Application and effect evaluation of gellan gum microgel emulsions in the cleaning of palm leaf manuscripts

Gellan gum is a microbial metabolic polysaccharide, featuring safety, non-toxicity, good stability, easy preparation and biodegradability. Microgel materials prepared from gellan gum possess both the water retention properties of microgels and the characteristics of the micrometer scale. To explore the effect of gellan gum microgel emulsions in the cleaning of palm leaf manuscripts, gellan gum microgel emulsions were prepared with a gellan gum content of 0.1% (mass fraction), the concentration of the accelerant (sodium chloride) of 0.05 mol/L, and the crosslinking temperature of 80 ℃. The shear modulus of the microgel emulsion was 2.5-5 Pa within the range of 0.1%-1% shear strain, and the gel particle size was about 2.35 μm, indicating that it has high softness and can penetrate the leaf stomata and character engravings of the palm leaf manuscripts for deep cleaning. The palm leaf manuscripts, both before and after cleaning, were analyzed by three-dimensional video microscopy, scanning electron microscopy (SEM), infrared spectroscopy, pH value measurements, electrical conductivity measurements, and bending strength measurements. The results show that the gellan gum microgel emulsion has a significant cleaning effect, removing microorganisms, oils and mud stains on the surface of the palm leaf manuscripts. No large crystals or filaments were observed in the SEM images, and the electrical conductivity of the soaking aqueous solution after washing the leaves with the microgel emulsion was very low (99.5 μS/cm), indicating that the residual amount of sodium chloride was minimal. Compared with cleaning with water or a water/ethanol mixture (with a volume ratio of 1∶1), cleaning with the microgel emulsion causes less physical damage to the palm leaf manuscripts. These results can provide a scientific basis for the application of gellan microgel emulsions in the non-invasive cleaning and protection of plant fiber cultural relics.