GB2076832A - Blends of polyethylene terephtalate based polyesters and styrene- maleic anhydride copolymers - Google Patents

Abstract

Thermoplastic blends comprising polyester containing at least 85 mole percent polyethylene terephthalate and styrene-maleic anhydride copolymer exhibit improved moldability and improved adhesive properties to a variety of substrates.

Description

SPECIFICATION Blends of polyethylene terephthalate based polyesters and styrene-maleic anhydride copolymers Background of the invention .High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described inter-alia in Whinfield et al, U.S. Patent No.

2,465,319 and in Pengilly, U.S. Patent No. 3,047,539. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.

The most commonly employed polyester prepared by those teachings is polyethylene terephthalate (PET).

This polymer's success in fiber and film applications has been due in part to the considerable improvement in properties obtained by stretching or extending the films and fibers whereby the polymer is obtained in an oriented, crystallized form of advantageous morphology. However, in spite of the excellent mechanical properties, resistance to chemical attack, ease of shaping, ready availability and attractive price of these polyesters, they have been used only to a very minor extent in the formation of three dimensional articles by various molding techniques.

The limited acceptance of polyethylene terephthalate as a molding resin may be traced primarily to the low rate and non-uniformity of crystallization which it inherently exhibits thereby causing sticking to the molds, to its tendency to form a molded shaped article having non-uniform surface characteristics, and to its tendency to undergo extensive shrinkage in the mold leading to distorted shaped articles. Because of the low rate of crystallization, an elevated molding temperature above the second order transition point (e.g. about 75"C) over an extended period of time must be employed to achieve a sufficient degree of internal crystallization. Without the development of the proper crystalline structure, the molded article tends to be limp and rubbery.The required used of elevated mold temperatures for extended periods, however, causes rapid and uneven shrinkage within the mold. The shape of the resulting product is therefore often distorted and different from the shape of the mold. Dimensional stability must therefore be sacrificed for control of proper crystalline development.

Attempts to overcome the disadvantages of polyethylene terephthalate have focused primariiy on controlling the crystal structure, e.g., by using two step molding cycles or by adding nucleating agents and molecular weight control. Thus, the properties of injection molded polyethylene terephthalate have been modified by the addition of polyolefins as illustrated by U.S. Patent Nos. 3,361,848; 3,504;080; and 3,769,260.

None of the polyolefins, however, include styrene-maleic anhydride copolymers. The utilization of nucleating agents has not, however, been widely adopted because they are effective only in a narrow temperature processing range and lead to non-uniformity in the resulting articles. While the incorporation of reinforcing fibers, such as glass fibers, will improve the level of physical properties obtained in the resulting molded articles (see for example U.S. Patent No. 3,368,995), they do not by themselves alleviate the non-uniform performance referred to above.

It also has been proposed, such as discussed in U.S. Patent No. 3,629,366, to form a polyethylene terephthalate molding composition which consists of at least two polyethylene terephthalates having differing viscosities.

Some polyalkylene terephthalates, other than polyethylene terephthalate, prepared from higher carbon number glycols such as polybutylene terephthalate, have been more successfully utilized as molding resins in the past because of their inherent ability to undergo crystallization at a more rapid rate than polyethylene terephthalate, leading to greater ease of moldability over a broad range of molding conditions.

Such polyesters have also been modified with additives such as styrene-maleic anhydride copolymers to improve mechanical strength properties of injection molded articles as illustrated by U.S. Patent No.

3,644,574. However, this patent discloses that the improvements sought to be obtained by the addition of the contemplated additives to polybutylene terephthalate are not obtained when the polyester is polyethylene terephthalate.

Polyesters such as polybutylene terephthalate have tended to be considerably more expensive than polyethylene terephthalate, however, which has limited their acceptance as molding resins to some degree.

In addition, polybutylene terephthalate has somewhat lower mechanical properties than polyethylene terephthalate in a molded article along with a lower heat distortion temperature.

Styrene-maleic an hydride copolymers have also been used as additives for polycarbonate resins and unsaturated polyesters as illustrated by U.S. Patent Nos. 3,862,988 and 4,038,341 respectively.

Separate and distinct from the molding properties of polyethylene are its surface energy characteristics.

Polyethylene terephthalate polyesters exhibit very low adhesive strength, when in the configuration, for example of fibers of films, on various substrates such as aluminum, copper, glass, steel, rubber, paper, good, chrome, organic polymers, mica, asbestos and the like.

