Manufacturing pu foam

Manufacturing Polyurethane Foams
Chandran.udumbasseri, Technical consultant
cudumbasseri@yahoo.co.in.
Introduction
Polyurethane foams are used as mattress, sofa covering, upholstery, automobile seats,
etc. Rigid polyurethane foam is used as insulators in cold storage equipments,
insulation packing, etc.
Process
Flexible polyurethane foam is made by continuous slab stock foaming method. The raw
materials, polyol, isocyanate, blowing agent, catalyst and surfactant are metered
continuously into a mixer. The mixed reactants are poured continuously into a paper
mold which moving on a conveyer belt. In the paper mold the mixed liquid foams and
expands to form a continuous block of foam. This block is cut and stored for one day to
cure the foam and cool. The cured are block cuttings are then cut to a variety of
shapes. These foams are having density in the range 15 to 50Kg/m3
.
Raw materials
The main raw materials are:
1. Polyol
2. Isocyanate
3. Blowing agent
4. Tin and amine catalyst
5. Silicone oil surfactant
6. Color/pigment
7. Fire retardant
Polyol
Flexible slabstock foams are made from polyether polyols. These are condensates of
propylene oxide and ethylene oxide. They are mainly triols. The hydroxyl values of
these polyols are in the range 36-56 mg KOH/g
Isocyanate
Toluene di iso-cyanate is used as raw material for flexible foams. 2.4 & 2.6 isomers are
present in the ration 80:20.
Blowing agents
The primary blowing agent which causes the foam to expand is carbon dioxide. Carbon
dioxide is produced by the reaction of iso-cyanate and added water.
Soft foams with density less than 21kg/m3
is produced by adding a secondary blowing
agent (trichlorofluoromethane or dichloromethane)
Catalyst
Amine: This type of catalyst (di-methyl amino ethanol or triethylene diamine) is used to
control rate of carbon dioxide formation (water and isocyanate reaction)
Stannous octoate: this catalyst promotes polyol and isocyanate reaction.
Silicone oil surfactant

Foaming process is controlled by the surfactant. The surfactant assists uniform mixing
of components and stabilizes the bubbles in the foam to prevent from collapsing
Chemistry
General reaction: RN=C=O + HO-R1
→ RNH-(OR1
)C=O (urethane link)
1. O=CN-R2
-NC=O + HO-R3
-OH+ O=CN-R2
-NC=O →
O=CN-R2
-NH(C=O)-O-R3
-O-(C=O)-NH-R2
-NC=O
CH3
N
O
N
O
OH
OH
n CH3
N
O
N
O
2,4 TDI Polyol 2,4 TDI
O
O
CH3
N
O
N
O
CH3
N
O
N
O
n
Urethane
The foaming process
1. Good mixing is necessary for homogeneous foam. Silicone surfactant assists
good mixing and lower surface tension of polyol.
2. During initial mixing tiny air bubbles are created a small amount of air is also
allowed to the mixing to have more such tiny air bubbles. As mixing proceeds
carbon dioxide or secondary blowing agent diffuses into these tiny bubbles and
enlarge them. The mix appears creamy. Time required to appear this creamy
appearance is called cream time.
3. Without surfactant the mixture appear to boil and the foam collapses
4. After 2 minutes of mixing, the gas reaction stops. Total volume is 30-50 times
that of original liquid volume. The polymer gels and spreads along the cell walls.
5. With 2-3 minutes of gel time the polymer strength increases
6. During curing time (one day) slow cross linking reactions take place and
strengthens the foam.
7. It is necessary to burst the cell walls after full rise time. If cell walls are not
broken then foam will not be having good resilience. The foam will appear tight.
This occurs when fast polymerization takes place.

