Thermoplastic resin composition and method for producing the same

Abstract

The present invention relates to a thermoplastic resin composition and a method for producing the same, and more particularly to an environmentally friendly thermoplastic resin composition that is biodegradable yet has excellent moldability and mechanical properties such as improved tensile strength and elongation, and can therefore be used as an environmentally friendly material in a variety of fields, and a method for producing the same.

Description

Technical Field

[0001] The present invention relates to a thermoplastic resin composition and a method for producing the same, and more particularly, to a biodegradable and environmentally friendly thermoplastic resin composition and a method for producing the same.

Background Art

[0002] Unlike thermosetting resins, thermoplastic resins have no intermolecular bonds (not cross-linked), which is advantageous for molding and processing. The easiest way to mold and process such thermoplastic resins is to utilize the thermal properties of thermoplastic polymers. Thermoplastic polymers change from a solid state to a liquid state at a temperature above the melting point, making it easy to mold them into the desired form. In industrial settings, injection machines and the like are generally used for molding such polymers. Specifically, it plays an important role in various plastic moldings, such as injecting a solid-state thermoplastic resin in the form of pellets or powder into a high-temperature injection machine to melt it, and then spinning it into a fibrous form through injection and a die.

[0003] As such thermoplastic resins, materials such as PET (polyethylene terephthalate), PE (polyethylene), and PP (polypropylene) have usually been mainly used. However, along with recent environmental problems, there has been a major issue regarding the industrial applications of biodegradable and environmentally friendly materials such as PLA (polylactic acid), PGA (polyglycolic acid), PLGA (polylactic-co-glycolic acid), PCL (polycaprolactone), PBAT (polybutylene adipate terephthalate), and PA (polyamide).

[0004] Biodegradable thermoplastic resins such as PLA have the problem of being very hard and brittle compared to existing petroleum-based plastics, which limits their application in various industrial fields. For this reason, methods that change the physical properties of the material by blending it with softer and more flexible polymers, or methods that impart ductility by incorporating nanocomposites into thermoplastic resins are mainly used. However, in the former case, although ductility can be greatly imparted by mixing and injection molding polymers with excellent ductility such as PEG, PEO, and PU, mixing polymers with different properties and chain extenders during injection presents process difficulties, such as the need to consider the compatibility and thermal properties between polymers. Furthermore, the physical properties of the polymers mixed together may reduce the biodegradability and biocompatibility of the original thermoplastic polymer.

[0005] On the other hand, the latter method involves mixing additives such as plasticizers during injection molding to alter the ductility and / or physical properties of the thermoplastic resin. While it has the advantage of inducing property changes with small amounts of additives and being based on the target substance, the latter method has drawbacks: most additives are difficult to mix and require additional processes; excessive additives lead to frequent yarn breakage during high-temperature spinning, resulting in poor spinning processability; and the post-processing properties are also poor due to the deterioration of the thermoplastic resin's physical properties.

[0006] Therefore, Korean Registered Patent No. 1992492 disclosed a thermoplastic cellulose derivative composition containing a cellulose ester, a plasticizer, and a hydrolysis inhibitor in order to improve the processability of thermoplastic resins, and Korean Registered Patent No. 01837493 disclosed an oxidative biodegradation additive composition containing a cellulose composition plasticized with a sodium bisulfite plasticizer in order to provide a thermoplastic cellulose resin with improved mechanical properties.

[0007] However, these thermoplastic resins also have problems, such as insufficient flexibility, resulting in rough surfaces during molding and easy breakage from external impacts. Furthermore, when mixed with existing biodegradable plastic raw materials to manufacture molded products, chemical decomposition occurs, aggregates are formed, and the resins are processed to have a hard appearance, limiting the potential for increasing the mixing ratio.

[0008] Therefore, there is a need to develop natural polymer thermoplastic raw materials that offer excellent moldability while significantly improving the mechanical properties of thermoplastic resins, such as elongation and tensile strength. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Korean Registered Patent No. 1992492 (Publication Date: June 19, 2014) [Patent Document 2] Korean Registered Patent No. 1837493 (Publication Date: July 29, 2016) [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The main objective of the present invention is to solve the above-mentioned problems and to provide a thermoplastic resin composition and a method for producing the same that is biodegradable, has excellent moldability, and exhibits improved mechanical properties such as tensile strength and elongation.

