WO2022119067A1

WO2022119067A1 - Biodegradable resin composition for fishing gear, fishing gear comprising the same, and manufacturing method thereof

Info

Publication number: WO2022119067A1
Application number: PCT/KR2021/008197
Authority: WO
Inventors: Su Bong Park; Bong Sung BAE; Bong Jin Cha; Jae Hyun Bae; Da Young Kang
Original assignee: Republic of Korea(National Fisheries Research and Development Institute)
Priority date: 2020-12-03
Filing date: 2021-06-29
Publication date: 2022-06-09
Also published as: CN115667360A; KR102279713B1

Abstract

The present invention relates to a biodegradable resin composition for fishing gear, fishing gear comprising the same, and a method for manufacturing the fishing gear. More specifically, the biodegradable resin composition for fishing gear according to the present invention is obtained by mixing an aliphatic dicarboxylic acid and an aliphatic diol and subjecting the mixture sequentially to esterification, transesterification, polycondensation, chain extension and solid-state polymerization reactions in the presence of a polyfunctional compound, and may have improved mechanical properties, processability, flexibility and elastic recovery properties. In addition, since the fishing gear of the present invention is manufactured using the biodegradable resin composition, it has flexibility and elasticity recovery comparable with those of nylon nets, and thus may not only improve fish catch, but also may prevent contamination of coastal waters by waste fishing gear dumped into the sea, protect the marine ecosystem, and minimize damage caused by ghost fishing.

Description

BIODEGRADABLE RESIN COMPOSITION FOR FISHING GEAR, FISHING GEAR COMPRISING THE SAME, AND MANUFACTURING METHOD THEREOF

The present invention relates to a biodegradable resin composition for fishing gear, a fishing gear comprising the same, and a method for manufacturing the fishing gear.

In general, fish are caught using fishing nets and fishing, and fishing using fishing nets may include gill nets, fish traps, trawls, dragnets, and surrounding nets. These fishing nets are combined with lines, sinkers, floats, and the like to manufacture fishing gears. Among these fishing gears, the gillnet fishing gear is a fishing method in which plastic floats are attached to the upper part of a fishing net, sinkers made of lead are attached to the lower part of the fishing net, and the fishing gear is placed on the top, middle or bottom of the sea so that a target organism can be gilled or entangled in the net. FIG. 1 is schematic view showing gill net fishing. Accordingly, the fishing net of the gill net fishing gear should have good flexibility.

FIG. 2 is an enlarged front view of a gill net fishing gear according to the present invention. FIG. 3 is a front view of the fishing net portion of the gill net fishing gear according to the present invention. Referring to FIGS. 2 and 3, in the gill net fishing gear, a fishing net having a square or diamond-shaped net serves as the body of a gill net 8, and floats 5 for deploying the fishing net upwards are connected to the upper end of the fishing net, and sinkers 6 for hanging the fishing net 3 downwards are connected to the lower end of the fishing net. When the gill net 8 is put into the sea, the fishing net 3 is spread up and down by the buoyancy of the floats 5 and the sinking force of the sinkers 6, so that a target organism may be caught. The depth of water at which the gill net 8 is placed is controlled by the length of buoy lines 2 that connect buoys 1, which float on the sea surface so as to indicate the placement position of the fishing gear, to the gill net.

On the other hand, trap fishing gear uses a method in which a cylindrical or conical frame is made using wires, wrapped with a fishing net, and then laid on the bottom of the sea, and then raised on the fishing boat. Fishing gears such as trolls, stow nets or dragnets use a method in which a wing net and a sack net are made as a fishing net, and the fishing gear is towed by a fishing boat so that a target organism enters the sack net. FIG. 4 is a schematic view showing trap fishing. Accordingly, a fishing net that is used for the trap gear should have good impact resistance.

FIG. 5 is an enlarged perspective view showing a trap fishing gear according to the present invention. Referring to FIG. 5, a cylindrical or conical frame 7 is made using a wire, etc., and a fishing net 3 is wrapped around the frame, thus manufacturing a fish trap 9. However, the fishing net 3 that is used in fishing gear, such as the conventional gill net 8 or fish trap 9, is made of a non-degradable aromatic polymer synthetic resin material in most cases. In particular, since the gill net 8 and the fish trap 9 are put in the sea for about 1 to 15 days and then picked up, a situation frequently occurs in which the buoy line 2 is cut by rough sea conditions or other fishing boats that operate while dragging fishing gear, so that the fishing net 3 applied to the gill net 8 or the fish trap 9 is lost along with the corresponding fishing gear.

When this situation occurs, problems arise in that, since the conventional fishing net 3 is made of a non-biodegradable aromatic polymer synthetic resin that is not biodegradable and as ghost fishing in which marine creatures are entangled or caught by lost fishing gears continues to repeat, a large loss of fishery resources occurs, and fishing gears accumulated on the bottom of the sea contaminate the spawning grounds and habitats of aquatic organisms.

In order to prevent the above problems, in recent years, various fishing nets 3 have been developed using biodegradable resins that are biodegradable in seawater. Representative examples thereof include a biodegradable aliphatic polyester-based resin composition, a fishing gear comprising the same, and a manufacturing method thereof, which are described in Korean Patent No. 10-415812. Specifically, according to the above patent, a fishing net 3 is produced using an aliphatic polyester-based resin as a biodegradable resin, and pollution of coastal waters by fishing nets abandoned in the sea and damage from ghost fishing are minimized by applying a material, which is naturally degradable in seawater, to the fishing net 3. However, problems arise in that the fishing net 3 has lower fishing performance than conventional nylon fishing nets due to poor flexibility and elastic recovery thereof, and the fishing net 3 is easily damaged in the process of raising the fishing gear.

In other words, in the case of the fishing gear comprising the gill net 8, fish should be easily gilled in the mesh of the fishing net 3, and when the gilled fish are removed, the fishing net 3 should return to its original state. In the case of the fishing gear comprising the fish trap 9, fish should easily enter the fish trap 9. However, in the case of the fishing net 3 made of the biodegradable aliphatic polyester-based resin composition having low flexibility and elastic recovery, the fishing performance thereof is low and thus the practical value thereof is low.

In addition, when the fishing net 3 is produced using the aliphatic polyester-based resin by spinning a netting twine for the fishing net 3 at a draw ratio of 5.0 to 6.0, knitting the spun netting twine into a net and then subjecting the net to hot-air drying, problems arise in that the strength, flexibility and elastic recovery required for the fishing net 3 are simultaneously lowered, the fishing performance thereof is lowered, and the fishing net 3 is easily damaged, resulting in a great reduction in the practical value thereof as fishing gear.

