Transcript Slide 1

Ultrasonic atomization of
wood resin-adhesives
Xuelian Zhang, Research Assistant
Douglas J. Gardner, Professor
The University of Maine
Lech Muszynski, Assistant Professor
Oregon State University
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Outline
• Background about current resin
application technology
• Problem and proposed work
• Ultrasonic atomization
• Aim of study
• Preliminary results
• Conclusions
• Acknowledgments
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Background---Oriented Strand Board
Debarking
Thawing pond
Wafer cutters
Dryer
Wafers
Blender
The liquid resin is
usually mixed with the
wood strands in the
rotating drum, sprayed
by spinning disk
atomizer
Forming machine
Forming panel
Press
Edge trimming and grading
Bundling and shipping
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
http://sres.anu.edu.au
Background---Resin efficiency
• Definition: using the least amount of resin necessary for
fabrication of quality products. (Burrows 1961)
• Empirical: finer resin droplets and uniform distribution
were found better than coarse resin droplets and wide
distribution in maximizing the resin efficiency.
D/
2
D
AEWC
(G. Smith 2005)
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Background---Size limitation
• If the resin droplets are too small, they may reside in the
lumen of a cell at the surface of wood substrates and
can not contact with an adjacent wood substrate .
The diameter of largest vessel elements of Populus tremuloides,
one of the typical wood species for OSB, is 50 ~100 µm; and that of
fibers is around 20~30 µm.
• Other than that, the resin would be airborne and drift
away easily if too small droplets are produced.
Sprayed pMDI resin droplets smaller than 20µm were found to be
aerosolized and easily inhaled, which would pose serious
environmental health and safety issues for mill personnel.
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Background---Resin efficiency
• Usually, the internal bonding
strength (IB) is considered as
a criteria of resin efficiency.
• 94um was predicted as
optimal average diameter.
(Smith 2003)
Wilson and Krahmer, 1976,
For. Prod. J 26(11):42-45
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Background---Spinning disk atomization
• State of the art
Typically, the resin is atomized using
spinning disk atomizers (introduced in
early 1980’s), which run from 10,000
rpm to15,000 rpm and break the liquid
resin into a spray of fine droplets by
centrifugal force.
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Spray characteristics of spinning
disk atomization
Average Particle Size Distribution
Volume frequency (%)
20
15
PMDI at 14,910rpm
PMDI at 10,441rpm
PMDI at 9,287rpm
10
PF at 14,832rpm
PF at 12,894rpm
PF at 10,068rpm
5
0
1
10
100
Droplet size (μm)
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
1000
Spray characteristics of spinning
disk atomization
Cumulative Frequency (%)
Average Particle Size Distribution
100
pMDI at 14,910rpm
75
pMDI at 10,441rpm
pMDI at 9,287rpm
50
PF at 14,832rpm
FP at 12,894rpm
25
PF at 10,068rpm
0
1
10
100
Droplet size (μm)
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
1000
Proposed work
•
Historically, two possible ways to improve resin
efficiency have been examined including:
① modifying the composition of the resin-adhesives;
② modifying the on-going manufacturing techniques
under process conditions.
•
Our project: to develop an improved resin application
system for wood strand based composite production
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Ultrasonic atomization
• A promising alternative solution is droplet
atomization based on an ultrasonic
principle.
 Smaller drop sizes which can be accurately
controlled;
 More uniform size distribution;
 High sphericity of droplets;
 Lower momentum associated with ejected
droplets; in other words, a soft, low-velocity
spray.
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Ultrasonic Atomization
• Ultrasonic atomization is a process of atomization of a
liquid under vibrations with a frequency in excess of 20
kHz.
• Nozzle is geometrically configured so excitation of PZT
plates creates standing longitudinal wave though nozzle,
with maximum vibration at nozzle tip.
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Atomization Mechanism
• As liquid issues from nozzle tip, a capillary wave is
generated on liquid surface
• Wave collapses into drops of uniform diameter when
capillary wave becomes unstable.
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Application limitation
• Ultrasonic atomization has been successfully utilized in
various fields, such as the medical, cosmetic, and
electronic industries. However, the liquid viscosity
empirically limits its application, 50 cP at max.
• For applying wood resin-adhesives, a similar type of
sonic atomizer was employed and it was determined that
it could only spray resin-adhesives at very limited flow
rate. (Lehmann 1965)
• No work has done about application of ultrasonic
atomization in the area of wood resin-adhesive
application.
