Semi-efficient Vulcanization System Research Articles

Effect of Compound Curing System on Properties of NBR/CM Blends

Abstract The effects of conventional vulcanization (CV), semi-efficient vulcanization (SEV), efficient vulcanization (EV), and equilibrium cure (EC) on the properties of nitrile rubber (NBR)/ chlorinated polyethylene (CM) blends were studied. The results showed that the SEV system had a faster vulcanization rate, larger torque, and larger vulcanization temperature coefficient, and the EC system had reversion resistance and a longer vulcanizing period. The modulus of the SEV system, the tensile strength of the CV system, and the elongation at the break of the EC system were high. The SEV system had good seawater and oil resistance; SEV > EV > CV >EC appeared in G’ and G”. The tanδ of the SEV system was larger than that of the EC system, but the tanδ of CV and EV system was close.

Enhancing Rubber Vulcanization Cure Kinetics: Lowering Vulcanization Temperature by Addition of MgO as Co-Cure Activator in ZnO-Based Cure Activator Systems.

Vulcanization is a chemical modification of rubber that requires a considerable amount of thermal energy. To save thermal energy, the kinetics of rubber vulcanization should be improved. In this article, the curing properties of rubber vulcanization are thoroughly investigated using the moving die rheometer (MDR) technique. To enhance the kinetics in different stages of ZnO-based sulfur vulcanization systems, small amounts of MgO were added. The results revealed that the small amount of 1 to 2 phr (per hundred grams of rubber) of MgO in the controlled 5 phr ZnO-based curing systems can significantly improve the curing kinetics. For example, the optimum curing time of 1 phr MgO added to the 5 phr ZnO-containing semi-efficient vulcanization system at different temperatures was more than half that of the controlled 5 phr ZnO-only compound. While maintaining a similar rate of vulcanization, the vulcanization temperature can be reduced by up to 20 °C by using MgO as a co-cure activator, which exhibits similar or better rheometric mechanical properties compared to the controlled compounds. With the addition of MgO as a co-cure activator, the vulcanization reactions become very fast, enabling vulcanization to be completed, even at the boiling point of water (100 °C) with an affordable curing time (<1 h). By reducing the vulcanization temperature, the scorch safety time can be enhanced in the ZnO/MgO-based binary cure activator-containing vulcanizates. Overall, MgO could be a potential candidate as a co-cure activator with ZnO for the vulcanization of rubber, offering better economical and eco-friendly methods.

Performance of Thermal-Oxidative Aging on the Structure and Properties of Ethylene Propylene Diene Monomer (EPDM) Vulcanizates.

A thermal-oxidative aging test at 120 °C was conducted on ethylene propylene diene monomer (EPDM) vulcanizates of the semi-efficient vulcanization system. The effect of thermal-oxidative aging on EPDM vulcanizates was systematically studied by curing kinetics, aging coefficient, crosslinking density, macroscopic physical properties, contact angle, Fourier Transform Infrared Spectrometer (FTIR), Thermogravimetric analysis (TGA) and thermal decomposition kinetics. The results show that the content of hydroxyl and carbonyl groups as well as the carbonyl index increased with increasing aging time, indicating that EPDM vulcanizates were gradually oxidized and degraded. As a result, the EPDM vulcanized rubber chains were crosslinked with limited conformational transformation and weakened flexibility. The thermogravimetric analysis demonstrates that the thermal degradation of EPDM vulcanizates had competitive reactions of crosslinking and degradation, and the thermal decomposition curve can be divided into three stages; meanwhile, the thermal stability of EPDM vulcanizates gradually decreased with increasing aging time. The introduction of antioxidants in the system can promote the crosslinking speed and reduce the crosslinking density of EPDM vulcanizates while inhibiting the surface thermal and oxygen aging reaction. This was attributed to the fact that the antioxidant can reduce the thermal degradation reaction level, but it is not conducive to the formation of a perfect crosslinking network structure and reduces the activation energy of thermal degradation of the main chain.

Mechanical properties of rubber vulcanizates containing Ethylene Propylene Diene Rubber waste at different types of vulcanization system

Ethylene Propylene Diene Rubber (EPDM) waste filled Natural Rubber (NR) that cured by using conventional vulcanization (CV), semi-efficient vulcanization (semi-EV) and efficient vulcanization (EV) system was successfully compounded by an internal mixer. The ratio of sulphur and accelerator is different for each vulcanization system, that finally affect the vulcanizate properties due to the different structural features of an accelerated sulphur vulcanizate of NR. 60 phr of pulverized EPDM waste was incorporated into 40 phr of NR in each vulcanization system. Studies about the usage of abundantly available EPDM waste as a potential filler is essential towards green environment and minimize landfill area in future. It is found that the cured rubber with CV system has the best properties due to high degree of crosslinking of polysulphidic crosslink. Tensile properties and abrasion resistance of the rubber compound indicated its mechanical properties were investigated. Density and hardness test were also done to study its physical properties. For tensile strength, CV system has 14% increment from EV system because of a stress-relieving mechanism that exhibited in this vulcanization system. As for tensile modulus, M500 for CV system shown 29% increment than EV system. As a result of the decreased chain flexibility caused by the increased crosslinking density in the CV system, the elongation at break of the vulcanizate is the lowest (174 mm) when compared to the EV system (336 mm). CV system shown highest Abrasion resistance index (ARI) i.e. 1820%. This indicate that very small amount of mass loss obtained for the CV cured rubber during the testing. CV system gives highest density and hardness values i.e. 1.0747 g/cm3 and 52.5 Shore A, respectively. Thus, the results indicated that NR containing EPDM waste cured by CV system is able to be utilized in the development of rubber compound with a compromise property.

Influence of the curing system on the physical-mechanical, dynamic properties, and aging resistance of ethylene–propylene–diene monomer formulations for applications at high temperatures

The effects of three curing systems on rheometric, morphological, physical-mechanical, thermal, and dynamic properties of ethylene–propylene–diene monomer (EPDM) composites was investigated. The influence of thermo-oxidative aging on crosslink density and physical-mechanical properties was studied. Based on a standard composition for application at high temperatures, EPDM formulations with semi-efficient vulcanization systems (ES), efficient vulcanization systems (ED), and peroxide curing systems (EP) were prepared. Experimental results indicated that EPDM compounds cured with efficient vulcanization systems exhibit the highest scorch time with an intermediate maximum torque value at 150°C. The filler dispersion in the elastomeric matrix was greater than 94%; however, the ED formulation showed a more pronounced decrease, with the increase in deformation indicating a greater filler–filler interaction. In comparison with those cured with peroxide and semi-efficient systems, EPDM formulations cured with an efficient system presented better thermal resistance and the crosslink density was sufficient to maintain the mechanical integrity, leading to an intermediate hardness value, tensile strength, modulus, and greater elongation at breaking. In summary, the results indicated that the efficient curing system was the most appropriate to be used in the envelope’s manufacture, due to the better performance of the mechanical properties associated with the better resistance to thermal aging.

Pengaruh Oleamida Terhadap Karakteristik Pematangan Karet Alam Terisi Silika

The purpose of this study was as a feasibility study of the utilization of oleamide as a new additive for natural rubber (NR) filled with silica using the semi-efficient vulcanization system. Silica fillers used as much as 30 parts per hundred parts rubber (phr). Oleamide was obtained from the synthesis of oleic acid with urea. Oleamide was inserted into the silica filled NR compounds with the varied composition of 0.0 phr; 2.0 phr; 4.0 phr; 6.0 phr, and 8.0 phr. The influence of oleamide on the curing characteristic of the silica filled NR compounds was observed. It was obtained that the oleamide functions as a curative and also a plasticizer. The greater the levels of oleamide added, the shorter the scorch time and optimum curing time were. Oleamide also decreased the minimum torque with addition up to 8.0 phr. The greater the levels of oleamide was, the lower the minimum torque was. Oleamide also increased the maximum torque and torque difference of the silica-filled NR composites at the addition of 2.0 phr. The 2.0 phr was the optimum composition of the oleamide.

