If you are referring to polyurethane finishes, the answer is that you don’t. What you do is apply the finish with a high quality brush and when it is dry you sand it, and apply the next coat. Each coat requires less finish and should be sanded with progressively finer paper. After two or three coats, you should have little or no problem with bubbles.
For a good alternative approach I strongly sugget that you read and follow the directions.
If you are referring to polyurethane finishes, the answer is that you don’t. What you do is apply the finish with a high quality brush and when it is dry you sand it, and apply the next coat. Each coat requires less finish and should be sanded with progressively finer paper. After two or three coats, you should have little or no problem with bubbles.
For a good alternative approach I strongly sugget that you read and follow the directions.
You are talking about PU Foam, not PU per se. I think they are just the result of isocyanate end groups reacting with water to give off CO2 .His is basic stuff that you can easily Google.
You are talking about PU Foam, not PU per se. I think they are just the result of isocyanate end groups reacting with water to give off CO2 .His is basic stuff that you can easily Google.
Polyurethane foam (insulation and seat cushions, for example) is typically a mixture of an isocyanate (e.g. pMDI) and a resin or polyol. When these two components are mixed there is an exothermic reaction which causes expansion and growth of the material. This growth is determined by the type of polyurethane being made/blended. When this expansion occurs there are little cells formed which either crack open (open cell) or are designed to stay closed (closed cell). Depending on the chemistry and type of application will determine the cellular structure. In the case of open cell, which is typically water blown, steam is created during application which 'blows up' the foam into a soft pillowy material. The cells where the water/steam were are left open creating these little bubbles/voids. The little voids (bubbles) trap air and act as insulators/resistors to heat flow (R-Value).
In the case of closed cell, and specifically chemical blown (e.g. 245fa), the little cells are filled with an inert gas which too acts as an insulator with higher resistance to heat flow (higher R-Value).
Polyurethane foam (insulation and seat cushions, for example) is typically a mixture of an isocyanate (e.g. pMDI) and a resin or polyol. When these two components are mixed there is an exothermic reaction which causes expansion and growth of the material. This growth is determined by the type of polyurethane being made/blended. When this expansion occurs there are little cells formed which either crack open (open cell) or are designed to stay closed (closed cell). Depending on the chemistry and type of application will determine the cellular structure. In the case of open cell, which is typically water blown, steam is created during application which 'blows up' the foam into a soft pillowy material. The cells where the water/steam were are left open creating these little bubbles/voids. The little voids (bubbles) trap air and act as insulators/resistors to heat flow (R-Value).
In the case of closed cell, and specifically chemical blown (e.g. 245fa), the little cells are filled with an inert gas which too acts as an insulator with higher resistance to heat flow (higher R-Value).
Only PU foams have bubbles, but parts made of PU are used in some products as rigid solid material. The bubbles in PU foams are generated as a result of a chemical reaction between some substances and water, producing a gas product and expanding the polymer. Many other polymers are foamed with some kinds of volatile substances, which all have bubbles. Check as an example this paper: Polystyrene foams. I. Processing-structure relationships.
Only PU foams have bubbles, but parts made of PU are used in some products as rigid solid material. The bubbles in PU foams are generated as a result of a chemical reaction between some substances and water, producing a gas product and expanding the polymer. Many other polymers are foamed with some kinds of volatile substances, which all have bubbles. Check as an example this paper: Polystyrene foams. I. Processing-structure relationships.
Those ‘bubbles’ are called ‘cells.’ There are solid polyurethanes (no cells), cellular polyurethanes (foams with visible cells), and microcellular products. In many cases, the foams are water-blown systems. Water in the polyol reacts with the isocyanate to produce carbamic acid. This is an unstable intermediate which decomposes into carbon dioxide and an amine. This reaction is exothermic and releases 47 kcal/mol of water. The carbon dioxide becomes the blowing agent and forms the cells, with the help of surfactants / cell control agents. The amine immediately reacts with another isocyanate radical to produce a urea.
Rigid systems are almost always over-indexed, meaning there are more –NCO (isocyanate) radicals in the A side than –OH (hydroxyl) radicals in the polyol and water in the B side. This is to insure that all the water and polyol gets reacted; any excess isocyanate will react with itself. Flexible systems are often under-indexed, but there are catalysts that preferentially drive the NCO-water reaction, insuring that all the water gets used. There are remaining hydroxyl groups that contribute to the required softness of the foam.
