What Are the Raw Materials of Flexible Polyurethane Foam?-Part 2

Catalysts

Polyurethane reactions typically use organotin compounds and some tertiary amines as catalysts. For example, dibutyltin dilaurate (T-12, DBTDL) and stannous octoate T9. Both are yellow liquids; the former is more toxic, the latter is non-toxic. Organotin catalysts effectively catalyze the reaction between —NCO and —OH groups. The dosage is generally 0.01%~0.1% of the solid content. Their structural formulas are as follows:

Dibutyltin Dilaurate (T-12, DBTDL)
[H9C4-CH-COO]2Sn (CH=C2H5)

Stannous Octoate
(H9C4)2Sn (OCOC11H23)2

Tertiary amine catalysts strongly catalyze the reactions of —NCO with —OH, H2O, and —NH2, but comparatively, their catalytic effect on —NCO and —OH is weaker than organotin catalysts. Tertiary amines are especially effective in catalyzing —NCO and H2O reactions, typically used in polyurethane foam plastics, foaming adhesives, low-temperature curing, and moisture-curing polyurethane adhesives. There are four types of tertiary amines: aliphatic (e.g., triethylamine), alicyclic (e.g., ethylene diamine), alkanolamines (e.g., triethanolamine), and aromatic amines. Among these, triethylene diamine is the most commonly used. Its structural formula is shown on the right. Triethylene diamine is crystalline at room temperature and inconvenient to use, so it is often prepared as a 33% solution in propylene glycol for easier handling.

Amines: Generally used are CS 90, AI, and A33 (in a ratio of 3:5). Their role is to promote the reaction between isocyanate and water, adjusting foam density, bubbles, and porosity, mainly to promote the foaming reaction.

Too much amine: causes cracking at edges and mid-bottom of the foam, splitting, or foam with holes or bubble eyes.

Too little amine: causes shrinkage, closed cells, and thick bottoms in the foam products.

About delayed amines:

Typically, amines and acids first form quaternary ammonium salts, which at room temperature do not catalyze the reaction, thus delaying catalysis. When the temperature rises, these salts decompose to release amine and acid, thereby catalyzing the reaction. The decomposition temperature depends on the acid used; stronger acids form more stable salts with higher decomposition temperatures.

TEGOAMIN SMP (amine catalyst) is a tertiary amine, a delayed catalyst for low-density sponge or molding, improving foam liquid flow and significantly shortening curing time. When using SMP or similar products, 33LV may be reduced or omitted. SMP is widely used in soft polyurethane block foam and cold molding systems. The amount varies with machine conditions; generally, 0.15 p.b.w. SMP is sufficient to perform well in formulations. It can increase foam hardness by 5-10%, which can be used to enhance hardness directly or, if hardness is to be maintained, reduce isocyanate index by about 2-3%, which is economically beneficial.

By adjusting the ratio of strong to weak acids and complexing with tertiary amines, delayed amines can be produced.

A1 Catalyst
Typical physical properties of A-1 catalyst: viscosity (20℃) 4.1 mPa.s, density (20℃) 0.902 g/cm³, flash point (closed/open cup) 74℃/77℃, refractive index (25℃) 1.4346, boiling point 186~226℃, vapor pressure (21℃) 1.3 Pa.

Characteristics and Uses

A-1 catalyst is mainly used for producing soft polyether-based polyurethane foams and can also be used in packaging rigid foam. It has a particularly strong catalytic effect on water, which can reduce foam density. Its effect on gas generation reactions is about 80%, while on gel reactions about 20%. The catalyst is highly active and used in small amounts. Adjusting its dosage controls foam rise and gel time. A-1 used with organotin catalysts improves production tolerance, ensuring consistent quality despite minor operational or metering errors, producing high-quality soft foam.

A-1 catalyst is widely used in various polyurethane foam formulations, especially suitable for producing high-resilience, semi-rigid, and low-density foams.

A33

Form: Liquid, specific gravity @ 20℃ 1.033

A tertiary amine compound that promotes the reaction between isocyanate and polyols to crosslink foam. Used in light sponge production. Contains 33% triethylene diamine in a dipropylene glycol solution.

Most amine catalysts are tertiary amines and do not participate in the reaction. After soft block foam forms, some amine catalysts volatilize during production; the remainder stays in the foam, contributing to VOCs and odor in soft foam.
Dosage: 0.15-0.2% of PPG.

Tin T9 (produced by Dow Corning, USA)

Tin: Has a strong catalytic effect on isocyanate and hydroxyl groups. Generally, stannous octoate T-9 is used. It is efficient and low in toxicity, with a molecular weight of 392.5, pure product is white or light yellow paste, soluble in petroleum ether but insoluble in water, with about 22% tin content. (T-19 is a highly active gel reaction catalyst mainly promoting gel reaction, i.e., the later-stage reaction, accelerating viscosity increase, reducing liquid film flow, and improving foam stability.)

T12 (D22, UL22): Molecular weight 631.55, relative density 1.02-1.06, tin content 18.6±0.6%, viscosity <50 mPa.s, flash point 440℃, soluble in common solvents and plasticizers, insoluble in water, highly toxic organic compound. Common in high resilience and memory foam.

Tin Dosage Reference
Dosage: For 30-hole PPG 0.15-0.25%, for 60-hole 0.2-0.5%.

