CA2111732A1

CA2111732A1 - Plant cellulose film and process of preparing the same

Info

Publication number: CA2111732A1
Application number: CA002111732A
Authority: CA
Inventors: Taogen Jin; Shuixin Tong; Mingzhen Li; Hualin Zheng; Yongwei Yu; Jianzhon Xu; Hongzhen Luo
Original assignee: Individual
Current assignee: China International Association For Promotion Of Science & Technology
Priority date: 1992-12-18
Filing date: 1993-12-17
Publication date: 1994-06-19
Also published as: DE4342723A1; KR940014563A; CN1088225A; CN1036140C; AU677243B2; AU5251393A; BR9305113A; GB2273458B; GB2273458A; JPH0770366A; GB9325981D0

Abstract

A B S T R A C T
The present invention relates to a plant cellulose film composed of by weight 50-90% of plant cellulose, 0.2-40% of modifier and 5-20% of water.
The plant cellulose film may contain herbicides, insecticides, germicides, fertilizing nutriments of N, P and K, trace elements and rare-earth elements. The plant cellulose film may be used as decomposable farming film and packaging material for goods, food such as sausages, fruits, vegetables, candies and cakes, pharmaceuticals and garbage, and carpets for man-made lawn. The plant cellulose and hemi-cellulose may also be used to make disposable cups, dishes, and food boxes. The method of preparing the plant cellulose film comprises the following process steps: concentrating, pressing, shredding, degrading xanthating and dissolving, filtering, ripening into viscose, spinning, coagulating, regenerating, desulphurizing, bleaching, plasticizing, pressing, drying, coating and winding into films.

