Source: https://patents.justia.com/patent/3935141
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US Patent for Environmentally degradable ethylene polymeric compositions Patent (Patent # 3,935,141 issued January 27, 1976) - Justia Patents Search
Justia Patents US Patent for Environmentally degradable ethylene polymeric compositions Patent (Patent # 3,935,141)
Jun 28, 1972 - Union Carbide Corporation
wherein X is hydrogen, alkyl of from 1 to about 10 carbon atoms or a substituted or unsubstituted phenyl and X.sup.1 is alkyl of from 1 to about 10 carbon atoms or a substituted or unsbustituted phenyl, said sterically hindered group being susceptible to proton donation. Generally the sterically hindered phenol will be one that does not volatilize or decompose appreciably below temperatures of about 200.degree.C.
A 6 .times. 12 inches two-roll mill with heat supplied by full stream at 190.degree.C. and heated for at least 15 minutes is used. With the bit as close as possible the ethylene base polymer is added and then during a period of about 1 minute the bite is opened after the ethylene polymer has begun to flux. The polypropylene or other auto-oxidative susceptible agent is added. Thereafter antioxidant and other filler (if applicable) are added. The polyvalent transition metal salt is then slowly added in about 30 seconds. The material is worked for 2 minutes until homogeneous, then pulled off the rolls and cut into squares about 2 by 2 inches. It is recognized that any of the other conventional additives usually present, such as pigment, slip agents, anti-block agents; etc. can be present if desired. Unless otherwise stated this method was used in the examples.
In the mixer method a 5 lb. Banbury mixer was employed with full steam on the shell and rotors for 5 minutes to achieve 190.degree.C. The ethylene base polymer and auto-oxidative susceptible agent, such as polypropylene, were added. The ram was moved downward at the full pressure of 80 psi and the Banbury operated at maximum forward speed for 3 minutes or until the materials are fluxed. The antioxidant, filler (if applicable), and polyvalent transition metal salt were added with the ram backed down to 10 psi and the Banbury at its slowest forward speed for one minute. The ram pressure was then readjusted to 80 psi and the Banbury was then operated at full forward speed for 2 minutes. Cooling water was then supplied to the shell and rotors and the mixer was operated at its slowest forward speed for one minute. Thereafter the compounded material was discharged, sheeted and diced.
After compounding by either the mixer or roll mill method the samples were compression molded by the following method. A mold lined with Mylar sheet was charged with the ethylene polymer composition. It was placed between preheated (190.degree.C.) plattens and low pressure (1 ton on 6 in..sup.2 ram) was applied for four minutes followed by full pressure (32 tons on 6 in..sup.2 ram) for two minutes. The plattens were then water cooled and the sample was recovered.
Weathering tests were conducted by placing a plurality of identical specimens from the same molded sheet in an Atlas XW Weatherometer that uses a carbon arc radiation source with Corex D filters to simulate solar light spectral distribution. The sample was maintained at a blackbody radiation temperature of 140.degree.F. over a four hour period, which included an 18 minute period of water spray. Water was permitted to accumulate at the bottom of the chamber to provide a humidified condition. The exposed samples are removed from the Weatherometer after certain periods of time and examined for embrittlement, percent elongation and FMIR. The period in hours that has transpired is recorded when the sample fails the test. Normally the samples are rated at the end of 20, 60, 100, 150, 200, 250, 350, 500, 750 and 1,000 hours of exposure. The specimen from the previous rating period is removed permanently from the Weatherometer at the end of the 60, 150, 250, 500 and 1,000 hours periods for complete evaluation. By this is meant that at the 20 hour period the first specimen is removed, rated and returned, at the 60 hour period it is permanently removed, rated and tested; at the 100 hour period the second specimen is removed, rated and returned, at the 150 hour period it is permanently removed, rated and tested. This procedure is continued in the time pairs until all of the specimens have been consumed and permanently removed. On occasion additional specimens were permanently removed, rated and tested at the 20 or 100 hour periods.
It was observed that as weathering exposure proceeds, surface cracking appeared. The cracks occur in polyethylene compositions generally after the onset of embrittlement, usually between 150 to 250 hours of exposure. Through the optical microscope, the crack patterns which appeared on the surface of severely oxidized samples were clearly visible. The cross section fracture surfaces of brittle specimens were observed through the optical microscope and at magnifications of 46 X to 300 X it was possible to determine which areas of the cross section were brittle. Scanning electron micrographs of the weathered specimen at a magnification of 500 X show that the cracks were formed by brittle failure resulting in very sharp clean cuts. Primary cracks are normal to the surface and are believed to be influenced by the internal stress disbtibution in the specimen, and will be parallel to the surface if the stress distribution in the specimen is uniform. Secondary cracks join the primary cracks, are ess-shaped, and slant inward at an angle less than 90.degree. to the surface. Tertiary cracks join primary and secondary ones and also are ess-shaped and likewise slant inwardly. This produces a network of cracks in which the spacing between the cracks progressively becomes smaller and results in particles on the order of 350 microns in width which can readily peel off or slough off due to the "slant faults" similar to that mechanism observed in exfoliating rocks.
