Chen Liang, Wu Lihui, Song Lixian, Xia Zhijie, Lin Yuanfei, Chen Wei, Li Liangbin
National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, 230029, China.
Nanoscale. 2020 Dec 23;12(48):24527-24542. doi: 10.1039/d0nr06003h.
The hierarchical structural evolution of natural rubber (NR) filled with different contents of nanoscale carbon black (CB) (10 phr-CB10 and 50 phr-CB50) after first loading and recovering for different times was investigated by X-ray nano-CT, wide-angle X-ray scattering (WAXS) and solid state NMR techniques. The CB filler structures as captured by X-ray nano-CT recover gradually with increasing recovering time, but the filler network with different CB contents shows dramatically different structure evolution. For CB10, limited by the filling content, CB particles mainly induces a hydrodynamic effect in spite of deformation or recovering. For CB50, the CB filler forms a 3D connected network, partially destructed during deformation, and the destructed part can be partially recovered during recovery. This suggests that the connected CB filler structure mainly acts as a network reinforcement, whereas the destructed part can induce a hydrodynamic effect. The different effects induced by different CB filling contents are also reflected by the NR matrix, which is reflected by the onset strains εc of strain-induced crystallization (SIC) of NR as captured by WAXS. For CB10, εc remains almost constant, i.e. εc = ca. 1.49, while that of NR with CB50 slightly decreases from initial ca. 1.12 to 0.96 with increasing recovering time up to 50 h. Also, the bound rubber fraction and entangled rubber network remain unchanged after deformation and under different recovery time as detected by the magic sandwich echo (MSE) FID and proton multiple quantum (MQ) NMR. These results demonstrate the key role of the CB filler network in determining the stress-softening behavior of reinforced rubber.
通过X射线纳米CT、广角X射线散射（WAXS）和固态核磁共振技术，研究了填充不同含量纳米级炭黑（CB）（10 phr-CB10和50 phr-CB50）的天然橡胶（NR）在首次加载和不同时间恢复后的层次结构演变。X射线纳米CT捕获的CB填料结构随着恢复时间的增加而逐渐恢复，但不同CB含量的填料网络显示出截然不同的结构演变。对于CB10，受填充量的限制，CB颗粒无论在变形还是恢复过程中主要诱导流体动力学效应。对于CB50，CB填料形成三维连通网络，在变形过程中部分被破坏，并且被破坏的部分在恢复过程中可以部分恢复。这表明连通的CB填料结构主要起网络增强作用，而被破坏的部分可以诱导流体动力学效应。不同CB填充量引起的不同效应也反映在NR基体中，这通过WAXS捕获的NR应变诱导结晶（SIC）的起始应变εc来反映。对于CB10，εc几乎保持不变，即εc = 约1.49，而对于含有CB50的NR，随着恢复时间增加到50小时，其εc从初始的约1.12略微降低到0.96。此外，通过魔术夹心回波（MSE）FID和质子多量子（MQ）核磁共振检测，在变形后和不同恢复时间下，结合橡胶分数和缠结橡胶网络保持不变。这些结果证明了CB填料网络在决定增强橡胶的应力软化行为中的关键作用。
