Natural Rubber Compounds Research Articles

Enhancement of water and salt penetration resistance into mortar cement composited with vulcanized natural rubber compound

AbstractVulcanized natural rubber compound plays an important role to be used as a reinforcement phase for mortar‐cement‐paste matrix. Natural rubber is an organic binder to increase good adhesion for the flexible‐film formation and waterproof membrane within the mortar matrix. Adding sulfur as a curing agent into natural rubber latex can increase chemical bridge bonding within the mortar cement paste matrix. Embedding vulcanized natural rubber 30 wt% (PMC‐30) with a sulfur curing system was employed to increase physical, chemical, thermal, and mechanical properties due to interconnective bonding. PMC‐30 possessed low water absorption of less than 10%. After 28 days of curing, they possessed a high thermal shock resistance, a low percentage of salt solution absorption, and no thermal deterioration. The mortar composite embedded with the vulcanized natural rubber compound 30 wt% (PMC‐30) was an alternative mortar composite formula suitable for use in the seawater, beaches, and salt contact areas due to the lowest percentage of salt solution absorption (1.94%), low water absorption (3.17% ± 0.74), good thermal shock resistance, and the highest flexural strength (6.72 ± 0.39 MPa). Therefore, adding the vulcanized natural rubber compound in mortar cement is a good way to improve the flexural strength and water resistance of mortar cement.

Correlations between lipid contents of natural rubber and tensile properties of natural rubber-based compound, using attenuated total reflection Fourier transform infrared spectroscopy

In this study, the lipid contents of different kinds of natural rubber were measured by attenuated total reflection–Fourier transform infrared spectroscopy. The correlation between these amounts were considered with the tensile properties of natural rubber compounds. The Pearson correlation coefficients were more than −0.9 for all cases, which confirms that the models are acceptable. These models were applied for the estimation of tensile properties in the case study. It was observed that the tensile strength, elongation at break, modulus 100%, and modulus 300% can be predicted by errors of about 4%, 17%, 18%, and 18% respectively. This is a simple, fast, and nondestructive way to estimate the tensile properties before the compound preparation.

Natural Rubber Composites Reinforced with Green Silica from Rice Husk: Effect of Filler Loading on Mechanical Properties

Natural rubber (NR) composites filled with silica are typically used for tire tread applications owing to their low energy consumption and low rolling resistance. Tire tread properties vary broadly depending on the compound formulation and curing conditions. Silica loading is recognized as a critical factor influencing the mechanical properties of the composites. In this work, we aim to investigate the effect of silica loading (10–50 phr) on the mechanical properties of NR composites. Silica was prepared from rice husk waste via chemical treatment and subsequent calcination at 600 °C. Prior to the compound mixing process, silica was modified by a silane coupling agent to improve compatibility with the NR matrix. The NR compounds reinforced with silane-modified silica from rice husk were prepared using a two-roll mill machine. The scorch and cure times increased as the silica loading increased. The mechanical properties of the NR composites, including tensile strength, elongation at break, modulus, hardness, and abrasion loss, were examined as a function of silica loading. Tensile strength increased and reached the maximum value at 20 phr but decreased at high loading owing to the agglomeration of silica in the NR matrix. With increasing silica loading, hardness and modulus increased, whereas elongation at break and abrasion resistance decreased slightly. These results indicate that NR composites filled with silica are stiffer and harder at a higher silica loading due to the strong interaction between silica and the NR matrix, inhibiting the segmental mobility of rubber chains. We anticipate that the compound formulation presented in this work could potentially be adapted to tire tread applications.

Self‐healing natural rubber based on dynamic disulphide exchange towards fatigue lifetime extension

AbstractDynamic disulphide exchange mechanism was introduced to promote self‐healing characteristics to natural rubber compound and the corresponding healing mechanism and mechanical properties are presented. The formation of reversible dynamic disulphide bonds within rubber molecular chains was evidenced via FTIR and the total crosslink density of dynamic disulphide crosslinks was quantitatively measured by equilibrium swelling test. Scanning Electron Microscopy (SEM) results revealed that the healed area of the fractured surface adhered well with minor scar on the contact surface, suggesting that intermolecular diffusion occur at the fracture surface. It was also found that the tensile strength and tear strength of the broken samples able to recover 91% and 103%, respectively, under thermal healing at 150°C for 10 min. The fatigue lifespan of the materials increased 154.9% compared with the conventional rubber. The successful fabrication of self‐healing natural rubber through dynamically reversible disulphide exchange mechanism would be expected to open up new opportunities for development of sustainable rubber products.

