WO2012026653A1

WO2012026653A1 - Biodegradable, photodegradable bio film containing rice hull and rice bran, and manufacturing method thereof

Info

Publication number: WO2012026653A1
Application number: PCT/KR2010/009350
Authority: WO
Inventors: Sang-Ik Han; Hang-Won Kang; Ki-Chang Jang; Woo-Duck Seo; Je-Bong Lee; Gi-Hwan Lee; Dong-Soo Park; Jun-Hyun Cho; Soo-Kwon Park; Hung-Gu Hwang; Hak-Dong Lee; Dae-Woo Byun; Kyung-Soon Shin; Woo-Shin Byun; Jun-Hyo Kwon
Original assignee: Republic Of Korea (Management : Rural Development Administration); Evergreen Co., Ltd.
Priority date: 2010-08-24
Filing date: 2010-12-27
Publication date: 2012-03-01
Also published as: KR101062012B1

Abstract

The present invention relates to a biodegradable, photo-degradable biofilm comprising rice hull and rice bran, and a method of its preparation. More particularly, the present presentation relates to a biodegradable, photo-degradable biofilm comprising rice hull and rice bran, starch, titanium dioxide and biodegradable polyester, which enables to retain a suitable strength to protect crops during their growth, thus being capable of reducing the cost normally required for collecting the leftover films used for covering field during cultivation and the handling cost thereof.

Description

BIODEGRADABLE, PHOTODEGRADABLE BIO FILM CONTAINING RICE HULL AND RICE BRAN, AND MANUFACTURING METHOD THEREOF

The present invention relates to a biodegradable, photodegradable biofilm comprising rice hull and rice bran, and a method of its preparation. The biodegradable, photodegradable biofilm of the present invention enables to retain a suitable strength to protect crops during their growth. Further, it has biodegradable, photodegradable properties, thus capable of reducing the cost normally required for collecting the leftover films used for covering field during cultivation and the handling cost thereof.

Recent increase in labor cost has resulted in increase in the use of various kinds of disposables including plastic containers for transplanting plug seedling, plastic films for mulching cultivation, etc. This has resulted in giving an extra burden on people involved in the related fields of collecting a huge amount of disposable wastes and also raised a serious environmental issue of soil contamination due to the remnants in the plastic containers. Further, those people have been exposed to contact with environmental hormones being released therefrom, a material known to block human endocrine system. In addition, these disposable containers and plastic films, when burnt to be abandoned, generate toxic gases which damage the air quality, and raise a serious environmental issue because they are hardly decomposed by microorganisms after they are buried.

To solve the above problem, numerous researches have been focused on to manufacture disposable containers by using a natural biodegradable polymer material such as starch, modified starch, and starch containing cellulose-based plant fiber; and a synthetic biodegradable material such as polylactic acid, aliphatic polyester, and biodegradable polyurethane. In particular, the natural biodegradable polymer material comprising starch has been favored as a disposable product because it is much cheaper than the synthetic biodegradable material.

Japanese Patent Application Publication No. Hei 8-311243 discloses a method for manufacturing a container by using a biodegradable foaming composition comprising a natural biodegradable polymer material such as starch and plant fiber, and aliphatic polyester and other additives.

Japanese Patent Application Publication No. Hei 7-97545 discloses a method for manufacturing a container manufactured by using a starch-containing biodegradable material by coating the surface of the container with a coating agent, wherein polylactic acid is dissolved in halogenated hydrocarbon.

Korean Patent No. 10-0574547 discloses a method for manufacturing a container manufactured by using a natural biodegradable polymer material such as pulp fiber powder, starch or the like, by coating the inner surface of the container with a coating agent comprising a natural biodegradable polymer material, acrylate copolymer, and a solvent.

Korean Patent No. 10-0830901 discloses a method for improving decomposition and preservation by gas phase depositioning a mixture on the biodegradable film. This method is focused on the improvement of film with regard to their decomposition and blocking of moisture. However, during their cultivation, field normally retain covering effect of soil due to the films covered thereon and thus it is necessary to take a preventive measure against the growth of weeds. Further, during fall and winter seasons when the cultivation of field crops end, biodegradable property of the protective films is required. Therefore, there is an urgent need for the development of a method which can resolve the above problems.

Korean Patent No. 10-0368738 discloses a bio/photodegradable film to be used for covering field crops during the cultivation, which comprises starch, an oxidizing agent and photodegradation controller, and polyethylene and aliphatic polymer as matrix resin. However, due to the presence of polyethylene, which is used for processability of a film, it was hard to achieve the complete decomposition of the film.

The present invention has been made in an effort to solve the above problems by discovering that a biodegradable and photodegradable film, which enables to retain a suitable strength to undergo growth environment for field crops and be completely degraded after a certain period of time, can be manufactured by using rice hull and rice bran, which are very commonly seen in Korea.

