Moisture absorption and Desorption in a UV cured urethane acrylate adhesive based on radiation source

摘要

A photopolymerizable urethane acrylate (UA) adhesive was cured using two different sources: a conventional UV-lamp and a UV-emitting light emitting diode (LED). Moisture uptake in cured specimens was characterized by immersion in deionized water at 21.8, 30, 37.5, and 45 degrees C for a period of 6 months. Additionally, desorption experiments were performed for selected specimens under vacuum at room temperature. Material degradation in the form of mass loss was observed in all samples after attainment of a maximum water uptake level, with the phenomenon being more pronounced at higher immersion temperatures. This degradation is attributed to leaching and dissolution of uncured monomers and lower weight molecular species from the samples. A two stage moisture uptake model is proposed to account for mass loss and excellent agreement between the tested mass loss and the loss-rate parameters determined from the model is shown. Performance of specimens was characterized with dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). It was found the LED source was not as effective in curing surfaces, due to which there is a higher level of mass and lower T-g from hygrothermal exposure as compared to the core regions of the LED cured specimens and the overall lamp cured specimens. (C) 2007 Wiley Periodicals, Inc.