Natural Rubber Vulcanizates Research Articles

Thermal and mechanical properties of PLA/ENR thermoplastic vulcanizates compatibilized with tetrafunctional double-decker silsesquioxanes

The influence of the addition of tetrafunctional double-decker silsesquioxanes (DDSQ-ether-4OH) on the compatibility, thermal and mechanical properties of polylactide and epoxidized natural rubber (PLA/ENR) vulcanizates was investigated. The apparent cross-linking density and thermal stability of PLA/ENR vulcanizates were also determined. The FTIR analysis confirmed the compatibilizing effect of DDSQ-ether-4OH and the formation of the PLA-g-ENR copolymer. A strong effect of ENR content and DDSQ-ether-4OH addition on the thermal and mechanical properties of the obtained vulcanizates was demonstrated.

Structure and properties of resole resin crosslinked vulcanizates of natural rubber grafted with polymethylmethacrylate

Structure and properties of resole resin crosslinked vulcanizates of natural rubber grafted with polymethylmethacrylate

Physical Properties Investigations of Natural Rubber Composites Using Cetyltrimethylammonium Bromide (CTAB) as Modifier of Local Clay Filler

Improved absorption of rubber backbone on filler surfaces is necessary to enhance the physical properties of rubber vulcanizate. One of the ways to repair the surface of the filler is through modifying using surfactant. Hence, this study aims to compare the physical properties of natural rubber vulcanizates using clay filler and modified clay with cetyltrimethylammonium bromide (CTAB). The processes that were followed to achieve the objectives of this research were the design of rubber formulas, mastication and milling of rubber, and testing of the physical properties of rubber vulcanization. The clay characterization and its modification using FTIR and XRD were also carried out. Characterization using FTIR and XRD showed that there was indeed a clay modification with CTAB. Natural rubber compounds were also analyzed using SEM. The torque on the rheometer for modified clay with CTAB is 12.34 kg-cm higher than for original clay, which is 7.05 kg-cm. Elongation at break and tensile strength for vulcanizate using CTAB-modified clay filler is lower than that using original clay, with 300% modulus and hardness increase. Thus, clay modification using CTAB as a filler has a good effect on the curing characteristics and physical properties of natural rubber vulcanization compared to only using local clay as a filler.

Polyurethane Glycerolysate as a Modifier of the Properties of Natural Rubber Mixtures and Vulcanizates.

Chemical recycling of polyurethanes can be realized in several different ways, but the most important methods are glycolysis and glycerolysis. Both methods permit recovery of polyols (when the process is realized with the mass excess of depolymerizing agent) or substitutes of polyols, which contain urethane moieties in the main chains and terminate mainly in hydroxyl groups (when the process is realized with the mass excess of depolymerized polyurethane). Oligomeric products with urethane groups in the chemical structure can also be used as modifiers of rubber mixtures and vulcanizates. The main aim of the presented work is to study the effect of polyurethane glycerolysate on the performance of natural rubber mixtures and vulcanizates. The influence of the modifier on the vulcanization kinetics and swelling of rubber mixtures, and the thermo-mechanical and mechanical properties of rubber vulcanizates, was studied. The prepared materials were also subjected to accelerated thermal aging in air. It was found that polyurethane glycerolysate affects the vulcanization process of rubber mixtures (for example, promotes the activation of vulcanization) and acts as an antidegradant under thermoxidative conditions (higher stability of mechanical properties was observed in comparison to a reference sample without modifier). The obtained results show that chemical recycling products can be valuable modifiers of natural rubber mixtures and vulcanizates, which extends the possible applications of polyurethane chemical recycling products.

Enhancement of hydrophobicity in natural rubber vulcanizates using diatomaceous earth

This study discusses an approach that gives the Natural Rubber (NR) vulcanizates an elevated hydrophobic character. The method used a chemically treated filler called diatomaceous earth (DE) to deliver the hydrophobic characteristics to NR. DE has a nanoscale roughness. It was chemically treated with hexadecyltrimethoxy silane to obtain low surface energy. The combination of nanoscale roughness and low surface energy gave superhydrophobic properties to DE. A series of treated-DE was made with varying silane percentages to find an optimum silane to DE ratio to get the maximum possible hydrophobicity. The optimum ratio was recorded as 38% w/w, and the treated DE displayed a superhydrophobic water contact angle (WCA) of 152°. The treated-DE was added to the rubber as a filler during the compounding process. The filler was added in varying amounts of 5 phr, 10 phr, 15 phr, and 20 phr to observe the changes in the hydrophobic property. The wettability and morphology of developed vulcanizates were measured using WCA measurements and scanning electron microscope (SEM) analysis, respectively. NR compounded with 20 phr filler exhibited an enhanced WCA of 136°, compared to the WCA of 92° of the NR vulcanizate with no treated-DE, and displayed improved tensile, and tear properties.

