CA1171576A - Stabilized ethylene/tetrafluoroethylene copolymers - Google Patents

Abstract

TITLE
Stabilized Ethylene/Tetrafluoroethylene Copolymers ABSTRACT OF THE DISCLOSURE
Presence of cuprous iodide or cuprous chloride provides protection to ethyiene/tetrafluoro-ethylene polymers against thermal degradation.

Description

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TITLE
Stabilized Ethylene/Tetrafluoroethylene Copolymers - FIELD OF THE INVENTION
This invention relates to an ethylene-tetrafluoroethylene copolymer which is stabilized against thermal deqradation, and more particularly to an ethylene~tetrafluoroethylene copolymer which is stabilized against thermal degradation by addition of CuI or CuCl.
BACKGROUND OF THE INVENTION
Ethylene-tetrafluoroethylene copolymers have good thermal, chemical, electrical and mechanical properties and are melt-processible. These copolymers are known to be heat-resistant thermoplastic resins which have a melting point of 260 to 300C. ~owev~r, the copolymers thermally deteriorate and become colored, brittle and foamed when heated to a temperature higher than the melting point for a long period of time. Accordingly, it is desirable to prevent the thermal deterioration of ethylene-tetrafluoroethylene copolymers during the conventional operation of injectlon molding and extrusion molding processes.
U.S. Patent ~,110,30~ discloses that a copper compound, such as metallic copper, cupric oxide or cuprous oxide, cupric nitrate, cupric chloride or copper alloys, stabilize the copolymers against degradation at elevated temperatures.
SUM~ARY OF THE INVENTION
It has now been found that cuprous chloride or cuprous iodide provide better protection to ethylene-tetrafluoroethylene copolymers (E/TFE
copolymers hereinafter~ against thermal degradation than the metallic copper or cupric oxides disclosed ~ l7~ 57 ~

in U.S. Patent 4,110,308, and therefore can be employed at lower concentrations, thus avoiding detrimental pigmentation and the like.
- Addition o cuprous chloride or iodide to an E/TFE copolymer allows the copolymer to be exposed to very high temperatures in air without rapid loss in weight, molecular weight deterioration, color or bubble generation. Such protection greatly improves E~TFE copolymers utility for such applications as rotomolding, surface coating, molding, and wire insulation, where high temperatures are involved in manufacture and/or use.
For example, in rotomolding the E/TFE powder is subjected to temperatures well above the melting 15 point for up to an hour with oxygen generally present. Under such conditions, untreated E/TFE
powders turn brown, foam, and become exceedingly brittle because of molecular weight reduction. The addition of small amounts of cuprous chloride or 20 iodide prevents such degradation.
DESCRIPTION
The ethylene-tetrafluoroethylene copolymers used in the invention can be prepared by various well-known polymerization methods such as emulsion 25 polymerization in an aqueous medium or suspension polymerization. The ratio of ethylene to tetrafluoroethyle~e units can be conventionally varied and it i~ possible to combine a small amount (e.g., up to 20 mole percent) of a copolymerizable 30 ethylenically unsaturated comonomer of 3-12 carbon atoms~ such 2s propylene, isobutylene, vinyl fluoride, hexafluoropropylene, chlorotrifluoroethylene, acrylic acid, alkyl esters thereof, chloroethyl vinyl ether, perfluoroalkyl ` ` ' 11'~.~.5~

