KR100683941B1 - Preparation of novel polylactide/clay nanocomposite with improved shear thinning and toughness - Google Patents

Abstract

Provided is a method for preparing novel polylactide/clay nanocomposite, wherein the polylactide/clay nanocomposite exhibits a high shear thinning phenomenon and good toughness. The method for preparing novel polylactide/clay nanocomposite having improved shear thinning and toughness comprises the steps of: preparing modified clay by introducing a copolymer of lactide and caprolactone into clay having hydroxyl groups at the surface through a ring opening polymerization; and melt-kneading the modified clay, a plasticizer of aliphatic polyester, and high-molecular-weight polylactide to prepare novel polylactide/clay nanocomposite.

Description

Preparation of Novel Polylactide / Clay Nanocomposite with Improved Shear Thinning and Toughness

1 is a graph showing shear thinning characteristics at 210 ° C. of a polylactide / clay nanocomposite and a comparative example using clays developed in the present invention.

Figure 2 is a graph showing the toughness of the polylactide / clay nanocomposite and the comparative example using the clay developed in the present invention.

The present invention aims at the application of polylactide to biodegradable general purpose resins by enhancing shear thinning and toughness of polylactide. The present invention comprises the steps of preparing a modified clay by introducing a copolymer of lactide and caprolactone to the clay having a hydroxyl group on the surface through a ring-opening polymerization reaction, a plasticizer of the electrically modified clay and aliphatic polyester, and Melt-kneading high molecular weight polylactide to prepare a novel polylactide / clay nanocomposite.

A novel clay / polylactide nanocomposite using melt kneading a surface modified clay with a copolymer of lactide and caprolactone and a plasticizer and a high molecular weight linear polylactide, and a preparation thereof. Polylactide is a biodegradable, biocompatible aliphatic polyester that has been used primarily for medical purposes such as drug delivery media, tissue engineering supports, and sutures.

Recently, polylactide has been recognized as an alternative to general purpose plastics such as polyethylene, polypropylene, and polystyrene due to its biodegradability, good mechanical strength, and environmentally friendly materials. However, despite the above advantages, polylactide has significant limitations in practical applications due to the poor processability and brittleness of the material itself.

Poor processability of polylactide, for example, low shear thinning, is one of the biggest problems in application to general-purpose plastics, and there is a problem in that existing polymer processing equipment such as extruders and injection molding machines that are currently commercialized cannot be easily used. In order to solve such a problem, researches for modifying polylactide are being actively conducted, and most representative examples thereof include branched polylactide synthesis and polylactide / clay nanocomposite production. In the case of branched polylactide, the shear thinning characteristics can be improved, but other disadvantages of polylactide, such as gas permeability, low heat distortion temperature, and brittleness, cannot be solved.

Recent studies to improve the shear thinning properties, gas permeability and heat deflection temperature of polylactide are focused on the preparation of polylactide / clay nanocomposite materials. The method for preparing the polylactide / clay nanocomposites is divided into two main methods.

The first is a method using a polymerization method and the second is a method using a melt kneading method. When the polylactide / clay nanocomposites are prepared by the polymerization method, the polylactide ends are fixed to the surface of the clay, which may cause considerable shear thinning even when the clay content is relatively low, but heterogeneous. Due to the reaction conditions, the molecular weight of the polylactide bonded to the clay surface is relatively small, which may lead to a decrease in mechanical strength. In the case of the melt kneading method, the mechanical strength can be maintained because the polylactide is already synthesized, but the polylactide chain and the clay surface are physically only interacted with each other in order to exhibit considerable shear thinning phenomenon. High clay content is required.