The stability of the samples prior to weathering was determined by Differentials Scanning Calorimetry (DSC). A du Pont 900 Thermal Analyzer with DSC module attachment and an external strip chart recorder were used for the isothermal DSC induction time studies. By measuring the length of time at 180.degree.C. or 200.degree.C. required for the heat of oxidation to be evolved, the stability of the compound can be determined. At 200.degree.C. well-stabilized commercial polyethylene has a 3 to 6 minute induction time. All induction times are given in minutes unless otherwise specified.
The DSC inductin time measurements were made as follows: Test batches of ethylene polymer compositions were prepared on a two roll mill on which were blended 100 gram batches of ethylene polymer and additives. Minimum fluxing temperatures were used to avoid premature oxidation effects. The fluxed mixtures were then pressed into plaques about 10 .times. 10 inches with a thickness of 10 mils on a heated hydraulic press. Circular specimens 0.20 inches in diameter were cut from the 10 mils plaques and then placed in aluminum sample holders of the Differential Scanning Calorimeter (DSC) cell. In each case the sample holder plus sample were then placed on the raised sample position while an empty aluminum sample holder was placed on the raised reference position. Nitrogen was passed through the assembled DSC cell at a gas flow rate of 500 ml./min. blanketing the sample and reference cells with an inert atmosphere. The sample and reference cells were then heated at a programmed rate of 80.degree.C. per minute to a preselected isothermal temperature. When equilibrium temperature was obtained, an accurate millivolt recorder (with a 1 inch per minute linear chart speed and a 0 to 25 millivolts chart span) began to record the amplified differential thermocouple signal from the DSC cell. After one inch of chart travel the nitrogen flow was rapidly stopped and air was passed through the DSC cell, also at a flow rate of 500 ml per minute. The sharp inflection in the exothermic direction of the recorded curve indicated the end of the induction period. Since the induction time is that period of time during which there is no exotherm or thermal oxidative degradation, it is a measure of the effectiveness of thermal stabilizing additives which have been compounded with the ethylene polymers. A direct comparison between controls and the compositions of this invention is therefore provided by this induction time measurement.
The exposure time required for embrittlement, hereinafter also referred to as "Embr.", to occur is listed in Table I, Parts A and B, as well as the time required for the surface carbonyl level to exceed 1.7, hereinafter also referred to as "FMIR R>1.7" and the ultimate elongation to fall below 20%, hereinafter also referred to as ".ltoreq. 20% Elong." The effect of the added polypropylene in Control C in promoting embrittlement is to reduce the exposure time required for embittlement to occur as compared to Control B without polypropylene. The effect of the cobalt metal salt in Control A is to reduce the exposure time required for embrittlement over that necessary in Controls B or C without cobalt. The effect of the combined system of this invention is to produce an interaction which promotes embrittlement at a much faster rate than is observed for any of the controls. This embrittlement effect is also polypropylene concentration dependent; that is the exposure time required for embrittlement to occur decreases as the polypropylene concentration increases and in all instances embrittlement of the ethylene polymer compositions of this invention proceeded faster than in Controls A, B or C.
