Microphotometric Detection of Particles/Inhomogeneities in Flowing Polymer Melts

By application of different unique microphotometric sensors it is possible to detect and quantify disturbing particles (gels, unmolten resins, black spots, additive agglomerates, bubbles) within a flowing polymer melt in realtime during extrusion processing. These particles result in disadvantageous optical and mechanical properties of a final polymer product. Sensors can be adapted inline and online to different extruders at various positions. This seems to give technical and economic benefit to quality control and process optimisation in polymer processing.     

Melt flow instabilities in polyethylene resins

The melt flow instabilities of four polyethylene (PE) pipe resins were investigated and critically compared. By comparing the flow curve obtained by capillary rheology measurements with the linear viscoelastic (LVE) data, the apparent slip was seen in the four polyethylenes. It was proposed that the high content of small chains could cause the significant wall slip, but the slip was not the origin mechanism of sharkskin melt fracture. The bimodal resins that had higher content of low molecular weight component first showed a matte surface at lower stresses. The matte surface remained until the extrudate converted to a wavy appearance as shear rates were increased. It was observed that the onset stress of sharkskin melt fracture was almost proportional to the plateau modulus. Furthermore, the chain relaxation time of the resins also influences the surface melt fracture behavior of the resin.     

Preparation and properties of star-branched PA12 with hexafunctional cyclotriphosphazene core

Using hexa(4-carboxylphenoxy)cyclotriphosphazene (HCPCP) with six carboxyl groups as the core, a new kind of star-branched PA12 with hexafunctional cyclotriphosphazene core was prepared in the ring-opening polymerization of ω-laurolactam. The relationship between the structure and properties of star-branched PA12 had been systematically investigated. Compared with linear PA12, star-branched PA12 has lower relative viscosity and higher melt flow rate while its mechanical properties can be almost retained by the use of star-branching and an appropriate molecular weight. Research on crystallization and rheological behaviors indicate that star-branched PA12 with appropriate molecular weight has the faster crystallization rate, the higher flowability and the lower processing temperature and pressure than linear PA12, which could be used as the easy processing polyamide resin for the rapid molding process.     

界面相互作用对尼龙6／聚乙烯共混物形态结构和流变行为的影响

利用扫描电子显微镜和动态力学分析仪研究了马来酸酐熔融接枝聚乙烯（ＰＥ－ｇ－ＭＡ）对尼龙６／聚乙烯（ＰＡ６／ＰＥ）共混物形态结构和动态力学行为的影响．结果表明，ＰＥ－ｇ－ＭＡ使ＰＡ６／ＰＥ共混物中ＰＡｅ的玻璃化转变峰向低温例偏移，这主要归因于ＰＥ－ｇ－ＭＡ改善了ＰＡ６和ＰＥ二者的相容性；但随着ＰＥ分散相中ＰＥ－ｇ－ＭＡ所占比重的增加，ＰＥ－ｇ－ＭＡ与ＰＡ６之间界面化学键合密度增大，使得ＰＡ６的玻璃化转变温度反而提高．同时，利用平行板流交仪研究了ＰＥ－ｇ－ＭＡ对ＰＡ６／ＰＥ共混物熔体流变行为的影响．ＰＥ－ｇ－ＭＡ使共混物熔体粘度和动态储能模量增大，这应归因于ＰＡ６／ＰＥ－ｇ－ＭＡ之间在熔融共混过程中的界面化学键合．     

A flow visualization technique for the determination of velocity profiles in dies with circular cross sections

A unique retainer/transparent quartz die assembly was designed and fabricated to fit on a melt extruder. It permitted visualization of polymer flow behavior during melt spinning. Tracer particles were mixed with polymer chips prior to extrusion. A laser beam was directed through a lens system and used to illuminate the tracer particles in the melt only in a thin, vertical cross section of the transparent quartz die. Streak photography was used to determine the cross-sectional velocity distribution of the melt as it passed through the die.     