The poor adhesion of polyethylene terephthalate is believed to be due in part to its surface energy characteristics. For purposes of analysis the surface energy characteristics of a solid polymer fiber or film can be considered to be the sum of separate dispersion (i.e., non-polar) and polar (Keesom) contributions.

The polar component or contribution includes various dipole interactions and hydrogen bonding, which for simplicity, are combined into a single term. The contribution of the dispersion component to the surface energy of polyethylene terephthalate is about 93% while the polar component contributes only about 7%. It is well known that a polymer wherein the polar contribution to the surface energy thereof is low in relation to the dispersion component will exhibit poor adhesive properties. Consequently, if polyethylene terephthalate can be modified to increase the polar contribution to its surface energy the adhesive properties thereof will be increased.

In the past the adhesive properties of polyesters have been improved by the incorporation of a polyolefin such as styrene as illustrated by U.S. Patent No. 3,657,389 to provide a hot-melt adhesive. None of the polyolefins described in this patent include styrene-maleic anhydride copolymers.

There has therefore been a continuing search for ways to modify certain polyesters such as polyethylene terephthalate to improve their moldability and adhesive properties. The present invention is a result of this search.

It is therefore an object of the present invention to provide a polyethylene terephthalate based polyester which can be molded under economically advantageous conditions to yield a product which exhibits improved mechanical properties, dimensional stability, and easier moldability.

It is another object of the present invention to improve the adhesive properties of a polyethylene terephthalate based polyester.

These and other objects and features of the invention will become apparent from the claims and from the following description when read in conjunction with the accompanying drawing.

Summary of the invention In one aspect of the present invention there is provided a composition comprising a blend of (1) a polyester comprising at least 85 mole percent polyethylene terephthalate and (2) styrene-maleic anhydride copolymer wherein the weight ratio of the polyester to the styrene-maleic anhydride in the blend is from about 99:1 to about 50:50 respectively.

In another aspect of the present invention there is provided a process for improving the moldability of a polyester comprising at least 85 mole percent polyethylene terephthalate which comprises intimately admixing with said polyester, styrene-maleic anhydride copolymer in an amount sufficient to achieve a polyester to styrene-maleic anhydride weight ratio in the mixture of from about 95:5 to about 50:50.

In a further aspect of the present invention there is provided a process for molding a polyester comprising at least 85 mole percent polyethylene terephthalate which comprises intimately admixing with said polyester, styrene-maleic anhydride copolymer in an amount sufficient to achieve a polyester to styrene-maleic anhydride weight ratio of from about 95:5 to about 50:50; and molding said mixture in accordance with a molding procedure which uses a mold temperature of less than the second order transition temperature of the polyester and not less than about 0 C.

In still a further aspect of the present invention there is provided a process for improving the adhesive properties of a polyester comprising at least 85 mole percent polyethylene terephthalate which comprises admixing styrene-maleic anhydride copolymer with said polyester in an amount sufficient to achieve a polyester to styrene-maleic anhydride weight ratio of from about 99:1 to about 80:20.

Brief description of the drawing The Figure is a Kaelble plot derived from the contact angles of a variety of liquids which are placed on a variety of film samples prepared by compression molding blends of polyethylene terephthalate and styrene-maleic anhydride copolymer.

Description of the preferred embodiment The molding and adhesive properties of certain polyesters are improved by blending therewith a styrene-maleic anhydride (SMA) copolymer.

More specifically, the polyester utilized in accordance with the present invention is at least 85 mole percent, typically about 85 to 100 mole percent and preferably about 90 to about 100 mole percent polyethylene terephthalate. Thus, although it is preferred that the polyester constitute a homopolyester wherein the acid component is derived from terephthalic acid and the glycol component is derived from ethylene glycol, co-polyesters wherein the glycol component further includes minor amounts (i.e., not greater than 15 mole percent of the glycol component) of other glycols such as diethylene glycol, neopentyl glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, etc., and the acid component further includes minor amounts (i.e., not greater than 15 mole percent of the acid component) of other dicarboxylic acids such as isophthalic acid, hexahydroterephthalic acid, bibenzoic acid, adipic acid, sebacic acid, azelaic acid, etc., may also be employed. Consequently the term "PET" as employed herein in intended to include both homo- and co-polyesters comprising at least 85 mole percent polyethylene terephthalate.

The polyesters may be crystalline or amorphous. A representative example of an amorphous PET based polyester includes the random copolyester derived from (1) a mixture of neopentyl glycol and ethylene glycol and (2) terephthalic acid.