Study of rheological characteristics and mechanical strength properties of natural rubber vulcanizates varying the type and content of carbon black

This paper presents a study about the influence of the size and content of two types of carbon black N220 and N550 with loading of 10–100 phr on the properties of the vulcanized natural rubber (NR).The mechanical characteristics such as the tensile strength, the tensile modulus, the elongation at break, the hardness, the abrasion resistance, and rheological properties of NR reinforced with carbon black were investigated. By analyzing the results of an N220 reinforced NR, the reinforcement gives improvement in tensile strengths when fillers are added up to 70 phr. However, and by referring of elongation at break, a fall of product elasticity is observed. . The increase of filler loading results a decrease in rheological properties; optimum cure time, scorch time, cure rate index (CRI). Furthermore, the increase of the filler loading leads to the increase in hardness for all the compounds. Compared the reinforcing ability of carbon black N220 scarcely inferior to carbon black N550.However, it seems that the rubber compound filled N220 or N550 gives comparable results on mechanical properties.

Effect of deep eutectic solvents on vulcanization and rheological behaviors of rubber vulcanizates

Deep eutectic solvents (DESs) are able to promote vulcanization of rubbers while the mechanisms remain unclear. Herein 4-methyl-5,7-dihydroxycoumarin (DHMC) as hydrogen bond donor (HBD) was used to synthesize DES by reaction with tetrabutylammonium bromide (TBAB) as hydrogen bond acceptor (HBA). The effects of DHMC, TBAB and DES on vulcanization of natural rubber (NR) and isoprene rubber (IR) were studied. It is shown that DES could participate in crosslinking network and adjust crosslinking density (vc) of the vulcanizates through physical and chemical interactions with NR non-rubber components, zinc oxide (ZnO) activator and N-cyclohexyl-2-benzothiazolesulfenamide (CZ) accelerator. Furthermore, DES influences linear and nonlinear rheological responses and mechanical behaviors of NR vulcanizates. The NR vulcanizates cured at 120 °C with 0.1–0.3 phr (part per hundred parts of rubber) DES exhibit higher tensile strengths and lower vc in comparison with the control one cured at 140 °C, which is assigned to the more homogenous crosslinking network in the former. This work provides an effective way to modulate the crosslinking network to produce high-strength vulcanizates at lowered vulcanization temperatures and ZnO amount, which is beneficial for the preparation of rubber products with high strengths and low hysteresis energies.

Synthetic Polyisoprene Rubber as a Mimic of Natural Rubber: Recent Advances on Synthesis, Nanocomposites, and Applications.

Up to now, rubber materials have been used in a wide range of applications, from automotive parts to special-design engineering pieces, as well as in the pharmaceutical, food, electronics, and military industries, among others. Since the discovery of the vulcanization of natural rubber (NR) in 1838, the continuous demand for this material has intensified the quest for a synthetic substitute with similar properties. In this regard, synthetic polyisoprene rubber (IR) emerged as an attractive alternative. However, despite the efforts made, some properties of natural rubber have been difficult to match (i.e., superior mechanical properties) due not only to its high content of cis-1,4-polyisoprene but also because its structure is considered a naturally occurring nanocomposite. In this sense, cutting-edge research has proposed the synthesis of nanocomposites with synthetic rubber, obtaining the same properties as natural rubber. This review focuses on the synthesis, structure, and properties of natural and synthetic rubber, with a special interest in the synthesis of IR nanocomposites, giving the reader a comprehensive reference on how to achieve a mimic of NR.

Preparation of Multifunctional Additive [MFA] from Castor Oil (CO) and Study of its Effects on the Physical Properties of Natural Rubber Vulcanizates

