A STUDY ON THE EFFECT OF
ZnO AND AMMONIA CONCENTRATION ON LATEX PROPERTIES,
GELLING TIME AND PHYSICAL PROPERTIES OF THE FILM
ZnO AND AMMONIA CONCENTRATION ON LATEX PROPERTIES,
GELLING TIME AND PHYSICAL PROPERTIES OF THE FILM
BY
MEERA
MEERA
І . INTRODUCTION……………………………………….
1. Hindustan Latex Ltd………………………………………
2. Male Contraceptive Condoms……………………………….
3. Natural Rubber Latex………………………………………
4. Testing Of Latex…………………………………………...
5. Preservation N R Latex……………………………………
6. Processing Of Latex……………………………………….
7. Latex Compounding………………………………………
8. Dipping Process…………………………………………..
І І.SCOPE OF THE EXPERIMENT…………………………..
1. Experimental Details………………………………………
2. Materials Used…………………………………………….
3. Parameters Tested………………………………………….
4. Frequency Of Testing………………………………………
5. Preparation Of Latex Compounding…………………………
6. Natural Ageing Of Latex Compound………………………..
7. Dilution Of Latex Compound………………………………
8. Preparation Of Mould Samples…………………………….
9. Leaching Of Mould Samples……………………………….
10. Vulcanization & Stripping…………………………………
11. Cutting Of Ring Samples…………………………………..
12. Ageing……………………………………………………
13. Test Details……………………………………………….
NATURAL RUBBER LATEX
Natural rubber is the nature’s most versatile product, which was discovered in Brazil, in South America 420 years ago, has an exudates mass caused due to drying of milky liquid oozing out of certain trees. This material has multifarious uses and there is hardly any segments of life does not use of rubber-based materials.
Guayule Shrub was probably the first known source of rubber, which was discovered in North America. Charles –de-la-Condamine, a French man first discovered Heavea Brasiliensis tree. Now Heavea Brasiliensis is the most important source of natural rubber and more than 97 % of natural rubber is produced from this tree. It obtained from the bark of the rubber tree by a process called tapping that a process of controlled wounding of the plant – a small portion of the bark is removed. This process opens the latex vessels and the latex flows out of the tree that is channeled into containers fitted to the bark.
Natural rubber latex is stable colloidal dispersion of 1,4 Cis Polyisoprene in an aqueous medium. The rubber content of field latex varies from 30-40%.
The size of the rubber particle varies from 0.025 to 0.3 microns. Natural rubber is a colloid with a specific gravity of 0.96 – 0.98 and a pH in the range of 6.5 – 7. The dispersed phase is mainly rubber and the dispersion medium is water. In addition to rubber and water, latex contains small quintiles of proteins, resins fats, fatty acids, other lipids and sterol esters, carbohydrates and mineral matter. Lipids in fresh latex consist of fats , waxes ,sterols , sterol esters & Phospholipids . Lipids associated with the rubber and non – rubber particles on latex play a key role in stability and colloid behavior of latex.
The natural rubber is a Polyisoprene. The structure of Polyisoprene is
CH3
│
▬( ▬CH2 ▬ C═ CH ▬CH2▬ ) n
In nature, Polyisoprene occurs as cis as well as trans form, the cis form is natural rubber and trans form is Gutta purcha.
CH2 H Trans (Gutta Purcha)
C ═ C
CH3 CH2
CH2 CH2 Cis form of (Natural
C ═ C rubber)
CH3 H
Composition of Heavea Latex
The following is the approximate composition of natural rubber latex.
Composition
In %
Rubber Hydrocarbon
30 -45%
Lutoid particles
10 – 20%
Protein substance
1 – 1.5 %
Resinous Substance
1 – 2.5 %
Applications
N.R latex is a general-purpose elastomer. Its high resilience, low heat build up& excellent dynamic properties coupled with out standing processability make it an ideal rubber for automatic tyres.
Engineering applications
Most engineering applications of natural rubber involves its use as a spring. The main reason for using in spring are ,
• Excellent resistance to fatigue.
• High resilience.
• Low heats build up.
• Reasonability good bonding with metal.
The typical engineering applications of natural rubber includes anti vibration mounting , flexible couplings , bridge bearings , lock fenders & rail pads .However the most important aspect of natural rubber is that it is economically friendly . I t is a product of nature & the energy requirement for its production is only a small fraction of that required for synthetic rubbers .While production of synthetic rubber causes , large scale production including releasing of large quantities of carbon into the atmosphere , production of natural rubber starts with fixing of the carbon from the atmosphere ,. There use of natural rubber has a definite positive impact on the environment.
