WO2018057156A1

WO2018057156A1 - Process for making an article from polyolefin and composition thereof

Info

Publication number: WO2018057156A1
Application number: PCT/US2017/047121
Authority: WO
Inventors: Eric J. HUKKANEN; Bryan E. BARTON; Shane L. Mangold; Gerald F. Billovits
Original assignee: Dow Global Technologies Llc
Priority date: 2016-09-20
Filing date: 2017-08-16
Publication date: 2018-03-29

Abstract

A method for preparing a polyolefin material comprising providing a crosslinked polyolefin material; surface treating the crosslinked polyolefin material with an acidic medium; heating the crosslinked polyolefin material at or below 140 degrees C. A stabilized polyolefin article comprising an empirical formula, CH_XS_YO_Z, where: 1.85 ≤ X ≤ 2.10; 0.000 ≤ Y ≤ 0.035; and 0.03 ≤ Z ≤ 0.20. An oxidized polyolefin article comprising an empirical formula, CH_XO_Z, where: 0.35 ≤ X ≤ 0.50; and 0.5 ≤ Z ≤ 0.6.

Description

PROCESS FOR MAKING AN ARTICLE FROM POLYOLEFIN AND

COMPOSITION THEREOF

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 and mass 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. Of particular interest is identifying an economical process for preparing stabilized articles from polyolefin precursors, such as stabilized articles which are suitable for subsequent processing to form carbonaceous articles. For example, maximizing mass retention, preventing filament fusion and improving tensile properties during the stabilization and carbonization steps are of interest.

SUMMARY

[0003] A method for preparing a polyolefin material comprising providing a crosslinked polyolefin material; surface treating the crosslinked polyolefin material with an acidic medium; heating the crosslinked polyolefin material at or below 140 degrees C.

[0004] A stabilized polyolefin article comprising an empirical formula, CH_XS_YO_Z, where: 1.85≤ X≤ 2.10; 0.000 < Y < 0.035; and 0.03≤ Z≤ 0.20.

[0005] An oxidized polyolefin article comprising an empirical formula, CHxOz, where: 0.35≤ X≤ 0.50; and 0.5≤ Z≤ 0.6. DETAILED DESCRIPTION

[0006] Unless otherwise indicated, numeric ranges, for instance "from 2 to 10," are inclusive of the numbers defining the range (e.g., 2 and 10).

[0007] Unless otherwise indicated, ratios, percentages, parts, and the like are by weight.

[0008] 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 moles of crosslinkable functional groups divided by the total number of moles of monomer units contained in the polyolefin.

[0009] 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.

[0010] Unless otherwise indicated, "alkene" refers to CI to CIO alkenes.

[0011] Unless otherwise indicated, "alkyne" refers to CI to CIO alkynes.

[0012] Unless stated otherwise, any method or process steps described herein may be performed in any order.

[0013] The present disclosure describes a method for preparing a polyolefin material. The polyolefin material is prepared by providing a crosslinked polyolefin material; surface treating the crosslinked polyolefin material with an acidic medium; heating the crosslinked polyolefin material at or below 140 degrees C, thereby providing a stabilized polyolefin material. The polyolefin material is further prepared by heating polyolefin material in an oxidizing environment at a temperature no greater than 500 degrees C, thereby providing an oxidized polyolefin material. The polyolefin material is further prepared by heating the polyolefin material in an inert environment, thereby providing a carbonaceous polyolefin material.

[0014] 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. [0015] The treated olefin 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.

[0016] The fabricated articles described herein are subjected to a crosslinking step. In one instance, the fabricated article has been melt blended with a treating agent prior to the crosslinking step. In one instance, the fabricated article has been melt blended without the use of a treating agent prior to the crosslinking step. A variety of methods for crosslinking polyolefins are known. In one instance, the fabricated articles 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.

[0017] As noted above, at least a portion of the polyolefin 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.

[0018] Crosslinking the fabricated article is 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. Where the fabricated article is a fiber, crosslinking can contribute to an

improvement in fiber properties, for example, increase shape retention. In one instance, the fabricated article is crosslinked such that it has at least 50 percent gel fraction. In one instance, the fabricated article is crosslinked such that it has at least 55 percent gel fraction. In one instance, the fabricated article is crosslinked such that it has at least 60 percent gel fraction. In one instance, the fabricated article is crosslinked such that it has at least 65 percent gel fraction. In one instance, the fabricated article is crosslinked such that it has at least 70 percent gel fraction.

