Research On The Pretreatment Of Cotton Fiber Using NaOH/Urea Aqueous System And Its Application

Cotton fiber is an important industrial raw material, and as the most pure cellulosic sources in the nature, it is widely applied to various industry sectors, such as the light industry, chemical industry, medicine industry, national defense industry. However, cotton fiber has a dense crystal structure and a high degree of polymerization, leading to the high crystallinity, which limits its effective utilization. Therefore, it is particularly important to reduce the crystallinity and improve the reactivity of cotton fiber. NaOH/urea aqueous system is a kind of non-derivative cellulose solvents with low cost, non-toxic, non-polluting and environment friendly, and it has a strong ability of dissolving cellulose. In this paper, the pretreatment of cotton fiber was conducted by using NaOH/urea aqueous system to reduce the degree of crystallinity of cellulose effectively, improve its accessibility and reactivity, and promote its further application.In this paper, the conditions of pretreatment process of cotton fiber using NaOH/urea aqueous system were studied. By controlling the temperature, alkali-urea ratio, solution dosage, reaction time and stirring speed, the moderate pretreatment of cotton fiber was realized and the dissolution was inhibited. The influence and its significant degree of the above factors on the pretreatment were analyzed and studied by single factor and orthogonal design experiment, respectively. The results showed that when the system temperature decreased or alkali-urea ratio, stirring time and stirring speed increased, the pretreating fiber ability of this solution system increased; and this ability would firstly increase and then decrease when solution dosage increased; and the influence degree sequence for these factors was temperature> alkali-urea ratio> solution dosage> mixing time, and among them, the temperature and alkali-urea ratio were significant factors, and solution dosage and stirring time were non-significant factors. At the same time, a mathematical model between fiber yield and temperature and alkali/urea ratio was established as follows: y=1.93z1-5.89z2+124.53 (r=0.992), wherein y represented the fiber yield, z1 represented system temperature, and z2 represented alkali-urea ratio.In this paper, the different structures and properties of pretreated cotton fibers were studied. The morphological structure and various properties of fibers under different pretreating degree were analyzed and characterized synthetically by using the determination of water retention value (WRV) and the degree of polymerization (DP) and various testing means, such as SEM, FQA, FT-IR, XRD, TG/DTG The results showed that with the increasing degree of pretreatment, the swelling properties of fiber increased and the average DP value decreased gradually; the surface morphology of pretreated fiber was gradually destroyed, and the microfiber on the surface decreased; the degree of kink and curl was also increasing. From FQA, fiber length and fines content decreased, and fiber width increased, while the kink and curl index firstly increased and then decreased. The crystallinity gradually decreased from original 81.52% to 33.41%; at the same time, the cellulosic crystal also gradually changed from cellulose â…  to cellulose â…¡; and the highest cellulose â…¡ relative content was 40.95%; in addition, the pretreatment process leaded to a decrease in fiber thermal stability.In this paper, the application properties of pretreated cotton fibers were studied and explored. In the same conditions, the beating and papermaking process were conducted using pretreated fibers under different pretreating degree to study the influence of the pretreatment on the beatability and paper performance of cotton fiber. The results showed that when compared with unpretreated fiber, the beatability and paper performance of pretreated cotton fibers were all poorer, but the thickness of handsheet was better. At the same time, in the same conditions, the cellulose acetate (CA) was prepared using various pretreated fibers to determine the reactivity of fibers, and the degree of substitution (DS) of CA was measured. The various CAs were also analyzed and characterized by using SEM, FT-IR and XRD. The results showed that when compared with unpretreated fiber, the reactivity of pretreated fiber all increased; the DS values of CAs were also increased, and among them,4# CA had the highest DS of 2.88; the chemical structures of CAs prepared from different material were almost same; and the crystallinity of CA decreased obviously, and the minimum was 15.12%.