Description

~1~ 17 32 PLANT CELLULOSE FILM AND PROCESS OF PREPARING T~E SAME

Field of Invention The present invention relates to plant cellulose film products and the process of preparing the same. In particular, the present invention relates to 5 decomposable cellulose farming films, decomposable cellulose farming films for weed-killing, decomposable cellulose farming films for insect/germ-killing, decomposable cellulose farming films with N, P, K and rare-earth elements, decomposable cellulose farming films with trace elements and rare-earth elements, and the process of preparing the same.
10 _ackground Cellulose films can be used as farming films and packages of goods, especially food, such as sausages, fruits, vegetables, candies and cakes, and pharmaceuticals. They can also be used as materials for making green carpets, garbage bags and dialysis bags.
It is well-known that there are various kinds of synthetic high molecular films and products developed since the early sixties. Polyethylene farming films and products of other synthetic high molecular materials have been used in almost every industry. The volume of the raw material used in making farming films of polyethylene in the early 1990's in China exceeded 50Q000 tons 20 with a coverage of over 50,000,000 Mu with an annual increase rate of 15%-20%.
The volume of the raw material used is expected to reach 700,000 ~o 1,000,000 tons with a coverage of 70,000,000 to 100,000,000 Mu by the 1995.
With an increased awareness of the environment and more and -2- 2.i.~ 732 more concerns of environmental pollution, scientists around the world are paying serious attention to the adverse effects on the environment and the normal growth of crops caused by high molecular synthetic plastic products and farming films of polyethylene. Such products have been used in large volumes, are hard to 5 retrieve, and do not decompose in the soil where they can be buried for a long time.
Since the early 1990's, statutory prohibitions and limitations have been made in some Western European countries, Japan and the U.S. with regard to using various kinds of high molecular plastic products that do not decompose 10 as packaging material. As a result, these countries have started to develop decomposable packaging materials and novel farming films that decompose by light.
It has long been desirable to replace synthetic high polymer compounds with decomposable films. One method has been to blow at a certain 15 temperature (170-200~C) a mixture of starch (20-150 ~lm) and polyethylene that contains over 30% of starch. As the particles of starch and the melt materials move at different speeds, an apertured film is formed, which is fragile and of low strength. Although this kind of starch film carries many hydroxy groups, which has good hydrophilicity and can be partially decomposed by microorganisms, the 20 polyethylene mixed with it carmot decompose. Moreover, its applicability is limited because of its thickness, low strength and transparency.
Another method has been to introduce the starch particles into a chemical chain so as to promote the mixing of the synthetic polymers. The films so formed are disclosed in U.S. 4337181, GB 1487050 and GB 1485833. Though 3 21~.17~2 these films can decompose, the method of preparing the film is complex and costly, and the films are low in tensile strength, relatively thick and cannot be stretched.
Light-decomposable films are synthetic high polymers wherein a 5 certain amount of photosensitizer is added during the filming process (EP230143) and the films are formed by blow-forming (calendaring) under hot melt. This type of film can decompose under ultraviolet rays. However, such decomposition is not complete, i.e. the synthetic high polymers cannot be completely decomposed into C2 and water. Moreover, when these high polymers are buried into the soil 10 without any sunlight shining on them, they simply cannot decompose.
When light-decomposable films are used as farming films, their decomposition and the season of growth of the crops should not be synchronous.
In other words, the covering farming films should be decomposed when the crops do not need to be covered any longer; and vice versa, there should be no 15 decomposition when the crops still need to be covered. However, the decomposition of the farming films made of light-decomposable films is hard to control because various conditions impact on the rate of decomposition, and many times results in the reduction of output of the crops (sometimes, because the decomposition period is not properly "synchronous" with the season of growth of 20 the crops.) Thus, the decomposition of light-decomposable films must be "controllable", which however, is quite difficult.
A decomposable film and method of making it are described in the specification of CN90109135.9, wherein a biologically decomposable film is formed by using synthetic polymers (olefins such as polyethylene or polypropylene) and bio-decomposable polymers (such as starch or cellulose) as the basic material.
However, as synthetic high polymers are also used in this film, the filming process is relatively complex. Moreover, even though the high polymers used may decompose, the time required for decornposition is quite long (the longest is two S years). Whether the remnants after the decomposition are toxic and harmful to the farmland is yet to be tested.
The specification of CN 90109250.9 describes a method of making regenerated cellulose films from cotton straw and peanut shells. Although "agricultural by-products" are used instead of synthetic high polymers in this 10 method, considerable po]lution is caused as the method uses a solution of copper-ammonia as a solvent to make the viscose. The treatment of the waste water is difficult. Further, non-cellulose comprises over 50~o of the raw materials.
Finally, the yield is low.
In view of the problems in preparing and developing decomposable 15 films in and outside China, in May of 1988 the inventors of the present invention began to study and develop farrning and forest films made of straw fibers that are inexpensive and decomposable, and filed with the Chinese Patent Office in June of 1990 a patent application entitle "A Farming/Forest Film of Straw Fibers and the Method of Making the Same", (Application No. 90103061.9 and Publication 20 No. CN 10580284,) which is cited here for reference. The straw farming film of that invention overcame the problems met by researchers in developing decomposable films. It has, among other things, the following advantages: the raw materials used are abundant, the film can be decomposed by microorganisms in the soil, and the film can preserve moisture and temperature in the soil. Thus, - s - ~ 7 3 2 such straw farming film can replace polyethylene farming fi]ms and other starch films and light-decomposable films available on the present market. The film can also replace many plastic products on the market which are made of synthetic high polymers, thereby solving the pollution problem caused by synthetic high S polymers that cannot decompose.
In recent years, on the basis of the above application and after a deep study, the inventors have improved upon the straw film and invented a plant cellulose film of the present invention which has substantive improvements and prominent technological advances in the material used, types, properties and the 10 process of the film as well.
Summan~ of the Invention The object of the present invention is to provide a plant cellulose film and its preparing process, which film can be used as farming films, packages of goods, especially packages of foods, green carpets, and materials for dialysis 15 bags and garbage bags as well. A plant cellulose film of the invention compAses plant cellulose, modifier(s) and water, with a composition of (by weight) Plant cellulose 50-90%
Modifier(s) 0.2-40%
Water 5-20%
20 Brief Description of Drawin s In drawings which illustrate the method of the present invention, Figure 1 is a flow chart of preparing and filming a plant cellulose viscose of the present invention; and Figure 2 is a flow chart of preparing and filming another type of plant -6- 71;~1732 cellulose viscose of the present inveiltion.
Detailed Description of the Invention According to the present invention, a plant cellulose film comprises plant cellulose, modifier(s) and water. The composition of the film is, by weight, 5 Plant cellulose 50-90%
Modifier(s) 0.2-40%
Water 5-20%
The raw material of the plant cellulose used in the plant cellulose film of the present invention comprises: crop straw such as straw of rice, wheat, 10 vegetable seeds, sunflower, maize, Chinese sorghum and soybean; crop shells such as shell of peanut and sunflower seeds; natural plant cel]ulose such as cotton velvet and hemp; wood such as birch, China fir, pine and bush; plant pulp and residue such as wood pulp and bagasse; grass such as Chinese alpine rush (eulaliopsi binata) and reed; and bamboos.
According to the present invention, the plant cellulose film comprises preferably 55-85% by weight of plant cellulose, and most preferably 60-80%.
The types of modifiers that may be used in the plant cellulose film of the present invention are various and comprises: aromatic esters such as di-n-~; 20 butyl phthalate, dicapryl phthalate, di-(2-ethyl he~yl) phthalate, di-iso-nonyl phthalate, diheptyl phthalate, butyl benzyl phthalate, di-iso-nonyl phthalate, butyodecyl phthalate, butyl phthalyl butyl glycollate, di-(2-ethyl hexyl)4, 5-epoxy tetrahydro phthalate, butyldecyl terephthalate; aliphatic esters such as dimenthyl glutarate, dibutyl glutarate, ethylene glycol di Cs-Cg fatty acid esters, '':

