M. Szesztay

DSC application for characterization of urea/formaldehyde condensates

Curing process was investigated for a variety of urea/formaldehyde (UF) resin adhesives suitable for particle boards and/or plywoods using DSC in anisothermal mode. In spite of the very different origins of the adhesives (both commercial and laboratory made) several common features in their thermal behaviour are noticed. The maximum curing reaction rate was detected in the range of 80–85°C. Elimination of formaldehyde was observed at 105–150°C. At temperatures higher than 150°C thermal decomposition of methylene linkage takes place which affects the mechanical properties of the adhesives. According to our results a good compromise can be found between product quality and curing rate (production efficiency) on the one hand, and environmental protection (low formaldehyd emission) on the other.ZusammenfassungDer Aushärtungsprozeß verschiedener UF-Harze für Spanplatten und Sperrholz wurde mit Hilfe der anisothermen DSC untersucht. Trotz der äußerst unterschiedlichen Herkunft der kommerziellen und im Labor synthetisierten Harze konnten ähnliche Reaktionen auf die thermische Behandlung festgestellt werden. Die maximale Aushärtungsreaktion lag zwischen 80 und 85°C. Freisetzung von Formaldehyd wurde zwischen 105 und 150°C beobachtet. Über 150°C zerfallen Methylenbindungen, wodurch die mechanischen Eigenschaften der Harze beeinträchtigt werden. Es läßt sich ein guter Kompromiß finden zwischen Produktqualität und Aushärtezeit (Produktivität) auf der einen Seite und Umweltschutz (geringe Formaldehydemission) auf der anderen.

DSC characterisation of urea/formaldehyde condensates, II. Experiences with high pressure DSC cell

At anisothermic thermograms registered when curing the urea/formaldehyde (UF) resins in high pressure DSC cell the endothermic effects, such as evaporation of water and elimination of formaldehyde shift to temperatures higher by about 40°C in comparison to the thermograms received using the cell without pressure. The temperature for the exotherma of curing remains unchanged. Due to the shift of decomposition temperature the elimination of formaldehyde takes place at more agreeable conditions: as the resin is more rigid the risk of additional endothermic effect connected with bubble blowing is diminished. The shift of water elimination temperature however disturbs at clear recognition of the base line of the endotherma. Preliminary treating of samples with inert gas before the measurements helps to improve the measurement conditions.ZusammenfassungDas thermische Verhalten beim Aushärten von UF-Harzen wurde unter hohem Druck in DSC-Meßzellen verfolgt. Es zeigte sich, daß die endothermen Effekte (Verdampfen von Wasser, Abgabe von Formaldehyd) unter Druck bei um 40°C höheren Temperature erfolgen. Dagegen bleibt der Temperaturbereich der exothermen Reaktionen unverändert. Aufgrund dieser Verschiebung erfolgt die Abgabe von Formaldehyd unter günstigeren Bedingungen als ohne Druck: das Harz ist in diesem Zustand fester und das Risiko zusätzlicher endothermer Effekte (z. B. Platzen von Dampfblasen) ist geringer. Dagegen wirkt sich die höhere Temperaturs der Wasserabspaltung störend aus für das eindeutige Erkennen der Basislinie. Eine vorangehende Behandlung mit Inertgasen verbessert die Versuchsbedingungen.

Crosslinking behaviour of diolmodified epoxies: 2. DSC measurements

SummaryDiglycidyl ether of bisphenol A (BADGE) reacts with aliphatic alcohols to form different products, depending on the type of accelerator. Using isothermal and dynamic DSC, magnesium perchlorate proved to be a more selective accelerator in comparison with N,N-Dimethylbenzylamine (DMBA). In the presence of DMBA, Arrhenius plots of log tc (tc-cure times) versus inverse cure temperature show a changing reaction order over a wide range of temperatures.

Kinetics of Radical Polymerization at High Conversion I. GPC Measurements of Molecular Mass Distribution

Abstract A series of poly(methyl methacrylate) (PMMA) samples was prepared with different monomer concentrations and to different degree of conversion in benzene, at 50°C. Average molecular weights and intrinsic viscosity values in the eluent (THF) measured by GPC using an online viscometer are reported. At monomer concentrations up to 50 mol %, no gel effect is observed even in the case of very high conversions (∼90%); both molecular weights and kinetic parameters which determine the length of the polymer chain remain practically unchanged independent of conversion. From monomer concentrations of 75 mol %, significant increase of both of these values is observed depending on conversion. The average branching numbers of polymer chains for all samples remain close to zero. The polydispersity values are generally near 1.7. These results denote that there is no significant chain transfer to polymer and the disproportionation probability in chain termination reactions agree with earlier results described in t...

Tracking of alkyd-resin condensation by GPC

SummaryCondensation process of pentaerythritol / phtalic-anhydride/ benzoic acid/synthetic fatty acid mixture was carried out according to two different schedules; the first was carried out in one step (I) at 210 °C, the other in two steps (II) feeding pentaerythritol into the mixture of the other components already preheated to 180 °C and then elevating the temperature to 210 °C. GPC chromatograms were taken during the process. It has been established that fractions with higher molecular mass are formed from fractions with lower molecular mass. It could be proved with a three-detector method that they become chemically homogeneous starting from molecular masses of about 10 000.

Kinetics of radical polymerization. XLVI: Kinetic investigation of the polymerization of styrene in solution by gel permeation chromatography

Abstract Molecular mass distribution was investigated for the polymerization of styrene initiated by AIBN at 50° in the presence of various solvents. Two types of solvents were chosen; in one, there is no chain transfer to solvent (Bz, DMF) whereas in CCl 4 the chain transfer should be considered. The molecular mass distributions of the systems were determined by GPC and they were also calculated from kinetic data in terms of the hot radical theory. The agreement of MMD curves obtained by both methods (GPC and kinetic) are within experimental error, sufficient.