WO2009062312A1

WO2009062312A1 - Stable vegetable or animal derived wax emulsions and uses therefor

Info

Publication number: WO2009062312A1
Application number: PCT/CA2008/002017
Authority: WO
Inventors: Maria Racota
Original assignee: Walker Industries Holdings Limited
Priority date: 2007-11-15
Filing date: 2008-11-17
Publication date: 2009-05-22

Abstract

A stable wax emulsion for imparting water repelling characteristics to wood panels and cellulose sheet products comprises a vegetable oil or animal fat based wax, an emulsifier and water. The vegetable oil based wax preferably comprises soya wax. The emulsifier preferably comprises lignosulphonic acid or salts thereof or polymers comprising monomers of an olefin and maleic anhydride. In a preferred embodiment, the polymer comprises a copolymer of an olefin and maleic anhydride.

Description

STABLE VEGETABLE OR ANIMAL DERIVED WAX EMULSIONS AND USES THEREFOR

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority from U.S. application number 60/988,261 , filed November 15, 2007, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION [0002] The present invention relates to stable vegetable or animal derived wax emulsions. More particularly, the invention relates to vegetable oil based wax emulsions including lignosulfonates or olefin maleic anhydride polymers. In one aspect, the vegetable oil comprises soya oil. BACKGROUND OF THE INVENTION [0003] Waxes are used in many industrial applications. Although waxes can be used in molten form, in many cases, they are purchased in the form of emulsions. For example, wax emulsions are used in the manufacture of gypsum wall boards for imparting water repellency characteristics. Such emulsions are taught in US Patent Nos. 5,968,237 and 6,890,976 and the entire contents of such references are incorporated herein by reference. Similarly, wax emulsions are known to be used in various other applications such as the coating of wood or paper products etc. With regard to composite wood panels, for example, wax emulsions may be applied as a water repellent surface coating or the wax emulsion may be incorporated into the precursor wood particle material (such as wood particles or chips etc.) prior to such material being pressed into boards. [0004] One of the problems faced in using wax emulsions is stability. A wax emulsion is referred to as being "stable" if it remains in the emulsified state without being separated into its components (i.e. separated into aqueous and non-aqueous phases). It has been often found that once a wax emulsion is prepared, it must be incorporated into the final formulation within a short period of time, before it becomes unstable. This poses difficulties for most manufacturers using wax emulsions since such emulsions are normally obtained from outside sources and, therefore, the emulsions must remain stable during the time between blending of the emulsion and its final use. This time period is in most cases relatively lengthy given the need for transport and storage of the product. For this reason, various wax emulsion formulations have been proposed to address stability problems and a number of prior art references are directed to specific formulations that have been found to exhibit desired stability characteristics. One the factors contributing to stability of a wax emulsion is the choice of the emulsifiers, surfactants, or stabilizers used in the formulation. As understood by persons skilled in the art, the choice of components used in an emulsion is highly dependent upon interactions between the components and, hence, predictability of stability is difficult.

[0005] Another issue relating to wax emulsions is that of supply. Waxes used in industrial wax emulsions are generally obtained from petroleum-based materials. Therefore, the cost and supply of such petroleum derived waxes are directly related to petroleum costs and production capacity. In addition, with the exception of FDA compliant paraffin waxes, other waxes derived from petroleum sources are unusable in applications involving human or animal consumption such as the coating of fruit and vegetables etc. or the coating of the packaging used to contain such items. For this reason, various attempts have been made to utilise waxes from vegetable matter into industrial wax emulsions. One source of waxes that has received much attention is soya beans. Soya beans are generally easy to grow and provide an inexpensive and renewable source of wax.

[0006] The following U.S. references recite soya wax emulsions: 4,666,522; 2006/0196391 ; 2006/0289138; and, 2007/0068642. However, the stability of the emulsions taught in these references is not well defined. Further, US 4,666,522 teaches an emulsion comprising lignosulphonate and a "wax, oil, fat, asphalt or mixtures thereof. However, this reference only teaches the use of soya oil as opposed to a wax.