8. If polymerization is slow the struts will be weak causing more of strut breaking
during cell wall breaking. This results in splitting in the foam. This occurs usually
at the top edges
First running of slabstock and data collection
The following data should be collected during the first running of the slabstock
machine.
Material- Formulation Throughput
Dial
Reading
Flow
meter
Temperatur
e
Jetsize
Injector
pressure
Machine condition
Basi
c
Actua
l
Theor
y
Actua
l
Run No
Barrel type
Polyol
Name:
Batch no:
OH value:
Water
content
Stirrer type
Lay down nozzle
Stirrer speed, rpm
Iso cyanate
Type:
Index;
Air injection, ml/min
Head pressure, atm
Conveyor speed,
m/min
Actvator-1
Water:
Amine:
Silicone;
Conveyor angle,
degree
Traverse speed,
m/min
Traverse width, m
Channel width, m
Activator-2
Tin
octoate:
Cream time, sec
Full rise time, sec
Gelation time, sec
Block height
shoulder,m
Block height crown,
m
Blowing
agent
Type :
Density, kg/m3
Hardness, N

Formulation and Calculation
Example formulation
Polyol 100.00
Isocyante 105.00
Water 003.30
Amine 000.40
Silicone surfactant 001.00
Stannous octoate (10%) 000.24
Blowing agent (TCFM) 006.00
Specification of polyol
OH value 42
Water, % 00.03
Polyol contains 0.03% of water
Isocyanate calculation
Isocyanate required (Eq wt = 87) =
Hydroxyl value is 42 mg.
So 42mg of KOH per gm of polyol for Saponification
= KOH = polyol = Equivalents of isocyanate
= = 6.51 parts of isocyanate for polyol
Water requirement
Required water = 3.3 parts
Water has two OH groups. So its equivalents is 18/2 = 9
No of equivalents of water = = 0.367 = = 31.91 parts of isocyanate
Actual water requirement = required – water in polyol = 3.3-0.03 = 3.27parts
Total iso cyanate = 6.51 + 31.91 = 38.42 parts
This is the exact quantity of iso cyanate required
The iso cyanate index is 105. It is 5% excess of the required quantity
38.42 x 1.05 = 40.34 parts of iso cyanate required

So the calculated formulation is,
Polyol 100.00
Isocyanate 040.34
Water 003.27
Amine 000.40
Silicone surfactant 001.00
Stannous octoate 000.24
TCFM 006.00
Stannous octoate is 10% solution in polyol
0.24 parts of stannous octoate in 100 gm polyol
For 0.24 parts = = 2.4 g polyol solution
0.24g stannous octoate + 2.16g polyol
Actual polyol to be added = 100-2.16 = 97.84
So for formulation
Polyol 97.84
Iso cyanate 40.34
Water 03.27
Amine 00.40
Silicone 01.00
Stannous octoate 02.40
TCFM 06.00
-------------------------------------------------
Total 151.25
============================

Through put
Cream time = 1 sec
Cream line = 0.5 meters for maximum block height from mixing head
Definitions:
Cream time: Time required for the chemical mixer to foam and reach its maximum
foam height
Cream line:
0.5 meters in 1.0 seconds
3 meter in 1 minute
Conveyor speed = 3 Meters/minute
Suppose block width is 1.5meters, height 0.8 meters and length 0.3 meters
Volume = 3x1.5x0.8 = 3.6m3
Density = 25Kg/m3
Weight of block = 25 x 3.6 = 90Kg
Output = 90Kg/min
Polyol through put
=
1. All added TCFM will evaporate
2. Carbon dioxide will escape
Carbon dioxide loss = 2 x water used (by weight)
Polyol through put =
= = 64.9Kg/min
If the used polyol is 3% less, then
=65 x 0.97 = 63.8kg/min
Through put factor = = = 0.652
Through put theoretical calculation
Polyol 97.84x0.652 = 63.800
Iso cyanate 40.34x0.652 = 26.300
Activator1 4.67 x 0.652 = 03.045

