RESUMO
Multi-leaf hollow-profiled fiber is a complex-shaped fiber with a hollow structure with at least three leaves arranged outside. In this work, spinning processes for the preparation of multi-leaf hollow-profiled fiber with complex cross-section patterns were proposed. Initially, the characteristics and preparation methods of multi-leaf hollow-profiled fibers were analyzed, and the key technologies for their preparation were studied. Further, micro-hole spinnerets were designed, and the numerical simulations of melt flow in the spinning channel were performed. Then, the preparation of six-leaf hollow profiled fibers was carried out to study the formation of the cross-sections. Finally, as an extension and application, an experimental verification of the melt spinning parameters' effects on eight-leaf hollow fiber preparation was conducted. From the results of the spinning experiments, it was found that when the volume flow rate of a single hole increased from 2.33 × 10-8 m3/s to 3.33 × 10-8 m3/s, the profile degree of the spun fiber increased from 30.93% to a maximum value of 40.99%. Furthermore, when the cooling speed increased from 0.6 m/s to 1 m/s, the profile degree increased from 29.56% to 41.63%. When the initial blowing height increased from 80 mm to 140 mm, the profile degree decreased from 40.99% to 27.13%. When the spinning temperature increased from 285 °C to 290 °C, the profile degree decreased from 40.99% to 38.56%. However, the winding speed had an insignificant effect on the cross-sectional shape of the spun fibers. Moreover, the spun fibers showed good performance and a natural three-dimensional crimp function.
RESUMO
In this work, a preparation method of three-component composite fibers with complex cross-sectional patterns was proposed, and the fibers with complex cross-sectional patterns were fabricated using melt spinning. Initially, inspired by the shape of a fishbone, a spinning pack with three-component melt channels was designed for spinning fibers with a "fishbone" cross-sectional pattern. Then, the numerical simulation of the melt flow in the channels of the spinning pack was performed using Polyflow software. The spinning pack structure was optimized by analyzing the flow velocity distribution and shear rate distribution of different components within the spinning pack channels. The results showed that smaller velocity fluctuations contribute to the clarity of the cross-sectional pattern. Thereafter, the spinning experiments were carried out based on the optimized spinning pack. The effect of the flow ratio between the three components on the cross-sectional pattern was discussed, and the three-component composite fibers with a clear "fishbone" cross-sectional pattern were obtained. Finally, in order to further study the effectiveness of the complex cross-sectional pattern fiber preparation proposed in this paper, another spinning pack for fibers with an "H-shaped" cross-sectional pattern was designed according to the aforementioned method, and spinning experiments were carried out. The SEM images of the cross-sections of fibers with "fishbone" and "H-shaped" cross-sectional patterns were obtained, verifying the feasibility of the method proposed in this paper. Moreover, the fibers with complex cross-sectional patterns obtained by this method have a certain anti-counterfeiting effect and can also be blended with other yarns to obtain fabrics with anti-counterfeiting effects.
RESUMO
In this work, a skin-core composite intelligent temperature-adjusting fiber was prepared using the composite melt spinning method, with polypropylene as the skin layer and T28-type paraffin as the core layer, in order to obtain clothing fibers with a bidirectional temperature adjustment function. A differential scanning calorimeter was used to test the phase-change latent heat of fibers with different amounts of paraffin injections, and an infrared thermal imager was used to monitor the skin-core composite intelligent temperature-adjusting fiber bundles and ordinary polypropylene fiber bundles under the same heating and cooling conditions. The temperature of the fiber bundle was considered to be a function of time. The results showed that with the increase in the amount of the paraffin injections, the proportion of the paraffin component in the fiber and the latent heat of the fiber phase transition also increased. When the paraffin injection amount was 1.5 mL/min, the melting enthalpy and the crystallization enthalpy reached 65.93 J/g and 66.15 J/g, respectively. Under the same conditions, the heating speed of the intelligent temperature-adjusting fiber bundle was found to be slower than that of the ordinary polypropylene fibers, and the maximum temperature difference between the two reached 8.0 °C. Further, the cooling speed of the former was also observed to be slower than that of the latter, and the maximum temperature difference between the two reached 6.7 °C.
RESUMO
After the High Frequency Oscillatory Ventilation (HFOV) has been applied in the invasive ventilator, the new technique of noninvasive High Frequency Oscillatory Ventilation (nHFOV) which does not require opening the patient's airway has attracted much attention from the field. This paper proposes the design of an experimental positive pressure-controlled nHFOV ventilator which utilizes a blower and a special valve and has three ventilation modes: spontaneous controlled ventilation combining HFOV, time-cycled ventilation combining HFOV (T-HFOV), and continuous positive airway pressure ventilation combining HFOV. Experiments on respiratory model are conducted and demonstrated the feasibility of using nHFOV through the control of fan and valve. The experimental ventilator is able to produce an air flow with small tidal volume (VT) and a large minute ventilation volume (MV) using regular breath tubes and nasal mask (e.g., under T-HFOV mode, with a maximum tidal volume of 100 ml, the minute ventilation volume reached 14,400 ml). In the process of transmission, there is only a minor loss of oscillation pressure. (Under experimental condition and with an oscillation frequency of 2-10 Hz, peak pressure loss was around 0%-50% when it reaches the mask.).
