Preparation method of high-dispersed carbon black master batch for polyethylene pipes

Abstract

The application belongs to the field of color master batch preparation, and particularly relates to a preparation method of high-dispersion carbon black master batch for polyethylene pipes. First, a pigment carbon black is modified by oxidation and coated by a complex coupling agent. Then, the treated carbon black is dispersed into a polyethylene carrier through a dense mixing and shearing processing method to obtain a high-dispersion carbon black master batch for polyethylene pipes. The preparation method improves the problems of low dispersibility of the carbon black master batch for pipes and great influence of high carbon black content on the mechanical properties of pipe mixing materials, and has practical application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of plastics, in particular to a preparation method of carbon black master batch for pipes. BACKGROUND

[0002] The general municipal plastic polyethylene pipe requires a service life of more than 50 years, and a certain content of carbon black pigment is generally added to color the pipe and effectively improve the ultraviolet resistance of the pipe material. The content and dispersion of carbon black play a crucial role in the weather resistance of polyethylene pipes. At present, all ISO, EN and national standards stipulate that black compounding materials must be used to produce PE100 grade gas pipes and water pipes. The carbon black content of the compounding material should use carbon black with a particle size of less than 25 nm, the carbon black content should not be less than 2.0%, and the carbon black dispersion should be ≤3 levels; the strict control of the national PE100 grade gas pipes and water pipes puts forward strict requirements for the production of carbon black master batch for pressure pipes.

[0003] The higher the dispersion of carbon black in the pipe material compounding material, the better the ultraviolet resistance of the pipe material, and the smallest effect on the mechanical properties of the pipe material.

[0004] In order to improve the uniform dispersion of carbon black in the compounding material, traditional carbon black master batch for pipes will add small molecular weight dispersing agents such as polyethylene wax, oxidized polyethylene wax, ethylene vinyl acetate wax, etc. during the preparation of the master batch; the addition of these small molecular agents will become the stress concentration point of the first destruction of the high molecular material, resulting in the decrease of the mechanical properties of the compounding material. CN110078995B discloses a preparation method of carbon black master batch for polyethylene pipes. The preparation method adds 5-20% of one or several small molecular dispersants such as polyethylene wax, ethylene bis-stearamide, EVA wax and oxidized polyethylene wax, which improves the dispersion performance of carbon black, but reduces the mechanical properties of the pipe material. In the preparation of black master batch for polyethylene HDPE pipe material, a melt shear dispersion process is used to produce HDPE pipe material special black master batch, which can only be used for PE63 grade pressure pipes due to the addition of small molecular dispersants in the preparation process.

[0005] In order to improve the uniform dispersion of carbon black in the mixed material, a coupling agent is added in the preparation of carbon black master batch to promote the uniform dispersion of carbon black, but the surface group of special pigment type carbon black is less, which cannot form a good organic-inorganic connection bridge with the coupling agent, resulting in that the dispersibility cannot meet the use requirement. CN113214555A discloses a preparation method of high-performance carbon black master batch. After the carbon black, the carbon black master batch carrier and the dispersant are melt blended, an aluminic ester coupling agent is added to improve the wettability of the resin to the surface of the carbon black, but after the blending, the carbon black is plasticized and coated by the carbon black master batch carrier resin, a small amount of groups on the surface of the carbon black and the carrier resin are partially bonded, the connection of the coupling agent to the carbon black and the carrier resin is weakened, and the coupling agent cannot effectively disperse the carbon black. SUMMARY

[0006] The present application aims to provide a preparation method of high-dispersion carbon black master batch for polyethylene pipes, which effectively increases the number of oxygen-containing functions on the surface of carbon black through pretreatment of carbon black, and increases the bonding efficiency of the coupling process of the functional groups on the surface of carbon black to the coupling agent through the blending of carbon black and coupling agent in advance, thereby improving the dispersion effect of carbon black in the pipe material.

[0007] To solve the above technical problems, the present application adopts the following two-stage technical scheme:

[0008] First stage: carbon black pretreatment

[0009] In this stage, the fixed feature carbon black is pretreated. The action mechanism mainly includes two steps: Ⅰ. Air and nitrogen dioxide mixed gas is adsorbed on the surface of carbon black to oxidize carbon black, and nitrogen dioxide adsorbed on the surface of carbon black is reduced on the surface of carbon black to form carbon-oxygen groups and nitric oxide Ⅱ. Nitric oxide is desorbed from the surface of carbon black and reacts with oxygen in the air to generate nitrogen dioxide; nitrogen dioxide / air mixed gas is used to oxidize carbon black, which aims to effectively increase the number of oxygen-containing functions on the surface of carbon black.

