Plant tannin and chitosan-templated cellulose for improved absorption of UV protective natural chromophores
Graphical abstract
Introduction
The stratospheric ozone layer filters out harmful ultraviolet radiation (UVR) and protects lives on earth. Rapid industrialization accelerating the depletion of the ozone layer and thus, increasing UV radiation levels at the earth's surface (Fang et al., 2019; Fuentes-León et al., 2020). Though the introduction of the Montreal Protocol in 1987 controlled the ozone layer depletion, the process is very slow, and it may take this century to return to pre-1980 levels and subjected to the controlled use and production of ozone-depleting compounds (Hossaini et al., 2017; Barnes et al., 2019). Exposure to UV radiation (UV–B) may cause skin cancer, malignant melanoma development and damage eye's lens. In this context, protective coverings like apparel, gloves, umbrella, curtain etc. against UV radiation could be an excellent preventive measure to mitigate the UV exposure. Cellulosic materials as a substrate for UV protective functionalization are advantageous because of their biodegradability, skin-friendliness, comfort, low cost etc. (Varghese and Mittal, 2017; Venkatesan and Periyasamy, 2019). Different fabrication techniques to produce cellulose-based UV protective products have been extensively reported by the researcher in the last couple of decades (Dubrovski and Golob, 2009; Wong et al., 2016). However, pristine cellulose is transparent to UV rays due to the absence of carbon-carbon double bonds in their chemical structure (Davis et al., 1997). To minimize the UVR transmission, UV-protective finishing such as UV absorbers (Oda, 2011), films (Sadeghifar et al., 2017), polymers (Tang et al., 2015), finishing agents (Alebeid and Zhao, 2017), etc. have been applied on the cellulose substrates. Though synthetic chemicals have outstanding UV protective characteristics, they are mostly not ecofriendly and lack biocompatibility for applications like skin coverings and food packaging. Long term exposure to synthetic chemicals poses the risk of skin infections and cancer (Anderson and Meade, 2014). Recently, different UV protective chromophores (UVPNCs) extracted from the biowaste of plant and fruits, leaves, flowers, herbs, and vegetables have proved their comparable UV shielding capacity with the synthetic chemicals (Islam and Mohammad, 2015; Haji and Naebe, 2020; Sanda and Liliana, 2021; Haule et al., 2019; Elsahida et al., 2019). These natural extracts are comprised of wide varieties of chromophores such as tannin, flavonoid, carotenoids, chlorophyll, anthocyanin, betacyanin, anthraquinone, curcuminoids, monascus, betalains, bixin etc. (Islam and Mohammad, 2015; Liman et al., 2020a). The UVPNCs possess distinct ionic nature, solubility, pH stability, protonation, molecular weight and geometry, thermal stability etc. which govern the chromophore-cellulose binding and UVR transmission. Therefore, it is of utmost importance to screen various UVPNCs and understand their reactive chemistry, adsorption behavior and shielding capacity for developing high performing UV protective cellulose-based materials. However, several challenges exist to use these UVPNCs for UV protective applications. The anionic nature of UVPNCs is the major challenge because they demonstrate poor reactivity to cellusate ion resulting in poor durability to laundering (Gulzar et al., 2015). Besides, the significant crystalline region of cellulose barely absorbs UVPNCs and shows poor UV shielding capacity (Liman et al., 2020b). Therefore, surface modification of cellulose is crucial to improve the fixation of UVPNCs.
Treating cellulose with metal ions endow functional sites which increase the bonding stability between cellulose and UVPNCs (Islam et al., 2021a). Unfortunately, these metallic ions (mordant) treatment is not viable due to the large residues of unreacted metals in the reaction bath. Besides, the dermal exposure of these metallic mordanted substrates in wet or sweating conditions leads to the migration of metals from substrates to human skin (Rovira et al., 2017). Therefore, different types of green cross-linkers for bio-activation of cellulose are being used by the researcher (İşmal and Yildirim, 2018). For example, tannin based polyphenolic compounds from pomegranate, myrobolan, emblica, gallnut, catechu etc. exhibited excellent performance against UVR (İşmal and Yildirim, 2018). Tannin based polyphenols have higher absorbance intensity in the UV region (200–400 nm), as a result, they could intrinsically impede the UV ray to penetrate inside the cellulose (Li et al., 2019). The major benefit of using these tannins based polyphenols as bio-activator of cellulose is that, they have both hydroxyl (-OH) and carboxylic (-COOH) sites in their molecular structures (Prabhu et al., 2011), which could enhance the chromophores absorption and demonstrate high UV protection (Islam and Mohammad, 2015).
