Lyocell熔喷非织造布纤网结构及纤维直径的研究

以纤维素/NMMO/水溶液为原料,制备了Lyocell熔喷非织造布。采用扫描电子显微镜分析了该熔喷纤网的形态结构,并研究了成网方式、气流初始温度及模头温度等对纤维形貌及直径的影响。结果表明,Lyocell熔喷纤网呈三维网状结构,存在"shots"、纤维间的融合与枝化现象,且得到的熔喷Lyocell纤维具有光滑的表面;成网方式和气流初始温度显著地影响熔喷Lyocell纤维的形貌;在一定的温度范围内,提高气流初始温度和模头温度,都能制备更细的熔喷Lyocell纤维。     

聚丙烯非织造布熔喷过程的计算流体力学模拟研究进展

聚丙烯非织造布采用熔喷工艺制成,在过滤、阻菌、吸附、防水等方面性能优异,有着非常广阔的市场前景。熔喷工艺中的聚合物拉伸过程复杂且迅速,难以用实验观察。因此,为降低熔喷布生产成本,提高成品质量,计算流体力学（computational fluid dynamics, CFD）方法被广泛应用于该工艺过程分析之中,包括模头中的流道分析、喷射流场分析等。其中,喷射流场分析是主要应用方向,可为喷丝板结构优化、喷射流场优化等问题提供解决方案。本文简要介绍了聚丙烯非织造布熔喷工艺原理及其特点,主要对该领域中应用CFD模拟的相关研究进展进行了综述。文中指出,目前熔喷过程的CFD模拟一般基于喷射流场中的气流,没有考虑黏性聚合物纤维对其影响。然而,黏性聚合物纤维在高速高温气流条件下会发生振动,对射流流场的影响不容忽视。熔喷非织造布的关键问题是减小聚合物纤维的直径,提高熔喷非织造布的质量。因此,研究的重点应逐渐由气流场转变为纤维流场。虽然CFD已被广泛应用于熔喷过程模拟,但熔融状态下聚合物纤维流场模拟研究仍需要在未来的工作中进行展开。     

熔喷法气流拉伸机理与喷射流场的研究进展

介绍了熔喷法非织造布的气流拉伸机理和空气喷射流场的研究进展,评价了聚合物熔喷气流拉伸的数学模型和空气喷射流场等对纤维直径的影响。指出今后的研究应探索建立熔喷法的三维拉伸模型和喷嘴气流喷射流场理论。     

双组分熔喷非织造布的开发与应用

双组分熔喷技术是一种新兴且有发展前途的技术,介绍了双组分熔喷非织造布技术的生产工艺过程及原理,分析了Hills公司和Nordson公司的双组分熔喷技术,并探讨了双组分熔喷产品的应用前景。     

熔喷非织造布技术发展概况及应用

介绍了熔喷非织造布技术的生产工艺过程及原理，分析了国内外熔喷技术的发展现状和发展趋势，探讨了熔喷产品的应用前景，并就其今后的发展提出了几点建议。     

熔喷/干法纤网在线复合汽车吸音棉的生产工艺

为了实现熔喷/干法纤网复合汽车吸音棉的在线生产,以开发300 g/m2的复合吸音棉为例,对熔喷工艺、干法纤网工艺以及熔喷/干法纤网在线复合等内容进行了分析介绍。结果表明:采用熔融指数150 g/min的聚丙烯切片,并控制好模头温度、热空气喷射角、热空气压力、接收距离等熔喷工艺参数,采用纤度为3.3 dtex的三维卷曲涤纶中空短纤维和阻燃涤纶短纤维组成的干法纤网,纤网加入熔喷丝的角度在75～83°之间时,能够得到较好的复合吸音棉材料。     

熔喷法非织造布生产技术的发展

介绍了几种典型的新型熔喷非织造布设备和熔喷数学模型及熔喷法非织造布原料的特点,探讨了熔喷法非织造布产品的应用。     

熔喷法用高熔融指数聚丙烯

1熔喷工艺熔喷法是一种一步生产非织造布的工艺(由切片到纤网)。在加工过程中,高速空气将从挤压机模头端出来的熔融态热塑性树脂吹到一个成网帘带上或成网滚筒上,形成细纤维自粘合纤网。高流速的熔体从一个带有一单排小孔的模头挤出,然后通过热空气喷嘴,将熔体吹成非常细的纤维     

聚丙烯熔喷布生产工艺及国内市场调研

探究了聚丙烯熔喷布的市场份额、应用领域、加工制造原理及过程.分析了医用口罩的构造及其各项标准,并简述了熔喷设备国内外现状.调研发现:我国熔喷工艺虽在非织造布总工艺中占比较小,但工艺成熟,生产设备齐全,熔喷布相关标准完善,国内外市场需求旺盛.     

