Small Rubber Particle Research Articles

Comparative Transcriptome Analysis Identifies Potentially Relevant Genes in Rubber Clones with a High Latex Yield (Hevea brasiliensis)

Since the 1950s, the rubber tree (Hevea brasiliensis) has significantly contributed to Malaysia's agricultural economy due to its capability to produce high-value natural rubber. Due to the presence of cis-1,4-polyisoprene, natural rubber exhibits unique properties such as flexibility, high elasticity, and efficient heat dispersion. Cis-1,4-polyisoprene is synthesized via two distinct metabolic pathways: the isoprenoid and rubber biosynthesis. RNA sequencing was performed on 12 specimens from the bark, leaf, and latex tissues of two rubber clones, RRIM 3001 (high latex yield) and RRIM 712 (low latex yield). After quality assessment, these specimens generated a mean of 73,816,244 clean reads. The differential expression analysis revealed that the Acetyl-CoA-Acetyltransferase (AACT) and Diphosphomevalonate Decarboxylase (MVD) genes (via the MVA pathway), as well as the Small Rubber Particle Protein (SRPP) and Rubber Elongation Factor (REF) genes (via the rubber biosynthesis pathway), were overexpressed in the bark, leaf, and latex tissues of RRIM 3001 compared to RRIM 712. The transcription factor Ethylene Response Factor (ERF) was also found to be more highly expressed in RRIM 3001 than in RRIM 712. Five rubber clones with random yield characteristics were used in quantitative amplification analysis to validate AACT, MVD, SRPP, REF, and ERF genes. The quantitative analysis shows that the five genes were consistently expressed with the yield characteristics of the five random rubber clones.

Transcriptomics and proteomics profiles of Taraxacum kok-saghyz roots revealed different gene and protein members play different roles for natural rubber biosynthesis

The Russian dandelion (Taraxacum kok-saghyz L. Rodin, TKS) is a potential crop for natural rubber production. Our proteomics results have revealed that both methylerythritol (MEP) and mevalonate (MVA) pathways are important for natural rubber biosynthesis (NRB) in TKS roots. In this study, morphological characteristics and rubber content in TKS roots during five development stages were determined and more laticifer cells, rubber particles, and natural rubber were observed in older TKS roots. Combination of transcriptomics and proteomics was further performed to gain an overall realizing of the principle developmental mechanism and metabolic regulation processes in TKS roots and determine the key genes and proteins for NRB. From the detected TKS roots, 34,710 genes and 3695 proteins were positively identified. Among them, 22194 genes and 2145 proteins were differentially expressed during root development, and their correlation coefficients were calculated. GO and KEGG analysis showed that most up-regulated genes and proteins were involved in carbon metabolic process. A total of 102 NRB-related gene and protein members, including 10 cis-isoprene transferases (CPT), 8 small rubber particle proteins (SRPP), 2 rubber elongation factors (REF), as well as one HRT1-REF bridging protein (HRBP), were identified. Our omics data revealed that different family members of genes and proteins play different roles for NRB in TKS roots. Among them, CPT7, SRPP5, SRPP6 and SRPP9 might play more important roles for NRB in TKS roots.

In-situ observation of spatial organization of natural rubber latex particles and exploring the relationship between particle size and mechanical properties of natural rubber

