CELLULOSE NANOCRYSTALS - THERMOSET RESIN SYSTEMS, APPLICATIONS THEREOF AND ARTICLES MADE THEREFROM

Abstract

The present describes wood adhesives reinforced with cellulose nanocrystals (CNC), in liquid and powder forms in which resin system are a phenol-formaldehyde polymer and/or lignin-phenol-formaldehyde polymer and polymeric methylene diphenyl diisocyanate (pMDI), and a method of making this polymer in liquid and powder from and the composite products that can be produced therefrom.

Claims

1. A method of producing a liquid thermoset resin with improved storage modulus comprising the steps of: providing a phenolic compound, providing a formaldehyde compound, providing cellulose nanocrystals, and providing a hydroxide base; mixing the phenolic compound and from 0.5 to 2% cellulose nanocrystals by weight of cellulose nanocrystals with water and the hydroxide base at a constant temperature making a phenolic blend; methylolating of the phenolic compound by adding the formaldehyde compound to the phenolic blend to start the polymerization through condensation and controlling the temperature producing a reaction mixture; and stopping the polymerization by cooling the reaction mixture until the mixture reaches a specific viscosity producing the thermoset resin with improved storage modulus by at least 25% at temperatures of about 30 C. to 210 C.

2. A method for producing a powder thermoset resin with improved storage modulus comprising the steps of providing a phenolic compound, providing a formaldehyde compound, providing cellulose nanocrystals, and providing a hydroxide base; mixing the phenolic compound and the formaldehyde compound with water making a phenolic blend; polymerizing the phenolic blend by adding the hydroxide base to the phenolic blend to start the polymerization and controlling the temperature producing a reaction mixture; stopping the polymerization by cooling the reaction mixture until the mixture reaches a specific viscosity to produce a phenolic resin; mixing 0.5 to 2% of the cellulose nanocrystals with the phenolic resin; and drying the phenolic resin to produce the thermoset resin

3. The method of claim 1 or 2, wherein the weight ratio of hydroxide base to phenolic compound is from 0.03:1 to 0.3:1.

4. The method of claim 1 or 2, wherein the phenolic compound is at least one of phenol and lignin.

5. The method of claim 1 or 2, wherein the formaldehyde compound is a para-formaldehyde.

6. The method of claim 1 or 2, comprising a molar ratio of formaldehyde compound: phenolic compound from 1.8:1 to 3.0:1.

7. The method of claim 1, wherein the phenolic compound is first mixed with water, and secondly with the cellulose nanocrystals, followed by the addition of the formaldehyde compound at a temperature of about 50 C. to about 60 C.

8. The method of claim 1, wherein the phenolic compound, the cellulose nanocrystals, water, the hydroxide base and the formaldehyde compound are mixed at a temperature of about 70 C. to about 90 C.

9. The method of claim 2, wherein the viscosity of the thermoset resin is about 70 cps to about 80 cps.

10. The method of claim 2, wherein the viscosity of the thermoset resin is about 100 cps to about 200 cps.

11. The method of claim 2, wherein the viscosity of the thermoset resin is about 250 cps to about 3000 cps.

12. The method of claim 2, wherein the phenolic resin is pulverized to produce the powder thermoset resin.

13. The method of claim 2, wherein the polymerizing of the phenolic blend is at a temperature of about 75 C. to about 95 C.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0050] FIG. 1 is a graph of storage modulus as a function of temperature (PPF0: 0% CNC in PF resin, PPF1: 0.5% CNC in PF resin, and PPF3: 2.0% CNC in PF).

DETAILED DESCRIPTION OF THE INVENTION

[0051] For easier understanding, a number of terms used herein are described below in more details:

[0052] Lignin generally refers to a group of phenolic polymers that give strength and rigidity to plant materials. Lignins are complex polymers, and tend to be referred to in generic terms. Lignins may include, for example, industrial lignin preparations, such as kraft lignin, lignosulfonates, and organosolv lignin from by-products of bio-ethanol process, and analytical lignin preparation, such as dioxane acidolysis lignin, milled wood lignin, Klason lignin, cellulolytic enzyme lignin, and etc.

[0053] Lignin component represents any lignin-containing materials. Lignin component can be derived from industrial lignin preparation, analytical lignin preparation, and etc, which are from renewable resources, especially from lignocelluloses. The lignin component can be a material or compositions, which is modified or treated or purified portion of lignin.

[0054] Lignocelluloses materials include all plant materials. For example, materials include wood materials (such as wood strands, wood fibers or wood chips or wood particles), grass materials (such as hemp or flax), grain materials (such as the straw of rice, wheat, corn), and etc.

[0055] A phenolic compound is defined as a compound of general formula ArOH, where Ar is phenyl (phenol), substituted phenyl or other aryl groups (e.g. tannins) and a lignin and combinations thereof. The phenolic compound may be selected from the group consisting of phenol, a lignin and combinations thereof.

