高分子材料体积拉伸流变加工技术进展

高分子材料加工产业对加工过程高效、环保、低能耗的发展需求,推动着聚合物塑化输运方法与原理的不断创新。在高分子材料电磁动态塑化加工成型方法的基础上,进一步提出了基于体积拉伸流变的高分子材料加工成型方法与技术。详细介绍了体积拉伸形变支配的叶片塑化输运设备和偏心转子塑化输运设备的基本结构与工作原理,并阐述了两者在高分子材料加工中的应用优势。研究结果表明,与传统螺杆式塑化输运技术相比,体积拉伸流变塑化输运技术具有缩短加工热历程、混炼效果好、制品性能优良、对物料适应性广等显著优势。高分子材料在加工领域新技术的发展,为开发新型塑料产品、提高产品性能并降低产品成本开拓了广阔的空间。     

基于拉伸流动的聚合物复合材料分散混合研究进展

相对常用聚合物成型加工设备通过剪切力场来实现对聚合物及其填充体系的分散混合,拉伸流场具有更好的分散混合效果及较高的分散效率.通过对成型加工设备结构进行优化设计,以及成型设备进行合理改造来实现高效分散的拉伸流场,并对拉伸流场的产生方式进行论述.     

Morphology and Properties of Polyethylene/Clay Nanocomposite Drawn Fibers

The influence of an elongational flow on the morphology of PE/clay nanocomposite drawn fibers was studied. An increase of the elastic modulus and the tensile strength as well as a decrease of the elongation at break are observed with increasing draw ratio. The applied elongational gradient orients the polymer chains and the clay particles along the spinning direction. When the applied flow results in the formation and the orientation of exfoliated nanoparticles, a pronounced increase of the mechanical properties is observed. The dispersed clay particles can be broken and oriented by the extensional flow, which might indicate a flow‐induced intercalated/exfoliated morphology transition.

     

聚合物/粘土纳米复合材料的研究进展

综述了聚合物/粘土纳米复合材料的制备、表征和性能。粘土经相容剂修饰成为有机土,层间距增大,层间微环境由亲水变为亲油,从而利于聚合物的插层。聚合物插层导致粘土片层剥离并分散于聚合物基体中,得到的聚合物/粘土纳米复合材料的机械和物理性能比原来的聚合物材料有了显著的提高。     

Rheological Properties of Different Film Blowing Polyethylene Samples Under Shear and Elongational Flow

Summary: The rheological behavior of polyethylenes is mainly dominated by the molecular weight, the molecular weight distribution and by the type, the amount and the distribution of the chain branches. In this work a linear metallocene catalyzed polyethylene (m‐PE), a branched metallocene catalyzed polyethylene (m‐bPE), a conventional linear low density polyethylene (LLDPE) and a low density polyethylene (LDPE) have been investigated in order to compare their rheological behavior in shear and in elongational flow. The four samples have similar melt flow index and in particular a value typical of film blowing grade. The melt viscosity has been studied both in shear and in isothermal and non‐isothermal elongational flow. The most important features of the results are that in shear flow the m‐PE sample shows less pronounced non Newtonian behavior while in the elongational flow the behavior of m‐PE is very similar to that of the linear low density polyethylene: the narrower molecular weight distribution and the better homogeneity of the branching distribution are reasonably responsible for this behavior. Of course the most pronounced non‐linear behavior is shown, as expected, by the LDPE sample and by the branched metallocene sample. This similar behavior has to be attributed to the presence of branching. Similar comments hold in non‐isothermal elongational flow; the LDPE sample shows the highest values of the melt strength and the other two samples show very similar values. As for the breaking stretching ratio the opposite is true for LDPE while m‐PE and LLDPE show higher values. The transient isothermal elongational viscosity curves show that the branched samples show a strain hardening effect, while LLDPE and m‐PE samples present a linear behavior.

Dimensionless flow curves of different polyethylene samples.     

Elongational flow-induced birefringence of polyacrylamide and poly(acrylamide-co-sodium acrylate)

Aqueous solutions of poly(acrylamide-co-sodium acrylate), in up to 1M NaCl, exhibited a flow-induced negative birefringence above a critical elongation flow rate in a crossed-slot device. Aqueous polyacrylamide, on the other hand, exhibited a positive birefringent pattern just above a critical elongation rate. At slightly higher elongation rates a negative birefringent thin-line region centred in the positive birefringent region appeared. This phenomenon was observed for all polyacrylamide concentrations tested (0.001 to 0.5 wt%; 0.5 to 20 times the quiescent overlap concentration). This change in birefringence sign can be qualitatively mimicked using a simple coil deformation model which includes contributions from intrinsic, microform and macroform optical anisotropy terms. Evidence is also given for this alternating birefringence sign pattern possibly being due to an elongational flow-induced change in the microstructure of the polyacrylamide.     