POTENTIAL SUSTAINABLE ANTIOXIDANTS FOR NATURAL RUBBER: HENNA AND ITS MAJOR COMPONENTS

ABSTRACT Unsaturated chain structure of natural rubber makes it a poor defense against thermo-oxidative aging. Synthetic antioxidants are commonly used in rubber compound recipes to prevent/retard aging of the rubber material during its service life. However, synthetic antioxidants cause some negative effects on human and environmental health; they tend to be replaced by natural alternatives. In this study, the short- and long-term antioxidant effects of henna and its basic active components, lawsone and gallic acid, have been investigated individually for natural rubber cured with semi-efficient sulfur vulcanization system. The composition of henna was determined by gas chromatography-mass spectrometry (GC-MS) analysis. Qualitative and quantitative analysis were performed using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) to highlight structural changes on aged vulcanizates. The authors attempted to correlate the suggested aging mechanism with rheological, mechanical, and morphological properties. Results showed that both lawsone and gallic acid were impressively successful regarding their anti-oxidation activity. In addition, henna, which contains a sufficient amount of lawsone and gallic acid, has been suggested as a competitive natural alternative to the common synthetic stabilization system for natural rubber, considering its sustainable commercial abundancy.

The properties of unfilled natural rubber in the existence of alkanolamide: swelling, mechanical and morphological properties

A study was carried out on the utilization of alkanolamide as a new curative additive in natural rubber (NR) compounds by using a semi-efficient vulcanization system. The alkanolamide was derived from the waste of cooking oil and incorporated into the unfilled-NR compound at 0.2, 0.4, 0.6, 0.8, and 1.0 phr. The effect of alkanolamide on swelling percentage, mechanical and morphological properties of the NR compounds were observed. It was found that the addition of the alkanolamide increased elongation at break of the NR compounds. The alkanolamide also increased tensile modulus, tensile strength, hardness and crosslink density of up to 0.6 phr of alkanolamide loading and then decreased with further increases in the alkanolamide loading. Scanning electron microscopy (SEM) micrographs proved that 0.6 phr loading of alkanolamide in the NR compounds exhibited the greatest matrix tearing line and surface roughness which correlated to a higher tensile strength of the NR compounds.

The properties of unfilled natural rubber in the existence of alkanolamide: rheological and crosslink density properties

Using a semi-efficient vulcanization system; a study was carried out on the utilization of alkanolamide as a curative additive in natural rubber (NR) compounds. The alkanolamide was incorporated into the unfilled-NR compound at 0.2, 0.4, 0.6, 0.8, and 1.0 phr. The effect of alkanolamide on rheological and crosslink density properties of the NR compounds were observed. It was found that the addition of the alkanolamide exhibited shorter scorch and cure times and higher elongation at break of the NR compounds. The alkanolamide also exhibited higher torque differences and crosslink density of up to 0.6 phr of alkanolamide loading and then decreased with further increases in the alkanolamide loading.

The effects of aminopropyltriethoxy silane on tensile and rheometric properties of silica-filled natural rubber vulcanizates

By using a semi-efficient vulcanization system; the effects of aminopropyltriethoxy silane on rheometric and tensile properties of silica-filled natural rubber (NR) composites were investigated. The NR composites were filled by silica filler at a fixed loading at 30.0 parts per hundred rubber (phr). The aminopropyltriethoxy silane was incorporated into the silica-filled NR composites. The aminopropyltriethoxy silane loadings were 1.0, 3.0, 5.0 and 7.0 phr. It was found that aminopropyltriethoxy silane functioned as a co-curing agent which reduced the scorch and cure times of the silica-filled NR composites. The higher the aminopropyltriethoxy silane loading, the shorter the scorch and cure times were. It was also found that aminopropyltriethoxy silanecaused in modulus and tensile improvements, exclusively up to a 5.0 phr of loading. The 5.0 phr of aminopropyltriethoxy silane was the optimum loading.

