Density dependent influence of grammage on tensile properties of handsheets

Experimental data are presented for the influence of grammage on the tensile index and specific elastic modulus of laboratory formed paper sheets formed from pine, spruce and birch Kraft fibres. The data show tensile index and specific elastic modulus to increase with grammage up to a grammage of around 60 g m(-2) and to typically decrease at higher grammages for sheets with density around 0.7 g cm(-3); no significant decrease is observed for sheets with density 1 g cm(-3). We observe that if tensile index exhibits a maximum with grammage, then so does specific elastic modulus. The data compare favourably with theory accounting for the competing influence of stress-transfer efficiency and the Weibull-type incidence of flows with changing grammage. An experimental procedure to determine the grammage of fibres is presented also allowing comparison of tensile data with theory and agreement is good. The treatment suggests that the incidence of weak spots in the sheet depends upon the degree of bonding such that at high density no dependence is observed.