Antibiotic Paper

Abstract

Cellulose fibers possess strong antibiotic properties (including antiviral properties) when they have a uniform content of a small amount of a 2-(C.sub.8 -C.sub.18 substantially straight chain) pseudourea. The fibers remain antimicrobial when in addition they contain a normally water-soluble thermosetting wet strength resin in thermoset state. Antibiotic bandages, diapers, bed sheets, boxes, surgeons' gowns, etc. can be prepared from paper composed of these fibers.

Parent Case Text

This is a continuation-in-part of my copending applications, Serial Nos. 773,954 and 42,749, respectively, filed November 6, 1968 and June 1, 1970, and now both abandoned.

Description

The present invention relates to cellulose fibers and fibrous cellulose structures having antimicrobial properties. More particularly, the invention relates to cellulose fibers, water-laid cellulose webs (including paper) and articles made therefrom having antimicrobial properties resulting from the presence therein of a uniformly adsorbed content of an ionic pseudourea, and to methods for the manufacture of said fibers and webs. For convenience, the term "antimicrobial" is hereafter used to describe the inhibiting of the life of all microbes including fungi, bacteria, protozoa and viruses.

Antimicrobial paper is paper composed of fibers which have an effective content of an agent which inhibits the growth thereon of some or all of the forms of life just mentioned. In the past, the principal use of such paper has been as mulch paper (paper which is spread on the ground to inhibit the growth of weeds and the evaporation of water), but such paper is coming to find important use for such purposes as bandages, boxes for bandages and other surgical equipment, diapers, surgical drape sheets, hospital gowns and bed sheets, and as the base for surgical adhesive tape. Such items are commonly supplied in sterile form, and during their period of use they must resist microbial growth. Paper which possesses antiviral properties is urgently desired, for example in connection with the care of patients with head colds, influenza and mumps.

Because of the long period of time during which it must maintain its integrity in the warmth and humidity of the environment, mulch paper must be highly and comparatively permanently resistant to microbial attack. Mulch paper is moist during much of its life at a temperature most favorable to the growth of microorganisms, and is subject to severe tearing forces (e.g., by the wind) from time to time. Mulch paper desirably maintains its identity and strength during the growing season and nevertheless should ultimately succumb to attack by microorganisms, i.e., it should be greatly weakened or disintegrated by them within two to three months after being plowed under ground at the end of the growing season. PaPer used for bandages, hospital sheets, surgical drape sheets and underwear should likewise possess wet strength.

The discovery has now been made that cellulose fibers which have an adsorbed content of a long chain alkyl pseudourea of borderline solubility such that it is substantially insoluble in water as the free base but is soluble in acid possesses antimicrobial properties alone and in the presence of wet strength resins in thermoset state, and these properties are retained when the paper is exposed to moist conditions for long periods of time at elevated temperatures such as are encountered in outdoor weathering. I have found that in preferred embodiments such as when the paper is sufficiently antimicrobial to strongly resist the growth of microbial life under incubating conditions, the fibers carrying a pseudourea of the type described remain substantially sterile.

The present invention in preferred embodiments provides improvements as follows:

1. Bulk fibrous cellulose ("cotton wool") carrying a pseudourea (or pseudothiourea) of the type described possesses antimicrobial properties when used as surgical and dental packing in wounds, and when employed as packing material in boxes has the property of maintaining the inside of the boxies substantially sterile with respect to yeasts, bacteria, protozoa, and lipophilic viruses. 2. Paper comprising the aforesaid fibers possesses similar antimicrobial properties and remains substantially sterile when employed as diaper material for babies, surgical drape sheets, hospital gowns bed sheets, etc.

3. The paper strongly resists attack by microorganisms found in agricultural fields, and this activity is not masked when the paper has an effective amount of a normally water-soluble wet strength resin in thermoset state. Moreover, the paper is readily permeable by water, and hence permits rain to penetrate into the ground, and is accordingly well-suited for use as mulch paper. The paper is substantially unaffected by the action of microorganisms when allowed to remain for three to five months on fields under temperature and humidity conditions highly conducive to the rapid growth of microorganisms (temperatures of 70.degree. F.- 90.degree. F. and relative humidity in excess of 50 percent).

