Abstract:
A method is provided for preparing a multifunctional additive involving irradiating raw cotton plant material with an electron beam source, continually blending the raw cotton plant material during the irradiating and micronizing the irradiated cotton plant material. The invention is improved wherein the irradiating and blending of the raw cotton plant material is performed while the raw cotton plant material is in rope form. Irradiated rope is suitably tensioned before micronizing to compensate for degradability of the rope incurred during irradiation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application based on U.S. patent application Ser. No. 09/861,842 filed May 21, 2001 now U.S. Pat. No. 6,506,712. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to multifunctional additives and methods for preparing and using the same. Specifically, multifunctional additives are produced by irradiating and subsequently fragmenting, or micronizing, plant materials, such as raw cotton. A multifunctional additive made in accordance with the method of the present invention has the following attributes: (1) anti-misting properties, (2) low coefficient of friction, (3) is suitable for use as a substitute for talc, as for example in cosmetics and other personal care products, and (4) is suitable as a substitute for asbestos in industrial applications. 
     BACKGROUND OF THE INVENTION 
     Radiation processing for modification and enhancement of polymeric material properties has been well documented in the prior art. In particular, electron beam processing has been used to improve thermal, chemical, barrier, impact, wear, and other properties of many inexpensive materials extending their utility to demanding applications typically dominated by higher cost materials. Electron beam processing may result in cross-linking, degradation, or a combination of the two, depending on the nature of the polymeric materials and the dosage of radiation applied. Results of electron beam processing of cross-linkable plastics has yielded materials with improved dimensional stability, reduced stress cracking, higher service temperatures, reduced solvent and water permeability. More specifically, radiation induced cross-linking in polyethylene has resulted in increased modulus, tensile and impact strength, hardness, deflection and service temperature stress/crack resistance, abrasion resistance, creep and fatigue resistance. In contrast, radiation processing can also induce degradative, or scissioning, effects in polymeric materials such as polytetrafluoroethylene (PTFE). Scrap or off-spec PTFE, degraded by electron beam processing, has been identified as useful in the production of abrasion-reducing additives. 
     PTFE has found a use as a friction-reducing additive in many areas, including the printing ink industry. PTFE additives provide ink formulations with anti-rub properties so that the inks are resistant to smearing and marring. However, PTFE cost is relatively high in comparison to other anti-abrasion additives and therefore PTFE use is often cost prohibitive. 
     Radiation processing has also been used in degrading high molecular weight cellulose ethers common polymeric materials into low molecular weight cellulose ethers producing low molecular weight cellulose ethers for varying uses. For example, U.S. Pat. No. 5,928,709 to Doenges et al. discloses a method of producing low molecular weight cellulose ethers by irradiation of a mixture of higher molecular weight cellulose ethers and an Arrhenius and/or Bronsted base. The resulting low molecular weight cellulose ethers are suitable as water-binding agents, thickeners and emulsion stabilizes. 
     Clays and talcs have also found traditional use in the reduction of friction. For instance, clays are currently used in down hole drilling fluids useful in reducing friction during drilling operations. Debris present in a down hole is cleared by pumping clay into the bore hole where the clay lowers the viscosity of the debris and aids in moving the clay to an exit. Ideally, the clay maintains the debris in a suspended mixture without building viscosity. In practice, a significant buildup in viscosity is experienced in this process and the efficiency of clearing debris from down holes using clay is significantly less than desired. The cost of suitable clays may also be prohibitive. 
     Talc has found wide use as a friction-reducer in personal care products, most notably mascaras and body powders. Although hypoallergenic in nature and therefore safe for contact with the human body, talc suitable for personal care products is expensive to manufacture. 
     The above-described background highlights the need for multifunctional additives with improved low COF characteristics obtainable at a reduced cost. Such additives should not only be economical to manufacture, but also derived from a cheap but plentiful raw material source. The method of manufacture should also be flexible to accommodate production of additives suitable for a variety of applications. 
     SUMMARY OF THE INVENTION 
     The invention relates to a method for preparing a multifunctional additive from a raw plant material and, in particular, cotton. The raw plant material is irradiated with an electron beam source to form an irradiated product. During the irradiation, the raw plant material is continually blended to provide a uniform radiation dosage to the raw plant material. Following irradiation, the irradiated product is fragmented, or micronized, to form the additive having an average diameter size less than that of the original raw plant material starting product. 
