Selected results are presented of new detailed experiments on progressively recycling virgin pulp in the form of handsheets and machine made paper. Laboratory beaten pulp has been made into handsheets, re-disintegrated and remade (1) over four recycles with rosin/alumsizing and touch up beating to maintain freeness, and (2) over three recycles without sizing or further beating. The same beaten pulp was made into paper on a pilot paper machine and remade over three cycles.
The work has shown clearly that, in the experiments, pilot machine recycling caused much smaller changes of sheet properties than is the case for handsheet recycling. However, the trends of change as recycling progresses are similar and it is likely that the same basic mechanisms are responsible. Differences of stock preparation and differences of formation make distinct contributions to the differences between handsheet and machine recycling. Changes in the chemical composition of the fibres occur during recycling and these were found to be more pronounced in the second handsheet recycling experiment than in the pilot machine trial. Loss of bonding strength is clearly related to a reduction of wet plasticity of the fibres. Machine recycling results support the handsheet data in suggesting a strong possibility that changes in fibre surface condition play an important part in loss of bonding strength, particularly at the first remaking.