Journal of Rubber Research最新文献

The preservative of natural rubber latex (NRL) is essentially a kind of bactericide or bacteriostat, mainly used for sterilisation or inhibit bacterial breeding, which will improve the pH of latex. To maintain the colloidal stability and consider the needs of reality manufacture, the NRL preservative also needs to have the advantages in terms of low price, ease to obtain and use, low toxicity, etc. In this study, a derivative of s-triazine (HT), a derivative of 2-methyl-4-isothiazolin-3-one (MI) and 2-methyl-5-chloro-4-isothiazolin-3-one (CMI) mixture (KS) are chosen as a non-ammonia preservative for NRL, which their effect on the structure and properties of NRL was investigated. The results of vulcanisation characteristics showed that the temperature dependence of the samples preserved by preservative HT was lower than that of ammonia and KS during the induction period (t₁₀). The test results of molecular weight and cross-linking density showed that the addition of preservative HT could protect the molecular chain structure of NR. In terms of physical and mechanical properties, the performance of sample HT is similar to that of sample ammonia, but after thermo-oxidative ageing at 100 °C for 24 h, the tensile strength retention rate of the sample preserved by the preservative HT can still reach 78%, which is higher than that of the ammonia preserved sample. Therefore, Preservative HT is a relatively better preservative. Its addition will not affect the structure of NRL and the prepared NR has good physical and mechanical properties as well as thermo-oxidative resistance. It can be considered to replace ammonia as the NRL preservative.

Rubber (Hevea brasiliensis) is a priority tree crop that produces natural rubber (NR), making it an important plantation commodity in the Philippines. However, NR production is confronted with major constraints, including rubber diseases resulting in low latex yield. Twenty-five rubber farms located in five major rubber-producing municipalities (Kidapawan, Antipas, Makilala, Matalam and President Roxas) of Cotabato, Philippines, were surveyed for prevalence of major rubber leaf diseases. Information on farm practices and environmental variables was collected. The majority of rubber farmers were smallholders with hectarage planted ranging between 1 and 15 hectares. The most planted clones are RRIM 600 and PB 260, which are high-yielding yet susceptible to many foliar pathogens. Six leaf diseases, viz. Oidium powdery mildew, Colletotrichum leaf disease, Corynespora leaf fall/spot, Phytophthora leaf blight, bird’s eye spot and algal spot, were documented in this study. Powdery mildew was the most prevalent in Cotabato with the highest percentage and severity of infections in all plantations, followed by Colletotrichum leaf disease. Information on disease prevalence in surveyed areas is important for disease management actions.

With an objective to produce superior quality natural rubber (NR) for preparing tyre treads, various coagulation techniques were attempted for NR latex such as mechanical stirring and heating, steam-induced, salt-induced and freeze–thaw process, from which their efficiency was compared with formic acid-coagulated natural rubber. The effect of coagulation methods on molecular weight and thermo-oxidative ageing of resulting rubber was evaluated. The processing and cure characteristics, rubber–filler interaction and mechanical properties of NR were also evaluated. Rubber separated by mechanical stirring followed by heating and freeze–thaw coagulation showed better retention of molecular weight coagulated NR field latex. FTIR spectrum detected a high amount of nitrogenous materials in rubber compared to acid-coagulated natural rubber. Gel permeation chromatography (GPC), Mooney viscosity and black incorporation time were used to characterise the rubber separated by different methods. Different coagulation techniques adopted have very little effect on the glass transition temperature (T_g). Technological and morphological properties of rubber obtained by stirring and freeze–thaw processes are superior compared to other processes.

Zinc oxide (ZnO) nanoparticles were synthesised by the co-precipitation method and the nanocrystals were found in the range 30–50 nm in size. Silicone rubber (SiR) nanocomposite samples were prepared using different concentrations (1, 3, 5, and 7 wt%) of zinc oxide (ZnO) nanoparticles through mechanical mixing and hot press moulding. The surface morphology of prepared silicone elastomer nanocomposites was studied using a scanning electron microscope (SEM) to investigate the smooth dispersion of ZnO nanoparticles inside the matrix and at higher concentration (7 wt%) agglomerates were formed. With increasing ZnO concentration, the mechanical properties of silicone rubber nanocomposite exhibited an increase in tensile strength, modulus, and decrease in elongation at break, which can be attributed to good distribution and reinforcing activity of nanoparticle in the elastomer matrix. At higher concentration (7 wt%), the rate of increase of mechanical properties was nominal due to the agglomeration of nanoparticles. The effect of ZnO nanoparticle concentration on the rheological properties of silicone rubber nanocomposites such as loss modulus, storage modulus, and complex viscosity was studied as a function of temperature and at different frequency 1, 10, and 100 Hz. The effect of ZnO nanoparticle concentration on the rheological properties showed an increase in loss modulus, storage modulus, and complex viscosity due to increase in volume fraction of nanofiller and reinforcement. The loss factor of silicone elastomer nanocomposites decreased with ZnO concentration which can be attributed towards better polymer–nanoparticle interactions. The addition of ZnO nanoparticles up to 5 wt% concentration level provided better rheological properties beyond which the rate of increase was marginal. Based on the results of morphology, mechanical and rheological properties of silicone rubber nanocomposites, 5 wt% ZnO nanoparticles may be considered as the percolation limit.

