Substitution of MBS Accelerator With A Non Carcinogenic Accelerator

Substitution of MBS Accelerator With A Non Carcinogenic Accelerator

 
Jadheer

ABSTRACT

This project is done in the field of rubber compounding .The accelerator MBS consumption is very high in tyre industry; this generates some harmful chemicals that are unhealthy to human being. High usage of this hazardous material may causes to cancer. So elimination of MBS accelerator from rubber compounding is very necessary.

The main objective of this project is to develop a Non-carcinogenic compound by using a Non-carcinogenic accelerator, in the place of MBS. For this purpose consider the accelerator TBBS/CBS, which are more matching with MBS in cost and availability.

In this project I studied the properties of regular MBS compound and various TBBS/CBS compounds. Then compare all the properties and select suitable one alternative to MBS.

INTRODUCTION

VULCUNISATION OF RUBBER:

The development of rubber technology got a real boost with the invention of vulcanization by Charles Goodyear. He found that if rubber was mixed with sulphur and heated, a change occurred, for which the term vulcanization was given. As a result of this by about 1850 a whole range of rubber products were available

Raw rubber looses its rubber-like properties at temperatures above 60 c. Also its wear resistance and tensile strengths are low. The process of vulcunisation can improve the quality of rubber. Raw rubber is heated during vulcunisation. During vulcanization, the rubber chains are cross-linked into a three dimensional network which gives the desired physical properties. This converted the raw rubber in to a non-tacky, highly elastic, tough material that was no longer soluble in solvents.

In the early stage of development, sulphur alone was used as the vulcanizing agent. The rubber was mixed with sulphur and was heated at high temperature and pressure for a very long time. But even after this the physical properties were poor. Manufacturers were anxious to reduce the time of heating and it was not long before metallic oxides such as those of zinc, calcium, magnesium and lead, were being incorporated for this purpose. The use of these inorganic accelerators continued until world war -1.

In the earlier days of the present century organic substances were found to reduce the time of vulcanization and also to improve the physical properties of the products. These substances were called accelerators.

The discovery of Mercaptobenz Thiazoles (MBT) IN 1921 was undoubtedly one of the outstanding landmarks. It was during the same period they found that zinc oxide enhanced the action of organic accelerators. Thus zinc oxide was regarded as an activator whose addition to a compound was highly desirable. Then started stearic acid was used as a co-ivator along with zinc oxide. This even improved the physical properties of the product.

CHEMISTRY OF VULCUNIZATION:

The chemistry of vulcanization is so complex that even though the main stages are proven there is still much to be learnt about the effect of different types of additives. Vulcanization is the process by with mainly plastic rubber is converted in to elastic rubber or hard rubber state. The process which is brought about by the liking of macromolecules at their reactive sites, this process is also known as cross linking. The sulphur is combined in the vulcanization network in a number of ways, it may be present as monosulphidic, disulphidic or polysulphidic but it may also be present as pendent sulphidic or cyclic monosulphidic & disulphidic.

Most of all properties of the vulcanisates are depends on these cross links in between the macromolecular structure. The system of vulcanization can mainly effect the concentration of these cross links. A conventional vulcanization with high sulphor to accelerator ratio is produce the poly-suphidic cross links. But the Efficient vulcanization system to using high accelerator the low or no sulphor & semi efficient vulcanization system with compromised concentration of sulphur to accelerator in between conventional and efficient vulcanization system can produce more mono & disulphidic cross links.

As the No. of moo & disulphidic cross links are increased, it will increases the ageing by oxidation resistance, thermal resistance, reversion resistance in natural rubber vulcanization and it also provides reduced compression set. But these systems show some draw backs i.e. inflexible processing safety, outdoor & poor initial vulcanisates properties, high cost & necessity for careful storage etc. So the application of this system is limited to few necessary situations. The modules, hardness etc. are increased by increasing the number of polysuphidic cross links, but these also reduces the elongation at break, fatigue life etc. of the polymer vulcanisate.

Not only the system of vulcanization but also the process of vulcanization is effects the vulcanisate properties. Over vulcanization is a dynamic process, not all the cross links survive the vulcanisation process. Instead existing cross link are broken down and new once are formed continuously. While the modules are rising more cross links are formed than are broken down. At the plateau stage, newly formed cross links are in balance with those that are broken down. And when reversion takes place more are broken down than are formed. This will caused to the variation of vulcanisate property of the natural rubber vulcanisate.

The degree of cross linking can show a marked influence in tensile stress, elongation at break, rebound resilience at the lower temperature, tear resistance, tension set, compression set, fatigue resistance (heat buildup), resistance to swelling etc. The degree of cross linking can also shows the less influence on, tensile strength, rebound resilience at room temperature, dynamic damping at room temperature, abrasion resistance, gas permeability, low temperature flexibility, electrical resistance etc.

