# Deposition Efficacy of Natural and Synthetic Antioxidants on Fabrics
## 1 Introduction  
Tannins are structurally different polyphenic secondary metabolites of plants. Besides their polyphenic character, they offer a wide range of interesting biological functional features, besides biocompatibility and biodegradability, namely antioxidant, antimicrobial and anti-inflammatory activities [1; 2; 3; 4; 5; 6; 7; 8; 9], that render them ideal for several applications such as topical cosmetics, and biomedical and healthcare products. Tannins have been used in textiles for several hundreds of years and nowadays their use as natural dyes in textile applications is rapidly growing because of the potential carcinogenicity and environmental effects of synthetic dyes [10; 11; 12; 13]. Moreover, tannin-rich natural extracts were used as a colouring as well as antimicrobial agents to treat cotton fabrics [14; 15]. Hence, on one side, natural extracts can be successfully used as natural dyes, and on the other side, they also impart an antimicrobial finish to cotton fabric, representing viable alternatives to the artificial and sometimes toxic antimicrobial agents for hospital textiles as well as agents to hinder malodorous species which may be formed by the enzymatic oxidation of fatty acids present in domestic laundry soils. The malodour draws its origin from the bacterial biotransformation of proteinaceous substrates and odourless physiological secretions containing long-chain fatty acids, sulphur-containing amino acids and hormones, into volatile odorousorganic compounds [16; 17]. Body soils left behind on fabrics will break down over time due to microbial action or autoxidation into malodorous byproducts which consumers describe as body, sweat, stale, or musty odours [18; 19; 20; 21]. The process can be suppressed by antioxidant agents that are able to interfere with the oxidation of organic body soil caused by microorganisms belonging to skin flora, thereby limiting the formation of malodour. In the US, 45.7% of consumers claim \"odour removal\" as a need in at least one out of their last ten loads (Procter and Gamble, unpublished data from a 2019 study involving 4995 representative US consumers). Odour removal is also a top unmet need in many other regions. Thus, more effective laundry detergent solutions are needed to eliminate odours from fabrics. Given that tannins possess significant antioxidant and enzyme complexing properties associated with a high propensity to form complexes, they can significantly contribute to malodour reduction. Furthermore, tannins deposited on fabrics can undergo stacking and thus trap the malodorous species on fabrics. Several studies aiming at evaluating the possible effects of polyphenics from plant extract on malodour have demonstrated their effective role as malodour-reducing agents [22; 23; 24; 25; 26; 27]. Existing literature suggests that condensed tannins are able to deposit on fabrics [28; 29; 30]. Their specific UV absorbance characteristics can also make tannins natural sunscreens [31; 32]. These specific characteristics make tannins an interesting starting point for the development of smart textiles, which, owing to their added properties, show sunscreen, antimicrobial and malodour control properties and enable prevention of malodour formation also in a re-blooming scenario. In this context, in a preliminary study aimed to assess the possibility of using pine bark extracts as natural active ingredients in smart textiles [21; 22; 23; 24; 25; 26; 27], we deposited on cotton samples two different pine tannins as well as common phenolic antioxidants, namely 3,5-di-_tert_-butyl-4-hydroxy toluene (BHT), methyl 3-(3,5-di-_tert_-butyl- 4-hydroxyphenyl)propanoate) (MfBHHP) and octadecyl 3-(3,5-di-_tert_-butyl-4-hydroxyphenyl)propanoate (Figure S1 in Supplementary Materials).