Study On The Preparation And Properties Of Chitosan Modified Polypropylene Fibers

Polypropylene(PP) is one of the four major synthetic fibres which possesses excellent comprehensive performance, such as lightweight, mildew resistance, chemical corrosion resistance, ease of processing. The usual spinning PP fibers have poor hydrophilicity and dyeable, which can be ascribed to the high neat degree of the molecular chain that the surface of the molecular chain don’t have polar groups. Thus, PP fibers often need to be modified to meet various applications.Chitosan(CTS) is the most abundant biopolymer in nature after cellulose with strong hygroscopicity, moisture retention, biodegradability, biocompatibility, broad-spectrum antimicrobial properties and so on, which has been applied in absorbable surgical sutures, nonwoven, hemostatic materials and antibacterial fabrics. However, the high cost and expensive price of pure spinning chitosan fibres have limited the application and development of chitosan in the field of ordinary textiles.This paper simulated the blending melt spinning using capillary rheometer, and chitosan modified polypropylene fiber(PP/CTS) were prepared through melt extruding method. The rheological properties of PP/CTS blending melt and the structure properties of the fiber were explored, so as to provide theoretical basis for the development and production of chitosan modified polypropylene fiber. Therefore, the performance of PP fibers can be improved,meanwhile, the application of chitosan in textile materials is expanded as well.1. The chitosan particles were produced by the dry ball-milling method, and the influence of the mechanical force on the structure and basic physicochemical properties of chitosan was investigated. The morphology of chitosan changed from plate, block and flocculent into gray fine powder during the dry ball mill operation. Particles present irregular flake and block and the layer structure of the surface is similar to "erosion" topography. The particle size of chitosan is rapidly reduced after ball milling, and after ball milling of 8 h, the average particle size reduce to 843.7 nm. The molecular weight of chitosan decrease and the crystalline structure is destroyed then tend to be amorphous state after grinding. However, the deacelation degree andmolecular structure have no obvious changes, and the hygroscopicity and water-soluble of chitosan particles are significantly improved. The color of chitosan changes from grey into yellow, brown and dark with the increase of thermal threatment temperature. The infrared absorption peak of chitosan have no obvious changes when the temperature is 200 oC. When the temperature increases to 300 oC, the disappearance of hydroxy and amino peak imply that the molecular structures are severely damaged.2. The rheological properties of PP/CTS melt blends were investigated by capillary rheometer. The apparent viscosity and shear stress of PP are increased with the addition of chitosan particles. Besides, adding more chitosan also raise the value of the non-newtonian index and the flow activation energy obviously of PP. Compared with pure PP, the shear viscosity of the blend with 4% of chitosan is increased from 37.10 Pa·s to 43.89 Pa·s, the shear stress is enhanced from 56.60 kPa to 61.77 kPa, and the viscous flow activation energy is increased by 125.6% at the shear rate of 1500.48 s-1. The blending melt of PP/CTS belongs to extensional thinning fluid. And, the extensional viscosity and extensional stress of the blends remarkably increase with the increase of chitosan particles. During the processing, the melt have slight degradation under low shear rate with the addition of chitosan. The melt possess good processing stability when the shear rate is higher than 1800 s-1.3. The chitosan modified polypropylene composite fibers were prepared by melt extrusion in which chitosan particles acting as modifier. The crystal form of PP have no changes while the crystal surface spacing and crystallite size decrease with the addition of chitosan. Accordingly,the crystallinity and crystal temperature of the composite fibers is improved. Thermogravimetric analysis showed that the thermal stability of the composite fibers is enhanced slightly. The fastest pyrolysis temperature is increased by 3.37 oC as the chitosan content is 3%. With the addition of the chitosan particles treated with titanate coupling agent, the crystal sizes of the composite fibers is much decreased and the crystallinity have further increased. Adding 1% of chitosan with or without coupling treatment, the crystallinity of the blends is increasesed by5.91% and 9.21%, respectively. In the meantimne, both of the hydrophilicity and moisture absorption of the composite fiber are enhanced when compared to pure PP.