[0019] As noted above, the surface of the crosslinked fabricated article is modified with a surface-treating agent and a subsequent heat treatment to yield a surface-treated fabricated article. The surface of the fabricated article is defined as the outermost portion of the fabricated article. The surface-treating agent is a chemical agent which is suitable for pacifying the surface of the fabricated article. The surface of the fabricated article is pacified when adjacent fabricated articles do not fuse together when heated, such as during the air-oxidation process described herein. In some embodiments, the surface of the fabricated article is pacified when adjacent fabricated articles are substantially not fused together when heated. In one instance, the surface-treating agent is an acidic medium. In one instance, the acidic medium is a sulfonating agent or a nitrating agent. In some embodiments, the sulfonating agent is an SO3 containing moiety. In some embodiments, the surface-treating agent is selected from the list consisting of sulfuric acid, fuming sulfuric acid, sulfur trioxide, and chlorosulfonic acid. In one instance, the sulfur trioxide is a gaseous sulfur trioxide or a halogenated compound containing sulfur trioxide. In one instance, the nitrating agent is nitric acid. Without being limited by theory, the surface- treating agent serves to prevent the fabricated article from fusing together when heated by pacifying the surface of the fabricated article. For example, where the fabricated article is a fiber, if the fabricated article is not treated with the surface-treating agent, the filaments which comprise the fiber will fuse together when heated. Treating the fiber with the surface-treating agent helps to prevent filament fusion. In one instance, the concentration of the sulfuric acid in the surface-treating agent is 90 percent or less. In one instance, the concentration of the sulfuric acid in the surface-treating agent is 98 percent or less. In one instance, the concentration of the sulfuric acid in the surface-treating agent is 10 percent or greater. In one instance, the concentration of the sulfuric acid in the surface-treating agent is 20 percent or greater. In one instance, the concentration of the sulfuric acid in the surface-treating agent is 30 percent or greater.

[0020] Following the surface-treating step the polyolefin material is heated. In one instance, the initial temperature of this heating step is at or below the melting point of the polymer resin. In one instance, the temperature of this heating step is at or above 120 °C. The temperature selected for this heating step is a function of the time of treatment. In one instance, this heating step is performed in an inert environment. In one instance, this heating step is performed in air.

[0021] In some embodiments, after treating the fabricated article with the surface treating agent, the fabricated article is subjected to a heating step and then is subsequently treated again with surface treating agent and subsequently subjected to an additional heating step and followed by one or more additional treatment with a surface treatment agent and heating step. For example, following the first treatment with a surface treatment agent the fabricated article is heated at 120 °C for 20 minutes, followed by treatment with a surface treatment agent, followed by heating at 130 °C for 20 minutes, followed by treatment with a surface treatment agent, followed by heating at 140 °C for 20 minutes. In some

embodiments, tension is applied during either or both of the surface-treatment or heating steps to maintain fiber tow length or reduce fiber tow shrinkage. In some embodiments, the surface-treated fabricated article is then washed with water.

[0022] In one instance, the crosslinking step and the surface-treatment step are performed simultaneously by selecting a compound which performs the functions of both the chemical agent and the surface-treating agent. For example, SO3 containing moieties are suitable for both crosslinking and surface treating a polyolefin fabricated article. In some embodiments, chemical crosslinking and surface treating of the fabricated article are performed in a single step by treating the fabricated article with an SO3 containing moiety. In some

embodiments, the conditions for this single-step treatment include treating the fabricated article with the surface-treating agent and heating the fabricated article step- wise, for example, heating at 120 °C for 20 minutes, followed by heating at 130 °C for 20 minutes, followed by heating at 140 °C for 20 minutes. In some embodiments, the fabricated article is then washed with water. In some embodiments, the fabricated article is first crosslinked, and is second surface-treated.

[0023] In one instance, following surface treatment, the surface-treated fabricated article is washed in a solvent. Suitable solvents may include toluene, xylene, or a high-temperature halocarbon. An example of a suitable high-temperature halocarbon is tetrachloroethane. In some embodiments, the temperature of the solvent is above room temperature. In one instance, the temperature of the solvent is at or is greater than 80 °C. In another instance, the temperature of the solvent is at or is less than 100 °C. Without being limited by theory, washing the surface-treated fabricated article with the solvent removes at least some of the portions of the fabricated article which were not crosslinked. It was observed that washing with the solvent reduces the instances of filament fusion. It is anticipated that where the crosslinking step is more efficient, meaning a greater percentage of the fabricated article is crosslinked, the need to wash with the solvent will be reduced. It is anticipated that washing with the solvent will be unnecessary where there is extensive crosslinking in the fabricated article. For example, where the fabricated article is 70-100% crosslinked, the solvent wash step may be unnecessary.

[0024] In one instance, following the surface treating and heating steps are repeated one or more times. In one instance, the surface treating and heating steps are performed such that the fabricated article reaches a gel fraction of at least 70 percent. The desired gel fraction can be achieved by either or both of repeating the surface treating and heating steps or adjusting the conditions of the surface treating and heating steps (for example, increasing the duration of the steps or increasing the temperature of the heating steps or increasing the concentration of the surface treating agent).

