Technological process of the flexible foam production (polyurethane)

The production process of polyurethane foam consists of the reaction of polyol with toluene-di-isocyanate in the presence of catalysts, water and blowing agents. The reaction takes place in three stages: the order expansion reaction, the gas formation reaction and the cross-linking reaction.

These reactions take place in very short times of a few minutes, after which the foam solidifies into a porous mass. Since the reaction is exothermic, vulcanization is not necessary. The production of PU foam can be carried out by the method of discontinuous and continuous production. The second one takes place in factory production (fomax - system). According to this system, the raw material from the tanks is dosed by means of the pump to the reactor, which is connected by means of flexible pipes to the trough from which the slurry is poured into the mobile trae (conveyor). The bottom of the conveyor and the sides of the conveyor are wrapped with paper which moves at the same speed as the belt. At the end of the conveyor belt, the cutting is performed to the desired length, and the blocks are transported to the surface for cooling. Blocks after 24 hours are put into further processing.

I. PHYSICAL AND CHEMICAL ASPECTS OF POLYURETHANE SPONGE FORMATION

Polyurethane foam has experienced a great development (growth) in the last two decades. Now the annual production is about 2.5 million tons per year, with 2.0 million tons of soft pulp. The advantages for the production of PU foam are conditioned by the technical suitability of two basic types of raw material: polyether polyols with 2 to 8 hydroxyl groups per molecule and average molecular weight of 2000 to 6000, aromatic polyisocyanates such as toluene diisocyanate (TDI) or diphenyl- methane diisocyanate (MDI). However, the continuous process of flexible PU foam can only be realized with the increased development of special catalysts and foam stabilizers that are polysilicon-polyether copolymers.

Among the catalysts stannus octoate plays a major role. Surface polysilioxane-polyether copolymers, however, are of outstanding importance, especially for the (one-shot) continuous process of the flexible tip. If these products are not of a high quality standard, the required level of production (product) of PU foam cannot be realized.

The findings described in these reports are mainly based on the general physical rules for the formation of foam and it was concluded that the surface activity of the substances is the main "responsibility" of their effectiveness.

FOAM FORMATION AND STABILIZATION

All foams are generally dispersions of gas in the liquid phase. There are two possibilities for their formation:

a) The gas is mechanically dispersed in the liquid (heterogeneous foam formation).

b) Gas is generated in the liquid phase, e.g. with chemical reaction (homogeneous foam formation).

PU foam in which the blowing gas is introduced by reaction of isocyanate with water or by evaporation to a non-reactive liquid having a low evaporation point represents primarily an example of homogeneous foam formation.

In further research, however, it has been found that in the formation of PU foam, the saturation of the liquid with the maximum possible amount of gas is not enough to cause the self-formation of the "embryo", i.e. the spontaneous formation of small bubbles in the liquid.

Contrary to what was expected, these studies show that all cells of the final plume must exist as small gas bubbles at the beginning of the reaction mixture and must arise during the mixing process. The formation of PU sponge is considered as successive heterogeneous and homogeneous formation. For the formation of small (good) cell foam it is very important to start with a thin (small) distribution of air with the reaction mixture so that the small bubbles formed by the mixing process remain stable and do not coalesce. Such a thin and relatively stable dispersion of air is generally obtained by using surface-active compounds such as polysiloxane-polyether copolymers. These compounds reduce (decrease) the surface tension, however, they also reduce the free energy contained in the thermodynamically unstable dispersed system. According to the equation

DF=c A (c- interfacial tension; A-surface of the system)

The free energy of gas-liquid dispersion decreases with decreasing surface tension, but increases with decreasing bubble size.

As the foaming reaction begins, the small spherical bubbles present in the reaction mixture grow with the continuous diffusion of gas into them. The shape of the bubbles remains spherical until the gas volume of the system reaches 75% of the total volume. At this point, corresponding to a foam density of about 250 kg/m3, the geometric arrangement of the bubbles represents approximately a hexagonal spherical density packing in the liquid template. When the relative gas volume exceeds this critical point, the spherical foam transforms into a polyhedral system consisting mostly of pentagonal dodecahedron cell shapes. These cells are formed by compression which form a polyhedral frame in which most of the material (which forms the foam) is concentrated, and thins the membranes that form the horizontal surface of the two neighboring cells.

PU foam is mainly produced in a final density of 25 kg/m¬3. Polyhedral foam stabilization is therefore technically the most important. The stability of the polyhedral foam is mainly dependent on the stability of the cell membranes. Interpretations of the mechanism of how polyhedral foam membranes are stabilized in the presence of SURFACTANT (surfactants) are based on the classic Gibbs-Marangani effects.

According to this theory, the concentration of surfactant molecules on the surface decreases when the membranes expand as the foam increases. This causes higher surface tension on the expanded parts of the membranes. The resulting surface tension gradient causes the surfactant molecules to move along the surface. This movement of the surfactant molecules leads to the spontaneous migration of most of the molecules, which prevents the thinning of the membranes. Thinning and eventual destruction of membranes, however, can occur if surfactant molecules are present in too high a concentration. With increasing surfactant concentration, the expanded surface area can be increasingly replaced by the diffusion of surfactant molecules from the inner parts of the membranes.

