CHANGES IN TRANSMISSION CHARACTERISTICS OF POLYMETHYLMETHACRYLATE ANDCELLULOSE-(III) ACETATE DURING EXPOSURE TO ULTRAVIOLET-LIGHT

Ultraviolet-transparent polymethylmethacrylate (PMMA) and cellulose (I II) acetate (CA) (often used as a cut-off filter in UVB [280-320 nm] b iological effect studies) were exposed to a 20 W Philips TL 12 lamp to examine changes in transmission characteristics due to UVB exposure. Transmission of UVB and biologically weighted UVB (UVBBE(DNA)) through PMMA were similar, 88.3 and 83.5%, respectively. The absorption chara cteristics of PMMA did not change with time at any of the UV irradianc e levels applied. However, transmission of UVB and UVBBE(DNA) through new CA differed considerably: 59% versus only 11%, respectively. Also, spectral absorption characteristics changed with time due to degradat ion of CA, at a rate that was dependent on the incident UVB irradiance . The decrease in transmission through CA of both UVB and UVBBE(DNA) c an be described by exponential functions. The CA that was wrapped arou nd the UV lamp showed dramatic changes in UV absorption over the first few hours of use. However, when CA was placed at a longer distance fr om the light source initial degradation was less. It is concluded that PMMA can be applied in UV effect studies as a reasonable alternative for quartz. The CA should, however, be used with care, because the lar ge transmission decreases that were observed strongly hamper an accura te calculation of (biologically weighted) UVB dose rates.