Additionally, different biopolymers derived from starch (Balakrishnan et al., 2018) and crustacean shells (Fortunati et al., 2018) have also been used to improve the UV shielding capacity of cellulosic polymer. Among them, chitosan is a polysaccharide and comprised of β-1,4-linked polymer of 2-amino-2-deoxy-d-glucose (Ebnesajjad and Modjarrad, 2014). Chitosan is obtained by alkaline deacetylation of chitin which is mostly derived from marine sources, e.g., crustacean shells (Fortunati et al., 2018). The amino group (-NH2) in the chitosan backbone creates cationic functional sites in cellulose and improve the reactivity of cellulose towards anionic natural chromophores. Furthermore, treating cellulose with tannin based polyphenols and chitosan endow π- π and lamellar stacking of cellulose crystals and reorient the inter and intramolecular H-bonding configuration (Hu et al., 2017; Sampath et al., 2017). The reoriented H-bonding leads to higher surface area and anchoring sites for better fixation of UVPNCs. Thus, tannins and chitosan could impart several multi-functional properties in cellulose such as UV shielding, antimicrobial, and anti-creasing properties, etc. (Islam and Mohammad, 2015; Massella et al., 2019). Therefore, the activation of cellulose with natural cross-linkers and the proper understanding of the impregnation mechanism of activated cellulose surface with UVPNCs is important to achieve higher UV shielding property. To the best of our knowledge, no study has investigated the influence of plant-tannin and chitosan cross-linker in cellulosic molecular arrangement reorientation and their corresponding impregnation mechanism with UVPNCs extracted from banana floral stem (BFS).
In this study, we used BFS extract as a source of UVPNCs, which principally comprised of several chromophores namely condensed tannins, flavonoids, anthraquinones, anthocyanins and beta-cyanines. The active UVPNCs were confirmed by the phytochemical screening of BFS extracts and their exhaustion and fixation behaviors were determined for the proper understanding of inherent impregnation behavior of UVPNCs into cellulose. Besides, different types of natural (tannin enrich plant polyphenols, chitosan biopolymer) and commercial cross-linkers (metallic salts, commercial tannic acid) were used to modify the molecular orientation of the cellulosic chain which was expressed in term of total crystallinity index (TCI), lateral order index (LOI), hydrogen bond intensity (HBI), hydrogen bonding energies (EH), hydrogen bonding distances (R) and asymmetric factor (AF). The UV shielding ability of plant tannins and chitosan templated UVPNCs impregnated cellulose was determined and further compared with different metallic salts and commercial tannins. Lastly, the bonding durability of UVPNCs impregnated cellulose substrates were evaluated through different colorfastness properties.
Section snippets
Materials
A cellulosic (cotton) knitted fabric was used as a substrate with a thickness of 0.78 mm, and areal density of 175 gm−2. The substrate was treated with 5 g/L NaOH and 10 g/L H2O2 at boiling temperature for an hour to remove oil, wax and non-cellulosic impurities from the surface for achieving adequate absorbency. The treated cellulose substrate has a whiteness index of 68.38, lightness (L*) of 93.68, redness (a*) of −0.30, blueness (b*) of 3.67, chroma (c*) of 3.68, hue (h*) of 94.74,
Phytochemical screening of banana floral stem extract
Different qualitative phytochemical tests were performed to confirm the presence of several active UVPNCs in the BFS extract as shown in Table 1. The selection of proper solvent is necessary to identify the chemical interaction of specific chromophores and hence three extraction processes were used to identify UVPNCs extracted from BFS. After hot water extraction and evaporation of water at 80, the yield of crude BFS extract was estimated at around 8.48%. The presence of tannin, flavonoids,
Conclusion
This study reported an efficient and sustainable impregnation method of cellulose using plant tannins and chitosan for imparting higher UV shielding functionality. UV protective natural chromophores (UVPNCs) derived from BFS extract have intrinsic fixation rate of 53–63% that was further improved by bio-templating of cellulose. Furthermore, different typical metallic salts and commercial tannic acid were also applied to compare the acceptability of the performance of plant tannin and chitosan.
CRediT authorship contribution statement
M. Tauhidul Islam: Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Validation, Software, Visualization, Writing – original draft. Md Reazuddin Repon: Resources, Investigation, Data curation. Md Luthfar Rahman Liman: Formal analysis, Investigation, Data curation, Software, Visualization, Writing – original draft. Md Milon Hossain: Supervision, Writing – review & editing. Md Abdullah Al Mamun: Project management.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors are thankful to the Institute of Radiation and Polymer Technology, Bangladesh Atomic Energy Commission and the Centre for Advanced Research in Sciences, University of Dhaka, Bangladesh for providing different characterization facilities. We also highly acknowledge the Department of Chemistry, Mawlana Bhashani Science and Technology University, Tangail, Bangladesh for their laboratory supports in exhaustion and fixation study of this research work.
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