Despite the movement along the surface, this process will not promote the necessary comigration of most of the molecules from the imprinted parts to the membranes. Thus there will be a surfactant concentration limit at which a maximum of foam stability is expected. As the surfactant concentration increases, the stability of the foam should decrease. Practical experience does not agree with this concept. In the production of flexible PU foam, it is known that increasing the concentration of the surfactant leads more (more often) to the overall stabilization than to the reduction of the stability of the foam.

According to Plateau's theory, foam stability is mostly caused by suction which is exerted on the membranes by means of supports. In polyhedral foam, each strut is shared by three neighboring cells. The transoms themselves and those parts of the membranes where they join are concavely curved. Due to the curvature of the liquid-gas surface at the transoms or Plate boundaries, the pressure at the transoms is lower than at the membranes. This pressure difference, which is greater in line growth than gravity growth, leads to drying (dehydration) of liquid from the membranes in the direction of the transoms. The profile view of the borders of the Plateau, and the pressure ratios are given in fig.1. The absorption of the edges of the Plateau is neutralized (opposed) by the dispersion (expansion) of the foam. The fact that the expansion itself has the effect of stabilizing the foam can be demonstrated with a simple experiment. The rapid formation of cream (foam) in which the stabilizer is missing gives cream (foam) which reaches approximately the same height as when the stabilizer is added, but then collapses spontaneously.

Regardless of the cooperation during the mixing and nucleation process, the main task of stabilizers should be not in the dynamic stabilization of the foam growth, but (rather) in the static stabilization after the period of foam growth, until the foam liquid crystallizes, forming a stable polymeric network.

OPENING OF PORES (CELLS)

The opening of flexible PU foam cells occurs spontaneously and almost completely at the end of rising. Formulations (recipes) containing completely different raw materials and catalysts can be processed (processed) in such a way that only a small part of the cell membranes remain completely or partially intact.

Until now the cell opening mechanism of PU foam has received little attention and has remained undefined (doubtful). This is surprising since, especially in the production of flexible foam, the formation of open cell foam in sufficient quantities is of the greatest technical importance.

For the most part the opening of the cells of the PU foam has been considered as mechanical destruction of the cell membranes. It has been concluded that during foam formation the viscosity of the foam material increases and resists (impedes) more and more the transmission of gas (gas pressure) to the expansion cells. Eventually the pressure inside the cells is believed to have increased enough to force equalization of pressure with the surrounding atmosphere causing the cell membranes to break down. If this mechanism will contain all the procedures that increase the stability or viscosity of the material (formation of foam) by chemical or physical interactions, it should favor the effectiveness of the cell opening process. At least they should not have a harmful (opposite) effect.

However, the opposite is observed in the practical process. Favoring the polymer formation reaction by increasing the stannous octoate concentration or by introducing polyols or cross-linking agents with higher activity in the formulation (recipe) produces closed-cell sponges more often than open-cell sponges. The same behavior is observed when the concentration of foam stabilizers is increased. Formulations in which the raw material and catalysts are chosen in such a way that the formation of the polymer is slow, in which case the internal pressure increase of the expanding gas can be more easily transmitted, give the opposite of the open cell foam. .From these experiences it can be concluded that there is a small difference between the opening of the cells and the collapse of the foam. It appears that cell opening results from a selective instability of cell membranes and stability of the polyhedral framework. Phenomenal, the opening of the cells can be considered as a partial collapse.These observations argue the assumption that, apart from the nuclear phase, the function and effectiveness of polysilicon-polyether copolymers as a stabilizer of flexible PU foam, seem predominant in the context of the cell opening process.

If the opening of the cells does not occur with pressure that causes the mechanical destruction of the membranes, but occurs when the material is not independent and probably still fluid, its mechanism will be explained by the properties and structure of the foam material at that stage and especially from the physical interaction that the stabilizer creates with the polymer binder.

Interpreting the efficacy of foam stabilizers and the mechanism of cell opening, therefore, requires a detailed knowledge of the chemical constitution of the foam polymer at the time of cell (pore) opening. This means an explanation of the chemical reactions that occur during the rising period. Until now, assumptions about the chemical reaction sequence in the growth of PU foam are mostly derived from the results of the reactions of aromatic isocyanates with alcohols, water or amines and from the findings of ir-spectroscopic research.

CHEMISTRY OF POLYURETHANE FOAM FORMATION

The formation of PU foam is based on the reactions of isocyanates with alcohols and water. When the polyether polyol used has more than two hydroxyl and hydroxy groups of equivalent weight above 700, their reaction leads to the formation of the elastomeric, three-dimensional polymer network. The reaction between isocyanate and water is of twofold importance. First, it produces CO2 which swells the foam, and secondly the aromatic amines which are formed in that case can react in urea. Urea segments can form a microdisperse (separated) solid phase and thus reinforce the elastomeric polymethane polyether polymer, acting as a chemical filler material.

