Green Rubber Research Articles

High-performance volatile organic compounds free silica-filled butadiene rubber green nanocomposites using ionic liquid peroxide vulcanization

Manufacturing green rubber nanocomposites with higher performance and without volatile organic compounds (VOCs) is a big bottleneck for academics and the industry. Bis(3-triethoxysilylpropyl) tetra sulfide or Si69 silane is the most commonly used for green tires while during tire production it releases VOCs which are dangerous for people's health. Herein we elucidate that ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate can mediate physical and chemical reactions among silica and butadiene rubber (BR) and replace Si69 to fabricating rubber nanocomposites with free VOCs cured by Di cumyl peroxide (DCP). The findings reveal that IL chemically reacts with BR and that combining IL and Si69 shows similar tensile properties (φ = 0.079- 0.147) and higher strain at break in comparison with that containing Si69. Moreover, IL synergistically impacts silica-filled BR nanocomposites viscoelastic, thermal, and dielectric properties. It influences the Payne effect by reducing loss modulus improving weak strain overshoot markedly (the ΔG''/G''0 and tanδ0 values of the vulcanizate containing IL/Si69 are 465% higher and 42.8% lower than that containing Si69) and thermal stability and dielectric properties. Compared with BR nanocomposites containing Si69 at the same amount, IL significantly reduces the tangent value and dissipation energy, providing a simple method to fabricate green rubber nanocomposites with tunable reinforcement behaviors.

Identification of the Sex Pheromone of the Asparagus Moth, Parahypopta Caestrum (Lepidoptera, Cossidae)

Chemical, electrophysiological, and field trapping experiments were carried out to identify the female-produced sex pheromone of the asparagus moth, Parahypopta caestrum, a very serious pests of asparagus cultivations in southern Europe. Gas chromatography coupled with mass spectrometry and electroantennogram detection (GC-MS-EAD) analysis of hexane and solid-phase microextraction (SPME) extracts of sex pheromone glands of calling females consistently detected four compounds eliciting EAG responses in male moth antennae. According to their GC retention times, mass spectra, and comparative EAG analyses with reference standards, these EAD-active compounds were identified as (Z)-9-tetradecenol (Z9-14:OH), (Z)-5-tetradecenyl acetate (Z5-14:Ac), (Z)-7-tetradecenyl acetate (Z7-14:Ac), and (Z)-9-tetradecenyl acetate (Z9-14:Ac), respectively. In the SPME extracts from the head-space of individual abdominal tips, Z9-14:Ac, Z5-14:Ac, Z7-14:Ac, and Z9:14 OH were detected in the ratio of 82:9:5:4. In EAG dose-response experiments, Z9-14:Ac was the strongest antennal stimulant at different doses tested. In field trapping experiments, Z9-14:Ac, Z7-14:Ac, and Z5-14:Ac proven to be essential for male attraction and a their 85:5:10 blend loaded onto green rubber septum dispensers was significantly more effective than single-, two-, and any other three-component blend of these compounds. The addition of Z9-14:OH to the optimal blend resulted in a significant reduction of male catches. The attractive blend here identified allowed for an effective and accurate monitoring of P. caestrum flight activity in southern Italy.

Conventional and Green Rubber Plasticizers Classified through Nile Red [E(NR)] and Reichardt’s Polarity Scale [ET(30)

After a survey on polymer plasticization theories and conventional criteria to evaluate polymer–plasticizer compatibility through the solubility parameter, an attempt to create a polymer–plasticizer polarity scale through solvatochromic dyes has been made. Since Reichardt’s ET(30) dye is insoluble in rubber hydrocarbon polymers like polyisoprene, polybutadiene and styrene–butadiene copolymers and is not useful for the evaluation of the hydrocarbons and ester plasticizers, the Nile Red solvatochromic dye was instead used extensively and successfully for this class of compounds. A total of 53 different compounds were evaluated with the Nile Red dye and wherever possible also with Reichardt’s ET(33) dye. A very good correlation was then found between the Nile Red scale E(NR) and Reichardt’s ET(30) scale for this class of compounds focusing on diene rubbers and their typical hydrocarbons and new ester plasticizers. Furthermore, the E(NR) scale also shows a reasonable correlation with the total solubility parameter calculated according to the Van Krevelen method. Based on the above results, some conclusion was made about the compatibility between the diene rubbers and the conventional plasticizers, as well as a new and green plasticizer proposed for the rubber compounds.

