Index is most often considered a dimensionless value (not a percent), as it is the ratio of the equivalent amount of isocyanate used relative to the theoretical equivalent amount times 100. Above 100 means an excess of isocyanate; less than 100 means a shortage, or an excess of polyol. Some people use poor (though accurate) terminology and say ‘poly rich’ rather than saying ‘under-indexed.’ The 100 factor is often unused, so it is written or said as 1.00 rather than 100.
Meaning, as previously stated, an index of 100 (or 1.00) is perfect stoichiometry: every reactive site in the isocyanate / A- side is reacted with every hydroxyl site in the polyol / B side, which includes any water present in the polyol as a blowing agent. Nothing is left over nor unreacted. The ratio may or may not be 100:100.
Very few systems run at an index of 1.00. Most rigid systems are over-indexed, and run at 1.05 to 1.15 or higher. For a trimer, a low index is 2.0 (200) or so; a high-index trimer is >3 (or >300). We run a few rigid systems at 1.31; none are less than 1.15. This insures that all the polyol and water (if water-blown) are reacted, and the remaining isocyanate will react with itself. This contributes to increased dimensional stability, and other properties. We have an 80D aliphatic system that we run at 0.95 to improve ductility.
Most flexible systems – foams in particular, and many elastomers – run at less than 100. We have one flexible foam system that we run at various ratios to achieve indices from 45 to 70, depending on the properties that we want.
Equivalent weight calculations are used to determine the stoichiometric ratio; the index is user-defined, and based on the material, required properties, etc. You’ve also probably noticed that I use 100 and 1.00 interchangeably. Most will know what you mean either way.
Index is most often considered a dimensionless value (not a percent), as it is the ratio of the equivalent amount of isocyanate used relative to the theoretical equivalent amount times 100. Above 100 means an excess of isocyanate; less than 100 means a shortage, or an excess of polyol. Some people use poor (though accurate) terminology and say ‘poly rich’ rather than saying ‘under-indexed.’ The 100 factor is often unused, so it is written or said as 1.00 rather than 100.
Meaning, as previously stated, an index of 100 (or 1.00) is perfect stoichiometry: every reactive site in the isocyanate / A- side is reacted with every hydroxyl site in the polyol / B side, which includes any water present in the polyol as a blowing agent. Nothing is left over nor unreacted. The ratio may or may not be 100:100.
Very few systems run at an index of 1.00. Most rigid systems are over-indexed, and run at 1.05 to 1.15 or higher. For a trimer, a low index is 2.0 (200) or so; a high-index trimer is >3 (or >300). We run a few rigid systems at 1.31; none are less than 1.15. This insures that all the polyol and water (if water-blown) are reacted, and the remaining isocyanate will react with itself. This contributes to increased dimensional stability, and other properties. We have an 80D aliphatic system that we run at 0.95 to improve ductility.
Most flexible systems – foams in particular, and many elastomers – run at less than 100. We have one flexible foam system that we run at various ratios to achieve indices from 45 to 70, depending on the properties that we want.
Equivalent weight calculations are used to determine the stoichiometric ratio; the index is user-defined, and based on the material, required properties, etc. You’ve also probably noticed that I use 100 and 1.00 interchangeably. Most will know what you mean either way.
If I were given a random B-side; that is, a blend of two or more polyols, chain extender(s), blowing agent, catalyst package (front & back end), etc., the first thing that I’d need to do is establish the hydroxyl value (OH value, or OHV). That’s the measure of the amount of hydroxyl groups available for reaction, calculated according to the hydroxyl number of the components, or determined in a wet analytical method (ASTM D 4274-88).
If I calculate the OH value based on the measured OHV of the components, it’s referred to as the theoretical system OHV. Or I can get a measured value for the system with a wet analytical method. In either case, it’s defined as the number of milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl content of 1.0 gram of polyol.
So now I know the hydroxyl value. I can convert that to equivalent weight with the following formula: 56,100 / OHV = Equivalent Weight. The latter is defined as molecular weight divided by the number of reactive sites taking part in the reaction. Think of it as somewhat analogous to Avogadro’s number: the equivalent weight for any polyol (or any isocyanate) is the weight in grams that has the exact same number of reactive sites.
