Influence of the Chemical Structure of Flexible Blocks on the Mechanical Properties of Poly(Urethane-Ureas) in a Humid Atmosphere

Abstract

Sorption of moisture on segmented poly(urethane3ureas) with flexible segments of various chemical structures and the effect of a humid atmosphere on the mechanical properties of these materials were studied. Poly(urethane3urea) prepared from mixtures of oligoethers shows advantages from the viewpoint of preservation of high strength in a humid atmosphere.Block polyurethane elastomers, so-called segmented polyurethanes (SPUs), are widely used in various branches of industry thanks to their high strength, good deformation characteristics, and resistance to a number of solvents [1]. Depending on the destination, polyurethane items can operate in air or in direct contact with water (e.g., polyurethane coatings of squeeze rolls in paper-making industry).Published data on the behavior of SPUs in moist media mainly concern the moisture transfer in these materials [235] and changes in the structure [2, 5, 6] and glass transition point [5, 6] of moistened polyurethanes. Experiments were performed with thin polyurethane films prepared from solution; in this case, correct estimation of changes in mechanical properties on moistening is complicated by intense moisture exchange with the surrounding medium. Data on the mechanical properties of the films are limited to the results of their mechanical tests before moistening [3]. Therefore, it is unclear to what extent the mechanical characteristics of various SPUs vary on moistening and how the extent of their variation depends on the polymer structure.Studies in this direction are necessary for understanding how the mechanical characteristics of polyurethanes change on moistening and for choosing formulations of polyurethane materials suitable for operation in moist media.In this study we examined the influence of the relative air humidity, varied in a wide range, on the mechanical properties of SPUs with various flexible segments. Our main goal was to reveal what structure of flexible blocks would provide the highest strength of the polyurethane material in a humid atmosphere. EXPERIMENTALWe used segmented poly(urethane3ureas) with poly(tetramethylene oxide) flexible blocks (SPUM-1), poly(propylene oxide) segments (SPUM-2), mixed polyether blocks (SPUM-3), and mixed polybutadiene3poly(tetramethylene oxide) flexible segments (SPUM-4). To prepare SPUMs, we took prepolymers based on oligo(tetramethylene oxide)diol (M~1700), oligo(propylene oxide)diol Laprol 2102 (M~1950), and polybutadienediol (M~2100, SKU-DF-2 prepolymer). The molecular weight of the oligomeric diols was estimated from the content of hydroxy groups. The prepolymers were prepared by the reactions of appropriate diols with toluylene-2,4-diisocyanate. The prepolymers and their mixtures (in preparation of SPUMs with mixed flexible segments) were cured with 3,3`-dichloro-4,4`-diaminodiphenylmethane (Diamet Kh) by the procedure described in [7].The molar ratio of the prepolymers (or their mixture) to Diamet Kh was 1.03, and the molar ratio of the NCO and OH groups in the synthesis of the prepolymers, 2.1.The isotherm...

Influence of Moisture Sorption on the Physical and Mechanical Properties of Plasticised Poly(Ether Urethane Ureas)

“…Use of the IR-spectroscopy method established that the degree of microphase separation of flexible and rigid segments in non-plasticised polyurethane urea based on polytetramethylene oxide diol is about 3 times greater than in SPUU-1 with polypropylene oxide flexible segments [5]. It was shown that as the polarity of the flexible chains falls, with the resulting rise in the degree of microphase separation in the polymer there is an increased role for the reinforcing filler in shaping the mechanical properties of the material and ensuring the stability of these properties in a damp environment [6].…”

“…There is information pointing to a substantial impact of moisture on the mechanical properties of segmented polyurethane ureas (SPUUs) based on polyethers. The greatest deterioration in the strength and elasticity properties is seen in the case of materials with polypropylene oxide flexible blocks (segments) based on oligo(propylene oxide)diols or their pre-polymers [6]. There is also a considerable deterioration in the properties of elastomers with polytetramethylene oxide flexible segments.…”

Behaviour of Segmented Polyether Urethane Urea in a Humid Atmosphere after Mechanical Loading

“…With reduction in the content of rigid phase and increase in the polarity of the flexible phase, not only should the moisture absorption by the material increase, but also its strength should decrease at the same air humidity as a result of weakening of interchain interaction in the flexible phase in the presence of moisture [10], which also occurs when predeformed SPUU specimens are moistened.…”