[0010] The alkoxyl group in the monoalkoxy titanate coupling agent and the functional groups on the surface of carbon black such as hydroxyl group are de-alcoholized and bonded, the carbon black particles are coated (see coupling coating mechanism), and the long molecular chain structure in the coupling agent is dispersed in the polyethylene resin, so as to effectively disperse the carbon black particles into the master batch carrier resin, increase the bonding efficiency of the coupling process of the functional groups on the surface of carbon black to the coupling agent, and improve the dispersion effect of carbon black in the resin carrier.

[0011]

[0012] Coupling coating mechanism

[0013] The specific pretreatment process of carbon black in this stage is as follows: (1) the carbon black produced by the furnace process has an oil absorption value of 60-130 ml / g and a specific surface area of 50-120 m 2The special pigment carbon black with oil absorption value of 60-130 ml / g and specific surface of 50-120 m Figure 1 / g is placed in the fluidized bed reaction bed layer (the structure of the fluidized bed is shown in );(2) the temperature is raised to 100-500℃ at a rate of 10℃ / min under nitrogen atmosphere;(3) after the temperature is raised to the target temperature, the gas is switched to a mixture of air and nitrogen dioxide to perform surface oxidation treatment on the carbon black;(4) the carbon black after oxidation treatment is placed in a stirrer and stirred for 2-30 min, the stirring speed is 10-500 r / min;(5) the required coupling agent is sprayed into the stirred carbon black, and after continuous stirring for 0.1-2 h, the stirring speed is 10-1000 r / min, to obtain the treated carbon black.

[0014] Second stage: master batch preparation

[0015] The purpose of this stage is to use the integrated processing method of melt shear to combine the mechanical shearing effect and the high-efficiency coupling reaction between the carrier resin and the post-treated carbon black through the coupling agent, so that the carbon black is uniformly dispersed in the color master batch, and the high-dispersion carbon black master batch for pipelines is obtained.

[0016] The specific operation process of this stage is as follows: the high-density polyethylene with specific mass and specific specification is placed in a plasticizing machine at 150-190℃ for plasticizing for 10-20 min, after plasticizing, the carbon black after pretreatment and plasticizing aid are added, and the temperature is 150-190℃, the plasticizing speed is 20-60 r / min, and the plasticizing time is 10-30 min, after plasticizing, the plasticizing material automatically enters the forced feeder, and is extruded and granulated in the single-screw extruder, to obtain the carbon black master batch for pressure pipelines.

[0017] The carbon black raw material used in the above technical solution is a pigment type special carbon black produced by furnace process, and the oil absorption value is 60-130 ml / g, and the specific surface is 50-120 m 2 / g;preferably the oil absorption value is 70-110 ml / g, and the specific surface is 80-120 m 2 / g;the 325 mesh residue is less than 20 ppm, and the ash content is less than 0.2%;

[0018] The polyethylene in the above technical solution is high-density polyethylene, the melt index of the high-density polyethylene is 5-50 g / 10 min, the weight average molecular weight is less than 80000, the number average molecular weight is less than 15000, and the molecular weight distribution is less than 8;

[0019] The coupling agent in the above technical solution is a titanate coupling agent;The titanate coupling agent is a monoalkoxy titanate, and the alkyl type is isopropyl, specifically titanium isopropyl triisostearate, and the amount of the coupling agent is 0.5-5 wt% of the weight of the carbon black;

[0020] The equipment for the carbon black pretreatment in the technical scheme comprises a fluidized bed reactor and a high-speed stirrer;

[0021] The gas for the carbon black pretreatment in the technical scheme is a mixture of nitrogen dioxide and air, and the volume ratio of NO2 to air in the gas mixture is 5-30%:95-70%;

[0022] The mixing aid in the technical scheme is an antioxidant and a lubricant;

[0023] The processing temperature of the internal mixer in the technical scheme is 140-190 DEG C, the mixing speed is 10-80 r / min, and the mixing time is 10-60 min; preferably, the mixing temperature is 150-170 DEG C, the mixing speed is 20-60 r / min, and the mixing time is 10-30 min;

[0024] The antioxidant in the technical scheme is one or more of hindered phenolic antioxidants and phosphite antioxidants;

[0025] The lubricant in the technical scheme is one of zinc stearate and EBS.

