The authors wish to thank the finacial support given by Coordenação para o
Aperfeiçoamento do Pessoal de Ensino Superior (CAPES) of the Ministry of Education
as well as to Látex Lemgruber S.A. for the donation of the natural rubber latex and to
Oxiteno do Brasil S.A. Indústria e Comércio for the donation of the surfactants.