     In the preferred embodiment of the invention, the method utilizes raw cotton as the raw plant material. 
     Prior to the irradiating step of the invention, a granulating step may be included wherein the raw plant material is granulated to reduce the diameter size of the raw plant material before irradiating. In one approach to the invention, the granulating step may reduce the raw plant material to about a ⅛ inch to about a ¼ inch diameter size prior to the irradiating step. 
     The irradiation step of the invention utilizes an electron beam source for delivering accelerated electrons to the raw plant material. A suitable dosage may be between about 30 megaRads to about 100 megaRads depending upon the particular application the resulting additive will be used in. A dosage of about 80 megaRads to about 100 megaRads is preferable where the additive will be used in friction-reducing applications. However, the total dosage is preferably administered in multiple low dosage passes. 
     The micronizing step of the invention is meant to reduce the size of the irradiated product and may be carried out with a jet classifying mill. The micronizing step is intended to reduce the average diameter size of the irradiated plant material to an average diameter size of about 3 microns to 4 microns with 99% of the average diameter sizes being below 10 microns. 
     In addition to a preparatory method, the invention is also directed to an additive, useful in reducing friction, providing anti-misting properties, and suitable as a substitute for talc and asbestos, produced from a raw plant material having been subjected to irradiation by an electron beam. During irradiation, the raw plant material is continually blended so that the raw plant material receives a uniform dosage of irradiation. The irradiated product is subsequently micronized to form an additive with a reduced diameter. The raw plant material used to product the additive is preferably raw cotton. 
     An additive according to the invention as described above is useful in reducing the coefficient of friction of a substance and may be mixed with the substance in a sufficient amount to effectively reduce the coefficient of friction of the substance/additive mixture. The substance may be a lubricant/grease, cosmetic formulation, or matting agent. 
     The invention further contemplates taking irradiated raw cotton plant material in rope form and feeding same through an idler compensating unit, an uncoiling and tensioning unit, a slack control unit and a cotton pinch roll feed unit. The irradiated rope product is then micronized as previously described. 
     After being micronized into powdered form, the irradiated rope is washed, agitated and dried so that the powdered cotton has a pH of 7.0. 
     Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings illustrate the best mode presently contemplated in carrying out the invention. 
     In the drawings: 
     FIG. 1 is a side view of a rope handling system in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferable raw plant material is raw cotton, possibly brought into the process in a baled form subsequent to harvest activities. Cotton is particularly desirable because no pretreatments of starting materials are necessary and raw natural products may be brought directly from their original source (e.g., harvest from a field) into the process, therefore reducing costly pretreatment steps such as etherification. 
     Cotton is a particularly attractive raw plant material for the invention as cotton is grown in about 80 countries, in a band that stretches around the world between latitudes 45° N to 30° S. After planting, seedlings appear five days later, with the first flower buds appearing after approximately six weeks. In another three to five weeks, these buds become flowers. The flowers are short lived and fall from the cotton plant, leaving behind a small seed pod, known as the boll. Each boll contains about 30 seeds, and up to 500,000 fibers of cotton. Each fiber grows its full length in three weeks and for the following four to seven weeks, each fiber gets thicker as layers of cellulose build up cell walls. Approximately ten weeks after flowering, the boll splits open and the raw cotton fibers are exposed to sunlight. As the fibers lose water and die, each fiber collapses into a twisted ribbon structure. Cotton is then picked by hand or by cotton harvesters. Cotton fibers are separated from the associated cotton seeds in a process called ginning. Following ginning, the cotton fiber is pressed into bales and wrapped for protection. 
     Prior to processing the raw cotton through the method according to the invention, the raw cotton fibers are debated, thus allowing the cotton fibers to be stretched into a thin sheet. The unbaled cotton sheet is cut or chopped into fairly small pieces, for example, about 2″×2″ in size. The cut pieces are then fed into a pelletizer or a compressor and compressed into pellets of about ½″ in size. 
     Alternately, if palletizing is not acceptable, the cut pieces may be chopped to form small squares in the range of ½″ to ¼″ in size. Chopping may be performed in a HOG or Cumberland chopper or similar equipment. 
     Thereafter, it is preferred to expose the raw cotton material to irradiation with electrons when the raw material is in a relatively dry state. Preferably, the raw material will have a water content of less than about 0.05% to 1.0% by weight of the raw material. 
