KR102029207B1 - Pla composite and preparing method thereof - Google Patents

Abstract

The present invention relates to a PLA nanocomposite material and a method for manufacturing the same, PLA nanocomposite material having an improved physical properties, and does not require the surface hydrophobization pretreatment process, melt kneading, solution mixing process, etc. of cellulose, PLA having an improved physical properties It relates to a method for producing a nanocomposite material.

Description

PLA composite material and manufacturing method thereof {PLA COMPOSITE AND PREPARING METHOD THEREOF}

The present invention relates to a PLA composite material and a manufacturing method thereof.

As fossil raw materials are depleted and consumers demand for eco-friendly materials, efforts are being actively made to utilize biomass. Biomass has various types of bio-based polymers, and cellulose has attracted attention in terms of reproducibility. Cellulose is a polymerized glucose unit, and is an organic compound that is common in nature.

Cellulose consists of crystalline nanofibers on natural biomass (FIG. 1). In particular, cellulose nanofibers are known to have a mechanical strength of one strand ranging from tens to hundreds of GPa. However, it is a high mechanical strength and eco-friendly bio material. Nanofibers are difficult to extract in the form of nanofibers because they are strongly crystallized by hydrogen bonds.

In order to extract from the cellulose in the form of nanofibers, a top-down seam method in which nanofibers are separated from each other, that is, a method of finely slicing or slicing a bulk material is required. Treatment of cellulose in water with an oxidizing agent comprising sodium hypochlorite (NaClO) or sulfuric acid in the presence of an N-oxyl compound catalyst represented by (2,2,6,6-tetramethylpiperidin-1-yl) oxidanyl (TEMPO) After that, a method of applying a dispersing force is known.

 This method only modifies the surface of the nanofibers and does not break the nanofiber crystal structure. The hydroxy groups with strong hydrogen bonds are eliminated and negative charges are generated to generate repulsive force. Accordingly, the nanofibers can be dispersed in an aqueous solution. Alternatively, if sulfuric acid is added to cellulose at a certain concentration, the surface of the nanofibers can be formed with chitin, chitosan, and cellulose by forming sulfonic acid (R-SO3H) groups on the nanofiber surface. Can be dispersed in The fibrous cellulose material thus produced is called "nanocellulose". Representative examples of nanocellulose include cellulose nanocrystals (CNC) and cellulose nanofibers (CNF). The CNC has a length of 150-200 nm and a diameter of 5-20 nm. CNF has a length of several μm (1-5 μm) and a diameter of about 10-20 nm. And nanocellulose is acidic after the chemical treatment mentioned above. Immediately after the preparation, the acidic state treats alkali hydroxides (eg, NaOH) for neutralization and therefore contains small amounts of alkali cations such as sodium (Na +) and potassium (K +).

As described above, since one strand of the nanocellulose fiber is a high-strength crystalline material, when the polymer composite material is manufactured by mixing the nanocellulose, the insufficient mechanical and thermal properties of the matrix polymer may be reinforced.

Reinforcing materials when polymer composite materials are made using nano fibrillated cellulose, which can make cellulose into a relatively mild process without the nanofiberization process including peeling and sea island to make nanocellulose. Due to the low aspect ratio, high mechanical reinforcement effects cannot be expected.

Therefore, it is possible to make a material that exceeds the physical properties of the existing composite material, which must produce a polymer composite material using nanocellulose. The difficulty of fabricating polymer nanocomposites using nanocellulose is that cellulose is generally a hydrophilic component having a hydroxyl group (-OH), so that it is difficult to mix with a generally hydrophobic polymer and plastic material. Even when mixed, they easily aggregate and lose their function as nanomaterials.

The method of increasing the miscibility of the nanocellulose with the polymer composite material is to make the nanocellulose hydrophobic through a complex surface hydrophobization modification process. This process leads to cost and production time delays from an industrial point of view. Surface modification reduces the aspect ratio of the nanocellulose to reduce the mechanical reinforcing effect.

There are two main ways to mix hydrophobically modified nanocellulose with a polymer. The first is to mix the polymer melt and nanocellulose in a heated state, which is very incompatible with the nanocellulose due to the high viscosity of the polymer melt. In addition, nanocellulose is thermally decomposed because it is exposed to heat for a long time. The second is to mix the polymer and nanocellulose by solution using an organic solvent. At this time, the use of organic solvent can cause environmental pollution.

In the present invention, 1) without the step of hydrophobized surface modification of the nanocellulose 2) to produce a PLA nanocomposite containing the nanocellulose through the in-situ direct polymerization method without a heat mixing process or a solvent mixing process.

