不相容聚合物共混物受限结晶行为的研究进展

不相容聚合物共混是一种获得综合性能优异的高分子材料的有效途径。当结晶聚合物作为分散相均匀地分布在不相容聚合物基体相中,并且其分散相数目大于活跃的异相成核物质数目时,在冷却过程中会发生受限结晶(分级结晶)现象。分散相中缺少活跃的异相成核物质是不相容共混物发生受限结晶的关键因素。从受限结晶的产生总结了近年来不相容共混物中受限结晶的研究进展,并概述了增容剂、填料、退火、分散相尺寸及其分布和结晶温度等因素对受限结晶行为的研究。     

聚对苯二甲酸乙二酯/聚丙烯不相容共混体系的结构流变学

通过熔融共混制备了不相容的聚对苯二甲酸乙二醇酯（PET）/聚丙烯（PP）复合体系,研究了复合体系的结构流变学。结果表明,PET/PP共混体系的不相容相形态显著影响其稳态和动态流变行为。当PP组分为分散相时,复合体系表现出动态形状松弛;当两组分呈多种相形态共存时,复合体系表现出强烈的低频区弹性响应;而当PET组分为分散相时,复合体系的剪切敏感性则相对较小。在较高剪切应力作用下,分散相液滴的凝聚是影响体系流变行为的控制因素,而在较低的剪切应力作用下,液滴的破碎则成为控制因素。     

乙烯—辛烯共聚物对RB／NBR共混胶性能的影响

通过聚合物共混来改善均聚物的性能是一种有效的、低成本的途径。一般情况下,聚合物相互间是不相容的,所以需使用相容剂来改善相容性。从理论上讲,相容剂能迁移到相间的界面处,从而降低界面张力,减少分散相尺寸并稳定共混胶的形态。     

周期性间断多副螺棱螺杆混沌混合性能

在普通单螺杆的计量段插入周期性间断多副螺棱以触发混沌混合,对其加工聚合物的分布混合与分散混合特征进行模拟,同时与普通单螺杆比较,并进行不相容体系共混实验。结果表明:周期性间断多副螺棱螺杆使物料在流道内的停留时间增长,停留时间概率密度曲线峰增宽,使得粒子承受的扰动频率增大,有效地降低了粒子的分离尺度;周期性间断多副螺棱螺杆的最大剪切速率均值高于普通单螺杆,在聚合物加工过程中产生混沌混合,增强了聚合物的拉伸折叠作用;采用扫描电镜观察PC/HDPE不相容共混物的脆断面形貌,分散相PC颗粒经历被拉伸成片状结构、破碎成更小的纤维状结构、进一步破碎成球状形态的演变过程,分散相破碎演变得早,分散相粒径细小,周期性间断多副螺棱螺杆挤出机就具有很好的混沌混合特征。     

PIB/PDMS/纳米SiO2共混体系形态迟滞研究

本文研究了不相容聚异丁烯(PIB)/聚二甲基硅氧烷(PDMS)共混物的形态迟滞现象以及添加纳米SiO2粒子的影响。通过数据分析及绘成函数图表,并与相应的理论模型进行对比,实验得到与文献报道一样的形态迟滞区域,在这个区域内,改变剪切速率,分散相尺寸大小没有明显的变化。加入亲水性纳米硅粒子后,形态迟滞区受破碎线位置的改变的影响而变大,而加入疏水性纳米硅粒子后,形态迟滞区受凝聚线位置的改变的影响同样出现变大的情况。经过进一步理论分析,推测这种变化可能与纳米硅粒子在PIB/PDMS共混物中的分布有关。     

超临界CO_2制备聚合物及其共混物的应用现状

综述了超临界CO2制备聚合物及其共混物的应用现状,主要包括超临界CO2降低单一聚合物和聚合物共混物的黏度、改变聚合物共混物相行为及其他性能的应用。超临界CO2降低聚合物熔体黏度可以使聚合物的成型温度降低,提高其加工性。在聚合物共混物中引入超临界CO2,能改变聚合物共混物微观相形态,分散相尺寸减小,进而达到改变其他性能的目的。     

填料对不相容聚合物共混物相结构的影响及其应用

主要综述了填料的引入对不相容聚合物共混物分散相结构、相反转及共连续相结构稳定性的影响.介绍了填料填充不相容聚合物共混体系的应用,尤其是在导电复合材料中的应用.还指出了今后研究中需要解决的一些问题.     