Property Improvements of Silica-Filled Styrene Butadiene Rubber/Butadiene Rubber Blend Incorporated with Fatty-Acid-Containing Palm Oil.

Using vegetable oils as a plasticizer or processing aid in green rubber products is becoming popular due to environmental concerns. However, differences in vegetable oil processing result in varying amounts of low-molecular-weight (low-MW) free fatty acids (FFAs) in their composition, which range from 2% to 30%. This research investigated how the properties of silica-filled styrene butadiene rubber (SBR) and butadiene rubber (BR) blends were affected by the presence of FFAs in palm oil (PO). The rubber compounds containing a 70/30 SBR/BR blend, 30 phr of silica, and 2 phr of bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT), and the vulcanizing agents were prepared and tested. The PO content was kept constant at 20 phr, while the number of FFAs, i.e., lauric acid (LA), palmitic acid (PA), and oleic acid (OA), in PO varied from 10-30%. The viscosity, dynamic mechanical properties, morphology, cure characteristics, and mechanical properties of the rubber blend were then measured. Regardless of the FFA types, increasing FFA content in PO decreased scorch time, cure time, minimum torque, and viscosity. As the FFA content increased, the torque difference and crosslink density also increased, which led to higher hardness, modulus, tensile strength, and abrasion resistance. The FFA types had a slight effect on the vulcanizate properties, even though LA showed slightly better mechanical properties than PA and OA. The results reveal that FFAs in PO not only improve processability but also function as a co-activator in silica-filled sulfur-vulcanized SBR/BR blend compounds.

Green Approaches in Rubber Recycling Technologies: Present Status and Future Perspective

As a consequence of massive production and consumption of rubbers, rubber blends, and rubber composites for myriad applications, elastomeric products have enormously accumulated and become an environmental threat. The disposal and burning of rubber wastes have been banned because of environmental and economic reasons. By contrast, a great deal of attention has been directed toward strategies enabling recycling and reuse of rubbers. Basically, conventional recycling methods suffer from several drawbacks such as the formation of dust, fumes, and toxic gases in the air, as well as contamination of underground water resources. Thus, green and sustainable formulations and processing methods nowadays are of priority and importance. Taking advantage of sustainable development horizons, scientific and technological aspects of waste rubber management such as processing techniques, properties of the resulting products, industrial applications, and compatibilization with other materials such as thermoplastics, thermosets, and rubbers are herein reviewed and discussed. A particular emphasis is placed on reactive extrusion as a highly flexible in situ compounding method enabling innovations and taking care of sustainability concerns. Finally, the current status of green rubber recycling and future opening doors ahead of this technology are highlighted.

Construction of Biomass Tea Polyphenol-Functionalized Halloysite Nanotubes Enabling Green and Sustained-Release Antioxidants for Highly Antiaging Elastomers

The strategy of using sustainable biomass resources instead of traditional petrochemical products has been established as an environmentally friendly way to achieve the “green rubber” industry. Meanwhile, rubber antioxidants possessing high efficiency, long-lasting protection, migration resistance, and green multifunctional properties have attracted intensive investigation for rubber protection. Herein, a naturally extracted substance of tea polyphenol (TP)-functionalized halloysite nanotubes (HNTs), which generates the slow release of free-radical capturing activity and excellent interfacial interaction in the natural rubber matrix, is fabricated by vacuum-pumping and surface-decorating methods (denoted as HNTs-s-TP). Interestingly, the nontoxic and natural antioxidant HNTs-s-TP exhibited remarkable thermo-oxidative aging resistance and stability in a natural rubber (NR) matrix compared to that of TP directly pumped into the tubes due to the further modification of the chemical anchor TP on the outer surface of HNTs. In addition, we have systematically investigated the mechanism for highly efficient and sustainable antioxidation in the rubber matrix via the natural antioxidant HNTs-s-TP derived from the constructed galloyl structure. We envision that this new natural antioxidant fabrication technology will provide significant insights into the innovation for the construction of green and eco-friendly functionalized rubber additives.

