Structure And Properties Of Polypropylene/Superfine Down Powder Composite Fibers

In textile industry, only the isotactic PP (iPP) is normally used to produce textile fibers due to the high degree of crystallinity of iPP fibers. Therefore, iPP fibers are well applicable for various fields including industrial sewing threads, bandage, carpeting, woven bags, and medical fabrics. However, the main disadvantage of iPP fibers is lack of dyeability, which restricts its available application in apparel industry. Compared to synthetic polymer, down fiber is usually more biocompatible, degradable, and environmental friendly. Poultry farms in China produced about 0.2 billion kg of down fiber every year. However, a large amount of down fiber is often processed into a low quality protein supplement for animal feed after usage. This is a huge waste of energy resources. In addition, down fiber showed a higher thermal stability than wool fiber. This means that superfine down powder (SDP) is better to be filler, which could improve the dyeing properties, moisture regain and water absorption of iPP fibers than superfine wool powder.The thermal properties of SDP were characterized by using TGA, DSC, TG-FTIR and FTIR. The effect of average size of powder on the thermal properties of down powder was also discussed. The average particle size of SDP was around 2.34μm. SDP contained nearly 14 times the specific surface area of down fiber. This meant that there were more hydrogen groups on the surface of SDP, which has higher moisture than down fiber. It was apparent the thermal stability of down powder decreased as the decrease in the average size of powder. According DSC curves, down fiber and SDP had four endothermal peaks, which can be explained as follows:peak 1 corresponds to the vaporization of moisture and bound water of samples; peak 2 is ascribed to crystal cleavage; peak 3 corresponds to destruction of crosslinks, such as-S-S-bonds, H bonds and salt links; peak 4 is ascribed to the thermal degradation of peptide bonds. It was evident that these peaks of SDP were different from those of down fiber, suggesting that the microstructure of down fiber changed during the process of grinding powder.The dyeing properties of SDP were different with those of down fiber due to the high specific surface area of SDP. Compared with down fiber, SDP showed higher dye up-take and lower K/S value. However, the K/S value of SDP was higher than that of down fiber when they dyed at 10% dye concentration and 28℃.SDP has hydrophilic surfaces that make it incompatible with polypropylene. The interfacial adhesion between powder and polymer is one of the major factors determining the ultimate mechanical properties of composites. SDP was modified by stearic acid to improve the weak interfacial adhesion between powder and iPP matrix and was named MSDP. The chemical reaction between SDP and stearic acid was characterized using the attenuated total reflection attachment on the Fourier transform infrared (ATR-FTIR). iPP/MSDP composites showed more uniform powder dispersion in iPP matrix, higher compatibility and better mechanical properties than PP/SDP composites. The addition of SDP led to a large increase in water absorption of iPP/SDP composites. However, the water absorption of iPP/MSDP composites decreased slightly compared to that of PP/SDP composites. Furthermore, the effects of SDP and MSDP on the micro-structural and thermal properties of different composites were also investigated respectively.Nonisothermal crystallization kinetics of pure iPP, iPP/SDP composites and iPP/MSDP composites were investigated. The data were analyzed by using nonlinear multi-variable regression method and fitted to Avrami and Mo'models. Ozawa models failed to provide an adequate description of the nonisothermal crystallization of all samples. The Mo'model proved to be the best fitting model among those investigated. The crystallization behavior studied with DSC showed that superfine down powder in iPP matrix acted as nucleating agents. Moreover, iPP matrix in composites shows a two-stage crystallization process:the primary stage is characterized by nucleation and spherulitic growth and the secondary stage is the characteristic of the perfecting of crystals. SDP decelerated the primary stage but speeded up the secondary stage, resulting in the decreased the crystallization rate of iPP matrix in general. The nucleating activity of pure iPP, iPP/SDP composites and iPP/MSDP composites were calculated by using Dobreva and Gutzowa equation. With the increase in SDP content, the nucleating activity of samples increased. The activation energies for nonisothermal crystallization of pure iPP, iPP/SDP composites and iPP/MSDP composites were calculated by using Kissinger and Takhor methods, respectively. With the increase in SDP content the activation energies for nonisothermal crystallization of samples increased, which meant lower crystallization rate of samples containing higher content of SDP.Porous iPP fibers were fabricated by melt extrusion and spinning of immiscible blends of thermal polyurethane (TPU) and iPP and subsequent removal of the TPU. The characteristics of the porous structure, such as pore size and pore interconnectivity, depend on the content of TPU and the spinning process. iPP/TPU composite fibers showed a lower spinning ability than pure iPP fibers. When TPU content was 30%, the pores of iPP fibers after the removal of TPU were interconnected without the loss of spinning ability. Therefore, iPP/TPU/SDP composites containing 30%TPU were prepared and then were spun to produce porous iPP/SDP composite fibers after the TPU was removed. For porous iPP/SDP composite fibers, with the increase in SDP content the pores were seem to be needles and those size increased, which meant that more SDP could be seen on the surface of porous iPP/SDP composite fibers. Porous iPP/SDP composite fibers showed improved moisture regain and dyeing properties but lower wet-washing fastness.To develop dyeable iPP fibers, SDP (SDP) was coated on the surface of iPP fibers post melt-spinning. Optical micrographs showed that the surface of powder-coated iPP fibers was roughness, and the amount and dispersion of coated SDP were found entirely dependent on melt-spinning temperature. With the increase in coated SDP content, the moisture and water absorption of powder-coated iPP fibers increased. Powder-coated iPP fibers could be, respectively, dyed by reactive red dye and acid red dye, and the observed enhancement of color strength (K/S value) and red value (a*) of powder-coated iPP fibers could be attributed to SDP coated on iPP fibers. It was worth noting that the removal of coated SDP affected the wet-washing fastness of powder-coated iPP fibers largely. In addition, the powder-coated iPP fibers were produced in a few minutes with lower cost and could have potential applications in textile industry.Isotactic PP was blended with dyed SDP to produce dyes into iPP fibers. The effects of the content and the K/S value of SDP on the K/S value of iPP/dyed SDP composite fibers were investigated. With the increase in dyed SDP content, the K/S values of iPP/dyed SDP blend fibers increased, especially when the amount of dyed SDP was over 8%. Higher K/S value of dyed SDP blended higher K/S value of iPP/dyed SDP composite fibers obtained.