Pine oleoresin and methyl cellulose-incorporated adaptive hydrogels with self-healing capability, suppressed...

Physically crosslinked hydrogels are promising soft materials nevertheless, excessive swelling resulting from their hydrophilic nature remains a major limitation that can adversely affect their dimensional stability and long-term performance. In this study, a novel physically cross-linked hydrogel matrix containing methyl cellulose (MC) and pine oleoresin (OLR) was developed to suppress the excessive swelling behavior and improve the thermal stability of polyvinyl alcohol (PVA)-based hydrogels while maintaining self-healing properties. Physically crosslinked hydrogels were produced in the presence of Na₂B₄O₇.10H₂O by supporting freeze-thaw cycles. OLR emulsion was added to the matrix at different ratios (0.25-1.00%), and the swelling degree, gel fraction, chemical structure, thermal, rheological, morphological, and color properties of the systems were investigated. The inclusion of MC increased the swelling capacity by about 300%, whereas OLR addition simultaneously lowered the swelling degree by up to 60%. Thermal analysis results showed that OLR ratios below 0.75% increased the onset degradation temperatures by 20-30°C and increased the char amount. Rheological analyses revealed that elastic characteristics (G' > G″) were dominant in all samples, and the hydrogels exhibited a high self-healing capacity ranging from 92 to 98%. Furthermore, cut-contact testing visually confirmed that damaged surfaces were repaired in a short time. These findings demonstrate that OLR is an effective bio-based filler for tailoring the swelling, viscoelastic, and thermal behavior of physically crosslinked hydrogels, offering a promising strategy for the development of multifunctional soft materials.