Protein-Based Adhesives for Particleboards

The main objective of this study was to elucidate the possibilities to use wheat gluten (WG) as a binder for particleboards, as well as soy protein isolate (SPI). The focus was on the effect of the adhesive formulation and the processing conditions, while the press parameters were kept constant. Some aspects of the dispersion and the preparation of the dispersions that were investigated are: the dispersing agent (sodium hydroxide 0.1 M or citric acid 0.05 M), the time (1, 3 or 5h) to prepare the dispersion, the temperature (room temperature, 50 or 80°C) during the preparation of the dispersions and the effect of storing (1, 2.5 or 4 days) the dispersions before application. Additionally, utilization of cross-linker polyamidoamine-epichlorohydrin (PAAE) and trimethylolpropane triacetoacetate (AATMP) were evaluated. Furthermore, the utilization of green particles versus dried particles was examined. The concentration (12, 16, 20 or 24%) of WG dispersion and the process for applying it to the particles were studied. Two application methods were evaluated, in application method 1 (appl. 1) all the dispersion was added to the particles in one step before the particles were dried. When application method 2 (appl. 2) was employed the dispersion was added in two steps, some of the dispersion was added before the drying and some after the drying. The considered board properties were internal bond (IB), thickness swelling (TS) and water absorption (ABS). The wetting, penetration and film formation of the WG dispersions on the wood was investigated employing different microscopy techniques. For the WG dispersions it looks as if a lower temperature is preferable for the preparation of the dispersion and that the time to prepare the dispersion is of no importance. Furthermore, storing the dispersions for more than one day before it was used as an adhesive for particleboards (PB) resulted in poorer boards. Using the right cross-linker, such as PAAE enhances the binding abilities of WG. According to this study it is beneficial to use dried particles instead of green particles. Additionally, the results show that the interaction between the concentration of WG dispersion and how it is applied is a significant factor, considering the IB value. However, in general the two step process (appl. 2) is preferable. The microscopy study reveals that this can be explained by the balance between wetting, penetration, and flow of the dispersion on the wood. The two step application results in less over-penetration when the viscosity of the dispersion is low.QC 20151209