Natural rubber (NR), an important source of elastomeric material, has superior comprehensive properties compared to synthetic high cis-1, 4-polyisoprene, which are attributed to its peculiar architecture. However, it is a challenge to identify the precise structure of NR, especially the structure of NR particles, as there are no direct characterization methods to perform in-situ investigation of structure of NR particles at an intact state. In this study, we used cryogenic transmission electron microscopy (cryo-TEM) to directly explore the morphology of NR particles existing in the latex without drying or chemical fixation. Then, the spatial organization of proteins and phospholipids on the surface of NR particles was visualized by stochastic optical reconstruction microscopy (STORM). The results show that NR particles are spherical particles with an average particle size of 88 ± 15 nm, and the exterior of NR particles is a mixed monolayer of proteins and phospholipids (ca. 4.6 ± 0.77 nm in thickness). Thus, a more complete model for the Hevea brasiliensis rubber particles was proposed. Moreover, we explicated the relationship between the particle size of NR particles, molecular characteristics, and mechanical properties of NR. The Mnand Mw of small rubber particles (SRPs) with a particle size of 106 nm are (1.56 ± 0.06) × 106 g/mol and (2.21 ± 0.07) × 106 g/mol respectively, which are much larger than those of the large rubber particles (LRPs) with a particle size of 628 nm (Mn: (0.41 ± 0.05) × 10 6 g/mol; Mw: (1.63 ± 0.10) × 106 g/mol). After vulcanization, the SRPs have better mechanical properties. Compared with LRPs, SRPs exhibit a 4.3-fold increase in tensile strength (from 5.7 to 24.6 MPa) and a 3.5-fold increase in toughness (from 12.9 to 44.9 kJ/m2). This work not only provides rational design for the new biomimetic synthetic rubber with unique hierarchical structures and excellent properties, but also offers a new possibility for tuning the mechanical properties of NR by preparation of LRPs/SRPs blend of various ratios.

Poly (Lactic Acid) (PLA)/Recycled Styrene Butadiene Rubber (rSBR) Composites

Recycled styrene butadiene rubber (rSBR) from waste car tires was used as a filler in poly(lactic) acid (PLA) to modify its properties. The compounds were prepared via twin-screw extrusion and molded by injection with different rSBR contents (0 to 25% wt.). Additionally, recycled rubber particle size was controlled between 125 and 1000 μm to determine the effect of this parameter. From the samples produced, a series of morphological, physical and mechanical characterizations were performed. As expected, rSBR addition decreased the PLA stiffness. Up to 5% rSBR, the flexural and elastic moduli were unchanged, but the tensile strength, elongation at break and impact toughness were decreased. The highest tensile strength, elongation at break and impact toughness were achieved for PLA/rSBR blends filled with small rubber particles (125-250 μm). According to the morphological analysis, this behavior was associated to better interfacial interactions between smaller rSBR particles (higher specific surface area) and PLA resulting in a more uniform filler distribution and better stress transfer from PLA to rSBR. Finally, to complete the mechanical properties of the materials, fatigue tests were carried out on different blends and the results were related to instrumented indentation to get some more local information.

Constructing Chemical Interface Layers by Using Ionic Liquid in Graphene Oxide/Rubber Composites to Achieve High-Wear Resistance in Environmental-Friendly Green Tires.

The harm caused by small rubber particles generated from tire abrasion to the atmosphere is receiving a continuing concern. For developing environmental-friendly tire tread materials with high wear resistance, building the strong interface between nano-fillers and rubber matrix is the primary challenge. Herein, ionic liquid (IL, 1-allyl-3-methylimidazole chloride) was used to modify graphene oxide (GO) by π-cation interaction and hydrogen bonding between IL and GO. Furthermore, an IL-GO/natural rubber (NR) masterbatch possessing fine dispersion of GO was prepared by the emulsion compounding method, and thereafter, a further compound with solution polymerized styrene butadiene rubber (SSBR) was fabricated for the tread rubber composite. Results showed that the double bond in the IL enhanced the cross-linking reaction during the vulcanization of rubber composites occurred at high temperature, leading to an elevated interfacial interaction between the IL-modified GO and the rubber macromolecules. Compared with silicon dioxide (SiO2)-filled NR/SSBR composites, the cross-link density, 300% modulus, and tear strength of the IL-GO/SiO2/NR/SSBR composites were increased by 10.2, 42.6, and 20.2%, respectively. Importantly, the wear resistance of the IL-GO/SiO2/NR/SSBR composites was improved by 17.3%, ascribing to the strong interface between IL-GO and rubber macromolecules.