For instance, assume two polyols: one with an equivalent weight of 165, and one with 145. That means that 165 grams of the former has the same number of reactive sites as 145 grams of the latter. Same with isocyanates.
Now I can determine how much isocyanate I need. Isocyanates have the chemical group –N:C:O, the reactive group of an isocyanate molecule. It’s measured as a weight percent, and the typical rigid isocyanate (polymeric MDI, or PMDI) has an NCO content of 31.2%. That’s converted to equivalent weight using the following formula: 4,200/NCO% = Eq.Wt. In this case, that’s an Eq.Wt. of ~135.
So, now we know that 165 grams of our polyol blend and 135 grams of PMDI have exactly the same number of reactive sites, and that a ratio (135:165 A:B) is perfect stoichiometry. That is, at that ratio, both sides have the exact same number of reactive sites, and the system is referred to as having an index of 100.
If it’s a rigid system (solid or foam), it’s usually over-indexed, meaning that there are more –N:C:O reactive sites than there are –O:H reactive sites. One reason for that is to insure that all of the components in the B side are reacted; any excess NCO will react with itself. It also improves certain physical properties.
Now the question is: What index do I want or need? Typical rigid systems usually run at 105 to 115 index, so I would use that factor on the iso side. If I want a 110 index (10% excess NCO): 1.10 x 135 = 148.5. So at an index of 110, my new ratio would be 149:165 A:B.
Many off-the-shelf systems are formulated to be mixed at 100:100 A:B. Remember that the index may or may not be 100; for rigid systems, it’s more than likely over 100. In this case, polyols are chosen and blended in proportions that achieve a 1:1 ratio at an index that the formulator has determined will yield the required physical properties (hardness, ductility, dimensional stability, etc.).
Check out my other posts, particularly the one on Index.
If I were given a random B-side; that is, a blend of two or more polyols, chain extender(s), blowing agent, catalyst package (front & back end), etc., the first thing that I’d need to do is establish the hydroxyl value (OH value, or OHV). That’s the measure of the amount of hydroxyl groups available for reaction, calculated according to the hydroxyl number of the components, or determined in a wet analytical method (ASTM D 4274-88).
If I calculate the OH value based on the measured OHV of the components, it’s referred to as the theoretical system OHV. Or I can get a measured value for the system with a wet analytical method. In either case, it’s defined as the number of milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl content of 1.0 gram of polyol.
So now I know the hydroxyl value. I can convert that to equivalent weight with the following formula: 56,100 / OHV = Equivalent Weight. The latter is defined as molecular weight divided by the number of reactive sites taking part in the reaction. Think of it as somewhat analogous to Avogadro’s number: the equivalent weight for any polyol (or any isocyanate) is the weight in grams that has the exact same number of reactive sites.
For instance, assume two polyols: one with an equivalent weight of 165, and one with 145. That means that 165 grams of the former has the same number of reactive sites as 145 grams of the latter. Same with isocyanates.
Now I can determine how much isocyanate I need. Isocyanates have the chemical group –N:C:O, the reactive group of an isocyanate molecule. It’s measured as a weight percent, and the typical rigid isocyanate (polymeric MDI, or PMDI) has an NCO content of 31.2%. That’s converted to equivalent weight using the following formula: 4,200/NCO% = Eq.Wt. In this case, that’s an Eq.Wt. of ~135.
So, now we know that 165 grams of our polyol blend and 135 grams of PMDI have exactly the same number of reactive sites, and that a ratio (135:165 A:B) is perfect stoichiometry. That is, at that ratio, both sides have the exact same number of reactive sites, and the system is referred to as having an index of 100.
If it’s a rigid system (solid or foam), it’s usually over-indexed, meaning that there are more –N:C:O reactive sites than there are –O:H reactive sites. One reason for that is to insure that all of the components in the B side are reacted; any excess NCO will react with itself. It also improves certain physical properties.
Now the question is: What index do I want or need? Typical rigid systems usually run at 105 to 115 index, so I would use that factor on the iso side. If I want a 110 index (10% excess NCO): 1.10 x 135 = 148.5. So at an index of 110, my new ratio would be 149:165 A:B.
