Fibre Degradation during Autoclaved Cellulosic Fibre-cement Composite Manufacture

A study was undertaken to determine the extent of pulp strength losses and dissolution of fibre components occurring within the composite during the manufacture of autoclaved cellulosic fibre-cement sheets. Softwood kraft pulp sheets were sandwiched between freshly-prepared fibre-cement composite sheets and the changes in the chemistry of the pulp sheets followed as the sandwiches went through the curing process. In this way, the chemical environment seen by the fibre during composite manufacture can be realistically simulated without needing to isolate the fibre from the cured composite. Results showed that the cellulose degree of polymerisation (DP) and fibre strength dropped during composite curing for both unbleached and fully bleached softwood kraft pulps. Most of the reduction in cellulose DP occurred prior to reaching the autoclaving temperature, with significant degradation of the unbleached fibre even occurring during initial curing at room temperature. Degraded fibre components, particularly hemicelluloses, migrated into the matrix during autoclaving, while inorganic materials from the matrix were incorporated into the fibre.