Introduction

Papyrus (Cyperus papyrus) is a fibrous material made up of 57.98–61.82% cellulose and 11.82–13.45% hemicellulose1,2,3. It also contains 12–34% lignin and 3% proteinaceous materials. Papyrus was commonly used as a writing material in ancient Egypt and widely in the Roman Empire4,5. Papyrus is prone to deterioration due to various factors such as temperature, humidity, light, air pollution, and improper storage6. Biodegradation is primarily caused by microorganisms like fungi and bacteria that break down cellulose materials. Biodeterioration (defined as any undesirable change in material characteristics due to biological agents) is a common issue in museums. Factors influencing it include material composition, environmental conditions, and museum maintenance practices7,8,9,10. Papyrus, a fragile material made from the pith of the papyrus plant, is susceptible to oxidation due to various factors in storage and indoor environments. High humidity levels can promote oxidation, while low humidity can cause brittleness. Extreme temperatures, exposure to light, poor air quality, and acidic materials can accelerate oxidation. Cellulolytic fungi, particularly in indoor environments, can cause severe deterioration, leading to fiber loss and destruction. Other fungal spoilage may result from permanent staining and mycelium penetration11.

Oxidation is a chemical reaction that involves the loss of electrons from a substance. In the case of papyrus, oxidation can occur when the material is exposed to oxygen in the air. This can lead to the breakdown of the cellulose fibers in the papyrus, causing it to become brittle and discolored over time.

Hydrolysis is another degradation process that can affect papyrus. It involves the breaking of chemical bonds in a substance through the addition of water molecules. In the case of papyrus, hydrolysis can occur when the material is exposed to high humidity or moisture. This can lead to the breakdown of the cellulose fibers in the papyrus, making it weak and prone to tearing12.

This study sheds light on the mechanism of papyrus deterioration through oxidation, which is a major problem for papyrus caused by various deterioration factors due to improper conditions. The oxidation of glucose residues in cellulose materials occurs simultaneously with the breakage of glycosidic bonds, leading to a reduction in the degree of polymerization (DP) and increased durability. Oxidation products can progress further, forming cross-links between neighboring macromolecules through hemiacetal and ester bonds. Lignin is more susceptible to oxidation by atmospheric oxygen compared to cellulose, making papyrus containing a high amount of lignin prone to oxidation and degradation.

Lignin may function as a protective shield for cellulose initially. Radicals, active oxygen forms, and carboxyl groups from lignin oxidation can lower the pH of papyrus, accelerate cellulose degradation, and pose a significant challenge for papyrus preservation13,14. Cellulose contains specific functional groups at the end of each glucose unit, including alcohol groups, secondary alcohol groups, and an aldehyde group. The oxidation of the main alcohol groups at the C6 atom can lead to the formation of an aldehyde group and then a carboxylic group. The secondary alcohol groups at the C2 and C3 atoms can be converted into ketone groups. The destruction of the glucopyranose ring can occur through the oxidation of aldehyde groups, which may further oxidize into carboxyl groups, breaking the carbon atom bonds. Additionally, the hydroxyl group on the final glucose unit’s C1 atom may oxidize, leading to the potential breakage of the glucopyranose ring in the nearby position15.

In recent years, essential oils have gained significant attention in the conservation field for their antibacterial, antifungal, and antioxidant properties. These oils are volatile aromatic liquids derived from different plant parts. Various publications have highlighted the successful use of essential oils such as Artemisia, Boldo, Camphor, Ravensara aromatica, Lavender, Tea Tree, Thuja, Clove, Camphor wormseed, Anise, Cumin, Garlic, Laurel, Oregano, Thyme, Cinnamon, and others16. Lavender oil is a natural biocide that is used in conservation to protect photographic prints from biodegradation. It is a safe alternative to synthetic chemicals that can be harmful to collections. In a study, camphor oil was also found to be effective in preventing fungal growth on archeological oil paintings. The oils are applied in a vapor phase in a controlled environment for 15–20 days to ensure preservation17,18. Lavender, a member of the Lamiaceae family, is native to the Mediterranean region, Africa, and Asia. It has been used as an herbal remedy for centuries19 and contains over a hundred constituents, with linalool, linalyl acetate, Lavandula acetate, camphor, and 1,8-cineole being the most common. The antioxidant activity of lavender essential oil has attracted the attention of researchers20. Additionally, the volatile components of Lavandula essential oils have been found to exhibit strong antifungal activity21. The camphor tree is native to China, Taiwan, and Japan. Its wood and bark are used to produce traditional oils. These oils, rich in camphor, have strong antifungal and antioxidant properties. The camphor oils extracted through steam distillation from the leaves are valuable due to their high content of camphor and linalool22 (chemical formula C10H16O9). The botanical names for the camphor tree are Laurus Camphora, Cinnamomum Camphora, or Camphora officinalis23.