Activator 2 02.4 x 0.652 = 01.565
Blowing agent 06.0 x 0.652 = 03.912
Calibrate all the streams within + 1% of the theoretical through put
Enter these actuals in throughput actual column.
Material- Formulation Throughput
Dial
Reading
Flow
meter
Temperatur
e
Jetsize,mm
Injector
pressure
Machine condition
Basi
c
Actua
l
Theor
y
Actua
l
Run No 5
Barrel type 1
Polyol
Name:
Batch no:
OH
value:42
Water 0.03
content
100 97.8
4
65 63.8 16
0
25 - Stirrer type 1
Lay down nozzle 1
Stirrer speed, rpm 380
0
Iso cyanate
Type:
Index;105
40.3
4
40.3
4
26.30 26.2
2
81 16.
5
25 5 - Air injection, ml/min 200
Head pressure, atm -
Conveyor speed,
m/min
3
Actvator-1
Water:-
0.03
Amine:DMEA
Silicone;
3.27
0.4
1.0 4.67 3.045 3.05
1
84
6
- - 1 - Conveyor angle,
degree
5
Traverse speed,
m/min
20
Traverse width, m 0.9
Channel width, m 1.1
Activator-2
Tin
octoate:
10%
0.24 0.24 1.565 1.55
9
79
7
- - 1 - Cream time, sec 9
Full rise time, sec 90
Gelation time, sec 110
Block height
shoulder,m
0.8
Block height crown,
m
0.85
Blowing
agent
Type :TCFM
6.0
6.0 3.912 3.90
0
- 0.4
9
12 - - Density, kg/m3 20
Hardness, N
Flow chart

Machinery and Accessories
1. Polyol and isocyanate
Tank capacity = 10000 Lts to 30000 Lts
2. Catalysts are fed from drums
3. TCFM is kept pressurized and below 23o
C (chilled at 15o
C)
Preparations
Activator-1
Required water and amine are mixed together until the amine dissolves completely.
Required silicone is then added and mixed.
Activator-2
Stannous octoate should not be allowed to get exposed to moisture as the material gets
hydrolyzed. Always fresh solution in polyol should be prepared. Hydrolyzed material in
polyol appears milky. Color change from yellow to dark brown occurs in hot climate.
This color change will not affect the activity of the material. Correct amount of material
is added to polyol and stirred well. Avoid any air entrapping.

Mixing
1. Start stirrer
2. Bring the polyol stream to the delivery
3. Bring blowing agent and activators to the delivery
4. Bring isocyanate to the delivery
All the above 4 steps should be accomplished in 5 sec.
At the end of the run
1. Stop iso cayante
2. Stop all streams
3. Flush the mixer with polyol or cleaning solvent
4. Stop stirrer
Production Results
Through put
1. Polyol 47.00Kg/min
2. TDI 27.00Kg/min
3. Activator1 02.98Kg/min
4. Actvator2 01.08Kg/min
Activator 1
Water 28.80
SC240 07.30
Amine 00.80
Activator 2
Polyol 36.0
T9 04.0
Color 02.2
1 minute feed composition
Water 02.3258
SC240 00.5895
Amine 00.0646
Polyol 00.9210
T9 00.1024
Color 00.0560

Formulation
Polyol = 47 + 0.921 = 47.921
Polyol 47.9210 100
Water 02.3258 04.853
SC240 00.5895 01.230
Amine 00.0646 00.135
T9 00.1024 00.214
Color 00.0560 00.117
TDI 27.0000 56.340
Iso cyanate index 1.06
Formulation
Polyol 38.325 100
Water 01.804 04.7070
SC-240 00.451 01.1768
Amine 00.045 00.1174
T9 00.082 00.2140
Color 00.075 00.1956
TDI 21.500 56.0900
Iso cyanate index 1.084
Density 18.2 Kg/m3
Test results of the foam
Parameter Results Specification
VORALUX-Polyol CARADOL-Polyol
Density, Kg/m3
18.4-18.5 18.0-18.4 18.5-19.0
ILD Value, 40%N 175-185 140-150 140
CLD Value,40%KPa 4.3-5.3 3.0 3.8
Tensile strength, KPa 92.0-95.0 94.0-98.0 146
Elongation, % 200-250 200-250 240
Tear strength, N/m 400-420 320-350 -

