Reducing formaldehyde emission of urea formaldehyde-bonded particleboard by addition of amines as formaldehyde scavenger
Introduction
As one of the wooden materials for buildings applications, particleboard is classified as reconstructed panels that are mainly used to manufacture furniture as well as for thermal and acoustic insulation [1]. Particleboard is one of the important major timber products in Malaysia. In the year 2017, the total revenue from the exportation of Malaysian major timber products was RM 23.2 billion [2]. Particleboard has contributed 1.88% of the total export value in 2017, which accounted for RM 437 million. The local production line in Asian countries, particularly Malaysia, is continuously influenced by the Japanese trends as Japan is a main and vital for demand of particleboard. Japanese Industrial Standard (JIS) has the most stringent standards in the world where only wood panels with emission level of F**** (≤0.3 mg/L) could be used unrestrictedly within the room, while the F*** (≤0.5 mg/L) and F** (≤1.5 mg/L) panels are only allowed provided that the room is spacious and have good ventilation [3]. According to Athanassiadou and Ohlmeyer [4], the respective emission level of F****, F*** and F** are more or less equivalent to European standard's SE0, E0 and E1.
Sick House Syndrome, a term derived from Sick Building System that was first recognised in the year of 1983 by World Health Organization as a medical condition, has been reported in residential houses and educational facilities throughout the world. The occupants experience various symptoms such as headache, nose and throat irritation and fatigue [5]. Formaldehyde, acetaldehyde, acetone and 2-ethyl-1-hexanol are the main indoor pollutants that were detected in buildings and are closely related to the occurrence of mucosal symptoms among users [6]. The formaldehyde levels present in indoor air are highly dependent on the formaldehyde sources, temperature, humidity and air exchange rate in the building. The main sources of indoor formaldehyde emission in the residential houses and educational facilities nowadays include wood floor finishes, wood-based products such as plywood, particleboard and medium density fiberboard, wallpaper and paints as well as cigarette smoke [7].
Urea formaldehyde is a major aminoplastic resins used for the fabrication of interior wood-based products due to its low cost and high reactivity [8]. A study by He et al. [9] revealed that urea formaldehyde (UF) resin is the main source that contributes to the formaldehyde emitted from wood-based panels. Urea and formaldehyde are highly reactive and could react rapidly to form a strong bond. Nevertheless, the reaction is reversible and therefore provides potential for long-term formaldehyde release [10]. Formaldehyde emits from formaldehyde-based adhesive bonded particleboard is mainly caused by the existence of unreacted free formaldehyde in the board. However, this type of release lasts only for a short period of time after manufacture. Another release mechanism that could continue throughout the entire working life of the board is through the hydrolysis of the aminoplastic bond when exposed to elevated temperature and relative humidity [11].
In the past decades, great effort in reducing formaldehyde emission from particleboard such as lowering the formaldehyde to urea (F/U) molar ratio in UF resin has been made. However, lowering F/U ratio inevitably lower the UF reactivity and subsequently, reduced the properties of the resulted panels [12]. In addition, lowering of F/U ratio has reached its limit when Maminski et al. [13] reported that the strength of joints made with UF resin with F/U ratio of 0.85 is 20% lower than the resin with an F/U ratio of about 1.1. To make matters worse, no significant reduction of formaldehyde emission was recorded. An additional amount of 15–20% of resin is needed in order to fulfill the performance standards. Although lowering F/U ratio is the most direct and economic method, other methods known to reduce formaldehyde emission including incorporation of formaldehyde catcher or scavenger, optimisation of processing parameters, and coating with nanoparticles modified water based varnish have also been adopted by several researchers [[14], [15], [16], [17]]. Recently, a study by Jiang et al. [18] has proved that particleboard thermally treated at mild temperature (50 or 60 °C) displayed significant reduction in formaldehyde emission. Ayrilmis et al. [19] incorporated microfibrillated cellulose (MFC) into different grades of urea formaldehyde (UF) resins (SE0, E0 and E1) and the formaldehyde emission of produced laminated veneer lumber (LVL) were determined. The results revealed that the modification by MFC only showed significant effect on SE0 grade UF resin in terms of formaldehyde emission reduction, while E0 and E1 grade UF resin did not indicate the same observation.
