WO2009002778A1

WO2009002778A1 - Additives to improve high temperature performance of polyesters

Info

Publication number: WO2009002778A1
Application number: PCT/US2008/067310
Authority: WO
Inventors: Thomas P. Mcandrew; Lawrence H. Judovits; Laurent B. Cartier; Nicholas J. Rodak
Original assignee: Arkema Inc.
Priority date: 2007-06-27
Filing date: 2008-06-18
Publication date: 2008-12-31

Abstract

The invention relates to the addition of organic salts to a polyester in order to improve high temperature performance of the polymer. In particular the modulus at a given temperature of polyesters, and especially crystalline poly(ethylene terephthalate) (CPET) is improved using small amounts of organic salts. The improved high temperature modulus allows for use at higher coooking temperatures, thus increasing the number of food-service applications for which CPET is suitable.

Description

ADDITIVES TO IMPROVE HIGH TEMPERATURE PERFORMANCE OF

POLYESTERS

Field of the Invention

The invention relates to the addition of organic salts to a polyester in order to improve high temperature performance of the polymer. In particular the modulus at a given temperature of polyesters, and especially crystalline poly(ethylene terephthalate) (CPET) is improved using small amounts of organic salts. The improved high temprature modulus allows for use at higher processing temperatures, thus increasing the number of food-service applications for which CPET is suitable.

Background of the Invention

Plastics, and in particular polyesters, are useful in food applications since they can be both frozen and heated without detrimental effects. One specifically useful application is in packaging for frozen foods, which can then be heated to serving temperature - especially in a microwave oven.

One problem with many of these polymers is that they can soften and deform at higher temperatures, decreasing their usefulness. One polyester that has found particular usefulness in food applications is crystalline poly(ethylene terephthalate) (CPET). The CPET can be melt compounded with functional polyolefins (FPO) to impart improved low-temperature performance.

The structure of CPET is shown in Diagram 1.

Diagram 1. Structure of Poly(ethylene terephthalate) hi order to increase the applications for which polyesters may be used, it is desired to increase the heat distortion temperature - allowing for higher cooking and pasteurization temperatures and thus decreasing the cooking or processing time.

Higher heat distortion polymers can also replace metals such as aluminum in certain applications.

PCT/US06/48643 describes the use of onium salts to increase the melting point of polyvinylidene fluoride. Surprisingly it has now been found that the addition of small amounts of specific organic salts to polyesters increases the high temperature performance of the polymers.

Summary of the Invention

The invention relates to a polymer blend comprising: a) at least 50 percent by weight of one or more polyesters b) from 100 ppm to 10 weight percent of one or more organic salts, based on the weight of the polyester, said organic salt having the formula:

[R₁R₂R₃R₄Y]⁺X^" wherein X^" is an anion that may be polyatomic, Y is selected from phosphorous or nitrogen and R₁, R₂, R₃, and R₄ are each individually H or a Ci_-20 group selected from alkyl, aryl, or alkylaryl groups. Ri, R₂, R₃, and R₄ may or may not be identical. Said cation may alternately be a heterocyclic imidazolium_.

The invention also relates to a process for improving the high temperature properties, such as modulus, by adding one or more organic salts to a polyester or a polyester blend.

Brief Description of the Drawings

Figure 1 - is a plot of the DMA Analyses for Example 1. The salt is Et(Ph)₃PBr. The complementary salt is Na(Ph)₄B.

Detailed Description of the Invention The invention relates to the addition of one or more organic salts to a polyester in order to improve high temperature performance of the polymer.

Polyesters, useful in the invention include, but are not limited to, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), APET, and polyethylene terephthalate-glycol modified (PETG). Preferred polyesters are PET and PBT. An especially preferred PET is crystalline poly(ethylene terephthalate) (CPET). The polyester of the invention may also be a blend of one or more polyesters and one or more non-polyester polymers, where the polyester represents at least 50 weight percent of the blend. The polyesters may contain usual additives, including but not limited to fillers, dyes, impact modifiers, and stabilizers. Organic salts of the invention include, but are not limited to phosphonium, , ammonium, and imidazolium salts. The salts used may be prepared by known synthetic methods such as nucleophilic substitution of an alkyl or aryl halide, with subsequent anion exchange. The organic salts useful in the invention have the formula:

[R₁R₂R₃R₄ Y]⁺X- where X^" may be a simple halogen anion such as iodide, bromide, chloride, or fluoride or a complex organic carboxylate anion such as acetate or succinate, or benzoate, or a complex inorganic anion such as hexafluorophosphate, sulfate, tetrafluoroborate, or an aluminosilicate; Y is selected from phosphorous or nitrogen and Ri, R₂, R₃, and R₄ are each individually H or a Ci_-20 group selected from alkyl, aryl, or alkylaryl groups. R₁, R₂, R₃, and R₄ may or may not be identical. Said cation may alternately be a heterocyclic imidazolium. Moreover, the groups R₁, R₂, R₃, and R₄ may bear one or more of oxygen, nitrogen, sulfur, and phosphorus centers wherein the organic cation may therefore contain functionality such as alcohol, carboxylic acid, ester, amide or other that may augment the desirable effects imparted by the organic salt additive. Specific examples of such salts include: ethyl triphenyl phosphonium bromide (ETP), ethyl triphenyl phosphonium hexafluorophosphate, stearyl triphenyl phosphonium bromide, and tetrabutyl ammonium hexafluorophosphate. Mixtures of organic salts may also be used.

