Refining

The main reason to refine is to increase the capability of the fibres to form hydrogen bonds. Unrefined fibres are stiff and the amount of OH groups on the fibre surface is low.

If paper is made from unrefined fibres the direct contact area between the fibres in a sheet will be small. There will be only a few hydrogen bonds created, the paper would be weak. During the refining the outer fibre walls are broken up to make it easier for the fibre to absorb water and to
swell. The outer surface area increases and the fibre becomes softer. The number of OH groups on the surface increases

Large areas of direct contact and many OH groups make it possible to form more hydrogen bonds. Consequently, a paper made from refined fibres is strong. Further in the process the fibre’s inner cavity, lumen, may fall in and the fibre will resemble a band. The fibre collapses.