WO1995034597A1

WO1995034597A1 - Propylene polymer compositions, methods therefor, and articles therefrom

Info

Publication number: WO1995034597A1
Application number: PCT/US1995/007227
Authority: WO
Inventors: Bruce Kaduk; Keith Dawes; George Pieslak
Original assignee: Raychem Corporation
Priority date: 1994-06-10
Filing date: 1995-06-05
Publication date: 1995-12-21
Also published as: CA2192546A1; KR970704006A; MX9606248A; EP0764182A1; JPH10501297A

Abstract

Certain propylene polymer compositions have been discovered which can be efficiently radiation crosslinked. The crosslinked compositions have markedly improved properties and can be made into heat recoverable articles.

Description

PROPYLENE POLYMER COMPOSITIONS, METHODS THEREFOR, AND ARTICLES THEREFROM

Technical Field of the Invention

This invention relates to propylene polymer compositions, methods of crosslinking them, and articles made from compositions so crosslinked.

Background of the Invention

Propylene homopolymer is preferred over ethylene homopolymer for many applications because of the higher flexural modulus associated with its higher crystalline melting point. However, propylene homopolymer has one disadvantage — while the properties of ethylene homopolymer can be improved by crosslinking, it generally is not possible to do so with propylene homopolymer. Common treatments such as peroxide or radiation (gamma or electron beam) are ineffective in the presence of oxygen because degradation and molecular weight reduction are the preferred reaction pathway for the free radicals generated. Better results are obtained by processing in a nitrogen atmosphere, but such processing is often impractical.

Crosslinked polymers can be made into dimensionally recoverable articles such as fiber, film, tubing, molded parts, and wrap-around sheets. A dimensionally recoverable article is one whose dimensional configuration may be made to change substantially when subjected to a treatment. Usually these articles recover towards an original shape from which they have previously been deformed, but the term "recoverable" as used herein also includes an article which adopts a new configuration, even if not previously deformed. A typical form of dimensionally recoverable article is a heat recoverable article, whose dimensional configuration may be changed by subjecting the article to heat treatment. In their most common form, heat recoverable articles comprise a shrinkable sleeve made from a polymeric material, such as polyethylene or poly(vinylidene fluoride).

In the production of heat recoverable articles, the polymeric material may be cross¬ linked at any stage in the production of the article that will enhance the desired dimensional recoverability. One manner of producing a heat-recoverable article comprises shaping the polymeric material into the desired heat-stable form, subsequently cross-linking the polymeric material, heating the article to a temperature above the crystalline melting point or, for amorphous materials the softening point, as the case may be, of the polymer, deforming the article, and cooling the article whilst in the deformed state so that the deformed state of the article is retained. Since the deformed state of the article is heat unstable, application of heat will cause the article to assume or try to assume its original heat-stable shape. Methods of making dimensionally recoverable articles are disclosed in Cook et al., US 3,086,242 (1963); Cook, US 3,597,372 (1971); Caponigro et al., US 4,200,676 (1980); and Peigneur et al., US 4,803,104 (1989).

Dimensionally recoverable articles made from propylene polymers have hitherto not been practically feasible, given the tendency of such polymers to degrade upon attempted crosslinking, despite their desirability in view of the higher melting point and superior mechanical properties of propylene polymers. Or, where a modicum of crosslinking is observed in a propylene polymer, the level of such crosslinking, as determined by hot modulus and elongation measurements as discussed below, is too low for practical use in dimensionally recoverable articles.

Summary of the Invention

We have discovered that certain propylene polymer compositions unexpectedly crosslink to an unexpectedly high level upon irradiation, so that hot modulus and other properties practically useful for making dimensionally recoverable articles are attained. The present invention contains a number of embodiments, summarized as follows.

In a first embodiment, there is provided a method of making a crosslinked propy¬ lene polymer composition which has high hot modulus and elongation and is suitable for making dimensionally recoverable articles therefrom, the method comprising the steps of:

(a) providing a propylene polymer composition having crystalline propylene blocks and comprising (i) 10 to 60 parts by weight of a first component which is (A) a propylene homopolymer having an isotactic index of at least 80 or (B) a crystalline propylene-ethylene copolymer having a propylene content of at least 85 weight %, based on the weight of the copolymer, and an isotactic index of at least 85 and (ii) 5 to 90 parts by weight of second component which is a copolymer of ethylene and propylene having an ethylene content of 15 to 70 weight %, based on the weight of the second component; and

(b) crosslinking the propylene polymer composition with high energy radiation to provide a crosslinked propylene polymer composition having a hot modu- is of at least 5 psi at 200 °C and an elongation of at least 150 %. The high energy radiation may be gamma-radiation or electron beam radiation. Optionally, the propylene polymer composition may further comprise 5 to 40 parts by weight of a third component which is a polymer containing ethylene repeat units and is insoluble in xylene at 25 °C.

In a second embodiment, there is provided a method of making a dimensionally recoverable article, comprising the steps of:

(a) providing a propylene polymer composition as described above; (b) forming the propylene polymer composition into a shaped article;

(c) crosslinking the propylene polymer composition with high energy radiation to provide a crosslinked propylene polymer composition having a hot modu¬ lus of at least 5 psi at 200 °C and an elongation of at least 150 %;

(d) heating the shaped article to an elevated temperature above the crystalline melting point of the propylene blocks;

(e) deforming the shaped article into a deformed state while at the elevated temperature; and

(f) cooling the shaped article while applying a constraint to hold the shaped article in its deformed state, until a lower temperature below the crystalline melting point of the propylene blocks is reached at which the shaped article retains its deformed state upon removal of the constraint.

In a third embodiment, there is provided a composition of matter which has high hot modulus and elongation and is suitable for making dimensionally recoverable articles therefrom, the composition comprising

(a) a propylene polymer composition as described above and

(b) an effective amount of a radiation crosslinking promoter; which composition of matter has been crosslinked by exposure to high energy radiation and, after crosslinking, has a hot modulus of at least 5 psi at 200 °C and an elongation of at least 150 %. Optionally, the composition of matter further comprises an effective amount of an antioxidant and retains at least one-half of the elongation after crosslinking, upon heat aging at 130 °C (preferably 150 °C) for 1 week.

In a fourth embodiment, there is provided a dimensionally recoverable article made from the crosslinked composition of matter described above. In a fifth embodiment, there is provided a combination comprising (a) a propylene polymer composition as described above and (b) a radiation crosslinking promoter in an amount effective to cause the propylene polymer composition to crosslink upon exposure to high energy radiation and to have, after such crosslinking, a hot modulus of at least 5 psi at 200 °C and an elongation of at least 150 %.

Description of the Preferred Embodiments

Our invention is based on our discovery that certain propylene polymer compositions unexpectedly respond positively to radiation crosslinking. Instead of degrading via chain scission or other mechanisms, these propylene polymer compositions crosslink effectively, attaining high hot modulus values and elongation, enabling deformation at elevated temperature and subsequent recovery upon the application of heat.

Fujii et al., US 4,454,306 (1984) discloses that certain propylenic block copolymers can be crosslinked by peroxide. However, as shown by the comparative examples herein- below, the amount of crosslinking from peroxide treatment is small and the resulting hot modulus is zero or very low. Generally, the elongation and tensile strength are also unsatis¬ factory for making heat recoverable articles. We have discovered that radiation cross¬ linking is much more effective. Such a result is most unexpected, as the prior art has hitherto viewed peroxide and radiation as functionally equivalent techniques.

The propylene polymer compositions of our invention have crystalline propylene blocks and comprise (i) 10 to 60 parts by weight of a first component which is (A) a propylene homopolymer having an isotactic index of at least 80 or (B) a crystalline propylene-ethylene copolymer having a propylene content of at least 85 weight %, based on the weight of the copolymer, and an isotactic index of at least 85 and (ii) 5 to 90 parts by weight of second component which is a copolymer of ethylene and propylene having an ethylene content of 15 to 70 weight %, based on the weight of the second component. The second component preferably is soluble in xylene at 25 °C. Preferably, the propylene polymer composition is substantially free of carbon-carbon unsaturation, such as would be introduced by a diene comonomer. Propylene polymer compositions of this invention preferably are characterized by a crystalline melting point indicative of polyethylene blocks (115 to 125 °C) and a crystalline melting point indicative of polypropylene blocks (155 to 165 °C), with the latter showing a larger exotherm. Optionally, the propylene polymer composition may further comprise 5 to 40 parts by weight of a third component which is a polymer containing ethylene repeat units and is insoluble in xylene at 25 °C.

Suitable propylene polymer compositions may be made by the techniques disclosed in Ceccin et al., US Patents Nos. 5,302,454 (1994); 5,298,561 (1994); and 5,077,327 (1991); Simonazzi et al., "An Outlook On Progress In Propylene-Based Polymer Tech¬ nology," Prog. Polym. Set, Vol. 16, pp. 303-329 (1991); Galli et al., "Advances In Ziegler- Natta Polymerization — Unique Polyolefin Copolymers, Alloys, And Blends Made Directly In The Reactor," Makromol. Chem. Macromol. Symp., Vol. 63, pp. 19-54 (1992); Klimek, "Property And Cost Advantages Of In-Situ Thermoplastic Olefins," SAE Inter¬ national Congress & Exposition (Feb.-Mar. 1995); Klimek, "In-Situ Thermoplastic Olefins For Automotive Injection And Blow Molding Applications," ECM/ Automotive TPO Con¬ ference (Oct. 1994); Klimek, "New Impact Copolymer Polypropylenes For FDA Applications," SPO '93 (Oct. 1993); the disclosures of which are incorporated herein by reference. Exemplary suitable commercially available propylene polymer compositions include KS 02 IP and Hifax CA 12E from Himont, Inc., of Wilmington, Delaware, and Quantum TP 1300 from Quantum Chemical Company, of Morris, Illinois.

Prior art documents relating to the crosslinking of propylene polymers have generally reported results of gel content (or fraction) measurements after attempted crosslinking, with the finding of a significant gel content being reported as a positive result. We have discovered that the finding of a gel content alone is not sufficiently diagnostic of the development of the physical properties required for a propylene polymer to be useful for making dimensionally recoverable articles. Rather, we have discovered that hot modulus, elongation, and tensile strength (especially the first two) are the critical parameters. A material which is found to have significant gel content may nevertheless have very poor hot modulus and/or elongation values, leaving it still unsuitable for making dimensionally recoverable articles.

The hot modulus or M₁₀₀ is a measurement of the tensile strength of a polymer at 100 % elongation and a specified temperature (normally above the crystalline melting point or T_m of the polymer). A sample is deemed to have failed, or have a zero M₁₀₀ value, if it breaks before it attains 100 % elongation. Herein, M₁₀₀ measurements are made at 200 °C. Crosslinked polymer compositions of this invention preferably have an M₁₀₀ of at least 5, more preferably at least 25, and most preferably at least 50 psi. Preferably, the M₁₀₀ is no greater than 200 psi. Dimensionally recoverable articles made from high M₁₀₀ polymer are desirable because such articles recover faster and with higher recovery forces and are less susceptible to amnesia.

The elongation of crosslinked propylene polymer compositions of this invention is at least 150 %, preferably at least 250 %. Preferably, the elongation is no greater than 2,000 %. Accordingly, crosslinked propylene polymer compositions according to this invention have a hot modulus of at least 5 psi at 200 °C and an elongation of at least 150 %. Further the tensile strength preferably is at least 1,500 psi, more preferably at least 2,500 psi. Preferably, the tensile strength is no greater than 10,000 psi. Thus, in a preferred subcombination, such compositions also have a tensile strength of at least 1,500 psi.

The high energy radiation for crosslinking can be in the form of accelerated electrons from an electron beam or gamma rays from a radioactive source (e.g., cobalt-60). Irradiation is generally carried out at about room temperature, but higher temperatures can also be used. The dosage employed depends upon the extent of crosslinking desired, balanced against the tendency of the polymer composition to be degraded by too high doses of radiation. Suitable dosages generally are in the range of 2 to 40 Mrads. We have further discovered that the polymer compositions of our invention are efficiently crosslinked in an air (oxygenated) atmosphere, without requiring an inert atmosphere such as nitrogen. This result is unexpected because it is known that oxygen can react with free radicals and interfere with the crosslinking process and lead to degradation, particularly in the case of the longer-lived, more oxidation susceptible propylene radicals. For applications where an adhesive is to be applied to the crosslinked material, high beam doses are preferably avoided, as we have found a tendency towards reduced adherability at higher beam doses.

The efficiency of radiation crosslinking may be increased by adding an effective amount of a radiation crosslinking promoter (or prorad) to the propylene polymer com¬ position, forming an intimate mixture or blend. Generally, prorads are compounds having at least two ethylenic double bonds, present as allyl, methallyl, propargyl, acrylyl, or vinyl groups. Examples of suitable prorads include triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), triallyl trimellitate, triallyl trimesate, tetraallyl pyromellitate, the diallyl ester of l,l,3-trimethyl-5-carboxy-3-(p-carboxyphenyl)indane, diallyl adipate, diallyl phthalate (DAP), diallyl isophthalate, diallyl terephthalate, 1,4-butylene glycol dimethacrylate, trimethylolpropane trimethacrylate (TMPTM), pentaerythritol trimethacrylate, glycerol propoxy trimethacrylate, liquid poly(l,2-butadiene), tri-(2-acryloxyethyl)isocyanurate, and tri-(2-methacryloxyethyl)isocyanurate, and the like, and combinations thereof. Preferred crosslinking agents are TAIC, TAC, and TMPTM. Other crosslinking agents which can be used are disclosed in US Pat. 3,763,222; 3,840,619; 3,894,118; 3,911,192; 3,970,770; 3,985,716; 3,995,091; 4,031,167; 4,155,823; and 4,353,961, the disclosures of which are incorporated herein by reference. Mixtures of crosslinking promoters can be used.

Preferably, the radiation crosslinking promoter is used in an amount of between 0.1 % and 10 %, more preferably between 1 % and 5 %, per cent by weight based on the weight of the propylene polymer composition.

An effective amount of an antioxidant may be added to the propylene polymer com¬ position to increase its thermal stability, forming an intimate mixture or blend therewith. Suitable antioxidants include alkylated phenols, e.g. those commercially available as Good- rite 3125™, Irganox B225™ Irganox 1010™ (pentaerythrityl tetrakis-3-(3,5-di- ert-butyl- 4-hydroxyphenyl)propionate, Irganox 1035™, Irganox 1076™ (octadecyl 3-(3,5-di-/ert- butyl-4-hydroxyphenyl)propionate), Irganox 3114™ (l,3,5-tris-(3,5-di-tert-butyl-4- hydroxybenzyl)isocyanurate), Topanol CA™ (l,l,3-tris-(5-tert-butyl-4-hydroxy-2- methylphenyl)butane), Irganox 1093™, and Vulkanox BKF™; organic phosphite or phosphates, e.g. dilauryl phosphite and Mark 1178™; alkylidene polyphenols, e.g. Ethanox 330™ (l,3,5-tris-(3,5-di-ter -butyl-4-hydroxybenzyl)mesitylene); thio-bis alkylated phenols, e.g. Santonox R™ (4,4'-thiobis-(3-methyl-6-.ert-butylphenol) and polymerized derivatives thereof; dilauryl thio-dipropionate, e.g. Carstab DLTDP™; dimyristyl thio- dipropionate, e.g. Carstab DMTDP; distearyl thiodipropionate (DSTDP), e.g. Cyanox STDP; amines, e.g. Wingstay 29, and the like. Combinations of antioxidants can be used. Preferably, the antioxidant is used in an amount of between 0.1 % and 5 %, more preferably between 0.2 % and 2 %, per cent by weight based on the weight of the propylene polymer composition. Especially preferred antioxidant packages include the following combina¬ tions (1-2 wt % of each ingredient): (a) Irganox 1010 and DSTDP, (b) oligomerized 4,4'- thiobis(2-(l,l-dimethylethyl)-5-methylphenol) and DSTDP, (c) Irganox 1010 and thiodipropionate polyester (e.g., Poly TDP 2000 from Eastman Chemical Products), and (d) oligomerized 4,4'-thiobis(2-(l,l-dimethylethyl)-5-methylphenol) and Poly TDP 2000; especially packages (a) and (c).

Other additives can also be added: UV stabilizers such as [2,2'-thio-bis(4-t-octyl- phenolato)] n-butylamine nickel, Cyasorb UV 1084, 3,5-di-t-butyl-p-hydroxybenzoic acid, UV Chek AM-240; flame retardants, both halogenated (such as decabromodiphenyl ether, perchloropentacyclodecane, and l,2-bis(tetrabromophthalimido)ethylene) and unhalogenated (such as alumina trihydrate, magnesium hydroxide, and magnesium carbonate); and pigments such as titanium dioxide and carbon black.

The prorad, antioxidant, and other additives may be combined with the propylene polymer composition by any of various blending techniques conventional in the art, such a milling, extrusion, Brabender mixing, and the like.

The propylene polymer compositions of our invention can be used alone or in combination with one or more other polymers, such as ethylene polymers (preferably ethylene-propylene copolymers), linear medium and low density polyethylene, EPDM rubber or high density polyethylene.

Deformation of the articles to their dimensionally recoverable shape can be accomplished by methods such as those disclosed in Cook et al., US 3,086,242 (1963) and Cook, US 3,397,372 (1971), the disclosures of which are incorporated herein by reference. The original dimensionally stable form may be a transient form in a continuous process in which, for example an extruded tube is expanded while hot (e.g. by application of an internal air pressure or an external vacuum) to a dimensionally unstable form but in other applications, a preformed dimensionally stable article is deformed to a dimensionally unstable form in a separate stage. For example, a tubular article may be heated in a bath of a hot fluid and deformed by insertion of a mandrel into the hot tubular article. After deformation, the deformed article is cooled to a lower temperature at which the deformed shape is stable. Recovery during the cooling step is prevented by applying a constraint such as air pressure or mechanical means (e.g., the mandrel); after cooling to the lower temperature, the constraint may be removed.

