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Production of biopolymer film, fibre, foam and adhesive materials from soluble s-sulfonated keratin derivatives

Production of biopolymer film, fibre, foam and adhesive materials from soluble s-sulfonated keratin derivatives description/claims

This invention relates to the preparation and use of soluble keratin derivatives in the production of a range of biopolymer materials such as films, fibres, foams and adhesives, and the improvement of those materials using further chemical treatments.

Keratins are a class of structural proteins widely represented in biological structures, especially in epithelial tissues of higher vertebrates. Keratins may be divided into two major classes, the soft keratins (occurring in skin and a few other tissues) and hard keratins, forming the material of nails, claws, hair, horn and (in birds and reptiles) is feathers and scales.

The hard keratins may in turn be further subdivided into structural types described as α-keratin, β-keratin, or feather keratin. Keratins of the α and β types have different predominant structural motifs in their proteins, in the former case supramolecular structures based on the α-helix secondary structure of protein chains, and in the latter case on the β-pleated sheet motif.

All keratins are characterised by a high level of the sulphur-containing diamino-acid cystine, which acts as a cross-linking point between protein chains. This feature of a high-level of interchain crosslinking through cystine gives the keratins, especially the hard keratins, their characteristics of toughness, durability, resistance to degradation, and desirable mechanical properties. Cystine contents vary widely in the keratins, which is reflected in their variation in mechanical properties.

Wool and hair are examples of hard α-keratin. However, even in a given α-keratin, there are many classes of structural protein present, and the mechanical properties arise from a sophisticated supramolecular organisation of proteins of many different types to create a complex morphology with a correspondingly complex mechanical behaviour.

An object of the invention is to provide biopolymer materials derived from soluble keratin derivatives and production methods for producing the biopolymer materials.

According to a broadest aspect of the invention there are provided materials derived from S-sulfonated keratin proteins, as herein defined, in the form of films, fibres, foams or adhesives. The S-sulfonated keratin proteins can be derived from wool keratin and be enriched in intermediate filament protein(s).

According to another aspect of the invention there is provided a process method for the formation of films from S-sulfonated keratin proteins in which a solution of the proteins is cast and the solution solvents evaporated to leave a protein film.

The solution(s) used can be aqueous based, including some proportion of organic solvents.

The films produced by this process method are inherently soluble in water or the solvent mix used for casting the film.

Another aspect of the invention describes a method for improving the wet strength of films, produced by the process method, by using chemical agents, such as thiols and phosphines, that remove the sulfonate group and allow the formation of disulfide bonds within the protein film. The disulfide bonds provide the film with wet strength. Another method of improving the wet strength of a film, produced by the process method, is described in which acidic solutions are used to treat the protein film, and through a process of protonation of the sulfonate groups and any other suitable polar groups within the protein, the film becomes insoluble in water and has significant wet strength.

Another aspect of the invention describes introduction of crosslinks into a film, produced by the process method, through the use of crosslinking agents such as those commonly used in protein modifications, that target a range of functional groups present within the protein.

A further aspect of the invention is a method for the production of protein films using a solution comprising a combination S-sulfonated keratin proteins and reduced keratin proteins or peptides containing reactive cysteine residues. The two species combine to form a crosslinked keratin network and subsequently a protein film with good wet strength properties. This approach of combining S-sulfonated and reduced keratins can also be applied to the production of keratin fibres, foams and adhesives.

A further aspect of the invention is a method for the production of keratin fibres through the extrusion of a solution comprising of S-sulfonated keratin proteins through a spinnerette into a coagulation bath that causes the protein to become insoluble. In particular the coagulation bath may contain reductants, such as thiols or phosphines, that cause the removal of the sulfonate group from the protein and lead to disulfide groups forming. In addition the coagulation bath can contain crosslinking agents, such as formaldehyde or glutaraldehyde, which cause the protein(s) to become insoluble on contact with the coagulation bath. In addition the coagulation bath can be at acidic pH, which also causes the protein solution to become insoluble.

A further aspect of the invention is a method for the production of keratin fibres through the extrusion of a solution comprising of S-sulfonated keratin proteins through a spinnerette into a hot environment through which the solvent is rapidly removed and a fibrous keratin material remains. Fibres produced in this way can be further processed through wet chemical treatments to improve the wet strength of the fibres through the formation of crosslinks, or by protonation of the protein in manners similar to those described above for keratin films.

A further aspect of the invention is a method for the production of keratin foams through the freeze drying of a solution of S-sulfonated keratin proteins. Foams produced in this way can be modified using similar methods to those described for keratin films, that is through the use of a reductant such as a thiol or phosphine to remove the S-sulfonate group, through the use of reduced keratin proteins or peptides to remove the S-sulfonate group, through the use of an acidic solution to protonate the S-sulfonate group and the protein, or through the use of crosslinking agents such as formaldehyde and glutaraldehyde to modify the protein.

A further aspect of the Invention is a range of keratin based adhesives, comprising at least in part a solution of S-sulfonated keratin proteins. These adhesives can be made to have superior wet strength properties through the use of reducing agents, such as thiols or phosphines. Alternatively wet strength can be imparted through the use of a reduced keratin protein or reduced keratin peptide, to create a crosslinked keratin network These two sets of reagents can form a ‘two pot’ adhesive.

The flexibility of the films, fibres, foams and adhesives produced by the methods described can be modified through the use of plasticizers such as those from the glycerol or polyethylene glycol families.

According to further aspect of the invention there is provided a film, fibre, foam or adhesive material derived from keratin derivates of high molecular weight as described and claimed in PCT/NZ02/00125 whereby the process includes a first stage digestion step of sulfonating a keratin source by oxidative sulfitolysis followed by a second stage repetitive aqueous extraction involving separation of soluble and insoluble keratin and subsequent re-extraction of the insoluble keratin to thereby produce a highly S-sulfonated keratin derivative. The protein keratin source can be a naturally occurring protein source.

According to yet a further aspect of the invention there is provided a film, fibre, foam or adhesive material derived from either highly S-sulfonated keratin intermediate filament proteins, soluble keratin peptides or a purified protein with little or no damage to the structural integrity of the protein as produced from an impure protein source as described above.

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• Utility Patent

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