Molding of the PU foam which is usually performed in a period of about 2 minutes requires a very careful balancing of the blowing reaction and the urethane reaction which can be processed spontaneously. For the soot formation process, therefore, it is of great importance to know the influence that conditions the reaction, the reactivity of the raw materials and, in particular, the variable action (variability) of the catalysts on the relative priorities of these reactions.

III. CHEMICAL REACTIONS IN THE FORMATION PROCESS OF POLY URETHANE FOAM- SPONGE

The chemical reactions of polyurethanes are based on the reactions of isocyanates with compounds containing active hydrogen. Isocyanates are compounds containing one or more highly reactive groups (-N=C=O). These groups react rapidly with hydrogen atoms that are bonded to atoms with higher electronegativity than the carbon atom. Some compounds that respond to these properties are given in Table 1.

Table 1. Active hydrogen compounds ordered by reactivity in the reaction with isocyanates:

Active hydrogen compounds	Typical structure	The relative degree of reactivity at 25⁰C unutilized
Aliphatic primary amines	R-NH₂	100.000
Aliphatic secondary amines	R₂-NH	20.000-50.000
Primary aromatic amines	A₂-NH₂	200-300
Primary alcohols	R-CH₂-OH	100
water	H-0-H	100
Carboxylic acids	R-COOH	40
Secondary alcohols	R₂-CH-OH	30
Urea	R-NH-CO-NH-R	15
Tertiary alcohols	R₃-C-OH	0.5
Urethanes	R-NH-C-O-R	0.3
Amides	R-C-NH₂	0.1

The reactivity of the isocyanate group can be explained by considering their resonance structures:

R – N – C = O «R – N = C = O «R – N = C - O

The electron density is expected to be greater on the oxygen atom and less on the carbon atom. This results in the oxygen atom having a high share of negative charge, while the carbon atom has a positive charge. The nitrogen atom has a medium share of negative charge. The normal reaction involves addition of the C=N double bond. the nucleophilic center from the compound with active hydrogen attacks the electrophilic carbon. The active hydrogen atom then bonds with the nitrogen atom. Electron withdrawing groups attacked by isocyanate molecules increase the reactivity of NCO groups towards nucleophilic groups. Electron donating groups reduce the activities of NCO groups. For this reason aromatic isocyanates are more reactive than aliphatic isocyanates. The formation of flexible PU foam is complex involving many components and at least two competing reactions.

III. 1 POLYMERIZATION REACTIONS

The reaction of the formation of polyurethane polymers takes place between an isocyanate and an alcohol according to the scheme:

R – N = C = O + R^’ – CH₂– OH ® R – N – C – O – CH₂ – R^’

Isocyanate alcohol urethane

This process is isothermal of adhesion where the associated heat of reaction is approximately 24 Kcal/mol of urethane. The hydrogen atom from the urethane group is capable of reacting with the other isocyanate molecule to form allophonate.

R – N – C – O – CH₂– R^’ + R – N = C = O Û R – N – C – O – CH₂– R^’

Urethane Isocyanate Alophonat

This reaction is continuous and leads to the formation of polymer bonds. The networks of polymer connections are shown in fig.1.

III. 2 GAS FORMATION REACTIONS

In order to form PU foam, it must be expanded or inflated with the introduction of gas bubbles. The conventional source of the gas is CO2 produced by the reaction of isocyanate with water.

R – N = C = O + H – O – H ® R – N – C – OH ® R – NH₂ + CO₂ + Q

The intermediate product of this reaction is thermally unstable carbonic acid, which spontaneously decomposes into amine and carbon dioxide. Diffusion of CO2 into previously nucleated bubbles in the reactive medium causes the medium to expand to form foam. Further reaction of the amine formed with the isocyanate gives the disubstituted urea.

R – N = C = O + R^’ – NH₂ ® R – N – C – N – R^’

Isocyanate amin disubstituted urea

Again, if the isocyanate molecules and amines are polyfunctional, polymer networks will result. Another possibility of polymer bonding is the reaction of hydrogen from disubstituted urea with free isocyanate to form the biurea bond.

R – N – C – N – R^’ + R – N = C = O Û R – N – C – N – R^’

Biurea

Since the reaction is irreversible, there are debates whether allophanates and biurets are present in the final polyurethane product. Blowing can also be achieved by physically adding non-reactive blowing fluids to the formulation (spiking recipe). The most commonly used blowing agents are fluorocarbons, methylene chloride and trichloroethane. The evaporation of these liquids by the exothermic reaction produces gas molecules which diffuse into the nucleation bubbles and contribute to the expansion of the bubble.

III. 3 FORMATION OF ISOCYANATE-AMINE COMPLEXES

This mechanism was first proposed by Baker and Holdsworth in 1947, which involved reversible nucleophilic attack of the carbon atom by amines to form the activated complex. In aromatic isocyanates, the carbonyl and aromatic groups have intermediate electron-withdrawing effects.

R^’ – N – C = O

isocyanate

NH₃ - tertiary amine

R^’ – N = C – O ® R^’ – N = C – O

NR₃

R^’ – N – C – NR₃ ® R^’ – N – C – O – R^’’ + N – R₃

With the formation of the amine complex, the nitrogen atom from the isocyanate group is activated and immediately reacts with the hydrogen atoms from the water or hydroxyl groups of the polyol.

