Einfluß der Kristallisationsbedingungen auf das Zug-Dehnungsverhalten von Polyäthylenterephthalat

Zusammenfassung Es wurde der Einfluß der Morphologie auf das Zug-Dehnungsverhalten und den Bruch von Polyäthylenterephthalat untersucht. Dazu wurden verstreckte und unverstreckte Folien fünf Stunden lang bei verschiedenen Temperaturen zwischen 100° und 240°C getempert. Zusätzlich wurden die Aufheiz- und Abkühlgeschwindigkeiten variiert. Die Proben wurden anschließend bis zum Bruch verstreckt. Sowohl bei den verstreckten als auch bei den unverstreckten Proben geht die Bruchdehnung als Funktion der Kristallisationstemperatur durch ein Minimum. Die verstreckten Proben besitzen einen bedeutend höheren Elastizitätsmodul und auch eine bedeutend höhere Bruchfestigkeit als die unverstreckten Proben. Desweiteren wurde festgestellt, daß das Streckverhältnis nach einer Kaltverstreckung entlang der Probe nicht einheitlich ist und daß eine Alterung des Materials das mechanische Verhalten der Proben wesentlich beeinflußt.

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Summary The influence of the morphology on the stress-strain curves and fracture of polyethylene terephthalate was studied. Undrawn and drawn samples of polyethylene terephthalate were crystallized at various temperatures between 100° and 240°C. Different heating and cooling rates were applied. Afterwards the samples were drawn until fracture occured. Both, for the undrawn as well as for the drawn samples it turned out that the elongation at break plotted as a function of the crystallization temperature goes through a minimum. For the drawn samples the fracture stress andYoungs modulus was larger than for the undrawn samples. It could be further shown that the draw ratio after cold drawing is not uniform and that aging effects considerably the mechanical behaviour of the samples.

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Wir danken der Deutschen Forschungsgemeinschaft für die finanzielle Unterstützung dieser Arbeit im Rahmen des SFB 41, sowie der Firma Kalle AG., Wiesbaden, für die Überlassung der Folien.     

Morphological changes in SBS block copolymers caused by oil extension as determined by absolute small angle x-ray scattering

A series of SBS block copolymers diluted with different amounts (0–60 wt%) of three different kinds of oil were investigated: 1) lithene PM (a low molecular weight polybutadiene); 2) a paraffinic mineral oil with its electron density close to that of the polybutadiene (PB) phase; 3) a highly aromatic mineral oil with an electron density close to the polystyrene (PS) phase. All the oils seem to go into the polybutadiene matrix. Paraffinic oil and lithene form a homogeneous phase with PB; the aromatic oil at low concentrations mixes with the PB phase with a high level of inhomogeneity, while at higher concentration partial phase separation occurs. In the undiluted polymer, styrene forms cylinders in hexagonal packing. The distance between cylinders (about 43 nm) is not significantly changed upon dilution up to 33 wt%. Previously proposed changes in the morphology of PS domains at larger oil contents can be related to observed changes in the long period, in the segment length distributions, and in the homogeneities of the phase (density fluctuations). The electron density difference obtained for pure SBS is lower than the theoretical one calculated from the densities of pure PS and pure PB. Dilution by paraffinic oil improves the phase separation.     

Influence of the surface morphology on the melting of polymer crystals. I. Loops of random length and adjacent reentry

A polymer crystal with a noncrystalline surface layer formed by chain loops of different lengths is considered. It is assumed that the length of each loop can be changed by longitudinal diffusion of the molecule through the crystal lattice. From the condition that the free energy of the system is minimum, the loop length distribution and the average loop length as function of temperature are calculated. In contrast to the results for loops of equal length, for the present model, a substantial thickness of the noncrystalline surface layer and a broad melting range is obtained also for the case of adjacent reentry. In order to get this result one has to take into account that even an “ideal fold” consists of at least four rigidly arranged CH2 groups in energetically unfavored conformation.     

On crystallization and phase separation phenomena in PEN/PHBA copolyesters

Two different etching techniques that reveal the semicrystalline morphology of polyesters have been developed and applied to an analysis of the phase structure of copolyesters made by reacting poly(hydroxybenzoic acid) (PHBA), and poly(ethylene naphtha-lene-dicarboxylate) (PEN). One technique is based on oxidation with acidic permanganate solutions and is used to study the macroscopic distribution of different phases. The other is based on sa-ponification with alkaline reagents and reveals more detailed structure within the various phases. Etching and electron microscopic examinations have been carried out for three different PEN-co-PHBA compositions. Three different types of solid phase are revealed: (1) a phase rich in PEN; (2) a phase containing roughly equal proportions of the two components, liquid crystalline at high temperatures; (3) a solid phase of crystalline HBA-rich molecules, which segregate into laminar regions. These observations are consistent with the previously published thermal, x-ray, and dynamic mechanical analyses of these materials.     

Zur Deutung der sogenannten a Orientierung in Polyäthylenterephthalat

Ohne Zusammenfassung     

Topological analysis of complex molecular surfaces

An algorithm for the calculation of local and global curvatures of molecular surfaces is presented. The analysis is based on a surface representation as a set of points in 3-D space (“dotted surface” representation). The surface data are used to subdivide the surfac into domains with different curvatures. All domains are characterized by a reference point with a corresponding curvature profile specifiying the topological properties in its neighborhood. The curvature profiles provide a method for a systematic comparison of the shapes of different molecules. Such a strategy is important for the treatment of molecular recognition problems. The enzyme-inhibitor complex trypsin/BPTI was chosen to demonstrate the scopes of the method.     

Parameter identification in a soil with constant diffusivity

We consider infiltration into a soil that is assumed to have hydraulic conductivity of the form K = K = K_se^h and water content of the form = K – _r. Here h denotes capillary pressure head while K_s, , and _r represent soil specific parameters. These assumptions linearize the flow equation and permit a closed form solution that displays the roles of all the parameters appearing in the hydraulic function K and . We assume K_s and _r to be known. A measurement of diffusivity fixes the product of and resulting in a parameter identification problem for one parameter. We show that this parameter identification problem, in some cases, has a unique solution. We also show that, in some cases, this parameter identification problem can have multiple solutions, or no solution. In addition it is shown that solutions to the parameter identification problem can be very sensitive to small changes in the problem data.     

Zum Mechanismus der Polymerkristallisation

Zusammenfassung Auf der Grundlage der Ergebnisse von Röntgenkleinwinkel-Streuexperimenten und elektroenenmikroskopischen Untersuchungen an verzweigtem Polyethylen wird ein neues Modell zum Ablauf des partiellen Kristallisierens und Schmelzens entwickelt. Im Modell wird der Aufbau der Lamellarstruktur als sukzessive Einschubkristallisation beschrieben, die durch die Konzentration an nichtkristallisierfähigen Einheiten in den amorphen Bereichen gesteuert wird. Die Kinetik der Einschubkristallisation läßt sich durch dilatometrische Experimente verfolgen. Aus vergleichenden Röntgenkleinwinkel- und Ramanstreuexperimenten kann auf eine Anreicherung der Cobausteine an den Lamellenoberflächen geschlossen werden.Preprint zur 30. Hauptversammlung der Kolloid-Gesellschaft, 6.–9. Oktober 1981 in Ulm.