The effects of crosslinker ratio and photoinitiator type on the properties of pnipam hydrogel

In this study, Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were produced from N-isopropylacrylamide (NIPAM), at three different concentrations of crosslinker, N,N´-methylenebisacrylamide (BIS) (0.50%, 0.35%, and 0.25%) using two types of photoinitiator, a hydrophilic photoinitiator (Irgacure 2959) and a hydrophobic photoinitiator (Irgacure 651). When Irgacure 651 was used photopolymerization process was completed in 20 min compared to two hours with Irgacure 2959. However, the resultant hydrogels were opaque suggesting a heterogeneous structure, which in turn led to low compressive strength. Besides, when hydrogel solution was prepared with Irgacure 651 in water/ethanol mixture 0.25% crosslinker ratio was not sufficient to form a hydrogel. Irgacure 2959 produced homogenous transparent hydrogels with a higher degree of swelling. When the crosslinker ratio decreased swelling capacity increased, but hydrogels became weaker. The decrease in compressive strength was particularly high at the 0.25% crosslinker ratio. The crosslinker ratio or photoinitiator type did not have any significant effect on the phase transition temperature. On the other hand, hydrogel samples prepared with Irgacure 651 in water/ethanol mixture showed a quicker response to swelling and deswelling. In conclusion, in terms of morphology, swelling capacity, and compressive strength the best results were obtained with the crosslinker ratio of 0.35% and Irgacure 2959. © 2022, The Polymer Society, Taipei.
Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, TÜBİTAK: 119M355
The authors would like to express appreciation for the support of the Scientific and Technological Research Council of Turkey (TÜBİTAK) [Project Number =119M355].