Besides dimensionally recoverable articles, the crosslinked propylene polymer compositions of this invention find utility as wire insulation, tape, film, fibers, tubing, and molded parts. They are also useful as coatings for crude oil transmission pipelines, which require serviceability at temperatures approaching 140 °C and chemical resistance. The coatings may be applied as a heat-shrinkable coating.

The practice of our invention may be understood by reference to the following examples, which are provided by means of illustration, not limitation. To measure Mj₀₀ values, an Instron tester was set up with an Eurotherm heated chamber at 200 °C and a 2 kg Instron Tension Load Cell. The jaw separation was 50.8 mm (2 in). The crosshead speed was 100 mm/min, with the variable speed control set at 50.8 % to give a 2.0 in/min speed. The extension return limit was set at 50.8 mm (2 in). Test specimens were cut from slabs 0.020 to 0.030 inch thick using a 6 x 0.125 inch strip die. The Instron tester was calibrated using a 100 g weight before the start of each testing period and periodically during the test periods. Each test specimen was measured for width and thickness before analysis using a micrometer. Each test specimen was preheated in the chamber for 3 min, then stretched to 100 % elongation. The tension at 100 % elongation was recorded and divided by the specimen's initial cross sectional area to give the M₁₀₀ value in lb/in² (psi).

To measure tensile strength and elongation, the procedure of ASTM D638-91 was generally followed and is summarized as follows: the Instron tester was set up with a 50 kg Tension Load Cell. The jaw separation was 50.8 mm (2 in). The crosshead speed was 100 mm/min with the variable speed control set at 50.8 % to give a 2.0 in/min speed. The extension return limit was set at 950 mm. Test specimens were cut from slabs 0.020 to 0.030 in thick using a dumbbell shaped D die per ASTM specifications with a reduced section dimension of 0.125 in. The Instron tester was calibrated with a 1,000 g weight before the start of each testing period and periodically during the test periods. Testing was done at ambient (room) laboratory temperature (20 to 25 °C). Each test specimen was measured for width and thickness before analysis using a micrometer. Two bench marks were marked on each specimen with a 1.0 inch (254 mm) separation, centered on the reduced section, in order to measure elongation. The specimens were stretched until break at a crosshead speed of 2 in/min. The elongation between the bench marks was measured with a hand-held ruler. The tension at break was recorded and divided by the specimen's initial cross-sectional area to give the tensile strength in lb/in² (psi). As used herein, the term "elongation" means the elongation at break, also referred to as the ultimate elongation. Similarly, the term "tensile strength" means the tensile strength at break, also referred to as the ultimate tensile strength.

Example 1

This example demonstrates the effective radiation crosslinking of Himont KS 02 IP, a propylene polymer composition according to this invention, compared to the ineffectiveness of peroxide crosslinking. The results are provided in TABLES I (electron beam radiation) and II (peroxide). TABLE I Electron Beam Crosslinking of Himont KS 02 IP Propylene Polymer Composition

Beam Dose M₁₀₀ at 200 °C Room Temperature Room Temperature

Specimen (Mrad) (psi) Elongation (%) Tensile Strength (psi)

A 10 29.0 ± 0.4 395 ± 11 1670 ± 34 B 10 27.9 ± 0.3 410 ± 8 1746 ± 28 C 30 67.8 ± 6.1 305 ± 26 2575 ± 179

Specimen A contained 4 % TAIC, 2 % Irganox 1010, and 1 % DSTDP. Specimen B contained 4 % TAIC, 1 % Irganox 1010, and 2 % TDP 2000. Specimen C contained 4 % TAIC.

TABLE II

Peroxide Crosslinking of Himont KS 02 IP Propylene Polymer Composition

M₁₀₀ at 200 Room Temperature Room Temperature Gel Content

Specimen °C (psi) Elongation (%) Tensile Strength (psi) (wt. %)

D 0 20 ± 10 720 ± 59 —

E 0 170 ± 10 1260 ± 73 52.5

F 0 90 ± 10 903 ± 75 —

G 14.2 ± 3.5 17 ± 6 800 ± 32 —

Specimen D contained 1.23 % Perkadox 14-40B-PD and 0.05 % dibenzothiazole disulfide. Specimen E contained 10.00 % Nisso Polybutadiene B-3000, 1.23 % Perkadox 14-40B-PD, and 0.05 % dibenzothiazole disulfide. Specimen F contained 0.50 % Irganox 1010, 0.50 % TAIC, and 0.50 % 2,5-dimethyl-2,5- di(t-butylperoxy)hexyne-3 (Lupersol 130, Pennwalt). Specimen G contained 0.50 % Irganox 1010, 0.50 % TAIC, and 0.50 % Lupersol 130.

It can be seen from TABLE I that all the radiation crosslinked samples exhibited a combination of high M₁₀o and high elongation values, making them useful for dimensionally recoverable articles. Further, the tensile strengths were also all high.

Turning now to the results in TABLE II, Specimen E is especially noteworthy: Even though it had a gel content of 52.5%, its M₁₀₀ was zero and its elongation was a relatively low 170 %, making it effectively useless for making dimensionally recoverable articles. The only peroxide-treated specimen to develop a measurable M₁₀₀ was Specimen G, but which had a very low elongation of only 17 %, again making it useless for dimensionally recoverable articles. Finally, the tensile strengths also were lower than those obtained in TABLE I. Example 2

In this example, the radiation and peroxide crosslinking of Quantum TP 1300 HC, another propylene polymer composition according to this invention, is studied, analogously to Example 1. The results are provided in TABLES III and IV.

TABLE III Electron Beam Crosslinking of Quantum TP 1300 HC Propylene Polymer Composition

Beam Dose M₁₀₀ at 200 °C Room Temperature Room Temperature

Specimen (Mrad) (psi) Elongation (*'• Tensile Strength (psi)

H 10 6.7 ± 0.2 535 ± 15 3090 ± 94 I 10 8.4 ± 0.5 540 ± 8 3160 ± 27 J 30 16.8 ± 0.2 330 ± 92 2880 ± 749

Specimen H contained 4 % TAIC, 2 % Irganox 1010, and 1 % DSTDP. Specimen I contained 4 % TAIC, 1 % Irganox 1010, and 2 % TDP 2000. Specimen J contained 4 % TAIC and 0.2 % Irganox B 225; Quantum TR 134 was a pre- commercialization version of Quantum TP 1300 HC.