[0025] Following the surface-treating step, including both treating with the surface treating agent and the heating step, the polyolefin material is treated with a stabilizing agent to provide a stabilized fabricated article. In one instance, the stabilizing agent is an oxidizing agent. In one instance, the oxidizing agent is oxygen. In one instance, the crosslinked fabricated article is treated with the stabilizing agent by exposing the crosslinked fabricated article to a heated oxidizing environment to yield a stabilized fabricated article. In some embodiments, the temperature for the oxidizing environment is at least 120 °C, preferably at least 190 °C. In some embodiments, the temperature for the oxidizing environment is no more than 500 °C, preferably no more than 400 °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 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 treated stabilized fabricated article which is a precursor for a carbonaceous article. Without being limited by theory, the stabilization process oxidizes at least a portion of the crosslinked fabricated article and causes changes to the hydrocarbon structure that increases at least a portion of the crosslink density while decreasing the hydrogen/carbon ratio of the crosslinked fabricated article. Without being limited by theory, the stabilized article has a modified surface as compared to a control article.

[0026] The present disclosure describes a stabilized polyolefin article comprising an empirical formula, CH_xS_YOz, where: 1.85≤ X≤ 2.10; 0.00 < Y < 0.035; and 0.03≤ Z≤ 0.20. In one instance, 1.9≤ X≤ 2.08. In one instance, 1.918≤ X≤ 2.062. In one instance, 0.00 < Y < 0.0209. In one instance, 0.001 < Y < 0.03. In one instance, 0.0424≤ Z≤ 0.148. In one instance, 0.035 < Z < 0.18.

[0027] The present disclosure describes an oxidized polyolefin article comprising an empirical formula, CHxOz, where: 0.35 < X < 0.50; and 0.5 < Z < 0.6. In one instance, 0.390≤ X≤ 0.418. In one instance, 0.37≤ X≤ 0.46. In one instance, 0.525≤ Z≤ 0.562. In one instance, 0.51 < Z < 0.58. [0028] 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.

[0029] The carbonaceous articles described herein are prepared by carbonizing the stabilized fabricated article by heat-treating the treated stabilized fabricated articles in an inert environment. The inert environment is an environment surrounding the 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.

[0030] 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 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.

[0031] 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 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 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.

[0032] In the Examples, overall mass yield is calculated as the product of oxidation mass yield and carbonization mass yield (calculated as provided below). PHR refers to parts per hundred resin (mass basis). 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. Definitions of measured yields:

Oxidation mass yield: Y_N =

mpE

Carbonization mass yield: Y_C =

mox

Overall mass yield: Y_M = YQ YQ

Overall mass yield (carbonaceous mass per initial mass of PE): Y_{M PE} = ^Y°^YC

^M%PE

Where mm is the initial mass of polyethylene; mox is the mass remaining after oxidation; mc_F is the mass remaining after carbonization; M%PE is the mass % of polyethylene in the origin formed article.

[0033] Soxhlet extraction is a method for determining the gel fraction and swell ratio 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 fraction (%) 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. The treated articles are submitted for elemental analysis to determine the carbon, hydrogen, nitrogen, sulfur, and oxygen content. A Thermo Model Flash EA1112 Combustion CHNS/O Analyzer is used for determining carbon, hydrogen, nitrogen, sulfur, and oxygen components.

[0034] Carbon fiber tensile properties (modulus, strength, strain) for single filaments/fibers are determined using a single column Instron model 5543 following procedures based on ASTM method C1557 (Standard Test Method for Tensile Strength and Young's Modulus of Fibers). A 5 N load cell with appropriate grips are used. Fiber diameter is determined by optical microscopy.

Polyethylene fiber preparation

[0035] An ethylene/octene copolymer (density = 0.955 g/cm3; MI = 30 g/10 min,

190°C/2.16 kg) is melt spun and hot-drawn to form five fiber tows (identified as PEF1, PEF2, PEF3, PEF4 and PEF5) with the following properties reported in Table 1.

Table 1

Polyethylene fiber crosslinking by batch electron beam exposure

[0036] Polyethylene fiber tows are crosslinked by electron beam exposure using the AEB Lab System (Advanced Electron Beams, Inc., Wilmington, MA). The batch-mode apparatus comprises of a sealed, high vacuum, electron emitter lamp with a maximum accelerating voltage of 150 kV and a maximum e-beam dose of 80 kGy per pass. A continuous fiber tow is wound around stainless steel pegs attached around the exterior of a similar 8" x 10" aluminum plate with the center section removed. Upon placement of the polyethylene tow in the AEB Lab System chamber, the sample is purged with high purity nitrogen gas from a gas cylinder until the oxygen concentration within the apparatus dropped below a pre-set value, typically 200 ppm. The tows are irradiated by programming the control computer to execute the required number of passes, transporting the mounted samples under the beam on each pass, to achieve the desired total dosage.

