Melt fracture of polyisobutylenes

The processability of different grades of polyisobutylene (PIB) was investigated using a capillary rheometer. Direct focus was given to the occurrence of melt fracture phenomena, such as sharkskin and gross melt fracture (GMF). The influence of molecular weight (MW) of PIB, temperature and die entrance angle on melt fracture was examined in detail. Due to their highly elastic nature, high MW PIBs were found to exhibit gross melt fracture instability even at low shear rates, rendering their processing an impossible task. An increase in temperature resulted in postponing both instabilities (sharkskin and gross) to higher shear rates, thus making their processing easier. Finally, decreasing the entrance angle below a critical value resulted in postponing the onset of GMF to higher shear rates.     

Thiophene-containing products of the Ugi reaction in an oxidation-triggered IMDA/aromatization cascade: a simple access to 3-oxoisoindolines

A novel approach to skeletally diverse 3-oxoisoindolines has been developed which includes preparation of Ugi adducts containing thiophene and fumaric acid residues. When treated with excess m-CPBA at room temperature, these precursors undergo a simple oxidative cycloaddition/aromatization transformation and the corresponding 3-oxoisoindoline products are isolated in fair chemical yield over two steps. The second step is thought to include S-oxidation/IMDA/S-oxidation/SO₂ extrusion/aromatization events.     

Hot deformation in nanocrystalline Ndben Feben B backward extruded rings

Radially oriented Nd-Fe-B rings are prepared by backward extrusion of fine grained melt-spun powder. Melt-spun powder with the nominal composition of Nd_30.5Fe_bal.Co_6.0Ga_0.6Al_0.2B_0.9 (wt%) is used as starting material. The effects of process variables, such as deformation temperature (T_d), strain rate (ε) and height reduction (Δh%), on the magnetic properties of the rings are investigated. A scanning electron microscope (SEM) equipped with an energy spectrum device is used to study the metallograph and microfracture of the extruded rings. The B_r and (BH)_max reach the optimum values at T_d=800℃, ε =0.01 mm/s, and Δh% =70%. It is found by SEM observations that the particle boundaries, which seemingly correspond to the interfaces of the starting melt-spun powders, emerge after the corrosion of metallography specimens. This is helpful for studying the effects of powder-powder interface on the local deformation and deformation homogeneity in the rings. For different spatial positions of the extruded rings, there are characteristic metallographies and microfractures. The upper end of the rings has the least deformation and worst texture, and therefore the worst magnetic properties. The magnetic properties in the radial direction increase slightly along the axis from the bottom to the middle, then steeply decrease at the upper end of the ring. The deformation and the formation-of-texturing processes are discussed. The deformation and the texturing formation of melt-spun Nd-Fe-B alloys probably involve grain boundary sliding and grain rotation, the solution-precipitation process and preferential growth of Nd₂Fe₁₄B nanograins along the easy growth a-axis.     

Rheological and mechanical properties of nylon 6 nanocomposites submitted to reprocessing with single and twin screw extruders

The effect of multiple extrusions on nanostructure and properties of nylon 6 nanocomposites was investigated. Nanocomposites at different silicate loadings were produced by melt compounding and submitted to further reprocessing by using single and twin screw extruders. Rheological, morphological and mechanical analyses were carried out on as-produced and reprocessed samples in order to explore the influence of the number and the type of extrusion cycles on silicate nanodispersion.Rheological measurements, correlated to TEM analyses, were used to probe the nanoscale arrangement developed with the reprocessing as well as the thermo-mechanical degradation involving both the neat matrix and the organoclay. The results have shown that the reprocessing by single screw extruder can modify the initial morphology since the re-agglomeration of the silicate layers can occur. On the other hand, a better nanodispersion was observed in the hybrids reprocessed by twin screw extruder. This was attributed to the additional mechanical stresses able to realizing a dispersive mixing that contributes to avoid re-agglomeration phenomena. The high shear stresses produced with twin screw geometry determined also a significant degradation of neat matrix, principally based on chain scission mechanism.A strong correlation between the rheological behaviour and mechanical properties was observed and all as-produced and reprocessed hybrids showed a substantial enhancement in tensile modulus with the adding of silicate. However, the entity of performance enhancements displayed by the reprocessed hybrids was found to be highly dependent on the degradation of both organoclay and polymer matrix as well as the silicate amount, the number and the type reprocessing.     