-7- ~111732 pentaerythritol fatty acid ester, diethyleneglycol di C7-Cg mixed acid esters, ethylene glycol butyrate, dioctyl sebacate, dicapryl sebacate, di-2-ethylhexyl maleate, butyl ester of epoxy fatty acids, 2-ethylhexyl ester of epoxy fatty acids, sorbitan monostearate, sorbitan monopalmitate, polyoxyethylene sorbitan trioleate, 5 polyoxyethylene sorbitan monolaurate, sorbitan trioleate and the like; hydrocarbon and its substituted compounds such as emulsified paraffin, chlorinated paraffin, mixture of chlorinated alkyl benzene sulfonate and chlorinated paraffin and the like; phosphate esters such as dibutyl phenyl phosphate, sodium hexametaphosphate, dipheyl octyl phosphate, tricresyl phosphates and the like;
10 polyhydric alcohol and its derivatives such as glycol, diethylene glycol, triethylene g]ycol, glycerin, sorbitol and the ]ike; ethanolomines such as ethanolamine, diethanolamine, triethanolamine and the like; vegetable oil such as soybean oi], peanut oil, rapeseed oil, palm oil, tung oil, castor oil, and the like; polyoxyethylene ethers such as alkyl phenyl polyoxyethylene, aliphatic alcohol polyoxyethylene 15 ether, high aliphatic alcohol poloxyethylene ether and the like; acrylic acid and its derivative copolymers such as polyacrylic acid, polyacrylamide, polymethyl-pentyl acrylate, acrylic acid-acrylamide copolymer, acrylic acid-C1-Cs acrylate copolymers;
polyaklylacrylic acid, polyalkylacry]amide, poly Cl-Cs alkylacrylate, alkylacrylic acid-C1-Cs alkylacrylate copolymers, polyvinyl alcohol and polyvinyl acetals such 20 las polyvinyl alcohol, polyvinyl formal-butyryl, polyvinyl acrylal and the like;
polyvinyl acetate and vinyl acetate copolymers such as polyvinyl acetate, vinyl acetate-C2-Cs olefins copolymers, vinyl acetate -acrylic acid and its derivative copolymers, vinyl acetate -- acryl olefin copolymers and the like; polyolefins and olefins copolymers such as polyethylene wax, oxide polyethylene, emulsified -~- 2111~3~

polyethylene, polyvinylidene chloride, vinyl chloride -- vinylidene chloride copolymer, polyvinyl perchloride and the like; poly acryl olefins and copolymers such as styrene -- butadiene copolymer, carboxylated styrene butadiene copolymer etc.; cellulose and starch such as carboxymethyl cellulose, hydroxyethyl cellulose, 5 denatured starch etc.; alkyd resins such as water soluble alkyd resins, and epoxy resins such as water soluble epoxy resins. Other modifiers comprise amino resins such as melamine -- formaldehyde resin, silicone, and sodium alginate and the like.

. . .
Out of the above modifiers, the following are preferred: achromatic 10 es~ers such as di-n-butyl phthalate, dicapryl phthalate, di-(2-ethyl hexyl) phthalate, di-iso-nonyl phthalate, butyl benzyl phthalate, butyl phthaly butyl glycollate, C4-Clo terephthalate etc.; aliphatic esters such as di-butyl sebacate, di-octyl sebacate, di-capryl sebacate, ethylene glycol di-C5-Cg fatty acid ester, sorbitan monostearate, sorbitan monopalmitate, di-2~ethylhexyl maleate, 2-ethylhexyl ester of epoxy fatty 15 acids; hydrocarbon and its substitutes such as emulsified paraffin, chlorinated paraffin; phosphate esters such as di-butyl phenyl phosphate, sodium hexametaphosphate, di-phenyl octyl phosphate; polyhydric alcohol and its derivatives such as glycol, di-ethylene glycol, triethylene glycol, glycerin; vegetable oil such as castor oil; polyoxyethylene castor oil, polyoxyethylene ethers such as 20 laliphatic alcohol polyoxyethylene ether; high aliphatic alcohol polyoxyethylene ether, copolymers such as polyacrylic esters and acrylate copolymers, vinyl acetate :
-- acrylate copolymers, ethylene -~ vinyl acetate copolymers styrene -- acrylate copolymers; polyolefins and olefins copolymers such as polyethylene wax, styrene -butadiene copolymer, carboxylated styrene butadiene copolymer, polyvinylidene -~ ~9~ 21~:l732 chloride, vinyl chloride - vinylidene chloride resins, and carboxymethyl cellulose, water soluble alkyd resins, water soluble epoxy resins, and melamine formaldehyde resins.
Each of the above modifiers can be used alone or together with 5 others according to the property of the film to be made. The amount of the modifier used is, by weight 0.2%-40%, based on the weight of the plant cellulose film, preferably 0.5%-20%, and most preferably 1-15%. The modes of use of the modifier are various, for instance, the relevant modifier from the above may be added into the viscose in a given ratio to form a film or after the regenerated 10 cellulose film has been formed, the film may be spun, coated or immersed with the modifier to form a complex film. The decomposable plant cellulose film formed is 8-20 u thick, and the test results of its properties of biology, optics, mechanics and its experimental results obtained on experimental farmland plots (eleven plots) with regard to different crops, weather and soil show that the film 15 is of good property.
I. Mechanical Propertv Longitudinal Tensile Strength 17.3-49.2 MPa Transverse Tensile Strength 13.3-30.4 MPa IT. Optical T'ropert~v Transmittance 83.2-91.1%
ITT. Biolo~ical ProPert~
When buried in wet soil of 15 cm deep, the film started to decomposei slightly in 40 days and finish decomposing in 80 days. When covering - 10- "

