METHOD OF FORMING DISINTEGRATABLE COHERENT MATERIALS AND MATERIALS SO FORMED

Abstract: Method of forming a coherent material capable of being controllably disintegrated comprising the steps of adding chitin, or a chitin derivative, to said material during the formation of said material and obtaining disintegration of said chitin-containing material by exposing said material to chitinase, and to materials formed by said method. The invention offers particular advantage when the coherent material is a plastics material or a solids material in particulate or divided form, in suspension in a liquid.

Description: METHQD OF FORMING DISINTEGRATABLE COHERENT MATERIALS AND MATERIALS SO FORMED DESCRIPTION The present invention relates to a method of forming coherent materials capable of being controllably disintegrated and to materials so formed. Many instances arise in which materials need to be made in coherent form, especially in the case of non- articulate materials, but in which it could be desirable if the material could then be controllably disintegrated either wholly or partly to destroy its coherent nature. Thus, many structural plastics in common use at the present day have the disadvantage that they degrade only slowly or at imperceptible rates. As a result, littering of the environment takes place by careless disposal of articles made of these plastics and, because of the virtual indestructable nature of the plastics, the litter tends to accumulate. It would, therefore, be desirable if plastics could be modified so that they will readily undergo degradation on disposal. The present invention seeks to provide a coherent material capable of being controllably disintegrated. According to the present invention there is provided a method of forming a coherent material capable of being con¬ trollably disintegrated comprising the steps of adding chitin, or a chitin derivative, to said material during the formation of said material and obtaining disintegration of said chitin- containing material by exposing said material to chitinase. Chitin is a skeletal material found in the majority of Invertebrata, especially Anthropoda, and it has the empirical formula C _H_,0-^N . It is therefore, a widely distributed natural material. Further, the enzyme chitinase which is capable of degrading the chitin is also a natural substance widely dispersed in nature. It is, for example, found in the oceans and soils. When found in nature the chitin is formed with the coherent material (the skelatal material). The present invention proposed the addition of chitin to the coherent material and is therefore different from chitin-containing materials found in nature. Of the chitin derivatives chitosan has been found to be particularly useful in some embodiments of the invention. The present invention further envisages a formable body of coherent material including chitin or a chitin derivative, that is to say a mass of coherent material with chitin or a chitin derivative distributed therethrough capable of being formed into a desired shape or configuration. Preferably, therefore, the method includes the steps of forming said chitin/chitin derivative-containing material into a body of filament, ribbon, strip, sheet, or solids form. The present invention affords particular advantage when the coherent material comprises a plastics material and the method includes the steps of polymerising the component monomer or monomers OMH of the plastics material in the presence of chitin or a chitin derivative. By polymerising the monomer or monomers concerned in the presence of chitin, the chitin is incorporated in the polymer molecules and distributed throughout the mass of the plastics material. When the coherent material comprises a plastics material and the chitin/chitin derivative is incorporated in the polymer molecules articles made from such materials, including filaments, ribbon, strip, sheet or solids forms and articles made therefrom can be controllably disintegrated simply by exposing the article to chitinase and, as stated above, as the enzyme chitinase is a natural substance found in the oceans and in many soils, chi in- containing articles buried or dumped in the sea when their use- ful life is finished will rapidly disintegrate without in any way damaging or contaminating the environment. Thus, plastics food containers, refuse bags, wrappings, and the like currently almost indestructable articles can be readily rendered disintegratable by the invention now proposed. As the enzyme chitinase is found in human blood the present invention can be safely used for temporary prosthetic devices such as bone spacers, splints and the like internal devices. Thus, it is known in surgery to employ splints internally of the body, plastics splints being readily mouldable are advantage- ous but, since the splints are not degradable by the body, they must be removed after the bones concerned have set. This means that the patient must undergo two operations, one for insertion of the splint and a second operation for removal of the splint. When the splint is made from a plastics material as proposed by the present invention the chitinase in the blood will effect controlled disintegration of the plastic splint, the disintegra¬ tion will be such that the body will not be inconvenienced or damaged by the disintegrated plastics material, and the second operation can thus be avoided. Further, if stitches or wound dressings are made from the coherent material with chitin/chitin derivative incorporated therein as proposed by the present invention the said material may be disintegrated by the body when exposed to blood or, when externally applied as a dressing to a wound not bleeding but wherein the removal of the dressing may be painful, the dressing may be disintegrated, painlessly, by application of a mild solution of chitinase thereto. There are instances in which it would be desirable after a body of material is formed, if parts of the body could be destroyed or if it could be made up in porous form, but in which the materials concerned would make this difficult or impossible. For instance, if a body were