Construction of renewable biomass cardanol functionalized spherical nanoparticles achieving favorable interfacial interaction and thermostability in styrene butadiene rubber matrix

AbstractTo expand the application of natural resources in the green rubber industry and reduce the dependence of rubber additives on the non‐renewable petrochemical resources, a novel cardanol‐based natural rubber additive (silica‐s‐LPCGE) is prepared. Compared with the directly adding of silica and LPCGE, silica‐s‐LPCGE is assisted to form an effective interfacial interaction between the rubber matrix and the filler during rubber vulcanization by the immobilized LPCGE on silica surface, to improve the mechanical property and processability of styrene‐butadiene rubber (SBR)/silica‐s‐LPCGE composites. Meanwhile, with the introduce of silica‐s‐LPCGE, the aging resistance and migration resistance of the SBR composites are also improved obviously. The preparation of this novel multifunctional supported natural biomass processing additive provides a new possibility for the preparation of green rubber additives.

Sustainable Composites Based on Natural Rubber and Biomass Resources

Abstract: For the past two decades, environmentally friendly natural rubber composites and nanocomposites reinforced with renewable and biodegradable natural fillers has attracted increasing attention of polymer researchers from both industrial and environmental viewpoints. The use of bio-based fillers in rubber materials has emerged as extremely promising in the progress of green rubber technology. The dispersion of bio-based fillers within the rubber matrix is the key parameter that decides the overall performances of bio-based rubber composites. An important criterion for obtaining superior properties in rubber composites is good interfacial adhesion between natural fillers and natural rubber matrix, along with good dispersion and distribution of fillers within the matrix. Natural fillers represent materials that are environmentally friendly, easily available, comprising of valuable lignocellulosic fractions and are from a bio-based feedstock. Recent developments in this area focus on renewable fillers such as cellulose, chitin and lignin in its micro and nanoforms. Additionally, recent studies have focused on the use of different type of biomass residue wastes in rubber composites with a view to adapt to the recent circular economy principles. This review presents an overview of various studies and highlights in the area of bio-based filler reinforced natural rubber composites and also discusses the applications of such materials in industrial sectors.

Effect of Agricultural Social Services on Green Production of Natural Rubber: Evidence from Hainan, China

It is vital to concentrate on conserving the ecological environment and promoting production efficiency in the process of planting natural rubber. Agricultural social services (ASSs) play an essential role in helping rubber farmers to achieve green production. Based on the survey data of 552 natural rubber farmers in Hainan Province, this study builds an index system regarding socialized services for rubber production from three factors: technology extension services, financial insurance services, and market information services. This research uses the slack-based measure (SBM) model and the Tobit model to analyze the green production efficiency (GPE) and the influences of rubber production socialized services on the rubber growers’ green production efficiency. Our results revealed that (1) the average green productivity of rubber planting in Hainan is approximately 0.41, which means that there is ample space for improvement; (2) ASSs have a significant positive effect on increasing the green rubber production efficiency; and (3) among ASSs, the technical extension service has the most significant effect on improving the green production efficiency of the growers. To further raise GPE of natural rubber, the socialized service system can be strengthened in terms of technology, capital, and information. ASSs have noticeable potential in improving the efficiency of rubber green production while ensuring economic, social, and ecological sustainability.

Reinforcing mechanism and experimental study of environmentally friendly potassium oleate in silica/natural rubber system

AbstractThis paper prepared potassium oleate/silica/natural rubber composites by atomization spray drying technology. This study compared the effects of the environmental protection accelerator potassium oleate and amine accelerator 1,3‐diphenylguanidine on the Payne effect, silane reaction index, vulcanization performance, mechanical properties, static and dynamic mechanical properties, and aging properties of silica/natural rubber. The results show that potassium oleate can promote the silane reaction and increase the silane reaction's efficiency. When potassium oleate formed the silica coating, the carboxyl group of potassium oleate and the hydroxyl group of silica were bonded to form a covalent bond, which reduced the polarity of silica and promoted the dispersion effect of silica in the rubber matrix and enhanced the compatibility with rubber. Compared with the original formulation, after adding 3 phr of potassium oleate, the fracture elongation of vulcanized rubber was increased by 17.2%, tensile product increased by 57.3% and rolling resistance decreased by 54.6%. After adding 3 phr of 1,3‐diphenylguanidine, the fracture elongation of vulcanized rubber was increased by 1.1%, tensile product increased by 51.1% and rolling resistance decreased by 48.6%. In contrast, the anti‐aging performance of the rubber composites with potassium oleate was better than that of 1,3‐diphenylguanidine. This study opens up a new way to apply a new green rubber accelerator and prepare high‐performance rubber composites.

