Tensile Stress—Strain Measurements for Characterization of Gum Elastomers and Filled Compounds

Abstract

For a gum elastomer in its amorphous, isotropic state, shear modulus and tensile modulus are related with a factor of three. This relation is maintained in the range of temperature and time scale defining the rubbery region of the material behavior. When a large deformation is imposed, for example, in tensile stress—strain measurements, the above relation may still be preserved, if the nonlinear behavior can be linearized. The strain—time correspondence principle is the linearization scheme of this work. When a gum elastomer contains various structural constraints, the factor three relation does not apply, even after the application of the above linearization scheme. Example of constraints are excessive amounts of long branches, gel, molecular associations, and reinforcing fillers. These constraints usually make the factor larger than three. This is because the constraints make the large, elongational deformation more difficult to achieve compared to shear deformation. An example of gum elastomer in this work is a polyethylacrylate containing a significant amount of gel. With this polymer, both the presence of gel and the molecular association act as the constraints. However, when 50 phr of carbon blacks are added, the fillers do not act as strong constraints as they do when they are in the diene rubbers. This is because the polyethylacrylate is known to have a weaker affinity to carbon black compared to the diene rubbers. Triblock copolymers, styrene—isoprene—styrene, were examined according to the above treatment; 25% polystyrene copolymer exhibited crosslink-like behavior by the polystyrene domains. However, 14% polystyrene copolymers acted as if they are no crosslinks. When these copolymers are diluted to 44% with an addition of 56% tackifier, the ratio of tensile to shear modulus became less than three. The styrene domains must have effective crosslinks at the small shear deformation, but at large tensile deformations such crosslinks must not be present.

Structure development in silica-filled polyacrylate rubber composites during mixing

“…It is generally recognized that, in the frequency region where the rubberlike plateau zone appears, the increase of GЈ with is due to the increase of network structure in the system. 21,22 As shown in Figure 5, the size of agglomerates became smaller with mixing temperatures up to 120°C, which enhanced the development of network structure and simultaneously improved GЈ at a given due to the homogeneous dispersion of silica. When the mixing temperature exceeded 120°C, a part of the network structure might be broken by the chain scission, which reduced the GЈ at a given as well as the small change of GЈ with .…”

Segmental Dynamics of Interfacial Poly(methyl acrylate)-d3 in Composites by Deuterium NMR Spectroscopy

“…Others probe larger scale translational diffusion, as in fluorescence photobleaching, , or segmental dynamics, as in ESR or NMR. , Often, these techniques have been applied where the polymer was at an interface with air. Much less has been done on composite materials, although the effects of the filler are clearly evident in dynamic mechanical studies of filled systems …”

Effect of mica addition on the properties of natural rubber and polybutadiene rubber vulcanizates

“…Fillers are also used to reduce cost or to impart certain characteristics such as modulus, abrasion resistance, tear resistance, and tensile strength. [1][2][3] Another consequence of incorporating a filler into a polymer is the considerable change in the dynamic properties one can achieve in the final composites. 4 Carbon black is unquestionably the universal reinforcing filler, even though silicas are also often used.…”