Tyre is a dynamic product; the property of a tyre vulcanizate mainly depends on its degree of cross linking, the system of vulcanization used, the vulcanization process and the ageing conditions, heat buildup etc. on the service should affects the properties of tyre vulcanizates .

Theory of sulphur vulcanization;

Sulphur contained in the vulcanization network in a number of ways. As cross links it may be present as monosulphide, disulphide, or polysulphide, but it may be also be present as pendent sulphides, or cyclic monosulphides and disulphides.By the use of chemical probes, the relative amount of mono, di, and poly sulphide material can be assessed, and by measuring the degree of cross links as well, the pendent and intra molecular sulphur can be estimated. From this information and the amounts of nitrogen and sulphur combined with rubber and various stages of vulcanization, it is possible to deduce the general course of the vulcanization reaction.

The initial step in vulcanization seems to be the reaction of sulphor with the zinc salt of accelerator to give the zinc perthio salt XS, ZnSxX, where X is a group derived from the accelerator. This salt reacts with rubber hydrocarbon RH to give a rubber bound intermediate

X S_xZnS_xX+RH X S_xR+ZnS+HS_x-1 X

And a per thiol accelerator group which, with further zinc oxide to form a zinc perthio salt of lower sulphor content; this may, nevertheless again be an active sulphurating agent, forming intermediates XSx-1R. In this way each molecule of accelerator give rise to a series of intermediates of varying degrees of polysulphidity. The hydrogen atom which removed is like to be attached to a methylene group in the alpha position of double bond.

CH3

- CH2- C =CH- CH2 -

The intermediate XS_xR then react with molecule of rubber hydrocarbon RH to give cross link, and more accelerator is generated;

XS_xR+RH RS_x-1+XSH

Even this is not the whole story, for, on further heating, the degree of poly sulphidity of the cross link declines. This process is catalysed by XS_xZnS_xX and can result in additional cross links. It is also evident that the cross links which where initially at positions 4 and 5 undergo an allylic shift, with the result that new configurations appears;

At the same time, disappearance of cross links of disulphide and polysulphide type occurs, with formation of conjugated trienes;

This destruction of cross links is apparently associated with the formation of cyclic sulphides. A consideration of the above reaction leads to conclusion that, if desulphuration proceeds rapidly in the case of the mix depicted, the final network will be highly cross linked with mainly monosulphidic bonds, and there will be relatively new modification of the cyclic sulphide or conjugated triene type; such a crosslink is termed efficiently cross linked. If on the other hand, desulphuration proceeds slowly as in the case of the compound depicted, there will be opportunities for thermal decomposition, leading to reversion or loss of cross links and to networks containing modifications; further, the cross links which do survive will be di or poly sulphidic and hence will be liable to further decomposition. These cross links are inefficiently cross linked.

Examination of a system containing HAF black shows that a remarks made above for a pure gum system generally hold for a natural rubber compound containing active black. The presence of HAF black increases the overall rate of reaction of the rubber and sulphur, and promotes the desulphuration reaction, thus leading to increased cross link efficiency.

ROLE OF ACCELERATORS:

By definition "Accelerators" are basic substances, which reduce the vulcunisation time by increasing the rate of cure. They also improve the physical properties such as modulus of the vulcunisate. The most commonly used vulcanizing agent is sulphur. Along with this different types of accelerators are being used. The most popular accelerators are delayed action sulphenamides, thiazoles, thiuram sulphides, dithiocarbamates and guanidines. A sulphur donor such as a thiuram disulphide may replace part or all of the sulphur. The accelerator to sulphur ratio dictates the efficiency of vulcanization and, in turn, the thermal stability of the resulting vulcunizate.

Sulphur is combined in the vulcanization network in a number of ways.

DIFFERENT SYSTEMS OF SULPHUR VULCUNIZATION:

Depending upon the dosage of Sulphur and accelerator, there are three different systems

of vulcanization.

· Conventional System

· Efficient vulcunization system

· Semi-efficient Vulcanization System.

Ø
Conventional System

In rubber an accelerator to sulphur ratio typically of 1: 5. is called a conventional vulcanizing system and it gives a network in which about 20 sulphur atoms are combined with the rubber for each inserted chemical crosslink. Here, ;mainly polysulphidic linkages are formed. These compounds give good tensile strength, modulus etc. But they are:subject to reversion. They show poor heat resistance, in a typical Natural Rubber compound, the usual dosage will be 2-2.5 phr of sulphur and 0.5-1 phr of accelerator

Ø Efficient Vulcanization System

An accelerator to sulphur ratio of 5: 1 is typical of an efficient vulcanizing (EV) system where no more than 4 - 5 sulphur atoms are combined with the rubber for each chemical crosslink. Most of the crosslinks at optimum cure are monosulphidic or disulphidic and only a relatively smafl proportion of the sulphur is wasted in main chain modifications. Jhis combination provides very nuch enhanced thermal stability; both under aerobic and anaerobic conditions, but some mechanical properties may be impaired. These compounds show good reversion resistance.

