Creep in chipboard. 10. The effect of variable climate on the creep behaviour of a range of chipboards and one waferboard

Ten samples from each of ten brands of commercial chipboard, covering a range of UF, MUF and PF resins, were stressed over a 5-year period at 30% of their short term ultimate bending strength, under protected external conditions. No relationship could be established for the term of the experiment between fluctuations in creep deflection and changes in environmental conditions. Exceptionally, for two short periods of time, relationships were established and these were in line with current views on mechano-sorptive behaviour. Differences in relative creep between the ten brands were significantly greater than those occurring between samples of any one brand. Although there were significant differences in relative creep among the six brands of MUF bonded boards, the relative creep of all these boards was significantly lower than those brands made with UF and high-alkaline cured PF resins. While most of the MUF bonded samples survived the duration of the experiment, all UF and PF samples failed before the end of the 5-year period. For the first 6 months of the experiment, the mean relative creep under protected external conditions was equal to, or slightly less than, that obtained in matched samples tested under a constant environment of 20 degrees C 90% rh