TABLE I __________________________________________________________________________ Ethylene Polymer Exposure Times Required, Hours Composition, % by weight PART A PART B __________________________________________________________________________ FMIR FMIR LDPE PP Co Embr. R>1.7 .ltoreq.20% ELONG. Embr. R>1.7 .ltoreq.20% __________________________________________________________________________ ELONG. 70 30 0.10 60 60-150 20 20 60-150 0-20 80 20 0.10 20-60 60-150 20 20 60-150 0-20 90 10 0.10 60 60 60 20 20 0-20 95 5 0.10 100 60 100 60-100 20-60 60 98 2 0.10 150 60 150 100-150 20-60 100 99.6 0.3 0.10 150-250 60 150 150-250 20-60 100 99.8 0.1 0.10 150 60-150 150 60-250 60-100 60 100* 0 0.10 250 60 150 250 20-60 150 100** 0 0 >1000 >150 >500 1000 150 500 90*** 10 0 750 750 500 500 500 500 __________________________________________________________________________ *Control A **Control B, contains an amount of mineral spirits equal to that present in all other samples. ***Control C
TABLE II ______________________________________ Ethylene Polymer Exposure Times Required, Hours Composition, % PART A ______________________________________ FMIR LDPE Co Embr. R>1.7 .ltoreq.20% ELONG. ______________________________________ 96 2 200-250 150 250 97 1 200 150 150-250 98 0.10 100-150 100-150 150 98 0.075 100-150 100-150 150 98 0.050 150 100-150 150 98 0.025 100-150 150 150 98 0.010 150 150-200 150-250 PART B FMIR LDPE Co Embr. R>1.7 .ltoreq.20% ELONG. ______________________________________ 96 2 200-250 150 150-250 97 1 150-200 150 150-250 98 0.10 100-150 60 150 98 0.075 100-150 60 150 98 0.050 60-100 60 150 98 0.025 100-150 150 150 98 0.010 100 60 60-150 ______________________________________
Ethylene polymer compositions containing a 0.922 density LDPE as the base resin, polypropylene (98% isotactic) in amounts of 0%, 2%, 5% and 10% and 0.10% cobalt metal as cobalt naphthenate solution in mineral spirits were prepared. A control sample consisting of the base resin alone was also prepared. All of the above compositions contained the usual slip (oleamide), antiblock (silica), and antioxidant (2,6-ditert-butyl-4-methylphenol), system in the conventional amounts used in commercial LDPE. These compositions were extruded through a 1 inch NRM extruder at 400.degree.F and reextruded through the extruder until the composition had been reextruded five times. After each pass a 20 mils plaque was fabricated, tested for physical properties, and weathered according to the aforementioned procedures.
Ethylene polymer compositions containing of a 0.922 density LDPE as the base resin, 1.16% polypropylene as the auto-oxidative susceptible additive, (98% isotactic) and 0.05% of cobalt metal as the following salts: (1) solid cobalt acetate, (2) cobalt octoate solution in mineral spirits, (3) cobalt naphthenate solution in mineral spirits, and (4) the cobalt salts of a mixture of branched C.sub.8 and C.sub.9 acids in mineral spirits, known as cobalt Nuxtra. These compositions were fabricated into 20 mils plaques and weathered according to the aforementioned procedures. The exposure times required for embrittlement to occur, surface carbonyl level to exceed 1.7, and ultimate elongation to drop below 20% are listed in Part A of Table III. All of the cobalt salt forms were active and promoted accelerated embrittlement in 200 hours exposure or less. The salts dispersed in mineral spirits show enhanced activity, with the naphthenate being the most active form in the 1.16% polypropylene compositions.
Ethylene polymer compositions identical to the above in every way, but containing a 0.922 g/cc density polyethylene base resin, 6.48% polypropylene as the auto-oxidative susceptible additive and 0.10% cobalt metal from each of the same cobalt salts were prepared. The exposure times required for the above phenomena to occur are listed in part B of Table III. All of the cobalt salt forms were active and promoted accelerated embrittlement in 200 hours exposure or less. The salts dispersed in mineral spirits show enhanced activity in the 6.48% polypropylene compositions. All of the octoate, naphthenate, or mixed branched C.sub.8 and C.sub.9 acid salts of cobalt show comparable effectiveness in causing accelerated embrittlement in combination with polypropylene in the preferred range of 1 to 6.5% in low density polyethylene.
