Abstract Understanding the ultrastructure and chemical characterization of pulp fibers is highly important in utilizing wood as a raw material in a wide scope of applications, such as forest biomass-based biorefineries and low-cost renewable materials. The observation of the ultrastructure is not possible without advanced microscopy and spectroscopy techniques. Therefore, this study focuses on exploring the ultrastructure of pulp fibers with helium ion microscopy (HIM) and scanning electron microscopy (SEM). For the analysis of chemical characterization in the pulp fibers, Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) were performed. For these studies, the pulp fiber samples were obtained mainly from three different wood species, i.e. spruce, birch and eucalyptus. They were received in the never dried state and dried with a critical point drier (CPD) to minimize pore collapse. The spectroscopy results showed a strong signal from crystalline cellulose and confirmed the absence of lignin after Kraft pulping and bleaching. However, with XPS about 2% of lignin was detected in eucalyptus pulp. The results obtained with the microscopy techniques are compared and indicating the nanofibril size, shape, surface roughness as well as their orientation in pulp fibers. To our knowledge, this is the first time that HIM is applied to study the ultrastructure of pulp fibers and compared against more conventional microscopy and spectroscopy techniques. The main differences between HIM and SEM were found to be related to the focusing and magnification. The individual nano- and microfibrils as well as their bundles were more easily visible with HIM than with SEM. Also, with HIM it was possible to get the total area in focus at once which was not the case with SEM. The increased understanding of the ultrastructure and chemical composition of wood pulp enhance the development of novel wood-based products and processes for their manufacture.

中文翻译：

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纸浆纤维的化学表征和超微结构研究

摘要 了解纸浆纤维的超微结构和化学特性对于在广泛的应用中利用木材作为原材料非常重要，例如基于森林生物质的生物精炼厂和低成本的可再生材料。如果没有先进的显微镜和光谱技术，就不可能观察到超微结构。因此，本研究的重点是利用氦离子显微镜（HIM）和扫描电子显微镜（SEM）探索纸浆纤维的超微结构。为了分析纸浆纤维的化学特性，进行了拉曼光谱、傅里叶变换红外光谱 (FT-IR) 和 X 射线光电子能谱 (XPS)。对于这些研究，纸浆纤维样品主要来自三种不同的木材种类，即云杉、桦木和桉树。它们以从未干燥的状态接收并用临界点干燥器 (CPD) 干燥以最大限度地减少孔隙塌陷。光谱结果显示来自结晶纤维素的强信号并证实在牛皮纸制浆和漂白后没有木质素。然而，使用 XPS 在桉树浆中检测到大约 2% 的木质素。用显微镜技术获得的结果进行了比较，并表明了纳米原纤维的尺寸、形状、表面粗糙度以及它们在纸浆纤维中的取向。据我们所知，这是 HIM 首次应用于研究纸浆纤维的超微结构，并与更传统的显微镜和光谱技术进行比较。发现 HIM 和 SEM 之间的主要区别与聚焦和放大倍数有关。使用 HIM 比使用 SEM 更容易看到单个纳米和微原纤维以及它们的束。此外，使用 HIM 可以立即获得整个区域的焦点，而 SEM 则不是这种情况。对木浆超微结构和化学成分的深入了解促进了新型木基产品及其制造工艺的开发。