Moisture crosslinking and properties of ethylene-vinyl acetate rubber

Ethylene-vinyl acetate rubber (EVM) is commonly crosslinked by peroxides due to its saturated main chain. Nevertheless, it is usually accompanied by side reactions to bring unexpected bubbles in products. So, it is necessary to find an alternative and environment friendly crosslinking for EVM. Herein, a silane of γ -aminopropyltriethoxysilane (APTES) containing amino groups was adopted as monomer to graft on the matrix of a modified polymer of EVM named ethylene-vinyl acetate-glycidyl methacrylate terpolymer elastomer (EVM-GMA). EVM-GMA-g-APTES was prepared through melt blending followed by the moisture crosslinking, which was achieved in a 90 °C water bath with the aid of catalyst dibutyltin dilaurate (DBTL). It was found that the characteristic absorption peak belonging to the Si–O–C bond of the purified samples appeared at 1077 cm −1 on the infrared spectrum, indicating the reaction between amino groups in APTES and epoxy groups in EVM-GMA happened successfully. Besides, the moisture curing curves of EVM-GMA-g-APTES compounds kept rising over time, which denoted that the chemical crosslink occurred and the Si–O–Si networks had been formed. Additionally, the modulus and tensile strength of moisture crosslinked samples were elevated remarkably with the increasing APTES content, and the samples with 2.5 phr APTES had relatively rational mechanical properties. Moisture crosslinking was feasible for EVM-GMA since the mechanical performance of the moisture crosslink was better than that of the peroxide crosslink system at a similar crosslink density. It was carried out successfully for the grafting reaction between ethylene-vinyl acetate-glycidyl methacrylate terpolymer elastomer (EVM-GMA) matrix and γ -aminopropyltriethoxysilane (APTES), and moisture cured EVM-GMA-g-APTES compounds were acquired through 90 °C a water bath, which showed excellent mechanical properties than that of peroxide crosslinked at a similar crosslinking density. • The grafting reaction between APTES and EVM-GMA happened successfully. • Various characterization methods (FTIR, EDS and RPA) were used to investigate the grafting mechanism of EVM-GMA-g-APTES. • The moisture crosslinked EVM-GMA-g-APTES has unique mechanical properties. • A new approach to develop green rubber crosslinking.

Facile strategy for the preparation of green graphene rubber with enhanced interfacial interaction and thermal management capability

AbstractThe development of high‐performance green rubber materials with excellent comprehensive properties is very important for the environment and resources. Graphene has excellent electrical, mechanical, and thermal properties and is regarded as the most promising functional filler for rubber composites. In this work, a facile and efficient strategy was used to prepare graphene rubber materials with balanced integrated properties by chemical modification of graphene oxide (GO) with gelatin (Gel). Gel molecules as bridges could not only connect with GO by chemical bonds, but also physically entangle with natural rubber (NR) molecules. The optimized dispersibility of GO and the enhanced interfacial interaction between GO and NR together enable graphene rubber to exhibit excellent integrated properties, such as tensile strength of 29.7 MPa and heat build‐up of 1.9°C only at 1 phr of Gel‐rGO (G‐rGO) content. Additionally, finite element simulation was used to evaluate the temperature field distribution of graphene rubber tires, and the temperature of the NR/Gel‐rGO (NR/G‐rGO) tread was 17.3°C lower than that of NR/GO. This work will provide effective strategies for the preparation of high‐performance graphene rubber materials.

Investigating the potential of sustainable use of green silica in the green tire industry: a review.