Too much tin: rapid gelling, increased viscosity, poor resilience, poor breathability causing closed-cell formation and flashing. Increasing dosage moderately can produce relaxed open-cell foam; further increase leads to tight foam causing shrinkage and closed cells.

Too little tin: insufficient gelling causes cracking during foaming, cracks at edges or top, with mold release and rough edges.

Observe the foam top’s open-cell rupture patterns: dense large bubbles suggest reducing T9 dosage, smooth surface suggests increasing T9.

Lab tin foaming dosage should be reduced by 10-15% for machine production.

Reducing amine or increasing tin increases polymer bubble wall strength when gas generation is high, reducing hollow or cracking.

Whether polyurethane foam has ideal open-cell or closed-cell structure mainly depends on the balance between gel reaction speed and gas expansion rate during foaming. This balance can be adjusted by varying tertiary amine catalysts and types/amounts of foam stabilizers and additives.

Catalyst Usage Instructions

Primarily adjust gel and foam reaction speeds and inhibit side reactions. Generally, increasing catalyst concentration speeds reactions, shortens cure time, and reduces foam cell size, density, and compression modulus. Excess catalyst causes foam shrinkage and cracking. Reduce catalyst if cracking at bottom; increase T9 if cracking at upper/middle sections. Early foaming causes coarse bubbles, cracks, or collapsed foam. Early gelling causes low flowability, high density, closed cells, and foam shrinkage.

For products with low hydroxyl value, low TDI index, and low density, more catalyst is needed. For products with high hydroxyl value, high TDI index, and high density, less catalyst is used.

Tin Catalyst Use Notes
Because organotin catalysts are sensitive to external factors and prone to hydrolysis, phenomena such as whitening time, non-stick time, and demolding time extension may occur, leading to catalyst failure. Therefore, in high-water formulations for low-density foam, the choice and amount of catalyst must be careful, limiting high-dose usage. Important points:

When using high water content to prepare low-density foam, choose organotin catalysts with better hydrolysis resistance if possible, add them before production, mix well, and avoid long-term high-temperature storage with high-water polyols.

During production, if polyol mixtures with organotin catalysts become stratified or turbid, foaming tests must be done to observe whitening and gel times to check catalyst failure due to hydrolysis.

Organotin catalysts must be stored, transported, and used in acid-free, alkali-free, dry containers, sealed, and protected from water, acid, or alkali impurities during use.

In winter or low temperatures, preheat T12 slightly before use to maintain catalytic activity.

Soft block polyether polyol foams typically use tertiary amine catalysts with organotin catalysts. Gel catalysts may be diluted pure compounds like triethanolamine or bis(dimethylaminoethyl) ether or optimized blends. Typical tin catalysts for soft block foaming are pure or diluted stannous octoate. Diluted products (including amines and tin) solve raw material handling, metering accuracy, and pumping viscosity issues. High-performance blends improve processing, broaden formulation range, and reduce foam physical property variation in specialized foam equipment.

Polyurethane Catalyst Products List (USA)

Amine Catalysts
*DABCO 33LVR A-33: 33% triethylenediamine dipropylene glycol solution, industrial standard product.
*DABCO 8154: 8154 delayed triethylenediamine-type catalyst, can improve foam flowability.
*DABCO BDMA: BDMA reduces brittleness and surface curing in high moisture formulations.
*DABCO BL-11 A-1: 70% dipropylene glycol solution of bis(dimethylaminoethyl) ether, "foaming" catalyst.
*DABCO BL-17: BL-17 bis(dimethylaminoethyl) ether derivative with delayed reaction effect.
*DABCO BL-22: BL-22 complex amine with strong "foaming" effect, can replace BL-11.
*DABCO Crystalline solid amine: solid triethylenediamine, industrial standard product.
*DABCO CS-90: CS-90 complex amine with strong "foaming" action, improves foam density gradient and open-cell effect, reduces corner cracking in box foams (improves holes and rough foam structure caused by MC usage).
*DABCO DMAEE: DMAEE low odor surface curing catalyst, used with main base catalysts like 33LV.
*DABCO DMEA: DMEA mild and balanced catalyst, shorter cream time.
*DABCO S-25: S-25 gel catalyst, 25% triethylenediamine, 75% 1,4-butanediol mixture.
*DABCO T: T foaming catalyst with low atomization, used in packaging materials.
*POLYCAT12 (PC12): tertiary amine catalyst, lower reactivity, can increase foam hardness.
*POLYCAT17 (PC17): balanced, low atomization catalyst, improves surface curing, especially suitable for headrests and similar products.
*POLYCAT48 (PC48): special balanced catalyst that helps improve flowability and dimensional stability, especially for low-density formulations. Can be used alone or combined with other catalysts.

T9: stannous octoate, standard tin catalyst for soft foam;
T12: dibutyltin dilaurate (DBTDL), weak gel tin catalyst, highly toxic

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Effect of Different Catalyst Dosages on Foaming Time of Soft Foam

General block foam formulations have foaming times of 5–12 seconds, with total foaming times typically around 80–160 seconds. Foaming time can be adjusted by the amounts of organotin and amine catalysts. See the table below:

The first part is about TDI, please click the following link to read: https://www.sabtechmachine.com/what-are-the-raw-materials-of-flexible-polyurethane-foam-part-1.html

The third part is about Catalysts, please click the following link to read: https://www.sabtechmachine.com/what-are-the-raw-materials-of-flexible-polyurethane-foam-part-3.html