聚丙烯（PP）作为一种耐高温、非交联的高性能绝缘材料，既可以提升高压直流电缆的工作温度，又能在达到使用寿命后回收利用，是高压直流电缆绝缘材料的理想选择。但纯PP材料的机械特性较差，抗老化性能较弱，故学者们进行了大量的研究以改善其性能。目前PP的老化机理尚不明确，老化改性效果差，也没有针对性的老化模型，为此本文开展了聚丙烯直流电缆绝缘材料老化特性及机理的深入研究。 本文对纯PP材料进行了热老化、电老化及电热老化三种加速老化试验，探究了不同老化方式下PP机械性能与电气性能的老化规律。试验表明，在热老化和电热老化结束后PP的断裂伸长率劣化幅度大于10%，已经超过了国标要求。通过差示扫描热分析、红外光谱分析、空间电荷测量等测试，从微观层面上探究了PP材料在不同老化条件下的老化机理，揭示了热氧反应是热老化和电热老化的主要诱因，而在电老化则主要是由PP内部空间电场畸变造成的。为改善PP的机械特性和抗老化能力，通过共混改性的方式制备了聚丙烯/弹性体（PP/PBC）复合材料。PP/PBC的机械性能相对于PP有了较大的改善，但直流击穿场强却降低了9.6%。相同条件的加速老化试验后，PP/PBC在电老化及电热老化条件下机械特性和电气特性分别下降了14.8%和14.5%，均高于同等条件下PP性能衰减的幅度。差示扫描热分析、红外光谱分析、空间电荷测量等测试表明，加入PBC使得PP材料引入了更多浅陷阱，电老化及电热老化过程中空间电荷向材料内部渗透严重，使得材料内部老化场强更高，加剧了PP/PBC性能劣化的程度。为此进一步在PP/PBC中加入纳米ZnO，制备了PP/PBC/ZnO纳米复合材料。PP/PBC/ZnO纳米复合材料的直流击穿场强提升了9.2%，且相对于PP和PP/PBC而言，三种老化方式下机械性能和电气性能的劣化幅度均低于10%，体现出优异的抗老化能力。微观层面的分析表明，纳米ZnO的引入一方面提高了PP的结晶度，抑制了由高温引起的热氧反应；另一方面在界面处形成了大量的深陷阱，抑制了空间电荷向材料内部的扩散，从而对热老化、电老化和电热联合老化都有较强的抵抗能力。依据老化过程中机械特性的老化规律，建立了三种PP材料在不同老化条件下热老化模型、电老化模型以及电热联合老化模型。并据此对PP直流电缆在优化工况下的预期寿命进行了初步预测。在15kV/mm的工作场强下，使用PP/PBC/ZnO绝缘材料可使聚丙烯直流电缆能以120℃的工作温度运行30年。

Polypropylene (PP) is a kind of high-temperature resistant, non-crosslinked, high-performance insulation material. It can not only improve the working temperature of HVDC cable, but also be recycled after reaching the service life. Pure PP has poor mechanical properties and anti-aging performance, so scholars have conducted a lot of researches to improve its performance. Presently, the aging mechanism of PP is not clear, and the modification is poor. Besides, there is no aging models for PP. Therefore, this paper carried out an in-depth study on the aging characteristics and mechanism of PP DC cable insulation materials.In this paper, thermal aging, electrical aging and electrothermal aging tests were carried out on pure PP materials, and the aging rules of mechanical and electrical properties of PP after different aging tests were explored.The results showed that the deterioration of PP elongation at break after thermal aging and electric aging is greater than 10%, which has exceeded the national standard requirements.The aging mechanism of PP materials under different aging conditions was revealed by DSC, IR, space charge measurement and other tests. The results showed that the thermo-oxygen reaction was the main inducement of thermal aging and electrothermal aging, while the electrical aging was mainly caused by the distortion of the space electric field in PP.In order to improve the mechanical properties and anti-aging ability of PP, polypropylene/elastomer (PP/PBC) weas prepared by blending modification.Compared with PP, the mechanical properties of PP/PBC have been greatly improved, but the electrical properties have been reduced by 9.6%. After the accelerated aging tests under the same conditions, the mechanical and electrical properties of PP/PBC deteriorated by14.8% and 14.5%. Differential scanning thermal analysis, infrared spectrum analysis, space charge measurement and other tests showed that the addition of PBC added more shallow traps to PP, and the space charge penetration into the material was serious in the process of electric aging and electric thermal aging, which aggravated the deterioration of PP/PBC performance.Therefore, PP/PBC/ZnO nanocomposites were prepared by adding nano-ZnO into PP/PBC.The electrical properties of PP/PBC/ZnO nanocomposites have been greatly improved. Compared with PP and PP/PBC, the deterioration of mechanical properties and electrical properties of PP/PBC nanocomposites after the three aging tests were significantly reduced. The microscopic analysis showed that, the introduction of nano-ZnO could improve the crystallinity of PP and inhibit the thermal oxygen reaction caused by high temperature on the one hand.On the other hand, a large number of deep traps were formed at the interface, which inhibited the diffusion of space charge to the interior of the material, and thus had a strong resistance to thermal aging, electrical aging and electro-thermal combined aging.The thermal aging model, electrical aging model and electrothermal combined aging model of three PP materials under different aging conditions were established.Based on this, the life expectancy of PP DC cable under specific working conditions is preliminarily predicted.PP/PBC/ZnO insulation can be used to run the DC cable at 120℃ for 30 years with field strength of 15kV/mm.