Study On The Formation Mechanism And The Structure And Properties Of Large-Diameter Polymer Monofilaments

Large-diameter polymer monofilaments have excellent mechanical properties and may find a variety of prospect engineering applications. The typical products are poly(phenylene sulfide)(PPS), polyvinylidene tetrafluoroethylene (PVDF), poly(ether imide) (PEI), and poly(ether ether ketone) (PEEK), they are all indispensable industrial high-tech fibers. The production process of melt-spinning polymer fibers with its diameter ranged from 0.08 mm to 5 mm are remarkably different from those of the conventional staple fibers and conjugated filaments, which may consist of single-hole high-capacity polymer melt extrusion, liquid cooling and multi-step drawing. There hasn’t been any in-depth study on, the melt-spinning of large-diameter polymer monofilament in China up to now. In order to change the status of the long-term import of large-diameter polymer monofilament, it becomes essential and important to carry out the study on the formation mechanism and the structure and properties of large-diameter melt-spun polymer monofilaments.In this dissertation, the large-diameter single component and bi-component core-sheath monofilaments of polyethylene(PE), polypropylene(PP), poly(ethylene terephthalate) (PET), polyamide 6 (PA6), PPS, poly(lactic acid)(PLA), thermoplastic elastomer (TPEE) and PVDF and their blends were produced with self-designed spinning and post-treatment system including the extrusion spinning, liquid cooling, and multi-step drawing. The microstructure and properties of these products were investigated with X-ray,differential scanning calorimetry (DSC), scanning electron microscopy (SEM), dynamic viscoelasticity analysis (DMA) and tensile test. The relationship between melt-spinning parameters and the structure-property of resultant monofilaments, especially the formation mechanism, die drawing and multi-step roller drawings were focused in detail.On the basis of classical theory of melt-spinning polymer fibers, the effects of technical parameters, including the cooling rate, the drawing ratio of viscous flow and the spinning tension, on the microstructure and mechanical properties of as-spun large-diameter monofilament, and their effects on the spinning stability, were carefully studied, with special attention on the temperature variation along the spinning path and the radial temperature distribution based on liquid cooling technique.The effects of the polymer blend ratio and the dosage of compatibilizer into the polymer blends of PP/PE, PP/PA6, PET/PBT, PPS/PA66 on the polymer compatibility and the structure and properties of polymer blend monofilaments were investigated to address the cooling effect on the spinning stability due to the complicated thermal conductivity and heat capacity of the multiphase system. The effects of drawing ratio, drawing temperature, and the allocation of drawing ratio in the multi-stage drawing technique and proprietary die drawing technique, as well as cooling parameters on the roundness and mechanical properties of large-diameter monofilament were focused as well.The core-sheath monofilaments of the polymer systems of PA6/PET, PLA/PA6 and TPEE/PA6 were developed with the emphasized spinneret composite component technique and liquid cooling conditions in order to eliminate skin structure. High roundness PET monofilament with the diameter ranged from 3 to 6 mm was circumvented by using extrusion coating. In addition, in the consideration of functional modifications of the large-diameter polymer monofilament, such as electric conductivity, flame retardant and antibacterial, the effect of the additives on the mechanical properties of the large-diameter polymer monofilament was also studied briefly.The major findings of the study are listed as follows:The major difference between the liquid cooling and the air cooling techniques was caused by heat transfer mechanism, namely, the convection process was decisive in conventional melt-spinning, whereas the conduction process was determinative within as-spun monofilament. The results on the melt spinning of bi-component of PP and PPS indicated that the diameter and mechanical properties of resultant filaments depended strongly not only on single-hole extrusion capacity and spinning parameters, but also on the skin structure determined by heat conductive coefficient and liquid cooling conditions. This should be one novel viewpoint to explain the melt-spinning of large-diameter monofilament and would show its academic value.Under the given conditions, the maximum diameter of resultant monofilament depended on polymer themselves, the maximum diameter of PP 0.6mm, PE 2.0mm, PET 3.5mm, PA6 6mm and PPS 5mm were got. When the monofilament diameter was fixed at 0.20mm, the effects of liquid cooling temperature on the spinning stability and mechanical properties were studied, the optimum liquid cooling temperature depended on polymer themselves, they were 60-80℃for PET,8-12℃for PA6,20-30℃for PP, and 70-80℃for PPS respectively.At the given weight ratio of PP to PE blend of 80:20, the disadvantages of breaking, bifurcation and fibrillation of polypropylene were eliminated and the monofilament toughness was improved by adding the compatibilizer of 0.5-1.0 wt% maleic anhydride grafted ethylene vinyl acetate copolymer (EVA) or polyolefin elastomer (POE). The compatibility between PP and PA6 was also enhanced by dosaging 1.5-2.0 wt% PP-g-maleic anhydride. When the cooling temperature was 25-30℃and the cooling height was 30cm, the steady-state spinning of PP/PA6 blend was effectively achieved. The knot strength of the resultant monofilament increased from 3.6cN/dtex to 4.8cN/dtex. The two blend monofilaments of polypropylene have been commercially used as high efficiency filter materials.The total draw ratio of 6 was assumed for the melt-spun PET monofilament with the intrinsic viscosity 1.05 dl/g, the tensile strength was reached to 5.8cN/dtex after single-stage post drawing while to 7.5cN/dtex after three-stage post drawings. After the off-line proprietary die drawing, the polyamide monofilament with its diameter 4-6 mm was obtained with greatly improved roundness, and it can meet the fisheries, recreation, special transportation needs.The study of cooling mechanism and the practice of the melt-spinning of large-diameter monofilaments can provide a guide for the manufacturing of production equipment and the selection of processing techniques of large-diameter polymer monofilaments in China, especially composite spinneret component, multi-stage drawing, extrusion coating and proprietary die drawing. A series of polymer monofilaments with diameter at 3mm, PPS/PA66 monofilaments, PLA/PA6 and TPEE/PA6 skin-core composite monofilaments, were firstly produced in China.12 items of China’s national invention patents were applied. Among them,10 items were open to debate, and the item skin-core composite monofilament for paper making has been patented.