Source: http://www.google.com/patents/US6916549?ie=ISO-8859-1
Timestamp: 2014-07-11 13:42:28
Document Index: 522433335

Matched Legal Cases: ['Application No. 60', 'art 2', 'art 4', 'art 5', 'art 5', 'art 5', 'art 5']

Patent US6916549 - In situ fluoropolymer polymerization into porous substrates - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsThe present invention relates to in situ polymerization of fluoropolymer into porous substrates, to improve resistance to degradation by wetting and staining, and wood, to improve resistance to degradation, staining and warping....http://www.google.com/patents/US6916549?utm_source=gb-gplus-sharePatent US6916549 - In situ fluoropolymer polymerization into porous substratesAdvanced Patent SearchPublication numberUS6916549 B2Publication typeGrantApplication numberUS 10/379,811Publication dateJul 12, 2005Filing dateMar 5, 2003Priority dateOct 27, 1998Fee statusPaidAlso published asUS6558743, US20030162030Publication number10379811, 379811, US 6916549 B2, US 6916549B2, US-B2-6916549, US6916549 B2, US6916549B2InventorsJohn Russell Crompton, Jr., James M. Donatello, Kiu-Seung Lee, Charles Winfield Stewart, Robert Clayton WhelandOriginal AssigneeE. I. Du Pont De Nemours And CompanyExport CitationBiBTeX, EndNote, RefManPatent Citations (31), Non-Patent Citations (5), Referenced by (1), Classifications (22), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetIn situ fluoropolymer polymerization into porous substratesUS 6916549 B2Abstract The present invention relates to in situ polymerization of fluoropolymer into porous substrates, to improve resistance to degradation by wetting and staining, and wood, to improve resistance to degradation, staining and warping.
CROSS REFERENCE TO RELATED APPLICATIONS This application is a division of U.S. application Ser. No. 09/409,173, filed on Sep. 30, 1999, now U.S. Pat. No. 6,558,743, This application claims the benefit of Provisional Application No. 60/105/798, filed Oct. 27, 1998.
FIELD OF THE INVENTION This invention relates to the polymerization of fluoropolymers into substrates comprising wood and wood by-products substrates. The fluoropolymer/substrate network that results is present on the surface of the substrate and is also deposited into the substrate at appreciable depths. The substrate/fluoropolymer networks provide a protective coating for the substrate.
TECHNICAL BACKGROUND OF THE INVENTION Wood, like other porous materials has a host of uses. Common uses for wood include use as a building material and for the production of furniture. Materials comprising wood may degrade by staining and wetting. Materials comprising wood degrade by staining, wetting and warping. It is desirable to treat porous wood substrates such that they are more resistant to degradation. It is also desirable to treat wood such that the wood is more resistant to decay and degradation by staining, wetting and warping, and to improve durability while maintaining the appearance of wood.
SUMMARY OF THE INVENTION Disclosed in the present invention is a process for preparing a fluoropolymer/substrate composition, comprising:
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a depiction of a block of redwood as described in Example 2 in the present invention.
DETAILED DESCRIPTION OF THE INVENTION The present invention discloses a process for the in situ polymerization of fluoromonomer into porous substrates such as wood and wood by-products.
When wood substrates are used in the present invention, the fluoro-monomer polymerizes inside the pores of the wood so as to partially or fully block the pores. The process has been demonstrated with a preferred group of wood substrates comprising cedar, cherry, oak, pine, poplar, redwood, and walnut for which, in Example 1 below, �8% to 25% of the void space available to water was filled with polytetrafluoroethylene (PTFE). In view of the broad range of woods with which this process has been demonstrated, the process should work well with most if not all woods.
In this invention, the preferred initiator solution comprises a solution of hexafluoropropylene oxide dimer peroxide [hereinafter referred to as �DP�] in Freon� E1. It is further preferred that the fluoromonomer used in this process is tetrafluoroethylene. TFE polymerizes to form PTFE.
In the preferred embodiment of the process where the substrate is wood, the wood is soaked in a solution of free radical initiator. The wood is then removed from the initiator solution and the free liquid is allowed to drain away. By �free liquid� is meant solution that is not absorbed by the substrate during soaking. The initiator-soaked wood is then placed in an apparatus suitable for polymerization. The apparatus is filled with gas phase fluoromonomer, and the polymerization allowed to run. The preferred initiator when wood is used as a substrate is DP. The polymerization apparatus can be a simple plastic bag for atmospheric pressure polymerization or an autoclave for polymerization at pressures up to several hundred psi.
EXAMPLES Example 1 Polymerization of (PTFE) into Different Woods Decreased Water Absorption, Increased Durability A. Polymerization of TFE into Wood
A saw was used to cut samples of cedar, cherry, oak, pine, poplar, redwood, and walnut into cubes which measured roughly 0.75 inches on a side. Using glass jars, three cubes of each wood were soaked for 1 hour in �50 ml of 0.185 M hexafluoropropylene oxide dimer peroxide (1, DP) at −15� C.