Preservation of NR latex
It has been noted that natural rubber latex is the contents of a specialized type of cell in the Hevea Brasiliensis tree. It is a complex biochemical system. NRL consist of negatively charged rubber particle in an aqueous serum. It also contains non rubber constituents like proteins, carbohydrate etc which make them a suitable media for the growth of micro organism. So chemical changes occur shortly after the latex leaves the tree. The first of these changes is that the latex coagulates within a few hours. This process is known as spontaneous coagulation. Spontaneous coagulation is to be distinguished from the second of the obvious changes. This is putrefaction, which sets in at a later stage, with the development of bad odors. Preservation of latex is necessary to prevent both these processes occurring. Preserved latex may be field latex or concentrate latex.
Attributes of a good preservative
1.It should preserve the latex against spontaneous coagulation and putrification.It should destroy or in-activate the micro organisms.
2.It should increase the colloidal stability of the latex. This can be achieved by increasing the pH and hence the preservative should preferably be an alkali.
3.It should deactivate or remove traces of metal ions present in the latex.
4.It should not be harmful to the people or should not have adverse reaction with rubber or the container of latex.
Latex preservatives
Various chemicals have been used as preservatives among which ammonia is the most commonly used chemical.
1) Ammonia
Ammonia is a bactericide and it prevents the microbial action on latex. Moreover being an alkali it increases the pH of the system. Also ammonia reacts with the fatty acid present in the latex to form an anionic soap which increases the colloidal stability of the system.
2) Sodium Sulphite
Sodium Sulphite is used as an anticoagulant on the cup and bucket, especially when the latex is to be used for the production of a form of dry natural rubber known as pale crepe. As the name of this product implies, it is essential to keep discoloration of this type f natural rubber to a minimum. In this connection, it may be noted that sodium Sulphite is used as an enzyme inhibitor in the manufacture of pale crepe, the objective is again being to minimize discolouration.Excess use pf sodium Sulphite in latex retards drying of sheet rubber and gives rise to tackiness.
3) Potassium Hydroxide
The only practically important alternative to ammonia as a sole preservative of NR latex is KOH. This is used for the preservation of 75% m/m evaporated NR latex concentrate. It is an effective bactericide by virtue of its high alkalinity. For the same reason, it gives latex which is colloidally very stable.
High Ammonia preservation System
This is the most commonly used system in India. Here Ammonia at a concentration of 0.7% by wt is added to the centrifuged latex. This system will maintain its stability for long periods. But for field latex the non-rubber constituents are more and hence Ammonia concentration of 1% is used to preserve field latex.
Low Ammonia preservation System
One limitation of the high ammonia system is its low ZnO stability which is more important in the manufacture of some products. In such cases low ammonia systems are preferred. In low ammonia system ammonia is used at a concentration of 0.2% by Wt .Along with it chemicals like boric acid, sodium pentachlorophenate, ZDC are used. The most commonly used low ammonia system is LATZ.Here 0.025% of TMTD & 0.025% ZnO and 0.2% ammonia ( all by wt) is used.
Processing of latex
About 3 to 4 hours after tapping, the latex is collected from the tree, treated with a stabilizer to prevent premature coagulation, and brought to a factory or small holder central processing center. About 82 to 85% of latex extruded by the tree is collected in this way as field latex.
On arrival at factory the latex is sieved and blended. Field latex is either concentrated by removing part of the water to give latex concentrate, or it is deliberately coagulated processing into dry rubber.
Concentration of NR latex
The process of latex concentration involves the removal of a substantial quantity of serum from field latex ,thus making the latex richer in rubber content. Concentration of latex is necessary for the following reason:
Economy in transportation
Preference for high DRC by the consuming industry
Better uniformity in quality
Higher degree of purity
Latex may be concentrated to 60% DRC usually by creaming,centrifuging,evaporation or electro decantation or alternatively coagulated and dried. Creamed latex and evaporated latex are still in production. Centrifuged latex is the standard latex of commercially available in bulk.
Centrifuged Latex
Centrifuged latex concentrate accounts for more than 90% of total latex concentrate. The main types are available, one is known as high ammonia latex concentrate where the preservative is solely ammonia at a concentration of about 07%.The other is known as low ammonia latex concentrate, where the ammonia content is limited to 02% and is supplemented by secondary preservatives.
In centrifuging, latex is subjected to centrifugal force, several thousand times the gravitational force, in a bowl rotating at high speeds whereby individual rubber particles tend to separate into a layer surrounding the axis of rotation leaving an outer serum layer having a comparatively low rubber content. Each layer is removed through annular spacing around the axis of rotation. By controlling the time to which latex is subjected to such forces and by controlling the conditions of operations, latex having an original DRC of 30-38% can be concentrated to DRC of 60 or more.
Creamed Latex
Creamed latex is produced by adding a creaming agent, usually ammonium alginate, to the field latex preserved with a higher concentration of ammonia together with secondary preservatives.By creaming, DRC of about 66 to 68% is obtained.
Evaporated Latex
Evaporated latex is produced by passing field latex, preserved with KOH, through heated film evaporators at reduced pressure repeatedly until the desired rubber concentration is obtained.
