Preparation, Structure And Properties Of Bamboo Lyocell Fiber

Lyocell process is a simple and environmental-friendly process for the production of regenerated cellulose fiber.It adopts N-methylmorpholine-N-oxide monohydrate （NMMO·H₂O）,a non-toxic solvent,to directly dissolve cellulose and then uses a dry-jet wet spinning method to spin the fiber.In the process,no derivatization,such as alkalization and xanthation in the case of viscose fibers,is required.Furthermore, Lyocell fibers are distinguished by high crystallinity,high degree of orientation,and well-oriented amorphous regions,resulting in a very high dry and wet tensile strength, a high wet modulus and high loop tenacity.Due to the restriction of wood resource in China,using wood as main raw material of Lyocell fiber could not meet demand for Lyocell fiber.However,bamboo resource is abundant in our country.If Lyocell fibers could be made from bamboo,it not only provides a cheap material for Lyocell fiber but also exploits a new application of bamboo.Moreover,compared to the fibers from cotton and wood,bamboo cellulose fiber made from bamboo has significantly different properties,such as good drapability,good dyeing property,soft,cool,comfortable feelings,and lustrous looking,etc.So far,regenerated bamboo cellulose fiber was prepared by viscose process at home and abroad.Lyocell Fibers made from bamboo cellulose has not been reported yet. Hence,exploratory researches on bamboo Lyocell fiber were done in this paper.Firstly,the bamboo pulps were analyzed and characterized by viscosimetry method, gel permeation chromatography（GPC） and Fourier transform infrared spectroscopy （FTIR） and the results were compared with wood pulp.It was found from the FTIR spectra that bamboo pulp was mainly consist of cellulose,same as wood pulp,but contained higher lignin than wood pulp and a little unknown substances which didn’t exist in wood pulp,the paper grade bamboo pulp had higher DP,broader MWD and higher content of hemicellulose than that of fiber grade bamboo pulp.Furthermore,the study of bamboo pulp with different DP dissolved in NMMO·H₂O showed that the dissolving property of the paper grade bamboo pulp with high DP exhibited more inferior than that of the fiber grade bamboo pulp.Therefore,the paper grade bamboo pulp could not be directly used as raw material for producing Lyocell fiber.Bamboo cellulose/NMMO·H₂O solutions were prepared by dissolving bamboo celluloses with different DP in NMMO·H₂O and the rheological behaviors of these solutions were investigated with HAAKE RS150L rheometer.The results showed that bamboo cellulose spinning dopes were shear thinning fluids.With the increase of the average degree of polymerization of bamboo cellulose pulps,the flow curves moved upward,the critical shear rate and the non-Newtonian index（n） decreased,while the apparent viscosity,the viscous flow activation energy,the zero shear viscosity and the structural viscosity index increased.With the increase of temperature,the apparent viscosity decreased,the non-Newtonian index increased.Moreover,the rheological behaviors of the alkali treated bamboo cellulose/NMMO·H₂O solutions were affected by the average degree of polymerization of bamboo cellulose,the content of hemicellulose and impurity in the pulp.In addition,the comparison of the results from theological data and GPC showed that it was feasible to predict the MW and MWD of cellulose by using rheological method.On basis of aforementioned investigations,the fiber grade bamboo pulp was preferentially selected as raw material for preparing bamboo Lyoccell fiber,bamboo Lyocell fiber was preparing with this pulp by Lyocell process in our laboratory and the influence of spinning parameters on structure and property of bamboo cellulose fiber were systemically investigated.The results showed that the spin parameters had greatly effected on the structures and properties of bamboo Lyocell fiber.Firstly,the mechanical property of the fiber enhanced with the increase of the cellulose concentration in spinning dope.Secondly,the crystallinity and orientation of bamboo Lyocell fiber increased and accordingly the tensile strength and initial modulus increased with the increase of draw down ratio,whereas the linear density and elongation at break decreased with the increase of draw down ratio.When the draw ratio was kept constant,the higher the spinning speed,the higher the orientation in amorphous region and crystallinity,the higher the tensile strength and initial modulus will be,while the orientation in crystalline region and the linear density were not changed basically.In addition,the crystallinity,orientation in crystalline region and initial modulus increased and the orientation in amorphous region,total orientation and tensile strength slightly decreased with the increase of the temperature of coagulation bath.Moreover,the gap length also affects the mechnical properties of the fiber and the optimum gap length is 5 cm.Generally speaking,paper grade bamboo pulp has high molecular weight,it is difficult to be dissolved in N-methylmorpholine-N-oxide monohydrate（NMMO·H₂O）. In order to reduce its molecular weight,improve its dissolving property in NMMO·H₂O and obtain the cheap bamboo pulp with good spinnability for Lyocell process,the paper grade bamboo pulp was irradiated in air by ⁶⁰Coγ-ray,then the molecular weight（MW） and the molecular weight distribution（MWD） of the irradiated bamboo cellulose were measured by viscosimetry and gel permeation chromatography （GPC）,and the crystalline structure was studied by Fourier transform infrared spectroscopy（FTIR） and wide angle X-ray diffraction（WAXD）.The results showed that the average degree of polymerization（（?）） of the irradiated bamboo cellulose decreased and its MWD became narrow continuously with the increase of absorbed dose,the most significant degradation of the bamboo cellulose took place in the range of the absorbed dose up to 15kGy.However,the results from WAXD and FTIR showed that the crystalline structure such as crystallinity and crystalline form did not change obviously,and this implies that the crystalline structures of the bamboo cellulose were not destroyed in our case.It could be deduced from the relationship between（?） and absorbed doses（D） that G（s） of the bamboo cellulose was 0.94μmol·J^-1,which indicated that the bamboo cellulose was easily degraded by ⁶⁰Coγ-ray radiation. Therefore,it was possible economically to degrade the bamboo cellulose by irradiation. Furthermore,it was found from spinning experiment that the dissolving property and the spinnability of the irradiated bamboo cellulose was remarkably improved and that the fiber made from the bamboo cellulose could be applied in apparel industry.The comparison of the wear behavior of bamboo Lyocell fiber and the other regenerated cellulose fiber was carried out.The results showed that the bamboo Lyocell fiber had many similarities in structure and properties compared with the conventional Lyocell fiber,such as smooth surface,approximate circular cross section, and easy fibrillation,its crystallinity,tensile strength and initial modulus are higher than the bamboo viscose fiber,its ratio of wet tensile strength to dry tensile strength is higher than that of bamboo viscose fiber,and its hygroscopic,dyeing and anti-fibrillation property all are better than conventional Lyocell fiber.Furthermore, the bamboo Lyocell fiber also has excellent negative ion effect and nature antibacterial property.The handle of the fabrics weaved with bamboo lyocell fiber and wood lyocell fiber respectively were evaluated by KES system,the results showed that the former had better wear performance,such as fluffy,slippery,tender and has a good sense of seeing as well as good hanging ability.