Aliphatic-aromatic copolyesters

Abstract: This invention relates to random aliphatic-aromatic copolyesters, as well as fibers, molded objects, and films prepared therefrom.

Description: Field of Invention This application is a divisional application of EP-A-0 559 785 (92 901 494.2). This invention concerns random aliphatic-aromatic copolyesters which are useful as molded or extruded plastic objects, fibers, or films. Moreover, various additives can be added to the random aliphatic-aromatic copolyesters to enhance properties such as water vapor transmission rates or biodegradability. Background of the Invention Polyhydroxyalkanoates (PHA), such as polyhydroxybutyrate (PHB), polycaprolactone (PCL), or copolymers of polyhydroxybutyrate and polyhydroxyvalerate (PHBV), have been known for at least twenty years. With the exception of polycaprolactone, they are generally prepared biologically and have been reported to be biodegradable (M. Kunioka et al., Appl. Microbiol. Biotechnol. , 30, 569 (1989)). Polyesters prepared from aliphatic diacids or the corresponding carboxylic ester of lower alcohols and diols have also been reported to be biodegradable. For example, Fields and Rodriguez ("Proceedings of the Third International Biodegradation Symposium", J.M. Sharpley and A.M. Kaplan, Eds., Applied Science, Barking, England, 1976, p. 775) prepared polyesters from C2-C12 diacids coupled with C4-C12 diols and found that many were biodegradable. Aliphatic polyesters have been used in very few applications mainly because of their low melting points and low glass transition temperatures (generally less than 65°C and -30°C, respectively). At room temperature, the physical form of many of the aliphatic polyesters is as a thick, viscous liquid. Therefore, aliphatic polyesters are not expected to be generally useful. On the other hand, aromatic polyesters, such as poly(ethylene terephthalate), poly (cyclohexanedimethanol terephthalate), and poly(ethylene terephthalate-co-isophthalate), have proven to be very useful materials. Aromatic polyesters, however, are generally very resistant to biodegradation (J. E. Potts in "Kirk-Othmer Encyclopedia of Chemical Technology", Suppl. Vol, Wiley-Interscience, New York, 1984, pp. 626-668). Block copolyesters containing both aliphatic and aromatic structures have been prepared and have been shown to be biodegradable. Examples of aliphatic-aromatic block copolyester-ethers include the work of Reed and Gilding ( Polymer , 22, 499 (1981)) using poly(ethylene terephthalate)/ poly(ethylene oxide) where these block copolymers were studied and found to be biodegradable in vitro. Tokiwa and Suzuki have investigated block copolyesters such as those derived from poly(caprolactone) and poly(butylene terephthalate) and found them to be degraded by a lipase ( J. Appl. Polym. Sci. , 26, 441-448 (1981)). Presumably, the biodegradation is dependent upon the aliphatic blocks of the copolyesters; the blocks consisting of aromatic polyester are still resistant to biodegradation. Random aliphatic-aromatic copolyesters have not been investigated in this regard. There have been reports of the preparation of a biodegradable barrier film for use in disposable articles. Comerford et al. (U.S. Patent 3,952,347) have disclosed that finely divided biodegradable materials such as cellulose, starch, carbohydrates, and natural gums may be dispersed in a matrix of nonbiodegradable film forming materials which are resistant to solubility in water. Wielicki (U.S. Patent 3,602,225) teaches the use of barrier films made of plasticized regenerated cellulose films. Comerford (U.S. Patent 3,683,917) teaches the use of a cellulosic material coated with a water repellent material. Aliphatic-aromatic copolyesters comprising repeat units such as adipic acid, terephthalic acid and 1,4-butanediol are known (US-A-4,419,507). However, US-A-4,419,507 places emphasis on four component copolyesters whereas the present invention in principle concerns a three component copolyester. There is only one example in this reference with a three component copolyester, however, comprising glutaric acid. Copolyesters comprising as an essential component glutaric acid are not claimed in the present patent. There exists in the market place the need for thermoplastics which are useful in molding, fiber, and film applications. For these applications, it is desirable that the thermoplastic blend be processable at a low melt temperature and have a high glass transition temperature. These thermoplastics should not contain volatile or extractable plasticizers. Moreover, there is a need in the marketplace for a biodegradable material for use in disposable articles such as diapers, and razors. As