the soil, slight cracks appear in 60 days and the film starts splitting open and ~
decomposes quickly in 100 days. ;
When the film was immersed in soil and water for continuous decomposition for 15 days during inside experiments, the rate of decomposition S was 3-4.69%.
_d Tests Experiments on peanut, cotton, soybean, maize and water melon ;
show that the production of these crops has a]l been greatly increased. The general increase rate being 20%, and the highest increase rate of maize being 10 50%
It is a further object of the present invention to provide plant cellulose films that kill weeds, insects and germs and have compound fertilizingingredients of N, P or K and trace elements/rare-earth elements. The methods of preparing these multifunctioned films are the same with that of preparing the15 above plant cellulose films, except that chemical substances of special functions are added by way of spinning, coating or immersing. `
Weed ~ Killing Farming F lm of Cellulose The week-killing cellulose farming film of the present invention comprises water, soluble herbicides of 0.05-1 g/m2. One or a mLxture of more 20 than one of the following herbicides are used generally according to different crops and weeks: glufosinate, gramoxone (paraquat), difenzoquat, dalapon, bialaphos, alloxyelim-sadium, acifiuorfen sodium and sodium pentachlorophenate. ~;
~n_e~t~Killing Cellulose Farming Film This type of film of the present invention has insecticides that are 2 ~ 1 1 7 ~ 2 ~ ~
water soluble. One or a mixture of more than one of the following insecticides are added in the film: monocrotophos, phosphamidon, mevinphos, omethoate, 2-dimethoxy phosphinyl imino-1, 3-dithiofive ring, methamidophos, acephate soluble powder, 2-(dimethoxy phosphimide)-1,3 dithio five ring, insect grass, 2-N, N-5 dimethylamino-1, 3-bis (thiosulfato sodium) propane, thiocylcam soluble powder, bandane and cyhexatin. The amount of the insecticides used is controlled at 50-2000 PPm/m2.
Germ-Killing Cellulose Farmin~ Film The type of film of the present invention has germicides that are 10 water soluble and non-toxic. One or a mixture of more than one of the following germicides is used in this film, whose amount used is generally 50-2000 PPm/m2:
folpet-AM, Sodium P-amino bengensulfonate, phosethyl A1, and p-phthalic acid.
Plant Cellulose Farmin~ Film With Compound Fertilizer Containin~ N~ P~ K
This film may contain a single fertilizing ingredient like N, P or K, 15 or compound fertilizers. A solution with the fertilizing ingredient is fixed onto the surface of the film by way of spinning, coating or immersing. The fertilizing ingredient goes into the soil when the film decomposes or the water vapor on the film surface drops into the soil carrying the fertilizing ingredients for the nutrition of crops. When operating, the solid fertilizers are first dissolved in water, then 20 fixed to the surface by spinning, coating or immersing. The fertilizing ingredient falls onto the soil or onto the soil or onto the leaves of the crops together with the water vapor of the film during the decomposition process of the film or during the growth of the crops so that the nutrients for the crops is increased, which gives the increase of the production. The fertilizing nutrient includes one or a mixture of 2 1 ~ ~ 7 3 2 more than one of the following: urea, ammonium sulphate, ammonium hydrocarbonate, ammonium nitrate, ammonium chloride, single superphosphate, fused calcium-magnesium phosphate, calcium phosphate secondary, diammonium hydrogean phosphate, potassium chloride, potassium dihydrogen phosphate, S potassium chloride, potassium dihydrogen phosphate, which are all water soluble.
The effective concentration of the fertilizing nutrient on the film surface (N:P:K
= 6:3:1) is generally 200-1000 PPm/m2.
Plant cellu!ose Farmin~ Film with Trace/Rare Earth Elements .. .. .
The film with trace elements is prepared by dissolving one or a 10 mixture of salts of the following elements: iron, manganese, zinc, magnesium nickel, cobalt, copper and tin, extracting the elements from the salts, making a solution with the elements and fixing the solution onto the surface of the film by way of immersing, coating or spinning. The film with rare-earth element is prepared by fixing mixed rare-earth elements onto the surface of the film in the 15 same way as the above. The content of the trace elements and rare-earth elements used may be controlled at 0.05-10 PPm/m2.

. ,.
The process of preparing the above plant cellulose farming film of the present invention involves making the plant cellulose viscose and filming.
In particular, the process comprises the following steps:
20 1. The plant cellulose in the plant cellulose raw material is concentrated and purified into a dry pulp or wet pulp, which is immersed and stirred in a - ~;
solution of alkali to dissolve hemi-cellulose, and the pressed alkali cellulose is shredded;

2. The alkali cellulose is warmed to promote itS chain scission and : ;' :

2~ L1732 degradation;
3. The degraded alkali cellulose is added, when being stirred under vacuum of 600-700 mm Hg, with CS2 for sulfonation. After a solution of alkali is added, the cellulose is stirred until the cellulose is fully dissolved. Then a modifier is added and stirred to uniform the mixture and provide a light-yellow viscose.

4. The viscose is filtered to eliminate impurities;

5. The viscose is defoamed by suction and is then ripened;

6. The ripened viscose is spun;
10 7. The viscose is coagulated in a coagulating bath;
8. The coagu]ated cellulose film is regenerated in a regenerating bath of sulfilric acid and washed with water;
9. The regenerated film is desulphurized in an alkali solution and washed with water;
15 10. The desulphurized film is bleached and washed with water;
11. The bleached fi]m is plasticized to improve its plasticity;
12. The plasticized film is pressed to reduce the moisture content and the thickness and to increase the strength of the film;
13. The pressed film is dried under hot wind;
20 14. The dried film is coated on its surface with a surface modifïer(s) to provide a plant cellulose film and 15. The cellulose film is wound up.
The following is a detailed description of the method of the present invention given in connection with the above flow charts.