Korean Patent Publication No. 2011-0101376

An object of the present invention is to provide a PLA nanocomposite having improved physical properties.

The present invention does not require surface hydrophobization pretreatment of cellulose, melt kneading, solution mixing, and the like, and an object of the present invention is to provide a method for producing PLA nanocomposite having improved physical properties.

1. A PLA composite material comprising a matrix comprising polylactic acid chains and nanocellulose interspersed between the chains.

2. according to the above 1, which is prepared by polymerizing a lactic acid or a derivative thereof under a mixture of nanocellulose, PLA composite material.

3. In the above 1, wherein the matrix is prepared through a direct polymerization (direct polymerzation) that is directly polymer in the lactic acid without passing through the lactide intermediate, PLA composite material.

4. In the above 1, wherein the matrix further comprises a polymer chain containing a repeating unit represented by the following formula (3), PLA composite material:

[Formula 3]

Wherein n is an integer from 1 to 10.

5. according to the above 1, wherein the nano cellulose is 0.01 to 20% by weight of the total weight of the composite material, PLA composite material.

6. In the above 1, wherein the nanocellulose is cellulose nanocrystals, cellulose nanofibers or a mixture thereof, PLA composite material.

7. In the above 1, wherein the nano cellulose is 2 to 200 nm in diameter containing cellulose, PLA composite material.

8. according to the above 1, wherein the nanocellulose contains less than 3000ppm monovalent cation, PLA composite material.

9. A method for producing a PLA composite material, comprising directly condensing lactic acid or a derivative thereof under mixing of nanocellulose.

10. In the above 9, wherein the nanocellulose is contained in 0.01 to 20% by weight of the total weight of the mixture, the production method of PLA composite material.

11. In the above 9, wherein the polymerization of the monomer of the formula 4 at the time of the polymerization together, the production method of PLA composite material:

[Formula 4]

(Wherein X is F, Br, Cl or I, R is H, COOH, an alkyl group having 1 to 4 carbon atoms, n is an integer of 1 to 10).

12. Product manufactured by including the PLA composite material of any one of 1 to 8.

PLA composite material of the present invention has improved physical properties such as high glass charge temperature, high tensile strength, low thermal expansion coefficient.

The production method of the PLA composite material of the present invention does not require hydrophobization pretreatment of nanocellulose, melt kneading, solution mixing, etc., and also improved during manufacturing without undergoing the lactide intermediate production process necessarily performed in the general PLA polymerization method PLA nanocomposites having the physical properties can be prepared.

1 is a cellulose nanofiber constituting cellulose
Figure 2 schematically shows the PLA direct polymerization method and indirect polymerization method.
3 is an atomic force microscope (AFM) image of cellulose nanocrystals (CNC).
4 is an AFM image of cellulose nanofibers (CNF).
5 is a photograph in which cellulose nanocrystals and nanofibers are dispersed in 1,4-butanediol and succinic acid.
6 is a photograph of cellulose nanocrystalline and nanofibers dispersed in chloroform.
7 is a transmission electron microscope (TEM) photograph of a cross section of a PLA composite in which cellulose nanocrystals are dispersed.

Hereinafter, the present invention will be described in more detail.

PLA composite material of the present invention comprises a matrix comprising a polylactic acid chain and nanocellulose interspersed between the chain.

Polylactic acid is a polymer having a repeating structure represented by the following formula (1). This may be obtained, for example, by condensation polymerization of lactic acid or a derivative thereof.

[Formula 1]

.

.

The molecular weight of the polylactic acid according to the present invention is not particularly limited, and for example, the number average molecular weight may be 500 to 1,000,000.

If necessary, the matrix according to the present invention may further include a polymer chain comprising a repeating unit represented by the following formula (3).

[Formula 3]

Wherein n is an integer from 1 to 10.

The repeating unit represented by Formula 3 may be included in a chain separate from the polylactic acid chain or may be included in the polylactic acid chain.

Cellulose is composed of crystalline nanofibers having a diameter of several tens of nanometers on the biomass, and the strength of these nanofibers is 80 to 120 GPa, and high mechanical reinforcing effects can be expected when used as a composite material.

Cellulose is a polymer having a repeating unit represented by the following formula (2).

[Formula 2]

In Formula 2, n is 10 to 35,000.

The nanocellulose according to the invention penetrates into the polylactic acid matrix and is interspersed between the polylactic acid chains. As nanocellulose is interspersed between the polylactic acid chains, it is possible to bind the polylactic acid molecular chain to increase the glass transition temperature, increase the tensile strength, and decrease the thermal expansion coefficient.

