Polyolefins are well known commercial polymers, used for a variety of products such as packaging films and extruded and molded shapes. They are produced by polymerization of olefin monomer over transition metal coordination catalysts, specifically titanium halide containing catalysts or single site catalysts. Most commonly used polyolefins include polypropylene, polyethylene and polybutene. The olefin polymer usually has certain limitation in its use for applications, such as wires and cables, due its low surface hardness and structure stability.

It is known that certain polyolefins, especially polyethylene and its copolymers, would be modified either by organic peroxides or by high energy irradiation to improve its hardness and dimensional stability. The organic peroxide is commonly mixed with polyolefin polymers which are extruded to obtain partially crosslinked polyolefins. For example, U. S.

Pat. ITao 9079776 discloses the use of an organic peroxide for crossliaing of polyethylene g and other elastomeric polyolefins. One disadvantage of using an organic peroxide is the scorch formation during the crosslinking reaction due to the localized the heat generation during the crosslinking reaction. Various approaches have been attempted, as disclosed in U.S. Pat. Nos. 2,292,791 and 5,245,084, to prepare a scorch resistant composition by adding free radical inhibitors and curing promoters into the composition.

It is well known that organic peroxides are unstable chemicals which are difficult for transportation, storage or application. In addition, all the organic peroxides will release toxic by-products upon degradation in a chemical reaction. The most common degradation by- product is t-butyl alcohol. These toxic by-products exclude the use of the final polymer products in many applications, such as, toys, food packaging, medical device, etc.

High energy irradiation, such as electron beam, gamma radiation, and plasma treatment etc., have been used to modify the polyolefins properties by partially crosslinking the polymer composition. U. S. Pat. No. 6,494, 917 disclosed a crosslinking method by using either electron beam irradiation or organic peroxide initiation to prepare medical implants with stable shape and size. But the high energy irradiation process requires the use of expensive equipment, such as, an electron beam generator, and sophisticated handling procedures.

Therefore, there is a need to crosslink olefin polymers without using expensive irradiation source and with reduced toxic by-products.

Accordingly, it is an object of this invention to eliminate the above mentioned difficulties in handling the organic peroxides and to avoid the toxic by-products resulted from their use.

It is another object of this invention to increase the dimensional stability of olefin polymers using a batch or a continuous process without the direct use of a high-energy irradiation source.

In accordance with the present invention, a process for making crosslinked polyolefins by using reactive, peroxide-containing olefin polymers is disclosed. The present invention relates to a process making crosslinked olefin polymers comprising: a) preparing an olefin polymer mixture which comprises: I. about 0.5% to about 20.0% by weight of a reactive, peroxide-containing olefin polymer material (A); and II. about 80.0% to 99.5% by weight of an ethylene polymer material (B) ; wherein the gum of components I + 11 is equal to 100 b) extruding or compounding in molten state the olefin polymer mixture, thereby producing a melt mixture; and optionally c) pelletizing the melt mixture after it is cooled.

Olefin polymers suitable as a polymer starting material for the reactive, peroxide- containing olefin polymers are propylene polymer materials, ethylene polymer materials, butent-l polymer materials, or mixtures thereof.

The polymer starting material can be: (a) a crystalline homopolymer of propylene having an isotactic index greater than about 80%, preferably about 90% to about 99.5% ; (b) a crystalline, random copolymer of propylene with an olefin selected from ethylene and C4-CIo a-olefins wherein the polymerized olefin content is about 1-10% by weight, preferably about 1% to about 4%, when ethylene is used, and about 1% to about 20% by weight, preferably about 1% to about 16%, when the C4-Clo oc-olefin is used, the copolymer having an isotactic index greater than about 60%, preferably at least about 70%; (c) a crystalline, random terpolymer of propylene and two olefins selected from ethylene and C4 CE a-olefins wherein the polymerized olefin content is about 1-5% by weight, preferably about 1% to about 4%, when ethylene is used, and about 1% to about 20% by weight, preferably about 1% to about 16%, when the C4-Clo a-olefins are used, the terpolymer having an isotactic index greater than about 85%; (d) an olefin polymer composition comprising: (i) about 10% to about 60% by weight, preferably about 15% to about 55%, of a crystalline propylene homopolymer having an isotactic index at least about 80%, preferably about 90 to about 99.5%, or a crystalline copolymer of monomers selected from (a) propylene and ethylene, (b) propylene, ethylene and a C4-C8 a-olefin, and (c) propylene and a C4- C8 a-olefin, the copolymer having a polymerized propylene content of more than about 85% by weight, preferably about 90% to about 99%, and an isotactic index greater than about 60%; (ii) about 3% to about 25% by weight, preferably about 5% to about 20%, of a copolymer of ethylene and propylene or a C4-C8 a-olefin that is insoluble in xylene at ambient temperature ; and (iii) about 10% to about 80% by weight, preferably about 15% to about 65%, of an elastomeric copolymer of monomers selected from (a) ethylene and propylene, (b) ethylene, propylene, and a c4-C8 α-olefin, and (c) ethylene and a C4-C8 α-olefin, the copolymer optionally containing about 0.5% to about 10% by weight of a polymerized diene and containing less than about 70% by weight, preferably about 10% to about 60%, most preferably about 12% to about 55%, of polymerized ethylene, and being soluble in xylene at ambient temperature and having an intrinsic viscosity of about 1.5 to about 4.0 dl/g; wherein the total of (ii) and (iii), based on the total olefin polymer composition is about 50% to about 90% by weight, and the weight ratio of (ii)/ (iii) is less than about 0.4, preferably 0.1 to 0.3, and the composition is prepared by polymerization in at least two stages; (e) homopolymers of ethylene; (f) random copolymers of ethylene and an a-olefin selected from Cg-Cio a-olefins having a polymerized a-olefin content of about 1 to about 20% by weight, preferably about 1% to about 16%; (g) random terpolymers of ethylene and two C3-CIo a-olefins having a polymerized a-olefin content of about 1% to about 20% by weight, preferably about 1% to about 16%; (h) homopolymers of butene-1 ; (i) copolymers or terpolymers of butene-1 with ethylene, propylene or Cs-Cio a olefin, the comonomer content of up to about 15 mole %; and (j) mixtures thereof.

Preferably, the polymer starting material is selected from: (a) a crystalline homopolymer of propylene having an isotactic index greater than about 80%, preferably about 90% to about 99.5% ; and (b) a crystalline, random copolymer of propylene with an olefin selected from ethylene and C4-Clo a-olefins wherein the polymerized olefin content is about 1-10% by weight, preferably about 1% to about 4%, when ethylene is used, and about 1% to about 20% by weight, preferably about 1% to about 16%, when the C o a-olefin is useå9 the copolmer having an isotactic inaex greater than about 60%, preferably at least about 70%; Most preferably, the polymer starting material is a propylene homopolymer having an isotactic index greater than about 90%.

The useful polybutene-1 homo or copolymers can be isotactic or syndiotactic and have a melt flow rate (MFR) from about 0.1 to 150 dg/min, preferably from about 0.3 to 100, and most preferably from about 0.5 to 75.

These butene-1 polymer materials, their methods of preparation and their properties are known in the art. Suitable polybutene-1 polymers can be obtained, for example, by using Ziegler-Natta catalysts with butene-1, as described in WO 99/45043, or by metallocene polymerization of butene-1 as described in WO 02/102811, the disclosures of which are incorporated herein by reference.

Preferably, the butene-1 polymer materials contain up to about 15 mole % of copolymerized ethylene or propylene. More preferably, the butene-1 polymer material is a homopolymer having a crystallinity of at least about 30% by weight measured with wide- angle X-ray diffraction after 7 days, more preferably about 45% to about 70%, most preferably about 55% to about 60%.

Typically, the polymer starting material for the reactive, peroxide-containing olefin polymer is exposed to high-energy ionizing radiation under a blanket of inert gas, preferably nitrogen. The ionizing radiation should have sufficient energy to penetrate the mass of polymer material being irradiated to the extent desired. The ionizing radiation can be of any kind, but preferably includes electrons and gamma rays. More preferred are electrons beamed from an electron generator having an accelerating potential of 500-4,000 kilovolts.

Satisfactory results are obtained at a dose of ionizing radiation of about 0.1 to about 15 megarads ("Mrad"), preferably about 0.5 to about 9.0 Mrad.

The term"rad"is usually defined as that quantity of ionizing radiation that results in the absorption of 100 ergs of energy per gram of irradiated material regardless of the source of the radiation using the process described in U. S. Pat. No. 5,047, 446. Energy absorption from ionizing radiation is measured by the well-known convention dosimeter, a measuring device in which a strip of polymer film containing a radiation-sensitive dye is the energy absorption sensing means. Therefore, as used in this specification, the term"rad"means that quantity of ionizing radiation resulting in the absorption of the equivalent of 100 ergs of energy per gram of the polymer film of a dosimeter placed at the surface of the oleiin material being irradiated, whether in the form of a bed or layer of particles, or a film, or a sheet.

The irradiated olefin polymer material is then oxidized in a series of steps. The first treatment step consists of heating the irradiated polymer in the presence of a first controlled amount of active okygen greater than 0.004% by volume but less than 15% by volume, preferably less than 8% by volume, more preferably less than 5% by volume, and most preferably from 1.3% to 3.0% by volume, to a first temperature of at least 25°C but below the softening point of the polymer, preferably about 25°C to 140°, more preferably about 25°C to 100°C, and most preferably about 40°C to 80°C. Heating to the desired temperature is accomplished as quickly as possible, preferably in less than 10 minutes. The polymer is then held at the selected temperature, typically for about 5 to 90 minutes, to increase the extent of reaction of the oxygen with the free radicals in the polymer. The holding time, which can be determined by one skilled in the art, depends upon the properties of the starting material, the active oxygen concentration used, the irradiation dose, and the temperature. The maximum time is determined by the physical constraints of the fluid bed used to treat the polymer.

In the second treatment step, the irradiated polymer is heated in the presence of a second controlled amount of oxygen greater than 0.004% by volume but less than 15% by volume, preferably less than 8% by volume, more preferably less than 5% by volume, and most preferably from 1.3% to 3.0% by volume to a second temperature of at least 25°C but below the softening point of the polymer. Preferably, the second temperature is from 80°C to less than the softening point of the polymer, and greater than the first temperature of the first step. The polymer is then held at the selected temperature and oxygen concentration conditions, typically for about 90 minutes, to increase the rate of chain scission and to minimize the recombination of chain fragments so as to form long chain branches, i. e. , to minimize the formation of long chain branches. The holding time is determined by the same factors discussed in relation to the first treatment step.

In the optional third step, the oxidized olefin polymer material is heated under a blanket of inert gas, preferably nitrogen, to a third temperature of at least 80°C but below the softening point of the polymer, and held at that temperature for about 10 to about 120 minutes, preferably about 60 minutes. A more stable product is produced if this step is carried out. It is preferred to use this step if the reactive, peroxide-containing olefin polymer material is going to be stored rather than used immediately, or if the radiation dose that is used is on the high end of the range described above. The polymer is then cooled to a fourth temperature of about 50°C over a period of about 10 minutes under a blanket of inert gas, preferably nitrogen, before being discharged from the bed. In this manner, stable intermediates are <BR> <BR> formed that can be stored at room temperature for long periods of time without further degradation.

As used in this specification, the expression"room temperature"or"ambient" temperature means approximately 25°C. The expression"active oxygen"means oxygen in a form that will react with the irradiated olefin polymer material. It includes molecular oxygen, which is the form of oxygen normally found in air. The active oxygen content requirement of this invention can be achieved by replacing part or all of the air in the environment by an inert gas such as, for example, nitrogen.

The preferred method of making the reactive, peroxide-containing polyolefin material is to carry out the treatment by passing the irradiated polymer through a fluid bed assembly operating at a first temperature in the presence of a first controlled amount oxygen, passing the polymer through a second fluid bed assembly operating at a second temperature in the presence of a second controlled amount of oxygen, and then maintaining the polymer at a third temperature under a blanket of nitrogen, in a third fluid bed assembly. In commercial operation, a continuous process using separate fluid beds for the first two steps, and a purged, mixed bed for the third step is preferred. However, the process can also be carried out in a batch mode in one fluid bed, using a fluidizing gas stream heated to the desired temperature for each treatment step. Unlike some techniques, such as melt extrusion methods, the fluidized bed method does not require the conversion of the irradiated polymer into the molten state and subsequent re-solidification and comminution into the desired form. The fluidizing medium can be, for example, nitrogen or any other gas that is inert with respect to the free radicals present, e. g. , argon, krypton, and helium.

The concentration of peroxide groups formed on the polymer can be controlled easily by varying the radiation dose during the preparation of the irradiated polymer and the amount of oxygen to which such polymer is exposed after irradiation. The oxygen level in the fluid bed gas stream is controlled by the addition of dried, filtered air at the inlet to the fluid bed.

Air must be constantly added to compensate for the oxygen consumed by the formation of peroxides in the polymer.

Without bound by theory, the reactive, peroxide-containing olefin polymer material of the invention contains peroxide linkages that degrade during compounding to form various oxygen-containing polar functional groups, e. g., carboxylic acids, ketones and. esters. In addition, the number average and weight average molecular weight of the reactive, peroxide- containing olefin polymer is usually much lower than that of the corresponding olefin polymer used to prepare the same, due to the chain scission reactions during irradiation and oxidation.

The concentration of peroxide groups formed on the polymer can be controlled easily by varying the radiation dose during the preparation of the reactive, peroxide-containing olefin polymer and the amount of oxygen to which such polymer is exposed after irradiation.

The oxygen level in the fluid bed gas stream is controlled by the addition of dried, filtered air at the inlet to the fluid bed. Air must be constantly added to compensate for the oxygen consumed by the formation of peroxides in the polymer.

Alternatively, the reactive, peroxide-containing olefin polymer materials could be prepared according to the following procedures. In the first treatment step, the polymer starting material was treated with 0.1 to 10 wt% of an organic peroxide initiator while adding a controlled amount of oxygen so that the olefin polymer material is exposed to greater than 0.004% but less than 21% by volume, preferably less than 15%, more preferably less than 8% by volume, and most preferably 1.0% to 5.0% by volume, at a temperature of at least 25 °C but below the softening point of the polymer, preferably about 25 °C to about 140 °C. In the second treatment step, the polymer is then heated to a temperature of at least 25 °C up to the softening point of the polymer, preferably from 100 °C to less than the softening point of the polymer, at an oxygen concentration that is within the same range as in the first treatment step. The total reaction time is typically about 0.5 hour to four hours. After the oxygen treatment, the polymer is treated at a temperature of at least 80 °C but below the softening point of the polymer, typically for 0.5 hour to about two hours, in an inert atmosphere such as nitrogen to quench any active free radicals.

Suitable organic peroxides include acyl peroxides, such as benzoyl and dibenzoyl peroxides; dialkyl and aralkyl peroxides, such as di-tert-butyl peroxide, dicumyl peroxide; cumyl butyl peroxide; l, l,-di-tert-butylperoxy-3, 5,5-trimethylcyclohexane ; 2,5-dimethyl- 1, 2,5-tri-tert-butylperoxyhexane, and bis (alpha-tert-butylperoxy isopropylbenzene), and peroxy esters such as bis (alpha-tert-butylperoxy pivalate; tert-butylperbenzoate; 2,5- dimethylhexyl-2, 5-di (perbenzoate); tert-butyl-di (perphthalate); tert-butylperoxy-2- ethylhexanoate, and 1, 1-dimethyl-3-hydroxybutylperoxy-2-ethyl hexanoate,. and peroxycarbonates such as di (2-ethylhexyl) peroxy dicarbonate, di (n-propyl) peroxy dicarbonate, and di (4-tert-butylcyclohexyl) peroxy dicarbonate. The peroxides can be used neat or in diluent medium.

The typical peroxide concentration of the reactive, peroxide-containing olefin polymers is ranging from about 10 to about 100 milli-equivalent of peroxide in one kilogram of the reactive, peroxide-containing olefin polymer (meg) O The ethylene polymer material (B) in the present invention can be : (i) ethylene homopolymer ; (ii) random copolymers of ethylene and one or more alpha-olefin selected from C3-Cl2 alpha-olefins having a polymerized alpha-olefin content of up to about 20% by weight, preferably about 1% to about 16% ; (iii) random terpolymers of ethylene and two C3-Cl2 alpha-olefins having a polymerized alpha-olefin content of up to about 20% by weight, preferably about 1% to about 16%; and (iv) mixtures thereof.

Suitable equipment for conducting crosslinking process include but not limited to single screw extruder, twin screw extruder, Ferrell Continuous Mixer (FCM), Banbury mixer, a kneading machine, or an autoclave, etc.

In the crosslinked olefin polymer composition, the reactive, peroxide-containing olefin polymer material can be present in an amount of about 0.5 to about 20% by weight, preferably about 1 to about 15%, more preferably about 2 to about 6%. The balance of the composition up to 100% by weight is the ethylene polymer material.

The polymer composition of the present invention may also contain conventional additives, for instance, anti-acid stabilizers, such as, calcium stearate, hydrotalcite, zinc stearate, calcium oxide, and sodium stearate.

Unless otherwise specified, the properties of the olefin polymer materials, compositions and other characteristics that are set forth in the following examples have been determined according to the test methods reported below: Melt Flow Rate ("MFR"): ASTM D1238, units of dg/min ; 230° C ; 2.16 kg; Polymer material with a MFR below 100, using full die; Polymer material with a MFR equal or above 100, using l/2 die ; unless otherwise specified.

Isotactic Index Defined as the percent of olefin polymer insoluble in xylene.

The weight percent of olefin polymer soluble in xylene at room temperature is determined by dissolving 2.5 g of polymer in 250 ml of xylene at room temperature m a vessel equipped with a stirrer, and heating at 135°C with agitation for 20 minutes. The solution is cooled to 25°C while continuing the agitation, and then left to stand without agitation for 30 minutes so that the solids can settle. The solids are filtered with filter paper, the remaining solution is evaporated by treating it with a nitrogen stream, and the solid residue is vacuum dried at 80°C until a constant weight is reached. These values correspond substantially to the isotactic index determined by extracting with boiling n-heptane, which by definition constitutes the isotactic index of polypropylene.

Peroxide Concentration: Quantitative Organic Analysis via Functional Groups, by S.

Siggia et al. , 4th Ed. , NY, Wiley 1979, pp. 334-42.

Molecular Weight: The samples are prepared at a concentration of 70 mg/50 ml of stabilized 1,2, 4 trichlorobenzene (250jug/ml BHT). The samples are then heated to 170 degC for 2.5 hours to solubilize.

The samples are then run on a Waters GPCV2000 at 145 degC at a flow rate of 1.0 ml/min. using the same stabilized solvent.

Three Polymer Lab columns were used in series (Plgel, 20/mi mixed ALS, 300 X 7.5 mm).

Gas Chromatograph determination of reaction byproduct: Weigh accurately 7-8 g polymer sample into a 50 ml serum vial.

Add 25 ml methylene chloride by pipette and cap the vial tightly with a teflon-lined septum seal (crimp the cap tightly to ensure seal is secure). Place the vial in a ultrasonic bath at room temperature. Remove a portion of the extract and analyze by Gas Chromotograph (Agilent 5890 or equivalent).

In this specification, all parts, percentages and ratios are by weight unless otherwise specified. The reactive, peroxide-containing olefin polymer materials are prepared according to the following procedures.

Preparation 1 A polypropylene homopolymer having a MFR of 9.0 dg/min and I. I. of 96.5%, commercially available from Basell USA Inc. was irradiated at 0.5 Mrad under a blanket of nitrogen. The irradiated polymer was then treated with 1.45% by volume of oxygen at 80°C for 60 minutes and then with 1.45% by volume of oxygen at 140°C for an additional 60 minutes. The oxygen was then removed. The polymer was then bheated at 140°C under a blanket of nitrogen for 60 minutes, cooled and collected. The MFR of the resultant polymer material was 325 dg/min. The peroxide concentration was 12. 3 meq/kg of polymer.

Preparation 2 A reactive, peroxide-containing olefin polymer was prepared from a propylene homopolymer, commercially available from Basell USA Inc., having a MFR of 9.0 dg/min and I. I. of 96.5%, in the presence of an organic peroxide, t-butyl-peroxy-2-ethyl-hexanoate (Lupersol PMS), commercially available from ELF Atochem. 2000 grams of the propylene homopolymer was treated with 6.0% by volume of oxygen at 100 °C in a gas circulated reactor and 100 grams of the organic peroxide was added at a flow rate of 4g/min while the temperature was kept at 100 °C and oxygen concentration of 6.0% by volume. The mixture was kept at 100 °C and the oxygen concentration of 6.0% by volume for 60 minutes after the addition of the organic peroxide was completed. The mixture was then heated up to 140 °C and held at that temperature for 60 min. The oxygen was then removed. The polymer was then treated at 140°C under a blanket of nitrogen for 60 minutes, cooled and collected. The MFR of the resulting material was about 16000 dg/min.

Example 1 This example demonstrates a crosslinking reaction characteristics of an ethylene polymer material in the presence of a reactive, peroxide-containing olefin polymer.

The ethylene polymer material was a random copolymer of ethylene and butene, with a butene content of 9% having a MFR of 3. 82 dg/min and density of 0. 916 g/cm commercially available from Haldia Petrochemicals LTD.

A high melt flow rate (MFR) olefin polymer used in the comparative samples was a propylene homopolymer, having a MFR of 525 and I.I. of 97.0, commercially available from Basel LJSA Inc.

All materials were simultaneously dry-blended and bag mixed with Irganox B225 antioxidant and calcium stearate. Irganox B225 antioxidant is a 1: 1 blend of Irganox 1010 antioxidant and Irgafos 168 tris (2, 4-di-t-butylphenyl) phosphite anitoxidant and is commercially available from Ciba Specialty Chemicals Corporation. The composition of each sample is shown in Table 1. The amounts given for the stabilizers are in parts per hundred parts of the polymer composition.

The mixed composition was then added into the heated chamber of a melt flow index machine and held at 230 °C for a specified period of time before measuring its melt flow rate.

The samples 1 and 2 with a reactive, peroxide-containing olefin polymer exhibited a significant decrease in the melt flow rate with the increase of the reaction time indicating the ethylene polymer material was effectively crosslinked.

In order to show that the decrease in melt flow rate did not result from the effect of heat and time, two comparative samples were prepared using a high melt flow olefin polymer in place of the reactive, peroxide-containing olefin polymer. The comparative samples 1 and 2 did not show any significant changes in the melt flow rate of the polymer mixture with the increases of the holding time from 6 minutes to 30 minutes.

Table 1 Comparative Comparative Composition Sample 1 Sample 2 Sample 1 Sample 2 Ethylene polymer material 90 90 90 90 (wt%) High MFR olefin polymer 10 10 (wt%) Reactive, peroxide-containing olefin polymer of Preparation 1 10 10 (wt%) Irganox B-225 antioxidant 0. 1 0. 1 0. 1 0. 1 (pph) Calcium stearate (pph) 0. 05 0. 05 0. 05 0.05 Time held at 230 °C (min) 6 30 6 30 MFR (dg/min) 14. 9 14.7 14.6 8.60 Example 2 This example also shows the crosslinking reaction of an ethylene polymer material with a reactive, peroxide-containing olefin polymer.

The ethylene polymer material, the high melt flow rate (MFR) olefin polymer, and the reactive, peroxide-containing olefin polymer are the same as those in Example 1, except that the content of the ethylene polymer material used in the experiments was increased from 90 wt% to 95 wt%.

The experimental results are summarized in Table 2. Although the melt flow rates of the polymer mixture decreases as compared with those in Example 1, the comparative samples 1 and 2 did not show any significant changes in the melt flow rate with the increases of the holding time from 6 minutes to 30 minutes. The samples 1 and 2 with a reactive, peroxide-containing olefin polymer exhibited a significant decrease of the melt flow rate with the increase of the reaction time indicating the polymer was effectively crosslinked.

Table 2 Composition Comparative Comparative Sample 1 Sample 2 Sample 1 Sample 2 Ethylene polymner material 95 95 95 95 (wt%) High MFR olefin polymer 5 5 (wt%) Reactive, peroxide-containing olefin polymer of Preparation 1 5 5 (wt%) Irganox B-225 antioxidant 0. 1 0. 1 0. 1 0. 1 h) Calcium stearate (pph) 0. 05 0. 05 0. 05 0. 05 Time held at 230 °C (min) 6 30 6 30 MFR (dg/min) 7. 80 7. 85 8. 64 4. 60 Example 3 This example demonstrates the crosslinking reaction of an ethylene polymer material in the presence of a reactive, peroxide-containing olefin polymer.

The ethylene polymer material in this experiment and the high melt flow rate (MFR) olefin polymer used in the comparative samples, were the same as those used in Example 1.

The reactive, peroxide-containing olefin polymer was prepared by Preparation 2 and had a high melt flow rate.

All materials were simultaneously dry-blended and bag mixed with Irganox B225 antioxidant and calcium stearate. The composition of each sample is shown in Table 3. The amounts given for the stabilizers are in parts per hundred parts of the polymer composition.

The mixed composition was then added into the heated chamber of a melt flow index machine and held at 230 °C for a specified period of time before measuring its melt flow rate.

The comparative samples 1 and 2 did not show any significant changes in the melt flow rate of the polymer mixture with the increases of the holding time from 6 minutes to 30 minutes.

The samples 1 and 2 with a reactive, peroxide-containing olefin polymer exhibited a significant decrease of the melt flow rate with the increase of the reaction time indicating the polymer was effectively crosslinked.

Table 3 Comparative Comparative Composition Sample 1 Sample 2 Sample 1 Sample 2 Ethylene polymer material 95 95 95 95 (wot%) High MFR olefin polymer 5 5 (wt% 4 Reactive, peroxide-containing olefin polymer of Preparation 2 5 5 (wt%) Irganox B-225 antioxidant 0.1 0.1 0.1 0.1 Calcium stearate (pph) 0. 05 0. 05 0. 05 0.05 Time held at 230 °C (min) 6 30 6 30 MFR (dg/min) 7. 80 7. 85 11. 7 6. 80 Other features, advantages and embodiments of the invention disclosed herein will be readily apparent to those exercising ordinary skill after reading the foregoing disclosures. In this regard, while specific embodiments of the invention have been described in considerable detail, variations and modifications of these embodiments can be effected without departing from the spirit and scope of the invention as described and claimed.