Ultrasonic treatment to improve the quality of recycled pulp fiber

The effect of ultrasound on the quality of recycled fibers was investigated . Ultrasound was applied to recycled pulp fiber suspension before ink remov al by conventional flotation. The ultrasonic treatment induced an increase in the sedimentation volume of the fiber, which implies that the flexibilit y and bulkiness of the fiber increase. The water retention value of the ult rasonically treated fiber recovered from the loss caused by the recycling. These facts are due to a beating effect of the treatment. The paper sheets prepared from the ultrasonically treated fiber suspension showed higher she et density, tensile strength, and brightness than that from an untreated fi ber suspension. The process, which consists of ultrasonic treatment for 1 m in following flotation deinking, requires about 1.4 times as much energy as the conventional flotation deinking process, but it induced 20% improvemen t in brightness. The results indicate that the ultrasonic treatment is effe ctive in improving recycled fiber quality.