聚对苯二甲酸丙二酯熔体拉伸流变性能研究

使用毛细管流变仪研究了PTT熔体在单轴拉伸流场中的流变性能。结果表明,PTT熔体拉伸流动属于拉伸变稀型,熔体的拉伸粘度随拉伸应力增加而降低,随相对分子质量提高,熔体的拉伸变稀现象更加明显。熔体的相对分子质量越高,拉伸速率对熔体的拉伸粘度影响越大。随拉伸速率提高,熔体的拉伸应力增大,拉伸粘度减小,易产生拉伸共振现象。因此,PTT熔体纺丝时应该采取较低的喷头拉伸倍数,即适当提高熔体挤出时的纺丝速度,或降低卷绕速度,以此降低熔体拉伸比和防止拉伸共振现象,改善纺丝成形的稳定性。     

聚烯烃纤维

951162二在聚丙烯/聚乙烯共混物熔纺时拉伸共振的研究Park Jung Hwi…;Hanguk Somyu Konghakho-吧ehi,1993,30,(3),p.217一225(英)对聚丙烯(I)/低密度聚乙烯(亚)共混物以不同比例熔纺纤维拉伸共振作了研究。当l含量增加时,系统变得更加稳定,因此得到更高的临界拉伸比和更短的共振周期。随I的挤出速率增加,Doax/D。,:对拉伸比作图的斜率增加,当l含量增加时,该斜率稍有降低。(张桂水) 951163Danaklon购买BottroPHigh performanee Textiles,1994,(7),p.13(英)丹麦的主要化纤制造公司,最近取得了对HccelsAG的德国主要子公司Faserwerk Bo…     

特种纤维及其他合成纤维

982163芳纶微细长丝纱的工艺和性质Van der Werff H.…;CFI Man一Made Fiber YearBook 1997,p.31一37(英)评述了Twaron长丝纱(Akzo产对位芳纶)的纺丝工艺,详述了制备dpf<1.odtex Twaron长丝纱的可能性。聚合物浓度的降低,使Twaron长丝的机械性能强烈地劣化。干喷湿纺时,可采用增加在空气间隔区拉伸比的办法,有效地降低单丝线密度(d pf)并同时改善机械性质。聚合物浓度和空气间隔区拉伸比二者对长丝模量的影响,由理论模量可定量地作充分的了解。空气间隔区拉伸比的最大值,借助拉伸共振的出现加以确定。然后在空气间隔区的最大拉伸比条…     

塔器的风诱导共振分析和预防设计方法研究

随着塔设备的高径比越来越大,也越来越容易发生风诱导共振现象.由于空塔的系统阻尼比可能远低于操作工况下塔设备的系统阻尼比,空塔更容易发生"共振"事故,且振幅越大,危险系数越高.介绍了风诱导共振的机理,总结了塔器发生具有较大危害的共振现象的四个必要条件,并据此分析了几个主要的防振措施,提出了基于共振预防的塔器设计校核方法,...     

用毛细管流变仪测量橡胶的工艺性能

采用Rosand RH10毛细管流变仪对橡胶材料进行了流变表征,研究了该橡胶样品在各个剪切速率下的流动性,获得剪切黏度-剪切速率以及拉伸黏度-拉伸速率曲线;研究了橡胶样品在不同剪切速率、不同长径比口模下的模口胀大比,并观察了挤出物熔体破裂现象;研究了剪切速率和口模长径比与熔体破裂程度关系,此外还表征了该橡胶样品的应力松弛现象。这些流变数据为材料结构表征以及后期加工工艺提供了重要的参考数据。     

干-喷湿纺聚丙烯腈纤维拉伸工艺研究

研究了干 -喷湿纺聚丙烯腈 (PAN)初生纤维的喷丝头拉伸比和三级拉伸 (空气拉伸、DMF浴拉伸、热水和沸水拉伸、干热拉伸 )工艺中各拉伸比对纤维性能的影响。结果表明 :提高喷丝头拉伸比可明显地降低初生纤维的线密度 ,提高强度 ;三级拉伸工艺中各拉伸比的提高均有利于PAN纤维线密度的减小及其强度、声速取向度和抗张模量的提高 ;合理调配三级拉伸中各拉伸比可制得强度超过 7.0cN/dtex的PAN纤维     

