Spruce wood specimens were bonded with one-component polyurethane (PUR) and urea-formaldehyde (UF) adhesive, respectively. The adhesion of the adhesives to the wood cell wall was evaluated at two different locations by means of a new micromechanical assay based on nanoindentation. One location tested corresponded to the interface between the adhesive and the natural inner cell wall surface of the secondary cell wall layer 3 (S3), whereas the second location corresponded to the interface between the adhesive and the freshly cut secondary cell wall layer 2 (S2). Overall, a trend towards reduced cell wall adhesion was found for PUR compared to UF. Position-resolved examination revealed excellent adhesion of UF to freshly cut cell walls (S2) but significantly diminished adhesion to the inner cell wall surface (S3). In contrast, PUR showed better adhesion to the inner cell wall surface and less adhesion to freshly cut cell walls. Atomic force microscopy revealed a less polar character for the inner cell wall surface (S3) compared to freshly cut cell walls (S2). It is proposed that differences in the polarity of the used adhesives and the surface chemistry of the two cell wall surfaces examined account for the observed trends.

中文翻译：

---

使用纳米压痕评估木材细胞壁粘附的基本位置依赖性差异

云杉木试样分别用单组分聚氨酯 (PUR) 和脲醛 (UF) 粘合剂粘合。通过基于纳米压痕的新微机械分析，在两个不同位置评估了粘合剂对木材细胞壁的粘附。测试的一个位置对应于粘合剂和次生细胞壁层 3 的天然内细胞壁表面之间的界面（S3），而第二个位置对应于粘合剂和新切割的次生细胞壁层 2 之间的界面（S2 ）。总体而言，与 UF 相比，PUR 有降低细胞壁粘附的趋势。位置分辨检查显示 UF 对新切割的细胞壁 (S2) 具有极好的粘附力，但对内细胞壁表面 (S3) 的粘附力显着降低。相比之下，PUR 对内细胞壁表面的粘附性更好，对新切割的细胞壁的粘附性较差。与新鲜切割的细胞壁 (S2) 相比，原子力显微镜显示内细胞壁表面 (S3) 的极性较小。建议所用粘合剂的极性和所检查的两个细胞壁表面的表面化学的差异解释了观察到的趋势。