Effect of Cross-Linker Length on the Absorption Characteristics of the Sodium Salt of Cross-Linked Polyaspartic Acid

For the development of biodegradable superabsorbent polymers, the effect of the cross-linking length on the absorption characteristics of the Na salt of polyaspartic acid (PAspNa) was demonstrated using different concentrations of diamine cross-linking agents bearing carbon chains of different lengths, viz., ethylenediamine, 1,6-hexamethylenediamine, 1,8-diaminooctane, 1,10-diaminodecane, and 1,12-diaminododecane were used as cross-linking agents. The absorption of PAspNa was measured in deionised water and in a 0.9% aqueous NaCl solution. Under the conditions tested, when the alkyl chain of PAspNa was too short or too long, the absorbency was low and the cross-linking length was optimum. The success of the cross-linking reaction was confirmed by FT-IR spectroscopy. The degree of cross-linking was estimated and the ideal concentration for maximum water absorption was determined by elemental analysis. The sample obtained by cross-linking 1,8-diaminooctane at a concentration of 0.11 g/g polysuccinimide (PSI) showed the highest absorption. The thermal properties of each material were determined by dynamic scanning calorimetry. Therefore, the length of the cross-linking agent was found to strongly influence water absorption.

Automated summary

The effect of cross-linking length on the absorption characteristics of polyaspartic acid sodium (PAspNa) was investigated by using different concentrations of diamine cross-linking agents with carbon chains of varying lengths. It was found that the absorbency of PAspNa was optimum when the alkyl chain length was at an intermediate level. The successful cross-linking reaction was confirmed using FT-IR spectroscopy, and the degree of cross-linking and the ideal concentration for maximum water absorption were determined.