It can be said that essential oils contain natural compounds that act as antioxidants, preventing oxidation and degradation of the papyrus fibers. The oils create a protective barrier on the surface of the papyrus, reducing its susceptibility to chemical reactions with environmental deterioration factors. The antimicrobial properties of essential oils inhibit the growth of fungi and bacteria that can accelerate chemical deterioration. Few studies have examined the long-term effects of essential oils on some heritage materials and the extent to which they reduce the impact of chemical, physical, or biological reactions. One example of such studies is the work done by ref. 24, who proved that essential oil had good resistance against some fungi isolated from archeological papyrus. They also confirmed that no undesirable properties were detected in thermally aged papyrus experiments associated with essential oils. Reference 25 stated that essential oils are safe for both conservators and the environment. They have proven that essential oils can resist fungi and also do not affect the surface appearance or mechanical properties of cellulose fibers. Reference 26 reported that camphor oil is a potential candidate for use in controlling fungal deterioration in different materials of cultural heritage.

This study aims to assess the antioxidant properties of camphor and lavender oils on papyrus to protect it from deterioration caused by oxidation. The study utilizes scanning electron microscopy (SEM) to observe changes in fiber morphology, infrared spectrum analysis to track alterations in functional groups post-treatment, and XRD to measure the impact on cellulose crystallinity. Additionally, color change measurements will be used to demonstrate the effectiveness of lavender and camphor oils as antioxidants on papyrus.

Methods

Papyrus sheets are produced in the Qaramous village in the Sharkia Governorate of Egypt. The samples were cut to the required dimensions or weight for each analysis and investigation4.

Lavender and camphor oils were purchased from the unit of pressing and extracting natural oils, National Research Centre (NRC), Dokki, Giza, Egypt. The purity was 100%. The steam distillation method was used for the extraction of oils.

Tween 80 was purchased from El-Gomhouria Company in Egypt. It helps improve the solubility of poorly water-soluble compounds by forming micelles in aqueous solutions. This property makes it a valuable ingredient for mixing essential oils with water, as used in this study27.

In the beginning, three concentrations of lavender and camphor oils were prepared for a preliminary study to explore the appropriate concentration to be used in the experimental study. Concentrations of 0.5%, 0.75%, and 1.0% of the oils were prepared, and an equivalent amount of Tween 80 was added to them, followed by the addition of distilled water to make the solution up to 100 ml. The solution was stirred for 15 min to ensure complete dissolution and mixing.

After visually evaluating the three prepared concentrations, it was found that the 0.5% concentration was the best and was used in the experimental study for evaluation after the application of oils on the samples subjected to heat and light aging. This concentration was prepared using the same method described here. The spray method was used to treat the aged untreated samples (5 cm2) with the prepared oil. The samples were then left to dry naturally at room temperature.

Accelerated tests are designed to find materials that can be safe for long-term use and would not cause degradation of treated artefacts28. Accelerated heat aging was conducted at 85 °C for 240 h following ISO 5630-3.199629 to simulate deteriorated and oxidized samples. This aging time is equivalent to 50 years of natural aging as per the ISO standard. This technique was used to prepare aged, untreated samples and was also used for the treated samples.

Artificial aging by light for 120 h, equivalent to 50 years of natural aging by UV lamp (Mercury-ARC Lamp (E40 - Mix F 500 W) at a distance of 15 cm from the samples30 at the National Institute for Standards (NIS) in Giza, Egypt. This method was only applied to the treated samples. All samples were exposed to artificial heat and light aging to evaluate the resistance of papyrus samples treated with oils to oxidation processes.

Visual assessment for the preliminary study

Visual estimation with the naked eye and using a digital camera (Samsung camera 38MP, f/2.2 lens) is an important step to evaluate the effect of three initial concentrations of the oils used (0.5%, 0.75%, 1.0%) on the color of the treated papyrus samples31,32.

Surface morphology investigation with scanning electron microscope (SEM)

The surface morphology of the samples was observed using a scanning electron microscope (JEOL, JSM 5400 LV EDX link ISIS-Oxford, high vacuum) at the SEM unit of Assiut University, Egypt. The samples were coated with gold using Physical Sputter Coating (PSC) for better visualization.