Enhancement of the properties of carbon-black-filled natural rubber compounds containing soybean oil cured with peroxide through the addition of coagents

Due to the hazard of the commercial rubber processing oil such as distillate aromatic extract (DAE), many rubber researchers play attention to find the green alternatives. Vegetable oils seem to gain a lot of attraction for this. It is not just only due to their environmentally friendly nature but also their abundance and affordable cost. The use of soybean oil (SBO) for the carbon black-filled rubber compounds was focused here and comparatively discussed with the use of DAE. Furthermore, this work also proposed the way to improve the mechanical properties and environmental endurance of the rubber compounds containing SBO by adding coagents. There were two types of coagent including trimethylolpropane trimethacrylate (TMPTMA) and triallyl isocyanurate (TAIC) used here. It was found that the cure time, cure rate index, and cure reaction rate constant of SBO-added rubber compounds with and without coagents were higher than those of DAE-added rubber compounds, whereas the activation energy of SBO-added rubber compounds was lower than the one with DAE. Without coagent, the mechanical properties of rubber compounds with DAE and SBO are equal. However, the addition of coagents improved the mechanical properties of rubber compounds containing SBO. The modulus at 100% strain, modulus at 200% strain, and tensile strength of TMPTMA-added rubber compounds increased by 41%, 48%, and 15%, respectively, whereas the rubber compounds with TAIC increased by 7%, 8%, and 20%, respectively, when compared to the one with SBO alone. Interesting, the SBO-added rubber compounds with and without coagents showed better thermal aging and ozone resistances than the DAE-added rubber compounds. All results showed that the presence of coagents especially TMPTMA gave the SBO-added rubber compound with the superior performance to the DAE-added rubber compound and the SBO-added rubber compound without coagent.

The effect of different forms of iron substances on the aging properties of carbon‐black filled natural rubber

AbstractThe effect of iron‐containing substances with different forms on the properties of carbon‐black filled natural rubber compound is discussed. The ionic iron substances (FeCl2, FeCl3, Fe(SA)3) have a detrimental effect on the rubber. Based on the oxidation induction temperature values, the relative deteriorating effects of ionic iron substances on the rubber are in the order: Fe(SA)3 > FeCl3 ≈ FeCl2. Not only are the metal ions (Fe2+, Fe3+) with adjacent stable oxidation states catalytically active in degrading rubber, but also the counterions have an influence on the effect of oxidation, particularly the stearic anion. Ionic iron materials can decrease the molecular weight, especially for the case of Fe(SA)3 as measured by gel permeation chromatography. Due to the degrading effect on the rubber molecules, Fe(SA)3 brings about a torque decrease in moving die rheometer and evident decrease of the Mooney viscosity at 100°C, which is different from the effects of Fe2O3 and 304L‐Fe. The insoluble iron substances behave more like hard fillers. Additionally, Fe(SA)3 remarkably alters the bound rubber content and the tensile properties after aging via two different process (scission and crosslinking). Overall, this work has a thorough comparison of effect of iron‐containing materials on rubber aging and provides useful inspiration to protect the rubber from deterioration by foreign reagents and regulating the rubber stability and degradation rate via introducing degradative metal ions.

Leather-like composite materials prepared from natural rubber and two leather wastes: Wet blue leather and finished leather

In this study, leather-like composites were prepared from natural rubber (NR) and two different types of leather waste, namely wet blue leather (WBL) and finished leather (FL). Compounding was carried out on an internal mixer and two-roll mill, and curing was further conducted on a compression molding machine. The effects of leather type and content from 20 to 80 parts per hundred of rubber (phr) on cure characteristics, mechanical properties (hardness and tensile properties) and thermal stability of the as-prepared composites were investigated and compared with those of the unfilled NR compound. The curing rate and crosslink density of all composites were found to be lower than those of the unfilled NR. All WBL-filled NR composites exhibited higher tensile strength than the unfilled NR, while all FL-filled NR composites had lower values. Meanwhile, the hardness and modulus at 200% strain of all composites were increased with increasing leather waste contents compared to those of the unfilled NR. The composites containing low WBL loadings (20 and 40 phr) demonstrated higher elongation at break over the unfilled NR, while the other composites exhibited lower values. Besides, the thermal stability of all NR composites was deteriorated, but still largely retained.