[0007] US 2005/0269728 teaches an emulsion formulation for enhancing the mechanical strength and dimensional stability of composite wood panels comprising an emulsion of a triglyceride, a wax, a surfactant, and a binding agent. It is noted that the primary focus of this reference is a stable wax-containing emulsion that is compatible with resins and binding agents used in the wood panel industry. This reference distinguishes between the triglyceride and wax components based on their degree of saturation, as measured by iodine values ("IV"), as known in the art. The triglyceride component is indicated as having a low (0-70) IV, indicating a low degree of unsaturation, and it is specified that such component is made by hydrogenation of an oil. The reference suggests numerous combinations and sources/types of oils and waxes for use in the emulsions, one source being soya. Various possibilities are also provided for the surfactant component of the emulsion, with lignosulphonates being one option. However, the reference only illustrates an emulsion formed with linseed oil (as the triglyceride component) and paraffin wax. There is no teaching in this reference of a stable emulsion comprising soya wax. [0008] US 2006/0264519 teaches a wax emulsion comprising paraffin or montan waxes combined with lignosulphonic acid or salts thereof as the emulsifier. This reference does not discuss the use of plant or animal derived waxes.

[0009] A need exists for an improved vegetable oil wax or an animal derived wax emulsion having desired stability characteristics and/or an ability to be used in various applications.

SUMMARY OF THE INVENTION [0010] In one aspect, the present invention provides an aqueous emulsion formed from a wax and an emulsifier. In one embodiment, the wax component comprises a vegetable oil based wax or an animal fat. In another aspect, the invention provides an aqueous emulsion formed from an oil, such as a vegetable oil, and an emulsifier.

[0011] In a preferred embodiment, the emulsifier comprises one or more lignosulphonates or olefin maleic anhydride (OMA) polymers.

[0012] In one aspect, the lignosulphonate component is provided in the form of a salt of lignosulphonic acid. In a further aspect, the salt comprises a calcium, sodium or ammonium salt.

[0013] In another aspect, the OMA polymer comprises an alpha-olefin maleic anhydride copolymer. In a further aspect, the OMA polymer comprises a copolymer formed with an olefin having 6 to 36 carbon atoms.

[0014] In another aspect, the preferred vegetable wax is soya wax. In a further aspect, the soya wax comprises a hydrogenated soya oil.

[0015] Thus, in one embodiment, the invention provides an aqueous emulsion comprising water, soya wax and an emulsifier chosen from one or more lignosulphonates and one or more olefin maleic anhydride polymers.

[0016] Thus, in one aspect, the invention provides a stable wax emulsion for imparting water repelling characteristics to cellulose based products, the emulsion comprising - a vegetable wax or animal fat; - an emulsifier chosen from the group consisting of lignosulphonic acid or salts thereof and polymers comprising monomers of an olefin and maleic anhydride; and, - water. [0017] In other aspects, the invention provides uses of such emulsions and wood based panels or cellulosic products incorporating or coated with such emulsions having water repelling characteristics.

DETAILED DESCRIPTION OF THE INVENTION [0018] In the present disclosure, the following terms will be understood to have the associated meanings:

[0019] "Wax", as used herein, the term wax will be understood to mean the hydrogenated forms of naturally occurring vegetable oils and/or animal fats. One preferred wax is soya wax, obtained from hydrogenated soya oil. Examples of soya waxes that can be used in the present invention are those sold under the following trade names: HP-C100™, HP-C300™, HP-SFS™, HP-SFP™ (from Hase Petroleum Wax Co.); NatureWax™ S-113™ and S-155™ (from Cargill); and SYB-010™ (from Archer Daniels Midland Co.). It will be understood that the waxes that can be used in the present invention are not limited to these examples. Further, the term "wax" is not intended to limit the invention to a component that is necessarily solid at room temperature.

[0020] "Iodine value", or "IV", is a measure of the iodine absorbed in a given time by a chemically unsaturated material. The IV number is used to measure the degree of unsaturation (i.e. the number of double bonds) of a compound or mixture.