纤维素溶液吹膜过程中拉伸黏度的测定

通过非等温吹塑薄膜挤出实验研究了纤维素的NMMO(N-甲基吗啉-N-氧化物，亦称N-甲基氧化吗啉)溶液在不同工艺条件下的拉伸流动行为。讨论和推导了挤出过程中的理论数学模型，测定了纤维素溶液在加工过程中膜泡半径和膜厚随加工方向的变化，并对沿加工方向上拉伸速率和表观拉伸黏度的变化进行了探讨。研究表明：质量份数为9％的纤维素溶液在加工过程中拉伸黏度受拉伸速率与温度的综合影响，沿加工方向呈现先微降，再渐升的趋势；在加工过程中随着牵引速度和膜泡内外压力差(△P)的增大，膜泡的厚度变小，拉伸速率变大，拉伸黏度变小。     

高聚物/黏土纳米复合材料阻燃性能的研究进展

综述了近几年来高聚物／黏土纳米复合材料阻燃性能的研究进展，介绍了其结构、制备、阻燃机理及表征方法，并与常规阻燃剂进行了阻燃性能比较，发现在机械、加工、环保等方面，高聚物／黏土纳米复合材料均优于常规阻燃剂，同时对其研究与应用做了展望。     

聚合物/蒙脱土纳米复合材料研究及其应用进展

主要介绍了聚合物／蒙脱土纳米复合材料的制备方法、国内的研究和应用进展以及国外的应用领域。     

Rheology of a low‐filled polyamide 6/montmorillonite nanocomposite

The rheological properties of a polyamide 6/clay nanocomposite with a low loading of clay (1 wt %) were studied. Linear viscoelastic measurements in oscillatory and steady shear with small strain amplitudes were carried out. The nanocomposite exhibited a higher elastic modulus, viscous modulus, and complex viscosity than neat polyamide 6 during dynamic and steady shear tests. Moreover, the addition of clay resulted in a reduction of the critical strain amplitude, an increase of the loss angle, and a reduction of the frequency at the intersection of the elastic and viscous moduli. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

熔融插层法制备聚合物/黏土纳米复合材料研究进展

对国内外熔融插层法制备聚合物／黏土纳米复合材料(PCN)的研究进展进行了介绍。介绍了影响PCN结构形态的几种因素;对熔融插层法制备PCN的热力学、动力学的研究进行了总结;介绍了熔融插层的机理和几种理论模型。并对聚合物／黏土纳米复合材料的开发及应用前景作出了展望。     

Elongational flow studies of the conformation of DNA molecules in the globular state

Elongational flow‐induced birefringence of a T4‐phage DNA aqueous solution was measured with changing NaCl and polyethylene glycol (PEG) concentrations. DNA molecules are known to manifest a coil–globule transition with increasing PEG concentration. At certain PEG concentrations near the critical concentration of the transition, the globular DNA solution, which was expected to be nonbirefringent, showed flow‐induced birefringence. Strain‐rate dependence of the birefringence intensity, having a critical strain rate, was similar to that of the flexible polymer chain that manifests the coil–stretch transition. The flow‐induced birefringence pattern, however, suggested that the globular DNA molecules were rigid and optically anisotropic. At the critical strain rate, the globular DNA molecules in the solution of the particular PEG concentration were considered to collapse nonadiabatically to an optically anisotropic and mechanically rigid conformation. The overall shape of the collapsed conformation of the globular DNA was estimated to be an ellipsoid with an aspect ratio of about 0.7. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1351–1358, 2000     

Percolated Network Structure Formation and Rheological Properties in Nylon 6/Clay Nanocomposites

To understand the effect of the percolated clay network structure formed by the exfoliated clay layers in nanocomposites, the clay network structure in nylon‐6‐based nanocomposites is characterized using TEM and FFT analyses. A MMT volume fraction between 0.013 and 0.014 is the percolation threshold for strong network formation. The volume spanning MMT network leads to a very high flow activation energy as compared with that of neat nylon 6, resulting in the pseudo‐solid like response under molten state in N6CNs. A canonical NVT‐MD simulation was conducted in the system made up by nylon 6 molecules/Si(OH)₄ molecules. The formation of the strong interfacial interaction between nylon 6 molecules and Si(OH)₄ molecules induced by OH groups is suggested.