用于过滤介质的熔喷法纳米纤维

将纳米纤维用作过滤的一大好处就是其超高的表面积。表1给出了熔喷法纳米纤维、典型的标准熔喷纤维和熔纺纤维表面积的比较。表1PP纺粘、熔喷及纳米纤维表面积比较在20世纪50年代初期,Wente、Wyly等人开始采用熔喷法来制造细旦纤维。第一条商业化熔喷法生产线,其专利技术由Exxo     

挤压造粒环模模板压缩孔深度的研究

我厂于１９９７年引进１台ＫＹＷ２５型环模挤压造粒机,采用干法工艺生产,设计产量为３００ｋｇ／ｈ。开机后一直存在产量低、模孔堵塞严重、模板使用寿命短等问题,致使生产无法正常进行。经反复考察整机,并研究模板压缩孔深度的影响。最后确定了最佳孔深范围,有效地...     

Design of extruder dies using thermoplastics melt properties data

The procedures developed in this paper enable the die designer to estimate the dimensions of the die at the exit and to define a flow channel within the body of the die appropriate to the required dimensions and output rate of the extruded product. Design procedures are given for predicting die swell (and hence die exit dimensions) from a knowledge of product dimensions, output rate and the basic shear, elasticity, and viscosity data. Within the body of the die the length and included angle of a convergent tapered section should be such that the critical tensile deformation rate is not exceeded. At the die entry the taper angle is related to the tensile and shear viscosities. Analytical expressions based on flow data are given for predicting pressure drops resulting from flow through circular and slot dies of constant cross-section and through conical and wedge-shaped dies. A numerical example shows how the theory may be applied to the design of a die for a thin-walled tube. For the resultant die design, the likely effects are predicted to changes in output rate and melt temperature for the chosen material, of changes in grade of the same type of polymer, and of changes in polymer type.     

New slit die rheometer: some results with a butadiene-styrene block copolymer

The slit die rheometer described, is a modification of the extrusion part of a Zwick rheometer (piston apparatus with constant applied pressure). The new slit has a variable depth, and pressure-temperature transducers are flush mounted at the die wall. The duct is 85 mm long and has a rectangular cross-section, 10 mm wide; four depths are available (0.50, 0.75, 1.00 and 1.50 mm). The hydraulic system gives pressures ranging from ～80 to 430 kg/cm², and the volumetric flow rate is determined by collecting extrudate samples. Some results are presented on Solprene 415, a butadiene-styrene block copolymer. Parabolic pressure profiles are accepted along the longitudinal distance of the die. A method is proposed to linearize the pressure gradient, in order to calculate the wall shear stress. A flow curve is obtained which is not strictly described by a power law relation.     

Experimental investigation of the rheological behaviors of polypropylene in a capillary flow

The rheological characterization of polymer melts is strongly related to their material properties. In this study, we focused on the rheological behaviors of a polypropylene (PP) melt through a capillary die. With an advanced twin‐bore capillary rheometer with dies measuring 1.0, 0.5, and 0.25 mm in diameter, experiments were performed over a shear‐rate range of 3 × 10² to 5 × 10³ s^?1 at three temperatures, 210, 220, and 230 °C. The results demonstrate that the geometry dependence of the PP viscosity relied on the die diameter and the temperature of the PP melt. The viscosity values of the PP melt in the 0.25‐mm diameter die were higher than were those in the 0.5‐ and 1.0‐mm dies at 220 and 230 °C. However, the viscosity values in all of the tested dies were similar at 210 °C. The tendency for the viscosity to decrease as the temperature of the polymer melt increased weakened in the 0.25‐mm diameter die. As a result, the pressure applied to the PP melt in the 0.25‐mm diameter die increased; this caused a decrease in the free volume between molecules. On the basis of the Barus equation, the contribution of pressure to the changed viscosity in each die at each of the tested temperatures was calculated and was found to be as high as 32.86% in the 0.25‐mm die at 230 °C. Additionally, the effect of the wall slip on the geometry dependence of the PP viscosity in the tested dies was investigated with a modified Mooney method. The values of the slip velocity revealed that wall slip occurred only in the 0.25‐mm die at 210 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43459.     