The relationship between EuSRPP1 gene expression and rubber biosynthesis in Eucommia ulmoides Oliver (Du-zhong)

Because of the unique properties, trans-polyisoprene rubber (TPI) has gradually realized that it has great development potential. Eucommia ulmoides Oliver (E. ulmoides Oliver), also named Du-zhong, is one of the few woody plants producing TPI. The significant expansion of small rubber particle protein and rubber elongation factor (SRPP/REF) genes in E. ulmoides Oliver may be associated with the producing of TPI. To understand the relationship between EuSRPP1 gene expression and rubber biosynthesis in E. ulmoides Oliver, in this study, an overexpression transgenic (OT) vector of EuSRPP1 driven by the act promoter and an RNA interference (RNAi) expression vector of EuSRPP1 were constructed. Then, Agrobacterium-mediated genetic transformation of E. ulmoides Oliver was conducted to obtain the OT and RNAi seedlings. Quantitative Real-time Polymerase Chain Reaction (qRT-PCR) showed that the EuSRPP1 expression levels in OT seedlings significantly increased, and were 2.53 × and 3.68 × higher in OT-1 and OT-2 seedlings, respectively, than the wild-type (WT) seedlings, Meanwhile, the expression levels of E. ulmoides Isopentenyl Diphosphate Isomerase (EuIPPS) and E. ulmoides Farnesyl Diphosphate Synthase (EuFPS) genes in OT plants, which are related to rubber biosynthesis synthesis, were also up-regulated. To the contrary, EuSRPP1 gene expression levels in the RNAi-1 and RNAi-2 seedlings significantly decreased, which were 3.92% and 42.38% of the WT seedlings, respectively. EuIPPS and EuFPS genes expression levels in the RNAi seedlings were also down-regulated. The TPI content analysis revealed that the TPI content in the overexpression EuSRPP1 callus increased to 1.85 × that of the WT callus, whereas that in the RNAi callus decreased to only 52% of the WT callus. Molecular weights of rubber were significantly different in OT callus (2.31 × 106 Da) and RNAi callus (0.36 × 106 Da). Observation of the rubber particles revealed that the rubber particle electron density was higher in OT seedlings, and the immunogold localization results showed that EuSRPP1 was localized to rubber particles. These results indicate that the EuSRPP1 expression level influences the chain elongation, particle development, and content of rubber in E. ulmoides Oliver.

Avoiding unconscious injection of vial-derived rubber particles during intra-articular drug administration

ObjectiveVial coring describes the occurrence of small rubber particles, which are formed by needles when perforating vial stoppers. These particles may be aspirated along with the drug. Unconscious injection of rubber particles may increase the risks associated with intra-articular injections. This study aimed to analyze the frequency of this phenomenon and possibilities to avoid its occurrence. Method800 vials of 2 ​mL, filled with sodium chloride, were divided into 4 groups (n ​= ​200 each). Aspiration through the rubber stopper was performed with a 18-Gauge needle and the fluid was ejected onto a 10 ​μm filter paper through a 18-Gauge needle (group one) and a 23-Gauge needle (group two). In group three a 23-Gauge needle was used for aspiration and ejection. In group four, aspiration was performed using 18-Gauge needles with implemented 5 ​μm filters. Subsequently, a microscopic analysis of the filter papers was performed. ResultsIn none of the 800 specimen, a rubber particle was detected by naked eye. Microscopically, 20 (10%) rubber particles were detected in group one, 21 (11%) in group two and 65 (33%) in group three. In group four, no particles were visualized. ConclusionThis study shows the occurrence of rubber particles in 10–33% of the cases, when standard needles are used for the aspiration of drugs. We therefore recommend using industrially prefilled syringes, filter needles or removing the rubber stopper before withdrawing drugs from vials for intra-articular injections.

Optimization of a protein extraction method from natural rubber sheets made of Hevea brasiliensis latex

A method to extract proteins from natural rubber (NR) samples has been developed to characterize the protein composition of NR by SDS-PAGE electrophoresis. While the incubation of NR pieces in aqueous buffers did not provide satisfactory results (no protein bands detected by SDS-PAGE), the solubilization of NR pieces in an organic solvent, prior to centrifugation and protein extraction from the obtained pellet, was found efficient to highlight protein bands by SDS-PAGE. Pure cyclohexane was used to solubilize NR pieces and resulted in a low share of nitrogen in the pellet (29%). The addition of 10% (v/v) ethanol to cyclohexane allowed to significantly increase this share to 73% and to detect 13 protein bands by SDS-PAGE. The molecular weights of the four most intense bands suggest the presence in NR of the following proteins: rubber elongation factor, small rubber particle protein, hevamine, and β-1-3 glucanase.

