CA2161070A1 - Sealant composition for the long-term sealing of weather-exposed end grain surfaces of solid wood products - Google Patents

Abstract

A sealant composition for the long-term sealing of weather-exposed end grain surfaces of lumber and other solid wood products comprises an incompletely cured, viscous, polymeric material and a viscosity-adjusting liquid carrier therefor. Polymeric materials specified are Acrylic emulsion polymers Catalyzed silicone resins Isocyanate-crosslinked vinyl and synthetic rubber emulsion polymers Moisture-cured polyurethane resins Catalyzed epoxy resin polysulfide resin blends Catalyzed polysulfide resins After application, the composition cures under ambient conditions.

Description

~ -- 2161070 SEALANT COMPOSITION FOR THE LONG-TERM SEALING
OF WEATHER-EXPOSED END GRAIN SURFACES OF
SOLID WOOD PRODUCTS
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to sealant compositions for the long-term sealing of weather-exposed, end grain surfaces of solid wood products; to a method of sealing such end grain surfaces; and to the end-grain-surface-sealed wood products of the method.

2. Description of the Prior Art Examples of solid wood structural products to which the present invention pertains are bridge timbers and decks, bridge and highway guard rails and posts, exposed glued laminated timbers in structural applications, railroad cross ties and trestle members, piling in any location, pier timbers and decking, retaining wail and staircase timbers, wood foundation members, highway sound barriers, elevated walkways and covers, and the like.
As is well known, when such structural products are used in locations where they are subject to weathering, the wood of which they are fabricated deteriorates and loses strength in a comparatively short time. The most vulnerable points of attack by weathering are the end grain surfaces provided by the sawn ends of the wooden structurural members, whether square-cut or bias-cut, in any configuration.

` 216107~`

Water uptake into the end grain of wood is many times the rate and amount that is absorbed across the grain. Exposed end grain surfaces upturned into the rain continue to absorb and, by capillarity, "pump" water deep into the wooden member with each rainfall. When so doing, the cut ends of the individual wood fibers, like microscopic drinking straws, perform exactly the same function they did in the living tree before it was harvested and machined into structural components: namely, they transport water up the entire length 10 of the tree stem. While this water transport function is essential in the living tree to promote life and growth, it becomes a problem and a serious limitation to the subsequent use of wood as a structural building material in any weather-exposed location.
Fig. 1, an anatomical diagram of the cross-section of solid wood, shows this phenomenon. Virtually all wood fibers are oriented to the vertical surface (end grain) for water transport. Thus, it presents a "sealing problem" quite unique among cut wood surfaces.
In Fig. 1 the parallel, lengthwise orientation of the various classes of wood fibers is clearly evident, as is their tubular structure. In the diagram, the numeral 1 represents the tubular canals; the numeral 2 the epithelial cells; the numeral 3, thick-walled, longitudinal parenchyma; and the 5 numeral 4, earlywood tracheids. All are longitudinally ~ 2161070 `-, oriented hollow tubes which, when cut through by the sawing operation, afford easily accessible passageways to the interior of the structural member for the penetration of ground and atmospheric water.
After having absorbed substantial amounts of water, exposed wood end grain surfaces are subject to a variety of natural forces that weaken and destroy the wood structure.
These include:
1. Cracks and splits resulting from repeated wetting, drying and shrinkage of the wood.
2. Freeze-thaw splitting resulting from ice formation and expansion, a phenomenon which occurs within individual wood fibers as well as in whole wood.

3. Actual loss of wood substance and thus volume through gradual leaching out of hemicelluloses, extractives and other partially soluble wood components including, over time, liqnin itself.

4. Further loss of wood substance and volume by photodegradation of both lignin and cellulose through the action of sunlight in combination with absorbed moisture.

5. Attack on the wet wood by mold and fungi to produce rot in various forms.
Efforts to protect wood from these destructive forces and 25 thus lengthen its useful life have given birth to a major wood `-- 2161070 --~ ` .

preserving industry. This industry employs both water-borne and solvent-borne solutions of chemicals that are lethal to mold and rot life forms. These solutions are injected into wood by means of combined vacuum-pressure cycles while the wood members are submerged in treating solution. The cycle time usually is several hours. As a result of this highly energetic treatment, the treating solutions penetrate into the wood members only to a depth of about one-half inch across the grain, while penetrating into the end grain a distance of one 10 or two feet. End grain absorption of fluids into wood is 25 to 50 times greater than cross-grain absorption, thus underscoring the need for specialized end grain protection.
The advantages obtained by pressure treatment of wood timbers in the treating plant can be largely nullified by 15 practices employed in the field. When pressure-preservative treated timbers are cut to size more than 2 feet away from the end of their original treated length, only the outer marginal half-inch or so of the cut end surface is protected. The entire center area is exposed by the cut and constitutes raw 20 wood. Thus, in spite of expensive preservative treatment, as much as three quarters of the cut end grain surface is left unprotected and rendered vulnerable to excessive water uptake and splitting or rotting on exposure. The same is true for the inner surfaces of any job site holes drilled for bolts or 25 other fasteners.

~-` 216107D

It accordingly is apparent that conventional wood preservative protection in fact protects only an outside shell of each structural component. For complete protection, it must be coupled with application of an appropriate end grain surface sealant, either in the factory or in the field, thereby providing an effective barrier to the gross absorption of water into potentially unprotected areas.
It is the general purpose of the present invention to provide such an end grain sealant composition.