Thus, the conventional biodegradable aliphatic polyester-based resin composition has problems in that the economic efficiency of fishing using the fishing net 3 is low due to the lack of the strength, flexibility, and elastic recovery properties required for the fishing net 3, and the composition adversely affects the improvement of the business balance of fishing operations. Due to these problems, there is a need for additional research and development of a material for the fishing net 3 as well as a process for producing the fishing net 3.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a biodegradable resin composition for fishing gear having improved mechanical properties, processability, flexibility and elasticity recovery while having a higher molecular weight than a conventional aliphatic polyester resin composition.

Another object of the present invention is to provide a fishing gear manufactured using the biodegradable resin composition, which is biodegradable, environmentally friendly, improves fish catch by having flexibility and elasticity recovery comparable with those of nylon nets, prevents damage to a fishing net, and minimize damage caused by ghost fishing.

Still another object of the present invention is to provide a method of manufacturing fishing gear using the biodegradable resin composition.

In one aspect, a biodegradable resin composition for fishing gear may be obtained by subjecting an aliphatic dicarboxylic acid and an aliphatic diol sequentially to esterification, transesterification, polycondensation, chain extension and solid-state polymerization reactions in the presence of a polyfunctional compound represented by the following Formula 1:

[Formula 1]

wherein n is an integer ranging from 1 to 11, and m is an integer ranging from 1 to 30.

The polyfunctional compound may be obtained by mixing DL-malic acid and ethylene glycol or a polyethylene glycol having a weight-average molecular weight (Mw) of 150 to 500 g/mol at a molar ratio of 1:1 to 1:1.5 and subjecting the mixture to an esterification reaction.

The polyfunctional compound may be a reaction accelerator which is added to the esterification reaction during the production of the biodegradable resin composition. The polyfunctional compound acts as a reaction accelerator in the esterification process for synthesis of the biodegradable resin, so that the biodegradable resin composition having a number-average molecular weight and weight-average molecular weight more suitable for fishing gear compared to conventional aliphatic polyester resins may be easily and quickly obtained. This increase in the reaction rate has an economic advantage due to high productivity.

In addition, since the high-temperature polycondensation reaction time is shortened due to the use of the polyfunctional compound, the biodegradable aliphatic polyester resin according to the present invention has a lower concentration of end carboxyl groups than a conventional biodegradable aliphatic polyester resin, and thus advantageously has excellent durability. In addition, since the polyfunctional compound has steric hindrance in the molecular structure and functional groups at different positions, and thus has different reaction activities. Thus, the polyfunctional compound has advantages in that it is easily handled and the reaction thereof is easily controlled. That is, as the polyfunctional compound is used as a reaction accelerator, it is possible to increase the reaction rate and solve the problems that it is difficult to control the reaction of polyfunctional compounds such as citric acid and glycerol, which are used as conventional reaction promoters, and gelling of these compounds easily occurs. In addition, since citric acid and glycerol that are used as conventional reaction accelerators have high reactivity that is difficult to control, they easily combine with the reactive sites of the reactants, so that the active reactive sites of the product after the polycondensation reaction are small. However, the polyfunctional compound of the present invention has a relatively high concentration of residual active reactive sites, and thus the efficiency of the chain extension and solid-state polymerization reactions that are sequentially performed after the polycondensation reaction is high, making it possible to obtain an aliphatic polyester having a desired molecular weight.

In addition, the polyfunctional compound may form side chains in the main chain of the molecular structure of the biodegradable resin, thus not only improving the tear strength of the biodegradable resin, but also imparting excellent processability to the biodegradable resin composition by widening the molecular weight distribution of the biodegradable resin.

The polyfunctional compound may be obtained by mixing DL-malic acid and ethylene glycol or a polyethylene glycol having a weight-average molecular weight (Mw) of 150 to 500 g/mol at a molar ratio of 1:1 to 1:1.5, preferably 1:1.1 to 1:1.4, more preferably 1:1.15 to 1:1.3, most preferably 1:1.2, and subjecting the mixture to an esterification reaction. At this time, when the molar ratio between DL-malic acid and ethylene glycol or polyethylene glycol is out of the above range, the polyfunctional compound represented by Formula 1 may not be properly synthesized.

The polyfunctional compound may be produced according to the following Reaction Scheme 1. Preferably, the polyfunctional compound may be obtained by mixing DL-malic acid and ethylene glycol and subjecting the mixture to an esterification reaction.

[Reaction Scheme 1]

The polyfunctional compound may be mixed in an amount of 0.1 to 3 g, preferably 0.8 to 2.5 g, more preferably 1 to 2 g, most preferably 1 to 1.5 g, per mole of the aliphatic dicarboxylic acid. At this time, if the mixing amount of the polyfunctional compound is less than 0.1 g per mol of the aliphatic dicarboxylic acid, the esterification reaction of the aliphatic dicarboxylic acid and the fatty acid diol will not sufficiently occur and the reaction rate may be slow. On the other hand, if the mixing amount of the polyfunctional compound is 3 g, the overall reaction rate may increase, but the polyfunctional compound may cause gelling of the obtained resin, thus causing a gel or a fish eye in a product produced using the resin, or in severe cases, making it impossible to discharge the resin from the reactor.

The aliphatic dicarboxylic acid may be a compound represented by the following Formula 2.

[Formula 2]

ROOC-(CH₂)_n-COOR

wherein n is an integer ranging from 0 to 10, and R is hydrogen or a methyl group.

In a specific example, the aliphatic dicarboxylic acid may be at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelic acid, sebacic acid, 1,4-cyclohexyldicarboxylic acid, and esterified derivatives thereof. Preferably, the aliphatic dicarboxylic acid may be obtained by mixing succinic acid and adipic acid at a molar ratio of 95: 5 to 99: 1, more preferably 97: 3 to 98: 2, most preferably 98: 2.

In a specific example, the aliphatic diol may be at least one selected from the group consisting of ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, and 1,2-cyclohexanedimethanol. Preferably, the aliphatic diol may be obtained by mixing 1,4-butanediol and ethylene glycol at a molar ratio of 95: 5 to 99: 1, most preferably 98.8: 1.2 to 98: 2.

The aliphatic dicarboxylic acid and the aliphatic diol may be mixed together at a molar ratio of 1: 1.1 to 1.5, preferably 1: 1.15 to 1.4, more preferably 1: 1.15 to 1.3, most preferably 1: 1.2 to 1.25. At this time, if the molar ratio between the aliphatic dicarboxylic acid and the aliphatic diol is less than 1: 1.1, the esterification reaction or the transesterification reaction may not be smoothly performed, and thus the color of the obtained resin composition may be adversely affected. On the other hand, if the molar ratio is greater than 1: 1.5, the production cost may increase due to a decrease in the degree of vacuum in the reaction process, thus lowering economic efficiency.