This experiment focuses on the synthesis of Multifunctional Additives (MFA) from Castor seed oil (CO) and pure Oleic acid (OA) respectively. These multifunctional additives (CO-MFA and OA-MFA) were investigated as potential substitutes for process oil, activator, co-activator, and accelerator in the formulation of a natural rubber vulcanizate. During processing, the castor seed oil was characterized for acid value (AV), free fatty acid (FFA) and saponification value (SV) and subsequently reacted with 1, 6-hexane diamine to obtain a mixture of salts termed castor oil-based multifunctional additives (CO-MFA), similarly, a pure oleic acid was also reacted with 1, 6-hexane diamine to obtain a pure salt termed oleic acid-based multifunctional additive (OA-MFA). These compounds were investigated as substitutes for process oil/stearic acid, process oil/stearic acid/zinc oxide, process oil/MBT, and process oil/stearic acid/zinc oxide/MBT in the formulation and compounding of natural rubber vulcanizate. The pre-mastication of the rubber and subsequent mixing with additives was carried out in a Banbury Internal Mixer at a rotor speed of 50 rpm for 7 mins while the vulcanization was achieved on a compression molding machine at a temperature of 140oC for 15 mins. The various vulcanizates samples were evaluated for tensile properties, compression set, abrasion resistance, and hardness. The use of castor seed oil-based multifunctional additives (CO-MFA) as a substitute for process oil/stearic acid/zinc oxide/MBT gave the highest value of tensile strength (12.24 MPa) as against the conventional rubber compound (4.21 MPa).

Effect of green synthesized zinc oxide nanoparticles as cure activator on the mechanical properties of natural rubber vulcanizate

Effect of green synthesized zinc oxide nanoparticles as cure activator on the mechanical properties of natural rubber vulcanizate

Microstructure Evolution and Strain Softening of Carbon Black Filled Natural Rubber Vulcanizates

Microstructure Evolution and Strain Softening of Carbon Black Filled Natural Rubber Vulcanizates

Effect of the thermoplastic types and ratios for the 3D printed thermoplastic natural rubber vulcanizates: Mechanical, dynamical, thermal, printed-structural properties

Since the crosslinked natural rubber (NR) products contain chemical crosslinks, the materials have loosened the biodegradable and environmentally friendly properties. Combination of NR and thermoplastic, so called thermoplastic natural rubber (TPNR), can be a proper approach for solving this evident through new technological processing. Therefore, the three-dimensional 3D printing TPNR based on polypropylene (PP) and high-density polyethylene (HDPE) thermoplastics were carried out. Blending ratios of 70:30 and 80:20 have investigated, while the dynamically cured system was applied to the blends. This aims to the NR applications and solves the end-cycled of NR waste which cannot be recycled. Relating the molecular structure of the blends, the crosslinked NR particles are dispersed and distributed in the PP phase, while the superior toughness of HDPE provides high elongation at break and impact strength. However, the high crystallinity of PP combined with its low toughness and high stickiness makes it a more broadly applicable 3D printing material than HDPE. It was found that the complexed 3D printing of PP/NR at 80:20 showed the highest compressive strength relative to pure PP. This indicates the improvement of the intrinsic properties of the blends. This improvement can be advantageous for the NR product platform when it is incorporated in PP and parts are produced by 3D printing.

Research of strain induced crystallization and tensile properties of vulcanized natural rubber based on crosslink densities

Natural rubber (NR) has excellent mechanical properties than synthetic rubber for its strain induced crystallization (SIC) property. It is known that crosslink density has significant influences on SIC, but mechanism of SIC enhanced tensile properties based on crosslink densities has not investigated clearly. In this study, vulcanizates of NR and NR devoid of non-rubber components, characterized by varying crosslink densities, are prepared. Mechanical and crystallization properties and the structure evolution of the systems occurring during stretching are analyzed by conducting tensile tests and using the in-situ (WAXD) technique. Results reveal that the crosslink density significantly affects the mechanical properties and SIC of the NR materials. The maximum tensile strength is recorded when the crosslink density is 1.84 × 10−4 mol/cm3. The structural evolution of the NR vulcanizates characterized by varying crosslink densities is reported, and the strengthening mechanism associated with the systems is proposed. The stretching process associated with the NR vulcanizates can be divided into three stages, namely stages I, II, and III, based on the crystallization process. The NR vulcanizates characterized by low crosslink densities are primarily reinforced by a series of crystallites in stage II of stretching. Stress upturn is realized following the formation of a large number of crystallite networks in stage III. NR vulcanizates characterized by high crosslink densities form parallel reinforcements with the surrounding network post crystallization in stage II, and this can be attributed to the presence of a large number of crosslink chains in the system. Stress upturn can be realized even in the presence of a small number of crystallite networks in stage III. Furthermore, the results indicate that the process of crystallization significantly affects the elongation at break. The influence of crystallization on the elongation at break has different results divided by a critical crosslink density 0.75 × 10−4 mol/cm3. When the crosslink density is lower than the critical crosslink density, the ideal elongation at break is smaller than real elongation at break. While that is higher than the critical crosslink density, the ideal elongation at break is higher than the real. This is because crystallization in stages II and III determine the final elongation at break.