III. 4 ORGANOMETALLIC CATALYSIS

The polymerization or gelation reaction between the isocyanate and the polyol is accelerated by organometallic catalysts. Of the large number of metals available, tin compounds are the most widely used. These compounds act as Lewis acids and generally react with basic isocyanate and polyol moieties. There are three complementary mechanisms in the formation of the active complex. First the polyol is activated by forming a complex with the tin catalyst

L₄Sn + R^’’ – OH Û L₄Sn …. O Û L₄Sn – O – R^’’ + H⁺

Comp of Sn polioli Catalized complex

L – symbolizes the substituted ligands in the Sn molecule

The product tin - alcohol (alkoxide) reacts with isocyanates, in which case carbonates are formed, which further react with additional polyols to obtain polymer molecules.

L₄Sn …. O – R^’’ + R^’ – N = C = O ® L₄Sn – N – C – O – R^’’ ®

® R^’ – N – C – O – R^’’ + L₄Sn … O – R^’’

The second mechanism involves the activation of isocyanate molecules.

L₄Sn + 2R^’ – N = C = O Û

L₄Sn + 2R^’ – N – C – O – R^’’

The final mechanism represents the reaction between the organometallic compound and the amine catalyst. The formed tin-amine complex then accepts polyol molecules, in which case tin alkoxide is formed. The carboxylate group that is released releases the position for the attachment of the isocyanate group. Further reaction of the complex with additional polyol creates polymer molecules. For flexible sponge, stannous octoate (tin(II)-2-ethyl hexoate) is the preferred as a catalyst. The actual concentration level of tin octoate must be determined experimentally. The change in the concentration of tin (II) ocate affects the quality of the sputum that is presented in the table below.

A ¬ Collaps–Crack–Small Cracks–Songe –Tendency- Srinckage Good For Shriking And Total Net

Open Cells good Closed Totaly

GOOD Closed

Increase of Stano - Octate

Air Flow

IV. RAW MATERIALS AND COMPONENTS THAT PARTICIPATE IN THE PRODUCTION OF SPONGE

1. Polyol 3500/48

2. TDI 80/20 toluene diisocyanate

3. Silicone DC 198

4. Amini LV 33

5. Water - simple from the net

6. Freon F11

7. Methylene chloride

8. Niaksi Al

9. Stanooktoate

10. Color

11. Melamine

POLYOL 3500/48

Is a polyvalent alcohol with a molecular mass of 3500/48 OH groups, which is why it is a colorless liquid with a characteristic smell. Polyol comes in tanks and tankers with wagons or tanker trucks. If it is in tanks, the same should be deposited in spaces where the temperature is 17-220C. Filling and emptying from tanks or cisterns is done by means of a pump, and in order to prevent air sealing, the polyol inlet is adjusted so that the polyol flows from the side of the tank.

After filling the tank, the polyol must be allowed to rest before use so that all air bubbles come to the surface of the polyol and the temperature equalizes. Up to the polyol mixing head is guided metal pipes which are finished from mild steel and tightly sealed in the connection. Pipes with polyol must be colored in the same color as the tank, so that it does not lead to the mixture, which is quite dangerous, and that it does not lead to contamination. Working with polyol requires protective equipment, gloves, work clothes, etc. It is necessary to adhere to safety measures and fire prevention measures.

TDI TOLUENDISOCYANATE 80/20–

It is more widely used as isocyanate in all types of foams, regardless of whether it is the convection type or the heat resistant type. It comes in tanks or tanks with a temperature between 17- 22 ⁰C. At this temperature they entered the mixing head with metal pipes. The tanks would have to be specifically stored in some closed and ventilated space.

TDI is a colorless to pale yellow liquid with a characteristic unpleasant odor, is heavier than water and settles to the bottom when mixed with water. It reacts with water and the reaction speed is slow up to 50 ⁰C, and the higher the temperature, the reaction will be progressively faster. It also reacts with basic chemicals and acids. For the human body, it reacts to protein and poses a health risk. In the human body, it comes into contact with the organs for digestion, in direct contact with the skin or eyes by inhaling the vapor or mist.

Experience and observations from the field of occupational medicine in the isocyanate industry over 25 years have shown that use with TDI can be safe, but always requires caution in the event of excessive exposure and the resulting health risk. Wherever there is TDI, good ventilation must be ensured.

When the TDI in the tanks freezes then the melting is done with hot air instead of hot steam. Care must be taken that the water does not reach the isocyanate. Due to the high toxicity of TDI, full protective clothing must be worn while working with it, eye protection and breathing apparatus must be used.

- All persons working with TDI or with products containing TDI must be fully informed about the possible danger and trained in the action of normal use and the action of use in case of danger. The best decontamination agent from spilled isocyanate is: 90-95 part by mas water

- 3-8 parts by mass of concentrated ammonia

- 02-05 parts by mas detergent

Also, in those cases, the fire extinguisher must be notified.

