Decreasing formaldehyde emission from medium density fiberboard panels produced by adding different amine compounds to urea formaldehyde resin
Introduction
Amino resins being used to bond composite wood products have an extremely important role in forest products, such as in medium density fiberboard (MDF), particleboard (PB), oriented strand board (OSB), and plywood (PW).
About 90% or more of the world's board production is made with urea formaldehyde (UF) resins [1]. UF resins, the most well-known amino resins, have many advantages such as low cost, ease of use under a wide variety of curing conditions, the fastest reaction time in hot press, water solubility, low cure temperatures, resistance to microorganisms and to abrasion, excellent thermal properties, and their colorless qualities, especially the cured resin compared to other resins. However, UF resins are not suitable to produce boards with good exterior exposure resistance. The biggest drawback of UF resins also is that they release formaldehyde into the environment during curing when they are used as a binder component [1], [2], [3], [4].
Many products were produced with formaldehyde based resins, which emitted formaldehyde vapor and lead to consumer dissatisfaction and health related complaints. These emissions have caused various symptoms, the most common of which are irritation in the eyes and the upper respiratory tract [5], [6], [7]. When the human body is exposed to formaldehyde in high doses there is a risk of serious poisoning, and prolonged exposure can lead to chronic toxicity and even cancer [8], [9]. For these reasons, regulatory pressure has recently reduced or eliminated formaldehyde emissions from wood products on a world-wide scale.
One of the common effective methods to decrease the formaldehyde content of resin is to change the mole ratio of formaldehyde to urea in UF resin. Several workers declared that the emission of formaldehyde from wood based panels lessened as the mole ratio decreases, the other physical and mechanical properties were adversely affected [10], [11], [12], [13]. The other method has been the use of chemical additives called formaldehyde scavengers to reduce formaldehyde emitted from wood based panels. The most common scavengers are compounds containing primary or secondary amine such as urea, ammonia, melamine, and dicyandiamide [14]. It is known that urea is extensively used to decrease formaldehyde emitted from wood based panels bonded with thermosetting adhesive. Other formaldehyde scavengers such as tannin, resorcinol, peroxides, and ammonia treatment are expensive and not very effective. The addition of urea to resin does not cause problems in particleboard production. However, the formaldehyde scavengers must be carefully used, and they will adversely affect all properties of these panels [15], [16], [17], [18].
On the other hand, Ebewele et al. [19], [20] determined that the water resistance and flexibility of long-chain aliphatic primary diamines were improved by better glue line stress distribution in the cured UF resin network. For this reason, it is possible that using some amine compounds might enhance the mechanical and physical properties of MDF panels. The purpose of this study is to evaluate the applicability of urea (US), propylamine (PAS), methylamine (MAS), ethylamine (EAS), and cyclopentylamine (CPAS) compounds to reduce the levels of released formaldehyde from MDF panels bound with UF resin. The effects of these amine compounds on the mechanical and physical properties of these MDF panels were also investigated.
Section snippets
Materials
Hardwood fibers of 85% and softwood fibers of 15% obtained from Çamsan A.Ş., Turkey were used in this study. These fibers were screened to remove bundles of fiber, and were then dried at 100 °C to obtain a 2–3% moisture content.
Mechanical properties of MDF panels
Since water in amine solution also added to the UF resin, fiber mats burst in pressing with PAS (1.4%), MAS (1.4%), and CPAS (1.2–1.4%). However, it did not burst with fiber mats for urea added to UF resin. Fig. 1 shows the values of the some mechanical properties of MDF panels produced with UF resin by adding different amine compounds.
When a US chemical was added to the UF resin, the MOR values of MDF panels decreased compared to control panels, as can be seen in Fig. 1. It was determined that
Conclusions
Some amine chemicals were used to decrease formaldehyde emitted from MDF panels in this study. As a result, the addition of CPAS chemical changing ratios to UF resin had considerably positive effects on the mechanical and physical properties of MDF panels, and ensured a reduction in the formaldehyde released from these panels. Using US chemical as a formaldehyde scavenger had less effect than other amine chemicals in terms of formaldehyde. In addition, the physical and mechanical properties of
Acknowledgment
This work was supported in part by the Research Foundation at Karadeniz Technical University under Grant 2005.113.002.1.
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