The 2 important international specifications are the
SPECIFICATION OF CL-60 AS PER ISO AND ASTM
Parameter | Unit | Range | ISO | ASTM | |
1 | Total Solids (tsc) | % | min* | 61 | 61.3 |
2 | Dry Rubber (drc) | % | min | 60 | 59.8 |
3 | Non Rubbers (nrs) | % | max | 1.7 | 2 |
4 | Alkalinity as Ammonia – HA | % | min | 0.6 | 0.6 |
Alkalinity as Ammonia - LA | % | max | 0.29 | 0.29 | |
5 | Mechanical Stability Time (MST)# | sec | min | 650 | 650 |
6 | Coagulum Content | % | max | 0.03 | 0.05 |
7 | Copper | ppm | max | 8 | 8 |
8 | Manganese | ppm | max | 8 | 8 |
9 | Sludge Content | % | max | 0.1 | 0.1 |
10 | Volatile fatty Acid No (VFA) | No | max* | 0.06 | 0.06 |
11 | KOH No | No | max* | 0.7 | 0.8 |
12 | pH | Unit | Min | 10 | 10 |
# MST is tested 20 days after production Analysing the Tests separately
EPDM rubber products manufacturer in Kerala
TEST METHOD FOR TSC
TEST METHOD FOR DRC
TEST METHOD FOR ALKALINITY AS AMMONIA
Here we are testing the total alkali present and expressing it as Ammonia
The reagents required are
2 to 5 g of latex is weighed accurately into a conical flask containing 200 ml of distilled water 5 drops of Methyl red indicator is added and swirled well .This is titrated against 0.1N Hcl, the end point is when the colour changes from red to pink
The vol. of HCl used is noted
Normally the calculation is done by substituting in a formula
% of Alkalinity as Ammonia is calculated as
The basic starting point is
NHCl x VHCl = NCL60 x WCL60
If we rewrite this equation: (the unknown is Normality of CL60)
NCL60 = (NHCl x VHCl)/WCL60 hence
Wt of Ammonia = NCL60 x 17/1000
Wt of Ammonia = NCL60 x 17/1000
= [(NHCl x VHCl)/WCL60] x 0.017
% of Ammonia = 0.017x(NHClxVHCl)x100
WCL60
Eq: wt: of Ammonia - 17
MECHANICAL STABILITY TIME
Significance:
This test gives an indication at to how stable the latex is to agitation, the colloidal stability. The stability is crucial in the transport and stirring of CL60
Materials required
• Stirrer – 14000+200 rpm [MST apparatus earlier the KLAXON MST TESTER]
• Test beaker usually polycarbonate
• Glass rod
• Petri dish with water
Conditioning of Latex
Test Procedure
End point
Expression of result
DETERMINATION OF COAGULUM CONTENT Significance:
This estimates the coagulated rubber particles the skin formed and other foreign matter in latex. Coagulum can destabilise the latex as well as result in poor film formation
Materials requires
Test Procedure
Calculation
Coagulum Content% = Mass of dried coagulum x 100
Mass of latex taken
DETERMINATION OF MICRO COAGULUM CONTENT
This is a continuation of Coagulum determination and has the same significance as coagulum content
Calculation
Micro Coagulum Content% =Mass of dired micro coagulum x 100
Mass of latex taken originally
COPPER and MANGANESE were insisted by Customers when Iron pipes, brass or gun metal valves etc were used. Today they have all been replaced by Stainless Steel or PVC and Customers do not insist these test results.
Both Copper and Manganese are done spectrophotometrically
COPPER
A known weight of tsc film is ashed at 800 deg C and digested in Nitric Acid/Hydrochloric Acid mixture.
The colour generating compound is the complex of
Cu + ZDEC
Known solutions with Cu is made and the standard graph made
The Unknown ashed solution is complexed with ZDEC and reading taken ant 425 nm
From the graph the value is determined
MANGANESE
The standard calibration graph is first made using known quantities of Manganese
The reagents used are
This develops the permanganate colour
The colour is read spectrophotometrically at 525 nm
The value is read from the graph directly
SLUDGE CONTENT
Apparatus
Laboratory Centrifuge of rpm 2300 – 3000
With 50 ml centrifuge tubes
Chemical Used
Alcohol – Ammonia mixture
Ammonium hydroxide- 28 ml
Ethyl Alcohol 95% 946 ml
Water 2810 ml
Procedure
50 g each of latex is taken into the centrifuge tubes, the top closed and centrifuged for 20 min. The top sludge is removed and the latex above the sludge is carefully taken out using a pipette.