Therefore, an object of the present invention is to provide a method for manufacturing a biodegradable and photodegradable biofilm which has a suitable strength to protect field crops during the cultivation and is biodegradable as well as photo-degradable thereby reducing cost for collecting used biofilms and their treatment.

The present invention relates to a biodegradable, photodegradable biofilm comprising 20 ~ 50 wt% of rice hull, 5 ~ 15 wt% of rice bran, 1 ~ 15 wt% of starch, 0~5 wt% of titanium dioxide and 20 ~ 60 wt% of biodegradable polyester.

The present invention also relates to a method of manufacturing biodegradable, photodegradable biofilm comprising:

pulverizing rice hull and rice bran using a pulverizer;

adding the pulverized rice hull and rice bran along with starch and titanium dioxide into a mixer, and performing a milling to obtain a mixture for molding; and

extruding said mixture for molding along with biodegradable polyester at 120 ~ 190℃ to form a film with a thickness of 0.03 ~ 1.0 mm

The biodegradable, photodegradable biofilm of the present invention comprises rice hull, rice bran and starch which are readily available in the market. Further, biodegradable, photodegradable biofilm of the present invention, when used as a protective film for covering field crops during their cultivation, enables to maintain sufficient strength to protect them, and in six months later, when they are to be discarded after being used-up upon harvest of the crops, they start to proceed themselves with a slow biodegradation thus eliminating the worries for environmental contamination and the release of environmental hormones therefrom, while reducing the general cost which otherwise might have occurred to collect the used protective films and handling them thereafter.

FIG. 1 shows a picture of biodegradable, photodegradable biofilms comprising rice hull and rice bran manufactured according to the present invention.

FIG. 2 is a graph showing the result of tension test of the biodegradable, photodegradable biofilms manufactured according to Examples 1 ~ 3 of the present invention.

FIG. 3 is a graph showing the result of tension test of commercial protective films.

The present invention is described further in detail hereinbelow.

The biodegradable, photodegradable biofilm of the present invention comprising rice hull, rice bran and starch can retain suitable strength to protect field crops during their growth period to be covered therewith, and can slowly start to attend to its self biodegradation in soil around the time when the crop cultivation is completed, thus being freed from the worries of environmental contamination and cost and labor for handling the used biofilms.

The rice hull used for the manufacture of the biofilm gives strength to the biodegradable, photodegradable biofilm, and is used in the form of powder with a predeterminded particle size in order to promote easy decomposition of the biofilm during crop cultivation being protected with the film. More specifically, the rice hull is preferably to have a particle size capable of being sieved through 120 ~ 250 mesh sieve. In general, the smaller the particle size the greater the hardness of the biofilm. However, if the particle size of the rice hull powder is larger than the hole size of 120 mesh sieve, it will deteriorate processability and makes the surface of the biofilm rough. In contrast, although the smaller the particle size the better the quality of the biofilm, if the particle size of the rice hull powder is smaller than the hole size of 250 mesh sieve it will considerably increase the manufacturing cost due to the requirement of excess pulverization while the advantages in effect may not be obvious. Therefore, it is recommended that rice hull with at least two different kinds of particle size are used together to produce good quality biofilm in terms of hardness and softness. Rice hull is used in the amount of 20 ~ 50 wt% relative to the total composition of the biofilm. If the amount of the rice hull is less than 20 wt% it will deteriorate biodegradability of the biofilm thus not being suitable to be used as a protective film for field crops. In contrast, if the amount is greater than 50 wt% it will worsen the processability thus it may cause any unexpected problems during the biofilm manufacturing process.

Rice bran is used to render biodegradability and softness to the biofilm. The molecular structure of rice bran is more densed than that of rice hull, and thus it gives a better softness than the rice hull. Rice bran is also used in the form of powder with a predeterminded particle size as is the case with rice hull, in the range of 120 ~ 200 mesh sieve hole size. In general, the lower the particle size the better the biodegradability of the biofilm. If the particle size of the rice hull powder is bigger than the hole size of 120 mesh sieve it may deteriorate processability of manuafacturing the biofilm. In contrast, although the greater the particle size the better the softness of the biofilm, if the particle size of the rice hull powder is smaller than the hole size of 200 mesh sieve it will considerably increase the manufacturing cost due to the requirement of excess pulverization. Therefore, it is recommended that the rice bran content be maintained in the above range. Rice bran is used in the amount of 5 ~ 15 wt% relative to the total composition of the biofilm. If the amount of the rice bran is less than 5 wt% it will deteriorate biodegradability of the biofilm. In contrast, if the amount is greater than 15 wt% it will worsen the processability.

