Human hair is a keratin and melanin-rich natural fibre and considered as one of the largest waste material produced by humans. It has been estimated that about 300,000 tons of human hair are thrown away every year round the world. Although this is biodegradable, its accumulation in the waste stream due to the uncontrolled disposal is posing serious environmental problems. However, although the hair is dumped as waste, high-quality human hair and its various products are commercially exploited as well.
Fig: Integrated processing showing extraction of multiple products from waste human hair
India is one of the major exporters of human hair and during 2011-12 the Tirumala temple alone auctioned human hair worth US $ 2 billion. Considering the abundance, easy resourcing, excellent biocompatibility, immune friendly nature upon transplantation, favourable cellular interaction activity and biodegradability, etc., recently keratin extracted from human hair has emerged as an alternative biomaterial for a number of applications. Considering the stimuli-sensitive nature of the protein, various mild extraction methods to extract keratins from hair have been developed leading to a number of biomaterial applications for the protein fibre.
The market value of keratin is Rs 15000-20000/kg while melanin is more expensive than gold and sold around Rs 4000-5000/g. The common methods applied to solubilise human hair are acidic, basic and enzymatic hydrolysis; sulfitolysis is also a common method applied to dissolve keratin. But the toxicity of many of the used chemicals and uncontrolled drastic reaction conditions often result in the formation of keratin with low molecular weight, which degrades the quality and hence the application potential of the protein. Among various solvents, the use of ionic liquids is increasing to process various waste including human hair.
Scientists at the CSIR-Central Salt & Marine Chemicals Research Institute (CSMCRI), Bhavnagar have developed an integrated process for the production of keratin and melanin from Waste Human Hair (WHH) using a hydrated ionic liquid. The hydrated ionic liquid is found to completely solubilise 20-25% w/w of waste human hair.
Melanin and keratin with 10-22% and 36-38% yield were isolated from the solution. Due to the very good nitrogen content (5.00-6.99%) in the hydrated ionic liquid remaining after the isolation of melanin and keratin and evaporating water present in it, it can be used to fortify nitrogen-deficient liquid seaweed plant biostimulant and can be used as an agricultural nutrient for plant growth.