     Various sources of radiation may be utilized with the process according to the invention. Useful sources of radiation may be either continuous or pulsed electron beam accelerators currently available in the art. In general, any accelerator from the main types including electrostatic direct-current, electrodynamic DC, radio frequency linear accelerator, magnetic-induction LINACs and continuous wave machines may be used in the process. The dosage, or amount of energy absorbed, is measured in units of megaRads (MR or Mrad), where one MR is equal to one million ergs per gram, or kilograys (kGy), where one kGy is equal to one thousand joules per kilogram. The energy dose delivered to the raw material in the method is 30 to 100 MR. Preferably, dosages on the high end of that spectrum, 80 to 100 MR are preferred where the resulting irradiated materials will be used as anti-friction additives. 
     In accordance with the presently preferred embodiment of the subject invention, the radiation is produced by an electron accelerator. The electron beam is applied through a window to the pellets or small chopped pieces of cotton being carried on a tray system where the material is blended or turned after each pass through the beam window. The irradiation and blending may also be carried out in a ribbon type blender with the radiation applied through a beam window or with a beam horn. In a typical electron accelerator, a dosage of 2.5 MR is applied per pass of the product past the beam window. If the radiation dose is higher, the cotton may burn or degrade. Thus, with a total dosage of 80 MR, the material must be passed under the accelerator window thirty-two times. After each pass, the material must be turned over or blended before again being exposed to the radiation. 
     In contrast, a process according to the invention avoids the limitations in prior art techniques by providing for the raw plant material to be continually blended during the irradiating step. Multi-pass radiation with the material being turned or blended between each pass results in uniform radiation of the raw cotton. 
     Irradiation of the raw plant material forms an irradiated product which is subsequently guided to a micronizing step. Micronizing of the irradiated product is carried out by a micronizing mill, preferably a jet classifying mill such as a model 30 Roto-Jet manufactured by Fluid Energy Al-Jet Company. The jet mill is operated using an air flow of 1500-2000 CFM at 120 psi. This is a high speed grinding mill with an integral, independently driven dynamic classifier producing a narrow size distribution. Although size of the micronized irradiated product may vary depending on the ultimate application for the additive, the general particle range is from about 2 microns to about 10 microns for the applications disclosed herein. For friction-reducing additive applications, 99% of the particles will be below 10 microns in average diameter size with a minimal number of additive particles less than 2 microns in diameter and 0% below 1.0 micron. An average particle diameter of 3 to 4 microns is desirable for friction-reducing applications. 
     It has been discovered that in the process of carrying out the irradiation process described above that the manual debating and cutting of the raw cotton fibers and manual placing of the cut fibers into a tray before further chopping or pellitizing is extremely labor intensive. In addition, if the raw cotton segments are not constantly rotated, they burn. 
     In order to provide an improved system which overcomes the above noted drawbacks and enables a greater throughput, the raw cotton fibers are roped and then irradiated. The irradiated rope is then fed through various roller and tensioning structure before being micronized. 
     Referring now to FIG. 1, thereshown is a rope handling system  10  constructed in accordance with the present invention. The rope handling system  10  includes at least one and preferably a pair of spools  12  of rope coils  16 ,  18 , respectively, fabricated of raw cotton and irradiated according to the process described above. The spools  12 ,  14  or rope uncoiler units have non-driven shafts  20  rotatable in bearings (not shown). The height of each shaft  20  is such that the rope coil  16 ,  18  can be slid onto the shaft  20  from a pallet jack (not shown). Incorporated into the shaft assembly, between the bearings is a mechanical braking system (not shown) to prevent the rope coil  16 ,  18  from freewheeling and overfeeding the rope. The rope handling system  10  is designed to handle rope diameters typically in the ⅜ inch to ⅝ inch range. Each spool  12 ,  14  has the capacity for holding 1,000-50,000 feet of irradiated cotton rope thereon and is generally uncoiled at a rate of about 250 ft. per minute. Based on this uncoiling rate, and an assumed weight of 0.026 pounds per foot for ⅜ inch diameter rope, the instantaneous throughput would be 13 lbs. per minute or 875,000 lbs. per year. 