The microbial life against which the paper of the present invention possesses activity include the bacteria, (including sulfate-reducing bacteria), yeasts, fungi, and green algae, and lipophilic viruses.

The pseduoureas referred to have the formula

R represents a C.sub.8 -C.sub.18 substantially straight chain alkyl substituent. Suitable substantially straigh chain alkyl substituents include octyl, dodecyl, hexadecyl and octadecyl. The aforesaid pseudoureas dissolve in water containing a stoichiometric excess of hydrochloric acid, acetic acid, formic acid, trichloroacetic acid, nitric acid, phosphoric acid or other strong acid. The molecule as a whole is cationic.

The amount of pseudourea present in cellulose fibers and in the paper of the present invention depends upon the specific antimicrobial activity of the pseudourea present, the vitality of the microorganisms present, and the degree of antimicrobial activity which it is desired that the fibers (or paper, paperboard, etc. which have a content thereof) should possess. As a rule of thumb, I have found that in most instances, cellulose fibers possess perceptible antimicrobial activity when they contain as little as 0.1 percent of the pseudourea based on the dry weight of the fibers. On the other hand, I have found that the fibers need not contain more than about 3 percent by weight of the pseudourea for them to possess very satisfactory antimicrobial activity. My results to date indicate that satisfactory results are obtained when the fibers contain between about 0.3 percent and 0.5 percent by weight of the pseudourea as in this range the fibers (and the paper) possess very satisfactory antimicrobial activity yet over-use of the pseudourea is avoided. The optimum amount of pseudourea that need be present in any instance to procure the desired antimicrobial activity can be readily found by laboratory trial.

The pseudoureas referred to above are most conveniently applied by forming an aqueous suspension of cellulose fibers and adding to the suspension one or more of the aforesaid pseudoureas as a water-soluble salt. The pseudourea component of the salts are rapidly and substantively absorbed by the fibers and the amount of pseudourea which is present in the fibers of the final product can be determined by calculation based on Kjeldahl nitrogen analysis.

Thereafter the suspension is processed into paper or paperboard in any customary manner. The fibers are formed into a web web by flowing the suspension over a foraminous substrate, and the web is dried at an elevated temperature into the desired form.

For the manufacture of cotton wool the fibers in the suspension may be allowed to accumulate on the foraminous substrate so as to form a wet web of substantial thickness which may be dried, and the resulting batt carded so as to separate the fibers into a fluffy wool-like product.

For processing into paper, the suspension is formed into a wet web at some normal basis weight and the wet web is dried over steam-heated rolls.

In many instances when the end product is paper or paperboard, it is desired that such product possess wet strength properties. These properties can be imparted by adding any of the known cationic thermosetting wet strength resins for paper along with the pseudourea, or by applying the wet strength resin subsequently, for example at the size press, the paper being subsequently heated to develop the wet strengthening properties of the resin. Suitable resins include the melamine-formaldehyde resin colloid of Maxwell et al. U.S. Pat. No. 2,345,543, the polyamine-epichlorohydrin resins of Daniel et al. U.S. Pat. No. 2,595,935, and the polyamidepolyamine-epichlorohydrin resins of Keim, U.S. Pat. No. 2,926,154.

It may be desired that the paper and paperboard of the present invention possess superior dry strength without possessing permanent wet strength (to facilitate disposal of the paper after use). This can be accomplished by adding a water-soluble cationic or non-ionic dry strengthening agent along with pseudourea. Suitable polymers for this purpose are disclosed in Woodberry, U.S. Pat. Nos. 2,959,514 and 3,258,393.

The invention will be further illustrated by the following examples which illustrate embodiments of the invention and are not to be construed as limitations thereon.

EXAMPLE 1

The following illustrates the manufacture of antimicrobial cellulose fibers resulting from the presence thereon of a small amount of water-insoluble pseudourea.

