Yonghwan(Mark) Jang (PhD student) Kaichang Li (Professor) Department of Wood Science and Engineering Oregon State University, Corvallis, OR 97331, USA The International Conference on Wood Adhesives, October 9-11, 2013 Toronto, Ontario Canada
Outline Introduction Motivation Background Experiment and Results Conclusions
World production: 217 MMT/year The U.S. The largest producer and exporter in the world The second most valuable agricultural export Chemical composition Soybeans [http://www.jgi.doe.gov/news/news_1_17_08.html] Protein (40%), carbohydrates (35%), oil (20%), ash (5%) [http://www.scottsdalefitnessandhealth.com/top-5-reasonssoy-is-not-a-health-food.html]
Defatted soy flour Oil has been removed Soy flour Types of soy products Soy protein isolate (SPI): > 90% protein Soy protein concentrate (SPC): > 70% protein Soy flour (SF) : > 50% protein
Animal Timeline of soy-based adhesives Soybean Casein PF UF Soy Adhesives Peak UF Growing Soy-PAE Adhesive 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 1923 1938 UF Resins Introduced 1 st Patented Soy-Adhesive 2004 Soy-PAE for Interior Plywood [Source: Forest Products Society & Forest Products Laboratory]
Soy-PAE adhesive [Source: Li et. al., (2004)] SF and polyamidoamine-epichlorohydrin (PAE) Successful interior plywood Cost-competitive to UF Environmentally-friendly Superior strength and high water-resistance PAE resin The most expensive component Derived from petrochemicals
Motivation Replacement for PAE in soy-based adhesives Desirable features of a new curing agent Derived from natural or renewable materials Less expensive Easy to use Environmentally-friendly
Efforts for development of a PAE alternative at OSU A curing agent from glycerol and ammonia Epichlorohydrin currently derived from glycerol Soy flour-(curing agent) adhesive worked well for interior plywood (Jang et al, Int. J. Adhesion & Adhesives, 2011, 31: 754-759) Issue with this curing agent Fishy or amine smell
Efforts for development of a PAE alternative at OSU (cont d) A curing agent (polyepoxide) Generated from the reaction between glycerol and epichlorohydrin Effective Crosslinking agent for soy flour adhesives (Huang et al, Holzforschung, 2012, 66: 427-431) Issue with this curing agent Too expensive
Key features SF-MgO adhesive = + Soy Flour (SF) MgO No petrochemical-based products Safe to use [ GRAS (generally recognized as safe) products by FDA] [http://www.ecvv.com/product/2478968.html] Cost-competitive Comparable to soy-pae adhesive (strength and water resistance of wood composite panels) No known issues: Dream wood adhesive!
Magnesium oxide (magnesia) Porous surface Poor solubility in water: 0.62 mg in 100 ml Derived from (MgCl 2 )-rich brine, sea water or magnesite Abundant and readily available Applications: Food supplement Medicine (laxative) Desiccants for books Fillers for plastics and rubber
Investigation of water-resistance of plywood panels bonded with SF-MgO adhesives
Preparation of SF-MgO adhesives + + 36% solids content SF Pre-mixing DI water 10 min at RT
Preparation of 5-ply plywood panels Stand time Post-prepress Veneer assembly Cold-press Water-resistance test Plywood panel Hot-press
ANSI/HPVA HP-1-2009 Water-resistant Test Three-cycle soak test Two-cycle boil test Soaked in water for 20 h Boiled in water for 4 h 1st cycle Dried at 50 C for 19 h Dried at 63 C for 20 h Boiled in water for 4 h Soaking/drying cycle repeated for three cycles Requirement: 95% of specimens (19 out of 20) after the 1 st cycle must pass Dried at 63 C for 3 h 90% after the 2 nd cycle must pass
Conclusions All panels passed the three-cycle soak and the two-cycle boil tests. Strengths of panels are comparable to soy-pae adhesives. Effective cross-linking agent Adhesive works well for different veneers (yellow poplar, aspen, pines, white fir, maple).
Adhesion mechanism of SF-MgO adhesive
Proposed adhesion mechanisms Covalent linkages, hydrogen bonding, and mechanical interlocks all exist between SF and MgO.
Which fraction in SF is essential? Water resistance and shear strength Soy protein isolate (SPI) Insoluble Carbohydrates (IC) Glycinin (11S)
Preparation of different fractions Dispersion of SF Adjusted to ph 8.0 and centrifuged Alkali Extraction Supernatant Precipitate Insoluble Carbohydrates (IC)
Preparation of different fractions (cont d) Acid Treatment Adjusted to ph 4.5 and centrifuged Adjusted to ph 6.4 and centrifuged Precipitate Precipitate Soy protein isolate (SPI) Glycinin (11S) [Ref: Thanh and Shibasaki (1976) J. Agric. Food Chem. 24:1117-1121]
Preparation of adhesives + + DI water (9.32 ml) Pre-mixing SPI (3 g dry wt) MgO (0.5 g) Mixed at RT for 10 min Adhesive Ingredients Total Solids Content SF-MgO SPI-MgO 11S-MgO IC-MgO 36% 27% 30% 20%
7.5 cm 5.0 cm 1.5 cm 7.5 cm Preparation of Composites Maple veneer 17.5 cm Top Middle 0.5 cm 0.5 cm 7 cm 4 cm 7 cm Bottom Hot-press 10 kg/cm 2, 120 C, 5 min
Evaluation of shear strength The shear strength of wood composite was determined on an Instron TTBML testing machine.