Polyethylene fiber crosslinking by continuous electron beam exposure

[0037] Polyethylene fiber tows are crosslinked by electron beam exposure using a pilot- scale PCT Engineered Systems apparatus (Davenport, IA). The polyethylene fiber tow is fed continuously at 25 ft/min to the electron beam apparatus using Izumi winders. The pilot-scale system comprises a controlled atmosphere housing and a rotating 24 in diameter cooled roller. The polyethylene fiber tow is irradiated continuously by accelerated electron beams from an emitter mounted in the top of the housing. The accelerating voltage is 200 kV and the current is 295-300 mA. Electron beam irradiation dosage is determined by residence time.

Example 1

[0038] The fiber tow identified as PEF2 in Table lis crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 89.7%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish; confirmed by ATR-FTIR spectroscopy. Three (3) washed crosslinked fiber tows (identified as 1A, IB and 1C) are tied between two sections of commercial carbon fiber and undergo the following acid thermal treatment:

1. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 60 min. The tow is removed from the oven, and is observed to be black in color, and flexible.

Filaments are separable.

2. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 60 min.

3. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 130°C for 20 min. The tow is removed from the oven, and is observed to be black in color, and flexible.

Filaments are separable. 4. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 140°C for 20 min. After all treatments and carbon fiber leads are removed, the tow is removed from the oven, and is observed to be black in color, and flexible. Filaments are separable.

Example 1A

[0039] One fiber tow prepared according to Example 1, identified as 1A, is rinsed with 50 vol% sulfuric acid and deionized water and dried. A portion of 1A is heated in a nitrogen atmosphere using a TGA (10°C/min to 800°C). The final char yield is 10.4% of the initial mass at 800°C; 1 A loses 70.3% of the initial mass between 400-500°C. The mean elemental composition of 1A is 72.5 wt% carbon, 11.7 wt% hydrogen, 3.9 wt% sulfur, and 12.0 wt% oxygen (by difference). See Tables 2-6.

Example IB

[0040] One fiber tow prepared according to Example 1, identified as IB, is stabilized unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The mean elemental composition of IB is 57.7 wt% carbon, 2.0 wt% hydrogen, ND (<0.5) wt% sulfur, and 40.3 wt% oxygen (by difference). See Tables 7-11.

Example 1C

[0041] One fiber tow prepared according to Example 1, identified as 1C, is stabilized unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The fiber tow is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber tow is flexible and separable, indicating individual filaments. Individual filaments are mounted using a 0.28 inch gauge length and tensile tested.. Nine (9) filaments of 1C are tested to produce the following mean properties: diameter = 9.7 μιη, modulus = 9.16 GPa, tensile strength = 0.12 GPa, tensile strain = 1.96%. Example 2

[0042] The fiber tow identified as PEF3 in Table 1 is crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 89.4%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0043] Three (3) washed crosslinked fiber tows prepared according to Example 2 (identified as 2A, 2B and 2C) are tied between two sections of commercial carbon fiber and each undergo the following acid thermal treatment:

Filaments are separable.

4. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 140°C for 20 min. After all treatments and carbon fiber leads are removed, the tow is removed from the oven, and is observed to be black in color, and flexible. Filaments are separable.

Example 2A

[0044] One fiber tow prepared according to Example 2, identified as 2A, is rinsed with 50 vol% sulfuric acid and deionized water and dried. A portion of 2A is heated in a nitrogen atmosphere using a TGA (10°C/min to 800°C). The final char yield is 8.9% of the initial mass at 800°C; 2A loses 73.1% of the initial mass between 400-500°C. The mean elemental composition of 2 A is 73.1 wt% carbon, 11.9 wt% hydrogen, 3.4 wt% sulfur, and

11.5 wt% oxygen (by difference). See Tables 2-6. Example 2B

[0045] One fiber tow prepared according to Example 2, identified as 2B, is stabilized unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The mean elemental composition of 2B is 56.7 wt% carbon, 2.0 wt% hydrogen, ND (<0.5) wt% sulfur, and 41.4 wt% oxygen (by difference). See Tables 7-11.

Example 2C

[0046] One fiber tow prepared according to Example 2, identified as 2C, is stabilized unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. Sample 2C is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber tows are flexible and separable, indicating individual filaments. Individual filaments are mounted using a 0.5 inch gauge length and tensile tested. Eight (8) filaments of 2C are tested to produce the following mean properties: diameter = 8.0 μιη, modulus = 25.4 GPa, tensile strength = 0.18 GPa, tensile strain = 0.73%.

Example 3

[0047] The fiber tow identified as PEF4 in Table 1 is crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 91.0%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish; confirmed by ATR-FTIR spectroscopy. Three (3) washed crosslinked fiber tows (identified as 3 A, 3B, and 3C) are tied between two sections of commercial carbon fiber and undergo the following acid thermal treatment:

Filaments are separable. 2. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 60 min.

Filaments are separable.

Example 3A

[0048] One fiber tow prepared according to Example 3, identified as 3A, is rinsed with 50 vol% sulfuric acid and deionized water and dried. A portion of 3A is heated in a nitrogen atmosphere using a TGA (10°C/min to 800°C). The final char yield is 6.0% of the initial mass at 800°C; 3A loses 73.7% of the initial mass between 400-500°C. The mean elemental composition of 3A is 70.4 wt% carbon, 11.8 wt% hydrogen, 3.9 wt% sulfur, and 13.9 wt% oxygen (by difference). See Tables 2-6.

Example 3B

[0049] One fiber tow prepared according to Example 3, identified as 3B, is stabilized unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at

2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The mean elemental composition of 3B is 56.1 wt% carbon, 1.8 wt% hydrogen, ND (<0.5) wt% sulfur, and 42.0 wt% oxygen (by difference). See Tables 7-11.

Example 3C

[0050] One fiber tow prepared according to Example 3, identified as 3C, is stabilized unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at

2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The tow is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber tow is flexible and separable, indicating individual filaments. Individual filaments are mounted using a 0.28 inch gauge length and tensile tested. Two (2) filaments of 3C are tested to produce the following mean properties:

diameter = 6.9 μιη, modulus = 24.5 GPa, tensile strength = 0.14 GPa, tensile strain = 0.56%. Example 4

[0051] The fiber tow identified as PEF3 in Table 1 is crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 89.4%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0052] One (1) washed crosslinked fiber tow is tied between two sections of commercial carbon fiber and each undergo the following acid thermal treatment:

1. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 20 min. The tow is removed from the oven, and is observed to be black in color, and flexible.

Filaments are separable.

2. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 20 min.

Filaments are separable.

[0053] The tow is rinsed with deionized water and dried. The tow is stabilized

unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The tow is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber tows are flexible and separable, indicating individual filaments. Individual filaments are mounted using a 0.28 inch gauge length and tensile tested. Seven (7) filaments are tested to produce the following mean properties: diameter = 8.8 μιη, modulus = 33.2 GPa, tensile strength = 0.34 GPa, tensile strain = 1.00%. Example 5

[0054] The fiber tow identified as PEF3 in Table 1 is crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 89.4%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0055] One (1) washed crosslinked fiber tows is tied between two sections of commercial carbon fiber and each undergo the following acid thermal treatment:

1. The tow is dipped in chlorosulfonic acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 20 min. The tow is removed from the oven, and is observed to be black in color, and flexible.

Filaments are separable.

2. The tow is dipped in chlorosulfonic acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 20 min.

3. The tow is dipped in chlorosulfonic acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 130°C for 20 min. The tow is removed from the oven, and is observed to be black in color, and flexible. Filaments are separable.

4. The tow is dipped in chlorosulfonic acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 140°C for 20 min. After all treatments and carbon fiber leads are removed, the tow is removed from the oven, and is observed to be black in color, and flexible. Filaments are separable. [0056] The tow is rinsed with deionized water and dried. The tow is stabilized

unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The tow is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber tows are flexible and separable, indicating individual filaments. Individual filaments are mounted using a 0.5 inch gauge length and tensile tested. Seven (7) filaments are tested to produce the following mean properties: diameter = 10.2 μιη, modulus = 25.3 GPa, tensile strength = 0.20 GPa, tensile strain = 0.79%.

Example 6

[0057] The fiber tow identified as PEF3 in Table 1 is crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 89.4%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0058] One (1) washed crosslinked fiber tows is tied between two sections of commercial carbon fiber and each undergo the following acid thermal treatment:

1. The tow is dipped in 70 wt% nitric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 100°C for 20 min.

2. The tow is dipped in 70 wt% nitric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 100°C for 20 min.

3. The tow is dipped in 70 wt% nitric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 110°C for 20 min.

4. The tow is dipped in 70 wt% nitric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 20 min. After all treatments and carbon fiber leads are removed, the sample is removed, brown in color, and flexible. Filaments are separable. [0059] The tow is rinsed with deionized water and dried. The tow is stabilized

unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The tow is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting tow is analyzed using SEM. The tow is flexible and separable, indicating individual filaments.

Example 7

[0060] The fiber tow identified as PEF1 in Table 1 is crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 91.8%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0061] One (1) washed crosslinked fiber tows is tied between two sections of commercial carbon fiber and each undergo the following acid thermal treatment:

1. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension.

Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 20 min. The tow is removed from the oven, and is observed to be black in color, and flexible.

Filaments are separable.

[0062] The tow is stabilized unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The tow is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber tows are flexible and separable, indicating individual filaments. Individual filaments are mounted using a 0.28 inch gauge length and tensile tested. Nine (9) filaments are tested to produce the following mean properties: diameter = 9.1 μιη, modulus = 20.5 GPa, tensile strength = 0.13 GPa, tensile strain = 0.63%.

Example 8

[0063] The fiber tow identified as PEF2 in Table 1 is crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 89.7%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0064] One (1) washed crosslinked fiber tows is tied between two sections of commercial carbon fiber and each undergo the following acid thermal treatment:

Filaments are separable.

[0065] The tow is rinsed with 50 vol% sulfuric acid and deionized water and dried. A portion of the tow is heated in a nitrogen atmosphere using a TGA (10°C/min to 800°C). The final char yield is 2.0% of the initial mass at 800°C; the sample loses 85.6% of the initial mass between 400-500°C. The mean elemental composition of the surface treated sample is 81.7 wt% carbon, 13.6 wt% hydrogen, ND (<0.5) wt% sulfur, and 4.6 wt% oxygen (by difference). See Tables 2-6.

Example 9

[0066] The fiber tow identified as PEF1 in Table 1 is crosslinked with electron beam irradiation (400 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 74.4%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0067] One (1) washed crosslinked fiber tow is tied between two sections of commercial carbon fiber and undergoes the following acid thermal treatment:

Filaments are separable.

3. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension.

Air flow is 1.5 L/min. The tow is heated in the oven at 130°C for 20 min. The tow is removed from the oven, and is observed to be black in color, and flexible.

Filaments are separable.

[0068] The tow is rinsed with deionized water and dried. The tow is stabilized

unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The tow is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber tows are flexible and separable, indicating individual filaments. Individual filaments are mounted using a 0.5 inch gauge length and tensile tested. Ten (10) filaments are tested to produce the following mean properties: diameter = 10.8 μιη, modulus = 18.8 GPa, tensile strength = 0.19 GPa, tensile strain = 1.46%.

Example 10

[0069] The fiber tow identified as PEF2 in Table 1 is crosslinked with electron beam irradiation (400 kGy; 80 kGy/dose) to yield a crosslinked tow. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0070] One (1) washed crosslinked fiber tows is tied between two sections of commercial carbon fiber and undergoes the following acid thermal treatment:

Filaments are separable.

2. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 20 min. 3. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 130°C for 20 min. The tow is removed from the oven, and is observed to be black in color, and flexible.

Filaments are separable.

[0071] The tow is rinsed with 50 vol% sulfuric acid and deionized water and dried. A portion of the tow is heated in a nitrogen atmosphere using a TGA (10°C/min to 800°C). The final char yield is 2.0% of the initial mass at 800°C; the sample loses 85.6% of the initial mass between 400-500°C. The mean elemental composition of the surface treated sample is 75.1 wt% carbon, 13.0 wt% hydrogen, 2.0 wt% sulfur, and 9.9 wt% oxygen (by difference). See Tables 2-6.

Example 11

[0072] The fiber tow identified as PEF4 in Table 1 is crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 91.0%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0073] One (1) washed crosslinked fiber tows is tied between two sections of commercial carbon fiber and undergoes the following acid thermal treatment:

1. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 60 min.

2. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 18.5 hours. After all treatments and carbon fiber leads are removed, the tow is removed from the oven, and is observed to be black in color, and flexible. Filaments are separable.

[0074] The surface treated fiber is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber tow is flexible and separable, indicating individual filaments.

Individual filaments are mounted using a 0.5 inch gauge length and tensile tested. Fifteen (15) filaments are tested to produce the following mean properties: diameter = 8.8 μιη, modulus = 52.3 GPa, tensile strength = 0.61 GPa, tensile strain = 1.14%.

Example 12

[0075] The fiber tow identified as PEF1 in Table 1 is crosslinked with electron beam irradiation (1200 kGy; 80 kGy/dose) to yield a crosslinked tow with mean gel fraction of 88.7%, as determined by Soxhlet extraction. The crosslinked fiber tow is washed in deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0076] Three (3) washed crosslinked fiber tows, identified as 12A, 12B, and 12C, are tied between two sections of commercial carbon fiber and each undergo the following acid thermal treatment:

1. Each fiber tow is dipped in 30 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 20 min. The tow is removed from the oven, and is observed to be black in color, and flexible. Filaments are separable.

2. Each fiber tow is dipped in 30 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 20 min.

3. Each fiber tow is dipped in 30 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 130°C for 20 min. The tow is removed from the oven, and is observed to be black in color, and flexible. Filaments are separable.