[0026] Compared with the prior art, the implementation of the present application has the following beneficial effects:

[0027] Through the implementation of the scheme, high carbon black filling amount and high dispersion of the carbon black master batch for pipes can be prepared without adding small molecular weight dispersants.

[0028] The carbon black master batch product is used in polyethylene pipe mixing materials, and meets the requirements of GB / T 13663-2017 standard for polyethylene (PE) pipe systems for water supply. It can also be used in polyethylene pipe mixing materials for gas, and meets the requirements of GB / T 15558-2015 standard for buried polyethylene (PE) pipe systems for gas. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The fluidized bed of the carbon black pretreatment equipment of the present application is briefly shown in the figure;

[0030] Figure 2 The actual picture of the carbon black master batch for pressure pipes is shown in the figure;

[0031] Figure 3 The dispersion apparent grade diagram of the carbon black master batch in Example 1 is shown in the figure;

[0032] Figure 4 The dispersion apparent grade diagram of the carbon black master batch in Comparative Example 1 is shown in the figure. DETAILED DESCRIPTION

[0033] A preparation method of a high-dispersion carbon black master batch for polyethylene pipes comprises the following steps:

[0034] 1) Carbon black pretreatment: carbon black is placed in a fluidized bed reactor, a mixture of nitrogen dioxide and air is introduced, and the carbon black is oxidized at a suitable temperature range; the oxidized carbon black is placed in a blender and stirred, a coupling agent is added and stirred again to make the coupling agent evenly dispersed on the surface of the carbon black particles, and a pretreated carbon black is obtained;

[0035] 2) Mixing of carbon black masterbatch: polyethylene is placed in an internal mixer for plasticization, after plasticization, internal mixing aids and pretreated carbon black are added for internal mixing, after internal mixing, it is placed in a single screw extruder for extrusion and granulation, and a carbon black masterbatch for pressure pipeline is obtained.

[0036] In order to achieve the purpose of the present application, the technical scheme is further described in detail below with examples.

[0037] Example 1

[0038] 20 kg of Cabot P type carbon black is placed on the fluidized bed reaction bed, the fluidized bed reactor is gas replaced under the nitrogen atmosphere of 10 L / min, the replacement time is 20 min, then the temperature is raised to 300℃ at the temperature raising rate of 10℃ / min, after the bed temperature reaches the target temperature, it is stabilized for 30 min; the nitrogen atmosphere is switched to air-nitrogen dioxide mixed gas atmosphere, the air flow is 10 L / min, the nitrogen dioxide gas flow is 5 L / min, the thermal oxidation treatment is carried out, the treatment time is 2 h, then the atmosphere is switched to 10 L / min nitrogen atmosphere for purging, at the same time, the fluidized bed is cooled to room temperature, then the carbon black is taken out from the fluidized bed take-off port.

[0039] The oxidized carbon black is placed in a 50 L high-speed mixer, 1.5%wt titanium isopropyl titanate coupling agent is sprayed into the carbon black, and then the stirring is started. The stirring rate is 800 r / min, and the stirring time is 20 min. After stirring, the carbon black is transferred to a bucket for standby.

[0040] High-density polyethylene DMDA8920 15 kg is weighed and placed in a 175℃ 35 L internal mixer for plasticization for 10 min, after plasticization, pretreated carbon black 10 kg, zinc stearate 125 g, antioxidant 1010 15 g, antioxidant 168 30 g are added, and internal mixing is carried out at a temperature of 175℃ and an internal mixing speed of 5-10 r / min for 10 min, the temperature of the internal mixer is reduced to 155℃, and internal mixing is carried out again for 15 min, then the internal mixing material is extruded and granulated by a single screw extruder using a forced feeder, and a carbon black masterbatch for pipeline is obtained.

