WO2010065758A2

WO2010065758A2 - Soy adhesives

Info

Publication number: WO2010065758A2
Application number: PCT/US2009/066614
Authority: WO
Inventors: Kaichang Li
Original assignee: Oregon State University; Oregon State
Current assignee: Oregon State University; Oregon State
Priority date: 2008-12-03
Filing date: 2009-12-03
Publication date: 2010-06-10
Anticipated expiration: 2011-06-03
Also published as: WO2010065758A3

Abstract

Embodiments of a method and composition for making curing agents, soy- based adhesives including the curing agents, and lignocellulosic composites made with the adhesives are disclosed. One embodiment of a method for making a lignocellulosic composite includes: applying (i) soy protein and (ii) a curing agent to at least one lignocellulosic substrate; and bonding the composition-applied substrate to at least one other lignocellulosic substrate, wherein the curing agent is made by a method comprising: reacting (i) ammonia with (ii) epichlorohydrin, a chlorinated propanol or a mixture thereof at a temperature of 50 to 60°C. In another embodiment, the curing agent for making the lignocellulosic composite is prepared by reacting (i) ammonia with (ii) epichlorohydrin, a chlorinated propanol, or a mixture thereof to produce an intermediate and subsequently heating the intermediate to produce a curing agent.

Description

SOY ADHESIVES

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and benefit of U.S. Provisional Patent Application No. 61/200,817, filed December 3, 2008, which is incorporated herein by reference in its entirety.

FIELD

The present disclosure relates to soy adhesives for making lignocellulosic composites.

BACKGROUND

Lignocellulosic-based composites are formed from small dimension pieces of cellulosic material that are bonded with an adhesive (i.e., a binder). In general, solid wood is fragmented into smaller pieces such as strands, fibers, and chips. An adhesive composition then is added to the wood component. The resulting mixture is subjected to heat and pressure resulting in a composite. The adhesive mix typically is the only non-lignocellulosic component.

The most commonly used wood adhesives are phenol-formaldehyde resins (PF) and urea-formaldehyde resins (UF). There are at least two concerns with PF and UF resins. First, volatile organic compounds (VOC) are generated during the manufacture and use of lignocellulosic-based composites. For example, the California Air Resources Board (CARB) estimates that as much as 400 tons of formaldehyde is emitted from wood composite products bonded with UF resins each year in California An increasing concern about the effect of emissive VOC, especially formaldehyde, on human health has prompted a need for more environmentally acceptable adhesives. Second, PF and UF resins are made from petroleum-derived products. The reserves of petroleum are naturally limited. The wood composite industry would greatly benefit from the development of formaldehyde-free adhesives made from renewable natural resources. Soy protein was used as a wood adhesive for the production of plywood from the 1930' s to the 1960's. Petroleum-derived adhesives replaced soy protein adhesives due to the relatively low bonding strength and water resistance of soy protein adhesives. However, soy protein is an inexpensive, abundant, renewable material that is environmentally acceptable.

Improved soy protein adhesives have been developed that employ a polyamidoamine-epichlorohydrin adduct (PAE) as a curing agent, such as those disclosed in U.S. Patent No. 7,252,735. However, this PAE curing agent is derived from petrochemicals and is the most expensive component of the soy flour/PAE adhesive. Thus, it would be advantageous to develop a less expensive soy-based adhesive.

SUMMARY

Disclosed herein are embodiments of methods and compositions for making curing agents, soy-based adhesives including the curing agents, and lignocellulosic composites made with the adhesives.

One embodiment of a method for making a lignocellulosic composite disclosed herein includes : applying (i) soy protein and (ii) a curing agent to at least one lignocellulosic substrate; and bonding the composition-applied substrate to at least one other lignocellulosic substrate, wherein the curing agent is made by a method comprising: reacting (i) ammonia with (ii) epichlorohydrin, a chlorinated propanol or a mixture thereof at a temperature of 50 to 6O⁰C.

In another embodiment, the curing agent for making the lignocellulosic composite is prepared by reacting (i) ammonia with (ii) epichlorohydrin, a chlorinated propanol, or a mixture thereof to produce an intermediate and subsequently heating the intermediate to produce a curing agent. In certain embodiments, the curing agent is prepared in an aqueous medium.

An adhesive composition suitable for bonding lignocellulosic materials is prepared by mixing any of the curing agent embodiments with a soy protein. In particular embodiments, the adhesive composition includes a base.

A lignocellulosic composite is prepared by applying soy protein and any of the curing agent embodiments to a lignocellulosic substrate, which then is bonded to another lignocellulosic substrate. In particular embodiments, the lignocellulosic composite further includes a base and/or a boron compound. In some embodiments, a substantially formaldehyde-free composition is prepared from soy protein, a curing agent, and comminuted lignocellulosic materials.

The foregoing and other objects, features, and advantages will become more apparent from the following detailed description.

DRAWINGS

Figure 1 is a graph depicting test results for one embodiment of an adhesive disclosed herein.

