CA1108366A - Chitin films and fibers - Google Patents

Abstract

ABSTRACT
A new method for producing high strength films, fibers and other shaped articles from chitin has been discovered, whereby an anhydrous solution of chitin is made into the desired shape, the chitin is insolubilized with an organic non-solvent for the chitin and the resultant shaped article, if desired, is oriented, by cold drawing until its properties, such as tensile strength, are substantially enhanced. The films, fibers, and other shaped articles capable of being oriented or in oriented form, are novel and useful in such applications as food wrap and surgical sutures.

Description

3~ -This invention relates to films and fibers and a process of maXing same. This invention also relates to solutlons of chitin.
Chitin is a cellulose~like material that occurs widely in nature, for ex~mple in the cell walls of fungi and the hard shell of insects and crustaceans. The waste from shrimp, lobster and crab seafood industries, now used largely ~or its protein values in animal feed, contains 10 15 percent chitin and is a readily available source of supply.
More specifically, chitin is a mucopolysaccharide, poly-N-acetyl-D-glucosamine and like cellulose, o~ relati~ely high molecular weight. ~owever, in the natural state it occurs only in small flakes or as short ibrous material, e,g. from the carapace or tendons of crustaceans; there is no source, as with cotton in the cellulosics, that forms useful shaped articles without solution and reprecipitation or renaturing~
For many years efforts have been made to prepare films and fibers of chitin following c~llulose technology, but with limited success. Kunike, Soc. Dyers and Colourists; 42, 318 (1926), prepared chitin films and filaments hy dissol~ing chitin in aqueous acids, s~inning or casting, and subsequently coagulating ~ith a nonsolvent. Even though the filaments were dried under t~nsion their tensile strength was only about that of rayon.
Clark and Smith, J. Phys. Chem., 40 863 ~193~), used aqueous acids or lithium salts for solution and regeneration, but the films pxoduced were readily dispersed in water. Threads extruded from lithium thiocyan~te with tension applied during ~heir ~ormation were said to develop orientation, but an x-ray pattern - of a chitin sheet supported on a glass pla~e reprecipitated from lithium thiocya~ate solution, showed only the broad diffuse nodes of a strainedr non-crystallin~ material.
Somewhat later, Thor, U.S. Patents 2,168,374 and 2,168,373, August 8, 1939, described the preparation of chitin xanthate for 3~
regeneratirg chitin ~ilms and ~ibers. The patents me~tion the stretching o filaments in the gel state to lmprove physical properties, but not the drawing of solid chitin, required for fiber orientation. Thor, U.S. Patent 2~217,823, October 15, 1940, discloses some further details of his e~forts to produce commercially useful films and fibers from chitin, but covers only homogeneous mix~ures of chitin and cellulose coprecipitated from the mixed xanthates. Regerated chitin films were said to possess good s~rength in the dry stake, but became soft and slimy on wettiny, implying a lack of touglmess when wet.
Thor and Henderson, Am. Dyestuff Reporter, 29, 489 (1940) dascribe ~he preparation of regenerated chitin from chitin xanthate and summarize its properties. It formed films having a tensile strength of 9~49 kg/sq mm (dry) and 1.75 kg/sq mm (wet).
In summary, the prior art discloses attempts to produce useful articles by solution and regeneration of chitin, including stretching during fiber formation, as practiced commercially with rayon technology, but it does not teach how to carry out film or fiber prepaxation in such a manner as to achie~e a tough renatured product capable of high orientation and possessing tensile strength, resistance to watPr and other outstanding physical properties comparable wlth native chitin, as indicated in Table l.
Table 1 - Chitin Properties ~ .. . . . . .
Ten. Str.
Fiber k~/sq mm Reference Natural chitin 58 Clar~ and Smith Regenerated chitin 35 Xunike Silk 35~6 Clark and Smith Viscose rayon 25 Xunike Wool 14.5 Clark and Smith Film 30 Regenerated chi~in 9.49 Thor and Henderson Regenerated cellulose 9.10 Thor and Henderson It is an object of this invention to prepare highly oriented shaped articles from chiti~. Fur~her obj ects are the unsupported

