Influence of polyacrylamide on the methylene blue value of manufactured sand

The manufactured sand has become the main source of sand for construction in China. The effects of molecular weight and hydrolysis degree of anionic polyacrylamide（HPAM） on the methylene blue（MB） value of manufactured sand are investigated by methylene blue test. The mechanism of action between HPAM and MB is explored by means of cyclic voltammetry（CV） test, scanning electron microscope and Fourier transform infrared spectroscopy. The results show that with the increase of anionic polyacrylamide concentration, the methylene blue value of manufactured sand shows a stepwise increase trend. At the same hydrolysis degree and concentration, with the increase of molecular weight of HPAM, the number of amide groups in the molecular chain and the content of anionic active groups produced by hydrolysis increases, and the electrochemical active complexes formed by the combination with the cations（C₁₆H₁₈N₃S⁺） in the MB solution increase. The hydrogen bonding force between the oxygen-containing functional groups produced by HPAM hydrolysis and the benzene ring in the MB molecule is enhanced, resulting in an increase of the MB value. At the same molecular weight and concentration, with the increase of the hydrolysis degree of HPAM, the effective length of the molecular chain of the hydrolyzed HPAM increases, and the electrostatic attraction and hydrogen bonding force between the MB molecule and the HPAM molecule are enhanced, resulting in the increase of the MB value.