DETAILED DESCRIPTION

Embodiments of an adhesive composition can be made by reacting or mixing a soy protein with at least one substantially formaldehyde-free curing agent. The substantially formaldehyde-free compound may provide both curing for the adhesive composition and adhesion to the lignocellulosic substrate. In other words, the substantially formaldehyde-free compound may be a difunctional adhesion promoter in the sense that one compound can provide dual functions. The curing agent is a reaction product of (ii) ammonia with (ii) epichlorohydrin and/or a chlorinated propanol. The adhesive composition may be provided as a two-part system in which the protein comprises one part or package and the curing agent comprises the second part or package. All the parts or components of the composition may be in the form of aqueous solutions or dispersions. Thus, volatile organic solvents as carrier fluids can be avoided.

Soy protein is an exemplary protein for use in the presently described adhesives. Soybeans contain about 38 wt% protein with the remaining portion comprising carbohydrates, oils, ash and moisture. Soybeans are processed to increase the amount of soy protein in the processed product. Soy protein products of any form may be utilized in the disclosed adhesive compositions. The three most common soy protein products are soy flour, soy protein concentrate, and soy protein isolate (SPI). One difference between these products is the amount of soy protein. For example, in certain embodiments, soy flour may typically include approximately 45-55 wt% protein, soy protein concentrate includes at least about 65 wt% protein (dry weight), and SPI includes at least about 85 wt% protein (dry weight). According to certain embodiments of the adhesive composition, the soy protein is soy flour.

The curing agents are prepared from epichlorohydrin and/or chlorinated propanols, particularly 1,3-dichloropropanol or 1 ,2-dichloropropanol, and aqueous ammonia. Industrially, epichlorohydrin is manufactured from propylene. Propylene reacts with chlorine gas to form allyl chloride. The allyl chloride is converted to dichloropropanol with peroxide. Dichloropropanol reacts with sodium hydroxide to form epichlorohydrin, as shown below:

O H₂C=C-CH₃ + 1/2 Cl₂ - H₂C=C-CH₂CI + H₂O₂ ^Λ + H₂O propylene allyl chloride epichlorohydrin However, epichlorohydrin also can be prepared from glycerol, along with

1 ,2-dichloropropanol and 1,3-dichloropropanol as disclosed, e.g., in U.S. Patent Publication No. 2007/0112224. Glycerol is abundant and readily available, e.g., as a byproduct in biodiesel production. Thus, glycerol is a less expensive starting material than propylene for epichlorohydrin synthesis. Glycerol reacts with HCl in the presence of an acid catalyst to form 1,3-dichloropropanol and 1 ,2- dichloropropanol. Suitable catalysts are disclosed, for example, in U.S. Patent Publication No. 2008/0045728. Reaction of 1,3-dichloropropanol and 1 ,2- dichloropropanol with a base (e.g. , NaOH) produces epichlorohydrin, as shown below:

H₂ H₂

CI^C^OH

Cl

H₂ H₂ t i t 1 ,2-dichloropropanol

HO-^Cγ°-OH ^{+ 2 HCI} and + 2 H₂O

OH H₂ H₂ glycerol Cl^ C Cl

OH

1 ,3-dichloropropanol

NaOH

epichlorohydrin

In some embodiments, a curing agent is prepared by reacting epichlorohydrin, a chlorinated propanol, or a mixture thereof with aqueous ammonia (NH3). In certain embodiments, epichlorohydrin or chlorinated propanol is reacted with ammonia at NHyepichlorohydrin or NHychlorinated propanol molar ratios ranging from 5:1 to 1 :5, more particularly from 2: 1 to 1 :3. In certain embodiments, undesirable side reactions may occur in the presence of excess ammonia.

In one embodiment for making the curing agent, a mixture of epichlorohydrin (and/or chlorinated propanol) and aqueous ammonia is vigorously stirred in a sealed reaction at a predetermined temperature selected from 50 ⁰C to 60 ⁰C, particularly from 55 ⁰C to 60 ⁰C to produce, the curing agent. The reaction is exothermic. The reaction may be cooled to maintain a temperature range of 50 ⁰C to 60 ⁰C, particularly from 55 ⁰C to 60 ⁰C. The reaction is considered complete when the initial heterogeneous reaction mixture becomes a homogeneous solution. The reaction typically progresses for 20 minutes to 20 hours, although preferably the reaction is complete in 4 hours or less.

In another embodiment for making the curing agent, a mixture of epichlorohydrin (and/or chlorinated propanol) and aqueous ammonia is vigorously stirred in a sealed reaction at a predetermined temperature selected from 0 ⁰C to 65 ⁰C, such as from 25 ⁰C to 60 ⁰C to produce an intermediate product. In particular embodiments, the reaction temperature is 30 to 45 ⁰C, more particularly 40 ⁰C. If the temperature is too low, the reaction is slow to occur. At temperatures over 65 ⁰C, side reactions, such as replacement of a chlorine atom with an amino group, may occur. The reaction is exothermic. The reaction may be cooled to maintain a temperature range of 0 to 65 ⁰C, such as 25 to 60 ⁰C.

