Non-destructive detection of density and moisture content of heartwood and sapwood based on X-ray computed tomography (X-CT) technology

Density and moisture content (MC) are two of the most important wood performance indexes, which are highly correlated with many other physical and mechanical properties of wood. X-ray computed tomography (X-CT) technology was used to analyze the difference in the CT number of the heartwood and sapwood of Chinese white poplar (Populus tomentosa) and Masson pine (Pinus massoniana) under different MC. Additionally, the fitted models of CT number-density and CT number-MC were established and validated for the heartwood and sapwood of P. tomentosa and P. massoniana. The methodological improvement has been described in detail regarding the established models, which are contrasted and discussed with previous models. The results showed that the CT number-density fitted models of the heartwood and sapwood of P. tomentosa and P. massoniana adopted the linear model: \( D = k \times H + b \), where D is the density, H is the CT number, k is the slope, and b is the intercept. R² values obtained in the validation models were all higher than 0.98, indicating that the CT number-density fitted models can reliably predict wood density. The CT number-MC fitted models for the heartwood and sapwood of P. tomentosa and P. massoniana adopted the logarithmic model: \( M = \ln ((a + b \times H)^{100} ) \), where M is the MC, H is the CT number, and a and b are the correlation coefficients in the model. R² values obtained in the validation models were all higher than 0.95, indicating that this model is valid for the accurate prediction of wood MC. The fitted model parameters of heartwood and sapwood indicated that the X-CT technology was effective for identifying the difference in density and MC of heartwood and sapwood. Therefore, it is feasible to use non-destructive testing technology when studying density and MC of heartwood and sapwood based on X-CT technology. The study results provide reference data for the non-destructive testing of wood properties and reasonable utilization.