[0011] Another object of the present invention is to provide an environmentally friendly molded article formed from the thermoplastic resin composition. [Means for solving the problem]

[0012] To achieve the above objective, one embodiment of the present invention provides a thermoplastic resin composition characterized by containing 65% to 80% by weight of hydroxyethylcellulose and 20% to 35% by weight of glycerin, wherein the viscosity of an aqueous solution of 2% by weight dissolved in water is measured at 20°C using a Brookfield viscometer and is 4,000 cps to 250,000 cps.

[0013] In a preferred embodiment of the present invention, the thermoplastic resin composition may further contain one or more additives selected from the group consisting of antioxidants, lubricants, biodegradation accelerators, and strength enhancers.

[0014] In a preferred embodiment of the present invention, the lubricant may be one or more selected from the group consisting of sorbitol, magnesium stearate, calcium stearate, ethylene glycol, glycerol monostearate, and lecithin.

[0015] Another embodiment of the present invention provides a method for producing a thermoplastic resin composition, characterized by comprising the steps of (a) forming a mixture by adding 20% ​​to 35% by weight of glycerin to 65% to 80% by weight of hydroxyethylcellulose with a viscosity of 4,000 cps to 250,000 cps, and (b) kneading the mixture to plasticize it.

[0016] In another preferred embodiment of the present invention, the kneading in step (b) above may be characterized by being carried out at 50°C to 90°C at 300 rpm or more.

[0017] Another embodiment of the present invention provides a molded article formed from the above-described thermoplastic resin composition.

[0018] In another preferred embodiment of the present invention, the molded article may be characterized by having a tensile strength of 4.5 MPa to 6.5 MPa as measured in accordance with ASTM D638.

[0019] In another preferred embodiment of the present invention, the molded article can be characterized in that the elongation measured in accordance with ASTM D638 is 20 mm to 45 mm.

Advantages of the Invention

[0020] The thermoplastic resin composition according to the present invention has excellent moldability while having biodegradability, and not only the tensile strength but also the mechanical properties such as elongation are improved. Therefore, it has the effect of being applicable as an environmentally friendly material in various fields.

Brief Description of the Drawings

[0021] [Figure 1] It is a photographic image of the molded article produced in Example 3 taken with a digital camera. [Figure 2] It is a photographic image of the molded article produced in Example 7 taken with a digital camera. [Figure 3] It is a photographic image of the molded article produced in Example 10 taken with a digital camera. [Figure 4] It is a photographic image of the molded article produced in Comparative Example 1 taken with a digital camera. [Figure 5] It is a photographic image of the molded article produced in Comparative Example 4 taken with a digital camera.

Modes for Carrying Out the Invention

[0022] The advantages, features, and methods for achieving them of the present invention will become clear by referring to the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and can be realized in various different forms. However, this embodiment is provided only to make the disclosure of the present invention complete and to fully inform those with ordinary knowledge in the technical field to which the present invention pertains of the scope of the invention. The present invention is defined only by the scope of the claims.

[0023] In describing the present invention, if it is determined that a specific explanation of related known technologies may obscure the gist of the present invention, such detailed explanation will be omitted.

[0024] Wherever "includes," "has," "consists of," or "is composed of" is used in this specification, other parts may be added unless "only" is used. When a component is expressed singularly, it includes cases where it includes multiple components unless otherwise explicitly stated.

[0025] As used herein, "molded product" refers to a substance made into a specific shape, such as an extruded product or an injection-molded product.

[0026] The features of each of the various embodiments of the present invention can be partially or entirely combined or combined with one another, enabling a variety of technically diverse interlocking and driving processes. Each embodiment may be implemented independently of the others, or it may be implemented together in relation to one another.

