Hydroxypropyl methylcellulose as an effective consolidant for freeze-drying conservation of waterlogged bamboo slips

Abstract

To address the challenge of stabilizing highly degraded simulated waterlogged bamboo slips while preserving their original chemical characteristics, this study developed a mild consolidation strategy based on hydroxypropyl methylcellulose (HPMC) impregnation combined with freeze-drying. Simulated waterlogged bamboo slips were treated with different HPMC concentrations, impregnation temperatures, and durations, and the consolidation performance was systematically evaluated using dimensional stability measurements, mechanical testing, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), low-field nuclear magnetic resonance (LF-NMR), and scanning electron microscopy (SEM). The optimum treatment (5 wt% HPMC, 60 °C, 7 d) reduced volumetric shrinkage to 4.69%(corresponding to anti-shrinkage efficiencies (ASE) of 85.48–91.30%), increased the flexural strength to 4.65 MPa, and improved the surface hardness (Shore D) to 75.6–78.4, demonstrating substantial enhancement of both dimensional stability and mechanical performance. FTIR and XRD analyses suggested that HPMC did not induce chemical modification or cellulose phase transformation, indicating that the reinforcement was achieved through physical interactions involving hydroxyl groups and intermolecular associations rather than extensive covalent reactions, while preserving the intrinsic chemical identity of the bamboo substrate.LF-NMR analysis further revealed that HPMC consolidation altered the water-binding environment by reducing water mobility and increasing molecular confinement within the bamboo matrix, providing complementary evidence for enhanced interfacial stabilization during drying. SEM observations, together with freeze-dried HPMC controls, revealed that HPMC formed a continuous membrane-like network coating vascular bundles and parenchyma tissues, thereby enhancing interfacial bonding and mitigating structural collapse during freeze-drying. Furthermore, wet–heat aging (25 °C and 60% RH for 30 days) confirmed the durability of the HPMC-treated bamboo, with volumetric shrinkage maintained below 2%, negligible changes in hardness, and <8% reduction in bending strength, demonstrating the long-term environmental stability of the HPMC-derived network.These findings demonstrate that HPMC functions as both a physical binder and a structural scaffold, providing an effective, polysaccharide-based consolidation strategy for the long-term preservation of degraded waterlogged bamboo cultural heritage.

The authors' abstract, as published at the source. Journal of Cultural Heritage, 2026 · DOI ↗