to have internal hollows it might require a moulding technique of a complexity such as to render its production untenable on the ground of cost. The present invention affords a solution to a£ least some of these problems by providing a method of forming a coherent body, including chitin or a chitin derivative, into a desired form, forming a body of chitin/chitin derivative-free material of desired shape incorporating said chitin/chitin derivative containing material form, and subsequently exposing said chitin chitin derivative-containing material to chitinase to cause said material to disintegrate whilst leaving the chitin-free material intact. Thus, and by way of example, the chitin containing material -may comprise a core, inserted into a mould and which, after the mould has been filled with, for example, a plastics material, may be readily disintegrated to afford the chitin-free moulded article a configuration which could be otherwise achieved only by very complex moulds. In another embodiment the chitin containing material may be in the form of a sheet or laminate applied to a sheet or body of chitin free material and whereupon, when the chitin containing material has served its purpose,it may be readily removed with chitinase. One example of such a use is when the chitin containing material comprises a laminate applied to chipboard for use as a kitchen worktop or a piece of furniture, such as a cabinet* When conventional laminates are used they cannot be removed from the base without damaging the base, so that when a replacement laminate is required the laminate and the base must be replaced. When the laminate contains chitin as proposed by the present invention said laminate can be readily disintegrated, by the application of chitinase, without damage to the base, whereupon the base can be retained and a new laminate applied thereto. This laminate or coating form also offers considerable O PI advantage in painting, when the chitin may be incorporated in a "hard" or gloss paint and, when the paint is to be removed, disintegrated by the application of chitinase, thus avoiding the time taking sanding or heat stripping practices. T e invention also offers advantage for certain wall coverings, such as so called "washable" wallpapers and which, by their nature, prevent the penetration of water to the backing material, generally a paper backing. With such an arrangement the "washable" laminate may comprise the coherent material with chitin or chitin derivative therethrough, in which case the laminate may be disintegrated to allow access to the paper backing by simply washing the laminate with a dilute solution of chitinase. Alternatively, the coherent material with chitin in accordance with the invention may comprise the adhesive retaining the laminate with the backing, in which case annlication of a dilute solution of chitinase to the joints of adjacent sheets of wallpaper will cause rapid disintegration of the adhesive, thus allowing the laminate to be removed without damage. In one further example the coherent material including chitin may be used as a label or -protecting material applied to a fragile surface when the said material can be disintegrated without damaging said surface. The method proposed by the present invention is also useful for forming coherent bodies of solids in particle or divided form in suspension in liquids and according to this aspect of the invention the method proposed comprises the steps of adding chitin or a chitin derivative to the liquid, flocculating to allow the chitin to bind together particles of solids material, removing clear liquid to leave a sludge of chitin-bound solids material, and exposing the sludge to chitinase to biodegenerate the chitin, thus destroying the hydrous nature of the sludge, and removing liquid from the sludge. The above method has particular application to sewage and effluent treatment and wherein the chitin or chitin derivative acts as a most effective flocculent/coagulant aid. The use of inorganic salts to promote flocculation and rapid settlement of suspended matter in waste water treatment will yield sludges containing relatively high amounts of water, since most coagulants produce a voluminous and highly hydrated floe. Whilst these reagents help considerably in producing a clear supernatent liquor, the sheer volume of the separated sludge gives problems in disposal or subsequent drying for disposal. When chitin derivatives are used as the principal flocculant, however, a totally different mechanism becomes possible when treating the sludge. If the chitin flocculated sludge is further treated with chitinase there is a rapid biodegeneration of the chitin element so that the hydrous nature of the sludge is rapidly destroyed. Thus a further loss of water can be achieved rapidly and this effect can be further enhanced by the use of conventional dewatering materials. Thus the duplex system of using chitin or its derivatives as a flocculant/coagulant on the incoming water followed by chitinase treatment of the sludge produced, will enable both objectives of treatment to be achieved, OMPI i.e. a maximisation of clarification and a reduction in volume of sludge to suit disposal or drying of the sludge. Since the economics of sludge disposal are generally based on volumetric considerations, the duplex system offers considerable advantages over systems now in use. Inorganic salts, ferric chloride, chlorinated copperas, alum, sodium aluminate, for example, are permanent through the system, and whilst they are all effective when correctly used, they still retain their water holding properties even at the sludge stage. Further, if the precipitated matter is such that it can be recycled as animal food after suitable treatment, the nature of the flocculants used becomes critically important. High levels of iron salts, for example, can detract from the usefulness of treated sludge when used as a source of food. Chitin and chitinase, however, offer no such problems since both materials can be shown to be safe in such systems. The amount of chitin/chitin derivative used to bind the particulate material will