The reaction is considered complete when the initial heterogeneous reaction mixture becomes a homogeneous solution. The reaction typically progresses for 20 minutes to 20 hours. The intermediate product may include a mixture of different compounds. For example, although not bound by any theory, the main products of this reaction may include compounds with the following formulas: N(CH₂CHOHCH₂Cl)₃ (compound (I)), HN(CH₂OHCH₂Cl)₂ and H₂NCHOHCH₂Cl. At an epichlorohydrin/ammonia molar ratio of 3:1, compound (1) was the main product:

epichlorohydrin N(CH₂CHOHCH₂CI)₃ (1)

The intermediate product then is subjected to a second additional heating step to produce a final curing agent product. For example, the prepared intermediate is heated at a temperature selected from 65 ⁰C to 98 ⁰C, more particularly, from 70 ⁰C to 80 ⁰C. The second heating step may occur at a pH selected from 6 to 14, particularly pH 8-10. In some embodiments, the second reaction is carried out for 20 minutes to 5 hours. The resulting curing agent may have a solids content of 5 to 80, more particularly 25 to 60, wt%. Although not bound by any theory, it is believed that the second heating step may cause a portion of the intermediate product to cyclize. For example, the product (which may be a mixture of different compounds) of the second heating step may include at least one of the following compounds:

In another embodiment, the intermediate product may be reacted further with ammonia and additional epichlorohydrin to produce compounds such as those shown below. For example, in a first step the intermediate product may be reacted with a molar excess (e.g., a 2 to 4-fold excess) of ammonia at 10 to 98 ⁰C for 1 to 24 hours to produce a second intermediate (4). The second intermediate then can be reacted with a molar excess (e.g., a 4 to 10-fold excess) of epichlorohydrin at 10 to 98 ⁰C to produce a third intermediate (5). The third intermediate may be further heated at 65 to 98 ⁰C to produce a final curing agent product (6).

At least one boron compound, a group IA oxide or hydroxide, or a group HA oxide or hydroxide may also be included as a base in the adhesive composition. The boron compound may be any compound or material that includes at least one boron atom or species. "Group IA" and "group HA" refer to the element classifications in the Periodic Table of the Elements. Although not bound by any theory, it is believed that a boron species not only acts as a base to buffer the pH of the adhesive, but also can potentially chelate with hydroxyl groups, thus serving as a crosslinking agent for the soy protein or lignin. The group IA or group HA species can potentially facilitate the reactions between the curing agent and soy flour and the reactions between the curing agent and lignocellulosic components. The metal ions of group IIA species can potentially chelate with a plurality of carboxylic acid groups, thus serving as a crosslinking agent for the soy protein or lignin.

In particular examples the boron compound may be boric acid, a boron salt, or a borate ester. As is understood by those of ordinary skill in the art, boric acid, borate salts and borate esters can be produced from numerous other boron compounds, including without limitation, metaborates, acyl borates, anhydrous borates, borax, boron hydrides, and the like. Specific examples of borate salts or borate esters include sodium borate, anhydrous sodium borate, sodium tetraborate, sodium boro formate and sodium borohydride. Similarly, a person of ordinary skill in the art will recognize that boron compounds can be provided as various salts and in various hydration states, including without limitation, KB₅Η₂O, Na₂B₄O₇-IOH₂O, Na₂B₄O_r5H₂O, Mg₃B₇O₁₃Cl, K₃B₃O₆, CaB₂O₄, and the like. About 0.1 to about 15 wt%, more particularly about 0.1 to about 5 wt% of the boron compound(s) may be included in the adhesive, based on the combined dry weight of soy protein and curing agent. In particular examples the group IA oxide or hydroxide or group IIA oxide or hydroxide may be a hydroxide or oxide of calcium, sodium or potassium. Illustrative compounds include sodium hydroxide, potassium hydroxide, calcium hydroxide, or calcium oxide. The amount of group IA oxide or hydroxide, or group IIA oxide or hydroxide added to the mixture may vary. For example, about 0.1 to about 20 wt%, more particularly about 0.1 to about 10 wt% of the base(s) may be included in the adhesive, based on the combined dry weight of soy protein and curing agent.

The adhesive composition also may include additives and fillers found in lignocellulosic adhesives such as bactericides, insecticides, silica, wax, wheat flour, tree bark flour, nut shell flour and the like.

The ingredients of the adhesive composition may be mixed together in any order and at standard temperature and pressure (i.e., about 25°C and about 1 atmosphere). Typically, the ingredients are water soluble or water dispersible. The solids content of the resulting final adhesive mixture may be from 5 to 65 wt.%, more particularly from 25 to 50 wt %. Each (or only one) part of the adhesive system could be provided to the end user in the form of a concentrate that is diluted by the end user to the appropriate mix ratios and solid contents.