Slabstock foam
A typical formulation
Requirement
Foam of density 25Kg/m3
Strength medium
Formulation
Polyol with OH value equal to 42.0mg KOH /g and water content 0.03%
Isocynate TDI
Activator 1: water, amine, silicone oil blend
Activator 2: stannous octoate in 10% polyol
Blowing agent: TCFM11
Basic formulation
Polyol 100parts by weight
TDI 105 Isocynate Index
Water 3.3 parts by weight
Dimethyl amino ethanol 0.4 parts by weight
Silicone oil 1.0 parts by weight
Stannous octoate 0.24 parts by weight
Blowing agent 6.0 parts by weight
Log sheet-1
Foam Grade: 25Kg/m3
and medium hardness
Component Material Formulation parts by
weight
Basic Actual
Polyol Grade:
OH value: 42.0 mg KOH/g
Moisture: 0.03%
100
TDI Grade:
Isocynate Index: 105
Eq weight: 87
40.34
Activator 1 Water = 3.3-0.03
Amine
Silicone oil:
3.27
0.4
1.0
Activator 2 Stannous octoate in 10%
polyol
0.24
Blowing agent TCFM11/Methylene
Chloride
6.0

The Isocynate index taken is 105
Total Isocyanate required = =40.34 parts by weight
Total aqueous activator 1
Water 3.3-0.03 = 3.27 parts by weight
Amine 0.4 parts by weight
Silicone oil 1.0 parts by weight
-----------------------------
Total 4.67 parts by weight
Activator 2
10% dilute solution in polyol = = 2.4 parts by weight
Polyol
Polyol in stannous octoate = 2.4 – 0.24 = 2.16
Reduce this amount from 100, 100-2.16 = 97.84 parts by weight

Log sheet -2
Foam Grade: 25Kg/m3
and medium hardness
weight
Basic Actual
Polyol Grade:
Moisture: 0.03%
100 97.84
TDI Grade:
Eq weight: 87
40.34 40.34
Amine
Silicone oil:
3.27
0.4
1.0
4.67
polyol
0.24
2.4
Chloride
6.0 6.0
Through put
Cream time = 10seconds (for automatic)
For manual cream time can be 15 seconds or so
Maximum block height cream line= 0.5 meters from mixing head
1 meter 30 seconds
2 meter 1minute
Output
Foam volume
Length 1.95 meters
Width 1.45 meters
Height 1.1 meters
Foam volume = 3,11 m3
Density taken = 25Kg/m3
Weight of foam produced = 3.11x25 = 77.75 Kg
This is total output in one minute
Polyol through put
Total output x =
Gas loss 2xwater weight = 2x3,3 = 6.6

Blowing agent = 6.0
Total ingredients = 97.84+40.34 +4.67+2.4+6.00 = 151.25
Polyol through put = 77.75x = = 56.07 kg/minute
Log Sheet 3
Foam Grade: 25Kg/m3
and medium hardness
weight
Through put
kg/minute
Basic Actual Theory
Polyol Grade:
Moisture: 0.03%
100 97.84 56.07
TDI Grade:
Eq weight: 87
40.34 40.34
Amine
Silicone oil:
3.27
0.4
1.0
4.67
polyol
0.24
2.4
Chloride
6.0 6.0
Some formulations from actual production using automatic machine
F1 F2 F3 STD Teat
Values
Polyol 100 100 100
Water 4.7070 4.66 4.53
SC240 1.1768 1.18 1.147
Amine 0.117 0.129 0.126
T9 0.214 0.246 0.246
Color 0.1956 0.113 0.112
TDI 56.09 55.9 52.09
Index 1.084 1.09 1.042
Density Kg/m3
18.2 17.4-17.5 18.5-18.8 18-19
ILD 40%N 140-150 180-185 175-185 140
CLD 40%Kpa 3-3.2 5.2-6 4.3-5.3 3.8
Tensile, Kpa 94-98 120-125 92-96 146
Elongation, % 100-120 110-120 100-110 240
Tear strength N/m 320-350 330-350 400-420 -