[0041] Example 2

[0042] Put 20 kg Cabot P-type carbon black on the fluidized bed reaction bed, under the atmosphere of 10 L / min nitrogen, the fluidized bed reactor is replaced by gas, the replacement time is 20 min, then heated to 300℃ at a rate of 10℃ / min, after the bed temperature reaches the target temperature, stabilize for 30 min; nitrogen atmosphere is switched to air and nitrogen dioxide mixed gas atmosphere, where the air flow is 10 L / min, the nitrogen dioxide gas flow is 5 L / min, heat oxidation treatment is carried out, the treatment time is 2 h, then the atmosphere is switched to 10 L / min nitrogen atmosphere for purging, at the same time, the fluidized bed is cooled to room temperature, then the carbon black is taken out from the fluidized bed.

[0043] Put the oxidized carbon black in a 50L high-speed mixer, spray 1.0%wt titanium isopropyl titanate coupling agent into the carbon black, then start stirring. The stirring rate is 800 r / min, and the stirring time is 20 min. After stirring, the carbon black is transferred to the barrel for standby.

[0044] Take 15 kg of high-density polyethylene HMN55180, put it in a 175℃ 35L internal mixer for plasticization for 10 min, after plasticization, add 10 kg of pretreated carbon black, 125 g of zinc stearate, 15 g of antioxidant 1010 and 30 g of antioxidant 168, and carry out internal mixing at a temperature of 175℃ and an internal mixing speed of 5-10 r / min for 10 min. Reduce the temperature of the internal mixer to 155℃, and then carry out internal mixing for 15 min. Then, the internal mixing material is extruded and granulated by a single screw extruder using a forced feeder to obtain a carbon black master batch for pipes.

[0045] Example 3

[0046] Put 20 kg of Jiangxi Black Cat Special Carbon Black M6330 on the fluidized bed reaction bed, under the atmosphere of 10 L / min nitrogen, the fluidized bed reactor is replaced by gas, the replacement time is 20 min, then heated to 300℃ at a rate of 10℃ / min, after the bed temperature reaches the target temperature, stabilize for 30 min; nitrogen atmosphere is switched to air and nitrogen dioxide mixed gas atmosphere, where the air flow is 10 L / min, the nitrogen dioxide gas flow is 5 L / min, heat oxidation treatment is carried out, the treatment time is 2 h, then the atmosphere is switched to 10 L / min nitrogen atmosphere for purging, at the same time, the fluidized bed is cooled to room temperature, then the carbon black is taken out from the fluidized bed.

[0047] Put the oxidized carbon black in a 50L high-speed mixer, spray 1.0%wt titanium isopropyl titanate coupling agent into the carbon black, then start stirring. The stirring rate is 800 r / min, and the stirring time is 20 min. After stirring, the carbon black is transferred to the barrel for standby.

[0048] Take high density polyethylene DMDA8920 15 kg, placed in 175℃ 35L plasticizing mixer 10 min, after plasticizing, add pretreated carbon black 10 kg, zinc stearate 125 g, antioxidant 1010 15 g, antioxidant 168 30 g, at a temperature of 175℃, mixing speed of 5-10r / min for 10 min, reduce the temperature of the mixer to 155℃, and then mixing for 15 min, the mixing material using forced feeder, single screw extruder extrusion granulation, get carbon black masterbatch for pipeline.

[0049] Comparative example 1

[0050] Take high density polyethylene DMDA8920 15 kg, placed in 175℃ 35L plasticizing mixer 10 min, after plasticizing, add black cat pigment type carbon black M6330 10 kg, zinc stearate 125 g, antioxidant 1010 15 g, antioxidant 168 30 g, at a temperature of 175℃, mixing speed of 5-10r / min for 10 min, reduce the temperature of the mixer to 155℃, and then mixing for 15 min, the mixing material using forced feeder, single screw extruder extrusion granulation, get carbon black masterbatch for pipeline.

[0051] Comparative example 2

[0052] Take high density polyethylene DMDA8920 15 kg, placed in 175℃ 35L plasticizing mixer 10 min, after plasticizing, add black cat pigment type carbon black M6330 10 kg, zinc stearate 125 g, antioxidant 1010 15 g, antioxidant 168 30 g, at a temperature of 175℃, mixing speed of 5-10r / min for 10 min, add titanium isopropyl triisostearate coupling agent 150 g, kneading 3 min, reduce the temperature of the mixer to 155℃, and then mixing for 15 min, the mixing material using forced feeder, single screw extruder extrusion granulation, get carbon black masterbatch for pipeline.