~ 14 - ~ 7 3 2 -~
Prep~ration of Plant cellulose Viscose (1) Alkali Immersing, Pressing and Shredding ;;
According to the type of the raw material used, first, the cellulose ~ -in the raw material is concentrated and purified to get a dry pulp (or pulp dregs) 5 or wet pu]p of cellulose. If a wet pulp is obtained, the mois~ure content should be controlled at 10-60%, and the pu]p is immersed in alkali with a concentration of 14-25%, such as NaOH, and stirred for 40-120 minutes at 40-140 r.p.m. After surplus alkali is pressed out, hemicellulose is extracted to make disposable containers, such as cups, food boxes and instant-meal boxes, and the alkali 10 solution is recyc]ed after the extraction. The alkali cellulose which has been pressed, is then degraded in an aging drum after it is shredded.
(2) Degrading Alkali Cellulose at Control1ed Temperature ~ ~;
In the aging drum, the pressed and shredded alkali cellulose is warmed to 20-100C, preferably to 40-80C, and best to 45-65C, for 1-3 hour(s) 15 to control the polymerization degree of the cellulose at about 200-600, and keep the cellulose at 10-30C for 0.5-2 hours to prevent the cellulose from further degrading under high temperature.
(3) Sulfonating -- Dissolving After degradation, the alkali cellulose is put into a reaction tank 20 where it is sealed and stirred. Under a vacuum of 600 mm Hg, CS2 of 15-45%
(WT) by the weight of the cellulose is added into the alkali cellulose to react for , .....
1-2.5 hour(s). When the y value of the cellulose xanthate reaches 20-40, alkali solution of 10-15% is added and stirred at a low speed for 1.5-4 hours. When the cellulose is completely dissolved, a modifier is added and stirred evenly to provide a light-yellow cellulose viscose, whose cellulose content is managed at 5-9%, alkali content 4-7.5%, and viscosity is 30-90 seconds measured by the falling ball method.
(4) Filtering the Viscose The viscose may be filtered twice so as to prevent impurities from getting into the filming process and to increase the quality of the fi]m.
(5) Defoaming and Ripening the Viscose The viscose may be defoamed under vacuum. During the process of vacuum defoaming, hydrolysis saponification happens inside the viscose and 10 xanthic acid is formed. The degree of the formation of the xanthlc acid is measured with a salt solution. When the ripening degree reaches 4-8, filming may be performed. The ripening period is generally 30-80 hours and the temperature is 8-30C.
In preparing the viscose of the present invention, the steps of the 15 alkali immersing, shredding, chain scission and degradation, sulfonation, and dissolution of the plant cellulose may be combined into one step (see Figure 2) and the viscose is prepared using a unified machine for viscose preparation. The composition of the viscose so prepared is the same with that by the above method, and the choice of the method is made mainly based upon the quality of ` ' ~ 20 the plant celluiose.
Filmin~
Referring to Figures 1 and 2, the filming of the present plant cellulose viscose is continuously made on a casting machine whose linear velocity is 10-60 m/sec, film thickness is 8-20 ,u preferably 12-14 u, and film breadth is ,~ off`

- 16- 21~732 : :

about 1.5 m.
1) Spinning Spinning is important ~o the quality of filming. When operating, the crack should be 0.15-0.25 mm and the pressure of the cavity is 0.05-0.2 MPa.
2) Coagulating The coagulating bath contains sulphuric acid of 90-180 g/l, sodium su]phate of 180-240 g/l and some defoaming stabilizer of 20-80 g/l. The coagulating temperature is 40-60C.
3) Regenerating The regenerating bath is a solution of sulphuric acid of 50-130 ~.
The regenerating temperature is 40-70C.
4) Desu1pherizing ~;
The regenerated cellulose film is desulphurized under 60-90C in a desulphurizing tank that contains an alkali solution of 0.15-0.80 g/l.
5) Bleaching The desulphurized film is bleached under 20-30C in a bleaching tank that contains calcium hypochlorite, sodium hypochlorite or by using an ozone generator. The effective Cl and O contained are 0.3-1.2 g/l 6? Plasticizing The bleached film is plasticized by using diethylene glycol or glycerin of 8-17% and silica sol of 0.5-2.0% to change the feel and plasticity of the film.

7) Pressing The plasticized cellulose film that contains moisture is pressed by using two rollers that are of different hardness to reduce the moisture and "' - 17- 2~ 732 thickness, and to increase the strength and intensity of the fi]m so as to reduce the energy consumed in evaporating the moisture during the subsequent drying step.
During the above filming process, in order to prevent the mixing of the solution of upper step with the solution of subsequent step from regenerating S to bleaching and to ensure that the concentration of the solution does not change significantly, a washing tank of 40-60C is respectively arranged between each processing step.

8) Dlging The pressed film is dried by evaporating its moisture with the aid 10 of a flow of hot air during the period when the film moves into the drying roller.
The linear velocity of the drying roller is the same with that of the casting machine, and the temperature of the flow of hot air is preferably not too high.
The temperature of the drying should be: low-high-low-cool. After the film is dried, 5-20% of moisture should remain in the film body.