Electro decantation process
This process is carried out in a special rectangular tank containing 1cm apart many groves in which cellophane sheets are fixed. The two electrodes are fixed at each end of the tank. Natural rubber latex is poured in the tank and electrics current is applied. The particles float to the top as a cream, which is removed from time to time. Latex with a solid content of 60-62% is obtained.
Advantages of centrifuged latex in the manufacture of dipped goods
There are several important features which must be recognized in natural product, which are:
High total solids of 60 to 70 %that is ammonia or fixed –alkali stabilized.
The latex is readily available in high ammonia forms, which permit deliberate stability control, necessary in latex dipping.
It is excellent wet gel strength.
It can be prevulcanized prior to use.
It can be straight, coagulant, or heat sensitized dipped.
Rapid drying and curing characteristics is typical, unlike most synthetic lattices.
LATEX COMPOUNDING:-
The first step of condom production is the compounding of latex. Compounding is done to make the latex suitable for moulding operations and for making the final product confirming to requirements of the end user. The process of mixing various compounding ingredients with latex is known as compounding.
Compounding involves choosing the amounts and type of vulcanizing ingredients, activator, accelerator, antioxidant, fillers and pigments and mixing them together when these are vulcanized under appropriate conditions a rubber article appropriate to the requirements specified is obtained. Some times other special purpose additives like viscosity modifier, plasticizer etc are added.
All ingredients added to the latex should be brought into a physical state that is comparable to the latex before they are added.
Ingredients like water soluble organic acids, salts of polyvalent metal, acidic materials etc should not be added to the latex as they lead to coagulation.
Compounding ingredients added to latex may be water-soluble or water insoluble. Water soluble ingredients can be added o latex as solutions in water. But water insoluble ingredients must be added as dispersions or emulsions. Solid ingredients are converted into dispersion before adding to latex. This can be achieved by using equipments like ball mill/attritor. Dispersing agents, wetting agents, protective colloids are also added during the preparation of dispersion to get stable dispersions. The pH of all additives are adjusted to alkaline pH(8-9) before adding to the latex.
Latex Compounding Ingredients
1) Stabilizers & surface-active agents.
Latex stabilizers like alkali’s (KOH, ammonia), protective colloids like casein and numerous surface active agents such as carboxylates, sulphonates...etc are used. Stabilizers are first added in to the latex during its compounding to prevent coagulations of latex compounds, while stripping, storage or during addition of chemicals
2) Vulcanizing agents.
Mainly sulphur is used as vulcanizing agent .Sulphur for the use of latex should be of good quality ,and finely dispersed in an aqueous medium . A Sulphur donor like TMTD is also used.
Vulcanization is an irreversible process during which a rubber compound, through a change in its chemical structure becomes less plastic and more resistant to swelling by organic liquids and the elastic properties are improved or extended over a greater range of temperatures, when cross links are inserted between the adjacent polymer chains.
Vulcanizing agents used for natural rubber are
1. Sulphur
2. Peroxides
3. Sulphur chloride
4. Sulphides (TMTD)……….etc
3) Accelerators
Accelerators enhance the rate of vulcanization. At higher temperature it can cut the vulcanization time from hours to minuets or seconds. Different type of accelerators are used for vulcanization .They are
1. Guanidines
Diphenyleguanidines
Diortho tolyl guanidines
2.Thiazoles
Mercapto benzothiazol(MBT)
Zinc salt of Mercapto benzothiazol(ZMBT)
Sodium dibutyl dithio carbamate
3.Thiuram disulphide
Tetra methyl Thiuram disulphide
Tetra methyl Thiuram mono sulphides.
4.Dithiocarbamates
SDBC
ZDBC & ZDEC
4) Activators
ZnO is commonly used as activator.. It can also help to increase the rate of vulcanization.
5) Antioxidents
They reduce degradation from sunlight, heat etc.antioxidants oppose oxidation and in a number of cases suppress many undesirable reactions, promoted either by oxygen or peroxides.
Eg; Antioxidant SP, Wigstay L (reaction product of p-cresol & di-cyclopentadiene)
DIPPING PROCESS
The dipping process consist essentially in the immersion of a former into suitably compounded latex, followed by slow withdrawal in such a way as to leave a uniform deposit of latex on the former. The thickness of the deposit may be reinforced with subsequent coatings. The process is completed by drying, leaching & vulcanizing the deposit. It is usually desirable to form a rolled bead at the neck of the article, inorder to reinforce the thin rubber to deposit against tearing.
There are different dipping methods are used ;
1. Simple dipping
2. Coacervant dipping
3. Heat sensitized dipping
4. Electro deposition
Simple dipping
By simple dipping is meant dipping without the assistance of any coagulants. A deposit forms by virtue of the viscosity of latex and of its tendency to wet out of the former. Single dip process gives very thin deposits. Single dipping is usually practiced as a multi-dip process, allowing partial or complete drying between the successive dips .The thickness of the composite deposit is approximately proportional to the number of dips.
