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

NO

N

O

OH

OH

n CH3

NO

N

O

2,4 TDI Polyol 2,4 TDI

O

OCH3

NO

N

O

CH3

NO

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

Dia

l

Re

ad

ing

Flo

w

me

ter

T

em

pera

tur

e

Je

t siz

e

Inje

cto

r

pre

ssu

re

Machine condition Basi

c

Actual

Theor

y

Actual

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

Dia

l

Re

ad

ing

Flo

w

me

ter

Te

mp

era

tur

e

Jet

siz

e,

mm

Inje

cto

r

pre

ssu

re

Machine condition Basic

Actual

Theory

Actual

Run No 5

Barrel type 1

Polyol Name: Batch no: OH value:42 Water 0.03 content

100 97.84

65 63.8 160

25 - Stirrer type 1

Lay down nozzle 1

Stirrer speed, rpm 3800

Iso cyanate Type: Index;105

40.34

40.34

26.30 26.22

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

3.051

846

- - 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

1.559

797

- - 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

3.900

- 0.49

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 23oC (chilled at 15oC)

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 -