The polyester component of the blend may be formed by any of the polymerization techniques known in the art. For instance, terephthalic acid or a dialkyl or diaryl ester of terephthalic acid (e.g., dimethyl terephthalate or diphenyl terephthalate) may be reacted with ethylene glycol to form polyethylene terephthalate. A catalyst such as antimony oxide is commonly employed during the polymerization.

The polyethylene terephthalate based component preferably exhibits an intrinsic viscosity (I.V.) of about 0.5 to 1.0 dl/gm, and in a particularly preferred embodiment, an intrinsic viscosity of about 0.6 to 0.95 dl/gm.

The l.V. of the polymer may be determined by the equation

where llr is the "relative viscosity" obtained by dividing the viscosity of a dilute solution of the polymer by the viscosity of the solvent employed tmeasured at the same temperature), and C is the polymer concentration in the solution expressed in grams/100 ml. The intrinsic viscosity may be conveniently determined from a solution of 0.1 gram of polymer in 100 ml. of ortho-chlorophenol at 250C. The polyethylene terephthalate component commonly exhibits a glass transition temperature of about 75"C, and a melting point of about 250 to 265"C, e.g., about 260oC.

The additive component of the present invention comprises a styrene-maleic an hydride copolymer.

The styrene-maleic anhydride copolymer employed is a thermoplastic polymer which is commonly known in the art and is commerically available. The copolymer can vary in molecular weight over a wide range and in the proportions of styrene and maleic an hydride which comprise it.

Generally, the styrene-maleic anhydride copolymer can be prepared by reacting maleic an hydride with styrene at elevated temperatures, preferably in the presence of a peroxide catalyst. See, for example, U.S.

Patent No. 2,971,939, which is incorporated herein be reference.

The molar ratio of styrene to maleic anhydride present in the polymer can vary over a wide range. It is preferred to utilize styrene-maleic an hydride copolymers wherein the molar ratio of styrene to maleic anhydride is on the order of about 1:1, to about 15:1, preferably about 7:1 to about 15:1 (e.g., 13:1), respectively. However, it should be understood that the copolymer can contain somewhat lower amounts of styrene or higher amounts thereof.Furthermore, it should be understood that when the term "styrene maleic an hydride copolymer" is used herein and in the claims, it includes within its meaning copolymers that contain substituents on the benzene ring or the alkenyl portions of the styrene, and also polymers which in the polymeric chain contain small amounts of other materials such as, for example, alpha-methyl styrene.

It should also be appreciated that mixtures of different styrene-maleic anhydride copolymers may be used in the compositions within the scope of this invention.

The styrene-maleic anhydride copolymer should have a molecular weight within the preferred range of from about 2,000 to about 20,000.

The blends of the present invention may be formed through the utilization of any technique which is capable of initially producing a substantially uniform admixture. Preferably, a blending technique is selected which results in no substantial degradation of the constituent component molecules and is carried out in the substantial absence of moisture. Melt blending may be conveniently selected preferably with the components being intimately admixed while at a temperature of about 250 to 300"C in the absence of moisture. The blend may be initially mixed in the solid state (i.e., as pellets or chips) and further blended to form an intimate admixture in the molten state.Alternatively, the blends may be prepared by dissolving the polyester and styrene-maleic anhydride components in a suitable solvent preferably a polar solvent which facilitates surface enrichment as described herein, and recovering the blend by precipitation (e.g., through the addition of a non-solvent) or by evaporation of the solvent. Suitable apparatus wherein the desired admixture may be accomplished include a Plastigraph mixer, a melt extruder fitted with one or more mixing sections, or any other equipment designed to thoroughly mix polymeric materials while in the melt or in solution. After admixture, the resulting blend may be pelletized, or fabricated into any form required for further processing in accordance with standard techniques.

The amount of styrene-maleic anhydride copolymer which is blended with the polyester will depend on the intended end use of the blend and the purpose of adding the copolymerto the polyester.

For example, when the styrene-maleic anhydride is added to the polyester to improve adhesive properties, amounts as low as 1% of the SMA copolymer, by weight, based on the weight of the two components of the blend, can be employed to increase the polar contribution of the surface energy of the polyester as defined herein. By way of explanation and without wishing to be bound by any particular theory it is believed that the SMA in the PET/SMA blends is oriented with the polar groups at the surface thereof instead of buried in the interior of the blend as is normally observed with other polymers containing polar groups and that SMA copolymer will accumulate on the solid surface of the polymer blend.Thus, the modification of the surface 'energy by the SMA copolymer can be quite pronounced even when employed in small quantities due to the surface enrichment and orientation of the polar groups.

