Chlorine dioxide bleaching of soda-anthraquinone jute pulp to a very high brightness.
Bleaching of soda-anthraquinone jute pulp by chlorine dioxide (ClO2) was studied to reach a target brightness of above 88% for the purpose of using less bleaching chemicals. The performance of either chlorine dioxide or peroxide in the final bleaching to boost brightness was also studied. The experimental results revealed that the final brightness depended on ClO2 charge in the Do and D1 stages. The brightness reversion was lower when the final stage brightening was done by peroxide. The use of Mg(OH)2 in the D1 and D2 stages improved the final brightness due to the formation of less chlorate and chlorite during the Mg(OH)2- based ClO2 brightening stages. The strength properties of pulp bleached by peroxide in the final stage was slightly better than that from ClO2 as the final ClO2 bleaching stage.
Pulp properties and effluent characteristics from the Mg(OH)2-based peroxide bleaching process
Softwood TMP was subjected to peroxide bleaching under various conditions, with either magnesium hydroxide (Mg(OH) 2 ) or sodium hydroxide (NaOH) as the alkali source. The optical and physical strength properties of the bleached pulps were compared, as were the charge characteristics. The Mg(OH) 2 process was found to yield brightness and strength results similar to those of the conventional process, but the pulp from the Mg(OH) 2 process had a higher light-scattering coefficient. The bleached pulp from the Mg(OH) 2 process was lower in total carboxylic group content, but its surface charge density was close to that of pulp from the NaOH process. A lower COD load in the bleaching effluent from the Mg(OH) 2 process was found to be caused by the decreased formation of acetic acid and methanol and by the lower dissolution of lignin. Application: Using magnesium hydroxide as a substitute for sodium hydroxide can improve the bleaching effluent characteristics in the bleaching of mechanical pulps.
Live birth in the Devonian period
The extinct placoderm fishes were the dominant group of vertebrates throughout the Middle Palaeozoic era, yet controversy about their relationships within the gnathostomes (jawed vertebrates) is partly due to different interpretations of their reproductive biology. Here we document the oldest record of a live-bearing vertebrate in a new ptyctodontid placoderm, Materpiscis attenboroughi gen. et sp. nov., from the Late Devonian Gogo Formation of Australia (approximately 380 million years ago). The new specimen, remarkably preserved in three dimensions, contains a single, intra-uterine embryo connected by a permineralized umbilical cord. An amorphous crystalline mass near the umbilical cord possibly represents the recrystallized yolk sac. Another ptyctodont from the Gogo Formation, Austroptyctodus gardineri, also shows three small embryos inside it in the same position. Ptyctodontids have already provided the oldest definite evidence for vertebrate copulation, and the new specimens confirm that some placoderms had a remarkably advanced reproductive biology, comparable to that of some modern sharks and rays. The new discovery points to internal fertilization and viviparity in vertebrates as originating earliest within placoderms.