The organic salt is present in the composition at from 100 ppm to 10 and preferably 0.3 0.1 to 8 weight percent, based on the weight of the polyester.

While not being bound by any particular theory, it is believed the addition of the organic salts increases the crystalinity level of the polyester, resulting in better heat distortion properties.

In some cases, the addition of the organic salt to a polyester results in a reduction of the polyester molecular weight due to hydrolysis or catalysis. This effect can be offset by the addition of a complementary salt, such as sodium tetraphenyl borate for ETP.. Ethyl triphenyl phosphonium tetraphenyl borate and tetrabutyl ammonium tetraphenyl borate would also be useful. Other complimentary salts can be used for with similar results with other organic salts, and several complimentary salts may for useful with any specific organic salt of the invention.

The organic salt may be blended with the polyester by several means, including but not limited to known methods of melt blending or solution blending, hi one embodiment the organic salt is mixed with polyester in a melt-extruder. In a preferred embodiment the polyester is dried prior to blending with the organic salt.

The polyester/organic salt blend of the invention may also include carbon nanotubes, for further improvement of the high temperature properties.

Examples

CPET was dried at about 110⁰C for about 16 hours under partial vacuum (0.25 atm). The salt/CPET compounds were melt mixed on a DSM midi extruder (for experimental use - twin screw - 15 cc capacity) at 28O⁰C for 10 minutes. Prior to injection molding, extrudates were dried at about 100⁰C for 16 hours under partial vacuum (0.25 atm). Injection molding was performed by melting at 285⁰C for 5-10 minutes, with injection into a mold at 8O⁰C. Injection molded pieces were dried at about 100⁰C for 16 hours under partial vacuum (0.25 atm) prior to DMA analysis.

Table 1. DSC Results.

Data for Et(Ph)₃PBr is average of two DSC experiments. Value for Increase (%) is a comparison to plain CPET.

DSC results are shown in the Table 1. Several points are noted:

• presence of salts did not change Tm.

• presence of salts did change Tc - raising it slightly. This indicates that salts serve as nucleating agents - since on cooling crystallization begins at a higher temperature. • presence of salts did change crystallinity level - raising it appreciably. While increase in crystallinity level can be expected to translate into improved performance at higher temperature, the critical experiment is DMA - which provides values of storage modulus as a function of temperature.

Results of DMA analysis are shown in Figure 1. DMA analysis was performed using a heating rate of 3°C/min from ambient temperature to 255⁰C at 1 Hz with a dual cantilever clamp.

It is noted that the presence of 0.5% Et(Ph)₃PBr by itself improved storage modulus - giving better performance at higher temperatures. It is also noted that the presence of 0.5% Et(Ph)₃PBr and 0.5% Na(Ph)₄B produced an even larger improvement in storage modulus.

Claims

What is claimed is:

1. A polymer blend comprising: a) at least 50 percent by weight of one or more polyesters b) from 100 ppm to 10 weight percent of one or more organic salts, based on the weight of the polyester, said organic salt having the formula:

[R₁R₂R₃R₄Y]⁺X^" wherein X^" is an anion that may be polyatomic, Y is selected from phosphorous or nitrogen and R₁, R₂, R₃, and R₄ are each individually H or a Cj_-20 group selected from alkyl, aryl, or alkylaryl groups. R₁, R₂, R₃, and R₄ may or may not be identical.

2. The polymer blend of claim 1 , wherein said polyester is selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), APET, and polyethylene terephthalate-glycol modified (PETG).

3. The polymer blend of claim 1, wherein said organic salt is selected from the group consisting of phosphonium, ammonium, and imidazolium salts.

4. The polymer blend of claim 3, wherein said organic salt is ethyl triphenyl phosphonium bromide, ethyl triphenyl phosphonium hexafluorophosphate, stearyl triphenyl phosphonium bromide, tetrabutyl ammonium hexafluorophosphate, or a mixture thereof.

5. The polymer blend of claim 1, wherein said organic salt is present at from 0.3 to 8 weight percent, based on the weight of the polyester.

6. The polymer blend of claim 1, wherein said organic salt is present at from 0.3 to 1 weight percent, based on the weight of the polyester.

7. The polymer blend of claim 1, further comprising a salt complimentary to said organic salt, in an amount about equal to that of the organic salt.

8. The polymer blend of claim 6, wherein said organic salt/complimentary salt pair is ethyl triphenyl phosphonium bromide/sodium tetraphenyl borate.

9. A process for improving the high temperature modulus properties of a polyester comprising admixing from 100 ppm to 10 weight percent of one or more organic salts, based on the weight of the polymer, said organic salt having the formula:

[RiR₂R₃R₄Y]⁺X^" wherein X^" is an anion that may be polyatomic, Y is selected from phosphorous or nitrogen and Ri, R₂, R₃, and R₄ are each individually H or a Ci_-20 group selected from alkyl, aryl, or alkylaryl groups. R₁, R₂, R₃, and R₄ may or may not be identical.