Novel application of Zn‐containing Zeolitic Imidazolate Frameworks in promoting the vulcanization and mechanical properties of natural rubber composites

AbstractThree kinds of Zn‐containing Zeolitic Imidazolate Frameworks (Zn‐ZIFs, including ZIF‐8, ZIF‐11 and ZIF‐14) based on the zinc ions coordinating with different imidazolate ligands were added into the natural rubber (NR) using the DM and TMTD binary accelerators system, respectively. The influences of Zn‐ZIFs on the sulfur vulcanization behaviors and mechanical properties of NR matrix were evaluated. The results indicated that the addition of ZIF‐8 or ZIF‐14 could realize the fast vulcanization of NR at 130°C (the ordinary vulcanization temperature of NR is above 150°C), while ZIF‐11 did not show the obvious accelerating performance. Amongst the three Zn‐ZIFs, ZIF‐8 benefited NR matrix for the acquirement of the highest tensile strength and the largest crosslinking density. As an optimal additive, ZIF‐8 with 0.6 phr distinctly improved the physical‐mechanical, thermo‐oxidative aging resistance and dynamic mechanical properties of NR composites. It proved that Zn atom and its coordination porous network in Zn‐ZIFs played synergistic effects in accelerating vulcanization and enhancing mechanical properties of NR matrix besides its role of reinforcement filler. Then the above ZIF‐8/DM/TMTD vulcanization system was used to prepare the UHMWPE fibers/NR composites. The mechanical properties of the UHMWPE/NR composites were significantly improved in contrast to the pure NR matrix.

Structure and mechanical properties of natural rubber vulcanized with various zinc oxide nanoparticles

AbstractEffect of zinc oxide (ZnO) nanoparticles on vulcanization mechanism of natural rubber and crosslinking structure of its vulcanizate was investigated by rubber‐state NMR spectroscopy. Natural rubber was compounded with various ZnO nanoparticles (c‐ZnO, NC105, NC205, NC23, NC234(STA), and AZ12N), stearic acid, N‐tert‐butyl‐2‐benzothiazole sulfonamide (TBBS), N‐(1,3‐dimethylbutyl)‐N′‐phenylenediamine (6PPD), and sulfur. Vulcanization of the compounded natural rubber was analyzed with a moving die rheometer. The resulting natural rubber vulcanizates were characterized by swelling method, rubber‐state NMR spectroscopy, and tensile test. The rubber‐state NMR measurements revealed that natural rubber was efficiently vulcanized with NC205 and AZ12N but not with c‐ZnO, NC234, and NC234(STA). A relationship between the structure of vulcanized natural rubber and surface activity, surface structure, and particle size of the ZnO nanoparticles was investigated in this study. The mechanical properties of vulcanized natural rubber were found to depend on not only strain‐induced crystallization but also amount of effective CS linkages.

Enhanced wear resistance of sustainable tire materials with plasma modified pyrolysis carbon black

In this study, pyrolysis carbon black (CBp) was pre-treated by the combination of air jet milling and Ar plasma technology to obtain the reinforcing filler, MP-CBp. The modification effect was verified by XPS, Raman spectroscopy and TEM images. The increment of introduced activation groups and the augmentation of surface area conferred MP-CBp an impressive reinforcement to natural rubber (NR) matrix. The excellent reinforcement of MP-CBp was attributed to the formation of strong filler network according to the mechanical properties. Besides, the tribological studies conducted under various load conditions revealed that the NR component filled with MP-CBp presented intensively improvement on the ground traction and the wear resistance. The addition of 60 phr MP-CBp intensified 20% dry traction, 33.3% wet traction and decreased 27.7% specific wear rate of NR vulcanizates. This strategy to modify CBp with cleanliness Ar plasma technique provides novel insights into not only the surface treatment of CBp, but also the manufacture of sustainable wear-resistant tire materials, which can tremendously promote the recycled utilization of waste tires.

