Abstract Recently, epoxy resins with outstanding cryogenic performance have attracted much attention for low-cost space exploration. Since the structure-property relationship is the foundation of materials design, the present study investigates the effect of the stoichiometric ratio of active-hydrogen to epoxy-group ([H]/[E]) on the crosslinked network structure and cryogenic properties of a polyurethane modified epoxy resin (PUE). The average molecular weight (Mc) and integrity of the crosslinked network structure in PUE thermosets are studied by dynamic mechanical analysis and FTIR. Cryogenic properties including the coefficient of thermal expansion (CTE) and tensile properties of all PUE thermosets are determined. The results show that increasing the [H]/[E] stoichiometric ratio from 0.7 to 1.3 can decrease the Mc of PUE thermosets cured at low temperature. The crosslinked network structure of PUE thermosets with lower Mc possesses smaller CTE. The tensile strength of the thermosets at 77 K is increased to about 105 MPa when the [H]/[E] stoichiometric ratio reaches 1.3. And appropriately excessive content of curing agent is necessary to get optimum mechanical properties at RT and 77 K for these low-temperature cured PUE thermosets. Finally, the influence of the [H]/[E] stoichiometric ratio on the fracture mechanism of PUE thermosets is discussed in terms of the morphological characteristic of the propagation zones on the fracture surface of the tensile samples as well.

中文翻译：

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化学计量比对低温固化环氧树脂交联网络结构和低温性能的影响

摘要 近年来，具有优异低温性能的环氧树脂在低成本太空探索中备受关注。由于结构-性能关系是材料设计的基础，本研究研究了活性氢与环氧基的化学计量比 ([H]/[E]) 对交联网络结构和低温性能的影响。聚氨酯改性环氧树脂（PUE）。通过动态力学分析和 FTIR 研究了 PUE 热固性材料中交联网络结构的平均分子量 (Mc) 和完整性。低温特性包括所有 PUE 热固性材料的热膨胀系数 (CTE) 和拉伸特性。结果表明，将 [H]/[E] 化学计量比从 0.7 增加到 1。3 可以降低低温固化PUE热固性材料的Mc。具有较低 Mc 的 PUE 热固性材料的交联网络结构具有较小的 CTE。当 [H]/[E] 化学计量比达到 1.3 时，热固性塑料在 77 K 下的拉伸强度增加到约 105 MPa。对于这些低温固化的 PUE 热固性材料，需要适当过量的固化剂含量才能在 RT 和 77 K 下获得最佳机械性能。最后，从拉伸样品断裂面上扩展区的形态特征讨论了[H]/[E]化学计量比对PUE热固性塑料断裂机理的影响。当 [H]/[E] 化学计量比达到 1.3 时，热固性塑料在 77 K 下的拉伸强度增加到约 105 MPa。对于这些低温固化的 PUE 热固性材料，需要适当过量的固化剂含量才能在 RT 和 77 K 下获得最佳机械性能。最后，从拉伸样品断裂面上扩展区的形态特征讨论了[H]/[E]化学计量比对PUE热固性塑料断裂机理的影响。当 [H]/[E] 化学计量比达到 1.3 时，热固性塑料在 77 K 下的拉伸强度增加到约 105 MPa。对于这些低温固化的 PUE 热固性材料，需要适当过量的固化剂含量才能在 RT 和 77 K 下获得最佳机械性能。最后，从拉伸样品断裂面上扩展区的形态特征讨论了[H]/[E]化学计量比对PUE热固性塑料断裂机理的影响。