| At present, the melt-blown nonwovens technology is developing very rapidly all over the world. However, most of the melt-blown nonwovens are made from the petroleum-base raw materials. The large usage of these non-biodegradable materials can cause increasingly serious environmental problems. So it is preferred that the degradable polymers are used as the raw materials of melt-blown nonwovens.Lyocell melt-blown nonwovens are precisely the environment friendly nonwovens because of its abundant source, biodegradability, ease of processing, good strength and absorbency and so on. The correlational research has been done for more than ten ygais ahroad and important progress has been made.However,up to now, there is no report on Lyocell melt-blown technology at home. So the work in this thesis is of great significance.In this paper, the rheological properties of all kinds of the cellulose/NMMO·HaO solutions were analyzed firstly by HAAKE rheometer. The results showed that these spinning dopes were shear thinning liquid. With the increasing of average degree of polymerization (DP) of cellulose pulps, cellulose content and impurity content in dopes, the apparent viscosity of dopes increased and it decreased when temperature rose. The fluidity of solutions was enhanced by filtering, which was good to the melt-blowing process. With the increasing of average DP of cellulose pulps and the cellulose content in dopes, the viscoelasticity of solutions rose and the melt-blown spinnability of dopes got worse.On basis of the aforementioned analysis on rheological behaviour, the preliminary exploration on Lyocell melt-blown nonwovens was carried out with traditional melt-blown equipment equipped with single screw extruder. The results showed that the melt-blown spinnability of dopes was improved obviously with the decrease of average DP of cellulose pulps and the cellulose content in dopes. The resultant Lyocell melt-blown nonwovens had the similar characteristics of those made from thermoplastic resins. The Lyocell webs possessed a three-dimentional network structure. There were shorts, fiber fusion and branching in webs. In addition, good webs were gained using the wet web forming way under the specific experimental conditions. However, there were a series of shortcomings in this melt-blowing system which couldn’t deal with the dopes well.Therefore, the further exploration was made with the new purpose-built equipment. The results showed that the surface of the obtained fiber was smooth when the pump capacity was very small while it would get rough and pebbled when the pump capacity increased. The Lyocell melt-blown nonwovens had excellent absorption performance because they could absorb about8times their weight in water. With the roller traversing speed increasing, the mean fiber diameter of webs kept unchanged. When increased the die to collector distance, webs’thickness and degree of crystallinity increased, mean fiber diameter, maximum, average and minimum pore size decreased at first and then increased while breaking tenacity increased at first and then decreased. The increase of pump capacity would increase the fiber diameter while no significant change in pore size of webs had been observed in a certain pump capacity range. When hot air temperature rose, mean fiber diameter decreased at first and then increased while breaking tenacity decreased. The rising of die temperature would decrease the mean fiber diameter, maximum, average and minimum pore size of webs while degree of crystallinity and breaking tenacity increased. When air velocity increased, mean fiber diameter decreased at first and then increased, maximum, average and minimum pore size of webs decreased rapidly, degree of crystallinity increased at first and then decreased while breaking tenacity increased. Besides, the fiber diameter irregularity of Lyocell melt-blown nonwovens was very high and its coefficient of variation (CV) was between30%and50%.The above results revealed that, the new purpose-built equipment could overcome the shortcomings which existed in the traditional melt-blown system and it could produce better Lyocell melt-blown nonwovens using cellulose solutions with high viscosity. |
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