A micro-mechanical modelling study of drying restraint effects on the hygro-mechanics of paper sheets

In this contribution we show how fibre activation and micro-buckling of fibre walls may explain, quantitatively, differences in the hygro-mechanical response of paper sheets due to the presence or absence of mechanical restraint during their fabrication. To this end, both effects are incorporated in an idealised micro-mechanical model of the fibre network. The model is used to predict the response of the network to wetting-drying cycles, as a function of the degree of restraint during production. Restrained-dried networks are predicted to exhibit an irreversible hygroscopic strain upon first wetting and a different reversible hygro-expansivity coefficient, compared with freely-dried networks, which match well with experimental values reported in the literature.