Many off-the-shelf systems are formulated to be mixed at 100:100 A:B. Remember that the index may or may not be 100; for rigid systems, it’s more than likely over 100. In this case, polyols are chosen and blended in proportions that achieve a 1:1 ratio at an index that the formulator has determined will yield the required physical properties (hardness, ductility, dimensional stability, etc.).
Check out my other posts, particularly the one on Index.
Polyurethane product is usually varnish and is used to finish natural wood. Serves to protect and add a shine to the surface. Not used over painted surfaces,but try it -it might work. Try it on a scrap piece first.
Polyurethane product is usually varnish and is used to finish natural wood. Serves to protect and add a shine to the surface. Not used over painted surfaces,but try it -it might work. Try it on a scrap piece first.
I think perhaps you mean measure rather than calculate, but you would need special apparatus for that. If you want a general idea you can ask some of the major suppliers of the raw materials; Bayer was a supplier through much of my career when I dealt with PU. Or you could look up the prior art in any Patent for PU foam. The US site is brilliant for that sort of thing and is free on-line.
I think perhaps you mean measure rather than calculate, but you would need special apparatus for that. If you want a general idea you can ask some of the major suppliers of the raw materials; Bayer was a supplier through much of my career when I dealt with PU. Or you could look up the prior art in any Patent for PU foam. The US site is brilliant for that sort of thing and is free on-line.
You remove it by using a chemical paint and varnish stripper followed by scraping and sanding. What fun!
You remove it by using a chemical paint and varnish stripper followed by scraping and sanding. What fun!
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VOTE
Polyurethane is a versatile polymer which can be fabricated into wide range of applications.
This thermoset polymer can be synthesized by reacting di isocyanates with polyols in prsence of catalyst or exposure to ultraviolet rays.
It can be further blown by blowing agent to make polyurethane foams
Polyurethane is a versatile polymer which can be fabricated into wide range of applications.
This thermoset polymer can be synthesized by reacting di isocyanates with polyols in prsence of catalyst or exposure to ultraviolet rays.
It can be further blown by blowing agent to make polyurethane foams
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Index is most often considered a dimensionless value (not a percent), as it is the ratio of the equivalent amount of isocyanate used relative to the theoretical equivalent amount times 100. Above 100 means an excess of isocyanate; less than 100 means a shortage, or an excess of polyol. Some people use poor (though accurate) terminology and say ‘poly rich’ rather than saying ‘under-indexed.’ The 100 factor is often unused, so it is written or said as 1.00 rather than 100.
Meaning, as previously stated, an index of 100 (or 1.00) is perfect stoichiometry: every reactive site in the isocyanate / A- side is reacted with every hydroxyl site in the polyol / B side, which includes any water present in the polyol as a blowing agent. Nothing is left over nor unreacted. The ratio may or may not be 100:100.
Very few systems run at an index of 1.00. Most rigid systems are over-indexed, and run at 1.05 to 1.15 or higher. For a trimer, a low index is 2.0 (200) or so; a high-index trimer is >3 (or >300). We run a few rigid systems at 1.31; none are less than 1.15. This insures that all the polyol and water (if water-blown) are reacted, and the remaining isocyanate will react with itself. This contributes to increased dimensional stability, and other properties. We have an 80D aliphatic system that we run at 0.95 to improve ductility.
Most flexible systems – foams in particular, and many elastomers – run at less than 100. We have one flexible foam system that we run at various ratios to achieve indices from 45 to 70, depending on the properties that we want.
Equivalent weight calculations are used to determine the stoichiometric ratio; the index is user-defined, and based on the material, required properties, etc. You’ve also probably noticed that I use 100 and 1.00 interchangeably. Most will know what you mean either way.
Index is most often considered a dimensionless value (not a percent), as it is the ratio of the equivalent amount of isocyanate used relative to the theoretical equivalent amount times 100. Above 100 means an excess of isocyanate; less than 100 means a shortage, or an excess of polyol. Some people use poor (though accurate) terminology and say ‘poly rich’ rather than saying ‘under-indexed.’ The 100 factor is often unused, so it is written or said as 1.00 rather than 100.