Coacervant dipping
In this method a fluid coacervant like acetic acid is used to assist the build up of a deposit. It can be worked into two ways, according as the former is
dip first into the coacervant or first into the latex compound .The thickness of the deposit obtained is determined by the dwell time and by the stability of the latex towards the particular coacervant, which is used.
Heat sensitized dipping
The principle is to employ a heated former and to compound the latex in such a way that it is heat sensitive. The deposit builds up around the former as heat is conducted
A way into the surrounding latex .The thickness of the deposit depends on many factors like the degree of heat sensitivity of the latex, the temperature of the former and the heat capacity of the former.
Electro deposition
Since the latex particle usually carry a negative charge , it is possible to assist deposition by causing the particles to migrate towards the (positive polarity ) under the influence of a potential gradient.
SCOPE AND OBJECTIVE OF THE EXPERIMENT
SCOPE AND OBJECTIVE
Though dipped goods can be manufactured from post vulcanisable lattices (not pre vulcanized),a certain extend of prevulcanisation is generally given to increase the productivity and to get the required processing characteristics.ZnO is commonly used as the activator for NR latex vulcanized with Sulphur.ZnO along with organic accelerator increases the rate of vulcanization to levels that are required by various industrial applications.Moreover ZnO gives protection against thermal degradation and increases the modulus of the product.
Ammonia is used in natural rubber latex as a preservative because it acts as a stabilizer and bacteriacide. During compounding and post compounding operation some amount of ammonia is lost due to evaporation. To compensate this loss additional ammonia and other stabilizers are incorporated into the latex during compounding .Moreover ammonia is added to various compounding ingredients (eg:Sulphur dispersion,accelerator solution etc..) to adjust pH to the required level.The concentration of ammonia can effect the stability of the latex and hence the processing behavior. Also ammonia plays an important role in ZnO thickening of latex compound,which influences the compound stability and flow characteristics.Thus concentration of ammonia and ZnO are very critical as far as processing of latex compound is considered.
The main objective of my project work was to study the effect of ZnO and ammonia concentration on the properties of compounded latex,gelling time and physical properties of the film.
ZnO is added at different phr and the quantity of ammonia is also varied and the properties of the compounded latex with different formulations were studied.When ZnO is added during compounding,it combines with the ammonia present in the latex to form Zinc Amine complex.The formation of Zinc Amine complex may lead to the changes in viscosity of latex.
A brief outline of my project work is as follows:Nine formulations of combinations of ZnO and ammonia were tried.For each compounding, natural ageing, dilution etc….was given
All tests (HST,MST,TS,VISCOSITY,PH,ALKALINITY) were carried out.Hand dipped samples were then made.Ring samples were taken from these samples and Tensile strength,Elongation at break and modulus tested.The Gelling Time of the lattices of different formulations were observed.The physical properties of the film(Before Ageing and After Ageing) were also studied.
EXPERIMENTAL DETAILS
Materials Used
Concentrated latex manufactured by supplier namely Thiruvambady Estate (TE) latex was used in the study.
• Raw latex: TE
• Sulphur
• ZnO
• Antioxidant
• Accelerator-1
• Accelerator-2
SPECIFICATION OF RAW LATEX
Sl.No Test Items Specification
1. Appearance Clear milky white colour
without grey/yellow.
2. Odour No putrefactive odour after
the neutralisation of ammonia with
Boric Acid.
3. DRC(%) 60.0 min by wt.
4. TS - DRC (%) 1.0 Max.
(NRC)
5. Total Alkalinity (%) 1.8-2.5
(Titration Method)
6. Viscosity(B-type 50-85
viscometer at
25 deg.C
and 60% TS) (CP).
7. VFA No. 0.05max.
(KOH g/100g
solid )
8. MST (Second) 800-1600
9. pH value at 25deg .C 10-11.5
SPECIFICATION OF COMPOUNDING INGRADIENTS
SULPHUR
Test item Specification
Appearance Light yellow powder
Moisture 1% max.
Residue on 100 mesh sieve (%) 0.05 max.
Residue on 200 mesh sieve (%) 3.5 max.
Ash content 1% max.
Sulphur content (purity) 99% min.
ZnO
Test item Specification
Appearance White powder
Zinc oxide content 99% min. by wt.
Ignition loss 1% max. by wt.
Insoluble matter against HCl 0.1% max.
ANTIOXIDANT
Test Item Specification
Appearance Free flowing, cream coloured
powder
Ash 3 % max
Melting point 95 °Cmin.
Moisture 0.5 % max
Residue on sieve (100 mesh) 0.5 % max
Residue on sieve (200 mesh) 1.0 % max
ACCELERATOR - 1
Test item Specification
Physical form liquid
Colour reddish brown
Density, Mg/m3 0.99 +/- 0.02
Solubility* One part dissolves in two parts.