- 2 -films, ibers and other shaped articles themselves, either as cast, extruded or formed, or after having been cold drawn to achieve a high degree of orientation and substantial enhancement of their properties. A further ob~ect is to provide a method for producing the shaped articles in such a way that the chitin is laid down with a substantial portion of it in crystalline form, comparable with the well ordered natural chitins~ capable of being cold drawn to enhance its properties. Another object is to provide a superior solution and renaturing process or producing unsupported ~ilms, continuous ~ilaments and other shaped articles from chitin, such thàt those articles shall ha~e physical properties and utility substantiall~ improved over those ~f the prior art, which are comprise~ almost wholly o~ amorphous chitin.
Like certain other natural a~d synthetic polymers, chitin may occur in amorphous, s~retched amorphous, partially crystalline and unoriented, and crystalline, oriented forms. Broadly these are described as different degrees of order or organizationO
~ibrillar chîtin, for example, from the tendons of crustaceans ~Clark and Smlt~) is of the highest natural occurring order; it is highly crystalline as shown by double refraction along the fiber axis and the characteristic Maltese Cross with a polarizing microscope, and its x-ray pattern shows the sharp multi-nodal pattern typical of known crystalline, oriented fibers. Amorphous portions of natural chitin and most reconstituted chitins show no Maltese Cross with a polarizing microscope and only broad, difuse concentric rings in their x-ray patterns. They may show some double ref action under a polarizing microscope arising from the strain of stretching. Similarly, there are striking di~ferences in the specif~c gravity of the different orms of chitin, ranging from about 1.35 for the amorphous material to about 1.49 for the highly crystalline fibrils. There are, of course I grada~ions and

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overlap in the degree of order or organizations of the chitin, both in the natural and renatured states, and such differences are found in natural chitins even from different areas of the same animal. The distinctions are determined by a ~ombination of physical measurements, such as those indicated above.
The problem confronting the investigator then is to devise a method for converting a solution of chitin, in which the chitin is fully dissolved or dispersed, and without order or organization, into a shaped article with a high or at least conkrolled degree of crystallinity and/or orientation. We have found that we can accomplish these objectives and produce products of the desired qualities by a multis~age process that involves controlling the molecular structure and maximizing the properties of the chitin products.
The presen~ invention in one aspect, resides in a process for manufacture of a shaped object of renatured chitin containing renatured crystalline chitin in an amount , .
sufficient for said shaped object to be cold drawn; which comprises forming an anhydrous solution of natural chitin, forming the solution into the shape desired and coagulating the chitin from the solution with an anhydrous coagulating medium so as to obtain the shape desired and to form fibrils, crystallites or spherulites in the coagulated structureO
In another aspect, this invention resides in a shaped object of renatured chitin containing renatured crystalline chitin in an amount sufficient for said shaped ob~ect to be cold drawn.
The above aspects of the invention are disclosed and claimed in Canadian Patent Application No. 250,379 of Austin et al, filed April 15, 1976, of which the present application is a divisional.
~ .
~ - 4 -In a further aspect, this invention resides in a method of post-forming a shaped article of renatured chitin containing renatured crystalline chitin, which comprises subjecting it to inelastic stress in the solid state whereby permanent orientation is induced.
In yet a further aspect, the present invention resides in a shaped article from renatured chitin having an X-ray fiber pattern, ~g. multi-nodal pattern grouped around two axes normal to each other, characteristic of an oriented fiber.
More specifically, the process of the invention comprises the following steps 1. Chitin is dissolved in a solvent comprising dichloracetic acid or trichloracetic acid, such as the chloracetic acid systems in the U.S. Patent 3,892,731 of July 1, 1975, by P.R. Austin, usually in combination with at least one other anhydrous organic solvent.
2. The chitin in the solution of step 1 is coagulated or renatured, in the form of a fiber, film~ tube or other shape by addition of an excess of an anhydrous organic liquid which is a non-solvent for chitin.
3. The coagulated shaped object is neutralized and/or leached with an alkaline reagent, preferably in a anhydrous system, then washed with water until it is neutral, and then driedO ~.
40 Optionally, the shaped chitin object obtained as described in steps 1, 2, and 3, is oriented by subjecting it to cold drawing in the solid state to a length at least 25 ; greater than its original dimension.
The following examples illustrate, but in no way limit, the practic~ of this invention.