聚苯乙烯/聚乙烯的反应性挤出共混

多官能团单体;聚苯乙烯/聚乙烯的反应性挤出共混     

Effect of surface composition on the flowability of industrial spray-dried dairy powders

The surface composition of four industrial spray-dried dairy powders (skim milk powder, whole milk powder, cream powder and whey protein concentrate) was estimated by electron spectroscopy for chemical analysis (ESCA), and its influence on powder flowability was studied. It was found that skim milk powder flows well compared to the other powders because the surface is made of lactose and protein with a small amount of fat, whereas the high surface fat composition inhibits the flow of whole milk, cream and whey protein powders. However, the poor flowability of the powders with high surface fat coverage was drastically improved by removal of fat present on the surface through a brief wash with petroleum ether. The results obtained indicate that, although there are several parameters including particle size, which influence the flowability of powders, the flowability of powders is strongly influenced by the surface composition of powders, particularly for fat-containing powders.     

Reactive blending of PE‐GMA/PA6 effect of composition and processing conditions

Blends of ethylene‐glycidyl methacrylate copolymer (PE‐GMA) and polyamide 6 (PA6) were prepared in a corotating twin screw extruder. Two processing temperatures were used in order to disperse PA6 in two forms: at high temperature in the molten state in molted PE‐GMA Matrix (emulsion type mixture) and at lower temperature as fillers in molted PEGMA matrix (suspension type mixture). Processed blends were analyzed by scanning electron microscopy and dynamic mechanical experiments to probe the reactivity in the extruder and the compatibilization phenomena. The dependence of the morphology and the rheological properties of PE‐GMA/PA6 blends on blend composition and screw rotational speed was also investigated and is discussed in the paper. The results show that dispersion of the two polymers in the molten state leads to a higher level of interfacial reaction. They also show that whatever the screw rotational speed and the temperature of extrusion are, the rate of interfacial reaction in PE‐GMA/PA6 blends is higher for 50/50 PE‐GMA/PA blends than for 70/30 PE‐GMA/PA blends. Copyright © 2015 John Wiley & Sons, Ltd.     

A novel method for making ultra-fine metal fibers and particles

A novel method based on plastic processing and equipment for preparing ultra-fine metal fibers and particles is reported. With this new method, metal fibers and particles can both be produced on the same equipment and the surfaces of the fibers and particles can be protected from oxidation by the polymers or solvents during the preparation process. Metal-alloy powders with lower melt point were filled into polymer by an extruder, followed by a die-drawing process at a temperature lower than the melt temperature of the metal alloy. Metal fibers or particles were obtained after the polymer matrix was washed away. Metal alloy fibers can be obtained when a polymer that strongly interacts with metal alloy, such as a special polyvinyl alcohol with a low alcoholysis degree, is used as the polymer matrix. Metal-alloy particles can be obtained when a polymer with weak interaction with metal alloy, such as polyethylene (PE), is used as the polymer matrix. Based on the principle of this new method, it is possible to produce finer or even nano-sized metal fibers and particles with higher melting points.     

Nanoporous structure of ultrahigh-molecular-weight polyethylene reactor powder

The influence of the catalyst system and synthesis conditions on the morphology and molecular dynamics of reactor (nascent) powders of ultrahigh-molecular-weight PE synthesized over supported Ziegler-Natta catalysts in laboratory reactors was studied by means of electron microscopy and ¹H broadline NMR spectroscopy. For comparison, commercial reactor powders were studied as well. The type of the catalyst system and the temperature of slurry polymerization have a substantial effect on the supermolecular structure of the nascent polymer. The proton NMR spectra of the reactor powders synthesized at low temperatures display a narrow component. An analysis of its behavior at low temperatures and different humidities led to the conclusion that the signal is due to water localized in nanopores of 2–4 nm in size in the nascent polymer. The role of nanopores in the sintering of reactor particles is discussed.     

