Journal of Rubber Research最新文献

Hevea brasiliensis, or the Para rubber tree, is a major commercial source of natural rubber (NR). The rubber tree is susceptible to various fungal attacks, which affect NR production and Corynespora cassiicola is one of the major pathogens affecting young and mature rubber trees. Corynespora leaf fall disease (CLFD) outbreaks often cause serious loss in latex productivity by adversely affecting tree health. Since fungicidal chemical control is uneconomical and unsustainable, improving host resistance is the most effective strategy for the long-term management of this disease. In this context, 78 Hevea genotypes were screened against two virulent isolates of two races of C. cassiicola (Race 1 and Race 2). The level of host resistance was determined in vitro using detached leaf bioassay and those genotypes that were found to be highly resistant were subjected to further evaluation under greenhouse conditions. Seven genotypes were classified as highly resistant against both races of C. cassicola in vitro, with less than 20% disease intensity. Subsequent assessment under greenhouse conditions identified three genotypes with less than 40% disease severity and corresponding rAUDPC value of less than 0.4 when challenged with both races of C. cassiicola. These resistant genotypes are suitable candidates to be included in breeding programmes aimed at the development of superior clones with durable resistance against Corynespora leaf fall disease.

A finite element model for analysing the sealing performance of three types of wellhead rotary blowout preventer rubber ring structures in use on site was established. By using this model, the stress, deformation and contact pressure distribution of the passive rubber ring during pre-tightening conditions were calculated when the inner annulus of the passive rubber ring passed through the 5-inch drill pipe body and the 7-inch joint. The distribution position, length, and magnitude of contact pressure on the contact surface between the three types of rubber rings and the outer wall of the drill string under different pressure penetration loads under rated working conditions were calculated. Overall, the sealing performance of the active rubber ring is the best while the sealing performance of the passive rubber ring is the worst. However, the passive rubber ring has a simple structure and does not require a hydraulic system, which makes it impossible to adjust the sealing strength of the rubber ring in real time based on the actual fluid pressure on site. On the other hand, the I-type rubber ring uses part of the rotating blowout preventer structure as the hydraulic chamber wall, which can thicken the rubber layer in contact with drill pipe. Therefore, passive rubber rings are more suitable for low fluid pressure drilling operations. When the fluid pressure at the lower part of the rubber ring exceeds the rated maximum fluid pressure, it will lead to a sharp decrease in the sealing performance of the rubber ring. Therefore, stricter control of the use of the rubber ring is needed during on-site use, especially in drilling conditions with wellhead fluid pressure. The research methods and achievements in the article provide theoretical guidance for the safety evaluation of rotary blowout preventers used in ultra deep wells unbalanced drilling.

Crumb rubber (CR) that had been used in an outdoor football stadium in the U.S.A. for over 10 years was sampled, analysed and compared to samples taken from an on-site, covered excess CR stockpile and from fresh CR that could be used to replace the used CR. These tests were accomplished to determine if the original CR properties had changed significantly, from new/un-used CR, which could have safety and performance implications if continued use of this CR was planned. A series of analytical and mechanical tests were performed to determine degradation effects over time that included Fourier-transform infrared spectroscopy (FTIR), solvent swell tests, differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), X-ray emission spectroscopy (XES), vertical impact, hardness and bulk density. Results inferred compositional differences and mechanical property changes between all three CR samples, with indications that the older CR was demonstrating concurrent increased crosslinking and molecular scissioning, with subsequent loss in resilience. The FTIR results indicated various polymer types present that originated from recycled automobile tyres as well as evidence of oxidation in the used CR. The DSC exhibited lower thermal enthalpy and higher glass transition temperatures confirming compositional changes in older samples. Both vertical impact and hardness tests showed a significant increase in hardness and lower resilience in the used CR. A significant decrease in average size in the used CR was revealed through sieving and microscopy, which indicated mechanical wear. Bulk density measurements of un-sieved used and stockpile CR showed a substantial increase in bulk density for the used samples. The fresh, new potential replacement CR appears to originate from a different supplier than the CR originally used on the sports surface (and accompanying stockpile CR) and possessed much higher resilience than the used CR.

This research aimed to design biocompatible polymeric surfactants as additives to natural rubber latex (NRL) and the mechanical properties of the latex films were evaluated thereafter. Both anionic and non-ionic surfactants, APS and NPS, were successfully synthesised from palm-based oleic acid by polyesterification, with their ester linkages verified by FTIR analysis. Both surfactants possess good thermal stability with thermal decomposition temperatures above 200 °C. They were biocompatible and non-cytotoxic, as evidenced by high cell viability > 80% for all tested cell lines. In general, the antibacterial activities of both surfactants were stronger against Gram-positive bacteria than Gram-negative bacteria. Surfactant solutions were prepared and compounded into NR latex to produce latex films. Both solutions exhibited good wetting properties with contact angles < 90°, low critical micelle concentration values ranging from 0.005 to 0.007 mol/L, low foaming ability, and reasonable foam stability above 80%. The unaged NR films compounded with APS demonstrated greater mechanical strengths than the control and NPS, recording the highest tensile strength of 28.65 MPa and the lowest modulus (M300) reflecting softness. Both latex films showed a slight reduction in mechanical properties after ageing. These results indicated that APS had a higher potential to modify NR latex film properties, in particular film softness. The surfactants also presented high potential as non-cytotoxic antimicrobial agents in NR compounding.

