Patent Publication Number: US-2010113673-A1

Title: Polymer nanocomposites and fabrication methods thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 97142029, filed on Oct. 31, 2008, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a polymer nanocomposite and more particularly to an amorphous polyester nanocomposite. 
     2. Description of the Related Art 
     Polyethylene terephthalate (PET) is a thermoplastic polyester engineered plastic, polymerized by esterization of diacid and diol, which is widely used in the essential goods industry, electronics industry and so forth. However, the molecular structure of polyethylene terephthalate is regular, such that it stacks easily into crystal structures, thus negatively effecting transparency, impact resistance and dyeability of the polyethylene terephthalate. Therefore, the inventors of the present invention disclosed, in Taiwan Patent Application No. 95148406, an amorphous polyester. For the amorphous polyester, 1,3 and/or 1,4-cyclohexanedimethanol (1,3/1,4-CHDM) was added into a diol monomer to fabricate an amorphous copolyester with a wide amorphous range. Additionally, the inventors of the present invention also disclosed, in Taiwan Patent Application No. 97128612, a random amorphous copolyester. For the random amorphous copolyester, a more rigid or a softer diacid or diol group was added into the monomers to form an amorphous copolyester with a wide shrink temperature range. 
     Although the above copolyester materials can be widely used in the essential goods industry and electronics industry, gas barriering effects of the copolyester materials are not satisfactory. Thus, an amorphous polyester material is desired, which has better gas barriering, heat shrink and transparency effects. 
     U.S. Pat. No. 6,767,951 discloses a polyester body mixed with a hydrophilic block copolymer and an unmodified layered clay by melting to form a polyester nanocomposite. U.S. Pat. No. 6,486,253 discloses using at least more than two kinds of organic cationic salts to modify clay, and mixing the modified clay into polyester to form a polymer nanocomposite with gas barriering effect. U.S. Pat. No. 6,486,252 discloses using an expanding agent to pre-swell a modified layered clay, and mixes the clay into polyester by melting to form a polymer nanocomposite with gas barriering effect. U.S. publication No. US20060141183 discloses using a sepiolite-typed clay mixed with at least one kind of polyester precursor, wherein the polyester precursor is polymerized to form a polyester nanocomposite with gas barriering effect. 
     However, the above polymer nanocomposites are fabricated based on a crystal polyester body. Accordingly, while the materials have gas barriering effect, requirements for transparency, impact resistance and dyeability are not satisfactory. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a polymer nanocomposite. The polymer nanocomposite comprises an amorphous polyester body and a plurality of layered structural materials mixed with the amorphous polyester body, wherein the layered structural materials have one or more than one kind of aspect ratio. 
     The invention further provides a method for fabricating a polymer nanocomposite. First, an amorphous polyester and a plurality of modified layered structural materials are provided, wherein the plurality of modified layered structural materials have one or more than one kind of aspect ratio. Then, the modified layered structural materials are mixed uniformly, and mixed into the amorphous polyester to form the polymer nanocomposite by a melting process. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a schematic cross section of a polymer nanocomposite according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. The description is provided for illustrating the general principles of the invention and is not meant to be limiting. The scope of the invention is best determined by reference to the appended claims. 
     The invention utilizes one or more than one kind of layered structural material mixed into an amorphous polyester body to form a polymer nanocomposite. The layered structural materials may be modified layered clay, which have one or more than one kind of aspect ratio. The modified layered clay is dispersed in the amorphous polyester at a nanometer sized scale. The amorphous polyester is polymerized by a diacid monomer and a diol monomer, wherein the diol monomer may contain 1,3 and/or 1,4-cyclohexanedimethanol (1,3/1,4-CHDM). 
     Referring to  FIG. 1 , a schematic cross section of a polymer nanocomposite  100  according to one embodiment of the invention is shown. A plurality of layered structural materials  104  and  106  are dispersed in an amorphous polyester body  102 . The layered structural material  104  is a modified layered clay with a small aspect ratio, and the layered structural material  106  is a modified layered clay with a large aspect ratio. A polymer chain  102   a  of the amorphous polyester is interposed between the layered clays  104  and  106 , such that the polymer nanocomposite  100  is achieved with nanometer size scale dispersion. 
     The invention utilizes one or more than one kind of layered clay with different aspect ratios mixed into the amorphous polyester through nanometer size scale dispersion. The structure of the layered clay has gas barriering effect. Moreover, the layered clay with more than one kind of aspect ratios can produce a random arrangement to increase the paths for gas to pass therethrough. Therefore, the gas barriering of the polymer nanocomposites are enhanced. Additionally, the polymer nanocomposites of the invention further have heat shrink and transparency effects. 
     In the polymer nanocomposites according to the embodiments of the invention, the layered structural materials are about 0. 1 to 20 weight %. In one embodiment of the invention, the layered structural materials may be several modified clays with two kinds of aspect ratios. One modified clay is a quaternary ammonium compound such as dimethyl distearyl ammonium chloride (DDAC) modified layered clay, referred to as a polymer grade nonoclay (PGN) (product of American Nanocor Inc.), having an aspect ratio of about 300˜500. The other is an organic modified layered clay, referred to as Cloisite 15A (C15A) (product of American Southern Clay Products Inc.), having an aspect ratio of about 75˜100, wherein an organic modified agent of C15A is dimethyl dehydrogenated tallow quaternary ammonium. In one embodiment of the invention, the two kinds of aspect ratios of the layered structural materials have a ratio of about 2 or more than 2. 
     The amorphous polyester is polymerized by a diacid monomer and a diol monomer, and can be represented by formula (I): 
     