Experimental investigation of the mechanical behaviour of gravel-granulated tyre rubber mixtures

Recycling and reuse of end-of-life tyres (ELTs) in civil engineering applications is an effective way to minimise environmental and health issues associated with such waste materials and concurrently reduce high demand of natural aggregates. In this study, direct shear tests were carried out to evaluate the strength and deformation properties of two types of gravel-granulated tyre rubber (G-GTR) mixtures under four levels of normal stress (6.5, 30, 60, and 100 kPa). Mixtures were prepared at different volumetric rubber content (VRC) of 0%, 10%, 25%, 40% and 100%, by using a combination of small and large rubber particles mixed with a rounded uniform gravel. The results indicated that VRC and normal stress are the main parameters that influence the mechanical behaviour of G-GTR mixtures, while, the effect of rubber size is more noticeable at lower VRC. Based on the experimental findings, a framework with compressibility and strength performance-based criteria for the selection of G-GTR mixtures as structural fills for geotechnical applications is proposed. It is recommended that, as long as one-dimensional compressive strains are acceptable, mixtures with VRC ≤ 40% are suitable materials for the majority of geotechnical engineering applications, since the friction angle is generally > 30°.

Laboratory Evaluation of Rubberized Binder and Mix Containing a Low Content of Devulcanized Rubber Modifier

This paper evaluates the mechanical properties of rubberized asphalt binder and mix containing 5% and 10% rubber. This rubberized asphalt binder was manufactured in a field-blend process using devulcanized rubber particles, finer than 250 microns, derived from waste tires. Comparison between the rubberized binder and the base binder test results showed that the rubberized binders had higher complex moduli and lower phase angles at the grade temperature. They also had a higher percentage recovery in the multiple stress creep recovery test, and a significant creep stiffness reduction in the bending beam rheometer test. Given the low rubber content and small rubber particle size, this rubberized binder can be used in dense-graded mixes, whereas asphalt rubber binders, with larger rubber particles and higher rubber content (>15%), must be used in gap- or open-graded mixes. This rubberized dense-graded mix met the volumetric design criteria at the same binder content as the control mix prepared with the unmodified base binder. Laboratory tests on the mix included repeated load triaxial, Hamburg wheel track, flexural dynamic modulus, and beam fatigue. The rubberized mixes had slightly lower stiffnesses than the control mix, but better resistance to moisture damage, rutting, and fatigue cracking. A strong linear correlation was found between the carbonyl area index and the rheological properties of the long-term aged binder and fatigue life of the mixes. Based on these findings, these rubber-modified binders can be considered for use in dense-graded mixes to improve overall performance and make use of waste tires.

Structural and Functional Annotation of Transposable Elements Revealed a Potential Regulation of Genes Involved in Rubber Biosynthesis by TE-Derived siRNA Interference in Hevea brasiliensis.

The natural rubber biosynthetic pathway is well described in Hevea, although the final stages of rubber elongation are still poorly understood. Small Rubber Particle Proteins and Rubber Elongation Factors (SRPPs and REFs) are proteins with major function in rubber particle formation and stabilization. Their corresponding genes are clustered on a scaffold1222 of the reference genomic sequence of the Hevea brasiliensis genome. Apart from gene expression by transcriptomic analyses, to date, no deep analyses have been carried out for the genomic environment of SRPPs and REFs loci. By integrative analyses on transposable element annotation, small RNAs production and gene expression, we analysed their role in the control of the transcription of rubber biosynthetic genes. The first in-depth annotation of TEs (Transposable Elements) and their capacity to produce TE-derived siRNAs (small interfering RNAs) is presented, only possible in the Hevea brasiliensis clone PB 260 for which all data are available. We observed that 11% of genes are located near TEs and their presence may interfere in their transcription at both genetic and epigenetic level. We hypothesized that the genomic environment of rubber biosynthesis genes has been shaped by TE and TE-derived siRNAs with possible transcriptional interference on their gene expression. We discussed possible functionalization of TEs as enhancers and as donors of alternative transcription start sites in promoter sequences, possibly through the modelling of genetic and epigenetic landscapes.

