Evaluation of the structural morphology of starch-graft-poly(acrylic acid) on its scale-inhibition efficiency

The development of phosphorus-free and biodegradable scale inhibitors has been paid considerable attention. Two series of starch-graft-poly(acrylic acid) (St-g-PAA) samples with different grafting ratios and grafted-chain distributions, that is, the number and length of grafted PAA chains on the starch backbone, were designed and prepared in this study. Fourier transform infrared and ¹H nuclear magnetic resonance spectra were used to further characterize the molecular structures of the St-g-PAAs. In addition to dose, the effects of the structural morphologies of St-g-PAA, namely, grafting ratio and grafted-chain distribution, on the scale-inhibition performance against calcium carbonate were investigated systematically. Structural morphology significantly influenced the scale-inhibition performance of St-g-PAA. St-g-PAA with relatively low grafting ratio (≤97%) displayed better scale-inhibition effect than samples with similar grafted-chain distributions. Meanwhile, under the similar grafting ratios, samples with higher number of branched chains with shorter grafted chains displayed better antiscaling performance. Thus, higher scale-inhibition rate and lower corresponding optimal dose were obtained. Different scale-inhibition mechanisms were involved in the effects of the structural morphology. These mechanisms were investigated in detail from the molecular levels using scanning electron microscopy and X-ray diffraction.