Change of color measurement

The color change of the samples was measured using an Optimatch 3100 (model number CE 3100, serial number 31013780698, SDL, UK). The average of six samples was used to measure the change in color of the samples studied. All samples were measured in the visible range under H. D65 light source, 10° viewing angle, 400 nm to 700 nm wavelength range, and 10 nm spacing. The color changes were expressed using the L, a, and b color coordinates of the CIELAB color space. In the CIELAB color space, the L axis ranges from 0 to 100, with 0 representing black and 100 representing white. The a-axis represents red (positive values) to green (negative values), while the b-axis represents yellow (positive values) to blue (negative values). The overall color change for all treated papyrus was calculated as ΔE using the Eq. (1)33:

$$\Delta E=\,\sqrt{{(\Delta L)}^{2}+{(\Delta a)}^{2}+\,{(\Delta b)}^{2}}$$
(1)

The differences in color index values before and after treatment are represented by (ΔL², (Δa)², and (Δb)².

pH measurement

The average of three samples was used to measure the pH value of the samples studied. A pocket-waterproof temperature tester from Romania was used to measure pH. The pH of the papyrus samples was determined using the cold extraction method, where 1 g of each sample was soaked in 100 mL of distilled water for 6 h. The pH meter was calibrated with pH 7 and pH 4 solutions. The pH values were adjusted following the ISO room temperature method (ISO 6588-1: 2012)34.

XRD analysis for measurement of papyrus crystallinity

The cellulose crystallinity of treated papyrus samples with oils was measured using XRD analysis. The X-ray bulb type used was Copper with a working wavelength of 1.541874. The working angle range was from 10 to 50 degrees, with working conditions set at KV 35-MA20. The crystallinity index was calculated using the equation provided by35:

$${I}_{\text{crys}}=\frac{{{I}}_{002}-{I}_{\mathrm{am}}}{{I}_{002}\,}\times 100$$

Where ICrys is the crystallization index, I002 is the intensity at a 2θ value of 22.6°, and Iam is the intensity at a 2θ value of 19°.

Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy

FTIR analysis was conducted to examine the chemical changes in control, treatment, and aged treated papyrus samples. The samples were analyzed using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectra on a Bruker Vertex 70 Platinum ATR scale with diamond crystal in the range of 4000–400 cm−1 and a resolution of 4 at the Archeological Research and Preservation Centre—Supreme Council of Antiquities, Ministry of Tourism and Antiquities, Egypt.

Results and discussion

Investigation of the surface morphology by a scanning electron microscope

The investigation of the surface morphology of the control sample under a scanning electron microscope (Fig. 1A) reveals a fascinating surface morphology. The fibers appear to have a distinct structure with a rough and irregular surface. The individual fibers show a twisted and intertwined pattern, giving them a unique and intricate appearance. The surface of the papyrus fibers shows a network of fine ridges and grooves. These features contribute to the overall texture of the fibers and play a crucial role in their strength and flexibility. The SEM images also highlight the presence of small pores and pits on the surface of the fibers, which may be related to the plant’s growth and development.

Fig. 1: Comparing the control samples with the treated samples with oils.
figure 1

Scanning electron microscope images to investigate the surface morphology of the untreated and treated papyrus samples before and after accelerated heat and light aging methods: A New papyrus sample (control), B Heat aged untreated sample, C Light aged untreated sample, D The treated sample with camphor oil, E The treated sample with camphor oil after heat aging, F The treated sample with camphor oil after light aging, G The treated sample with lavender oil, H The treated sample with lavender oil after heat aging, I The treated sample with lavender oil after light aging.

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Under the SEM, the heat-aged papyrus sample (Fig. 1B) showed visible alterations in its surface structure. The fibers appeared to be more brittle and fragile, with signs of degradation. Cracks and fissures were observed on the surface, indicating the weakening of the material due to accelerated heat aging.

Under the SEM, the accelerated light aging process (Fig. 1C) causes changes in the surface structure of the papyrus samples. These changes include alterations in the texture and overall appearance of the surface. The fibers of the papyrus may become more brittle or show signs of degradation, leading to a rougher or more uneven surface texture. Additionally, the accelerated light aging process also led to the formation of cracks, wrinkles, and other surface defects on the papyrus samples.

In Fig. 1D, the sample treated with camphor oil displayed a smooth and well-preserved surface with clearly visible fiber patterns. The fibers appeared stronger compared to the untreated sample that was subjected to heat aging. However, in Fig. 1E, after accelerated heat aging, the surface showed minimal changes, with oil accumulation leading to the fibers being visible underneath. In Fig. 1F, the treated sample that underwent light aging exhibited a slightly coarse and non-uniform surface morphology. Overall, the application of camphor oil seemed to have a protective effect on the fibers, even after accelerated heat and light aging methods.

