The Effect of Crosslinking Mixture Addition on the mechanical properties of PU Polymeric Matrix

Abstract

Polyurethanes are prepared by extending a prepolymer chains made from a macro diol and a diisocyanate and its mechanical properties could be improved by using special additives to enhance the crosslinking process. In this study, 15 hydroxyl terminated polybutadiene (HTPB) based poly urethanes were prepared using 1, 6- hexamethylene diisocyanate (HMDI) and crosslinking mixture (CM) consists of trimethylol propane (TMP) as a triol crosslinker and butane diol (BD) as a chain extender. Five different crosslinking mixtures were used through the combination between TMP: BD = 1:0, 0:1, 1:1, 2:1 and 1:2. The research investigated the impact occurred on the mechanical behaviour of PU formulations prepared by adding certain cross-linking additives with various content from 0 % to 5 % and the curing ratio NCO/OH maintained constant at 0.7. The strength-strain relationships of all the finished samples were determined by using a LLOYD testing machine. The mechanical properties have been plotted vs. crosslinking mixture content and TMP: BD percentage which could be utilized to choose an appropriate network forming agent formulation for a particular grain technology and implementation. It was concluded that both TMP and BD have a major influence on the mechanical behaviour which allow obtaining a wide range of strength and elongation capabilities. The tensile strength increased by the excess of triol addition while the strain had a lowering effect which was compensated by the existence of diol extender. Tailoring the mechanical characteristics was easy to make by using a suitable proportions of TMP and BD to obtain outstanding mechanical properties for fixed NCO/OH, especially elastic capabilities, compared to polyurethanes formulated without any crosslinking additives.