Tumbling fluidized-bed process parameters affecting quality of biopolymer coating on surface of pristine urea particles Babar Azeem a, ⁎, KuZilati KuShaari a, ⁎, Zakaria Man a , Sayed Ameenuddin Irfan b , Thanh H. Trinh a a Department of Chemical Engineering, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak Darul Ridzuan, Malaysia b Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak Darul Ridzuan, Malaysia abstract article info Article history: Received 20 January 2017 Received in revised form 7 July 2017 Accepted 31 July 2017 Available online 05 August 2017 When pristine urea particles are subjected to spray coating in a fluidized bed, the frequency of substrate particles to come across the spray zone changes due to various hydrodynamic factors of the fluidized bed giving rise to preferential coating. The heterogeneity of coating film on the surface of urea particles results in poor coating quality which ultimately affects the controlled-release properties of the coated product. In this study, the effect of tumbling fluidized bed process parameters is studied on coating quality and the Response Surface Methodol- ogy is employed for the optimization of process parameters for better results. In case of coating uniformity w.r.t. coefficient of variance (CV) of coating thickness, atomizing air pressure appears as the most influential parame- ter. The best coating uniformity in this case is achieved at 2.25 bar of atomizing pressure. The lowest and highest values of atomizing pressure resulted in higher CV of coating thickness. In case of coating uniformity w.r.t. change in coating mass, coating time appears the most influential parameter. Coating mass increases linearly with coating time. For coating uniformity in terms of CV of size distribution, atomizing pressure and fluidizing gas temperature are the most influential parameters. The best coating uniformity is witnessed at 85 °C and 1.90 bar. The optimum values of process parameters and response objectives can be used to scale-up the unit used. © 2017 Elsevier B.V. All rights reserved. Keywords: Fluidization Biopolymer Controlled-release urea Particulate technology Urea coating 1. Introduction Pristine urea is highly vulnerable to losses (30–70%) through ammonia volatilization, leaching and surface runoff when applied to soil without engulfment by a barrier layer [1]. Thus, nutrient use efficiency (NUE) of the plants is reduced in addition to environmental pollution through water eutrophication and stratospheric ozone depletion via escape of NH 3 , NO, N 2 O and N 2 into the atmosphere [2]. To offset these issues, controlled release coated urea (CRCU) is employed that is a purposely designed manure aimed at providing the nutrients in a controlled manner most preferably in synchrony with the metabolic needs of the plants. The CRCU is an environmentally friendly fertilizer that helps to enhance the NUE and eradicate environ- mental pollution. In addition, the single application of CRCU in one season diminishes the overall cost [3]. The CRCU is produced by the physical intromission of granular urea in an appropriate coating materi- al capable of impeding the spontaneous dissolution and manipulating the nutrient release kinetics as per set standards. Although billions of research dollars have been spent on the development of CRCU, yet the application of CRCU is limited to ornamental and horticultural plants. Synthetic polymers'-coated controlled-release urea (CRU) is used as an abatement strategy but it offers soil pollution due to non- biodegradability and toxicity of the polymers [2]. Starch is abundantly available naturally occurring polysaccharide polymer which is cheap, biodegradable, renewable, and environmentally friendly [1]. Starch alone, however, is ineffective to be used as coating material for CRF production because of its profound hygroscopic nature, poor mechani- cal properties and weak dimensional stability [4]. Starch blends with certain appropriate materials can be used to develop efficient control release devices. Borax or di sodium tetraborate can also be used as a crosslinker for the chemical modification of starches [5]. It can enhance the mechanical properties of starch films by crosslinking reaction with the hydroxyl groups of starch [6]. However, it is recommended that the quantity of borax should not exceed 10% in the starch films lest the adverse effect is experienced with respect to the starch film proper- ties [5]. In addition to work as a crosslinker, borax also contributes to the provision of boron which acts as an essential micronutrient for the plants in the soil [7]. When urea is coated in a fluidized bed, a certain degree of heterogene- ity of the coating mass or film thickness may arise which distorts the coat- ing quality. This can be attributed to the preferential coating of part of the substrate due to unequal opportunities to pass through the spray zone [8]. The investigation of urea coating quality in terms of coating uniformity (CU) is important due to substantial dependence of the controlled- Powder Technology 320 (2017) 714–725 ⁎ Corresponding authors. E-mail addresses: engineerbabar.icet@pu.edu.pk (B. Azeem), kuzilati_kushaari@utp.edu.my (K. KuShaari). http://dx.doi.org/10.1016/j.powtec.2017.07.095 0032-5910/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec