Abstract This work advances the development and use of sustainable polyurethane elastomers as green adhesives by providing insights into the mechanisms of humidity-induced changes on adhesive performance. Using a model adhesive prepared from equimolar ratios of castor oil and hexamethylene diisocyanate under facile reaction conditions, we show that the subtle changes in the chemical composition which occur with curing under different humidity environments significantly impact the cohesive integrity of the adhesives and, thus, their performances with different substrates. The curing chemistry was evaluated based on the isocyanate consumption, which was followed using Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry. Thermal, mechanical and adhesion properties were evaluated from thermogravimetric analysis, differential scanning calorimetry, rheology, tacking and lap shear tests. Moisture-cured adhesives were less covalently crosslinked, harder, more resistant to deformation, and recovered faster upon shear deformation compared to those cured otherwise. These mechanical properties complimented adhesive lap shear performance with substrates which formed covalent bonds during curing. For substrates with which covalent bonds could not form during curing, however, decreased internal cohesive integrity and associated increased hardness by urea formation resulted in poorer adhesive lap shear performance. This is contrary better tack performances obtained for the moisture-cured adhesives, attributed to their increased polarity and the energy dissipating ability.

中文翻译：

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对湿度引起的模型蓖麻油衍生聚氨酯粘合剂整体性能变化机制的分子见解

摘要 这项工作通过深入了解湿度引起的粘合剂性能变化机制，推动了可持续聚氨酯弹性体作为绿色粘合剂的开发和使用。使用由等摩尔比的蓖麻油和六亚甲基二异氰酸酯在易反应条件下制备的模型粘合剂，我们表明在不同湿度环境下固化时发生的化学成分的细微变化显着影响粘合剂的内聚完整性，因此，它们的不同基材的性能。根据异氰酸酯消耗量评估固化化学，然后使用傅立叶变换红外光谱和差示扫描量热法进行跟踪。通过热重分析评估热、机械和粘合性能，差示扫描量热法、流变学、粘性和搭接剪切测试。与其他方式固化的粘合剂相比，湿固化粘合剂的共价交联程度较低，更硬，更耐变形，并且在剪切变形后恢复得更快。这些机械性能与在固化过程中形成共价键的基材的粘合剂搭接剪切性能相得益彰。然而，对于固化过程中无法形成共价键的基材，降低的内部内聚完整性和相关联的因尿素形成而增加的硬度导致较差的粘合剂搭接剪切性能。这与湿固化粘合剂获得的更好的粘性性能相反，归因于它们增加的极性和能量耗散能力。与其他方式固化的粘合剂相比，湿固化粘合剂的共价交联程度较低，更硬，更耐变形，并且在剪切变形后恢复得更快。这些机械性能与在固化过程中形成共价键的基材的粘合剂搭接剪切性能相得益彰。然而，对于固化过程中无法形成共价键的基材，降低的内部内聚完整性和相关联的因尿素形成而增加的硬度导致较差的粘合剂搭接剪切性能。这与湿固化粘合剂获得的更好的粘性性能相反，归因于它们增加的极性和能量耗散能力。与其他方式固化的粘合剂相比，湿固化粘合剂的共价交联程度较低，更硬，更耐变形，并且在剪切变形后恢复得更快。这些机械性能与在固化过程中形成共价键的基材的粘合剂搭接剪切性能相得益彰。然而，对于固化过程中无法形成共价键的基材，降低的内部内聚完整性和相关联的因尿素形成而增加的硬度导致较差的粘合剂搭接剪切性能。这与湿固化粘合剂获得的更好的粘性性能相反，归因于它们增加的极性和能量耗散能力。这些机械性能与在固化过程中形成共价键的基材的粘合剂搭接剪切性能相得益彰。然而，对于固化过程中无法形成共价键的基材，降低的内部内聚完整性和相关联的因尿素形成而增加的硬度导致较差的粘合剂搭接剪切性能。这与湿固化粘合剂获得的更好的粘性性能相反，归因于它们增加的极性和能量耗散能力。这些机械性能与在固化过程中形成共价键的基材的粘合剂搭接剪切性能相得益彰。然而，对于固化过程中无法形成共价键的基材，降低的内部内聚完整性和相关联的因尿素形成而增加的硬度导致较差的粘合剂搭接剪切性能。这与湿固化粘合剂获得的更好的粘性性能相反，归因于它们增加的极性和能量耗散能力。