A Polymer Visualization System with Accurate Heating and Cooling Control and High-Speed Imaging
A visualization system to observe crystal and bubble formation in polymers under high temperature and pressure has been developed. Using this system, polymer can be subjected to a programmable thermal treatment to simulate the process in high pressure differential scanning calorimetry (HPDSC). With a high-temperature/high-pressure view-cell unit, this system enables in situ observation of crystal formation in semi-crystalline polymers to complement thermal analyses with HPDSC. The high-speed recording capability of the camera not only allows detailed recording of crystal formation, it also enables in situ capture of plastic foaming processes with a high temporal resolution. To demonstrate the system’s capability, crystal formation and foaming processes of polypropylene/carbon dioxide systems were examined. It was observed that crystals nucleated and grew into spherulites, and they grew at faster rates as temperature decreased. This observation agrees with the crystallinity measurement obtained with the HPDSC. Cell nucleation first occurred at crystals’ boundaries due to CO2 exclusion from crystal growth fronts. Subsequently, cells were nucleated around the existing ones due to tensile stresses generated in the constrained amorphous regions between networks of crystals.
The Constraints Aggregation Technique for Control of Ethanol Production
In the article a new method for control and optimization of the ethanol production process was presented. The fed batch reactor for ethanol production can be described by the system of the nonlinear differential-algebraic equations. The new control approach base on the direct shooting method, which leads to a medium- or large-scale nonlinear optimization problem. In the presented research, three main aims of the optimization with the differential-algebraic constraints are indicated. The first one is the minimization of the cost function, which represents a process performance index. The second and third aims are to provide consistent initial conditions for the system to be solved and to ensure the continuity of the differential state trajectories. For these reasons, the large number of decision variables and equality constraints, connected with both consistent initial conditions for the differential-algebraic system and continuity of the differential state trajectories, was treated using the constraints aggregation technique. The direct shooting approach together with constraints aggregation technique enables us to obtain a new form of the nonlinear optimization task.
Über die Druckabhängigkeit der viskoelastischen und physikalisch-chemischen Eigenschaften von Polymeren—IV: Isotherme- und Nicht-Isotherme Kristallisation
Zusammenfassung Es wird gezeigt, daβ die druckinitiierte isotherme Kristallisation nur eine beschrankte Aussage uber die Kristallisationskinetik erlaubt. Dagegen liefert die Nicht-Isotherme-Kristallisation klare Aussagen, wobei sich jedoch die Notwendigkeit ergibt, die bekannten Theorien der Nicht-Isothermen-Kristallisation zu erweitern. Beim Polyathylen und Polyoxymethylen ist die zur Keimbildung notwendige thermodynamische Triebkraft im untersuchten Bereich weitgehend druckunabhangig. Beim Polypropylen sind die Kristallisationskurven zwar superponierbar, jedoch ergibt sich fur die notwendige thermodynamische Triebkraft eine Druckabhangigkeit. Fur die Kristallisationskinetik wird festgestellt, daβ der Druck nur durch die von ihm beeinfluβbare Unterkuhlung wirksam werden kann.