桐油悬挂链辅助的高强自主愈合弹性体设计及其性能优化

Design of mechanically robust self-healing elastomers based on tung oil-derived dangling chains

为进一步优化自愈材料的力学性能和修复能力,着眼于如何利用天然可再生的林业生物质原料设计制备出兼具高强度与快速自愈效能的新型弹性体材料。以木本油脂——桐油为原料,通过高效氨解反应制备了反应型功能单体(TOD),将其作为“软段”构筑了系列含悬挂链和动态共价键的热塑性聚氨酯弹性体。进一步利用TOD脂肪酸链中共轭双键的氧化交联特性,通过在合成过程中热诱导其自发形成桥接网络结构,最终获得高强度自主愈合材料。采用核磁共振氢谱(~1H NMR)和傅里叶变换红外光谱(FT-IR)确定了TOD单体的化学结构,并证实了其在合成终点后的有效交联,从而贡献体系的机械性能,拉伸强度可达16.16 MPa,断裂应变为1 318%。对弹性体热力学性能分析表明,TOD的引入会显著提升聚合物的玻璃化转变温度,保证材料稳定的力学性能,同时与动态二硫键协同作用实现弹性体在室温环境下的高效自主愈合。制备的薄膜在室温愈合24 h后的愈合效率可达95.4%(以应力为参照)。结果表明:桐油悬挂链的非对称结构能够打破分子链的规整度,进而诱导二硫键在室温下更加快速地复分解,促使材料自愈。此外,由于体系中动态键合结构的存在,交联型聚氨酯在加工温度下表现出优异的热回收利用性能。经过验证,弹性体在多次物理回收后机械性能与初始值保持一致,未出现显著降低。这为木本油脂的高值化利用提供了一种新方法,并丰富现有高性能功能弹性体增强理论体系,也说明,油脂基功能型聚氨酯弹性体具有广阔的应用前景。

In order to optimize the mechanical properties and repair ability of self-healing materials,this study focused on how to design and prepare new elastomers with high strength and rapid self-healing performance using natural and renewable forestry biomass raw materials.To this end,a series of thermoplastic polyurethane elastomers containing suspended chains and dynamic covalent bonds were constructed using woody oil-based tung oil as a raw material,and reactive functional monomer(TOD) through the efficient ammonolysis reaction as a “soft segment”.By utilizing the self-healing properties of conjugated double bonds in the side chains of TOD fatty acids,the self-conjugated double bonds in the side chains of fatty acids were further exploited to form multiple cross-linked structures by simple thermal processing to obtain robust self-healing materials.The chemical structure of TOD monomer was determined by the ~1H nuclear magnetic resonance(~1H NMR),Fourier transform infrared(FT-IR) measurements,and its effective chemical cross-linking after thermal processing was confirmed,thus contributing to the enhancement of the mechanical properties of the system,with tensile strength up to 16.16 MPa and strain at break of 1 318%.Analysis of the thermomechanical properties of the elastomers showed that the introduction of a small amount of TOD would significantly increase the glass transition temperature(T_g) of polyurethanes containing dynamic disulfide bonds,ultimately achieving efficient healing of the polyurethanes in a room temperature environment while ensuring stable mechanical properties of the materials.The healing efficiency(with the stress as a reference) of the as-prepared films can be as high as 95.4% after 24 h of healing at room temperature,while the elastic recovery rate reaches 94.4%.The results showed that the asymmetric structure of the tung oil-derived dangling chain could break the regularity of the molecular chain,which in turn induced a more rapid metathesis of the disulfide bond at room temperature and contributed to the self-healing of the material.Owing to the presence of dynamic bond structure in the system,the obtained cross-linked elastomer exhibited stable re-processability at moderate temperature.It was verified that the mechanical properties of the elastomers remained consistent with the original values after several physical recycling and did not show any significant decrease.It is believed that this work opens new ideas for the high-value utilization of woody oils and is expected to enrich the theoretical system of high-performance elastomers.It was indicated that the oil-based functional polyurethane elastomers have a broad application prospect.