TABLE III ______________________________________ PART A Exposure Times Required, Hours ______________________________________ FMIR Co Salt Embr. R>1.7 .ltoreq.20% ELONG. ______________________________________ Acetate 200 >150 >150 Octoate 150-200 150 100-150 Naphthenate 150 100 100 Nuxtra 150-200 100 100-150 PART B Exposure Times Required, Hours ______________________________________ FMIR Co Salt Embr. R>1.7 .ltoreq.20% ELONG. ______________________________________ Acetate 200 >150 >150 Octoate 100 150 60 Naphthenate 100 100 60-100 Nuxtra 150 150 60-100 ______________________________________
TABLE IV ______________________________________ PART A Exposure Time Required, Hours ______________________________________ FMIR Salt Embr. R>1.7 .ltoreq.20% ELONG. ______________________________________ Co Octoate 150 60-150 60 Fe Octoate 100 60 60 Mn Octoate 150 150 150 Ce Naphthenate 150 150-250 Zn Octoate 250 150 Pb Octoate 250-500 150.sup.+ Zr Octoate 500 Ca Octoate 500 PART B Exposure Time Required, Hours ______________________________________ FMIR Salt Embr. R>1.7 .ltoreq.20% ELONG. ______________________________________ Co Octoate 150 60 60 Fe Octoate 150 60 150 Mn Octoate 150 150 150 Ce Naphthenate 150 150-250 Zn Octoate 250 150 Pb Octoate 250-500 Zr Octoate 500 Ca Octoate 500 250.sup.+ ______________________________________
TABLE V ______________________________________ Run 1 2 3 4 Control ______________________________________ LDPE,% 98 98 95 95 100 PP,% 2 2 5 5 0 Co,% 0.05 0.1 0.05 0.1 0 Fe,% 0.05 0 0.05 0 0 Exposure Time Required, Hours Embr. 60-100 150 100-150 100 >750 FMIR R>1.7 60 60 60 60 -- .ltoreq.20% ELONG. 60 150 60 100 -- ______________________________________
EXAMPLE XIII An ethylene polymer composition containing 98% of a 0.922 density polyethylene (LDPE) as base resin, 2% polypropylene (98% isotactic) as auto-oxidative susceptible additive and 0.075% cobalt metal as a cobalt octaote solution in mineral spirits was prepared according to the procedure aforedescribed. Another composition as above was prepared additionally including a stabilizer system consisting of 0.05% Topanol CA, and 0.15% dilauryl thiodipropionate. Control specimens (1) containing 2% polypropylene in the aforesaid LDPE and (2) neat LDPE, were also prepared. All of the aforementioned compositions were pressed into 20 mils plaques and weathered by the aforementioned procedures. All of the aforementioned samples were pressed into 10 mil plaques for isothermal DSC induction time analyses at 180.degree.C. according to the procedure as aforedescribed. The stabilized composition had an induction period of 14.1 minute at 180.degree.C. while the unstabilized composition had a 0.25 minute induction time at 180.degree.C. The controls had induction times at 180.degree.C. of 0.40 and 0.16 minute respectively.
Ethylene polymer compositions of (1) 90% of a 0.922 density LDPE as base resin, 10% polypropylene (98% isotactic) as auto-oxidative susceptible additive and 0.10% cobalt metal as cobalt naphthenate solution in mineral spirits, and (2) 98% of the LDPE, 2% polypropylene (98% isotactic) and 0.025% cobalt metal as above, were prepared both with a stabilization system containing (a) 0.05% of a primary hindered phenol anti-oxidant AO (i.e. Irganox-1010) having four sterically hindered phenol groups linked to a central carbon by fatty acid ester linkages; (b) 0.05% of dilauryl thiodipropionate (DLTDP) and (c) 0.05% of distearyl pentaerythritol diphosphite (DSPD). Control samples which did not contain the stabilization system were also prepared. The compositions were pressed into 20 mils plaques and weathered by the aforementioned procedures. They were also pressed into 10 mils plaques for isothermal DSC induction time analysis at 180.degree.C.
The exposure times required for embrittlement, surface carbonyl level to exceed 1.7 and ultimate elongation to drop below 20% are listed in Part A of Table VI. The isothermal DSC induction times obtained at 180.degree.C. are also reported in Part A of Table VI. The exposure time for the stabilized samples at which ultimate elongation deteriorates below 20% when compared with the exposure time required for the unstabilized control samples was found to be slightly longer. The presence of stabilizers in the second formulation has a more noticeable effect on these properties (elongation deterioration and surface carbonyl level build-up); but does not retard the embrittlement occurrence significantly. The isothermal DSC induction time data indicates that in the absence of weatherometer exposure these samples are quite stable and have considerable long induction times at 180.degree.C.
TABLE VI __________________________________________________________________________ PART A (Unirradiated) FMIR %PP %Co %AO %DSPD Embr. R>1.7 .ltoreq.20%ELONG. DSC Induction Time, __________________________________________________________________________ Min. 10 0.10 0.05 0.05 150 150 150 24.8 2 0.025 0.05 0.05 150 150-250 150-250 26.7 CONTROLS 10 0.10 0 0 150 150 60 0.10 2 0.025 0 0 150 150 150 0.14 PART B (5 Megareps irradiation) 10 0.10 0.05 0.05 150 150 60 0.12 2 0.025 0.05 0.05 150 150 60-100 0.13 __________________________________________________________________________
An ethylene polymer composition containing 95% as base resin, 5% polypropylene (98% isotactic) as the auto-oxidative susceptible additive and a mixture of 0.05% cobalt as cobalt octoate and 0.05% iron as iron octoate in mineral spirits solution was prepared that also contained a stabilization system consisting of 0.05% of a hindered phenol antioxidant (Irganox-1010), 0.15% of a thioester (dilauryl thiodipropionate) and 0.05% of distearyl pentaerythritoldiphosphite. A sample as above, but excluding the stabilization system, and a control sample containing only the aforesaid 5% polypropylene mixture in 95% LDPE were also prepared. Specimens were pressed as 20 mils plaques and weathered by the aforementioned procedures. Specimens were also pressed into 10 mils plaques for isothermal DSC induction time analysis at 180.degree.C. as aforedescribed.
