Study On Acetalization Of PVA/SP Blend Fibers With Non-Formaldehyde And Fabrication Of MWNTs/PVA Reinforced Fibers

Poly（vinyl alcohol） （PVA） fibers are one of the most important synthetic fibers with good moisture absorption and high strength etc.. However, its deficiencies, such as poor wet strength and high degree of shrinkage in hot water, have limited its application in certain areas. In recent years, with the development of the production of PVA fibers, researches on physical and chemical modifications of PVA have attracted increasing attention, one of which is to further improve its performances for textile use and put it into commercial run, another is to develop its non-textile use, and mainly focused on the PVA blends and composites research. Against these two points, this research just deals with soybean protein modified PVA fibers and MWNTs reinforced PVA composite fibers.During the spinning process, acetalization treatment with formaldehyde is important to reduce the Tiber shrinkage in boiling water while formaldehyde is harmful to persons’ health and environmental-unfriendly. In this work, new cross-linking agents were chosen to replace toxic formaldehyde for acetal treatment and Latin square experiments were designed to determine the cross-linking conditions. Compared to the formalization process, the conditions for the new cross-linking agents were relatively relaxed and reduced energy consumption. FTIR and ¹³C NMR results confirmed the reactions of PVA and protein molecules with such cross-linking agents. The strength of the resultant fibers reached 3.76 cN/dtex, showed an increase of 4% compared with the formalized fibers; the boiling water shrinkage reduced to 1%, improving the properties of resistance to hot water markedly; the content of protein residues in enzymatic hydrolyzed fibers was 90%, higher than that of the formalized fibers. Therefore, the effects of acetalization treated by new cross-linking agents were better than formalization treatment.There have been more and more researches about PVA reinforcing materials in recent years, and this paper just focuses on the preparation of PVA composite fibers with MWNTs as reinforcements to substitute for the harmful asbestos as reinforcing materials in the construction industry.By simply refluxing MWNTs with mixed acids, some functional groups, such as carboxylic groups, can be introduced on MWNTs. Such MWNTs were then used to prepare functionalized MWNTs （Fun-MWNTs） through esterification reaction with PVA. Electron microscopy showed that the functionalized MWNTs could disperse in DMSO homogenously and stably, and have good compatibility with PVA matrix.The static rheological properties were studied using HAKKE rheometer in order to choose reasonable spinning technology. The results showed that the solutions were shear-thinning non-Newtonian fluid. MWNTs played the role of cross-linking in the dope, which increased the degree of structure and decreased the spinnability. The activation energy of blend solutions varied with the addition of different MWNTs.PVA/Fun-MWNTs fibers were spun with dry jet wet spinning, the cross section of which was circular and compact. The strength of the resultant fibers reached 9.66 cN/dtex, the strength and modulus increased 63.4% and 7.4% respectively compared with the pure PVA fibers. Fun-MWNTs greatly enhanced their combination with PVA matrix, the interactions between them helped to transfer the load of the composite fibers, thus improving the mechanical properties of nanocomposites.