Aliquots are taken from an aqueous neutral suspension of well-beaten cellulose papermaking fibers at a consistency 0.6 percent and to these are respectively added sufficient of 10 percent by weight solutions of:

1. n-Decylpseudourea hydrochloride

2. n-Dodecylpseudourea nitrate

3. n-Dodecyl-N,N-dimethylpseudourea acetate

4. n-Hexadecylpseudourea trichloroacetate

to provide up to 0.5 percent of the urea derivative (as the free base), based on the dry weight of the fibers. The pH of the aliquots is then adjusted to 6, and the suspensions are gently stirred for a minute to permit the pseudourea to be adsorbed by the fibers. The pH of the suspension simultaneously decreases.

The resulting suspensions are formed into thick water-laid webs on a laboratory handsheet machine which are oven-dried at 190.degree. F., and the resulting webs are hand-carded using a textile carder. Fluffy resilient masses are obtained which resemble surgical cotton wool.

Samples of the cotton wool are respectively sprayed with suspensions of:

1. Aerobacter aerogenes

2. Bacillus cereus var. mycoides

3. Pseudomonas aeruginosa

4. Chaetomium globosum

5. i Penicillium citrinum

6. Penicillium expansum

7. Trichoderma viride

8. Aspergillus flavus

9. Fusarium moniliforme

10. Aspergillus niger

in a standard laboratory nutrient medium (agar-agar medium containing protein as source of nitrogen, carbohydrate, and calcium, magnesium, potassium and iron salts of the type normally present in said medium) to provide nutritional requirements for the microbial life thereon. The samples are allowed to stand for three days at 30.degree. C. and 75 percent relative humidity, to permit the fibers to exert their biocidal properties, and then are incubated on sterile agar plates, in comparison with control samples of cotton wool which contain no antimicrobial agent, to determine the extent to which the microbial life has been arrested. At the end of the incubation period the plates carrying the test cotton wool are substantially or completely free from microorganisms, whereas the control plates carry heavy growths of microorganisms.

EXAMPLE 2

The following illustrates the manufacture and use of mulch paper according to the present invention.

Into a furnish composed of a 50:50 mixture of hard wood and soft wood papermaking fibers at pH 4.5 at a consistency of 0.6 percent, as it passes through the machine chest in a paper mill, is metered a 5 percent by weight solution of n-dodecylpseudourea hydrochloride at a sufficient rate to provide 0.5 l percent of n-dodecylpseudourea (as the free base) based on the dry weight of the fibers and a solution of the melamine-formaldehyde wet strength acid colloid of Maxwell et al. U.S. Pat. No. 2,345,543 at the same rate. The furnish is processed into paper at a basis weight of 50 lbs. per 25" .times. 40"/500 ream, and the paper is dried at 190.degree. F.-250.degree. F. for about 1 minute. Kjeldahl nitrogen analyses of the paper show that the dry paper contains 60 percent -70 percent by weight of the dodecylpseudourea which had been added. From experience it is known that most of the remainder was adsorbed by the cellulose fibers, which were lost with the white water.

The resulting paper is transported to a pineapple plantation and is rolled upon the ground by an automatic pineapple seedling planter. Pineapple seedlings are then planted through approximately 1 inch diameter holes punched through the paper.

The paper largely prevents the growth of weeds around the seedlings, does not support microbiological growth during the period that the pineapples are growing, resists tearing when wet, and shortens the vegetation period of the pineapples. The paper loses virtually all its strength and disintegrates to fibrous state within three months after being ploughed under the ground.

EXAMPLE 3

The procedure of Example 2 is repeated except that the paper is applied as a mulch for watermelons, cauliflower, cabbage, celery, parsnips and tomatoes grown in a Florida soil. Similar results are obtained.

EXAMPLE 4

The following illustrates the remarkable antimicrobial properties possessed by a preferred paper of the present invention.