Alternatively, when the SMA copolymer is employed to modify the molding properties of the polyester it should be employed in amounts of not less than about 5%, by weight, based on the weight of the two components of the blend. As the amount of SMA copolymer increases up to 50% the mold temperatures, which can be employed to obtain acceptable mechanical properties, can be increasingly lowered below the second order transition of the polyester. Consequently, the lower the mold temperature the less the probability that shrinkage will occur. Obviously, the particular amount of SMA employed in the blend will also be affected by the overall mix of properties sought to be imparted to the molded product.

Accordingly, although any effective amount of the SMA copolymer may be employed in the blend it is preferred that such effective amount be sufficient to provide a PET to SMA weight ratio of from about 99:1 to about 50:50 (e.g., 95:5 to about 50:50), preferably from about 75:25, and most preferably from about 90:10 to about 80:20.

When the effect sought to be produced is an improvement in adhesion, such effective amounts will generally constitute a PET:SMA weight ratio of from about 99:1 to about 80:20, and preferably from about 95:5 to about 90:10.

When the effect sought to be produced is an improvement in the moldability of the blend in the sense that" lower mold temperatures can be employed thereby reducing shrinkage without sacrificing mechanical properties such effective amounts will generally constitute a PET:SMA weight ratio of from about 95:5 to about 50:50, preferably from about 90:10 to about 80:20.

The improvements obtainable by modification of the polyethylene terphthalate in the polymer blends described herein with respect to surface energy (i.e., adhesive properties) are determined by wettability measurements and surface energy analysis which isolate the dispersion and polar contributions of surface energies in the form of solid-vapor surface tension.

More specifically, the polar and dispersion interaction between a liquid in contact with a solid can be expressed by the following mathematical relationships:

wherein YLV = liquid-vapor suface tension in dynes/cm (i.e., the surface tension of the liquid in equilibrium with its vapor).

Ysv = solid-vapor surface tension (i.e., the surface energy of the solid in equilibrium with the vapor of the liquid).

a ssL = square roots of the respective (London) dispersion YdLv and (Keesom) polary v parts of YLV- αs# sss = square roots of respective dispersion ysdv and polar #SVp# parts of Ysv.

Wa = nominal work of adhesion.

6 = liquid-solid contact angle.

From these relationships, the nominal work of adhesion for a variety of liquids is determined from equation (3) by measuring the contact angles (6) of a drop of a variety of liquids which are placed on the surface of the solid polyester blend which has been provided in the configuration of a film. The liquids are selected so that they differ in the extent to which the polar forces contribute to their interactions with the polyester surface. The values for the nominal works of adhesion for each liquid are then substittuted into equation (5) where αL and ssL are calculated from the literature values of 3LVp and #LVd also obtainable for each liquid. A single linear plot is then made of Wa/2αL(y-axis) versus ssL/αL(x-axis) from the values obtained for each liquid on each film sample.The plot is then extrapolated to ssL/αL = 0 to determine αs which rquals (#SVd)1/2. The slope of the line identifies sss which equals (#SVp). The above analysis is referred to as the Kaelble method and is discussed in the following publications the disclosures of which are herein incorporated by reference: D.H. Kaelble, Physial Chemistry of Adhesion, Wiley -Interscience, New York (1971), pp. 139-170; D.H. Kaelble, 2 J. Adhesion, 66 (1970); P.J. Dynes and D.H. Kaelble, 6 J. Adhesion, 195 (1974); D.H. Kaelble et al, J. Adhesion 6, 239 (1974).

When the PET/SMA blends described herein are analyzed by the Kaelbie method it is found that the contribution of the polar component of the surface energy of the solid blend in equilibrium with the vapor of the chosen liquids is increased substantially in comparision with the polar component of the surface energy of the polyethylene terephthalate alone. Thus, while the polar and dispersion contributions to surface energy of PET alone are 2.88 dynes/cm. and 39.48 dynes/cm. respectively, the polar and dispersion contributions of the PET/SMA blends are found to be about 53.29 dynes/cm. and 3.06 dynes/cm. respectively. This constitutes about an 88% increase in the contribution of the polar component to the total surface energy.Moreover, the increase in polarity of the blend is believed to be exhibited even at low PET/SMA weight ratios of about 99:1 because apparently enough of the SMA in the blend will eventually migrate and concentrate at the surface of the solid polymer blend to bring about the transformation in polarity described herein. Surface enrichment occurs most readily when the PET/SMA blend is melted. Consequently, when the blend is desired to be used for its adhesive properties, it is desired to achieve mixing by a melt blending technique. Such surface enrichment can also occur during fiber and film formation where the mixture is heated above the melting point of both components in the blend.Surface enrichment may also occur when the components df blend are dissolved in the same solution and the solution cast onto a polar substrate so that the polar group of the SMA are induced to orient at the surface of the blend in contact with the substrate through attraction of the polar groups of the latter.

