title: Determining the critical relative humidity for moisture-induced phase transitions.
abstract: A new method to determine the onset relative humidity for a glass transition and crystallization processes in amorphous or partially amorphous materials was developed using dynamic gravimetric vapor sorption (DVS). Water vapor can act as a plasticizing agent in amorphous materials, thus lowering the glass transition temperature below room temperatures. Additional water sorption can lead to a crystallization event below the glass transition temperature. On spray-dried lactose the glass transition RH and crystallization RH values were 30 and 58% at 25 degrees C, respectively. Glass transition and crystallization RH values were also measured at 5, 15, 25, 35, and 45 degrees C on a spray-dried salbutamol sulfate sample. The glass transition RH values for the salbutamol sulfate sample ranged from 64.5% RH (5 degrees C) to 32.8% RH (45 degrees C) while the crystallization RH values ranged from 81.0% RH (5 degrees C) to 50.4% RH (45 degrees C). The results clearly show that the glass transition and crystallization humidity values decrease as the sample temperature increases.
authors.affiliation: Surface Measurement Systems Ltd., 2222 South 12th Street, Suite D, Allentown, PA 18103, USA. burnett@smsna.com
authors.forename: D J
authors.initials: DJ
authors.lastname: Burnett
authors.forename: F
authors.initials: F
authors.lastname: Thielmann
authors.forename: J
authors.initials: J
authors.lastname: Booth
mesh_terms: D000420:Albuterol / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D006813:Humidity; D007785:Lactose / Q000737:chemistry*; D044367:Phase Transition; D014835:Volatilization
chemical_list: D007785:Lactose; D000420:Albuterol