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Publication Date: 2014-Mar-25
Document File: 3 page(s) / 419K

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Methylene diphenyl diisocyanate (MDI) has been successfully introduced to fiber by dry blending during the medium density fiberboard (MDF) manufacturing process in (1) a fall chute, (2) a lump separator or air grader, (3) a blowline, and (4) between a transfer screw and a weigh belt. Therefore, it can be concluded that MDI resin can be introduced to the fiber in any part of the MDF manufacturing process.

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Page 01 of 3


     Blending resin (glue) into medium density fiberboard (MDF) fibers poses a particular problem that is unique among the composite panel industry (MDF, Particleboard, oriented strand board (OSB), and plywood). Because MDF fibers are so finely textured, they easily form entanglements that create nodules (or tightly wound balls) of fiber, as illustrated in Figure 1, that are difficult to penetrate with resin.

Figure 1: Nodularized MDF Fiber

     For this reason, MDF is typically resinated in a blowline, which is a pressurized pipe within which the MDF fiber is conveyed via super-heated steam after it goes through the refiner (where chips are ground down to fiber). Turbulence in the blowline assists the spread of the resin by rubbing and friction in the constant flow of the fibers past one another. Urea Formaldehyde (UF) based resins are tacky (or sticky), and therefore require lots of this turbulence in order to get good distribution on the fiber. Therefore, the resin is injected at the beginning of the blowline, so that it has a maximum amount of time and travel with the fiber in this turbulent environment. Unfortunately, the heat and steam will cause the UF resin to react partially while it is in the blowline. This is essentially a waste of resin, because the job of the resin is to cement the fibers together in the press. The press is much further down in the process, and since the fiber must also be dried after the blowline, the resin must also face further pre-curing reaction in the drier before making it to the press. This represents a significant cost, since the material must be over-resinated in order to make up for the loss. Resin cost can therefore be as high as 50% of the raw material cost of the final product.

     For this reason, MDF manufacturers have tried to find ways to resinate further down in the process in order to avoid the pre-cure issue. There is now a piece of equipment, EVOjet dry resin blending system, sold by Dieffenbacher that separates the fiber material to a very high degree, and sprays the UF resin at a highly atomized state, therefore ensuring good resin distribution. However, this is a large piece of expensive equipment that must be added to the process, which further requires extra piping and space, which is often at a premium at many MDF producing facilities. The equipment installation will cost multiple millions of dollars to accomplish the desired result. However, Dieffenbacher touts up to 50% resin savings, a testament to the amount of degradation caused by blowline blending.

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     Initially, Methylene Diphenyl Diisocyanate (MDI) was treated the same way as UF resin in MDF as customers have begun to look for alternatives to formaldehyde emitting resins. Over time, the industry is coming to understand that MDI is physically different from UF based resins. It is much easier to spread MDI resin on fiber than UF resin, particularly...