SUMMARY OF THE INVENTION
I have discovered, and it is the essence of the present invention, that an effective end grain sealant composition for the long-term sealing of weather-exposed end grain surfaces of solid wood products must be characterized as follows:

1. It necessarily is fluid at the time of application to permit wetting, spreading, leveling and absorption.
2. It necessarily is polar, to ensure total wetting of all the diverse elements of the wood surface, and polar bonding of the sealant to the wood. The polar groups or sites on the molecular structure of the sealant liquid must be from the category that bonds strongly chemically with the normally occurring chemically active sites on cellulose and lignin molecular structures. Ideally, the polar groups on the molecular structure of the sealant liquid are capable of .
bonding, not only to untreated wood, but also to wood that has been treated with aqueous or non-aqueous preservative solutions. This may be accomplished either through appropriate molecular attraction to the preservative substance itself, or by solvency sufficient to lift and penetrate the preservative film and reach native wood structure for bonding to it.
3. For film-forming capability it should have a polymeric content of at least 50% by weight. It must also have an application viscosity within a range that will permit absorbtion into the wood end grain sufficiently to develop a strongly anchored adhesive bond capable of resisting the large capillary-based lifting force of water being drawn out of wood by evaporation, or by ice crystal formation in the end grain beneath the film. These are very substantial forces, expressed in pounds per square inch. The bond between the wood and the sealant film needs to be strong enough to fail mainly in the wood structure, or within the film substance itself (if it is the weaker of the two).
4. However, the viscosity of the sealant fluid must be within a range that will leave an observable built-up film across the wood end grain surface when cured.
The critical lower limit of applied viscosity is that which will prevent total absorbtion of the sealant into the wood end grain, leaving no measurable protective surface film. The critical upper limit of viscosity is a value too high to spread and level efficiently, or too high to wet and penetrate wood end grain to the depth needed for essential film adhesion.

In practice, the viscosity of the sealant material should be such as to leave on the end grain wood surface a cured film at least several thousandths of an inch thick, preferably from about 0.005 inch to about 0.125 inch thick. In centipoises at 75F., a broad useful range of viscosity is from about 5000 to about 500,000 Brookfield.

It is noted that among the successful sealants in the low end of this viscosity range are those that on application quickly lose the solvent phase by absorbtion into end grain wood and thicken rapidly enough in place to form an adequate residual covering film. Successful lower viscosity sealants also include those with significant thixotropic properties that cause immediate thickening after they have been applied and have become quiescent, thus permitting both essential absorption and adequate residual surface film buildup.

` ' .
It is noted further that suitable viscosities can be achieved by manipulation of such factors as the molecular weight of an active polymer component, the percentage of non-volatile solids, filler/pigment-type and loading and the incorporation of thixotropic materials.

5. The sealant must be capable of curing to useful form under ambient conditions, i.e. at room temperature and, preferably, at temperatures down to near-freezing, in order to get practical latitude for on-site as well as factory application.

6. The cured sealant film must have long-term re-sistance to the elements of exterior exposure, including the sun's radiation, moisture, snow/hail/freezing and extreme drying in any combination. This exposure resistance may result from inherent chemical stability of the molecular structure of the sealant polymer, or from the incorporation of light-shielding pigments, or from the use of specialized fillers applied to or contained throughout the thickness of the applied film, or both.

Ultra-violet shielding or screening chemical compounds . 2161070 alone, dissolved in the sealant composition are not considered adequate to provide true long term protection for an otherwise sunlight-sensitive polymeric film. They may be present in an acceptable formulation, but cannot constitute the sole means of light-exposure protection due to gradual loss of function over time.

7. The cured sealant film must be heat stable and non melting to at least 180F. in order to withstand prolonged exposure under desert conditions, especially if used on dark-colored (treated) wood members which absorb more of the sun's heat.

8. The cured sealant film must be permanently elastomeric in order to follow without film rupture the daily changes in wood dimension due to moisture and temperature variation. The required degree of elastomeric elongation must be at least 50 percent, preferably from 100-300 percent by a standard film test.
Practically, the sealant film must be capable of bridging small cracks without loss of integrity, which normally indicates an elongation capability of at least 100%.

It is noted that, in the case of wood timbers incorporating boxed heart (pith center), as time goes on - - 216107~
-the timbers usually develop two or three primary stress-relieving splits as they dry in place. These splits may be up to 1/4 inch or more in width. It is apparent that they cannot possibly be bridged on a permanent basis by a flexible film of any kind.

However, the end grain sealant of the invention does seal all the many open end grain capillaries right up to the edge of these primary splits. Accordingly, only the parallel grain surfaces of the wood within the primary splits, which surfaces are of limited permeability to moisture, are exposed to the elements. The maximum obtainable sealing effect resulting from the application of the sealant compositions of the invention thus is obtained.

9. For permanence under use conditions its polymer component must be a thermosetting material, as opposed to a thermoplastic material.

lO. It must be capable of application to the end grain wood surfaces by commercial production techniques of brushing, roller coating, dipping, trowelling, etc.

11. It must be substantially wax free since, particularly under use conditions of high temperature, waxes become volatile and would be removed from the sealant composition by evaporation.

In summary, therefore, the fluid sealant composition of my invention for the long-term sealing of weather exposed end grain surfaces of solid wood products comprises a polymeric adhesive material in incompletely cured condition in 10 combination with a liquid carrier therefor used in relative proportions such as to impart to the final composition the characteristics noted above.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1, the single figure of the drawings, is a 15 schematic, fragmentary, top perspective view, greatly enlarged, of a typical wood (Southern Pine softwood), illustrating its gross structure.
DETAILED DESCRIPTION OF THE INVENTION
An exhaustive study of a very large number of 20 commercially available polymeric materials has revealed that the following polymeric material classes are suitable for use in the sealant compositions of my invention, used singly or in combination with each other:
Acrylic emulsion polymers Catalyzed silicone resins 216107!) Isocyanate-crosslinked vinyl and synthetic rubber emulsion polymers Moisture-cured polyurethane resins Catalyzed epoxy resin-polysulfide resin blends Catalyzed polysulfide resins A detailed characterization of these polymer classes follows:

. 2161070 ACRYLIC POLYMERS
Room temperature-curing acrylic solution or aqueous emulsion polymers and formulated coatings or caulks, usually as single-component systems.
Composition These wood end grain coating polymers are comprised of:
1. Solution or emulsion polymers of methacrylic acid esters in which the alcoholic reactant preferably contains from 4 to 12 carbon atoms. (The larger the number of carbon atoms, the 10 more elastic and less water absorptive the applied coating film.) Similarly, solution or emulsion polymers of acrylic acid esters in which the alcoholic reactant preferably contains from 2 to 10 carbon atoms.
2. Copolymers of the above esters with other monomers 15 containing hydroxyl, carboxyl, amido and vinyl functional groups, or combinations of these monomers. Typical of these, but by no means exhaustive, are: Butanediol monoacrylate, N-hydroxymethyl acrylamide and methacrylamide, hydroxyethyl and hydroxypropyl acrylate and alpha-beta unsaturated carboxylic 20 acids.
3. Finally, all of the above homo- and copolymers with cross-linking agents added. Typically, epoxides, polyisocyanates, and low molecular weight melamine- or phenol formaldehyde resins.

