Is accelerated aging a reliable approach to evaluate long term performance of structural adhesives?

Transcription

1 International Conference on Wood Adhesives, October 9-11, 2013, Toronto Is accelerated aging a reliable approach to evaluate long term performance of structural adhesives? Ying-Hei Chui and Meng Gong Wood Science and Technology Centre University of New Brunswick Fredericton, NB, Canada

2 Outline Background Objective Materials and Methods Results and Discussion Conclusions Acknowledgements 2

3 Background The long term performance of structural adhesives is a key performance attribute in evaluation of adhesive standards. An accelerated aging regime is used to simulate the long term weathering exposure before mechanical testing or delamination measurement. How reliable are these accelerated aging regimes in simulation of the true weathering exposure in the long term? 3

4 Objective To examine the reliability of the accelerated aging regimes in simulation of the true weathering exposure in the long term 4

5 Materials and Specimens Spruce lumber Shear block and structural size finger-joined lumber specimens Polyurethane (PUR) and phenol-resorcinol formaldehyde (PRF) 5

6 Block Shear Tests CSA O112.9 Evaluation of adhesives for structural wood products (exterior exposure) Test Clause MC at test Dry % Vacuum-pressure Wet Boil-dry-freeze Wet 6

7 Design of Experiment Weathering under the climate of eastern Canada (shear blocks and finger-joined lumber) Factor Level Adhesive type PUR PRF Exposure duration (months) Accelerated regimes (shear blocks only) Factor Level Adhesive type PUR PRF Treatment Wet Dry PVSW PVSD 2BFW 2BFD 8BFW 8BFD * Note: Replicates shear blocks (10) and finger-joined lumber (20) 7

8 Weathering site Fredericton, NB, Canada Aug. 29, 2006 Aug. 29,

9 Weathering site Fredericton, NB, Canada 9

10 Average temperatures in Fredericton, NB 10

11 Precipitation in Fredericton, NB 11

12 Mechanical testing Block shear tests (CSA O112.9) Tension tests (NLGA SPS1) on finger-joined lumber 12

13 Results: block shear tests (accelerated aging regimes) The performance of shear block specimens exposed to accelerated aging was similar between PUR and PRF in terms of shear strength. The shear strength decreased by 20% and 25% at wet (8 cycles) and dry (2 cycles) condition, respectively. 13

14 Results: block shear tests (weathering) Tested at dry condition. The long term performance of shear block specimens was similar between PUR and PRF in terms of shear strength. The shear strength decreased by 20% after 5 year exterior exposure for both adhesives used. 14

15 Results: fingerjoined lumber tests (weathering) Verification tests. Tested at dry condition. The UTS of finger-joined lumber bonded with PUR was larger than that with PRF regardless of exposure time. The UTS decreased by 10% and 20% when bonded with PRF and PUR, respectively. 15

16 Results: Median block shear strength (MPa) Accelerated aging regime PUR PRF CSA O112.9 requirement Dry Passed Vacuum-pressure Failed Boil-dry-freeze (8 cycles) Passed 16

17 Results When tested at wet condition, there was minimal strength change after V-P or 2-cycle boil-dry-freeze treatment, but a more substantial strength reduction occurred after 8-cycle one. When tested at dry condition, there was minimal strength change after V-P treatment, but a substantial strength reduction occurred after 2-cycle treatment. The strength reduction in finger joints was generally lower than that in shear blocks. 17

18 Conclusions 2-cycle boil-dry-freeze treatment could be equivalent to 60-month exposure in terms of shear strength when tested at dry condition. After 5-year exterior exposure, there was about 20% reduction in strength (shear blocks and finger-joined lumber). The accelerated aging regimes appearred to be suitable and reliable in simulation of the true weathering exposure in the long term. 18

19 Acknowledgements Natural Resources Canada under its Value-to-Wood Program Natural Sciences and Engineering Research Council of Canada (NSERC) 19

20 Thank you and Questions? 20