       
         
         
             
             
         
       
     
     In the formula (I), R′ is 1,3-cyclohexanedimethyl and 1,4-cyclohexanedimethyl, each of R 1  and R 2 , independently, is a bivalent aromatic or aliphatic group, and A, B, C, D, E and F are numbers of repeating units, wherein A is 0˜0.8, B is 0˜0.8, C is 0˜1, D is 0˜1, E is 0˜0.8, F is 0˜0.8, C+D&gt;0.2 and A+B+E+F&lt;0.8. The diacid monomer may be terephthalic acid (TPA) and an aromatic or an aliphatic diacid monomer. The diol monomer may be ethylene glycol (EG), 1,3 and/or 1,4-cyclohexanedimethanol and an aromatic or an aliphatic diol monomer. 
     In the formula (I), the aromatic diacid monomer is such as 5-tert-butylisophthalic acid (5tBIA), dimethyl-2,6-naphthalenedicaboxylate (NDC), 2,6-naphthoic acid, 2,7-naphthoic acid, 1,4-naphthoic acid, dimethyl-2,7-naphthalenedicaboxylate, dimethyl-2,3-naphthalenedicaboxylate or isoterephthalic acid (IPA). The aliphatic diacid monomer is such as succinic acid (SA), malonic acid or adipic acid. The diacid monomer based on 100 mole % can contain 0-100 mole % of the aromatic or the aliphatic diacid monomer. 
     In the formula (I), the aromatic diol monomer is such as 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane or 4,4-biphenol. The aliphatic diol monomer is such as propylene glycol, butylene glycol, polyethylene glycol (PEG) or polytetramethylene glycol (PTMO). The diol monomer based on 100 mole % can contain 0˜80 mole % of the aromatic or the aliphatic diol monomer. In the formula (I), by introducing a more rigid or a softer diacid or diol group, an amorphous polyester with a wide heat shrink temperature range of 40˜120° C. can be achieved. In one embodiment of the invention, the amorphous polyester of the formula (I) can have an intrinsic viscosity greater than 0.5 dL/g. 
     In one embodiment of the invention, a method for fabricating the polymer nanocomposite includes providing a modified clay with one or more than one kind of aspect ratio, uniformly mixing the modified clay by any ratio, and then mixing the modified clay into the amorphous polyester to form a mixture. Next, the mixture is melted and extruded through a twin screw extruder to form the polymer nanocomposite by a melting process. The temperature of the melting process is about 170-240° C., and the rotation rate of the twin screw extruder is about 200 to 800 rpm. 
     The composition, the fabrication method and related measurement results of the polymer materials for examples and comparative examples are described in detail as below. 
     EXAMPLE 1  
     166 grams of terephthalic acid (TPA) was taken as the diacid monomer. 62 grams of ethylene glycol (EG) and 43.2 grams of 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol were taken as the diol monomer, wherein 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol were 30 mole % in the diol monomer. After two steps of esterification and polycondensation, an amorphous polyester of polyethylene terephtalate glycol (PETG) was synthesized. 
     A dimethyl distearyl ammonium chloride (DDAC) modified layered clay of polymer grade nonoclay (PGN) (product of American Nanocor Inc.) and an organic modified layered clay of Cloisite 15A (C15A) (product of American Southern Clay Products Inc.) were uniformly mixed by a weight ratio of 1:1 to form a clay mixture. Then, 1 part by weight of the clay mixture was mixed into 100 parts by weight of the amorphous polyester (PETG) to form a mixture. The mixture was melted and extruded at a temperature of 170˜240° C. and a rotation rate of 500 rpm by a twin screw extruder to complete the polymer nanocomposite of Example 1. 
     EXAMPLES 2 AND 3  
     The amorphous polyester, the modified clay mixture and the fabrication method of the polymer nanocomposites of Examples 2 and 3 were the same as Example 1. The difference between Example 1 and Example 2 was that 3 parts by weight of the modified clay mixture was mixed into 100 parts by weight of the amorphous polyester (PETG) in Example 2. The difference between Example 1 and Example 3 was that 6 parts by weight of the modified clay mixture was mixed into 100 parts by weight of the amorphous polyester (PETG) in Example 3. 
     EXAMPLES 4 AND 5 
     The amorphous polyester, and the fabrication method of the polymer nanocomposites of Examples 4 and 5 were the same as Example 1. In the polymer nanocomposites of Examples 4 and 5, only one kind of the modified clay was used. The difference between Example 1 and Example 4 was that 6 parts by weight of the modified clay Cloisite 15A (C15A) was mixed into 100 parts by weight of the amorphous polyester (PETG) in Example 4. The difference between Example 1 and Example 5 was that 6 parts by weight of the modified clay polymer grade nonoclay (PGN) was mixed into 100 parts by weight of the amorphous polyester (PETG) in Example 5. 
     COMPARATIVE EXAMPLE 1  
     In Comparative Example 1, there was no clay added into the amorphous polyester. The amorphous polyester (PETG) of Comparative Example 1 was the same as Example 1. 
     Then, the polymer nanocomposites of Examples 1-5 and the polymer material of Comparative Example 1 were measured by a gas barriering test, a resistance to water test, a heat shrink test, a mechanical property test and a transparency test. An oxygen permeability (mm-c.c./m 2 -day), a water vapor permeability (mm-gm/m 2 -day), a 100° C. heat shrink percentage (%), a tensile strength (MPa), and a total light transmittance (%) were obtained through the above measurement and the measurement results are listed in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 The material characteristics of Examples 1~5 and Comparative 
               