[0056] In a preferred embodiment the phenolic compound is phenol. In another preferred embodiment the phenolic compound is a combination of phenol and a lignin. Starting materials are understood as all compounds and products added to produce the adhesive polymer disclosed herein.

[0057] A formaldehyde compound may be selected from the group consisting of formaldehyde and paraformaldehyde and combinations thereof. The paraformaldehyde has the formula HOCH2(OCH2)nCH2OH, in which n is an integer of 1 to 100, typically 6 to 10. Paraformaldehyde will be decomposed to formaldehyde before it methylolation reaction with phenol or lignin.

[0058] Cellulose nanocrystals (CNC) includes all cellulose nanocrystals made from different resources, such as wood (softwoods and hardwoods), plants (for example, cotton, ramie, sisal, flax, wheat straw, potato tubers, sugar beet pulp, soybean stock, banana rachis etc), tunicates, algae (different species: green, gray, red, yellow-green, etc.), bacterials [common studied species of bacteria that produces cellulose is generally called Gluconacetobacter xylinus (reclassified from Acetobacter xylinum)], and etc. CNC may also be defined as nanocrystalline cellulose (NCC).

[0059] One such cellulose nanocrystals (CNC) are a cellulosic rod-like shaped nanomaterial and are extracted from a variety of naturally occurring cellulose sources such as wood pulp, cotton, some animals, algae and bacteria.

[0060] NCCs or CNCs can be obtained by various processes but the most common extraction technique relies on a chemical hydrolysis of the cellulose source under harsh acidic conditions, which releases the rigid crystalline parts of the microfibrils. Typical dimensions for CNCs are generally from 3 to 20 nanometers in cross section and from several tens of nanometers up to several microns in length. CNC is characterized by a high degree of crystallinity with an axial ratio ranging generally between few tens up to several hundreds.

[0061] The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

[0062] Phenol-formaldehyde (PF) resins are known to be prepared from two main chemicals that are reacted at elevated temperatures through methylolation and condensation to form a phenolic polymer. The polymer formation is strongly related to the molar ratio of phenol to formaldehyde, and the pH at which the reaction is carried out. The phenolic resin is called Novolac resin when the molar ratio of formaldehyde to phenol is less than 1 and at low pH. The phenolic resin is called Resol type when the molar ratio of formaldehyde to phenol is higher than 1, and the pH is higher than 7. Resol type phenolic resins will crosslink, usually at elevated temperatures.

[0063] The basic purposes of the present invention is 1) to incorporate CNC into phenol-formaldehyde resin system or lignin-phenol-formaldehyde resin system in liquid form or powder form, 2) to improve the bonding properties and mechanical properties of wood composites made with such formulations either in liquid form or powder form, and 3) to improve mechanical and thermal properties of CNC-phenol-formaldehyde molded products and/or CNC-lignin-phenol-formaldehyde molded products made with such formulations in powder form.

[0064] More specifically, the collective purposes of the present invention are 1) to incorporate CNC into phenolic resin with low viscosity in liquid form and make CNC-phenolic resin in powder form through spray drying process, 2) to provide a process for preparing thermoset resin in powder form wherein a CNC is well distributed into lignin-phenol-formaldehyde resin and/or phenol-formaldehyde resin which CNC has strong intimate contact with lignin-phenol-formaldehyde resin and/or phenol-formaldehyde resin, which can be used as powder resin for wood composites and for molded components, 3) to incorporate CNC into phenolic resin (either lignin-phenol-formaldehyde resin or straight phenol-formaldehyde resin) in liquid form, which can be used for wood composites, and 4) to incorporate CNC into isocyanate and make CNC-isocyanate binder (adhesive) in liquid form for wood composites.

[0065] Below we described the general chemistry associated with forming the final resin mixtures.

[0066] CNC-Phenolic Resin Formulations in Powder Form

[0067] The first step of the process according to the invention consists of mixing lignin if applicable, with phenol, formaldehyde (or paraformaldehyde), and a base and letting the so obtained mixture react at elevated temperatures. The order of addition of the above starting compounds is not important, but it is preferred to load phenol first, then water, later on lignin, after that, formaldehyde in the form of para-formaldehyde, and then raise the temperature to 50-60 C., and then load sodium hydroxide in the form of a solution containing 50% by weight of sodium hydroxide. The so prepared mixture is heated to temperatures ranging between 60-75 C., preferably 70 C., for a period of 1 to 2 hours, for example. In this step, the methylolation reaction takes place in which formaldehyde reacts on the ortho position of the phenol and with available sites on the lignin.

[0068] The second step of process according to the invention consists of loading more sodium hydroxide in the form of a solution containing 50% by weight of sodium hydroxide in the system, and the temperature is maintained same as the first step. The period of time is, for example, 10 minutes to 1 hour. The methylolation reaction continues.

[0069] Such a two-stage processing is actually important. Indeed, the same process could be made in only one stage at different temperatures, such as 80-95 C., such processing may not produce the same resin, and the resin obtained in one stage may not have the same quality as the resin produced in two steps.

