Polyacrylate Elastomers Research Articles

Hydrolytic Stability of Urethane and Polyacrylate Elastomers in Humid Environments

An accelerated humidity test utilizing a combination of high temperature and high humidity has been used to determine the ability of urethane and polyacrylate elastomers to withstand humid environments. A wide variation was found in the hydrolytic stability of the materials tested, which would not have been dis closed by the usual short term low temperature humidity test. The degradation has also been found to occur at moderate humidities as well, although the quantitative relationships of degradation rate versus relative humidity level has not as yet been accurately defined.

Chemical Stress Relaxation of Polyacrylate Elastomers

Abstract The continually widening range of thermal stresses imposed on elastomeric parts used in the automotive and aeronautical fields intensifies both the need for more thermally versatile elastomers and the need for effective laboratory methods for evaluating elastomer performance. Because stress relaxation provides a means of gauging product performance under both high temperature and external stress that approximate conditions of use, this technique gives a good estimation of an elastomer's commercial potential and its adaptability to a particular application. To demonstrate the value of stress relaxation, the thermal stability of a polyacrylate elastomer crosslinked with various curatives and the effect of certain additives on thermal stability were studied. Polyacrylates are of major interest for applications that require a high degree of thermal stability because of their ability to perform well over wide temperature ranges (−25° to 400° F). These elastomers are mainly copolymers of ethyl acrylate and a chlorine containing monomer such as vinyl chloroethyl ether. Some newer types are based on ethyl and butyl acrylates and chlorine free monomers such as epoxides and substituted amines. Generally, polyacrylates are compounded and prepared for curing according to standard techniques and they can be crosslinked with a variety of curative systems. Curing is accomplished at between 300° and 400° F in times ranging from 45 seconds to 45 minutes, depending on the elastomer and curing recipe used. The thermal stability of these elastomers is frequently determined by measuring the percentage changes in physical properties, e.g., tensile strength, elongation, modulus, after oven or oil aging or both at elevated temperatures. However, heat aging is carried out with no external stresses applied to the test specimens and the physical measurements before or after aging are made at room temperature. Although this type of test has some value, the results do not necessarily reflect the behavior of the elastomers in practice, as is the case with stress relaxation.