     Each of the ropes  16 ,  18  is fed to an idler compensating unit  22  comprised of two non-driven idler rolls  24 ,  26 , the first idler roll  24  being a single groove design and the second idler roll  26  being a double groove design. Leading into each idler roll  24 ,  26  is a UMHW PE oblong funnel  28  to direct the rope  16 ,  18  into the groove and to compensate for the change in side-to-side angle as the rope pays off the spool  12 ,  14 . There is also a non-driven, hold down roll  30  above each idler roll  24 ,  26  to keep the rope captive in the idler roll groove. A spring loaded tensioning roll  32  is provided for each roll. This tensioning roll  32  will control the mechanical braking mechanism described above. 
     The ropes  16 ,  18  are next fed into an uncoiling and tensioning unit  34  comprised of an upper roll  36  and a lower roll  38 , each formed with two grooves and both rolls driven by a single variable frequency controlled drive motor. This unit  34  controls the feed rate of the overall system. A non-driven, hold down roll  40  is provided for each driven roll  36 ,  38 . The ropes  16 ,  18  then pass into a slack control unit  42  including a series of top fixed, non-driven, two grooved rolls  44  and a plurality of lower floating rolls  46  that move up and down depending on the relative feed rates of the uncoiling and tensioning unit  34  and a downstream cutter pinch roll feed unit  48 . The vertical portion of the floating rolls  46  is sensed and the feed rate of the uncoiling end tensioning unit  34  is slightly adjusted to maintain the position of the floating rolls  46  and provide the pinch roll feed unit  48  with a constant rope tension and feed rate. When the ropes  16 ,  18  are initially fed through the slack control unit  42 , the floating rolls  46  will rise to a position above the fixed rolls  44  to allow the operator to feed the two ropes across the tops of the fixed rolls  44  and into the downstream unit  48 . 
     The ropes  16 ,  18  exiting the slack control unit  42  enter the cutter pinch roll feed unit  48  which is formed from a knurled-driven roll  50  and a pressure pinch roll  52 . The speed of the driven roll  50  is controlled by a variable frequency drive unit to regulate the feed rate of the ropes  16 ,  18  into the cutter. The pinch roll  52  is forced against the knurled roll  50  by an air cylinder  54 , and the pressure on the ropes  16 ,  18  at the bite point is controlled by air pressure. For initial feeding of the rope  16 ,  18 , the air cylinder  54  and pinch roll  52  are retracted. The driven roll speed is slowed to the speed of the uncoiling and tensioning unit  34  for any major speed changes. 
     Ropes  16 ,  18  from the pinch roll feed unit  48  enter an inline cutter  56  having a rotary blade and six knives, a bed knife, a two-twenty horse power motor and a custom feed tube with six 6 ¾ diameter feed tubes. The cutter motor is controlled by a variable frequency drive unit. The rotary speed of the cutter  56  and the lineal feed rate of the pinch roll feed unit  48  determines the cut length of the fibers which is typically ¼ inch. There is a flex transition from the discharge of the cutter  56  into the suction feed tube of an air jet mill  58  and an integral dynamic classifier  60  where the irradiated rope pieces are micronized. 
     A control panel  62  is included in the system  10  to house disconnect breakers, a transformer, the three variable frequency drive units, a PLC with I/O modules and operator push buttons, selector switches and indicating lights. The panel further includes two start stop jog stations for use during initial threading of the rope  16 ,  18  through the system  10 . 
     It should be understood that all tensioning equipment and the rope handling system  10  is used to compensate for the degradability of the rope fiber incurred during irradiation. The tensioning of the rope  16 ,  18  is typically between 5 and 50 pounds from the beginning of the system  10  to the end of the system  10 . 
     Within some industries there are an applications that require acidity testing. This testing is mostly done in distilled water, by adding a powdered material such as cotton @ 1 to 10% levels with mild mixing and than taking pH reading. 
     It has been discovered that after Irradiation of the roped cotton, it leaves a residue on the fiber that registers a pH between 1.0 and 4.0. In order to sell product to applications that need it to be 7.0, a washing process must be included. 
     After micronization, the powdered cotton is than put through a washing and drying process as follows: 
     Material is put into a stainless steel vessel with either deionized or well water @ 50% levels. A mild cleaning surfactant is added @ 0.5 to 2.0% depending on pH levels and agitated for 10 to 20 minutes. Once agitated material is than sent to an air-drying system; where particles are airborne and introduced to warm airflow. Material is then discharged and tested for pH levels. 
     Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.