Various amine-based compounds such as urea, ammonia, melamine, dicyandiamide, and polyamides have been incorporated into formaldehyde-based resin to reduce its formaldehyde emission [20]. Nevertheless, studies on the addition of primary alkyl amines as formaldehyde scavenger are very limited. A study by Boran et al. [21] reported on the effectiveness of adding different amine compounds in the reduction of formaldehyde emission of medium density fiberboard bonded with urea formaldehyde (UF) resin. Another study by Ghani et al. [22] revealed that the addition of 1% propylamine into UF resin could reduce the formaldehyde emission of the particleboard from 0.7 mg/L to around 0.3 mg/L. Nevertheless, physical and mechanical properties of the produced particleboard were adversely affected. This study aims to produce UF-bonded particleboard with lower formaldehyde emission using three primary alkyl amines, namely methylamine, ethylamine and propylamine. The effects of incorporating different amines and dosages on the properties of urea formaldehyde resin were investigated. In addition, the mechanical, physical properties and formaldehyde emission of the resultant particleboard were also evaluated.
Section snippets
Preparation of materials
Rubberwood particles were obtained from a local particleboard plant, HeveaBoard Berhad, which is located in Gemas. The binding agents used in this study, urea formaldehyde (UF) resin type E1, was supplied by Aica Chemicals (M) Sdn. Bhd from Senawang. Three different types of amines, namely, methylamine, ethylamine and propylamine which were used as formaldehyde scavenger om this study were purchased from Evergreen Engineering & Resources. The hardener used in this study was ammonium sulphate
UF properties after addition of amines
Gelation time, viscosity, pH and free formaldehyde content of the UF resin after addition of different dosage of amines are listed in Table 1. The UF resin with the addition of 0.5, 0.7 and 1.0% of methylamine (M), ethylamine (E) and propylamine (P) were denoted as M0.5, M0.7, M1.0, E0.5, E0.7, E1.0, P0.5, P0.7 and P1.0, respectively.
The gelation time of the control UF resin was 65 s. After the addition of amines, the gelation time increased to a range of 240–306 s. Similarly, the viscosity of
Conclusion
This study examined the effects of incorporating of different amines into UF resin and its relation to the properties of the resultant particleboard. From the current study, amine-containing UF resin had higher pH values, gelation time and viscosity compared to the control UF resin. When the added amines react with the existing free formaldehyde in the UF resin, free formaldehyde content of the resin is reduced. Although TGA results showed that a fully cured amine-containing UF resins possess
Acknowledgement
This work was supported by the Research University Grant Scheme (RUGS) [grant numbers 9444600 & 9575500] and the Higher Institution Centre of Excellence (HICoE) [grant number 6369107].
References (50)
- et al.
A review of structural, thermo-physical, acoustical, and environmental properties of wooden materials for building applications
Build. Environ.
(2017) - et al.
Indoor environment pollutants and their association with sick house syndrome among adults and children in elementary school
Build. Environ.
(2018) - et al.
(2017) VOCs and aldehydes source identification in European office buildings – the OFFICAIR study
Build. Environ.
(2017) - et al.
Formaldehyde and VOC emissions at different manufacturing stages of wood-based panels
Build. Environ.
(2012) Urea–formaldehyde (UF) adhesive resins for wood
Int. J. Adhesion Adhes.
(1998)- et al.
Effects of urea-formaldehyde resin mole ratio on the properties of particleboard
Build. Environ.
(2007) - et al.
Influences of some factors on the formaldehyde content of particleboard
Build. Environ.
(2006) - et al.
Effect of some manufacturing variables on formaldehyde release from particleboard: relationship between different test methods
Build. Environ.
(2011) - et al.
Formaldehyde and volatile organic compound (VOC) emissions from particleboard: identification of odorous compounds and effects of heat treatment
Build. Environ.
(2017) - et al.
Formaldehyde emission and VOCs from LVLs produced with three grades of urea-formaldehyde resin modified with nanocellulose
Build. Environ.
(2016)