Abstract
Adding carbon black (CB) particles to elastomeric polymers is essential to the successful industrial use of rubber in many applications, and the mechanical reinforcing effect of CB in rubber has been studied for nearly 100 years. Despite these many decades of investigations, the origin of stiffness enhancement of elastomers from incorporating nanometer-scale CB particles is still debated. It is not universally accepted whether the interactions between polymer chains and CB surfaces are purely physical adsorption or whether some polymer–particle chemical bonds are also introduced in the process of mixing and curing the CB-filled rubber compounds. We review key experimental observations of rubber reinforced with CB, including the finding that heat treatment of CB can greatly reduce the filler reinforcement effect in rubber. The details of the particle morphology and surface chemistry are described to give insights into the nature of the CB–elastomer interfaces. This is followed by a discussion of rubber processing effects, the influence of CB on crosslinking, and various chemical modification approaches that have been employed to improve polymer–filler interactions and reinforcement. Finally, we contrast various models that have been proposed for rationalizing the CB reinforcement of elastomers.
Highlights
The term reinforcement can have a variety of meanings when considering the effects of adding nanometer-scale particles such as carbon black (CB) to an elastomer
The global production of carbon black is 15 million metric tons per year, and 93% of this material goes into rubber applications (automobile tires (73%) and non-tire rubber products (20%)), with the remaining 7% used in paints, coatings, inks, and plastics compounding (Figure 1) [5]
Convincing evidence for this mechanism included the observations of: (1) more bound rubber at lower mixing temperatures; (2) less bound rubber when free radical acceptors were included in the formulation; and (3) increased bound rubber when mixing was conducted in a nitrogen versus air environment due to radicalquenching activity of oxygen
Summary
The term reinforcement can have a variety of meanings when considering the effects of adding nanometer-scale particles such as carbon black (CB) to an elastomer. This graphene sheet is approximately 2.0 × 2.5 nm which is slightly larger than the crystalline domain as measured by X-ray diffraction for furnace CB. This work mainly focused on bound rubber results and did not show the corresponding stress–strain reinforcement effects Convincing evidence for this mechanism included the observations of: (1) more bound rubber at lower mixing temperatures (higher shear stress breaks more polymer chains); (2) less bound rubber when free radical acceptors were included in the formulation; and (3) increased bound rubber when mixing was conducted in a nitrogen versus air environment due to radicalquenching activity of oxygen. Data replotted from Hess and coworkers [88]
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