Thermal degradation behavior of a biodegradable polymer (PBS) has been investigated by conventional and MTGA methods. The kinetic parameters of degradation were calculated by a general analytical solution and by the Coats‐Redfern, Ozawa, Horowitz‐Metzger, and MTGA methods. The results reveal that the reaction mechanism at lower temperature is probably the F1 model through the reaction of random chain cleavage via cis‐elimination. However, the reaction mechanism at higher temperature is likely to be D1 model because of the dominant diffusion control effect.
A kinetic study of the dehydration and decomposition of -irradiated and unirradiated Na2[Co(C4H4O4)2]·7H2O has been studied using isothermal and dynamic thermogravimetric methods. The thermal dehydration occurs in one step regulated by a random nucleation model (A3), while the decomposition of anhydrous salt is controlled by a phase boundary controlled model (R3). The kinetic parameters obtained at three heating rates are in good agreement; however, the values of the kinetic parameters estimated isothermally are slightly different from those estimated dynamically. Irradiation enhanced both the dehydration and the decomposition reactions but did not modify their mechanisms. The activation energy decreases as the irradiation dose increases.
Zusammenfassung Unter Anwendung von isothermen und dynamischen thermogravimetrischen Methoden wurde eine kinetische Untersuchung der Dehydratation und der Zersetzung von -bestrahltem und unbestrahltem Na2[Co(C4H4O4)2]·7H2O durchgeführt. Die thermische Dehydratation erfolgt in einem Schritt, bestimmt durch ein Random-Keimbildungsmodell (A3), während die Zersetzung der wasserfreien Salze durch ein phasengrenzenkontrolliertes Modell bestimmt wird (R3). Die bei drei Aufheizgeschwindigkeiten erhaltenen kinetischen Parameter stehen in guter Übereinstimmung; jedoch weichen die isotherm geschätzten kinetischen Parameter etwas von den dynamisch ermittelten ab. Bestrahlung mehrt sowohl die Dehydratations- als auch die Zersetzungsreaktionen, beläßt deren Mechanismus jedoch unverändert. Die Aktivierungsenergie sinkt mit zunehmender Strahlungsdosis.
Poly(butylene succinate) urethane ionomer (PBSUIs) foams with nano‐microcellular morphology were fabricated using supercritical CO2 (sc‐CO2) at different parameters. Effect of urethane ionic group (UIG) content (ranged from 1% to 5%) on the rheology and crystallization of PBSUIs were evaluated by intrinsic, dynamic rheological, X‐ray diffraction, and differential scanning calorimetry measurements. The results show that the complex viscosity of PBSUIs vastly improved, while their intrinsic viscosity and crystallinity decreased. They also evidenced that CO2 promoted the formation of crystallites in the amorphous and increased the Xc of PBSU and PBSUIs foams. Scanning electron microscope was employed to explore the influences of UIG content and foaming parameters on the morphologies of PBSUIs microcellular foams, and it revealed that UIG content was the dominated factor. The cell size and cell densities of PBSUIs microcellular foams were smaller than 5.0 micrometers and higher than 1.5 × 1010 cells/cm3, respectively, even foamed at diverse variations of foam temperature and pressure. Interestingly, PBSUIs with 3% and 5% UIG content achieved microcellular foams in nano‐cells, high‐stretched elliptical shape. The mechanism was ascribed that these PBSUIs with high melt viscosities could retard the CO2 bubbles to merge during the foam process and induce the cells to stretch and orient in depressururization direction. This study proposed a novel method for fabricating PBS nano‐microcellular foams. 相似文献
Thermal stability and fire retardancy of poly(1,4‐butanediol succinate) (PBS) nanocomposites with sepiolite and 2 halloysites was investigated using thermogravimetric analysis. Despite detrimental influence on thermal stability, confirmed by the use of isoconversional methods, nanoclays improve PBS fire behavior, studied using pyrolysis combustion flow calorimetry and cone calorimeter. Combinations of nanoclays with ammonium polyphosphate (APP) and aluminum diethyl phosphinate at 20 wt% global loading were tested using cone calorimeter at 50 kW/m2. It was noticed that the formation of protective structures of metallic phosphates with APP improves fire performance. The influence of ternary compositions combining sepiolite, APP, and lignin on fire performance was investigated. The composition having equimassic loading of each component leads to strong reductions in peak of heat release rate and Maximum of Average Heat Release Evolved (MAHRE) through the formation of a cohesive protective residue, containing new types of metallic phosphates and reinforced by sepiolite particles. This composition also allows smoke release rate to be minimized. 相似文献
Pulsed IR laser ablation of poly(ethylene succinate) results in the formation of volatile products (mainly carbon oxides, hydrogen, C1-C4 hydrocarbons) and affords deposition of polymeric films. Composition, structure and molecular weight distribution of the latter products were examined by EDX-SEM, FTIR, UV and NMR spectroscopy and gel permeation chromatography and revealed to be virtually identical to the initial poly(ethylene succinate). The deposited films and poly(ethylene succinate) decompose in the same way, as proved by TGA analysis. The formation of the volatile products is accounted for by random cleavages of the polymer backbone. The deposition of the polymeric products is judged to be due to molecular ester group interchange and/or a sequence of the C-C bond homolysis and recombination of the produced radicals. 相似文献
A rapid and convenient method for acylation and large-scale synthesis of dehydroandrographolide succinate has been developed under microwave irradiation. It is a one-pot condensation and is compatible with dehydration and rearrangement of double bond in mild reaction conditions with good yield, high purity (up to 99.8%), time-savings, few pollutants and low cost. In addition, a number of acylation derivatives were synthesized under microwave irradiation. 相似文献