Semi-efficient Vulcanization Research Articles

Effect of epoxidised natural rubbers on curing characteristics of kaolin-filled natural rubber composites

Effects of 2 types of epoxidised natural rubbers (ENR 25, ENR 50), with twenty-five and fifty moles of epoxidation, on crosslinking density and cure characteristics of natural rubber (NR) composites, which were filled by kaolin filler, were investigated using a semi efficient vulcanisation system. The ENRs were added separately into composites at 5.0, 10.0, 15.0, 20.0 and 25.0 parts per hundred rubber. An observation was conducted to investigate the effects of the ENRs on curing and crosslinking density of the kaolin-filled NR composites. Results revealed that both ENR 25 and ENR 50 functioned as curatives and compatibilizers. They decreased both cure and scorch times and minimum torque but increased difference of torque and crosslinking density. The higher ENRs loadings; the lower were the cure time and scorch time, the higher were the torque difference and crosslinking density. At a similar addition, ENR 50 exhibited a more pronounced curative and compatibilization effects than ENR 25.

Crosslink density and rheometric behaviour of natural rubber/chloroprene rubber blends

Crosslinking density and rheometric behaviour of natural rubber (NR)/chloroprene rubber (CR) blends with blend ratios from 0.0 to 100.0% rubber were investigated utilizing the semi efficient vulcanization. The degrees of crosslinking density were calculated using FloryRehner equations. The rheometric properties were tested by utilizing moving die curemeter (MDR 2000). From the overall results, cure and scorch times of the rubbers blends enhanced with increases the CR content. Whilst, the maximum values of torque difference and crosslinking density were performed by the rubbers blend with the 50/50 blend ratio.

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.

Effects of lauryl alcohol addition on cure characteristics and tensile properties of silica-filled natural rubber composites

By using a semi-efficient vulcanisation system; the effects of the lauryl alcohol (LA) addition as a new rubber additive on cure characteristics and tensile properties of silica-filled natural rubber (NR) composites were investigated. The NR composite was filled with silica filler with a fixed loading, 30.0 phr. The LA is a fatty alcohol based on palm kernel oil and added into the silica-filled NR composites. The LA loadings were 1.0, 2.0, 3.0 and 4.0 phr. It was found that LA functioned as a co-curing (curative) and internal plasticiser. As a co-curing agent, LA increased the crosslink density and tensile strength up to 3.0 phr of loading. As an internal plasticiser, LA decreased the modulus tensile and increased elongations at break of silica-filled NR composites. The 3.0 phr of LA was the optimum loading.

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.

PENGARUH PENAMBAHAN LAURIL ALKOHOL TERHADAP SIFAT-SIFAT UJI TARIK KOMPOSIT KARET ALAM TERISI SILIKA


 By using a semi-efficient vulcanisation system; the effects of lauryl alcohol (LA) as a new rubber additive on tensile properties of silica-filled natural rubber (NR) composites were investigated. The NR composites were filled by silica filler with a fixed loading, 30.0 phr (part per hundred rubber). The LA is a fatty alcohol based on palm kernel oil and incorporated into the silica-filled NR composites. The LA loadings were 1.0 phr, 2.0 phr, 3.0 phr and 4.0 phr. It was found that LA functioned as an internal plasticiser. As an internal plasticiser, LA decreased the tensile modulus and increased elongations at break of silica-filled NR composites. It was also found that LA increased the crosslink density and tensile strength up to 3.0 phr of LA loading. The 3.0 phr of LA was the optimum loading.

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.

Comparison study: effect of un-vulcanized and vulcanized NR content on the properties of two-matrix filled epoxy/natural rubber/graphene nano-platelets system

This paper focus in comparing un-vulcanized and vulcanized NR as toughening agent in epoxy resin. The incorporation of graphene nano-platelets (GNP) into two-matrix system has yield conductive materials whilst maintained their polymeric characteristics. Filled systems were prepared via magnetic stirring method and dispersion of GNP in the filled systems using ultrasonic water bath. The aim of this study is to investigate the effect of NR content on physical, mechanical, thermal and electrical performances of un-vulcanized and vulcanized filled systems. There is a great improvement in mechanical properties of vulcanized filled systems as compared to un-vulcanized filled systems. The results showed that the addition of vulcanized NR content at 5 vol% has improved flexural strength, modulus and toughness by 41.28%, 11.9% and 36.26% as compared to un-vulcanized filled system, when comparing at the same NR content. This improvement is attributed to the semi-efficient vulcanization (semi-EV) has transformed soft-like NR phases into high elastic NR phases, at which small vulcanized NR phases acted as energy dissipating center that can bear higher applied load without chain slippage. The flexured and fractured surfaces of filled systems were investigated using scanning electron microscope (SEM) technique to determine particle sizes of NR phases and its toughening mechanism. The formation of more conductive pathways in the vulcanized filled systems was agreed by the XRD analysis. Vulcanized filled systems have higher cross-link density in which implied that vulcanized NR phases are resistant to chemical penetration and cannot be easily removed.

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.

Thermal Insulator Made from Solid Natural Rubber: Part 1 - Formulation of Rubber Compounding, Appropriate Forming Condition and Basic Properties

Closed cell rubber sponge applied as thermal insulator made from solid natural rubber (NR) was prepared by using Supercell DPT as a blowing agent. Rubber chemicals and STR 20, solid NR, were mixed on a two roll mill prior to prepare the specimen by hot press machine. Curing behaviors of the compounded solid NR with various types of sulfur and peroxide vulcanizations were characterized with moving die rheometer (MDR) at 150 and 170°C. Tensile and compressive strengths of the rubber insulator were measured by universal tensile testing machine followed by ASTM D412 and ASTM D395, respectively. Bubble size of the blown up rubber was inspected by an average maximum length of the bubble by using optical microscope. It should be notice from the experimental that all rubber formula both of sulfur and peroxide systems showed loading percentages to completely expand in a mold by about 38 to 48. Rubber insulator blown up with Supercell DPT used by semi-efficient vulcanization (semi-E.V.) unconcealed predominant results among all curing systems so that further investigations of the formulation as heat stuff will be discussed in next paper

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.

Influence of accelerator/sulphur and co-agent/peroxide ratios in mixed vulcanisation systems on cure characteristics, mechanical properties and heat aging resistance of vulcanised SBR

The influence of accelerator/sulphur and co-agent/peroxide ratios on cure characteristic and vulcanisate properties in mixed vulcanisation of styrene butadiene rubber (SBR) was investigated in this work. Accelerator/sulphur ratio was investigated with three alternative sulphur curing systems, namely conventional, semi-efficient and efficient vulcanisation (EV) systems. Zinc dimethacrylate (ZDMA) was used as a co-agent to enhance the performance of peroxide and to provide ionic linkages. Ionic linkages contributed by ZDMA create bridges between two polymer chains. The ZDMA/peroxide ratio was varied from 2 to 10. The concentration of dicumyl peroxide was held fixed while the ZDMA content was varied. Cure characteristics, mechanical properties, dynamic mechanical properties and heat aging resistance were investigated in relation to the crosslink structure. Increasing the ZDMA/peroxide ratio significantly increased density of ionic linkages, especially in combination with the EV system. The combination of EV system with high ZDMA/peroxide ratio provided the highest ionic crosslink density and the lowest polysulphidic crosslink density: this enhanced the mechanical properties, the dynamic mechanical properties and the thermal stability of SBR vulcanisates.

Effect of ENR50/STR5L Blends on Properties of Foodstuff Conveyor Belts Compound

Natural rubber blending with nitrile rubber is the important raw material employed for the foodstuff conveyor belts formulation. This research involves the replacement of nitrile rubber with epoxidised natural rubber (ENR) aiming for food safety precaution and cost saving on the materials. This work included the investigation on the ratio of ENR with 50% epoxidation (ENR50) and natural rubber (Standard Thai Rubber 5L,STR5L). The ratios of ENR50:STR5L were 100:0, 75:25, 50:50, 25:75 and 0:100. The effect of fillers, i.e. silica (SiO2) and magnesium carbonate (MgCO3) on the properties of rubber blends was also investigated. The vulcanizing system was semi-efficient vulcanization (Semi-EV). The study was further focused on the morphological characterization and mechanical properties. It was found that increasing the proportion of ENR50 and STR5L at 50% produced better mechanical property, however, the elongation at break increased once the ENR50 was down at 25%. Thus, this enhanced the property of the foodstuff conveyor belts compound.