The transformation in the polarity induced by the SMA copolymer will result in an increase in the adhesive properties of the blend.

With respect to the molding properties of PET/SMA blends it has been found that the good mechanical strength properties of molded articles such as tensile strength, tensile modulus, flexural strength and flexural modulus, can be achieved without raising the temperature of the mold above the second order transition temperature of the polyester. in accordance with typical molding procedures e.g., injection molding, a polymer is heated above its melting point, e.g., about 280 to about 300"C, and the molten polymer is forced by hydraulic pressure from a heated chamber into a closed mold cavity. Typically, in the prior art the mold cavity is maintained, in the case of polyethylene terephthalate, at a temperature of at least 140"C and the polymer allowed to remain in the mold cavity for a period of about 40 seconds.The heating of the mold cavity is necessary to insure complete crystallization of the polyethylene terephthalate otherwise the polymer will be limp and rubbery. Alternatively, if the mold cavity is not heated, the molded article must be heat-set or tempered at a temperature of about 140"C for periods of up to two hours to insure complete crystallization and develop good mechanical properties.

It has been found that when PET/SMA blends are molded, particularly injection molded, the temperature of the mold cavity can vary from below the second order transition temperature of the polyester, to not less than about 0 C, typically from about 0 to about 600C, preferably from about 2 to about 25"C. While the polymer blend at these low mold cavity temperatures does not completely crystallize, it has been found that complete crystallization is not necessary to achieve good mechanical properties.Consequently, molded articles do not have to be subsequently heat-set or tempered and since the mold cavity temperature is maintained below the second order transition temperature, the problem of shrinkage and distortion of the shape of the molded article is substantially eliminated without sacrificing mechanical properties. A further advantage of employing SMA as the additive is that SMA is less expensive than PET. Consequently, a considerable savings in cost is obtained by employing the PET/SMA blend.

Broadly, the PET/SMA blend of the present invention may optionally incorporate one or more additional ingredients uniformly dispersed therein which may serve as a nucleating agent, flame retardant, filler, colorant, or reinforcing medium. Such non-polyester components may be incorporated within the blend either simultaneously with its formation or subsequent thereto. For instance, a nucleating agent (1- 10%), flame retardant (10-20%), filler (1-50%), colorant (1-20%), or reinforcing medium (1-50%) may be dispersed within the blend in the associated concentration percentages by weight based upon the weight of the polyester blend components.Suitable nucleating agents, flame retardants, fillers or reinforcing media can be organic and/or inorganic in nature and may be particulate or fibrous in configuration.

Particulate fillers tend to impart lower cost and improved aesthetic properties to the blend. Suitable particulate fillers include clays, silicates, phosphates, etc. Such particulate fillers preferably have a particle size of about 0.1 to 50 microns.

Suitable fibrous reinforcing media include glass fibers, asbestos fibers, carbon fibers (e.g., graphite fibers), or any other high modulus reinforcement. Such fibrous reinforcing media preferably are provided in short discrete lengths having an aspect ratio of at least 10 but may also be relatively continuous in length. The fibrous reinforcing media tend to further improve modulus, strength and stability properties of the blend.

Halogen or phosphorous containing materials may be added to impart fire resistance to the blend.

Asbestos, and other similar materials, may serve to reduce dripping and burning upon exposure to flame.

Commercially available drip retarding agents include a polytetrafluoroethylene, preferably of large particle size. Suitable nucleating agents, include finely divided inorganic or polymeric substances such as talc, sodium silicate, polypropylene, etc. with the particle size preferably being less than 2 microns.

The filler, reinforcing medium, or other additive most conveniently may be introduced into the polyester blend at the time of its formation or immediately thereafter while the blend is still molten.

The blends of the present invention exhibit improved physical properties, as well as significantly different properties than what one skilled in the art would expect. Fibers, films, orthree-dimensional shaped articles readily may be formed from the blend described herein by conventional melt formation procedures.