be dependant upon the volume of particulate matter per unit volume of the liquid and the size of the particulate matter but the actual amount of chitin to be used can be readily determined by simple experiment. When the chitin is added to a plastics material the chitin is preferably used in amounts between Λ and 20# by weight of the monomer or monomers and more preferably in amounts of from ~% to 10# by weight of the monomer(s). The greater the amount of chitin the more quickly disintegratable is the material in which it is O H incorporated. The present invention will now be described, by way of example only, with reference to the following example. In the example, a plastics material consisted of polymethyl- methacrylate and the momomer was polymerised in the presence of different amounts of chitin as indicated hereinbelow. The monomer was polymerised in each instance to produce a semi¬ circular strip of plastics material some 5.Ocm long. After ten minutes setting time, the test strips, and control stripe formed by polymerising the monomer without the chitin, were subjected to a pressure test using a fulcrum placed in the centre of each strip and applying equal weight to each end of the strip. The purpose of this test was not to test the strips to destruction, but to identify if a structural weakness was in the test strips and this proved not to be the case. An amount of chitinase (strain 50?) was dissolved in sterile water to give a 1/lOOth molar concentration and the solution was maintained at 20 C. The test strip were then immersed in the chitinase solution and examined every twenty minutes for loss of rigidity or structural form. In this connection, the molecular turnover number for the chitinase was 3 assumed to be about 10 . The results of these tests along with the different concentrations of chitin used in producing the test strips are shown in the table below:- RESULTS. Concentration chitin Time colla-pse of structural stability 1.09. 120 minutes 2. # 80 5.03- 20 10.0# 20 Control No effect As will be evident from the Table, the chitinase has the effect on the test strips of weakening them to the point where they suffered structural collapse; the time given in the table being the times at which collapse took place. These results clearly demonstrate that the plastics material incorporating the chitin is readily degradable by the action of chitinase. Thus, the incorporation of chitin in plastics and other materials capable of being bound by chitin or a chitin derivative opens up the possibility of making disposable articles readily degradable, but without affecting their structural integrity for the period of time that they are actually in use. V-- c. v Tv. Wli

Claims: CLAIMS 1. A method of forming a coherent material capable of being controllably disintegrated comprising the steps of adding chitin, or a chitin derivative, to said material during the formation of said material and obtaining disintegration of said chitin-containing material by exposing said material to chitinase. 2. A method as claimed in Claim 1 including the steps of forming said chitin/chitin derivative-containing material into a body of filament, ribbon, strip, sheet, or solids form. 3- A method as claimed in Claim 1 or 2 comprising the steps of forming the coherent material including chitin or chitin derivative into a desired form, forming a body of chitin/chitin derivative-free material of desired shape incorporating said chitin/chitin derivative- containing material form, and subsequently exposing said chitin/chitin derivative-containing material to chitinase to cause disintegration of the chitin/chitin derivative-containing material whilst leaving the chitin-free material intact. k. A method as claimed in Claim 1, 2 or 5 in which the chitin/ chitin derivative-containing coherent material comprises a plastics material and the method includes the steps of ■ polymerising the component monomer or monomers of the plastics material in the presence of chitin. 5» A method as claimed in Claim 1 for use when the coherent material is in particulate or divided form in suspension in a OMP1 liquid comprising the steps of adding the chitin or chitin derivative to the liquid, agitating the liquid to allow the chitin/chitin derivative to act as a flocculant/coagulant with respect to the coherent material, removing solids-free liquid to leave a residual sludge of chitin/chitin derivative containing coherent material, and exposing said sludge to chitinase to dis¬ integrate said sludge. 6. A method as claimed in Claim 5 including the step of reducing the liquid content of the disintegrated sludge. 7. A method as claimed in Claim 5 or β for de-watering sewage comprising the steps of adding chitin or a chitin derivative to the sewage, agitating the sewage to allow the chitin/chitin derivative to bind together solids particles in the sewage, dewatering to leave a sludge of chitin bound solids, applying chitinase to the sludge to disintigrate the chitin bound sludge, and then effecting a de-watering of the sludge. 8. A body of coherent material including chitin or a chitin derivative distributed throughout the mass of said body. 9. A body as claimed in Claim 1 comprising a plastics material with the chitin/chitin derivative dispersed therethrough. 10. A body as claimed in Claim 9 in which the chitin/chitin derivative is incorporated in the polymer molecules. 11. A composite body comprising a body as set forth in Claim 8 9 or 10 in filament, ribbons, strip, sheet, or solids form in combination with a chitin free body in filament, ribbons, strip, sheet or solids form. OMPI Λ~ W1PO ^ *N A T -1~- 12. A body as claimed in Claim 8, in the form of an adhesive. 13. A body as claimed in Claim 8, 9, 10, 11 or 12 in which the chitin/chitin derivative comprises 1# to 20# by weight of the body. Λ . A body as claimed in Claim 13 in which the chitin/chitin derivative comprises from % to 10 by weight of the body. OMPi

Inventors: EVEREST-TODD SELWYN, EVEREST-TODD, SELWYN
Applicants: WHEATLEY CHEMICAL CO LTD, WHEATLEY CHEMICAL COMPANY LIMITED
Application year: 1983
Main classification: C08L5
IPC codes: C02F11, C08L5