Cure The crosslinking and bonding mechanism for the entire family of acrylic polymers is initially loss of solvent phase, usually water, accompanied by room-temperature reaction in the coalescing film among the many functional groups present to crosslink and cure the polymer and bond it to the wood surfaces.
Examples Alkyl esters of acrylic or methacrylic acid having an 10 alkyl ester portion containing 1 to 12 carbon atoms as well as aromatic derivatives of acrylic and methacrylic acid, and including, methyl acrylate and methyl methacrylate, ethyl acrylate and ethyl methacrylate, butyl acrylate and butyl methacrylate, propyl acrylate and propyl methacrylate, decyl 15 acrylate and decyl methacrylate.
Commercial Examples Are:
1. "White Lightning"
Acrylic latex with silicone, white caulk; also, Ultra Performance, clear caulk White Lightning Products Corp.
Atlanta, GA 30310 2. "50 Year"
Acrylic sealant with silicone, clear caulk Macklanburg - Duncan Inc.

Oklahoma City, OK 73118 -t 3. "Alex Plus"
Acrylic latex caulk plus silicone DAP, Inc.
Dayton, OH 45401 4. "Polyseamseal Clear"
All purpose acrylic adhesive caulk Darworth CO.
Simsbury, CT 06070 (Ensign-Bickford Industries) 10 5. TC 20-2"
Formulated acrylic latex caulk (type 8) Rohm & Haas Co.
Philadelphia, PA 19105 ` 21filO70 ``

, SILICONE RESINS
Room temperature vulcanizing (RTV) polysiloxane liquid rubbers and formulated caulks, mainly single-component systems.
Composition These wood end grain coating polymers are comprised of silanol-terminated polydimethylsiloxane of about 300 to 1600 dimethylsiloxane chain units (20,000 to 120,000 molecular weight), generally formulated with inorganic fillers and 10 pigments.
Cure Typically, these polymers are cured at room temperature with methylethylketoxime as Methyl-tris (methylethyketoximo) silane and/or cyclohexylamine as Methyltris (cyclohexylamino) 15 silane. Other silane-terminated amines, alcohols, aldoximes and amides are also used commercially as curing agents.
Bonding to wood surfaces is attained through the chain-terminating silanol polar groups, and also through silane-activated hydrogen atoms on the polymeric structure, plus 20 added functional cross-linking groups.
Examples 1. "Silicone XL"
100% Silicone Caulk, Oxime RTV Cure, clear Macklanburg-Duncan, Inc.
Oklahoma City, OK 73118 2. "GE Silicone II" (50 year durability) Silicone caulk, clear General Electric Company Waterford, NY 12188 3. "Dow Corning DAP"
100% Silicone Sealant Dow Corning Corp.
Midland, MI 48686-0994 `- 2161070 `-.

ISOCYANATE-CROSSLINKED VINYL AND SYNTHETIC RUBBER EMULSION
POLYMERS
Room temperature-curing two-part formulated liquid adhesive systems.
Composition These coating polymers are primarily formulated two-part wood adhesives which perform equally well as wood end grain sealants. Their elasticity, as demonstrated by the property of percentile elongation tested according to ASTM 698, just 10 defines the minimum limit of flexibility needed for adequate end grain sealant performance under the terms of my invention. Mixed adhesive viscosity is initially in the range of 6,000 to 10,000 centipoises, gradually thickening with age to 20,000 to 30,000 centipoises and ultimately to a solid 15 cure. The mixed composition can be applied successfully over the range of viscosities or it can be thinned moderately with additional water to render it suitable for coating and self-leveling.
As listed in their Material Safety Data Sheets under the 20 Generic ID "Aqueous Polymeric Emulsions", these compositions consist of an aqueous emulsion component, generally described as a "Vinyl Polymer" or an "Acrylic-Aromatic Vinyl Polymer"
optionally together with a "Synthetic Rubber Latex" and an inorganic filler. The molecular weight ranges for the 25 emulsion polymers are unspecified. The second component, the ~- 2161070 .

cross-linking agent, is Poly (methylenephenylene) polyisocyanate.
Cure The curing mechanism, basically consists of crosslinking the vinyl or multipolymer aqueous emulsion phase with a polymeric diisocyanate of sufficiently limited water solubility that it can attain bulk reaction with the vinyl reactive sites before extensive urethane formation and the evolution of significant amounts of carbon dioxide gas from 10 the applied glue (or coating) film. Thus, the curing reaction is more a true isocyanate (NCO) polymer-building reaction than polyurethane reaction with water, initially forming polyureas as the principal polymeric backbone of the hardened structure.
Excellent adhesion to wood is attained through the NCO groups 15 of the terminal isocyanate molecules and assorted available functional groups on the vinyl/emulsion polymeric structure.
Where acrylic emulsions are included in the composition, small amounts of alkaline (amide) curing catalyst may also be included.
20 Examples 1. "Isoset WD3 - A320"*
Isocyanate-crosslinked aqueous polymeric emulsion (vinyl, synthetic rubber latex) 2. "Isoset WD3 - A322"*
Isocyanate-crosslinked agueous polymeric emulsion (vinyl, synthetic rubber latex) 3. "Isoset WD3 - CM402"*
Isocyanate-crosslinked aqueous polymeric emulsion (vinyl, acrylic) 4. "Isoset WD3 - C154"*
Isocyanate-crosslinked aqueous polymeric emulsion (acrylic, aromatic vinyl) 5. "Isoset WD3 - C120"*
Isocyanate-crosslinked aqueous polymeric emulsion (vinyl, acrylic-vinyl) 6. "KE-500" Wood laminating adhesive Isocyanate-crosslinked aqueous polymeric emulsion (vinyl, synthetic rubber latex) Oshika Shinko Co., Ltd.
Itabashi-Ku, Tokyo, 173 Japan 7. High Viscosity Cold Cure Adhesive Isocyanate-crosslinked aqueous polymeric emulsion (component 4397-1086, 94%, component 670-13, 6%) ICI polyurethanes (a division of International Chemicals, Inc.) West Deptford, NJ 08066 * All from Ashland Chemicals, Inc.
Columbus, OH 43216 2161071~