Ø Semi Efficient Vulcanization System

The Semi E.V. system comes in between the C.V. and E.V.system. The dosage of sulphur and accelerator, the physical proper tied obtained are all in between the other two systems.

Accelerators can be categorized in various ways. Depending upon the rate of vulcanization, they can bo classified as:-

· Slow

· Moderately fast

· Ultra

· Delayed action accelerator

In 1938 Bayer was the first to introduce commercial sulphenamides. These are delayed action accelerators. They are the reaction products of 2- Mercaptdbenzthiozole with basic substances. Sulphenamide types of accelerators are in vogue for almost nearly a century in tyre Industries. They have advantages of scorch safety, faster rates of curing, easy processability and better ultimate product properties. The sulphenamides become very popular because they available in spectrum of curing speed i.e. fast-slow(CBS, TBBS, MBS, DIBS, and DCBS).

VULCUNIZATION ACCELERATORS:

Sulphur by itself is a slow vulcunising agent. Large amounts of sulphur, high temperature and long heating periods are needed, thus obtain unsatisfactory crosslink efficiency with unsatisfactory strength and aeiging properties. Thus only with vulcunization accelerators the quality can be achieved.

There are some types of rubber accelerators. They are used in combination with each other in accordance with vulcanizing and/or acid-base conditions. Some examples classified by chemical structure are as below;

1. Thiazole

a. 2-Mercaptobenzothiazole

b. Dibenzothiazole disulfide

c. 2-Mercaptobenzothiazole Zinc salt

2. Sulphenamide

a. N-Cyclohexyl-2-benzothiazole sulfenamide

b. N-Oxydienthylene-2-benzothiazole sulfenamide

c. N-tert-butyl-2-benzothiazyl sulfenamide

3. Guanidine

a. Diphenyl guanidine

b. Di-o-tolylguanidine

4. Thiuram

a. Tetramethyl thiuram disulfide

b. Tetraethyl thiuram disulfide

c. Tetramethyl thiuram monosulfide

d. Isobutyl thiuram disulfide

e. Tetrabenzylthiuram disulfide

f. Dipentamethylene thiuramtetrasulfide

5. Dithiocarbamate

a. Zinc dimethyl dithiocarbamate

b. Zinc diethyl dithiocarbamate

c. Zinc dibutyl dithiocarbamate

d. Zinc N-ethyl-dithiocarbamate

e. Zinc dibenzyl dithiocarbamate

f. Copper dimethyl dithiocarbamate

6. Xanthates

a. Zinc isopryl xanthate

b. Sodium isopryl xanthate

c. Zinc butyl xanthate

7. Aldehyde amine

a. Hexamethylene tetramine (hexamine)

b. Ethylidene aniline

c. Diphenyl guanidine

8. Morpholine di sulphide

a. Bis-morpholine disulphide

MATERIALS USED:-

Master batch compound:

The Master batch compound weigth may be approximately 184.55gm. It was prepared by adding all ingredients to the rubber except sulphur, accelerator and retarder.

ACCELERATOR:-

The accelerator used here is of sulphenamide type. Also accelerators used by tyre industries are generally of sulphenamide type. These type of accelerators are used in tyre industry, as because of the fact that sulphenamides are accelerators with delayed onset vulcunization. Sulfenamides are special classes of accelerators that provide for a long delay period before the onset of the network formation. Sulfenamides and sulfenimides are commercially important classes of accelerators. Delayed action and fast cure characteristics are important in the preparation of large components made of rubber, such as tires. Large items require a great deal of processing to prepare the final form. Once in the final form and in the curing press, vulcanization should commence rapidly to allow for high productivity. The accelerator differs according to the type of amine used. The delayed action provided by the sulfenamide and sulphenimide accelerators allows time for processing before the onset of vulcanization.


Typical sulfenamide accelerators are :-

1. MBS (morpholino thio benzo thiazole sulphenamide).

2. CBS (cyclo hexyl benz thiazyl sulphenamide).

3. TBBS (N-tert: butyl benz thiazyl sulphenamide).

In these sulpheneamides are generally used in the tyre industry. This is because of the fact that sulphenamides are accelerators with delayed onset vulcunization. The accelerator differs according to the type of amine used.The scorch resistance of rubber compound is not much reduced as the proportion of the sulphenamide is increased, however the degree of vulcunization is increased and the total curing time reduced. If the sulphur content is raised, the scorch tendency and the degree of vulcunization are raised and the total curing time is reduced. As the amount of sulphur is reduced, the additional amount of accelerator required for agiven hardness is initially small but it increases greatly when only a very small proportion of sulphur is present. In such cases some dithio carbamates or thiuram accelerators are added so that total amount of accelerator can be kept relatively small. When the sulphur content is normal the addition of ultra accelerators as secondary accelerators considerably raises modulous.