The biodegradable resin composition may have a melting point of 85 to 120℃, a number-average molecular weight (Mn) of 35,000 to 80,000, a weight-average molecular weight (Mw) of 150,000 to 350,000, a melt flow index of 0.5 to 10 g/10 min as measured at 190℃ and a load of 2.16 kg, and an acid value of 0.5 mg KOH/g to 5 mg KOH/g. Preferably, the biodegradable resin composition may have a melting point of 100 to 118℃, a number-average molecular weight (Mn) of 45,000 to 70,000, a weight-average molecular weight (Mw) of 160,000 to 280,000, and a melt flow index of 1 to 8 g/10 min as measured at 190℃ and a load of 2.16 kg. More preferably, the biodegradable resin composition may have a melting point of 105 to 116℃, a number-average molecular weight (Mn) of 50,000 to 65,000, a weight-average molecular weight (Mw) of 180,000 to 250,000, and a melt flow index of 2 to 6 g/10 min as measured at 190℃ and a load of 2.16 kg.

In another aspect, the present invention provides a fishing gear manufactured using the biodegradable resin composition. Here, the fishing gear may be a gill net fishing gear ting or a trap fishing gear.

In still another aspect, the present invention providing a method for manufacturing fishing gear. In one embodiment, the method for manufacturing fishing gear according to the present invention comprises steps of:

(a) producing a polyfunctional compound represented by the following Formula 1 by an esterification reaction of DL-malic acid and ethylene glycol or a polyethylene glycol having a weight-average molecular weight (Mw) of 150 to 500 g/mol:

[Formula 1]

wherein n is an integer ranging from 1 to 11, and m is an integer ranging from 1 to 30;

(b) producing a reaction product by esterification and transesterification reactions of an aliphatic dicarboxylic acid and an aliphatic diol in the presence of the polyfunctional compound of step (a); (c) producing an aliphatic polyester resin composition by a polycondensation reaction of the reaction product produced in step (b); (d) introducing the resin composition, produced in step (c), into a twin screw extruder or a kneader, and then introducing one chain extender compound selected from among an isocyanate compound and a carbodiimide compound, followed by a chain extension reaction; (e) producing a biodegradable resin composition by solid-state polymerization of the resin composition, produced in step (d), at a temperature lower than the melting point of the resin composition; (f) spinning the biodegradable resin composition, produced in step (e), into a netting twine; and (g) knitting the netting twine, spun in step (f), into a net.

In another embodiment, the method for manufacturing fishing gear according to the present invention comprises steps of:

(a) producing the polyfunctional compound represented by Formula 1 by an esterification reaction of DL-malic acid and ethylene glycol or a polyethylene glycol having a weight-average molecular weight (Mw) of 150 to 500 g/mol at a molar ratio of 1:1 to 1:1.5 in the presence of a catalyst at 180 to 210℃ for 60 to 180 minutes; (b) mixing an aliphatic dicarboxylic acid and an aliphatic diol at a molar ratio of 1:1.1 to 1:1.5 and producing a reaction product by esterification and transesterification reactions of the mixture in the presence of the polyfunctional compound of step (a) at 185 to 235℃; (c) producing an aliphatic polyester resin composition by a polycondensation reaction of the reaction product, produced in (b), at 235 to 255℃ at a vacuum level of 0.1 to 2 Torr for 100 to 240 minutes; (d) introducing the resin composition, produced in step (c), into a twin screw extruder or a kneader, and then introducing 0.05 to 1 part by weight of one chain extender compound selected from among an isocyanate compound and a carbodiimide compound, followed by a chain extension reaction at 100 to 180℃; (e) producing a biodegradable resin composition by solid-state polymerization of the resin composition, produced in step (d), at a temperature of 70℃ to 100℃, which is lower than the melting point of the resin composition; (f) spinning the biodegradable resin composition, produced in step (e), into a netting twine; and (g) knitting the netting twine, spun in step (f), into a net.

Hereinafter, each step of the method for manufacturing fishing gear will be described in detail.

Step (a)

Specifically, step (a) is a step of producing the polyfunctional compound represented by Formula 1 by an esterification reaction of DL-malic acid and ethylene glycol or a polyethylene glycol having a weight-average molecular weight (Mw) of 150 to 500 g/mol:

Preferably, step (a) is a step of producing the polyfunctional compound represented by Formula 1 by an esterification reaction of DL-malic acid and ethylene glycol or a polyethylene glycol having a weight-average molecular weight (Mw) of 150 to 500 g/mol at a molar ratio of 1:1 to 1:1.5 in the presence of a catalyst at 180 to 210℃ for 60 to 180 minutes.

For the esterification reaction in step (a), DL-malic acid and ethylene glycol or a polyethylene glycol having a weight-average molecular weight (Mw) of 150 to 500 g/mol may be introduced into a reactor equipped with a reflux column, and then may be subjected to an esterification reaction with stirring at a slowly increasing temperature. At this time, the final increased temperature and the reaction in the esterification reaction may be 180 to 210℃ and 60 to 180 minutes, preferably 185 to 205℃ and 90 to 150 minutes, more preferably 190 to 200℃ and 100 to 150 minutes, most preferably 200℃ and 110 to 130 minutes. If the final increased temperature is lower than 180℃ or the reaction time is shorter than 60 minutes, the esterification reaction may not proceed smoothly. On the other hand, if the final increased temperature is higher than 210℃ or the reaction time is longer than 180 minutes, ethylene glycol boils and evaporates, and hence the molar ratio in the reaction mixture may be out of the desired range, and a good-quality polyfunctional compound may not be obtained due to thermal decomposition of the obtained product.

The catalyst that is used in step (a) may be at least one selected from the group consisting of monobutyltin oxide, titanium propoxide, and tetrabutyl titanate, but is not limited thereto. After the catalyst is introduced in an amount of 0.01 to 0.2 g, more preferably 0.01 to 0.05 g, per mole of DL-malic acid, the polyfunctional compound may be obtained by completely removing a theoretical amount of water while maintaining the temperature of the reactor at 180 to 210℃.

Step (b)

Step (b) is a step of producing a reaction product by esterification and transesterification reactions of an aliphatic dicarboxylic acid and an aliphatic diol in the presence of the polyfunctional compound of step (a).

Preferably, step (b) is a step of mixing an aliphatic dicarboxylic acid and an aliphatic diol at a molar ratio of 1:1.1 to 1:1.5 and producing a reaction product by esterification and transesterification reactions of the mixture in the presence of the polyfunctional compound of step (a) at 185 to 235℃. This step is preferably performed at a temperature of 185 to 235℃, more preferably 190 to 200℃, most preferably 195°C. If the temperature is lower than 185℃, the esterification reaction and the transesterification reaction may not sufficiently occur, and on the other hand, if the temperature is higher than 235℃, the resulting product may be thermally decomposed.

In step (b), the aliphatic dicarboxylic acid may be a compound represented by the following Formula 2.

