The thermal stability of papermaking pulps under conditions of accelerated ageing was examined. Degradation was found to be extremely complex and influenced both by the technical processes of papermaking and by the experimental methods used. At moderate temperatures as used for accelerated ageing, the folding endurance test was a sensitive measure of degradation. Methods of reducing the variability of the test were considered and a new technique capable of handling widely different results was developed and evaluated.
Several papermaking pulps were artificially aged and the resultant loss of strength attributed to the interaction between a gradual fibre strength reduction and a rapid increase in interfibre bonding. Excessive initial interfibre bonding decreased handsheet stability. Softwood sulphite and kraft pulps were more stable than a birch kraft pulp, but the behaviour of sulphite pulps varied greatly. The presence of lignin or of high hemicellulose content was not of itself sufficient to cause rapid ageing.