Fibers may be formed utilizing conventional melt spinning. For example, filaments with commercially attractive properties may be prepared at melttemperature of about 255 to about280 C and spinning speeds of about 1000 to about 1500 feet per minute followed by hot drawing at about 80 to about 1 00 C at a draw ratio of about 2.5:1 to about 6:1. Films similarly may be formed utilizing conventional melt casting or melt extrusion.

Three dimensional articles may be prepared with any coventional injection molding apparatus. Typical injection molding conditions employ a melt temperature of about 260 to about 300"C, to mold temperatures as described herein, and cycle times of about 15 to about 30 seconds. Screw speeds may typically range from about 60 to 90 rpm, and injection pressures of about 8,000 to about 13,000 psi conventionally may be selected.

The high adhesive properties of the blends described herein resulting from surfaces which are highly polar make them particularly suitable as tire cords since they bond well to rubber. Films used to prepare blends exhibit good adhesion to both polar and non-polar substrates such as steel aluminum, chrome, glass, paper, wood, organic polymers, mica and asbestos and can therefor be used in preparing such products as packaging film, and in uniaxially or biaxially stretched film applications such as backing for photographic film, backing for audio tapes, and backing for adhesive tapes.

Blends of the present invention find their greatest utility in the production of attractive, economical, smooth surfaced, three-dimensional, rigid shaped articles. Surprisingly such three-dimensional articles exhibit smooth, glossy surface characteristics, and are tough and resilient The smooth, glossy surface characteristics commonly are retained even when the shaped article incorporates glass fibers or other fibrous reinforcing media.

Typical three-dimensional articles which can be prepared include articles formed by injection molding, compression molding, transfer molding, foam molding, thermofoaming and laminates.

The invention is additionally illustrated in connection with the following Examples which are to be considered as illustrative of the present invention. It should be understood, however, that the invention is not limited to the specific details of the Examples. All parts and percentages in the Examples and the remainder of the specification are by weight unless otherwise specified.

Example I Polyethylene terephthalate (PET) is selected which has been formed by melt polymerization of terephthalic acid with ethylene glycol and exhibits an intrinsic viscosity as described herein of about 0.9 dl/gm.

Styrene-maleic anydride copolymer prepared by conventional procedures using a sytrene/maleic anhydride ratio of 93.7, and available from Arco polymers under the tradename Dylark 232TM is then granulated and mechanically blended with the above described polyethylene terephthalate, which has also been previously granulated, at various PET/SMA weight ratios as shown at Table I. Each mechanical blend is dried in a vacuum oven at about 1 00 C, and extruded in a screw fed extruder (Plasti-Corder from C.W.

Barbender Instruments, Inc.) to form strands which are cut into pellets of approximately 1/8 inch diameter.

The pellets are dried in an oven at 100"C overnight and injection molded into molds maintained at a temperature of about 4.5"C to give bars for testing. Each test bar,aswell as a control bar comprising only polyethylene terephthalate is tested for tensile strength and tensile modulus (ASTM D 638), flexurai strength and flexural modulus (ASTM D790). The results are summarized at Table As may be seen from the data of Table I the PET of run 5 when employing a mold temperature of about 4.5 C is unable to be tested because it is limp and rubbery. Consequently, run 6 is conducted by maintaining the temperature of the mold at 140 C.The resulting sample when tested provides a basis for comparing the mechanical properties of the various blends with PET molded in a conventional manner. The mechanical properties of the samples of runs 1 to 4 are comparable to run 6. No shrinking of the samples is observed for runs 1 to 4.

TABLE I PET/SMA Tensile Tensile Flex Flex Run Weight Strength Modulus Strength Modulus No. Ratio (psi) (psi x 106) (psi) (psi x 106) 1 90/10 8200 0.34 11000 0.35 2 80/20 6800 0.35 10800 0.35 3 60/40 6400 0.34 10400 0.35 4 50/50 6000 0.34 10100 0.35 5 100/0 - - - - - - - - COULD NOT BE TESTED @ 6* 100/0 7400 0.34 11000 0.35 *Mold temperature maintained at 140 C instead of 4.5 C.

Example 2 Example 1 is repeated with the exception that the PET:SMA blend has incorporated therein 30% by weight glass fibers 3/16" in length. The results are summarized at Table II.

As may be seen from the data of Table II the mechanical properties of the molded rods are improved even further by the incorporation of the glass fibers.

