Wilma K. Dierkes

COOPERATIVE EFFECTS OF EPOXIDE FUNCTIONAL GROUPS ON NATURAL RUBBER AND SILANE COUPLING AGENTS ON REINFORCING EFFICIENCY OF SILICA

Polar functionality attached onto natural rubber has a significant impact on the reinforcing efficiency of silica. Parallel studies involving various levels of epoxidation on natural rubber (ENR) in the absence of bis-(triethoxysilylpropyl) tetrasulfide (TESPT) coupling agent, as well as a combination of ENRs with different loadings of TESPT, provide a better understanding of the various factors that influence the properties of silica-filled ENR compounds. Based on the overall properties, the best possible combination to optimize processability, to reduce filler–filler interaction, and improve vulcanization rate as well as vulcanizate properties, is to use ENR with an epoxide content in the range of 20–30 mol%, together with a small portion of TESPT, that is, 2–4 wt% relative to the silica content. This leads to a reduction of approximately 60–80% of TESPT when compared with the conventional NR compounds, where the optimal loading of TESPT was 9.0 wt% relative to the silica content.

Comparative Investigation on the Reclamation of NR Based Latex Products with Amines and Disulfides

Abstract The latex industry has expanded over the years to meet the world demands for gloves, condoms, latex thread, etc. Due to the strict specifications for the products and the unstable nature of the latex, as high as 15% of the final latex products are rejected. Since waste latex rubber (WLR) represents a source of high quality rubber hydrocarbon, it is a potential candidate for generating reclaimed rubber of superior quality. In the present investigation, two reclaiming agents for WLR vulcanizates were studied in a thermo-mechanical reclaiming process. Parameters investigated were the concentration of the reclaiming agents, as well as reclaiming temperature and time required for proper reclamation. The efficiency of the reclamation process was studied by measurement of the Mooney viscosity, sol-gel analysis and swelling measurements. The ratio of main-chain scission to crosslink scission was studied and the distribution of mono-, di-, and polysulfidic crosslinks was analyzed by thiol-amine reactions....

A Mechanistic Approach to EPDM Devulcanization

Abstract The extensive utilization of rubber in a wide variety of products causes a problem in terms of waste. Reclaiming of end-of-life products or production scrap is a potential solution. A high quality reclaim would preferably be obtained by devulcanization, to leave the polymer chains intact. Reclaiming of natural rubber is common practice, although the fundamental knowledge about de- and re-crosslinking is rather limited. EPDM-based rubber is even more unexplored in terms of reclaiming and re-utilization. This paper gives a mechanistic insight into the thermal reclaiming of two differently vulcanized EPDM compounds, using hexadecylamine (HDA) as devulcanization agent. Reclaim from conventionally vulcanized EPDM, mainly polysulfidic of nature, shows the largest decrease in remaining crosslink density with increasing HDA concentration and at lower reclaim temperatures. After reclaiming at the lower limit of the experimental temperature window applied: 225 °C, the concentration of remaining di- and pol...

OPTIMIZATION OF RUBBER FORMULATION FOR SILICA-REINFORCED NATURAL RUBBER COMPOUNDS

The rubber formulation plays a significant role in the properties of NR compounds filled with silica. In this work, the influences of various silicas, silane coupling agents, and diphenylguanidine (DPG) on the properties of compounds and vulcanizates—that is, cure characteristics, Mooney viscosity, flocculation kinetics, bound rubber content, Payne effect, tan δ at 60°C, tensile properties, and tear properties—are investigated. The results demonstrate that compound viscosity and curing behavior, as well as vulcanizate properties of the silica-filled NR, are much improved by incorporating silane coupling agents. Bis-triethoxysilylpropyltetrasulfide clearly gives better overall properties than the disulfide-based silane bis-triethoxysilylpropyldisulfide, except for scorch safety. DPG acts as a synergist to sulfenamide primary accelerators, as well as activator for the silanization reaction. Highly dispersible (HD) silicas can significantly enhance the degree of dispersion and so lead to higher filler–rubber interaction. As a consequence, the HD silicas provide better dynamic and mechanical properties for filled NR vulcanizates compared with conventional counterparts. The optimal quantities of both silane coupling agent and DPG required in the formulation are correlated to the cetyl trimethylammonium bromide specific surface area of the silicas. Furthermore, the results reveal that the silica structure as characterized by the dibutylphthalate adsorption also strongly influences the reinforcing efficiency

Effect of Plasma Polymerization on the Performance of Silica in NBR, EPDM and NBR/EPDM Blends

Abstract The surface modification of precipitated silica powders by plasma-polymerization with acetylene monomer in order to improve their performance in NBR, EPDM and NBR/EPDM rubber blends, by matching the surface energies of the silica fillers of the rubbers, is the subject of this study. Silica, used as reinforcing filler for elastomers, is coated with a polyacetylene (PA) film and characterized by water penetration measurements, Cetyltrimethyl Ammonium Bromide (CTAB) area, Thermo Gravimetric Analysis (TGA), Time of Flight-Secondary Ion Mass Spectroscopy (ToF-SIMS) and Scanning Electron Microscopy with elemental analysis by Energy Dispersive X-ray spectroscopy (SEM/EDX). All techniques show the evidence of a PA-film deposition on the surface of silica. The properties of NBR, EPDM and blends based on NBR and EPDM, filled with untreated, PA- and silane-treated silica, are investigated by measurement of the Payne effect, the bound rubber content and weight loss related to bound rubber, the reinforcement ...