POLYURETHANE RESINS
Room temperature-curing liquid polyurethane and polyisocyanate resins and formulated coatings or caulks, separately catalyzed or single-component systems.
Composition 1. Commercially, these wood end grain coating polymers are most often the reaction products of the following di- or polyisocyanates - Toluene diisocyanate (TDI) mixed isomers.
~ Diphenylmethane-4, 4' diisocyanate (MDI) and higher homologs.
Polymethylenepolyphenylisocyanate (PAPI) andhigher homologs.
- Triphenylmethane Triisocyanate.
- Hexamethylene dissocyanate with appropriate (both lower and higher molecular weight) polyalcohols, polyether glycols, polyesters and polybutadiene glycols. For adhesive and sealant purposes, the reaction product of toluene diisocyanate and polypropylene glycol is 20 frequently encountered.
2. The generic designation "Polyurethane Prepolymer", prepared by reacting an excess of diisocyanate with polyol, is often encountered in Material Safety Data Sheets together with a trade secret number to maintain proprietary rights over the 5 exact reaction chemistry employed. Thus, the specific - 2161070 `--reactants can only be named in general terms. For wood end grain sealant applications, however, the controlling selection factors remain fluidity, adhesiveness, moderate flexibility and room temperature cure; that is, performance properties rather than chemistry. A suitable molecular weight range for these properties as wood end grain sealants is about 700 upward to several thousand. The formulated polyurethane prepolymers may contain moderate quantities of acrylic polymers for enhanced weathering capabilities; i.e., to help 10 the polyurethanes better resist ultraviolet auto-oxidation.
Cure Di- or polyisocyanates themselves, as well as isocyanate-terminated prepared polymers, strongly bond to any surface containing activated hydrogen atoms in its structure, in this 15 case wood. This fact, plus their outstanding ability to wet and penetrate almost any surface has led to their well-known broad-spectrum adhesive capability. Bonding occurs fairly slowly at room temperature but rapidly with applied heat or catalysis. In addition, isocyanates react with moisture when 20 present (atmospheric or surface) to form amines which immediately react with other multi-functional isocyanates in the composition to form NCO-terminated polyureas, called polyurethanes, which proceed to hard, irreversible cure while bonding to adjacent wood surfaces. This is the primary 25 adhesive mechanism. A variety of catalysts, mostly organic 2161070 ``--alkalies and organo-metallic complexes, can greatly accelerate the curing and bonding reactions of both prepared diisocyanate resins and moisture-generated (polyurethane) polymers, and are generally employed.
Examples 1. "3M PM1906" Industrial Adhesive Polypropylene Glycol-Toluene Diisocyanate Polymer 3M Company, St. Paul, MN 55144-1000 2. "Scotch-Seal 5200" White Marine Adhesive/Sealant Polyurethane Prepolymer with Acrylate Polymer, N.J. Trade Secret Registry No. 04499600-5575P.
3M Company, St. Paul, MN 55144-1000 3. "Scotch-Grip 5230" Wood Adhesive Polyurethane Prepolymer "CAS No. 9057-91-4' Moisture-curing polyurethane prepolymers 3M Company, St. Paul, MN 55144-1000 4. "Vulkem 116" Polyurethane Sealant Aromatic polyisocyanate resin Mameco International, Inc.
Cleveland, OH 44128 5. Emulsion Polyurethanes Aqueous, self-curing polyurethane laminating adhesives Morton International, Inc.
Woodstock, IL 60098 2161070 ~-, 6. "Scotch-Weld 3535 B/A" Industrial Adhesive Polyester-polyol crosslinked polyurethane prepolymer-Isocyanate polymer resin 3M Company, St. Paul, MN 55144-lOOO