Electrospinning of ultrahigh‐molecular‐weight polyethylene nanofibers

The electrospinning method has been employed to fabricate ultrafine nanofibers of ultrahigh‐molecular‐weight polyethylene for the first time with a mixture of solvents of different dielectric constants and conductivities. The possibility of producing highly oriented nanofibers from ultrahigh‐molecular‐weight polymers suggests new ways of fabricating ultrastrong, porous, and single‐component nanocomposite fibers with improved properties. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 766–773, 2007     

The effect of temperature gradients on the sharkskin surface instability in polymer extrusion through a slit die

The sharkskin surface instability is commonly observed in the extrusion of polymer melts. We present a series of experiments in which a specifically designed rectangular slit die with insulated and independently heated sides and is used to induce precise temperature gradients across a flowing polyethylene melt. Our previous experiments demonstrated that the character of the surface distortions produced by the sharkskin instability was a function of the die wall temperature and therefore the extrudate had viscoelastic properties at the surface. In this paper, we explore the role of temperature and viscoelastic property gradients near the capillary wall. The amplitude of the sharkskin instability is quantified and plotted against apparent shear and extension rates. Analysis of the data demonstrates that the amplitude and frequency of the instability is independent of bulk temperature and temperature gradient and is dependent only on wall temperature. The data are normalized using a dimensionless Weissenberg number based on the extension rate to collapse the data collected over all temperatures and gradients onto a single master curve. We conclude with an example of a rectangular extrudate exhibiting varying surface roughness due to differential die heating and discuss the implications of our observations on the sharkskin surface instability mechanism and on commercial applications.     

Automated solvent system screening for the preparative countercurrent chromatography of pharmaceutical discovery compounds

A fully automated countercurrent chromatography system has been constructed to rapidly screen the commonly used heptane/ethyl acetate/methanol/water solvent system series and translate the results to preparative scale separations. The system utilizes “on‐demand” preparation of the heptane/ethyl acetate/methanol/water solvent system upper and lower phases. Elution‐extrusion countercurrent chromatography was combined with non‐dynamic equilibrium injection reducing the screening time for each heptane/ethyl acetate/methanol/water system to 17 min. The result enabled solvent system development to be reduced to under 2 h. The countercurrent chromatography system was interfaced with a mass spectrometer to allow selective detection of target components in crude medicinal chemistry reaction mixtures. Mass‐directed preparative countercurrent chromatography purification was demonstrated for the first time using a synthetic tetrazole epoxide derived from a routine medicinal chemistry support workflow.     

A Facile Method to Prepare Double‐Layer Isoporous Hollow Fiber Membrane by In Situ Hydrogen Bond Formation in the Spinning Line

A double‐layer hollow fiber is fabricated where an isoporous surface of polystyrene‐block‐poly(4‐vinylpyridine) is fixed on a support layer by co‐extrusion. Due to the sulfonation of the support layer material, delamination of the two layers is suppressed without increasing the number of subsequent processing steps for isoporous composite membrane formation. Electron microscope‐energy‐dispersive X‐ray spectroscopy images unveil the existence of a high sulfur concentration in the interfacial region by which in‐process H‐bond formation between the layers is evidenced. For the very first time, our study reports a facile method to fabricate a sturdy isoporous double‐layer hollow fiber.

     

IUPAC-LDPE的流变性测试实验之间的相对滑动

以IUPAC—LDPE熔体在150℃下详细的流变学表征实验和毛细管挤出实验为基础考察了该熔体在挤出实验中的滑动问题．根据相对滑动特性给出了判断相对滑动存在和计算相对滑动速度的方法．用Wagner模型，PSM模型和Osaki模型计算的表观剪切速率，在10s^-1时的毛细管壁面剪切应力比毛细管挤出实验给出的应力值高出约15％-17％，这个结果意味着IUPAC—LDPE熔体在挤出实验中存在滑动现象．在表观剪切速率为0．1，1．0和10s^-1时，挤出实验条件下的流动与根据在旋转流变仪上测定的流变特性用PSM模型计算的流动相比，它们之间存在的相对滑动速度分别为0．004，0．071和1．343mm／s．用Wagner模型和Osaki模型计算的相对滑动速度与PSM模型的结果相近．     

Validation of an in-line Raman spectroscopic method for continuous active pharmaceutical ingredient quantification during pharmaceutical hot-melt extrusion

A calibration model for in-line API determination was developed based on Raman spectra collected during hot-melt extrusion. This predictive model was validated by calculating the accuracy profile based on the analysis results of validation experiments. Furthermore, based on the data of the accuracy profile, the measurement uncertainty was determined. Finally, the robustness of the model was evaluated.