     

熔融插层制备聚合物／层状粘土纳米复合材料研究进展

从流变性能、加工操作过程对熔融插层制备聚合物纳米复合材料的影响、分散机理的研究进展等方面对熔融插层制备聚合物 /层状粘土进行了综述 ,并对今后的研究提出了展望。     

Rheological behavior of polypropylene/layered silicate nanocomposites prepared by melt compounding in shear and elongational flows

Melt rheology and processability of exfoliated polypropylene (PP)/layered silicate nanocomposites were investigated. The nanocomposites were prepared by melt compounding process in the presence or absence of a PP‐based maleic anhydride compatibilizer. PP/layered silicate nanocomposites showed typical rheological properties of exfoliated nanocomposites such as nonterminal solid‐like plateau behavior at low frequency region in oscillatory shear flow, higher steady shear viscosity at low shear rate region, and outstanding strain hardening behavior in uniaxial elongational flow. The melt processability of exfoliated PP/layered silicate nanocomposites was significantly improved due to good dispersion of layered silicates and increased molecular interaction between the PP matrix and the layered silicate organoclay. Small‐angle X‐ray scattering and transmission electron microscopy results revealed that the layered silicate organoclay was exfoliated and good interaction between PP matrix and organoclay was achieved by using the PP‐g‐MAH compatibilizer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3506–3515, 2007     

The Influence of Macroscopic Elongational Flow on Dispersion Processes in Agitated Tanks

The influence of elongational and shear gradients in the macroscopic flow field in agitated tanks on dispersion processes is investigated. Measurements of droplet size distribution for a liquid‐liquid dispersion process using phase‐Doppler anemometry (PDA) reveal that axial‐flow impellers, such as the 24°‐pitched‐blade turbine and propeller, produce smaller droplets than the Rushton turbine at the same average specific power and energy input. These results stand in contradiction to the usual assumption that only the maximum turbulent shear stress determines the breakup process and the Rushton turbine is well known to produce higher turbulent shear stresses. Particle image velocimetry (PIV) measurements of the macroscopic flow field indicate that the 24°‐pitched‐blade turbine and propeller produce larger areas with higher elongational gradients. Therefore, the proposed consideration of particle breakup due to macroscopic elongational flow in addition to turbulent stresses improves the understanding of dispersion processes in agitated tanks.     

Fiber Suspensions in Complex Geometries: Flow/Orientation Coupling

A Galerkin finite element solution is developed for the flow of fiber suspensions. Primary variables are velocity, pressure, and a second‐order tensor describing the fiber orientation. The model treats the orientation as three‐dimensional, includes fiber—fiber interaction effects, and uses an orthotropic closure approximation. The flow and orientation are strongly coupled through an orientation‐dependent constitutive equation. We explore the effect of this coupling on the fluid mechanics of fiber suspensions by studying three flows: an axisymmetric contraction, an axisymmetric expansion, and a center‐gated disk. Coupling enhances the corner vortex in the contraction, in quantitative agreement with published experiments and calculations. The expansion results demonstrate that the aligned‐fiber approximation is not valid for this flow. In the center‐gated disk the effects of coupling are modest and are only noticeable near the center of the disk. This supports the use of decoupled models for injection molding in thin cavities.     

Rheology of natural fibers thermoplastic compounds: Flow length and fiber distribution

The presented study investigates the flow length and the corresponding fiber content distribution in the injection‐moulded natural fiber reinforced thermoplastics and its relation to fiber type and processing parameters such as injection pressure, temperature, injection rate and mould tempering by increasing die temperature. In this research, polypropylene compounds with nominally 30 wt % hemp and sisal fibers are investigated. The influence of the injection pressure (500 and 1000 bar), melt temperature (180°C, 200°C, and 220°C), and die temperature (23°C and 80°C) on the fiber content distribution all over the sample is investigated. An increasing linear trend of fiber content along the spiral length is observed as an evidence of a fiber/polymer multiflow system. A pattern for fiber content distribution with respect to the fiber length along the injected spiral can be distinguished, where the longer fibers are usually found at the end of the injected part and the shorter fibers remain near mould entrance point. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39861.     

Experimental methods in chemical engineering: Rheometry

Rheometry is an experimental technique that measures the relationship between stresses, strains, and their derivatives of fluids and deformable materials. Capillary and Couette viscometers were among the first instruments used to study rheology but now sophisticated shear and extensional rheometers are widely available for quality control, research, and product development. Here, we introduce the basics of rheology, define material functions, and describe conventional instruments, physical principles, applications, and uncertainties. In 2016 and 2017, the Web of Science indexed 8400 articles that mention rheometry and a bibliometric map assigned the keywords into five clusters of research: behaviour and viscosity, mechanical properties and morphology, rheological properties and microstructure, polymers and nano-particles, and visco-elastic properties and mixtures. Journal of Rheology, Construction Building Materials, Food Hydrocolloids, Soft Matter, Rheologica Acta, and Journal of Applied Polymer Science publish at least 80 articles per year that mention rheometry.