Use of Central Composite Design for Optimization of ultrasonic pre-treatment parameters on chemical deinking of old newspaper

To reuse recycled cellulosic fibers in paper production, contaminated particles and other impurities of the fibers can be greatly removed using a de-inking stage which is considered as a supplementary step in waste paper recycling technology. The effect of using ultrasonic pretreatment on the deinking of old newspapers was investigated utilizing the common conventional chemical method across this research work. Experimental design method was served to optimize the amount of ultrasonic bath temperature and sonication time. Therefore, 13 tests were designed using Response Surface Methodology (RSM) and Central Composite Design with Design Expert 7.0.0 Trial software. Ultrasonic bath temperature and sonication time at three different levels (1, 0 and 1+) and two axial points (α + and α-) were used as independent variables, and the optical and mechanical properties of handsheets were used as dependent variables. Response surfaces and contour plots were served to show the interaction between the independent variables and the response variable. ANOVA test showed that the quadratic model is the best model to explain the interaction among the studied variables. The predicted values of the obtained model had much conformity with the experimental results (R2=0.98). According to ANOVA results, it can be concluded that the effect of each of the variables on the optimal properties is significant and the ultrasonic time is the most effective factor on the response. According to the results, the proposed optimum conditions to achieve the highest amount of mechanical and optical properties (43.43) are the ultrasonic bath temperature 47 oC and the ultrasonic time of 31 min.