Design of Elastomeric Bridge Bearing Pad Compound Formula Based on Hydrogenated Natural Rubber

Laminated elastomeric bearing pad which is commonly produced by natural or chloroprene rubber is functioned as isolation system in bridge or flyover structures. In the research, hydrogenated natural rubber (HNR) was evaluated its feasibility to be used as base elastomer on steel-laminated bearing pad production by designing rubber compound formula. The compounding procedures of HNR applied various vulcanization system and carbon black filler types. The physical and mechanical tests result showed that only hardness parameter could fill the standar quality requirement of commercial elastomeric bearing pad as stated in AASHTO M251 in the range of 50 "“ 70 Shore A scale. The tensile property and compression set value of the HNR vulcanizates were under the requirement. This was due to low rubber-filler interaction and rigidity of crosslink network. The low interaction was more evident with increasing carbon filler particle size. By adjusting semi efficient vulcanization system and used N220 as carbon filler in designing compound formula,HNR was regarded as alternative promosing base elastomer for elastomeric bridge bearing pad manufacture. Nevertheless, it was necessary to improve the procedure to achieve better tesile property and compression set parameter.

Effect of Different Vulcanizing Systems on SMR-L/Waste Latex Compound Blends

Abstract Natural rubber (NR) is widely used in the industry to produce various products. It requires excellent physical, mechanical and thermal properties to prolong its performance for indoor and outdoor applications. Different sulphur vulcanization systems such as conventional vulcanization (CV), semi-efficient vulcanization (SEV) and efficient vulcanization (EV) systems have different sulphur intake thus give different cross-link density (CLD) and subsequently end properties of the NR vulcanizate. To conserve natural resources, industrial waste such as waste latex compound (WLC) can be utilized to form rubber-rubber blend with the NR. In this study, the effect of different vulcanizing system on the properties of SMR-L/WLC blend was investigated. By comparing the properties of 75:25 SMR-L/WLC blend with 100:0 SMR-L/WLC blend, the effect of WLC loading was also studied. Generally, 100:0 and 75:25 SMR-L/WLC blend with CV system has the best physical and mechanical properties in tensile strength, elongation at break, M100, M300 and hardness. This is due to higher polysulphidic cross-links in CV system which facilitate structural networks rearrangement. This enable the test specimens to withstand higher force. For heat retention properties, both blends showed EV system has better heat retention properties. EV system consists of mainly monosulphidic cross-links with higher thermal stability because the monosulphidic bond is stronger than the polysulphidic bond. The loading of WLC has affect the end properties of rubber vulcanizate. In general, WLC improved the physical and mechanical of vulcanizate but may improve or deteriorate the heat retention. WLC is partially vulcanized rubber thus, presence of WLC lead to higher crosslink density. However, during heat ageing test, the structural changes of the blend vulcanizate results in lesser changes in M100 and M300 but more changes in tensile strength and elongation at break. As conclusion, there is an optimum rubber vulcanizate properties need to be obtained by either using different sulphur vulcanization system or the WLC to have a balance in physical, mechanical and thermal properties.

Tuning of accelerator and curing system in devulcanized green natural rubber compounds

These days sustainable ecosystem warrants cleaner, safer and easier mobility of resources in a production cycle. In a response of such call, in this present work, sulphur crosslinked natural rubber (NR) is successfully devulcanized using bis(3-triethoxysilyl propyl) tetrasulfide (TESPT) - a dual function disulfide chemical. It is observed that the mono-, di- and poly sulfide crosslinks, those determine the final performance of the composites, can be controlled by using various chemicals like N-cyclohexyl-benzothiazyl-sulphenamide (CBS), tetramethylthiuram disulfide (TMTD), 2-mercaptobenzothiazol (MBT) and N-tert-butyl-2-benzothiazyl-sulphonamide (TBBS). Subsequently different vulcanizing systems like conventional, efficient and semi efficient vulcanization systems were also studied. Furthermore, in the optimization of vulcanizing system, semi-EV showed the highest mechanical properties compared to that of the CV and EV system. The study shows a unique correlation between the crosslink density, (mono-, di- and polysulfide) and the mole % uptake of the solvent with time. It also shows the dependence of the fraction of immobilized polymer chain and the segmental dynamics of the composites on the crosslink density.