Both the stabilized and the unstabilized plaques embrittled after 60 hrs exposure in the weatherometer. The control sample of LDPE and polypropylene only embrittled after 500 hours exposure. The stabilized sample had a 19.6 minutes DSC induction time at 180.degree.C., while the unstabilized sample had a 0.76 minute DSC induction time. The control sample had a 0.28 minute DSC induction time.
Specimens as above were irradiated prior to testing. Both the irradiated-stabilized and the irradiated-unstabilized samples embrittled after 60 hours of exposure in the weatherometer and the control embrittled after 250 hours of exposure. The irradiated-stabilized sample had a 1.4 minute DSC induction time at 180.degree.C. The irradiated-unstabilized sample had a 0.11 minute DSC induction time and the irradiated control had a 0.20 minute induction time.
This example demonstrates the use of several different antioxidants in ethylene polymer compositions containing 95% of a 0.928 density LDPE as the base resin, 5% polypropylene (98% isotactic) as the auto-oxidative susceptible additive and a mixture of 0.05% cobalt as cobalt octoate and 0.05% iron as iron octoate in mineral spirits. Each composition contained 0.05% of each of the following sterically hindered phenol antioxidants: Irganox 1010, Santox R, Topanol CA, Irganox 1076, and Ionol. Test specimens were prepared as 10 mils plaques and the isothermal DSC induction time measured at 180.degree.C. The DSC induction times were 9.8, 12.5, 6.2, and 3.5, respectively, for the compositions containing the indicated antioxidants.
An ethylene polymer composition containing 98% of a 0.928 density polyethylene as the resin, 2% polypropylene (98% isotactic) as the auto-oxidative susceptible additive and a mixture of 0.025% cobalt as cobalt octoate and 0.025% iron as iron octoate in mineral spirits was prepared using 0.05% of the antioxidant Irganox 1010. A second sample as above, but additionally containing 0.05% of distearyl pentaerythritol diphosphite was prepared. A third sample identical with the second sample, but additionally including 0.15% of dilauryl thiodipropionate was prepared. Test specimens were prepared from each as 10 mils plaques and the isothermal DSC induction times at 180.degree.C. measured. The DSC induction times at 180.degree.C. for the first, second and third samples were, respectively, 7.9, 10.0 and 15.0 minutes
An ehtylene polymer composition containing 99% of a 0.928 density polyethylene as base resin, 1% polypropylene (98% isotactic) as auto-oxidative susceptible additive and a mixture of 0.0125% cobalt metal as cobalt octoate and 0.0125% iron as iron octoate (0.025% mixture) and additionally including 0.05% of the hindered phenol antioxidant, Irganox-1010, and 0.05% of distearyl pentaerythritol diphosphite was prepared. A second sample as above, but containing 98% polyethylene, 2% polypropylene and 0.05% of the above organic metal salts mixture was prepared. A third sample as above, but containing 95% polyethylene, 5% polypropylene and 0.10% of the above organic metal salts mixture was prepared. Test specimens were fabricated as pressed 10 mils plaques and the isothermal DSC induction times at 180.degree.C. and 200.degree.C. were measured. The samples were aged in a forced air oven at 43.degree.C. (100.degree.F) for 1500 hours without showing any significant loss in isothermal DSC induction time at 200.degree. C. However when exposed to a UV lamp for 8 hours, the isothermal DSC induction times at 180.degree.C. decreased by 99.5%, 99.0% and 86.0% respectively, and there was found to be no measurable induction time at 200.degree.C., indicating loss of stability of the compositions exposed to UV.
Ethylene polymer compositions similar to those described in Example XVIII were prepared containing 0.10% of the hindered phenol antioxidant and 0.10% of distearyl pentaerythritol disphosphite. The test plaques having increased antioxidant content showed the same stability behavior upon oven aging at 43.degree.C. (110.degree.) for 1500 hours, and the same percentage loss of DSC induction time at 180.degree.C. after 8 hours of ultraviolet exposure as reported in Example XVIII.
Test plaques of the compositions of Example XVIII were irradiated by a van de Graaff generator to impart a 5 megarep dose. This irradiation resulted in an 80% to 55% decrease isothermal DSC induction time at 180.degree.C.
