Slip flow of non-plasticized PVC compounds

Measurements on seven rigid PVC compounds were carried out with a slit rheometer working in combination with an injection moulding machine. Plastication of the compounds occurred in the screw of the plastication unit, which also forced the melt through the die with a controlled forward velocity. The rectangular slit had a length of 90 mm and a widthB of 20 mm. The heightH could be varied between 0.8 and 3.3 mm. Pressures and temperatures were recorded at several positions in and before the die. Measurements were carried out at shear rates from 10 to 2000 s^–1.When the reduced volume output was plotted against the wall shear stress _W , only four compounds showed master curves independent ofH, which is indicative of wall adhesion. In the other cases this plot did not produce such a master curve, but the plot of the mean velocity against _W was independent ofH (slip curve). This indicated that slip flow prevailed with a slip velocityv _G When, in the case of wall slip, the smooth inner surfaces of the die were replaced by surfaces with grooves perpendicular to the direction of flow, slip flow was prevented and the flow curves were shifted to much higher values of _Wc Above a critical value of the wall shear stress ( _Wc ) at which slip flow began, the output became nearly independent of _W . From the measurements made below _Wc a vs. relation for the shear flow could be derived, which was used to calculate the superimposed shear flow . Exact values of the slip velocity were then given by . Wall slip only occurred for compounds with a high shear viscosity, which corresponds to a high molecular weight (K-value).Dedicated to Professor H. Janeschitz-Kriegl on the occasion of his 60th birthday.     

Rheologische Messungen an Kunststoff-Schmelzen mit einem neuen Rotationsrheometer

Zusammenfassung In der vorliegenden Arbeit wird ein neues Rotationsrheometer vorgestellt und über Messungen an zwei Polymethylmethacrylat-Formmassen berichtet. Bei dem Rheometer handelt es sich um ein Couette-Rheometer mit feststehendem Innenzylinder als Meßkörper. Der Meßkörper ist beidseitig eingespannt. In dem geschlossenen Meßraum können die Schmelzen bis zu einem Druck von 500 bar belastet werden.Der zeitliche Verlauf der Schubspannung in den Schmelzen wird in Abhängigkeit von Temperatur und Druck aufgezeichnet.

---

Summary A new type of rotational rheometer is described, and results for two samples of polymethylmethacrylate are reported. The rheometer consists of a Couette system with fixed inner cylinder, supported at both ends for torque measurements. Pressure may be varied up to 500 bar. Shear stresses have been recorded as a function of time, temperature and pressure.

---

Nomenklatur C [kp cm^–2 s^–1] Steigung der Anlaufkurve im Nullpunkt - D [kp cm rad^–1] Direktionsmoment - E ₀ [kcal mol^–1] Aktivierungsenergie der Newtonschen Viskosität - G [kp cm^–2] Schubmodul - G [—] Griffith-Zahl - l [mm] Länge des Meßkörpers - p [kp cm^–2] Druck - R _i [mm] Radius des Innenzylinders - R _a [mm] Radius des Außenzylinders - t _max [s] Zeit, bei der das Maximum in der Anlaufkurve auftritt - T [°C] Temperatur - ₀ [cm² kp^–1] Druckkoeffizient der Newtonschen Viskosität - [s^–1] Schergeschwindigkeit - ₀ [kp s cm^–2] Newtonsche Viskosität - (g cm²] Trägheitsmoment des Meßkörpers - v ₀ [s^–1] Eigenfrequenz des Meßsystems - _max [kp cm^–2] maximale Schubspannung - _st [kp cm^–2] stationäre Schubspannung Mit 7 Abbildungen und 1 Tabelle     

Die temperatur- und druckinvariante Darstellung der Scherviskosität von geschmolzenem Polymethylmethacrylat

