Microencapsulated PMDI Adhesives For Bonding Wood

Transcription

1 Microencapsulated PMDI Adhesives For Bonding Wood Wood Adhesives October 11th 2013, Toronto Andreas Zillessen, Fraunhofer WKI, Braunschweig, Germany Andreas Sengespeick, Fraunhofer UMSICHT, Oberhausen, Germany

2 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

3 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

4 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

5 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 wt%

6 Properties of the Microcapsules Diameter µm (ø 300 µm) Wall thickness µm NCO-content 27% (pure pmdi 32%) Storage stability min. 12 month Good pourability B. Plinke

7 Properties of the Microcapsules - mechanical activation - Friction test with a scalpel under an optical microscope Mechanical activation induces the release of the liquid core

8 NCO-content by IR spectroscopy ~ 2200 cm -1 : NCO

9 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

10 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

11 Converted NCO-groups in % Reactivity in Water Comparison emdi and Microcapsules MK Reihe 1 MK Reihe 2 MK Reihe 3 emdi 10 emdi time [min] Measured by CO 2 emission in water

12 Behavior under high temperatures High temperatures do not activate the MCs NCOs are deactivated by air moisture

13 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 N/mm² 4 N/mm² 4-6 N/mm² Embrittelment occurs after cold water treatment Addition of plasticizing components

14 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

15 Penetration Behavior comparative values 1K-PUR pmdi Y. Xu 2009

16 Variation of the Pressing parameters Pressure N/mm² Temperature C Pressing time min Moisture 12% EMC, addition of H 2 O Applied quantity 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.

17 Shear strength after addition of 40% of plasticizing components Shear strength in N/mm² 7d standard climate rubber powder PEG (s) wood failure 3% 18% 4d cold water wood failure 0% 75% 6h hot water wood failure 3% 44%

18 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

19 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

20 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

21 Thank You! A. Ritter, M. Brodel, U. Schliephake, W. Bürger, V. Ebeling B. Plinke Tank You for Your Attention!