Cure characteristics, crosslink density and degree of filler dispersion of kaolin-filled natural rubber compounds in the presence of alkanolamide

The effects of alkanolamide (ALK) addition on cure characteristics, crosslink density and degree of filler dispersion of kaolin-filled natural rubber (NR) compounds were investigated. The kaolin filler was incorporated into NR compounds with a fixed loading, 30.0 phr. The ALK was prepared from Refined Bleached Deodorized Palm Stearin (RBDPS), a waste product of cooking oil production, and diethanolamine. The ALK is an oily material and added into the filled NR compounds as a rubber additive at different loadings, 0.0, 3.0, 5.0 and 7.0. The kaolin-filled NR compounds with and without ALK were vulcanized using a semi-efficient vulcanization system. It was found that ALK decreased the scorch and cure times and improved filler dispersion of the kaolin-filled NR compounds. The higher the ALK loading, the shorter were the scorch and cure times. It was also found that ALK increased the crosslink density of kaolin-filled NR compound up to 5.0 phr of loading. Due to its oily properties, The ALK acted as an internal plasticizer which decreased the minimum torque and improved the degree of kaolin dispersion in NR phases. The higher the ALK loading; the lower the minimum torque and better the filler dispersion.

Investigation of thermo-oxidative ageing effects on the fatigue design of automotive anti-vibration parts

Elastomeric parts found in automotive anti-vibration systems are usually massive. Ageing therefore leads to heterogeneous properties, usually induced by several mechanisms due to the availability, or not, of oxygen in the part’s bulk. To better understand the effects of oxygen in the degradation process and on the fatigue properties, this paper aims at studying the ageing of a rubber material (semi-efficient vulcanization system) in aerobic (with oxygen) and anaerobic (without oxygen) conditions for a wide range of temperatures, relevant for under hood applications. The material studied here is a fully formulated compound NR/IR blend reinforced with carbon black. A specific protocol to perform ageing under anaerobic conditions was set up and validated. Numerous tests have been carried out to evaluate the consequences of ageing on monotonic tension and fatigue properties. A comparison of these consequences and of their kinetics is finally presented for ageing with or without oxygen.

CURE CHARACTERISTICS OF DEVULCANIZED RUBBER:THE ISSUE OF LOW SCORCH

ABSTRACT We investigate the reasons behind the observed low scorch during the revulcanization of devulcanized rubber. Mechanically devulcanized carbon black filled natural rubber vulcanizates originally cured by conventional vulcanization (CV), semiefficient vulcanization (semi EV), efficient vulcanization (EV), and peroxide systems as well as buffing dust obtained from pre-cured tread with known formulation were used. Revulcanization of these devulcanized samples using sulfur/sulfonamide system led to the following observations; irrespective of the type of sulfur cure system used for the initial vulcanization of the rubber, (i) the devulcanized samples cured without pre-vulcanization induction time and (ii) devulcanized samples prepared from peroxide vulcanized rubber cured with scorch safety. Based on the earlier reports that solvent extraction of devulcanized rubber did not improve the scorch time during revulcanization, the role of zinc bound non-extractable moieties was investigated using devulcanized rubber prepared from activator-free vulcanizates, which disproved the role of such moieties. This confirmed that the scorch reducing moieties should be attached to the rubber main chain, which can be unreacted crosslink precursors and cyclic sulfides left after the initial accelerated sulfur vulcanization of the original sample. The ability of pre-vulcanization inhibitor to induce scorch safety when devulcanized rubber is revulcanized as such, without adding any virgin rubber, proved that mercaptobenzothiazole (MBT) generated from crosslink precursors is the cause of low scorch. Acetone extracted devulcanized rubber samples prepared from tetramethyl thiuramdisulfide (TMTD) cured natural rubber, which does not follow the MBT pathway when revulcanized, cured with scorch safety, which further proved the role of MBT. Based on the previous reports and our results, it is obvious that powdering of rubber vulcanizate and devulcanization processes have no role on the low process safety of these materials, but it is inherent to the initial accelerated sulfur vulcanization chemistry undergone by these materials.