[0053] Comparative example 3

[0054] Put 10 kg of black cat pigment type carbon black M6330 in a 50L high speed mixer, spray 1.5%wt of titanium isopropyl triisostearate coupling agent into the carbon black, and then start stirring. The stirring rate is 800r / min, and the stirring time is 20 min. After stirring, the carbon black is transferred to the bucket for standby.

[0055] Take high density polyethylene DMDA8920 15 kg, placed in 175 ℃ 35L internal mixer for plasticization 10 min, after plasticization, add pretreated carbon black 10 kg, zinc stearate 125 g, antioxidant 1010 15 g, antioxidant 168 30 g, at a temperature of 175 ℃, internal mixer speed is 5-10 r / min under the internal mixing 10 min, reduce the temperature of the internal mixer to 155 ℃, then internal mixing 15 min, the internal mixing material is used by forced feeder, extruded and granulated by single screw extruder, get carbon black masterbatch for pipeline.

[0056] Comparative example 4

[0057] Put 20 kg of N115 type carbon black on the fluidized bed reaction bed, replace the gas in the fluidized bed reactor under the atmosphere of 10 L / min nitrogen, the replacement time is 20 min, then heat to 300 ℃ at a heating rate of 10 ℃ / min, after the bed temperature reaches the target temperature, stabilize for 30 min; switch the nitrogen atmosphere to air and nitrogen dioxide mixed gas atmosphere, the air flow is 10 l / min, the nitrogen dioxide gas flow is 5 l / min, heat oxidation treatment, the treatment time is 2 h, then switch the atmosphere to 10 L / min of nitrogen atmosphere for purging, at the same time, reduce the fluidized bed to room temperature, then take out the carbon black from the fluidized bed take-off port.

[0058] Put the oxidized carbon black in a 50L high-speed mixer, spray 1.5%wt of titanium isopropyl titanate coupling agent into the carbon black, then start stirring. The stirring rate is 800 r / min, and the stirring time is 20 min. After stirring, the carbon black is transferred to the barrel for standby.

[0059] Take high density polyethylene DMDA8920 15 kg, placed in 175 ℃ 35L internal mixer for plasticization 10 min, after plasticization, add pretreated carbon black 10 kg, zinc stearate 125 g, antioxidant 1010 15 g, antioxidant 168 30 g, at a temperature of 175 ℃, internal mixer speed is 5-10 r / min under the internal mixing 10 min, reduce the temperature of the internal mixer to 155 ℃, then internal mixing 15 min, the internal mixing material is used by forced feeder, extruded and granulated by single screw extruder, get carbon black masterbatch for pipeline.

[0060] The flowability of the carbon black masterbatch in the examples and comparative examples was tested using a Zwick melt indexer; the carbon black content was tested using a PE company simultaneous thermal analyzer; the carbon black oxidation induction period was tested using a Mettler DSC; the tensile elongation at break, tensile yield strength and dispersion were tested after mixing 6 wt% of the carbon black masterbatch with high-density polyethylene pipe material QZP-10N (94 wt%). The mixing equipment was a twin-screw extruder with a length-diameter ratio of 52 and a screw diameter of 16 mm. Among them, the mechanical tensile elongation at break and tensile yield strength were tested using an Instron tensile tester, and the test standard was ASTM-638; the dispersion was tested according to the GB18251 standard, and the test equipment was an Olympus optical microscope. The test data of the specific examples and comparative examples are as follows:

[0061]

[0062] In Comparative Example 1, no coupling agent was introduced, and the carbon black was not pretreated, resulting in a masterbatch with a poor size dispersion and apparent dispersion grade (see Figure 3 In Comparative Example 2, the pigment carbon black was not pretreated, and the titanate coupling agent was directly added to the component for mixing to prepare the carbon black masterbatch. The carbon black was not pretreated, and the carbon black particles were not effectively coated during the mixing process, resulting in a masterbatch with a poor size dispersion and apparent dispersion grade. In Comparative Example 3, the carbon black was directly coated with a single coupling agent for modification. Due to the small number of functional groups on the surface of the pigment carbon black, efficient coupling and coating modification could not be achieved, resulting in a masterbatch with a poor size dispersion and apparent dispersion grade. In Comparative Example 4, a rubber carbon black with a high oil absorption value and a high iodine absorption value was used, and the pigment carbon black defined in the present patent was not used. In the preparation of the masterbatch, the carbon black could not be effectively dispersed, the dispersion was > 6, and the apparent dispersion grade was C2. The carbon black particles that were not effectively dispersed had a serious impact on the mechanical properties of the mixed material, and the tensile elongation at break was only 340%.