An integrative transcriptomic and genomic analysis reveals novel insights into the hub genes and regulatory networks associated with rubber synthesis in H. brasiliensis

Rubber tree (Hevea brasiliensis) is an important tropical plant that produces natural rubber; however, the hub genes and regulatory networks associated with rubber synthesis remain largely unclear. In this work, 129 publically available RNA-seq datasets were collected to perform gene co-expression network analysis in rubber tree. In total, 25 co-expressed gene modules (M1-M25) were identified, and the molecular functions and hub genes of each module were systematically analyzed. Associations between modules and tissues/stresses revealed that modules were significantly associated with stresses in the tissues where the modules were specifically highly expressed. Notably, module M7 was highly expressed in latex and dramatically responsive to ethylene, jasmonate, and tapping panel dryness treatments. Besides, the genes from M7 were significantly enriched in isoprenoid metabolism, indicating a great contribution of this module to rubber biosynthesis. The co-expression network of rubber biosynthesis genes from M7 revealed that small rubber particle protein 1 (SRPP1), cis-prenyltransferase 2 (CPT2), and rubber elongation factor 1 (REF1) were the most connected hub genes participating in rubber biosynthesis. Two candidate cis-regulatory motifs and three transcription factors that might regulate rubber biosynthesis were further identified. Genomic evolutionary analysis suggested that the expansion of two independently evolved REF/SRPP clusters, II (containing SRPP1) and V (containing REF1), was critical for rubber synthesis. Together, this integrative transcriptomic and genomic analysis provides novel insights into the hub genes and regulatory networks underlying rubber synthesis in H. brasiliensis.

Film formation process of natural rubber latex particles: roles of the particle size and distribution of non-rubber species on film microstructure

Natural rubber (NR) films from various mixing ratios of large- (LRP) and small rubber particles (SRP) were prepared through latex and solution casting methods. Film-forming behaviours of the resulting films were investigated by monitoring their surface characteristics using atomic force microscopy (AFM). When the SRP portion was higher, the surface of the latex-cast films was found to be smoother as smaller particles protruded out of the surface less than larger ones did. AFM phase micrographs revealed a hexagonal shape of packed rubber particles (RPs) of the LRP film, while the RPs in the other samples were sphere-like. After aging under ambient conditions, the packed RPs were flattened while retaining their RP boundaries, creating a supporting framework within the rubber matrix. On the contrary, when the rubber film was cast from a toluene solution, the characteristic of RP boundaries disappeared and became aggregates of the membrane components on the film surface. The latex-cast films performed much better in mechanical strength than the solution-cast films did due to the destruction of the supporting framework arisen from the non-rubber components at the RP boundaries of the solution-cast film. An inhomogeneous density distribution produced by the non-rubber aggregates in the latex-cast films was observed in small angle X-ray scattering measurements.

A label-free shotgun proteomics analysis of macadamia nut.

In this study, we present a systematic proteomic overview of macadamia nut using a label-free shotgun proteomic approach. We identified 947 proteins in 723 clusters and gene ontology analysis revealed proteins across 46 functional categories including carbohydrate metabolism (10%), protein metabolic processes (5%), amino acid metabolism (4%), transport (4%), stress response (3%), lipid metabolism (3%), protein folding (3%) and defense response (1.4%). The defense response proteins accounted for 24% of the total peptide abundance. The vicilin-like macadamia antimicrobial peptides 2-3 (MiAMP2) was the most abundant protein, followed by glyceraldehyde-3-phosphate dehydrogenase 3, 11S legumin-like protein, 2-phospho-D-glycerate hydrolase and heat shock 70kDa protein among others. The cascading of amino acid and carbohydrate metabolic pathways in macadamia nut were constructed against reference maps from KEGG and proposed for the first time. Results were also indicative of useful protein candidates with possible allergenic potential and cross-reactivity in macadamia nut. The in-silico analysis revealed homology and linear epitope similarities to known allergens such as conglutin β allergen from lupin, Jug r2 vicilin allergens from walnut, Ara h3 11S globulin from peanut, small rubber particle protein Hev b3, hevein, enolase 2, HSP 70kDa Cla h4, Der f28 allergen, and methylglyoxalases. Label-free shotgun proteomics reveal valuable insights into the genetic and biological makeup of macadamia nut proteome and provide guidance on protein candidates with allergenic potential for further immunological investigation. Data are available via ProteomeXchange with identifier PXD015364.