Among the sulphenamide accelerators MBS and TBBS are most suitable for efficient vulcunisation system. The thermal instability of benzothiazole sulphenamide bond is the reason for limited shelf life of these materials. The processing safety increases from CBS to TBBS, MBS and highest with DCBS. Also TBBSgives the highest stress values. Addition of Zno is necessary for the activation of benzthiazole sulphenamides. In compounds with CBS, addition of stearic acid is recommended, to increase the stress value. Addition of stearic acid is necessary in compounds containing TBBS, MBS, CBS and DCBS to achieve higher cross link densities.

ACTION OF SULPHENAMIDE ACCELERATORS:

During vulcanization their molecules are split by heat. A 2- Mercaptobenzthiozole residue and a base are formed. The base activates the residue after which the vulcanization process proceeds extremely fast.

The main characteristics of the sulphenamides are very good processing safety, good cure rate and good reversion resistance. They also give vulcunizates with good physical properties.

A tread compound requires good processing safety during mixing and extrusion. During curing the tread gets direct contact with the heated mould. Since its thickness is high, and rubberbeing a poor conductor of heat, it takes some time for heat to get uniformly distribute to the inside. Thus the tread compound demands good reversion resistance. The sulphenamides with their delayed action and good reversion resistance makes a good choice and they are the most commonly used accelerators for the tread compounds.

MBS:-

MBS is the Morpholino Benz Thiazol Sulphenamide. This is most widely used in tyre formulation because of ease in processing and balanced spectrum of product properties besides its lower cost. The main disadvantage of MBS is that it is suspected due to its carcinogenic nature.

Structure of MBS:-

Property:-MBS is insoluble in benzene, ethyl acetate, methyl alcohol etc and soluble in water, dil: acid and alkali.

Specific gravity à 1.34-1.4

Melting point à 75-90 degree c

Moisture content à 0.3% (max)

Ash content à 0.25% (max)

Insoluble in methanol à 0.3% (max)

RETARDER

N-cyclohexyl thio phthalimidine (CTP (PVI))

Property: The material is white or yellowish crystalline powder dissolves in acetone, benzene,

oluene, ethyl ether, ethyl acetate as well as warm carbon tetra chloride, ethyl alcohol and

leptane. It is slightly dissolves in gasoline. But it is insoluble in kerosene and water

Appearance:- white or light yellow¹ crystal

1. Melting point (°C) 89-94°c

2. Heat loss 0.40 (max)¹

3. Ash content 0.20 (max)

SCOPE OF THE WORK:

The importance of replacement of MBS in tyre compounding

Amongst all the available sulphenamides, morpholino-thio-benzothiazole sulphenamide (MBS) is most widely used in tyre formulation because of ease in processing and a balanced spectrum of product properties besides jts lower cost. However of late, in advanced countries the use of MBS has been reduced significantly due to its suspected carcinogenic nature. Although many rubber Industries are still using the aforesaid material but in near future its application/will be stopped for safety reasons by government regulations

Morphoiine is released during vulcanization processes, using morphoiine-containing accelerators such as 2-N- morpholinothlo benzothiazole (MBS). Some of the amine is released into the atmosphere and some is bound to the rubber. Even^;the accelerator itself can contain free amine. The morpholine content of MBS is < 0.4%. by weight. This level can be higher if the accelerator is not stored properly and is exposed to heat or moisture.

MBS use in the manufacture of rubber additives results in an indefinable amount of morpholine being released into the hydrosphere or geosphere not only during manufacturing processes but also through tyre abrasion and disposal of used tyres.

Morpholine does not appear to be mutagenic or carcinogenic in-animals. However, it can be easily nitrosated to form A/-nitrosomorpholine .(NMOR), which is mutagenic and


carcinogenic in several species of experimental animals. Morpholine fed to rats sequentially with nitrite, caused an increase in tumours, mostly hepatocellular carcinoma and. sarcomas of the liver and lungs. It is therefore prudent to consider,exposure to morpholine increasing, thecarcinogenic risk in exposed, populations. .

Occupational exposure to morpholine rqay occur in several industries. Rubber products may also contribute to overall exposure. There afe few data on exposure of workers to morpholine. All reported values are below 3 mg/m3. "Occupational exposure to NMOR has been found in the rubber industry, where concentrations up to 250 ng/m3 have been measured. The. compound is absorbed by Inhalation: and. skin absorption In a 13-week inhalation study, morpholine (0.09-0,9 g/m3, 6 h/day, 5 days/week) has been reported to cause dose-related lesion of nasalmucosa and pneumonia at the higher exposure levels (0,36 andO.9 riig/mS) in the conditions p'f short-term and long-term inhalation, the critical effects appear to be irritation of the eyes; respiratory tract and the phenomenon known as blue Vision or glaucopsia have been described in occupational exposure High exposures to morpholine causes severe damage to the liver and kidneys of rats and guinea-pigs.