` 2161070 EPOXY RESIN - POLYSULFIDE RESIN BLENDS
Room temperature-curing, separately catalyzed, liquid epoxy resins, blended and co-reacted with liquid polysulfide resins within a combining range of 30-70 to 70-30 parts by weight.
Composition The epoxy wood end grain coating polymer components are most frequently comprised of the diglycidyl ether of Bisphenol A and higher homologs; i.e., Bisphenol A reacted with 10 epichlorohydrin, in a molecular weight range of 340 to about 420. (Higher molecular weights are solids at room temperature and can only be employed in solvent solution. Functional solvents, also called reactive diluents, such as alkyl glycidyl ethers are frequently used under these conditions as 15 the viscosity-reducing solvent so the entire solvated higher molecular weight epoxy resin system becomes bulk-curable and thus does not depend on solvent loss from the coating film to develop a full cure). These epoxy resins may also be reaction products of epichlorohydrin with Bisphenol F, polyhydroxy alphatic alcohols, phenolic novolac resins or resorcinol as long as they meet the coating requirements for fluid viscosity and room temperature cure. All are adequately adhesive to wood.
Cure These polymers are typically cured at room temperature 21 6107 0 `--with aliphatic polyamines, epoxy resin-polyamine adducts, organic acid anhydrides, polysulfide resins, poly-mercaptans or combinations of these hardeners. ("Lewis acids" such as Boron Tri-fluoride are occasionally employed but are more difficult to handle.) Bonding to wood surfaces is primarily attained through terminal epoxy (oxirane) groups, since the functionality of the polysulfide resin component is virtually consumed through co-reaction.
Epoxy Resin Examples (For polysulfide copolymer resins, see "Polysulfide Resins".) 1. "Epon 815" Adhesive Coating Modified Bisphenol A/Epichlorohydrin resin containing N-Butyl Glycidyl Ether Shell Oil Co.
Houston, TX 77210 2. "Epon 825"
Bisphenol A/Epichlorohydrin Based Epoxy Resin Shell Oil Co.
Houston, TX 77210 20 3. "DER 332"
Bisphenol A/Epichlorohydrin Based Epoxy Resin Dow Chemical U.S.A.
4. "Araldite 6005"
Bisphenol A/Epichlorohydrin Based Epoxy Resin Ciba-Geigy Corp.
Hawthorne, NY 10532 .
POLYSULFIDE RESINS
Room temperature-curing liquid polysulfide resins, separately catalyzed, and also formulated into single-component caulks.
Composition Commercially, these wood end grain coating resins are most often produced as the reaction products of bis-chloroethyl-formal with sodium polysulfide to a high molecular weight, then chain-segmented into a workable fluid viscosity 10 range and simultaneously mercaptan-terminated to provide the requisite curing sites. The molecular weight range is normally 3000 to 4500, although a broader range of 1000 to about 8000 is commercially available for special applications.
These resins may also be thio-ether polymers or mercaptan-15 terminated polyoxypropylene-polyurethane reaction products of about the same molecular weight and curing mechanism. All have essentially the same rheological and cured properties as straight polysulfide resins.
Cure Typically, these wood end grain coating polymers are cured with active oxidizing agents such as lead dioxide or cumene hydroperoxide together with an amine catalyst. They are also frequently cured by co-reaction with epoxy resins to yield products of intermediate (controllable) levels of 25 flexibility. (Normal combining range, 30-70 to 70-30.) 216107~

Bonding to wood surfaces is attained through terminal mercaptan polar groups as well as the active sites on cross-linking additives such as epoxy, phenolic or phenyl silane resins.
Examples 1. "LP-3" Adhesive/Coating Sealant Polysulfide polymer Morton International, Chemical Division Chicago, IL 60606-1292 2. "LP-2" Adhesive/Sealant Polysulfide polymer Morton International, Chemical Division Chicago, IL 60606-1292 .
The second major component of the herein described sealant composition is a liquid carrier, used for the purpose of viscosity adjustment. As examples there may be cited the following:
1. Water (in aqueous emulsion systems).
2. The liquid monomer or lower polymer of the polymeric material employed.
3. Liquid aromatic hydrocarbons, such as toluene and xylene.
4. Liquid aliphatic hydrocarbons, such as n-hexane.
10 5. Low-boiling petroleum distillation fractions, such as mineral spirits and naphthas.
6. Chlorinated organic solvents, such as perchlorethylene.
These and other suitable liquid carriers are employed in amount sufficient to impart to the sealant composition a 15 spreadable viscosity of from 5000 to 500,000 centipoises Brookfield at 75F.
In addition to the foregoing pair of principal components, there may be employed in combination therewith a variety of property-modifying agents.
For example, a plasticizer may be included in the formulation in order to improve film flexibility, especially in the case of those polymeric materials grossly lacking in this physical property. It is to be noted however that their employment is a trade-off. As film flexibility is gained, 25 other important properties such as film toughness and exposure - `- 21 61070 durability are reduced proportionately. In addition, the plasticizers evaporate slowly over time, especially on harsh exposure. Accordingly, the sealant compositions in which they are used may become gradually embrittled and lose their usefulness for the intended purpose as time goes on.
Examples of suitable plasticizers are the following:
Phthalates: dibutyl, dioctyl, benzylbutyl, ditridecyl.
Adipates; benzyl octyl, di-(2 ethylheptyl).
Phosphates: triphenyl, trichloroethyl Silicones: dimethyl, methylphenyl.
Polyethyleneglycol octanoates Dipropylene glycol dibenzoate.
Triethyleneglycol di-(2 ethylhexonate) Dibutyl sebacate Butylene glycol Polybutene Paraffinic oils Petrolatum Sorbitol Castor oil derivatives Epoxidized soybean oil Light-shielding pigments or specialized fillers may be included in the formulation or applied to a partially cured film in order to improve the long-term resistance of the 25 sealant film during exterior exposure to the sun's radiation, moisture, snow/hail/freezing and extreme drying, in any combination.
Examples of light-shielding pigments are as follows:
Leafing aluminum pigment Finely ground mica flakes Carbon blacks Graphite powders and flakes Titanium dioxide pigment Iron oxide pigments Powdered acrylic plastics Powdered, unplasticized vinyl chloride plastics Refined clays Light-stable colored pigments generally Powdered nut shell fillers Powdered siliceous diatoms (diatomite) The foregoing and other such materials are used in amount of from 0.1 to 10% by weight of the fluid sealant composition.
Although the expedient of using a liquid carrier in controlled amount may be used to control the viscosity of the 20 sealant composition to a practical spreadable level, in the case of certain excessively fluid polymeric materials it may be desirable or necessary to employ a thixotropic additive further to control this property. A sealant liquid can have a fairly thin "agitated" viscosity for purposes of easy 25 application, and yet have a considerably higher "quiescent"