[0070] The third step of process according to the invention consists of raising the temperature to 75-95 C. for condensation reaction of methylolated lignin with methylolated phenol, preferably 80-85 C. for a certain period of time. At this stage, controlling the reaction temperature is important. Otherwise, a proper viscosity may not be achieved. The viscosity is varied for different applications, such as around 70-80 cps for spray drying to make powder resin, around 100-200 cps for OSB with solids content around 45-50%, around 250-3000 cps or over for plywood making.

[0071] In applications, the amounts of raw materials added at each stage, the temperature at which the addition is carried out and/or the molar ratios of formaldehyde to phenol may vary depending on the needs. In practices, the molar ratio of formaldehyde to phenol preferably ranges from 1.8:1 to 3.0:1. More preferably, the molar ratio ranges from 2.2:1 to 2.8:1 to achieve better results; the weight ratio of base (sodium hydroxide and/or potassium hydroxide) to phenol or lignin (if applicable) ranges from 0.03:1.00 to 0.30:1.00. More preferably, the weight ratio ranges from 0.08:1.00 to 0.15:1.00 to achieve better results.

[0072] The fourth step of process according to invention consists of a) preparing the CNC aqueous dispersion through soaking the required amount of CNC in water for a few hours to make sure the CNC is well dispersed in water (it could become gel-like liquid if the CNC concentration reaches to 3-5% wt) with different methods, such as sonication, high shear mixing etc.; b) transferring pre-prepared CNC dispersion into phenol-formaldehyde resin (PF) or lignin-phenol-formaldehyde (LPF) resins and adjusting the solids content to 25-30% wt through the addition of water if necessary; c) mixing the mixture of CNC-phenolic resin (CNC-PF and/or CNC-LPF) with a high shear mixer under 2000 RPM or higher for 10 min or sufficient time to obtain uniform CNC-PF (post blending) or CNC-LPF (powdered CNC-PF and/or CNC-lignin-PF) system.

[0073] The fifth step of the process according to invention consists of converting the liquid CNC-LPF and/or CNC-PF system into a powder form with a certain feed rate (depending on the capacity of the spray-dryer). The outlet temperature was set at 85-95 C. through a pulverization spray dryer.

[0074] It is also possible to add part of CNC dispersion in the first step of the process of mixing lignin if possible, with phenol, formaldehyde (or paraformaldehyde), and a base and letting the so obtained mixture react at elevated temperature, and continue with second, third steps of process. In this case, the CNC is incorporated with phenolic resin system via in-situ polymerization. It also can combine fourth step and fifth step of the process to convert the liquid CNC-LPF and/or CNC-PF system into powder form.

[0075] CNC-Phenolic Resin Formulations in Liquid Form

[0076] The steps of the process according to the invention consist of similar first three steps as CNC-phenolic resin formulation in powder form described in previous section above except CNC was added in the first step in powder form.

[0077] Below we list some specific examples of the general chemistry just described.

Example 1

[0078] Preparation of Phenol-Formaldehyde Adhesive in Liquid Form for Making Powder Resin

[0079] In this example, all materials are counted by weight parts to prepare a formulation of phenol (98%): 750 parts by weight, paraformaldehyde (91%): 645 parts by weight, sodium hydroxide (50 wt %): 195 parts by weight, and water: 1550 parts by weight. The n value for formaldehyde is 1 to 100, and preferably 6 to 10.

[0080] In a 4-L reaction vessel, phenol, paraformaldehyde, and part of water (850 parts) were added to make a medium having a solids content around 50 wt %. The system was heated to around 50 C., and the first part of sodium hydroxide (75 parts) was added. The system was heated to approximately 70 C. and was kept at this temperature for one and a half hours. Subsequently, the second part of sodium hydroxide (60 parts) and water (300 parts) were added, with the temperature maintained at approximately 70 C. for another half an hour. Afterwards, the temperature was increased to 80-90 C., and the viscosity was monitored. When the viscosity of the resin system reached to 20-30 cps, pH was monitored and around 20 parts of sodium hydroxide (50% wt) were added to bring pH to over 10. When the viscosity reached to 70-100 cps and pH around 10.4, the reaction was terminated by cooling the reactor to approximately 30 C. The contents were transferred to a container and stored in a cold room for later use. The adhesive was coded PF. The viscosity of PF was 100 cps and the pH of the PF was 10.45.

Example 2

[0081] Preparation of Lignin-Phenol-Formaldehyde Adhesive in Liquid Form for Making Powder Resin

[0082] In this example, all materials are counted by weight parts to prepare a formulation of phenol (98%): 660 parts by weight, kraft softwood lignin from black liquor (prepared by Pulp & Paper Division of FPInnovations) (partially oxidized kraft lignin obtained from the LignoForce System) (90%): 350 parts by weight, paraformaldehyde (91%): 565 parts by weight, sodium hydroxide (50 wt %): 400 parts by weight, and water: 1730 parts by weight.