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.

Cure Characteristics and Physical Properties of <i>Imperata</i> <i>cy</i><i>lindrica</i> Activated Carbon Filled SMR L Compounding

The potential of activated carbon as a filler in rubber compound has been reviewed .Cure characteristics and physical properties ofImperataCylindricaactivated carbon filled natural rubber of Standard Malaysian Rubber (SMR L) were studied. SMR L was used as the elastomer and the composition of filler loading were varied from 0-50 parts per hundred rubber (phr). A semi-efficient vulcanization system was used throughout the study. The cure characteristics of the rubber compound was determined by using rheometer. The samples of hardness and resilience were measured by durometer shore A and Wallace Dunlop Tripsometer. Cure characteristics showed that cure time, t90and scorch time,t2increased as increased filler loading which indicate poor interaction between rubber and filler which slow down the vulcanization time. Minimum torque,MLand maximum torque,MHincreased as increased filler loading due to the low processability of the SMR L compounds. Crosslink density and hardness exhibit increment as increased filler loading due to increase rigidity of the SMR L compounds. The resilience will decrease correspondingly as increased in rigidity of the compounds.

Effects of curing systems on the mechanical and chemical ageing resistance properties of gasket compounds based on ethylene-propylene-diene-termonomer rubber in a simulated fuel cell environment

Ethylene-propylene-diene-termonomer (EPDM) rubber based fuel cell gasket compounds have been designed and explored the effects of various vulcanization systems on different properties. Three types of sulphur-accelerated vulcanization systems such as conventional vulcanization (con), semi-efficient vulcanization (sev) and efficient vulcanization (ev) and also a peroxide vulcanization system were employed in this study. The curing characteristics, tensile, hardness and compression set properties of the cured compounds were evaluated. The crosslink density was assessed by equilibrium swelling method in dodecane. The chemical stability of the cured EPDM compounds was also evaluated through an accelerated durability test (ADT) using a solution (1 M H2SO4 + 10 ppm HF) very close to the fuel cell atmosphere. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) were employed to investigate the chemical and physical changes of the cured EPDM compounds before and after exposure to the ADT solution over time. The results indicate that the EPDM compounds cured with peroxide exhibit the highest crosslink density with lowest compression set value at both room temperature and at elevated temperature. The FTIR and the corresponding SEM results show no significant chemical degradation of the peroxide cured EPDM compounds due to ADT ageing.

Devulcanization and Recycling of Waste Automotive Epdm Rubber Powder by Using Shearing Action and Chemical Additive

In automotive applications, ethylene-propylene-diene rubber (EPDM) is used to manufacture various components and therefore recycling scrap rubber is a major issue. The primary aim of this study was to develop a new method for devulcanizing waste automotive EPDM rubber powder by using shearing action and chemical additive and recycle the devulcanized powder. A semi-industrial twin screw extruder with a shearing action and reactor along with 2-mercaptobenzothiazole-disulfide (MBTS) chemical were used to devulcanize the waste powder at two different feed screw speeds and main rotor speeds at a constant temperature of 220°C. To recycle the devulcanized powder, different amounts of the devulcanized powder were mixed with a commercial EPDM-based automotive rubber strips compound to produce blends. The blends, commercial compound and devulcanized powder were cured with a semi-efficient (SEV) vulcanization system and their viscosity, cure and mechanical properties measured. For the blends, the Mooney viscosity was unchanged with 40 wt%, crosslink density with 20 wt%, tensile strength and elongation at break with 10 wt%, and compression set with 20 wt% of the devulcanized powder. Interestingly, the hardness benefitted from 50 wt% of the devulcanized powder in the blends. The scorch and optimum cure times shortened and the cure rate index rose when the loading of the devulcanized powder in the blends was raised. This new method offered a major new route for devulcanizing and recycling the waste powder.