Ammonia Alcohol mixture is poured into the tubes and the process is repeated till the supernatant liquid is clear
The sludge is then transferred quantitatively into a weighed 200 ml beaker
The water is evaporated on a hot plate and dried at 70+2oC and weighed
Calculation
% of Sludge = mass of sludge x 100
mass of latex
VOLATILE FATTY ACID NO. (VFA NO)
Definition
Volatile fatty Acid No is defined as the Number of Grams of Potassium Hydroxide required to neutralize the Volatile fatty Acids in a latex sample containing 100 g of total solids
Significance
VFA indicates the quality state of the latex at that time with particular reference to the microorganisms present that produce fatty acids.
Apparatus
Reagents
Markham Still
Principle
2CH3COOH + Ba(OH)2 Ba(CH3COO)2 + H2O
Acetic Acid and other similar organic acids react with Barium Hydroxide to give Barium Acetate of similar salts plus water.
Significance
The strong acid releases any complexed weak acids
Do not heat at this stage because the volatile acids will be released
The Distillation
Calculation
67.32 X N x V X 50 + W(100 –drc
W x tsc 100D
Where:
N = Normality of Ba(OH)2
V = Volume of Ba(OH)2
W = weight of sample
D = density of serum (1.02)
KOH Number
Definition
KOH Number is defined as the number of grams of Potassium Hydroxide equivalent all the acid radicles in latex containing 100 g of total solids
Significance
KOH Number is an indication of the age of a well preserved latex.
Apparatus
Reagents
Procedure
= M (100 – TSC) (TA – 0.5)
189
M = Weight of Latex
TA = Total Alkalinity in water phase
1 ml 5% formaldehyde = 0.0189 g of Ammonia
Vol of KOH | pH | 1st diff | 2nd diff |
5 | 9.11 | ||
0.13 | |||
6 | 9.24 | 0.03 | |
0.16 | |||
7 | 9.4 | 0.05 | |
0.21 | |||
8 | 9.61 | 0.07 | |
0.28 | |||
9 | 9.89 | 0.11 | |
0.39 | |||
10 | 10.3 | ### | |
0.25 | |||
11 | 10.5 | ### | |
0.19 | |||
12 | 10.7 | ### | |
0.16 | |||
13 | 10.9 |
The end point can be found from
1st differential deflection point or
2nd differential intersection point
Calculation
KOH NO: = N x V x 561
W x tsc
Where
N = Normality of KOH
V = Volume of KOH at end point
W = weight of latex sample
pH
Method
pH is determined electronically using a pH meter and glass electrode
Procedure
Result
The result is expressed as
pH at 27oC = xx.xx
CHEMICAL STABILITY TESTS
The Chemical Stability tests are
These tests are important for manufacturing products like Gloves, Condoms, Catheters, Balloons etc.
Brookfield Viscosity
Brookfield Viscosity denotes the shear viscosity of a liquid. The viscosity of latex is determined at 60 tsc using spindle 2 rotating at 60 rpm at a temperature of 25 + 2oC
Apparatus
Procedure
Container
Expression of result
The result is expressed as
Brookfield Viscosity sp2, 60 rpm, 60 tsc, 25+2oC, cps
(spindle 2 rotating at 60 rpm and the latex having a tsc of 60%, temperature adjusted to 25+2oC
Units is centipoise (cps)
Zinc Oxide Viscosity (ZOV5 and ZOV60)
Significance and objective
Zinc oxide Dispersion causes destabilization and thickening of latex. Latex with Zinc Oxide dispersion added normally has higher viscosity than one without Zinc Oxide. The Viscosity is measured after 5 minutes and 60 minutes to estimate the thickening.
Procedure
ZOV5 = BV after 5 min of addition of ZnO x 100
Original BV
ZOV60 = BV after 60 min of addition of ZnO x 100
Original BV
Zinc Oxide Stability Time (ZST)
Significance
ZST signifies the stability of latex to agitation after the addition of dispersion. A low value if not good
Apparatus
Procedure
Zinc Oxide Heat Stability
Result
The result is the time taken from the start of heating to the time of complete coagulation expressed in seconds
FORD CUP VISCOSITY
Significance
Ford Cup viscosity is the flow viscosity of latex and is measured by passing specified quantity of latex through an orifice of specified dimension.