Water-resistance of composites WSAD Three-cycle Water-Soaking- And-Drying Test US Voluntary PS1-95 (exterior application) BWT Two-cycle Boiling-Water Test 1st cycle Soaked in water for 24 h Dried in a fume hood for 24h Boiled in water for 4 h Dried at 63 C for 20 h Boiled in water for 4 h Cooled down in water BWT/W Soaking/drying cycle repeated for three-cylces Dried in a fume hood for 24h BWT/D
Shear Strength (MPa) Effect of different fractions with MgO on adhesive performance 10 9 8 7 6 5 SF-ONLY SF-MgO SPI-MgO 11S-MgO IC-MgO 4 3 3/10 DL 2 1 0 DL DL DL DL DL Dry WSAD BWT/D BWT/W Type of shear test Adhesives: the weight ratio of 8/1 (fraction/mgo) DL: all specimens were delaminated
Shear Strength (MPa) Effect of different fractions with MgO on adhesive performance (cont d) 10 9 8 7 6 5 SF-ONLY SF-MgO SPI-MgO 11S-MgO IC-MgO 4 3 3/10 DL 2 1 0 DL DL DL DL DL Dry WSAD BWT/D BWT/W Type of shear test Adhesives: the weight ratio of 6/1 (fraction/mgo) DL: all specimens were delaminated
Shear Strength (MPa) Effect of different fractions with MgO on adhesive performance (cont d) 10 9 8 7 6 5 SF-ONLY SF-MgO SPI-MgO 11S-MgO IC-MgO 4 3 3/10 DL 2 1 0 DL DL DL DL DL Dry WSAD BWT/D BWT/W Type of shear test Adhesives: the weight ratio of 4/1 (fraction/mgo) DL: all specimens were delaminated
Shear Strength (MPa) Effect of different fractions with MgO on adhesive performance (cont d) 8 7 6 5 SF-ONLY SF-MgO SPI-MgO 11S-MgO IC-MgO 4 3 3/10 DL 2 1 0 DL DL DL DL DL Dry WSAD BWT/D BWT/W Type of shear test Adhesives: the weight ratio of 2/1 (fraction/mgo) DL: all specimens were delaminated
Shear Strength (MPa) Effect of different fractions with MgO on adhesive performance (cont d) 8 7 6 5 SF-ONLY SF-MgO SPI-MgO 11S-MgO IC-MgO 4 3 3/10 DL 3/10 DL 2 1 0 DL DL DL DL DL Dry WSAD BWT/D BWT/W Type of shear test 3/10 DL Adhesives: the weight ratio of 1/1 (fraction/mgo) DL: all specimens were delaminated 1/10 DL
Conclusions SF-MgO, SPI-MgO and 11S-MgO were much better adhesives than SF-only and IC-MgO in terms of shear strength and water-resistance For SF-MgO: Dry strength WSAD strength> BWT/D strength at all ratios For SPI-MgO: Dry strength< WSAD strength BWT/D strength at 8/1, 6/1 and 4/1 ratios For 11S-MgO: Dry strength WSAD strength BWT/D strength at 8/1, 6/1 and 4/1 ratios
Conclusions (cont d) All laminates bonded with IC-MgO delaminated after the 2 nd cycle of the WSAD and BWT. The protein in SF was essential for the superior water resistance
Water-solubility of SF in SF-MgO adhesives
Sample preparation and water-solubility (WS) SF-MgO adhesive Cured at 103 C for 8 h Freeze-dried Ground and sieved (U.S. No. 80 mesh) Magnetically stirred at 200 rpm for 2 h Dispersed in DI water Centrifuged Precipitate was freezedried
Calculation of Water-solubility (WS) WS(%) = WS(%) = æ ç è æ ç è M - O M O M - O M - O M M M i i m ö 100 ø ö 100 ø for SF-only samples for SF-MgO samples M 0 : the weight of initial dry matter M i : the weight of insoluble dry matter M m : the weight of initial dry MgO in SF-MgO
WS (%) of SF Water-solubility (WS) of SF in samples 75 65 55 45 35 Freeze-dried Cured 25 SF-ONLY Samples SF-MgO Data are the mean of 4 replicates The error bars represent one standard deviation
Conclusions Water-resistant complex between SF and MgO was formed. The curing at elevated temperature was essential for high water resistance of the SF-MgO adhesive.
Summary MgO is an effective crosslinking agent for soy flour adhesives. Protein in soy flour plays an important role in high water-resistance and shear-strength. SF and MgO form a water-resistant complex at elevated temperature.