perfluorovinyl ethers, hexafluoroacetone, perfluorobutyl ethylene, and the like. The ratio of ethylene to tetra1uoroethylene units in the - copolymer may vary over wide limits. For example, the mole ratio of tetrafluoroethylene to ethylene units may be from 40/60-70/30, and preferably from about 45/55-60/40.
The cuprous chloride or iodide provides outstanding oxidation inhibition for E/TFE resins over the concentration range of 0.05 to 500ppm, preferably 5-50ppm, as copper. The protection is the same through this range whether at Sppm or 50ppm.
Copper in other forms is not as potent at lower concentrations; for example, Cu powder, Cu2O, and CuO all provide protection but become effective only at higher concentrations of 50ppm or more. There are important advantages gained at the lower ~oncentrations: (1) pismentation by the additive is minimized, (2) conversion of the halide to black 20 ~upric oxide at high temperatures is not as noticeable, (3) problems such as surface roughening, haziness, and electrical flaws are avoided.
E/TFE resins stabilized with CuI or CuCl can be heated in air above their melting point and 25 maintained there for 2 hours and more without significant losses in molecular weight (toughness) or color.
Another advantage of using the halides~ and particularly CuI, is their ability to greatly 30 stabilize E/TFE melts during processing; thereby allowing greater holdup times without losses in end-product molecular weight.
Inclusion of the cuprous halides in E/rFE
resins also improves stress cracking resistance in a.~t~6 high temperature applications. Color degradation is also slowed remarkably. For example, 5ppm CuI
retains 90 percent of its initial room temperature - elongation after 215 hours of aging at 230C, whereas 5 a control tno Cu) lasts for only 27 hours, and a sample containing 50ppm Cu metal powder lasts just 70 hours. Use of cuprous chloride or iodide in E/TFE
finished articles provides good prote~tion agains thermally induced cracking for up to 400 hours of 10 aging at 230C. Better protection shouid be expected at lower temperatures.
It is preferable to optimize the particle size, the specific surface area, and the particle distribution of the cuprous halide in accordance with 15 the desired properties of the copolymer composition.
For example, it is preferable to use a cuprous halide having a relatively small average particle diameter, usually less than 100 micron and preferably about 1-50 micron. It is also preferable to have a sharp 20 particle distribution.
Various methods can be employed for blending the cuprous halide with the E/TFE. Eor example~
commercially available CuI or CuCl powder can be blended with the copolymer in a mixer. An aqueous 25 slurry or organic solvent slurry of ethylene-tetrafluoroethylene copolymer and CuI or CuCl can also be prepared.
EXAMPLES
In the Examples, the E/TFE copolymer 30 designated E/TFE-I was a copolymer of ethylene/tetrafluoroethylene/hexafluoroacetone (21.3/72.9/5.8 wt percent) having a melt viscosity of 18 X 10 poise and a melting point of 262C. The copolymer was in the form of a partially compacted 35 friable powder.

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The E/TFE copolymer designated E/TE~E-II was a copolymer of ethylene~tetrafluoroethylene/per-fluorobutyl ethylene (18.9/79.35/1.75) having a melt viscosity of 5.85 X 104 poise, in powder form.

The following powdered additiYes were employed:
~1) cuprous iodide, CuI

(2) copper metal

(3) cupric oxide, CuO

(4) ~-A12O3

(5) ZnO

(6) CuI/KI mixture adsorbed on ~-A12O3

(7) cupric nitrate adsorbed on ~-A12O3

(8) CuI/KI mixture The different powdered additives were added to E/TFE-I powder in a blender along with enough trifluoro-1,1,2-tri~chloroethane (F-113) solvent to produce a fluid slurry. After mixing at high speed 20 for 1 minute, the slurry was poured into a pan ~nd the F-113 was allowed to evaporate. The resultan~
powder cake was then dried for 1 hour under vacuum a~
120C.
Evaluations - Two grams of each mixture were ?S weighed onto a watch glass and all the mixtures prepared were heated together at 300C for two hours in an oven using constantly circulating air. At 300C, the E/TFE-I powder is well above its melting point of 262C. The cooled mixtures were examined 30 for signs of degradation such as color generation, foaming, and cracking.
Results - The results are tabulated below in order of good to bad performance:

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These results show cuprous iodide (Example 13 give outstanding protection against oxidation. Its performance is much better than that ~ for any of the other tested additives (Comparisons 5 A-~). Based on the visual observations, CuI, CuI/KI/~12O3, Cu(NO3)2 adsorbed on ~-A1~03 in unwashed form, and copper metal powder rendered some protection, but CuO, Cu(NO3)2 adsorbed on ~ ~12O3 in washed form, ~A12O3, ZnO, and CuI/KI actually accelerated E/TFE-I
degradation.
~ EXAMPLE 2 Experimental - E/TFE~I powder samples were prepared in the same way described in Example 1.
15 Samples containing CuI, CuCl, CuBr, Cu, Cu2O, CuO, at 5, 50, 500, and 1000ppm as copper were studied.
Other additives tested were CuC12.2H2O and CuBr2 at 5, 50, and 500 ppm as copper plus CuF2.2H2O as 50ppm coppex mixed with 749ppm XI, 20 1000 and 300ppm ~-A12O3, 100 ppm of Cu(NO3)2fi~-A12O3 mixtures both washed ~nd unwashed, and 1000ppm of CuI~KI/~-A12O3 mixtures both washed and unwashed.
The additive particle size distributions 25 were measured using the Sedigraph and Coulter Counter techniques. The average particle size in microns for each additive type follows: Cu metal powder, 42 ;
Cu2O, 13 ; CuO, 7 ; CuI, 19.7 ; CuC12 2H2O, 14.6 ; ~-A1~03, 11.4 .
Each sample, in the amount of 2 grams, was placed on a watch glass, weighed, and then subjected to two hours of heat aging at 300C in circulating air.. Once cooled, each sample was photographed and then weighed to determine the amount of any weight as7~

