Abstract
Unfortunately, papyrus has not been sufficiently studied regarding improvement of the mechanical or optical properties, which degrade under the impact of aging factors over time. The aims of this research were studying the effects of hydroxypropylcellulose (HPC) loaded with 0.25% of ZnO nanoparticles (NP) at different concentrations (1% and 2%) on papyrus sheet properties before and after aging. Various analyses were used, such as visual assessment by a universal serial bus (USB) digital microscope, mechanical properties, Fourier-transform infrared (FTIR) analysis, color change, and pH measurement. A dramatic increase in mechanical properties was observed after treatment. Besides, FTIR illustrated increasing of CH2 and OH stretching, which contribute to increasing the cellulose crystallinity index. There was no significant change in pH values after treatment or ageing. Slight changes of optical characteristics were observed for treated samples, after the artificial aging of the treated samples, the mechanical measurements showed that the values of tensile strength and elongation were close to the values of the standard sample, which may contribute to preventive protection of ZnO NP for treated samples from the artificial ageing.
Download PDF
Full Article
Hydroxypropyl Cellulose Loaded with ZnO Nanoparticles for Enhancing the Mechanical Properties of Papyrus (Cyperus papyrus L.) Strips
Rushdya Rabee Ali Hassan,a Salwa Moustafa Amer Mahmoud,a Marina Atef Nessem,a Reham Tarek Abdel Aty,a Mariam George Ramzy,a Eldessoky S. Dessoky,b Ahmed Abdelkhalek,c and Mohamed Z. M. Salem d,*
Unfortunately, papyrus has not been sufficiently studied regarding improvement of the mechanical or optical properties, which degrade under the impact of aging factors over time. The aims of this research were studying the effects of hydroxypropylcellulose (HPC) loaded with 0.25% of ZnO nanoparticles (NP) at different concentrations (1% and 2%) on papyrus sheet properties before and after aging. Various analyses were used, such as visual assessment by a universal serial bus (USB) digital microscope, mechanical properties, Fourier-transform infrared (FTIR) analysis, color change, and pH measurement. A dramatic increase in mechanical properties was observed after treatment. Besides, FTIR illustrated increasing of CH2 and OH stretching, which contribute to increasing the cellulose crystallinity index. There was no significant change in pH values after treatment or ageing. Slight changes of optical characteristics were observed for treated samples, after the artificial aging of the treated samples, the mechanical measurements showed that the values of tensile strength and elongation were close to the values of the standard sample, which may contribute to preventive protection of ZnO NP for treated samples from the artificial ageing.
Keywords: Papyrus; Consolidation; Hydroxypropyl cellulose; ZnO nanoparticles; FT-IR
Contact information: a: Conservation Department, Faculty of Archaeology, Cairo University, Giza 12613, Egypt; b: Department of Biology, College of Science, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia; c: Plant Protection and Biomolecular Diagnosis Department, ALCRI, City of Scientific Research and Technological Applications, New Borg El Arab City, Alexandria 21934, Egypt; d: Forestry and Wood Technology Department, Faculty of Agriculture (El-Shatby), Alexandria University, Alexandria 21545, Egypt;*Corresponding author: zidan_forest@yahoo.com
INTRODUCTION
Since the time of ancient Egypt, papyrus (Cyperus papyrus, Cyperaceae) has been used in the creation of writing materials and the production of laminated layers, where the natural juices occurring in papyrus strips are sufficient to bond them into a sheet (Owen and Danzing 1993; Leach 2009).
Papyrus is composed of fibrous materials (Elnaggar et al. 2015), which are 97% cellulose, hemicellulose, and lignin and 3% proteinaceous materials (Menei 2015). The lignin content ranges from 12% to 34% (Katuščak et al. 2006). Papyrus is made using part of the papyrus stem: its outer shell is removed (Leach 2009; Taha et al. 2019), and the stem is formed to strips, which are moistened with water and placed on a board (Scora and Scora 1991; Taha et al. 2019). Then, another layer of strips is placed on top of them at right angles (Owen and Danzing 1993). They are squeezed together by wrapping them with a cylinder and are then dried (Basile 1972). During manufacturing and handling of papyrus, the sheets can become contaminated with salt particles or dirt, which have negative effects when the consolidated materials are applied and especially affect the mechanical strength (Elnaggar et al. 2015).
Unfortunately, there are also several degrading factors affecting papyrus, such as high temperature, humidity, light, air pollution gases, manufacturing processes, and poor storage (Franceschi 2011), which cause decomposition by oxidation and acidification. The latter leads to the weakness and fragility of the papyrus (Ibáñez Domínguez 2019). Therefore, consolidation of the papyrus surface fibers is often necessary before further treatment is begun.
