Rubber Chemistry and Technology最新文献

This work addresses the critical technological challenge of producing butadiene-based synthetic rubbers with the required skid resistance through anionic polymerizations at positive temperatures. The effects of adding different polar modifiers—bis[2-(N,N-dimethylamino)ethyl] ether (BDMAE), ditetrahydrofurylpropane, tetramethylethylenediamine, sodium stearate, sodium palmitate, and sodium tert-amilate—into the monomer feed in anionic solution polymerizations of 1,3-butadiene are investigated. Different feed concentrations and combinations of polar modifiers were tested to achieve high yields and vinyl contents with initial temperature of 40 °C. The reactions were evaluated according to the obtained temperature and pressure profiles and physico-chemical characterizations of the obtained polymer, with the aid of statistical analyses. The results clearly showed the positive effects of using polar modifiers in the feed. Particularly, the combination of BDMAE and sodium salts provided products with high vinyl contents (>50 mol%) with high yields (>80 wt%), leading to high temperature peaks (>90 °C), as desired to enhance skid resistance. Moreover, the performed statistical analyses and proposed mathematical modeling revealed the existence of multivariate and complex correlations among the analyzed process variables. The findings from this investigation can be pivotal for advancing industrial applications in the production of skid-resistant synthetic rubber.

Rubber engineering design analysis requires a fundamental understanding of the mechanical behavior of polymers, especially in their unvulcanized state. It necessitates the establishment of a three-dimensional constitutive material to account for the observed mechanical behavior. This law is required to produce realistic descriptions of the viscoelastic performance in a mathematically simple form that is easy to implement in engineering applications. This article describes the theory of the Tschoegl–Chang–Bloch time-dependent nonlinear viscoelastic constitutive law. The experimental verification of this law is provided under different deformation fields and multiple load steps. Laboratory test procedures to obtain the parameters required to describe the material under consideration are provided in detail. A recursive form of the constitutive law, suitable for finite element application, is derived and coded in the finite element commercial code Abaqus via the user subroutine UMAT. Comparisons between the experimental observations, the theoretical results, and the numerical data are drawn for simple test models examined under creep or shear relaxation conditions. The excellent agreements observed indicate the suitability of the governing law in analyzing viscoelastic problems of unvulcanized carbon black–filled rubbers.

The sulfide polymers of variable and controlled sulfur content, obtained by anionic copolymerization of elemental sulfur and thiiranes (styrene sulfide and cyclohexene sulfide), were applied as curatives (sulfur donors) in the vulcanization process of styrene–butadiene rubber. The activity of polysulfides as curatives was investigated based on rheometric measurements of the vulcanization process and calculations of curing parameters using kinetic data. The crosslink density and structure related to the mechanical properties of the vulcanizates under static and dynamic conditions were studied. The overall suitability of polysulfides as crosslinking agents for diene rubbers was investigated.

Decades of elastomeric fracture phenomenology resulting from the work of Thomas and Smith demonstrated the remarkable fact that rubbers are stronger and tougher at lower temperatures. The prevailing explanation relates the fracture behavior to polymer viscoelasticity. Given the recent insight and evidence that toughness is influenced by material strength, we examine elastomeric fracture with a different perspective and conclude that chain scission dictates fracture characteristics, including its temperature dependence. Working within selected temperature ranges, stretching is shown to be entirely elastic at a stretching rate less than 0.17 s⁻¹. We demonstrate that the same temperature and rate dependencies of strength and toughness, observed by Thomas and Smith, also occur in our crosslinked polybutadiene and styrene–butadiene rubber. The temperature effects on rate dependence of strength and toughness are found to be much stronger than that prescribed by the Williams–Landel–Ferry shift factor a_T. Moreover, crack propagates, upon either stepwise stretching or during creep, at a much lower speed at lower temperature that cannot be rationalized with polymer relaxation dynamics. Our new interpretation is that a carbon–carbon bond is stronger at a lower temperature. Because backbone bonds are more stable, a higher degree of network stretching occurs before rupture at lower temperatures.