Developing a Rubber basedNanocomposite

Polymer compounds such as Natural Rubber (NR), which consists of compounds such as isoprene, are capable of being processed for the manufacture of a range of rubber based products for a large variety of applications. The properties of a natural rubber compound are susceptible to enhancements in their properties through the incorporation of nanofillers into its matrix. This study addresses the preparation of a natural rubber based nanocomposite that utilizes graphene as a nanofiller for the facilitation of the required enhancement in the rubber compounds properties. The nanocomposite specimens used in the study were prepared by means of acid-coagulation. The acid-coagulation formulation utilized was adapted from methodologies employed in commercial applications. The enhancement in the rubber properties due to the incorporation of the nanofiller was validated by means of mechanical testing. Prior to the testing, the applicable standard for tensile property testing was identified to be ASTM D412. Through the acclaimed standard, a mould to facilitate the preparation of the required specimens was 3D printed from PETG. The primary aim of the study was to determine the effect of large concentrations of graphene (beyond 2.5wt %).The results from the mechanical testing of the acid-coagulated samples exhibited enhancements in the elongation at break and tensile strength between unfilled NR and the graphene filled NR nanocomposite. With the incorporation of 5wt% of graphene, the elongation at break of the rubber increased to 687%, showing a 25% increase. The tensile strength of the rubber increased to 4.07 MPa, showing an enhancement of 102% in comparison to the pristine rubber compound. KEYWORDS: Natural Rubber, Graphene, Acid-Coagulation, Tensile strength, Elongation at break.

Effects of the Diamine Chain End Functionalized Liquid Butadiene Rubber as a Processing Aid on the Properties of Carbon-Black-Filled Rubber Compounds.

The implementation of vehicle electrification and autonomous driving technologies has recently emphasized the importance of abrasion resistance and fuel efficiency of truck bus radial (TBR) tire treads that undergo high loads and long driving times. In this study, a functionalized liquid butadiene rubber (F-LqBR) was introduced to replace the treated distillate aromatic extracted (TDAE) oil as a way to improve abrasion resistance and fuel efficiency in the TBR tire tread compound and to solve the oil migration. First, radical polymerization was used to synthesize nonfunctionalized LqBR (N-LqBR) and amino-LqBR with an amine group at the chain ends. The synthesized LqBRs were then substituted in place of TDAE oil to manufacture carbon-black-filled natural rubber (NR) compounds and to evaluate their physical properties. The results show that LqBRs improved the migration resistance and enhanced the abrasion resistance by lowering the glass transition temperature (Tg) of the compound. In particular, amino-LqBR improved carbon black dispersion in the rubber matrix through a chemical bond between the functional group of the carbon black surface and the base rubber. In conclusion, amino-LqBR successfully served as a processing aid in a carbon black-filled NR compound while simultaneously enhancing its fuel efficiency and abrasion resistance.

Rice Husk Ash Extraction Applied for Biosilica Reinforced Tire Tread Filler Compound

In the agricultural countries, rice husk is an abundant waste, especially as one of the largest sources of silica (SiO2) production that can be produced. By complete combustion, to about 87% - 97% SiO2 content can be produced from rice husks. Alkaline solution is used as a solvent in the solid-liquid extraction production of rice husk ash SiO2. The mass of 10 grams of rice husk ash was weighed for the extraction process added with 80 ml of potassium hydroxide (KOH) solution with 10%, 15% and 20% various concentration to extract the SiO2 content. In a systematic study, for 60 minutes the rice husks were soaked and washed using HCl and then heated in a muffle furnace. The results of this study showed that all samples are succeeded in homogenizing SiO2 with purity close to 90%. Furthermore, through Energy-Dispersive X-ray Spectroscopy (EDS) analysis was proven these results obtained through solid-liquid extraction of KOH from rice husks. Natural SiO2, known as biosilica, is useful and has potential in reinforcing compounds, including applications as filler in tires and natural rubber compounds.

