WO2017112389A1

WO2017112389A1 - Method for making an article from polyolefin

Info

Publication number: WO2017112389A1
Application number: PCT/US2016/064691
Authority: WO
Inventors: Eric J. HUKKANEN; Bryan E. BARTON
Original assignee: Dow Global Technologies Llc
Priority date: 2015-12-22
Filing date: 2016-12-02
Publication date: 2017-06-29

Abstract

The present disclosure describes a method for producing an article comprising providing a polyolefin-derived crosslinked article having an initial gel fraction, G_i; treating the crosslinked article with a treating agent at a temperature below the melting point of the crosslinked article to provide a treated article having a final gel fraction, G_f, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction: R = G_f/G_i; and wherein the ratio R is: 1.010 < R <1.200.

Description

METHOD FOR MAKING AN ARTICLE FROM POLYOLEFIN

BACKGROUND

[0001] Previously, carbonaceous articles, such as carbon fibers, have been produced primarily from polyacrylonitrile (PAN), pitch, or cellulose precursors. The process for making carbonaceous articles begins by forming a fabricated article, such as a fiber or a film, from the precursor. Precursors may be formed into fabricated articles using standard techniques for forming or molding polymers. The fabricated article is subsequently stabilized to allow the fabricated article to substantially retain shape during the subsequent heat-processing steps; without being limited by theory, such stabilization typically involves a combination of oxidation and heat and generally results in dehydrogenation, ring formation, oxidation and crosslinking of the precursor which defines the fabricated article. The stabilized fabricated article is then converted into a carbonaceous article by heating the stabilized fabricated article in an inert atmosphere. While the general steps for producing a carbonaceous article are the same for the variety of precursors, the details of those steps vary widely depending on the chemical makeup of the selected precursor.

[0002] Polyolefins have been investigated as an alternative precursor for carbonaceous articles, but a suitable and economically viable preparation process has proven elusive. For example, filament fusion is a known problem when preparing polyolefin precursors.

Further, shape retention is another known problem when preparing polyolefin precursors. Processes for fabricating polyolefin precursors which overcome these limitations are desired.

STATEMENT OF INVENTION

[0003] The present disclosure describes a method for producing an article comprising providing a polyolefin-derived crosslinked article having an initial gel fraction, G,; treating the crosslinked article with a treating agent at a temperature below the melting point of the crosslinked article to provide a treated article having a final gel fraction, G/, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction: R = G_j/Gf, and wherein the ratio R is: 1.010 < R < 1.200.

DETAILED DESCRIPTION

[0004] Unless otherwise indicated, numeric ranges, for instance "from 2 to 10," are inclusive of the numbers defining the range (e.g., 2 and 10). [0005] Unless otherwise indicated, ratios, percentages, parts, and the like are by weight.

[0006] Unless otherwise indicated, the crosslinkable functional group content for a polyolefin resin is characterized by the mol% crosslinkable functional groups, which is calculated as the number of mols of crosslinkable functional groups divided by the total number of mols of monomer units contained in the polyolefin.

[0007] Unless otherwise indicated, "monomer" refers to a molecule which can undergo polymerization, thereby contributing constitutional units to the essential structure of a macromolecule, for example, a polyolefin.

[0008] In one aspect, the present disclosure describes a process for producing an article from a polyolefin resin. In one instance, the article is a stabilized article. In one instance, the article is a carbonaceous article. Unless stated otherwise, any method or process steps described herein may be performed in any order. Polyolefins are a class of polymers produced from one or more olefin monomer. The polymers described herein may be formed from one or more types of monomers. Polyethylene is the preferred polyolefin resin, but other polyolefin resins may be substituted. For example, a polyolefin produced from ethylene, propylene, or other alpha-olefin (for instance, 1-butene, 1-hexene, 1-octene), or a combination thereof, is also suitable. The polyolefins described herein are typically provided in resin form, subdivided into pellets or granules of a convenient size for further melt or solution processing.

[0009] The polyolefin resins described herein are subjected to a crosslinking step. Any suitable method for crosslinking polyolefins is sufficient. In one instance, the polyolefins are crosslinked by irradiation, such as by electron beam processing. Other crosslinking methods are suitable, for example, ultraviolet irradiation and gamma irradiation. In some instances, an initiator, such as benzophenone, may be used in conjunction with the irradiation to initiate crosslinking. In one instance, the polyolefin resins have been modified to include crosslinkable functional groups which are suitable for reacting to crosslink the polyolefin resin. Where the polyolefin resin includes crosslinkable functional groups, crosslinking may be initiated by known methods, including use of a chemical crosslinking agent, by heat, by steam, or other suitable method. In one instance, copolymers are suitable to provide a polyolefin resin having crosslinkable functional groups where one or more alpha-olefins have been copolymerized with another monomer containing a group suitable for serving as a crosslinkable functional group, for example, dienes, carbon monoxide, glycidyl methacrylate, acrylic acid, vinyl acetate, maleic anhydride, or vinyl trimethoxy silane (VTMS) are among the monomers suitable for being copolymerized with the alpha- olefin. Further, the polyolefin resin having crosslinkable functional groups may also be produced from a poly(alpha-olefin) which has been modified by grafting a functional group moiety onto the base polyolefin, wherein the functional group is selected based on its ability to subsequently enable crosslinking of the given polyolefin. For example, grafting of this type may be carried out by use of free radical initiators (such as peroxides) and vinyl monomers (such as VTMS, dienes, vinyl acetate, acrylic acid, methacrylic acid, acrylic and methacrylic esters such as glycidyl methacrylate and methacryloxypropyl trimethoxysilane, allyl amine, p-aminostyrene, dimethylaminoethyl methacrylate) or via azido-functionalized molecules (such as 4-[2-(trimethoxysilyl)ethyl)]benzenesulfonyl azide). Polyolefin resins having crosslinkable functional groups may be produced from a polyolefin resin, or may be purchased commercially. Examples of commercially available polyolefin resins having crosslinkable functional groups include SI-LINK sold by The Dow Chemical Company, PRIMACOR sold by The Dow Chemical Company, EVAL resins sold by Kuraray, and LOTADER AX8840 sold by Arkema.

[0010] As described above, the polyolefin resin is processed to form a fabricated article. A fabricated article is an article which has been fabricated from the polyolefin resin. The fabricated article is formed using known polyolefin fabrication techniques, for example, melt or solution spinning to form fibers, film extrusion or film casting or a blown film process to form films, die extrusion or injection molding or compression molding to form more complex shapes, or solution casting. The fabrication technique is selected according to the desired geometry of the target article, and the desired physical properties of the same. For example, where the desired article is a fiber, fiber spinning is a suitable fabrication technique. As another example, where the desired article is a film, compression molding is a suitable fabrication technique.

[0011] As noted above, at least a portion of the polyolefin resin is crosslinked to yield a crosslinked fabricated article. In some embodiments, crosslinking is carried out via chemical crosslinking. Thus, in some embodiments, the crosslinked fabricated article is a fabricated article which has been treated with one or more chemical agents to crosslink the crosslinkable functional groups of the polyolefin resin having crosslinkable functional groups. Such chemical agent functions to initiate the formation of intramolecular chemical bonds between the crosslinkable functional groups or reacts with the crosslinkable functional groups to form intramolecular chemical bonds, as is known in the art. Chemical crosslinking causes the crosslinkable functional groups to react to form new bonds, forming linkages between the various polymer chains which define the polyolefin resin having crosslinkable functional groups. The chemical agent which effectuates the crosslinking is selected based on the type of crosslinkable functional group(s) included in the polyolefin resin; a diverse array of reactions are known which crosslink crosslinkable functional groups via intermolecular and intramolecular chemical bonds. A suitable chemical agent is selected which is known to crosslink the crosslinkable functional groups present in the fabricated article to produce the crosslinked fabricated article. For example, without limiting the present disclosure, if the crosslinkable functional group attached to the polyolefin is a vinyl group, suitable chemical agents include free radical initiators such as peroxides or azo-bis nitriles, for example, dicumyl peroxide, dibenzoyl peroxide, t-butyl peroctoate, azobisisobutyronitrile, and the like. If the crosslinkable functional group attached to the polyolefin is an acid, such as a carboxylic acid, or an anhydride, or an ester, or a glycidoxy group, a suitable chemical agent can be a compound containing at least two nucleophilic groups, including dinucleophiles such as diamines, diols, dithiols, for example ethylenediamine, hexamethylenediamine, butane diol, or hexanedithiol. Compounds containing more than two nucleophilic groups, for example glycerol, sorbitol, or hexamethylene tetramine can also be used. Mixed di- or higher- nucleophiles, which contain at least two different nucleophilic groups, for example ethanolamine, can also be suitable chemical agents. If the crosslinkable functional group attached to the polyolefin is a mono-, di- or tri- alkoxy silyl group, water, and Lewis or Bronsted acid or base catalysts can be used as suitable chemical agents. For example, without limiting the present disclosure, Lewis or Bronsted acid or base catalysts include aryl sulfonic acids, sulfuric acid, hydroxides, zirconium alkoxides or tin reagents.

[0012] Crosslinking the fabricated article is generally preferred to ensure that the fabricated article retains its shape at the elevated temperatures required for the subsequent processing steps. Without crosslinking, polyolefin resins typically soften, melt or otherwise deform or breakdown at elevated temperatures. Crosslinking adds thermal stability to the fabricated article. The degree of crosslinking of the crosslinked fabricated article is expressed in terms of gel fraction. The gel fraction is determined by Soxhlet Extraction as described herein. In the methods described herein, the crosslinked fabricated article is provided having an initial gel fraction (Gi) equal to or greater than 60 percent. In one instance, the initial gel fraction is greater than or equal to 70 percent. In one instance, the initial gel fraction is greater than or equal to 75 percent. In one instance, the initial gel fraction is greater than or equal to 80 percent. In one instance, the initial gel fraction is greater than or equal to 85 percent. In one instance, the initial gel fraction is greater than or equal to 90 percent. In one instance, the initial gel fraction is greater than or equal to 95 percent.

[0013] In the methods described herein, the crosslinked fabricated article is (1) treated with a nitrogen-containing compound (NCC) and (2) optionally treated with an oxidizing agent to yield a stabilized fabricated article. The NCC includes a nitrogen source. Following treatment with the NCC, the fabricated article has a final gel fraction (G_/). In one instance the oxidizing agent is oxygen. Any suitable nitrogen-containing species which deposits nitrogen in the fabricated article may be used in the NCC. Examples of suitable NCCs include ammonia and ammonia derivatives. Ammonia derivatives include, but are not limited to, ammonium salts, amines, imines, amides, imides, carbamides, carbimides, enamines, amino boranes, and ammonium hydroxide. In one instance, the NCC is gaseous. In one instance, the gaseous NCC flows over the fabricated article. For example, in one instance the gaseous NCC is ammonia carried in an inert atmosphere. In one instance, the NCC is a liquid. In one instance, the fabricated article is dipped, immersed, sprayed, or otherwise treated with the liquid NCC. In one instance, the crosslinked fabricated article is treated with the NCC and the oxidizing agent simultaneously. In one instance, the crosslinked fabricated article is first treated with the NCC and is subsequently treated with the oxidizing agent. In one instance, the crosslinked fabricated article is treated first with the NCC, second with the oxidizing agent, and then this sequence is repeated one or more times. In one instance, the crosslinked fabricated article is first treated with the oxidizing agent to partially oxidize the crosslinked fabricated article, and then is subsequently treated with the NCC and the oxidizing agent. The crosslinked fabricated article is exposed to the NCC such that nitrogen source interacts sufficiently with the fabricated article to provide the improved characteristics described herein. In one instance, the crosslinked fabricated article is exposed to the NCC at a temperature below the melting temperature of the crosslinked fabricated article. In one instance, the crosslinked fabricated article is exposed to the NCC at a temperature at or below 120 °C.

[0014] The crosslinked fabricated article is optionally treated with the oxidizing agent at elevated temperature. In some embodiments, the temperature for treating the crosslinked fabricated article with the oxidizing agent is at least 100 °C, more preferably at least 120 °C, most preferably at least 190 °C. In some embodiments, the temperature for treating the crosslinked fabricated article with the oxidizing agent is no more than 450 °C. In one instance, the temperature for terracing the crosslinked fabricated article is from 120 to 300 °C. In one instance, the crosslinked fabricated article is introduced to a heating chamber which is already at the desired temperature. In another instance, the crosslinked fabricated article is introduced to a heating chamber at or near ambient temperature, which chamber is subsequently heated to the desired temperature. In some embodiments the heating rate is at least 1 °C/minute. In other embodiments the heating rate is no more than 15 °C/minute. In yet another instance, the chamber is heated step wise, for instance, the chamber is heated to a first temperature for a time, such as, 120 °C for one hour, then is raised to a second temperature for a time, such as 180 °C for one hour, and third is raised to a holding temperature, such as 250 °C for 10 hours. The stabilization process involves holding the crosslinked fabricated article at the given temperature for periods up to 100 hours depending on the dimensions of the fabricated article. The stabilization process yields a nitrogen- treated stabilized fabricated article which is a precursor for a carbonaceous article. Without being limited by theory, the stabilization process oxidizes the crosslinked fabricated article and causes changes to the hydrocarbon structure that increases the crosslink density while decreasing the hydrogen/carbon ratio of the crosslinked fabricated article.

[0015] Unexpectedly, it has been found that treating the crosslinked fabricated article with nitrogen improves mass retention of the stabilized article. It has also been found that treating the crosslinked fabricated article with a nitrogen-containing species improves form- retention of the subsequently produced carbonaceous article.

[0016] In another aspect, the present disclosure describes a nitrogen- treated stabilized fabricated article which is formed from a polyolefin precursor (resin). In one instance, the nitrogen-treated stabilized fabricated article is formed according to the process described herein.

[0017] In yet another aspect, a carbonaceous article and a process for making the same are provided. Carbonaceous articles are articles which are rich in carbon; carbon fibers, carbon sheets and carbon films are examples of carbonaceous articles. Carbonaceous articles have many applications, for example, carbon fibers are commonly used to reinforce composite materials, such as in carbon fiber reinforced epoxy composites, while carbon discs or pads are used for high performance braking systems.

[0018] The carbonaceous articles described herein are prepared by carbonizing the stabilized fabricated article by heat-treating the nitrogen-treated stabilized fabricated articles in an inert environment. The inert environment is an environment surrounding the nitrogen- treated stabilized fabricated article that shows little reactivity with carbon at elevated temperatures, preferably a high vacuum or an oxygen-depleted atmosphere, more preferably a nitrogen atmosphere or an argon atmosphere. It is understood that trace amounts of oxygen may be present in the inert atmosphere. In one instance, the temperature of the inert environment is at or above 600 °C. Preferably, the temperature of the inert environment is at or above 800 °C. In one instance, the temperature of the inert environment is no more than 3000 °C. In one instance, the temperature is from 1400-2400 °C. Temperatures at or near the upper end of that range will produce a graphite article, while temperatures at or near the lower end of the range will produce a carbon article.

[0019] In order to prevent bubbling or damage to the fabricated article during carbonization, it is preferred to heat the inert environment in a gradual or stepwise fashion. In one embodiment, the nitrogen-treated stabilized fabricated article is introduced to a heating chamber containing an inert environment at or near ambient temperature, which chamber is subsequently heated over a period of time to achieve the desired final temperature. The heating schedule can also include one or more hold steps for a prescribed period at the final temperature or an intermediate temperature or a programmed cooling rate before the article is removed from the chamber.

[0020] In yet another embodiment, the chamber containing the inert environment is subdivided into multiple zones, each maintained at a desired temperature by an appropriate control device, and the nitrogen-treated stabilized fabricated article is heated in a stepwise fashion by passage from one zone to the next via an appropriate transport mechanism, such as a motorized belt. In the instance where a nitrogen-treated stabilized fabricated article is a fiber, this transport mechanism can be the application of a traction force to the fiber at the exit of the carbonization process while the tension in the stabilized fiber is controlled at the inlet. Some embodiments of the invention will now be described in detail in the following Examples.

[0021] In the Examples, overall mass yield is calculated as the product of oxidation mass yield and carbonization mass yield (calculated as provided below). MI refers to melt index which is a measure of melt flow rate. Wt% refers to parts per 100 total parts, mass basis. PE refers to polyethylene.

[0022] The methods provided herein provide fabricated articles having improved properties as compared to previous methods of preparing fabricated articles from polyolefin resins. For example, the methods provided herein provide fabricated articles having reduced filament fusion. Filament fusion is a known problem when preparing carbonaceous articles from polyolefin precursors. The improvement described herein is achieved by carefully controlling the gel fraction of the crosslinked article (initial gel fraction, G,) and the nitrogen-treated article (final gel fraction, G_/) minimizes filament fusion. It has been found that controlling the reaction conditions to provide a ratio (R) in the range of 1.010 < R≤ 1.200, where R is defined as G/G, minimizes filament fusion. The duration of time needed to treat the crosslinked article with the treating agent may vary depending on the crosslinking method or the type of polyolefin resin used. As such, by measuring the R value, one of skill in the art can determine the duration of the nitrogen-containing compound treatment step to minimize filament fusion.

[0023] The present disclosure provides a method for producing an article comprising: (a) providing a polyolefin-derived crosslinked article having an initial gel fraction, G,; (b) treating the crosslinked article with a treating agent to provide a treated article having a final gel fraction, G_/, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction: R = G/G,, and wherein the ratio R is: 1.010≤R≤ 1.200.

[0024] The present disclosure also provides a method for producing an article comprising: (a) providing a polyolefin-derived crosslinked article having an initial gel fraction, G,; (b) treating the crosslinked article with a treating agent to provide a treated article having a final gel fraction, G_/, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction R: = G/G, and wherein the ratio R is: 1.010 < R≤ 1.200; and (c) treating the crosslinked article with an oxidizing agent to provide a stabilized article, the oxidizing agent comprising oxygen.

[0025] The present disclosure further provides a method for producing an article comprising: (a) providing a polyolefin-derived crosslinked article having an initial gel fraction, G,; (b) treating the crosslinked article with a treating agent to provide a treated article having a final gel fraction, G_/, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction R: = G/G, and wherein the ratio R is: 1.010 < R < 1.200; and (c) treating the crosslinked article with an oxidizing agent to provide a stabilized article, the oxidizing agent comprising oxygen, wherein steps (b) and (c) are performed sequentially. [0026] The present disclosure further provides a method for producing an article comprising: (a) providing a polyolefin-derived crosslinked article having an initial gel fraction, G,; (b) treating the crosslinked article with a treating agent to provide a treated article having a final gel fraction, G_/, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction R: = G/G, and wherein the ratio R is: 1.010 < R < 1.200; and (c) treating the crosslinked article with an oxidizing agent to provide a stabilized article, the oxidizing agent comprising oxygen, wherein steps (b) and (c) are performed concurrently.

[0027] The present disclosure provides a method for producing an article comprising: (a) providing a polyolefin-derived crosslinked article having an initial gel fraction, G,; (b) treating the crosslinked article with a treating agent to provide a treated article having a final gel fraction, G_/, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction: R = G/G,, and wherein the ratio R is: 1.037 < R < 1.090.

[0028] The present disclosure also provides a method for producing an article comprising:

(a) providing a polyolefin-derived crosslinked article having an initial gel fraction, G,; (b) treating the crosslinked article with a treating agent to provide a treated article having a final gel fraction, G_/, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction R: = G/G, and wherein the ratio R is: 1.037 < R < 1.090; and (c) treating the crosslinked article with an oxidizing agent to provide a stabilized article, the oxidizing agent comprising oxygen.

[0029] The present disclosure further provides a method for producing an article comprising: (a) providing a polyolefin-derived crosslinked article having an initial gel fraction, G,; (b) treating the crosslinked article with a treating agent to provide a treated article having a final gel fraction, G_/, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction R: = G/G, and wherein the ratio R is: 1.037 < R < 1.090; and (c) treating the crosslinked article with an oxidizing agent to provide a stabilized article, the oxidizing agent comprising oxygen, wherein steps (b) and (c) are performed sequentially.

[0030] The present disclosure further provides a method for producing an article comprising: (a) providing a polyolefin-derived crosslinked article having an initial gel fraction, G,; (b) treating the crosslinked article with a treating agent to provide a treated article having a final gel fraction, G_/, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction R: = G/G, and wherein the ratio R is: 1.037 < R < 1.090; and (c) treating the crosslinked article with an oxidizing agent to provide a stabilized article, the oxidizing agent comprising oxygen, wherein steps (b) and (c) are performed concurrently.

[0031] Soxhlet extraction is a method for determining the gel content and swell ration of crosslinked ethylene plastics, also referred to herein as hot xylenes extraction. As used herein, Soxhlet extraction is conducted according to ASTM Standard D2765-11 "Standard Test Methods for Determination of Gel Content and Swell Ratio of Crosslinked Ethylene Plastics." In the method employed, a crosslinked fabricated article between 0.050 - 0.500 g is weighed and placed into a cellulose-based thimble which is then placed into a Soxhlet extraction apparatus with sufficient quantity of xylenes. Soxhlet extraction is then performed with refluxing xylenes for at least 12 hours. Following extraction, the thimbles are removed and the crosslinked fabricated article is dried in a vacuum oven at 80 °C for at least 12 hours and then weighed, thereby providing a Soxhlet-treated article. The gel content (%) is then calculated from the weight ratio (Soxhlet-treated article)/(crosslinked fabricated article). The TGA Method for determining percent stabilization by sulfonation is as follows: a TA Instruments Thermal Gravimetric Analyzer (TGA) Q5000 or Discovery Series TGA is used. Using ~ 10-20 mg for the analysis, the sample is heated at 10 °C/min to 800 °C under nitrogen. The final weight of the sample at 800 °C is referred to as the char yield. The VTMS content of the VTMS grafted resins was determined by 13C NMR.

Example 1

[0032] An ethylene/octene copolymer (density = 0.941 g/cm3; MI = 34 g/10 min,

190°C/2.16 kg) is reactive extruded with vinyl trimethoxysilane (VTMS) to form a VTMS- grafted ethylene/octene copolymer (MI = 19 g/10 min, 190°C/2.16 kg; 1.4 wt% grafted silane content determined by Fourier transform infrared spectroscopy FT-IR) precursor resin. The VTMS-grafted precursor resin is melt spun to form fibers with the following properties: 1573 filaments, 1941.6 total denier, 2.221 gf/den, 11.385% elongation-to-break. The fiber is fed continuously to a series of stirred tank reactors to crosslink the fibers.

Reactor 1 contains 95-98% sulfuric acid maintained at 100°C. Reactor 2 contains 50% sulfuric acid maintained at room temperature. Reactor 3 contains deionized water maintained at room temperature. Residence time in each reactor is 60 min. This Example provides a crosslinked fiber having an initial gel fraction (G,) of 64.4%, as determined by Soxhlet extraction. Example 1A

[0033] The crosslinked fiber of Example 1 is soaked in a 25-28 wt% ammonium hydroxide solution for 5 min. The fiber is removed from the solution and dried in air, followed by subsequent drying in a heated (80°C) vacuum oven overnight. The final gel fraction (G_/) of the fiber is 68.2%, as determined by Soxhlet extraction.

Example IB

[0034] The crosslinked fiber of Example 1 is soaked in a 25-28 wt% ammonium hydroxide solution for 1 h. The fiber is removed from the solution and dried in air, followed by subsequent drying in a heated (80°C) vacuum oven overnight. The final gel fraction (G_/) of the fiber is 69.2%, as determined by Soxhlet extraction.

Example 1C

[0035] The crosslinked fiber of Example 1 is soaked in a 25-28 wt% ammonium hydroxide solution for 24 h. The fiber is removed from the solution and dried in air, followed by subsequent drying in a heated (80°C) vacuum oven overnight. The final gel fraction (G_/) of the fiber is 69.9%, as determined by Soxhlet extraction.

Example ID

[0036] The crosslinked fiber of Example 1 is treated for 5 min in a tubular reactor at room temperature with 3 seem ammonia and 97 seem nitrogen. The final gel fraction (G_/) of the fiber is 68.2%, as determined by Soxhlet extraction.

Example IE

[0037] The crosslinked fiber of Example 1 is treated for 60 min in a tubular reactor at room temperature with 3 seem ammonia and 97 seem nitrogen. The final gel fraction (G_/) of the fiber is 68.4%, as determined by Soxhlet extraction.

Example IF

[0038] The crosslinked fiber of Example 1 is treated for 5 min in a tubular reactor at 80°C with 3 seem ammonia and 97 seem nitrogen. The final gel fraction (G_/) of the fiber is 68.5%, as determined by Soxhlet extraction.

Example 2

[0039] An ethylene/octene copolymer (density = 0.941 g/cm3; MI = 34 g/10 min,

190°C/2.16 kg) is reactive extruded with vinyl trimethoxysilane (VTMS) to form a VTMS- grafted ethylene/octene copolymer (MI = 19 g/10 min, 190°C/2.16 kg; 1.4 wt% grafted silane content determined by Fourier transform infrared spectroscopy FT-IR) precursor resin. The VTMS-grafted precursor resin is melt spun to form fibers with the following properties: 1573 filaments, 1941.6 total denier, 2.221 gf/den, 11.385% elongation-to-break. The fiber is fed continuously to a series of stirred tank reactors to crosslink the fibers. Reactor 1 contains 95-98% sulfuric acid maintained at 110°C. Reactor 2 contains 50% sulfuric acid maintained at room temperature. Reactor 3 contains deionized water maintained at room temperature. Residence time in each reactor is 104 min. The initial gel fraction (G,) of the fiber is 70.9%, as determined by Soxhlet extraction.

Example 2A

[0040] The crosslinked fiber of Example 2 is soaked in a 25-28 wt% ammonium hydroxide solution for 5 min. The sample is removed from solution and dried in air, followed by subsequent drying in a heated (80°C) vacuum oven overnight. The final gel fraction (G_/) of the fiber is 76.8%, as determined by Soxhlet extraction.

Example 2B

[0041] The crosslinked fiber of Example 2 is soaked in a 25-28 wt% ammonium hydroxide solution for 1 h. The sample is removed from solution and dried in air, followed by subsequent drying in a heated (80°C) vacuum oven overnight. The final gel fraction (G_/) of the fiber is 77.2%, as determined by Soxhlet extraction.

Example 2C

[0042] The crosslinked fiber of Example 2 is soaked in a 25-28 wt% ammonium hydroxide solution for 24 h. The sample is removed from solution and dried in air, followed by subsequent drying in a heated (80°C) vacuum oven overnight. The final gel fraction (G_/) of the fiber is 77.3%, as determined by Soxhlet extraction.

Example 3

[0043] An ethylene/octene copolymer (density = 0.955 g/cm3; MI = 30 g/10 min,

190°C/2.16 kg) is melt spun to form fibers with the following properties: 1573 filaments, 1696.7 total denier, 1.255 gf/den, 17.157% elongation-to-break. The fiber tow is crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield two crosslinked articles, the average initial gel fraction (G,) thereof is 88.1%, as determined by Soxhlet extraction. Example 3A

[0044] The crosslinked fiber from Example 3 is treated for 30 min in a tubular reactor at 100 °C with 3 seem ammonia and 97 seem air under 100 g applied tension. The fiber tow retained 99% of the original length. The final gel fraction (G ) of the fiber is 91.5%, as determined by Soxhlet extraction. Example 3B

[0045] The crosslinked fiber from Example 3 is treated for 30 min in a tubular reactor at 120 °C with 3 seem ammonia and 97 seem air under 100 g applied tension. The fiber tow retained 45.6% of the original length. The final gel fraction (G_/) of the fiber is 93.8%, as determined by Soxhlet extraction.

Example 3C

[0046] The crosslinked fiber from Example 3 is treated for 30 min in a tubular reactor at 100 °C with 3 seem ammonia and 97 seem nitrogen under 100 g applied tension. The fiber tow retained 97% of the original length. The final gel fraction (G_/) of the fiber is 92.5%, as determined by Soxhlet extraction.

Example 3D

[0047] The crosslinked fiber from Example 3 is treated for 30 min in a tubular reactor at 120 °C with 3 seem ammonia and 97 seem nitrogen under 100 g applied tension. The fiber tow retained 48% of the original length. The final gel fraction (G_/) of the fiber is 93.5%, as determined by Soxhlet extraction.

Example 3E

[0048] The crosslinked fiber from Example 3 is treated for 30 min in a tubular reactor at 120 °C with 100 seem air under 100 g applied tension. The fiber tow retained 42% of the original length. The final gel fraction (G_/) of the fiber is 92.2%, as determined by Soxhlet extraction.

Example 3F

[0049] The crosslinked fiber from Example 3 is treated for 120 min in a tubular reactor at 120 °C with 100 seem nitrogen under 100 g applied tension. The fiber tow retained 42% of the original length. The final gel fraction (G_/) of the fiber is 92.7%, as determined by Soxhlet extraction.

Example 4

[0050] An ethylene/octene copolymer (density = 0.955 g/cm3; MI = 30 g/10 min,

190°C/2.16 kg) is melt spun to form fibers with the following properties: 1573 filaments, 1696.7 total denier, 1.255 gf/den, 17.157% elongation-to-break. Two fiber tows are crosslinked with electron beam irradiation (800 kGy; 80 kGy/dose) to a yield two crosslinked articles with an average initial gel fraction (G,) of 85.9%, as determined by Soxhlet extraction. Example 4A

[0051] The crosslinked fiber from Example 4 is treated for 30 min in a tubular reactor at 100°C with 3 seem ammonia and 97 seem air under 100 g applied tension. The fiber tow retained 97.3% of the original length. The final gel fraction (G_/) of the fiber is 89.1%, as determined by Soxhlet extraction.

Example 4B

[0052] The Crosslinked fiber from Example 4 is treated for 30 min in a tubular reactor at 120°C with 3 seem ammonia and 97 seem air under 100 g applied tension. The fiber tow retained 33.3% of the original length. The final gel fraction (G_/) of the fiber is 90.5%, as determined by Soxhlet extraction.

Example 4C

[0053] The crosslinked fiber from Example 4 is treated for 30 min in a tubular reactor at 100°C with 3 seem ammonia and 97 seem nitrogen under 100 g applied tension. The fiber tow retained 92.3% of the original length. The final gel fraction (G_/) of the fiber is 90.8%, as determined by Soxhlet extraction.

Example 4D

[0054] The crosslinked fiber from Example 4 is treated for 30 min in a tubular reactor at 120°C with 3 seem ammonia and 97 seem nitrogen under 100 g applied tension. The fiber tow retained 104% of the original length. The final gel fraction (G_/) of the fiber is 89.1%, as determined by Soxhlet extraction.

[0055] The following Table provides the initial gel fraction (G,), final gel fraction (G/) and R values for the Examples.

Table 1

Claims

WHAT IS CLAIMED IS:

1. A method for producing an article comprising:

(a) providing a polyolefin-derived crosslinked article having an initial gel fraction,

(b) treating the crosslinked article with a treating agent at a temperature below the melting point of the crosslinked article to provide a treated article having a final gel fraction, G/, the treating agent comprising a nitrogen-containing compound, wherein a ratio, R, is defined as the ratio of the final gel fraction to the initial gel fraction:

R = ¾ and

wherein the ratio R is: 1.010 < R < 1.200.

2. The method of claim 1 , wherein the nitrogen-containing compound is ammonia or an ammonia derivative.

3. The method of claim 2, wherein the ammonia derivative is one or more of

ammonium salts, amines, imines, amides, imides, carbamides, carbimides, and ammonium hydroxide.

4. The method of claim 1 , wherein the treating agent further comprises water.

5. The method of any one of claims 1-4, further comprising (c) treating the crosslinked article with an oxidizing agent to provide a stabilized article, the oxidizing agent comprising oxygen.

6. The method of claim 5, wherein steps (b) and (c) are performed sequentially.

7. The method of claim 5, wherein steps (b) and (c) are performed concurrently.

8. The method of claim 5, further comprising repeating steps (b) and (c) one or more times.

9. The method of claim 5, wherein the oxidizing agent further comprises water vapor.

10. The method of claim 1, wherein step (b) is performed in an inert environment.

11. The method of claim 1 , wherein step (b) is performed in an oxic environment.

12. The method of claim 1, wherein R is 1.037 < R < 1.090.

13. The method of claim 1, wherein step (b) is performed at or below 120 °C.