The papyrus sample treated with lavender oil (0.5%) (Fig. 1G) showed a smooth surface with the oil covering it, resulting in a less visible fiber structure. However, the fibers appeared strong underneath. After heat aging (Fig. 1H) and light aging (Fig. 1I), the surface remained smooth, the fibers appeared strong, and no changes were observed after aging.

The results proved that the surface morphology of papyrus samples treated with camphor and lavender oils showed better results compared to the aged untreated samples when examined using scanning electron microscopy (SEM) for some reasons as follows:

Firstly, the application of camphor and lavender oils on the papyrus samples likely helped to preserve the structural integrity of the fibers. These oils retained their original fiber structure better, leading to clearer and more defined surface morphology under SEM.

Secondly, the oils have also functioned as a protective coating on the surface of the papyrus samples, shielding them from the effects of both accelerated heat and light aging that can cause deterioration of the surface morphology. This protective layer could have helped to maintain the surface features of the samples, making them more distinguishable and easier to analyze under SEM.

Additionally, the oils may have contributed to the overall cleanliness of the fiber’s surface, which provides a clearer view of the underlying morphology and details of the papyrus fibers when examined using SEM.

Color change measurement

When assessing the efficacy of treatment methods on papyrus samples, color change measurement is crucial, especially during the preliminary investigation to establish the ideal concentration. When applied to papyrus samples, color change measurement provides valuable information about how camphor and lavender oil treatment affect the sample’s appearance. Color change measurement is employed as a baseline to ascertain the initial color characteristics of the treated papyrus samples before their exposure to accelerated heat and light aging techniques.

For comparing the color changes brought on by aging, this baseline data is helpful. By measuring the color change, researchers can objectively determine how well the camphor and lavender oil treatments protect the original color of the papyrus samples. Using accelerated aging techniques increases the significance of measuring color change. It allows scientists to assess the extent of color alterations brought about by aging. It is necessary to know this information to comprehend the treatment’s long-term stability and durability. The ability of the camphor and lavender oil treatments to successfully protect the papyrus samples from heat and light-induced discoloration and degradation can be ascertained by examining the color changes. Measurement of color change also provides useful information for conservation initiatives. The change of color measurement can be explained as follows:

According to the preliminary study findings, the results showed that the heat-aged sample had an L* value of 78.48, slightly lower than the control samples (79.23). It was suggested that the papyrus material may be darker due to heat aging. High temperatures have the potential to cause chemical reactions in organic materials like papyrus that change the material’s color and appearance. The samples treated with lavender and camphor oils gave an L* value less than the control and heat-aged untreated samples. The L* value decreased with increasing concentration of oil.

The chemical reactions that took place during the treatment process can be used to explain the decrease in Lightness (L* value) of the papyrus samples treated with lavender and camphor oils when compared to the control and aged untreated samples. When the papyrus samples were treated with the chemical solution, the chemicals likely reacted with the components of the papyrus, causing changes in its color and lightness. It was suggested that this could have been caused by one or more of the following mechanisms:

The oxidation of the organic compounds found in the papyrus is one theory as to how this reaction might occur. It’s possible that oxidizing agents in the chemical solution interacted with the organic molecules in the papyrus to form new compounds with distinct optical characteristics. As a result, the treated papyrus samples’ Lightness (L* value) may decrease.

The structure of the papyrus fibers may have changed because of the chemical treatment, changing how light scattering occurs in them. This might also have something to do with the apparent decrease in lightness treated.

The material’s surface properties may have changed as a result of the oil’s interaction with the papyrus fibers, causing a decrease in lightness.

To give the appearance of darkness, the oils may have added more pigments or compounds that absorbed light.

Furthermore, as demonstrated by the results, the lavender oil-treated papyrus samples showed a lower lightness (L* value) than the camphor oil-treated papyrus samples. This could be the result of one or more of the following causes:

The natural qualities of the oils. The treatment of papyrus can take on a different appearance due to the stronger scent and darker color of lavender oil. The darker color of lavender oil may have contributed to the lower lightness value observed in the samples treated with it.

Papyrus fibers may have become less light as a result of an interaction between the chemical components of lavender oil, which include substances like linalyl acetate and linalool. However, the lighter color and distinct chemical makeup of camphor oil may have had a less noticeable impact on the treated papyrus samples’ lightness.

There may be a noticeable variation in the lightness values of the treated papyrus samples due to the molecular structure of the compounds in lavender oil absorbing or scattering light differently than the components in camphor oil.

