Aqueous protein-containing polymeric emulsions from chemically modified thermosetting aliphatic polyketones were pre-pared in an one-pot process, by adding a given amount of soy protein to a polyketone-based emulsion. Several factors affecting the production, stability and performance of the emulsions as wood adhesives were studied. Emulsions containing proteins could be prepared at 45 and 40 wt% total solids contents, a composition not possible to achieve by just using a polyketone. The resulting emulsions were stable for at least two months at ambient temperature. The average particle size of the emulsions containing proteins was in almost all cases higher than the reference adhesive with no protein added except for the sample with 60 wt% protein intake from the sequential addition protocol. The viscosity of the protein-containing emulsions was higher than the one of the reference sample (no protein added) and it decreased in time. In agreement with these trends and with the results as a function of the addition protocol, a possible explanation of the role of the protein in the emulsion is proposed but needs further study (currently performed) to be confirmed.
From a practical point of view, all the prepared protein-containing emulsions passed the European standard (EN-314) wood test with higher shear strength than required. The presence of up to 40 wt% proteins in the basic adhesive formulation results in a slight increase of the average particle size as well as of the viscosity. This protein intake represents a kind of optimum for this system, thus allowing to substitute as much as possible of the unmodified PK with proteins and still retaining the same emulsion structure and stability as well as wood-adhesive performance. Furthermore, broader glue lines (improved glue penetration in the wood) were observed in the presence of proteins (i.e. with respect to the reference polyketone-based adhesive) in particular for systems with low solids contents, which can be prepared only when using proteins in the basic formulation.
The main advantage of using soy protein in the polyketone-base formulation is that the properties and performance as wood adhesive are not changed and that they could be prepared at different solids contents. Besides, the use of soy proteins is an advantage from economic point of view as it is low-cost filler. Research on the application of different types of proteins as well as other biomaterials in the polyketone-based wood adhesive is ongoing.