TABLE II Heat Deflection Tensile Notched Unnotched Tempera PET/SMA Strength Elonga- Tensile Flexural Flexural Izod Impact Izod Impact ture( ) Run Weight at Break tion() Modulus Strength Modulus Strength() Strength() at 264 No. Ratio (psi) (%) (psi x 106) (psi) (psi x 106) (ft-Ibs.) (ft-Ibs.) psi( C) 1 90/10 10900 1.15 1.13 18000 1.26 0.75 4.33 81 2 70/30 11000 1.19 1.11 17000 1.21 0.72 3.64 81 3 50/50 10900 1.20 1.08 17000 1.16 0.79 4.89 89 ()ASTM D 638 ()ASTM D 256 ( )ASTM D 648 Example 3 The following example is conducted to illustrate the effect of blending an SMA copolymer with polyethylene terephthaiate on the surface energy characteristics of the resulting blend.

Granules of polyethylene terephthalate and styrene-maleic anhydride are mechanicaily blended at various PET/SMA weight ratios and extruded to form pellets in accordance with Example 1. The pellets are then compression molded at 280"C between Kapton sheets to form films 10 mils thick. Each film sample is subjected to a Kaelble analysis as described herein. More specifically each film sample is placed on a microscope slide to keep it flat. A drop of liquid having an appropriate surface tension is applied to the surface of each film sample with a 1 cc Fisherbrand syringe and the contact angle at the three phase liquid-solid-air boundary is measured directly in degrees with a Rame-Hart contact angle goniometer.A second and third drop of the same liquid is added to the first and the angle measurement is observed after the addition of each drop. This procedure is repeated two to four times until an accurate average of the contact angle is obtained for the specific liquid, as indicated when the advancing contact angles after each drop agree within a few degrees. The observed contact angles for doubly distilled water, formamide, methylene iodide, PG-P-1200 (a polyglycol available from Dow Chemical Co.), and ethylene glycol are shown at Table II along with the corresponding PET/SMA weight ratios for each film sample. The contact angles are arranged at Table II such that the angle measurements in each row represents a single series of successive drops applied to the same spot on the film.Each row of contact angles represents a different area of film to which the series of drops is applied. The average contact angle for each liquid on each film sample is used to compute Wa/2 aL in accordance with Equation (3) and the values obtained for each liquid are used as the y-coordinates in a Kaelble plot as shown at the figure. The literature values of (3L and aL for each liquid are employed to define pL/aL and 2aL, as shown at Table II. The value of PL/aL for each liquid is employed as the x-coordinate. The value 2aL is used in conjunction with the contact angles to determine the y-coordinates.

The values of Wa/2aL determined for each solvent at the three different concentrations are shown in Table Ill.

The contact angles and y-coordinates determined therefrom for methylene iodide are disregarded in drafting the linear plot because it is found to interact with the film samples.

A single straight line is drawn which represents the three film samples having different PET/SMA ratios.

The slope of the line, i.e., ps, is determined from the plot illustrated by the Figure to be 7.30, while the y-intercept, i.e., aS is determined to be 1.75. From the squares of the slope and they-intercept of the plot, the polar (ysv) and dispersion (ydv) components of the solid-vapor surface tension are determined to be 53.29 dynes/cm. and 3.06 dynes/cm. respectively with the total (ysv) being 56.35 dynes/cm. The corresponding values of pure PET are 2.88 dynes/cm. (Ysv) and 36.59 dynes/cm. (dv) The above values show that the polarity, i.e., v5Vl ysvl of the surface of the PET film is increased from 0.07 to 0.95 by the addition of styrene-maleic anhydride copolymer. This is caused by the substantially increase in the polar contribution of the surface energy of the blended PET. Thus, the modification of the surface properties of the film samples at each PET/SMA ratio, is believed to be caused by the concentration of the styrene-maleic anhydride at the surface of the film by a phenomena known as surface enrichment and by the outward orienation of the polar groups as described herein. Such surface enrichment occurs even at low SMA concentrations. Consequently, even a small addition of SMA to the PET leads to a substantially large modification in the solid surface properties thereof.