Further dilutions turn cloudy.
ACCELERATOR- 2
Test item Specification
Appearance Yellow or reddish brown
Translucent liquid.
Content 50.0 % min.
Specific gravity 1.09 - 1.14
Solubility Soluble in water.
FORMULATION DETAILS
Table 1&2 show the details of the Phr & the quantity of the latex during compounding.
Table 1:PHR of ingredients
Ingredients Formulat
ion 1 Formulat
ion 2 Formulat
ion 3 Formulat
ion 4 Formulat
ion 5 Formulat
ion 6 Formulation 7 Formulation 8 Formulation9
NR latex 100 100 100 100 100 100 100 100 100
Vulcanizing
agent 1 1 1 1 1 1 1 1 1
Activator 0.5 0.5 0.5 0.75 0.75 0.75 1 1 1
Antioxidant 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
Accelerator
1 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
Accelerator
2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
Stabiliser 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05
Table 2: Quantity of Ingredients added
Ingredients Formulat
ion 1 Formulation2 Formulation 3 Formulat
ion 4 Formulat
ion 5 Formulat
ion 6 Formulation7 Formulation 8 Formulation 9
NR latex 3kg 3kg 3kg 3kg 3kg 3kg 3kg 3kg 3kg
Vulcanizing
agent 64.2g 64.2g 64.2g 64.2g 64.2g 64.2g 64.2g 64.2g 64.2g
Activator 31.6g 31.6g 31.6g 47.4g 47.4g 47.4g 63.3 63.3g 63.3g
Antioxidant 31.4g 31.4g 31.4g 31.4g 31.4g 31.4g 31.4 31.4g 31.4g
Accelerator 1 15g 15g 15g 15g 15g 15g 15g 15g 15g
Accelerator 2 6.67g 6.67g 6.67g 6.67g 6.67g 6.67 6.67g 6.67g 6.67g
Ammonia 600ml (0.75%) 600ml (0.75%) 600ml
(0.75%) 600ml
(1%) 600ml
(1%) 600ml
(1%) 600ml
(1.15%) 600ml
(1.15%) 600ml
(1.15%)
PARAMETERS TESTED
1) Compounded Latex
AMMONIA
Ph
VISCOSITY
TS
HST
MST
Gelling time
2) Dipped sample
TENSILE STRENGTH
ELONGATION AT BREAK
MODULUS
Frequency of testing
• For twelwe days alternatively( for compounded latex)
• Before Ageing & After Ageing (for TS, EB% Modulus)
DETTMINATION OF ALL TEST:
1. Total alkalinity
As the alkalinity of the system depends upon the NH3 concentration the ammonia concentration used in this study.
Procedure:
About 1.3 gm of latex is weighed accurately and is transffered to a beak containing 200 mi of distilled water. It is stirred and a few drops of Methyl orange indicator added and is titrated against standard 0.1 NHCL in the burette . At the end point a permanent yellow colour appears.
Calculations:
% of NH3=Normality of HCL х 0.017 хVolume of HCL consumed
Weight of latex
2. pH
Caliberate the Ph meter: Take any convenient size of sample and adjust the temperature to arrange from 20ºC by midly agitating the sample the Ph and record both the temperature and Ph of the latex sample .
3. Viscosity .
Viscosity of latex is determined by means of a viscometer which measures the torque produced on a specified spindle ritating at constant rotational frequency and at a low shear rate while immersed to a specific depth in latex.
Procedure:
Pour the sample into the beaker the water bath maintained at 25 ºC or 27ºC and stir the sample gently until the temprature is 25 ±2ºC or 27±2ºC record the precise tmperatue. Immediately attach the spindle securely to the motor shaft and attach the guard into the sample in such a way to avoid air being trapped until the surface of the sample is at the mid point of the groove on the spindle shaft . The spindle shall be placed vertically in the sample and in the centre of the beaker .Select the rotational frequency of the instrument.
Switch on yhe viscometer motor and take the equilibrium reading to the nearest unit scale division .20 – 30 sec may ellapse before equilibrium reading is attained . Calculate the viscosity of latex expressd In Cp.
3. Total solids:
Procedure :
A suitable mass of sample is taken the dish a little distilled water is added and distributed over the bottom of the dish . With the dish uncovered the specimen is placed in a vented clear oven for 16 hrs at 70 degree centigrade. Then it is taken out cool in a desicator to room temperature and weighed . Repeat drying and weighing until the mass is constant.
Calculation: % of total solids = C – A х 100
B – A
Where A – Mass of weighing dish
B – Mass of dish + original sample mass
C – Mass of dish + dry sample.
5. Heat stability time:
HST is the minimum time required for the complete coagulation of 50 ml of the completed latex at 90 ± 2ºC.
