| In melt blowing, the molten polymer is attenuated into fine fibers by the action of the high-velocity air, and with the air flowing the fibers are randomly gathered on the collector to form nonwoven webs. Due to its ability of producing superfine fibers, the melt blowing technology attracts the researchers' much attention. For fiber, researches both theoretical and experimental, have been done on polymer air drawing mechanism, and for web only experimental researches have been done. But the melt blowing is a one-step technology, and the produced product is the fiber aggregation, i.e., the web, not a single fiber. Therefore, the web, especially the web structure (pore size, pore shape) that greatly influences the product filtration properties is more important. However, study on the web structure is lack of theoretical foundation. For this reason, a series of items are studied with the action of airflow on the fiber motion in the flow field of the melt blowing, which essentially determines the web structure, being taken as the main subject. This study is an important component of the theory of melt blowing process, and is a guide of how to improve the web quality.The work of the thesis covers three parts.The first part mainly deals with the foundation and solution of the one-dimensional air drawing model of polymer. Considering it is needed to know distributions of the air velocity and air temperature along the die centerline (or spinline) when the theoretical model of polymer drawing is solved, the more accurate empirical formulas including more die geometry parametersare firstly developed in this part to obtain such distributions. Based on this, the currently used solutions of the theoretical model (or determinations of the initial rheological force) are improved, and a new solution is presented. A more stable and objective method is found by comparison between all the methods. This part is the basis of the second part in which the fiber motion in the air flow field is simulated because the needed fiber diameter and the initial fiber velocity for this simulation is obtained through solving the drawing model.In the second part, fiber movement in the air field of the melt blowing is numerically simulated, and the analysis of airflow action on fiber motion is carried out, and further the web structure. The simulation procedure of fiber movement includes the numerical simulation of the air flow field, the proposition of the fiber model, the development of the force balance equation for fiber movement and the calculation of fiber movement. In the work, the temperature is not concerned for simplification. The fiber is modeled as a "sphere-spring" chain, and its movement in the air field is regarded as a one-way coupling problem. The simulation results of fiber motion accord well with the experimental results borrowed from literatures and conducted with high-speed photography in this paper. Meanwhile, the effects of the initial air velocity, the air jet angle on the fiber movement are studied, and the influence of these two parameters as well as the DCD (die-to-collector distance) on the web structure is analyzed. The analysis results agree well with the experimental work reported by the published literature.In the third part, the effects of the added accessory air on adhesive meltblown web are experimentally examined based on the analysis results of the fiber motion. The web structure characteristics, such as pore area, pore perimeter are measured with image measuring software, and then pore size and pore shape (pore aspect ratio and pore roundness) are analyzed. It is shown that the accessory air, which can control the fiber movement, helps improve theproduced web quality. In addition, four main melt blowing parameters, the melt throughput, the primary air velocity, the accessory air velocity and the DCD are discussed in terms of their influence on fiber diameter and fiber diameter distribution, which settles base for the future optimization of the melt blowing process.
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