The observed variations in lightness values are probably the consequence of these variations in oil properties, which also affected the papyrus samples’ visual appearance.

The results indicated that the a* values consistently leaned towards the red color spectrum. The heat-aged untreated samples showed a* value of 6.97 compared to 6.13 for the control sample. The red color (a* value) of the heat-aged untreated papyrus sample was higher than the control sample due to the following reasons:

Thermal decomposition

The untreated papyrus sample underwent thermal degradation as a result of the heat aging process, which altered its chemical composition. The red color component of the sample was probably impacted by this degradation, which led to a high in the a* value.

Oxidation

The untreated papyrus samples’ color properties may have been changed by oxidation reactions brought on by the heat aging process.

Alterations in structure

The untreated papyrus samples’ light absorption and reflection characteristics may have been impacted by structural alterations brought on by the high temperatures experienced during heat aging. The higher a* value indicates that these changes might have played a role in the observed increase in the intensity of the red color.

Thermal stress

The untreated papyrus sample may experience thermal stress during the heat aging process, which changes its chemical and physical characteristics. The sample’s red color components may have been disturbed by this stress, which would explain the higher a* value in comparison to the control sample.

Consequently, the increase in the red color (a* value) of the untreated papyrus sample in comparison to the control sample was probably caused by a combination of thermal degradation, oxidation, structural alterations, and thermal stress during heat aging. The control and heat-aged untreated samples had higher* values than the treated samples with different oil concentrations. This could be the result of the following factors:

Lavender essential oil is known for its high levels of linalool and linalyl acetate, with moderate amounts of terpinene-4-ol, lavandulyl acetate, and lavandulol, and varying levels of eucalyptol (1,8-cineol) and camphor36. Camphor oil, on the other hand, is rich in camphor, cineol-1,8, and limonene37. These compounds interact with papyrus fibers. The red color (a* value) of the treated papyrus samples increased compared to the control and aged untreated samples.

Volatile organic compounds found in lavender and camphor oils can permeate papyrus fibers and react with the materials’ chromophores to change the intensity of the red color.

The chemical constituents of lavender38,39,40,41,42 and camphor oils40,41, such as linalool and camphor, can enhance the red hue of the papyrus by either increasing the absorption of red light or altering the molecular structure of the chromophores responsible for the red color.

The reason the treated samples remained redder than the control and aged untreated samples could be due to a chemical reaction that occurs between the oils and the papyrus fibers, stabilizing the red color and preventing it from fading or changing over time.

The ability of lavender and camphor oils to preserve and enhance the red hue of the papyrus material is responsible for the increase in red color (a* value) of the treated papyrus samples. These unique chemical properties of oils explain this phenomenon.

The results indicated that the control sample, heat-aged untreated sample, and treated samples with oils at various concentrations all exhibited a yellow color. The b* value of the control sample was 20.34, which decreased to 21.50 in the heat-aged untreated sample. This may be due to one or more of the following reasons:

Heat exposure may alter the chemical appearance of papyrus, causing the color that gives it its yellow hue to increase.

The color properties of papyrus can be impacted by high temperatures, as they can hasten the degradation of organic compounds within it.

There could have been a shift towards a different color spectrum as a result of the heat creating new compounds or changing the molecular structures of already existing ones.

The papyrus samples’ yellow color can also be attributed to oxidation reactions brought on by heat.

The prolonged exposure to heat may have caused physical changes in the papyrus fibers, affecting their ability to reflect light and altering the perceived color.

After heat aging, the untreated sample had a total color difference (ΔE) of 1.61. The samples treated with lavender oil showed ΔE values of 1.00, 1.99, and 2.42 at concentrations of 0.5%, 0.75%, and 1.0%, respectively. For the samples treated with camphor oil, the ΔE values were 1.13, 1.65, and 1.51 at concentrations of 0.5%, 0.75%, and 1.0%, respectively. The data indicated that the total color changes were minimal at the first concentration of lavender and camphor oils, less than 2. Additionally, the ΔE values at the second and third concentrations of camphor oil were less than 3, while they exceeded 3 for the samples treated with lavender oil at the same concentrations.

Based on the results of color change, which is one of the most important criteria for selecting treatment materials, a concentration of 0.5% was chosen for both lavender oil and camphor oil, as the color change results were less than 2, to ensure no color changes. The color changes cannot be seen with the naked eye up to 3. Previous studies35,42 have demonstrated that a total color difference of less than 3 is imperceptible to the naked eye. Although the overall color change for the concentrations with camphor oil did not reach 3, they were excluded to ensure no color change. The value L* value was higher in these concentrations compared to the control and heat-aged untreated samples.

