A theory for the elastic modulus of paper

A review has been made of the previous attempts to formulate a theory for the elastic modulus of paper in terms of fibre properties. The suggestion is made that, by considering the case of uniaxial stress, previous authors have attempted a problem that is too complex for the present state of knowledge. It is suggested that the case of equal biaxial strain is theoretically simpler and that verification of such a theory can be made more reliably. The biaxial theory is developed and the elastic modulus is written in terms of the moduli of the fibres and the bonded area of the sheet. The biaxial modulus has been measured for three levels of fibre bonded area for one pulp and these admittedly sparse data are in agreement with the theory.