Homogenization of Green SiO2 from Rice Husk Burn through Potassium Hydroxide Solid-Liquid Extraction

In the agricultural countries, rice husk is an abundant waste, especially as one of the largest sources of silica (SiO2) production that can be produced. By complete combustion, to about 87% - 97% SiO2 content can be produced from rice husks. Alkaline solution is used as a solvent in the solid-liquid extraction process of rice husk ash. The mass of 10 grams of rice husk ash was weighed for the extraction process added with 80 ml of potassium hydroxide (KOH) solution with 10%, 15% and 20% various concentration for 60 minutes to extract the SiO2 content. The solution was added with 1 N hydrochloric acid (HCl) solution to precipitate the SiO2, after the extraction process was complete. The SiO2 formed is then separated from the rest of the solution by filtration. Next step is the drying process which aims to remove the moisture content of the resulting SiO2. In a systematic study, for 60 minutes the rice husks were soaked and washed using HCl and then heated in a muffle furnace. The results of this study showed that all samples are succeeded in homogenizing SiO2 with a purity close to 90%. Furthermore, through X-Ray Fluorescence (XRF) analysis was proven these results obtained through solid-liquid extraction of KOH from rice husks. Green SiO2, known as biosilica, is useful and has potential in reinforcing compounds, including applications as filler in tires and natural rubber compounds.

Use of Liquidambar Orientalis Mills in natural rubber compounds as an alternative to synthetic resins

Phenolic resins are useful additives that provide various functions for rubber compounds during compounding and vulcanization, as well as after cure. Natural resins are considered as strong alternatives to synthetic ones due to environmental concern. Liquidambar Orientalis Mills is an endemic plant and grows in many different geographies including Turkey. In this study, the phenolic resin obtained from Liquidambar Orientalis Mills has been studied regarding its functions in a generic natural rubber compound. It was incorporated into the rubber compound with and without selected gum and phenolic resins so that mainly obtaining competitive adhesion properties. Both individual and collaborative effects of the natural resin were evaluated. Rheological, thermal, morphological, mechanical and adhesion properties of the compounds were studied comparatively along with the non-linear cure kinetics. Liquidambar Orientalis Mills has been found to be a good alternative to both gum and phenolic resins in rubber compounds. Besides, significant improvement could be achieved for particularly rubber–steel adhesion.

Improving the dispersion and reinforcing properties of peroxidated corn stover and sugarcane bagasse fibers in natural rubber compounds

The performance of peroxidated powdered fibers of corn stover and sugarcane bagasse as fillers in natural rubber was evaluated in this study. Powdered corn stover and sugar bagasse fibers were subjected to the conventional peroxidation treatment for conversion to more hydrophobic fillers with enhanced tensile properties. The physicochemical properties of the peroxidated fibers were assessed using standard methods. Morphological properties, thermal stability, and functional groups were also assessed. The treated and untreated fibers were then used as fillers in natural rubber compounding using the two-roll mill, compression moulding and subjected to physico-mechanical characterization. There was improved dispersion of the peroxidated fibers in the polymer matrix, which meant significant improvement in the reinforcement and mechanical properties of the natural rubber compounds. A morphological study of the composites showed that natural rubberperoxided fiber composites have very good dispersion in the rubber matrix. The mechanical properties showed that the composites have improved properties with the highest tensile strength of 44.55 MPa, modulus at 100% elongation of 6.11 MPa, elongation at break of 294%, hardness of 74.30 IRHD.

Treatment of natural rubber with bio-based components: A green endeavor to diminish the silica agglomeration for tyre tread application

Production of green tyres by replacing carbon black (CB) with silica in natural rubber (NR) has gathered attention in automotive industries in the recent past. Incorporating high dosages of silica in NR by solid-state mixing is a huge challenge. In green tyre technology, abrasion resistance index (ARI) is crucial alongside rolling resistance, wet grip, and heat build-up. In this study, two new non-silane coupling agents have been introduced to replace bis(3-Triethoxysilylpropyl)disulfide (TESPD). Amidst them, chemical-A (sorbitol) as an alternate coupling agent of TESPD effectively achieved most properties except ARI. Hence, the naturally obtainable sustainable and cost effective chemicals A and B (B-sorbic acid) are incorporated during mastication, acting as blocking agents. Consequently, chemical-A as a blocking agent executed remarkable improvement in crucial properties, including ARI. Furthermore, the optimization study of sorbitol is accomplished based on curing time, FTIR, and XPS analysis. Subsequently, using similar quantity (0.5 phr) sorbitol in silica-CB filled NR compound evidenced better performances as tyre tread compound.