[0027] In one embodiment, the present invention relates to a biodegradable thermoplastic resin composition characterized by containing 65% to 80% by weight of hydroxyethylcellulose with a viscosity of 4,000 cps to 250,000 cps, and 20% to 35% by weight of glycerin.

[0028] Generally, cellulose derivatives such as hydroxyethylcellulose have a polymer structure composed of strong hydrogen bonds, which causes thermal decomposition below their melting point, making them difficult to mold and process into plastics.

[0029] Therefore, in this invention, by adding glycerin to hydroxyethyl cellulose, a cellulose derivative having a specific viscosity, in a specific content, the strong hydrogen bonds of the hydroxyl groups of hydroxyethyl cellulose are weakened, the distance between chains is widened, creating an environment where micro-Brownian motion is likely to occur, thereby lowering the glass transition temperature of hydroxyethyl cellulose and providing flexibility. This plasticization process results in a natural polymer thermoplastic resin with excellent moldability and significantly improved mechanical properties such as elongation and tensile strength.

[0030] To avoid repetition, each of the aforementioned components will be described later in the section on the method for producing the thermoplastic resin composition.

[0031] In another embodiment, the present invention relates to a method for producing a biodegradable thermoplastic resin composition, characterized by comprising the steps of (a) mixing 65% to 80% by weight of hydroxyethylcellulose with a viscosity of 4,000 cps to 250,000 cps with 20% to 35% by weight of glycerin, and (b) kneading the mixture to plasticize it.

[0032] The method for producing the thermoplastic resin composition according to the present invention is to first add glycerin to hydroxyethylcellulose [(a) step].

[0033] The aforementioned hydroxyethyl cellulose (HEC) is a white or pale yellowish-white powdered water-soluble polymer component that possesses the best flame resistance and pH stability among cellulose derivatives, as well as colloidal properties, water retention, and temperature resistance. It is recognized as a raw material that can be used in a wide variety of products in various industries.

[0034] In the present invention, the hydroxyethylcellulose is a base resin and may be hydroxyethylcellulose having a viscosity of 4,000 cps to 250,000 cps. In this case, the viscosity of the hydroxyethylcellulose is the viscosity measured at 20°C using a Brookfield viscometer in an aqueous solution of hydroxyethylcellulose dissolved in water (hydroxyethylcellulose: 2% by weight).

[0035] If the viscosity of the hydroxyethylcellulose is less than 4,000 cps, there is a risk of insufficient mixing with glycerin, resulting in poor extrusion and browning. Furthermore, there is a risk of glycerin dissolving after extrusion, causing stickiness. If the viscosity exceeds 250,000 cps, the viscosity during mixing with glycerin is too high, resulting in poor extrusion and unstable extrusion, and there is a risk of browning due to carbonization.

[0036] Furthermore, the hydroxyethylcellulose can be mixed in an amount of 65% to 80% by weight relative to the total weight of the composition. If the hydroxyethylcellulose content is less than 65% by weight, there is a risk that an excessive amount of glycerin will be present, making the mixture sticky and difficult to pelletize, and that the mixture will form into a lump that is difficult to feed into equipment such as an extruder after plasticization. If it exceeds 80% by weight, there is a risk that plasticization by glycerin will not be carried out sufficiently, and that it will not be possible to manufacture a thermoplastic resin.

[0037] Such hydroxyethyl cellulose can be used as a compatibilized product or manufactured and used. Any known manufacturing method in the art can be applied without limitation as a method for producing hydroxyethyl cellulose. For example, cellulose can be reacted with an alkalizing agent to obtain alkalized cellulose, and then the obtained alkalized cellulose can be subjected to an etherification reaction.

[0038] On the other hand, glycerin can be obtained as a by-product when manufacturing soap or fatty acids from natural resins, but recently it is synthesized by treating propylene with chlorine to produce epichlorohydrin, which is then hydrolyzed. It is used in a variety of fields, including rubber, toothpaste, cosmetics, chemicals, paints, cellophane, printing inks, and confectionery.