Several materials are used for cellulosic conservation as supports, such as starches, gums, cellulose ether, and proteins (Hamburg 1988). The preparation of durable and efficient materials for conserving cellulosic supports is of great importance, and new technologies have emerged for conservation processes, including nanotechnologies (Giorgi et al. 2002; Ali et al. 2018; Hassan and Mohamed 2018; Salem et al. 2019; Salim et al. 2020), which allow production of minute objects as small as a nanometer (Hahn 2011).
Zinc oxide (ZnO) nanoparticles (NPs) have been used for many purposes, such as wear proofing for rubber composites (Chen et al. 2017), strong UV absorption in cosmetics and sunscreen (Jiang et al. 2018), antimicrobial agents, and UV blocking and deodorant in the textile industry (Raguvaran et al. 2015). Zinc oxide NPs with cotton fabrics or paper sheets showed good antimicrobial properties (Sricharussin et al. 2011, Khojasteh Khosro et al. 2016; Khalaji et al. 2019). Zinc oxide NPs have a good self-cleaning function on surfaces when applied in the presence of UV light, where it prevents dust or dirt accumulation on the surface (El-Fekyet al. 2014).
The authors found a general lack of studies of the use of ZnO as a consolidating agent. Most of the papers mentioned it as an antifungal and antibacterial agent. Consequently, this study used hydroxypropyl cellulose (HPC) as a loading material for ZnO NPs in the process of consolidation for the papyrus. The most important property of HPC is its solubility in water and polar solvents, and it is used to strengthen fragile and weak materials (Martin et al. 2011) and as an adhesive (Gill and Boersma 1997). It was subjected to acid hydrolysis and can be made alkaline to a pH of 6 to 8 with ammonium hydroxide, such that it can protect water-soluble colors (Hamburg 1988). This study evaluated the effects of HPC and HPC loaded with ZnO NPs on the mechanical and optical properties of the papyrus under accelerated aging.
EXPERIMENTAL
Transmission Electron Microscopy (TEM) Examination of ZnO NPs
The morphological analysis of the prepared ZnONPs (Sigma-Aldrich, Darmstadt, Germany) was performed via TEM using a JEM-1230 electron microscope (JEOL Ltd., Tokyo, Japan) operated at 60 kV. Before taking a TEM image, the sample was diluted at least 10 times by water. A drop of well-dispersed diluted sample was placed onto a copper grid (200 mesh and covered with a carbon membrane) and dried at ambient temperature (Abo Elgat et al. 2020).
Papyrus Samples and Accelerated Ageing
Papyrus plant was obtained from the village of Al-Qaramous, Abu-Kabir, Sharqia Governorate, Egypt. The papyrus specimens (Fig. 1) were prepared according to the method of strips stated by relevant studies of archaeological papyrus. The specimens were exposed to artificial aging at the National Institute of Standards (NIS), Giza, Egypt. The thermal aging was at 80 °C, and the relative humidity was 65% (ISO 5630-31996). Brushes were used in the application of consolidation materials. The specimen with the best results was subjected to a second period of accelerated aging (80 °C and 65% relative humidity. The time frame for the accelerated ageing (1st and 2nd time) was 5 days, which corresponds to 120 h and 50 years of the artificial aging (ISO 5630-3 1996). Aging was performed for all the original samples to reach a state similar to the archaeological samples, and then the treatment process was performed. All samples were evaluated using pH measurement – infrared spectroscopy – digital microscope examination, color change and mechanical properties. Based on all these multiple analyses, the best concentration was chosen, which was subjected to accelerating ageing for the second time, which makes the study integrated and smooth in a logical scientific way (Kolar et al. 2003; Kamel et al. 2004; Princi et al. 2005).
Fig. 1. (A) The treatment of papyrus samples with HPC; (B) treated samples with HPC loaded with ZnO NPs in different concentrations by the brushes; (C) during application; and (D) after application
HPC and ZnONPs
Hydroxypropyl cellulose (Klucel G, CTS Srl, Altavilla Vicentina, Italy) and ZnO NPs were chosen as consolidates. Concentrations of 1% and 2% of HPC in 95% ethyl alcohol were used. The steps of preparation as the following: i) 1% of HPC:100 mL of ethyl alcohol were added inside a glass flask and 1 grams of hydroxypropyl cellulose (Klucel G) was measured and added to it. The mixture was stirred until complete dissolution ii) 2% of HPC: 100 mL of ethyl alcohol were added inside a glass flask and 2 grams of hydroxypropyl cellulose (Klucel G) was measured and added to it. The mixture was stirred until complete dissolution. The ZnO NP powder (Sigma-Aldrich, Darmstadt, Germany) was added to the 1% and 2% HPC solutions at a ratio of 0.25 wt% based on the weight of dry HPC after mixing, and the mixture was stirred again for 30 min. The solutions were homogenized using a high-shear homogenizer at 10,000 rpm (CAT high-speed homogenizer, Gmbh, Shanghai, China). The prepared consolidation solutions were applied to the papyrus samples by brushing (the aim of this paper is presenting a new consolidate for archeological papyrus. In the field of conservation of papyrus, the conservators use the brush in most the conservation treatment because papyrus is a very sensitive weak object. Therefore, immersion treatment is not recommended). Then, the samples were left to dry at room temperature. Samples were evaluated via several analyses.