Cube #1: A cube from part A above containing polymerized PTFE Cube #2: A cube from part A above containing polymerized PTFE, the surface of which has been lightly sanded to remove most visible traces of PTFE. In the discussion that follows these lightly sanded cubes are referred to as �PTFE/wood blocks�. Cube #3: A cube untreated except that it has been put under pump vacuum overnight to mimic the final devolatilization step of part A above. In the discussion that follows the blocks that were not chemically treated are referred to as the �control� blocks. For each wood type, all three cubes were simultaneously immersed in distilled water in the same glass jar. In every case the control block showed an immediate darkening when immersed in water whereas the PTFE/wood blocks retained much of their natural color and appearance. The cubes were then periodically withdrawn, patted damp dry, weighed to determine the amount of water absorbed, and reimmersed in the water. A comparison of water absorption data of the control and PTFE/wood blocks after 600 cumulative hours of immersion in water is shown in Chart 2.
The soaking experiments described in part B of this Example were continued for 8 to 9 months at room temperature. After the wood cubes were removed from the water, the surfaces were wiped damp dry with a tissue. The PTFE containing wood samples were uniformly less darkened and less �wet� looking as recorded in the Chart 4 below.
Example 2 Evidence for PTFE Penetration Inches Deep into Redwood The experiments below establish that TFE polymerizes in wood at least inches below the wood surface and that, while deposition along the grain may be mildly favored, penetration occurs in other directions as well. Gaseous monomer, such as TFE, penetrates wood particularly easily.
Two redwood blocks were cut so as to detect anisotropy in the penetration and polymerization of TFE. The first block measuring 10.8 cm�2.6 cm�1.8 cm was cut so that the grain of the wood ran in the 10.8 cm direction. It is referred to hereinafter as the �lengthwise� block. A second block measuring 11.0 cm�2.7 cm�1.8 cm was cut so that the grain of the wood ran in the 2.7 cm direction. It is referred to as the �crossgrain� block. It is supposed that if TFE can penetrate wood substrates only along the direction of the grain of the wood, then TFE must travel 5.4 cm to get to the center of the lengthwise block but only 1.35 cm to get to the center of the crossgrain block. The two blocks could thus differ greatly in PTFE weight gain and how any PTFE is distributed spatially. Each block was weighed and then soaked for 1 hour at −15� C. in 0.16 M DP in Freon� E1. The blocks were briefly air dried and then transferred to separate 400 ml stainless steel autoclaves. Each tube was charged with 50 g of TFE and heated for four hours at 40� C. The blocks were recovered, lightly sanded to remove loose PTFE from the surface, dried for at least 4 days under pump vacuum, and reweighed. The lengthwise block increased in weight from 17.9 g to 30.3 g for a 69% weight gain. The crossgrain block increased in weight from 16.0 g to 28.7 g for a 79% weight gain. The volume of PTFE picked up per ml of wood was 0.103 ml of PTFE for the crossgrain sample and 0.108 ml for the lengthwise sample. These results are likely the same within experimental error and are not much different from the 0.13 ml of PTFE per ml of wood reported above for the much smaller redwood cubes in Example 1. This experiment provided the first indication that grain direction did not dominate deposition, that PTFE deposition is not limited primarily to the wood surface, and that sample size did not dramatically affect results up to dimensions of several inches.
A similar analysis was then done on the lengthwise block. As shown in FIG. 2, the block (block 20 of FIG. 2) was first cut in half to create two new faces (blocks 21 and 22 of FIG. 2). One of the new faces was scanned with the beam of an electron microscope in energy dispersive mode to measure relative fluorine concentration as shown by the direction of the arrows in FIG. 2. Three scans were performed in the 1.8 cm direction (scans #9, #10, and #11) and three scans were performed in the 2.6 cm direction (scans #12, #13, and #14). All six scans performed were perpendicular to the wood grain. High and low fluorine concentrations alternated irregularly across the full width of all six scans. There was no discernable preference for fluorine at the surface. One of the two 5.4 cm�2.6 cm�1.8 cm blocks created by the first cut was cut into half again. Two additional blocks were created (blocks 23 and 24 of FIG. 2) that measured �5.4 cm�2.6 cm�0.9 cm. The fresh cut face of one of the blocks was scanned three times along the grain of the wood, traveling each time the 5.4 cm distance from what had been the center of the original block to an outside end (scans #CE 15, #CE 16, and #CE 17). The fluorine concentrations increased 10 to 20 times from the center to the outer face of the block. Fluorine concentrations measured much lower at the center of the block for scan #CE16, than when scanned end on as in scans #9 through #14 of FIG. 2. Combustion analysis was used to resolve the inconsistency.