The nanocellulose may be obtained by dissolving cellulose. The sea island may be performed according to a method known in the art, for example, sulfuric acid treatment, TEMPO oxidation, mechanical peeling, etc., but is not limited thereto.

Nanocellulose is a nanofiber composed of cellulose, for example, cellulose nanocrystals, cellulose nanofibers or a mixture thereof, but is not limited thereto.

In the case of cellulose nanocrystals, for example, the length may be 50 nm to 500 nm, specifically 100 nm to 300 nm, and the diameter may be 2 nm to 200 nm, specifically 5 nm to 20 nm, but is not limited thereto.

In the case of cellulose nanofibers, for example, the length may be 0.1 μm to 10 μm, specifically 0.5 μm to 7 μm, and the diameter may be 2 nm to 200 nm, specifically 5 nm to 20 nm, but is not limited thereto.

The nanocellulose may include monovalent cations such as sodium and potassium.

Monovalent cations can be included, for example, up to 3000 ppm in nanocellulose. If the content is more than 3000ppm the mechanical properties of the PLA composite material may be lowered. Specifically, the nanocellulose according to the present invention may include 2 ppm to 3000 ppm monovalent cation, but is not limited thereto.

The content ratio of polylactic acid and nanocellulose is not particularly limited, and for example, nanocellulose may be included in an amount of 0.01 to 20% by weight of the total weight of the PLA composite material, preferably 0.1 to 15% by weight, more preferably. It may be included in 3 to 10% by weight. If the content of the nanocellulose is less than 0.01% by weight, the effect of improving the physical properties due to the addition of the nanocellulose may be insignificant, and if it is more than 20% by weight, it may be hard but easily broken. Can be.

The method of implementation is not particularly limited so as to be interspersed between the polylactic acid chains of the nanocellulose. For example, in the preparation of the polylactic acid by direct polymerization of the lactic acid (or a derivative thereof), the nanocellulose may also be added together in- It can be implemented by situ polymerization.

In the case of in-situ polymerization by mixing nanocellulose together in the preparation of polylactic acid by direct polycondensation of lactic acid, nanocellulose penetrates into PLA matrix at the molecular level and binds PLA chain to increase glass transition temperature. The tensile strength may increase, and the coefficient of thermal expansion may decrease.

In FIG. 2 and the following Reaction Scheme 1, the direct polymerization method is illustrated. Figure 2 shows the general method of making lactic acid into a dimer called lactide and then polymerizing it to produce polylactic acid (indirect polymerization, lactide, a dehydration dimer of 2 molecules of lactic acid, and ring-opening polymerization). As described above, the direct polymerization method according to the present invention means a method of polymerizing polylactic acid directly by esterification and transesterification of lactic acid (direct condensation of lactic acid), which is illustrated at the top of FIG. 2. Direct condensation polymerization includes a melt polymerization method and a deshrinkment polymerization method occurring in a solvent, and the two methods can be used without limitation.

Specific conditions and the like are shown in Scheme 1, but this is only an example and is not limited to these conditions.

Scheme 1

The addition time of the nanocellulose in the present invention is preferably before the start of the polycondensation reaction, but may be added to the reaction system at any stage before the start of the esterification reaction or the transesterification reaction and during the reaction.

The glass transition temperature of the PLA composite material of the present invention may be, for example, 60 ℃ to 90 ℃, but is not limited thereto.

The tensile strength may be, for example, 40 MPa to 60 MPa, specifically 40 MPa to 55 MPa, but is not limited thereto.

The coefficient of thermal expansion may be, for example, the coefficient of expansion (CTE) measured between −60 ° C. and 100 ° C., ranging from 130 μm / m ° C. to 180 μm / m ° C., specifically 135 μm / m ° C. to 180 μm / m ° C. However, it is not limited thereto.

In addition, the present invention provides a method for producing a PLA composite material.

The method for producing a PLA composite material of the present invention includes the step of directly condensation lactic acid or derivatives thereof under the mixing of nanocellulose.

As described above, indirect polymerization is generally used as a method for producing polylactic acid, but the method of the present invention directly condensates lactic acid or a derivative thereof under mixing of nanocellulose.

In the mixture of lactic acid or derivatives thereof and nanocellulose, since the nanocellulose is mixed with the monomers, the polylactic acid matrix is formed with the nanocellulose interspersed between the chains when the polylactic acid chain is formed. Since lactide does not disperse nanocellulose as a lipophilic substance, it is not easy to scatter between chains by the general polymerization method through the lactide process. Accordingly, when manufacturing the composite material by the indirect polymerization method, the mechanical and physical properties are significantly lower than the PLA composite material produced by the direct polymerization method.

