In this paper, several families of mangrove woods were examined with respect to qualification for dissolving pulps. The results obtained were as follows.
(1) The mangrove wood of the family Rhizophoraceae showed better properties cited below than Japanese hardwoods. The woods of Rhizophoraceae had higher specific gravity and were easier in cooking and bleaching. Most genera of the family contained a large amount of EDTA ash, which was normalized with the elimination method as described in the second and the third reports of this series. In the other properties of pulps, the woods of Rhizophoraceae were more excellent than Japanese hardwoods. In industrial viscose process, the compressibility of sodium cellulose and the filterability of viscose from Rhizophoraceae pulps were more excellent than those from LDP. Two species of the genus Bruguiera of Rhizophoraceae, B. parvifora and B. sexangula, had low content of EDTA ash and suitable reactivity. Two families of Combretaceae and Sonneratiaceae were adequate to dissolving pulps, having the same properties of pulps as those of LDP. The mangrove woods of other families surveyed in this paper were inadequate to dissolving pulps owing to some defects in pulping, pulp quality or reactivity. Among the families of mangrove, the family Rhizophoraceae has the widest distribution in Southeast Asia, and the genus Rhizophora (Bakau and Bakauan) is abundant in the same family. Therefore, the mangrove of Rhizophoraceae is most promissing as a resource for dissolving pulp woods.
(2) Microscopical observation of the woods of Rhizophora (Bakauan) and Bruguira (Langgadai) showed the features such as longer fibers, thicker cell walls, and smaller lumens than those of Japanese hardwoods. The ray parenchyma cells of Rhizophora wood contained a large amount of Ca-oxalate crystals.
(3) In chemical components of Rhizophora wood, the contents of lignin, pentosan, resin and water soluble matters were all lower than those of Japanese hardwood except the content of EDTA ash.