It can also be added that the concentrations of 0.75% and 1.0% were rejected because, at higher concentrations, the oils may have interacted more strongly with the papyrus, causing a more noticeable color change. The increased concentration of the oils could have also led to a more pronounced chemical reaction with the papyrus material itself, resulting in a more significant alteration in color.

It can be added that the treated samples of antioxidant oils (lavender and camphor oils) at a concentration of 0.5% exhibited less change in the total color value compared to the control and heat-aged untreated samples due to their ability to inhibit oxidation processes. Antioxidant compounds present in these oils, such as linalool in lavender oil and camphor in camphor oil, effectively scavenge free radicals and prevent the degradation of color in the samples42,43,44,45.

When exposed to oxidative stress, colors in the samples undergo chemical reactions that lead to changes in their structure and appearance. However, the presence of antioxidants in the oils intercepts the free radicals generated during oxidation and neutralizes their damaging effects on the color pigments. This protective mechanism helps maintain the original color intensity and stability of the samples, resulting in less overall change in the total color value.

Furthermore, the antioxidant properties of lavender and camphor oils contribute to their ability to preserve the color quality of the samples by delaying the onset of oxidation reactions. By inhibiting the formation of reactive oxygen species and other oxidative byproducts, these oils effectively extend the shelf life of the color pigments and prevent color deterioration.

To evaluate the protective effects of lavender and camphor oils on papyrus against oxidation from accelerated heat and light aging, samples were treated with a 0.5% concentration of these oils. The results of the accelerated heat aging were discussed earlier. During accelerated light aging, exposure to UV radiation led to bleaching of the samples, resulting in a slight increase in lightness (L* value)46 compared to the control sample. The increase in lightness of the papyrus sample compared to the control may be attributed to:

UV radiation breaks down the chromophores present in the papyrus fibers, leading to a reduction in the intensity of color pigments. This breakdown results in a lighter appearance of the papyrus sample.

The exposure to UV radiation causes photochemical reactions that alter the chemical structure of the papyrus fibers, leading to a bleaching effect. This bleaching effect contributes to the increase in lightness (L* value) of the papyrus sample.

UV radiation accelerates the degradation of lignin and other organic compounds present in the papyrus, which are responsible for the yellowing or darkening of the material. As these compounds degrade under UV exposure, the papyrus becomes lighter in color.

The prolonged exposure to UV radiation can also lead to the oxidation of organic compounds in the papyrus, further contributing to the lightening effect by breaking down the molecules responsible for the darker hues.

The accelerated light aging process using UV radiation effectively simulates the natural aging of the papyrus material, causing chemical changes that result in a significant increase in lightness (L* value) compared to the control sample that did not undergo such accelerated aging.

The L* value of the sample treated with lavender oil was 80.51, while the aged treated samples recorded 78.48 for heat aging and 80.68 for light aging. For the sample treated with camphor oil, the L* value was 80.14, compared to 78.48 for heat aging and 80.68 for light aging. Overall, there were no significant changes in the L* value (Table 1).

The a* value of the untreated sample after light aging was 6.53, which was less than the control and heat-aged untreated samples. The a* value of the treated sample with lavender was lower than the control and the aged untreated sample. The a* value of the aged treated samples increased compared to the untreated sample (Table 1).

Table 1 Change of color measurement as a preliminary study of papyrus samples treated with camphor and lavender oils at different concentrations
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The b* value of the untreated sample after light aging was 16.50, which was lower than the control and heat-aged untreated sample. This value decreased in the aged treated sample compared to the heat and light aged treated samples.

The total color difference (ΔE) of the untreated sample exposed to light aging was 5.48.

The samples treated with lavender oil showed an ΔE of 3.64, and with camphor, it was 4.07, indicating good results. The total color changes of the heat-aged samples showed less change compared to the light-aged samples (Table 2).

Table 2 Change of color measurement of papyrus samples treated with lavender and camphor at 0.5% before and after different accelerated aging methods
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pH measurement

The measurement of pH is vital for assessing the stability and condition of treated papyrus samples with lavender and camphor oils before and after accelerated heat and light aging methods.

Measuring pH before aging can provide important information about the initial state of the treated samples and help determine the effectiveness of the oil treatment in preserving the papyrus. A stable and balanced pH level indicates that the oils have successfully penetrated the fibers of the papyrus and are providing protection against thermal and light aging.

After accelerating aging, pH measurement becomes even more important as it can reveal any changes in the chemical composition of the treated samples due to the aging process. A significant shift in pH towards acidity or alkalinity may indicate that the oils have degraded or reacted with the papyrus fibers, potentially leading to accelerated deterioration.

