Financial support from the Basque Government (IT-776-13), the
Spanish Ministry of Economy and Competitiveness (MINECO)
(MAT2013-43076-R) and FCT/MEC and FEDER under Program
PT2020 for financial support to LSRE (Project UID/
EQU/50020/2013) is gratefully acknowledged. We also wish to
acknowledge the ‘‘Macrobehaviour-Mesostructure-Nanotechnolog
y” SGIker units from the University of the Basque Country, for their
technical support. A.S.-E. thanks the University of the Basque Country
for Ph.D. grant (PIF/UPV/12/201).
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.