SYLYCON DC-198 –

Is silicone oil which is added to the specified percentage for soft polyurethane foam. It is a gray colored oily liquid, it is non-toxic, it comes in 200 kg tanks. It is deposited in closed spaces at a temperature of 20 ⁰C and then emptyed into small plastic tanks. From the plastic tank to the mixing head goes with special pipes. This oil should be handled with care, adhering to all protective measures, especially measures against fire. The inlet temperature to the head is between 17-22 ⁰C.

AMINE LV-33 –

It is an additive that enters the content of the recipe, it is similar to silicone oil, its color is slightly lighter, i.e. light gray, it is viscous, in terms of viscosity it is similar to silicone. Comes in 200 kg tanks. and is stored in a closed space at a temperature of up to 22 ⁰C, and from there it goes to the head for mixing with special pipes.

WATER –

The content of the recipe for the benefit of soft PU foam also includes water from the city network. The water is mainly used by the water supply, so it does not need special filtration or any additional cleaning. It is added in a certain percentage and what that percentage will be depends on the percentage of water in the polyol.

FREON F11 –

Its chemical name is trichlorofluoromethane, a colorless liquid with high evaporation. It boils at a temperature of 23.7 ⁰C and turns into gas. It is used in the molding process of soft PU foam as a means of creating gases or steam and has the following technical properties: molecular weight 137.4, boiling point along 760 mm HG column 23.7 ⁰C, freezing point -111 ⁰C, density in –15⁰C is 1.57 x 103 kg/m3 while the density at 30⁰C is 1.46 x 103 kg/m3. Viscosity at –15⁰C =0.65 Cp. It has no self-combustion properties but is used as an extinguishing agent.

METHYLENE CHLORIDE –

The technical or foam type of methylene chloride can be used as an auxiliary tool for obtaining gases or vapors during the pouring of soft PU foam. Standard types of methylene chloride can cause the foam material to lose color, therefore VERTIFOAM INTERNATIONAL proposes that they not be used as auxiliaries. Methylene chloride is quite suitable for use as a cleaning solvent. For use in the recipe, technical or foam types with a small moisture content are necessary.

If levels with more than 10 parts by mass of methylene chloride are used in the formulation, VERTIFOAM INTERNATIONAL proposes the use of glycerin as an additional foam stabilizer. Technical characteristics: appearance; colorless evaporating liquid, water content 0.02%, boiling point during 760 mm HG 40⁰C, molecular weight 84.9, viscosity at 20⁰C 0.448 Cp. Methylene chloride is quite toxic and when working with it, all available tools and a respirator must be used. It is inserted into the mixing head at a temperature between 18 ⁰C and 22⁰C.

NIJAKS A1 (Amine) –

It is 75% dimethylaminoethyl ether and 30% dipropylene glycol. Dense oily liquid with a gray color, used as an additive during the pouring of soft foam. In addition to the standard additives, its addition to the mixing head improves the hardness and elasticity of the soft PU foam. Coming in tanks of 200 kg, and stored in a closed and tempered space. It enters the mixing head with a component temperature of 18-22 ⁰C.

STANOOKTOATE T-9 –

is a tin product which is used as a catalyst for the catalysis of the polyurethane reaction. Other tin catalysts are often used in temperature resistant formulations. It is soluble in polyvalent alcohol and most organic solvents, and insoluble in H200 alcohol. It must be kept closed, because it loses its activity if it is exposed to air, especially humid air.

The technical characteristics are as follows:

- tin content - 28%

- stano content – 97% of tin content

- visual appearance - pale colorless liquid

-flash point-428 ⁰C

Comes in 200 kg tanks, emptied into 100 kg tanks. , from where it is conveyed with special pipes to the mixing head. Protective equipment must be used when working with it.

COLOR -

Colors are added as needed. In our case, it will be added to the red T-15 types; T-18-yellow. The primary use of color is to determine the type and type of soft foam. These colors are pigmented and soluble in water. Typical inorganic coloring agents include: titanium dioxide, iron oxide, and chromium oxide.

MELAMINI-

It is powdery matter. Easily dissolves in all solvents as well as in water. It is used as an anti-flame agent in soft soap. It is added as a solution, dissolved in methylene chloride, mixed with the polyol and introduced into the mixing head.

It should be dry, grain-free and readily soluble in methylene chloride. It is added from 30-50% depending on the standard.

V. THE ROLE AND INFLUENCE OF THE COMPONENTS ON THE FORMATION OF THE SPONGE (Polyurethane Foam)

POLYOL

Polyols are the product of the polymeric reaction of an organic oxide and a compound containing two or more active hydrogens. Active hydrogen components initiate the polymerization which continues until the desired polyol is obtained. Dihydroxyl polyols or diols are obtained when one or more oxides are polymerized on the initiator which has two active hydrogens. If initiators with three functional groups such as glycerol are used, the addition of oxides forms linear chains that grow in three directions and the trihydroxyl polyol or triol is the result of the reaction. The properties of the obtained polyol depend greatly on the solution of the combination of oxides used. Since Dow possesses four basic oxides it is ideal for making a wide spectrum of polyols. The oxides and their formulas are given below.