U-3160单向碳纤维织物预浸前的整理改进

针对U-3160单向碳纤维织物组织结构松弛,存在布面不平整和纤维弯曲现象,在预浸前对其进行了必要的整理改进,从而有效减少了其预浸料中碳纤维的弯曲现象。结果表明,其复合材料的主要力学性能比未改进前有明显提高：纵向抗拉伸强度1599MPa,比改进前提高了15％;纵向抗拉伸模量133GPa,比改进前提高了9％;纵向抗压缩强度1153MPa,比改进前提高了21％;纵向抗压缩模量111GPa,比改进前提高了1．8％。达到了同类进口材料的实际水平。     

基于POLYFLOW模拟不同微孔形状及拉伸速率的共挤出流动

以聚酰胺6(PA6)和聚对苯二甲酸乙二醇酯(PET)两种聚合物为原料,应用POLYFLOW软件模拟并列型PA6/PET熔体共挤出过程的现象,讨论了2种熔体在不同入口角、不同长径比的微孔结构下的挤出胀大比的变化规律。结果表明:长径比较小时,入口角对挤出胀大比有一定的影响;长径比较大时,入口角对挤出胀大比几乎没有影响;随着长径比的增加,挤出胀大比逐渐减小。随着拉伸速率的增加,挤出胀大比减少;拉伸速率过大时,容易产生熔体破裂,因此,适当的拉伸速率可以减小挤出胀大比。     

喷头拉伸对三角形PAN纤维湿法凝固成形的影响

采用三角形喷丝孔,在二甲基亚砜(DMSO)水溶液凝固成形过程中,研究了不同喷头拉伸比对聚丙烯腈(PAN)初生纤维的截面形状和表面形貌、声速、结晶度以及力学性能的影响。结果表明:当喷头拉伸比增大到0.9倍时,初生纤维的截面的"角部钝化"现象消失,截面变形为和喷丝孔相似的形状;与此同时,初生纤维的力学性能也发生了显著的变化;而且,随着喷头拉伸比的增加,初生纤维的声速取向、结晶度及晶粒尺寸都逐渐增加。     

拉伸工艺参数与纤维拉伸张力和不匀率关系的研究

通过实验方法研究拉伸工艺条件和纤维拉伸张力及不匀率的关系。结果表明，拉伸比、拉伸速度和拉伸温度对纤维张力、张力波动和不匀率均存在着明显的影响。随着拉伸比、拉伸速度的提高和拉伸温度的降低，拉伸张力增大。增大拉伸比、拉伸速度和拉伸温度能有效地减小张力波动和不匀率。     

Studies on the mechanism of draw resonance in melt spinning

The physical mechanism of draw resonance of polymer fluids in melt spinning has been studied. It is proposed, according to the cross-sectional area dependence of the local draw ratio of the filament along the spinline, that filament drawing can be divided into three modes which are given in the main text. In particular, it is found that the nonuniformizing draw mode is the necessary condition of draw resonance. The mechanism is certified through the analytical solution of isothermal melt spinning under uniform spinning stress and the critical draw ratio of isothermal and uniform tension melt spinning. The mechanism was employed to analyze the promotive and suppressive factors of draw resonance in a real spinning system and the development of filament unevenness along the spinline.     

Numerical simulations of draw resonance in melt spinning of polymer fluids

This article deals with numerical simulations of draw resonance of polymer fluids by employing direct difference methods to solving the governing equations in melt spinning. The stability of each difference method was studied by a comparison of the results obtained from simulations with the theoretical solutions or values. The numerical simulation confirms that the critical draw ratio of draw resonance in an isothermal and uniform tension spinning of a Newtonian fluid is between 20 and 21. The cross-sectional area of a spinline in draw resonance was found to decrease monotonically from a spinneret toward a take-up bobbin, although the taken-up filament shows periodical variation. This study has also illustrated the mechanism of draw resonance previously proposed by the author. © 1993 John Wiley & Sons, Inc.     

Studies on melt spinning. VI. The effect of deformation history on elongational viscosity,spinnability, and thread instability

The effect of deformation history on the elongational behavior and spinnability of polypropylene melt was investigated by carrying out isothermal melt-spinning experiments. For the study, spinnerettes of different die geometries were used to investigate the effect, if any, of the entrance angle, the capillary length-to-diameter (L/D) ratio, and the reservoir-to-capillary diameter (D_R/D) ratio on the elongational behavior of molten threadlines. An experimental study was also carried out to investigate the phenomenon of draw resonance in the extrusion of polypropylene melts through spinnerettes of different die geometries. Draw resonance is the phenomenon which gives rise to pulsations in the threadline diameter when the stretch ratio is increased above a certain critical value. The results of our study show that the critical stretch ratio at which the onset of draw resonance starts to occur decreases as the L/D ratio is decreased, as the entrance angle is increased, as the D_R/D ratio is increased, as the melt temperature is decreased, and as the shear rate in the die is increased. Of particular interest is the observation that, at 180°C, the severity of fiber nonuniformity increases as the stretch ratio is increased, whereas at 200°C and 220°C, the severity of fiber nonuniformity first increases and then decreases as the stretch ratio is increased considerably above the critical value. A rheological interpretation of the observed onset of draw resonance is presented with the aid of the independently determined rheological data.     

