| Polyester is the most widely used synthetic fiber, but the fabrics from polyester yarn are usually used in clothing because they are soft and light. How to expand the application of PET fibers is of high commercial interest, such as forming a composite yarn with coated flexible resin layer. Polyvinyl chloride (PVC) is the world's second largest general resin with extensive use because of its low price, UV resistance, flame retardance, insulation, abrasive resistance, etc. In this thesis a series of PVC blends were prepared under certain conditions, which are used as cover layer. The PVC blends were coated on the high-strength polyester multifilament, the fabrics woven from this special PVC/PET composite yarn can be used in many leisure areas, for example, bench chair and table mat in restaurant.Because of the chloride (Cl) atom in PVC chain, PVC is excellent of flame resistance. However for the strong polarity of Cl, the intermolecular force is quite strong, thus the low temperature performance is poor because the molecular chains would be frozen that leads to embrittlement and hardening in cold environment. The different PVC formulations and PVC blended with polyethylene (PE) were used to improve the cold resistance in this work. For the incompatibility of PE and PVC, the organic materials ethylene-vinyl acetate copolymer (EVA) and inorganic material nano calcium carbonate (nano-CaCO3) were used as compatibilizer, respectively. The compatibility, cold resistance, thermal stability and mechanical properties were discussed, and the proper processing conditions were also analysised in this thesis. The results indicate both different methods can improve the cold resistance of PVC to some extent. The glass transition temperature (Tg) and the brittle temperature can be reduced by adding dioctyl adipate (DOA) as the plasticizer instead of dioctyl phthalate (DOP). But DOA should be used as a secondary plasticizer with DOP for the best performance. The brittle temperature is-31.7℃of PVC/PE/EVA (100/10/10, mass ratio), and EVA is applied as the compatibilizer of PVC and PE. However with the fixed PE content, the larger amount of EVA, the lower brittle temperature of PVC/PE.Conglomeration of nano-particles has been deemed as one of the main obstacles in the preparation of polymer based nano-materials, thus the surface modification of nano-CaCO3 is necessary. Titanate coupling agent was used to decrease the surface tension and surface energy so that the nano-CaCO3 can disperse uniformly in the matrix. When the content of nano-CaCO3 is 5wt%, the brittle temperature of PVC/PE blends is lowest with the value of-35℃, as well as good thermal stability and mechanical properties. The morphology of PVC and PE phase detected via optical microscope also shows the perfect compatibility of PVC/PE.The Thermal Gravimetric Analysis (TGA) concludes that there are two stages of the thermal degradation of both PVC and PVC/PE blends. The first stage is almost the same with similar apparent activation energy (E) while the apparent activation energy of the PVC/PE blends is increased significantly for the second stage. Both the initial decomposition temperature in equilibrium state is over 220℃. The PVC/PE/nano-CaCO3 blends show the best thermal stability, under the same heating rate, the initial decomposition temperature is 20℃higher than those for PVC and PVC/PE blends. The study of optimum extruding temperature reveals that the processing temperature of PVC, PVC/PE/EVA, PVC/PE/nano-CaC03 increases in turn.Polyester multifilament was coated with PVC (different formulas with different plasticizer), PVC/PE/EVA (100/10/10, mass ratio) and PVC/PE/nano-CaCO3 (5wt%) by single screw extruder. Concentricity of the coated yarn can be well controlled. The breaking strength of all the ccoated yarns was over 3cN/dtex, and the best breaking strength was 3.6cN/dtex when the clad layer is PVC/PE/nano-CaCO3. |
