Abstract：
Nanocelluloses are emerging as natural materials with favourable properties for coating industry and can be applied by state-of-the-art spraying technology. While additional functionalities are commonly introduced through chemical modification, the surface microstructuring of nanocellulose coatings with high throughput methods remains unexplored. Here, a femtosecond laser is used for texturing spray-coated coatings made of cellulose nanofibrils (CNF) or cellulose nanocrystals (CNC). For coating thickness of 1.5 to 8 μm, processing limits were determined with maximum ablation energy linearly increasing with coating thickness and minimum ablation energy decreasing or increasing depending on the apparent coating density. Within applicable processing window of pulse rate and power setting, the operational ranges were determined for creating one-dimensional and two-dimensional surface patterns, requiring a higher laser energy for CNC compared to CNF coatings and yielding thinnest possible resolved patterns of 17 μm as determined by the laser spot diameter. The laser ablation under low energy corresponds to an increase in surface roughness and intensifies surface hydrophilicity, while the line patterns are able to pin water droplets with rising water contact angles up to 90°. Present feasibility study opens future possibilities for managing surface properties of nanocellulose coatings in applications where tuning of surface hydrophilicity is required.
摘要：
纳米纤维素作为天然材料正在出现，具有涂料行业的有利性能，可以通过最先进的喷涂技术应用。虽然通常通过化学修饰引入额外的官能团，具有高通量方法的纳米纤维素涂层的表面微结构化仍未开发。这里,飞秒激光用于纹理化由纤维素纳米原纤维(CNF)或纤维素纳米晶体(CNC)制成的喷涂涂层。对于1.5至8μm的涂层厚度，确定加工极限，最大烧蚀能量随涂层厚度线性增加，最小烧蚀能量根据表观涂层密度而减少或增加。在脉冲速率和功率设置的适用处理窗口内，确定了创建一维和二维表面图案的操作范围，与CNF涂层相比，CNC需要更高的激光能量，并产生最薄的可能分辨的17μm图案，由激光光斑直径确定。低能量下的激光烧蚀对应于表面粗糙度的增加，并增强表面亲水性，而线条图案能够以高达90°的上升水接触角钉住水滴。目前的可行性研究为在需要调整表面亲水性的应用中管理纳米纤维素涂层的表面性能开辟了未来的可能性。