loss. The samples, as a group, were then subjected to another 2 hour aging in the 300C oven, cooled, photographed, and weighed again. This procedure was repeated six times giving the samples 12 hours of exposure time in the 300C oven.
Results - Wide differences in sta~iLity were evident after the first two hour exposure. The control resln with no additives turned dark brown and foamed excessively. Of those samples containing 5ppm copperr the CuI and CuCl ones exhibited no color change or foaming. The CuC12~2H~O sample displayed no foaming but incurred slight yellowing and some weight lossO Of the remaining samples, CuBr prevented foaming but allowed some yellowing, while 15 Cu metal, Cu2O, CuO, and CuBr2 allowed some foaming and considerable color development.
At 50ppm copper, all the additives except Cu2O, CuO, CuF2.2H2O and Cu metal prevented both color and bubble formation. At 500 and lOOOppm, 20 all the additives gave good protection.
The CuI sa~ples containing 500 and lOOOppm copper turned grey and black, respectively, after the first two hour aging~ The darkening is due not to degradation of the polymer, but is instead the result 25 of cupric oxide (black) formation. These samples did not darken further with continued oven exposures.
Evidence for CuO formation was also seen in the CuCl, CuBr, and Cu~O samples. Vf these, the CuI was the most reactive toward oxygen.
The weight loss with time for the various samples is tabulated in Table 1.
At 5ppm copper, Table 1 shows a wide range of additive effectiveness with CuI being the most powerful inhibitor followed in order of decreasing activity by CuCl, CuC12.2H2Or CuBr, Cu2O, CuBr2 and CuO. The CuI and CuCl compounds are by far the most effective additives: (1) they protect the longest against color forma~ion t4 6 hours), (2) 5 prevent foaming up to 6 hours for CuI and 4 hours for CuCl, (3) maintain the initial low rate of weight loss the longest and (4) give the lowest ultimate (12 hours) weight loss.
At 50ppm, the order of effectiveness remains 10 essentially the same. Here the sample containing copper metal gives the least protection. The overall order of effectiveness from best to poorest:
CuI CuCl, CuBr CuC12.2H2O, Cu2O CuBr2, CuO, and Cu metal.
At 500ppm, all the additives showed some effectiveness. However, at this loading, many of the additives pigment the resin. This pigmentation is undesirable in many applications. The CuO turns the resin geey, the CuI tan, and the Cu2O pink. From 20 the pigmentation standpoint, CuCl lends the least - color with the maximum protection and does not ! J
blacken to CuO nearly as much as the CuI. Of all the additives, copper metal pigments least but does not render ade~uate protection for the E/TFE-I.
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Expe imental - E/TFE-I samples were the same ones used in Example 2. Stabilized E/TFE-II samples were prepared the same way as the E~TFE-I samples tsee Example 1), but several changes were made from the Example 1 procedure: (1) the powder samples were weighed directly into heat-cleaned (300C for 2 hours) aluminum weighing dishes rather than into watch glasses, in order to allow easy removal of the polymer discs after heat aging; (2) a larger sample (S.5 grams) was used to supply enough polymer for MV
measurements; and (2) the samples were photographed a~ainst a white b.~ckground in order to better compare color changes and differences.
Each sample was weighed into its aluminum dish usin~ a gravimetric balance. All the samples were heat aged together in an air circulation oven set at 300~C. After aging, the samples were again weighed to determine the degree of weight loss. Each sample was then separated from the aluminum dish, photographed with the other samp]es.