For the first time, an agricultural waste-based nanomaterial, psyllium husk nano-ash (PHNA) was applied as an environmentally friendly, cost-effective and naturally occurring green nano-filler for the development of natural rubber (NR) nanocomposite. Fourier transformed infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy, field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) were performed to characterise the psyllium husk-based PHNA. The cure properties including rheometric torque difference (R_∞) and curing rate index (CRI) were found to increase due to the addition of only 3 parts per hundred parts of rubber (phr) of PHNA into the NR matrix. The mechanical properties like moduli at 100% and 300% elongation, tensile strength (TS), percentage of elongation at break (%EB) and elasticity of the NR composites were found to be improved in the presence of the 3 phr of the PHNA. The dispersion of the PHNA particles in the rubber matrix was confirmed by the FESEM analysis. The NR-PHNA compatibility was studied by the conformational entropy change (∆S) and the elastic Gibbs free energy change (∆G). Thermal stability of the NR composite was also enhanced due to incorporation of the PHNA and this was confirmed by oxidative thermal ageing experiment and thermo-gravimetric analysis (TGA).

In this paper, walnut shell filler of 75–150 µm and 45–75 µm size was used in rubber compound with different loadings (2,3, and 5 phr). At 2, 3, and 5 phr loading, small-size WNS powder (45–75 µm) has higher modulus at 300%, tensile strength and elongation at break than larger-size powder (75–150 µm); however, modulus at 300% is lower than blank compound. As the amount of WNS filler increases, the elongation at break with modulus at 300% and tensile strength decrease. The goal of using silane is to improve the interfacial interaction between WNS filler and the rubber matrix. Larger-size WNS filler using Si69 compound demonstrated higher modulus at 300% with higher elongation at break and tensile strength compared to non-silanised compound; however, modulus at 300% remained lower than blank compound. The silanised compound with both WNS fillers demonstrated slightly higher rebound resilience at 100 °C, slightly lower heat build-up, and slightly lower tan delta at 60 °C than the blank compound. It was demonstrated that small-size WNS filler with silane could partially replace N330 carbon black (3 phr) in natural rubber-based tire tread compound due to its bio-based, biodegradable, renewable and sustainable properties.

Due to continuous progress in science and technology and the pressure to seek low cost, green materials for electrochemical devices have led to discover the possibility to use natural rubber (NR) as a polymer for electrolytes. This study reports about modifying Sri Lankan NR and using it for a solid polymer electrolyte in fabricating super capacitors with natural graphite electrodes. Solid polymer electrolyte was prepared using methyl grafted NR as the polymer and magnesiumtrifluoromethanesulfonate as the salt. The composition, 1 NR: 0.80 magnesiumtrifluoromethanesulfonate showed the maximum room temperature conductivity of 3.36 × 10^–3 Scm⁻¹. Capacitive features were dominant at low frequencies. Initial single electrode specific capacitance was about 32 Fg⁻¹ whereas the initial single electrode specific discharge capacitance was about 12.8 Fg⁻¹. Even though the values are not very high, they are highlighting the suitability to launch further studies to enhance performance of super capacitors with NR based electrolytes.

Silicone rubber foam (SRF) is a kind of polymer material with excellent performance but flammable. The flame-retardant SRF was prepared with diatomite (Dia) and hexaphenoxycyclotriphosphazene (HPCTP) as flame retardants. Cone calorimetry tests (CCT), scanning electron microscopes (SEM) and mechanical tests were used to investigate the effects of Dia and HPCTP on the flame retardancy, smoke suppression and mechanical properties of SRF. The results showed that Dia and HPCTP had a synergistic effect on flame retardancy and smoke suppression. With the addition of 5 wt% Dia and 5 wt% HPCTP, the peak heat release rate (PHRR), the total heat release rate (THR), the peak smoke release rate (PSPR) and the total smoke production (TSP) of SRF decreased by 54.43, 37.64, 62.3 and 58%, respectively. With the addition of Dia and HPCTP, the thickness of the carbon layer became thicker, the cracks became smaller and the microstructure became denser. In addition, when the contents of 5 wt% Dia and 5 wt% HPCTP were added, the mechanical properties of SRF were the best; the tensile strength increased to 0.195 MPa, and the elongation at break increased by 109.85%. It provided a new flame-retardant method for SRF.

Room temperature vulcanised (RTV) silicone rubber is widely used in daily life. Ordinary and traditional flame-retarding RTV silicone rubber are easy to turn into brittle char layer or ashes without any self-supporting and bonding ability after experiencing a combustion process, which could not inhibit the secondary disasters after fire. To improve the fire-resistance performances of RTV silicone rubber, a new single component ceramifiable RTV silicone rubber was prepared in this work. The tack-free time, mechanical properties and thermal properties of different formulations were tested. The flexural strength and adhesion strength of the ceramic residues were studied by orthogonal designed experiments, which exhibited the maximum of 8.80 and 0.300 MPa after sintering at 1000 °C, respectively. The ceramifying process of the single component ceramifiable RTV silicone rubber at high temperatures was also investigated. These results will provide a basis for the development of fire-resistant silicone adhesive with better performance that can meet the actual needs.