[Formula 2]

ROOC-(CH₂)_n-COOR

The aliphatic dicarboxylic acid and the aliphatic diol may be mixed together at a molar ratio of 1:1.1 to 1.5, preferably 1:1.15 to 1.4, more preferably 1:1.15 to 1.3, most preferably 1: 1.2 to 1.25. At this time, if the molar ratio between the aliphatic dicarboxylic acid and the aliphatic diol is less than 1:1.1, the esterification reaction or the transesterification reaction may not be smoothly performed, and thus the color of the obtained resin composition may be adversely affected. On the other hand, if the molar ratio is greater than 1:1.5, the production cost may increase due to a decrease in the degree of vacuum in the reaction process, thus lowering economic efficiency.

Step (b) may further include a catalyst at the initial stage or late stage of the esterification reaction and the transesterification reaction. The catalyst may be at least one selected from the group consisting of titanium isopropoxide, calcium acetate, antimony trioxide, dibutyltin oxide, antimony acetate, tetrabutyl titanate, and tetrapropyl titanate, but is not limited thereto.

The catalyst may be mixed in an amount of 0.01 to 0.5 g, more preferably 0.03 to 0.2 g, most preferably 0.1 g, per mole of the aliphatic dicarboxylic acid. If the content of the catalyst is less than 0.01 g, the esterification reaction and the transesterification reaction may be delayed or may not occur sufficiently. On the other hand, if the content of the catalyst is more than 0.5 g, side reactions may occur or the reverse reaction rate may increase, thus causing color change of the reactants and deterioration in physical properties of the reactants.

Step (b) may further include a stabilizer at the initial stage or late stage of the esterification transesterification reactions. The stabilizer may include at least one selected from the group consisting of trimethyl phosphate, phosphoric acid and triphenyl phosphate, but is not limited thereto.

The stabilizer may be mixed in an amount of 0.01 to 0.5 g, more preferably 0.03 to 0.2 g, most preferably 0.1 g, per mole of the aliphatic dicarboxylic acid. If the content of the stabilizer is less than 0.01 g, the esterification reaction and the transesterification reaction may not occur sufficiently, and on the other hand, if the content of the stabilizer is more than 0.5 g, the stabilizer may interfere with the progress of the reactions, thus slowing the reaction rate, and a biodegradable resin composition having a sufficiently high molecular weight cannot be obtained.

Step (c)

Step (c) is a step of producing an aliphatic polyester resin composition by a polycondensation reaction of the reaction product produced in step (b).

Preferably, step (c) is a step of producing an aliphatic polyester resin composition by a polycondensation reaction of the reaction product, produced in (b), at 235 to 255℃ at a vacuum level of 0.1 to 2 Torr for 100 to 240 minutes. In this step, the polycondensation temperature and pressure may be 235 to 255℃ and 2 Torr or less, preferably 240 to 245℃ and 0.1 to 2 Torr, most preferably 245℃ and 1 to 1.5 Torr. If both the polycondensation temperature and vacuum conditions are not satisfied, the polycondensation reaction may not be performed properly, or the resulting product may be decomposed by oxidation at high temperature, and hence the color of the biodegradable resin composition may be poor or a resin having a desired molecular weight can be obtained.

The biodegradable aliphatic polyester resin composition obtained through step (c) has a number-average molecular weight (Mn) of 12,000 to 30,000, and a melt flow index of 30 g/10 min to 65 g/10 min as measured at 190°C and a load of 2,160 g.

Step (d)

Step (d) is a step of introducing the resin composition, produced in step (c), into a twin screw extruder or a kneader, and then introducing one chain extender compound selected from among an isocyanate compound, a carbodiimide compound and a modified styrene acrylic copolymer, followed by a chain extension reaction.

Preferably, step (d) is a step of introducing the resin composition, produced in step (c), into a twin screw extruder or a kneader, and then introducing 0.05 to 1 part by weight of one chain extender compound selected from among an isocyanate compound, a carbodiimide compound and a modified styrene acrylic copolymer, followed by a chain extension reaction at 100 to 180℃.

Specifically, the resin composition of step (c) may be subjected to a chain extension reaction in the range of 100 to 180℃. If the resin composition obtained in step (c) is subjected to a chain extension reaction at a temperature higher than the upper limit of the above-described range due to the high melt flow index thereof, the rate of a pyrolysis reaction, which is a reverse reaction, may increase along with an increase in the chain extension reaction rate, resulting in excessive widening of the molecular weight distribution of the resin composition, and the mechanical properties of the resin composition may deteriorate due to oxidation products and short polymer chains produced by the pyrolysis reaction, and the storage stability thereof may be reduced due to rapid hydrolysis. On the other hand, if the chain extension reaction is performed at a temperature lower than the lower limit of the above-described range, the resin composition may not be sufficiently melted in the reaction step, and thus the reaction may not occur sufficiently, so that the effect of the reaction cannot be obtained.

The chain extender that is used in step (d) may be one compound selected from among an isocyanate compound, a carbodiimide compound, and a modified styrene-acrylic copolymer. In this case, the isocyanate compound used may be one selected from the group consisting of 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate. The carbodiimide compound as another chain extender may be one selected from the group consisting of 1,3-dicyclohexylcarbodiimide, HMV-8CA, HMV-10B commercially available from Nisshinbo, Raschig's STABILIZER 9000, STABILIZER 7000, bis-(2,6-diisopropyl-phenylene-2,4-carbodiimide), and poly-(1,3,5-triisopropyl-phenylene-2,4-carbodiimide). The modified styrene-acrylic copolymer as another chain extender may be one selected from the group consisting of BASF's Joncryl ADR-4468C, ADR-4400, ADR-1300, and ADR-1350.

The biodegradable aliphatic polyester resin composition obtained through step (d) has a number-average molecular weight (Mn) of 20,000 to 40,000, and a melt flow index of 25 g/10 min to 45 g/10 min as measured at 190°C and a load of 2,160 g.

Step (e)

Step (e) is a step of producing a biodegradable resin composition having an increased molecular weight by solid-state polymerization of the resin composition, produced in step (d), at a temperature lower than the melting point of the resin composition. Preferably, step (e) is a step of producing a final biodegradable resin composition by solid-state polymerization of the resin composition, produced in step (d), at a temperature of 55℃ to 100℃, which is lower than the melting point of the resin composition.

In the solid-state polymerization of step (e), a dehumidifying dryer or vacuum dryer to which dehumidified air is supplied may be used as a reactor. More preferably, the reaction is carried out in a vacuum dryer capable of maintaining a vacuum level of less than 1 Torr. This is advantageous in terms of shortening the reaction time. The final biodegradable resin composition obtained through the solid-state polymerization may be suppressed from side reactions due to the reaction at a temperature below the melting temperature, and may have improved storage stability due to improvement in hydrolysis resistance at the end of the resin composition, and may have improved mechanical properties and processing performance due to low contents of residual monomers and low-molecular weight oligomers, an increased degree of crystallinity and an increased molecular weight.