Zusammenfassung An Polymethylmethacrylaten mit zahlenmittleren Molekulargewichten zwischen 8000 und 145000 g/Mol wurde die Scherviskosität bei Temperaturen im Bereich von 130–190 °C und bei Drücken bis zu 1000 kp/cm² in Abhängigkeit vom Schergefälle gemessen. Trägt man die an ein und derselben Probe gemessenen relativen Viskositäten/ ₀ (₀ untere Newtonsche Viskosität) über ₀· doppeltlogarithmisch auf, so erhält man eine einzige temperatur- und druckinvariante Kurve (master curve). Mit sinkendem Molekulargewicht machen sich jedoch bei großen Abszissenwerten zunehmend Abweichungen von der Temperatur- und Druckinvarianz bemerkbar. Die an Proben mit verschiedenem Molekulargewicht ermittelten invarianten Kurven weisen Wendepunkte auf, die sich mit wachsendem Molekulargewicht immer mehr zu niedrigeren Werten von/ ₀ verlagern. Durch Verschieben in Abszissenrichtung kann man die Kurven bis zu ihren Wendepunkten miteinander zur Deckung bringen und erhält auf diese Weise einen begrenzten Bereich der Molekulargewichtsinvarianz.Die Temperatur- und Druckinvarianz läßt sich sowohl mit den vonPrandtl undEyring als auch mit den vonF. Bueche entwickelten Modellen für das Fließen von Hochpolymeren begründen. Aus der Temperatur- und Druckinvarianz folgt, daß der Temperatur- und der Druckkoeffizient der Viskosität mit zunehmendem Schergefälle in gleicher Weise abnehmen und ein Minimum durchlaufen, wie auch experimentell bestätigt wird.

---

Summary The shear viscosity of polymethylmethacrylates (number average molecular weights from 8000 to 145000 g/mole) was measured in dependence of shear rate in the temperature range from 130–190 °C and with pressures up to 1000 kp/cm². If for one specimen ₀ ( ₀ lower Newtonian viscosity) is plotted over ₀· , both in logarithmic scales, one gets a curve, which is independent of temperature and pressure (master curve). With decreasing molecular weights increasing deviations from the master curve are found. The master curves found with specimens of different molecular weights have inflection points, which shift to lower values of ₀ with increasing molecular weight. By shifting of the whole curves in direction of the abscissa the parts until to the inflection point might be reduced to a single plot which is independent of molecular weight.The independence of temperature and pressure might be derived from the models developed by eitherPrandtl andEyring orF. Bueche for the flow in high polymers. From this follows that the temperature- and the pressure-coefficient of viscosity will similarly decrease with increasing shear rate until to a minimum, which was experimentally verified.

---

---

Erweiterte Fassung eines auf der Jahrestagung der Deutschen Rheologen am 21. Mai 1968 in Berlin gehaltenen Vortrags.

---

Herrn Dr.H. Kausch und Herrn Dipl.-Ing.H. Schönewald sind wir für wertvolle Diskussionen zu Dank verpflichtet. Der Arbeitsgemeinschaft industrieller Forschungsvereinigungen e.V. (AIP) danken wir für die finanzielle Unterstützung dieser Arbeit.     

MALDI-TOF imaging mass spectrometry of artifacts in “dried droplet” polymer samples

Matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) imaging of polystyrenes with various molecular masses was applied to study spatial molecular mass distribution of polymers in sample spots prepared by the “dried droplet” method. When different solvents and target surfaces were examined, a segregation of single homologous polymers was observed depending upon the evaporation rate of the solvent. For the observed patterns left by the evaporating droplet, a hypothesis is offered taking into account different hydrodynamic interactions and diffusion. The results illustrate that spot preparation using the conventionally “dried droplet” method is prone to artifacts and should be avoided for reliable and reproducible MALDI mass spectrometry experiments with regards to the determination of molecular masses and mass distributions.     

Isolation and structural characterization of capistruin, a lasso peptide predicted from the genome sequence of Burkholderia thailandensis E264

Lasso peptides are a structurally unique class of bioactive peptides characterized by a knotted arrangement, where the C-terminus threads through an N-terminal macrolactam ring. Although ribosomally synthesized, only the gene cluster for the best studied lasso peptide MccJ25 from Escherichia coli consisting of the precursor protein McjA and the processing and immunity proteins McjB, McjC, and McjD is known. Through genome mining studies, we have identified homologues of all four proteins in Burkholderia thailandensis E264 and predicted this strain to produce a lasso peptide. Here we report the successful isolation of the predicted peptide, named capistruin. Upon optimization of the fermentation conditions, mass spectrometric and NMR structural studies proved capistruin to adopt a novel lasso fold. Heterologous production of the lasso peptide in Escherichia coli showed that the identified genes are sufficient for the biosynthesis of capistruin, which exhibits antimicrobial activity against closely related Burkholderia and Pseudomonas strains. In general, our rational approach should be widely applicable for the isolation of new lasso peptides to explore their high structural stability and diverse biological activity.