Keynote Presentation: Automotive Outlook: Uncertainty, Recovery, Transformation
SPEAKER: Jeff Schuster, President, Americas Operation and Global Vehicle Forecasting, LMC Automotive
Characterization of Dynamic Mechanical and Dielectric Properties of Rubber Compounds by Simultaneous High Force DMA and DEA
Dynamic Mechanical Analysis (DMA) measures the viscoelastic properties of polymers, elastomers, rubber compounds, etc., under a controlled temperature and/or frequency program. A sinusoidal force is applied to the sample as input. This results in a sinusoidal deformation on sample as output. The sample’s response to the load is measured, which exhibits a time delay as phase shift.
Dielectric Analysis (DEA) explores the dielectric property of materials by applying a sinusoidal alternating voltage with variable frequency to two electrodes. The specimen acts as the dielectric between two electrodes. An AC current flows through the specimen and is measured as output. Based on the adjusted voltage and the recorded current, the complex sample impedance can be calculated. It describes dielectric behavior of material and depends on time, frequency, temperature, molecular mobility within the material, etc.
Molecular mobility caused by thermal activation is influenced by external mechanical constraints, as are molecular transport and relaxation processes. Static and dynamic sinusoidal sample deformations change dielectric behavior of material. For example, a vulcanized “virgin” rubber compound has never been subject to mechanical constraints. In the case of static and/or dynamic-mechanical load is applied, the structure, size and location of the carbon black cluster changes, which results in changes in the migration path density. As a result, conductivity and permittivity decrease as load increases. Simultaneous high force DMA and DEA, Netzsch GABO DiPLEXOR® can monitor the migration processes of the charge carriers within the sample driven by the electrical field and analyze the activated internal migration.
SPEAKER: Yanxi Zhang, Ph. D., Technical Sales Support, Netzsch Instruments North America
Mechanism of Oxidation in Natural Rubber at Lower Temperatures
The oxidation mechanism of natural rubber was studied using several techniques. In our prior paper we showed that there was a subtle but measureable change in the oxidation mechanism about 50°C using the ultra-sensitive oxygen consumption technique. In a subsequent paper we found that the crosslink distribution (sulfur types – polysulfidic, disulfidic, and monosulfidic) in beltcoat (conventional cured natural rubber compound) had a different crosslink distribution depending on the aging temperature. The beltcoat compound extracted from an oven-aged (65°C) tire was compared to the beltcoat compound extracted from a normal service tire (23°C – the average annual temperature in Phoenix, Arizona). The structure of the crosslinks formed at high temperature were predominantly carbon-carbon crosslinks. In contrast, the structure of the crosslinks formed at lower temperature were different. The chemical structure of the crosslinks formed during oxidation at lower temperature were possibly sulfoxide or peroxide linkages. The crosslink distribution test was the method developed by Campbell and Saville. This crosslink distribution test method which has traditionally been used to look at types of sulfur linkages has now been employed to look at the mechanism of oxidation. The chemical structure of the crosslinks formed during oxidation were examined at temperatures intermediate between 23°C and 65°C for elucidation of the mechanism of oxidation. The chemical structures of the formed crosslinks were found to depend strongly on temperature.
An additional study was initiated to further understand the proposed mechanism of sulfoxide, peroxide, and hydroperoxide formation at lower temperatures but not at higher temperatures. To investigate this we compared specimens aged constantly at one temperature to specimens which were aged with cycling (alternating between high and low temperature).
SPEAKER: Ed Terrill, Ph.D., Applied Research Fellow, Akron Rubber Development Laboratory, Inc.