The biodegradable resin composition of the present invention, finally produced by performing the solid-state polymerization in step (e), may have a melting point of 85 to 120℃, a number-average molecular weight (Mn) of 35,000 to 80,000, a weight-average molecular weight (Mw) of 150,000 to 350,000, a melt flow index of 0.5 to 10 g/10 min as measured at 190℃ and a load of 2.16 kg, and an acid value of 0.5 mg KOH/g to 5 mg KOH/g. Preferably, the biodegradable resin composition has a melting point of 100 to 118℃, a number-average molecular weight (Mn) of 45,000 to 70,000, a weight-average molecular weight (Mw) of 160,000 to 280,000, and a melt flow index of 1 to 8 g/10 min as measured at 190℃ and a load of 2.16 kg. More preferably, the biodegradable resin composition has a melting point of 105 to 116℃, a number-average molecular weight (Mn) of 50,000 to 65,000, a weight-average molecular weight (Mw) of 180,000 to 250,000, and a melt flow index of 2 to 6 g/10 min as measured at 190℃ and a load of 2.16 kg.

In addition, according to the present invention, an additive that is commonly used in the art may be additionally added to step (b) or step (c) as needed during the production of the biodegradable resin composition in order to improve performance, or may be added during mixing which is performed using a twin-screw extruder or a kneader after step (c).

Specifically, the additive may be at least one selected from the group consisting of an antioxidant, a UV stabilizer and a lubricant. The antioxidant is preferably a phenol-based antioxidant, and specifically, Adekastab AO series, Irgafos series, or a mixture thereof may be used as the antioxidant. The antioxidant may be mixed in an amount of 0.1 to 1.0 parts by weight based on 100 parts by weight of the aliphatic polyester resin composition.

The ultraviolet stabilizer may be a HALS-based compound having an amine group, and the ultraviolet stabilizer may be mixed in an amount of 0.1 to 0.8 parts by weight based on 100 parts by weight of the aliphatic polyester resin composition. The lubricant may be an amide-based PE wax, and the lubricant may be mixed in an amount of 0.1 to 1.0 parts by weight based on 100 parts by weight of the aliphatic polyester resin composition.

Step (f)

Step (f) may be a step of introducing the biodegradable resin composition, produced in step (e), into a spinning apparatus 300, and spinning the composition into a netting twine. The spinning in step (f) is a process of melting the biodegradable resin composition at a temperature higher than the melting point thereof, extruding it through a nozzle having a small diameter, and cooling and solidifying the extruded composition to obtain elongated solid fiber (hereinafter referred to as 'filament').

The spinning step may comprise: a melting step of melting the biodegradable resin composition in a cylinder of a spinning system; an extrusion step of extruding the molten biodegradable resin composition through a nozzle of the spinning system; a cooling step of cooling the filament, extruded in the extrusion step, through a cooling tank; a stretching step of stretching the cooled filament by passage through stretching roller; and a winding step of winding the stretched filament on a bobbin.

FIG. 6 schematically shows a spinning apparatus for fishing gear according to the present invention. Referring to FIG. 6, the spinning apparatus 300 comprises: a hopper 310 into which chips are introduced; a cylinder 320 coupled to the lower portion of the hopper and configured to melt the chips transferred to the inside through the hopper; a spinneret 330 communicating with the cylinder and configured to extrude the material, melted in the cylinder, into a filament type; a cooling tank 340 configured to cool the filament extruded through the spinneret; transfer rollers configured to transfer the filament to subsequence processes; first to

fourth stretching rollers

350, 360, 370 and 380 configured to stretch the filament; and stretching tanks (wetting tank, first electric heater tank, and second electric heater tank) installed between the first to fourth stretching rollers, respectively, and configured to improve the physical properties of the stretched multifilament.

Since the hopper 310 is configured to communicate with the cylinder 320, the chips introduced into the hopper are melted in the cylinder. The cylinder 320 is provided with a heater for heating the inside of the cylinder and configured to melt the chips, and the resin melted in the cylinder is externally extruded through the spinneret 330 by a piston provided inside the cylinder.

In an embodiment of the present invention, a spinneret having 40 nozzle holes, each having a diameter of 1.6mm, is used. Since a plurality of nozzle holes are formed in the spinneret, filaments extruded through the spinneret are extruded as a bundle and wound on rollers. In addition, the temperature of the cylinder 320, the temperature of the piston head, and the temperature of the spinneret is changed depending on the composition of the resin composition. A cooling tank and a transfer roller are disposed under the spinneret 330 and cool the filament spun from the spinneret. The filament cooled in the cooling bath 340 is subjected to a multi-step stretching process using stretching rollers and wound on the bobbin 390, and the filament is stretched by a difference in speed between first to

fourth stretching rollers

350, 360, 370 and 380, and the tensile strength of the filament is determined through the stretching action.

The stretching step may comprise: a first stretching step in which the filament cooled in a cooling tank 340 passes through first stretching rollers 350 and then passes through a wetting tank 352; a second stretching step in which the filament that passed through the wetting tank 352 in the first stretching step passes through second stretching rollers 352 and then passes a first electric heater tank 362; a third stretching step in which the filament that passed through the second stretching step passes through third stretching rollers 370 and then pass a second electric heater tank 372; and a fourth stretching step in which the filament that passed through the third stretching step is relaxed in fourth stretching rollers 380. Each of the stretching steps includes stretching tanks such as a wetting tank and an electric heater tank. In this case, the stretching tank may use a gas, a liquid, or a combination thereof.

In addition, since the four steps of stretching the filament by the stretching rollers are used, the strength of the filament is increased by gradually stretching the filament. The fourth stretching rollers may be rotated at a reduced speed compared to the third stretching rollers and may serve to reduce (relax) the stress of the filament. In addition, the filament that passed through the fourth stretching rollers may be wound on a bobbin.

When the biodegradable resin composition is extruded using the spinning apparatus, it is preferable that the temperature inside the cylinder is 198 to 225℃, the temperature of the piston head is 210 to 230℃, and the temperature of the spinning nozzle is 210 to 240℃.

If the temperature inside the cylinder, the piston head temperature, and the temperature of the spinning nozzle are lower than the lower limits of the above respective ranges, problems may arise in that the resin is not sufficiently melted in the system, and hence filament breakage occurs easily during spinning of the netting twine, and when the resin is discharged from the spinning nozzle, uniform stretching is not achieved, and thus variation in the diameter of the filament occurs. On the other hand, if each temperature is higher than the upper limit of the above-described range, gas may be generated when the resin is extruded from the spinneret, resulting in filament yarn or deterioration in the physical properties due to thermal decomposition of the resin.

In addition, it is preferable that the temperature of the cooling tank is 5℃ or below, the temperature of the wetting tank is 65 to 70℃, the temperature of the first electric heater tank is 80 to 90℃, and the temperature of the second electric heater bath is 75 to 85℃.