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Two parts of red crab O~lio chionecetes chitin was dis-solved in 87 parts by weight of a solvent system compri~ed of 40 percent by weight of trichloracetic acid, 40 percent chloral hydrate and 20 percent methylene chloride, with mechanical agitàtion for a period of 30 minutes. The solutlon was ~ery viscous and was filtered through wool felt~ A ribbon of ~he solution was flowed on glass and then immersed in acetone to coagulate it. The ace~one was removed and replaced with fresh aceto~e several times at 15-munute intervals. The clear, co-agulated band had substantial ten~ile strength. It was neutrallzed and washed with a 5 perc~nt sodium hydroxide and potassium hydro-xide mixture in 2-propanol, washed with water and air-driedO The x-ray pattern of this material revealed disti~ct, concentric : Debye rings closely similar to those of natural crystalline, unoriented alpha-chitin ~Carlstrom, J. Biophys. Biochem~ Cytol., Vol. 3, p. 669-683, 1957) and to the red crab ~Lake from which it was preparedO
The above ribbon was then cold drawn wit~ necking down, to twice its initial le~gth. The resultant oriented ribbon could he tied into a knot and pulled tight without breaking~ With further extension, breaking occurred at some imper~ection rather than at the knot. This renatured, cold-drawn xibbQn had an x-ray diEfraction pattern of an oriented fiber, characterized by three main layer lines along the vertical. axis (drawn through strong nodal points), two strong row lines laterally, and three weaker though distinct row lines that can be drawn laterally ~rom the ;~ center through the 1PSS distinct ~odal points. This pattern fits well with that of natural fibrous alpha-chitin ~Rudall~ K.M., Advances in Insect Physiolo~y, Vol. 1, Academic Press, New ~ork, 1963). The cold~drawn ribbon on obser~ation with a polarizing microscope was highly birefringent and showed extinction along the fiber axis u~der crossed Nicols.

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c' Another solution of chitin prepared as descxibed in the forepart o this example was extremely viscous and flowed very slowly to form a film, which was coagulated with excess acetone, neutralized and washed with 5 percent potassi~Lm hydroxide-sodium hydxoxide mixture, in 2-propanol, and flnally washed with water.
The use of an alcoholic system for neutralization appeared superiox to an aqueous system. The film, observed under the microscope showed the presence o~ many fibrils in an apparently amorphous mat.
~
A solution of red crab chitin was prepared hy dissolvi~g 2 parts (~y weight) of chitin in 87 parts of a solvent systPm com-prised of 40 percent (by weight) trichloracetic acid, 40 percent chloral hydrate and 20 percent methylene chloride ~ith mechanical agitation for 30 minutes, followed by filtration through wool felt.
A portion of the viscous chitin solution was extruded through an orifice into acetone to yield a mono~ilament and another portion was poured onto glass in the form of a ribbon, ~hich were then immersed in acetone. In each case the products were washed several times with fresh acetone during a one-hour period, retained acid neutralized by treating with S percent by weight sodium hydroxide~
potassium hydroxide solution in 2-propanol at room temperature, and washed with water until neutral~ The materials were subseq-uently extracted with methylene chloride for ~our hours. The samples were then tested with the results given below.