The starch used in the present invention serves as a binder, and it is preferred to use undenatured starch. The undenatured starch is a negative ionic natural starch which does not require any physical or chemical treatment. Therefore, it can make the manufacturing process simple and reduce the manufacturing cost. Examples of the undenatured starch include corn, glutinous corn, potato, tapioca, sweet potato, rice, glutinous rice, wheat, barley, and other seeds and cuts comprising less than 40 wt% of amylase. Preferably, starch derived from at least one selected from corn, potato, wheat, rice, tapioca and sweet potato. The above undenatured starch is normally charged with 500 meq or higher negative charge and thus tends to aggregate together, which weakens the bonding energy among molecules thereby deteriorating overall strength and water-resistance. In the present invention, however, rice hull and rice bran are used in powder form, as described previously, thus preventing aggregation of starch molecules thereby improving the overall mechanical properties of the film such as tensile strength, resistance or the like. The amount of starch to be used in the present invention is 1 ~ 15 wt%. If the amount is below 5% it may decrease adhesion thus not being suitable to be used as a binder. In contrast, if it is used more than 15 wt% it will result in reducing the amount of rice hull and rice bran thus deteriorating the mechanical strength of the film.

Titanium dioxide(TiO₂), one of the major constituents of the present invention, is typically used as an emusifiable concentrate or involved in crystal formation in a crystalline oil and smoothen the glaze surface. In the present invention, it is used to render photodegradability on films. The amount of titanium dioxide to be used in the present invention is 0~5 wt% relative to the total film composition. If it is used more than 5 wt% it may cause problems in terms of productivity, softness and strength.

Biodegradable polyester is used in the present invention to give elasticity and tensile strength to the film. The biodegradable polyester to be used in the present invention is at least one selected from the group consisting of polylactide, polyglycolic acid, poly hydroxy butyric acid, polycaprolactone, polybutylene succinate adipate polymer, terpolymer of terephthalic acid and adipic acid and 1,4-butanediol, polyhydroxyalkanoate and polycaprolactone. The biodegradable polyester is preferably used in the amount of 20 ~ 60 wt% relative to the total film composition. If the amount used is less than 20 wt% it will deteriorate biodegradability. In contrast, if the amount exceeds 60 wt% it may cause problems of softness, milling and increase in manufacturing cost.

In the present invention, in the process of manufacturing the biofilm, calcium carbonate(CaCO₃) may be further added in order to expedite degradation upon necessity. Calcium carbonate is preferably added in the range of 0.5 ~ 30 wt% relative to the total film composition. If its content is less than 0.5 wt% it may not be able to attain the intended effect of degradation. In contrast, if its content is greater than 30 wt% it may result in deterioration of the softness of the biofilm and too early degradation not suitable for crop cultivation of the biofilm. Therefore, it is preferred that calcium carbonate is used in the range of 30 wt% or less.

Further, other conventional additives such as processing agent, releasing agent, preservative, inorganic filler, white agent, drying agent, heat stabilizer, and fluorescent agent may be added as necessary within the scope that the addition may not damage the object of the present invention.

The present invention also relates to a method of manufacturing a biodegradable, photodegradable biofilm. The method is described herein below.

First, rice hull and rice bran are pulverized using a conventional pulverizer to be suitable for the biodegradable, photodegradable biofilm to be prepared. The pulverized rice hull and rice bran are added into a mixer along with starch and titanium dioxide, subjected to milling for 20 ~ 30 minutes to obtain a mixture for molding. The mixture is then extruded for molding along with biodegradable polyester at 120 ~ 190℃ to form a film with a thickness of 0.03 ~ 1.0 mm.

The biodegradable, photodegradable biofilm prepared according to a composition of the present invention has the advantages as a protective film. First, it can reduce the growth of weeds by covering the field with the film during their cultivation. Second, due to the biodegradable, photodegradable properties of the film, it starts to be degraded in soil after a certain length time thus eliminating the worries of release of environmental hormones as well as environmental contamination. Further, due to biodegradation nature, it can contribute to the reduction of costs associated in the collecting of used protective films and their treatment thereafter.

The present invention is described further in detail herein below in conjunction with the examples, however, they should not be construed as limiting the scope of the present invention.

[Examples]

Example 1

30 wt% of the rice hull powder passing 120 ~ 150 mesh sieve, 10 wt% of rice bran powder passing 120 ~ 150 mesh sieve, 5 wt% of corn starch and 3 wt% of titanium dioxide were added into a mixer and subjected to a roll mixing milling to obtain a mixture for molding. Thus obtained mixture for molding was added into a twin extruder along with 52 wt% of polylactide, processed under pressure at 180℃ to obtain a biodegradable, photodegradable biofilm with a thickness of 0.05 mm.