CH₂ - CH₂ CH₂ – CH – CH₃ CH₂ – CH – CH₂ – CH₃

Ethylene oxide propylene oxide 1,2 –Butylen oxide

CH₂ – CH – CH₂ -Cl

(grops)

Oxide units (in the polyol molecule) can be represented by general formulas.

R₁ = H, CH₃, C₂H₅, CH₂Cl

R₂ = H, CH₃

Polyether polyols derived from propylene oxide are terminated by secondary hydroxyl. When using ethylene oxide R and R¬2 the representative hydrogen atoms and the polyol is an unbranched polymer without side chains. The terminal hydroxyl is the primary hydroxide. When other oxides are used, one or two Rs organic radicals and the obtained polyol contain side chains across the molecule. Differences in string character are responsible for changes in the physical properties of the polyol. E.g., polyol based on ethylene oxide, due to its molecular symmetry is waxy solid with molecular weight around 600. While polyol based on propylene oxide is viscous liquid even at molecular weight of several thousand.

VORANOLL POLYOL GRADE

Voranoll polieter poliolet janë të përshtatshme për pajisjet e prodhimit të shpuzës në bloqe dhe me derdhje. Kufiri i peshës molekulare prej 3000-6000 mundëson përdorimin e Voronoll polioleve për shumë kërkesa. Poliolet standarde përdoren për aplikime të përgjithshme, poliolet tjera me reaktivitet të gjëra, peshë molekulare dhe funksionalitet të ndryshëm mundëson blerësin të ketë kërkesa speciale dhe aplikim special. Këto shtrihen nga shpuzat super të buta, të buta, deri në shpuzë të fortë, pa i dëmtuar vetitë fizike dhe të procesit.

VORALLUX POLYOL GRADE

Vorallux specialty polyols are developed for a range of special applications in the wood industry. Within the vorallux range Dow – offers narrow copolymer polyols which contain graphite particles of styrene acronitrile.

Depending on the copolymer application, different polyols are available with characteristics that are optimized to obtain sponges with broad properties. Flexible (soft) blades and reduced burning properties using formulations that increase these factors provide softness and comfort, while hard blade formulations provide the high level of processing and high strength needed for demanding applications.

ISOCYANATES

All isocyanates used in the polyester industry contain at least two isocyanate groups. The most used isocyanate is toluene-di-isocyanate and diphenyl methane 4,4'-diisocyanate (MDI) Voranate-80 type I Toulene diisocyanate Voranate T-80 Type II Toulene diisocyanate. They are two representatives of the family of qualitative isocyanates produced by DOW. . These products are mixtures of 2,4 and 2,6 isomers in the ratio 80-20 by weight. Type I is at a lower rate of activity and Type II is at a higher rate of activity. TDI is also present in the 65-35 isomeric grade known as T-65. This can be used for hard sponges. MDI is present in distilled and undistilled form. While pure MDI is a pale yellow solid, melting point 37-38⁰C, undistilled MDI is a yellow to brown solution containing 55% diphenyl methane diisocyanate 4,4' and 2,4 isomer, 25% triisocyanate and 20% high polyisocyanate known as polymethylene polyphenyl isocyanate (PMPPI). Bouth MDIs have lower vapor pressures than TDI and are less toxic. Blends of pure MDI with TDI 80/20 or TDI 65/35 are used in the production of elastic sponges.

Determination of the amount of TDI based on the amount of water in the recipe and the number of hydroxyl groups of the polyol

For 100 kg polyol with 48 [OH^-], hydroxil groups

48 [OH^-] x 0.155 = 7.44

5,1 [water] x 9.666 = 49.2996

56.7366

Index of TDI is taken from 1,06 : 1,13 depending on the characteristics of the sponge

56,7366 x 1,13 = 64, 112 kg TDI

Realized density 18 kg /m³

SUPERFICIAL SILOXANE

Superficial siloxane is silicone glycol copolymer used in conventional polyurethane foam production.

The synthesis of surface siloxane looks like this:

(CH₃)₃Si–O–[-Si–O]-[-Si-O]-Si(CH₃)₃ + H₂C=CHCH₂O(CH₂CH₂O)_m(CH₂CH)_nH®

(CH₃)₃Si-O-[-Si-O]_X-[Si-O]_Y-Si(CH₃)₃ Superficial siloxane structure

despite the behavior of the foam

CH₂O(CH₂CH₂O)_m(CH₂CHO)_nH

The functions enabled by superficial siloxane are:

a) Emulsifies incompatible components

b) Enables pore nucleation

c) Stabilizes the foam mass

d) Controls the drainage of the pore walls or their absence

a) Emulsifies and stabilizes incompatible components. Polyols are usually incompatible with isocyanates. For this, it allows even the best mix.

b) It reduces voids (cracks) in the foam and creates the same physical properties of the foam.

c) It increases the elasticity of the surface. This enables the membranes to be protected against clotting.

Influence of molecular weight on foam behavior

destabilized stabilized

--------Molekular weight of siloxan----®

d) Controlled pore opening with the help of:

- surface concentration

- concentration of the catalyst Tin (stanooctate)

- temp. recanters

- film layer of controlled drainage.

