Reclaimed rubber refers to the process of physically and chemically treating waste rubber and vulcanized scrap from the rubber industry—such as crushing, heating, and mechanical processing—to remove sulfur and turn it from an elastic state into a plastic and sticky form that can be reshaped and vulcanized again. Compared with natural and synthetic rubber, reclaimed rubber has better flow properties, and in formulations of reclaimed rubber products, additives have a significant effect on the compound, especially carbon black and plasticizers.
1. The effect of carbon black on the flow of reclaimed rubber
Carbon black is the most commonly used reinforcing agent in the production of reclaimed rubber products. During processing, it forms certain physical and chemical bonds with the reclaimed rubber, which hinders the movement and sliding of rubber molecular chains. Therefore, adding carbon black to reclaimed rubber increases the compound's viscosity. The more carbon black used, the higher the apparent viscosity; with the same amount of carbon black, viscosity increases as particle size decreases and as the structure of the carbon black increases.
At lower shear rates, carbon black has a larger effect on viscosity; at higher shear rates and temperatures, the viscosity of filled and unfilled compounds is nearly the same and is mainly determined by the properties of the reclaimed rubber.
2. The effect of plasticizers on the flow of reclaimed rubber
Rubber plasticizers can improve processing performance. Using plasticizers appropriately in reclaimed rubber formulations can reduce viscosity, elastic and brittle temperatures, and significantly improve flow, making the compound softer, with lower extrusion swell and higher extrusion speed, which helps rolling, extrusion, and molding operations. Within a certain range, the more plasticizer added, the lower the viscosity, and the better the flow of the reclaimed rubber compound.
In practical production, ester plasticizers, paraffin, ethylene glycol, stearates, modified fatty acids, low molecular weight polyethylene wax, and thermoplastic resins can all effectively lower the viscosity of reclaimed rubber compounds and improve their flow.
When producing rubber products with reclaimed rubber, flow is not determined by a single factor but by the combined effects of the reclaimed rubber’s own properties, carbon black type and amount, and plasticizer type and amount. When designing formulations for reclaimed rubber products, you can’t just chase low viscosity or high flow, as this may reduce compound strength, hardness, extrusion dimensional stability, and final product performance. For reclaimed rubber products that need good processing flow, it’s important to choose the right carbon black particle size and structure according to the process requirements and adjust with plasticizers to balance reinforcement and processing performance.
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