A MOISTURE-CURING ONE-COMPONENT POLYMER COMPOSITION COMPRISING A NATURAL GROUND CALCIUM CARBONATE (GCC)

Abstract

The present invention relates to a moisture-curing one-component polymer composition comprising a polymer material and a natural ground calcium carbonate (GCC), a cured product obtained by curing the moisture-curing one-component polymer composition, a process for preparing such a moisture-curing one-component polymer composition as well as a process for preparing such a cured product and the use of a natural ground calcium carbonate (GCC) for decreasing the processing time for preparing such a moisture-curing one-component polymer composition and/or increasing the elongation at break of such a cured product.

Claims

1. A moisture-curing one-component polymer composition comprising a polymer material and a natural ground calcium carbonate (GCC), the natural ground calcium carbonate (GCC) having i) a weight median particle size d.sub.50 value measured by the sedimentation method of ≤0.8 μm, and ii) a specific surface area (BET) of at least 10 m.sup.2/g as measured using nitrogen and the BET method according to ISO 9277:2010, and iii) a residual moisture content of ≤0.2 wt.-%, based on the total dry weight of the natural ground calcium carbonate (GCC).

2. The moisture-curing one-component polymer composition according to claim 1, wherein the natural ground calcium carbonate (GCC) is selected from the group consisting of marble, limestone, dolomite, chalk and mixtures thereof.

3. The moisture-curing one-component polymer composition according to claim 1, wherein the natural ground calcium carbonate (GCC) has i) a weight median particle size d.sub.50 value measured by the sedimentation method of ≤0.6 μm, and/or ii) a top cut (d.sub.98) measured by the sedimentation method of 0.3 to 3.0 μm, and/or iii) a specific surface area (BET) of from 10 to 40 m.sup.2/g as measured using nitrogen and the BET method according to ISO 9277:2010, and/or iv) a residual moisture content of ≤0.15 wt.-%, based on the total dry weight of the natural ground calcium carbonate (GCC).

4. The moisture-curing one-component polymer composition according to claim 1, wherein the natural ground calcium carbonate (GCC) is treated with at least one surface-treatment agent selected from the group consisting of I) a phosphoric acid ester blend of one or more phosphoric acid mono ester and/or salts thereof and/or one or more phosphoric acid di-ester and/or salts thereof, and/or II) at least one saturated or unsaturated aliphatic linear or branched carboxylic acid and/or salts thereof, and/or III) at least one mono-substituted succinic anhydride consisting of succinic anhydride mono-substituted with a group selected from a linear, branched, aliphatic and cyclic group having a total amount of carbon atoms from at least C2 to C30 in the substituent and/or salts thereof, and/or IV) at least one polydialkylsiloxane, and V) mixtures of one or more materials according to I) to IV).

5. The moisture-curing one-component polymer composition according to claim 1, wherein the polymer material is a moisture-curing polymer material.

6. The moisture-curing one-component polymer composition according to claim 1, wherein the polymer composition comprises the natural ground calcium carbonate (GCC) in an amount ranging from 20 to 65 wt.-%, based on the total weight of the polymer composition.

7. The moisture-curing one-component polymer composition according to claim 1, wherein the polymer composition further comprises a crosslinking agent and plasticizer as additives and optionally further additives such as colouring pigments, fibers, e.g. cellulose, glass or wood fibers, dyes, waxes, lubricants, oxidative- and/or UV-stabilizers, curing agents, adhesion promoter, antioxidants, rheological modifier such as PVC, and other fillers, such as carbon black, TiO.sub.2, mica, clay, precipitated silica, fumed silica, talc or calcined kaolin.

8. The moisture-curing one-component polymer composition according to claim 4, wherein the at least one surface-treatment agent is present on the natural ground calcium carbonate (GCC) in an amount ranging from 0.5 to 4.5 wt.-% based on the total weight of the natural ground calcium carbonate (GCC).

9. The moisture-curing one-component polymer composition according to claim 1, wherein the polymer composition is a sealant or adhesive composition.

10. A cured product obtained by curing the moisture-curing one-component polymer composition of claim 1, wherein the cured product has an elongation at break of more than 600%, determined according to ISO 37:2011.

11. A process for preparing a moisture-curing one-component polymer composition as defined in claim 1, wherein the process comprises the steps of a) providing a polymer material, b) providing a natural ground calcium carbonate (GCC) having i) a weight median particle size d.sub.50 value measured by the sedimentation method of ≤0.8 μm, and ii) a specific surface area (BET) of at least 10 m.sup.2/g as measured using nitrogen and the BET method according to ISO 9277:2010, and a residual moisture content of ≤0.2 wt.-%, based on the total dry weight of the natural ground calcium carbonate (GCC), c) providing a crosslinking agent and a plasticizer, d) optionally providing further additives such as colouring pigments, fibers, e.g. cellulose, glass or wood fibers, dyes, waxes, lubricants, oxidative- and/or UV-stabilizers, curing agents, adhesion promoter, antioxidants, rheological modifier such as PVC, and other fillers, such as carbon black, TiO.sub.2, mica, clay, precipitated silica, fumed silica, talc or calcined kaolin, and e) contacting the components of step a), step b), step c) and optional step d) in any order.

12. The process according to claim 11, wherein in contacting step e) firstly the natural ground calcium carbonate (GCC) of step b) is contacted under mixing, in one or more steps, with the plasticizer of step c) and the mixture obtained is contacted under mixing, in one or more steps, with the polymer material of step a) and the crosslinking agent of step c).

13. The process according to claim 12, wherein the crosslinking agent is contacted under mixing, in one or more steps, with the mixture obtained by contacting the natural ground calcium carbonate (GCC) with the plasticizer before, during or after said mixture is contacted with the polymer material.

14. The process according to claim 12, wherein the further optional additives of step d) are contacted under mixing, in one or more steps, with the mixture obtained by contacting the natural ground calcium carbonate (GCC) with the plasticizer before, during or after said mixture is contacted with the polymer material and the crosslinking agent.

15. A process for preparing a cured product, wherein the process comprises the steps of i) providing the moisture-curing one-component polymer composition in accordance with in claim 11, and ii) curing the composition of step i) such that the cured product is formed; wherein the cured product has an elongation at break of more than 600%, determined according to ISO 37:2011.

16. A method of using a natural ground calcium carbonate (GCC)-comprising the step of: preparing a moisture-curing one-component polymer composition and/or increasing the elongation at break of a cured product comprising a natural ground calcium carbonate (GCC) having i) a weight median particle size d.sub.50 value measured by the sedimentation method of ≤0.8 μm, and ii) a specific surface area (BET) of at least 10 m.sup.2/g as measured using nitrogen and the BET method according to ISO 9277:2010, and a residual moisture content of ≤0.2 wt.-%, based on the total dry weight of the natural ground calcium carbonate (GCC), wherein the processing time for preparing the moisture-curing one-component polymer composition and/or increasing the elongation at break of the cured product, is decreased as compared to the processing time for preparing the moisture-curing one-component polymer composition and cured product, in the absence of the natural ground calcium carbonate (GCC) having i) a weight median particle size d.sub.50 value measured by the sedimentation method of ≤0.8 μm, and ii) a specific surface area (BET) of at least 10 m.sup.2/g as measured using nitrogen and the BET method according to ISO 9277:2010, and a residual moisture content of ≤0.2 wt.-%, based on the total dry weight of the natural ground calcium carbonate (GCC).

17. The moisture-curing one-component polymer composition according to claim 1, wherein the polymer material is selected from the group comprising polyurethane, silyl-modified polyurethane, polyurea, silyl-modified polyurea, silicone, polyether polymers with terminal silane groups, polysulfide polymers with terminal silane groups, poly(meth)acrylate, and mixtures thereof.

Description

EXAMPLES

1. Measurement Methods

[0350] In the following, measurement methods implemented in the examples are described.

Particle Size Distribution

[0351] The weight median particle size d.sub.50 (wt) and weight top cut particle size d.sub.98 (wt) is determined by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field. The measurement is made with a Sedigraph™ 5120, Micromeritics Instrument Corporation. The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and sonicated.

[0352] The processes and instruments are known to the skilled person and are commonly used to determine the particle size of fillers and pigments.

Specific Surface Area (SSA)

[0353] The specific surface area was measured via the BET method according to ISO 9277:2010 using nitrogen as adsorbing gas on a Micromeritics ASAP 2460 instrument from Micromeritics. The samples were pretreated in vacuum (10.sup.−5 bar) by heating at 150° C. for a period of 60 min prior to measurement.