Therefore, when the polymerization method and the melt kneading method are applied simultaneously under the optimum conditions, it is thought that the shear thinning phenomenon can be increased and the mechanical strength can be maintained with a relatively low clay content. In addition, polylactide has properties similar to those of polystyrene, which has brittleness such that the elongation is limited to within 10%. Accordingly, it is difficult to develop a film grade resin. In order to solve the brittleness of the polylactide, the polylactide is plasticized or copolymerized. In this case, since the viscosity of the polylactide is low in the entire shear range, the melt strength and the yield / tensile strength at room temperature are lowered. There is this.

Therefore, when the polylactide / clay nanocomposite is prepared by the polymerization method and the melt kneading method, if the molecular weight of the polymer that is chemically bonded to the clay surface is properly controlled, the polymer on the clay surface may be mixed with It is thought to be able to act as an internal thickener / plasticizer since it can entangle / untie chains. At this time, the polymer chemically bonded to the clay surface should have flexibility and compatibility with the polylactide as a substrate.

In this regard, in the case of nanocomposite using melt kneading of clay and high molecular weight polylactide copolymerized with lactide and caprolactone on the surface, shear thinning similar to polypropylene and elongation of 3% to 150% (Korean patent, application no. 10-2005-0090702). However, the toughness is still insufficient compared to non-degradable general purpose resins such as polyethylene and polypropylene.

Accordingly, the present invention includes a composition showing a shear thinning property and toughness suitable for general purpose resins and a method for producing the same according to the polymerization and melt kneading methods in the production of polylactide / clay nanocomposites.

The prior art related to the present invention relates to a polymer composition and a method for preparing the same, USP 6,472,460, and a polyacrylide / clay nanocomposite prepared by melt kneading and evaluation of shear thinning properties of the prepared nanocomposite Maiti, M. Okamoto, K. Yamada, Ueda, Vol. 35, No. 8, p. 3104, 2002). Preparation and characterization of clay / polylactide nanocomposites using polymerization method (Macromolecular Rapid Communication, M. A. Pail, M. Alexandre, P. Degee, C. Calberg, R. Jerome, P. Dubois, Vol. 24, p. 561, 2003). Preparation, Characterization and Characterization of Polylactide / Clay Nanocomposites Using Melt Kneading Method after Bonding (Journal of Applied Polymer Science, S. Lee, C.-H.Kim, J.-K. Park, in press, 2006). Therefore, they are characterized by the melt kneading and the plasticization of novel polylactide / clay nanocomposites prepared using clays and plasticizers chemically bonded to substrates of polylactide and lactide / caprolactone copolymers, and polylactide as a substrate. It is about toughness evaluation, and its technical structure differs from this invention.

The present invention provides a polylactate using a clay and a plasticizer whose surface is modified with a copolymer of a lactide and a caprolactone, and a high molecular weight polylactide so as to significantly improve the exclusive dissolution and toughness of the polylactide even in low content clay. It is an object of the present invention to provide a Tied / Clay nanocomposite composition and a manufacturing method.

The present invention comprises the steps of preparing a modified clay by introducing a copolymer of lactide and caprolactone through ring-opening polymerization reaction to a clay having a hydroxyl group on the surface;

A novel polylactide with improved shear thinning and toughness comprising melt kneading the modified clay and the aliphatic polyester, and a high molecular weight polylactide to prepare a novel polylactide / clay nanocomposite. A method for producing the clay nanocomposite is shown.

The catalyst used in the ring-opening polymerization is a tin, Al or rare earth-based organometallic catalyst, the catalyst content may be used 0.01% to 1.0% relative to the number of moles of the monomer added for the polymerization reaction.

The monomer introduced into the clay having a hydroxyl group on the surface through the ring-opening polymerization is a lactide-based cyclic monomer selected from one or more of L-lactide, D-lactide, DL-lactide or racemic lactide And a mixture of caprolactone series cyclic monomers selected from one or more of ε-caprolactone or γ-caprolactone.

The high molecular weight polylactide used in the melt kneading above may be a number average molecular weight of 50,000g / mole to 500,000g / mole and the ratio of L-lactide and D-lactide in the polylactide 0 to 1 .