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Aim of study
•
To explore the applicability of the innovative
atomization method, ultrasonic atomization, for wood
resin-adhesive spray.



to determine whether wood resin-adhesives could be
effectively atomized using a bench-scale ultrasonic atomizer;
to measure the spray characteristics of ultrasonically atomized
resin- adhesive;
to determine the maximum flow rate of the ultrasonically
atomized resin-adhesive.
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Experimental
• Materials:
Trade name
Viscosity
Molecular weight
distribution
(cP.s at 25°C) Mn
PF
Dynea BB-634
pMDI Huntsman Rubinate 1840
246
Mw
800 2060
Mz
4130
233
• Equipments
Masterflex pump feeding system + Sono-tek Ultrasonic
atomizer (25 kHz) + Malvern drop size analyzer system
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Experimental
Ultrasonic atomizer
Masterflex Pump
Malvern
instrument
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Power generator
Results and discussion
• Ultrasonic atomized PF resin
Max flow rate
(ml/min)
0.15
Power input (watts)
6.6
Avg.
12
STDEV
Avg.
15
STDEV
Avg.
STDEV
Dv10 (μm)
62.78
1.80
54.04
2.76
52.46
3.11
Dv50 (μm)
91.98
3.85
84.76
5.51
82.20
5.66
Dv90 (μm)
154.81
10.19
160.79
9.32
152.72
8.62
91.92
1.68
94.21
0.95
92.62
1.55
100.91
4.47
96.48
4.90
92.89
5.24
Transmission(%)
D[4][3] (μm)
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Results and discussion
Average Particle Size Distribution
100
20.00
15.00
10.00
5.00
0.00
50
0
0
2
14
95
Particle Diameter (um)
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
661
Cumulative
Volume(%)
Volume
Frequency(%
)
Note:PF+36ml/min+12watts
Results and discussion
• Ultrasonic atomized pMDI resin
Max flow rate
(ml/min)
0.7
Power input (watts)
4.3
Avg.
5
STDEV
Avg.
8
STDEV
Avg.
STDEV
Dv10 (μm)
33.55
2.53
61.52
2.44
51.22
2.51
Dv50 (μm)
61.46
4.51
91.13
4.14
78.65
4.51
Dv90 (μm)
110.18
6.15
152.55
7.89
140.86
8.91
Transmission(%)
92.54
2.56
94.32
1.85
93.86
1.29
D[4][3] (μm)
67.83
3.85
99.67
4.16
88.19
4.23
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Results and discussion
Average Particle Size Distribution
20.00
15.00
10.00
5.00
0.00
100
50
0
0
2
14
95
Partilce Diameter (um)
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
661
Cumulative
Volume(%)
Volume
Frequency(%
)
Note: pMDI+36ml/min+5watts
Spinning disk atomization VS.
ultrasonic atomization
Uniformity of resin droplet distribution
Range=Dv0.9- Dv0.1
Relative span=Range/Dv0.5
Relative span
(Dv0.9-Dv0.1)/Dv0.5
6.00
5.00
4.00
Spinning disk
atomization
3.00
Ultrasonic atomization
2.00
1.00
0.00
0
20
40
60
80
100
Dv0.5
Ultrasonic: Bigger size and more uniform distribution
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Potential cost saving
Price
($/lb)
Adhesive demand
from OSB (MM lb)
2005
2005
2010
0.429~0.559 1250
1600
5.36~6.99
6.86~8.94
1600
12.63~14.38
16.16~18.40
Year
PF
pMDI
1.01~1.15
1250
Potential cost saving (MM $)
if 1% less saved
2005
2010
If 10% less ? 100 MM $!!!
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Conclusions
• ++ Both PF and pMDI resin were successfully sprayed
using a Sono-tech ultrasonic atomizer.
• ++ There is great application potential for of ultrasonic
atomization of wood resin-adhesives.
• --The limitation from throughput rate needs to be further
studied.
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Acknowledgements
• This research was funded in part by Henry Company
and the USDA McIntire Stennis Grant Improved
Adhesive Application System For Wood Strand-Based
Composites, Wood based composite fellowship;
• Dynea resins for supplying the liquid PF resin, Huntsman
for supplying pMDI resin;
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu
Thanks!!!
AEWC
Advanced Engineered Wood Composites Center
University of Maine, Orono, ME 04469
www.aewc.umaine.edu