Amount of Surface-Treatment Layer

[0354] The amount of the treatment layer on the magnesium and/or calcium ion-containing material is calculated theoretically from the values of the BET of the untreated magnesium and/or calcium ion-containing material and the amount of the one or more compound(s) that is/are used for the surface-treatment. It is assumed that 100% of the one or more compound(s) are present as surface treatment layer on the surface of the magnesium and/or calcium ion-containing material.

Residual Moisture Content

[0355] The residual moisture content was determined by thermogravimetric analysis (TGA). The equipment used to measure the TGA was the Mettler-Toledo TGA/DSC1 (TGA 1 STARe System) and the crucibles used were aluminium oxide 900 μl. The method consists of several heating steps under air (80 mL/min). The first step was a heating from 25 to 105° C. at a heating rate of 20° C./minute (step 1), then the temperature was maintained for 10 minutes at 105° C. (step 2), then heating was continued at a heating rate of 20° C./minute from 105 to 400° C. (step 3). The temperature was then maintained at 400° C. for 10 minutes (step 4), and finally, heating is continued at a heating rate of 20° C./minute from 400 to 600° C. (step 5). The residual moisture content is the cumulated weight loss after steps 1 and 2.

Shore A Hardness

[0356] Shore A hardness was determined according to DIN 53505.

Maple/Maple Lap Shear

[0357] Maple/Maple Lap Shear was determined according to DIN EN 14293:2006-10. For determining the shear strength of soft adhesives two mosaic parquet finger were lap bonded with the thickness of the adhesive gap being approximately 1 mm. After conditioning (14 days, 23±1° C., 50±5% relative humidity), the test specimens were clamped in a tensile testing machine and a tensile force was applied until breakage.

Skin Formation Time

[0358] To measure the skin formation time, a round bead of composition of approximately 3 mm diameter was applied on a polyethylene film substrate under standard conditions (23±1° C., 50±5% relative humidity). The skin formation time (Skin time, skin-overtime, SOT. skinning time) was determined as the elapsed time from the application to the bead to the time it took to leave no residue on a LDPE pipette, when lightly tapped on the surface of the composition.

Mechanical Properties

[0359] To determine the mechanical properties, films of about 2 mm thickness were produced by extruding the composition from an adhesive cartridge into a negative PTFE mould of 2.0 mm thickness, 35 mm width and 250 mm length. The composition was allowed to cure for 7 days under standard conditions. Dumbbells of dimensions according to ISO 37:2011, Table 2, Type 2 were punched out of the films and tested for tensile strength, elongation at break and modulus of elasticity (at 100% elongation) in accordance with ISO 37:2011.

Sag Resistance (Boing Sag Test)

[0360] The sag resistance (or Boeing sag test) referred to herein conforms to ASTM Specification D 2202-73 and measures the ability of a joint sealant composition to retain shape when placed in a vertical receptacle called a flow test jig. The sag resistance value as referred to in the Specification and claims hereof is the amount of sag or slump of the sealant composition in inches as indicated by the test jig after 5 minutes at standard conditions (23±1° C., 50±5% relative humidity)

2. Examples

[0361] Inventive and comparative 1K polymer compositions as set out in the following table 1 were prepared.

Filler Material

GCC1 (Marble)

[0362] A natural ground calcium carbonate material (GCC) surface treated with 3.6 wt.-% stearic acid and characterized by: a weight median diameter d.sub.50 of 0.3 μm, a specific surface area (BET) of 13 m.sup.2/g, a moisture content<0.08%, a moisture absorption<2500 ppm, Loss of weight at 400° C.>1.0%.

GCC2 (Chalk)

[0363] GCC2 is a commercial grade natural ground calcium carbonate material (GCC) surface treated with 2.5 wt.-% stearic acid which is sold under the name Omyabond 302 by Omya International AG. GCC2 is characterized by: a weight median diameter d.sub.50 of 0.3 μm, a specific surface area (BET) of 20 m.sup.2/g, a moisture content>0.4%, a moisture absorption>3000 ppm, Loss of weight at 400° C.>1.0%.