Histone deacetylase interacts with a WRKY transcription factor to regulate the expression of the small rubber particle protein gene from Hevea brasiliensis

Small rubber particle protein (SRPP) is an abundant rubber particle-associated protein that serves as a co-factor in the biosynthesis of natural rubber in Hevea brasiliensis. However, knowledge of SRPP gene (HbSRPP) expression in transcriptional regulation remains limited. In this work, the yeast one-hybrid experiment was performed to obtain the transcription factors that regulated HbSRPP and further study the natural rubber biosynthesis at the transcriptional level. A group I-type WRKY transcription factor (designated as HbWRKY14) was obtained, and expression analysis results showed that HbWRKY14 was highly expressed in latex. Moreover, methyl jasmonate and ethrel upregulated HbWRKY14 expression. HbWRKY14 can bind to the promoter of HbSRPP and showed capability to suppress the HbSRPP promoter. Thus, HbWRKY14 functions as a negative regulator of HbSRPP expression. Furthermore, H. brasiliensis histone deacetylase (named HbHDA3) interacted with HbWRKY14 and such interaction might relieve the HbWRKY14-mediated HbSRPP transcription inhibition.

Enhancing viscoelastic and mechanical performances of natural rubber through variation of large and small rubber particle combinations

There have been several reports investigating independent properties of large- (LRP) and small rubber particles (SRP). This work envisaged that, when co-existing, they could offer exceptional viscoelastic and mechanical properties from both components. Latex samples of various mixing ratios were prepared and properties of their rubber films were investigated against those of pure LRP and SRP to find that those containing 10–30% SRP were the best in mechanical strength and elasticity. This could be due to the combination of stronger phospholipid linkages in the LRP and void-filling ability of the SRP. The presence of SRP was shown to enhance curability in the vulcanised samples resulting in better mechanical performance of the vulcanisates. The 70/30 (LRP/SRP) blend showed the best thermal aging resistance among the vulcanisates. This suggested that the mixing ratios of the LRP and SRP contents were tunable to improve desirable properties of rubber products of interest, both green and cured.

Proteomic Landscape Has Revealed Small Rubber Particles Are Crucial Rubber Biosynthetic Machines for Ethylene-Stimulation in Natural Rubber Production.

Rubber particles are a specific organelle for natural rubber biosynthesis (NRB) and storage. Ethylene can significantly improve rubber latex production by increasing the generation of small rubber particles (SRPs), regulating protein accumulation, and activating many enzyme activities. We conducted a quantitative proteomics study of different SRPs upon ethylene stimulation by differential in-gel electrophoresis (DIGE) and using isobaric tags for relative and absolute quantification (iTRAQ) methods. In DIGE, 79 differentially accumulated proteins (DAPs) were determined as ethylene responsive proteins. Our results show that the abundance of many NRB-related proteins has been sharply induced upon ethylene stimulation. Among them, 23 proteins were identified as rubber elongation factor (REF) and small rubber particle protein (SRPP) family members, including 16 REF and 7 SRPP isoforms. Then, 138 unique phosphorylated peptides, containing 129 phosphorylated amino acids from the 64 REF/SRPP family members, were identified, and most serine and threonine were phosphorylated. Furthermore, we identified 226 DAPs from more than 2000 SRP proteins by iTRAQ. Integrative analysis revealed that almost all NRB-related proteins can be detected in SRPs, and many proteins are positively responsive to ethylene stimulation. These results indicate that ethylene may stimulate latex production by regulating the accumulation of some key proteins. The phosphorylation modification of REF and SRPP isoforms might be crucial for NRB, and SRP may act as a complex natural rubber biosynthetic machine.

