Eco-friendly rubber filler
doi:10.1038/nindia.2011.117 Published online 15 August 2011
Researchers have produced a new filler material for rubber products using modified nanocrystals obtained from maize starch.
Carbon black, although widely used as filler for rubber products, is an environmentally hazardous material. The researchers have found eco-friendly alternatives in natural materials such as starch — a biodegradable polymer produced by many plants.
They converted waxy maize starch into starch nanoparticles (SNPs) through acid hydrolysis. They produced three sets of bionanocomposites by mixing SNPs, hexamethylene diisocyanate (HMDI)-modified SNPs and organic-acid-treated SNPs with natural rubber.
The efficacy of the bionanocomposites was studied through exposure to high temperatures and subsequent comparison with carbon black.
Of all the bionanocomposites, the HMDI-modified SNPs demonstrated the highest mechanical strength. The unmodified SNPs were hydrophilic in nature. Natural rubber, on the other hand, is hydrophobic, yielding a poor adhesion between SNPs and natural rubber. After modification, the SNPs became hydrophobic, with a particle size of 70–100 nm.
The modified SNPs showed greater strength and elongation because their hydrophobic nature and small particle size allowed improved dispersion and better compatibility with natural rubber. The starchy fillers did not deteriorate the thermal stability of the nanocomposites.
The thermal stability of the nanocomposites may result from the dispersion of the nanoparticles and strong interaction between the nanoparticles and rubber molecules.
"The study opens up a new and green alternative to make filler material for rubbers," says lead researcher Sonal Thakore. Starch nanoparticles and their derivatives can also be used as drug delivery systems, she adds.
- Valodkar, M. et al. Organically modified nanosized starch derivatives as excellent reinforcing agents for bionanocomposites. Carbohydr. Polym. 86, 1244-1251 (2011) | Article |