4. Each fiber tow is dipped in 30 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 140°C for 20 min. After all treatments and carbon fiber leads are removed, the tow is removed from the oven, and is observed to be black in color, and flexible. Filaments are separable. Example 12 A

[0077] The fiber tow prepared according to Example 12 and identified as 12A is oxidized in air at 10°C/min to 350°C in a TGA. The tow is further carbonized in nitrogen at 10°C/min to 800°C in a TGA. Separable, individual, and hollow carbon fibers are observed by SEM. Example 12B

[0078] The fiber tow prepared according to Example 12 and identified as 12B is oxidized in air at 10°C/min to 400°C in a TGA. The tow is further carbonized in nitrogen at 10°C/min to 800°C in a TGA. Separable, individual, and solid carbon fibers are observed by SEM. Example 12C

[0079] The fiber tow prepared according to Example 12 and identified as 12C is stabilized unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The tow is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber tows are flexible and separable, indicating individual filaments. Individual filaments are mounted using a 0.5 inch gauge length and tensile tested. 20 (20) filaments are tested to produce the following mean properties:

diameter = 10.8 μιη, modulus = 30.0 GPa, tensile strength = 0.20 GPa, tensile strain = 0.65%.

Comparative Example 1

[0080] 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 fiber tows with the following properties: 1573 filaments, 1976.1 total denier, 2.22 gf/den, 12.32% elongation-to-break. The prepared fiber tows are continuously treated in a vessel containing an isopropanol solution with 5 wt% of an aryl sulfonic acid, Nacure B201, supplied by King Industries, for 30 min. The treated fiber tows are allowed to dry cure for 3 days. The fiber tows are subsequently moisture cured at 80 °C (100% relative humidity) for 5 days. The gel fraction is determined to be 58.2% by Soxhlet extraction. [0081] The crosslinked fiber tow is washed in isopropanol followed by deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0082] One (1) washed crosslinked fiber tow is tied between two sections of commercial carbon fiber and each undergo the following acid thermal treatment:

3. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 130°C for 20 min.

4. The tow is dipped in 96 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 140°C for 20 min. After all treatments and carbon fiber leads are removed, the tow is removed from the oven, and is observed to be black in color.

[0083] The tow is stabilized unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The tow is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber sample is brittle and fused. No individual filaments are separable.

Comparative Example 2

[0084] 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 fiber tows with the following properties: 1573 filaments, 1976.1 total denier, 2.22 gf/den, 12.32% elongation-to-break.

The prepared fiber tows are continuously treated in a vessel containing an isopropanol solution with 5 wt% of an aryl sulfonic acid, Nacure B201, supplied by King Industries, for 30 min. The treated fiber tows are allowed to dry cure for 3 days. The fiber tows are subsequently moisture cured at 80 °C (100% relative humidity) for 5 days. The gel fraction is determined to be 60.8% by Soxhlet extraction.

[0085] The crosslinked fiber tow is washed in isopropanol followed by deionized water for 1 hour at 60°C to remove the fiber spin finish.

[0086] Two (2) washed crosslinked fiber tows, identified as C2A and C2B, are tied between two sections of commercial carbon fiber and each undergo the following acid thermal treatment:

1. The tow is dipped in 50 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 60 min.

2. The tow is dipped in 50 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with lOOg tension. Air flow is 1.5 L/min. The tow is heated in the oven at 120°C for 60 min.

3. The tow is dipped in 50 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 130°C for 20 min.

4. The tow is dipped in 50 wt% sulfuric acid for 5-10 seconds and placed on Pigmat® to remove excess acid. The tow is placed in air convection oven with 20g tension. Air flow is 1.5 L/min. The tow is heated in the oven at 140°C for 20 min. After all treatments and carbon fiber leads are removed, the tow is removed from the oven, and is observed to be black in color.

Comparative Example 2A

[0087] The gel fraction of C2A after surface treatment is 68.9%, as determined by Soxhlet extraction.

Comparative Example 2B

[0088] The fiber tow C2B is stabilized unconstrained in a quartz boat in a batch tube furnace. Air is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 400°C and subsequently cooled to room temperature. The tow is carbonized unconstrained in a quartz boat in a batch tube furnace. Nitrogen is continuously fed at 2000 seem. The tube furnace is heated at 4°C/min from room temperature to 1150°C and subsequently cooled to room temperature. The resulting carbon fiber sample is brittle and fused. No individual filaments are separable.

[0089] Tables 2 through 11 report the elemental analysis for a portion of the preceding examples.