Plaques of the compositions of Example XVIII were irradiated by exposure to the intense light emanating from an argon swirl-flow plasma arc having 30% of the light content below 4000 A. for a 6 second exposure; this resulted in a 28% to 43% decrease in isothermal DSC induction time at 180.degree.C.
Plaques of the compositions of Example XVIII were irradiated by ultraviolet light from a mercury lamp for 8 hours; this resulted in a 99.5% to 86% decrease in isothermal DSC induction time at 180.degree.C.
An ethylene polymer composition containing 98% of a 0.922 density LDPE as base resin, 2% polypropylene (98% isotactic) as the auto-oxidative susceptible additive, 0.05% cobalt as cobalt octoate, and 0.05% of the hindered phenol antioxidant, Irganox-1010, was prepared. Test samples were pressed as 10 mils plaques in the manner aforedescribed and irradiated with dosages of 0, 1, 2, 5, 7 and 10 megareps by the van de Graaff accelerator. These specimens were examined by isothermal DSC analysis for induction times at 180.degree.C. and it was found that a dose of 1, 2, 5 and 10 megareps is sufficient to reduce the isothermal DSC induction time at 180.degree.C. by 55%, 73%, 84% and 99%, respectively, when compared to the unirradiated composition.
TABLE VII __________________________________________________________________________ Exposure Times Required, Hours PART A FMIR SURFACE %PE %PEO %Co Embr. R>1.7 .ltoreq.20%ELONG. CRACKS __________________________________________________________________________ 98 2 0.05 500 250 500 99.5 0.5 0.05 500 60 60-150 150 CONTROLS 100 0 0 >1000 98 2 0 750 100 0 0.05 250 150 150 500 PART B FMIR SURFACE %PE %PEO %Co Embr. R>1.7 .ltoreq.20%ELONG. CRACKS __________________________________________________________________________ 98 2 0.05 500 150 250 250 99.5 0.5 0.05 150 60 60 150 CONTROLS 100 0 0 1000 150 500 98 2 0 750 100 0 0.05 250 60 150 250 __________________________________________________________________________
Ethylene polymer compositions containing ethylene acrylic acid (EAA) copolymer have an acrylic acid content of 2% as base resin with 0.05% cobalt metal as the following salts: solid cobalt acetate, cobalt octoate solution in mineral spirits, cobalt naphthenate solution in mineral spirits, and the cobalt salts of a mixture of branched C.sub.8 and C.sub.9 acids, known as Nuxtra, were prepared. Compositions of an EAA copolymer having a 7% acrylic acid content with 0.10% cobalt metal as these same metal salts were also prepared. The compositions were pressed into 20 mils plaques and weathered by the aforementioned procedures. The exposure times required for embrittlement to occur, the ultimate elongation to drop below 20%, and cracking to occur are listed in Part A of Table VIII. In the 2% AA copolymer samples all forms of cobalt salts tested were active in promoting accelerated degradation. In the 7% AA copolymer samples embrittlement occurs less rapidly, but the appearance of surface cracks occurs earlier than for the 2% AA copolymer samples. All forms of cobalt as listed above are active in promoting degradation.
TABLE VIII __________________________________________________________________________ Exposure Times Required, Hours PART A %AA %Co Co Salt Embr. .ltoreq.20%ELONG. CRACKING __________________________________________________________________________ 2 0.05 Acetate 250 150 200 2 0.05 Octoate 100 100 200 2 0.05 Naphthenate 100 100 200 2 0.05 Nuxtra 150 100-150 200 7 0.10 Acetate >250 150 7 0.10 Octoate >250 100 7 0.10 Naphthenate >250 150 7 0.10 Nuxtra >250 150 PART B %AA %Co Co Salt Embr. CRACKING Unexposed Embr. __________________________________________________________________________ 2 1.0 Acetate 150 250 .ltoreq.3 mos 2 0.1 Acetate 150 250 .ltoreq.3 mos 2 0.05 Acetate 150 200 .ltoreq.3 mos 2 0 500 7 1.0 Acetate 500 100 .ltoreq.3 mos 7 0.1 Acetate 250 150 4-6 mos 7 0.05 Acetate 500 150 3-4 mos 7 0 500 __________________________________________________________________________
Ethylene polymer compositions were produced containing a low density polyethylene as the base resin (0.922 g/cc) and the following concentrations, in percent by weight of the composition, 2% of isotactic polypropylene as the auto-oxidative susceptible additive, and transition metal atoms and antioxidants as shown in the table. The homogeneous compositions were then compression molded to obtain 10 mils plaques and these were tested for thermal stability by the DSC induction time method at 200.degree.C. All of the compositions were weathered in an Atlas XW Weatherometer and all embrittled and had ultimate elongations of less than 20% by 150 hours of exposure. The unmodified polyethylene had an original ultimate elongation value of about 400% and this showed no visible change after 150 hours of exposure. The data and results are set forth in TAble IX.
