Interlaboratory test programme - reproducibility in xenon are weathering

Four different grades of polypropylene (PP) and four different grades of po lyamide (PA) were exposed to an accelerated xenon are weathering test in ac cordance with ISO 4892 part 2. Eight laboratories participated in the test with the goal of finding the range of inter-laboratory precision when the t est conditions are specified as exactly as possible. After weathering of PA samples for 1000 h, the agreement between laboratories concerning mechanic al properties was good. The main colour change was loss of yellowness. Afte r re-exposure, the results indicated that colour changes produced by the va rious weathering devices were less variable than the primary data suggested . The laboratories showed reasonable agreement in terms of the ranking orde r of gloss retention of the four formulations. However, the actual levels o f gloss retention clearly varied widely between laboratories. The PP sample s were exposed for various periods of time, each formulation being evaluate d after two different exposure levels. The agreement between laboratories c oncerning mechanical properties was very much dependent upon which part of the lifetime curve the samples were taken from. The main colour change in u npigmented and white formulations was yellowing. Colour changes produced in the black test pieces were generally small. There was appreciable variatio n between test laboratories, although the same ranking orders tended to eme rge. FTIR-spectroscopy showed increased intensity of the carbonyl band corr esponding to the effects of photooxidation. A deposit of amorphous silica w as detected as a broad absorption band in the 960-1260 cm(-1) region. The a mount of silica deposit on samples exposed at different laboratories varied greatly, especially on samples exposed for 1000 and 1500 h. Both PP and PA samples showed signs of silica deposition, especially in crazing sites. (C ) 2000 Elsevier Science Ltd. All rights reserved.