The appearance of the perforated pores (cells) and cells controlled through surface siloxane looks like:

The determination of the theoretical amount of silicon in the recipe is calculated as follows:

0.9 part Sc-240 silicone for 100 parts polyol; Plus 0.1 part for every 0.5 part water; over 3.5 parts of water; plus 0.2 parts for every 5 parts blowing agent (Freon or Methylene Chloride)

Technical characteristics of Silicone Sc-240

MDxD'yM

(EO)m(PO)nH

Type Silicone Glycol Copolymer

Physical properties low viscosity fluid

Viscosity at 25 ⁰C 950 Cp

Specific gravity 25 ⁰C 1.03g/cm³

Flash point 141 ⁰C

STANOUSOCTATE

General description

STANOOCTATE catalyst, is a tin catalyst for the continuous production of PU foam (the role of this catalyst is explained in Organometallic Catalysis pg. 10). DABCO T-9 catalyst is preferred over stannous octate products because of its uniform activity and excellent stability, enabling more economical, high-rate, high-volume production.

Typical properties:

Total tin content 28.0%

Percentage of stannous in total tin 97

Color (Gardner) 3

Physical state (aggregate) at 25⁰C clear liquid

Visual appearance colorless to pale yellow

Pour paint Below 25⁰C

Lbs/gal (25⁰C) 10.5

Viscosity, Brookfield (25⁰C) 250 cs or 312 Cps

Flash point 142⁰C

Specific gravity (25⁰C) 1.25 g/cm³

Applications

DABCO T-9 Catalyst can be used for flexible, semi-flexible and rigid polyether foam. DABCO T-9 Catalyst has been used successfully as a catalyst for urethane coatings and urethane fillers.

Storage

All stannous (stannic) catalysts are sensitive to air (especially humid air) and when exposed to it will gradually lose their activity due to the reduction of the stannous (stannate) compound. The stannous compound in DABCO T-9 Catalyst is protected from damage by the stabilization method. Also, each DABCO T-9 Catalyst power is filled with a (protective) layer of nitrogen before sealing.

DABCO T-9 Catalyst has superior deposition stability (as shown in the figure below). However, it should not be exposed to air for long periods of time. In order to maintain the activity of DABCO T-9 Catalyst, it is recommended that when an incomplete container is disposed of, it should be filled with nitrogen.

THE INFLUENCE OF AMIN CATALYSTS ON THE STRUCTURE OF POLYURETHANE FOAM (SPONGE)

As with other plastic materials, the addition of catalysts and additives to the basic mass greatly affects the characteristics of the final product and thus expands the possibility of using the polyurethane material. There is the opinion that the impact and importance of additional substances in the processing of polyurethanes is much greater than in other plastic materials, there is a justification looking at the fact that polyurethane is presented as a final product in the form of: flexible foam, semi-hard foam, hard foam, like elastomer, glue, paint, etc.

Polyurethane products are also applied within the density range of 16 kg/m3 up to 400 kg/m3, which in practice requires the application of special catalysts and additives. With the use of those catalysts, these densities can be obtained and in the middle of the PU the material contains a microporous structure, while on the surface it is a compact mass.

1. The basic reaction to create polyurethane is the reaction of polyol with di isocyanate. By the name polyol we mean the group of polymers prepared in block or by static polymerization of the smallest defined organic unit, polyvalent alcohols or ethers. Di isocyanates are mainly: toluene di isocyanate (mixture of 2,4 and 2,6 isomers in the ratio 80:20) or methylene diphenyl isocyanate.

Toluene di isocyanates CH₃ – C₆H₃ - (NCO)₂

Methylene di isocyanate OCH------- C₆H₄ - CH₂ - C₆H₄ - NCO

2. The most commonly used polyurethane (flexible and hard) should have a porous structure. To achieve that structure, certain catalysts and additives must be used at the time of polyurethane creation (reaction of polyol and isocyanate). From this we can conclude that the catalysis reaction is concurrent with or precedes the basic reaction, which in polyurethane chemistry we call the cross-linking reaction.

Through the above-mentioned reactions in the creation of the PU foam shape, the reactions of: swelling, growth, and stabilization take part. The swelling ratio is dictated by the percentage of water in the recipe and goes according to the given mechanism:

H₂O + R – NCO ------ RNH = C – O --------RNH₂

The reaction is exothermic and the percentage of water must be carefully controlled. The same blowing result can be obtained by adding air or Freon to the mixture.

The stabilization reaction is achieved by the addition of the organometallic compound (mainly tin octoate) which regulates: the size and shape and thickness of the pore walls, and also stabilizes the foam so as to prevent collapse in the mature phase.