[0021] "Stability" as used herein refers to the quality or property of a wax emulsion to resist separation into its components. [0022] "Composite wood panel", or "panel", as used herein, will be understood to mean any form of wood or cellulosic material-based panel. "Composite wood panel" will be understood to include particleboard, fibreboard, such as medium density fibreboard (MDF) and high density fibreboard (HDF), flakeboard, chipboard, oriented strand board (OSB), waferboard and other similar products wherein wood based material is mixed with adhesive and formed into a flat panel. [0023] "Wood particles" will be understood to mean known wood or cellulosic material commonly used in manufacturing composite wood panels. This term will, therefore, be understood to include wood particles, wood chips, wood shavings, wood wafers, wood strands, sawdust or other similar materials.

[0024] "Dispersion", as used with respect to the present invention, will be understood to mean a wax emulsion comprising a continuous aqueous phase and dispersed phase comprising the wax material. As known, the term "dispersion" may be used in the reverse, namely, to identify an aqueous phase dispersed within a continuous non-aqueous phase. However, for the purposes of the present description, the invention will be described in terms of the former meaning. [0025] "Solids" or "solids content" as used herein will be understood to refer to the amount (expressed as a weight percentage) of non-volatile material in the emulsion. More accurately, these terms refer to the total amount of material (including wax, urea, emulsifiers and stabilizers) that remain after evaporation or drying to a constant weight.

[0026] "Lignosulphonate" refers to a reaction product of lignin, which is inherently obtained during sulphite pulping of wood, and is a principle constituent of spent sulphite liquor. Generally, the lignosulphonate comprises a calcium, sodium or ammonium salt of lignosulphonic acid. In one embodiment, the lignosulphonate comprises the product available under the trade names Polyfon™, such as Polyfon H™, available from MeadWestvaco Corporation, Arbo™, such as Arbo A02™ (an ammonium salt) available from Tembec, and Norlig™ TSFL (also an ammonium salt) available from Borregaard LignoTech. However, various other examples of lignosulphonates will be known to persons skilled in the art. In addition, the term lignosulphonate will also be understood as including the acid (i.e. lignosulphonic acid) as well as salts thereof.

[0027] Olefin maleic anhydride copolymer", or "OMA", - refers to a copolymer formed from olefin, such as alpha-olefin, and maleic anhydride monomers according to the following reaction:

[0028] In one embodiment, the OMA component of the formulation comprises a copolymer of alpha-olefin and maleic anhydride such as that commercially available under the trade name Luxco OMA 30™ from Luxco Wax of Hayward, California, USA. However, various other examples of OMA will be known to persons skilled in the art. For example, in one embodiment, the term OMA will also be understood as encompassing graft polymers such as those formed by grafting esters (or half esters) of maleic anhydride to an ethylene or olefin based polymer (for example Ceramer 67™ manufactured by Baker Hughes Incorporated, Texas, USA. In another embodiment, the term OMA will be understood as including graft copolymers such as those formed by grafting esters of maleic anhydride to the OMA copolymers mentioned above. An example of such graft polymer is commercially available under the trade name Ceramer 1608™ (manufactured by Baker Hughes Incorporated, Texas, USA), which is a graft copolymer formed by grafting a monoisopropyl ester of maleic acid onto a copolymer of propylene and maleic anhydride.

[0029] PEG 600 is a polyethylene glycol, used to improve dispersibility and stability of the emulsion. PEG 600 is used in some of the paraffin wax formulations described herein and exhibits its positive effect on emulsion shear stability. In a preferred though not essential aspect of the invention, the subject emulsion formulations include a polyethylene glycol, such as PEG 600.

[0030] The emulsion formulation of the invention may optionally comprise an amine such as mono-ethanolamine (MEA). However, other amines like triethanolamine (TEA), aqua ammonia (or aqueous ammonia), morpholine, and one or more other amines or combinations of same may also be used.