Example 2

15 wt% of rice hull powder passing 200 ~ 250 mesh sieve, 15 wt% of rice hull powder passing 150 ~ 200 mesh sieve, 5 wt% of rice bran powder passing 120 ~ 150 mesh sieve, 10 wt% of corn starch and 3 wt% of titanium dioxide were added into a mixer and subjected to a roll mixing milling to obtain a mixture for molding. Thus obtained mixture for molding was added into a twin extruder along with 52 wt% of polylactide, processed under pressure at 185℃ to obtain a biodegradable, photodegradable biofilm with a thickness of 0.05 mm.

Example 3

10 wt% of rice hull powder passing 200 ~ 250 mesh sieve, 20 wt% of rice hull powder passing 150 ~ 200 mesh sieve, 10 wt% of rice bran powder passing 120 ~ 150 mesh sieve, 10 wt% of corn starch and 3 wt% of titanium dioxide were added into a mixer and subjected to a roll mixing milling to obtain a mixture for molding. Thus obtained mixture for molding was added into a twin extruder along with 47 wt% of polylactide, processed under pressure at 185℃ to obtain a biodegradable, photodegradable biofilm with a thickness of 0.03 mm.

Comparative Example

As a control, a low density polyethylene(LDPE) film Seagull Gold Plastic Co. with a thickness of 0.03 mm for agriculture was used.

Category	Example 1	Example 2	Example 3
rice hull (sieved through 200~250 mesh sieve) (wt%)	-000	15	10
rice hull (sieved through 150~200 mesh sieve)(wt%)	-	15	20
rice hull (sieved through 120~150 mesh sieve) (wt%)	30	-	-
rice bran (sieved through 120~150 mesh sieve) (wt%)	10	5	10
Starch (wt%)	5	10	10
titanium dioxide (wt%)	3	3	3
polylactide (wt%)	52	52	47

Test of Physical Properties

In order to study the mechanical properties of the films manufactured in the above Examples 1 ~ 3 and the commercially available LDPE, the respective samples were collected according to KS M3001, and analyzed by using Instron (Zwick Co., Germany). The results of the samples for Examples 1 ~ 3 are shown in FIG. 2 and that for the commercial LDPE, which were analyzed by using four samples) is shown in FIG. 3. The results were analyzed by comparing standard force(N) and strain(%). As shown in FIGs. 2 ~ 3, the films manufactured in Examples 1 ~ 3 had excellent intensity for primary breakpoint in the range of 9 ~ 14, superior to that of that of the commercially available agricultural film of Comparative Film, which was in the range of 5.4 ~ 5.9 N. The intensity for secondary breakpoint of the films manufactured in Examples 1 ~ 3 were in the range of 15 ~ 20N, with the tensile force being maintained at 50% strain, thus showing excellent mechanical strength and tensile force. The maximum tension force was 280 ~ 320%. In contrast, the agricultural film of Comparative Film, under the pressure of 6 N or higher of force, increased its tensile force to 300%, even up to 600% maximally, thus showing that it is extendable under a small force and not readily breakable.

From the foregoing, it was confirmed that the biodegradable, photodegradable biofilm of the present invention has a suitable strength to be used as a protective film capable of replacing the conventional low density polyethylene film thereby resolving the issues of environmental contamination, release of environmental hormones, cost for collecting and treating the used films.

Claims

A biodegradable, photodegradable biofilm comprising:
20 ~ 50 wt% of rice hull;
5 ~ 15 wt% of rice bran;
1 ~ 15 wt% of starch;
1~5 wt% of titanium dioxide; and
20 ~ 60 wt% of biodegradable polyester.
The biodegradable, photodegradable biofilm according to claim 1, wherein said biofilm further comprises 0.5 ~ 30 wt% of calcium carbonate.
The biodegradable, photodegradable biofilm according to claim 1, wherein said rice hull is in the form of powder of passing 120 ~ 250 mesh sieve, and rice bran is in the form of powder of passing 120 ~ 200 mesh sieve.
The biodegradable, photodegradable biofilm according to claim 1, wherein said starch is an undenatured starch selected from the group consisting of corn, glutinous corn, potato, tapioca, sweet potato, rice, glutinous rice, wheat and barley.
The biodegradable, photodegradable biofilm according to claim 1, wherein said biodegradable polyester is selected from the group consisting of polylactide, polyglycolic acid, poly hydroxy butyric acid, polycaprolactone, polybutylene succinate adipate copolymer, terpolymer of terephthalic acid, adipic acid and 1,4-butanediol, polyhydroxyalkanoate and polycaprolactone.
A method of manufacturing biodegradable, photodegradable biofilm comprising:
pulverizing rice hull and rice bran using a pulverizer;
adding the pulverized rice hull and rice bran along with starch and titanium dioxide into a mixer, and performing a milling for 20 ~ 30 minutes to obtain a mixture for molding; and
extruding said mixture for molding along with biodegradable polyester at 120 ~ 190℃ to form a film with a thickness of 0.03 ~ 1.0 mm.