The high water solubility qf morpholine and its low volatility (under environmental condition) make this hydrospherepre-dominant enviornmental sink. Morpholine is inherently biodegradable and, although degradation is slow, there are no data to suggest accumulation in the hydrosphere. However, it seems unlikely that current levels of morpholine emission cause any significant damage to the wider environment.

How MBS become carcinogenic?

Morpholine'(1_:oxa-4-azacyclohexane) is a colorless, oily, hygroscopic, volatile liquidwith a characteristic amine ("fishy")-odor. Morpholine can undergo a variety of reactions. It behaves chemically as a secondary amine. Under environmental and Physiological conditions, solutions of nitrite or gaseous-nitrogen oxides/e.gJ,'N2O3, N2O4, NOx reacts with dilute solutions of morpholine and forms the proven animal carcinogen. N-nitrosomorpholine (NMOR). Nitrogen oxide. (NO) levels may be of importance in nitrosation. The conditions of nitrbsation, in particular pH, play a significant role.

Due to its carcinogenic properties the formation of NMOR frorn morpholine has to be taken into account when assessing health and environmental aspects of morpholine.

In aqueous solutions, the reaction is as follows:

2HNO2 N2O3+H2O

N2O3 NO + NO2

The rate of reaction of the nitrosation of morpholine by nitrile is greatest at a pH value of 3.4, where the rate constant is 0.42 mol-12s-1. An increase in the pH value has been shown to result in a decrease in the rate of nitrosation with nitrile, and the rate was almost zero at pH>7. In contrast, nitrosation with gaseous nitrogen oxides (N2O3, N2O4, NOx) can take place over the whole pH range found that, under certain conditions the yield of NMOR at pH 7 was ten times higher than at pH 2, but there was no further increase beyond this pH. Enhancement of the nitrosation of morpholine by nitrogen dioxide was reported in the presence of iodine, vanillin and related phenols and halides, particularly bromide.

OBJECTIVE OF THE WORK:

Comparing the other sulphenamide accelerators, TBBS/CBS are more match able with MBS in cost and availability. Also TBBS, being a primary amine derivative of MBT and does not liberate nitrosamine to harmful to health and environment during vulcunisation of tires and during its service life. So the objective of the present investigation is to explore the potentials of using TBBS/CBS in place of MBS in the formulation of different tyre components without sacrificing the properties.

OUT LINE OF THE WORK

In this study a compound with MBS accelerator (0.5phr), Sulphur (2.25phr), CTP (O.2phr) was considered. Replacement of this compound with slightly faster accelerator TBBS/CBS and same phr of sulphur and retarder were used. So the reduced amount of TBBS/CBS was used. TBBS is a faster accelerator, so the requirement of accelerator can be reduced, to get equivalent properties. Then the properties of MBS and TBBS/CBS batches were compared.

Batch R... MBS -0.5Phr, Suiphur-2.25, CTP-0.2 - CONTROL BATCH

The compounds were evaluated for rheometer characteristics and the

vulcanizate properties like Tensile properties, Tear strength, and hardness are evaluated.

MIXING & VULCUNIZATION (Curing):-

Mixing is a process of homogenizing various ingredients or additives to the raw rubber in correct proportions so as to obtain desired properties to the finished product, which can also aid processing in most economic manner. Processing is the foundation upon which every further step is based in any rubber industry. Mixing is the most critical component of rubber processing. The aim of mixing is to produce a product that has the ingredients dispersed and distributed sufficiently thoroughly that will process satisfactory in the next process, cure efficiently and give the required properties for the end application. Mixing requires deciding for the given formulation what equipment to use, and the times, speeds, pressures, temperatures and procedures that are required to make an intimate mixture of ingredients into an adequately mixed compound.

FORMULATIONS:-

01 . TRIAL-1:-

NO:	INGREDIENTS	Phr
01	Master batch	184.55
02	TBBS	0.5
03	Insoluble sulphur	2.25
04	Retarder	0.2

02 . TRIAL-2:-

NO:	INGREDIENTS	Phr
01	Master batch	184.55
02	MBS	0.5
03	Insoluble sulphur	2.25
04	Retarder	0.2

03 . TRIAL-3:-

NO:	INGREDIENTS	Phr
01	Master batch	184.55
02	CBS	0.5
03	Insoluble sulphur	2.25
04	Retarder	0.2

04 . TRIAL-4:-

NO:	INGREDIENTS	Phr
01	Master batch	184.55
02	TBBS	0.45
03	Insoluble sulphur	2.25
04	Retarder	0.2