Identifying breach mechanism during air-gap spinning of lignin–cellulose ionic-liquid solutions

To be able to produce highly oriented and strong fibers from polymer solutions, a high elongational rate during the fiber-forming process is necessary. In the air-gap spinning process, a high elongational rate is realized by employing a high draw ratio, the ratio between take-up and extrusion velocity. Air-gap spinning of lignin–cellulose ionic-liquid solutions renders fibers that are promising to use as carbon fiber precursors. To further improve their mechanical properties, the polymer orientation should be maximized. However, achieving high draw ratios is limited by spinning instabilities that occur at high elongational rates. The aim of this experimental study is to understand the link between solution properties and the critical draw ratio during air-gap spinning. A maximum critical draw ratio with respect to temperature is found. Two mechanisms that limit the critical draw ratio are proposed, cohesive breach and draw resonance, the latter identified from high-speed videos. The two mechanisms clearly correlate with different temperature regions. The results from this work are not only of value for future work within the studied system but also for the design of air-gap spinning processes in general. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47800.     

Studies on melt spinning. III. Flow instabilities in melt spinning: Melt fracture and draw resonance

An experimental study has been carried out to investigate threadline instabilities in melt spinning. Two types of melt threadline instabilities, draw resonance and melt fracture, were observed under both isothermal and nonisothermal spinning conditions. Polymers investigated were polypropylene and polystyrene. Draw resonance was observed as an increase of the take-up speed above a critical value. It was also observed that an increase in take-up speed reduces the severity of melt fracture, whereas once draw resonance occurs the amplitude and frequency of the pulsing thread diameter increases with the take-up speed. The phenomenon of draw resonance was investigated by taking motion pictures of the pulsing molten threadline spun vertically downward. Furthermore, a stability analysis was carried out to explain the experimentally observed draw resonance.     

Studies on melt spinning. V. Draw resonance as a limit cycle

The exact wave form of draw resonance in isothermal spinning of Newtonian liquids was sought by solving numerically the simultaneous partial differential equations¹ of melt spinning in their original nonlinear form without recourse to perturbation. When the draw-down ration of spinning exceeded 20, solution of the equations became a limit cycle, a sustained oscillation having amplitude and period independent of initial conditions. As the draw down ratio was further increased, the amplitude of the limit cycle grew very rapidly, and the wave form became close to a pulse train predicting an extreme thinning of the thread at regular intervals along the thread. The above solution for Newtonian liquids agreed well with experiment with respect to oscillation period. Agreement, however, was poor in amplitude, indicating that possibly the amplitude of draw resonance is affected by deviations of polymer viscosity from Newtonian.     

Studies on melt spinning. VIII. The effects of molecular structure and cooling conditions on the severity of draw resonance

The effects of molecular structure and cooling conditions on the severity of draw resonance was investigated by carrying out carefully controlled melt spinning experiments. For the study, two types of polymeric materials were used: one which exhibits viscoelastic behavior (high-density polyethylene, polypropylene, and polystyrene), and the other which exhibits almost Newtonian behavior [nylon-6 and poly(ethylene terephthalate)]. In order to investigate the effect of cooling on the severity of draw resonance, different methods of cooling the molten threadline were employed. In one set of experiments, isothermal chambers of various lengths (3, 6, and 12 in.) were attached to the spinnerette face, so that the molten threadline, upon exiting from the spinnerette, began to cool in the ambient air only after it had passed through the isothermal chamber. This method of cooling is called “delayed cooling,” providing both an isothermal region (inside the isothermal chamber) where only stretching occurs, and a nonisothermal region (outside the isothermal chamber) where both stretching and cooling occur simultaneously. In other experiments, the temperature profile of the molten threadline was controlled by adjusting the temperature of the heated chamber. This method of cooling provides a gradual drop of the threadline temperature, compared to the more sudden drop when spinning into a cold environment provided at the spinnerette exit. The severity of draw resonance was recorded on movie film, and the thread tension was measured with a low-force load cell transducer and recorded on a chart recorder. The temperature of the threadline along the spin direction was measured using a fiber optical probe attached to a Vanzetti Infrared Thermal Monitoring System (Model TM-1). It was found that the severity of draw resonance depended on the molecular structure and the way the molten threadline was cooled. Of particular interest is the observation that, for the viscoelastic materials investigated, cooling destabilized the molten threadline outside the isothermal chamber. This gave rise to more severe resonant behavior, at and above the critical draw-down ratio, in contradiction to the theoretical prediction by Fisher and Denn. It was observed, also, that the elasticity of the materials tended to destabilize the molten threadline (i.e., it increased the severity of draw resonance), again in contradiction to the theoretical prediction of Fisher and Denn. It is believed that morphological changes of polymers may play an important role in the occurrence of draw resonance when a melt threadline is stretched under cooling. Our study indicated that a good understanding of draw resonance of viscoelastic fluids requires more careful study than the classical hydrodynamic stability analysis reported by Fisher and Denn. They based their analysis on several convenient and yet unjustified assumptions, and solely on phenomenological considerations. We suggest that future theoretical analysis of draw resonance be carried out by considering a fluid model with a nonlinear memory function in order to properly account for the deformation history of the fluid, and the relaxation and cooling processes in the die swell region and the region below it.     

