Recycled packaging paper fibers enhanced by ozonation

Today, brown cellulosic paper packaging exhibits a recycling rate of 87% in France. However, to maintain consistent quality after recycling, virgin fibers or starch are typically blended with recycled fibers to compensate for the loss of strength due to hornification and repeated mechanical stresses. Moreover, these solutions lead to process and environmental issues.

This PhD thesis explores a chemical sustainable strategy for upcycling recycled fibers and strengthening paper without additive using ozone oxidation. Ozone is a clean oxidant that operates at room temperature, leaves no chemical residue, and selectively introduces oxygen-containing groups, particularly carboxyl groups, onto lignin. Since old corrugated containers (OCC) are mainly composed of kraft pulp with highly reactive lignin, ozone is expected to increase lignin hydrophilicity, enhancing interfiber hydrogen bonding and improving paper strength. Ozonation has been successfully applied on a recycled pulp made of OCC: with 2% ozone, the tensile and burst strengths were increased by more than 10%. To better understand the effect of ozone, contaminant-free model pulps are laboratory-recycled and then ozonated. This shows that the mechanical properties of the fiber web lost during recycling can be restored by introducing COOH groups onto lignin and partial reopening of the fiber lumen. Other strategies, such as the use of crosslinking agents, aminoalkoxysilanes and refining are investigated for comparison. All the upcycled pulps are also re-pulped and reused for papermaking, to determine if improvements are maintained through further recycling.

The main conclusion is that ozonation and refining are the only efficient routes with clear paper strength gain. However, refining is known for its high energy consumption, making ozonation a novel sustainable alternative for the upcycling of recycled fibers.