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在250～400℃空气中对自由状态下对位芳纶进行等温热老化处理,采用万能材料试验机、红外光谱法、广角X射线衍射法、声速法和特性黏数法表征了老化过程中力学性能和结构的变化.结果表明,在老化初期,由于分子链的解取向,强度随时间快速下降;随后的热分解使强度随老化时间继续降低,符合二级反应动力学模型,其热老化表观活化能为32.4kJ/mol.老化样品的强度随温度升高显著下降,但高于350℃时热交联反应变得明显,同时结晶度增大和结晶结构完善,使强度的损失速率减小.老化样品的模量随老化温度的升高而增大,低于350℃时,非晶态分子链的解取向占优,模量较未热老化样品低;升高至350℃时,结晶结构完善占优,表现在第二类晶格畸变参数降低、表观微晶尺寸增大,特别是微晶横向融合使a,b轴方向尺寸显著增大,模量明显高于未老化样品.
The isoprenoid aging of para-aramid in free state was carried out in the air at 250 ~ 400 ℃. The properties of the aramid during aging were characterized by a universal testing machine, infrared spectroscopy, wide-angle X-ray diffraction, Mechanical properties and structural changes.The results show that in the early aging, the intensity decreases rapidly with time due to the orientation of the molecular chains. The subsequent thermal decomposition decreases the strength with the aging time, which accords with the second-order kinetics model, the thermal aging The apparent activation energy was 32.4 kJ / mol. The strength of aged samples decreased significantly with increasing temperature, but the cross-linking reaction became obvious when the temperature was higher than 350 ℃, while the crystallinity increased and the crystal structure was perfect. The modulus of aged samples increases with the increase of aging temperature. When the temperature is lower than 350 ℃, the solution orientation of amorphous molecular chains is dominant and the modulus is lower than that of non-aged samples. When the temperature is up to 350 ℃, Crystal structure perfection dominated, the performance of the second type of lattice distortion parameter decreases, the apparent crystallite size increases, especially the microcrystalline transverse fusion so that a, b axis direction size significantly increased modulus was significantly higher than the unaged samples .