Undoubtedly, with the increasing emission of greenhouse gases and non-biodegradable wastes as the consequence of over energy and material consumption, the demands for environmentally friendly products are of significant importance. Green tires, a superb alternative to traditional tires, could play a substantial part in environmental protection owing to lower toxic and harmful substances in their construction and their higher decomposition rate. Furthermore, manufacturing green tires using green silica as reinforcement has a high capacity to save energy and reduce carbon dioxide emissions, pollution, and raw material consumption. Nevertheless, their production costs are expensive in comparison with conventional tires. In this review article, by studying green tires, the improvement of silica-rubber mixing, as well as the production of green silica from agricultural wastes, were investigated. Not only does the consumption of agricultural wastes save resources considerably, but it also could eventually lead to the reduction of silica production expenses. The cost of producing green silica is about 50% lower than producing conventional silica, and since it weighs about 17% of green silica tires, it can reduce the cost of producing green rubber. Accordingly, we claim that green silica has provided acceptable properties of silica in tires. Apart from the technical aspect, environmental and economic challenges are also discussed, which can ultimately be seen as a promising prospect for the use of green silica in the green tire industry.

Synergistic effect of cuttlebone particles and non‐rubber components on reinforcing ability of natural rubber and synthetic isoprene rubber composites

AbstractThe comparison of the reinforcing ability of cuttlebone (CTBO) particles in natural and synthetic isoprene rubber (NR and IR, respectively) composites were investigated. The CTBO particles could reinforce in both NR and IR composites. However, the improvement of tensile properties in CTBO‐filled NR composites was higher than that of IR composites due to the presence of non‐rubber components in NR. The non‐rubber components promoted the strong interfacial adhesions with filler and rubbery matrix to increase the bound rubber content. These results affected the increase of the stress softening degree, hysteresis loss, residual strain during cyclic deformation and the volume fraction of constrained rubber region (immobilized area of rubber) in CTBO‐filled NR composites. The atomic force microscopy evidently revealed good compatibility between the CTBO particles and the NR matrix due to the presence of organic components from CTBO particles and from non‐rubber components in NR. Accordingly, the CTBO particles and non‐rubber components play important roles in improving the properties of green rubber composite materials.

Biomass antioxidant silica supported tea polyphenols with green and high-efficiency free radical capturing activity for rubber composites

To achieve simultaneous environment protecting, high-efficiency rubber antioxidant is still an enormous and long-term challenge in green rubber industry. Hence, a novel biomass antioxidant (denoted as silica-s-TP) was obtained by silica supported with green tea polyphenols exhibited prominent anti-aging functionality. Silica-s-TP hybrid particles were uniformly dispersed in rubber matrix with remarkable interfacial interaction, and the high-efficiency free radical capturing activity was stem from the construction of polyphenol structure on silica surface. Therefore, silica-s-TP brought to simultaneously enhance the performance of anti-aging property of SBR composites and surpass the achievements of the commercial antioxidants. Interesting, the biomass antioxidant silica-s-TP exhibited remarkable free radical-scavenging activities and stability in SBR matrix than the TP directly added in SBR matrix, due to the chemical anchor TP on silica surface. Such clay surface treatment technology with natural antioxidant may also bring to a new path for the preparation of green and eco-friendly functionalization rubber additives.

Influence of Oligopeptide Length and Distribution on Polyisoprene Properties.

The tuning of binding modes of polar groups is the key step to mimicking the structure and properties of natural rubber through the molecular design of synthetic polyisoprenes. Herein, the ordering and binding distances of oligopeptides could be altered systematically by changing their lengths and distribution along the polyisoprene chain, which impose huge impacts on the mechanical properties and chain dynamics of green rubber. In detail, a series of peptide-functionalized polyisoprenes with terminal blocks (B-2A-PIP, B-3A-PIP) or random sequences (R-2A-PIP, R-3A-PIP) are fabricated by using dipeptides (2A) or tripeptides (3A) as crosslinkers to explore the mechanism of terminal interaction on mechanism properties and chain dynamics. B-4A-PIP and R-4A-PIP served as control samples. It is found that the increased oligopeptide length and the block distribution improves the mechanical properties and confine the chain movement by elevate the contents of ordered and compact microstructures, which is indicated by XRD, broadband dielectric spectroscopy (BDS) and consistent with the result of molecular dynamics simulation. New relaxation signals belonging to oligopeptide aggregates are found which showed elevated dielectric strengths upon temperatures increase. Additionally, it also reveals that the binding modes of oligopeptide do not significantly influence the entanglements of polyisoprene.