~ensile Strength Elongation N2 C12 Material k~/s~ mm* % ~ ~

Filament 63 13 5.03 9.45 Ri~bon 104 44** 5.03 9.45 - * Break dimension; Instron TT-CM tensile testing machine ** Cold draw It will bP noted that the chitin retains solvent tenaciously and that even after neutralization and extraction with methylene ^ 6 --chloride the samples contained portions of the original chitin solvents employed as indicated ~y their chlorine content. Never~
~heless, the material could be cold drawn to give a very trong filament, which is birefringent and showed a marked nodal pattern by x-ray diffraction, indicating fiber orientation. The extruded filament was perhaps partially ordered by extrusion stress and showed lower elongation, without the striking enhancement of tensile streng~h induced by cold drawing.
E ~
Two parts of red crab chitin ~as dissolved in 87 parts of a solvent ~uxture comprised o 40 percent trichloracetic acid / 40 percent chloral hydrate and 2 0 percent methylene chloride .
Solution was accelerated by gentle warming and stirring for 30 minute~ . A very thick~ viscous solution was obtained which was iltered through felt.
One portion of the chitin filtrate solution ~as doctored onto glass to a thickness of about one-sixteenth inch. It was immexsed in acetone to coagulate and wash it, and given three successi~e fresh acetone washes each lasting 15 minutes. It was ~hen ~eutra-~0 lized and washed with a 5 percent solution of potassium hydroxidein 2 propanol and finally with water to pH of 7~ The film was tough, clear and ductil~, and part of it was cold drawn to two times its lenyth. Films neutralized with aqueous potassium hydroxide appeared weaker than those prepared in an anhydrous system. Observation of the undrawn film under a polarizing micro-5cope showed the presence of fibrillar material interspersed in a generally amorphous chitin matrix. The scanning electron micro-scope revealed small bundles of fibrils embedded in an amorphous mat. The dra~n film, above, upon x-ray analysis, showed a marked nodal pattern ~ery similar to that of the dxa~n ribbon o Example I, although not as intense.
A second portion of the aboYe ~iscous chitin solution was 3~ ~
placed in a vessel ~ith a single ~ine orifice and the solution was extruded under pressure into an excess o~ acetone. Fine mono-filaments were produced that were clear and coh~,rent and retained thPir entity with both appreciable strength and elasticity. They were wa~hed successively with acetone, 5 percent potassium hydro-xide in 2-propanol, and water as descxibed above for film preparation. The renatured chitin filaments wexe strong, ~emi-clear and easily cold drawn to ~wo or three times their initial length. One sample, 0.5 ~nO in diameter was drawn to a fiber of 0.25 mm. in diameter. The presence o~ moisture in the filament facilitated the cold drawing.
Examination of the undrawn extruded filament ~ith the scan-ning electron microscope revealed surface striations with axial furrows, apparently a collapsed tubular structure. An x~ray analysis of the filament gave a patt,ern with sharp concentric Debye rings and also nodes at both the vertical and lateral positions, indicating high crystallinity together with some fiber orientatio~ duri~g extrusion.

To 87 parts of 40 percent trichloracetic acid/40 percent chloral hydrate/20 percent methylene chloride solution, 2.0 parts of red crab chitin (Opilio chionecetes~ were added. This chitin . .
had been prepulverized to pass through a ~4~mesh screen. This solution was magnetically stirred for 45 minutes, adding small port,ions of methylene chloride as the solution became too ~iscous to stir until 5-10 parts of methylene chloride had been added.
This viscous solu~ion was filtered free of undissolved material ~hrough felt and then ~hrough glass fiber mat. ~t was then immediately cast upon gLass and doctored to an even thickness.