Through put
Density 22 Kg/m3
Cream time = 10seconds (for automatic)
For manual cream time can be 15 seconds or so
Maximum block height cream line= 0.5 meters from mixing head
1 meter 30 seconds
2 meter 1minute
Output
Foam volume
Length 1.95 meters
Width 1.45 meters
Height 1.1 meters
Foam volume = 3,11 m3
Density taken = 22Kg/m3
Weight of foam produced = 3.11x22 = 68.42 Kg /minute
This is total output in one minute
Polyol through put
Total output x =
Gas loss 2xwater weight = 2x3,3 = 6.6
Blowing agent = 6.0
Total ingredients = 97.84+40.34 +4.67+2.4+6.00 = 151.25
Polyol through put = 68.42 x = = 49.37 kg/minute
Taking 3% Polyol then actual polyol through put is 49.37x0.97 = 47.87 kg/minute
Calculate through put factor = = = 0.489
Multiply formulation actual values by throughput factor and enter in through put theory
column.
Multiply all other values (TDI< Activators & Blowing agent), except that of polyol, by a factor of
accuracy + 0.5%

Log Sheet 4
Foam Grade: 22Kg/m3
weight
Through put
kg/minute
Basic Actual Theory Actual
Polyol Grade:
Moisture: 0.03%
100 97.84 49.37 47.87
TDI Grade:
Eq weight: 87
40.34 40.34
19.73 19.63
Amine
Silicone oil:
3.27
0.4
1.0
4.67
2.28 2.27
polyol
0.24
2.4
1.17 1.16
Chloride
6.0 6.0 2.93 2.92
Through put actual
Polyol 47.87 Kg/minute
TDI 19.63 Kg/minute
Activator 1 2.27 Kg/minute
Activator 2 1.16 Kg/minute
Blowing agent 2.92 Kg/minute
Note:
1. Density can also be reduced by increasing water.

Relation between water % and Density of RPU foam
Below is given an equation that can be used to calculate water % to calculate the density
W% = 3.7063 * D -1.126
Where W is water % in the formulation and D is the required density in lbs/ft3
Density , lbs/ft3
Density , Kg/m3
W %
1.56 25 2.245
1.50 24 2.3513
1.44 23 2.466
1.37 22 2.5937

Density measurement of flexible PU foam
Relation: Mass, Volume and Density
Density is expressed in g/cc; Kg/m3
; lbs/ft3
Conversion gm/cc to Kg/m3
=
1 kg/m3
= 0.001 g/cm3
2 kg/m3
= 0.002 g/cm3
3 kg/m3
= 0.003 g/cm3
4 kg/m3
= 0.004 g/cm3
Conversion Kg/m3
to lbs/ft3
1 kg/m3
= 0.06242796 lb/ft3
2 kg/m3
= 0.124856 lb/ft3
3 kg/m3
= 0.187284 lb/ft3
4 kg/m3
= 0.249712 lb/ft3
Measurement
Cut out exactly flexible foam with dimensions
Length = 1ft
Width = 1ft
Height = 1ft

Weigh the cubic foam on a weighing balance
Calculation
Density in lbs/ft3
=
A mattress of 4 pounds per cubic foot means that a cube of this mattress measuring
a foot in each direction weighs four pounds.

Typical ranges of density for different foam applications.
Importance of density value
1. Density does give any indication of fitness of the foam
2. Density does give quality and durability of the mattress
3. A dense mattress is heavier and difficult to move but it is more durable.
4. Fitness is measured by ILD (Indentation Load Deflection). The higher
the ILD value the firmer the mattress.

How Dense Should a Good Mattress Be?
That depends on several factors, including what type of mattress you prefer and
how much you weigh. In general, a good-quality memory foam mattress should
have a density of at least four pounds.
A standard mattress need not be as dense to be of good quality. Double-sided
mattresses should be at least 1.5 pounds per cubic foot of density, and single sided
mattresses should be 1.8 pounds per cubic foot. If you're a heavy person, consider
going with a mattress that is two pounds per cubic foot at the minimum, so that it
lasts longer and is comfortable.
Buying a mattress can be difficult. Knowing what to look for in terms of density
can help you to start asking the right questions.

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