According to one approach, the soy protein component, the curing agent, the base, and additives/fillers are mixed together a short time prior to use. The composition may have an open time of up to about 5 days. As used herein, "open time" denotes the time from mixing of the two parts to the time at which the mixed composition cures to a point that it is no longer workable. In another approach, all the ingredients of the adhesive composition are pre-mixed together in a one-part system that is then supplied to an end user. In the one-part system, the adhesive composition can be applied to a substrate without the need for mixing together multiple different components. The adhesive compositions are heat-curable. In other words, heating the adhesive mixture forms covalent bonds between the individual molecules of the adhesive composition and covalent and/or hydrogen bonds between molecules of the adhesive mixture and the lignocellulosic particles. Such curing typically occurs during the hot pressing step of the composite formation. Thus, the cure temperature of the adhesive composition is tailored so that it coincides with the heating temperatures used in composite formation. Such cure temperatures may range, for example, from about 80 to about 220⁰C, more particularly from about 100 to about 160⁰C. The adhesive mixture typically is not heated until after it has been applied to the lignocellulosic substrates. Lignocellulosic composites that can be produced with the adhesives described herein include particleboard, plywood, oriented strand board (OSB), waferboard, fiberboard (including medium-density and high-density fiberboard), parallel strand lumber (PSL), laminated strand lumber (LSL), laminated veneer lumber (LVL), and similar products. In general, these composites are made by first blending comminuted lignocellulosic materials with an adhesive that serves as a binder to adhere the comminuted lignocellulosic materials into a unitary densified mass. Examples of suitable lignocellulosic materials include wood, bamboo, straw (including rice, wheat and barley), flax, hemp and bagasse. The comminuted lignocellulosic materials can be processed into any suitable substrate form and size such as chips, flakes, fibers, strands, wafers, trim, shavings, sawdust, straw, stalks, shives, and mixtures thereof. The lignocellulosic materials are mixed together with the adhesive composition serving as a binder, and formed into a desired configuration to provide a pre-bonded assembly. The pre-bonded assembly then is subjected to heat and elevated pressure to provide the lignocellulosic composite product. For example, the pre-bonded assembly may be subjected to temperatures of from about 120 to 225°C in the presence of varying amounts of steam, generated by liberation of entrained moisture from the lignocellulosic materials.

The amount of adhesive mixed with the lignocellulosic particles may vary depending, for example, upon the desired composite type, lignocellulosic material type and amount and specific adhesive composition. In general, about 1 to about 15, more particularly about 3 to about 10, weight percent adhesive may be mixed with the lignocellulosic material, based on the total combined weight of adhesive and lignocellulosic material. The mixed adhesive composition may be added to the comminuted lignocellulosic particles by spraying or similar techniques while the lignocellulosic particles are tumbled or agitated in a blender or similar mixer. For example, a stream of the comminuted lignocellulosic particles may be intermixed with a stream of the mixed adhesive composition and then be subjected to mechanical agitation.

In certain embodiments, a lignocellulosic composite composition may be made by mixing together soy protein, the curing agent, and comminuted lignocellulosic materials. The components may be mixed in order. For example, the soy protein and curing agent may be pre -mixed prior to mixing with the comminuted lignocellulosic materials. Alternatively, the soy protein and comminuted lignocellulosic materials may be pre -mixed, or the curing agent and the comminuted lignocellulosic materials may be pre -mixed. The adhesive compositions also may be used to produce layered lignocellulosic composites. Soy protein and a curing agent may be applied to at least one lignocellulosic substrate, which is then bonded to at least one other lignocellulosic substrate. A base and borate also may be applied to the lignocellulosic substrate. The soy protein, curing agent, base and borate may be mixed together and then applied to the lignocellulosic composite. For example, the adhesive compositions can be used to produce plywood or laminated veneer lumber (LVL). The adhesive composition may be applied onto veneer surfaces by roll coating, knife coating, curtain coating, or spraying. A plurality of veneers are then laid-up to form sheets of required thickness. The mats or sheets are then placed in a heated press (e.g., a platen) and compressed to effect consolidation and curing of the materials into a board. Fiberboard may be made by the wet felted/wet pressed method, the dry felted/dry pressed method, or the wet felted/dry pressed method.

The presently disclosed adhesives provide a strong bond between the lignocellulosic substrates. The adhesives also provide structural composites with high mechanical strength. In addition, the curing agent and the adhesive compositions are substantially free of formaldehyde (including any compounds that may degenerate to form formaldehyde). For example, the curing agent and the adhesive compositions do not contain any formaldehyde (and formaldehyde- generating compounds) that is detectable by conventional methods or, alternatively, the amount of formaldehyde (and formaldehyde-generating compounds) is negligible from an environmental and workplace regulatory standpoint. The specific examples described below are for illustrative purposes and should not be considered as limiting the scope of the appended claims.

Example 1 Preparation of curing agents from epichlorohydrin and ammonia

Epichlorohydrin (833 g, 9.0 mole), 29% aqueous ammonia (179 g, 3.0 moles), and water (300 ml) were stirred in a resin kettle with sufficient cooling to keep the temperature at around 40 ⁰C for about one hour. The reaction mixture was initially milky and then became a homogeneous solution. The resulting curing agent was designated as CA#1. The CA#1 was acidified with 1 N sulfuric acid to pH 3 for long term storage. The CA#1 was treated at 75 ⁰C for one hour to form a new curing agent (CA#2). The acidified CA#1 was adjusted to pH 9.5 with 1 N NaOH before the heat treatment at 75 ⁰C.

Comparative Example 2

Preparation of soy flour/CA#l adhesives

Soy flour (100 mesh and protein dispersibility index 90), CA#1, sodium hydroxide and water were mixed in a KitchenAid mixer for 5 minutes. The dry weight ratio of soy flour/C A# 1 was 7:1. The dry weight ratio of NaOH/(soy flour + CA#1) was 0.03:1. The total solids content of the adhesive was 36 %.

Example 3 Preparation of soy flour/CA#2 adhesives

Soy flour (100 mesh and protein dispersibility index 90), CA#2, sodium hydroxide and water were mixed in a KitchenAid mixer for 5 minutes. The dry weight ratio of soy flour/C A#l was 7:1. The dry weight ratio of NaOH/(soy flour + CA#1) was 0.03:1. The total solids content of the adhesive was 36 %.

