Measuring effect of the blooming of chemical curatives on the rate of cyclic fatigue crack growth in natural rubber filled with a silanized silica nanofiller

Two rubber compounds with different amounts of chemical curatives were prepared by mixing natural rubber with a high loading of a sulfur-bearing silanized precipitated amorphous white silica nanofiller. The chemical bonding between the filler and rubber was optimized via the tetrasulfane groups of the silane by adding a sulfenamide accelerator and zinc oxide. The rubber compounds were cured and stored at ambient temperature for 65 days before they were tested. One compound showed extensive blooming as a function of storage time. Thin tensile strips of the rubber vulcanizates containing an edge crack were repeatedly stressed at constant strain amplitude and test frequency at ambient temperature and crack length c was measured as a function of the number of cycles n. The cut growth per cycle, dc/dn, was calculated and plotted against the tearing energy, T. The blooming of the chemical curatives increased dc/dn by up to an order of magnitude at a constant T. This was due to the reagglomeration of the chemical curatives in the rubber and also within a thin layer approximately 15 to μm in size beneath the rubber surface. Under repeated stressing, cracks grew through the relatively weak agglomerated areas in the rubber and this caused the rate of crack growth to increase at a constant T

Two advanced styrene-butadiene/polybutadiene rubber blends filled with a silanized silica nanofiller for potential use in passenger car tire tread compound

Styrene-butadiene rubber (SBR) and poly- butadiene rubber (BR) were mixed together (75:25 by mass) to produce two SBR/BR blends. The blends were re- inforced with a precipitated amorphous white silica nano- filler the surfaces of which were pretreated with bis(3- triethoxysilylpropyl)-tetrasulfide (TESPT). TESPT is a sul- fur-bearing bifunctional organosilane that chemically bonds silica to rubber. The rubbers were primarily cured by using sulfur in TESPT and the cure was optimized by adding non-sulfur donor and sulfur donor accelerators and zinc oxide. The hardness, Young’s modulus, modulus at different strain amplitudes, tensile strength, elongation at break, stored energy density at break, tear strength, cyclic fatigue life, heat build-up, abrasion resistance, glass transition temperature, bound rubber and tan d of the cured blends were measured. The blend which was cured with the non-sulfur donor accelerator and zinc oxide had superior tensile strength, elongation at break, stored energy density at break and modulus at different strain amplitudes. It also possessed a lower heat build-up, a higher abrasion resistance and a higher tan d at low tem- peratures to obtain high-skid resistance and ice and wet- grip. Optimizing the chemical bonding between the rubber and filler reduced the amount of the chemical curatives by approximately 58% by weight for passenger car tire tread. This helped to improve health and safety at work and reduce damage to the environment

Safety and efficacy of Favipiravir in moderate to severe SARS-CoV-2 pneumonia

Background: We examined the safety and efficacy of a treatment protocol containing Favipiravir for the treatment of SARS-CoV-2. Methods: We did a multicenter randomized open-labeled clinical trial on moderate to severe cases infections of SARS-CoV-2. Patients with typical ground glass appearance on chest computerized tomography scan (CT scan) and oxygen saturation (SpO2) of less than 93 were enrolled. They were randomly allocated into Favipiravir (1.6 gr loading, 1.8 gr daily) and Lopinavir/Ritonavir (800/200 mg daily) treatment regimens in addition to standard care. In-hospital mortality, ICU admission, intubation, time to clinical recovery, changes in daily SpO2 after 5 min discontinuation of supplemental oxygen, and length of hospital stay were quantified and compared in the two groups. Results: 380 patients were randomly allocated into Favipiravir (1 9 3) and Lopinavir/Ritonavir (1 8 7) groups in 13 centers. The number of deaths, intubations, and ICU admissions were not significantly different (26, 27, 31 and 21, 17, 25 respectively). Mean hospital stay was also not different (7.9 days SD = 6 in the Favipiravir and 8.1 SD = 6.5 days in Lopinavir/Ritonavir groups) (p = 0.61). Time to clinical recovery in the Favipiravir group was similar to Lopinavir/Ritonavir group (HR = 0.94, 95% CI 0.75 � 1.17) and likewise the changes in the daily SpO2 after discontinuation of supplemental oxygen (p = 0.46) Conclusion: Adding Favipiravir to the treatment protocol did not reduce the number of ICU admissions or intubations or In-hospital mortality compared to Lopinavir/Ritonavir regimen. It also did not shorten time to clinical recovery and length of hospital stay. © 2021 Elsevier B.V

Effect of the blooming of chemical curatives on the dynamic behaviour of silanised silica-filled natural rubber-to-metal bonded bobbins

Rubber is viscoelastic in nature and used in a variety of industrial applications. Rubber mounts are used to dampen vibration and shock. Damping, fatigue and dynamic properties of rubber mounts depend to a large extent on chemical ingredients mixed with the rubber. Natural rubber is the most widely used polymer for conventional mounts. Apart from natural rubber, different fillers and rubber chemicals are also present in conventional formulation of rubber mounts. Conventionally, five different classes of chemical curatives are used in rubber industries, which include curing agents, primary and secondary accelerators as well as primary and secondary activators. When chemical curatives are present in excessive amounts in rubber, they migrate to the rubber surface and form a bloomed layer. In this work, two rubber formulations were used for preparing rubber-to-metal bonded bobbin mounts. The formulations were primarily based on natural rubber with 60 parts per hundred rubber by weight (p.h.r.) precipitated amorphous white silica nanofiller. The surface of silica was pre-treated with bis(3-triethoxysilylpropyl)-tetrasulphane (TESPT) coupling agent to chemically bond silica to the rubber. The rubber was cured primarily by reacting the tetrasulphane groups of TESPT with the rubber chains using a sulphenamide accelerator and the cure was then optimised by adding zinc oxide as an activator. The ratio of the accelerator to activator in one compound was 6 p. h.r./0.3. p.h.r. and the compound showed extensive blooming of the accelerator on the rubber surface when stored at ambient temperature for up to 60 days. However, the blooming was reduced significantly by changing the ratio of the accelerator to activator to 3 p.h.r./2.5. p.h.r., which was subsequently used to prepare a second compound. Dynamic and static properties of the bobbins were subsequently measured. Both compounds showed very low phase angle (δ) and spring rate ratio K d /K s (K d : dynamic spring rate; K s : static spring rate). Notably, the compound with the high accelerator to activator ratio had superior aforementioned properties, but the dynamic fatigue life of the bobbin reduced noticeably due to a gradual deterioration of the bond caused by the migration of the accelerator to the bonded interface