50 cc of latex is taken in a water beaker . It is then kept in the thermo set 90 ± 2ºC and is stirred continuously with a glass rod . Time for complete coagulation is noted using a stop watch . This gives the HST.
6. MST (MECHANICAL STABILITY TIME)
PRINCIPLE:
A test portion of latex concentrate is diluted to 55% (m/m) total solids content and stirred at high speed. The time required to initiate visible flocculation is recorded, this being regarded as a measure of the mechanical stability
TEST PROCEDURE:
Carry out the determination in duplicate and within 24 h of first opening the sample bottle. If the total solids content and alkalinity of the latex are not known, determine them in accordance with ISO 124 and ISO 125, respectively.
Dilute 100g of latex, in a glass beaker, to 55.0% (m/m) +/- 0.2% (m/m) total solids content with the appropriate ammonia solution. Without delay, warm the diluted latex with gentle stirring to 36 to 37 oC over a water bath. Immediately filter the diluted and warmed latex through the wire cloth and weigh 80.0g +/- 0.5 g of the filtered latex in to the container Check that the temperature of the latex is 35oC +/- 1 oC.
Place the container in position and stir the latex, ensuring that the rotational frequency of the stirrer is 14000 +/- 200 rev/min throughout the test, until the end point is passed.
The arrival of the end-point is preceded by a marked decrease in the depth of the vortex around the stirring shaft.
Determine the end-point by removing a drop of the latex at intervals of 15 s and spreading the sample gently on a suitable surface, for example the palm of the hand, a glass microscope slide, the surface of water or the stainless steel wire cloth. Take the end-point as the first appearance of flocculum. Confirm the end-point by the presence of an increased amount of flocculum in a sample taken after stirring the latex for an additional 15 s.
Procedure for Gelling Time
A test drop of latex is allowed to fall through a glass plate. The glass plate should be kept at an angle of 45º from the horizontal plane and the temperature of the glass plate is maintained at 45º C.A drop of latex is allowed to fall through the glass plate, with the help of a syringe .The time required by the drop to stop the flow is recorded as the gelling time
PROCEDURE FOR TENSILE STRENGTH
• The stripped condoms are cut to get samples in the form of a ring (ring samples ). They are cut using a die.
• Hand dipped products are cut to get ring samples . Altogether 60 ring samples are cut from condoms.
• Then ring samples are cut from condoms are made from each formulation . Half of them are kept for ageing.
• The other half of the ring samples are used to contact tests on tensile strength , EB( Elongation at Break)
• The ring samples are clamped and stretched in an UTM (Universal Testing Machine).
AGEING
The ring samples are kept for ageing in an ageing oven at 70C for seven days. They are taken out after the required period and conditioning is given to the samples.
PREPARATION OF LATEX COMPOUND
Latex compounding is done in Test Tank. Test Tank is a jacketed vessel, the capacity of which is about 25 kg. It contains a stirrer in it, which has three blades. The speed of the stirrer can be varied from 0 to 50 rpm.Usually during compounding and pre-vulcanization the rpm is maintained at 20 rpm. It also contain two valves , one valve is used as steam inlet and the other valve is for passing chilled water for the purpose of cooling.
The test tank is cleaned thoroughly with water and is dried prior to compounding. Before operating it, the stirrer and the valves are checked .
Latex after weighing is sieved through a voil cloth and is loaded to the test tank. The chemicals are added in the required order to the tank.ie first stabilizers, accelerators, antioxidant, activator and vulcanizing agent. These chemicals are added into the latex at regular intervals. After the addition of each chemical the latex is mixed for 5 minutes before adding the next chemical so as to get thorough mixing. The chemicals are added after sieving through the voil cloth.
After addition of all chemicals it is stirred continuously for 2-3 hours. Then heating is given by passing steam through the steam line .The temperature of the latex is maintained in the range of 55 2C by a temperature controller. Heating is given until the latex attains the required cure 55C .Usually heating is given for 8-11hours when latex is cured to the required level .Cure is tested by the chloroform method. Then the steam is cut. After giving cooling the compounded latex is unloaded and is kept in a room for maturation for one day.
NATURAL AGEING OF LATEX COMPOUND
Compounded latex was kept for natural ageing. It was kept covered for few days until it gets cured. Continuous stirring was maintained during this period, from this day own words the cure of the latex is tested using chloroform.
CHLOROFORM TEST
5 ml of compounded latex is taken in a beaker and to it ; 5 ml of chloroform is also added .It is then immediately stirred using a glass rod the coagulation gets completed . T he coagulam is allowed to stand 1 to 2 minutes and numerically rated as follows:
• If the coagulam forms a tacky lump and breaks stringy, it is judged as under cure.
• If the coagulam forms an under lump and breaks shortly, it is judged as normal cure.
• If the coagulam forms non-tacky large agglomerates, it is judged as optimum cure.
• I F the coagulam forms small dry crumbs, it is judged as over cure.