As shown in FIG. 2, the redwood �lengthwise block� was cut into three pieces. A piece measuring �5.4 cm�2.6 cm�0.9 cm and weighing about 4.5 g was digested chemically by heating it to reflux with 10 ml of concentrated sulfuric acid. Additional sulfuric acid was added to reduce the wood to an oily black residue. The carbon responsible for the black color was then burned away by the gradual addition of concentrated nitric acid. The residue was diluted with water, filtered, and dried. A white fibrous PTFE deposit was recovered. The residue accounted for 35.6% of starting sample weight, which was similar to the fluorine levels measured by combustion analysis. At 100� to 20,000� magnification, electron microscopy detected rod shaped structures 20μ-60 μ across and of indefinite length. At 20,000� magnifications, the rods showed a spongy fine structure. Such spongy morphology is often seen when TFE is polymerized in the gas phase. Perhaps the void spaces in wood function as microscopic gas phase polymerization reactors for TFE. In this invention, the polymerization appears to have filled the pores in the wood substrates with spongy PTFE deposits rather than having deposited the PTFE as a conformal coating on the walls of the pores.
Example 3 Evidence for PTFE Penetration Inches Deep into Oak Two oak blocks were cut so as to detect anisotropy in the penetration and polymerization of TFE. The first block which measured 12.1 cm�2.5 cm�1.9 cm, was cut so that the grain of the wood ran in the 12.1 cm direction. It will be referred to hereafter as the �lengthwise� block in this Example (block 40 of FIG. 4). A second block which measured 2.1 cm�2.5 cm�1.9 cm was cut so that the grain of the wood ran in the 2.5 cm direction. It will be referred to hereafter as the �crossgrain� block in this Example (block 30 of FIG. 3). To the extent that the TFE gas can penetrate the wood only along the direction of the grain, the TFE must travel 6.05 cm to get to the center of the lengthwise block but only 1.25 cm to get to the center of the crossgrain block. The two blocks could thus differ greatly in PTFE weight gain and how any PTFE is distributed spatially.
Each block was weighed and then soaked for 1 hour at −15� C. in 0.16 M DP in Freon� E1. The blocks were briefly air dried and then transferred to separate 400 ml stainless steel autoclaves. Each tube was charged with 25 g of TFE and heated for four hours at 40� C. The blocks were recovered, lightly sanded to remove loose PTFE from the surface, dried for at least 4 days under pump vacuum, and reweighed. The lengthwise block increased in weight from 44.36 to 47.98 g for an 8.1% weight gain. The crossgrain block increased in weight from 42.54 g to 49.81 g, or a 17.1% weight gain. The crossgrain sample picked up 0.05 ml of PTFE/ml of oak and the lengthwise sample picked up 0.03 ml of PTFE/ml of oak. This compares to 0.048 ml of PTFE per ml of oak in the case of the 0.75″ oak cubes of Example 1. The �2� greater deposition of PTFE in the crossgrain block suggested a mild preference for penetration in the direction along the wood's conductive tissues by which food and nutrients travel.
Three scans were performed in the 2.5 cm direction as indicated by the arrows #26, #27, #28 of FIG. 4 and three scans were performed in the 1.9 cm direction, indicated by the arrows #29, #30, and #31 of FIG. 4. All six scans were performed perpendicular to the wood grain. High and low fluorine concentrations alternated irregularly across the full width of all six scans. There was no discernable preference for fluorine at the surface. One of the two 6.05 cm�2.5 cm�1.9 cm blocks that was created by the first cut was cut in half again to create two more blocks (blocks 43 and 44 of FIG. 4). The blocks measured �6.05 cm�2.5 cm�0.95 cm each. The fresh cut face of one was scanned three times along the grain of the wood, traveling each time the �6.05 cm distance from what had been the center of the original block to an outside end, as indicated in arrows #CE32, #CE33, and #CE34 of FIG. 4. While the scans indicated by arrows #CE32, #CE33, and #CE34 showed very little fluorine towards the center of the block, high fluorine concentrations were detected at the center of the block in scans #26 to #31 of FIG. 4. As in the redwood block of Example 2, the same dependence of fluorine concentration upon scan direction was seen and elemental analysis was used to support the higher fluorine concentrations. It was concluded that there was a mild preference for TFE polymerization along the direction of the wood grain and that penetration easily occurred to depths of at least 6 cm.