It doesn’t take much water for rigid systems. A 10-pound-per-cubic-foot (PCF) rigid foam may have only 0.25% water. A 10 PCF flexible foam might have as much as 1.5%.
The challenge in creating solid polyurethanes is keeping the water out, to prevent bubbles/cells from forming in the finished product. Nitrogen blankets and desiccant cartridges are used on drums, day tanks, and other containers, as the raw materials tend to be hygroscopic. Moisture in the air will react with isocyanates and form crystals – not optimal.
Those ‘bubbles’ are called ‘cells.’ There are solid polyurethanes (no cells), cellular polyurethanes (foams with visible cells), and microcellular products. In many cases, the foams are water-blown systems. Water in the polyol reacts with the isocyanate to produce carbamic acid. This is an unstable intermediate which decomposes into carbon dioxide and an amine. This reaction is exothermic and releases 47 kcal/mol of water. The carbon dioxide becomes the blowing agent and forms the cells, with the help of surfactants / cell control agents. The amine immediately reacts with another isocyanate radical to produce a urea.
Rigid systems are almost always over-indexed, meaning there are more –NCO (isocyanate) radicals in the A side than –OH (hydroxyl) radicals in the polyol and water in the B side. This is to insure that all the water and polyol gets reacted; any excess isocyanate will react with itself. Flexible systems are often under-indexed, but there are catalysts that preferentially drive the NCO-water reaction, insuring that all the water gets used. There are remaining hydroxyl groups that contribute to the required softness of the foam.
It doesn’t take much water for rigid systems. A 10-pound-per-cubic-foot (PCF) rigid foam may have only 0.25% water. A 10 PCF flexible foam might have as much as 1.5%.
The challenge in creating solid polyurethanes is keeping the water out, to prevent bubbles/cells from forming in the finished product. Nitrogen blankets and desiccant cartridges are used on drums, day tanks, and other containers, as the raw materials tend to be hygroscopic. Moisture in the air will react with isocyanates and form crystals – not optimal.
If you are referring to polyurethane finishes, the answer is that you don’t. What you do is apply the finish with a high quality brush and when it is dry you sand it, and apply the next coat. Each coat requires less finish and should be sanded with progressively finer paper. After two or three coats, you should have little or no problem with bubbles.
For a good alternative approach I strongly sugget that you read and follow the directions.
If you are referring to polyurethane finishes, the answer is that you don’t. What you do is apply the finish with a high quality brush and when it is dry you sand it, and apply the next coat. Each coat requires less finish and should be sanded with progressively finer paper. After two or three coats, you should have little or no problem with bubbles.
For a good alternative approach I strongly sugget that you read and follow the directions.
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You are talking about PU Foam, not PU per se. I think they are just the result of isocyanate end groups reacting with water to give off CO2 .His is basic stuff that you can easily Google.
You are talking about PU Foam, not PU per se. I think they are just the result of isocyanate end groups reacting with water to give off CO2 .His is basic stuff that you can easily Google.
More
VOTE
Polyurethane foam (insulation and seat cushions, for example) is typically a mixture of an isocyanate (e.g. pMDI) and a resin or polyol. When these two components are mixed there is an exothermic reaction which causes expansion and growth of the material. This growth is determined by the type of polyurethane being made/blended. When this expansion occurs there are little cells formed which either crack open (open cell) or are designed to stay closed (closed cell). Depending on the chemistry and type of application will determine the cellular structure. In the case of open cell, which is typically water blown, steam is created during application which 'blows up' the foam into a soft pillowy material. The cells where the water/steam were are left open creating these little bubbles/voids. The little voids (bubbles) trap air and act as insulators/resistors to heat flow (R-Value).
In the case of closed cell, and specifically chemical blown (e.g. 245fa), the little cells are filled with an inert gas which too acts as an insulator with higher resistance to heat flow (higher R-Value).