纳米纤维用PP/CAB共混母粒中分散相尺寸的影响因素研究

利用相分离的方法制备热塑性聚丙烯(PP)纳米纤维,将不相容的PP和醋酸丁酸纤维素(CAB)两种聚合物在双螺杆挤出机中共混,制备出合适的母粒用于熔融静电纺丝。通过不同条件下的实验,研究了影响PP分散相粒子尺寸大小的因素,利用扫描电子显微镜观察了共混物的形态,并通过旋转流变仪测量了共混物在不同温度和不同剪切速率下的流变行为。结果表明,PP含量和熔融温度对分散相粒子尺寸的影响最为显著,其次为共混时间,螺杆转速的影响最小;当PP质量分数为20%,熔融温度为210℃,螺杆转速为25 r/min,共混时间为4 min时,可得到尺寸较小的PP分散相粒子。将上述条件下制备的母粒通过熔融静电纺丝技术制备PP/CAB纤维,经丙酮处理除去CAB,得到的PP纳米纤维的平均直径为320 nm左右,与直接熔融静电纺丝制备的PP纤维(平均直径为3.5μm左右)相比,纤维的直径降低了一个数量级,使得纤维细化。     

无机粒子对聚合物共混物相容性及相结构的影响

综述了无机粒子的引入对部分相容聚合物共混体系相行为和相结构演变的影响,同时介绍了无机粒子的引入对不相容聚合物共混体系热力学相容性和相结构演变(包括分散相的尺寸和形状、相转变及共连续结构的稳定性)的影响,并指出了今后研究中需要解决的一些问题。     

共聚焦拉曼成像技术研究PE-LD/EVOH共混物的三维相结构

利用共聚焦拉曼成像技术研究了低密度聚乙烯（PE-LD）/乙烯-乙烯醇共聚物（EVOH）共混物中各相在压塑样品水平方向、深度方向和三维空间的分布情况,首次获得了PE-LD/EVOH共混物的三维相结构,并直观地将相区与共混物化学成分相对应。结果表明,PE-LD/EVOH共混物为不相容体系;当EVOH的质量分数为20%时,其作为分散相,以较规则的圆柱体形态分散于PE-LD基体中,圆柱直径尺寸在3～6μm范围内。加入马来酸酐接枝聚乙烯（PE-gMAH）作为相容剂后,共混物的相态结构发生显著变化,分散相形状由规则变为不规则,截面的平均尺寸减小到约2μm,这说明PE-g-MAH可显著增强PE-LD与EVOH两组分间的界面相容性。     

Development of polymer blend morphology during compounding in a twin-screw extruder. Part I: Droplet dispersion and coalescence—a review

The theoretical and experimental data on the breakup of droplets are reviewed. Several factors influence development of droplets: flow type and its intensity, viscosity ratio, elasticity of polymers, composition, thermodynamic interactions, time, etc. For Newtonian systems undergoing small, linear deformation, both the viscosity ratio and the capillary number control deformability of drops. On the other hand, the breakup process can be described by the dimensionless breakup time and the critical capillary number. Drops are more efficiently broken in elongational flow than in shear, especially when the viscosity ratio λ ? 3. The drop deformation and breakup seems to be more difficult in viscoelastic systems than in Newtonian ones. There is no theory able to describe the deformability of viscoelastic droplet suspended in a viscoelastic or even Newtonian medium. The effect of droplets coalescence on the final morphology ought to be considered, even at low concentration of the dispersed phase, ?_d ? 0.005. Several drop breakup and coalescence theories were briefly reviewed. However, they are of little direct use for quantitative prediction of the polymer blend morphology during compounding in a twin-screw extruder. Their value is limited to serving as general guides to the process modeling.     