05 . TRIAL-5:-

No:	INGREDIENTS	Phr
01	Master batch	184.55
02	CBS	0.45
03	Insoluble sulphur	2.25
04	Retarder	0.2

06 . TRIAL-6:-

NO:	INGREDIENTS	Phr
01	Master batch	184.55
02	TBBS	0.4
03	Insoluble sulphur	2.25
04	Retarder	0.2

07 . TRIAL-7:-

NO:	INGREDIENTS	Phr
01	Master batch	184.55
02	TBBS	0.4
03	Insoluble sulphur	2.25
04	Retarder	0.2

Mixing is done in a two roll mill. All the batches are mixed one by one and stored. Trial numbers are given to them and are passed for testing. First the rheological properties are tested. For physical testing, the final batch compound must be get vulcunised.

Vulcunization was carried out using a hydraulic press having 12" ram size. The moulds were always preheated to the vulcunization temperature. The moulding were cooled up on removal from the mould to room temperature and conditioned at ambient temperature for 24 hrs before testing.

Cure time	Temperature
45 minutes	142 c

DETAILED DESCRIPTION OF PROCEDURES:

FINAL BATCH COMPOUND:

Final batch compound is prepared in the mill room using a two roll mill. Here first the master batch compound is make up in the two roll mill. After that other ingrediants like accelerator, retarder, and insolule sulphur are added and then again mixed. After that it is sheeted out and taken out for testing.

OSCILATING DISC RHEOMETER:

Introduction:

This test method covers the determination of rheometric properties such as optimum cure time (T90), Scorch Time (TS2), Minimum Torque (ML) & Maximum Torque (MH), of rubber compounds.

Reference Document / Standard : ASTM D 2084

Apparatus Model and Make : R100/1990 / Monsanto International, USA

Terminologies used:

Cure rate index:

It is a measure of rate of vulcanization based on the difference between optimum vulcanization and incipient scorch time.

Maximum torque:

It is a measure of stiffness or shear modulus of fully vulcanized test specimen at the vulcanization temperature.

Minimum torque:

It is a measure of stiffness of the unvulcanized test specimen taken at the lowest point of curve.

Scorch time:

It is a measure of processing safety of the compound. It denotes the time available for safe processing of the compound.

Time to a percentage of full cure:

It is an inverse measure of cure rate based on time to develop some percentage of the highest torque.

Use:

To determine the vulcanization characteristics of Vulcanisable rubber compounds used for quality control & research and development

Cure meter:

Consists of a specimen chamber, closure mechanism, a temperature control system, rotor drive and a torque measuring system.

Specimen chamber:

Consist of platen dies, and a biconical disk.

Platens:

Two platens made of aluminum alloy, each containing an electric heater and each having, in the center, a cavity to accommodate a die. From the side, there is a well for inserting a temperature sensor.

Dies:

The dies shall be fabricated from a non deforming tool steel having a minimum Rockwell hardness of HRC 50. Holes shall be drilled in both the upper and lower die member to enable temperature sensor to be inserted. The top and bottom surfaces of the die cavity shall contain rectangularly shaped grooves arranged radialy about the center and spaced at 20^o intervals. The lower die shall have a hole in the center to allow for the insertion of the disk stem. A suitable low friction seal shall be provided in this hole to prevent material leaking from the cavity.

Disk:

The biconical disk shall be fabricated from a non deforming tool steel having a minimum Rockwell hardness of HRC 50.The standard frequency of the rotary oscillation of the disk shall be constant at 1.7 Hz (100 cycles per minute)

The amplitude of the unloaded disk oscillation shall be constant at 1.00 ± 0.03^o about the centre position, that is, a total arc of 2 ^o.

Die closing mechanism:

The dies shall be closed and held closed during the test by a pneumatic cylinder with a force of 11.0 ± 0.5 KN (2500 ± 100 lbf).

Torque measuring system:

The torque measuring system shall consist of a device, that produces a signal that is directly proportional to the torque required to oscillate the disk. A recorder to record the maximum amplitude signal from the torque transducer shall be provided. The recorder shall have a full scale deflection response time on the torque scale of 1s or less and shall be capable of recording the torque with an accuracy of ± 0.5% of the torque.

Procedure:

· Bring the temperature of both die members to the test temperature with the disk in place and the die cavity in the closed position.

· Place the recorder pen to zero torque line on the chart.

· Position the pen to the 0 time position on the chart by pressing the reset button on the recorder.

· Select the correct torque range.

· Open the dies, place the specimen on the top of oscillating disc and close the dies.. This cycle must be completed within 20 seconds to minimize temperature change.

· Start the recorder immediately after the platens are closed.

· Test completion:

· Test is completed when the predetermined time has elapsed, or when a specified condition has been met (i.e. 1 or 2 lbf/in. reversion)

· Open platens, remove test specimen using the brass screwdriver, and clean the dies and disc with the brass brush.