Polyurethane foam (insulation and seat cushions, for example) is typically a mixture of an isocyanate (e.g. pMDI) and a resin or polyol. When these two components are mixed there is an exothermic reaction which causes expansion and growth of the material. This growth is determined by the type of polyurethane being made/blended. When this expansion occurs there are little cells formed which either crack open (open cell) or are designed to stay closed (closed cell). Depending on the chemistry and type of application will determine the cellular structure. In the case of open cell, which is typically water blown, steam is created during application which 'blows up' the foam into a soft pillowy material. The cells where the water/steam were are left open creating these little bubbles/voids. The little voids (bubbles) trap air and act as insulators/resistors to heat flow (R-Value).
In the case of closed cell, and specifically chemical blown (e.g. 245fa), the little cells are filled with an inert gas which too acts as an insulator with higher resistance to heat flow (higher R-Value).
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Only PU foams have bubbles, but parts made of PU are used in some products as rigid solid material. The bubbles in PU foams are generated as a result of a chemical reaction between some substances and water, producing a gas product and expanding the polymer. Many other polymers are foamed with some kinds of volatile substances, which all have bubbles. Check as an example this paper: Polystyrene foams. I. Processing-structure relationships.
Only PU foams have bubbles, but parts made of PU are used in some products as rigid solid material. The bubbles in PU foams are generated as a result of a chemical reaction between some substances and water, producing a gas product and expanding the polymer. Many other polymers are foamed with some kinds of volatile substances, which all have bubbles. Check as an example this paper: Polystyrene foams. I. Processing-structure relationships.
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Those ‘bubbles’ are called ‘cells.’ There are solid polyurethanes (no cells), cellular polyurethanes (foams with visible cells), and microcellular products. In many cases, the foams are water-blown systems. Water in the polyol reacts with the isocyanate to produce carbamic acid. This is an unstable intermediate which decomposes into carbon dioxide and an amine. This reaction is exothermic and releases 47 kcal/mol of water. The carbon dioxide becomes the blowing agent and forms the cells, with the help of surfactants / cell control agents. The amine immediately reacts with another isocyanate radical to produce a urea.
Rigid systems are almost always over-indexed, meaning there are more –NCO (isocyanate) radicals in the A side than –OH (hydroxyl) radicals in the polyol and water in the B side. This is to insure that all the water and polyol gets reacted; any excess isocyanate will react with itself. Flexible systems are often under-indexed, but there are catalysts that preferentially drive the NCO-water reaction, insuring that all the water gets used. There are remaining hydroxyl groups that contribute to the required softness of the foam.
It doesn’t take much water for rigid systems. A 10-pound-per-cubic-foot (PCF) rigid foam may have only 0.25% water. A 10 PCF flexible foam might have as much as 1.5%.
The challenge in creating solid polyurethanes is keeping the water out, to prevent bubbles/cells from forming in the finished product. Nitrogen blankets and desiccant cartridges are used on drums, day tanks, and other containers, as the raw materials tend to be hygroscopic. Moisture in the air will react with isocyanates and form crystals – not optimal.
Those ‘bubbles’ are called ‘cells.’ There are solid polyurethanes (no cells), cellular polyurethanes (foams with visible cells), and microcellular products. In many cases, the foams are water-blown systems. Water in the polyol reacts with the isocyanate to produce carbamic acid. This is an unstable intermediate which decomposes into carbon dioxide and an amine. This reaction is exothermic and releases 47 kcal/mol of water. The carbon dioxide becomes the blowing agent and forms the cells, with the help of surfactants / cell control agents. The amine immediately reacts with another isocyanate radical to produce a urea.
Rigid systems are almost always over-indexed, meaning there are more –NCO (isocyanate) radicals in the A side than –OH (hydroxyl) radicals in the polyol and water in the B side. This is to insure that all the water and polyol gets reacted; any excess isocyanate will react with itself. Flexible systems are often under-indexed, but there are catalysts that preferentially drive the NCO-water reaction, insuring that all the water gets used. There are remaining hydroxyl groups that contribute to the required softness of the foam.
It doesn’t take much water for rigid systems. A 10-pound-per-cubic-foot (PCF) rigid foam may have only 0.25% water. A 10 PCF flexible foam might have as much as 1.5%.
The challenge in creating solid polyurethanes is keeping the water out, to prevent bubbles/cells from forming in the finished product. Nitrogen blankets and desiccant cartridges are used on drums, day tanks, and other containers, as the raw materials tend to be hygroscopic. Moisture in the air will react with isocyanates and form crystals – not optimal.
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