Particle size and particle–particle interactions on tensile properties and reinforcement of corn flour particles in natural rubber

• Particle size of corn flour was significantly reduced to ∼300 nm.
• Hydrolyzed corn flour significantly increases the strength of natural rubber.
• Negatively charged corn flour particles reduced the particle agglomeration.
• Reinforcement factors can be described by anisotropic reinforcement elements.

Renewable corn flour has significant reinforcement effect in natural rubber. The corn flour was hydrolyzed and microfluidized to reduce its particle size. Greater than 90% of the hydrolyzed corn flour had an average size of ∼300 nm, a reduction of 33 times compared to un-hydrolyzed corn flour. Compared to un-hydrolyzed corn flour composites, the composites filled with 10–40% hydrolyzed corn flour had a significant increase in tensile strength (29–48%), Young’s modulus (16–74%), and toughness (33–55%), but a decrease in elongation (4–29%). The 300% modulus also increased 2–3 times. Particle agglomeration at higher filler concentration observed by swelling study was significantly reduced after corn flour was oxidized to introduce particle–particle repulsion with negatively charged carboxylic acid functional groups. The oxidized corn flour was also found to interfere with sulfur crosslinking process and behaved like a scorch retarder. Reinforcement factor at linear viscoelastic region can be described by mechanical models for anisotropic reinforcement elements. The aspect ratio of the reinforcement elements also decreased as the temperature increased, indicating polymer softening within the reinforcement elements.

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