In the above, the number average molecular weight of the copolymerized polymer of lactide and caprolactone chemically bonded to the clay surface may be one of 15,000 g / mole or more.

The inorganic content of the novel polylactide / clay nanocomposite may be 0.1% to 10% based on the weight of the polylactide substrate.

In the above content of the caprolactone cyclic monomer may be used that is 30wt% to 70wt% relative to the total monomer weight.

The amount of the plasticizer in the above may be used 0.1wt% to 50wt% relative to the weight of the substrate polylactide.

The plasticizer may be any one or more selected from low molecular weight lactic acid, glycerol, triacetin, or citrate.

The molecular weight of the plasticizer in the above may be used that is 100g / mole to 10,000g / mole.

The plasticizer may be used by selecting two or more compounds from a low molecular weight lactic acid-based, glycerol-based, triacetin-based, or citrate-based materials.

The ring-opening polymerization in the above is largely composed of the following two steps. First, in order to increase the reaction yield, the clay having a hydroxyl group on the surface is pretreated using the ring-opening polymerization catalyst. The pretreatment is to activate the hydroxyl group on the clay surface, so that the ring-opening copolymerization reaction of the lactide monomer and the caprolactone monomer proceeds only at the clay surface. Second, after adding the lactide monomer and the caprolactone monomer to the pretreated clay, the reaction system is heated to perform a clay surface modification reaction.

The clay and the plasticizer prepared by the above method are melt kneaded with polylactide having a number average molecular weight of 50,000 or more to finally prepare a novel polylactide / clay nanocomposite. In the plasticizer, a low molecular weight lactate, glycerol, triacetin, and citrate materials may be used.

Meanwhile, the present invention includes a novel polylactide / clay nanocomposite having improved shear thinning and toughness prepared by the aforementioned method.

Hereinafter, the present invention will be described in more detail with reference to Examples. These embodiments are only examples for describing the present invention, but the scope of the present invention is not limited thereto.

<Example 1>; Preparation of Clay with Surface Modified by Copolymer of L-Lactide and ε-Caprolactone

와 L-락티드 단량체 및 ε-카프로락톤을 tin(Ⅱ) octoate를 촉매로 하여 반응시킨다. 글로브 박스 내에서 수분이 제거된 240mL의 자일렌에 분산되어 있는 건조

8.64g에 0.6mmole의 tin(II) octoate를 첨가한 후 50℃에서 1일 동안 교반하였다. To modify the clay into a structure suitable for the present invention

And L-lactide monomer and ε-caprolactone are reacted with tin (II) octoate as a catalyst. Drying dispersed in 240 mL xylene removed with water in the glove box

0.6mmole tin (II) octoate was added to 8.64 g, and the mixture was stirred at 50 ° C. for 1 day.

43.2 g of L-lactide and 43.2 g of ε-caprolactone were added to the activated clay, and the reactor temperature was raised to 135 ° C., followed by a ring-opening polymerization reaction for 7 days. After completion of the reaction, the reaction mass is precipitated in excess of diethyl ether and the precipitate is filtered to remove unreacted L-lactide and ε-caprolactone.

The unreacted precipitate is dispersed in tetrahydrofuran, centrifuged at 4,000 rpm for 5 minutes, the supernatant is separated, and the precipitate is washed with tetrahydrofuran. After repeating the centrifugation and washing three times, the precipitate is dried in a vacuum oven for 60 days at 60 ℃ to remove residual solvent.

Purified compounds were characterized using Thermal Gravity Analyzer (TGA), Gel Permeation Chromatography (GPC), Differential Scanning Calorimetry (DSC), and Nuclear Magnetic Resonance (NMR). The synthesis conditions and characterization results of the modified clays are shown in Table 1-1 and Table 1-2.

