Tear and tensile strength development of PGW and CTMP pulps mixed with PLA or viscose fibres

The objective was to evaluate the effects on paper properties when replacing a minor share of wood fibre by synthetic fibre. The aim was to increase tear strength and stretch while minimizing the loss of tensile strength in paper consisting of mechanical pulp. Tested synthetic fibres included PLA and viscose fibres mixed with mechanical or chemi-mechanical pulp.Even at relatively low proportions, the synthetic fibres contributed to a significant increase of tear strength in the wood fibre based papers. With the highest tested proportion (20%) the increase of tear index in PGW based stock was 243% with PLA and 177% with viscose fibre. However, a simultaneous decrease in tensile strength and tensile stiffness was observed. The stretch at break remained unchanged. Thickness reduction of the synthetic fibres resulted in an increase of tear strength. The effect is due to the high fibre length of synthetic fibres, producing mechanically well entangled networks, coupled with the high enough strength of the synthetic fibres.