Improving the Performance of Wood Adhesive with Waste Rubber Tire

Reclaimed rubber (RR) from waste tires was introduced as a wood adhesive by blending with epoxidized natural rubber (ENR). To improve the polarity of RR and compatibility with ENR, maleic anhydride (MA) was grafted onto RR chains. Influences of RR and RR-g-MA (maleic anhydride grafted reclaimed rubber) on the adhesion of wood adhesive along with their properties such as crosslinking, mechanical properties, thermal stability, and wettability were studied. It was found that RR and RR-g-MA affect the vulcanization of ENR by increasing crosslink density. Especially, in the case of using RR-g-MA generates a new form of an ester linkage. The higher crosslink density together with the formation of ester linkages results in superior thermal stability by the addition of RR-g-MA. In addition, the incorporation of RR exhibited an increase in the lap shear strength when compared with the pure ENR. This improvement is due to the increased crosslink density because the presence of RR resulted in the enhanced cohesive strength of rubber adhesive. Additionally, the incorporation of RR-g-MA showed higher efficiency to improve the adhesion of rubber adhesive. The addition of RR-g-MA has not only enhanced the cohesive strength of rubber adhesive, but also increased the adhesive strength from the interaction between the hydroxy group in cellulose on the wood surface and the polar functional group (i.e., oxirane rings of ENR, maleic group of RR-g-MA and ester group of ester linkage) of rubber adhesive. Therefore, the cohesive fracture was observed in ENR/RR-g-MA adhesive. HIGHLIGHTS The worn-out rubber tire as a mass waste can be utilized to develop effective adhesives The addition of maleic anhydride grafted reclaimed rubber caused to generate new ester linkage between epoxidized natural rubber chains The epoxidized natural rubber vulcanizates with maleic anhydride grafted reclaimed rubber showed superior thermal stability The addition of maleic anhydride grafted reclaimed rubber enhanced the adhesive strength of rubber adhesive from the interaction between hydroxy group in cellulose on the wood surface and the polar functional group of rubber adhesive GRAPHICAL ABSTRACT

Effect of water on the accelerated sulfur vulcanization of natural rubber

Water present in natural rubber was found to play a role in forming carbon-carbon crosslinking junctions before forming carbon-sulfur crosslinking junctions when its effect on the accelerated sulfur vulcanization was investigated by analyzing low–molecular weight products through various instrumental analytical techniques. Samples were prepared by mixing deproteinized natural rubber (DPNR) with various moisture contents with stearic acid, ZnO, sulfur, and N-tert-butylbenzothiazole-2-sulfenamide, and they were vulcanized at 150 °C for various cure times. Low–molecular weight products such as 2,2′-dibenzothiazole disulfide (MBTS), 2-mercaptobenzothiazole (MBT), ZnMBT, Zn2+ and sulfur linked to the rubber were extracted from the vulcanized natural rubbers using benzene and dioxane, and subsequently measured by high-performance liquid chromatography, UV–visible spectroscopy, inductively coupled plasma atomic emission spectroscopy, and combustion analysis. The water present in natural rubber was found to strongly affect the production and formation rate of the low–molecular weight products in the accelerated sulfur vulcanization of natural rubber. As the result it suggests that the water promotes the formation of the C-C linkages, and then it sequentially promotes the formation of the C-S linkages.

Potential Utilization of Ground Eggshells as a Biofiller for Natural Rubber Biocomposites.

The aim of this work was application of ground eggshells in various amounts by weight as a biofiller for natural rubber (NR) biocomposites. Cetyltrimethylammonium bromide (CTAB), ionic liquids (ILs), i.e., 1-butyl-3-methylimidazolium chloride (BmiCl) and 1-decyl-3-methylimidazolium bromide (DmiBr), and silanes, i.e., (3-aminopropyl)-triethoxysilane (APTES) and bis [3-(triethoxysilyl)propyl] tetrasulfide (TESPTS), were used to increase the activity of ground eggshells in the elastomer matrix and to ameliorate the cure characteristics and properties of NR biocomposites. The influence of ground eggshells, CTAB, ILs, and silanes on the crosslink density, mechanical properties, and thermal stability of NR vulcanizates and their resistance to prolonged thermo-oxidation were explored. The amount of eggshells affected the curing characteristics and crosslink density of the rubber composites and therefore their tensile properties. Vulcanizates filled with eggshells demonstrated higher crosslink density than the unfilled sample by approximately 30%, whereas CTAB and ILs increased the crosslink density by 40-60% compared to the benchmark. Owing to the enhanced crosslink density and uniform dispersion of ground eggshells, vulcanizates containing CTAB and ILs exhibited tensile strength improved by approximately 20% compared to those without these additives. Moreover, the hardness of these vulcanizates was increased by 35-42%. Application of both the biofiller and the tested additives did not significantly affect the thermal stability of cured NR compared to the unfilled benchmark. Most importantly, the eggshell-filled vulcanizates showed improved resistance to thermo-oxidative aging compared to the unfilled NR.

Effect of ionic liquid on structure and properties of carbon black filled natural rubber vulcanizates

Effect of ionic liquid on structure and properties of carbon black filled natural rubber vulcanizates