Research and Development resume activities on the project called Ri-Leather, which began in autumn 2019, and which bears the signature of SSIP as a scientific partner, led by the chemical products company Real Color. The consortium also includes the companies set up in ATI (temporary joint ventures): Conceria Montebello, Conceria Corradi and Biodermol. Funded by the Veneto Region (POR FESR 2014-2020 measure 1.1.4), the project aims to introduce innovative chemical products and tanning processes, from the depilation/liming phase, to tanning and retanning, in order to reduce the environmental impact and introduce new eco-sustainable products to the market, aimed at improving creative productions.
The objectives of the project are:
* Reduction of purification sludge and wastewater COD, through the introduction of a new enzymatic /oxidative hair removal system with “recovery” of the hair
* Consistent reduction of polluting and dangerous substances such as sulphides in the hair removal treatment
* Reuse of intact hair and free of hazardous substances for the production of padding and insulating panels and technical fabrics
* Reuse and recycling of tanned leather residues and characterisation and enhancement of the same in terms of biodegradability of crust leather
* COD reduction of the retanning process waste.
The innovative phases of the project are specifically:
a) depilation and liming with the “recovery” of the hair by means of new depilatory chemicals, which through the combination of enzymatic action and chemical oxidation, ensure that an intact hair is obtained that is not hydrolyzed, clean and free of dangerous substances. The recovered hair can be easily compacted, dried and available for subsequent processing (eg making materials for padding, acoustic and thermal insulation in the furniture and green building sectors or technical fabrics for leather goods and footwear).
b) revaluation of waste deriving from the trimming/buffing of tanned leathers through the development of an innovative recycling process of the wet white organic tanning agent, coming from waste, and its subsequent reuse in the same tanning/retanning sector. The project is in fact aimed at the development of new products of protein origin capable of guaranteeing a more effective retanning action and considerably reducing the dispersion of substances in the process baths that cause an increase in the COD of the wastewater. In particular, through a specific hydrolysis process the aim is to separate the organic tanning agent from the protein part; the obtained and separated tanning agent will be characterised to perform its retanning functions more effectively, while the protein part deriving from the deconditioning treatment will be used, after specific chemical modification, in the retanning phase as an additive and auxiliary for the reduction of the COD of the wastewater deriving from the retanning itself.
The part concerning liming involves the Montebello Tannery and the Biodermol company as well as SSIP.
Why talking about liming, a technologically consolidated process that seems to have already said everything about the new discoveries? Although true, we must acknowledge that in most cases tanning industries still use the traditional method of reductive hair removal with sulfur.
While this process is reliable and effective, the environmental problem essentially linked to two parameters remains unchanged: that of air (odours, dangerousness of hydrogen sulphide) and wastewater, which in the case of destructive liming contributes to the quantity of post-purification sludge by almost 20%.
The objective of this study is to find an alternative solution, to avoid this problem, and also to go through an easier process:
* that operates at a reduced pH level and that allows to recover, or rather reuse, a hair that is not hydrolyzed or intact,
* with less swelling and the possibility of avoiding the subsequent deliming phase.
* that in any case does not require dedicated reaction environments such as corrosion resistant drums or equipped with cooling systems.
The main purpose of the liming phase is to remove hair and we could divide it into hair removal and swelling, usually processed simultaneously. Swelling is rather a consequence of the intentional opening and cleaning of collagen fibres with the elimination of some unwanted substances, such as unstructured proteins and the epidermis. Liming could be explained as an open up to allow the elimination of the aforementioned and substantially free up space for tanning and other substances in subsequent processes.
The proposed solution derives from the synergy of several technologies, namely:
• Enzymes for hair loosening
• Enzymatic activators or cofactors (metals, salts)
• Energetic oxidant as a result of a «sharpening» effect
• pH swab test
The first goal is to cause non-destructive hair removal, targeting therefore the adhesion substances of the hair and epidermis.
Hair removal with «recovery» works on the side of the hair follicle up to the bulb and on the Malpighian layer of junction between the dermis and the epidermis; area of pre-keratins (soft keratines). This task is carried out by chemical agents that mainly work on the disulfide bridge of keratins, called “sharpening” agents which can be reducing agents, such as sulphide, or oxidants, which are those considered in this study.
The second one is the open up goal which we intend to exploit, instead, through an enzymatic catalysis process.
The enzymes of our interest essentially consist of two classes: selective proteases, above all on Proteoglycans, and lipases on fats.
Proteglycans are very complex substances characterised by a protein and a polysaccharide part. The polysaccharide part is a glycosaminoglycan characterised by disaccharide units having an amide group in the C1 position.
In the hide, proteoglycans are present in connective tissue cells and in the extracellular matrix such as Dermatan sulfate, Chondroitin Sulphate and Keratan sulfate.
In the combined enzymatic and oxidative process, enzymes of the aforementioned species were used together with auxiliaries such as salts and some metal ions to increase their effectiveness.
It has been noted that moderate salt concentrations (Mg2Cl, KCl) accelerate the penetration and activity of enzymes.
Furthermore, metals such as Ca, Mg, K facilitate a more effective bond between enzyme and target proteoglycans, decreasing the activation energy of the transition state.
Another development on enzymes concerned their protection or encapsulation which allows them to maintain their stability, before their application in water, thus allowing them to be combined with other depilatory, reductive or oxidative agents, which are otherwise aggressive and denaturing.
The coatings used can be organic such as alginate or inorganic such as silica.
The primary action of hair removal, or the “sharpening” effect of reducing agents such as sulphide, effectively only act on pre-keratins (soft keratins).
In reality, the depilation could be possible with caustic soda alone, but the contraindications are considerable, such as the exothermic effect, the considerable swelling unless a consistent quantity of salt with an osmotic effect was added.
It should be remarked that for the most common reducing agent, sulphide, the action is only carried out on the cortex; there is no keratin in the marrow, while these would be too resistant on the cuticle.
In a future article dedicated to the project, there will be a discussion about the action mechanism of the depilatory agent alternative to sulphide and how it has been effectively used in synergy with the enzymatic action.
edited by Marco Nogarole, Technical and Business Service Manager of the Arzignano District (Veneto region) of the SSIP