Effect of marangoni stresses on the deformation and coalescence in compatibilized immiscible polymer blends

The effect of physical compatibilization on the deformation and coalescence of droplets in immiscible polymer blends is discussed. Evidence is provided for the existence of concentration gradients in block copolymers along the interface during deformation. This causes complex changes in droplet shapes during deformation and relaxation. These concentration gradients also result in Marangoni stresses, which stabilize the droplets against deformation and breakup. Coalescence experiments have been performed, varying both the compatibilizer concentration and the shear rate. Existing coalescence models have been evaluated. An empirical extension of Chesters' partially mobile interface model is presented, that treats the effects of Marangoni stresses on the coalescence process as a higher effective viscosity ratio.     

Theory of competition between breakup and coalescence of droplets in flowing polymer blends

The Smoluchowski equation for the breakup and coalescence of dispersed droplets has been solved for flowing polymer blends. A scaling form for the distribution of droplet sized derived and published for a system of clusters with fragmentation and coagualation was used in our dervation. Equations are developed here for the average droplet size and for the characteristic time of transition to steady state flow of blends with a high content of the dispersed phase. Expressions reasonably describing the average size of droplets for all concentrations were obtained by a theory modification. Measured dependences of droplet size on the blend composition can be matched only if simultaneous collisions of three and more droplets are considered. The results of the theory indicate that the mechanism of droplet breakup (formation of pieces with the same or different volumes) has only a small effect on their average size in concentrated systems. The dependence of droplet size on the shear rate in flow is determined by properties of the blend components, and is generally nonmonotonic.     

Prediction of average droplet size in flowing immiscible polymer blends

The paper is focused on calculation of the average droplet size in immiscible blends during their steady flow. Available theoretical and experimental results of studies of the droplet breakup and coalescence are utilized to derive the equations describing dynamic equilibrium between the droplet breakup and coalescence. New expression for the coalescence efficiency, reliably reflecting recent theoretical results, is proposed. The equation for the average steady droplet size, controlled by the stepwise breakup mechanism and coalescence of droplets with not very different sizes, is derived for blends containing up to 10–20 vol % of the droplets. For blends with above approximate 20 vol % of the droplets, the breakup by the Tomotika mechanism and coalescence in highly polydisperse system is modeled. Results of the derived equations are compared with experimental data; qualitative agreement is found for the dependence of the droplet size on the amount of the dispersed phase. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45250.     

Development of fibrillar morphology in immiscible PP/PS blends under shear flow

The formation dynamics of fibrillar morphology in dilute immiscible polypropylene (PP)/polystyrene blends under simple shear flow is investigated using optical‐shear technique. Two strategies in generating fibrillar droplets under shear flow, namely temperature quench and shear jump, are studied. It is found that the shear‐induced deformation of PP droplets is closely related to the total shear strain and changes of rheological properties of components during the temperature quench or shear‐jump process. The shape evolution of fibrillar droplets under shear flow displays large deviation to the prediction of affine deformation theory based on Newtonian fluids and that of three deformation models, which consider the viscoelastic properties of components. The possible effect of droplet coalescence, breakup, and interfacial slip on the deviation between the experimental data and the prediction values for droplet deformation are discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Coarsening in molten quiescent polymer blends: The role of the initial morphology

Coarsening of the phase dimensions in polymer blends under quiescent conditions is studied in blends of different morphologies; the dependence of the rate and extent of coarsening on the initial morphology is demonstrated. In blends with a droplet/matrix structure, coarsening via coalescence is found only above the percolation threshold for spherical particles (16 vol%). The rate of coalescence in the droplet/matrix structure is shown to obey the theory of Fortelny and Zivny for coalescence of droplets in quiescent media, and no constant level of the phase dimensions is reached. Below a volume fraction of 0.16 limited coarsening is found only for fibrillar and co-continuous morphologies. This coarsening is in fact the result of a restructuring because retraction and breakup occur, leading to a droplet/matrix morphology in which the droplet diameter is approximately twice the diameter of the original fiber. Breakup and retraction are completed in a short time relative to coalescence. At higher volume fractions in co-continuous structures (>30 vol%), these structures do not break up, and coarsening is found to take place by retraction only. No constant level of the phase dimensions is reached in the latter case.     