[0039] In the present invention, the glycerin plays a role in mixing with hydroxyethylcellulose to interfere with the strong hydrogen bonding caused by the hydroxyl groups of hydroxyethylcellulose, thereby increasing the distance between cellulose polymer chains and creating an environment conducive to micro-Brownian motion. It can be added in an amount of 20% to 35% by weight relative to the total weight of the composition.

[0040] If the glycerin content is added at less than 20% by weight of the total weight of the composition, it will not adequately interfere with the strong hydrogen bonding by the hydroxyl groups of hydroxyethylcellulose and increase the distance between cellulose polymer chains to create an environment conducive to micro-Brownian motion. As a result, it will not be able to lower the glass transition temperature or impart flexibility to the resin. If it exceeds 35% by weight, an excess of glycerin may dissolve, causing stickiness and making pelletization difficult.

[0041] Subsequently, the mixture of hydroxyethylcellulose and glycerin can be kneaded and plasticized [(b) step].

[0042] The kneading of the mixture can be carried out at 50°C to 90°C at 300 rpm or more, preferably at 70°C to 90°C at 300 rpm to 600 rpm, so as to facilitate the plasticization of hydroxyethylcellulose. The kneading time can be appropriately adjusted according to the content of the mixture and the degree of plasticization, preferably at 30 to 60 minutes.

[0043] When kneading is performed under the above conditions, the glass transition temperature and melting point can be lowered to facilitate the micro-Brownian motion of hydroxyethylcellulose, thereby improving the plasticization efficiency of hydroxyethylcellulose even with a small amount of glycerin.

[0044] The aforementioned mixing can be carried out by any method, either by using a mixer alone or by using an extruder in conjunction with the extrusion described later.

[0045] At this time, the kneading machine is not particularly limited and any kneading machine commonly used in this field can be used without restriction. For example, it may be a high-speed agitator, mixer, or blender.

[0046] On the other hand, in the method for producing the thermoplastic resin composition of the present invention, additives may be further added and mixed before and / or after the kneading (plasticizing) step, as needed.

[0047] The aforementioned additive may preferably be one or more selected from the group consisting of antioxidants, lubricants, biodegradation accelerators, and strength enhancers, and is a component commonly used in the field. The present invention does not particularly limit the selection of the aforementioned additive.

[0048] Specifically, among the additives mentioned above, the antioxidant plays a role in preventing thermal decomposition during the thermoplasticization and molding of hydroxyethylcellulose, and is a common antioxidant usable in this field. For example, it may be in the form of tetrakismethylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)methane or tris(2,4-di-t-butylphenyl)phosphate, either alone or in mixture form.

[0049] Furthermore, the lubricant is intended to improve the lubrication properties of the thermoplastic resin, and any ordinary lubricant usable in the field can be used without limitation. In terms of miscibility with the thermoplastic resin composition of the present invention and lubricity, it is preferably one or more selected from the group consisting of sorbitol, magnesium stearate, calcium stearate, ethylene glycol, glycerol monostearate, and lecithin.

[0050] Furthermore, the biodegradation accelerator and strength reinforcer can be any ordinary biodegradation accelerator and strength reinforcer capable of promoting the biodegradation of thermoplastic resins or reinforcing the strength of the resin, and the biodegradation accelerator can be a fatty oil such as soybean oil, castor oil, linseed oil, sunflower oil, or coconut oil, fatty acids such as caproic acid, capric acid, lauric acid, oleic acid, olenic acid, or linoleic acid, or fatty acid esters such as ethyl oleate, ethyl linoleate, or isooctylate, used alone or in a mixture of two or more, and the strength reinforcer can be a glass fiber, carbon fiber, or the like.

[0051] Such additives can be selected without restriction on the content used in normal use, as long as they do not impair the desired physical properties of the thermoplastic resin composition of the present invention. Preferably, each additive may be independently present in an amount of 0.01 to 10 parts by weight per 100 parts by weight of the thermoplastic resin composition of the present invention.

[0052] The method for producing a thermoplastic resin composition according to the present invention further includes an extrusion step and a cutting step of extruding and cutting the kneaded (plasticized) composition, thereby enabling the composition to be obtained in a form that is easy to commercialize.