PCC

[0364] PCC is a commercial (synthetic) precipitated calcium carbonate sold under the name of UltraPflex 100, by Specialty Minerals Inc.. The PCC is a stearate surface treated precipitated calcium carbonate with nominal primary particle size d.sub.50 of 70 nm and BET surface area of 21 m.sup.2/g, a moisture content>0.3%, a moisture absorption>3000 ppm, Loss of weight at 400° C.>1.0%

GCC3 (Limestone)

[0365] GCC3 is a commercial grade natural ground calcium carbonate material (GCC) surface treated with 1 wt.-% stearic acid which is sold under the name Omyalite 95T by Omya International AG. GCC3 is characterized by: a weight median diameter d.sub.50 of 0.9 μm, a specific surface area (BET) of 8 m.sup.2/g, a moisture content ≤0.2%, a moisture absorption>2500 ppm, Loss of weight at 400° C.>1.0%

GCC4 (Limestone)

[0366] GCC4 is a commercial grade natural ground calcium carbonate material (GCC) surface treated with 1.8 wt.-% stearic acid which is sold under the name Hydrocarb 120T by Omya International AG. GCC4 is characterized by: a weight median diameter d.sub.50 of 0.5 μm, a specific surface area (BET) of 22 m.sup.2/g, a moisture content≤0.5%, a moisture absorption>2500 ppm, Loss of weight at 400° C.>1.0%

TABLE-US-00001 TABLE 1 Inventive and comparative compositions Compounds by parts by Comparative Comparative Comparative Comparative weight Inventive 1 A B C D A Desmoseal 25.5 25.5 25.5 25.5 25.5 M280 (Prepolymer) B Incozol BH 1.1 1.1 1.1 1.1 1.1 (Latent crosslinking agent) C Mesamoll 25.5 25.5 25.5 25.5 25.5 (Plasticizer) D1 Marble 46.9 (GCC1) D2 Chalk 46.9 (GCC2) D3 (Synthetic) 46.9 precipitated calcium carbonate (PCC) D4 Limestone 46.9 (GCC3) D5 Limestone 46.9 (GCC4) E GLYEO 1.1 1.1 1.1 1.1 1.1 (Adhesion promotor)

[0367] The sealant compositions were prepared by mixing the components at room temperature. Sealants components A, B, C, D1-D5 and E are defined above.

[0368] The inventive 1K-PU composition was prepared by mixing plasticizer C and inventive product D1 in a 150 ml speed mixer cup (PP 250 ml) according to Table 1 above. The mixture was stirred in a SpeedMixer DAC 600.1 FVZ at 2300 rpm for 30 seconds at ambient temperature. Components A, B and E were added in the amounts according to Table 1 above. The mixture was stirred in a SpeedMixer DAC 600.1 FVZ at 2300 rpm for 30 seconds at ambient temperature.

[0369] The comparative A 1K-PU composition was prepared by mixing plasticizer C and product D2 in a 150 ml speed mixer cup (PP 250 ml) according to Table 1 above. The mixture was stirred in a SpeedMixer DAC 600.1 FVZ at 2300 rpm for 30 seconds at ambient temperature. Components A, B and E were added in the amounts according to Table 1 above. The mixture was stirred in a SpeedMixer DAC 600.1 FVZ at 2300 rpm for 30 seconds at ambient temperature.

[0370] The comparative B 1K-PU composition was prepared by mixing plasticizer C and product D3 in a 150 ml speed mixer cup (PP 250 ml) according to Table 1 above. The mixture was stirred in a SpeedMixer DAC 600.1 FVZ at 2300 rpm for 30 seconds at ambient temperature. Components A, B and E were added in the amounts according to Table 1 above. The mixture was stirred in a SpeedMixer DAC 600.1 FVZ at 2300 rpm for 30 seconds at ambient temperature.

[0371] The comparative C 1K-PU composition was prepared by mixing plasticizer C and product D4 in a 150 ml speed mixer cup (PP 250 ml) according to Table 1 above. The mixture was stirred in a SpeedMixer DAC 600.1 FVZ at 2300 rpm for 30 seconds at ambient temperature. Components A, B and E were added in the amounts according to Table 1 above. The mixture was stirred in a SpeedMixer DAC 600.1 FVZ at 2300 rpm for 30 seconds at ambient temperature.