, viscosity after application for the purpose of limiting the depth of absorption into wood end grain. Examples of suitable Thixotropic agents which may be employed for the desired purpose are the following:
Attapulgite clays Cabosil (colloidal silica) Thixcin GR (Inorganically modified derivative of castor oil) Thixatrol ST (Organic derivative of castor oil) Bentone (Bentonite-based organo-clay) Graphite flakes Polyacrylamides (hydrophilic shear-rate sensitive polymers) These are employed in amount sufficient to impart to the 15 fluid sealant composition the desired application viscosity.
Bioactive materials may be used in the amount necessary to control mold, fungus and rot in associated wood members.
Examples are:
Soluble borates Ammonium bifluoride Tributyltin compounds Quaternary ammonium salts Copper-8-quinolinolate Isothiazolone compounds Orthophenyl phenol Chorothalonil Chlorinated phenols (where permitted by law) It is to be noted that although a very minor proportion 216107n -of paraffin or other wax may be employed for the purpose of imparting the property of enhanced water repellancy to the herein described compositions, it is necessary for long-term satisfactory performance that the compositions of my invention be substantially wax free. The presence of wax interferes with the desired effective adhesion by chemical bonding of the polymeric materials to the wood. Furthermore, the heat of the summer sun, which can raise the temperature of in-service wood members to 150F., or even higher, will evaporate paraffin out 10 of the sealant coating so that its effect becomes truly temporary. Thus, a significant paraffin content generally indicates the temporary service nature of a coating composition in which it is contained.
To formulate the wood end grain sealant composition of my 15 invention, the polymeric component, the liquid carrier and any selected additives are introduced into a suitably efficient mixer and intimately mixed to uniformity. For a storable liquid intermediate, the catalyst or hardening agent is withheld. For immediate application, it is included in the 20 mix. If a thixotropic agent has been included, the mixed viscosity is judged on the basis of a desired application viscosity value in the range of 5000 to 500,000, preferably S000 to 50,000 centipoises, measured after several minutes of standing (to attain quiescent conditions), measured at 5 RPM
5 with a Brookfield Viscosimeter No. 7 spindle at 75F.

2161070 ~
;
Application to the end grain wood surface to be treated is made simply by brushing on, roller coating, dipping or trowelling, using conventional apparatus and procedures, and using sufficient sealant to result in the formation of a coating at least .005 inches thick.
Unless special equipment and procedures are employed, spray coating techniques are of limited application because of the high viscosity which characterizes the compositions versus the very much thinner viscosity required for spraying. Almost without exception, the surface holdout of the coating is lost with spray application.
EXAMPLES
The wood end grain sealant composition of my invention and their manner of application are illustrated in the following examples in which a large number of candidate compositions were evaluated under laboratory test conditions selected to duplicate actual (and severe) exposure conditions as closely as possible.
To establish the breadth of their usefulness, the sealant compositions were evaluated on three wood species, Douglas Fir, Ponderosa Pine and Southern Yellow Pine; also on these three wood specimens which had been subjected in a preliminary operation to three different wood preservative treatments, i.e.: borate diffusion, copper-chrome-arsenic water-borne vacuum-pressure treatment, and pentachlorophenol dissolved in light oil applied in a vacuum-pressure treatment. Each candidate sealant composition was tested on each of the above .
wood species and preservative treatment combinations.
The elongation characteristics and tensile strength of each sample film in cured condition were measured by ASTM Test method 638-90, "Standard Test Method for Tensile Properties of Plastics".
The samples (as films on wood blocks) then were subjected to the following rigorous testing procedures:
1. Atlas Xenon Weatherometer exposure for 1200 hours utilizing a continuous cycle of 18 minutes of water spray plus 10 Xenon lamp irradiation followed by 222 minutes of Xenon lamp irradiation alone. Effects on sealant films were observed and recorded every 100 hours. ASTM G26-93 "Operating Light and Water Exposure Apparatus txenon arc type) For Exposure of Non-Metallic Materials."
2. Water exposure cycles, a variation of ASTM D1183-92, "Standard Test Methods for Resistance of Adhesives to Cyclic Laboratory Aging Conditions." The modified procedure consisted of 24-hour cold water immersion, followed immediately in this water-saturated condition by 24 hours of 20 freezing at 0F., followed immediately by 24 hours of forced-air oven drying at 175-180F., followed by a 24-hour period of relaxation at room temperature. The effects of each completed cycle were served and recorded.
The results are given in the following tables in which:

.
The nomenclature in the "Treatment" column is as follows:
D. Fir is Douglas fir.
S. Pine is Southern yellow pine.
P. Pine is Ponderosa pine.
U indicates untreated wood specimens.
B indicates waterborne Borate preservative treatment by diffusion.
CCA indicates waterborne chrome-copper-arsenic vacuum-pressure preservative treatment.
Penta-Oil indicates solvent borne vacuum-pressure preservative treatment with pentachlorophenol dissolved in a light oil.
The "Sealant Film Weight" values listed are the number of grams of liquid sealant composition applied to 3 1/2-inch 15 square Douglas fir specimens (12.25 square inch area) and to 4-inch square pine specimens (16 square inch area). The difference in surface area between the test specimens cut from the two species groups is the reason that the film weights applied to the pine specimens are proportionately larger. In 20 fact, the film application rates per square inch are close to the same for both species groups. For all species, the test specimens were cut squarely across the grain of the wood with a circular saw and were 1 1/2 inches thick. Only one end grain surface of each specimens was coated. The other end 25 grain surface and the edges remained "raw" and absorptive, as - - 216107~ ~

they would in actual use.
In the "Film Failure" (hours) column the +1200 entries indicate that the sealant films were still intact and adequately protective at the termination of the Weatherometer test cycle of 1200 hours and could have undergone longer exposure if the test were continued.
Similarly, the 25+ entries in the "Failure Cycle" column under the Soak-Freeze-Dry test indicate that many of the end grain sealant specimens could have undergone additional cycles 10 of this exposure test. These successful samples seemed to have "settled into" the exposure cycle stresses and could have continued indefinitely. In my opinion, this behavior indicates true "long-term" exposure capability.

216107~

These examples illustrate the application of acrylic emulsion polymers to the sealant compositions of the invention.
In a variable speed propeller type laboratory mixer were placed 100 gm Rohm & Haas 100% acrylic latex formulated caulk single component and 15 gm water.
These two components were mixed until uniform.
The resulting sealant composition was characterized as follows:
non-volatile content 51%
Viscosity 67,000 cp Cured elongation 1145%
Cured Tensile strength 695 psi The sealant was applied to six different wood samples and tested for resistance to long-term weather exposure, as described above. The results were as given in Table 1.

` 216107~
.

