Journal of Rubber Research最新文献

Additive manufacturing (AM) involves creating prototypes by depositing and solidifying material by the placement of material in X, Y, and Z axes in a 3D space. The emergence of AM using elastomers has allowed the production of complex and customised parts with intricate geometries and modified properties as per specific needs of engineers cum designers. For successful 3D printing (3DP), it is crucial to use a material that is suitable for the specific application and printing process. Elastomers are unique polymers that are resilient, flexible and capable of deforming under stress. Fused deposition modelling, stereolithography and selective laser sintering printing are the most common 3DP techniques for elastomers. The use of elastomers in AM is limited due to technological, material and processing constraints. Despite challenges, elastomers have great potential in AM and can be applied in various industries namely automotive, aerospace, healthcare and consumer goods. However, there is a growing interest in expanding the range of elastomers that can be 3D printed. Researchers are experimenting with different approaches to enhance the printability of elastomers such as modifying material composition, material design, optimising printing parameters, control of chemical composition and 3DP techniques. Recent advancements in the structure, properties and printing techniques of elastomers show wide scope for improving their printability. Several elastomeric materials that can be 3D printed include thermoplastic elastomer, thermoplastic polyurethane, liquid silicone rubber, etc. This review paper aims at providing an overview of the current state of AM of elastomers, including the challenges and limitations. It discusses recent advancements and suggests ways to enhance the printability of elastomers in near future, which can help researchers and industry professionals to explore new and unique AM applications.

The presence of ammonia as a preservative in natural rubber (NR) latex concentrate induces a variety of problems in the NR latex foam manufacturing process, consequently leading to inconsistency in the quality of the end products. To overcome these issues, a novel ammonia-free NR (AFNR) latex concentrate that uses palm oil-based polymeric surfactants as an alternative preservative has been developed. This study explores the feasibility of using AFNR latex to produce latex foam shoe insoles. In this investigation, the AFNR latex was foamed into extra-high-density (EHD) and high-density (HD) foams using the Dunlop batch foaming process. The study found that HD latex foam is softer than EHD latex foam, with the Shore F hardness of HD latex foam and EHD latex foam being 57 and 77, respectively. The study also discovered that the peak pressure value and rebound resilience properties of HD latex foam shoe insoles, which were fabricated at 7 mm thickness, are 41% and 6% lower than those of EHD latex foam, respectively. Additionally, EHD latex foam and HD latex foam have different morphological characteristics, with EHD latex foam having a thicker cell wall, smaller pore size, and being less porous compared to HD latex foam. Taking these properties into consideration, HD foam could be the ideal choice for shoe insole applications, such as sports shoes.

In this work, the nanocomposites based on epichlorohydrin rubber (ECO) and graphene oxide (GO) have been prepared by solvent blending followed by open mill mixing, which is known to be an effective way of dispersing nanofillers within a polymer matrix. The successful dispersion of GO sheets within the ECO matrix has been confirmed by high-resolution transmission electron microscopy and atomic force microscopy. The incorporation of 1.5 vol.% of GO sheets into the ECO matrix enhances the breaking stress and stress at 200% strain values of ECO by 67% and 139%, respectively, which is due to the strong interfacial interactions between the polar groups in ECO and the oxygen-containing functional groups on the surfaces of GO sheets. This general finding is further corroborated by the fact that ECO's glass transition temperature increased from − 18 to − 14 °C with a 1.5 vol% GO content. The initial degradation temperature, the maximum degradation temperature and the percentage residue of ECO consistently increase with the concentration of GO due to the enhanced interfacial interaction between ECO and GO through chemical bonding, which delays the initial degradation by hampering the process of degradation. The uniform dispersion of GO sheets within the ECO matrix, along with improved interactions between GO sheets and ECO, results in the formation of a densely interconnected network of GO layers within the ECO chains. Consequently, this enhances the oil and fuel resistance of the ECO-GO nanocomposites. The fascinating results and outcomes of this investigation will pave the way for the development of fuel and oil-resistant materials with improved physico-mechanical properties.

Eucommia ulmoides rubber particles (EuRPs) are organelles that synthesise and store E. ulmoides rubber (EuR). In this study, the lipids dynamic change of EuRPs from leaf tissue at different growth period were investigated. The results showed that there were 1149 lipid species belonging to 39 lipid classes that were identified; TGs, DGs and Cers were the most abundant among all lipids of EuRPs. Lipid expression analysis demonstrated that the expression intensity of TGs was almost 1 × 10⁴-fold and 10-fold higher than those of MGs and DGs, respectively. Among sphingolipids, the expression intensity of SoP, CerG2, GM3, SM and GerG3 increased throughout the duration of investigation (August–November 2021). Further analysis found that the Cers species accounted for 9.40% of total lipid species and the number of Cers species in EuRPs isolated from leaves in August was the most, with gradual decline in the following 3 months. Meanwhile, hierarchical clustering indicated that there were seven types of highly abundant lipid species in leaf EuRPs from September to November, i.e. SQDG (18:3/18:3), SQDG (34:3), SQDG (17:5/23:2), DGDG (38:12), Co (Q9), TG (16:0/16:0/18:3) and TG (39:1). Compared with leaf EuRPs in August, there were 79, 101 and 107 lipid species which showed significant differential expression in September, October and November. Based on the high expression intensity of SQDG in EuRPs, the correlation between the genes mediated in EuR or SQDG biosynthesis was further analysed, whereby the results indicated co-expression of some genes, which implies the synergistic regulatory role in SQDG EuR biosynthesis.

Friction properties of rubber compounds are important for tyre tread applications as tyre is the only contact between the road and the car. Although epoxidised natural rubber (ENR) is widely reported to have a good grip property, there is limited information on its friction properties. In this study, the effect of substrate surface roughness on dry friction properties of tread rubbers based on silica-filled ENR 25 (ENR 25/silica), ENR 50 (ENR 50/silica) and NR (NR/silica) were assessed. Tensile strength, tear strength, hardness, dynamic properties and abrasion resistance were also examined. The friction properties upon sliding on a non-textured aluminium oxide plate and aluminium oxide abrasives with grit sizes of P320, P180, P120 and P60 were determined using the TE 75 Production Rubber Friction Tester at 5N, 10N, 15N and 20N of normal load. Meanwhile, surface roughness analysis on the sample surfaces was conducted using a 3D laser interferometer microscope. From this study, NR /silica tread had better physical strength, while ENR 50/silica had higher hardness and tensile modulus. On dynamic mechanical properties, the ENR 50/silica possessed the highest tangent delta value and all tangent delta values increased with a change of frequency from 1 to 10 Hz. With regard to friction properties, the coefficient of friction of all tread rubbers decreased with the increase in substrate roughness. The change in tread rubber surface roughness varied depending on the coefficient of friction, physical strength and substrate roughness. Throughout this study, the effect of surface roughness on dry friction properties of silica-filled ENR tread rubbers and its factors were successfully identified.

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).