In addition, since the lactide is not formed, polymerization is possible in one step, and since hydrophilic lactide or a derivative thereof is directly polymerized in a mixed state with the nanocellulose, hydrophobic modification of the nanocellulose is unnecessary. This has the advantage of simplicity.

As the lactic acid, one or more of L-lactic acid and D-lactic acid may be used.

It is preferable that the optical purity of the lactic acid used as a monomer is 95% or more, It is more preferable that it is 98% or more, It is especially preferable that it is 99% or more. When lactic acid is L-lactic acid, it is preferable that content of D-lactic acid is 2.5% or less, It is more preferable that it is 1.0% or less, It is especially preferable that it is 0.5% or less. When lactic acid is D-lactic acid, it is preferable that content of L-lactic acid is 2.5% or less, It is more preferable that it is 1.0% or less, It is especially preferable that it is 0.5% or less.

When polylactic acid is poly-L-lactic acid, it is preferable that L-lactic acid component contains 70 mol% or more of the repeating units of a polymer, It is more preferable that 90 mol% or more is contained, 95 mol% or more contains It is more preferable to carry out, and it is especially preferable to contain 98 mol% or more.

When polylactic acid is poly-D-lactic acid, it is preferable that the D-lactic acid component contains 70 mol% or more of the repeating units of a polymer, It is more preferable that it contains 90 mol% or more, Contains 95 mol% or more It is more preferable that it is, and it is especially preferable to contain 98 mol% or more.

When the polylactic acid is a stereo complex-polylactic acid, a mixture or block copolymer or a multi-block copolymer or a graft-block copolymer, a gradient-block copolymer, or a mixture of poly-L-lactic acid and poly-D-lactic acid It is desirable to form a mixed form.

Lactic acid derivatives include, but are not limited to, for example, chlorinated acylation, anhydride, esterification, amidation, nitrilation derivatives, and the like.

In the process of the invention, additional monomers can be polymerized together during the polymerization.

Further monomers include, for example, polyhydric alcohols, polyhydric carboxylic acids, hydroxy carboxylic acids, compounds containing polyhydric alcohols and polyhydric carboxylic acid functionalities, polyhydric carbonates, lactones, lactams, mixtures thereof, and the like. . The carboxylic acids mentioned above can be replaced with aliphatic esters which can be synthesized through ester reaction of carboxylic acids with aliphatic alcohols.

Additional monomers may also illustrate monomers of the general formula (4).

[Formula 4]

(Wherein X is F, Br, Cl or I, R is H, COOH, an alkyl group having 1 to 4 carbon atoms, n is an integer of 1 to 10).

Additional monomers may be included in the range of, for example, 30% by weight or less of the total monomers.

Nanocellulose may be in the above range.

The content of nanocellulose in the mixture (lactide or derivatives thereof and nanocellulose) is not particularly limited, and is, for example, 0.01 to 20% by weight, preferably 0.1 to 15, more preferably 3 to 10% by weight of the total weight. May be included as a%.

Polymerization while removing water or alcohol from the mixture may form a PLA composite material interspersed with nanocellulose between the matrix and the chain including the polylactic acid chain.

The polymerization conditions are not particularly limited and may be performed, for example, at 100 ° C to 180 ° C heating conditions. Specifically, in the mixture, an organic sulfonate and tin compound, a titanium compound, a germanium compound, an antimony compound, an aluminum compound, a magnesium compound, a compound containing a sulfonic acid functional group, a compound containing a phosphoric acid functional group, and a Brx A polycondensation catalyst such as ted acid or a mixture thereof is added to a catalyst made by the addition of these components within the range of the addition amount which does not cause problems in the properties, processability, and product of the composite as described above, It can be polymerized by first heating while stirring within the temperature range, by heating and secondary heating in the temperature range.

The first heating may be specifically performed at 120 ° C to 180 ° C for 1 hour to 5 hours, but is not limited thereto.

The secondary heating may be specifically performed at 100 ° C. to 160 ° C. for 5 hours to 15 hours, but is not limited thereto.

The method for producing a PLA composite material of the present invention may further comprise the step of mixing the lactic acid or derivatives thereof with nanocellulose.

Nanocellulose can be mixed with lactic acid or a derivative thereof, for example in powder form.

In the mixing, stirring, homogenization, and sonication may be performed to disperse the nanocellulose.

Specific examples of the mixing conditions, but may be stirred at 10 to 100rpm under 100 ℃ to 200 ℃ heating conditions in a nitrogen atmosphere, but is not limited thereto.

