This project offers a methodology for the analysis of resistographic profiles obtained from samples of wood and the extraction of precise data from these profiles. Tests were conducted on healthy samples of wood from six different species, as well as on “old” wood in use as part of timber structures with an age of 80-120 years. Based on the data collected using the resistograph, a series of variables was determined, and statistically analysed. An analysis of the data reveals the close relation between the resistographic variables and wood density (R2> 90%). Equally, in the case of healthy wood, an analysis of the defined variables permits the identification of the species of the sample with a very high probability and, therefore, its indirect resistance values.

Grading tests were performed on 338 poplar wood samples (Populus × euramericana I-214) with dimensions of 150×50 mm², 150×80 mm², and 200×100 mm² prepared for structural utilization. The non-destructive testing methods included ultrasound (Sylvatest) and induced vibrations (Portable Lumber Grader) combined with visual grading criteria. Additionally, screw withdrawal resistance was tested by the instrument Fakopp. These results were compared with those obtained by a four-point bending test according to the EN 408 (2004) standard. Ultrasound and induced vibrations overestimated the quality of this type of wood. Correlation equations are proposed to determine the true characteristics for each testing method. It can be concluded that poplar timber from clone I-214 has acceptable flexural strength, but a comparatively low elastic modulus, whereby it is not graded within a high strength class according to the EN 338 (2009) standard.

There is growing interest in the development of non-toxic, natural wood preservation agents to replace conventional chemicals. In this paper, the antifungal activities of silver nanoparticles, chitosan oligomers, and propolis ethanolic extract were evaluated against white-rot fungus Trametes versicolor (L.) Lloyd, with a view to protecting Populus spp. wood. In order to create a more realistic in-service type environment, the biocidal products were assessed according to EN:113 European standard, instead of using routine in vitro antimicrobial susceptibility testing methods. Wood blocks were impregnated with the aforementioned antifungal agents by the vacuum-pressure method in an autoclave, and their biodeterioration was monitored over 16 weeks. The results showed that treatments based on silver nanoparticles, at concentrations ranging from 5 to 20 ppm, presented high antifungal activity, protecting the wood from fungal attack over time, with weight losses in the range of 8.49% to 8.94% after 16 weeks, versus 24.79% weight loss in the control (untreated) samples. This was confirmed by SEM and optical microscopy images, which showed a noticeably higher cell wall degradation in control samples than in samples treated with silver nanoparticles. On the other hand, the efficacy of the treatments based on chitosan oligomers and propolis gradually decreased over time, which would be a limiting factor for their application as wood preservatives. The nanometal-based approach is thus posed as the preferred choice for the industrial treatment of poplar wood aimed at wood-based engineering products (plywood, laminated veneer lumber, cross-laminated timber, etc.).

Chitosan and chitosan oligomers are receiving increasing attention due to their antimicrobial properties. In the present study, they were assayed as a preventive treatment against white-rot decay of Populus wood (very important in economic and environmental terms), caused by Trametes versicolor fungus. Their capacity to incorporate different chemical species into the polymer structure with a view to improving their anti-fungal activity was also assessed by mixing oligo-chitosan with propolis and silver nanoparticles. The minimum inhibitory concentration of medium-molecular weight chitosan (MMWC), chitosan oligomers (CO), propolis (P), nanosilver (nAg), and their binary and ternary composites against T. versicolor was determined in vitro. Although all products exhibited anti-fungal properties, composites showed an enhanced effect as compared to the individual products: 100% mycelial growth inhibition was attained for concentrations of 2.0 and 0.2 mg·mL⁻¹ for the CO-P binary mixture, respectively; and 2 µg·mL⁻¹ for nAg in the ternary mixture. Subsequently, MMWC, CO, CO-P and CO-P-nAg composites were tested on poplar wood blocks as surface protectors. Wood decay caused by the fungus was monitored by microscopy and vibrational spectroscopy, evidencing the limitations of the CO-based coatings in comparison with MMWC, which has a higher viscosity and better adhesion properties. The usage of MMWC holds promise for poplar wood protection, with potential industrial applications.