By spinning the biodegradable resin composition under the spinning conditions of step (f), it is possible to impart mechanical strengths such as tensile strength comparable with that of a nylon net.

Step (g)

Step (g) may be a step of knitting the netting twine, spun in step (f), into a net. In step (g), the netting twine may be knitted into a fishing net through stretching 6.0 to 7.3 times while passing through the first to fourth stretching rolls. The net manufactured through step (g) may be used as a gill net fishing gear or a trap fishing gear.

The biodegradable resin composition for fishing gear according to the present invention may be obtained by mixing an aliphatic dicarboxylic acid and an aliphatic diol and subjecting the mixture sequentially to esterification, transesterification, polycondensation, chain extension and solid-state polymerization reactions. Thus, by reducing the polycondensation reaction rate, it is possible to produce a biodegradable resin having excellent productivity and economic efficiency and having a high molecular weight.

In addition, the biodegradable resin composition for fishing gear according to the present invention is obtained by essentially performing a chain extension reaction and a solid-state polymerization reaction, and thus may have a high molecular weight and improved mechanical properties, processability, flexibility and elasticity recovery properties, compared to conventional aliphatic polyester resin compositions.

In addition, the fishing gear according to the present invention has flexibility and elasticity recovery comparable with those of nylon nets, and thus may improve fish catch. In addition, it is biodegradable, and thus may prevent contamination of coastal waters by waste fishing gear dumped into the sea, protect the marine ecosystem, and minimize damage caused by ghost fishing. Furthermore, it is possible to improve the convenience and economic feasibility of fishing using the fishing gear.

The effects of the present invention are not limited to the above-mentioned effects. It should be understood that the effects of the present invention include all effects that can be inferred from the following description.

FIG. 1 is schematic view showing gill net fishing.

FIG. 2 is an enlarged front view of a gill net fishing gear according to the present invention.

FIG. 3 is a front view of the fishing net portion of the gill net fishing gear according to the present invention.

FIG. 4 is a schematic view showing trap fishing.

FIG. 5 is an enlarged perspective view showing a trap fishing gear according to the present invention

FIG. 6 schematically shows a spinning apparatus for manufacturing fishing gear according to the present invention.

The above objects, other objects, features and advantages of the present invention will be readily understood through the following preferred embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments disclosed herein are provided so that this disclosure will be thorough and complete, and will fully convey the spirit of the present invention to those skilled in the art.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples.

Production Example: Production of Polyfunctional Compound

After substituting a 1,000 ml round-bottom flask with nitrogen, 268.16 g of DL-malic acid, 148.96 g of ethylene glycol and 0.02 g of tetrabutyl titanate as a catalyst were introduced into the reactor and then subjected to an esterification reaction at 120℃ for two hours. When the theoretical amount of water generated as a byproduct of the reaction reached 2 moles, the reaction was determined to be complete, and the reaction was terminated, thus producing a polyfunctional compound. The process for producing this polyfunctional compound is shown in the following Reaction Scheme 2:

[Reaction Scheme 2]

wherein m is an integer ranging from 1 to 30.

Example 1

A 100-L reactor was substituted with nitrogen, and 23.14 kg of succinic acid, 0.58 kg of adipic acid, 22.3 kg of 1,4-butanediol, 0.155 kg of ethylene glycol and 300 g of the polyfunctional compound obtained in the Production Example were introduced into the reactor. The reaction temperature was increased and finally set to 205℃, and then a theoretical amount of water was discharged. At this time, 10 g of dibutyltin oxide and 10 g of titanium isopropoxide were added as a catalyst, and 20 g of trimethyl phosphate was added as a stabilizer. Thereafter, the temperature of the reactor was increased, and a polycondensation reaction was performed at a temperature of 245℃ under a reduced pressure of 1.5 Torr for 180 minutes to obtain an aliphatic polyester resin composition. Then, 100 kg of the resin composition obtained through the polycondensation reaction and 500 g of 1,6-hexamethylene diisocyanate were mixed together using a supermixer, and then subjected to a chain extension reaction using a twin screw extruder having a diameter of 58 mm at 160℃. Thereafter, the reaction product obtained through the chain extension reaction was introduced into a solid-state polymerization apparatus equipped with a vacuum pump, and subjected to a solid-state polymerization reaction at 80℃ for 8 hours to obtain a final biodegradable resin composition. The biodegradable resin composition was introduced into a spinning apparatus and spun into a netting twine of 0.284 mm in diameter at a draw ratio of 6.5. Then, the netting twine was knitted into a double knotted net having a mesh size of 51 mm by means of a knitting machine, and then the net was heat-treated in a wetting tank at 85℃ for 16 minutes, thus producing a fishing net.

Example 2

A 100-L reactor was substituted with nitrogen, and 22.67 kg of succinic acid, 1.17 kg of adipic acid, 22.3 kg of 1,4-butanediol, 0.155 kg of ethylene glycol and 300 g of the polyfunctional compound obtained in the Production Example were introduced into the reactor. The reaction temperature was increased with stirring and finally set to 205℃, and then water was discharged. At this time, 4 g of tetrabutyl titanate, 8 g of dibutyltin oxide and 8 g of titanium isopropoxide were added as a catalyst, and 15 g of trimethyl phosphate was added as a stabilizer. Thereafter, the temperature of the reactor was increased, and a polycondensation reaction was performed at a temperature of 245℃ under a reduced pressure of 1.5 Torr for 183 minutes to obtain an aliphatic polyester resin composition. Then, 100 kg of the resin composition obtained through the polycondensation reaction and 500 g of 1,6-hexamethylene diisocyanate were mixed together using a supermixer, and then subjected to a chain extension reaction using a twin screw extruder having a diameter of 58 mm at 160℃. Thereafter, the reaction product obtained through the chain extension reaction was introduced into a solid-state polymerization apparatus equipped with a vacuum pump, and subjected to a solid-state polymerization reaction at 85℃ for 12 hours to obtain a final biodegradable resin composition. The biodegradable resin composition was introduced into a spinning apparatus and spun into a netting twine of 0.284 mm in diameter at a draw ratio of 6.6. Then, the netting twine was knitted into a double knotted net having a mesh size of 51 mm by means of a knitting machine, and then the net was heat-treated in a wetting tank at 85℃ for 16 minutes, thus producing a fishing net.

