Coloring of massive wood is still a major challenge in high-end wood processing, which aims to provide solid wood at a broad range of colors to furniture manufacturers. Here we report that water-saturation of supercritical carbon dioxide (scCO₂)—a promising green dyeing medium—greatly improves solid wood dyeing. This has been demonstrated for disperse blue 134 and three European hardwood species, namely, birch (Betula pendula), beech (Fagus sylvatica), and oak (Quercus robur). Variation of dyeing temperature (45–100 °C) and pressure (10.0–30.0 MPa) revealed that 20.0 MPa and 100 °C pose an optimal parameter combination. Coloration of the interior of small wood cubes (2 cm³), expressed as ΔE color change within the CIELAB color space, was here 40.6 (±1.2) for birch, 28.7 (±3.1) for beech, and 16.3 (±4.4) for oak. Since these values are significantly higher compared to water-free scCO₂, it can be concluded that water—even if poorly soluble in scCO₂—was effectively transported throughout the semiporous wood matrices. This causes the latter to swell, which efficiently improves the accessibility of individual cell wall constituents by dyeing reagents, for example. Three-point bending tests indicate that water-saturated scCO₂ dyeing effectuates some morphological or chemical alterations to the wood structure, since a moderate loss of both flexural strength and stiffness (15–20%) was found. Nevertheless, the proposed approach which can be adapted to a broad variety of biobased materials represents a green, sustainable, and highly versatile process, as it is free of organic solvents and waste products.

中文翻译：

---

木材在水饱和超临界二氧化碳中的无溶剂染色

大块木材的着色仍是高端木材加工中的主要挑战，高端加工旨在为家具制造商提供各种颜色的实木。在这里，我们报告说，超临界二氧化碳（scCO ₂）的水饱和-一种很有前途的绿色染色介质-大大改善了实木染色。分散蓝色134和三种欧洲硬木物种，即桦木（Betula pendula），山毛榉（Fabus sylvatica）和橡木（Quercus robur）的效果已得到证明。染色温度（45–100°C）和压力（10.0–30.0 MPa）的变化表明20.0 MPa和100°C是最佳的参数组合。小木块（2 cm ³）内部的着色，表示为ΔECIELAB颜色空间内的颜色变化，桦木为40.6（±1.2），山毛榉为28.7（±3.1），橡木为16.3（±4.4）。由于与无水的scCO ₂相比，这些值要高得多，因此可以得出结论，即使难溶于scCO _2的水也可以有效地输送到整个半孔木材基质中。这导致后者膨胀，例如通过染色试剂有效地改善了单个细胞壁成分的可及性。三点弯曲测试表明，水饱和的scCO ₂染色会影响木材结构的某些形态或化学变化，因为发现弯曲强度和刚度均适度降低（15-20％）。然而，由于该方法不含有机溶剂和废品，因此可以适用于多种生物基材料，它代表了一种绿色，可持续和高度通用的方法。