Sıcaklık Taramalı Gerilim Gevşemesi (Tssr) Yöntemi ile Vinil Metil Silikon (Vmq) Elastomerinin Çapraz Bağ Yoğunluğunun Belirlenmesini Sınırlayan Koşullar
Özet
The main purpose of this study is to determine the relaxation behavior of vinyl methyl silicone (VMQ) elastomers with different hardnesses in a temperature scanning tensile relaxation (TSSR) instrument and to investigate the conditions that limit the detection of crosslink density (XLD) with this instrument. In earlier studies performed on TSSR with vinyl methyl silicone with different hardnesses such as 50, 60, 70 Shore A, it was observed that XLDs could not be calculated. This study was carried out on the basis of the approach why XLD value could not be observed with these polymers until this time and caused by the limiting conditions. In order to examine the effect of hardness and molecular mass on the relaxation properties of VMQ, mixtures were prepared with VMQ from 10 Shore A to 60 Shore A hardness. In order to compare the curing properties and crosslinking efficiency of VMQ mixtures, mixtures were formed using different co-agents such as TAIC (trialyl isocyanate) and ZDA (zinc acrylate), and XLDs were calculated using different methods. Moving Die Rheometer (MDR) was used to
examine the curing characteristics of mixtures and using different co-agents and to determine the optimum curing conditions. Curing degrees were determined by examining the minimum torque (ML) and maximum torque (MH) values at different hardnesses. For silicones with the same hardness, mixtures containing TAIC and ZDA were compared, and the effect of co-agents on curing properties was investigated. Taking into account the rheological properties, test samples were created and relaxation properties were tested in the TSSR instrument. For the isothermal relaxation stage, which is the first stage of the test, the relaxation behavior of the mixtures for 2 hours at 23° C was examined. In the second stage of the test, non-isothermal relaxation, the temperature and relaxation behavior of the mixtures were examined, and the XLD values obtained from the instrument were evaluated. In addition to the XLD values obtained from the instrument, the slopes of the non-isothermal relaxation curves were found with an external software and XLD was calculated with the help of rubber-elasticity equations and compared with the XLD values obtained from the instrument. In order to verify the obtained XLD values, frequency scanning studies were carried out with the rubber process analyzer (RPA) and the XLD values were calculated. In the light of the data obtained as a result of the studies, the situations where XLD could’nt be obtained from the TSSR were examined and possible causes were examined. As a result of all these studies, it has been observed that stretched VMQ elastomers with increased XLD have higher relaxation, isothermal relaxation and stretching amounts in response to high stress. In non-isothermal tests, it was observed that as the hardness increased, there was a decrease in the initial increase slope in the tension zone. Depending on the number of functional vinyl groups they contain, the XLD of ZDA containing elastomers were found to have higher XLD compared to the mixtures containing TAIC. Studies have also shown that the XLD value is a critical parameter for VMQ in TSSR applications. It was determined that the XLD values obtained as a result of the studies carried out with the RPA method were very close to the values obtained by the TSSR method. This showed that the TSSR method can be used for VMQ provided that the XLD value remains below a certain value.