Example 4 Preparation of plywood

Either soy flour/C A#l adhesive or soy flour/C A#2 adhesive was applied to two sides of a yellow-poplar or aspen veneer (2 ft x2 ft; moisture content 12%) by a roller coater with the adhesive spread rate of about 8 mg/cm². The adhesive-coated veneer was stacked between two uncoated veneers with the grain directions of two adjacent veneers perpendicular to each other. The stacked 5-ply veneers were put on a table for 5 minutes, cold-pressed at 100 psi for 5minutes, put on a table again for 5 minutes and hot-pressed at 150 psi at 130 ⁰C for 6 minutes. After hot-press, the panel was stored at ambient environment for at least 24 hours before it was evaluated for its shear strength and water-resistance. Example 5 Determination of water resistance

Curing agents and soy-based adhesives were prepared as described in

Examples 1 and 2. Five-ply plywood panels were prepared with yellow poplar veneer under hot-press conditions of 130 ⁰C, 150 psi and 6 minutes.

The water-resistance of the plywood panels was determined with a three- cycle soak test in accord with the American National Standard for Hardwood and Decorative Plywood; Hardwood Plywood & Veneer Association; 2004

(ANSI/HP VA HP-I). ANSI/HP VA HP-I is the commonly accepted standard for evaluating the water-resistance of interior plywood. The following is a detailed testing procedure defined by the standard. Twenty plywood specimens (2 in x 5 in) cut from each plywood panel were soaked in water at 24 ± 3 ⁰C for 4 hours, and then dried at 49 ⁰C to 52 ⁰C for 19 hours. All specimens were inspected to see whether they were delaminated. This soaking/drying cycle was repeated until three cycles were completed. According to the standard, a plywood panel meets water-resistance requirement for interior applications if 95% of the specimens, i.e., 19 out of the 20 specimens do not delaminate after the first soaking/drying cycle and 85% of specimens, i.e., 17 out of 20 specimens do not delaminate after the third soaking/drying cycle. The ANSI/HP VA HP-I specifically provides the following definition of delamination: any continuous opening between two layers has to be longer than two inches and deeper than 0.25 inch and wider than 0.003 inch.

Table 1 illustrates the results. The panels formed with CA#1 did not meet the standard. After the second cycle, 5-6 specimens had delaminated. However, panels formed with the heat-treated curing agent CA#2 met the standard with none of the specimens delaminating after three cycles. Table 1

Example 6

Two-cycle boil test

Curing agents and soy-based adhesives were prepared as described in Examples 1 and 2. Five-ply plywood panels were prepared with yellow poplar veneer under hot-press conditions of 130 ⁰C, 150 psi and 6 minutes.

In accordance with the American National Standard for Hardwood and Decorative Plywood; Hardwood Plywood & Veneer Association; 2004 (ANSI/HP VA HP-I), the following two-cycle boil test can be used to evaluate whether plywood panels can meet one of the water-resistance requirements for exterior applications. The 76 mm by 76 mm (3 inches by 3 inches) specimens are submerged in boiling water for 4 hours and then dried at a temperature of 63 ± 3 ⁰C (145 ± 5 ⁰F) for 20 hours with sufficient air circulation to lower the moisture content of the specimens to a maximum of 12 percent of the ovendry weight. They are boiled again for 4 hours, dried for three hours at a temperature of 63 ± 3 ⁰C (145 ± 5 0F), and then examined for delamination. An observed delamination greater than 25.4 mm (1 inch) in continuous length constitutes failure of the specimen. Within any given lot of test samples, 90 of the individual specimens must pass.

Table 2 illustrates the results of the two-cycle boil test of plywood formed with CA#1 with all eight specimens delaminating after the test. Dramatically improved results were obtained with the heat-treated curing agent CA#2. None of the specimens from panel 1 delaminated after the test. Four out of eight specimens from panel 2 delaminated.

Table 2

Example 7

Materials

Soy flour (SF) (7% moisture content) was provided by Cargill Incorporated (Minneapolis, MN); Epichlorohydrin(99%) and ammonium hydroxide (28%-30% wt% solution OfNH₃ in water) were purchased from Acros Organics(Morris Plains, NJ); Yellow-poplar, maple, white fir, pine and aspen veneer were a gift from Columbia Forest Products (Portland, OR).

Preparation of curing agents (CA) from epichlorohydrin and ammonium hydroxide The following is a representative procedure for the preparation of a CA.

Ammonium hydroxide (28-30%, 89.44 g, 1.5mol, 102 mL) and epichlorohydrin (99%, 456 g, 4.5mol, 354 mL) were added to the water (150 mL) and stirred at 600RPM in a 2 L resin kettle equipped with a condenser, a thermometer and an inside cooling coil which was connected with a cooling circulator. The temperature of the mixture increased slowly at the beginning and then dramatically went up as time passed. When the temperature reached the predetermined one, turned on the cooling circulator and maintained the temperature by switching on or off the circulator. The mixture was milky once stirred because epichlorohydrin is not soluble in water. When the mixture became clear, it was further stirred for half hour. The product was stored at room temperature. The solids content of the product is about 50% after extraction with ethyl acetate. The resulting CA was acidified with 1 N sulfuric acid to pH 3 for long term storage.