an example, unlike films prepared from polymers such as PHB, the material should be amenable to both solvent casting and melt extrusion. In melt extruding this material, coextrusion with other thermoplastics should not be a requirement. The barrier properties of this new biodegradable material should be adequate so that coating with a water insoluble polymer is not required. The new material should disperse completely in the environment and not require coating with a water soluble polymer. The mechanical properties of the material should be such that films or low modulus but of high tensile strength can be prepared. Summary of the Invention The present invention provides an essentially linear, random, semicrystalline, biodegradable aliphatic-aromatic copolyester which has an inherent viscosity of about 0.5 to 1.8 deciliters/gram as measured at a temperature of 25°C for a 0.5 g sample in 100 mL of a 60/40 parts by weight solution of phenol/tetrachloroethane wherein the aliphatic-aromatic copolyester is comprised of repeat units of the following structures: wherein R 11 and R 12 are derived from 100 mole % 1,4-butanediol and wherein the diol components of the copolyester are substantially derived from glycols other than diethylene glycol; R 13 is derived from adipic acid wherein the mole % of R 13 is from 40 - 60 % of the dicarboxylic acid components; and R 14 is a 1,4-disubstituted. C 6 -aryl wherein the mole % of R 14 is from 60-40% of the dicarboxylic acid components; wherein a polyester obtained by a process wherein before or during the first condensation stage 0.005-0.1 molar percent, based on the total acid component, of a C 6-10 -aryl or C 7-20 -alkaryl ester of phosphorous acid or of phosphoric acid is added to the reaction mixture; and, after termination of the second condensation stage, adding 0.01-0.2 molar percent, based on the total acid component, of hypophosphorous acid, is disclaimed (cf. US-A-4,328,059). Further embodiments are set forth in the claims. Of course, many of the AAPEs of this invention which do not require blending are also useful in film applications. While these AAPE do not have as high as a melting point as poly(ethylene terephthalate), the AAPE have higher melting points that are generally observed with aliphatic polyesters and are therefore useful in many applications, particularly those requiring biodegradability. These copolyesters have been shown to be degradable even though they are semicrystalline and contain substantial amounts of aromatic groups. These AAPEs are also particularly useful in molded parts, extruded objects, fibers, non-wovens, and foamed objects which benefit from being biodegradable. Films and fibers made from these copolyesters can be oriented. Orientation in many of these copolymers is accompanied by improved physical properties and a change from being opaque to being clear. AAPE films can be oriented uniaxially or biaxially and can be oriented in a blown film operation. The AAPEs of this invention are useful in packaging applications where thin films are desirable. Many of the AAPEs of this invention are particularly useful as thin barrier films where they must function as a barrier and/or be biodegradable. For example, these AAPEs are useful as protective barrier films and may be used in disposable absorbent articles such as infant diapers, incontinence briefs, sanitary napkins, tampons, bed liners, bedpan liners, bandages, and the like. It is preferred that the films of the invention have a tangent modulus of 1723.7 to 6,895 MPa (2.5 x 10 5 psi to 0.01 x 10 5 psi), a tensile strength of at least about 3447,4 kPa (0.5 x 10 3 psi), an average tear force of at least about 275.8 g/mm (7.0 g/mil), and an elongation at break of at least about 5%. Also preferred is wherein said films have a thickness of 0.00254 mm (0.1 mil) to 0.503 mm (20 mil) and a water vapor transmission rate less than about 500 g mil/m 2 -24 hours. The AAPEs of this invention can also be used in the other parts of disposable diapers. In addition to being used as a protective barrier film, these AAPEs can be used as tabs, nonwovens, fibers, tape, and other parts needed in the construction of a diaper. We have found that films prepared from these AAPEs have desirable moisture barrier properties. With the blends, the specific rates can be modified by modification of the blend composition. The water vapor transmission rates can also be controlled by the amount of aromatic dicarboxylic acid monomer present in the aliphatic-aromatic copolyester components . The AAPEs of this invention are also useful as molded plastic parts or as solid, foamed plastic objects. Examples of such parts include eyeglass frames, toothbrush