Study On The Mechanism Of Wheat Straw Oxygen-base Pulping

As we all know,Chinese non-wood fibrous raw materials are most resourceful in the world.However,the majority of them was abandoned and burnt in the field,resulting in a waste of resources as well as the air pollution.Making use of crop stalks has to be brought into pulping and papermaking,to diminish the negative impact of excessive dependent on wood resources on the environment with the fast development of paper industry in China.Furthermore,exploitation and adoption of new technology is vitally important to break the bottlenecks for straw paper industry.Alkali-oxygen method has always regarded as a new clean pulping technology excellent for straw,but its elementary systematic theory is not fully understood so that no commercial process is running in existing pulping mills.In this thesis,alkali-oxygen pulping of wheat straw was studied for its mechanism,with the aid of analyses of the chemical composition and structure from the treat straw or pulp and the relative black liquors.The summarizedResults are as follows:1)Alkali precooking of wheat straw in the presence or absence of oxygen was carried out individually at 5 different temperatures from 85? to 125 8 · It was shown that the former removed more lignin,hemicellulose,and less minerals,also gained the same delignification degree at the temperature lower than 20?.?2)A greater proportion of the macromolecular hemicelluloses in the straw would be dissolved in the black liquor after the precooking temperature mounted into 115?.The presence of oxygen can accelerate the formation of low-molecular carbohydrates,with increasing temperature.3)Alkali-oxygen pulping of wheat straw was performed at 4 different temperatures from 95?to 125? for 7 different periods ranging from 0 min to 140 min.The increase of the temperature also elongation of the time would promote the delignification and the dissolution of hemicelluloses from the straw,resulting in the decrease of the pulp yield,in spite of remaining more minerals onto fibers.The increase of macromolecular lignin and hemicelluloses in proportion means that degradation of them into low molecules was moderate.But the delignification selectivity decreased at 125?,led to a fast dissolution of macromolecular hemicelluloses.4)The cooking at 95? did not delignify enough to separate the straw into pulp fibers.That at 105? can delignify at a even rate pacing with the consumption of the alkali during the whole period,but it may take a longer period to get the pulp we need.The delignification rate at 115? or higher was fast in initial,and slowed down in mid late period,being basically in line with the diminishment of the alkali.The anticipant pulp can be obtained at 115? for 120min.