TABLE IV Peroxide Crosslinking of Quantum TP 1300 HC Propylene Polymer Composition

Mjoo at 200 Room Temperature Room Temperature Gel Content

Specimen °C (psi) Elongation f^0/ Tensile Strength (psi) (wt. %)

K 0 6±3 1177±88 13.9

Specimen K contained 1.23 % Perkadox 14-40B-PD and 0.05 % dibenzothiazole disulfide.

As in the case of Example 1, radiation crosslinking produced polymer with acceptable M₁₀₀ and elongation values, but peroxide crosslinking was ineffective.

Example 3

In this example, the crosslinking of propylene polymers of this invention in blends with other polymers is demonstrated. Results are provided in TABLE V. TABLE V

Electron Beam Crosslinking of Propylene Polymer Blends

Polymer Formulation ^a Elonga¬ Tensile

1st Compo¬ 2nd Compo¬ 3rd Compo¬ Beam Mioo at tion at Strength nent (parts by nent (parts by nent (parts by Dose 200 °C 23 °C at 23 °C weight) weight) weight) (Mrad) (psi) (%) (psi)

Himont KS Quantum TP None 10 10 287 2336 021P (20) 1300 HC (73) 30 33

Himont KS Quantum TP None 10 12 360 2477 021P (47) 1300 HC (46) 30 38

Himont KS Moplen Coat None 10 7 323 2823 021P (40) EP/60^b (53) 30 34

Quantum TP Vistalon None 10 16 380 3017 1300 HC (83) 3708 ° (10) 30 43

Quantum TP Chevron None 5 15 355 2150 1300 HC (73) 9606 ^d (20) 15 51 340 2933

Quantum TP Chevron 9606 Vistalon 3708 5 17 490 2593 1300 HC (68) (20) (5) 15 54 290 2817

Each polymer formulation contained the following additive package: 4 parts by weight

TAIC, 1 part by weight Irganox 1010, and 2 parts by weight TDP 2000.

An ethylene-propylene copolymer.

An EPDM rubber.

A high density polyethylene.

Example 4

We performed experiments comparing gamma (cobalt-60 source) and electron beam radiation on various propylene polymers: Himont KS 02 IP, Profax PD 199, Profax SV 256M, and Quantum TR 134. According to nuclear magnetic resonance (NMR) and diffe¬ rential scanning calorimetry (DSC) analysis, Himont KS 02 IP is believed to have isotactic propylene blocks with a T_m of 161 °C and largely amorphous ethylene blocks which nevertheless have a measurable crystallinity content (less than 5 %) and a T_m of 119 °C. The overall crystallinity is about 25 %. The T_m's of the ethylene and propylene blocks correspond closely to those of the respective homopolymers. Profax PD 199 is a propylene homopolymer, with a T_m of 163 °C by DSC. Profax SV 256M is an propylene-ethylene random copolymer. Quantum TR 134 is a heterophasic propylene-ethylene copolymer. Profax 199 and SV 256M are comparative samples not according to this invention.

TABLE VI provides results obtained upon gamma-irradiation in a nitrogen atmosphere. The results show that, of the four polymers, the Himont KS 02 IP and the Quantum TR 134 consistently showed the desired combination of M₁₀o and elongation needed for making heat recoverable articles.

TABLE VI

Irradiation of Propylene Polymers with Gamma Rays under Nitrogen ^a

Beam Mi oo at Room Tempera¬ Room Tempera¬

Propylene Dose 200 °C ture Elongation ture Tensile

Polymer (Mrad) (psi) (%) Strength (psi)

Profax PD 199 0 0 760 ± 70 5500 ±720

10 1.9 ±0.2 470 ± 264 4870 ±150

10 9.2 ± 0.5 301 ± 277 5050 ±105

30 4.4 ± 0.4 111 ±135 4890 ±150

30 37.2 ± 2.7 16±8 4970 ±330

Profax SV 256M 0 0 840 ±30 5680 ±130

10 1.3 ±0.2 669 ± 71 4500 ± 320

10 6.9 ± 0.6 663 ± 34 ^b 4760 ±190

30 35.8 ±2.4 495 ± 80 4240 ±190

30 0 278 ± 84 ^b 4120 ±410

Quantum TR 134 0 0 680 ±115 3230 ±560

10 18.4 ±1.4 535 ±27 4660 ±270

10 32.2 ±1.9 522 ±18 4930 ±105

30 22.6 ±1.1 498 ±11 4330 ±135

30 43.5 ±2.7 479 ±61 4320 ±265

Himont KS021P 0 0 135 ±5 735 ±40

10 89.4 ±3.9 498 ±114 3800 ±225

10 130.1 ±6.1 423 ± 62 3810 ±145

30 88.0 ±6.7 401 ± 16 3635 ± 240

30 98.4 ±0.9 ^c 327 ± 24 3110±430 a Data is average of 5 samples unless noted otherwise. b Based on 3 samples Based on 2 samples

The additive packages used in conjunction with the above materials is listed in TABLE VI(a): TABLE VI(a)

Additive Packages

Mioo at Antioxi¬ Chain trans¬

Propylene Beam Dose 200 °C dant ^a Prorad fer agent

Polymer (Mrad) (psi) (wt. %) (wt %) (wt. %)

Profax PD 199 0 0 0 0 0

10 1.9 ±0.2 0 2 ^c 0

10 9.2 ± 0.5 0 4 ^d 0

30 4.4 ± 0.4 0.2 2 ^c 1.0

30 37.2 ± 2.7 0.2 4 ^d 1.0

Profax SV 256M 0 0 0 0 0

10 1.3 ±0.2 0.2 2 ^e 0

10 6.9 ± 0.6 0.2 4 ^d 0

30 35.8 ±2.4 0 2 ^c 1.0

30 0 0 4 ^d 1.0

Quantum TR 134 0 0 0 0 0

10 18.4 ±1.4 0 2 ^c 1.0

10 32.2 ±1.9 0 4 ^d 1.0

30 22.6 ±1.1 0.2 2 ^c 0

30 43.5 ±2.7 0.2 4 ^d 0

Himont KS 021P 0 0 0 0 0

10 89.4 ± 3.9 0.2 2 ^c 1.0

10 130.1 ±6.1 0.2 4 ^d 1.0

30 88.0 ±6.7 0 2 ^c 0

30 98.4 ±0.9 0 4^d 0

Irganox B225. Tetrachlorobenzene. Triallylisocyanurate (TAIC). Trimethylolpropane trimethacrylate (TMPTM).