Example 3

A 100-L reactor was substituted with nitrogen, and 22.90 kg of succinic acid, 0.876 kg of adipic acid, 22.07 kg of 1,4-butanediol, 0.310 kg of ethylene glycol and 300 g of the polyfunctional compound obtained in the Production Example were introduced into the reactor. Then, the reaction temperature was increased and finally set to 195℃, and then water was discharged. At this time, 6 g of tetrabutyl titanate, 7 g of dibutyltin oxide and 7 g of titanium isopropoxide were added as a catalyst, and 14 g of trimethyl phosphate was added as a stabilizer. Thereafter, the temperature of the reactor was increased, and a polycondensation reaction was performed at a temperature of 240℃ under a reduced pressure of 1.5 Torr for 192 minutes to obtain an aliphatic polyester resin composition. Then, 100 kg of the resin composition obtained through the polycondensation reaction and 500 g of 1,6-hexamethylene diisocyanate were mixed together using a supermixer, and then subjected to a chain extension reaction using a twin screw extruder having a diameter of 58 mm at a temperature of 170℃. Thereafter, the reaction product obtained through the chain extension reaction was introduced into a solid-state polymerization apparatus equipped with a dehumidifying device, and subjected to a solid-state polymerization reaction at 80℃ for 12 hours to obtain a final biodegradable resin composition. The biodegradable resin composition was introduced into a spinning apparatus and spun into a netting twine of 0.284 mm in diameter at a draw ratio of 6.6. Then, the netting twine was knitted into a double knotted net having a mesh size of 51 mm by means of a knitting machine, and then the net was heat-treated in a wetting tank at 85℃ for 17 minutes, thus producing a fishing net.

Comparative Example 1

Poly butylene succinate (PBS), which is a commercially available biodegradable resin composition which is currently used as a resin for biodegradable fishing gear, was introduced into a spinning system and spun into a netting twine having a diameter of 0.284 mm at a draw ratio of 6.6. Then, the netting twine was knitted into a double knotted net having a mesh size of 51 mm by means of a knitting machine, and then the net was heat-treated in a wetting tank at 85℃ for 17 minutes, thus producing a fishing net.

Comparative Example 2

A resin composition composed of a 95:5 (wt/wt) mixture of PBS (poly butylene succinate) and PBAT (polybutylene adipate-co-terephthalate), which is currently commercially sold as a resin composition for biodegradable fishing gear, was introduced into a spinning system and spun into a netting twine having a diameter of 0.284 mm at a draw ratio of 6.6. Then, the netting twine was knitted into a double knotted net having a mesh size of 51 mm by means of a knitting machine, and then the net was heat-treated in a wetting tank at 85℃ for 18 minutes, thus producing a fishing net.

Experimental Example 1: Measurement of Molecular Weight, Melting Point and Melt Flow Index

The number-average molecular weight, weight-average molecular weight, melting point and melt flow index of each of the resin compositions produced by the methods of Examples 1 to 3 and the currently commercially available products used in Comparative Examples 1 and 2, were evaluated by the methods described below. The results of the evaluation are shown in Table 1 below.

[Evaluation methods]

(1) Number-average molecular weight and weight-average molecular weight

The number-average molecular weight and weight-average molecular weight distributions were measured by column chromatography using a system equipped with polystyrene at a temperature of 35℃. At this time, the developing solvent used was chloroform, the concentration of the sample used was 5 mg/mL, and the flow rate of the solvent was 1.0 mL/min.

(2) Melting point

The melting point was measured using a differential scanning calorimeter at a temperature ranging from 20℃ to 200℃ at a temperature increase rate of 10℃ per minute under a nitrogen atmosphere.

(3) Melt flow index

The melt flow index was measured according to the ASTM D1238 standard under the conditions of 190℃ and 2,160 g.

	Number-average molecular weight	Weight-average molecular weight	Melting point (℃)	Melt flow index (g/10 min)
Example 1	62,240	183,500	112.2	2.7
Example 2	63,800	233,150	110.1	2.4
Example 3	61,600	213,290	110.3	2.7
Comparative Example 1	54,800	148,860	115.6	2.8
Comparative Example 2	53,200	80,430	124.8	3.1

From the results in Table 1 above, it could be seen that Examples 1 to 3 had a higher number-average molecular weight and weight-average molecular weight and a lower melt flow index than Comparative Examples 1 and 2, suggesting that Examples 1 to 3 had excellent physical properties and processability. On the contrary, in the case of the biodegradable resin compositions of Comparative Examples 1 and 2, which do not contain the polyfunctional compound, the number-average molecular weight and the weight-average molecular weight were significantly lower than those of Examples 1 to 3, suggesting that the resin compositions of Comparative Examples 1 and 2 had poor extrusion formability, mechanical properties and durability.

Experimental Example 2: Evaluation of Mechanical Properties

The mechanical properties of the fishing nets produced in Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated by the methods described below. The results of the evaluation are shown in Table 2 below.

(1) Diameter

10 strands were cut to a length of 1 m, and then the sum weight thereof was measured to four places of decimals. The measured value was substituted into the following Equation (1).

[Equation 1]

Diameter (mm) =

w: Weight (g) of 10 m monofilament yarn;

ð: 3.14159; h: 10; c: 1.26 (specific gravity)

(2) Linear strength and elongation

The strength and elongation of each sample were measured using a constant-speed tensile tester (Instron 3365, USA) according to the KS K 0412 (2005) test method. The measurement was performed up to 1/1,000 g every 0.1 sec, and the measured value was stored in a PC, and then analyzed.

(3) Evaluation of flexibility

The flexibility was tested by the Brandt method, and each specimen was prepared by uniformly winding each sample 20 times on a cylinder of 4 cm in diameter and peeling it off. The flexibility measuring device measured the force applied when pressing the specimen at 4 cm and compressing it to 2.5 cm.

	Linear strength (kg_f/mm²)	Elongation (%)	Flexibility (g)	Diameter (mm)
Example 1	51.07±0.42	23.40±0.72	13.59	0.284
Example 2	48.11±0.48	27.28±0.68	14.58	0.284
Example 3	48.32±0.52	28.15±1.08	13.88	0.284
Comparative Example 1	48.48±0.70	21.82±0.48	18.28	0.284
Comparative Example 2	47.74±0.70	24.32±0.52	16.24	0.284

From the results in Table 2 above, it was confirmed that Examples 1 to 3 had improved linear strength, elongation and flexibility compared to Comparative Examples 1 and 2, and particularly, had significantly increased flexibility. Accordingly, it could be seen that, when Examples 1 to 3 are applied to gill net fishing gear or trap fishing gear, the fishing net can be prevented damaged even if fish are gilled in the mesh of the net or enter the inside of the fishing net, due to the improved flexibility thereof. On the contrary, it was confirmed that Comparative Examples 1 and 2 showed generally lower linear strength and elongation values than Examples 1 to 3, and had lower flexibility.

Experimental Example 3: Evaluation of Fishing Performance

Using the nets produced in Examples 1 to 3 and Comparative Examples 1 to 2, biodegradable gill net fishing gears were manufactured in a conventional manner. The fishing performance per width of each of the biodegradable gill net gears was tested for yellow corvina in the sea. The results are shown in Table 3 below.