Degradation by Electron Beam Irradiation of Some Composites Based on Natural Rubber Reinforced with Mineral and Organic Fillers.

Composites based on natural rubber reinforced with mineral (precipitated silica and chalk) and organic (sawdust and hemp) fillers in amount of 50 phr were obtained by peroxide cross-linking in the presence of trimethylolpropane trimethacrylate and irradiated by electron beam in the dose range of 150 and 450 kGy with the purpose of degradation. The composites mechanical characteristics, gel fraction, cross-linking degree, water uptake and weight loss in water and toluene were evaluated by specific analysis. The changes in structure and morphology were also studied by Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy. Based on the results obtained in the structural analysis, possible mechanisms specific to degradation are proposed. The increasing of irradiation dose to 450 kGy produced larger agglomerated structures, cracks and micro voids on the surface, as a result of the degradation process. This is consistent with that the increasing of irradiation dose to 450 kGy leads to a decrease in crosslinking and gel fraction but also drastic changes in mechanical properties specific to the composites’ degradation processes. The irradiation of composites reinforced with organic fillers lead to the formation of specific degradation compounds of both natural rubber and cellulose (aldehydes, ketones, carboxylic acids, compounds with small macromolecules). In the case of the composites reinforced with mineral fillers the degradation can occur by the cleavage of hydrogen bonds formed between precipitated silica or chalk particles and polymeric matrix also.

Unfilled Natural Rubber Compounds Containing Bio-Oil Cured with Different Curing Systems: A Comparative Study

This study focuses on the properties of unfilled natural rubber compounds containing bio-oils cured with a peroxide curing system and then discusses the comparisons to those cured using the sulfur system from our previous work. Two types of bio-oils, i.e., palm oil and soybean oil, were used, and distillate aromatic extract (DAE)-based petroleum oil was employed as a reference. The bio-oils caused no significant change in the vulcanization of rubber compounds cured using peroxide. However, the compounds containing bio-oils and cured with sulfur showed a faster vulcanization than the ones with DAE. The bio-oils strongly affected the crosslink density of rubber compounds in both curing systems. The use of bio-oils caused a low crosslink density due to the possible implication of curing agents to bio-oil molecules. The properties of rubber compounds dependent on the different levels of crosslink density were also investigated. The results revealed that when the crosslink density increased, the modulus, tensile strength, and hardness of the rubber compounds increased and the elongation at break and compression set decreased. The use of bio-oils in the rubber compounds cured with different curing systems gave low modulus at 300% strain, tensile strength, and hardness but high elongation at break and compression set when compared to the ones with DAE. However, no significant change was observed for the compression set of the rubber compounds cured using sulfur. With the presence of bio-oils, the properties of rubber compounds cured with sulfur system deteriorated less than those of the ones cured with peroxide.

Assessment of Physico-mechanical Properties of Natural Rubber and Modified Natural Rubber Vulcanizates with Watermelon Rind as Fillers

Natural Rubber (NR) has a relatively low tensile modulus and strength, hence the need for reinforcing fillers to increase its tensile strength, hardness and abrasion resistance. In this study, NR was deproteinized, epoxidized and depolymerized. The functional groups of the NR and the modified NR were determined using Fourier Transform Infrared (FT-IR) spectroscopy. Watermelon Rind (WR) was used as fillers to replace Carbon Black (CB) in the compounding process. The shells were collected, dried, milled and sieved to 75 µm mesh size. Powdered WR was carbonized at 250oC for 1.5 hrs to obtain Carbonized Watermelon Rind (CWR). The Uncarbonized Watermelon Rind (UWR) and CWR powder were characterized based on particle size, loss on ignition, volatile matter, moisture and ash content. The UWR and CWR were used to replace CB at 0, 50 and 100% for the NR and modified NR compounding. The physico-mechanical properties of the different vulcanizates were determined for the effect of modification on the NR. The FT-IR result of the NR samples showed the presence of O-H, C-H, C=C stretching with C=H wagging bands used as the fingerprint region of NR. The results of the physico-mechanical properties revealed that an increase in shell content in the NR decreased its tensile strength and elongation but improved the physico-mechanical properties of the modified NR. This study showed that watermelon rind can be a viable alternative source of carbon filler for improved physico-mechanical properties of modified natural rubber.