[0031] The present invention provides a wax emulsion formulation, in particular a vegetable or animal based wax formulation, that exhibits desired stability characteristics. More particularly, the formulation comprises a soya wax. In one embodiment, the invention essentially comprises a vegetable wax or animal fat and an emulsifier chosen from lignosulphonates (LS) and/or olefin maleic anhydride (OMA) copolymers (or graft polymers thereof etc.) In a preferred embodiment, the vegetable wax is soya wax.

[0032] The emulsions of the present invention can be used in various applications as will be known to persons skilled in the art. For example, they may be used to impart water repellent characteristics to composite wood panels such as plywood, oriented strand board (OSB), MDF, partideboard and the like. In one aspect, the emulsions may be sprayed or otherwise applied to the exterior surfaces of the boards as a water repellent coating. Alternatively, for example in the manufacture of OSB or partideboard, the emulsions may be mixed into the precursor wood flakes, chips or particles prior to pressing and formation of the boards. In the latter case, the emulsions may be incorporated into the adhesive formulation used to form the boards.

[0033] In another aspect, the emulsions of the present invention can be used to coat cellulosic sheet or board products such as paper or cardboard. In one example, the emulsion may be applied to the surface of cardboard or corrugated board used in making boxes. Such coating serving the purpose of repelling water. [0034] In another aspect, the emulsions of the invention can be used in the manufacture of gypsum boards or panels. In one example of such a use, the emulsions may be incorporated into the gypsum slurry used to make such boards.

[0035] Examples

[0036] The invention will now be described in terms of specific examples. It will be understood that the purpose of all examples contained herein is solely to illustrate the invention and that such examples are not intended to limit the invention in any way.

[0037] 1) Preparation of Emulsions

[0038] Various emulsions were prepared to assess stability characteristics. In preparing the emulsions, a two step process was followed comprising the steps of dispersion (to mix the various components) and homogenization (to reduce particle sizes).

[0039] The purpose of the dispersion step was to thoroughly mix the solutions forming the emulsion and to uniformly disperse any particles contained therein throughout the solution. That is, this step serves to mix the aqueous components (water and amine emulsifier) and non-aqueous components (wax and lignosulfonate or OMA) to form an emulsion comprising a continuous aqueous phase and a dispersed non-aqueous phase. The dispersion procedure involved the following steps: - A "water solution" comprising water and monoethanolamine (MEA) was prepared in a stainless steel mixing container. - A "wax pre-blend" comprising the wax (e.g. soya wax) and OMA was also prepared. - The wax pre-blend is added to the water solution and the blend dispersed with a disperser. [0040] The purpose of the homogenization step was to break apart large globules of substances in the mixture and to create a homogenous liquid. The homogenized emulsion was then cooled to 25°C in a cold water bath.

[0041] 2) Stability Tests for Emulsions

[0042] The stability of the various emulsions was measured by subjecting the formulations to high shear stresses using the disperser for a maximum of 3 minutes and then monitoring the emulsions for a period of time (24 hours). [0043] The samples were monitored for any changes such as: foaminess, cheesy composition, and/or wax fallout and the scale shown in Table 1 below was used to rank the results. In the course of these tests, samples that exhibited a shear stability of 4 or 5 were considered to be acceptable.

[0044] Table 1

[0045] 3) Particle Boards Manufactured Using Emulsions

[0046] The emulsions prepared for the comparative stability tests were also used in manufacturing wood particle board samples (typically 6" x 6" samples). The samples were then subjected to water absorption and thickness swell tests pursuant to ASTM standards.

[0047] The board samples were made according to the following procedure. First, the resin (adhesive) and wax emulsion was added to wood particles and the blend was mixed in a tumbler container. A weight mixture was added to the heated plate mould and was pressed at a predetermined pressure, temperature and time. The boards were then tested according to ASTM D1037.

[0048] The water absorption and thickness swell tests were conducted according to ASTM standard D-1037-96a. In these tests, the amount of water absorbed (after 2 hours and 24 hours) was measured as a percentage increase in weight of the board. The thickness swell was measured as a percentage increase (after 2 hours and 24 hours) in the thickness of the board.

[0049] In the test data provided below, the abbreviations and/or trade names listed in Table 2 are used.

