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Fambri, Luca; Pegoretti, Alessandro; Kolařı́k, Jan; Gavazza, C.; Penati, A.

doi:10.1023/a:1010118808415

Cited by 16 publications

(11 citation statements)

References 14 publications

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“…For instance, PBAc specimens stored at room conditions and heated to 250°C lost 5% of their initial weight in 46 min, whereas dried material required 150 min, as previously reported. 10 The isothermal method requires a preliminary test to determine an appropriate range of temperature to study. It can easily provide information in a relatively short time, and it can be used to study kinetic data of the various degradation stages after selection of the proper temperature range.…”

Section: Resultsmentioning

confidence: 99%

“…A convenient temperature range was approximately chosen as the interval in which the corresponding degradation reached about 2.5-5% (␣ ϭ 0.025-0.05) during dynamic thermooxidation at 10°C/min. In previous work 10 the interval of 250 -300°C was selected for PU-PPG and PUPBAc, and degradations up to 5% of weight loss (␣ ϭ 0.05) were examined. As a result of the fact that waterborne polyurethanes were more prone to degradation, in the present work, the selected temperature range was lowered to 190 -250°C for both PUR types.…”

Section: Resultsmentioning

confidence: 99%

“…The A ISO constant encompasses steric and entropic effects and formally represents the time t ␣ required to reach a certain degree of degradation at infinite temperature; the higher its value, the higher the resistance to thermooxidation. 10 On the other hand, A DYN formally represents the heating rate ␤ at which a certain percentage of weight loss occurs at infinite temperature; the lower its value, the higher the material stability. The kinetics of the thermooxidation process depend on both activation energy and the pre-exponential factor.…”

Section: Kinetic Analysismentioning

confidence: 99%

“…The evaluation of the kinetics parameters can be derived from isothermal and dynamic data, as reported/shown by various researchers. [1][2][3][4][5][6][7][8][9][10] The choice of testing method can affect the results, and quite large differences can be found as a result of the different analytical approaches that treat the thermal-degradation data, even for simple polymers. For instance, in the case of the nonoxidative degradation of polyethylene, the dynamic method recently proposed by Park et al 11 gave apparent activation energies and overall reaction orders rather dissimilar from those reported in the literature for similar material; [12][13][14][15][16] the researchers also comment that the values calculated according to the previous methods were significantly different from each other.…”

Section: Introductionmentioning

confidence: 99%

“…28 -30 In a previous article, the different thermal stabilities of polyether-and polyester-based polyurethanes were measured using the criterion of the required time to reach 5% weight loss during the isothermal experiments. 10 The objective of the present article is to evaluate the resistance to thermooxidation of different classes of normal and waterborne polyurethane films (PURs) by means of two different methods based on TGA, that is, an isothermal and a dynamic method.…”

Section: Introductionmentioning

confidence: 99%

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Thermooxidative stability of different polyurethanes evaluated by isothermal and dynamic methods

Fambri

Pegoretti

Gavazza

et al. 2001

J of Applied Polymer Sci

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ABSTRACT:Two methods for the evaluation of resistance to the thermooxidation of different classes of polyurethane films (PURs) throughout thermogravimetric analyses were used. Normal and waterborne polyurethanes were characterized using either isothermal or dynamic heating. In the isothermal method, the times required to reach degradations of 0.025, 0.05, and 0.10 were determined at several temperatures in the interval of 190 -250°C. In the dynamic method, heating rates of 0.5, 1, 2, 5, and 10°C /min were used in the range of 30 -500°C, and degradations of 0.025, 0.05, 0.10, 0.20, and 0.40 were considered. From the Arrhenius plots, activation energies were evaluated ranging between 130 and 230 kJ/mol for normal PURs and between 80 and 170 kJ/mol for waterborne PURs depending on the method, temperature interval, and degree of degradation. Advantages and disadvantages of the two methods were compared. The isothermal method requires a preliminary test, and it was more useful for degradation studies up to 0.05. The dynamic method offered evidence for the presence of different degradation processes, and it was more suitable for the evaluation of kinetics parameters at higher degrees of degradation.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Kinetic Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Thermooxidative stability of different polyurethanes evaluated by isothermal and dynamic methods

Fambri

Pegoretti

Gavazza

et al. 2001

J of Applied Polymer Sci

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Hydrolytic resistance of model poly(ether urethane ureas) and poly(ester urethane ureas)

Pegoretti

Fambri

Penati

et al. 1998

J. Appl. Polym. Sci.

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Poly(ester urethane ureas) (PesURUs) and poly(ether urethane ureas) (PetURUs) synthesized from diphenylmethane-4,4Ј-diisocyanate and poly(butylene adipate) diol, and poly(tetramethylene oxide) diol or poly(propylene oxide) diol, respectively, were hydrolyzed at 70°C for various periods up to 16 weeks. Differences in thermal and mechanical properties of as-received dry samples are correlated with the number and strength of hydrogen bonds formed between urea/urethane groups of hard segments and polyester or polyether groups of soft segments. Gel permeation chromatography measurements show that the molar mass of linear PesURUs markedly decreases with the hydrolysis time, whereas that of linear PetURUs remains almost unaffected. PesURU crosslinked by polymeric isocyanate has lower crystallinity, but shows somewhat better resistance to hydrolysis than its linear counterpart because of its more stable three-dimensional molecular structure. Water uptake at 37°C, dynamic mechanical thermal analysis, and differential scanning calorimetry thermograms determined for redried hydrolyzed specimens concurrently show that advancing hydrolysis accounts for decrease in the crystallinity (if any) of soft polyester segments, in the efficacy of hydrogen bonding and in crosslinking density. Experimental data indicate that hydrolytic resistance of PetURUs is primarily determined by (1) the hydrolytic stability of individual types of present groups, (2) steric hindrances affecting the access of water molecules to these groups, and (3) the hydrophilicity of backbones.

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