TABLE IX __________________________________________________________________________ Run a b c d e f g h __________________________________________________________________________ Transition metal atom, % cobalt (1) 0.05 0.025 .revreaction. iron (2) -- -- -- -- 0.025 .revreaction. Antioxidant, % A 0.05 .revreaction. B -- 0.075 -- -- -- 0.075 -- -- C -- -- 0.075 -- -- -- 0.075 -- D -- -- -- 0.1 -- -- -- 0.1 DSC Induction Time at 200.degree.C. minutes 5.8 8.2 13.5 19.6 2.5 3 7.5 4.6 __________________________________________________________________________ Run i j k l m n o __________________________________________________________________________ Transition metal atom, % cobalt (1) -- -- -- -- 0.05 .revreaction. iron (2) 0.05 .revreaction. -- -- -- Antioxidant, % A .revreaction. -- -- -- B -- 0.1 -- -- 0.075 -- -- C -- -- 0.075 -- -- 0.075 -- D -- -- -- 0.1 -- -- 0.1 DSC Induction Time at 200.degree.C. minutes 0.05 1.5 1.5 -- 0.08 0.8 0.1 __________________________________________________________________________ (1) 12% cobalt octoate solution in mineral spirits (2) a 50/50 mixture of 12% cobalt octoate and 9% iron Nuxtra mineral spirits. A tetrakis [methylene 3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane B distearyl pentaerythritol diphosphite C adduct of tri(nonylphenyl)phosphite and 1,1,3-tri(5-t-butyl-4-hydroxyl-2-methylphenyl)butane D a mixture of pentaerythritol and the thiodipropionate ester of 1,1,3-tris-(5'-tert-butyl-4'-hydroxy-2'-methylphenyl)butane.
The degradable ethylene polymer compositions were produced by compounding on a two roll mill 97.5 parts of the first masterbatch and 2.5 parts of the second masterbatch. Plaques 10 mils thick were compression molded from the homogeneous blends. Upon weathering all embrittled and all had ultimate elongations of less than 20% by 150 hours of exposure. The DSC induction times at 200.degree.C. in minutes, for each composition tested are set forth below:
Run minutes Run minutes ______________________________________ a 9.6 g 3.0 b 13.6 h 9.8 c 13.3 i 0.05 d 18.9 j 0.15 e 3.0 k 1.0 ______________________________________
The degradable ethylene polymer compositions were produced by compounding on a two roll mill 9.75 parts of the first masterbatch, 2.5 parts of the second masterbatch and 87.75 parts of the third masterbatch. Plaques 10 mils thick were compression molded from the homogeneous blends. Upon weathering all embrittled and all had ultimate elongations of less than 20% by 150 hours of exposure. The DSC induction times at 200.degree.C., in minutes, for each composition tested are set forth below:
Run minutes Run minutes ______________________________________ a 8.5 g 3.8 b 14 h 8 c 11.7 i 0.05 d 19 j 0.1 e 2.9 k 1.1 ______________________________________
Masterbatch 1 2 3 4 Polyethylene 96.0 96.8 97.0 97.96 Cobalt metal 2.0 2.0 2.0 2.0 Antioxidant A 2.0 1.2 1.0 0.04 (Table IX) DSC Induction Time, in minutes, of blends: at 200.degree.C. 11.5 0.1-1.3 0.1 0.1 at 180.degree.C. -- 0.25-3.6 0.2 0.27 at 170.degree.C. -- 6.4 0.15 -- at 160.degree.C. -- -- -- 0.2
The masterbatches per se, before blending with the additional polyethylene and polypropylene, showed DSC induction times at 200.degree.C. in excess of 60 minutes for 1, 2 and 3 and of 37 minutes for 4. The data shows that the masterbatches are far more stable than the degradable compositions prepared from them even though they have a higher metal atom content.
The dry blended degradable ethylene polymer composition produced in Part 1 of Example XXXVII was hot extruded on a one inch extruder to form a uniform sheet from 20 to 30 mils thick. A portion of the sheet was then compression molded to form a 10 mils plaque which had a thermal stability by the DSC induction time method at 200.degree.C. of 25.9 minutes. Another portion of the sheet was compounded on a hot two roll mill and then compression molded to form a 10 mils plaque which had an induction time of 28.3 minutes.