When the nanocellulose is mixed with lactic acid or a derivative thereof, it can be dispersed with high stability. For example, nanocellulose precipitates may not occur when observed after 6 hours of mixing. Therefore, it does not require a surface hydrophobization modification process for improving the miscibility with the polymer, and does not require a process such as melt kneading or organic solvent solution.

In addition, the present invention provides a product prepared by including the PLA composite material.

PLA composite material of the present invention is excellent in mechanical and thermal properties can be variously applied to all products using a polymer resin.

Hereinafter, the present invention will be described in detail with reference to Examples.

Example

1. Measurement of the length of nanocellulose using atomic force microscopy (AFM)

It was purchased from the University of Maine, which produces and sells two types of nanocellulose. (http://umaine.edu/pdc/cellulose-nano-crystals/). CNC (Cellulose nanocrystal) products are 150-200 nm in length and 5-20 nm in diameter (Composites Part B: Engineering Volume 79, 15 September 2015, Pages 521529). CNF (cellulose nanofiber) products are several μm (1-5 μm) long and 10-20 nm in diameter (Progress in Organic Coatings 76.2 (2013): 477-481). The CNC and CNF received the product in powder sprayed form. CNF and CNF were each dispersed in water to 0.1%, applied to a silicon wafer, and dried. And the diameter was measured by Veeco Dimension 3100. As a result, it was confirmed that the nanocellulose having a diameter of several nanometers as the product information (Figs. 3 and 4).

2. Confirmation of Dispersibility of Lactic Acid (Lactic Acid) of Nanocellulose

The CNC and CNF were dispersed in lactic acid to 1% by weight and left for a week. Then it was confirmed whether two nanocellulose precipitated (Fig. 5). As can be seen in Figure 5, both the CNC and CNF-dispersed lactic acid dispersion was transparent and was dispersed without precipitation even after one week. However, the CNC and CNF were dispersed in 1% by weight of lactide and left for a week. Then it was confirmed whether two nanocellulose precipitated (Fig. 6). As can be seen in Figure 6 both the CNC and CNF dispersed lactide dispersion was precipitated. Therefore, it is not possible to produce CNC and CNF nanocomposites during polymerization via existing lactide.

The particle diameters of CNC and CNF of the lactic acid dispersion in which CNC and CNF were dispersed were measured by a particle size analyzer (Table 1). As can be seen from Table 1, it can be seen that CNC and CNF are dispersed at several tens of nanometers in two solvents.

Particle Size of CNC and CNF in CNC and CNF-Dispersed Lactic Acid Dispersions

Sample Particle size Lactic acid dispersed by 1% by weight of CNC 107 nm Lactic acid dispersed with 1% by weight of CNF 241 nm

3. Direct polymerization after dispersing nanocellulose in lactic acid (lactic acid)

The CNC and CNF powders were placed in 100 g of lactic acid and then dispersed for 10 minutes with a bath sonicator. Lactic acid dispersions in which CNC and CNF were dispersed were placed in a reactor. In order to dry the moisture, the mixture was heated to 120 ° C. in a nitrogen atmosphere and stirred at 50 rpm to obtain a lactic acid mixed dispersion containing CNC and CNF. Para-toluene sulfonic acid (P-Toluenesulfonic acid monohydrate) 1.5 g was added to the water-removed L-lactic acid, the reactor temperature was set to 140 ℃ after reaction under reduced pressure of 200 torr to obtain a pre- oligomer. After manufacturing 400um fine powder by using a high speed rotary mixer, dried in a freeze dryer for 24 hours and reacted at 120 ° C for 12 hours in a solid-phase reactor while maintaining a moisture content of 200ppm without contact with external air. To make it. All reactions were replaced with nitrogen to prevent internal oxidation and side reactions. The content of nanocellulose (CNC and CNF) was prepared from 0% to 35% in the total weight of the mixed dispersion, and the types of samples are summarized in Table 2.

The number average molecular weight (Mn) of PLA constituting the completed PLA nanocomposite was analyzed by gel permeation chromatography (GPC).

The number average molecular weight (Mn) of PLA constituting the complex with the pure PLA was polymerized to a similar level (Table 2). This allows a direct comparison in the evaluation of mechanical and physical properties.