Soak-Sealant Freeze-Film Atlas Dry Exposure Example Material Weight Weatherometer Test No. Tested (Grams) Film Test (Failure Cycle) 1 U-D Fir 4.9 1200 +25 2 B-D Fir 5.5 1200 +25 3 CCA-D.Fir 4.5 1200 +25 4 U-S.Pine 6.0 1200 +25 B-S.Pine 5.9 1200 +25 6 Penta-P.Pine 5.0 1200 +25 .

These examples illustrate the application of silicone resins in the sealant compositions of the invention.
In a variable speed, propeller type, laboratory mixer were placed 100 gm Macklanburg-Duncan Co., Silicone Caulk clear Oxime RTV Cure single component; and 20 gms of Xylene.
These components were mixed to uniformity.
The resulting sealant composition was characterized as 10 follows:
Non volatile content 83%
Viscosity 167,200 CPS
Cured elongation 300%
Cured Tensile strength 80 psi The sealant was applied to six different wood samples and subjected to tests measuring resistance to long-term exposure, as described hereinabove. The results are summarized in Table Soak-Freeze-Sealant Dry Exposure Film Atlas Test Example Material Weight Weatherometer Failure No. Tested (Grams) Film Test Cycle 7 U-D Fir 6.4 1200 +25 8 B-D Fir 5.9 1200 +25 9 CCA-D. Fir 5.8 1200 +25 U-S Pine 7.7 1200 +25 11 B-S Pine 7.3 1200 +25 12 Penta-P Pine 7.5 1200 +25 These examples illustrate the application of isocyanate-cross linked vinyl emulsion polymers to the sealant compositions of the invention.
In a variable speed propeller type laboratory mixer were placed 100 g Ashland Chemical A320 vinyl butadiene emulsion.
18 gm Ashland Chemical CX47 MDI isocyanate crosslinker 15 gm water After mixing to uniformity, the composition had the following characteristics:
Non-volatile content 59%
Viscosity 5900 cps.
Cured elongation 50%
15 Cured Tensile strength 1925 psi The composition was applied to six different wood test samples and the resulting coated samples subjected to exposure tests as outlined above. The results are summarized in Table 3.

Soak-Sealant Atlas Freeze-Film Weatherometer Dry Exposure Example Material Weight (Film Failure- Test No. Tested (Grams) Hours) Test Failure Cycle 13 U-D. Fir 6.7 1200 +25 14 B-D Fir 7.6 1200 +25 25 15 CCA-D.Fir 6.6 1200 22 16 U-S.Pine 8.8 1200 10 17 B-S. Pine 9.0 1200 +25 18 Penta-P.Pine9.0 1200 +25 216107~

These examples illustrate the application of polyurethane resins to the sealant compositions of the invention.
Used as received were 100 gm 3M Co. 89847-75 B moisture- Cure polyurethane caulk (single component) No solvent carrier was reguired.
The as-is sealant composition had the following 10 characteristics:
Non-volatile content 100~
Viscosity 31,700 cp.
Cured elongation 350%
Cured tensile strength 200 psi The exposure test results when the above composition was applied to six different wood samples are given in Table 4.

Soak-Sealant Atlas Freeze-Film Weatherometer Dry Exposure Example Material Weight (Film Failure- Test 20 No. Tested (Grams) Hours) Test Failure CYcle 19 U-D. Fir 7.3 1200 +25 B-D. Fir 7.0 1200 +25 21 CCA-D.Fir 6.9 1200 +25 22 U-S. Pine 9.1 1200 +25 23 B-S Pine 9.3 1200 +25 24 Penta P. 9.2 500 +25 Pine 2161070 `-The following examples illustrate the application of epoxy resin-polysulfide resin blends to the sealant compositions of the invention.
In a variable speed propeller type laboratory mixer were placed 60 gm Shell Chemical Co. Epon 825 Epoxy Resin;
90 gm Morton Int'l Chemical Div. LP2C Polysulfide Resin;
6 gm Dow Chemical Co. DEH 20 Curing Agent (Diethylene Triamine Crosslinker).

These constituents were mixed to uniformity. The resulting sealant composition had the following characteristics Non-volatile content 100%
Viscosity 6900 cp.
Cured elongation 110%
Cured tensile strength 1488 psi The sealant composition was applied to six different wood samples and tested for durability as outlined above. The results are given in Table 5.

Soak-Sealant Atlas Freeze-Film Weatherometer Dry Exposure Example Material Weight (Film Failure- Test No. Tested (Grams) Hours) TestFailure Cycle U-D Fir 7.2 +1,200 +25 26 B-D Fir 6.6 +1,200 +25 27 CCA-D.Fir 7.2 +1,200 +25 28 U-S. Pine 9.7 +1,200 7*

29 B-S. Pine 9.1 +1,200 4*
Penta-P.Pine 9.6 +1,200 +25 * Excessive absorption into rapid-growth pith areas of Southern pine samples. Early radial splits were present in these areas.
Where a significant surface film remained, performance was passing.

i These examples illustrate the application of catalyzed polysulfide resins to the sealant compositions of the invention:
In a variable speed propeller type laboratory mixer were placed 100 gm Morton Int'l Chemical Div. LP2C
polysulfide resin.
8 gm Witco Corp. Cumene Hydroperoxide Crosslinker 1.5 gm Morton International EH330 Amine Catalyst 10 gm Alcoa Dry Leafing Aluminum pigment.
These constituents were mixed until a uniform composition was obtained. Its characteristics were as follows:
Non-volatile content 92%
Viscosity 35,280 cp Cured elongation 300%
Cured tensile strength 125 psi The composition was applied to six different wood samples and subjected to exposure tests with results as given in Table 20 6.

Soak-Sealant Atlas Freeze Film Weatherometer Dry Exposure Example Material Weight (Film Failure- Test No. Tested (Grams) Hours) Test Failure Cycle 31 U-D Fir 7.5 1200 +25 32 B-D Fir 7.5 1200 +25 33 CCA-D.Fir 7.4 1200 +25 34 U-S. Pine 9.6 1200 2*
B-S Pine 9.4 1200 3*
36 Penta-P.Pine9.5 1200 +25 * Excessive absorption into rapid-growth pith areas of Southern pine samples. Early radial splits were present in these areas.
Where a significant surface film remained, performance was passing.

