Vanja Kosar

Cure modeling of polyester thermosets in the copper mold

Abstract The cure of unsaturated polyester was studied experimentally and by using a model of the process. The kinetic parameters were calculated from the heat flow–time curves obtained by differential scanning calorimetry (DSC, Netzsch—Simultaneous Thermal Analyzer DSC 200), working in DSC (dynamic) mode. The temperature–time histories were studied in a cylindrically shaped copper mold. Taking into account the heat transferred due to conduction through the resin, as well as the kinetics of heat generated in the cure reaction, a numerical model was constructed. The contributions to the rise in temperature from heat conduction and chemical reaction are different in different parts of the composite, which can explain the temperature–time, or conversion–time histories. Introduction of a carbon-base filler reduced the amount of heat released in the composite and, as a result, lowered the temperatures through the resin. Finally, a good agreement between experimental data and the predicted mathematical model of the curing process in the mold was observed.

Modeliranje procesa umreženja izolacije izoliranih vodiča energijskih kabela

Sažetak Uobičajeno je da većina proizvođača u pogonu eksperimentalno određuje radne uvjete procesa umreženja i hlađenja proizvoda. Međutim, takav pristup ima manjkavosti prilikom proizvodnje novih proizvoda kada je potrebno predvidjeti nove radne uvjete. Isto tako, kada se upotrebljavaju drugi izolacijski materijali, potrebno je provesti niz nezavisnih eksperimenta za njihovu karakterizaciju. Sve to može dovesti do pogrešaka pri projektiranju nove opreme i proizvoda. S tim u svezi u ovom je radu predložen matematički model i provedena simulacija procesa kontinuiranog umreženja u vulkanizacijskoj cijevi. U procesu proizvodnje energijskih izoliranih vodiča izolacija od umreživog polietilena nanosi se na vodič pri temperaturi nižoj od temperature umreženja. Vodič s nanijetim slojem polimera kontinuirano se vodi kroz vulkanizacijsku cijev pod tlakom dušika da bi se izolacija zagrijala na temperaturu raspada peroksidnog inicijatora odnosno temperaturu reakcije umreženja. Promjena radnih uvjeta u cijevi utječe na fizička svojstva izoliranih vodiča i posebno na njegova konačna primjenska svojstva. Značajke izolacijskog materijala s obzirom na brzinu umreženja određuju ukupni kapacitet linije odnosno brzinu prolaza izoliranog vodiča, pri čemu je često ograničavajući faktor kapacitet ekstrudera. Svrha ovoga rada bila je provjera primjenjivosti modela i programske podrške za različite proizvodne linije u tvornici kabela Elka d. o. o. Zagreb.

Dynamic simulation of high-pressure tubular reactor for low-density polyethylene production

Low-density polyethylene, one of the most important polymer products, is commonly produced in high-pressure free radical polymerization processes. A dynamic model of the high-pressure polymerization of ethylene initiated by oxygen in tubular reactor is introduced, and a dynamic optimization problem is formulated for process start-up strategies. The present study proposes a kinetic model based on an assumed reaction mechanism. The model describes the rates of oxygen decomposition and propagation of free radical ethylene polymerization. The mass and heat balance equations in an adiabatic tubular reactor operated at a constant pressure of 2.4 kbars and a temperature range of 110–300°C are presented. Simulations of polymerization process predict temperature of the reaction mixture, response time for cooling water, and also conversion along the reactor length. Response time was obtained using different inputs of controlled variables. Values obtained from these simulations are compared with real data from the process unit (Polietilen, Dioki ®, Zagreb, Croatia) and a model validation is confirmed. Improvement in reactor productivity and better understanding of few different start-up procedures is achieved.