为了开发可持续和环保的材料,纤维素是合成聚合物的有希望的替代品。然而,天然纤维素,与许多合成聚合物相比,不能用传统技术熔融加工,因为,在加热时,它会在融化之前降解。一种提高纤维素热塑性的方法,纤维素纤维的形式,是通过化学改性,例如,二醇纤维素纤维。为了更好地理解这种改性纤维在熔融加工过程中分子相互作用的重要性,我们对不同改性程度的二醇纤维素纳米晶进行了分子动力学研究。我们研究了纳米晶体的结构以及它们在机械剪切过程中与相邻纳米晶体的相互作用,我们的模拟表明,压力,界面刚度,氢键网络,剪切过程中的纤维素构象高度依赖于改性程度,水晶之间的水层,和温度。通过以水作为增塑剂的纤维挤出,对样品中具有不同改性程度和/或含水量的二醇纤维素的熔融加工进行了实验研究。当增加样品中的改性程度和/或水含量时,熔融加工更容易。这与分子建模得出的结论一致。将天然纤维素改性为二醇纤维素后,测得的两种晶体之间的摩擦,在某些情况下,减半(与天然纤维素相比),并且随着温度的升高而降低。我们的结果表明,改性纳米纤维素纤维的分子模型可以提供有关这些材料的结构-性能关系的基本信息,因此对于开发新的纤维素基生物材料很有价值。
In the quest to develop sustainable and environmentally friendly materials, cellulose is a promising alternative to synthetic polymers. However, native cellulose, in contrast to many synthetic polymers, cannot be melt-processed with traditional techniques because, upon heating, it degrades before it melts. One way to improve the thermoplasticity of cellulose, in the form of cellulose fibers, is through chemical modification, for example, to dialcohol cellulose fibers. To better understand the importance of molecular interactions during melt processing of such modified fibers, we undertook a molecular dynamics study of dialcohol cellulose nanocrystals with different degrees of modification. We investigated the structure of the nanocrystals as well as their interactions with a neighboring nanocrystal during mechanical shearing, Our simulations showed that the stress, interfacial stiffness, hydrogen-bond network, and cellulose conformations during shearing are highly dependent on the degree of modification, water layers between the crystals, and temperature. The melt processing of dialcohol cellulose with different degrees of modification and/or water content in the samples was investigated experimentally by fiber extrusion with water used as a plasticizer. The melt processing was easier when increasing the degree of modification and/or water content in the samples, which was in agreement with the conclusions derived from the molecular modeling. The measured friction between the two crystals after the modification of native cellulose to dialcohol cellulose, in some cases, halved (compared to native cellulose) and is also reduced with increasing temperature. Our results demonstrate that molecular modeling of modified nanocellulose fibers can provide fundamental information on the structure-property relationships of these materials and thus is valuable for the development of new cellulose-based biomaterials.