[0050] Table 2

[0051] Table 3 summarises the characteristics of the waxes used in the tests. [0052] Table 3

[0053] 4) Emulsions of Soya Wax and OMA [0054] The results from the above tests using emulsions of soya wax and OMA are summarized in Table 4 [0055] Table 4 Emulsions of Soya Wax and OMA

[0056] Table 4: Emulsions of Soya Wax and OMA (Continued):

[0057] Table 4: Emulsions of Soya Wax and OMA (Continued)'

[0058] Table 4: Emulsions of Soya Wax and OMA (Continued):

[0059] Table 4: Emulsions of Soya Wax and OMA (Continued):

[0060] 5) Emulsions of Soya Wax and Lignosulphonates

[0061] The results from the above tests using emulsions of soya wax and lignosulphonates are summarized in Table 5.

Table 5 Emulsions of Soya Wax and Lignosulphonate

[0062] 6) Emulsions of Animal Fat Formulations

[0063] The results from the above tests using emulsions of animal fat (tallow) are summarized in Table 6. [0064] Table 6: Emulsions of Animal Fat (Tallow) Based Wax Formulations

[0065] 7) Comparison of Soya Wax/OMA and Paraffin Wax

[0066] In order to compare the effectiveness of the present invention and that of paraffin wax based emulsions, trials were conducted using various totes of formulation 5.52B (soya wax + OMA) and paraffin wax formulations. In both cases, emulsions of the respective waxes (prepared according to the above method) were used. Table 7 summarizes the results from these comparative tests (values shown are averages of various trials).

[0067] Table 7

[0068] Discussion of Test Data

[0069] In comparing run numbers 5.51, 5.52 and 5.53 with run number 4.95 (from Table 4), it is noted the presence of OMA improves the stability of the emulsion containing soya wax alone (i.e. without paraffin wax). Table 4 illustrates stable emulsions comprising soya wax and OMA. Table 5 clearly shows stable emulsions comprising soya wax and lignosulphonate.

[0070] In addition, the particle board test results clearly illustrate that the emulsions of the invention, comprising soya wax and either OMA or lignosulphonate, provide acceptable water repellent characteristics.

[0071] The above data also illustrate that a stable emulsion can also be obtained using a combination of soya wax and paraffin wax.

[0072] In the above tests, paraffin wax emulsion was considered as a control in designing the vegetable oil-based wax emulsions or the emulsions using both paraffin and soy waxes. A new emulsifier has been used (OMA30) and a stabilizer (PEG 600), in order to improve product stability.

[0073] Both OMA 30 and lignosulphonate salts were found to result in stable emulsions, as can be seen in formulations 5.52B, 5.53E, 5.132B, 5.43B, 5.43C, 5.58B, 5.57A, and 5.65E. However, their chemical composition and their behaviour as emulsifiers are different. OMA30 is a highly polar (hydrophilic) co-polymer with long alkyl (hydrophobic) side chains. This duality allows the co-polymer to act as a compatibility agent. Salts can be obtained by the reaction of the anhydride group with bases like: amines or metal hydroxides.

[0074] On the other hand, lignin molecules enhance wetting by lowering the interfacial tension resulting in a reduction in surface energy. Stabilization of wax emulsion results from the adsorption of lignin molecules at the wax droplet surface, this action results in a charge build up at the wax-water interphase, causing a mutual repulsion between emulsion particles having the same charge. In addition, the hydrophilic surface coating of lignin creates a protective layer around each droplet resulting in increased stability. Therefore, lignosulphonates are considered as emulsion stabilizers preventing the once formed droplets from creaming, coming into contact with each other and fusing to form large drops. In addition, being charged particles, they will have an electrostatic effect and as a result further reducing the likelihood the drops will come into contact.

[0075] As can be seen in the above data, the ratio between OMA 30 and soya wax was altered in order to obtain a good stability. 1-5% on total solids content would be the recommended range for OMA 30. The maximum solids content for a good stability is 45%, using OMA and 50% to 57% using lignosulphonates. For example, samples 4.172G, 5.53D and 5.44A at 50% and 57% do not exhibit good stability.