9) Modifying the Film Surface The surface of the dried film is coated by a coating machine with 2-5 ,u of one or more than one of the following: surface modifier, insecticide, herbicide and germicide, or with fertilizing nutrient of N, P or K, trace elements and rare-earth elements.
The following are examples of the present plant cellulose film. It will be clearly understood that the invention in its general form is not limited to the examples.
Example 1 An absolutely dIy pulp of rice straw of 1000 g (having 70% a -18 ~ 1 7 3 ~ : ~

cellulose) was pressed by a pressing machine to retain 35% of the moisture, then immersed and stirred in 70 liters of 20% of NaOH for 60 minutes, and then pumped into a small-hole pressing machine by a slurry pump, with the NaOH
content in the pressed alkali cellulose being about 14% and cellulose content 5 being about 30%. After being shredded by a shredding machine, the alkali cellulose was added into an aging drum at 50C and aged for 1.5 hours. The temperature was maintained for 1 hour by using tap water. The alkali cellulose was sent into a sulfonating tank to be stirred at a low speed (12 rpm), sealed and pumped into a vacuum of 600 mm HG, added with 16û ml of CS2 (the amount 10 was 30% of the cellulose) to react for 1.5 hours until the y value of cellulose reaches in excess of 30. A NaOH solution of 11% was added to dissolve the cellulose xanthate formed. 1he rotational speed was quickened to 24 rpm to make a cel]ulose viscose of over 5% of NaOh and 8% of cellulose, whose viscosi~
was 40 seconds (by falling ball method). Into the viscose, meanwhile, di-octyl 15 terephthalat of 8% by the cellulose weight was added and stirred for about 2 hours. After it was substantially dissolved, the viscose was pumped by gear type pump into the post-dissolving tank and stirred for another 2 hours at 150 rpm.
The post-dissolving tank was cooled by a cooling water. When substantially no small particles of viscose were seen from the sample obtained, the viscose was 20 pumped by a gear type pump into the middle ~ank to be filtered. The filtered viscose was sent into a defoaming viscose storage tank to be defoamed, a vacuum of 600 mm Hg was pumped and the viscose was aged at a constant temperature of 20C. After 40 hours the ripening degrees was measured. The filming was carried out when the ripening degree was about 6.

The viscose was driven into the coagulating tank when the casting machine moved at a speed of 30 m/sec and the crack of the spinner was 0.20 mm, where the concentration of H2SO4 in the coagulating bath was about 145 g/l, N2SO4 about 210 g~ and the temperature was 45C. The viscose was coagulated 5 quickly into a film in the tank and went into a regeneration tank having 80 g/l of H2SO4 and a temperature of 55C to be regenerated, washed with water and sent into a desulphurizing tank of 75C and 0.5 g/l of NaOH to be desulphurized.
After the film was washed on the surface, it was sent into a b]eaching tank having sodium hypochlorite of 0.5 gll to be bleached at 25C
After being washed, the film went into a plasticizing tank of 12% of diethylene glycol and 1% of silica sol to be plasticized. After being pressed, the moisture of the film was 2.5 times of the weight of the film. The film was then dried by a drying system with changing temperature from 50C-90C-50C-room temperature until its moisture content was 9%. Finally, onto the surface of the 15 film triethylene glycol of 5~o by the cellulose weight was coated, and a plant cellulose of 630 g was obtained, whose yield was 87%, moisture content was 10%, thickness was 14.4 ,u, transparency was 86%, water vapour permeability was 3.50 g/m2 hour (20C), longitudinal tensile strength was 19.5 MPa, and transverse tensile strength was 15.4 MPa.
! . 20 Example 2 The operation was the same as that of Example 1, except that wheat straw replaced rice straw, a modifier of sorbitan monostearate replaced di-octyl terephthalate. The film so prepared had a weight of 600 g, a yield of 85.7%, a moisture content of 9%, a thickness of 13.60 ,u, a transparency of 86.3%, water -20- ~li732 ~ ::

