Effect of drying and rewetting cycles on the structure and physicochemical characteristics of softwood fibres for reinforcement of cementitious composites

The changes produced in cellulosic fibres when they are subjected to successive drying and rewetting cycles could have an important impact on the resistance and durability of cement mortar composites based on these fibres. In this paper, unbleached, oxygen delignificated, semi-bleached, and fully bleached softwood pulps have been subjected to drying and rewetting cycles and the corresponding dried pulps characterized. The morphological structures and thermal stabilities were investigated with X-ray diffraction and thermogravimetric analysis. While the water retention values decrease significantly with drying and rewetting cycles, an overall increase in the crystallinity index and in the thermal stability was found in the hornificated pulps. Natural fibres from cotton linters were also studied and the results compared with the fibres from these softwood pulps.