Universal Serial Bus (USB) Digital Microscope
A USB digital microscope (200×) (model PZ01; Shenzhen Super Eyes Co., Ltd., Guangdong, China) was used for visual assessment of experimental samples.
Fourier-transform Infrared (FTIR) Analysis
Fourier-transform infrared analysis was used to monitor the chemical composition and changes that occurred in the papyrus due to treatment. The samples were analyzed with an FTIR spectrometer (Model6100, Jasco, Tokyo, Japan). The spectra were obtained in the transmission mode with a triglycine sulfate (TGS) detector using the KBr method and represent 2-mm/s co-added scans in the spectral region from 4000 cm-1 to 400 cm-1, with a resolution of 4 cm-1 (Salim et al. 2020).
Color Change in the CIELAB System
The colors of the samples were measured with an Optimatch 3100 (Model No. CE 3100. Serial No. 31013780698, SDL, UK). All samples were measured in the visible region, i.e., a wavelength range from 400 nm to 700 nm, with an interval of 10 nm using a D65 light source and an observed angle of 10°. The colorimetric coordinates L, a, and b of the CIELA B color space were used to express color change. The CIELAB color space is organized in a cubic form. The L axis runs from top to bottom. The maximum for L is 100, which represents white. The minimum for L is zero, which represents black. The a and b axes have no specific numerical limits. Positive a is red, while negative a is green. Positive b is yellow, while negative b is blue (Sehlstedt-Persson 2005; Calienno et al. 2015; Hassan 2015a). The total color change of all treated papyrus was expressed as ΔE, according to the following Eq. 1,
(1)
where (∆L)², (∆a)², and (∆b)² are the differences between the values of the color indices before and after treatment.
pH Measurement
pH values were measured by a cold extraction method according to ASTM D778-97 (2002) at room temperature using a pH meter. The samples were cut, with 50 g for one sample, and were put in 40 mL of distilled water (pH = 7) for the measurement of the papyrus acidity (ISO 187 1990; Salim et al. 2020). The samples were soaked for 6 h.
Mechanical Properties Measurement
Before measurement, all papyrus samples (15 cm in length and 1.5 cm in width) were conditioned according to ISO 187 (1990), at a temperature of 23 °C and a relative humidity of 50% for 24 h (ISO 1924-3 2005). The mechanical properties of the samples were performed in compliance with ISO 187 (1990).
Using a testing machine (H5KT, SDL Atlas, Borås, Sweden) at the National Institute for Standards (NIS), at 25 °C and a cross-head speed of 50 mm/min. The mean values of tensile strength and elongation were calculated from 3 measurements with a precision in the ±10% range. The sample was cut in the machine direction. The brushes were used in applying the treatment.
RESULTS AND DISCUSSION
TEM of ZnO NPs
Electron microscopy is an excellent tool for characterizing features of NPs (Ao et al. 2006). The ZnO NPs were spherical, according to the TEM results shown in Fig. 2.
Fig. 2. Image of TEM examination of the prepared ZnO NPs (A), (B) confirmed that the size of partials is 0.26 nm.
It is clear from Fig. 2 that the synthesized ZnO NPs were single-crystal particles, with moderate agglomeration and a reasonably narrow particle size distribution. It was also noted that, at room temperature, they exhibited clear crystal faceting, suggesting substantial crystallinity. In addition, the particle sizes and the size distribution were much lower than that already reported by mechanic-chemical reaction (Gedamu et al. 2014). Furthermore, particle size measurements from the TEM images were higher than those obtained from X-ray diffraction (Scherrer’s formula), as the size reached 21 nm (Look 2001; Emamifar et al. 2010).
USB Digital Microscope
No visual change was detected by the naked eye, but the microscope examination showed black impurities (Fig. 3). These impurities may be a result of the papyrus manufacturing process (Scora and Scora 1991; Leach 2009). Figure 3 shows that the fibers became less transparent, compared to the untreated sample, which indicates increased thickness of the treated fibers from the absorption of HPC inside the cells of the cellulose fibers in the papyrus. The digital microscopy examination showed that the industrial aging processes did not affect the fibers, and the fibers were coherent. However, slight brightness was observed on the papyrus surface after ageing.
FTIR Analysis
The IR spectra of the reference sample showed the same basic structure as all the cellulosic samples (Calienno et al. 2015; Hassan et al. 2020; Salim et al. 2020). Results are listed in Table 1.
Table 1. Changes in Functional Groups of Treated Papyrus