[0372] The comparative D 1K-PU composition was prepared by mixing plasticizer C and product D5 in a 150 ml speed mixer cup (PP 250 ml) according to Table 1 above. The mixture was stirred in a SpeedMixer DAC 600.1 FVZ at 2300 rpm for 30 seconds at ambient temperature. Components A, B and E were added in the amounts according to Table 1 above. The mixture was stirred in a SpeedMixer DAC 600.1 FVZ at 2300 rpm for 30 seconds at ambient temperature.

[0373] The results for the inventive and comparative 1K polymer compositions are shown in the following tables 2 and 3.

TABLE-US-00002 TABLE 2 Sag resistance and storage stability of the inventive and comparative 1K polymer compositions Properties of Inventive Comparative Comparative Comparative Comparative compositions 1 A B C D Sag <0.5 <0.5 >10 <1 >10 resistance (mm) after 7 d days easily solid, not solid, not solid, not solid, not storage at extrudable extrudable extrudable extrudable extrudabl room temperature after 7 d days still solid, not solid, not solid, not solid, not storage at extrudable extrudable extrudable extrudable extrudable 50° C.

TABLE-US-00003 TABLE 3 mechanical properties of the inventive and comparative 1K polymer compositions Properties of Inventive Comparative Comparative Comparative Comparative compositions 1 A B C D Skin time 150 70 N/A N/A 80 (minutes) 100% Tensile 0.2 0.2 N/A 0.7 0.4 modulus (MPa) Tensile strength 1.9 1.9 N/A N/A 2.1 (MPa) Elongation at 840 600 N/A 635 340 break (%)

[0374] Inventive 1K sealant compositions 2 and 3 as set out in the following table 4 were prepared.

TABLE-US-00004 TABLE 4 Inventive sealant compositions 2 and 3 based on HDI* and MDI** Inventive 2 Inventive 3 parts by parts by Components [g] weight.sup.# [g] weight.sup.# Plasticizer Mesamoll (Lanxess) 14.700 100 0.000 0 Plasticizer DIDP (ExxonMobil) 0.000 0 14.500 100 Pigment paste TiO.sub.2 Dispersion 9.800 66.7 9.600 66.2 Filler GCC1 44.800 304.8 44.100 304.1 Moisture P-Toluenesulfonyl 0.8 5.4 10.8 74.5 scavenger isocyanate (Sigma Aldrich) Polyol Desmophen 2061 BD 8.200 55.8 8.100 55.8 (Covestro) Polyol Desmophen 5034 BT 13.300 90.5 13.100 90.3 (Covestro) Solvent Xylene (Sigma 3.300 22.4 3.200 22.1 Aldrich) Diisocyanate Desmodur H 2.540 17.3 0.000 0 (HDI*) (Covestro) Diisocyanate Rubinate 9433 0.000 0 4.000 27.6 (MDI**) (Huntsman) Catalyst Coscat 83 (Palmer 0.042 0.29 0.042 0.29 Holland) Moisture P-Toluenesulfonyl 0.500 3.4 0.500 3.6 scavenger isocyanate (Sigma Aldrich) Stabilizer Eversorb 90 0.500 3.4 0.500 3.6 (Everlight Chemical) Adhesion Dynasylan GLYEO 1.000 6.8 1.000 6.9 promoter (Evonik) Catalyst Dibutyltin dilaurate 0.500 3.4 0.500 3.6 (Sigma Aldrich) *Hexamethylenediisocyanate **Methylenediphenyldiisocyanate .sup.#normalized to 100 parts by weight of the polymer

[0375] A pigment paste was prepared by pre-dispersing an equal weight of TiO.sub.2 dispersion (Kronos 2500) and corresponding plasticizer Mesamoll (Lanxess) or DIDP (ExxonMobil; CAS-68515491). The mixture was homogenized at 2300 rpm for 30 seconds. In a second step, the so prepared pigment paste and the GCC 1 of the present invention were homogenously mixed in a planetary mixer (PC Laborsystems) for 10 minutes under the following conditions: 1000 rpm stirring with a dissolver at a temperature between 30° C. and 70° C. at full vacuum (−0.8 atm or less). Thereafter the stirring speed was reduced to 200 rpm and the mixer was vented to reach ambient pressure. Moisture scavenger was added, and the vacuum restored and stirring at 200 rpm was continued for another 15 minutes. Thereafter, the mixer was vented again and the polyol, solvent, diisocyanate and catalyst were added and stirred for about 60 minutes in a temperature window of 70° C. to 75° C. at 200 rpm. The mixture was let to cool down to a temperature of 30° C. to 40° C. and the remaining compound, adhesion promotor and stabilizer were added and the mixture was homogenized for 15 minutes at 200 rpm in a light vacuum (−0.2 atm). Thereafter the mixture was discharged and transferred into a sealant cartridge for testing and storage.

