Studies of fibre hemp and flax pulps as a feedstock for Australian newsprint production

The primary aim of the pulping trials described here was to investigate the potential of using flax (Linum usitatissimum L.) and hemp (Cannabis sativa L.) bark and whole stem pulps as alternative reinforcing agents in the Aus tralian newsprint industry. Pulps were also made from the core fraction to assess its suitability as a supplement to the short fibred eucalypt compone nt of the existing newsprint blend. Existing cold caustic soda (CCS) and th ermomechanical (TMP) pulping processes were trialed. The behaviour of the h emp core pulps was analogous to that of eucalypt except that properties dev eloped more with chemical addition. These pulps were typically of low tear index and high tensile index. Tensile index tended to increase with the use of a higher concentration of sodium hydroxide. The flax CCS core pulps had superior tear strength but had lower tensile strength, lower brightness an d were very yellow in colour compared with the equivalent CCS hemp pulp and eucalypt CCS. The properties and behaviour of hemp and flax CCS bark pulps were similar and could potentially be blended or used interchangeably. The bark fibres of hemp and flax are capable of forming paper of very high tea r index but with lower tensile index and tensile energy absorption than wou ld be desired from a softwood kraft pulp. Accurate and uniform fibre cuttin g would be required to overcome the tendency of the bark fibre to tangle an d block screens. Whole stem pulp properties were generally intermediate to those of separate core and bark fibre.