Zwitterionic environment-friendly organic chrome-free tanning agent and preparation method thereof

The invention relates to a zwitterionic environment-friendly organic chrome-free tanning agent and a preparation method thereof. The preparation method comprises the following steps: firstly, preparing a prepolymer from polyisocyanate, a cationic hydrophilic monomer and an organic acid compound, then adding a mixed aqueous solution of hydrosulphite and sulfite to terminate and emulsify the prepolymer, and finally adjusting the solid content and the pH value to obtain the zwitterionic organic chrome-free tanning agent. The zwitterionic organic chrome-free tanning agent developed by the invention is safe and environment-friendly, the tanned wet white leather is high in moist heat stability and free of free formaldehyde, the problem of follow-up chemical material combination caused by the fact that the wet white leather obtained by a common organic tanning system is not resistant to yellowing and insufficient positive charges is solved, and particularly the problem that the wet white leather cannot resist yellow