After several acetone (dried with Drieri~e) washes, reprecipitation of clear, tough films was evident. These films had good strength, pliability and cold drawing capability. They were then extracted *Trade Mark 3~ ~;
for 12 hours in a soxhlet.apparatus with equal parts by volume of methylene chloride and acetone and were then immersed for storage in acetone (dry) or dried in air for testing. These extracted, dried films maintained their good characteristics and still had cold drawing capability. The specific gravity of these films fell in the 1. 46 - 1. 47 g;~ml. range. Elemental analysis sho~ed that they contalned 5.10 percent nitrogen and 9.54 percent chlorine. Ater treatment of a portion of the extracted, dried films in a boiling solution of one percent sodium hydroxide in }O ~-propanol, ele~ental a~ysis revealed that the nitrogen content was 6.56 percent and the chlorine content had dropped to 0.67 percent ~pure chitin has a nitrogen content of 6.9 percent); the sp~ gr. was 1.42 - 1.45.
Viewing the extracted, dried film under ~he polarizing micro-scope revealed a high degree of relative birefringence and the existence of Maltese Cross interference patterns, indicative of a : high degree ofsPherUlitic crystall nity.
X~ray diffraction analysis of the extracted, dried film ga~e a pattern of concentric Debye rings, visually consistent with that fxom the source chitin. Mathematical analy~is o~ the d-. spacings tabulated below was in good agreement ~ith the source material, confirming that the product approached renatured chitin.
d-Spacing (Angstroms) ;: Rea Crab_ChitinRenatured_Film_ : 11.00 11.00 11.02 10.34 9.64 9.70 7.86 7.45 7.~5 6.81 --- 6.81 - 5.38 5.47 5.~8

4.87 4.75 ~o8~
4.30 ~.07 4.32 3.89 3~82 3.93 To evaluate the cold drawing properties of the extracted, dried film, a portion was cold drawn by hand, with an extension of about 85 percent. The hand-dra~n film was cut into strips of constant width with a razor blade; the samples were conditioned _ g _ .

~ ) a~ ambient temperature and 50 percent relative humidi.ty and were tested for tensile strength and elongation. Based on their original dimensi~ns, their tensile strength varied between 52-58 kg/sq mm; total elongation was approximately 125 percent which included cold drawing by hand and machine. Retesting of these totally drawn materials revealed an average t nsile strength of 75 kg/sq mm with one sample at high as 95 kg/sq mm; residual elongation was about 4 pexcent.

E~ æ~
Two parts of red crab chitin, 125 parts of dichloracetic acid and 54 parts of methylene chloride were stirred intermittently for one hour at room temperature to swell and dissolve the chitin.
The system b~came very viscous, but still contained undissolved gel particles that were removed by filtration through wool felt.
The clear filtrate was flowed on glass, methylene chloride allowed to evaporate during 20 minutes and acetone added carefully to cover the thickened chitin so~ution without disturbing its continuity. After 15 minutes the acetone and extracted solvents were decanted and the film covered with fresh acetone. The extraction, decantation and acetone replacement was repeated;
the total time of acetone extraction was one hour and the film was stored in acetone, and then dried in air. Th~ air-dried film was treated with 2 percent aqueous sodium carbonate solution at room temperature for 30 minutes and then washed with water.
The film was air dried and kept at high humidity, as moisture acts as a plasticizer for the ~ilm.
Narrow sections of the chitin film were cold drawn ~y hand to about 25 percent elongation and showed the ~ollowing charac~er-istics of crystallinity and orientation: some drawn sections had a dumbell shape, indicating the necking down o cold drawing;
broken SectlonS at times left ~ails of fibrillar chitin; drawn portions appeared more transparen~ than the original film; over-~ 10 ~