The Apparatus
The apparatus consists of a vessel of capacity 100 ml and an orifice at the bottom. Based on the size of the orifice the FC is numbered
The preparation of sample
The Procedure
The Ford Cup selected (usually B3 for Latex) is placed on the stand and levelled. The bottom is closed with the finger and filtered (80 mesh) latex poured into it. The latex should be free of air bubbles. The edge of a glass plate or rod is run on the top of the cup so that the excess latex flows into the side. The cup outlet is opened by removing the finger; simultaneously starting a stop watch. The stopwatch is stopped at the point when the continuous flow breaks. This is the end point
Expression of Result
MAGNESIUM
Significance
Magnesium in Latex varies with
Mg++ is an hinderance to MST development and good film formation in the product.
Method
Mg++ being a divalent ion it is estimated by EDTA titration
Reagents
EDTA 0.01M: Dissolve 3.72 g of EDTA in water and make up to 1 litre. A few drops of KOH is added while dissolving
MgSO4 std solution 0.01M: Dissolve 2.46.48 g in 1 litre water
Ammonia-Ammonium Chloride buffer: Dissolve 5.35 g of Ammonium Chloride in 20 ml water add 35 ml 10 M Ammonia and make up to 100 ml.
Eriochrome Black T Indicator: 1 g of EBT in 50 ml EtOH plus 4.5 g of Hydroxyl Amine Hydrochloride
Procedure
Standardisation of EDTA
20 ml standard magnesium solution is pipetted into a china dish (china dish because the white background will show the colour change better) 10 ml of buffer solution is added followed by 2 drops of Erio T indicator. This is titrated against EDTA.
The end point is colour change from Wine Red to Blue
The normality of EDTA is calculated
Estimation of Magnesium
Weigh 5 g of latex into a conical flask and add 10 ml of buffer followed by 2 to 3 drops of Erio T indicator
Titrate against EDTA till the colour changed from Wine Red to Blue
Note the reading
A blank to be done and the value deducted from the above
Interference of Zn ions
This value actually gives the total divalent ions present
If Zinc Oxide is used as a preservative there is likely to be interference
A factor equivalent to the Zinc in ZnO used can be deducted to give Mg present
Zn can be masked using KCN but it being a high poison the use is not recommended
Calculation
% of Mg present (Mg%)= 24.305 x VEDTA X MEDTA X 100
1000 x WLATEX
ppm of Mg = Mg% x1000000 = Mg% x 10000
100
SOME IMPORTANTS POINTS IN TITRIMETRY
Standard Solution:
A known weight of a reagent in a definite volume ia a standard solution
Molar Solution:
When 1 gram molecular weight of a reagent is dissolved in 1 litre it is called a Molar Solution (M)
Normal Solution:
When 1 gram equivalent is dissolved in 1 litre it ia called a Normal Solution (N)
Molar weight & Equivalent Weight
Molar weight is the gram molar weight of a substance & Equivalent weight is the gram molecular weight divided by its valance or combining power
Molar weight of H2SO4 = 2+32+64 = 98
Equivalent wt of H2SO4= 98/2 = 49 (because the valency or combining power is 2)
Standard Solutions
Take an example of standard HCl (1+35.458)
Molecular weight = 36.458
Equivalent weight = 36.458
36.458 g HCl in 1000 mL water = 1.00N solution
When you divide reagent by a number the Normality is also divided by that number
36.458/2 g HCl in 1000 mL water = 1.00/2 N solution
18.229 g HCl in 1000 mL water = 0.50 N solution
When you divide water by a number the Normality is multiplied by that number
18.229 g HCl in 1000/2 mL water = 0.50 x 2 N solution
18.229 g HCl in 500 mL water = 1.00 N solution
CALCULATIONS
Some basic points t be noted in calculations are
1. The chemical you are considering should be confirmed by CAS No. and molecular weight:
MgSO4 has a molecular weight of [24+32+(16x4)]
= (24+32+64)
= 120
= 120+126
= 246
NORMALITY CALCULATIONS
N1 X V1 = N2 X V2
hence N1 = N2 X V2
V1
Take an example of Mg determination
If N1 (Mg)=0.0056 (Eq wt of Mg = 24.305)
Using the formula N = Eq wt/1000
Mg in 1000 ml will be 0.0056 x 24.305 = 0.136108
Mg in 100 ml (%) will be = 0.136108 x 100 = 0.0136108
1000
Mg ppm will be = 0.0136108 x 1000000 = 136.108
100
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