Studies on natural rubber containing kaolin modified with hexamethylenediamine derivative of phosphorylated cashew nut shell liquid prepolymer

Kaolin was modified with a solution of phosphorylated cashew nut shell liquid prepolymer (PCNSL) containing hexamethylenediamine (HMDA). The organomodified kaolin was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and infrared spectroscopy (FTIR). Processability characteristics and physico-mechanical properties of natural rubber (NR) compositions of conventional vulcanization (CV), semi efficient vulcanization (SEV) and efficient vulcanization (EV) systems containing 6phr (parts per hundred rubber) of the HMDA-PCNSL modified kaolin and unmodified kaolin have been studied. Compositions containing the organomodified kaolin showed improved cure characteristics and vulcanizate properties such as hardness, tensile strength, tear strength, abrasion resistance and thermal stability along with lower heat build-up and compression set which could be advantageous for applications such as tire treads.

EFFECT OF DEVULCANIZATION ON CROSSLINK DENSITY AND CROSSLINK DISTRIBUTION OF CARBON BLACK FILLED NATURAL RUBBER VULCANIZATES

ABSTRACTCarbon black filled natural rubber (NR) vulcanizates were devulcanized at ambient temperature in a two roll mill. The effect of cure system, that is, conventional vulcanization (CV), semiefficient vulcanization (semi EV), and efficient vulcanization (EV) systems, used for vulcanization of the original sample, on the efficiency of devulcanization was studied. The efficiency of devulcanization expressed as percentage devulcanization of the samples calculated from residual crosslink density measurements was correlated with the sol fraction of the devulcanized samples based on Horikx analysis. Using chemical probe analysis, we determined (i) the crosslink distribution pattern of the original sample, (ii) the extent to which the different types of crosslinks—that is, polysulfidic, disulfidic, and monosulfidic crosslinks—have been debonded or broken during the shearing process in the two roll mill, and (iii) the pattern of bond formation during revulcanization. Mechanical shearing predominantly breaks the majority crosslink type (polysulfidic crosslinks in CV and semi EV cure systems and disulfidic crosslinks in EV samples). Irrespective of the significant reduction in total crosslink density in all three sets of samples, chain shortening reactions similar to the post-crosslinking chemical reactions at curing temperatures also occur during mechanical shear at ambient conditions, which increased the absolute value of monosulfidic links in CV and semi EV systems. However, in the devulcanized EV system, the absolute value of polysulfidic crosslinks increased, which might be due to the re-crosslinking of the cleaved bonds. All the devulcanized samples were revulcanized, and the mechanical and morphological properties were analyzed. The percentage retention of the vulcanizate properties after revulcanization of the devulcanized samples correlated very well with efficiency of devulcanization.

Karakteristik termogravimetri dan kinetika dekomposisi EPDM dengan bahan pengisi carbon black

The thermal characteristics of a material are important to learn in order to know the thermal stability of the materials. Ethylene propylene diene monomer (EPDM) is a synthetic rubber that is widely used in industry due to its resistance to aging, ozone, and chemicals. The kinetic parameters and thermal decomposition of vulcanized EPDM were studied using thermogravimetric method with various vulcanization systems (efficient, semi-efficient, and conventional vulcanization system) and various carbon black (CB) as filler (50, 60, and 70 phr). Decomposition consist of two stages; the oxidation of EPDM and volatile matter loss then decomposition of EPDM. Kinetic parameters of the thermal decomposition were approximated by the Coats Redfern equation. Activation energy and decomposed mass increases with decreasing content of CB. Vulcanized EPDM with CB as filler has fairly good resistance against thermal decomposition. The decomposition process can be viewed in detail in this paper. Keywords: EPDM, thermal decomposition, kinetic, thermogravimetric, carbon black.

Effect of vulcanization system and carbon black on mechanical and swelling properties of EPDM blends

EPDM (Ethylene propylene diene monomer) is one of synthetic rubber that widely used in automotive. It must be vulcanized and added by other materials before used. The aim of this study is to investigate the effect of vulcanization system and the addition of carbon black (CB) to the mechanical properties and swelling characteristic of EPDM. This research used three vulcanization system, conventional vulcanization (CV), efficient vulcanization (EV) and semi-efficient vulcanization (SEV) with the variation of carbon black 50, 60, 70 phr (per hundred resin). This research showed that EV system resulted faster vulcanization time and lower delta torque than SEV and CV systems. This system also performed the highest tensile strength, elongation, and tear strength, while SEV system resulted the highest hardness. Furthermore, the conventional vulcanization system resulted the lowest swelling index.