[0053] The extrusion step may be carried out via an extruder, and the extruder is not particularly limited; any extruder commonly used in this field can be used without restriction. For example, a single-screw extruder with one screw or a multi-screw extruder with multiple screws can be used. Considering uniform mixing of the material, ease of processing, and economics, it is preferable to use a twin-screw extruder with two screws.

[0054] In this case, the temperature of the extruder can be set to 70°C to 200°C, preferably 130°C to 180°C, so that extrusion can be carried out efficiently without decomposition of the thermoplastic resin, and the screw rotation speed of the extruder can be 20 rpm to 300 rpm, preferably 20 rpm to 200 rpm. Such extrusion conditions have the advantage that the processing rate per unit time is appropriate, the process efficiency is excellent, and sufficient extrusion is possible without causing problems such as thermal decomposition of the resin components.

[0055] The extruded material can be cut into a form that is easy to handle and facilitates the manufacture of molded products, such as via a pelletizer, and is preferably in the form of pellets.

[0056] Furthermore, the method for producing the thermoplastic resin composition of the present invention may also be effective to further include a cooling step of cooling through a cooling water bath between the extrusion and cutting steps, and it is preferable to perform a drying step of drying at 50°C to 80°C for 4 to 8 hours after the cutting step.

[0057] The thermoplastic resin composition produced according to the present invention in this manner is biodegradable, has excellent elongation and tensile strength, and is easy to mold and mix with petroleum-based thermoplastic resins, making it applicable as an additive to a wide variety of thermoplastic resins.

[0058] In another embodiment, the present invention relates to a molded article formed from the thermoplastic resin composition.

[0059] The molded articles according to the present invention are formed from the thermoplastic resin composition described above and can be manufactured into various molded products by various molding methods such as injection molding, extrusion molding, vacuum molding, and casting molding. Such molding methods are well known to those with ordinary skill in the art to which the present invention pertains.

[0060] The molded articles formed by this molding method have, for example, a tensile strength of 4.5 MPa to 6.5 MPa and an elongation of 20 mm to 45 mm as measured by ASTM D638, and are excellent in mechanical properties and formability, as well as being biodegradable, so they can be usefully used in food, electrical / electronic products, automobile parts, building materials, household goods, toys, agricultural materials, marine materials, and the like.

[0061] In describing the thermoplastic resin composition, its manufacturing method, and molded article of the present invention, it should be explicitly stated that other conditions and equipment not explicitly mentioned can be appropriately selected within the range of practices commonly used in the art, and are not particularly limited. [Examples]

[0062] The present invention will be described in more detail below through specific examples. The following examples are merely illustrative to aid in understanding the present invention, and the scope of the present invention is not limited thereto.

[0063] <Example 1> As a cellulose derivative, 80% by weight of hydroxyethylcellulose (Lotte Fine Chemical, HEC B100K) with a viscosity of 100,000 cps was added to 20% by weight of glycerin, and the mixture was plasticized by high-speed mixing at 300 rpm for 30 minutes. Then, a molded product in a strand shape was manufactured using a twin-screw extruder with a screw speed of 30 rpm [main motor speed 200 rpm to 250 rpm].

[0064] <Examples 2-10> The manufacturing process was the same as in Example 1, but the conditions in Table 1 below were changed to produce a molded product in a strand shape.

[0065] <Comparative Examples 1-10> The manufacturing process was the same as in Example 1, but the conditions in Table 1 below were changed to produce a molded product in a strand shape.

[0066] [Table 1]

[0067] [Example of experiment] The properties of the test specimens produced in Examples 1-10 and Comparative Examples 1-10 were measured using the following method, and the results are shown in Table 2 and Figures 1-5 below.