Table 1-1. Synthesis Conditions of Modified Clay (Clay- g -P (CL- co -LL))

Synthesis condition

CL ^a LL ^b Reaction temperature Reaction time 8.62 g 43.2 g 43.2 g 135 ℃ 7 days

a: ε-caprolactone, b: L-lactide

Table 1-2. Characterization Results of Modified Clay (Clay- g -P (CL- co -LL))

Characterization result Mineral content Yield ^c Polymer bound to clay surface Mw [PDI] T _g , T _m CL / LL ratio Average chain length CL LL 9.3 wt% 97% 25,000 g / mole [1.3] 16 ℃, None 1 / 0.9 [mole%] 1.83 2.44

c: ratio of polymers chemically bonded to the clay surface among the polymerized polymers

Example 2 Measurement of Compatibility between Polymer (P (CL- co- LL)) Bonded to Clay Surface and Polylactide

In order to confirm the compatibility between P (CL- co- LL) and polylactide, the change of glass transition temperature and melting point according to the composition of P (CL- co- LL) / polylactide blend was investigated using DSC. And the results are shown in Table 2.

Table 2. Glass Transition Temperatures According to Composition of P (CL- co- LL) / Polylactide Blend

P (CL- co- LL) composition (wt%) Glass transition temperature [℃] Melting point [℃] 0 61 152 20 51 142 50 40 140 100 16 -

As shown in the Table 2, the blend has a single glass transition temperature and melting point are flexible P (CL- co -LL) P ( CL- co -LL when viewed as reducing the glass transition temperature and melt viscosity increase of the composition according to ) And polylactide are considered to be compatible in the entire composition range.

Example 3 Melt Kneading of Clay- g- P (CL- co- LL), Triacetin (Plasticizer) and High Molecular Weight Polylactide

Clay- g- P (CL- co- LL) prepared in Example 1 was 10 wt% of triacetin and high molecular weight polylactide, inorganic content 3wt%, plasticizer content 10wt%, mixer speed 40rpm, mixing time 15 Table 3 shows the results of melt kneading using a Brabender mixer under the conditions of minutes and a mixing temperature of 180 ° C.

<Example 4>

Melt using a Brabender mixer under the same conditions as in Example 3 except that Clay- g- P (CL- co- LL) was triwtine and 20 wt% of high molecular weight polylactide and 20 wt% of plasticizer. The result of kneading is shown in Table 3.

Table 3. Melt-kneading Conditions for Clay- g- P (CL- co- LL), Triacetin, and High Molecular Weight Polylactide

division Code Mineral content Plasticizer content Mixer speed Mixing time Mixing temperature Example 3 Clay- g- P (CL- co- LL) / PL ^a -10wt% 3wt% ^b 10wt% ^c 40 rpm 15 minutes 180 ℃ Example 4 Clay- g- P (CL- co- LL) / PL ^a -20wt% 3wt% ^b 20wt% ^c 40 rpm 15 minutes 180 ℃

a: high molecular weight pure polylactide [M _n : 85,000, PDI: 2.3, D-lactide: 6.6%]

b: Clay- g -P (CL- co -LL) content is 27.9wt%

c: wt% relative to substrate polylactide

<Example 5>; Plasticization Measurement of Clay- g -P (CL- co -LL) / PL

Clay- g -P (CL- co -LL) / to the PL measuring the plasticizer, and the plasticizer was added 10wt%, the plasticized Clay- g -P glass transition temperature of the (co CL- -LL) / PL It was examined using DSC and the results are shown in Table 4.

<Example 6>

20 wt% of a plasticizer was added, and the glass transition temperature was measured in the same manner as in Example 5, and the results are shown in Table 4.

Table 4. Glass Transition Temperatures of Plasticized Clay- g- P (CL- co- LL) / PL

Plasticizer content [wt%] Glass transition temperature [℃] Example 5 10 38 Example 6 20 24

As shown in Table 4, the plasticized clay- g -P (CL- co- LL) / PL represents a single glass transition temperature and the clay- g -P (CL It can be seen that plasticization of co -LL) / PL has sufficiently occurred.