Example 4 Protection of Wood A. High Pressure Process
A 30 mm�40 mm rectangle was cut from each of the six types of wood in a package of Band-it� Real Wood Variety Veneer (Cloverdale Company, Inc., P.O. Box 400, Cloverdale, Va. 24077). While the exact identities of the woods were unknown, their visual appearance suggested common woods such as walnut, pine, maple, and redwood. All six rectangles were notched so as to enable later identification and weighed. The strips were soaked for one hour at −15� C. in 0.165 M DP in CF3CFHCFHCF2CF3, briefly air dried, loaded into a 20.3 cm�25.4 cm zip lock polyethylene bag (Brandywine Bag Co., part number 301630) equipped with a polypropylene gas inlet valve, and the bag was clamped shut. The bag was taped to a rectangular wire frame attached in turn to an ordinary laboratory stirrer motor. The bag was evacuated/purged three with N2 and two times with TFE and then inflated loosely with TFE gas. For the next �18 hours the bag and its contents were slowly tumbled using the stirrer motor mounted in a horizontal position. The wood strips were unchanged in visual appearance. The strips were devolatilized for 72 hours under pump vacuum and reweighed. The strips had a weight gains of 0.9 wt % to 7 wt % as shown in Chart 5, column 2. Drops of water were placed on the wood and advancing contact angles measured about 10 minutes later. Advancing contact angles were uniformly high, 120� to 127� (Chart 5, column 3), indicative of PTFE at the surface. The behavior of the untreated control samples containing no polymerized PTFE was markedly different. While reasonably high contact angles of 90 to 122� were observed for the untreated control wood samples initially (Chart 5, column 5), these contact angles could be observed only briefly because the water droplets started to spread out over the surface after only about 15 seconds to 2 minutes (Chart 5, column 6). The PTFE treated and the control samples were next submerged in water at room temperature and then air dried to observe what effect the PTFE treatment had on warpage.
Example 5 Liquid Phase Perfluoromonomer A. In Wood Under Inert Atmosphere
A cube of redwood, �1.9 cm on a side and weighing 2.27 g was immersed in the PMD/DP solution left over from part A of this Example for 1 hour at −15� C. The redwood cube was removed, allowed to drain and then transferred to a 20.32 cm�25.4 cm zip lock polyethylene bag (Brandywine Bag Co., part number 301630) equipped with a polypropylene gas inlet valve. The bag was clamped shut, inflated and evacuated three times with nitrogen, inflated and evacuated three times with TFE, loosely inflated with TFE, and allowed to sit over a three days. The cube was removed along with 2.9 g of PTFE. Most of the PTFE removed was loose but some of it was scraped off of the redwood cube. After devolatilizing for 9 days under pump vacuum at room temperature, the cube weighed 4.51 g for a 99 percent weight gain. One side of the cube was light sanded revealing an attractive silvery brown surface darker in appearance than at the start. A drop of water placed on the surface remained on the surface of the cube for about two hours until it evaporated. A drop of water placed on an untreated redwood cube wet the surface of the cube within a minute and took about 30 minutes to soak into the cube, having spread out into a visibly large wet area on the cube.
Example 6 Penetration and Deposition of Fluoropolymer Lumber is most often cut with the wood grain running lengthwise. For monomer and initiator to thoroughly penetrate a long board, much of this penetration must either occur perpendicular to the wood grain or else monomer and initiator must be able to enter at the ends and travel rapidly down the wood grain. The experiments below show that significant penetration and PTFE deposition occurs perpendicular to the wood grain.
A block of pine measuring 14.5 cm�2.6 cm�1.9 cm and with the grain running lengthwise was cut roughly in half creating two new blocks: Block A measuring �7.0�2.6�1.9 cm and weighing 16.1 g and Block B measuring �7.4�2.6�1.9 cm and weighing 17.2 g. Using Epoxy-Patch� cement (Hysol Engineering Adhesives, The Dexter Corporation, Seabrook, N.H.) 2.6�1.9 cm patches of aluminum foil (Reynolds Wrap�, Reynolds Metal Company, Richmond, Va.) were glued to the far ends of Block A. After 3 days of drying, Block A (plus foil) weighed 16.5 g. The purpose of the aluminum foil was to block entry and travel by initiator and monomer in the direction of the wood grain to test for ease of perpendicular penetration. Blocks A and B were immersed for 1 hour at −15� C. in �0.16 M DP in CF3CF2CF2OCFHCF3 solvent. The blocks were removed, briefly drained, chilled on dry ice, and loaded into a chilled (less than −20� C.) 400 ml autoclave. The autoclave was evacuated and loaded with 50 g of TFE. After four hours at 40� C., the wood blocks were recovered, trace loose PTFE wiped off the surface with a tissue, and the blocks were dried under pump vacuum for 3 days. Block A weighed 23.9 g for a 46% weight gain and Block B weighed 25.0 g for a 45% weight gain. Thus, PTFE deposition was not particularly dependent upon the direction of the wood grain; or upon which wood surfaces (end grain or non-end grain) were exposed to initiator and TFE.
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