[0068] <Measurement method> (1) Measurement of moldability: The flowability during extrusion immediately after ejection was evaluated visually. If extrusion was easy and the extruded material was in good condition, it was recorded as "good" in Table 2; if it was not extruded, it was recorded as "poor". (2) Measurement of the condition of the molded product: The color, surface roughness, and stickiness of the extruded product were measured using an optical microscope (SOMETECH SV-55) immediately after extrusion at 60x magnification, and the results are shown in Table 2 and Figures 1 to 5. (3) Measurement of tensile strength: To measure the tensile strength of the thermoplastic resin, test specimens were prepared in accordance with the ASTM D638 standard, and then the tensile strength was measured using a Universal Test Machine (UTM, Instron Model 4465). The tensile speed was 10 mm / min, and measurements were taken 7 times. The upper and lower limits were discarded, and the average of 5 measurements was calculated and recorded in Table 2. (4) Measurement of elongation: To measure the elongation of thermoplastic resins, test specimens were prepared in accordance with ASTM D638 standards, and the elongation was measured using a Universal Test Machine (UTM, Instron Model 4465). The grip distance and gauge distance were fixed at 40 mm, and the speed was 10 mm / min. Seven measurements were taken, discarding the upper and lower limits, and the average of five measurements was calculated and recorded in Table 2.

[0069] [Table 2]

[0070] Table 2 and Figures 1 to 5 show that the molded articles produced in Examples 1 to 10 exhibited good moldability, excellent color and surface condition after extrusion, and high tensile strength and elongation. In contrast, the molded articles produced in Comparative Examples 1 to 10 were either not extruded and therefore could not be measured, or even if extruded, the molded articles had a rough appearance, exhibited stickiness and browning, and had low tensile strength and elongation.

[0071] In particular, in the case of the extruded molded products in Comparative Examples 1 and 7-9, they did not melt and therefore could not be extruded. In the case of the extruded molded product in Comparative Example 4, the browning phenomenon was very severe, and a molded product with a rough surface was produced. Furthermore, in the case of the extruded molded product in Comparative Example 5, the browning phenomenon was severe and the tensile strength was found to be poor. In the case of the extruded molded product in Comparative Example 10, the transparency was good, but the elongation rate was poor.

[0072] Therefore, the thermoplastic resin composition according to the present invention exhibits excellent moldability and improved mechanical properties such as tensile strength and elongation. Furthermore, because it contains cellulose derivatives and glycerin as active ingredients, it can be used in an environmentally friendly manner and is therefore useful in a wide range of fields.

[0073] Although the present invention has been described above with reference to limited embodiments and drawings, it goes without saying that the present invention is not limited thereto, and that various modifications and variations are possible within the equivalent scope of the technical concept of the present invention and the following claims by persons with ordinary skill in the art to which the present invention pertains.

Claims

1. A thermoplastic resin composition characterized by containing 65% to 80% by weight of hydroxyethylcellulose and 20% to 35% by weight of glycerin, wherein the viscosity of an aqueous solution dissolved in water at 2% by weight is measured at 20°C using a Brookfield viscometer to 4,000 cps to 250,000 cps.

2. The thermoplastic resin composition according to claim 1, further comprising one or more additives selected from the group consisting of antioxidants, lubricants, biodegradation accelerators, and strength reinforcing agents.

3. The thermoplastic resin composition according to claim 2, characterized in that the lubricant is one or more selected from the group consisting of sorbitol, magnesium stearate, calcium stearate, ethylene glycol, glycerol monostearate, and lecithin.

4. (a) A step of forming a mixture by adding 20% ​​to 35% by weight of glycerin to 65% to 80% by weight of hydroxyethylcellulose, which has a viscosity of 4,000 cps to 250,000 cps when an aqueous solution of 2% by weight dissolved in water is measured using a Burkfield viscometer at 20°C, (b) A method for producing a thermoplastic resin composition, comprising the step of kneading the mixture to make it plastic.

5. The method for producing a thermoplastic resin composition according to claim 4, characterized in that the kneading in step (b) is carried out at 50°C to 90°C at 300 rpm or more.

6. A molded article formed from the thermoplastic resin composition according to any one of claims 1 to 3.

7. The molded article according to claim 6, characterized in that the molded article has a tensile strength of 4.5 MPa to 6.5 MPa as measured in accordance with ASTM D638.

8. The molded article according to claim 6, characterized in that the molded article has an elongation of 20 mm to 45 mm as measured in accordance with ASTM D638.

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