Erosion and breakup of polymer drops under simple shear in high viscosity ratio systems

The deformation and breakup of a single polycarbonate (PC) drop in a polyethylene (PE) matrix were studied at high temperatures under simple shear flow using a specially designed transparent Couette device. Two main breakup modes were observed: (a) erosion from the surface of the drop in the form of thin ribbons and streams of droplets and (b) drop elogation and drop breakup along the axis perpendicular to the velocity direction. This is the first time drop breakup mechanism (a), “erosion,” has been visualized in polymer systems. The breakup occurs even when the viscosity ratio (η_r) is greater than 3.5. although it has been reported that breakup is impossible at these high viscosity ratios in Newtonian systems. The breakup of a polymer drop in a polymer matrix cannot be described by Capillary number and viscosity ratio only; it is also controlled by shear rate, temperature, elasticity and other polymer blending parameters. A pseudo first order decay model was used to describe the erosion phenomenon and it fits the experimental data well.     

在无机分散剂存在下苯乙烯悬浮聚合宏观成粒的特征

以苯乙烯悬浮聚合为体系,考察羟基磷酸钙(HAP)或HAP与聚乙烯醇(PVA)复合为分散剂体系时,各种因素如分散剂浓度、油水比、搅拌速度等与瞬时液滴大小及分布之间的关系,并分析讨论瞬时液滴分散、合并的过程特征.结果表明,悬浮苯乙烯液滴聚合宏观成粒的特征与分散剂的分散机理无关,仅体现液滴分散、合并的过程特点.当采用分批加分散剂时,实验观察到瞬时液滴大小分布呈由单峰过渡到双峰,再发展成单峰分布的特征,从而找出了以分批加分散剂方式制备窄分布聚合物颗粒的理论依据.     

Drop Deformation and Breakup Mechanisms in Viscoelastic Model Fluid Systems and Polymer Blends

This paper reviews the dispersion mechanisms in viscoelastic systems under relatively high shear rate conditions. In particular, two non‐Newtonian deformation and breakup mechanisms were revealed by flow visualization in a transparent Couette shearing setup. The first one is the dispersed droplet elongation perpendicular to the flow direction. This was observed only for viscoelastic drops and had been associated to normal force buildup in the droplet. The second deformation/breakup mechanism was observed in very high viscosity ratio polymer systems. It consists in erosion at the drop surface. Clouds of very small ribbons and sheets were developed around the drop then stretched and finally broken into very small droplets, rapidly distributed in the matrix.     

The role of organically modified layered silicate in the breakup and coalescence of droplets in PBT/PE blends

In this study, we investigated the effect of organically modified nanoclay (organoclay) on the morphology of immiscible polymer blends (PBT/PE) with various compositions of PBT ranging from 1 to 90 wt%. When a small amount of organoclay between 1 and 3 phr is added to the blend, the thin clay tactoids of the thickness of the order of 10 nm are located at the interface between PBT and PE phase. As its content is increased, the additional organoclay positions in a specific component depending on its affinity with the component. The addition of a small amount of organoclay results in the effective size reduction for PBT/PE blend. The organoclay located at the interface forms the interfacial phase with a non-homogeneous distribution of clay along the interface and changes the interfacial tension, which result in the coalescence suppression of the droplets. Rigid organoclay with a high aspect ratio allows the blend morphology with long-term thermal stability by suppressing the Brownian motion. This ability of the organoclay to suppress the coalescence of the droplets effectively reduces the droplet size. On the other hand, additional organoclay results in the rheological properties of particular component being increased, which means the change in the viscosity ratio. The change in the viscosity ratio, together with the coalescence suppression effect, affects the determination of the droplet size, depending on the location of the organoclay. Therefore, the organoclay suppresses the coalescence of the droplets at the interface, while simultaneously influencing the breakup of the droplets due to the change of viscosity ratio.