title: Permeation of urea through various polyurethane membranes.
abstract: BACKGROUND
  Controlled-release systems using polymer membranes are very important in agriculture for labour-saving and effective delivery of pesticides and other agents. Polymer-coated granules are one of the most useful formulations, and a study of the factors for polymer design is necessary to achieve various release patterns. A permeation study using plain membranes was carried out in order to clarify parameters, and the results were compared with the release from polymer-coated granules.
  
  
  RESULTS
  The permeation coefficient of urea through a plain polyurethane membrane decreased significantly as the urethane and alkyl side chain content increased. The glass transition temperature and crosslink density of the polyurethanes hardly influenced its permeability. The release rate from polyurethane-coated granules was also reduced by alkyl side chains. However, it was faster than that through a plain membrane because of capsule expansion by continuous water penetration and structural changes in the membrane.
  
  
  CONCLUSIONS
  The release rate of urea through a polyurethane plain membrane and from polyurethane-coated granules can be controlled by changing the chemical properties of the membrane. In addition, physical properties such as the glass transition temperature T(g) or crosslink density should be considered to assess the release profile from polyurethane-coated granules.
authors: Department of Materials Science, Graduate School of Science and Technology, Nagasaki University, Nagasaki, Japan. watanabea3@sc.sumitomo-chem.co.jp
authors: Atsushi
authors: A
authors: Watanabe
authors: Yoshihiro
authors: Y
authors: Takebayashi
authors: Toshiro
authors: T
authors: Ohtsubo
authors: Mutsuhisa
authors: M
authors: Furukawa
mesh_terms: D016503:Drug Delivery Systems / Q000379:methods*; D008567:Membranes, Artificial; D010539:Permeability; D011108:Polymers / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry*; D014508:Urea / Q000737:chemistry*
chemical_list: D008567:Membranes, Artificial; D011108:Polymers; D011140:Polyurethanes; D014508:Urea