Recycling waste rubber particles for the maintenance of different states of railway tracks through a two-step stoneblowing process

Abstract Injecting recycled rubber particles under the sleeper through a two-step stoneblowing technique (partially replacing the small stones with rubber) could improve the performance of ballasted railway tracks. In addition, this results in fewer environmental impacts associated with maintenance whilst recycling an abundant waste material (End-of-Life-Tyres, or ELTs). Nonetheless, to continue the development of this solution before its widespread application, this paper assesses the volumes and dosages of rubber to be used during the correction of various levels of irregularities and track states. The aim is to extend the service life of the track whilst optimizing performance by the inclusion of the elastic particles (particularly in transition sections where gradual variation of track behavior is required). For this purpose, innovative laboratory tests were used to study the effect of applying various quantities of rubber (recycled from ELTs) over small stones to correct three different levels of settlement. This paper presents the resulting guide values for the volumes of small stones and rubber particles to be added. These values depend on the level of track settlement to be corrected and the need for resilience according to the section and characteristics of traffic to be supported. Further, it appears that it is preferable to add the rubber after the compaction of the layer of small stones, which results in a lower tendency towards settlement and irregularities. Therefore, the current findings indicate that a two-step stoneblowing process (adding appropriate quantities of rubber) could be a cleaner technique for improving track behavior and reducing environmental impacts associated with maintenance.

Uncovering mechanisms of rubber biosynthesis in Taraxacum koksaghyz - role of cis-prenyltransferase-like 1 protein.

The Russian dandelion Taraxacum koksaghyz synthesizes considerable amounts of high-molecular-weight rubber in its roots. The characterization of factors that participate in natural rubber biosynthesis is fundamental for the establishment of T.koksaghyz as a rubber crop. The cis-1,4-isoprene polymers are stored in rubber particles. Located at the particle surface, the rubber transferase complex, member of the cis-prenyltransferase (cisPT) enzyme family, catalyzes the elongation of the rubber chains. An active rubber transferase heteromer requires a cisPT subunit (CPT) as well as a CPT-like subunit (CPTL), of which T.koksaghyz has two homologous forms: TkCPTL1 and TkCPTL2, which potentially associate with the rubber transferase complex. Knockdown of TkCPTL1, which is predominantly expressed in latex, led to abolished poly(cis-1,4-isoprene) synthesis but unaffected dolichol content, whereas levels of triterpenes and inulin were elevated in roots. Analyses of latex from these TkCPTL1-RNAi plants revealed particles that were similar to native rubber particles regarding their particle size, phospholipid composition, and presence of small rubber particle proteins (SRPPs). We found that the particles encapsulated triterpenes in a phospholipid shell stabilized by SRPPs. Conversely, downregulating the low-expressed TkCPTL2 showed no altered phenotype, suggesting its protein function is redundant in T.koksaghyz. MS-based comparison of latex proteomes from TkCPTL1-RNAi plants and T.koksaghyz wild-types discovered putative factors that convert metabolites in biosynthetic pathways connected to isoprenoids or that synthesize components of the rubber particle shell.

Pre‐Vulcanization of Large and Small Natural Rubber Latex Particles: Film‐Forming Behavior and Mechanical Properties

AbstractThe pre‐vulcanized large rubber particle (LRP) and small rubber particle (SRP) latices are independently prepared to investigate their film‐forming process and mechanical properties after being cast into films. The surface morphologies and roughness of both LRP and SRP films are found to be dependent on crosslink densities. The networks inside each rubber particle (RP) restrict particle deformation resulting in residual contour of RP within the film surface. For highly crosslinked RP, the collapse of the top surface of the RPs in the LRP films appears to create many “crater‐like” structures within the film surfaces, while they present only protruding particles within the SRP and blend films. This seems to indicate that LRPs are easier to coalesce and form film than SRPs. Additionally, dynamic and mechanical properties and strain‐induced crystallization (SIC) behaviors of the latex films, are effectively enhanced after pre‐vulcanization. The pre‐vulcanized LRP films perform better tensile properties and SIC than the SRP can.