Naturally occurring plant cellulose, our most abundant renewable resource, consists of fibers of long polymer chains that are tightly packed in parallel arrays in either of two crystal phases collectively referred to as cellulose I. During mercerization, a process that involves treatment with sodium hydroxide, cellulose goes through a conversion to another crystal form called cellulose II, within which every other chain has remarkably changed direction. We designed a neutron diffraction experiment with deuterium labelling in order to understand how this change of cellulose chain direction is possible. Here we show that during mercerization of bacterial cellulose, chains fold back on themselves in a zigzag pattern to form crystalline anti-parallel domains. This result provides a molecular level understanding of one of the most widely used industrial processes for improving cellulosic materials.

天然存在的植物纤维素是我们最丰富的可再生资源，由长聚合物链纤维组成，这些长聚合物链纤维紧密排列在两个晶相中的任何一个晶相中，统称为纤维素 I。在丝光处理过程中，该过程涉及用氢氧化钠处理，纤维素会转化为另一种称为纤维素 II 的晶体形式，其中所有其他链的方向都发生了显着变化。我们设计了一个带有氘标记的中子衍射实验，以了解纤维素链方向的这种变化是如何可能的。在这里，我们表明，在细菌纤维素的丝光化过程中，链以锯齿形模式向自身折叠，形成结晶反平行结构域。