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Douglas-fir (Pseudotsuga menziesii) has distinctly colored heartwood as a result of extractive deposition during heartwood formation. This is known to affect natural durability and treatability with preservatives, as well as other types of wood modification involving infiltration with chemicals. The distribution of extractives in sapwood and heartwood of Douglas-fir was studied using fluorescence microscopy. Several different types of extractive including flavonoids, resin acids, and tannins were localized to heartwood cell walls, resin canals, and rays, using autofluorescence or staining of flavonoids with Naturstoff A reagent. Extractives were found to infiltrate the cell walls of heartwood tracheids and were also present to a lesser extent in sapwood tracheid cell walls, especially in regions adjacent to the resin canals. Förster resonance energy transfer measurements showed that the accessibility of lignin lining cell wall micropores to rhodamine dye was reduced by about 50%, probably as a result of cell wall-bound tannin-like materials which accumulate in heartwood relative to sapwood, and are responsible for the orange color of the heartwood. These results indicate that micro-distribution of heartwood extractives affects cell wall porosity which is reduced by the accumulation of heartwood extractives in softwood tracheid cell walls.

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Rationale A combination of stable carbon (δ13C) and hydrogen (δ2H) isotope ratios and carbon content (% C) was evaluated as a rapid, low‐cost analytical approach to authenticate bioplastics, complementing existing radiocarbon (14C) and Fourier transform infrared (FTIR) analytical methods. Methods Petroleum‐ and bio‐based precursor materials and in‐market plastics were analysed and their δ13C, δ2H and % C values were used to establish isotope criteria to evaluate plastic claims, and the source and biocontent of the samples. 14C was used to confirm the findings of the isotope approach and FTIR analysis was used to vertify the plastic type of the in‐market plastics. Results Distinctive carbon and hydrogen stable isotope ratios were found for authentic bio‐based and petroleum‐based precursor plastics, and it was possible to classify in‐market plastics according to their source materials (petroleum, C3, C4, and mixed sources). An estimation of C4 biocontent was possible from a C4‐petroleum isotope mixing model using δ13C which was well correlated (R2 = 0.98) to 14C. It was not possible to establish a C3‐petroleum isotope mixing model due to δ13C isotopic overlap with petroleum plastics; however, the addition of δ2H and % C was useful to evaluate if petroleum‐bioplastic mixes contained C3 bioplastics, and PLS‐DA modelling reliably clustered each plastic type. Conclusions A combined dual stable isotope and carbon content approach was found to rapidly and accurately identify C3 and C4 bio‐based products from their petroleum counterparts, and identify instances of petroleum and bio‐based mixes frequently found in mislabelled bioplastics. Out of 37 in‐market products labelled as bioplastic, 19 were found to contain varying amounts of petroleum‐based plastic and did not meet their bio‐based claims.