3. The foam growth reaction is mainly dictated by the group of organic compounds that contain the group of amines based on which we call amine catalysts. The following table lists the most popular amine catalysts:

Tetra Ethyl Methane Diamine

CH₃CH₂ CH₃CH₂

N – CH₂ - N

CH₃CH₂CH₃CH₂

Pyridine C₅H₅N

N-ethyl Morpholine

CH₃ - CH₂ – N O

Triethyl Amine

N(CH₃CH₂)₃

Tetra methyl 1,3 –Propane

(CH₃)₂ – N – C – C – C – N(CH₃)₂

1,4 Diazabicyclo – (2.2.2’) Octane (Triethylenediamine)

N N

The activity of the amine catalyst is mainly dictated by these two characteristics:

- if the tertiary amine is more alkaline it is more active

- if the stereo barriers are smaller, the amine activity increases

For example, tetraethyl diamine has large stearic hindrances and therefore has less activity, while pyridine shows less activity due to its lower basicity.

4. In addition, it has been shown that the catalytic reaction is competitive with the basic reaction between the polyol and the diisocyanato. In fact, the reactivity of the isocyanate groups is exploited by their ability to react with the amine.

R – N = CO + -NH₂ -------- NH – C - NH

For example, reaction mechanism of Dapco amine catalyst

R – N = C =O + N (CH₂CH₃) N ------- R – N = C = O +

ROH------N (CH₂CH₃) N --------- R – N – C – 0 – R + Dapco

The reaction between the isocyanate and the amine as seen creates a complex (intermediate) which reacts more actively with the polyol than the pure isocyanate. It can be seen that the amine is released in the reaction, which enables the great action in a small percentage.

5. Although the reaction given in the previous point has gained full validation in practice, further research has brought us to new discoveries. It has been observed that the influence of amine and certain organic acids relatively easily form amine salts.

N (CH₂ – CH₂)₃ N + R – COOH ----------- R – C – O N (CH₂ – CH₂) – N O – C - R

The mixture of amine salts and amines react with isocyanate in the following manner

R – C – O - HN (CH₂CH₂)₃–HNO– C– R+ RNCO-----R – NH – C = O+ CO₂+ Dapco

From the reaction it can be seen that the isocyanate comes into contact and reacts first with the so-called hidden amine and as a secondary reaction with the pure amine. This has the consequence of increasing the time of the first phase of the reaction, the so-called gelation. The full length of the reaction, which is proven by experiment, remains unchanged or even shortened.

For example, the use of pure amine in flexible sponge products, the gelation is carried out for 20 sec, while the total reaction time is 125 sec. With the use of the amine-salt-amine combination, the gelation was slowed down to 28 sec, while the total reaction time was 115 sec. The distribution of the overall reaction time between the first and the second stage is obtained which is effectively used for the production of thicker castings, castings in complicated molds, the production of high-growth hard spigots. With the application of this combination, casting is improved so that the order of the mass in the mold shortens the time of removing the model from the apparatus.

6. Also, the researches with some less reactive amines have been expanded using these combinations with more reactive catalysts. The combination of amines with different activity solves the problem of casting in large molds and shortens the time of adhesion of the PU mass. Thus, e.g. with the combination of dimethylethanolamine and DABCO satisfactory results are obtained. DABCO catalyst takes the foaming reaction, while DMEA takes the free acid neutralization reaction in the second stage. The lack of the above-mentioned system is the hydrolysis of stanooctate, which very quickly breaks the activity of the catalyst. The reaction of some morphemic conjugates in combination with an active catalyst is particularly interesting, due to the property that such a system almost perfectly balances the cross-linking reaction.

BLOWING AUXILIARY ELEMENTS

The blowing elements can be used in the formulation of the recipe to reduce the density of the foam and the hardness (increase the elasticity), which cannot be achieved with the use of water and TDI alone. Until recently, Freon (trichlorofluoromethane) was used as a frying element, while today Methylene Chloride (MCl) is used. The technology for using MCl as a blowing element has been developed since 1970. The reason for replacing Freon with MCl has been its impact on the ozone layer, which is why it is banned in many countries in use. The blowing element has the function of absorbing the heat from the exothermic reaction, evaporating and creating the gas needed to expand the foam to a lower density. Since it is non-reactive and does not contribute anything to the polymer structure, the blowing agent gives a softer foam than without it.

METHYLENE CHLORIDE (MCL)

The formula CH₂Cl₂

Name: Dichloromethane. Methylene chloride

Appearance: Methylene chloride is a colorless, non-flammable liquid with a characteristic odor

Use: Methylene chloride is a low-boiling liquid that is added as the blowing agent of the foam, and enables the chemical reaction to release carbon dioxide. It is also used for cleaning and removing various fats due to its excellent solvent properties.

Physical properties:

Density (20⁰C) 1.323-1.327 kg/dm3

Water mg/kg max. 100

Color Apha max. 5

Free chlorine mg/kg max. 1

Evaporation point 40⁰C

There is no burning point

Physical properties low viscosity fluid

The ratio between water, methylene chloride and Freon

1 kg of water = 10 kg of Freon = 7 kg of methylene chloride

WATER

Water is a source of active hydrogens. Only demineralized water can be used in the production of sponge-polyurethane foam. The isocyanate reacts with water to give carbon dioxide gas and polyurea molecules. The gas diffuses into the pore core and allows the foam to expand. Polyurea molecules contribute to the final properties of the polymer.