An investigation into sintering of PA6 nanocomposite powders for rotational molding

The objective of this work is to study the sintering behavior of polyamide 6 (PA6) powders and PA6 nanocomposites by means of thermomechanical (TMA) and dimensionless analysis in view of its technological application in rotational molding. TMA analysis was used to monitor the bulk density evolution of PA6 powders and PA6 nanocomposites when heated above the melting temperature. Experimental TMA results indicate that the sintering of PA6 and PA6 nanocomposites occurs in two different steps, namely powder coalescence and void removal. Furthermore, TMA analysis showed that relevant degradation phenomena occur during the sintering of PA6 and PA6 nanocomposites, leading to gas formation in the molten polymer. The suitability of these materials in rotational molding was then assessed by defining a processing window, as the temperature difference between the endset sintering and the onset degradation. The heating rate dependence of the processing window was explained by means of dimensionless analysis, showing that powder coalescence is influenced by the viscosity evolution of the matrix, whereas void removal is influenced by the gas diffusivity inside the molten matrix. Therefore, the diffusion activation energy correlates the endset sintering temperature to the heating rate. On the other hand, the onset degradation temperature depends on the heating rate, due to the characteristic activation energy of the degradation process. Accordingly, the width of the processing window mainly depends on the values of the activation energies for diffusivity and degradation. The width of the processing window for neat PA6 was found to be too narrow to candidate this polymer for rotational molding. The addition of nanofiller causes a narrowing of the processing window, whereas the PA6 matrix modified with a thermal stabilizer showed a sufficiently broad processing window, compatible for use in rotational molding.     

Studies on crystal transition of polyamide 11 nanocomposites by variable-temperature X-ray diffraction

Polyamide I1 （PAll） and its nanocomposites with different organoclay loadings were prepared by melt-compounding and subsequent pelletizing. The crystal phase transitions of PAl 1 and its clay nanocomposites were investigated by variable-temperature X-ray diffraction. It was found that the Brill transition of the nanocomposite was 20 K higher than that of the neat PAl 1 for both heating and cooling processes. The PAl 1 d-spacings of the nanocomposites were observed to be smaller than those of the neat PAl 1 for melt crystallization. The constraints imposed by the addition of layered clay, restricting the thermal expansion of the polymer chains, are probably responsible for such a reduction of the d-spacing.     

Application of thermal analysis techniques to study the oxidation/reduction phenomena during sintering of steels containing oxygen-sensitive alloying elements

For the consolidation of steel parts manufactured by powder metallurgy (PM) techniques, removal of the surface oxides covering metallic powder particles is a necessary prerequisite. In PM steels with conventional compositions, reduction of the oxides is easily achieved in traditional sintering furnaces. However, processing steels containing alloying elements with a high oxygen affinity represents a big challenge that requires a deeper understanding of the chemical processes occurring during sintering. In the present work, thermogravimetry analysis coupled with mass spectrometry is used to describe the oxidation/reduction phenomena that take place when sintering steel powders and how these processes are modified by the addition of admixed particles containing oxygen-sensitive elements. Carbothermal reduction processes are studied using pure oxides (Fe₂O₃, MnO₂, Cr₂O₃ and SiO₂) as well as water-atomized Fe powders mixed with small amounts—4 mass/%—of Cr, Mn and Si powders or Fe–Mn–Si–(Cr) master alloy powders. The results show that there is an oxygen transfer from the base iron particles to the oxidation-sensitive elements—“internal getter effect”—taking place mostly through the gas phase. Different alloying elements (Cr, Mn, Si) show different temperature ranges of susceptibility to oxidation. Combination of these oxygen-sensitive alloying elements in the form of a master alloy powder reduces their sensitivity to oxidation. Also, the use of master alloys promotes the concentration of the oxides on the surface of the alloying particles and not in the grain boundaries of the surrounding iron particles—as occurs when using Mn carriers—which should have a beneficial impact on the final mechanical performance.     

激光烧结制备尼龙12/累托石纳米复合材料

将有机累托石与尼龙12粉末混合,采用激光烧结(SLS)技术制备了尼龙12累托石纳米复合材料,这是一种使纳米复合材料的制备与材料的成型同时进行的方法.利用X射线衍射(XRD)、红外光谱(FTIR)、扫描电镜(SEM)等手段对复合材料的结构进行了表征,并对其力学性能及热性能进行了研究.结果表明,尼龙12分子在激光烧结过程中插入到累托石层间,形成的复合材料在拉伸强度、弯曲强度、冲击强度等力学性能及热稳定性能方面均优于尼龙12烧结试样.     