PLA / nanocellulose composites made by in-situ polymerization

PLA nanocellulose content PLA number average molecular weight Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 285,041 CNC 0.05% 279,987 CNC One% 281,644 CNC 15% 236,943 CNF 0.05% 284,396 CNF One% 277,337 CNF 15% 290,911 CNF 35% 280,090

4. Measurement of glass transition temperature of PLA nanocellulose composite polymerized in Example 3

The glass transition temperature of the PLA nanocomposite was measured with a differential scanning calorimetry (DSC) Discovery DSC 2500 containing pure PLA and nanocellulose, namely CNC and CNF, prepared in Example 3. . Scanning from -60 ° C to 100 ° C. As the cellulose was added, it was confirmed that the glass transition temperature increased. It is believed that the nanocellulose has penetrated the PLA matrix at the molecular level, and the glass transition temperature is increased in proportion to the content of the two types of nanocellulose by binding the PLA molecular chain.

Glass transition temperature of PLA / nanocellulose composite produced by in-situ polymerization method (-means minus temperature)

PLA nanocellulose content Glass transition temperature (℃) Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 62 CNC 0.05% 66 CNC One% 67 CNC 15% 67 CNF 0.05% 65 CNF One% 66 CNF 15% 68 CNF 35% 66

5. Measurement of Tensile Strength of PLA Nanocellulose Composite Polymerized in Example 3

The tensile strength of the pure PLA and CNC, or the PLA composite material interspersed in the CNF matrix prepared in Example 3 was measured according to the ASTM D638 method by the universal testing macine (UTM) INSTRON 5582 UTM.

It can be seen that the tensile strength increased with increasing nanocellulose content (Table 4).

Tensile Strength of PLA / nanocellulose Composites Prepared by In-situ Polymerization

in-situ polymerized PLA nanocellulose content Tensile Strength (MPa) Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 39 CNC 0.05% 45 CNC One% 48 CNC 15% 50 CNF 0.05% 41 CNF One% 43 CNF 15% 48 CNF 35% 38

6. Measurement of coefficient of thermal expansion (CTE) of PLA nanocellulose composite polymerized in Example 3

The coefficient of thermal expansion of the pure PLA and PLA composite material made in Example 3 was measured according to the ASTM E831 method with a coefficient of thermal expansion (CTE) TA Instruments Model 2940. As a result, it was confirmed that pure PLA of 185 μm / m ° C. decreased up to about 40-50 with increasing nanocellulose content (Table 5).

Thermal Expansion Coefficient of PLA / nanocellulose Composites Prepared by In-situ Polymerization

in-situ polymerized PLA nanocellulose content CTE (㎛ / m ℃) Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 185 CNC 0.05% 177 CNC One% 151 CNC 15% 141 CNF 0.05% 182 CNF One% 174 CNF 15% 166 CNF 35% 134

7. Sodium Content of PLA Nanocellulose Composites Polymerized in Example 3

Sodium content of the pure PLA and PLA composite material prepared in Example 3 was measured using ICP-MS (inductively coupled plasma-mass spectroscopy). The sodium content of the PLA composite made in the present invention was found to have about 2-2500 ppm.

Sodium Content of PLA / nanocellulose Composites Prepared by In-situ Polymerization

in-situ polymerized PLA nanocellulose content Sodium content at total composite weight (ppm) Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 0 CNC 0.05% 39 CNC One% 317 CNC 15% 2398 CNF 0.05% 5 CNF One% 241 CNF 15% 1856 CNF 35% 2366

Example 8. Cross section of the PLA nanocellulose composite polymerized in Example 3 was observed by transmission electron microscope (TEM)

The cross section of the PLA composite prepared in Example 3 was observed using a transmission electron microscope (TEM). After microtoming the composite to obtain a sample that can observe the cross-section, it was stained with Uranyl acetate. In the electron micrograph of FIG. 7, it can be seen that nanocellulose having a diameter of about 5-20 nm is well dispersed in the matrix.

Comparative Example 1-1. Mixing Nanocellulose on a heated PLA Melt

Pure PLA synthesized in Example 3 was melt mixed with two kinds of nanocellulose using a HAAKE ™ MiniJet Pro Piston Injection Molding System. Nanocellulose powder dried at 200 ° C. in a nitrogen atmosphere was added and mixed for 10 minutes. To prepare a melt mixed PLA nano cellulose composite material of the type shown in Table 7.

Types of PLA / nanocellulose composites made with melt blending

PLA nanocellulose composite by melt mixing method Nano cellulose type Nano cellulose weight ratio Pure PLA 0% CNC 0.05% CNC One% CNC 15% CNF 0.05% CNF One% CNF 15%

Comparative Example 1-2. Evaluation of Physical Properties of PLA Composites Fabricated by Melt Mixing Method

The glass transition temperature, thermal expansion coefficient, and tensile strength of the melt mixed PLA nanocellulose composite material synthesized in Comparative Example 1 were measured in the same manner as in Example. In Example 4, the composite prepared by the in-situ method increased the glass transition temperature by 3-5 ° C., whereas the PLA nanocellulose composite material mixed in the melt phase increased only by about 1 ° C. (Table 8).

