Microencapsulated PMDI Adhesives For Bonding Wood Wood Adhesives October 11th 2013, Toronto Andreas Zillessen, Fraunhofer WKI, Braunschweig, Germany Andreas Sengespeick, Fraunhofer UMSICHT, Oberhausen, Germany
Outline Introduction Aim of the project Synthesis of the microcapsules Properties of the microcapsules Bonding wood with the microcapsules First results with 2 component systems Summery and Outlook
PMDI, 1K-PUR-Prepolymers and 2K-PUR PMDI 1K-PUR-prepolymer 2K-PUR NCO R NCO + H 2 O - CO 2 NH 2 R NH 2 + NCO R NCO NCO R NCO + OH R OH NCO R NH CO O R NCO + H 2 O m NCO R NCO + OH R OH NCO R NH CO O R NCO n NCO R NH CO NH R NCO n NCO R NH CO O R NCO n n >>> m; component 1 component 2 O C N O C N n N C O n = 0-9 pmdi
Aim of the Project Open times/pressing times 1 : 2,5 Mechanical activation of the adhesives Bonding on Demand long open times plus high reactivity
Synthesis of the Microcapsules Straightforward dropping process of pmdi into 1,4-butanediol Addition of surfactants, an amine and a fluorescent dye The capsule formation can be controlled by temperature and the stirring rate PMDI content 12.5-33 wt%
Properties of the Microcapsules Diameter 50-500 µm (ø 300 µm) Wall thickness 0.5-2 µm NCO-content 27% (pure pmdi 32%) Storage stability min. 12 month Good pourability B. Plinke
Properties of the Microcapsules - mechanical activation - Friction test with a scalpel under an optical microscope Mechanical activation induces the release of the liquid core
NCO-content by IR spectroscopy ~ 2200 cm -1 : NCO
Molecular weight distribution by GPC microcapsules pmdi Low molecular weight fraction in the MCs Decrease of the monomer content of the pmdi Increase of the oligomer content
Molecular weight distribution by GPC Mikrokapseln microcapsules Low molecular weight fraction in the MCs Decrease of the monomer content of the pmdi Increase of the oligomer content PMDI 1K-PUR
Converted NCO-groups in % Reactivity in Water Comparison emdi and Microcapsules 70 60 50 40 30 20 MK Reihe 1 MK Reihe 2 MK Reihe 3 emdi 10 emdi 0 450 425 400 375 350 325 300 275 250 225 200 175 150 125 100 75 50 25 0 time [min] Measured by CO 2 emission in water
Behavior under high temperatures High temperatures do not activate the MCs NCOs are deactivated by air moisture
Shear strength of joints bonded with pure MCs by hot pressing pretreatment Shear strength after standard climate Shear strength after cold water Shear strength after hot water Requierments EN 204 / D4 Test results 10 N/mm² 11.1 ± 0.7 N/mm² 4 N/mm² 1.8-2.9 N/mm² 4 N/mm² 4-6 N/mm² Embrittelment occurs after cold water treatment Addition of plasticizing components
Penetration Behavior The penetration of the pmdi into the wood structure can be controlled by the encapsulation. Joint thickness at 250 g/m²: 0.21 mm 0.41 mm Joint thickness at 400 g/m²: 0.26 mm 0.50 mm
Penetration Behavior comparative values 1K-PUR pmdi Y. Xu 2009
Variation of the Pressing parameters Pressure 0.3 0.7 N/mm² Temperature 120 180 C Pressing time 10 20 min Moisture 12% EMC, addition of H 2 O Applied quantity 120 400 g/m² Pressing pressures of at least 0.7 N/mm² are required to activate the MCs. Applied quantities of 250 g/m² are required.
Shear strength after addition of 40% of plasticizing components Shear strength in N/mm² 7d standard climate rubber powder PEG (s) 5.0 14.0 wood failure 3% 18% 4d cold water 4.3 6.8 wood failure 0% 75% 6h hot water 2.9 6.6 wood failure 3% 44%
Cold setting two component systems first results EPI-Dispersion A-components of PUR-Systems Different polyols and emulsions Conventional resins Bonding strength are not yet sufficient Stoichiometric adaption of the A component Miscibility is critical Microstructure of the adhesive joint
Summery PMDI can be microencapsulated by means of a dropping process in 1,4-butanediol The mechanical activation of the capsules occurs through pressing The capsules cannot be activated by temperature With PEG as a second component good bonding strengths can be achieved trough hot pressing
Outlook further steps Optimization of the yield of the encapsulation process Variation of the capsules wall thickness Determination and optimization of a suitable A- components for cold setting adhesives
Thank You! A. Ritter, M. Brodel, U. Schliephake, W. Bürger, V. Ebeling B. Plinke Tank You for Your Attention!