[0063] In the examples, the pigment carbon black was modified by oxidation and coated with a composite coupling agent, and then the treated carbon black was dispersed in the polyethylene carrier by mixing and shearing, resulting in a polyethylene pipe carbon black masterbatch with a carbon black content of 28-41%, a carbon black content of 2.3-2.5% in the mixed material, a carbon black dispersion of ≤2, and an apparent dispersion grade of A2 or higher (see Figure 4). The mechanical property of the mixed material is less affected by the master batch, the tensile elongation at break is all greater than or equal to 640%, the tensile yield strength is greater than or equal to 25 MPa, and the oxidation induction time is greater than or equal to 20 min; it meets the standard requirements of GB / T 13663-2017 polyethylene (PE) pipe system for water supply, the carbon black content is 2.0-2.5 wt%, the carbon black dispersion is less than or equal to 3, the tensile elongation at break is greater than or equal to 350%, the tensile yield stress is greater than or equal to 21 MPa, and the oxidation induction time is greater than or equal to 20 min. It meets the standard requirements of GB / T 15558-2015 buried polyethylene (PE) pipe system for gas, the carbon black content is 2.0-2.5 wt%, the carbon black dispersion is less than or equal to 3, the apparent dispersion grade is above B, the tensile elongation at break is greater than or equal to 350%, the tensile yield stress is greater than or equal to 21 MPa, and the oxidation induction time is greater than or equal to 20 min.

[0064] The above is only an embodiment of the present application, any equivalent change and modification made according to the patent application scope of the present application shall be within the scope of the present application.

Claims

1. A process for the preparation of a high dispersibility carbon black masterbatch for polyethylene pipes, characterized by, The method comprises the following steps: 1) carbon black pretreatment: carbon black is placed in a fluidized bed reactor, a mixture of nitrogen dioxide and air is introduced, and the carbon black is oxidized at a suitable temperature range; the oxidized carbon black is placed in a blender for stirring, a coupling agent is added and stirred again to make the coupling agent uniformly dispersed on the surface of the carbon black particles, and a pretreated carbon black is obtained; 2) mixing of carbon black master batch: polyethylene is plasticized in an internal mixer, after plasticization, additives and pretreated carbon black are added for mixing, after mixing, it is placed in a single screw extruder for extrusion and granulation, and a carbon black master batch for pressure pipeline is obtained; The carbon black raw material used was a pigment type special carbon black produced by a furnace process, having an oil absorption number of 60-130 mL / g, a specific surface area of 50-120 m 2 / g; a 325 mesh residue of less than 20 ppm, and an ash content of less than 0.2 wt%; The coupling agent is a titanate coupling agent; the titanate coupling agent is a monoalkoxy titanate, and the alkyl type is isopropyl, including: titanium isopropyl triisostearate; the amount is 0.5-5wt% of the weight of the carbon black.

2. The production method according to claim 1, characterized by, The polyethylene is high-density polyethylene; wherein the melt index of the high-density polyethylene is 5-50g / 10min, the weight average molecular weight is less than 80000, the number average molecular weight is less than 15000, and the molecular weight distribution is less than 8.

3. The preparation method according to claim 1, characterized in that, In the mixture of nitrogen dioxide and air, the volume ratio of NO2 to air is 5-30%:95-70%.

4. The method of claim 1, wherein, The oxidation treatment temperature is 100-500℃, and the oxidation treatment time is 0.1-24h.

5. The preparation method according to claim 1, characterized in that, The additive is an antioxidant and a lubricant.

6. The method of claim 1, wherein, The processing temperature of the internal mixer is 140-190℃, the mixing speed is 10-80r / min, and the mixing time is 10-60min.

7. The method of claim 5, wherein: The antioxidant is one or more of hindered phenolic antioxidants and phosphite antioxidants.

8. The method of claim 5, wherein: The lubricant is one or more of calcium stearate, zinc stearate and EBS.

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