Protein-based adhesives for particleboards

The aim of this study was to elucidate the possibilities of using soy protein isolate (SPI) and wheat gluten (WG) as binders for particleboards. One-layer particleboards were produced in laboratory scale. Parameters regarding the formulation of the adhesive and the gluing process were investigated, while the press parameters were kept constant. The considered factors were: the use of protein as a dispersion and/or as a dry protein powder, the temperature during the preparation of the dispersion, the time for preparing the dispersion, the storage time of dispersion prior to gluing, and the use of dried core particles or green particles. The board properties evaluated were: internal bond (IB), thickness swelling (TS) and water absorption (ABS). The results were statistically evaluated and SIMCA-P+ software was employed as a multivariate analyzing tool. The results show that protein adhesives can work as adhesive for particleboard. The results also reveal that it is preferable to use the dispersion as a binder rather than the dry protein. Furthermore, in the case of the SPI, the time for preparing the dispersion is a significant parameter; it appears that longer dispersion time results in enhanced board properties. According to the results, the temperature during the preparation does not seem to have any impact on the gluing properties of the SPI dispersions. On the other hand, in the case of WG dispersions, the temperature has an impact on the properties of the adhesive, favouring lower temperature, while the time is insignificant. Additionally, if the dispersion has been stored for more than 1 day before it is used, it results in boards with poorer mechanical and water resistance properties. The utilization of the green chips, instead of the dried core particles, is clearly a disadvantage, especially regarding the water resistance of the particleboards. It appears that SPI is superior to WG when it comes to the water resistance as well as the mechanical properties of the boards. However, it is not possible to compare these two proteins explicitly, since SPI contains a higher percentage of protein. Additionally, WG contains more starch, which is known to give poorer water resistance properties.