ISSN:
0323-7648
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The relaxation behavior of polyamide 4 was investigated as a function of absorbed moisture using dynamic mechanical measurements. Two relaxations, α at 81 °C and γ at - 111°C, were observed in the “dry” sample at a frequency of 1 Hz. The addition of water resulted in the depression of the α relaxation (αw) of the “wet” polyamide and the appearance of a second α relaxation (αd), slightly depressed from that of the “dry” specimen, reflecting the movements of the polymer chains after water has evaporated during the heating scan of the experiment. A second run was performed, resulting in the appearance of a single relaxation peak (α) at temperature very close to that of “dry” polyamide 4. Additionally, a β transition was observed whose temperature decreased with increasing water content. Similar results were obtained for specimens of polyamide 6. From plots of the depression of the glass transition temperature, ΔTg, as a function of the ratio of the number of water molecules to the number of accessible amide groups in the amorphous regions, R, one observes a sharp depression in the glass transition temperature with increasing water content up to some critical value, above which additional water molecules do not significantly change the glass transition temperature. Based on existing models for the sorption of water in polyamides, we propose a model whereby the environment of the polymer - water complex varies with the amount of water added to the system. At low water contents, both loosely and tightly bound water exist at the sorption centers, or amide groups. Above the critical water concentration, additional water molecules form clusters at these sorption centers. Additional aspects of the model explain the appearance of two α or primary relaxation peaks (αw and αd) due to the changing environments as a consequence of the heating scan of the dynamic mechanical measurements.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/actp.1995.010460502
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