Study On The Humidifying Process Before Crimping And Low Modulus Mechanism Of Cellulose Diacetate Filament

Cellulose diacetate, as the second category of regenerated cellulose fiber, has been used incigarette filter industry due to numerous advantages such as odorless, non-toxic, excellentabsorption and filter function. During the production of cellulose diacetate, crimping is a veryimportant process. However, because of the relatively high modulus, cellulose diacetate always bedamaged by the friction of clamps and rollers of crimping machine and form many fiber crumbswhich are called flying. Flying can not only increase the burden of filter stick formation, but alsoimpair the health of the workers. A variety of processes are being developed to decrease the initialmodulus of cellulose diacetate before crimping. Among all different methods, humidifying processhas received considerable attention because of its simplicity and effectiveness.In this paper, humidifying process was added to the cellulose diacetate filament beforecrimping. Deionized water and spinning oil were added to the filament by self-made ultrasonicwave atomizer humidifying machine. Then the mechanical properties of diacetate tow and fiberwere tested. The as-prepared filament exhibit low initial modulus. The modulus-strain curves withdifferent humidifying parameter were fitted. These curves demonstrate the relationship betweenthe microstructure of the filament and the initial modulus.Firstly, Three kinds of diacetate fiber with linear density of6.0D、3.9D and2.4D are tested inmorphology structure、tensile property、thermal property and surface property. The experimentalresults show that the fiber surface cleanliness of2.4D diacetate fiber is the worst, there are moreoil、matting agents and flying depositing on the surface. The results of X-ray diffraction showthat with the decrease of linear density the crystallinity increases after the first decrease. Theresults of TG show that3.9D diacetate fiber has the largest degradation rate, which means thethermal stability is worse. This result matches to the result by XRD analysis. The results of tensile tests show that2.4D diacetate fiber has a relatively higher initial modulus and breaking stress andthe lower breaking strain, which means2.4D diacetate fiber is more easily damaged by the frictionof crimping machine and form more flying.Secondly, deionized water was added to the filament by the self-made ultrasonic waveatomizer humidifying machine, which could disperse the water into little drops with the diameterof1-10um. Then the moisture content and mechanical properties of diacetate tow and fiber weretested. The moisture content increases with the raise amount of atomized water. There is aconspicuous inflection in the curve with the moisture content of24.28%. The initial modulusdecreases with the raise of moisture content. The initial modulus of diacetate tow drops to2.49cN/tex from the original3.12cN/tex. The drop percentage is20.2%. The initial modulus ofdiacetate fiber drops to27.20cN/dtex from the original30.94cN/dtex. The drop percentage is12.1%. When the moisture content is28.43%, the diacatete fiber has the lowest initial modulusand the highest breaking stress which can avoid damage to the largest extent. As a consequence,the moisture content should be controlled at about28.43%in the actual production process.Thirdly, spinning oil was added to the filament. Then the mechanical properties of diacetatetow and fiber were tested. The initial modulus of diacetate tow drops to2.62cN/tex from theoriginal3.12cN/tex. The drop percentage is16.0%. The initial modulus of diacetate fiber drops to27.90cN/dtex from the original30.94cN/dtex. The drop percentage is9.8%. Compared withdeionized water, the initial modulus also decreases, but the drop percentage is smaller.Finally, modulus-strain curve is the first derivative of stress-strain curve. In order to eliminatethe fluctuation of the derivative curve, the real stress-strain curve was interpolated by45pointswith Origin. Then the interpolated real stress-strain curve was polynomial fitted. Themodulus-strain curve was the first derivative of the polynomial fitted real stress-strain curve. Thevalue of the maximum peak is defined as the initial modulus. The initial modulus will decreaseand the corresponding strain will increase with the raise of moisture content. These curvesdemonstrate the relationship between the microstructure of the filament and the initial modulus.