By monitoring the pH of the treated papyrus samples before and after accelerated aging, researchers can gain insights into the long-term effectiveness of the oil treatment and make informed decisions about the preservation and conservation of these valuable artifacts.

The results (Table 3) showed that the pH value of the control sample was 8.7. The high pH value of the control sample may be due to some additive materials during the manufacturing process. References 47,48 reported that papyrus sheets were treated with different materials to prepare the surface for writing. She also reported that the Nile River contains hydrated aluminum silicates, organic matter, iron oxides, and quartz. She also said that clay suspended in water can be added during the papyrus manufacture to make papyrus fibers denser and less absorbent. She confirmed that the elemental analysis proved that clay addition was provided in the manufacturing process. It can be added that papyrus sheets are often soaked in water during the manufacturing process to make them pliable and easier to work with. This water can contribute to the alkaline sheet, as water with a pH above 7 is considered alkaline.

Table 3 pH measurement of the treated papyrus samples with lavender and camphor oils at a concentration of 0.5% before and after heat and light accelerated aging
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The results also showed that the heat and light aging methods affected the pH value, which was recorded as 8.0 for the heat-aged untreated sample and 7.5 for the light-aged sample. The decrease in pH value may be due to the deterioration of cellulose (the main component of papyrus), which releases acidic substances that can lead to the decreased pH value. The oxidation process can lead to the formation of acidic byproducts. These byproducts can contribute to the decrease in pH of the papyrus. The hydrolysis process caused by aging can also promote hydrolysis, a chemical reaction where water molecules break down the papyrus fibers. This process can release acidic components.

The results indicated that the pH of the sample treated with lavender oil was 7.3, slightly lower than the initial value of 7.2 and the value of 7.4 after accelerating heat and light aging. For the sample treated with camphor oil, the pH was 7.6, which decreased to 7.5 after both heat and light aging. This decrease in pH may be attributed to the aging process, which accelerates the chemical reaction between the oils and the papyrus, potentially releasing acidic substances and causing a slight pH decrease.

XRD analysis

The results of the XRD analysis (XRD) are presented in Fig. 2 and Table 4. The results show that the initial WAXS diffractograms of untreated papyrus samples and those treated with camphor oil may be the same. This finding suggests that the treatment with camphor oil does not particularly affect the size and shape of crystallites in the papyrus, but the treatment slightly increases the crystallite size of the longitudinal dimension. While the results show that there is a significant change in the initial WAXS diffractograms of untreated papyrus samples and those treated by the lavender oil, The results show that treatment by the lavender oil caused the crystallite size of the longitudinal dimension of papyrus samples to decrease markedly; also, their lateral dimension and crystallinity index changed (see Fig. 2).

Fig. 2: X-ray diffraction analysis of the untreated and treated papyrus samples before and after aging.
figure 2

X-ray diffraction analysis of the untreated and treated papyrus samples before and after accelerated heat and light aging methods: (A) New papyrus sample (control), (B) Heat aged untreated sample, (C) Light aged untreated sample, (D) The treated sample with camphor oil, (E) The treated sample with camphor oil after heat aging, (F) The treated sample with camphor oil after light aging, (G) The treated sample with lavender oil, (H) The treated sample with lavender oil after heat aging, (I) The treated sample with lavender oil after light aging.

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Table 4 The crystallinity index of cellulose of the treated papyrus samples with lavender and camphor oils at a concentration of 0.5% before and after heat and light accelerated aging
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The results show that there is little change in the crystallinity index of cellulose of treated and untreated papyrus after aging by heat or ultraviolet radiation. This may be due to the occurrence of glycosidic bond breakage that causes a decrease in the crystallinity index of cellulose when exposed to heat or ultraviolet radiation46. The camphor oil treatment was superior to the lavender oil treatment. For the samples treated with camphor oil, there was no noticeable decrease compared to the standard sample, indicating the extent of thermal and chemical stability of camphor oil even after exposure to aging, as the crystallinity index of cellulose in the sample treated with camphor oil was 54.5% while it was 59.8% in the heat aged untreated sample. In the case of UV aging, there was a slight increase from 54.2% in the light-aged untreated sample to 58.9%. In contrast to the lavender oil treatment, which caused a decrease in the samples from 59.8% in the heat aged untreated sample to 40.4% in the treated sample, and the samples treated with lavender oil after UV aging had a severe decrease in the crystallinity index of cellulose from 54.2% in the light aged untreated sample to 32.6% in the heat treated sample. Because of unstable to UV aging that caused a decrease in the crystallinity index of cellulose in the light aged untreated sample, so lavender oil did not produce high efficacy as an antioxidant when compared to camphor oil, indicating that lavender oil is not thermally or UV stable (Fig. 2 and Table 4).

