Why does groundwood pulp give paper good opacity but lower strength?

Groundwood pulp provides paper with high opacity and bulk, which are desirable qualities for printing, because the process of creating the pulp results in fibres that are fragmented and contain a significant amount of debris, known as fines.1

However, groundwood pulp results in lower strength for two primary reasons:
* Fibre Characteristics: The fibres produced through mechanical grinding are relatively short compared to those in chemical pulps.1
* Limited Bonding: Because the fibres are fragmented and retain all the original chemical constituents of the wood—including lignin, hemicellulose, and resins—they possess only a moderate ability to bond to one another.1

In the context of papermaking, the strength of a sheet is heavily dependent on the length of the fibres and their ability to form strong interfibre bonds. Consequently, papers made with groundwood pulp often require the addition of small percentages of chemical wood pulp to achieve the necessary durability for their intended use.23