· Due to the adhesive qualities of some rubber it may be necessary to remove the biconical-oscillating disc. The following procedure is accomplished

· Loosen the collet by pressing on the knob located on the right side of the rheometer, and turn it counter clockwise until disc can be removed with the brass screw driver.

· Remove the rubber specimen, using the brass screwdriver.

· Replace the disc, press in on the knob on the right side of the rheometer and turn it clockwise until it is tight.

· Close the platens and allow temperature to stabilize before beginning a new test.

TENSILE PROPERTIES:

Introduction:

This method is used to determine physical properties of rubber compounds in tension. Dumb bell shaped specimens are cut from a cured 6"×6" pad and pulled on a constant rate of extension tester at a jaw separation of 20 ± 2 inch/minute.

The resulting stress/strain curve is analyzed to determine tensile, modulus and elongation properties of the compound.

Reference Document / Standard:

ASTM D 412

Apparatus Model and Make:

Instron Corp. / Instron 3365

Terminologies Used:

Elongation:

Elongation represents the increase in length of the sample at ruptures, calculated as a percent of the original length. Percentage elongation is given by the relation

% EB = L - Lo

Lo

Where 'L' is the length in mm between the bench market at break 'L' is the initial length in mm between the bench mark.

Tensile Strength:

As all rubber products undergo stress during use, most compounds are designed to meet the tensile strength requirements. Tensile strength is a measure of the ability of a material to withstand forces that tend to pull it apart and to determine to what extend the material stretches before breaking. Tensile strength is given in Kg / Cm² by the relationship,

Tensile strength = F / A

Where 'F' is the force in kg at breakage & 'A' is the initial cross sectional area in cm².

TEAR STRENGTH:

Introduction
:

Tear strength is defined as the force per unit thickness required o propagate a nick or cut in a direction perpendicular to the direction of applied stress, or to initiate tearing in a direction normal to the direction of stress..

Reference Document / Standard:

ASTM D 624

Apparatus Model and Make:

Instron Corp. / Instron 3365

Procedure
:

· The gauge of the test piece is measured and they are inserted into the grip of the tensile testing machine. And is stretched until it fails.

· Because of the lower force involved, gripping is less difficult than with tensile tests.

· However, smaller force means that a sensitive load-measuring device is needed and the rate of change of force will rise and fall alternatively.

· All the current standard specify a stretching of 500 mm/min, the same as for tensile test.

Calculation
:

Tear strength is calculated by dividing the load in Kg by the thickness in cm of the specimen & expressed as Kg / cm.

Tear strength = F / A

Where 'F' is the force in Kg at the loading time, 'T' is the thickness of the specimen in Cm

HARDNESS TEST:

Introduction:

Shore A hardness is a measure of the resistance to penetration of an indenter of specified size and shape, forced into the test specimen. The hardness is measured in shore A hardness units ranging from 0 to 100.

This test method permits hardness measurements based on either initial indentation or indentation after a specified period of time, or both.

Reference Document / Standard:

ASTM D 2240

Apparatus Model and Make:

Gold 1997 / TRSE Instruments and Equipments, Chennai

Theory
:

Hardness tester (Durometer) is used to determine the hardness of the specimen. Hardness is defined as the resistance offered by a specimen to the penetration of a hardened steel truncated cone (shore A). The shore A Durometer is used for measuring softer materials.

This test method is based on the penetration of the specified indenter forced into the material under specified conditions. The indentation hardness is inversely related to the penetration and is dependant on the elastic modulus and Viscoelastic behaviour of the material. The shape of the indenter and the force applied to it influence the result obtained so that there may be no simple relationship between the result obtained with either another type of Durometer or another instrument for measuring hardness. This test method is an empirical test indented primarily for control purpose. No simple relationship exists between indentation hardness determined by this method and any fundamental property of the material tested.

Apparatus
:

Hardness measuring apparatus or Durometer consisting of the following components

o Presser foot with a hole having a diameter between 2.5 and 3.2 mm centered at least 6 mm from any edge of the foot.

o Indenter formed from hardened steel rod with a diameter between 1.15 and 1.4 mm to the shape and dimension.

o Indicating device on which the amount of extension of the point of indenter may be lead in terms of graduations ranging from zero for full extension of 2.46 to 2.54 mm to 100 for zero extension obtained by placing presser foot and indenter in firm contact with a flat piece of glass.

o Calibrated spring for applying force in the indenter in accordance with one of the following equations:

Force N = 0.55 + 0.075 H_A

Where,

H_A is hardness reading on shore A.

Test specimen:

The specimen should be at least 6 mm thick and should have as even surface, which should be sprinkled with the talcum powder before testing thinner samples may be piled up to get the thickness of 6 mm. But the hardness so determined on each specimen is only indicative and not definite.