[0083] In a 4-L reaction vessel, phenol, kraft softwood lignin, paraformaldehyde, some of the sodium hydroxide (80 parts), and some of the water (1400 parts) were added to make a medium having a solids content around 50 wt %. The system was heated to approximately 70 C. and was kept at this temperature for one and a half hours. Subsequently, the second portion of sodium hydroxide (100 parts) and remaining water were added, with the temperature maintained at approximately 70 C. for another half an hour. Afterward, the temperature was increased to 80-90 C., and the viscosity was monitored. When the viscosity of the resin system reached to around 50 cps, some sodium hydroxide was loaded to being up the pH to over 10. Viscosity of resin was checked every 20 minutes. When the viscosity reached to 70-100 cps, the reaction was terminated by cooling the reactor to approximately 30 C. The contents were transferred to a container and stored in a cold room for later use. The adhesive was coded LPF. The viscosity of LPF was 97 cps and the pH of the LPF was 10.26. Another batch was synthesized under the same condition and two batches were mixed together. [Phenol (660 parts), kraft softwood lignin (360 parts), paraformaldehyde (565 parts) mentioned in previous paragraph were loaded in except part of sodium hydroxide and part of water].

Example 3

[0084] Preparation of CNC-Lignin Phenol-Formaldehyde Composites in Powder Form and CNC-Phenol-Formaldehyde Composites in Powder Form

[0085] The PF made in Example 1 and LPF made in Example 2 were used to prepare nano-crystalline cellulose-phenol-formaldehyde (CNC-PF) and cellulose nanocrystals-lignin-phenol-formaldehyde (CNC-LPF) adhesives through post-blending with CNC dispersion in phenolic resin and drying through a spray dryer. The LPF (and/or PF) was divided into several portions, in which one was used as a control, and other portions for adding different levels of CNC. The procedure is described as follows: [0086] 1) Soaking and dispersing the required amount of CNC in water overnight; [0087] 2) Transferring CNC water dispersion into phenolic resin and adding water to solids content about 28% (detailed in Table 1); [0088] 3) Mixing the mixture of CNC-LPF in liquid form and/or CNC-PF in liquid form at a speed of 2000 RPM for 10 minutes with a high shear mixer to obtain uniformly distributed CNC-LPF or CNC-PF resin formulations; [0089] 4) Drying the uniformly distributed CNC-LPF and/or CNC-PF formulations with a pulverization spray dryer (Model: BE-1037, Series: Bowen) from Incotech Inc. (Bennires, Quebec, Canada) (outlet temperature of 88-91 C. and feed rate of 48 gram per minute). (please see Table 1 for detailed information of CNC-LPF and CNC-PF powder)

TABLE-US-00001 TABLE 1 Information about spray drying of CNC-phenolic resin CNC Mixture load- before CNC in MC of Powder Liquid resin ing.sup.1 drying.sup.2 Yield powder powder.sup.3 Code Code Solid (%) (%) Solid (%) % % % PLPF0 LPF 41 0 29.5 88.3 0 4.4 PLPF1 LPF 41 0.20 28.9 88.5 0.5 4.5 PLPF2 LPF 41 0.40 29.4 86.2 1.0 4.4 PLPF3 LPF 41 0.80 29.4 83.6 2.0 4.0 PLPF4 LPF 41 1.60 29.7 79.4 3.9 4.6 PPF0 PF 39 0 27.7 74.8 0 5.7 PPF1 PF 39 0.20 27.8 83.2 0.5 5.9 PPF3 PF 39 0.80 28.0 74.6 2.0 5.8 .sup.1Based on the weight of liquid resin; .sup.2before drying, solid content was measured for mixture at 121 C. for 2 hours; .sup.3(actual powder weight powder weight after oven dry at 103 C. for 24 hours)/powder weight after oven dry at 103 C. for 24 hours 100

Example 4

[0090] Oriented strand board (OSB) panels made with CNC-LPF composite powder adhesive, and CNC-PF composite powder adhesive

[0091] Three-layer OSB panels were made with CNC-phenolic resins prepared in Example 3. These resins were only used in surface layers and 100% commercial phenolic powder resin was used in the core layer, under the pressing conditions listed in Table 2. Detailed information about the resins in surface and core layers is listed in Table 3.

