimensional properties such as solubility, morphology, porosity and size