Example 8 The CA prepared from the Example 7 was treated at 75 ⁰C for one hour to form a new CA. If an acidified CA was used for the heat treatment, it was adjusted to pH 9.5 with 1 N NaOH before the heat treatment at 75 ⁰C.

Example 9 Preparation of SF-CA adhesives

The following is a representative procedure for the preparation of SF-CA adhesives. A CA prepared with above procedures (242 g, 121 g dry CA ), water (1470 mL) and 20% NaOH solution (145g) were sequentially added to a KitchenAid mixer and mixed for 1 min at room temperature. SF (920 g, wet weight, 847 g dry weight) was added and further mixed for 5 min. The total solids content of the resulting adhesive was 36%.

Example 10

Preparation of plywood A SF-CA adhesive was applied to two sides of a yellow-poplar or aspen veneer (2 ft x2 ft; moisture content 12%) by a roller coater with the adhesive spread rate of about 8 mg/cm². The adhesive-coated veneer was stacked between two uncoated veneers with the grain directions of two adjacent veneers perpendicular to each other. The stacked 5-ply veneers were put on a table for 5 minutes, cold-pressed at 100 psi for 5minutes, put on a table again for 5 minutes and hot-pressed at 150 psi at 130 ⁰C for 6 minutes. After hot-press, the panel was stored at ambient environment for at least 24 hours before it was evaluated for its shear strength and water- resistance. Example 11

Three-cycle soak test

The water-resistance of the plywood panels was determined with a three-cycle soak test in accord with the American National Standard for Hardwood and Decorative Plywood; Hardwood Plywood & Veneer Association; 2004 (ANSI/HP VA HP-I). The three-cycle soak test is the commonly accepted standard for evaluating the water-resistance of interior plywood (the type II plywood). The following is a detailed testing procedure defined by the standard. Twenty plywood specimens (2 in x 5 in) cut from each plywood panel were soaked in water at 24 ± 3 ⁰C for 4 hours, and then dried at 49 ⁰C to 52 ⁰C for 19 hours. All specimens were inspected to see whether they were delaminated. This soaking/drying cycle was repeated until three cycles were completed. According to the standard, a plywood panel meets water-resistance requirement for interior applications if 95% of the specimens, i.e., 19 out of the 20 specimens do not delaminate after the first soaking/drying cycle and 85% of specimens, i.e., 17 out of 20 specimens do not delaminate after the third soaking/drying cycle. The ANSI/HP VA HP-I specifically provides the following definition of delamination: any continuous opening between two layers has to be longer than two inches and deeper than 0.25 inch and wider than 0.003 inch.

Summary of Results

The effect of reaction temperature on reaction time

The reaction of epichlorohydrin and ammonia in water is highly exo-thermal. The reaction temperature has to be properly controlled to obtain a useful CA. The reaction time is defined as the time between the beginning of mixing the reaction mixture and the time when the reaction mixture became a clear homogeneous solution. The effect of the reaction temperature on the reaction time is shown in Table 3. The reaction time decreased dramatically with the increase of the reaction temperature. The effect of NaOH on the water resistance and dry shear strengths of 5-ply aspen plywood panels bonded with SF-CA adhesives.

Although not bound by any theory, NaOH may be helpful for generating azetidinium groups and epoxy groups, so the effect of addition of NaOH in preparation of SF-CA adhesives was studied. The curing agent prepared at 50 ⁰C without further heat treatment was used to make plywood panels. Based on our previous experience on making plywood panels, aspen has smaller variability than other species like yellow poplar. Therefore aspen was used to investigate the effect of NaOH. The results were shown in Table 4 and Figure 1. The panels with NaOH had no failed specimens after the three-cycle soak test. One panel without NaOH had no failed specimens and another had three failed specimens after the three-cycle soak test. But all four panels passed the three-cycle soak test. The dry shear strength of plywood panels with NaOH was significantly higher than that of panels without NaOH. Therefore, NaOH (3 wt% based on dry weight of SF and CA) was included in SF-CA adhesives in all subsequent investigations.

Effects of the heat treatment of a CA at 75 ⁰C for one hour and the reaction time on the water resistance of plywood panels bonded with SF-CA adhesives.

Heat treatment of a prepared CA (i.e. subjecting the intermediate CA to a second heating step) may be helpful to form an azetidinium group that is a key functional group reacting with soy protein. Effects of a second heat treatment of CA at 75 ⁰C for one hour and the reaction temperature on the water resistance of plywood panels bonded with SF-CA adhesives are shown in Table 5 and Table 6. When the CA was first prepared at 45 ⁰C, the further heat treatment of the CA did not make any difference on the water resistance of 5-ply aspen plywood, i.e., all plywood panels passed the three-cycle soak test. However the heat treatment greatly improved the water resistance of 5-ply yellow poplar plywood panels. When the CA was heat- treated, the yellow poplar plywood panels bonded with the SF-CA adhesive passed the three-cycle soak test. However, the plywood panels did not pass the soak test when the CA was not heat-treated (Table 5). When the CA was prepared at 45 ⁰C, all aspen plywood panels passed the three- cycle soak test no matter whether the CA was heat-treated or not (Table 5). The heat-treatment of the CA enabled the 5-ply yellow poplar plywood panels to pass the three-cycle soak test. Without the heat-treatment of the CA, the yellow poplar plywood panels did not pass the three-cycle soak test (Table 5).