Bromide and Chloride Ionic Liquids Applied to Enhance the Vulcanization and Performance of Natural Rubber Biocomposites Filled with Nanosized Silica.

In this study, the possibility of using ionic liquids (ILs) as auxiliary substances improving the vulcanization and physicochemical properties of natural rubber (NR) biocomposites filled with nanosized silica was investigated. Hence, the influence of ILs with bromide and chloride anions and various cations, i.e., alkylimidazolium, alkylpyrrolidinium and alkylpiperidinium cation, on the curing characteristics and crosslink density of NR compounds was determined. Furthermore, the effect of nanosized silica and ILs on the functional properties of the obtained vulcanizates, including mechanical properties under static and dynamic conditions, hardness, thermal stability and resistance to thermo-oxidative aging, were explored. Applying nanosized silica improved the processing safety of NR compounds but significantly increased the optimal vulcanization time compared to the unfilled rubber. ILs significantly improved the cure characteristics of NR compounds by increasing the rate of vulcanization and the crosslink density of NR biocomposites. Consequently, the tensile strength and hardness of the vulcanizates significantly increased compared to that without ILs. Moreover, the use of nanosized silica and ILs had a favorable impact on the thermal stability of the vulcanizates and their resistance to prolonged thermo-oxidation.

The Influence of Colloidal Properties of Carbon Black on Static and Dynamic Mechanical Properties of Natural Rubber.

The influence of carbon black (CB) structure and surface area on key rubber properties such as monotonic stress-strain, cyclic stress–strain, and dynamic mechanical behaviors are investigated in this paper. Natural rubber compounds containing eight different CBs were examined at equivalent particulate volume fractions. The CBs varied in their surface area and structure properties according to a wide experimental design space, allowing robust correlations to the experimental data sets to be extracted. Carbon black structure plays a dominant role in defining the monotonic stress–strain properties (e.g., secant moduli) of the compounds. In line with the previous literature, this is primarily due to strain amplification and occluded rubber mechanisms. For cyclic stress–strain properties, which include the Mullins effect and cyclic softening, the observed mechanical hysteresis is strongly correlated with carbon black structure, which implies that hysteretic energy dissipation at medium to large strain values is isolated in the rubber matrix and arises due to matrix overstrain effects. Under small to medium dynamic strain conditions, classical strain dependence of viscoelastic moduli is observed (the Payne effect), the magnitude of which varies dramatically and systematically depending on the colloidal properties of the CB. At low strain amplitudes, both CB structure and surface area are positively correlated to the complex moduli. Beyond ~2% strain amplitude the effect of surface area vanishes, while structure plays an increasing and eventually dominant role in defining the complex modulus. This transition in colloidal correlations reflects the transition in stiffening mechanisms from flexing of rigid percolated particle networks at low strains to strain amplification at medium to high strains. By rescaling the dynamic mechanical data sets to peak dynamic stress and peak strain energy density, the influence of CB colloidal properties on compound hysteresis under strain, stress, and strain energy density control can be estimated. This has considerable significance for materials selection in rubber product development.

Study on volume change and scanning electron microscope observation of carbon black‐filled natural rubber upon stretching

AbstractThe volume of natural rubber vulcanizates varied slightly during stretching. Hydrostatic weighing method was adopted in this study to study the volume change. By measuring the volume change of natural rubber compounds filled with different grades and different loadings of carbon black during extension, the corresponding volume variation–elongation (ΔV/V–ε) curves were created, and the differences of ΔV/V–ε curves among different carbon black compounds were discussed. The stress differences between different samples were normalized and the ΔV/(Vσ)–ε curves were plotted. Scanning electron microscope was utilized to observe the emergence and variation process of cavities in various stretched states. X‐ray diffraction was used to explore the change of crystallinity of the rubber after stretching to a certain elongation. Based on the experimental results, the damage at the filler‐rubber matrix interface and within the fillers agglomerates would be discussed.