Current Projects

Our research interests and pursuits are targeted toward the design and development of environmentally benign dyes (and dyeing processes) for a variety of applications, as many dyes and processes for coloration of textiles, human, and other materials poise toxicity concerns. For example, some precursors employed to develop permanent hair dyes during their application (e.g., p-phenylenediamine/PPD and resorcinol) are moderate to strong/extreme skin sensitizers. Key in advancing research aimed at designing and developing less toxic alternatives is not only an understanding of dye and substrate structure-property relationships and dye-substrate interactions, but the deployment of traditional and non-traditional approaches/methods. Also, key is a holistic approach to assessing the benign character of proposed alternatives. In the case of hair dyes this means not only assessing the dyes for their impact on human health but also their impact on aquatic systems, since they can leach into the environment. See below for current project highlights.

Analysis of metal complexable monoazo dyes for sustainable human hair coloration

Monoazo dyes that have been applied as 2:1 dye:metal complexes to textiles at high temperature (100^oC) have been demonstrated by our laboratory to form such complexes in human hair in situ under mild and more practical conditions for the dyeing of human hair [1]. This is accomplishable by employing environmentally benign metal ions such as Al³⁺ or Fe³⁺ as a post-treatment applied at 40^oC on previously dyed fibers. The idea to form such complexes in hair was inspired by the primary mechanism that renders conventional permanent hair dyes “permanent” or wash resistant, i.e., the formation of oligomeric or higher molecular weight chemical structures in the hair fiber that become mechanically entrapped. Indeed, conventional permanent hair dyes (indo dyes) are formed inside hair upon the oxidative coupling of precursors such as p-phenylenediamine/PPD and resorcinol that can diffuse into the core of the fiber. Our goal is to develop an alternative permanent hair dye technology that also mechanically entraps the dye in hair.

Of the dyes we have explored as alternative permanent hair dyes, arylazonaphthol dye with and without metal applied displayed good wash resistance compared to a commercial permanent hair dye standard [2]. In the case of applying arylazonaphthol dye without metal ion (i.e., the dye ligand), this result is believed to be due to the nature of the sulfonamide (-SO₂NH₂) auxochrome that renders the dye less soluble in water compared to traditional acid dyes that contain sulfonate (-SO₃Na) or sulfonic acid (SO₃H) groups. And, in the case of applying arylazonaphthol dye with metal ion (i.e., the metal complexed dye), this result is believed to be in addition due to the mechanical entrapment of the complexed dye within hair as a consequence of its higher molecular weight. Results from a Salmonella/microsome mutagenicity assay employed and acute toxicity tests with Daphnia similis (48h) and Parhyale hawaiensis (96h) conducted in collaboration with the Laboratório de Ecotoxicologia e Genotoxicidade at UNICAMP revealed the arylazonaphthol dye and other monoazo dyes belonging to the same family displayed a low environmental hazard potential [2]. Of interest is to continue exploring the potential of the dyes.

T.N. Williams, M. Szymczyk, and H.S. Freeman. “In situ Chelation of Monoazo Dyes in Human Hair Keratin Fibers Using Environmentally Benign Metal Ions,” ACS Appl. Bio Mater., 2021, 4 (8), pp 6195–6202. DOI: 10.1021/acsabm.1c00512
T.N. Williams, F.I. Vacchi, A. dos Santos, G. de Aragão Umbuzeiro, and H.S. Freeman. “Metal-complexed monoazo dyes as sustainable permanent hair dye alternatives—Toxicological and durability properties,” Dyes Pigm., 2022, 197, pp 10819. DOI: 10.1016/j.dyepig.2021.109819

Exploration of biocolorants for sustainable textile and human hair coloration

The global demand for biocolorants suitable for the coloration of hair, textiles, food, and other materials is rapidly increasing to overcome adverse effects that can result from the consumption of some synthetic dyes (e.g., cancer). As their name implies, biocolorants are dyes derived from biological sources such as plants or microorganisms (bacteria, yeast, fungi, and algae), and they are either extracted from their source or biosynthesized. In addition to displaying a wide variety of colors, many biocolorants are biodegradable and can display antimicrobial, anti-inflammatory, and other properties, expanding their application beyond aesthetics. Indeed, many have found use in biosensing applications.

The use of biocolorants produced using microorganisms is more attractive than the use of plant sources, because the need to compete with farmland is eliminated. Also, the production of biocolorants from microorganisms such as fungi can be controlled in a laboratory setting by tuning process conditions (e.g., pH, nitrogen source, light). Biosynthesis of desirable colorants can increase their yield and purity and eliminate the need to consume solvents to extract them. More importantly, their biosynthesis does not involve the consumption of petroleum based starting materials. In addition, several of the colorants may be employable in waterless dyeing applications. Given the plethora of microbial species available, this is a large area of research, and our laboratory intends to fill the gap. Stay tuned for our progress!

Keywords: sustainability, green chemistry, dyes, dyeing, hair dyes, textiles, chemistry, biosynthesis