The composite fabricated by the in-situ method measured in Example 5 increased the tensile strength by 5 to 10 MPa, whereas the PLA nanocellulose composite material mixed in the melt phase increased only by 1 to 2 MPa. 9).

The composite prepared by the in-situ method measured in Example 6 has a CTE value of 40-50 μm / m ° C. or more, whereas the PLA nanocellulose composite material mixed in the melt phase is only about 5-10 μm / m ° C. It did not decrease (Table 10).

The improvement of mechanical and physical properties of the composite material produced by the melt mixture measured in the comparative example is significantly lower than that of the composite material produced by the in-situ polymerization method of Examples. This proves that the dispersibility of nanocellulose by the in-situ polymerization method is very excellent.

Glass Transition Temperature of PLA / nanocellulose Composite Made by Melt Mixing

Melt mixing method PLA nanocellulose content Glass transition temperature (℃) Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 62 CNC 0.05% 62 CNC One% 63 CNC 15% 63 CNF 0.05% 62 CNF One% 63 CNF 15% 63

Tensile Strength Values of PLA / nanocellulose Composites Prepared by Melt Mixing

Melt mixing method PLA nanocellulose content Tensile Strength (MPa) Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 39 CNC 0.05% 40 CNC One% 40 CNC 15% 40 CNF 0.05% 41 CNF One% 40 CNF 15% 41

CTE Values of PLA / nanocellulose Composites Prepared by Melt Blending

PLA nanocellulose composite by melt mixing method CTE (㎛ / m ℃) Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 185 CNC 0.05% 183 CNC One% 182 CNC 15% 180 CNF 0.05% 184 CNF One% 183 CNF 15% 179

Comparative Example 2-1. Fabrication of in-situ polymerized PLA / nanocellulose composite using lactide solution

The CNC and CNF powders were placed in 100 g lactide and dispersed for 10 minutes with a bath sonicator. The lactide dispersion in which CNC and CNF were dispersed was placed in a reactor. In order to dry the water, the mixture was heated to 120 ° C. in a nitrogen atmosphere and stirred at 50 rpm to obtain a lactide mixed dispersion containing CNC and CNF. Para-toluene sulfonic acid (P-Toluenesulfonic acid monohydrate) 1.5 g was added to the lactide from which water was removed, and then the reactor temperature was set at 140 ° C., and the reaction was carried out under a reduced pressure of 200 Torr to obtain a pre-oligomer. After manufacturing 400um fine powder by using a high speed rotary mixer, dried in a freeze dryer for 24 hours and reacted at 120 ° C for 12 hours in a solid-phase reactor while maintaining a moisture content of 200ppm without contact with external air. To make it. All reactions were replaced with nitrogen to prevent internal oxidation and side reactions. The content of nanocellulose (CNC and CNF) was prepared from 0% to 15% of the total weight of the mixed dispersion, and the types of samples are summarized in Table 11.

Types of PLA / nanocellulose complexes made by lactide polymerization

PLA nanocellulose composite through lactide polymerization Nano cellulose type Nano cellulose weight ratio Pure PLA 0% CNC 0.05% CNC One% CNC 15% CNF 0.05% CNF One% CNF 15%

Comparative Example 2-2. Evaluation of Physical Properties of PLA Composites Fabricated by Lactide Polymerization

The glass transition temperature, thermal expansion coefficient, and tensile strength of the PLA nanocellulose composite material prepared by the lactide polymerization method synthesized in Comparative Example 2 were measured in the same manner as in Example.

In Example 4, the composite prepared by the in-situ method increased the glass transition temperature by 3-5 ° C., whereas the PLA nanocellulose composite material mixed in the mixed phase increased only by about 1 ° C. (Table 12).

The composite fabricated by the in-situ method measured in Example 5 increased the tensile strength by about 5-10 MPa, whereas the PLA nanocellulose composite material mixed in solution phase increased or decreased only by about 0-1 MPa ( Table 13).

The composite prepared by the in-situ method measured in Example 6 has a CTE value of 40-50 μm / m ° C. or more, whereas the PLA nanocellulose composite material mixed in the solution phase is only about 5-10 μm / m ° C. It did not decrease (Table 14).

The improvement in mechanical and physical properties of the composite material produced by the solution mixture measured in Comparative Example 2 is significantly less than the composite material produced by the in-situ polymerization method of the embodiment. This proves that the dispersibility of nanocellulose by the in-situ polymerization method is very excellent.