Results - The weight loss results are tabulated in Tables 2 and 3.
The weight loss results for both E/TFE-I and E/TFE-II are largely parallel. A concentration dependence is evident for the Cu, Cu2O and CuO
additives, whereas CuI and CuCl show no concentration dependence over the wide range of 5 to 500ppm 30 copper. More important, the CuI and CuCl are far more potent stabilizers than copper or its oxides at low concentrations.

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~, Experimental - CuI or CuCl was blended with E,'TFE-I or II powder by tumble blending for 1 hour.
- The blends were then extruded through a 28mm twin screw extruder.
The extruded samples were compression molded (at 300C) into 4" X 4" ~ 0.010" films. These films were cut into 2" X 4" halves, and one half were subjected to thermal agin~ in air at 230C for a 10 specif ied time. The other half were not aged and served as a control. A new film sample was molded for each aging cycle. The unaged and aged samples were measured for color, degree of oxidation by absorption in the 1755 cm 1 region (carbonyl region), and percent elongation at both room temperature and 200C.
The E/TFE-I sampies extruded were ones containing: a control ~no additive), 5ppm Cu as CuI, 50ppm Cu as CuI, 500ppm Cu as CuI, 5ppm Cu as CuCl, 20 50ppm Cu as CuCl, 50ppm Cu metal powder, 50ppm Cu as Cu2O. The E/TFE-II samples extruded were ones containing: 0.25ppm Cu as CuI, 5ppm Cu as CuI, 5ppm Cu as Cu2O, and 50ppm Cu as Cu2O. The E/TFE-II
powder served as a control.
Results - are shown in Table 4.

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Claims (18)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An ethylene/tetrafluoroethylene copolymer composition having good thermal stability which comprises a) an ethylene/tetrafluoroethylene copolymer which con-tains 40 to 70 mol percent tetrafluoroethylene units and complementally 60-30 mol percent ethylene units and b) from 0.05 to 500 ppm, based on parts of a) and b), cuprous iodide or cuprous chloride (as copper) free of other inorganic halide salts.

2. The composition of Claim 1 wherein the copolymer contains units of ethylene, tetrafluoroethylene and hexafluoroacetone.

3. The composition of Claim 1 wherein the copolymer contains units of ethylene, tetrafluoroethylene and perfluorobutyl ethylene.

4. The composition of Claim 2 wherein the cuprous compound is cuprous iodide.

5. The composition of Claim 2 wherein the cuprous compound is cuprous chloride.

6. The composition of Claim 3 wherein the cuprous compound is cuprous iodide.

7. The composition of Claim 3 wherein the cuprous compound is cuprous chloride.

8. The composition of Claim 4 or Claim 6 where-in the cuprous iodide is present in an amount of from 5 to 50 ppm.

9. The composition of Claim 5 or Claim 7 where-in the cuprous chloride is present in an amount of from 5 to 50 ppm.

10. An ethylene/tetrafluoroethylene copolymer composition having good thermal stability which comprises a) an ethylene/tetrafluoroethylene copolymer which con-tains 40 to 70 mol percent tetrafluoroethylene units and complementally 60-30 mol percent ethylene units and up to 20 mol percent units of at least one copolymerizable ethylenically unsaturated comonomer of 3-12 carbon atoms, and b) from 0.05 to 500 ppm, based on parts of a) and b), cuprous iodide or cuprous chloride (as copper) free of other inorganic halide salts.

11. The composition of Claim 10 wherein the copolymer contains units of ethylene, tetrafluoroethylene and hexafluoroacetone.

12. The composition of Claim 10 wherein the copolymer contains units of ethylene, tetrafluoroethylene and perfluorobutyl ethylene.

13. The composition of Claim 11 wherein the cuprous compound is cuprous iodide.

14. The composition of Claim 11 wherein the cuprous compound is cuprous chloride.

150 The composition of Claim 12 wherein the cuprous compound is cuprous iodide.

16. The composition of Claim 12 wherein the cuprous compound is cuprous chloride.

17. The composition of Claim 13 or Claim 15 wherein the cuprous iodide is present in an amount of from 5 to 50 ppm.

18. The composition of Claim 14 or Claim 16 wherein the cuprous chloride is present in an amount of from 5 to 50 ppm.