33~
drawn s~ctions whitened, indicating lack o~ adequate moistureand resul~ant inhomogeneities in the drawn film; portions tGughened and curled on drawing between tight fingernails; with the polarizing microscope the drawn film showed high birefringence and parallel extinction, and imperfect Maltese Crosses evidenced by characteristic light spots in the film, indicating spherulitic crystallinity.
The examples above were selected to illustrate significan~
aspec~s of ~he inveniion, but are not to be considered limiting.
Thus to one skilled in the art, many variations of the operations and choice of materials will be evident and are considered within the cope of this inventionO Several such variations and alter-natives are indicated herewith~
~ hitin from red crabs has been used in the examples and is so called alpha-chitin, but it is known that chitin from other crabs, e.g., blue, rock, king and Dungeness crabs, and from lobsters, shrimp, crayfish and other crustaceans is of the alpha type and such chitin sources may also be used to prepare the products of this invention. Chitin from other structure~ such as the cell walls of fungi and the hard shell of insects may be the same or of the beta or gamma type of chitin, which differ mainly in molecular spacial arrangement and only slightly in chemical structure, but since they all revert to a random structure in solution, their conversion (renaturing) to a strong film, fiber or other shaped structure maXes any of the chitins, whatever their source, suitable for use in this invention. The chitins may vary slightly chemically, dPpending on source and method of separation from shell and proteinaceous materials, for example; such variations may include molecular weight, partial hydrolysis of ~he acetamide group and/or the presence o water of hydration.
However, such chitins will still be insolu~le in dilute acetic acid, whish distinguishes them from the chitosans, obtained from chitins purposely hydrolysed to a substantial degree. Chitins of high molecular weight are preferred in carrying out this invention.
Natural chitin includes an amorphous form, associated or aggregated particles containing spherulitic crystalline materlal and showing the ~ypical Maltese Cross with a polarizing micro-scope, ibrils having a spheruli~ic strustuxe with one very long axis (showing Debye rings with x-ray analysis and parallel extinction under crossed Nicols with a polarizing microscope), and oriented fibers giving characteristic nodal x-ray patterns.
There are of course overlaps and gradation in ~hese structures.
Each of these forms has i~s counterpart in reprecipitated or renatured chitin ovex a range of products including powders, unsupported film, ~ibrils and oriented fibers~
The specific solvents employed to dissolYe the chitin are selected as a matter of convenience and economics. Although such solvents are normally dry, adventitious moisture entering the system as absorbed water in or on the chitin, or as a hydrate or azeotrope of one of the solvents is frequently tolerated and may at times be advantageous. Solv2nts ~hat are particularly useful in combination with the chloracetic acids mentioned above in dissolving chitin include formic acid, acetic acid, glycollic acid, chloral, chloxal hydrate, nitromethane, chlorinated aliphatic hydrocarbons such as methylene chloride and tetrachlorethane.
The proportions of the chloracetic acids in the solvent mixture can vary widely, amounts ranging from 25 percent to 80 percent by weight of the mixture are suitable. More than one a~Xiliary ~ ;
solvent can be employed in the sol~ent mixture. Thu~, for example, a mixture of 40 percent, by weight, trichloracetic acid, 40 percent chloral hydrate, and 20 percen~ methylene chloride is especially preferred. The concentration of chitin in the solution can also vary widely. Solutions containing less than 0.5 percent, - 12 ~

