Controllable synthesis of polyaspartic acid: Studying into the chain length effect for calcium scale inhibition

Polyaspartic acid (PASP) has been disclosed as a green and degradable antiscalant for inhibiting the calcium scale for >30 years. Although the chain length of PASP has been known as one of the key factors to influence the inhibition performance of both CaCO3 and CaSO4 scale, the very limited methods for the controllable synthesis of PASP make it hard to examine the core cause. Herein, a simple two-step method has been established for the synthesis of PASPs (PASP-1-PASP-6) with narrow dispersity (D) and controllable chain length (from 12 to 36). The static antiscaling experiments show that while PASP-4 with chain length of 24 has the best inhibition performance against CaCO3 scale, PASP-1 with the chain length of 12 gives the best result against CaSO4 scale. Furthermore, detailed scale-inhibition study shows that with the variation of chain length of PASP, the core cause for determining the antiscaling effect of CaCO3 or CaSO4 scale is different. While the antiscaling effect for CaCO3 scale inhibition involves chelation, dispersion, lattice distortion, and threshold effect, the effect for CaSO4 scale inhibition only includes chelation, dispersion and threshold effect. No lattice distortion effect was observed for the latter. This study not only proves the best chain length of PASP for CaCO3 and CaSO4 scale inhibition for the first time, but also is meaningful for guiding the design of other new green polymer-based antiscalants.