Glass Transition Temperature of PLA / nanocellulose Composite Made by Lactide Polymerization

Lactide Polymerization PLA Nanocellulose Content Glass transition temperature (℃) Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 62 CNC 0.05% 62 CNC One% 62 CNC 15% 63 CNF 0.05% 62 CNF One% 62 CNF 15% 63

Tensile Strength Values of PLA / nanocellulose Composites Prepared by Chloroform Solution Mixing

Solution mixing method PLA nanocellulose content Tensile Strength (MPa) Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 39 CNC 0.05% 40 CNC One% 40 CNC 15% 40 CNF 0.05% 39 CNF One% 39 CNF 15% 40

CTE Values of PLA / nanocellulose Composites Prepared by Lactide Polymerization

PLA nanocellulose composite by solution mixing CTE (㎛ / m ℃) Nano cellulose type Nano cellulose weight ratio Pure PLA 0% 185 CNC 0.05% 183 CNC One% 180 CNC 15% 177 CNF 0.05% 184 CNF One% 183 CNF 15% 181

Comparative Example 3-1. In-situ polymer polymerization after dispersing microcellulose in lactic acid

Microcellulose having a micro size diameter was purchased from Sigma Aldrich (Microcrystalline Cellulose or Sigmacell Cellulose). According to Sigma Aldrich, it has a diameter of about 20 μm (http://www.sigmaaldrich.com/catalog/product/sigma/s3504?lang=en&region=US). The microcellulose was added to lactic acid and dispersed for 10 minutes with a bath sonicator. The lactic acid dispersion in which the microcellulose was dispersed was placed in a reactor. The polymerization was carried out in the same manner as in Example 3.

Comparative Example 3-2. Glass transition temperature measurement of PLA microcellulose composite

The glass transition temperature of the pure PLA and PLA composite material prepared in Comparative Example 3-1 was measured by TA differential scanning calorimetry (DSC) Discovery DSC 2500 (Table 15). Scanning from -60 ° C to 100 ° C. In Example 4, the nanocellulose composite prepared by the in-situ method increased the glass transition temperature up to 5 ° C. or more, whereas the PLA microcellulose composite material did not increase (Table 15).

Glass Transition Temperature of PLA / Microcellulose Composite Made by In-situ Polymerization

in-situ polymerized PLA microcellulose content Glass transition temperature (℃) Microcellulose Microcellulose Weight Ratio Pure PLA 0% 62 Microcellulose 0.05% 62 Microcellulose One% 62 Microcellulose 15% 62

Comparative Example 3-3. Tensile strength measurement of PLA microcellulose composite

Tensile strength of the pure PLA and PLA composite material prepared in Comparative Example 3-1 was measured according to the ASTM D638 method by the universal testing macine (UTM) INSTRON 5582 UTM. In-situ nanocellulose composites increased the tensile strength by about 5-10 MPa, whereas in-situ microcellulose composites increased by only about 0-1 MPa (Table 16).

Tensile Strength of PLA / Micro cellulose Composites Prepared by In-situ Polymerization

in-situ polymerized PLA microcellulose content Tensile Strength (MPa) Complex type Microcellulose Weight Ratio Pure PLA 0% 39 Microcellulose 0.05% 39 Microcellulose One% 40 Microcellulose 15% 40

Claims (10)

PLA composite comprising a matrix comprising a linear polylactic acid chain backbone and nanocellulose interspersed between the chains.
The composite material according to claim 1, which is prepared by polymerizing lactic acid or a derivative thereof under a mixture of nanocellulose.
The composite according to claim 1, wherein the matrix is prepared by direct condensation of lactic acid without passing through the lactide intermediate.
The composite material according to claim 1, wherein the matrix further comprises a polymer chain comprising a repeating unit represented by the following Formula 3:
[Formula 3]

Wherein n is an integer from 1 to 10.
The composite material according to claim 1, wherein the polylactic acid has a number average molecular weight of 236,943 or more.
The composite material according to claim 1, wherein the nanocellulose is contained in an amount of 0.01 to 20% by weight based on the total weight of the composite material.
The composite material of claim 1, wherein the nanocellulose is cellulose nanocrystals, cellulose nanofibers, or a mixture thereof.
The composite material according to claim 1, wherein the nanocellulose comprises cellulose having a diameter of 2 nm to 200 nm.
The composite material according to claim 1, wherein the nanocellulose contains 3000 ppm or less of monovalent cations.
Claims 1 to 9 of the product prepared by comprising the PLA composite material.

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