	Catch (kg yellow corvina/width)
Example 1	2.20
Example 2	2.40
Example 3	2.65
Comparative Example 1	2.05
Comparative Example 2	2.10

From the results in Table 3, it was confirmed that the gill net fishing gears of Examples 1 to 3 had better fishing performance than those of Comparative Examples 1 and 2. In addition, it was confirmed that the biodegradable gill net fishing gears produced in Examples 1 to 3 were not broken even in the process of lifting the nets by manpower and machine, and thus were highly practical. On the contrary, in the case of Comparative Examples 1 and 2, the catch was relatively small compared to Examples 1 to 3, and the fishing nets were broken in the process of lifting the nets by manpower and machine.

[Description of reference numerals]

1: Buoys

2: Buoy lines

3: Fishing net

3a, 3b: Protecting net

4a, 4b: Hanging line

5: Floats

6: Sinkers

7: Frame

8: Gill net

9: Fish trap

300: Spinning apparatus

310: Hopper

320: Cylinder

330: Spinneret

340: Cooling tank

350, 360, 370, 380: First to fourth stretching rollers

362: First electric heater tank

372: Second electric heater tank

390: Bobbin

Claims

A biodegradable resin composition for fishing gear having excellent flexibility and elastic recovery properties, the biodegradable resin composition being obtained by subjecting an aliphatic dicarboxylic acid and an aliphatic diol sequentially to esterification, transesterification, polycondensation, chain extension and solid-state polymerization reactions in the presence of a polyfunctional compound represented by the following Formula 1:

[Formula 1]

wherein n is an integer ranging from 1 to 11, and m is an integer ranging from 1 to 30.
The biodegradable resin composition of claim 1, wherein the polyfunctional compound is obtained by mixing DL-malic acid and ethylene glycol or a polyethylene glycol having a weight-average molecular weight (Mw) of 150 to 500 g/mol at a molar ratio of 1:1 to 1:1.5 to obtain a mixture and subjecting the mixture to an esterification reaction.
The biodegradable resin composition of claim 1, wherein the polyfunctional compound is mixed in an amount of 0.1 to 3 g per mole of the aliphatic dicarboxylic acid.
The biodegradable resin composition of claim 1, wherein the aliphatic dicarboxylic acid is at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelic acid, sebacic acid, 1,4-cyclohexyldicarboxylic acid, and esterified derivatives thereof.
The biodegradable resin composition of claim 4, wherein the aliphatic dicarboxylic acid is obtained by mixing succinic acid and adipic acid at a molar ratio of 95: 5 to 99:1.
The biodegradable resin composition of claim 1, wherein the aliphatic diol is at least one selected from the group consisting of ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, and 1,2-cyclohexanedimethanol.
The biodegradable resin composition of claim 6, wherein the aliphatic diol is obtained by mixing 1,4-butanediol and ethylene glycol at a molar ratio of 95: 5 to 99: 1.
The biodegradable resin composition of claim 1, wherein the aliphatic dicarboxylic acid and the aliphatic diol are mixed together at a molar ratio of 1:1.1 to 1.5.
The biodegradable resin composition of claim 1, which has a melting point of 85 to 120℃, a number-average molecular weight (Mn) of 35,000 to 80,000, a weight-average molecular weight (Mw) of 150,000 to 350,000, a melt flow index of 0.5 to 10 g/10 min as measured at 190℃ and a load of 2.16 kg, and an acid value of 0.5 mg KOH/g to 5 mg KOH/g.
A fishing gear manufactured using the biodegradable resin composition according to claim 1.
The fishing gear of claim 10, which is a gill net fishing gear or a trap fishing gear.
A method for manufacturing fishing gear, the method comprising steps of:

(a) producing a polyfunctional compound represented by the following Formula 1 by an esterification reaction of DL-malic acid and ethylene glycol or a polyethylene glycol having a weight-average molecular weight (Mw) of 150 to 500 g/mol:

[Formula 1]

wherein n is an integer ranging from 1 to 11, and m is an integer ranging from 1 to 30;

(b) producing a reaction product by esterification and transesterification reactions of an aliphatic dicarboxylic acid and an aliphatic diol in the presence of the polyfunctional compound of step (a);

(c) producing an aliphatic polyester resin composition by a polycondensation reaction of the reaction product produced in step (b);

(d) introducing the resin composition, produced in step (c), into a twin screw extruder or a kneader, and then introducing one chain extender compound selected from among an isocyanate compound and a carbodiimide compound, followed by a chain extension reaction;

(e) producing a biodegradable resin composition by solid-state polymerization of the resin composition, produced in step (d), at a temperature lower than a melting point of the resin composition;

(f) spinning the biodegradable resin composition, produced in step (e), into a netting twine; and

(g) knitting the netting twine, spun in step (f), into a net.
The method of claim 12, comprising steps of:

(a) producing the polyfunctional compound represented by Formula 1 by an esterification reaction of DL-malic acid and ethylene glycol or a polyethylene glycol having a weight-average molecular weight (Mw) of 150 to 500 g/mol at a molar ratio of 1:1 to 1:1.5 in the presence of a catalyst at 180 to 210℃ for 60 to 180 minutes;

(b) mixing an aliphatic dicarboxylic acid and an aliphatic diol at a molar ratio of 1:1.1 to 1:1.5 to obtain a mixture and producing a reaction product by esterification and transesterification reactions of the mixture in the presence of the polyfunctional compound of step (a) at 185 to 235℃;

(c) producing an aliphatic polyester resin composition by a polycondensation reaction of the reaction product, produced in (b), at 235 to 255℃ at a vacuum level of 0.1 to 2 Torr for 100 to 240 minutes;

(d) introducing the resin composition, produced in step (c), into a twin screw extruder or a kneader, and then introducing one chain extender compound selected from among an isocyanate compound and a carbodiimide compound, followed by a chain extension reaction at 100 to 180℃; and

(e) producing a biodegradable resin composition by solid-state polymerization of the resin composition, produced in step (d), at a temperature of 70℃ to 100℃, which is lower than the melting point of the resin composition.
The method of claim 12 or 13, wherein the catalyst in step (a) is at least one selected from the group consisting of monobutyltin oxide, titanium propoxide, and tetrabutyl titanate.
The method of claim 12 or 13, wherein step (b) further includes at least one selected from the group consisting of titanium isopropoxide, calcium acetate, antimony trioxide, dibutyltin oxide, antimony acetate, tetrabutyl titanate, and tetrapropyl titanate, at an initial stage or late stage of the esterification and transesterification reactions.
The method of claim 12 or 13, wherein the biodegradable resin composition produced in step (e) has a melting point of 85 to 120℃, a number-average molecular weight (Mn) of 35,000 to 80,000, a weight-average molecular weight (Mw) of 150,000 to 350,000, a melt flow index of 0.5 to 10 g/10 min as measured at 190℃ and a load of 2.16 kg, and an acid value of 0.5 mg KOH/g to 5 mg KOH/g.
The method of claim 12, wherein the fishing gear is a grill net fishing gear or a trap fishing gear.