- 21filO7~`-From a consideration of the results of the foregoing laboratory exposure tests in which the test samples were given a passing grade, together with a large number of other tests carried out with a variety of other polymeric compositions in which the test samples were given a failing grade, it may be concluded as follows:
1. Non-polar (thus, non-adhesive) sealant films, no matter how durable otherwise, failed by detaching from the énd grain wood block specimens early in the soak-freeze-dry test.
lO 2. Low viscosity, totally absorbed sealant compositions failed early due to film failure in either the Weatherometer or the soak-freeze-dry test (or both). The failure mechanism was most often excessive end grain splitting.
3. Highly polar and adhesive compositions of several 15 polymeric species generally performed well, except as limited by other performance properties such as film rigidity, which led to early excessive splitting.
4. Sealant viscosities ranging from 423,500 cps. down to 5100 cps. at 75F. were successfully applied and performed 20 well. Sealant viscosities as low as 1500 cps. at 75F. were tested and judged too fluid (flowed readily off inclined surfaces) to be practical.
5. Non-elastomeric sealant compositions, although otherwise adequately film-forming and adhesive to wood, failed 5 early due to excessive splitting.

2~61070 6. As a group, the successfully adhesive, film-forming and elastomeric sealant compositions tended to perform well on both untreated fir and pines and also on the preservative-treated wood specimens.
7. For the purpose of enhancing the long-term exposure resistance of somewhat light-sensitive but otherwise successfully-performing end grain sealant adhesive polymers (epoxies, polysulfides), the incorporation or application of appropriate light-shielding pigments and fillers such as leafing aluminum pigment and finely-ground mica flakes accomplishes this purpose very satisfactorily, providing fully adequate service life.
8. A thixotropic sealant liquid can have a fairly thin "agitated" viscosity for purposes of easy application and yet have a considerably higher "quiescent" viscosity after application for the purpose of limiting the depth of absorption into wood end grain.
9. In summary, application of the end grain sealant compositions of the invention results in the production of a wood product having end grain surfaces sealed with a polymeric film having a thickness of at least about .005 inch, preferably from about .005 to about .125 inches, which has been absorbed into and chemically bonded to the interior wood structure to a depth of from about 1/64 to about 1/8 inch. A
5 sealant coating is not particularly effective as an unabsorbed 21 filO7!1 surface film even if adhesively bonded to the top few wood cells. It is too easily subject to lifting rupture and physical damage by normally encountered physical forces. Nor is it as effective when so deeply absorbed into end grain that a solid film barrier is no longer presented.
Having thus described my invention in preferred embodiments, I claim:

Claims (19)

1. A substantially wax-free, fluid, sealant composition for the long-term sealing of weather-exposed end grain surfaces of solid wood products including lumber, timbers, piling, railroad ties, glued-laminated beams, decking and the like, comprising:
a) a polymeric material in incompletely cured condition having the following characteristics:
(1) capability of curing after application and under ambient conditions to a solid, durable, weather-resistant, tough yet durably elastomeric, end grain sealant layer, having an elongation capacity of at least 50%.
(2) capability of polar bonding to wood during curing to insure substantially complete wetting of the end grain wood surface and the formation of strong and durable chemical bonds between the sealant layer and the wood, (3) having a polymeric material content of at least 50%, and b) a liquid carrier therefor, used in amount sufficient to impart to the said composition a spreadable viscosity of from 5000 to 500,000 Brookfield at 75°F.

2. The sealant composition of claim 1 having a viscosity of from 5,000 to 50,000 0 at 75°F.

3. The sealant composition of claim 1 including a thixotropic material used in amount sufficient to control the application viscosity of the composition to a level of from 5,000 to 500,000 Brookfield at 75°F.

4. The sealant composition of claim 3 wherein the thixotropic material comprises cabosil.

5. The sealant composition of claim 1 having after curing an elongation capability of at least 100%.

6. The sealant composition of claim 1 including a light-shielding quantity of a pigment.

7. The sealant composition of claim 6 wherein the pigment comprises from 0.1 to 10% by weight of finely ground mica.

8. The sealant composition of claim 6 wherein the pigment comprises from 0.1 to 10% by weight of leafing aluminum pigment.

9. The sealant composition of claim 1 including a plasticising quantity of a plasticising agent for the polymeric materials.

10. The sealant composition of claim 9 wherein the plasticising agent comprises a phthalate plasticizer.

11. The sealant composition of claim 1 wherein the polymeric material comprises a member of the group consisting of Acrylic emulsion polymers Catalyzed silicone resins Isocyanate-crosslinked vinyl and synthetic rubber emulsion polymers Moisture-cured polyurethane resins Catalyzed epoxy resin-polysulfide resin blends Catalyzed polysulfide resins

12. The sealant composition of claim 11 wherein the polymeric material comprises an acrylic emulsion polymer.

13. The sealant composition of claim 11 wherein the polymeric material comprises a catalyzed silicone resin.

14. The sealant composition of claim 11 wherein the polymeric material comprises isocyanate-cross-linked vinyl and synthetic rubber emulsion polymers.

15. The sealant composition of claim 11 wherein the polymeric material comprises a moisture cured polyurethane resin.

16. The sealant composition of claim 11 wherein the polymeric material comprises a catalyzed epoxy resin-polysulfide resin blends.

17. The sealant composition of claim 11 wherein the polymeric material comprises a catalyzed polysulfide resin polymer.

18. The method which comprises applying to an end grain surface of a solid wood product the sealant composition of any one of claims 1-17 and permitting the sealant to cure in situ to a solid, end-grain-sealing condition, the sealant composition being employed in amount sufficient to deposit across the end grain surface a sealant layer having a thickness of at least .005 inch, securely bonded by chemical bonds to the underlying wood.

19. The end-grain-surface-sealed product of the method of claim 18.