Mixtures of cobalt octoate in solution in mineral spirits and the proper amounts of antioxidant were coated onto finely divided silica to produce freeflowing dry powders that were used to prepare degradable ethylene polymer compositions. Three degradable compositions were prepared by compounding on a two roll mill and then 10 mils thick plaques were produced by compression molding. The degradable compositions and their DSC induction times at 200.degree.C. are set forth below:
Composition 1 2 3 ______________________________________ Polyethylene (0.922 g/cc),% 97.3 97.2 97.2 Polypropylene, % 2 2 2 Cobalt metal, % 0.05 0.05 0.05 Antioxidant (see Table IX) A 0.05 0.05 0.05 B -- 0.075 -- C -- -- 0.075 DSC induction time, min. 17.1 13.5 18.1 ______________________________________
Since degradation is accompanied by a sharp rise in melt index, this property was used to determine whether or not degradation had occurred. The granular materials were stored in air at 80.degree.C. and samples were withdrawn at intervals for melt index measurement. It was observed that the granules of Part 2 showed a sharp rise in melt index and odor development between the fourth and sixth week of storage while the granules of Part 1 showed no signs of melt index rise or odor development. The results are set forth below:
Melt index, dgm/min. Part 1 Part 2 ______________________________________ Unaged 2.01 1.92 One week 2.15 2.13 Two weeks 1.94 2.05 Three weeks 1.66 1.88 Four weeks 1.92 2.21 Six weeks 2.13 7.55 ______________________________________
Melt index. dgm/min. Part 1 Part 2 ______________________________________ On removal 2.13 7.55 One week later 1.93 35.7 Two weeks later 1.99 47.2 ______________________________________
TABLE X __________________________________________________________________________ Hours required for Hours required for cracking failure __________________________________________________________________________ Run a b c d a b c d Polypropylene,% 0 1 2 5 0 1 2 5 Ethyl acrylate content of copolymer, % 1.7 200 .fwdarw. 750 500 500 250 7.7 >750 500 500 350 350 250-350 .fwdarw. 200 12 >750 350 .fwdarw. 350 250 250-350 .fwdarw. 15 350 .fwdarw. 500-750 250 .fwdarw. 18 .rarw. >750 .fwdarw. 350 500 250 .fwdarw. 25 >750 >750 >500 350 250-350 200 250 250 __________________________________________________________________________
TABLE XI __________________________________________________________________________ Composition a b c d e f g h i j __________________________________________________________________________ Ferrous stearate, % 0 0.1 0.15 0.25 0 0.1 0.15 0.25 0.1 0.25 Antioxidant, % A 0.02 0.02 0.03 0.05 0.02 0.02 0.03 0.05 0.04 0.1 C .04 .04 .06 .1 .04 .04 .06 .1 .08 .2 UV Stabilizer, % E 0 0 0 0 .1 .1 .15 .25 .4 .1 Titanium dioxide, % 0 0 0 0 0 0 0 0 0 0 __________________________________________________________________________ Composition k l m n o p q r s t __________________________________________________________________________ Ferrous stearate, % 0 0.1 0.15 0.25 0 0.1 0.15 0.25 0.1 0.25 Antioxidant, % A 0.02 0.02 0.03 0.05 0.02 0.02 0.03 0.05 0.04 0.1 C .04 .04 .06 .1 .04 .04 .06 .1 .08 .2 UV Stabilizer, % E 0 0 0 0 .1 .1 .15 .25 .4 .1 Titanium dioxide, % 2 2 2 2 2 2 2 2 2 2 __________________________________________________________________________ A and C - See Table IX E - 2-(2'hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole
2984641 May 1961 Wolinsky
3341357 September 1967 Field
3575904 April 1971 Clarke
3592792 July 1971 Newland et al.
3825627 July 1974 McGaugh
Chemical & Engineering News Guillets, May 11, 1970, p. 61. "Polyethylene," by Raff et al., p. 99, Interscience Publ., N.Y., 1956. "Autoxidation and Antioxidants," by Lundbe rg, Vols. I & 11, Interscience Publ., N.Y., 1964. Mechanisms of Oxidation of Organic Compounds," by Waters, John Wiley & Sons, N.Y., 1964, pp. 13-14.
Patent number: 3935141
Filed: Jun 28, 1972
Inventors: James Edward Potts (Bernards Township, NJ), Stephen Watson Cornell (Dunellen, NJ), Albert Martin Sracic (Gladstone, NJ)
Attorney: James J. O'Connell
Application Number: 5/267,255
Current U.S. Class: 260/23H; 260/23AR; 260/23S; 260/312R; 260/328A; 260/332R; 260/336PQ; 260/457P; 260/4575; 260/4585; 260/459R; 260/459NC; 260/4595; 260/897A; 260/897R; Promoting Degradability Of Polymers (260/DIG43)