TABLE III Liquid contact angles PET/SMA Weight D.Dist.H2O Formaldehyde CH2I2 PG-P-1200 Ethylene Glycol Run Ratio ssL/αL=1.53 ssL/αL=0.90 ssL/αL=0.22 ssL/αL= 0.53 ssL/αL=0.81 No. In Blend 2αL=9.34 2αL=11.37 2αL=13.93 2αL=9.90 2α;L=10.83 1 90/10 40 43 43 45 58 58 58 62 52 47 45 45 30 27 29 29 45 48 56 56 38 42 40 41 65 65 63 63 40 44 44 44 34 29 32 34 58 60 61 62 44 45 45 45 55 57 59 59 50 43 45 41 37 40 40 40 62 62 58 60 51 52 55 56 59 53 58 61 54 54 47 48 34 23 24 27 60 58 58 58 48 48 52 48 61 61 61 61 42 40 42 42 59 59 59 59 Averages 46.50 59.65 46.44 33.75 57.90 2 50/50 41 41 43 46 58 58 59 59 21 21 25 28 18 24 24 24 45 44 43 41 40 40 38 37 59 59 59 57 28 23 20 16 16 14 19 20 51 53 51 51 37 40 41 43 55 49 51 53 29 28 31 25 18 24 22 18 44 50 56 54 44 46 45 46 49 50 51 48 27 29 39 46 41 41 49 49 53 54 54 53 26 25 25 40 Averages 42.40 54.40 27.60 20.08 48.58 3 10/90 46 48 48 49 64 64 60 61 31 32 31 31 10 12 13 16 31 27 27 25 43 45 37 42 58 58 58 58 21 - - 22 12 14 11 13 40 49 47 51 46 49 46 46 60 61 60 58 29 29 34 43 14 16 16 15 51 50 54 53 42 49 49 47 60 58 60 63 29 22 26 31 17 19 19 18 49 49 51 51 63 65 59 59 27 28 24 25 10 17 21 20 Averages 46.60 60.35 28.06 15.15 42.08 TABLE IV .............................................................. Wa/2αL...............................................................

PET/SMA D. Dist. H2O Formamide CH212 PG-P-1200 Ethylene Glycol 90:10 13.20 7.72 6.16 5.79 6.83 50:50 13.55 8.10 6.88 6.13 7.41 10:90 13.15 7.66 6.86 6.21 7.77 The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular forms disclosed, since these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the invention.

Claims (13)

1. A composition comprising a blend of (1) a polyester comprising at least 85 mole percent polyethylene terephthalate and (2) a styrene-maleic anhydride copolymer wherein the weight ratio of the polyester to the styrene-maleic anhydride in the blend is from about 99:1 to about 50:50 respectively.

2. The composition of claim 1 wherein the weight ratio of the polyester to the styrene-maleic anhydride copolymer is from about 95.5 to about 75:25.

3. The composition of claim 2 wherein the polyester is a homopolymer of polyethylene terephthalate.

4. A process for improving the moldability of a polyester comprising at least 85 mole percent polyethylene terephthalate which comprises intimately admixing with said polyester styrene-maleic anhydride copolymer in an amount sufficient to achieve a polyester to styrene-maleic anhydride weight ratio in the mixture of from about 95:5 to about 50:50.

5. The process of claim 4 wherein the polyester is a homopolymer of polyethylene terephthalate and said weight ratio is from about90:10to about 80:20.

6. A process for molding a polyester comprising at least 85 mole percent polyethylene terephthalate which comprises intimately admixing with said polyester styrene-maleic anhydride copolymer in an amount sufficient to achieve a polyester to styrene-maleic anhydride weight ratio of from about 95:5 to about 50:50; and molding said mixture, in accordance with a molding procedure which uses a mold temperature of less than the second order transition temperature of the polyester and not less than about 0 C.

7. The process of claim 6 wherein the polyester is a homopolymer of polyethylene terephthalate, said weight ratio is from about 90:10 to about 80:20, admixture is achieved by melt blending, and the mold temperature is from about 0 to about 60 C

8. A process for improving the adhesive properties of a polyester comprising at least 85 mole percent polyethylene terephthalate which comprises admixing styrene-maleic anhydride copolymer with said polyester in an amount sufficient to achieve a polyester to styrene-maleic anhydride weight ratio of from about 99:1 to about 80:20.

9. The process of claim 8 wherein said polyester is a homopolymer of polyethylene terephthalate, said weight ratio is from about 95:5 to about 90:10, and admixture is achieved by melt blending the two components of the mixture.

10. A composition substantially as hereinbefore described with reference to the Examples.

11. A process for improving the moldability of a polyester substantially as hereinbefore described with reference to the Examples.

12. A process for improving the adhesive properties of a polyester substantially as hereinbefore "described with reference to the Examples.

13. A process for molding a polyester substantially as hereinbefore described with reference to the Examples.