TABLE-US-00002 TABLE 2 OSB panel manufacturing conditions with CNC-phenolic powder resin Target panel density (OD basis) 40 lbs/ft.sup.3 Mat dimension 20 in 23 in Target panel thickness 11.1 mm ( 7/16 in) Mat composition: face/core/face 25/50/25 Resin dosage Face: 3% Core: 3% Wax dosage Face: 1% Core: 1% Face wafer moisture before resin and wax 2% Core wafer moisture before resin and wax 2.5% Core moisture after resin and wax 3.5% Face moisture after resin and wax 7-8% Press temperature ( C.) 220 C. Total press time 150 seconds (daylight to daylight) Close time 25 seconds Degas 25 seconds Replicate 2

TABLE-US-00003 TABLE 3 OSB panels with different resin formulations MC of MC of Solid CNC face mat core mat No. Face resin % % % Core resin % 1 Com. PF1 55.3 0 7 Com. PF3 4 2 PLPF0 95.6 0 7 Com. PF3 4 3 PLPF1 95.5 0.49 7 Com. PF3 4 4 PLPF2 95.4 0.98 7 Com. PF3 4 5 PLPF3 96.0 1.95 7 Com. PF3 4 6 PLPF4 95.4 3.90 7 Com. PF3 4 7 PPF0 94.3 0 7 Com. PF3 4 8 PPF1 94.1 0.49 7 Com. PF3 4 9 PPF3 94.2 1.98 7 Com. PF3 4 10 Com. PF2 96.0 0 7 Com. PF3 4 Com. PF1: commercial liquid PF (surface); Com. PF2: commercial powder PF (surface); PLPF: powder CNC-lignin-PFs via spray drying; PPF: powder CNC-PF resins via spray drying; Com. PF3: commercial power PF for core

[0092] The physical and mechanical properties of OSB panels, including 24-h thickness swelling (TS), 24-h water absorption (WA), internal bond (IB) strength, modulus of elasticity (MOE) and modulus of rupture (MOR) were measured according to CSA 0437.1-93 standard and the results are illustrated in Tables 4, 5, and 6.

TABLE-US-00004 TABLE 4 Mechanical and physical properties of OSB panels made with CNC-phenolic resins Density 24-h TS.sup.1 24-h WA.sup.2 Density IB.sup.3 No. Face resin (kg/m.sup.3) (%) (%) (kg/m.sup.3) (MPa) 1 Com. PF1 671 16 23.4 3.2 38.1 3.3 655 13 0.33 0.07 2 PLPF0 677 15 19.5 1.9 31.9 0.8 643 22 0.35 0.05 3 PLPF1 677 17 18.3 1.9 32.1 0.3 650 15 0.32 0.05 4 PLPF2 678 15 19.8 0.4 33.7 2.7 648 18 0.34 0.05 5 PLPF3 661 21 18.0 1.4 33.9 0.2 644 18 0.39 0.09 6 PLPF4 665 19 17.7 0.6 31.8 0.5 646 8 0.36 0.07 7 PPF0 642 4 18.3 0.2 36.2 1.2 649 20 0.32 0.10 8 PPF1 678 10 17.9 0.6 33.5 1.0 648 25 0.41 0.04 9 PPF3 621 30 17.1 1.5 38.2 3.9 670 34 0.35 0.08 10 Com. PF2 622 30 19.5 1.0 39.2 3.6 648 12 0.41 0.07 .sup.1 & 2Average of two specimens per panel; .sup.3average of 8 specimens per panel

TABLE-US-00005 TABLE 5 Static bending properties of OSB panels made with CNC-phenolic resins (tested under dry condition).sup.1 Face resin Density MOE MOR No. code CNC (%) (kg/m.sup.3) (MPa) (MPa) 1 Com. PF1 0 632 61 2843 606 18.1 8.0 2 PLPF0 0 688 28 4102 534 29.5 5.6 3 PLPF1 0.5 629 19 2767 311 18.3 5.4 4 PLPF2 1.0 631 16 3305 149 19.1 2.1 5 PLPF3 2.0 652 31 3940 1430 28.3 10.5 6 PLPF4 3.9 640 9 4199 564 31.3 7.1 7 PPF0 0 656 29 3943 339 24.5 3.0 8 PPF1 0.5 640 29 3669 836 24.7 8.9 9 PPF3 2.0 651 31 3621 659 26.1 4.0 10 Com. PF2 0 669 26 3596 859 23.3 5.0 .sup.1Average of 4 specimens per panel, in which two specimens were tested under top face up, and two specimens were tested under top face down,

TABLE-US-00006 TABLE 6 Static bending properties of OSB panels made with CNC-phenolic resins (tested under wet condition).sup.1 Face resin Density MOE MOR No. code CNC (%) (kg/m.sup.3) (MPa) (MPa) 1 Com. PF1 0 654 24 1326 403 6.7 1.8 2 PLPF0 0 636 17 1528 142 8.1 1.9 3 PLPF1 0.5 656 19 1773 204 10.2 1.2 4 PLPF2 1.0 649 37 2036 422 12.0 3.4 5 PLPF3 2.0 644 16 1977 238 12.0 2.8 6 PLPF4 3.9 647 37 2172 350 12.5 2.9 7 PPF0 0 654 13 2259 465 11.9 2.7 8 PPF1 0.5 645 24 1920 316 10.9 3.6 9 PPF3 2.0 644 9 2053 378 11.9 1.9 10 Com. PF2 0 635 17 1697 346 10.6 1.4 .sup.1Average of 4 specimens per panel, in which two specimens were tested under top face up, and two specimens were tested under top face down. Specimens were soaked in water at 20 C. for 24 hrs before testing.

