The impact of formaldehyde on human health causes great concerns nowadays. As it was one of the cheapest cross linking agents and a by-product of bio-process, finding an adhesive or resin product or material without formaldehyde and its derivatives is very challenging. Thus, one has to use a systematic method to work out the issue of reducing formaldehyde emission. However, as more people understand the challenge of reducing formaldehyde emission and endorsing the cost increase in developing new products with no or low formaldehyde emission, it provides a great opportunity to upgrade product line and develop new products.
In this project, bio-polymer, epoxy, polyvinyl acetate (PVA), urea formaldehyde (UF), phenol formaldehyde (PF), melamine urea formaldehyde (MUF), diphenylmethane diisocyanate (pMDI) resins and a new resin formulation developed at Mississippi State University (MSU) together with bio-based resins derived from bark, soy bean protein, lignin and wood have been tested. Epoxy, MSU, MUF, PF, pMDI, PVA, UF resins and soy bean protein and bark based PF resins were used for panel performance evaluation.
PVA and epoxy resins did not show any advantages in panel performance. MSU resin has potential in reducing panel free formaldehyde emission. PF resin will help improve panel modulus of elasticity (MOE) and modulus of rupture (MOR), thickness swelling (TS), water absorption (WA) and linear expansion (LE). It was found that MSU, MUF, PF and MDI resins offer great possibilities for medium density fiberboard (MDF) and particleboard applications.
A commercially available MUF resin was found especially suitable for particleboard application, in terms of low free formaldehyde emission and panel strength.
Mixing MDI with UF resin in particleboard application has potentially in improving panel internal bond strength (IB), MOE, and MOR performances and reducing panel TS and LE. It also has the potential to improve panel productivity.
A new three-layer with high surface or face moisture content (MC) concept was developed in this project. This concept was evaluated using different types of panel, especially high density fiberboard (HDF), MDF, and particleboard. The following variables were evaluated: UF face resin contents, panel face layer MC contents, MDI resin contents in panel core layer, hot press times, hot press temperatures, panel face and core ratio and types of face resins. At 11.1 mm (7/16 inch) panel thickness, the concept can mainly be applied successfully in making particleboard panels at a face:core ratio of 40:60, at 6% resin in face and 9% resin in core layers, with UF, PF, MDI, a combination of UF and MDI and a combination of UF, MDI and PF resins, with face MC up to 20% and core MC 6%, hot pressed at 180°C and 130 seconds. The particleboard panels made had improved panel performance, especially in terms of surface quality, when compared with panels made using conventional processing. To better use the concept, resins with hydrolysis resistance may be required.
Further, the three-layer with high face MC process concept was used to make HDF without resin in face layers. The same concept has also been applied to MDF panel manufacturing. It was found that the concept can be more easily adopted with MDI resin in MDF operation. With high MC in the face and with a small amount of resin in the core layer, one should be able to make HDF to meet the performance requirement. Generally, the experiment has shown that the new process concept has big potential in reducing panel operation cost with improved performance.
It was recommended that FPInnovations should do further work with the panel industry to allow the research results to be transferred to industry as soon as possible. Any resin with a renewable feature has great potential. Bark and wood should be considered first throughout the process to convert soy bean protein, wood and bark into resin or parts of resin.