Recycling and deinking processes cause fiber damage because of hornification phenomena and increased external fibrillation. Mechanical refining has been used for many years to enhance the mechanical properties of paper. Biorefining of pulp using enzymes is receiving increasing interest for energy reduction at the refining step of the paper-making process. Moreover, enzymes have also been used for the enhancement of mechanical properties without affecting the drainage rate. As an alternative to mechanical refining treatment, a combination of an enzymatic treatment and cellulose nanofibril (CNF) addition was explored to enhance the mechanical properties of paper. The tests were carried out on a deinked pulp (DIP) suspension made of 50% old newspapers (ONP) and 50% old magazines (OMG). Various enzyme charges and CNF amounts were added to the mixture of ONP and OMG. All pulps (treated and untreated) were characterized from a morphological point of view, and the paper sheets made thereof were mechanically characterized. The combination of the enzymatic treatment with the addition of 3% CNF provided sufficient tensile strength for the paper to be used in high-performance applications

The authors wish to acknowledge the financial support of the Economy and Competitiveness Ministry of the Government of Spain to project CTQ2013–48090–C2–2–R.