When the CA was prepared at 35 ⁰C followed by the heat treatment, both aspen plywood and yellow poplar plywood passed the soak test (Table 5). When the CA was prepared at 30 ⁰C followed by the heat treatment, aspen plywood panels passed, only one of two yellow poplar plywood panels passed the soak test (Table 5).

Results from Table 5 revealed that the second step heat treatment of CA prepared in the reaction temperature range of 30 ⁰C to 45 ⁰C is beneficial.

When the CA was prepared at 50 ⁰C or 55 ⁰C, all plywood panels (7-ply, aspen plywood and yellow poplar plywood) passed the soak test, regardless of whether the heat treatment was employed (Table 6). When the CA was prepared at 60 ⁰C, aspen plywood panels passed the three cycle soak test with or without the heat treatment of the CA. However, the heat treatment of the CA prepared at 60 ⁰C dramatically reduced the water resistance of the yellow poplar plywood panels and only allowed one of two 7-ply passed the soak test (Table 6). Results from Table 6 demonstrated that the heat treatment of the CA prepared at 50 ⁰C or 55 ⁰C did not have impacts on the water resistance of all plywood panels. However, the heat treatment of the CA prepared at 60 ⁰C had negative impact on the water resistance of yellow poplar plywood and the 7-ply.

Effects of chemical addition order and heat treatment on the water resistance of plywood panels bonded with SF-CA adhesives. Results from all previous tables were based on the CAs that was prepared by mixing epichlorohydrin and ammonium hydroxide all at once at the beginning of the reaction. The CAs were also prepared by the slow addition of epichlorohydrin to ammonium hydroxide or the slow addition of ammonium hydroxide to epichlorohydrin during the reaction. The effects of the different addition order and the heat treatment on the water resistance of plywood panels are shown in Table 7. When the CA was prepared by the slow addition of epichlorohydrin to ammonium hydroxide followed with or without the heat treatment, both 7-ply and 5 -ply aspen plywood panels passed the three-cycle soak test. However, only one of two 5 -ply yellow poplar plywood panels passed the three-cycle soak test (Table 7).

When the CA was prepared by the slow addition of ammonium hydroxide to epichlorohydrin without the heat treatment, both 5-ply aspen plywood panels passed the three-cycle soak test. However, only one of two 5-ply 7-ply plywood panels and and only one of two yellow poplar plywood panels passed the three-cycle soak test (Table 7). When the CA was prepared by the slow addition of ammonium hydroxide to epichlorohydrin followed by the heat treatment, only one of two 7-ply plywood panels passed. All 5-ply aspen plywood and 5-ply yellow poplar plywood passed the three-cycle soak test though.

Results from Table 6 and Table 7 demonstrated that the mixing of epichlorohydrin and ammonium hydroxide all at once at the beginning of the reaction was a better method of preparing a CA than the slow addition of one chemical to another.

Table 3. The effect of the reaction temperature on the reaction time

The reaction time includes 30 min of extra stirring time at a predetermined temperature after the solution became clear. Table 4. The effect of addition of NaOH on the water resistance of 5-ply aspen plywood

Table 5. Effects of the heat treatment of a CA and the reaction temperature on the water resistance of plywood panels bonded with a SF-CA adhesive.

Table 6. Effects of the heat treatment of a CA and the reaction temperature on the water resistance of l wood anels bonded with a SF-CA adhesive.

*7-ply=maple/white fir/pine/white fir/pine/white fir/maple Table 7. The effect of different chemical addition order on the water resistance of l wood anels bonded with SF-CA adhesives CA was re ared at 55 ⁰C

In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.

Claims

What is claimed is:

1. A method for making a lignocellulosic composite, comprising: applying (i) soy protein and (ii) a curing agent to at least one lignocellulosic substrate; and bonding the composition-applied substrate to at least one other lignocellulosic substrate, wherein the curing agent is made by a method comprising: reacting (i) ammonia with (ii) epichlorohydrin, a chlorinated propanol or a mixture thereof at a temperature of 50 to 6O⁰C.

2. The method of claim 1 , wherein the reaction for making the curing agent is at a temperature of at least 55 ⁰C.

3. A method for making a lignocellulosic composite, comprising: applying (i) soy protein and (ii) a curing agent to at least one lignocellulosic substrate; and bonding the composition-applied substrate to at least one other lignocellulosic substrate, wherein the curing agent is made by a method comprising: (a) reacting (i) ammonia with (ii) epichlorohydrin, a chlorinated propanol or a mixture thereof at a temperature of 0 to 65⁰C to produce an intermediate; and subsequently (b) heating the intermediate at a temperature of 65 to 98 ⁰C to produce a curing agent.

4. The method of any one of claims 1 to 3, wherein ammonia is reacted with epichlorohydrin.

5. The method of any one of claims 1 or 4, wherein the curing agent has a solids content of 5 to 80 wt%.

6. The method of claim 3, wherein step (a) is exothermic, and the method further comprises cooling the step (a) reaction to maintain the reaction temperature.

7. The method of any one of claims 1 to 6, wherein the ammonia and the epichlorohydrin or chlorinated propanol are mixed together to form a reaction mixture in an aqueous medium, and the reaction mixture is a heterogeneous mixture prior to the reaction.

8. The method of any one of claims 1 to 7, wherein the reaction for making the curing agent is performed until the reaction mixture becomes a homogeneous composition.