vapour permeability of 3.6 ~/m2hour (20C), a longitudinal tensile strength of 18.6 MPa and a transverse tensile strength of 16.2 MPa.
Example 3 The operation was the same as that of Example 1, except that wood S pu]p replaced rice straw, a modifier of di-butyl phenyl phosphate replaced di-octyl terephthalate. The film so prepared had a weight of 610 g, a yield of 89.0%, a moisture content of 9%, a thickness of 12.80 ,u, a transparency of 90.2%, a water vapour permeability of 3.8 g/m2hour, a longitudinal tensile strength of 23.9 MPa, and a transverse tensile strength of 18.5 MPa.
10 Exnmple 4 First, a film was prepared according to the method of Example 1.
Immersed and stirred in 10 liters of water for 15 minutes were 1000 g of urea, 2000 g of calcium dihydrogen phosphate and 1000 g of potassium dihydrogen phosphate. 20 litres of triethylene glycol was added into 2 litres of the 15 solution. 2 liters of this mixture solution was applied onto the surface of 20 m2 of the film, with the concentration of the N.P.K. coating being about 1000 PPm/m2 and the ratio of N:P-K being 6:3:1. The film so obtained had a thickness of 16 ,u, a transparency of 85%~ a longitudinal tensile strength of 19.2 MPa and a transverse tensile strength of 15.1 MPa.
' 20 Example 5 First, a film was prepared according to the method of Example 1.
10 litres of a solution of effective monocrotophos of 200 PPm were prepared. Water soluble alkyd resins were added into 2 litres of that solution, and the mixture solution was applied onto the surface of 20 m2 of the film. The film - - 21 - 2 ~ 1 1 7 3 2 ~-so obtained has 100 PPm/m2 of effective monocrotophos, a thickness of 16 ~, a transparency of 85%, a longitudinal tensile strength of 18.4 MPa and a transverse tensile strength of 14.8 MPa.
Example 6 The operation was the same as that of Example 1, except that the amount of di-octyl terephthalate added in the viscose was 10% of cellulose instead of 8%. 623 g of film was obtained with a yield of 88.9%, a moisture content of 18%, a thickness of 18.3 ~ a transparency of 91.6%, a water vapour permeability of 3.52 g/m2hour (20C), a longitudinal tensile strength of 20.3 MPa, a transverse 10 tensile strength of 15.8 Mpa.
Example 7 The operation was the same as that of Example 1, except that the amount of di-octyl terephthalate added in the viscose was 14% of ce]lulose instead of 8%. 604 g of the film was obtained with a yield of 85.8%, a moisture content of 12%, a thickness of 15.1 ,u, a transparency of 87.4%, a water vapour permeability of 3.76 g/m2hour (20C), a longitudinal tensile strength of 21.5 MPa, a transverse tensile strength of 16.9 MPa. f Example 8 The operation was the same as that of Example 1, except that the ;
20 amount of di-octyl terephthalate added in the viscose was 20% of cellulose instead of 8%. 678 g of the film was obtained with a yield of 86.3%, a water content of 6%, a thickness of 10.2 ,u, a transparency of 85.1%, a water vapour permeabilityof 3.84 g/m2hour (20C), a longitudinal tenslle strength of 24.1 MPa, a transverse tensile strength 19.0 MPa.

Claims

1. A plant cellulose film, of which the composition comprising, by weight:
plant cellulose 50-90%
modifier 0.2-40%
water 5-20%

2. A plant cellulose film according to Claim 1, wherein said plant cellulose is selected from one or a mixture of more than one of the following: crop straw, shell of crop seed, natural plant cellulose, wood, grass and bamboo.

3. A plant cellulose film according to Claim 1, wherein said plant cellulose is selected from one or a mixture of more than one of the following: rice straw, wheat straw, bagasse, Chinese alpine rush, wood pulp, cotton velvet, reed and bamboo.

4. A plant cellulose film according to Claim 1, wherein said modifier is selected from one or a mixture of more than one of the following: aromatic esters, fatty acid esters, hydrocarbon and its derivatives, phosphate esters, polyhydric alcohol and its derivatives, vegetable oil, poloxyethylene ethers, acrylic acid and its derivative copolymers, polyvinyl alcohol and polyvinyl acetals, polyolefins and olefins copolymers, cellulose and starch, alkyd resins, epoxy resins, amino resins, silicone and sodium alginate.

5. A plant cellulose film according to Claims 1 or 4, wherein said modifier is selected from one or a mixture of more than one of the following: d-in-butyl phthalate, dicapryl phthalate, di-(2-ethyl hexyl) phthalate, di-iso-nonyl phthalate, butyl benzyl phthalate, butyl phthalyl butyl glycollate, C4-C10 terephthalate, di-butyl sebacate, di-octyl sebacate, di-capryl sebacate, ethylene glycol di-C5-C9 fatty acid ester, sorbitan monostearate, sorbitan monopalmitate, di-2-ethylhexyl maleate, 2-ethylhexyl ester of epoxy fatty acids, emulsified paraffin, chlorinated paraffin, di-butyl phenyl phosphate sodium hexametaphosphate, di-phenyl octyl phosphate, diethylene glycol, triethylene glycol, glycol, glycerin, castor oil, polyoxyenthylene castor oil, aliphatic alcohol polyoxyethylene ether, high aliphatic alcohol polyoxyethylene ether, polyacrylic esters and acrylate copolymers, vinyl acetate--acrylate copolymers, ethylene--vinyl acetate copolymers, styrene--acrylate copolymers, polyethylene wax, styrene--butadiene copolymers, carboxylated styrene butadiene copolymers, polyvinylidene chloride, vinyl chloride--vinylidene chloride copolymers, carboxymethyl cellulose, water soluble alkyd resins, water soluble epoxy resins and melamine formaldehyde resins.

6. A plant cellulose film according to Claims 1 or 4, wherein the amount of said modifier used in preferably 0.5-20%, and most preferably 1-15%.

7. A plant cellulose film according to Claims 1 or 4, wherein the amount of said plant cellulose used is preferably 55-85%, and most preferably 60-80%.

8. A plant cellulose film according to Claim 1, wherein the longitudinal tensile strength is 17.3-49.2 MPa and the transverse tensile strength is 13.3-30.4 MPa.

9. A plant cellulose film according to Claim 1, wherein the film further contains herbicide comprising one or a mixture of more than one of the following:
glufosinate, gramoxone, difenzoquat, dalapon, bialaphos, alloxydim-sadium, acifiuorfen sodium, sodium pentachlorophenate, and the amount of herbicide used is 0.05-1 g/m2 based on the area of the film.