Table 2

Surface C (wt%) H (wt%) N (wt%) S (wt%) O (wt%) Treated

Example

1A 72.5 11.7 ND (<0.5) 3.9 12.0

2A 73.1 11.9 ND (<0.5) 3.4 11.5

3A 70.4 11.8 ND (<0.5) 3.9 13.9

8 81.7 13.6 ND (<0.5) ND (<0.5) 4.6

10 75.1 13.0 ND (<0.5) 2.0 9.9

Table 3

Surface H/C (wt/wt) N/C (wt/wt) S/C (wt/wt) N/H (wt/wt) O/C (wt/wt) Treated

Example

1A 0.161 0.000 0.053 0.000 0.165

2A 0.163 0.000 0.047 0.000 0.157

3A 0.168 0.000 0.056 0.000 0.198

8 0.167 0.000 0.000 0.000 0.056

10 0.173 0.000 0.027 0.000 0.131

Table 4

Surface C (mol%) H (mol%) N (mol%) S (mol%) O (mol%) Treated

Example

1A 32.7 62.6 0.0 0.7 4.0

2A 32.4 63.2 0.0 0.6 3.8

3A 31.5 63.1 0.0 0.7 4.7

8 33.0 65.6 0.0 0.0 1.4

10 31.5 65.0 0.0 0.3 3.1 Table 5

Surface H/C N/C S/C N/H O/C

Treated (mol/mol) (mol/mol) (mol/mol) (mol/mol) (mol/mol)

Example

1A 1.918 0.0 0.0200 0.0 0.124

2A 1.950 0.0 0.0177 0.0 0.118

3A 2.001 0.0 0.0209 0.0 0.148

8 1.991 0.0 0.0 0.0 0.0424

10 2.062 0.0 0.0101 0.0 0.0987

Table 6

Table 7

Oxidized C (wt%) H (wt%) N (wt%) S (wt%) 0 (wt%) Example

IB 57.7 2.0 ND (<0.5) ND (<0.5) 40.3

2B 56.7 2.0 ND (<0.5) ND (<0.5) 41.4

3B 56.1 1.8 ND (<0.5) ND (<0.5) 42.0

Table 8

Oxidized H/C (wt/wt) N/C (wt/wt) S/C (wt/wt) N/H (wt/wt) O/C (wt/wt)

Example

IB 0.0350 0.0 0.0 0.0 0.700

2B 0.0350 0.0 0.0 0.0 0.730

3B 0.0327 0.0 0.0 0.0 0.749 Table 9

Oxidized C (mol%) H (mol%) N (mol%) S (mol%) 0 (mol%)

Example

IB 51.5 21.5 0.0 0.0 27.0

2B 50.9 21.3 0.0 0.0 27.9

3B 51.2 20.0 0.0 0.0 28.8

Table 10

Oxidized H/C N/C s/c N/H O/C

Example (mol/mol) (mol/mol) (mol/mol) (mol/mol) (mol/mol)

IB 0.418 0.0 0.0 0.0 0.525

2B 0.418 0.0 0.0 0.0 0.548

3B 0.390 0.0 0.0 0.0 0.562

Table 11

Claims

WHAT IS CLAIMED IS:

1. A method for preparing a polyolefin material comprising:

(a) providing a crosslinked polyolefin material;

(b) surface treating the crosslinked polyolefin material with an acidic medium;

(c) heating the crosslinked polyolefin material at or below 140 degrees C.

2. The method for preparing a polyolefin material of claim 1, wherein the crosslinked polyolefin material has at least 70% gel content

3. The method for preparing a polyolefin material of any one of claims 1 to 2, wherein the acidic medium is a sulfonating agent or nitrating agent.

4. The method for preparing a polyolefin material of claim 3, wherein the sulfonating agent is sulfuric acid, chlorosulfonic acid, fuming sulfuric acid, or sulfur trioxide.

5. The method for preparing a polyolefin material of claim 4, wherein the sulfur trioxide is a gaseous sulfur trioxide or a halogenated compound containing sulfur trioxide.

6. The method for preparing a polyolefin material of claim 3, wherein the nitrating agent is nitric acid.

7. The method for preparing a polyolefin material of any one of claims 1 to 6, wherein steps (b) and (c) are repeated one or more time.

8. The method for preparing a polyolefin material of any one of claims 1 to 7, further comprising:

(d) heating the polyolefin material in an oxidizing environment at a temperature no greater than 500 degrees C.

9. The method for preparing a polyolefin material further comprising:

(e) heating the polyolefin material in an inert environment at a temperature no greater than 3000 degrees C.

10. A stabilized polyolefin article comprising an empirical formula, CH_XS_YO_Z, where:

1.85≤X≤2.10;

0.000 <Υ<0.035; and

0.03≤ Z≤ 0.20.

11. The stabilized polyolefin article of claim 10, where:

1.918≤X< 2.062;

0.000 < Y < 0.0209; and

0.0424 <Z<0.148.

12. An oxidized polyolefin article comprising an empirical formula, CHxOz, where:

0.35≤X<0.50; and

0.5≤Z≤0.6.

13. The oxidized polyolefin article of claim 12, where:

0.390 <X<0.418; and

0.525 <Z<0.562.