Tween 20-cinnamic acid conjugate as a UV-absorbing emulsifier

Cinnamic acid (CA) was covalently attached to the head of Tween 20 in order to prepare a UV absorbing emulsifier. The molar ratio of Tween20 to CA of the Tween 20-CA conjugate was calculated to be 1:1.3 on 1H NMR spectrum. The interfacial tensions of Tween 20-CA conjugate solution were lower than those of Tween 20 solutions in the full range of concentration tested (0.0005–0.01% (w/v)), indicating that the interfacial activity of Tween 20-CA conjugate is higher than that of Tween 20. The dimerization degree of Tween 20-CA conjugate in 180 min was about 77% and it was higher than that of free CA. The molar extinction coefficient of Tween20-CA conjugate at 280 nm was 14,391.8 M−1 cm−1, not markedly different from that of CA. Emulsion prepared using Tween20-CA conjugate was much more stable for 70 h in terms of oil droplet size change than emulsion prepared using Tween 20, possibly because the interfacial activity of Tween 20-CA conjugate was higher than that of Tween 20. The oil droplet size of emulsions prepared using Tween 20-CA conjugate increased during UV irradiation period (100 min), however, the increment was not so great that the droplet size was kept below 7 μm. It is believed that Tween 20-CA conjugate can be used as a UV-absorber.