[0093] From Table 4, it can be seen that the addition of CNC into lignin phenolic resins could reduce the thickness swelling from 19.5% for the OSB made with PNCLPF0 (without CNC) to 17.7% for the OSB made with PNCLPF4 (CNC: 3.90%). The water absorption (WA) and internal bond (IB) strength were basically the same for the OSB made with and without CNC. Addition of CNC into phenolic resin did not significantly improve the MOE and MOR for the OSB panels at dry conditions (Table 5); however, it improved the wet bending strength of the OSB made with lignin phenolic resins from average values of 1528 MPa (MOE of OSB made with PNCLPF0) and 8.1 MPa (MOR of OSB made with PNCLPF0) to average values of 2172 MPa (MOE of OSB made with PNCLPF4) and 12.5 MPa (MOR of OSB made with PNCLPF4).

Example 5

[0094] In-Situ Polymerization of CNC Phenol-Formaldehyde Resin in Liquid Form

[0095] CNC was formulated with phenol (99 wt %) 150 parts by weight; formaldehyde (40% wt %) 240 parts by weight; sodium hydroxide (50 wt %) 55 parts, CNC (powder) 2.6 parts, and water 120 parts.

[0096] In a 1-L reactor vessel, phenol, one third of the caustic, two thirds of the water, and CNC were added and the system was heated to around 60 C. Subsequently, one half of the formaldehyde solution was added over 30 minutes and another one fourth of water was added. At this point, the system temperature was raised to 65-70 C. and kept constant for 30 minutes. The temperature was then raised to 80-85 C., kept at this level for one hour, and then decreased to 65-70 C. At this point, the remaining formaldehyde was added over 30 minutes as well as the remaining water. The system was kept at 65-70 C. for another 30 minutes. Subsequently, the remaining sodium hydroxide was added and the temperature was kept at 80-85 C. until the required viscosity (350 cps) was reached.

[0097] The reaction was terminated by cooling the system with cooling water to around 30 C. The resulting products were transferred to a container and stored in a cold room (4 C.) before use. The adhesive was coded as CNC-PF. The CNC content was 1 wt % based on the solids content of the polymer adhesive.

[0098] Yellow birch veneer strips (1.5 mm thick120 mm wide240 mm long) were cut from the veneer purchased from a local mill (with the long direction being parallel to the wood grains), and stored at 30 C. for certain time, then conditioned at 20 C. and 20% relative humidity (RH) for two weeks. The adhesive polymer formulations prepared above were applied to one side of each face layer (the manufacturing condition for 3-ply plywood panel making is given in Table 7). After manufacturing, the panels were conditioned at 20 C. and 20% RH until reaching consistent moisture content. These three-ply plywood samples were then cut into testing specimen sizes (25 mm wide80 mm long) for a plywood shear test. At least thirty specimens were cut from each plywood panel. Half of the specimens was tested in the pulled open mode while the other half of the specimens was tested in the pulled closed mode. The cross-section of the test samples was 25 mm by 25 mm. Specimens were tested wet after 48 hours of soaking in 20 C. running water.

TABLE-US-00007 TABLE 7 the 3-ply plywood composites manufacturing conditions Wood species Yellow birch Thickness of veneer 1.5 mm Plywood 3-ply plywood Resin spread rate on face ply 200-220 g/m.sup.2 Open assembly time 2-20 minutes Close assembly time 2-10 minutes Temperature 150 C. Pressure 1500 kPa Pressing time 5 min Pressure release time 30 sec.
The test results are listed in Table 8 as follows:

TABLE-US-00008 TABLE 8 Three-ply plywood properties with/without CNC Test after Test after 48 hr soaking boiling-drying-boiling Shear Wood Shear Wood strength failure strength failure Code (MPa) (%) (MPa) (%) Commercial PF 1.79 0.42 64 1.73 0.41 50 PF (lab-synthesized) 1.88 0.53 88 2.06 0.46 29 CNC-PF 2.58 0.61 66 2.16 0.56 51

[0099] It can be seen that the CNC-PF resin improved the bonding strength of 3-ply plywood after 48 hours soaking, in which the average value of bonding strength increased by about 37% comparing with the lab-synthesized PF resin; CNC-PF resin also improved the bonding strength after boiling-drying-boiling treatment.

Example 6

[0100] Post-Blending of Cellulose Nanocrystals with Lignin-Phenol-Formaldehyde Resin in Liquid Form

[0101] The lignin based phenol-formaldehyde resin was synthesized under the condition similar to Example 2. However, the pH of the resin was about 11.4. The CNC was post-blended with such resin as shown in Table 9. For all formulations, a high shear mixer was applied and all formulations were mixed at 2000 RPM for 15 minutes. CNCLPF0 was the sample without CNC. CNCLPF1 was prepared by: 1) dispersing CNC in water to make high concentration dispersion, and 2) adding the required lignin-phenol-formaldehyde resin in the CNC dispersion and 3) mixing them with a high shear mixer. CNCLPF2 and CNCLPF3 were prepared in the same way except CNC content: 1) directly adding the CNC in the resin, 2) using glass rod to mix CNC in resin, and 3) using a high shear mixer to obtain uniform formulation.