Areas identified as escape zones for Pseudocercospora ulei, the causal agent of South American Leaf Blight (SALB), are being sought for the development of profitable rubber growing, as high-yielding Asian clones can be grown there without suffering repeated defoliation caused by epidemics of the disease. A performance trial with 10 clones was set up in 2006 in such an escape zone in Ecuador with non-American clones whose high production potential is acknowledged elsewhere in the world, some of which are recommended on a commercial scale. Production results over seven years, between 2013 and 2019, indicated a very high potential for this material in this new region, reaching average yields of 2.5 t/ha/year for clones PB 280, PB 312 and PB 314, and 1.85 t/ha/year for the control clone RRIM 600, despite a very pronounced 5-month dry season. However, the risks of wind damage and tapping panel dryness were found to be very high for PB 312 and PB 314. Clone PB 280 proved to perform best overall, with 93% of trees in production and one of the lowest Tapping Panel Dryness (TPD) rates. This clone, distinguished by its medium high latex metabolism and a high sucrose reserve, presents a highly promising alternative for the cultivation of rubber trees in escape zones. This is particularly relevant in situations where the phytosanitary risk associated with P. ulei is constrained.

A novel accelerator, cerium cysteine (Ce-Cys) was synthesised by double replacement reaction. The complex was characterised by FT-IR analysis, thermal analysis, EDTA titration and elemental analysis, respectively, to determine that the molecular formula of the complex was Ce (Cys)₃Cl₃·3H₂O. Cure characteristics, crosslink density, mechanical properties and thermo-oxidative ageing of NR compounds were investigated. The research revealed that the vulcanisates containing Ce-Cys manifested high scorch time, outstanding mechanical properties, and better thermo-oxidative ageing properties. Furthermore, based on kinetic calculations, it was concluded that as the amount of Ce-Cys increased, the reactivity of the crosslink precursor increased while the activation energy decreased.

Natural rubber (NR) is an invaluable material, in great demand for manufacturing of broad-ranging products. Its performance and properties have been widely studied by incorporating with different ingredients and inorganic fillers including clay minerals to develop many products, one of which is rubber floor mat. Nevertheless, the study on the pottery clay with NR from Cambodia is limited. This study investigated on the mechanical, impact absorption and morphological properties of clay-filled NR at different loadings for floor mat application. It was found that the effect of clay loadings on hardness of rubber composites was insignificant while the value of tensile strength and elongation at break before ageing was reduced to about 10 MPa and 720%, respectively, as clay loadings increased. For tensile properties after ageing, heat resistance property was obtained at clay loading of 20 and 30 phr. The value of tear strength was reduced as clay loading increased by reasons explained through SEM images that revealed agglomeration of clay filler within the rubber matrix accountable for the reduction in mechanical properties. The impact energy absorption showed optimum level at 10 phr of clay loadings at the value of 3.0 Joules. Compared to two types of commercial floor mats, the compounded composites showed superior performance in tensile properties and impact absorption ability.

Pestalotiopsis leaf fall disease (PLFD) has been on the increase in recent years, resulting in diminished latex yield in many rubber producing countries. Thus far, some reports have pointed to the presence of fungal pathogen(s) other than Pestalotiopsis sp. in the diseased leaves. To decipher the diversity of fungal pathogens, a total of 110 early-stage and another 110 late-stage symptomatic leaves were sampled from 12 Hevea clones in seven different areas in Malaysia during wintering and wet seasons at different times of the year. A total of 487 fungal isolates were obtained; 241 were from the early-stage and 246 from the late-stage symptomatic leaves. These isolates were clustered into 11 morphotypes based on colony appearance and microscopic observation of the spore. The diversity analysis revealed significant differences in morphotype richness and evenness when comparing different rubber clones, seasonal effects, and locations by which the fungal isolates were sampled. Five isolates representative of the five predominant morphotypes associated with PLFD were analysed using the Internal Transcribed Spacer (ITS) markers and BLAST analysis. Their closest relative species were identified as Colletotrichum conoides, Neopestalotiopsis surinamensis, Lasiodiplodia theobromae, Phyllosticta fallopiae and Letendraea cordylinicola. This study enhanced our understanding of PLFD, particularly the diversity and distribution of fungal communities associated with the disease across different rubber clones, seasons, and locations in Malaysia. The identification of these fungal isolates associated with PLFD symptoms paves the way for further research into their pathogenicity and the development of targeted management strategies to mitigate the disease.

Non-linear rheological behaviours of high fluorine content fluoroelastomer (HF-FKM) mixtures with varied carbon black (CB) filling amounts were investigated. Non-linear viscoelastic characteristics of HF-FKM mixture are characterised by large amplitude oscillatory shear (LAOS) tests, correlations between rheological behaviour and CB content were then discussed. Each non-linear viscoelastic parameter of HF-FKM mixture presents a three-stage characteristic with increasing CB content, corresponding to ranges of 0–20 phr, 25–30 phr, and 35–45 phr. Three stages of viscoelasticity characteristics for HF-FKM mixtures were considered to depend on the alteration of CB-elastomer network structure with increasing CB content, corresponding to the states where continuous phase of gum, CB-elastomer mesophase and excessive CB agglomerates predominate in mixture compound, respectively. After vulcanisation, samples with 30 phr CB content show the best resilience performance against thermal ageing, contributing to the existence of CB-elastomer mesophase. Samples with 25 phr CB content possess the second lowest compression sets at 225 and 250 °C ageing conditions but perform no better than those with 35 phr at 275 °C. The reason is presumed to be that the presence of excessive CB agglomerates in HF-FKM vulcanisate reduced irreversible deformation of the CB-elastomer network under compression at elevated temperatures.