Can Encapsulated Fragrant Oil Protect Old Manuscripts?

Fragrant oils have uses beyond the pleasure of smelling them. In palm-leaf manuscripts, which carry writing on palm leaves and form part of traditions in South and Southeast Asia and elsewhere, oils such as clove oil have been used to keep the leaves flexible. Once the oil evaporates, however, its effects become harder to sustain.

A study published by Ding and colleagues in 2025 tackled this problem by enclosing clove oil in tiny capsules and combining them with fine cellulose particles. The aim was not to make the fragrance seem stronger, but to develop a material that would preserve the strength and resistance to breakage of brittle leaves for longer.

Using artificially deteriorated samples instead of historical artifacts

The experiments used modern palm-leaf manuscripts made by traditional methods and obtained in Yunnan Province. Chemical treatment and heating made them brittle, producing samples that simulated deteriorated manuscripts. This was not a study that tested a new material by applying it to historical manuscripts themselves.

Alongside the new material, the researchers prepared clove oil alone, fine cellulose particles alone, a combination without an oil-encapsulating shell, and a combination without oil. They compared appearance and mechanical properties against untreated samples.

A shell around the oil, and cellulose to support the leaf

The material has three components: clove oil, an acrylic polymer called PMMA, and cellulose nanowhiskers. The last are slender, needle-like particles made of cellulose, the principal constituent of plant fibers.

First, small oil-containing droplets are dispersed in water and stabilized with cellulose particles. As the solvent used in preparation evaporates, PMMA forms a shell around the oil. The cellulose particles also form a network-like structure connecting the resulting capsules.

Electron microscopy revealed spherical structures with an oil-containing core and a shell. Particle sizes varied, but the selected conditions produced capsules on the order of several hundred nanometers. The authors proposed that, as the solvent evaporates, small capsules form as though being squeezed out from the surfaces of the original droplets.

After comparing different proportions of oil and shell material, the researchers found that the selected formulation encapsulated about 51% of the oil initially added. Oil accounted for about 35% of the finished solid material. These two figures have different denominators.

How quickly does the oil come out?

Oil release from the capsules was examined in water. The selected formulation released about 56% in the first two hours and about 63% by four hours. Release was initially rapid and then slowed.

From comparisons with mathematical models, the authors interpreted diffusion, the gradual movement of oil driven by concentration differences, as the main mechanism. Results for release into water cannot, however, be directly substituted for the rate of release into the air from a dry manuscript or the length of time a person can smell the oil.

In a separate experiment, mass changes were measured over seven days at around room temperature. The new material lost about 2.9% of its mass, compared with about 33.1% for oil alone. Because the new material also contains relatively nonvolatile shell material and cellulose, the denominator is not the same as that for retention of the oil itself. Nevertheless, the authors regarded the result as supporting improved oil retention.

Greater tensile strength without a major change in appearance

No conspicuous change in appearance was observed in simulated manuscripts impregnated with the new material. Oil alone, by contrast, made the surface glossy, while the shell-free and oil-free combinations left conspicuous white residues. These latter two conditions were excluded from subsequent mechanical tests.

Compared with untreated samples, tensile testing showed increases of about 44% in tensile strength, about 102% in a measure of the ability to absorb energy before fracture, and about 58% in elongation at break for the new material. These measurements used 9–12 specimens per condition.

Clove oil alone also produced improvements, but those with the new material were greater. Cellulose particles alone increased deflection under bending but produced little improvement in tensile measures. The evaluation distinguishes flexible bending from improvements across multiple mechanical properties.

Do the effects survive hot, humid conditions?

Durability was examined by accelerating deterioration at 80°C and 65% relative humidity. In samples treated with oil alone, much of the mechanical improvement was lost after one day.

Even after four days, samples treated with the new material retained tensile strength about 21% above the untreated baseline and an energy-to-fracture measure about 49% higher. Tensile measurements in this durability experiment used eight specimens per condition.

However, the four days of accelerated testing were not directly converted into an equivalent number of years in storage. Real manuscripts differ in deterioration, inks, and storage conditions. The study does not establish that the effects last for decades in historical materials, or that the treatment is harmless to every kind of material.

Combining support with gradual release

Under the microscope, the new material formed a thin film on the leaf surface, with capsules embedded in it. Some material also penetrated inside, distributed in a way that bridged gaps in the tissue. Fracture surfaces showed more evidence of fiber pullout than untreated samples, indicating a change in how the material broke.

The authors suggest that two functions work together: the surface film and internal bridges support the structure, while oil released from the capsules maintains flexibility. A distinctive feature of the study is that the encapsulating material itself provides reinforcement, rather than simply trapping the oil for longer.

Although the material is expected to be compatible with the leaves, application to cultural heritage requires further study of issues such as long-term chemical stability and whether the treatment can be removed when necessary. This should not be taken as a method for applying clove oil to books at home or to valuable manuscripts.

Summary

Enclosing clove oil in polymer shells and combining it with cellulose particles improved the strength and resistance to breakage of simulated palm-leaf manuscripts. Under hot, humid test conditions, the effects also lasted longer than those of oil alone.

The approach uses the properties of a fragrant oil while controlling its release and supporting the leaves with the material itself. The authors describe this combination as a promising way to make reinforcement of palm-leaf manuscripts more durable. The study gives fragrance-encapsulation technology a new role in a setting where volatility is a disadvantage.

References

Ding, J., Yu, J., Zhu, J., Zou, W., Zhang, Y., Feng, R., Zhao, X., Wang, S., Li, L., & Li, X. (2025). Controlled-release clove oil nanocapsules integrated with cellulose nanowhiskers for durable toughening of palm leaf manuscripts. npj Heritage Science, 13, 482. DOI: 10.1038/s40494-025-02065-3 / Full text. Original article: © The Author(s) 2025, CC BY-NC-ND 4.0.