Comparative Example 1 Melt Kneading of Clay- g- P (CL- co- LL) and High Molecular Weight Polylactide

Clay- g- P (CL- co- LL) prepared in Example 1 was melt kneaded using a high molecular weight polylactide and Brabender mixer, and its preparation conditions are shown in Table 5.

Table 5. Melt-kneading Conditions of Clay- g- P (CL- co- LL) and High Molecular Weight Polylactide

Code Mineral content Plasticizer content Mixer speed Mixing time Mixing temperature Comparative Example 1 Clay- g- P (CL- co- LL) / PL ^a -0wt% 3wt% ^b 0wt% 40 rpm 15 minutes 180 ℃

a: high molecular weight pure polylactide [M _n : 85,000, PDI: 2.3, D-lactide: 6.6%]

b: Clay- g -P (CL- co -LL) content is 27.9wt%

Example 7, 8 Shear Thinning Characteristics of Plasticized Clay- g- P (CL- co- LL) / PL

In order to measure the shear thinning characteristics of the nanocomposites prepared in Examples 3 and 4, the resin was compressed at 190 ° C. in a press to prepare disc shaped specimens of 1.5 cm in diameter and 0.5 cm in thickness. The prepared specimen was mounted on a 25 mm parallel plate with a thickness of 1 mm using a rotary viscometer (ARES, Rheometric Scientific).

When the temperature of the viscometer reached 210 ° C., the experiment was conducted under a constant tensile, dynamic shear condition of 10%. Experimental results of shear thinning of plasticized Clay- g- P (CL- co- LL) / PL are shown in FIG. 1. In the case of plasticized clay- g- P (CL- co- LL) / PL, the composite viscosity decreases with increasing plasticizer content, but the shear thinning is similar to that of polypropylene. It is believed that the polymers chemically bonded to the surface of the clay, but plasticized by, resulted in sufficient chain entanglement and loosening with the substrate polylactide in the low and high frequency bands, respectively.

Comparative Example 2 Shear Thinning Characteristics of Clay- g- P (CL- co- LL) / PL-0wt%

The resin was compressed at 190 ° C. in a press to measure the exclusive dissolution characteristics of Clay- g- P (CL- co- LL) / PL-0wt% prepared in Comparative Example 1. Was prepared. The prepared specimen was mounted on a 25 mm parallel plate with a thickness of 1 mm using a rotary viscometer (ARES, Rheometric Scientific). When the temperature of the viscometer reached 210 ° C., the experiment was conducted under a constant tensile, dynamic shear condition of 10%.

The shear thinning characteristic test results of Clay- g- P (CL- co- LL) / PL-0wt% are shown in FIG. 1. Clay- g -P (CL- co -LL) / PL-0wt% has had the complex viscosity is high as compared to plasticized Clay- g -P (CL- co -LL) / PL is the degree of shear thinning similar Able to know. This is thought to be the result of the polymers in which the unplasticized polymer chains in the nanocomposite are chemically bonded to the clay surface simultaneously with sufficient chain entanglement and loosening with the substrate polylactide in the low and high frequency bands, respectively.

Example 9,10 Toughness of Plasticized Clay- g- P (CL- co- LL) / PL

In order to measure the toughness of the nanocomposites prepared in Examples 3 and 4, a specimen was prepared according to ASTM D638-03, and then experiments were performed using INSTRON (Model-5583). The stress-strain curves of plasticized Clay- g- P (CL- co- LL) / PL are shown in FIG. 2.

The plasticized clay- g- P (CL- co- LL) / PL exhibited cold stretching behavior and rubbery behavior as the plasticizer content increased, and the conventional toughened polylock in yield / tensile strength It can be seen that the better than the ted. This is believed to be due to the introduction of modified clays.

