The use of p-MDI resin in MDF manufacture Tan, Rynehvee
Traditional manufacture of medium density fibreboard (MDF) involves the use of urea-formaldehyde (UF) resin as binder. After much study, formaldehyde emissions from this resin are found to cause negative health effects, that is, cancer, for humans and animals. Because of this, the Composite Panel Association recently published new lower limit on formaldehyde emissions, which made the use of UF resin costly from increasing the scavengers that minimize formaldehyde emissions from finished boards. MDF mills are now facing increased competitive pressure in keeping their emissions below the CARB Phase 2 limit and since then, different formaldehyde-free resins, may it be organic or synthetic, have been tried in place of UF resin. The use of polymeric methylene diphenyl diisocyanate (p-MDI) as binder for wood composite panels is not new. It is widely known as a binder for oriented strand board (OSB). MDF mills in Europe and North America are now converting their systems to use p-MDI to alleviate pressure from the new emission limit. p-MDI has a lot of benefits in the production process, and even though it is more expensive, its benefits have proven to outweigh the cost. Improvements on the product such as high internal bond strength, better MOE and MOR, additional moisture resistance, and less formaldehyde testing and monitoring are just some of the advantages in using p-MDI. This report concludes that despite these advantages, it is still important to understand how the resin reacts and cures when integrating this resin into a production process. It is necessary to have a gradual transition through multiple trials and document press settings and process modifications that produce on-spec MDF boards. When this is understood, the addition of catalyst and other additives that will improve the process can then be experimented on.
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