A sample of the paper of Example 2 is pressed upon a sterile Petri dish of agar upon which has previously been sprinkled an aqueous suspension of Aspergillus niger and other fungal spores. The dish is incubated at 30.degree. C. along with a control dish which contains no paper. After 48 hours the control dish carries a heavy growth of fungi, but the paper in the test dish shows no growth whatever.

EXAMPLE 5

A strip of the paper of Example 3 11/2inches .times. 2 inches is folded so as to form a strip approximately 1/2 inch .times. 2 inches. The strip is placed at the midpoint across a strip of adhesive plaster 2 inches .times. 2 inches, which is then cut to form a bandage of the bandaid type 1/2 inch .times. 2 inches. The bandage is applied over a cut and abraded area on the leg of a warm-blooded animal. The area heals without infection.

EXAMPLE 6

The following illustrates the virustatic and virucidal efficiency of the pseudoureas against typical lipophilic viruses.

A

Virus Used: Influenza B (National Institute of Health's Massachusetts Strain RMK-3)

80 mg. of 2-n-dodecylpseudourea acetate is dissolved in 200 ml. of warm distilled water giving a solution containing 400 p.p.m. of the agent. To 4.5 ml. of this solution is added 0.5 of the virus and shaken to form a uniform solution. The solution is maintained at 22.degree. C. for 10 minutes. Several dilutions are made to below 10.sup..sup.-1 biocide concentration and inoculated into rhesus monkey kidney cultures. A control is prepared consisting of 0.5 ml. of the virus in 4.5 ml. of Earl's lactalbumin hydrolysate medium.

The virucidal effectiveness of the solution is determined by the hemadsorption test wherein 3 days after inoculation the cell culture tubes are washed twice with 1.0 ml. of phosphate-buffered saline solution and 1 ml. of 0.4 percent guinea pig erythrocytes is added to each tube. The tubes are incubated for 20 minutes at 4.degree. C. and washed again with 1.0 ml. of the saline solution. The erythrocytes adsorbed the monkey kidney cells that are infected with influenza.

The procedure is repeated except that 2-n-dodecyl-N,N-dimethylpseudourea dihydrogen phosphate is used in place of the acetate.

The virus potency (log TCID.sub.50 /ml.) is 5.2 for the control and 2.2 for each of the tests with the pseudourea salts, where TCID represents Tissue Culture Infection Dose.

Each of the pseudourea salts is toxic to the virus concentrations at 10.sup..sup.-1. ##SPC1##

Example 7

The following illustrates the manufacture of an infant's diaper according to the present invention.

To an aqueous suspension of cellulose papermaking fibers at pH 4.5 and a consistency of 0.6 percent is added sufficient of an aqueous solution of n-(2-decyl)pseudourea acetate to provide 2 percent based on the dry weight of the fibers. The fibers are formed into a web on a screen and the web is allowed to air dry. The web is carded to form cotton wool which is formed into a batt about 18 inches .times. 18 inches .times. 1/4 inch. The batt is placed between two sheets of wet strength paper 18 inches .times. 18 inches, one of which is sized and the other is unsized. The edges of the two sheets are bound together with pressure-sensive adhesive tape.

Example 8

The following illustrates the antimicrobial effect of increasing amounts of a preferred antimicrobial agent as a function of the kinds of microbial life present.

A water-leaf paper sheet (paper containing no additive) of 40 lb. basis weight per 25" .times. 40"/500 ream is immersed in a 0.05 percent by weight solution of 2-n-dodecyl pseudourea ("PU") and removed. Surplus solution is allowed to drain off. The resulting wet web is dried for one minute on a laboratory drum drier having a drum temperature of 240.degree. F. and contains about 0.05 percent of the pseudourea by weight. The procedure is successively repeated with solutions of increasing strength, yielding papers of the psedudourea content shown in the table below.

The papers are then tested for their antimicrobial power against fungus (Aspergillus niger), and on a bacterium (Aerobacter aerogenes).

Results are as follows.