ALE formulation for thermomechanical inelastic material models applied to tire forming and curing simulations

Forming of tires during production is a challenging process for Lagrangian solid mechanics due to large changes in the geometry and material properties of the rubber layers. This paper extends the Arbitrary Lagrangian–Eulerian (ALE) formulation to thermomechanical inelastic material models with special consideration of rubber. The ALE approach based on tracking the material and spatial meshes is used, and an operator-split is employed which splits up the solution within a time step into a mesh smoothing step, a history remapping step and a Lagrangian step. Mesh distortion is reduced in the smoothing step by solving a boundary value problem. History variables are subsequently remapped to the new mesh with a particle tracking scheme. Within the Lagrangian steps, a fully coupled thermomechanical problem is solved. An advanced two-phase rubber model is incorporated into the ALE approach, which can describe green rubber, cured rubber and the transition process. Several numerical examples demonstrate the superior behavior of the developed formulation in comparison to purely Lagrangian finite elements.

Recent advances of natural fibers based green rubber composites: Properties, current status, and future perspectives

AbstractThe searching of suitable alternatives to petroleum‐based fillers is an uncompromising challenge in present day rubber research. Recently, natural fibers are the part of great attention of both academic and industrial researchers due to their easy availability, environmental friendliness, and biodegradability. Natural fiber is cellulose‐rich material, which is preferentially used as alternative filler in rubber technology. This article reviews current advances in natural fibers filled rubber composites in terms of mechanical, thermal, and biodegradable properties (2010–2020). The incorporation of unmodified natural fibers as filler is not able to offer desired reinforcement in rubber composites. Several surface modification methods can be introduced to improve the overall performances of natural fibers filled rubber composites. Finally, the review clarifies present status and future prospects of natural fibers based advanced rubber composites in automobile industry. The successful designing of natural fibers based sustainable rubber composites can introduce a new era in green rubber technology.

Assessment of Land Resources Potentials for Orientated Agriculture Land Use in Ham Thuan Bac district, Binh Thuan province.

Land resources potential assessment is a valuable method for orienting land use planning in the world as well as in Vietnam.The objectives of the study are (1) to assess land suitability and (2) to orient the effective use of agricultural land in the study area. Results indicated that Ham Thuan Bac has 107 land mapping units (LMU), in which includes 11 land-use types (LUTs) such as rice, corn, cassava and sweet potato, sugarcane, grass for livestock, vegetables, green dragon fruit, rubber, coffee, and other fruit trees. Agricultural land with high suitability (S1) and moderately suitable (S2) for mostly LUTs is small, however, marginally suitable (S3) and not suitable land (N) are quite large. More than 50% of the LUTs for growing rice, rubber, coffee, other fruit are not suitable; the remaining LUTs have unsuitable land ranging from 10.76% to 25.16% of agricultural land in the district. Based on land suitability classification, we propose to keep 8550 ha with S1, S2, and a part of S3 area to be irrigated for cultivating rice; 9071.7ha of dragon fruit land including 694.67 ha of S1 and 8377.03 ha of S2 land; and only cultivate annual crops, fruit trees and grazing grass on the land with suitble levels from S1 to S3 of the current status.The remainingareas ofS3 and N for riceand areas of S2 and S3for green dragon fruit under S2, S3with active and semi-active irrigation regimeswill be converted to annual crops and fruit trees and grass for livestock.

Novel Hybrid Biomass Anti-Aging Filler for Styrene-Butadiene Rubber Composites with Antioxidative and Reinforcing Properties.

Antioxidants are normally utilized to extend the service life of polymers due to the strong reducibility of the phenolic hydroxyl group of the hindered phenol structure. Inspired by this characteristic, we have introduced green tea polyphenol (TP) supported on a silica surface containing considerable phenolic hydroxyl groups to obtain a novel biomass anti-aging filler (BAF, denoted as silica-s-TP) to reinforce and improve the anti-aging property of rubber composites. The applying of silica-s-TP to enhance the thermal-oxidative stability and ultraviolet light (UV) aging resistance of styrene-butadiene rubber (SBR) was evaluated. The hybrid biomass anti-aging filler could not only uniformly disperse in the rubber matrix, giving rise to the excellent mechanical properties, but also enhance the properties of thermal-oxidative stability and UV aging resistance with the increasing silica-s-TP content of SBR distinctly. This study provides a mild and environmentally friendly strategy to prepare the functional biomass filler, which could be applied as not only a reinforcement filler but also an anti-aging additive in “green rubber”.