9. The method of any one of claims 1 to 8, wherein the mole ratio of ammonia to epichlorohydrin or chlorinated propanol is 5:1 to 1 :5.

10. The method of any one of claims 1 to 9, wherein the reaction for making the curing agent is performed for 20 minutes to 20 hours.

11. The method of any one of claims 1 to 10, wherein the reaction for making the curing agent is performed for 20 minutes to 5 hours.

12. The method of any one of claims 1 to 11, further comprising applying sodium hydroxide, calcium oxide, calcium hydroxide, and/or a boron compound to the at least one lignocellulosic composite.

13. The method of any one of claims 1 to 12, wherein the soy protein, curing agent and a base including sodium hydroxide, calcium oxide, calcium hydroxide, and/or a boron compound are mixed together and the resulting mixture is applied to the at least one lignocellulosic substrate.

14. The method of any one of claims 1 to 13, wherein the mix ratio of soy protein to curing agent is 100: 1 to 1 : 100, based on dry weight.

15. The method of any one of claims 1 to 14, wherein the bonding comprises heating at a temperature of 80 to 220 ⁰C.

16. The method of any one of claims 1 to 15, wherein the soy protein is in the form of a soy protein product, and the soy protein product is selected from soy flour, soy protein concentrate or soy protein isolate.

17. A method for making a lignocellulosic composite, comprising mixing together:

(i) soy protein;

(ii) a curing agent, wherein the curing agent is made by the curing agent- making method as recited in any one of claims 1 to 11 ; and (iii) comminuted lignocellulosic particles.

18. The method of claim 17, wherein the components (i) and (ii) are pre-mixed prior to mixing with component (iii).

19. The method of claim 17, wherein the components (i) and (iii) are pre-mixed prior to mixing with component (ii).

20. The method of claim 17, wherein the component (ii) and (iii) are pre-mixed prior to mixing with component (i).

21. The method according to claim 3, wherein the step (a) reaction temperature is 30 to 45 ⁰C.

22. A lignocellulosic composite made according to the method of any one of claims l to 21.

23. The composite of claim 22, wherein the composite is substantially formaldehyde-free.

24. A method for making an adhesive composition, comprising: mixing together (a) a soy protein, (b) a curing agent and (c) a base including sodium hydroxide, calcium oxide or a mixture thereof to produce an adhesive composition, wherein the curing agent is made by the curing agent-making method as recited in any one of claims 1 to 11.

25. The method of claim 24, wherein the mix ratio of soy protein to curing agent is 100:1 to 1 :100, based on dry weight.

26. The method of claim 24 or 25, wherein the adhesive composition includes 0.1% to 10 wt% of the base, based on the dry weight of the adhesive composition.

27. The method of any one of claims 24 to 26, wherein the adhesive composition has a solids content of 10 to 60 wt% prior to bonding lignocellulosic substrates.

28. The method of any one of claims 24 to 27, wherein the soy protein is in the form of a soy protein product, and the soy protein product is selected from soy flour, soy protein concentrate or soy protein isolate.

29. An adhesive composition comprising the reaction product of at least: (i) soy protein; and

(ii) a curing agent, wherein the curing agent is made by the curing agent- making method as recited in any one of claims 1 to 11.

30. The adhesive composition of claim 29, wherein the adhesive composition is substantially formaldehyde-free.

31. A composition, comprising a mixture of at least:

(i) soy protein; (ii) a curing agent, wherein the curing agent is made by the curing agent- making method as recited in any one of claims 1 to 11 ; and (iii) comminuted lignocellulosic particles.

32. The composition of any claim 31, wherein the composition is substantially formaldehyde-free.

33. A method for making a curing agent, comprising:

(a) reacting (i) ammonia with (ii) epichlorohydrin, a chlorinated propanol or a mixture thereof at a temperature of 0 to 65⁰C to produce an intermediate; and subsequently

(b) heating the intermediate at a temperature of 65 to 98 ⁰C to produce a curing agent.

34. The method of claim 33 wherein ammonia is reacted with epichlorohydrin.

35. The method of claim 33 or 34, wherein the curing agent has a solids content of 5 to 80 wt%.

36. The method of any one of claims 33 to 35, wherein step (a) is exothermic, and the method further comprises cooling the step (a) reaction to maintain the temperature range of 0 to 65 ⁰C.

37. The method of any one of claims 33 to 36, wherein the ammonia and the epichlorohydrin or chlorinated propanol are mixed together to form a reaction mixture in an aqueous medium, and the reaction mixture is a heterogeneous mixture prior to the reaction.

38. The method of any one of claims 33 to 37, wherein step (a) is performed until the reaction mixture becomes a homogeneous composition.

39. The method of any one of claims 33 to 38, wherein the mole ratio of ammonia to epichlorohydrin or chlorinated propanol is 5:1 to 1 :5.

40. The method of any one of claims 33 to 39, wherein step (a) is performed for 20 minutes to 20 hours.

41. The method of any one of claims 33 to 40, wherein step (b) is performed for 20 minutes to 5 hours.

42. The method of any one of claims 33 to 41, wherein the step (a) reaction temperature is 30 to 45 ⁰C.

43. A curing agent produced by any one of the methods of claims 33 to 42.

44. The curing agent of claim 43, wherein the curing agent is substantially formaldehyde-free.