TABLE-US-00009 TABLE 9 CNC-LPF for plywood application CNC (%) NVC .sup.1 (based on (based on Viscosity No. Resin type Code (%) liquid) solid) (cps) Remarks 1 Lignin PF CNCLPF0 40.5 0 0 1440 1) mixing 2 Lignin PF CNCLPF1 38.0 0.73 1.92 1620 1) CNC in water; 2) load in LPF; 3) 3 Lignin PF CNCLPF2 41.0 0.80 1.94 1560 1) CNC in LPF; 2) mixing 4 Lignin PF CNCLPF3 41.4 1.45 3.50 2340 1) CNC in LPF; 2) mixing .sup.1 Non-Volatile Content (NVC): measured at 125 C. for 105 min;

[0102] The 2-ply plywood samples with such formulations were made with cross-section of 10 mm by 20 mm. The temperature was 150 C. and the press time was 3 minutes. The detailed information on the panel making is listed in Table 10.

TABLE-US-00010 TABLE 10 2-ply Plywood composites making conditions Wood species Sliced yellow birch Thickness of veneer Plywood 2-ply Resin spread rate on face ply 1.1-1.2 mg/cm.sup.2 Temperature 150 C. Pressure 1000 kPa Pressing time 3 min Pressure release time 0

[0103] After samples were made, and they were stored in a conditioning chamber for one week and then 5 specimens for each formulation were tested after 48 hour soaking in water (around 20 C.), and tested wet at a 10 mm/min speed using an MTS testing machine. The testing results are shown in Table 11.

TABLE-US-00011 TABLE 11 Properties of two-ply plywood panel made with lignin PF with/without CNC CNC (%) Shear NVC .sup.1 (based on (Based on strength No. Code (%) liquid) solid) (MPa) Remarks 1 CNCLPF0 40.5 0 0 3.60 0.68 1) Mixing 2 CNCLPF1 38.0 0.73 1.92 3.61 0.31 1)CNC in water; 2) load in LPF; 3) 3 CNCLPF2 41.0 0.80 1.94 4.09 0.91 1) CNC in LPF; 2) mixing 4 CNCLPF3 41.4 1.45 3.50 4.25 0.74 1) CNC in LPF; 2) mixing

[0104] From Table 11, it can be seen that adding CNC in lignin-PF resins through post-blending can improve the wet shear strength, in which the average value increased by about 13.6% with 1.94% CNC in the resin (No. 3 in Table 11), and 18.1% with 3.5% CNC in the resin comparing with control (No. 1 in Table 11).

Example 7

[0105] Molded Compounds with CNC-PF Powder

[0106] The CNC-PF powders in Table 1 coded PPF0, PPF1 and PPF3 were used. The electric press with dimension of 12 inches by 12 inches was used to make the molded products under 150 C. for 3.5 minutes with aluminum mold of 6-7 mm in width, 50 mm in length, and 1 mm in thickness. The thermo-mechanical properties were evaluated by Dynamic Mechanical Analyzer (DMA Q 800 from TA Instruments) with following conditions: in dynamic mold, frequency of 1 Hz, strain of 0.1%, and heating rate of 10 C./min from 25 C. to 250 C. The storage moduli of these materials are illustrated in FIG. 1.

[0107] From FIG. 1, it can be seen that with addition of small amount of CNC could significantly improve the storage modulus, in which 0.5% wt CNC increased the modulus by 25%-30% in different temperatures (from 30 C. to 210 C.), and 2.0% wt CNC increased the modulus by 48%-51% in different temperatures (from 30 C. to 210 C.)

[0108] CNC-pMDI Formulations

[0109] The first step of process according to invention consists of a) preparing the CNC aqueous dispersion through soaking the required amount of CNC in water for a few hours to make sure the CNC is well dispersed in water (it could become gel-like liquid if the CNC concentration reaches to 3-5% wt) with different methods, such as sonication, high shear mixing etc.; b) transferring pre-prepared CNC dispersion into polymeric MDI via mechanical mixing to form stable uniform CNC-pMDI emulsion system and adjusting the active component content to 40-70% wt through the addition of water if necessary.

[0110] Below we list some specific examples

Example 8

[0111] The spray-dried NCC powder was dispersed in water at different concentrations (0.5%-1.5%) by magnetic mixing, followed by mechanical mixing and ultrasonic mixing at room temperature. The resulting NCC suspensions were characterized as follows: 1) Viscosity measured by a viscometer (BrookfieldLVT), 2) Turbidity measured with a Micro 1000 IR Turbidimeter (Scientific Inc. Company), and 3) Birefringence (a specific property of non-aggregated NCC) checked under polarized light.