Model compound studies on the devulcanization of natural rubber using 2,3-dimethyl-2-butene

Abstract The mechanism of devulcanization of sulfur-vulcanized natural rubber with aromatic disulfides and aliphatic amines has been studied using 2,3-dimethyl-2-butene (C6H12) as a low-molecular weight model compound. First C6H12 was vulcanized with a mixture of sulfur, zinc stearate and N-cyclohexyl-2-benzothiazylsulfenamide (CBS) as accelerator at 140 °C, resulting in a mixture of addition products (C6H11−Sx−C6H11). The compounds were isolated and identified by High Performance Liquid Chromatography (HPLC) with respect to their various sulfur ranks. In a second stage, the vulcanized products were devulcanized using the agents mentioned above at 200 °C. The kinetics and chemistry of the breakdown of the sulfur-bridges were monitored. Both devulcanization agents decompose sulfidic vulcanization products with sulfur ranks equal or higher than 3 quite effectively and with comparable speed. Diphenyldisulfide as devulcanization agent gives rise to a high amount of mono- and disulfidic compounds formed during...

Improved Aging Performance of Virgin EPDM Roof-Sheeting Compounds with Amine-Devulcanized EPDM Weatherstrip Material

Sulfur-cured EPDM building-profile material was reclaimed in a co-rotating twin-screw extruder using hexadecylamine as reclaiming aid. This reclaim was blended with increasing amounts of a virgin EPDM roof-sheeting masterbatch and cured at temperatures allowing for a reversion-free vulcanization. The trends in cure characteristics showed that increasing amounts of reclaim employed in the blends lowered the reversion-free cure temperature and the maximum torque values, while the vulcanization speed was increased. The insoluble fraction and crosslink density both decreased, while the ratio of mono- to di- and polysulfidic crosslinks increased with growing reclaim contents. A SEM-EDX morphology study of the blends, in order to evaluate the dispersion of the reclaim into the virgin rubber matrix showed, that even large amounts of reclaimed material resulted in homogeneous and smooth compounds. Tensile strength, modulus at 300% strain and hardness decreased, while elongation at break, tear strength and compression set at 70 degrees C increased with increasing reclaim ratios. Irrespective of the blend ratios, the mechanical properties all fulfilled the most stringent UEAtc specifications for EPDM roof-sheeting. Increasing reclaim contents improve the aging resistance and prolong the time before a practical limiting value for elongation at break of 250% for EPDM roof-sheeting purposes is reached.

Application of NR-based latex reclaim: The link between structure and properties

Abstract Natural rubber based waste latex rubber (WLR) that is reclaimed with diphenyldisulphide by a thermo-mechanical process is blended with virgin rubber in different proportion to study the change in mechanical and viscoelastic properties. Two types of WLR differing mainly in the amount of polysulfidic linkages are reclaimed and blended with a virgin rubber compound with and without adjustment of the curing system, the former in order to compensate for the extra input of sulfur and accelerators due to the addition of reclaim. The cure behavior, final crosslink density and distribution, mechanical properties and dynamic viscoelastic properties of the blends with reclaimed WLR are compared to the property profile of the virgin material. The morphology of the blends as well as sulfur distribution between the matrix and the reclaim particle is analyzed. With increasing concentrations of WLR reclaim, tensile strength, tear strength and elongation at break decrease, whereas modulus at 100% elongation, comp...

Modeling and Practice of Ethanol-devolatilization of Silica-silane Rubber Compoundsin an Internal Mixer

Abstract During mixing of a rubber compound containing silica and silane, the mixer is not only used for the dispersion of the filler and other ingredients, but also for a chemical reaction. These two functionalities of the mixer result in opposite processing requirements: A good dispersion is reached by high shearing forces, increasing the compound temperature. The silanization is not dependent on high shearing forces; it is positively influenced by high temperatures, but with an increasing risk of scorch. Another drawback is the equilibrium between the ethanol concentration in the vapor phase in the void space of the mixing chamber and in the rubber phase, which is limiting the reaction rate of the silanization. Devolatilization of the compound is a crucial factor for the efficiency of the silanization reaction. In this article a model for devolatilization of a rubber compound in an internal mixer is developed, including a chemical reaction replenishing the volatile component during the devolatilization process. The model is based on the penetration theory, with the main contribution to the devolatilization being convective mass transfer. The main influencing factors, theoretically deducted and practically verified, are temperature, mixer volume, fill factor, rotor speed, reaction time and partial pressure of the volatile component in the void volume of the mixer.

Effect of Multiwalled Carbon Nanotubes on the Properties of EPDM/NBR Dissimilar Elastomer Blends

In the presence of multiwalled carbon nanotubes (MWCNT), polar nitrile-butadiene rubber (NBR) and nonpolar ethylene propylene diene rubber (EPDM) blends were prepared following a melt mixing method. For the preparation of MWCNT filled EPDM/NBR blends, two mixing methods were used: direct mixing and the masterbatch dilution method. Various physical, mechanical, and morphological properties are explored to elucidate the dispersion behavior of MWCNTs. It was concluded that the preparation method influences the dispersion of the nanotubes in different rubber phases and the properties of these blends are controlled by the degree of dispersion of the nanotubes in the two phases. GRAPHICAL ABSTRACT