How does lignin affect the colour and durability of groundwood paper?

In the context of papermaking, groundwood pulp is produced by mechanically grinding wood, which retains all of the wood's original chemical constituents, including lignin.

Lignin significantly impacts the quality of groundwood paper in the following ways:

• Colour: Because groundwood pulp retains lignin and other natural colouring materials, the resulting paper lacks high whiteness. Furthermore, lignin is highly sensitive to light and heat; its presence causes the paper to undergo discoloration, typically yellowing over time. This is commonly observed in newsprint and certain book papers.1
• Durability and Strength: Papers containing groundwood pulp do not possess high strength. This is due to the fact that the fibres are fragmented during the mechanical grinding process and have only a moderate ability to bond with one another.1

While lignin is removed during the production of chemical wood pulp to improve purity and stability, its retention in groundwood pulp provides specific benefits such as increased bulk and good opacity, making it suitable for applications where long-term archival durability is not required.21