[0076] The recommended formulations using OMA were found to be those illustrated by trials 5.52B, 5.53E, and 5.132B at 45% solid content. The recommended formulations using lignosulphonate were found to be those illustrated by trials 5.43B, 5.43C, 5.57A, 5.58B, and 5.65E at 50% and 57% solid content.

[0077] Table 4 above also provides data illustrating desirable results using other olefin/maleic anhydride polymers. These formulations are identified as trial numbers 5.92C, 5.96C, and 5.98B.

[0078] Table 6 illustrates that the present invention provides desirable results when using animal fat derived waxes as well. As shown, desired results are obtained with tallow when in combination with either OMA or lignosulfonate (runs 5.132B and 5.65E). Although run number 4.172H of Table 6 provided good stability results, the viscosity of the formulation was found to be too high.

[0079] Finally, as shown in Table 7, the results for the soya wax emulsion (5.52B) compared well with the results for the paraffin wax emulsion. Thus, this example illustrates that the soya wax emulsions of the invention are as effective as paraffin wax in imparting the desired water repelling characteristics.

[0080] It will be understood that the above description has provided various emulsion compositions and has outlined the main or primary components thereof. It will also be understood that various other additives such as thickeners, pH control agents, colourants, etc. may optionally be used. The invention does not explicitly or implicitly include or exclude any such additive components that will be known to persons skilled in the art.

[0081] Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the purpose and scope of the invention as outlined in the claims appended hereto. Any examples provided herein are included solely for the purpose of illustrating the invention and are not intended to limit the invention in any way. Any drawings provided herein are solely for the purpose of illustrating various aspects of the invention and are not intended to be drawn to scale or to limit the invention in any way. The disclosures of all prior art recited herein are incorporated herein by reference in their entirety.

Claims

WE CLAIM:

1. A stable wax emulsion for imparting water repelling characteristics to cellulose based products, the emulsion comprising:

- a vegetable wax or animal fat;

- an emulsifier chosen from the group consisting of lignosulphonic acid or salts thereof and polymers comprising monomers of an olefin and maleic anhydride; and,

- water.

2. The emulsion of claim 1 wherein the vegetable wax is a vegetable oil based wax and the animal fat is tallow.

3. The emulsion of claim 2 wherein the soya wax is derived from hydrogenated vegetable oil.

4. The emulsion of claim 1 wherein the vegetable wax is a soya oil based wax.

5. The emulsion of any one of claims 1 to 4 wherein the emulsifier is lignosulphonic acid or a salt thereof.

6. The emulsion of any one of claims 1 to 4 wherein the emulsifier is a polymer comprising monomers of an olefin and maleic anhydride.

7. The emulsion of claim 6 wherein the polymer is an olefin maleic anhydride copolymer.

8. The emulsion of claim 6 wherein the polymer is a graft polymer comprising maleic anhydride monomers grafted to an olefinic polymer.

9. The emulsion of claim 7 wherein the copolymer includes maleic acid moieties grafted thereto.

10. The emulsion of any one of claims 1 to 9 wherein the wax component includes a paraffin wax.

11. The emulsion of any one of claims 1 to 10 wherein said emulsion comprises a continuous aqueous phase and a dispersed phase comprising said wax or animal fat and the emulsifier.

12. The emulsion of claim 11 wherein said continuous aqueous phase further comprises an amine emulsifier component.

13. The emulsion of claim 12 wherein the amine component is chosen from amine emulsifiers, monoethanolamine, triethanolamine, aqua ammonia; morpholine and combinations thereof.

14. Use of the emulsion according any one of claims 1 to 13 in the manufacture of composite wood panels or cellulose based sheets.

15. Use of the emulsion according any one of claims 1 to 13 in the manufacture of gypsum wall boards.

16. Use of the emulsion according any one of claims 1 to 13 as water repellent additive or coating on composite wood panels or cellulose based sheets.

17. A composite wood panel having incorporated therein or thereon a wax emulsion according to any one of claims 1 to 13.