TABLE VII provides the results obtained upon irradiation with an electron beam in a nitrogen atmosphere. The data pattern is the same as with gamma, with the Quantum and Himont materials being consistently superior. TABLE VII

Irradiation of Propylene ^'. 'olymers with Electron Beam under Nitrogen ^a

Propylene Beam Mioo Room Tempe¬ Room Temperature

Polymer Dose at200°C rature Elongation Tensile Strength

(Mrad) (psi) (%) (psi)

Profax PD 199 0 0 760 ±70 5500 ±720

10 0.7 ±0.1 677 ± 38 4720 ±105

10 3.4 ± 0.2 290 ± 275 3920 ±900

30 5.8 ±0.1 lO±O 4455 ± 80

30 30.5 ±0.1 25 ±5 ^b 4920 ±250

Profax SV 256M 0 0 840 ± 30 5680 ±130

10 2.5 ±2 675 ± 43 4730 ±205

10 9.4 ± 0.4 572 ± 77 4265 ± 755

30 0 ^c 445 ±18 4295 ±110

30 0 ^c 363 ± 32 4140 ±195

Quantum TR 134 0 0 680 ±115 3230 ±560

10 15.9 ±0.9 567 ±21 4260 ±150

10 14.2 ± 0.6 545 ± 33 4275 ± 475

30 16.1 ±0.2 448 ± 23 3295 ±210

30 0 c 373 ± 23 3145 ±185

Himont KS 021P 0 0 135 ±5 735 ± 40

10 57.6 ± 3.2 437 ± 33 3135 ±100

10 55.1 ±1.9 403 ± 90 2860 ± 280

30 55.9 ±0 408 ± 14 2940 ±60

30 68.3 ±1.1 393 ± 29 3285 ±335 ^a Data is average of 3 samples unless noted otherwise. ^b Based on 2 samples ^c All samples broke at less than 100% elongation

Example 5

TABLE VIII provides the results obtained upon irradiation with an electron beam in air, which is simpler and therefore more desirable from a process point of view. However, the oxygen may intercept free radicals created by the radiation, interfering with the crosslinking process. Therefore, irradiation in air is a more demanding test of the crosslinkability of a polymer. The results in TABLE VIII follow the pattern of TABLES VI and VII. TABLE VIII

Irradiation of Propylene Polymers with Electron Beam in Air

Beam Mioo Room Tempera¬ Room Temperature

Propylene Dose at200°C ture Elongation Tensile Strength Polymer (Mrad) (psi) (%) (psi)

Profax PD 199 0 0 760 ± 70 5500 ± 720

10 0.7 ±0 592 ± 32 4385 ± 385

10 1.5 ±0 593 ± 55 4305 ± 440

30 3.7 ±0.3 5±0 4360 ± 205

30 14.5 ±1.5 5±0 4870 ± 540

Profax SV 256M 0 0 840 ± 30 5680 ±130

10 1.6 ±0.2 658 ± 53 4230 ± 45

10 3.1 ±0.5 433 ±316 3910 ±1055

30 16.7 ±0.6 160 ±148 3115 ±470

30 0 ^a 150 ±132 3360 ±475

Quantum TR 134 0 0 680 ±115 3230 ± 560

10 8.0 ±1.0 537 ±13 4480 ±100

10 13.5 ±0.9 453 ± 45 4105 ±500

30 9.5 ± 0.7 458 ± 38 3310 ±150

30 16.8 ± 0.2 330 ± 92 2880 ± 750

Himont KS 021P 0 0 135 ±5 735 ± 40

10 38.5 ±2.3 453 ±6 3335 ± 580

10 45.9 ±0.7 468 ± 16 3270 ± 580

30 45.9 ±2.4 343 ± 12 2810±310

30 67.8 ±6.1 303 ± 26 2575 ± 100

All samples broke at less than 100% elongation

Example 6

TABLE IX studies the effect of beam dose and various additive packages on the radiation crosslinking in air of the propylene ethylene block copolymers. Two additive packages were used. One package consisted of a prorad alone (A). The other package contained a prorad, a chain transfer agent, and an antioxidant (B). The results show that, in the presence of prorad, electron beam radiation gives practically useful M₁₀₀ and elongation values at dosages as low as 2 Mrad. TABLE IX

Electron Beam Irradiation of Himont KS 02 IP in Air —

Effect of Beam Dosage and Additive Package

Beam Mioo Room Tempera¬ Room Tempe¬

Additive Dose at 200 °C ture Elongation rature Tensile Package (Mrad) (psi) (%) Strength (psi)

None 0 0 135 ± 35 735 ± 40

2 2.4 ± 0.3 130 ± 105 795 ± 40

5 6.3 ± 0.4 150 ± 25 815 ± 20

10 8.0 ± 0.5 300 ± 100 1080 ± 150

20 17.4 ± 0.7 375 ± 150 1385 ± 280

A 2 28.2 ± 1.2 625 ± 0 3475 ± 35

5 36.8 ± 0.8 560 ± 28 3600 ± 500

10 53.4 ± 1.2 500 ± 35 3310 ± 165

20 64.7 ± 5.7 305 ± 149 2080 ± 660

B 2 8.2 ± 0.1 450 ± 71 1180 ± 115

5 24.3 ± 1.2 556 ± 4 2675 ± 75

10 58.1 ± 1.4 463 ± 18 3405 ± 145

20 86.3 ± 4.7 390 ± 21 3330 ± 515

A 4 % trimethylolpropane trimethacrylate (prorad)

B 0.2 % Irganox B225 (antioxidant) plus 1 % 1,2,4,5-tetrachlorobenzene (chain transfer agent) plus 4 % triallylisocyanurate (prorad)

Example 7

Typically, the thermal stability of an irradiated propylene polymer is poor because of the occurrence of radiation-induced degradative processes in competition with radiation- induced crosslinking. To evaluate the thermal stability of irradiated propylene polymers, samples were hung in an 130 °C air circulating oven for one week. If a sample degraded to such an extent that it fell off the hanger (i.e., was unable to sustain its own weight) or tensile and elongation measurements could not be made, it was deemed to have failed the test. Preferably, an aged crosslinked propylene polymer composition according to this invention still has an elongation of at least 100, more preferably at least 200 % and a tensile strength of at least 900, more preferably at least 1,500 psi.