表面修饰的钛酸钡纳米粉体的制备

采用水热法制备出表面包裹有硬脂酸的钛酸钡纳米粉体,并运用一系列手段对其微结构进行了表征.结果表明:产物粒径较小,粒度分布较窄,单分散性较好,其表面为非极性,同时表现出良好的流动性能.认为钛酸钡纳米粉体表面极性的改变是由于其表面包裹了一层硬脂酸,并且包裹层降低了粉体间的相互作用力,从而提高了粉体的流动性.     

Impact properties,phase structure,compatibility, and fracture morphology of polyamide‐1010/thermoplastic poly(ester urethane) elastomer blends

Blends of polyamide‐1010 (PA1010) and a thermoplastic poly(ester urethane) elastomer (TPU) were prepared by melt extrusion. The impact properties, phase structure, compatibility, and fracture morphology under impact were investigated for PA1010/TPU blends. The results indicated that TPU enhanced the impact strength of PA1010, and the best impact modification effect of the blends was obtained with 20 wt % TPU. The phase structure was investigated with scanning electron microscopy, and the compatibility was investigated with dynamic mechanical analysis and small‐angle X‐ray scattering. The study of the fracture morphology of PA1010/TPU blends indicated that the fracture surface of the blends had special features, consisting of many fibrillar elastomer particles and a conglutination–multilayer structure, as well as many small tubers on this structure. These fracture phenomena could not be found on the fracture surface of pure PA1010. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1177–1185, 2005     

Sintering of hydroxyapatite lath-like powders

Hydroxyapatite powders, which consisted of lath-like single-crystalline particles, were calcined at two different temperatures. Green and calcined powders were used for sintering HAp ceramic samples under uniaxial pressing. Powders and sintered samples were studied using various analytical techniques in order to determine how calcination affects the particle properties and the sintering behavior of HAp powders. It was found that calcination decreases the particles length and changes the particles morphology from lath-like to spherical shape. The relative density increases with increasing calcination temperature and aging time. It was found that long aging time favor the formation of thermally stable HAp particles, whereas a shorter one results in the formation of β-calcium phosphate during thermal treatment. Sintering of compacted powders begins at temperatures greater than 900°C, with a trend to increase the onset temperature as the calcination temperature is increased.     

高耐压HDPE自增强管挤出系统及试样的结构与性能

本文针对管件在输送压力流体时的特殊应力状态,提出了管材周向自增强的构想,据此设计出了自增强挤出系统.该系统利用芯棒旋转,使大分子链沿管周向取向并在适当的压力、温度条件下生成串晶结构,从而大大提高了管材的周向强度及模量.利用DSC、WAXD和SEM等检测手段对试件的凝聚态结构进行分析,找到了周向强度提高的理论依据.     

A comparison of theoretically determined and experimentally measured velocity distributions of poly(ethylene terephthalate) flow in a capillary

A streak photographic technique was used to determine the velocity distribution in a capillary produced by the flow of poly(ethylene terephthalate) (PET). This uniquely designed quartz die assembly, which was fitted onto a melt extruder, permitted visualization of polymer flow behavior during melt spinning. Aluminum tracer particles were mixed with polymer chips prior to extrusion. A laser beam was directed through a lens system that illuminated the tracer particles in the melt only in a thin, vertical cross section of the transparent quartz die. A pressure-drop analysis was also performed on PET, under the same experimental conditions, to determine rheological properties of the polymer. By using these rheological properties theoretical velocity distributions were calculated for PET and then compared with the profiles obtained by the streak photographic technique.     

Design of Blends with an Extremely Low Viscosity Ratio between the Dispersed and Continuous Phases. Dependence of the Dispersed Phase Size on the Processing Parameters

Summary: This work deals with the development of the dispersed phase morphology in immiscible blends of poly(ethylene glycol)/polyamide 66 (PEG/PA) with an extremely low viscosity ratio. The blends were obtained, under different operating conditions, by melt blending in an internal mixer. The objective was to examine the influence of the main processing parameters on the particles size of the minor phase (PEG). A model was elaborated to describe the dependence of the particle size on interfacial tension, PEG concentration, shear rate and viscosity ratio between the two blend components.