               
                 Example 1 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 oxygen 
                 water vapor 
                 100° C. heat 
                   
                   
               
               
                   
                 permeability 
                 permeability 
                 shrink 
                   
                 total light 
               
               
                   
                 (mm-c.c./m 2 - 
                 (mm-gm/m 2 - 
                 percentage 
                 tensile 
                 transmittance 
               
               
                   
                 day) 
                 day) 
                 (%) 
                 strength (Mpa) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 1 
                 7.107 
                 1.187 
                 43 
                 42 
                 82.41 
               
               
                 Example 2 
                 6.908 
                 1.144 
                 39 
                 43.5 
                 80.32 
               
               
                 Example 3 
                 5.663 
                 1.068 
                 38 
                 46 
                 77.59 
               
               
                 Example 4 
                 7.302 
                 1.106 
                 — 
                 48.5 
                 73.82 
               
               
                 Example 5 
                 6.583 
                 0.951 
                 — 
                 46.4 
                 74.83 
               
               
                 Comparative 
                 10.167 
                 1.627 
                 — 
                 42.1 
                 86.04 
               
               
                 Example 1 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, when comparing the polymer nanocomposite of Example 3 with the amorphous polyester (PETG) of Comparative Example 1, the oxygen permeability of the polymer nanocomposite of the invention was reduced by about 44%, the water vapor permeability was reduced by about 34%, and the tensile strength was increased by about 8.5%. Moreover, the 100° C. heat shrink percentage of the polymer nanocomposites of Examples 1˜3 achieved 38˜43% and the total light transmittance thereof achieved 77.59˜82.41%. Accordingly, the polymer nanocomposites of the invention enhanced the effects for gas barrier and mechanical strength. Meanwhile, the polymer nanocomposites of the invention also had heat shrink and transparency effects. Therefore, the polymer nanocomposites of the invention can be used for heat shrink films, packaging materials and encapsulants, such as, for example, the containers, the shrink films and the packaging materials for drinks, foods or cosmetics, the encapsulants for electronic products such as light emitting diode (LED), and the base materials for various products. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.