Resumo (PT):
Abstract (EN):
Hypothesis: The possibility of tailoring the final properties of environmentally friendly waterborne
polyurethane and polyurethane-urea dispersions and the films they produce makes them attractive for
a wide range of applications. Both the reagents content and the synthesis route contribute to the
observed final properties.
Experiments: A series of polyurethane-urea and polyurethane aqueous dispersions were synthesized
using 1,2-ethanediamine and/or 1,4-butanediol as chain extenders. The diamine content was varied from
0 to 4.5 wt%. Its addition was carried out either by the classical heterogeneous reaction medium (after
phase inversion step), or else by the alternative homogeneous medium (prior to dispersion formation).
Dispersions as well as films prepared from dispersions have been later extensively characterized.
Findings: 1,2-Ethanediamine addition in heterogeneous medium leads to dispersions with high particle
sizes and broad distributions whereas in homogeneous medium, lower particle sizes and narrow distributions were observed, thus leading to higher uniformity and cohesiveness among particles during film formation. Thereby, stress transfer is favored adding the diamine in a homogeneous medium; and thus
the obtained films presented quite higher stress and modulus values. Furthermore, the higher uniformity
of films tends to hinder water molecules transport through the film, resulting, in general, in a lower water
absorption capacity
Language:
English
Type (Professor's evaluation):
Scientific
No. of pages:
9