Comparative Example 3 Toughness of Clay- g- P (CL- co- LL) / PL-0wt%

In order to measure the toughness of the nanocomposite prepared in Comparative Example 1, the test piece was prepared according to ASTM D638-03 and then tested using INSTRON (Model-5583). The stress-strain curve of Clay- g- P (CL- co- LL) / PL-0wt% is shown in FIG. 2.

Clay- g- P (CL- co- LL) / PL-0wt% is relatively low in molecular weight (M _n = 25,000 g / mole) and is sufficiently flexible and compatible with polylactide. Therefore, it is thought that the plasticity of brittle polylactide can be sufficiently plasticized to improve the elongation of polylactide to about 150%, but it is still insufficient to replace non-degradable resins such as polyethylene and polypropylene.

The present invention solves the problems of low shear thinning and toughness, which is a problem in general-purpose resination of biodegradable polymers. Thus, the novel polylactide / clay nanocomposites are characterized by Since the plasticization of the polymer chains occurs properly, it shows high shear thinning phenomenon and excellent toughness. Therefore, the present invention can increase the application to biodegradable general purpose resins.

Claims (12)

Preparing a modified clay by introducing a copolymer of lactide and caprolactone into a clay having a hydroxyl group on a surface thereof through a ring-opening polymerization reaction; Shear thinning and toughness improvement comprising the steps of melt kneading the modified clay and the aliphatic polyester, and the high molecular weight polylactide to produce a novel polylactide / clay nanocomposite. Method for preparing a polylactide / clay nanocomposite. 2. The shear thinning according to claim 1, wherein the catalyst used for ring-opening polymerization is a tin, Al, or rare earth-based organometallic catalyst, and the catalyst content is 0.01% to 1.0% relative to the number of moles of monomers added for the polymerization reaction. And a method for producing a novel polylactide / clay nanocomposite with improved toughness. The monomer used in the ring-opening polymerization is a lactide-based cyclic monomer selected from one or more of L-lactide, D-lactide, DL-lactide or racemic lactide and ε-caprolactone or A method for preparing a novel polylactide / clay nanocomposite having improved shear thinning and toughness, characterized by a mixture of caprolactone series cyclic monomers selected from one or more of γ-caprolactone. The method according to claim 1, wherein the high molecular weight polylactide used for melt kneading has a number average molecular weight of 50,000 g / mole to 500,000 g / mole and the ratio of L-lactide and D-lactide in the polylactide is 0 to 1. A method for producing a novel polylactide / clay nanocomposite having improved shear thinning and toughness. The novel polylactide / clay nanocomposite having improved shear thinning and toughness according to claim 1, wherein the number average molecular weight of the copolymer of lactide and caprolactone chemically bonded to the clay surface is 15,000 g / mole or more. Manufacturing method. The novel polylactide / clay nano of claim 1, wherein the inorganic content in the novel polylactide / clay nanocomposite is 0.1% to 10% by weight of the polylactide substrate. Method for preparing a composite. The method of claim 3, wherein the content of the caprolactone cyclic monomer is 30 wt% to 70 wt% based on the total monomer weight. The method of claim 1, wherein the content of the plasticizer is 0.1 wt% to 50 wt% based on the weight of the substrate polylactide. [Claim 2] The novel polylactide / clay nano having improved shear thinning and toughness according to claim 1, wherein the plasticizer is at least one selected from the group consisting of low molecular weight lactate, glycerol, triacetin, or citrate. Method for preparing a composite. 10. The method of claim 9, wherein the plasticizer has a molecular weight of 100 g / mole to 10,000 g / mole. 10. The novel polyimide of claim 9, wherein the plasticizer is selected from two or more compounds selected from low molecular weight lactic acid, glycerol, triacetin, or citrate materials. Method for preparing lactide / clay nanocomposites. A novel polylactide / clay nanocomposite with improved shear thinning and toughness prepared by the method of any one of claims 1-11.

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