Effect of the drawing process on the wet spinning of polyacrylonitrile fibers in a system of dimethyl sulfoxide and water

The effect of the drawing process on the structural characteristics and mechanical properties of polyacrylonitrile (PAN) fibers was comparatively studied. The protofibers extruded from the spinneret were the initial phase of stretching, which involved the deformation of the primitive fiber with the concurrent orientation of the fibrils. Wet‐spun PAN fibers observed by scanning electron microscopy exhibited different cross‐sectional shapes as the draw ratio was varied. X‐ray diffraction results revealed that the crystalline orientation of PAN fibers increased with increasing draw ratio; these differences in the orientation behaviors were attributed to the various drawing mechanisms involved. The crystalline and amorphous orientations of the PAN fibers showed different features; at the same time, the tensile properties were strongly dependent on the draw ratio. However, the stream stretch ratio had most influence on the tensile strength and the orientation of PAN fibers for the selected process parameters. Electron spin resonance proved that the local morphology and segmental dynamics of the protofibers were due to a more heterogeneous environment caused by the sequence structure. Differential scanning calorimetry indicated that the size and shape of the exotherm and exoenergic reaction were strongly dependent on the morphology and physical changes occurring during fiber formation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1026–1037, 2007     

Dynamics and criteria for bubble instabilities in a single layer film blowing extrusion

In this paper, the performance of a new in‐line scanning camera system for the study of various bubble instabilities in film blowing extrusion is critically evaluated. Three commercial film‐grade polyethylenes, LmPE, LLDPE and LDPE, were used to generate the bubble instabilities. Reliable and objective criteria for differentiating various bubble instabilities such as draw resonance, helicoidal instability, and frost line height instability are proposed by using the new device. Detailed dynamics of each bubble instability was carefully investigated as a function of time in a broad range of the take‐up ratio (TUR), blow‐up ratio (BUR) and frost line height (FLH). In addition, effects of melt temperature and mass flow rates on dynamics of the bubble instabilities are discussed. It was found that the new system could capture the main characteristics of all bubble instabilities quantitatively. It was also found that magnitude and periodicity of radius variation during draw resonance of LmPE decreased as TUR increased at constant FLH and BUR. This implies that the origin of draw resonance in film blowing seems to be different from that observed in fiber spinning. In the case of helicoidal instability, eccentricity, which defines the deviation of the bubble center from the die center, decreased as TUR increased. However, the bubble could not be stabilized as expected. A graphical quantification approach to determine the stable zone in the bubble stability map is also discussed.     

Studies on blown film extrusion. III. Bubble instability

An experimental study has been carried out to investigate flow instabilities in blown film extrusion. Two types of flow instabilities were observed, depending on whether a bubble was under uniaxial or biaxial stretching. Under biaxial stretching, the phenomenon of a surface wave-type instability was observed, yielding wavy bubble shapes which very much resembled water waves at the free surface. Under uniaxial stretching, another type of instability, frequently referred to as draw resonance, was observed. It was also observed that, once draw resonance occurs, the amplitude and frequency of bubble diameter pulsing increased with stretch ratio. Quantitative information was obtained from a series of motion pictures taken of bubble diameter in both types of flow instability. It was observed further that an increase in extrusion melt temperature enhanced the severity of bubble instability.