$
by weight, to lO percent are useful. Chitin conc~ntrations of from l to 5 percent are preferred.
Because trichloracetic acid and chloral are held so tenac-iously by chitln, certain after-treatments may be employed to remove them more completely~ such as heating with dilute aqueous ammonia or other alkali or by soaking in such media over a long perlod. Alternatively, recourse may be had to the use of other solvents for chitin such as phenol, cresol or other phenolic compound in conjunction with a chloxinated or fluorinated solvent, an amide or a sulfoxide. Some of the ~luorinated solvents, although expensive, may be useful as chitin solvents by themselves or in conjunction with one or more of the oth~r solvents mentioned.
Ren~turing connotes the reforming of chitin from its solution to a solid structure possessing to a substantial degree the organization of ~atural crystalline chitin. Mere coagulation or precipi~ation as described in ~he prior art, or regeneration from the xanthate as i~dicated in the cited references yields only amorphous chiti~ showing no crystal structure with x-rays 2V or polarizing microscope, having a low speci~ic gravity and incapable of being cold drawn appreciably ~ithout breaking. The 5tretching of a coagulating fiber may give strain and orientation as indicated by parallel extinction under crossed Nicols, but the x-ray pattern shows the absence of crystalline structure (Clark ~ld gmlth, 1936~. Fibrous natural chitin has been described by Hackman and Goldberg, 1965l as comprising about 30 percent of crystalline, organi~ed molecular chitin. Such measurements are not precise, but at least a few percent of such oxganized material is re~uired before a renatured chitin structure can be cold drawn.
The renaturing of the chitin takes place principally in the insolubilization step using a non-sol~ent for the c~itin~
Commonly the chiti~ disso~vad in the organic solvent is extruded in aceton~ or other orgaIlic non-sol~ent for a sufficient time to penmit some degrea of crystalliæation--organization o the chitin to take place. There is a time-temperatureooncentration inter~
reLationship here that is optimized by suitable pilot trials~
It appears that the shaped article may first be "case hardened", that is, a skin is formed around the inner still-soluble system and the inso1ubilization and crystallization~organization then proceeds by diffusioIl o non-solvent in through the membrane and the chi~in solvent QUt to the excess of leachi~g solvent~ This action, together with subsequent neutralization ~if required) and drying involves some collapse of the structure wi~hin its skin becau~e of the reduced volume, with consequent emer~ence of a characteristic film or fiber morphology. Suitable coagulat-ing agents include aliphatic ketones; e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, and cyclo-pentanona; chlorinated aliphatic hydrocarbons; e.g., excess methylene chloride, carbon tetra-chloride, trichloroethylene, and tetrahydrofuran; hydrocarbons, e.g., cyclohexane, hexane, and petroleum ether. Alcohols such as ethyl alcohol~ isopropyl alcohol, n-bu,tyl alcohol can be used~ especially after pre-liminary coagulation o'f the chitin has been obtained by means of one of the a~ove-mentioned non~solvents.
With an acid solvent system for the chitin, a neutralization step is usually desirable. If the insolubilization in an organic solvent is essentially complete, then aqueous alkali or ammonia may be used for the neutralization. Depending on time and other processing conditions, however, it may be desirable to neutralize ' with a nonaqueous s~stem such as a]coholic alkali metal hydroxide, which permits insolubilization and crystallization to continue at the same time. Salts ~ormed during neutralization are finally leached with water to yield the salt-free chitin product.
Alkaline materials useful in the neutralization step include ~..
~ 14 -$~ii sodi~m carbonate, al~ali metal hydroxides; e.g., lithium, sodium and potassium hydroxides r pyridine and ammoniaO Pxeferably tha neutralization is carried out with a 1 to 5 percent, by weight, solution of one or more alkali metal hydxoxides in an aliphatic alcohol of up to four carbon atoms; e.g~, methyl, ethyl, iso-propyl and n-blltyl alcohol.
Cold drawing is an op~ration commonly applied to crystallin~
polymers to orient them and enhance their properties~ Thus polyethylene, nylon, polyethylene terephthalate and polyvinyl-idine chloride are all crystalline polymers capable of b~ing colddrawn and are frequently so oriented as to develop their optimum properties for various uses. For chitin fibers, drawing may be carried out between differential speed rolls, between a snub pin or mandrel and a fiber-advancing rGll, or other device that wiil : control their elongation in uniform manner to 25 percent or mora o the original length. Drawing to at least 2.0 times the original length gives objects having greatly improved properties.
If desired, the fibers may be moistened or humidified with . steam. The drawing may be carried out at any temperatuxe below the decomposition point of the fiber, but is customarily drawn between 0 and 150C. Plasticizers or humectants such as glycerol may be employed to facilitate the drawing.
With chitin film, a one-way stretc~ may be imparted as desc.ribed for fiber, but if desired a two-way cold drawing may be carried out, for example, b~ means of a tenter frame. Drawing of a sheet may also ~e accomplished by use of a ~lat iron shaped mandrel to serve as a focal poi~t for ~he drawing. Alternatively, ~ tuhi~g of chitin film may be blown ~o impart circl~mferential drawi.ng and orientation, and the blown film used as such or cut to flat film.
Depending upon the nature of the shaped article o chitin, ~he oold drawing step may b~ carried out by cold rolling, 3~ `

