基于成核剂自组装构筑木纤维表面枝状结构的木塑界面改善机制研究

Due to the large gap of polarity and surface free energy between wood and plastic, their interfacial wetting and adhesion are quite bad, leading to poor interfacial interaction, which is the key factor that restricts the development of high-performance composites. In this study, the self-assembly nucleating agent is applied as interfacial modifier for wood fiber/ polypropylene composite. On one hand, the nucleating agent can aggregate on wood fiber driven by hydrogen bonding; on the other hand, it acts as local nuclei and induce the crystallization of polypropylene. Thus, the nucleating agent plays the role of bridge between wood and plastic. Meanwhile, inspired by the structure of tree root, the self-assembly behavior of nucleating agent is regulated to construct branched root-like wood fibers, which inserts into the plastic (soil). As a result, mechanical interlocks between wood fiber and polypropylene can be formed, and the interfacial strength will be enhanced. This study mainly investigates the construction of the branched wood fiber, the formation of the interface between wood fiber and polypropylene, and the improvement of the properties of wood plastic composite. The relationships between interfacial microstructure，interfacial interaction and material properties are established. Finally, the mechanism of nucleating agent at the interface is revealed, which will provide scientific basis and fundamental support for the improvement of wood plastic composite interface and properties.

木材和塑料由于极性和表面自由能相差较大，二者复合时界面润湿和黏合较差，不能形成良好的界面结合，成为制约木塑复合材料性能提高的瓶颈。本项目采用具有自组装特性的成核剂来改善木纤维/聚丙烯复合材料界面，该成核剂一方面可以依靠氢键结合到木纤维表面，另一方面提供晶核诱导聚丙烯附生结晶，从而在木塑之间起到桥梁作用，有助于形成良好的界面结合；同时，受树根结构的启发，调控成核剂自组装在木纤维表面构筑枝状结构（“树根”），穿插在聚丙烯（“土壤”）中，在木纤维与聚丙烯间形成牢固的互锁结构，显著提高两相界面强度。重点研究木纤维表面枝状结构的构筑、引入自组装成核剂后木纤维/聚丙烯复合界面的形成、木塑复合材料性能的改善，建立微观结构、界面结合、材料性能之间的关系，从而明确成核剂自组装对界面改善的作用机制。该研究成果将为木塑复合材料的界面改善和性能优化提供科学依据和理论基础。

针对木塑复合材料中木材和塑料界面相容性差的问题，本项目通过引入具有自组装特性的成核剂以期改善木塑界面结合，选取β型成核剂先对聚丙烯进行共混改性，然后与木纤维经过挤出、模压制备木塑复合材料。研究结果表明，引入成核剂能够高效诱导聚丙烯产生β晶型，在成核剂加量为0.05%时β晶相对含量可达到80%，同时成核剂的引入能够提高结晶速率和温度，加快结晶过程，使得晶体数量增加，晶体尺寸降低；另一方面，部分成核剂分子由于氢键作用会聚集在木纤维表面，通过改变成核剂种类和加量可调控其在木纤维表面的自组装拓扑形态形成枝状结构，进一步提供晶核诱导塑料进行附生结晶，从而增强了界面结合。基于以上两方面作用机理，引入成核剂后木塑复合材料的韧性、热变形温度、结晶速率显著提高，当成核剂用量为0.3%时，复合材料的冲击强度和断裂伸长率分别提高28%和40%。本研究成果为木塑复合界面增强和性能优化提供一种简便有效的新思路，明确了引入自组装成核剂对木纤维/塑料复合界面的作用机制，实现了木塑复合材料的增韧，并有助于缩短其加工周期。