handles, toys, automotive trim, tool handles, camera parts, razor parts, ink pen barrels, disposable syringes, bottles, and the like. The plastic parts, especially those made by a foamed method which gives the plastic part increased surface area, of this invention are particularly useful in applications were it is desired that the plastic part be environmentally non-persistent. Injection molding bars made from the AAPEs of the invention typically have a flexural modulus of 344740 kPa to 68948 kPa (5.0 .x 10 5 psi to 0.1 x 10 5 psi), a flexural strength of 89632.4 kPa to 689.48 kPa (13 x 10 3 psi to 0.1 x 10 3 psi), and a notched Izod (23°C) of 1.0 to 25 ft-lb/in. It is preferred that the molding bars have a flexural modulus of 2620024 kPa to 1034213 kPa (3.8 x 10 5 psi to 1.5 x 10 5 psi), a flexural strength of 78600.72 kPa to 27579.2 kPa (11.4 x 10 3 psi to 4 x 10 3 psi), and a notched Izod (23°C) of 2 to 15 ft-lb/in. The AAPE's of this invention are also useful as fibers. Examples of fiber applications include cigarette filters, diaper topsheet, sanitary napkins, fishing line, fishing nets, fiber for producing surgical clothing, hygiene articles, absorbent fibers, and fibers for conveying liquids. We have found that, in addition to being spun from an appropriate solvent, the blends and/or AAPE of this invention can be melt-spun to produce fibers with excellent strength. The fibers can be oriented by drawing the fiber after spinning or by orientation during the spinning (cabinet orientation). Fibers produced from the blends and/or AAPEs have excellent shape retention even for fibers with complex cross-sectional shapes. We have also found that the fibers can be readily crimped. Fiber produced from the blends and/or AAPEs typically have a denier/filament (DPF) of 33.3-0.1 dtex (30-0.1). The preferred denier is 11.1-0.11 dtex (10-1.5 DPF). For fluid management, the fiber can contain hydrophobic agents or, optionally, can be coated with hydrophobic agents. The preferred AAPEs of this invention and products made therefrom have melting points between 75°C and 160°C. The more preferred range is between 80°C and 140°C. The fibers and films prepared from the AAPE's of the present invention are useful in applications where protective barrier films are desirable. For example, they may be used in absorbent articles such as infant diapers, incontinence briefs (adult diapers), sanitary napkins, tampons, bed liners, bedpans, and bandages. The biodegradable films, fibers, and AAPE 's of the invention are particularly useful in disposable articles because of environmental considerations. The films of the invention can also be used to make non-absorbent articles such as packaging materials (for example, foam sheets for packaging), food bags, trash bags, agricultural compost sheets, film base for tape and photographic film, as well as solid plastic articles such as syringes and camera cases. Biodegradable materials, such as the preferred barrier films of this invention, are materials that are comprised of components which, by microbial catalyzed degradation, are reduced in film or fiber strength by reduction in polymer size to monomers or short chains which are then assimilated by the microbes. In an aerobic environment, these monomers or short chains are ultimately oxidized to CO 2 , H 2 O, and new cell biomass. In an anaerobic environment the monomers or short chains are ultimately oxidized to CO 2 , H 2 , acetate, methane, and cell biomass. Successful biodegradation requires that direct physical contact must be established between the biodegradable material and the active microbial population or the enzymes produced by the active microbial population. An active microbial population useful for degrading the films and blends of the invention can generally be obtained from any municipal or industrial wastewater treatment facility in which the influents (waste stream) are high in cellulose materials. Moreover, successful biodegradation requires that certain minimal physical and chemical requirements be met such as suitable pH, temperature, oxygen concentration, proper nutrients, and moisture level. We have found that certain cellulose esters are biodegradable in conventional wastewater treatment facilities and in an in vitro enrichment system and hence are particularly useful in the preparation of blends to be used for barrier films and fibers in disposable articles. We have also found that many of the AAPEs degrade in a composting environment and hence are useful in the preparation of materials to be used as environmentally non-persistent materials. Examples illustrating AAPEs may be inferred from the experimental part of the parent patent application EP-A-0 559 785.