[0112] CNC suspension was mixed with emulsifiable pMDI, I-Bond MDF EM 4330 from Huntsman (here after E-MDI) with different ratio of CNC aqueous dispersion to E-MDI based on actual weight via mechanical means. The mixture of CNC-E-MDI emulsion is stable for certain period time.

[0113] An Automated Bond Evaluation System (ABES) was used to evaluate the bond strength development of NCC/E-MDI resin as a function of time at 120 C. measured by ABES. The test conditions with ABES are given as: [0114] a. Veneer: 117200.7 mm aspen [0115] b. Bonding area: 5 mm20 mm [0116] c. CNC dosage in glue: 2% CNC based on E-MDI [0117] d. Assembly time: no [0118] e. Pressing: 120 C. for 30-90 seconds [0119] f. Replicate: 5 at each bonding condition

TABLE-US-00012 TABLE 12 Properties of shear strength of AEBS made with E-MDI with/without CNC CNC (%).sup.3 Shear strength (MPa) NVC .sup.1 Spread rate.sup.2 (based on (Based on (cured at 120 C.) No. Code (%) (mg/cm.sup.2) liquid) solid) 30 sec 90 sec 1 E-MDI 100 1.80-1.92 0 0 0.96 0.18 1.28 0.22 2 E-MDI/water 50 1.36-1.40 0 0 2.31 0.39 4.44 0.98 3 E-MDI/CNC 51 1.36-1.38 1 2.0 3.20 0.46 5.50 0.98 .sup.1 NVC: non volatile content. E-MDI is treated as 100% active component .sup.2spread rate: calculated based on active components in which E-MDI treated as 100% active components .sup.2CNC content based on mixture of E-MDI resin and CNC either in liquid basis or solid (treated E-MDI as 100% solid)

[0120] It can be seen that incorporation of CNC into E-MDI could improve the bonding strength development

Example 9

[0121] The sodium forms of CNC, spray-dried CNC (code SD CNC), and freeze-dried CNC (code FD CNC), were dispersed in water first and then incorporated with E-MDI at loading level of 0.5-1.0% wt. based on E-MDI weight (same as example 8). The resulting adhesives (or binders) are used to manufacture strand boards. The panel manufacturing conditions are listed as follow:

Panel Dimension: 11.1 mm by 508 mm by 584 mm

[0122] Panel construction: random orientation/three layer
Mass distribution: 25/50/25
Wood species: 70% Aspen+30% high-density hardwoods
Target mat moisture: 6.5-7.5% in face layer and 5-7% in core layers
Slack wax content: 1.0% (on a dry wood basis) in face and core layers
Resin content in face: 2.5% E-MDI with/without CNC (on a dry wood weight)
Resin content in core: 2.5% regular polymeric MDI (on a dry wood weight)
Target board density: 62424 kg/m.sup.3 (390.5 lb/ft.sup.3) (oven dry basis)
Press temperature: 220 C. (platen)
Total press time: 150 seconds (daylight to daylight)

Replicates: 2

[0123] All strand board were conditioned in a chamber at 65% RH and 20 C until they reached the equilibrium moisture contents prior test. The internal bond (IB) strength, thickness swelling (TS) and water absorption (WA) of 24 hour soaking in running water at 20 C., dry modulus of rupture (MOR) and modulus of elasticity (MOE), and wet MOR and MOE after 24 hour running water soaking according CAS 0437-93 standard.

[0124] The mechanical properties of strand board made with E-MDI with/without CNC is illustrated as below:

TABLE-US-00013 TABLE 12 Properties of shear strength of AEBS made with E-MDI with/without CNC Unit No. 1 No. 2 No. 3 No. 4 No. 5 Properties Resin loading % 2.50 2.50 2.50 2.50 2.50 pMDI % 2.50 E-MDI % 2.50 2.488 2.488 2.475 CNC.sup.1 Freeze-dried % 0.012 Spray-dried % 0.012 0.025 Mechanical Properties IB MPa 0.50 0.42 0.47 0.44 0.52 MOR Dry MPa 40.51 39.50 34.10 39.00 31.60 Wet MPa 13.10 12.40 15.90 16.40 13.40 Retention % 32.34 31.39 46.63 42.05 42.41 MOE Dry MPa 5500 5326 4900 4988 4701 Wet MPa 2730 2628 3142 3152 2663 Retention % 49.64 49.34 64.12 63.19 56.65 TS % 18.20 17.70 17.30 16.50 14.50 WA % 24.40 21.80 22.00 24.40 20.00 .sup.1CNC content based on E-MDI content, CNC is 3% aqueous dispersion

[0125] It can be seen that addition of CNC into polymeric MDI can improve wet flexural strength (MOR) and also MOE. Addition of CNC could also reduce the thickness swelling (TS) and water absorption (WA).

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