Each specimen should be tested thrice at three spots, which should be at a distance of at least 5 mm from each other and 13 mm from any edge of the test plate. Vulcanized specimen should not be tested earlier than 3 days after vulcanization. Area of pressure foot to the extent of at least 6mm radius from the centre of an indenter in all directions should be in contact with specimen. Rounded, uneven or coarsely ground surface cannot be tested suitably.

Procedure
:

Place the specimen on a hard, even, horizontal surface. Hold the tester in a vertical position and apply it to the specimen which holding the presser foot parallel to the surface of the specimen.

Apply pressure with hand without shack until the pressure foot just makes a firm contact with the surface of specimen evenly. The reading is to be taken after about three seconds after this contact is made. This is particularly important for non-elastic rubber specimen.

To eliminate the human error, it is strongly advisable to use the tester with a specially designed tester stand. Three tests should be carried out on each specimen and the mean value of the three readings should be rounded off to a shore number. It is advisable to indicate derivations of individual reading from this mean value in test report.

TEST RESULTS AND DISCUSSION

Test results:

Rheo properties:

CC	AD	ML	MH	TS2	TC10	TC15	TC25	TC50	TC90
Trial-1	TBBS	8.2	31.61	10.72	11.02	11.80	13.02	15.88	25.42
Trial-2	MBS	9.11	30.5	12.72	12.85	13.83	15.25	18.50	30.10
Trial-3	CBS	9.18	31.66	10.37	10.55	11..30	12.42	15.08	24.22
Trial-4	TBBS	8.26	29.76	11.52	11.67	12.58	13.93	17.23	28.07
Trial-5	CBS	8.32	30.29	11.23	11.42	12.28	13.53	16.50	26.50
Trial-6	TBBS	8.58	30.28	12.00	12.17	13.08	14.45	17.73	28.73
Trial-7	CBS	8.34	29.67	11.60	11.68	12.58	13.92	17.13	27.92

CC - compound code, AD - Accelerator dosage, ML - Minimum torque,

MH - Maximum torque, TS2 - Scorch time, TC90 - 90% Cure time

PHYSICAL PROPERTIES:

TENSILE STRENGTH:

Compound code	Accelerator Dosage(phr)	Tensile strenth(kg/cm2)
Trial-1	TBBS(0.5)	235.2
Trial-2	MBS(0.5)	229
Trial-3	CBS(0.5)	229.3
Trial-4	TBBS(0.45)	232
Trial-5	CBS(0.45)	228.6
Trial-6	TBBS(0.4)	227.4
Trial-7	CBS(0.4)	225.3

TEAR STRENGTH:

Compound code	Accelerator Dosage(phr)	Tear strenth(N/m)
Trial-1	TBBS(0.5)	116.7
Trial-2	MBS(0.5)	106.3
Trial-3	CBS(0.5)	112.7
Trial-4	TBBS(0.45)	92.6
Trial-5	CBS(0.45)	114.5
Trial-6	TBBS(0.4)	98.8
Trial-7	CBS(0.4)	98.1

HARDNESS:

Compound code	Accelerator Dosage(phr)	Hardness (Shore A)
Trial-1	TBBS(0.5)	60
Trial-2	MBS(0.5)	60
Trial-3	CBS(0.5)	60
Trial-4	TBBS(0.45)	60
Trial-5	CBS(0.45)	60
Trial-6	TBBS(0.4)	59
Trial-7	CBS(0.4)	59

OVERALL ANALYSIS:

TBBS/CBS have better rheo properties as those accelerators shows good cure properties as compared to MBS. TBBS/CBS takes lower scorch time, cure time and also faster cure rate. Also the cure properties of these batches are better for processing safety.

By analysing the physical properties also we can conclude at the point that, TBBS/CBS can replace MBS. The tensile strength, tear strength, and hardness are also good as compared to MBS.

Also MBS is carcenogenic, we want to replace it by using an eco-friendly accelerator. Analysing of all batches shows that the Trial-1&3 batches are more comparable with control batch in physical as well as cure properties.

CONCLUSION:-

Since MOR is carcinogenic material its usage is banned in European & other foreign countries. So to adhere to the regulatory requirement this has to be eliminated from the product.

Ø Since the cure rate is matching with 0.4 phr of CBS & TBBS, this can be substituted for 0.5 phr MOR.

Ø There is a cost advantage of Rs:42 per batch (approx: 200Kg).

REFERENCES
:

1. Rubber Technology - By C.M. Blow.

2. Physical Testing Of Rubber (Second Edition) - By R.P. Brown.

3. Rubber Technology (Third edition) - By Maurice Morton.

4. Hand Book of Rubber Technology - By Hoffman.

5. Polymer Science - By Gowariker.

6. Tyre Technology - By Kovaic.