Nitrile rubber (NBR)/hydrogenated nitrile butadiene rubber (HNBR) blends with various ratios were compounded with internal mixer and two‐roll open mill. Mechanical properties and low‐temperature performance (TR10) of the NBR/HNBR blends after aging under different conditions were investigated. Furthermore, equilibrium swelling test and moving die rheometer (MDR) test were used to systematically investigate the effects of HNBR dosage on the crosslink densities and curing behaviors. Vulcanization torque and crosslink densities decreased with an increase in HNBR content. The crosslink density of pure HNBR is higher than that of pure NBR, which is related to the macromolecular structures of the rubber. Compression sets of the NBR/HNBR vulcanizates were correlated with HNBR dosage indicating a linear relationship. Low‐temperature performance of the NBR/HNBR blends was improved after being aged in the synthetic hydrocarbon hydraulic oils (SH‐1 and SH‐2). This work shows that the low‐temperature performance and oil resistance could be better balanced by blending NBR with HNBR, while the mechanical properties maintain relatively high level.
Equilibrium swelling and rheological tests were adopted to systematically investigate the effects of softener type and dosage on the crosslink densities. The results turned out that the chemical crosslink density could be distinguished from the physical crosslink density by comparing the results of equilibrium swelling and rheological tests. The liquid butadiene (LB) as a softener leads to the greatest reduction in crosslink density, followed by polyethylene wax (PW) and paraffinic oil (PO). The tensile strength decreases with increasing PO content while shows peak values with increase of LB and PW contents. The dependencies of chemical crosslink density on the aging time under 150°C are quite different for the three softeners, which can be expected from the double crosslinking networks consisting of small softener and large main crosslinking networks. Further investigation has been performed to correlate the tensile strength with chemical crosslink density of ethylene propylene diene monomer elastomer vulcanizates. Three different linear relationships can be obtained for the softeners independent of the aging time. It can now be expected from this study that the role of some new softeners in rubber compounds is not only confined to plasticization but also forms crosslinking networks in the peroxide‐cured rubbers.
Equilibrium swelling test is employed to study the swelling responses of natural rubber (NR) in various solvents, and to determine the total Hildebrand solubility parameter (δt) of NR. The three‐dimensional solubility parameters (HSP) of NR is obtained by virtue of software package as the result of being δd = 17.50 MPa1/2, δp = 3.20 MPa1/2, δh = 1.40 MPa1/2, and δt = 17.85 MPa1/2, respectively. The swelling ratio (q) is correlated with the energy difference (Ra) in order to deeply understand the swelling principle of NR, and the results turn out that q decreased with the increase of the Ra and it can be used to explain the abnormal swelling phenomena of methyl acetate and ethyl acetate. One of the possible applications of Ra is the prediction or explanation of diffusion behaviors of small liquids in the rubber matrix. Therefore, the diffusion coefficient (D) is calculated in accordance with the Fick's law model and attempted to correlate with the Ra value. Two qualitative relationships between D and Ra and χHSP can be preliminarily established now, which can provide an easy way to predict the diffusion behavior of fluids in rubber matrix.
In this work, effects of natural rubber (NR) content on the vulcanization and damping properties of chlorinated butyl rubber (CIIR) were studied. A new method to characterize the damping performance of the NR/CIIR blends by the rebound behavior of rubber ball was proposed. And an optical laser-based measurement was used to follow the movement of the rubber sample. The DMA results showed that better damping properties of the blends was obtained at higher proportion of CIIR in the blends at room temperature (20 C) and a frequency of 0.1-100 Hz. Furthermore, a propose
natriuretic peptide (BNP) was 548.4 pg/ml and gradually increased to 979.47 pg/ml. Comprehensive data suggest that the patient has cardiac insufficiency. Control of the ventricle rate to prevent stroke. Strictly control the 24-hour access volume to avoid water and sodium retention. Give medicines to strengthen the heart, diuresis, and improve heart function.On the 11th postoperative day, the patient had a sudden decrease in consciousness and a decrease in the muscle strength of the right limb (Grade II). Computed tomography showed low-density shadows in the left cerebral hemisphere and no obvious bleeding (Fig. 2B). Computed tomography angiography showed severe stenosis and occlusion in the M2 segment of the left middle cerebral artery, and the distal branches were significantly sparser than the opposite side (Fig. 2C). Computed tomography perfusion imaging (CTP) indicates partial core infarction of the left frontotemporal parietal lobe (Fig. 2D). The patient has a history of atrial fibrillation. Acute stroke is considered for this acute attack, but CV cannot be ruled out. For differential diagnosis and treatment without delay, cerebrovascular angiography is preferred. Intraoperative angiography showed that the left posterior traffic, the middle cerebral artery slender, the blood flow was slow, and the flow rate decreased significantly. Fasudil was injected intrathecally during the operation (Fig. 2E-H). Twelve days after the occurrence of CV, CT showed edema in the left cerebral hemisphere, the midline was in the middle, and the left lateral ventricle was slightly compressed (Fig. 2I). After acute left heart failure, the patient developed multifunctional failure, abnormal coagulation function, renal insufficiency, lung infection, shock, and finally respiratory and cardiac arrest.
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