TABLE X provides heat aging results for propylene ethylene block copolymers containing either additive package A or B. Very substantial retentions of the pre-aging elongation and tensile strengths are obtained. It is noted that additive package B, which contains an antioxidant, is more effective, as might be expected. However, the effectiveness of the antioxidant at such a low concentration level is noteworthy.

TABLE X

Heat Aging (1 Week at 130 °C) of Himont KS 021P Propylene Polymer

Electron Beam Irradiation in Air

Beam Room Tempe¬ Room Tempe¬ Pre-Aging

Additive Dose rature Elongation rature Tensile Elongation Package (Mrad) (%) Strength (psi) Retained (%)

A 0 24.5 ± 4.5 1085 ± 125 18.4

2 <10 650 ± 90 <1

5 <10 675 ± 30 <1

B 0 60.0 ± 9.5 1070 ± 100 44.9

2 202.5 ± 22.5 1685 ± 190 45.2

5 405.0 ± 16.5 2485 ± 60 72.5

A 4 % trimethylolpropane trimethacrylate (prorad)

Example 8

Hifax 12E from Himont was pressed into square plaques (6 x 6 in, 15.24 x 15.24 cm) about 40 mils (ca. 1 mm) thick at 200 °C and irradiated in air in an 1 Mev electron beam. For comparison purposes, some other propylene polymers or copolymers outside of the scope of this invention were similarly treated. The results are provided in Table XI.

TABLE XI

Irradiation of Propylene Polymers and Copolymers

Beam Room Tempe¬ Room Tempe¬ M.oo

Polymer Dose rature Elonga¬ rature Tensile at 200 °C

(Mrad) tion (%) Strength (psi) (psi)

Hifax CA 12E 10 223 975 7.5

20 317 1208 18.7

Hifax ETA 3131 * 10 150 2960 Melted

20 — — Melted

Hifax ETA 5081E ^a 10 430 2960 Melted

20 — — Melted

Orevac FT ^a 10 — — Melted

20 — — Melted ^a Control, not according to this invention.

Example 9

In this example, heat aging data after four weeks at 150 °C is provided (TABLE

XII).

TABLE XII

Heat Aging at 150 °C for Four Weeks

Property Himont KS Himont KS Quantum TP

021P ^a 021P ^b 1300 HC ^c

Before aging

Elongation (%) 396 412 536

Tensile Strength (psi) 1,670 1,746 3,089

After aging (4 weeks at 150°C)

Elongation (%) 202 216 228

% Original value retained 51.0 52.4 42.5

Tensile Strength (psi) 1,328 1,436 2,618

% Original value retained 79.5 82.2 84.8

T — . 9.3. wt . _ % pol ;ymer, ; 2. — wt rz %r Irganox 1010, 1 wt % DSTDP, and 4 wt % TAIC. 93 wt polymer, 1 wt % Irganox 1010, 2 wt % TDP 2000, and 4 wt % TAIC. 93 wt % polymer, 2 wt % Irganox 1010, 1 wt % DSTDP, and 4 wt % TAIC. Example 10

This example demonstrates the preparation of heat recoverable tape (which also can be made into a wrap-around sleeve) using the compositions of this invention. Himont KS 021P propylene copolymer containing 4 wt % TAIC and 1.5 wt % oligomerized 4,4'- thiobis(2-(l,l-dimethylethyl)-5-methylphenol) was extruded into tape (9 inches wide x 0.04 inch thick). This tape was irradiated with 30 Mrad in an electron beam to produce tape with an M₁₀o of 31 psi at 200 °C. The irradiated tape was expanded by 18% in a tape expander and then allowed to recover dimensionally by heating in a 200 °C oven for 15 min. The properties of the recovered tape were: tensile strength at break (23 °C), 2,090 psi; elongation at break (23 °C), 490 %; M₁₀₀, 31 psi. After heat aging at 150 °C for one week, the tensile strength was 1,140 psi and the elongation was less than 50 %. The tape was also made into a wrap-around sleeve product which was shrunk onto a 2 inch diameter pipe by heating with a propane torch.

Example 11

This examples demonstrates the preparation of dimensionally recoverable tubing using a polymer composition of this invention. A formulation consisting of 94.8 wt % Himont KS 02 IP propylene copolymer, 1.0 wt % tetrachlorobenzene, 0.2 wt % Irganox B225, and 4 wt % TAIC was compounded on a twin screw extruder. The compound was extruded into 3/32 inch tubing. The tubing was electron-beam irradiated and then expanded three times its initial diameter to give expanded tubing with a diameter of 9/32 inch. The expanded tubing was recovered in an oven at 200 °C for 3 minutes. The recovered tubing had the following properties (TABLE XIII):

TABLE XIII

Properties of Recovered Tubing

Beam Dose Tensile Strength Elongation Mioo (Mrad) (psi) (%) (psi)

Control ^a 4,240 790 n/a

4 3,270 700 l l

8 3,280 560 25

12 2,750 450 36

16 2,670 380 60 a T UTn 1beamed 1 and1 unexpanded sample While we do not wish to be bound by any theory, it is our belief that the unexpected crosslinkability we have observed is associated with the presence of both propylene and ethylene fractions in our compositions, with the crosslinking occurring primarily in the ethylene fractions and at a rate higher than the rate of degradation in the propylene fractions. The especially pronounced increase in crosslinking upon the addition of prorad may be associated with the preferential distribution of the prorad into the less crystalline ethylene phase, as opposed to the more crystalline propylene phase.