Fourier transform infrared analysis (FTIR)

FTIR data are presented in Fig. 3 and Table 5 for camphor oil, representing the signal peaks of the main compounds of camphor C-OH bending and C=C stretching observed at 1743 cm−1 and 897 cm−1. Additionally, C-H bending for lavender appeared at 1419 cm−1–1421 cm−1 48,49,50.

Fig. 3: The functional groups of the treated samples and the control samples.
figure 3

The treated papyrus samples with lavender and camphor oils at a concentration of 0.5% before and after heat and light-accelerated aging were compared to the control samples.

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Table 5 functional groups of standard samples compared to samples treated with camphor oil and lavender oil before and after UV and thermal aging
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It was clear from the data obtained (Fig. 3 and Table 5) that distinct regions of cellulose structure, which belong to O-H vibrations, appeared at the wavenumber of 3340 cm−1 for the unaged papyrus sample (control). This wavenumber shifted to lower values with heat (3309 cm−1) and light (3328 cm−1) treatments, respectively. The wavenumbers of the treated and aged treated samples with lavender oil ranged from 3327–3328 cm−1, indicating that no significant changes were observed. For the treated and aged treated samples with camphor oil, there was an increase in the wavenumbers, ranging from 3334 to 3348 cm−1. The band intensity of the O-H vibration was 0.01 for the control sample, 0.03, and 0.04 for the heat and light-aged untreated samples. All intensities of the treated and aged treated samples with oils used were 0.02, which indicated the stability of the treated samples against the artificial aging techniques used.

The wavenumber in the range of 2915 to 2920 cm−1 corresponds to C-H stretching vibrations. A distinct C-H band was observed at 2919 cm−1 for the control sample and at 2918 cm−1 for the heat-aged untreated sample. The wavenumbers of treated and aged treated samples with the oils used ranged from 2918 to 2920 cm−1, except for the light-aged treated sample with lavender at a concentration of 0.5%, which appeared at a wavenumber of 2915 cm−1. This indicated that no significant changes were observed. The intensities at this band were approximately the same except for the treated sample with lavender (0.93) at a concentration of 0.05%, and for the heat-aged treated sample (0.94) with camphor at a concentration of 0.5%.

The bands ranged from 1600 to 1643 cm−1 for the control, aged untreated samples, treated, and aged treated samples, respectively referred to as H-O-H deformation vibration, and also referred to as O-H in-plane bending vibration of adsorbed water, which was broad in the control sample compared to the heat and light-aged untreated samples. This was stronger than the control, indicating the loss of more water. The treated and aged treated samples with oils used shifted to higher wavenumbers compared to the aged untreated samples and ranged from 1612 to 1620 cm−1.

The bands at wavenumbers between 896 to 1155 cm−1 refer to various C-O stretching, C-O-C, and C-C-O bending vibrations. The wavenumbers and absorbance intensities at these bands are approximately the same in all samples studied and range from 1154 to 1159 cm−1 and from 896 to 899 cm−1.

The band ranging from 1416 to 1420 cm−1 is related to cellulose structure and refers to H-C-H and O-C-H in-plane bending vibrations. It was noticed that there were no significant changes in both wavenumbers and intensities at this band.

The data revealed pronounced alterations in the untreated samples subjected to heat and UV aging compared to the control group, likely attributable to oxidative processes triggered by thermal and ultraviolet radiation exposure. Conversely, negligible differences were observed between the treated and aged treated samples and the untreated samples exposed to heat and light aging. This suggests that the application of lavender and camphor oils had a minimal impact on the chemical composition and structural integrity of the papyrus material. The consistency of wavenumbers and intensities indicates that the oils did not compromise the molecular structure of the papyrus fibers at the tested concentration. The findings indicate that the application of essential oils is an effective method for protecting papyrus from the deterioration effects of artificial aging induced by ultraviolet radiation. These oils are distinguished by their eco-friendly nature and pose no health risks to conservators. Notably, camphor oil exhibits antioxidant properties without causing discernible color changes or adverse effects on fibers or cellulose crystallinity or pH values and the functional groups of papyrus, in comparison to standard samples subjected to artificial aging via ultraviolet exposure. Consequently, the use of essential oils emerges as an environmentally friendly technique and a foundational element for advanced studies aimed at preserving and protecting papyrus manuscripts from various deterioration factors.