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Investigation of ethanolamine stabilized natural rubber latex from Taraxacum kok-saghyz and from Hevea brasiliensis using zeta-potential and dynamic light scattering measurements

Krickl, Sebastian, Touraud, Didier, Kunz, Werner
Industrial crops and products 2017 v.103 pp. 169-174
Hevea brasiliensis, Taraxacum kok-saghyz, air, ammonia, dispersions, ethanolamine, latex, light scattering, odors, pH, particle size distribution, potassium carbonate, potassium hydroxide, preservatives, roots, rubber, stabilizers, toxicity, zeta potential
For pH adjustment and long-term preservation of natural rubber (NR11NR: natural rubber.) latex, the usage of ammonia or KOH is still state of the art. Unfortunately, ammonia has a bad odor, it is volatile and toxic and thus does not provide safe and comfortable handling during the processing of latex. KOH preserved latices on the other hand have a significant tendency to form potassium carbonate when getting in contact with air, which rapidly leads to a decrease of the pH value. To overcome these drawbacks, ethanolamine (ETA22ETA: ethanolamine.) is suggested as a substitutional stabilizer for latex from Hevea brasiliensis (HB33HB: Hevea brasiliensis.) and for latex from Russian dandelion, Taraxacum kok-saghyz (TKS44TKS: Taraxacum kok-saghyz.), a promising crop for an alternative and renewable source of NR latex. However, little is known about the colloidal stability of ETA stabilized latices. To this purpose, zeta-potential measurements were performed to evaluate and compare the electrostatic stability of ETA, ammonia, and KOH preserved latices. In addition, dynamic light scattering was used to determine the particle size distribution of the latex dispersions. The results suggest a comparable stabilizing efficiency of the three chosen preservatives. Zeta-potentials of HB latex were in the range between −93mV and −102mV. For TKS latex taken directly from dandelion roots, lower absolute values were obtained (−84mV to −93mV) as well as for TKS latex gained by extraction (−61mV to −65mV). However, all obtained zeta-potentials are in a range that guarantees sufficient colloidal stability. As a result, we found that ETA seems to be as suitable as ammonia or KOH for pH adjustment of TKS and HB latex, leading to comparable latex dispersion stability.