After maturation the compound is diluted to the required Ts as mentioned below & tested for ammonia, pH viscosity ,TS , HST, MST (all test) which are explained in detail , later in laboratory test methods.
DLUTION OF LATEX
Before making condoms, the cured latex should be diluted to the required TS, (521) .After diluting the latex , all tests are carried out (HST,MST,Viscosity,TS) .
PREPARATION OF MOULD SAMPLES
Borosilicate glass moulds are used for condom sample preparation .These moulds are cleaned by washing and kept in an air oven for drying (70C) .Then it was kept in room temperature to bring down the temperature. Diluted compounds after removing the surface skin was used for dipping.
• First dip was given with very slow withdrawal speed and the last drop dripping from the nipple portion was allowed to full down.
• Then the mould is inverted quickly and rotated so that the film formed on the mould will have uniform thickness through out.
• It was rotated over a hot plate to speed up the drying process .About 5 pieces were given the first dip and then started the second dipping process.
• For the second dip , the level of latex should be slighter lower than that of the first dip so that all the beading portion, the second dip level will be at a lower level .
• Initial drying was done after inverting the mould and rotating over a heated hot plate .For getting a hand made samples this is done manually.
• Five hand dip condoms were made from each latex compound. So altogether 30 mould samples were made .Beading is done by hand.
LEACHING OF MOULD SAMPLE
After drying, the product will firmly stick on to the moulds . In order to soften and to facilitate easy removal from the moulds , the product should be immersed in an alkali bath (1 % ammonia) at 70C . This can also remove unwanted and soluble substances present in the dipped samples.
VULCANIZATION AND STRIPPING
Vulcanization of the mould samples is done before stripping the products .All the moulds were kept on a metal stand and placed in an air oven kept at 80C for 60 mts .After vulcanization time is over , the moulds were taken out , cooled to room temperature and stripping is carried out with the help of silica powder.
CUTTING OF RING SAMPLES
The stripped condoms are cut to get samples in the form of a ring (ring samples ). They are cut using a die.
• Hand dipped products are cut to get ring samples . Altogether 60 ring samples are cut from condoms.
• Then ring samples are cut from condoms are made from each formulation . Half of them are kept for ageing.
• The other half of the ring samples are used to contact tests on tensile strength , EB( Elongation at Break)
AGEING
The ring samples are kept for ageing in an ageing oven at 70C for seven days. They are taken out after the required period and conditioning is given to the samples.
Conditioning is given for three days at 25 deg C and RH of 50% & then tensile properties are measured..
DATA TABULATIONS
FORMULATION 1
TEST PARAMETERS
2nd DAY
4th DAY
6th DAY
8th DAY
10th DAY
AMMONIA
0.5
0.5
0.5
0.5
0.5
Ph
10.6 10.6
10.6
10.55
10.5
VISCOSITY
14.5 14.5
14.6
14.6
14.6
TS
51.0
51.0
51.0
51.0
51.0
HST
940
900
920
900
900
MST 435 435 435 430 430
FORMULATION 2
TEST PARAMETERS
2nd DAY
4th DAY
6th DAY
8th DAY
10th DAY
AMMONIA 0.75 0.75 0.75 0.75 0.75
Ph 10.85 10.85 10.8 10.8 10.8
VISCOSITY 15.5 15.5 15.6 15.6 15.6
TS 51.0 51.0 51.0 51.0 51.0
HST 970 970 970 962 960
MST 445 445 440 440 440
FORMULATION 3
TEST PARAMETERS
2nd DAY
4th DAY
6th DAY
8th DAY
10th DAY
AMMONIA 0.9 0.9 0.9 0.9 0.9
Ph 11 11 10.95 10.95 10.9
VISCOSITY 14.4 14.4 14.5 14.5 14.5
TS 51.0 51.0 51.0 51.0 51.0
HST 1050 1035 1030 1030 1028
MST 435 435 435 430 430
FORMULATION 4
TEST PARAMETERS
2nd DAY