Growth After 48 % PU Hours at 80.degree.F. No. In Paper Fungus Bacterium Control None Heavy Heavy 1 0.05 Mod. Mod. 2 0.1 Do. Slight 3 0.2 Little Little 4 0.3 None None 5 0.5 Do. None 6 1.0 Do. Do.

Since 2-dodecylpseudourea is known to be a virucide, and since the above results show that this compound is adsorbed on paper in strongly biologically active form, it is expected that the paper described possesses strong antiviral properties as well.

Example 9

The following illustrates the manufacture of highly antimicrobial paper of excellent wet strength properties according to the invention.

To an aqueous suspension of unbleached softwood kraft fibers at 0.6 percent consistency and pH 6 in ordinary (non-aseptic) laboratory water is added with gentle stirring sufficient of a 5 percent by weight solution of 2-n-dodecylpseudourea hydrochloride to supply 3/4 percent of this compound based of the dry weight of the fibers. There is then added sufficient of a 1 percent solution of a water-soluble cationic thermosetting glyoxylated 95:5 molar ratio acrylamide:diallyl dimethyl ammonium chloride copolymer to supply 1 percent of the polymer based of the dry weight of the fibers.

The suspension is then formed into handsheets at 50 lb. basis weight which are dried for one minute on a drying roll having a surface temperature of 220.degree.F.

The resulting paper carries about 0.6 percent and 0.8 percent by weight of the respective agents, and has a TAPPI wet tensile of 9 lb. per inch.

A 6" .times. 6" sheet of the paper is then inoculated with stock laboratory cultures so as to place on the sheet cultures of a bacterium and a fungus, and the sheet is allowed to airdry at 80.degree.F. for 30 minutes. The sheet is then rolled in a plastic sheet and allowed to incubate in the dark for 48 hours. The sheet is then incubated and is found to be sterile.

Example 10

An experimental child's diaper (a commercial cloth diaper having pinned to the center a "pillow" composed of a batt of cellulose papermaking fibers between two sheets of wet strength paper, the fibers in the batt and the paper containing 1 percent of n-n-dodecylpseudourea by weight) is placed about a baby in approximately customary manner and left in position until soiled. The soiled pillow is removed and a sample incubated at 80.degree.F. No microbial growth develops.

Claims

I claim:

1. Cellulose fibers having a uniformly adsorbed effective content within the range of 0.01 percent - 3 percent based on the dry weight of the fibers as agent inhibiting the growth of microorganisms thereon of a 2-(C.sub.8 -C.sub.18 substantially straight chain alkyl) pseudourea.

2. Fibers according to claim 1 wherein the pseudourea is 2-n-dodecylpseudourea.

3. Antimicrobial paper consisting essentially of fibers according to claim 1.

4. Infants' diapers consisting essentially of a substantially square assembly of a batt of fibers according to claim 1 and two sheets of wet strength paper, one of which is sized and the other is unsized, said batt being positioned between said sheets of paper.

5. A process for the manufacture of antimicrobial paper which comprises forming an aqueous suspension of cellulose papermaking fibers, adding thereto a small but effective amount as antimicrobial agent of a salt of a 2-(C.sub.8 -C.sub.18 substantially straight chain alkyl) pseudourea, forming said fibers into a wet web, and drying said web at a temperature between about 190.degree. F. and 250.degree. F. to form paper.

6. A process according to claim 5 for the manufacture of paper which comprises forming an aqueous suspension of cellulose papermaking fibers, adding thereto sufficient of an acid solution of a 2-(C.sub.8 -C.sub.18 substantially straight chain alkyl polypseudourea) to deposit on said fibers an effective amount thereof within the range of 0.01 percent - 3 percent based on the dry weight of said fibers as antimicrobial agent, adding to said suspension 0.1 percent - 3 percent of a water-soluble cationic wet strength resin, forming said fibers into a web, and drying said web at a temperature between about 190.degree. F. and 250.degree. F.

7. A process according to claim 6 wherein the wet strength resin is a thermosetting resin containing amine-reactive substituents.