The foregoing detailed description of the invention includes passages which are chiefly or exclusively concerned with particular parts or aspects of the invention. It is to be understood that this is for clarity and convenience, that a particular feature may be relevant in more than just the passage in which it is disclosed, and that the disclosure herein in¬ cludes all the appropriate combinations of information found in the different passages. Similarly, although the various passages may relate to specific embodiments of the inven- tion, it is to be understood that where a specific feature is disclosed in the context of a par¬ ticular embodiment, such feature can also be used, to the extent appropriate, in the context of another embodiment, in combination with another feature, or in the invention in general.

Claims

ClaimsWhat is claimed is:

1. A method of making a crosslinked propylene polymer composition which has high hot modulus and elongation and is suitable for making dimensionally recoverable articles therefrom, the method comprising the steps of:

(a) providing a propylene polymer composition having crystalline propylene blocks and comprising

(i) 10 to 60 parts by weight of a first component which is (A) a propylene homopolymer having an isotactic index of at least 80 or

(B) a crystalline propylene-ethylene copolymer having a propylene content of at least 85 weight %, based on the weight of the copolymer, and an isotactic index of at least 85 and (ii) 5 to 90 parts by weight of second component which is a copolymer of ethylene and propylene having an ethylene content of 15 to 70 weight %, based on the weight of the second component; and

(b) crosslinking the propylene polymer composition with high energy radiation to provide a crosslinked propylene polymer composition having a hot modu¬ lus of at least 5 psi at 200 °C and an elongation of at least 150 %.

2. A method according to claim 1 , wherein the propylene polymer composition further comprises 5 to 40 parts by weight of a third component which is a polymer containing ethylene repeat units and being insoluble in xylene at 25 °C.

3. A method according to claim 1 , wherein the polymer composition is substantially free of carbon-carbon unsaturation.

4. A method according to claim 1, wherein the second component is soluble in xylene at 25 °C.

5. A method according to claim 1, wherein the polymer composition has a crystalline melting point between 115 and 125 °C and a further crystalline melting point between 155 and 165 °C, with the latter melting point exhibiting a larger exotherm.

6. A method according to claim 1 , wherein a radiation crosslinking promoter selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, triallyl trimesate, tetraallyl pyromellitate, the diallyl ester of 1,1,3- trimethyl-5-carboxy-3-(p-carboxyphenyl)indane, diallyl adipate, diallyl phthalate, diallyl isophthalate, diallyl terephthalate, 1,4-butylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, glycerol pro- poxy trimethacrylate, liquid poly( 1 ,2-butadiene), tri-(2-acryloxyethyl)isocyanurate, tri-(2-methacryloxyethyl)isocyanurate, and combinations thereof is intimately mixed with the propylene polymer composition prior to exposure to the high energy radiation.

7. A method according to claim 1 , wherein the high energy radiation is electron beam radiation.

8. A method according to claim 1, wherein the crosslinked propylene polymer composition has a hot modulus of at least 25 psi and an elongation of at least 250 %.

9. A method according to claim 1 , wherein the propylene polymer composition is combined with a further polymer selected from the group consisting of ethylene copolymers, EPDM rubber, linear medium density polyethylene, linear low density polyethylene, high density polyethylene, and combinations thereof.

10. A method according to claim 1 , wherein the propylene polymer composition further comprises a stabilizer package selected from the group consisting of (a) (penta- erythrityl tetrakis-3-(3,5-di-/er?-butyl-4-hydroxyphenyl)propionate and distearyl thiodipropionate, (b) oligomerized 4,4'-thiobis(2-(l,l-dimethylethyl)-5-methyl- phenol) and distearyl thiodipropionate, (c) (pentaerythrityl tetrakis-3-(3,5-di-t_τt- butyl-4-hydroxyphenyl)propionate and thiodipropionate polyester, and (d) oligomerized 4,4'-thiobis(2-(l,l-dimethylethyl)-5-methylphenol) and thiodipropionate polyester.

11. A method of making a dimensionally recoverable article, comprising the steps of: (a) providing a propylene polymer composition having crystalline propylene blocks and comprising

(B) a crystalline propylene-ethylene copolymer having a propylene content of at least 85 weight %, based on the weight of the copolymer, and an isotactic index of at least 85 and (ii) 5 to 90 parts by weight of second component which is a copolymer of ethylene and propylene having an ethylene content of 15 to 70 weight %, based on the weight of the second component;

(b) forming the propylene polymer composition into a shaped article;

(c) crosslinking the propylene polymer composition with high energy radiation to provide a crosslinked propylene polymer composition having a hot modu¬ lus of at least 5 psi at 200 °C and an elongation of at least 150 %; (d) heating the shaped article to an elevated temperature above the crystalline melting point of the propylene blocks;

12. A composition of matter which has high hot modulus and elongation and is suitable for making dimensionally recoverable articles therefrom, the composition comprising

(a) a propylene polymer composition having crystalline propylene blocks and comprising

(b) an effective amount of a radiation crosslinking promoter; which composition of matter has been crosslinked by exposure to high energy radiation and, after crosslinking, has a hot modulus of at least 5 psi at 200 °C and an elongation of at least 150 %.

13. A composition of matter according to claim 12, further having a tensile strength and an elongation which are at least as great as those of the corresponding uncrosslinked composition of matter.

14. A composition of matter according to claim 12, further comprising an effective amount of an antioxidant and retaining at least one-half of the elongation after crosslinking, upon heat aging at 130 °C for 1 week.

15. A composition of matter according to claim 12, having an elongation of at least 100 % and a tensile strength of at least 900 psi.

16. A dimensionally recoverable article, made from the composition of matter of claim 12.

17. In combination,

(i) 10 to 60 parts by weight of a first component which is (A) a propylene homopolymer having an isotactic index of at least 80 or (B) a crystalline propylene-ethylene copolymer having a propylene content of at least 85 weight %, based on the weight of the copolymer, and an isotactic index of at least 85 and (ii) 5 to 90 parts by weight of second component which is a copolymer of ethylene and propylene having an ethylene content of 15 to 70 weight %, based on the weight of the second component; and

(b) a radiation crosslinking promoter in an amount effective to cause the propylene polymer composition to crosslink upon exposure to high energy radiation and have, after such crosslinking, a hot modulus of at least 5 psi at 200 °C and an elongation of at least 150 %.

* * * * * * * * * *