Cucumber Biomass Powder as Reinforcing Scaffold for Poly(acrylic acid-co-acrylamide) Superabsorbent Hydrogels: Structure and Properties

Abstract

Unrefined cucumber biomass powder (CBP) was incorporated into a poly(acrylic acid-co-acrylamide) (P(AA-co-AM)) network to develop a superabsorbent hydrogel with enhanced gel network rigidity and swelling performance. CBP served as a renewable reinforcing scaffold, providing a multicomponent biomass matrix for physical reinforcement alongside abundant hydrophilic groups (–OH, –NH, and –CONH–). Spectroscopic and rheological analyses suggest that CBP integration significantly alters the gel network through complex multi-component interactions, as evidenced by FTIR peak shifts (3435 → 3442 cm−1, 1558 → 1567 cm−1) that are consistent with extensive interfacial hydrogen bonding and potential partial chemical integration, leading to a 97% increase in storage modulus (from 11.9 kPa to 23.4 kPa) with a corresponding decrease in tanδ from 0.36 to 0.26. Under optimized synthesis conditions, the composite exhibited 30 min free-swelling capacities of 2801.00 g/g in deionized water, 142.72 g/g in 0.9 wt% NaCl, and 65.04 g/g in synthetic urine, along with rapid kinetics (1637.49 g/g within 1 min) and partial residual swelling capacity (727.44 g/g retained after five cycles). Rheological analysis revealed that CBP incorporation enhances network stiffness while introducing a more strain-sensitive response at high deformations—a typical trade-off for rigidized gel networks. These findings demonstrate that unrefined model biomass can serve as an effective, low-cost reinforcing scaffold for functional hydrogels, offering a sustainable route for personal care or agricultural applications in gel materials design.