[0376] The mechanical properties of the inventive 1K sealant compositions 2 and 3 are set out in the following table 5.

TABLE-US-00005 TABLE 5 mechanical properties of the inventive compositions 2 and 3 Inventive 2 Inventive 3 Sag resistance (mm) <0.5 <0.5 Skin time (minutes) 170 50 Elongation at break (%) >626 >670 Tensile strength (MPa) 0.9 1.3 100% Tensile modulus 0.3 0.3 (MPa) Shore A 22 24

[0377] Inventive 1K sealant compositions 4 to 8 as set out in the following table 6 were prepared.

TABLE-US-00006 TABLE 6 Inventive sealant compositions 4-8 4 5 6 7 8 Components [g] [g] [g] [g] [g] Polyol Dongda DL 2000D (Shandong 5.00 7.50 5.00 5.00 5.00 Bluestar Dongda Co.) Polyol EP 330 NG (Shandong 8.10 12.20 8.10 8.10 8.10 Bluestar Dongda Co.) Solvent Xylene (Sigma Aldrich) 2.00 3.00 2.00 2.00 2.00 Filler GCC1 18.00 27.00 18.00 18.00 18.00 Diisocyanate Rubinate 9433 3.20 4.80 3.20 3.20 3.20 (MDI) (Huntsman) Catalyst Dibutyltin dilaurate 0.08 0.08 0.08 0.08 0.08 (Sigma Aldrich) Adhesion promoter Dynasylan GLYMO (Evonik) 0.40 0.60 0.40 0.40 0.40 Moisture scavenger p-Toluenesulfonyl isocyanate 0.20 0.00 0.2 0.2 0.2 (Sigma Aldrich) Moisture scavenger Additive OF (Borchers) 0.00 0.30 0.00 0.00 0.00 Latent hardener Incozol BH (Incorez) 1.10 0.00 0.00 0.00 0.00 Latent hardener Incozol EH (Incorez) 0.00 1.60 0.40 0.80 1.10

[0378] A mixture of the polyols and the GCC 1 (filler) of the present invention was homogenized at 2300 rpm for 30 seconds. In a second step, the so prepared mixture was homogenously mixed in a planetary mixer (PC Laborsystems) for 10 minutes under the following conditions: 1000 rpm stirring with a dissolver at a temperature between 30° C. and 70° C. at full vacuum (−0.8 atm or less). Thereafter, the stirring speed was reduced to 200 rpm and the mixer was vented to reach ambient pressure. Moisture scavenger was added, and the vacuum restored and stirring at 200 rpm was continued for another 15 minutes. Thereafter, the mixer was vented again and the solvent, diisocyanate and catalyst were added and stirred for about 60 minutes in a temperature window of 70° C. to 75° C. at 200 rpm. The mixture was let to cool down to a temperature of 30° C. to 40° C. and the remaining compounds, adhesion promotor and latent hardener were added and the mixture was homogenized for 15 minutes at 200 rpm in a light vacuum (−0.2 atm). Thereafter, the mixture was discharged and transferred into a sealant cartridge for testing and storage.

[0379] The mechanical properties of the inventive 1K sealant compositions 4 to 8 are set out in the following table 7.

TABLE-US-00007 TABLE 7 mechanical properties of the inventive compositions 4-8 4 5 6 7 8 Skin time (minutes) 15 20 10 10 10 Elongation (%) 368 335 618 502 548 Tensile Strength (MPa) 0.7 1.8 3.0 2.2 3.1 100% Tensile modulus 0.4 0.9 0.9 0.9 0.9 (MPa) Shore A 37 47 45 47 55 Maple/Maple Lap Shear Shear Strength (MPa) 2.2 2.1 2.2 3.2 2.5