Low Temperature Softening Modification Of Ramie

Ramie, the Chinese grass, has been planted in China for more than one century. The output oframie fibers in China occupies more than90%of the worldwide ramie yield. Ramie can adapt tovarious environments and grow on even barren hill lands. Ramie fiber has excellent propertiessuch as coolness, high permeability, moisture absorption, antibacterial function etc.. The ramiefibers and ramie fabrics are important industrial raw materials for various applications.However, ramie fibers have the high crystallinity and stiffness, as well as a large fiberdiameter and a low elongation. These properties lead to the poor spinnability, the easiness ofcrease and the poor dyeability. More importantly, the thick and rigid ramie fiber ends on thefabrics can apply a strong protruding force on skin and cause itchy feeling. This problem haslimited ramie fibers for applications requiring for the direct contact with skin. Modifications havebeen employed to ramie products in order to reduce the itching effect and to improve theirdyeability.In this research, a low temperature softening treatment with an alkaline/urea treatment bathfor ramie was developed. The influences of the types of softening agents, the agent concentration,the treatment temperature and time on the properties and structure of ramie fibers and fabrics wereinvestigated. Comparisons were made among the treatment effects of the conventional highconcentration alkali treatment at room temperature (HART, the traditional method), the mediumconcentration alkali/urea treatment at room temperature (MAURT) and the new treatmentdeveloped in this current study (Low concentration alkali/urea/boron salt/lubricant at lowtemperature, LAUBLLT). The main findings were summarized as follows:(1) The ramie fibers treated by LAUBLLT and the raw fibers were subjected to theinvestigations by the Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD),scanning electron micrographs (SEM), tests of mechanical properties and moisture regain, and theevaluation of the color strength (K/S value). The optimized treatment bath was with the weight ratio of7wt.%of NaOH,12wt.%of urea,3wt.%of Na2B4O710H2O and5wt.%glycerol. Theoptimized treatment condition was at10°C for10min. After the LAUBLLT treatment, thesurfaces of the modified fibers became rougher. The tensile stress decreased, but it was similarwith that of cotton fibers. The moduli of fibers were reduced to8.1±3.2GPa, close to that ofrayon fibers. The treatment temperature played a more important role to control the treatmenteffect than other parameters, such as the treatment time. The crystallinity of fibers was reducedfrom81.78%to50.02%. By comparing the FTIR profiles, it was revealed that the crystallineregions of treated fibers were reduced and the amorphous area was increased, which wasconsistent with XRD results. Compared to the raw sample, the moisture absorption of treatedramie fibers was enhanced and their dyeability was improved significantly.(2) The ramie fabrics treated by LAUBLLT and the original fabrics were subjected to theinvestigations by the XRD, SEM, tests of mechanical properties and moisture regain, and theevaluation of the color strength (K/S value). Fibrillation of fibers could be observed on the surfaceof fabrics after treatment. Yarns became more compacted. The mean tensile stresses of samplesvaried, but there were no statistically significant differences among the tensile stresses of treatedand untreated fabrics. The treatment temperature could significantly affect the initial moduli oftreated fabrics. After treatment, the moduli of the fabrics decreased. The bending lengths of all thetreated fabrics were substantially shortened from2.61cm to2.23–2.33cm, indicating that thefabrics became softer. The scratchiness value was reduced from3.13to around1.50, which was atthe mild scratchiness level. Moreover, at the same time, the color strength of the modified samples,indexed as the value of K/S, increased obviously. The dyeability improved greatly.Without any chemical reaction, the developed treatment in this study requires for limitedconsumption of the chemical agents and the agents can be reused. The treated fibers and fabricsbecame softer and more flexible. The scratchiness of treated ramie fibers and fabrics wassubstantially weakened. This treatment is low in price and environmental friendly, suggesting apotential for industrial applications.