تأثیر پیشتیمار آنزیمی خمیرکاغذ بازیافتی با توالی ترکیبی سلوالز و الکاز در رنگبری با پراکسید هیدروژن.

Background and Objectives: The use of recycled pulp in papermaking reduces the quality of the resultant papers. Hence, employing enzyme pre-treatment in isolation or in combination with sequential pulp bleaching methods can prove to be effective approaches for enhancing the quality of the end product derived from recycled pulp. This study was undertaken to examine the impact of cellulase and laccase enzyme pre-treatment sequences on the bleachability of the resultant pulp with hydrogen peroxide, as well as to assess the quality of the final pulp following the bleaching process. Materials and Methods: At first, the mixture of waste newspaper and magazine papers were deinked using enzyme pre-treatment (combined sequence of cellulase and laccase) as well as conventional chemical method. Enzymatic pre-treatment was done as experimental treatments C₁L₁ (cellulase usage: 0.1% and duration time: 10 minutes; laccase usage: 20u and duration time: 120 minutes), C₁L₂ (cellulase usage: 0.1% and duration time: 10 minutes; laccase usage: 40u and duration time: 120 minutes), C₂L₁ (cellulase usage: 0.1% and duration time: 20 minutes; laccase usage: 20u and duration time: 120 minutes) and C₂L₂ (cellulase usage: 0.1% and duration time: 20 minutes; laccase usage: 40u and duration time: 120 minutes) under specific process conditions. Additionally, control pulp samples (without the addition of chemicals or enzymes) and chemically deinked pulp samples were prepared. The bleaching of the deinked pulp was then conducted using a hydrogen peroxide bleaching system, which consisted of 2% hydrogen peroxide, 2% sodium hydroxide, 2% sodium silicate, 0.2% DTPA chelating agent, and 0.1% magnesium sulfate. The bleaching process took place in separate plastic bags, under specific process conditions of 10% consistency, a temperature of 70 °C, and a duration of 2 hours in a water bath. Finally, the optical and strength characteristics of the bleached pulp were assessed. Results: The findings revealed that incorporating enzyme pre-treatment during the deinking process enhances the overall efficiency of hydrogen peroxide bleaching. Consequently, the resulting papers exhibited superior optical and strength characteristics after bleaching, as compared to pulp that underwent conventional chemical-based deinking. Specifically, the application of C2L2 and C2L1 enzymatic pre-treatments, followed by bleaching with hydrogen peroxide, resulted in brightness improvements of 11.12% (equivalent to approximately 5 units) and 9.5% (equivalent to approximately 4 units), respectively. In these pretreatments, the whiteness of the paper increased by 31.92% and 24.54% (an increase of about 9 and 6 units), respectively. Also, the yellowness of the paper decreased by 40.19% and 44.25%, respectively, and the opacity of the paper reduced by 37.74% and 23.97%, respectively. Also, in experimental runs of C₂L₁ and C₂L₂, the paper tensile index increased 29.17% and 35.64%, respectively (40.64 Nm/g and 38.7 Nm/g, respectively), breaking length enhanced by 64.42% and 99%, respectively (5.92 km and 4.89 km), and the paper burst index also increased by 70.85% and 92.37% (3.81 mN.m² /g and 4.29 kPa.m² /g), respectively. The tear indices of the paper in these experiments were found to average approximately 6.82 mN.m ² /g and 6.62 mN.m ² /g, which are slightly lower compared to the chemically deinked pulp after bleaching. However, in the pretreatment utilizing the combined sequence C₂L₁, the tear index of the paper was nearly equivalent to that of the chemically deinked pulp. Conclusion: The findings demonstrate that the combined sequences of cellulase and laccase resulted in a substantial enhancement in the bleachability of pulp with hydrogen peroxide, surpassing that of chemically deinked pulp. Moreover, these enzymatic pre-treatment sequences led to the production of papers with superior optical and strength properties. Notably, the most favorable optical and strength characteristics were observed in the C₂L₂ and C₁L₂ enzymatic pre-treatment sequences following hydrogen peroxide bleaching. [ABSTRACT FROM AUTHOR]