Model reference optimal steady-state adaptive computer control of plastics extrusion processes

The first true hierarchical automatic optimal control scheme for plastics extrusion has operated satisfactorily in the laboratory. The process operator is only required to specify desired output rate and die inlet melt temperature set-points. The control variable set-points are continually set by computer in line with an optimal policy pre-programmed from off-line solutions using models for extruder and die behavior. Feedback and feedforward control strategies are used to hold the melt temperature and pressure at die inlet within close tolerances using control actions calculated via process models and applied by a hierarchical cascade controller. The methodology is described by reference to a specific 40 mm diameter screw extruder fitted with a variable geometry annular blow molding die head, processing specific polymers. However, the control procedures are completely general and can be applied to any extruder-die combination.     

Numerical simulation of a single-screw plasticating extruder

A fully-predictive steady-state computer model has been developed for a single-screw plasticating extruder. Included in the model are a model for solids flow in the feed hopper; a variation of the Darnell and Mol model for the solids conveying zone; a variation of Tadmor's melting model for the melting zone; an implicit finite difference solution of the mass, momentum, and energy conservation equations for the melt-conveying zone of the extruder and die; and a predictive correlation for the extrudate swell at the die exit. A temperature- and shear-rate-dependent viscosity equation is used to describe the melt-flow behavior in the model. The parameters in the viscosity equation are obtained by applying regression analysis to Instron capillary rheometer data. Given the material and rheological properties of the polymer, the screw geometry and dimensions, and the extruder operating conditions, the following are predicted: flow rate of the polymer, pressure and temperature profiles along the extruder screw channel and in the die, and extrudate swell at the die exit. The predictions have been confirmed with experimental results from a 11/2 in. (38 mm) diameter, 24:1 L/D single-screw extruder with a 3/16 in. (4.76 mm) diameter cylindrical red die. High- and low-density polyethylene resins were used.     

Entrance pressure drop studies of corn meal dough during extrusion cooking

The entrance pressure drop during extrusion cooking of corn grits was measured using a cylindrical die viscometer attached to a single screw extruder and compared with results obtained using low-density polyethylene (LDPE). The cylindrical die viscometer had a length to diameter ratio of 40 with half-entry angles of 30, 37.5, 45 and 90° with the horizontal. The entrance pressure drop at the die was measured as a function of extrusion temperature, product moisture content and the die entry angle. Results indicate that the flow behavior of corn grits and the entrance pressure drop were affected by product moisture content, process temperature and the shear history in the extruder. Entrance pressure drop also increased with wall shear stress for plastic melt, but for food biopolymer, the increase was observed provided shear history effects were minimized. Entrance correction increased with apparent shear rate for LDPE, but the reverse was true for corn meal. Using Cogswell's analysis, corn grits exhibit severe extension thinning behavior in entry flow.     

The copolymerization of methacrylates in a counter-rotating twin-screw extruder

The copolymerization of n-butylmethacrylate with 2-hydroxypropylmethacrylate was studied in a closely intermeshing counterrotating twin-screw extruder. The average molecular weight of the product can be increased by increasing the screw rotation rate or the die resistance or by decreasing the throughput or the barrel temperature. The conversion can be improved by decreasing the throughput, increasing the die resistance, and (within limits) increasing the barrel temperature, as well as through post-initiation. Compared with various classical polymerization processes, this situation requires that particular attention be paid to the occurrence of a gel effect, the existence of a thermodynamic ceiling temperature, and the reactivity ratio of the monomers used.     

管壁厚度对微挤出成型的影响分析

基于Bird-Carreau黏度模型,运用有限元方法对三维等温微管挤出成型流动模型进行了数值分析,主要研究了管壁厚度对微管挤出成型过程中挤出胀大、速度分布、剪切速率和口模压降等重要指标的影响。结果表明,当熔体入口体积流率相等时,随着管壁厚度的增大,挤出物挤出胀大率和横截面尺寸变化量增大;口模出口端面上熔体的二次流动增强,但挤出速度和剪切速率减小;熔体在口模内的压力降明显下降;适当增加管壁厚度,有利于提高微管挤出质量。     

二氧化碳活化法制备竹材基药用炭的研究

以竹炭为原料,二氧化碳为活化剂制备药用炭。系统研究了活化温度、活化时间、二氧化碳流量以及原料粒度对药用炭吸着力及得率的影响,并对过程反应机理进行了初步探索。得到了优化工艺条件,当活化温度950℃,活化时间120min,二氧化碳流量600mL／min,原料粒度3．35～4．75mm,所得药用炭的吸着力达到1．28,得率54．30％,其吸着力超过《中国药典（2005年版）》的要求。实验结果表明,采用竹炭可以制备高性能的药用炭。