The effect of cooking agents on Japanese paper

The strength and durability of koro papers made from fibre cooked in differ ent chemicals, such as wood ash, soda ash (sodium carbonate), lime (calcium hydroxide), and caustic soda (sodium hydroxide) were compared in order to determine what makes a more durable kozo paper The deterioration rate of fo lding endurance and original strength of tensile index showed that milder a lkali, such as wood ash and soda ash, have a more favourable effect on the durability of papers rather than stronger alkali, such as caustic soda and lime. Bleached paper was most unstable in strength and colour. These stabil ity differences were attributed to the degree of damage to the fiber during cooking and bleaching. Higher damage by stronger chemicals was also demons trated by chemical composition analysis. The above results proved the commo nly held belief that mild alkali is better than stronger chemicals in paper making.