4th DAY
6th DAY
8th DAY
10th DAY
AMMONIA 0.5 0.5 0.5 0.5 0.5
Ph 10.6 10.6 10.55 10.5 10.5
VISCOSITY 18.5 18.5 18.6 18.6 18.6
TS 51.0 51.0 51.0 51.0 51.0
HST 660. 660 650 650 650
MST 230 228 230 230 230
PARAMETERS
2nd day 4th day 6th day
8th day 10th day
AMMONIA
0.75
0.75
0.75
0.75
0.75
PH
10.8
10.8
10.8
10.8
10.75
VISCOSITY
18.4
18.4
18.5
18.5
18.5
TS
51
51
51
51
51
HST
740
740
740
730
738
MST 237 235 235 230 230
FORMULATION 5
FORMULATION 6
PARAMETERS
2nd day 4th day 6th day
8th day
9th day
AMMONIA
PH
VISCOSITY
TS
HST
MST
0.9
11
18.5
51
820
230
0.9
11
18.5
51
820
228
0.9
10.95
18.6
51
800
230
0.9
10.9
18.6
51
800
230
0.9
10.9
18.6
51
800
230
FORMULATION 7
PARAMETERS
2nd day 4th day 6th day
8th day 10th day
AMMONIA
PH
VISCOSITY
TS
HST
MST
0.5
10.6
20.5
51
490
215
0.5
10.6
20.5
51
485
210
0.5
10.6
20.6
51
480
210
0.5
10.55
20.6
51
480
210
0.5
10.5
20.6
51
480
210
FORMULATION 8
PARAMETERS
2nd day 4th day 6th day
8th day 10th day
AMMONIA
PH
VISCOSITY
TS
HST
MST
0.75
10.8
21.4
51
590
220
0.75
10.8
21.4
51
590
220
0.75
10.8
21.5
51
570
215
0.75
10.75
21.5
51
570
215
0.75
10.75
21.5
51
570
215
FORMULATION 9
PARAMETERS
2nd day 4th day 6th day
8th day 10th day
AMMONIA
PH
VISCOSITY
TS
HST
MST
0.9
11
20.5
51
690
210
0.9
11
20.5
51
690
215
0.9
10.95
20.5
51
690
215
0.9
10.9
20.6
51
660
210
0.9
10.9
20.6
51
640
210
RESULTS AND DISCUSSIONS
ZnO 0.5 phr ZnO 0.75 phr ZnO 1 phr
0.5 NH3 435 230 210
0.75NH3 440 237 215
0.9NH3 440 240 215
ZnO 0.5phr ZnO .75phr ZnO 1phr
0.5 NH3 900 650 480
0.75 NH3 970 740 570
0.9 NH3 1030 800 690
Results of Elongation of ring samples
FORMULATIONS ELONGATION
BA AA
1 st 779 752
2 nd 760 754
3 rd 768 745
4 th 727 710
5 th 735 705
6 th 729 722
7 th 678 632
8 th 652 620
9 th 675 645
• Histograph showing the Elongation of ring samples
Results of Tensile strength of ring samples:
FORMULATIONS Tensile Strength
BA AA
1st 21 19.5
2nd 22 20
3rd 21 20
4th 24 23
5th 25 23
6th 24 22
7th 26 24
8th 27 25
9th 26 25
• Histograph showing the tensile strength of ring samples
Results of Modulus of ring samples:
FORMULATIONS MODULUS
BA AA
1st 4.2 4
2nd 4.1 4
3rd 4.2 4.1
4th 4.5 4.3
5th 4.4 4.3
6th 4.5 4.4
7th 6.2 6.1
8th 6.1 6
9th 6.3 6.2
• Histograph showing the modulus of ring samples
ZnO PHR
.5 phr .75phr 1 phr
.5 NH3 21 24 26
.75 NH3 22 25 27
.9 NH3 21 24 26
.5 phr .75 phr 1 phr
.5 NH3 19.5 23 24
.75 NH3 20 23 25
.9 NH3 20 22 25
.5 phr .75 phr 1 phr
.5 NH3 779 727 678
.75 NH3 760 735 652
.9 NH3 768 729 675
.5 phr .75 phr 1 phr
.5 NH3 752 710 632
.75 NH3 754 705 620
.9 NH3 745 722 645
.5phr .75 phr 1 phr
.5 NH3 4.2 4.5 6.2
.75 NH3 4.1 4.4 6.1
.9 NH3 4.2 4.5 6.3
.5phr .75 phr 1 phr
.5 NH3 4 4.3 6.1
.75 NH3 4 4.3 6
.9 NH3 4.1 4.4 6.2
ZnO phr Gelling Time
.5 phr 39
.75 phr 24
1 phr 18
ZnO.0.5phr Zno.0.75phr Zno.1.0phr
Amm.0.5 14.6 18.5 20.4
Amm.0.75 15.6 18.6 20.5
Amm.0.9 14.5 18.6 21.5
0.5 0.75 1
0.5 14.6 18.5 20.4
0.75 15.6 18.6 20.5
0.9 14.5 18.6 21.5
CONCLUSION
► HST increases when concentration of ammonia is increased
►HST decreases when ZnO phr is increased.
► When ZnO is increased, gelling time decreases.
►There is a steep decrease in gelling time from 0.5 to 0.75 phr of ZnO.
► Change in concentration of Ammonia does not have much effect on change in gelling time.
►Increase in ZnO phr increases the viscosity of latex.
►MST increases with decrease in ZnO phr.
►Physical properties like Tensile strength and Modulus increases with increase in phr of
►ZnO, but Elongation at break decreases with increase in phr of ZnO.
►The change in concentration of Ammonia does not have any effect on the physical properties
Of the latex film
►The values of Tensile strength, Elongation and Modulus tend to drop on Ageing.
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