| Polymeric nanoparticles containing the fungicides tebuconazole and chlorothalonil were prepared with median diameters of ∼80 to ∼250 nm. The nanoparticles were prepared in high yield using a simple one-step emulsion preparation. The fungicides were dispersed within the nanoparticle matrix as a solid suspension. The nanoparticles were suspended in water and incorporated into southern yellow pine, a softwood, and birch, a hardwood, using conventional vacuum-pressure treatments. Biological tests confirmed that nanoparticle-treated pine and birch were effectively protected against Gloeophyllum trabeum and Trametes versicolor, common brown and white rot wood decay fungi, respectively. The release rate of the active ingredient (a.i.) was studied in water. The a.i. release rate was controlled by matrix polarity. The most hydrophilic matrix studied, polyvinylpyridine, released a.i. fastest, and the least hydrophilic matrix studied, polyvinylpyridine-co-styrene (30% styrene) released a.i. most slowly. The effect of nanoparticle porosity was also investigated by blending a hyperbranched polyester with polyvinylpyridine. The release rate increased with increased-branching, which was attributed to increased porosity, but the affect may have been the result of hydrolysis of the ester bonds in the hyperbranched polymer. Biological studies showed that the nanoparticle-treated wood was protected from fungal attack at appropriate levels of a.i. incorporation, but the efficacy did not correlate with the a.i. release rate. This suggested that the matrix plays some role in the biological efficacy beyond simply controlling the a.i. release.; The nanoparticle preparation method was shown to be versatile when two other commercial a.i.s, RH287 and chlorpyrifos, were able to be incorporated into nanoparticles with only minor procedural modifications. The method was also shown to be adaptable to a surfactant-free emulsion preparation method, which makes the use of nanoparticles in wood more industrially attractive. |
