Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Outline Background about current resin application technology Problem and proposed work Ultrasonic atomization Aim of study Preliminary results Conclusions Acknowledgments

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Background--- Oriented Strand Board Debarking Thawing pond Wafer cutters Dryer Wafers Blender Forming machine Forming panel Press Edge trimming and grading Bundling and shipping The liquid resin is usually mixed with the wood strands in the rotating drum, sprayed by spinning disk atomizer

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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 D/ 2 (G. Smith 2005)

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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.

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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.

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Spray characteristics of spinning disk atomization

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Spray characteristics of spinning disk atomization

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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.

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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.

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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. Atomization Mechanism

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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.

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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.

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Experimental Materials: Equipments Masterflex pump feeding system + Sono-tek Ultrasonic atomizer (25 kHz) + Malvern drop size analyzer system Trade name Viscosity Molecular weight distribution (cP.s at 25°C)MnMwMz PF Dynea BB pMDI Huntsman Rubinate

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Ultrasonic atomizer Malvern instrument Power generator Masterflex Pump Experimental

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Results and discussion Ultrasonic atomized PF resin Max flow rate (ml/min)0.15 Power input (watts) Avg.STDEVAvg.STDEVAvg.STDEV Dv10 (μm) Dv50 (μm) Dv90 (μm) Transmission(%) D[4][3] (μm)

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Results and discussion

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Results and discussion Ultrasonic atomized pMDI resin Max flow rate (ml/min)0.7 Power input (watts)4.358 Avg.STDEVAvg.STDEVAvg.STDEV Dv10 (μm) Dv50 (μm) Dv90 (μm) Transmission(%) D[4][3] (μm)

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Results and discussion

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Spinning disk atomization VS. ultrasonic atomization Ultrasonic: Bigger size and more uniform distribution Range=Dv0.9- Dv0.1 Relative span=Range/Dv0.5

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Potential cost saving Price ($/lb) Adhesive demand from OSB (MM lb) Potential cost saving (MM $) if 1% less saved Year PF0.429~ ~ ~8.94 pMDI 1.01~ ~ ~18.40 If 10% less ? 100 MM $!!!

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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.

Advanced Engineered Wood Composites Center University of Maine, Orono, ME 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;

Advanced Engineered Wood Composites Center University of Maine, Orono, ME Thanks!!!