10. A plant cellulose film according to Claim 1, wherein the film further contains insecticide of 50-2000 PPm/m2 based on the area of the said film and the insecticide comprises one or a mixture of more than one of the following:
monocrotophos, phosphamidon, mevinphs, omethoate, 2-dimethoxy phosphinyl imino-1,3-dithio five ring, methamidophos, acephate soluble powder, 2-(dimethoxy phosphimide)-1,3 dithio five ring, insect grass, 2-N, N-dimethylamino-1,3-bis (thiosulfato sodium) propane, thiocyclam soluble powder, bandane, and cyhexatin.

11. A plant cellulose film according to claim 1, wherein the film further contains non-toxic germicide of 50-2000 PPM/m2 based on the area of the said film and the germicide comprises one or a mixture of more than one of the following: folpet-am, sodium p-amino bensensulfonate, phosethyl A1, and p-phthalic acid.

12. A plant cellulose film according to Claim 1, wherein the film further contains fertilizing nutrient of N, P or K or a mixture of them of 200-1000 PPm/m2 based on the area of the said film, and preferably with a ratio of N:P:K
of 6:3:1, and the fertilizing nutrient comprises urea, ammonium sulphate, ammonium hydrocarbonate, ammonium nitrate, ammonium chloride, single superphosphate, fused calcium-magnesium phosphate, calcium phosphate secondary, diammonium hydrogean phosphate, potassium chloride, and potassium dihydrogen phosphate.

13. A plant cellulose film according to Claim 1, wherein the film further contains trace element and rare-earth element of 0.05-10 PPm/m2 based on the area of the said film, said trace element comprising one or a mixture of more than one of the following: iron, manganese, zinc, magnesium, nickel, cobalt, copper and tin.

14. A process of preparing plant cellulose film, comprising:

1) concentrating and purifying the plant cellulose raw material into a dry pulp or wet pulp, immersing and stirring said pulp in a solution of alkali to dissolve hemi-cellulose, pressing said cellulose and shredding said pressed cellulose;
2) warming the said alkali cellulose to promote its chain scission and degradation;
3) adding CS2 when said degraded alkali cellulose is stirred under a vacuum of 600-700 mm Hg for sulfonation, adding a solution of alkali and stirring for full dissolution, and adding a modifier with stirring to get a light-yellow viscose;
4) filtering said viscose to eliminate impurities;
5) ripening said viscose after said viscose is defoamed under vacuum;
6) spinning said ripened viscose;
7) coagulating said viscose in a coagulating bath;
8) regenerating said coagulated film in a regenerating bath of sulphuric acid, 9) desulphurizing said regenerated film in an alkali solution;
10) bleaching said desulphurized film;
11) plasticizing said bleached film to change its plasticity;
12) pressing said plasticized film to reduce the moisture content and thickness and to increase the strength of the film, and 13) drying said pressed film in a flow of hot air.

15. A process according to Claim 14, wherein said process further includes a step of coating a modifier on the surface of said pressed film.

16. A process according to Claim 15, wherein said modifier is coated onto said film surface by way of spinning, coating or immersing.

17. A process according to Claim 15, wherein said modifier is one or a mixture of more than one of the following: insecticides, herbicides, and germicides.

18. A process according to Claim 15, wherein said modifier is a fertilizing nutrient of N, P or K or mixture of them, trace elements and rare-earth elements are coated on the surface of said film.

19. A process according to Claim 14, wherein in step 1) the moisture content of said wet pulp is 10-60% and the concentration of said solution of alkali is 14-25%.

20. A process according to Claim 14, wherein in step 2) the warming temperature is 30-90°C and the degree of polymerization of cellulose is 200-600.

21. A process according to Claim 14, wherein in step 3) the amount of CS2 used is 15-45%(WT) by the weight of the cellulose, the amount of the cellulose contained in said viscose is 5.0-9.0% and the viscosity is 30-90 seconds.

22. A process according to Claim 14, wherein in step 5) the ripening temperature is 8-30°C and the ripening time is 30-80 hours.

23. A process according to Claim 14, wherein in step 6) the crack is 0.15-0.25 mm and the pressure of the cavity is 0.05-0.2 MPa.

24. A process according to Claim 14, wherein in step 7) the coagulating temperature is 40-60°C.

25. A process according to Claim 14, wherein in step 8) the regenerating temperature is 40-70°C.

26. A process according to Claim 14, wherein in step 9) the desulphurizing temperature is 60-90°C.

27. A process according to Claim 14, wherein in step 10) the bleaching temperature is 20-30°C.

28. A process according to Claim 14, wherein in step 13) 5-20% of moisture is kept in the film after said film is dried by a flow of hot air.

29. A process according to Claim 15, wherein the modifier coated on the surface of said film is one or a mixture of more than one of the following insecticide, herbicide, germicide, fertilizing nutrient of N, P or K or a mixture of them, trace element, and rare-earth element; and said coating is 2-5 µ thick.

30. A plant cellulose film according to Claims 1-13, which is used as farming film.

31. A plant cellulose film according to Claims 1-8 or 11, which is used as packaging material for goods, packaging material for food, drinks and pharmaceuticals and packaging material for sausages, fruits, vegetables, candies and cakes.

32. A plant cellulose film according to Claims 1 or 12, which is used as carpet and packaging material for garbage.

33. A plant cellulose film according to Claim 1, which is used as dialysis bag.