Formation of Fiber Structures of Blended Fibers (I) of Liquid Crystalline Polymers and Polypropylene

The formation process of blended fibers of liquid crystal polymer and polypropylene (the formation of fiber structure I Qin Yimin (Biochemical Materials Research and Development Center, Jiaxing University, Jiaxing 314001, Zhejiang, China). The results show that in the process of using liquid crystal polymer reinforced polypropylene fiber, the liquid crystal The concentration, viscosity of the phase, the shearing and drawing tension of the melt, the shape of the spinneret, the compatibilizer and other factors have a great influence on the formation of the liquid crystal phase structure at higher concentrations and greater tensile tensions. Under the effect, liquid crystal polymers can form microfibers with reinforcing effect in polypropylene fibers.

1 The basic principle of blended spinning The blending of polymer materials is an effective way to obtain new properties. 111 The thermodynamics of blending is very similar to that of low molecular materials. The free energy in the mixing process can be calculated by the following formula: Change; ASm is the change of entropy. In order to make the two polymers compatible, AFm must be less than zero. Due to the high molecular weight of polymers, the entropy change during mixing is small, and the mixing process of polymers is generally an endothermic process. AHm is a positive value, so it is difficult to meet the thermodynamic compatibility conditions. Most of the polymer blend systems are incompatible 121. When two or more polymer materials are evenly distributed, the following basic structural forms can be formed. 13:1) When AFm is less than zero, The two polymers are evenly distributed to form a compatible polymer material; 2) the polymer is distributed in the form of particles in another polymer; 3) the polymer is in microfiber form Distributed in another polymer; 4) Two kinds of macromolecules each forming an interconnected network are bound together.

The spinning of the blended polymer and the spinning of the single polymer are basically the same. In the actual spinning process, two kinds of polymer materials can be mixed at different stages in the spinning process. Two kinds of polymer chips are usually dry-blended when melt-spinning, melted and mixed in different parts of the spinning machine, and then spun into fibers. In some cases, the polymer may also be pre-mixed and melt granulated before melt spinning.

For solution spinning, three mixing methods are generally used: 1) The two polymers are dry blended in proportion and then dissolved in a solvent. 2) Dissolve 2 kinds of high polymers separately, and then mix 2 solutions of high polymer. 3) First a polymer is dissolved in a solvent, and then mixed with another polymer monomer, and then polymerize the second polymer 141. 2 liquid crystal polymer and polypropylene blends The fiber-optic liquid crystal polymer (LCP) is generally a polymeric material having a rigid and linear structure formed by polymerization of aromatic monomers. Meltable liquid crystals can form an anisotropic melt after melting. Under suitable conditions, high strength and high modulus fibers can be formed by drawing from a spinneret.

When LCP is blended with an isotropic polymer that is incompatible with itself, if LCP can form a microfibrillar structure during processing, it can perform in-situ reinforcement of the blended polymer material. effect. The LCP microfibers in the disperse phase can provide a good reinforcing effect and can be conveniently used in the extrusion molding of polymers.

Polypropylene (PP) is a high-performance polymer material.

Polypropylene fiber has the characteristics of convenient processing, high strength, acid and alkali resistance, and low cost. Polypropylene fibers have the disadvantages of lower melting point, poor thermal stability, lower modulus of fiber, and poor structural stability.

The high strength, high modulus and high thermal stability of LCP just make up for the weakness of polypropylene fiber. Through blend spinning, a small amount of LCP can effectively improve the overall performance of polypropylene fiber.

3 The formation of liquid crystal polymer and polypropylene blend fiber structure The melting point of liquid crystal polymer is generally much higher than the melting point of polypropylene. There are three kinds of widely used fused liquid crystals, namely VectraA900, VectraB950 and RodrnnLC3000. Their melting points are about 280, 280 and 240Q respectively, polypropylene has a melting point of 165. Before entering the spinneret, due to the melt entering a relatively stable laminar flow zone, the liquid crystal phase shrinks into a spherical structure under the action of surface tension. Microscope tests showed that the liquid crystal phase before entering the spinneret was essentially distributed in the polypropylene in a tiny spherical structure.

Before entering the spinneret, the liquid crystal phase is elongated by the effect of elongational flow. The shear flow of the melt through the spinneret has little effect on the extension of the liquid crystal phase. After the spinneret is ejected, the melt is further stretched. The spinneret stretches not only the primary fiber but also the stretched microfiber of the liquid crystal. The experimental results show that when the primary fibers fall freely at the spinneret, the microfibril of the liquid crystal phase has a large diameter and tends to shrink into a spherical shape under the effect of surface tension. However, under high tension, very fine liquid crystal microfibers can be formed in the polypropylene. The transition of the liquid crystal phase structure from the screw feed zone to the spinneret outlet is shown.

The feed zone of the feed screw zone ~~spinner>s pointed out that in the heating zone of the screw, with the melting of the polypropylene, the advancement of the screw contributes to uniform distribution of the liquid crystal chips in the polypropylene melt. As the temperature rises, the liquid crystal slices are first compressed into a sheet-like structure and split into more dispersions with the stirring shear of the screw. After cooling the screw through the different parts of the mix due to the LCP's price is much higher than polypropylene, liquid crystal polymer as a reinforcing material in the PP / LCP mixture is only a small amount of additives. However, the concentration of the liquid crystal phase in the mixture plays an important role in the structure of the microfibrils in the final product.

: At 2.5, due to the LCP concentration being too small, the LCP slice was split into small particles under the stirring shear action of the screw. Due to the limited volume, these particles are hardly affected by the shearing effect in the spinneret holes, on the other hand, it is difficult to form long microfibers. When the ratio of PP/LCP reaches 100 or 80, the formation of fine and long LCP microfibers can be observed clearly in the primary blended fibers, and the effect of PP is enhanced. When the concentration of LCP is further increased, the number of microfibers in the PP fiber increases, and a network can be formed by itself. When the LCP phase forms a network at a higher concentration, drafting of the primary blended fibers becomes difficult, and it is difficult for the PP phase to reach a higher degree of orientation, thereby reducing the overall performance of the blended fibers.

5 Conclusion In summary, in the process of blending liquid crystal polymers with polypropylene, the liquid crystal polymers that act as reinforcements are distributed in polypropylene fibers in the form of a dispersed phase. The structure of the liquid crystal phase is affected by factors such as concentration, viscosity, shear and tensile tension of the melt, spinneret shape, compatibilizer, and the like. Under the effect of higher concentration and greater tensile tension, liquid crystal polymers can form microfibers with reinforcing effect in polypropylene fibers.