extrusion and dra~in~ through a constricting die, or by stamping.
A~ with the crystalline polymers mentioned abo~e, the chitin shaped articles may be conditioned or set in predeter-mined form by heating them, as such or under tension or restraint in the desired form with or without the presence o~ moisture.
In this way not only tensile strength but residual elongation, ~lasticity, stiffness, shxinkage, recovery ~rom deformation, and shape can be controlled.
The pliability of the renatured chitin products can be enhanced by incorporation o~ plasticizers or humectants having a significant degree of compatibility with chitinO ~xamples of suitable materia~ for this use include glycerol, ethylene glycol, propylene giycol and sorbitol.
Because of their inertness to water, steam cterilization and storage conditions the films both as formed and as cold drawn are useful in food wrapping, such as sausage casings, oven products and dairy products. The undrawn films are partic-ularly useful where the film is subjected to temporary stress.
The fibers, particularly when oriented, are especially adapted to use as sewing thread and decorative fibers where their good ~ dyeability, strength and controlled elongation are advantageous.
- Use of the chitin a~ surgical sutures has been descxibed by L.L. Balassa, U.S. Patent 3,632,754, January 4, 1972, in part because of its ability to accelerate wound healing. The ~ oriented chitin fibers of this invention are particularly suited - for this purpose because of their enhanced tensile strength and elasticity.
It is apparent that changes and modifications may be made without departing from the invention in its broader aspectsO
The aim of the appended claims, therefore~ is ~o cover all such changes and modiications as fall within the true spirit and scope of the invention.

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Claims (14)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of post forming a shaped article of renatured chitin containing renatured crystalline chitin, which comprises subjecting it to inelastic stress in the solid state whereby permanent orientation is induced.

2. A method of post-forming a shaped article of renatured chitin containing renatured crystalline chitin, which comprises subjecting it to ineleastic stress in the solid state whereby the post-formed article is characterized by the multimodal x-ray diffraction pattern of an oriented fiber.

3. A cold drawn shaped object of renatured chitin containing crystalline chitin.

4. The cold drawn shaped object of claim 3 that has been cold drawn at least 25 percent of one of its original dimensions.

5. The cold drawn shaped object of claim 3 that has been cold drawn at least 25 percent of one of its original dimensions and has a specific gravity above 1.40.

6. A method of orienting a shaped object of renatured chitin containing renatured crystalline chitin in an amount sufficient for said shaped object to be cold drawn, which comprises subjecting it to inelastic stress in the solid state until it has been elongated to at least 25 percent greater than its original dimensions.

7. The method of claim 1 wherein the stress is applied by cold drawing, cold rolling, stamping, die extrusion or blowing.

8. The method of claim 6 wherein the stress is applied by cold drawing, cold rolling, stamping, die extrusion or blowing.

9. A shaped article from renatured chitin having an X-ray fiber pattern, eg. multi-nodal pattern grouped around two axes normal to each other, characteristic of an oriented fiber.

10. A cold drawn shaped article in accordance with claim 3, 4 or 5 which is in the form of a fiber or film.

11. A shaped article in accordance with claim 9 which is in the form of a fiber, film, tubing or stamping.

12. The shaped article of claim 9 that has been stressed to at least 1.4 times its original dimensions.

13. The shaped article made by the method of claim 7 wherein the article has been stressed to at least 1.4 times one of its original dimensions.

14. The shaped article made by the method of claim 7 and having an X-ray pattern substantially identical to that of oriented fibrous natural alpha-chitin.