Claims: An essentially linear, random, semicrystalline, aliphatic-aromatic copolyester which has an inherent viscosity of 0.5 to 1.8 deciliters/gram as measured at a temperature of 25°C for a 0.5 g sample in 100 mL of a 60/40 parts by weight solution of phenol/tetrachloroethane wherein the aliphatic-aromatic copolyester is comprised of repeat units of the following structures: wherein R 11 and R 12 are derived from 100 mole % 1,4-butanediol and wherein the diol components of the copolyester are substantially derived from glycols other than diethylene glycol; R 13 is derived from adipic acid wherein the mole % of R 13 is from 40-60% of the dicarboxylic acid components; and R 14 is a 1,4-disubstituted C 6 -aryl wherein the mole % of R 14 is from 60-40% of the dicarboxylic acid components; wherein a polyester obtained by a process wherein before or during the first condensation stage 0.005-0.1 molar percent, based on the total acid component, of a C 6-10 -aryl or C 7-20 -alkaryl ester of phosphorous acid or of phosphoric acid is added to the reaction mixture; and, after termination of the second condensation stage, adding 0.01-0.2 molar percent, based on the total acid component, of hypophosphorous acid is disclaimed. An essentially linear, random, semicrystalline aliphatic-aromatic copolyester which has an inherent viscosity of 0.5 to 1.8 deciliters/gram as measured at a temperature of 25°C for a 0.5 g sample in 100 mL of a 60/40 parts by weight solution of phenol/tetrachloroethane wherein the aliphatic-aromatic copolyester is poly(tetramethylene adipate-co-terephthalate) or poly(hexamethylene adipate-co-terephthalate), wherein the moles of terephthalate is 40 - 60%. The aliphatic-aromatic copolyester of Claim 2 wherein the aliphatic-aromatic copolyester is poly(tetramethylene adipate-co-terephthalate) copolyester wherein the mole % of terephthalate is 40-60%. The aliphatic-aromatic copolyester of Claim 2 wherein the aliphatic-aromatic copolyester is poly(hexamethylene adipate-co-terephthalate) copolyester wherein the mole % of terephthalate is 40-60%. The aliphatic-aromatic copolyester on any one of the preceding claims wherein the copolyester has a melting point of 75-160°C. Shaped article formed from the aliphatic-aromatic copolyester of anyone of claims 1 to 5. Shaped article of Claim 6 wherein said shaped article is selected from the group consisting of films, fibers or plastic objects. Shaped article of Claim 7 wherein said shaped article is a film. Shaped article of Claim 8 said film having a tangent modulus of 1723.7 MPa (2,5 x 10 5 psi) to 6,895 Mpa (0.01 x 10 5 psi), a tensile strength of at least 3441.4 kPa (0.5 x 10 3 psi), an average tear force of at least 275.8 g/mm (7 g/mil), and an elongation at break of at least 5%. Shaped article of Claim 8 said film having a thickness of 0.00254 mm (0.1 mil) to 0.508 mm (20 mil) and a water vapor transmission rate less than 12.7 g mm/m 2 -24 hours (500 g mil/m 2 -24 hours). The article of Claim 8 wherein said film is prepared by solvent casting, melt extrusion, or by a blown film process. The shaped article of Claim 8 wherein said film is uniaxially oriented. The shaped article of Claim 8 wherein said film is biaxially oriented. The shaped article of Claim 8 wherein said film is a protective barrier film. A blend comprising: (A) 50% to 99% of an aliphatic-aromatic copolyester according to anyone of claims 1 to 5, and (B) 1% to 50% of a biodegradable additive, said percentages being based on the weight of component(A) plus component (B). The blend of claim 15, wherein component (B) is starch.

Inventors: BARLOW FRED DEWEY JR, BUCHANAN CHARLES MICHAEL, DEATON BETTY J, GARDNER ROBERT MARSHALL, GEDON STEVEN CARL, WHITE ALAN WAYNE, WOOD MATTHEW DAVIE, BARLOW, FRED DEWEY, JR., BUCHANAN, CHARLES MICHAEL, DEATON, BETTY J., GARDNER, ROBERT MARSHALL, GEDON, STEVEN CARL, WHITE, ALAN WAYNE, WOOD, MATTHEW DAVIE, Buchanan, Charles Michael, c/o Eastman Chem. Co.
Applicants: EASTMAN CHEM CO, EASTMAN CHEMICAL COMPANY
Application year: 1991
Main classification: C08G63
IPC codes: C08L67, C08L1, A61L15, C08G63, C08L3