Meaning, as previously stated, an index of 100 (or 1.00) is perfect stoichiometry: every reactive site in the isocyanate / A- side is reacted with every hydroxyl site in the polyol / B side, which includes any water present in the polyol as a blowing agent. Nothing is left over nor unreacted. The ratio may or may not be 100:100.
Very few systems run at an index of 1.00. Most rigid systems are over-indexed, and run at 1.05 to 1.15 or higher. For a trimer, a low index is 2.0 (200) or so; a high-index trimer is >3 (or >300). We run a few rigid systems at 1.31; none are less than 1.15. This insures that all the polyol and water (if water-blown) are reacted, and the remaining isocyanate will react with itself. This contributes to increased dimensional stability, and other properties. We have an 80D aliphatic system that we run at 0.95 to improve ductility.
Most flexible systems – foams in particular, and many elastomers – run at less than 100. We have one flexible foam system that we run at various ratios to achieve indices from 45 to 70, depending on the properties that we want.
Equivalent weight calculations are used to determine the stoichiometric ratio; the index is user-defined, and based on the material, required properties, etc. You’ve also probably noticed that I use 100 and 1.00 interchangeably. Most will know what you mean either way.
More
VOTE
If I were given a random B-side; that is, a blend of two or more polyols, chain extender(s), blowing agent, catalyst package (front & back end), etc., the first thing that I’d need to do is establish the hydroxyl value (OH value, or OHV). That’s the measure of the amount of hydroxyl groups available for reaction, calculated according to the hydroxyl number of the components, or determined in a wet analytical method (ASTM D 4274-88).
If I calculate the OH value based on the measured OHV of the components, it’s referred to as the theoretical system OHV. Or I can get a measured value for the system with a wet analytical method. In either case, it’s defined as the number of milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl content of 1.0 gram of polyol.
So now I know the hydroxyl value. I can convert that to equivalent weight with the following formula: 56,100 / OHV = Equivalent Weight. The latter is defined as molecular weight divided by the number of reactive sites taking part in the reaction. Think of it as somewhat analogous to Avogadro’s number: the equivalent weight for any polyol (or any isocyanate) is the weight in grams that has the exact same number of reactive sites.
For instance, assume two polyols: one with an equivalent weight of 165, and one with 145. That means that 165 grams of the former has the same number of reactive sites as 145 grams of the latter. Same with isocyanates.
Now I can determine how much isocyanate I need. Isocyanates have the chemical group –N:C:O, the reactive group of an isocyanate molecule. It’s measured as a weight percent, and the typical rigid isocyanate (polymeric MDI, or PMDI) has an NCO content of 31.2%. That’s converted to equivalent weight using the following formula: 4,200/NCO% = Eq.Wt. In this case, that’s an Eq.Wt. of ~135.
So, now we know that 165 grams of our polyol blend and 135 grams of PMDI have exactly the same number of reactive sites, and that a ratio (135:165 A:B) is perfect stoichiometry. That is, at that ratio, both sides have the exact same number of reactive sites, and the system is referred to as having an index of 100.
If it’s a rigid system (solid or foam), it’s usually over-indexed, meaning that there are more –N:C:O reactive sites than there are –O:H reactive sites. One reason for that is to insure that all of the components in the B side are reacted; any excess NCO will react with itself. It also improves certain physical properties.
Now the question is: What index do I want or need? Typical rigid systems usually run at 105 to 115 index, so I would use that factor on the iso side. If I want a 110 index (10% excess NCO): 1.10 x 135 = 148.5. So at an index of 110, my new ratio would be 149:165 A:B.
Many off-the-shelf systems are formulated to be mixed at 100:100 A:B. Remember that the index may or may not be 100; for rigid systems, it’s more than likely over 100. In this case, polyols are chosen and blended in proportions that achieve a 1:1 ratio at an index that the formulator has determined will yield the required physical properties (hardness, ductility, dimensional stability, etc.).
Check out my other posts, particularly the one on Index.
If I were given a random B-side; that is, a blend of two or more polyols, chain extender(s), blowing agent, catalyst package (front & back end), etc., the first thing that I’d need to do is establish the hydroxyl value (OH value, or OHV). That’s the measure of the amount of hydroxyl groups available for reaction, calculated according to the hydroxyl number of the components, or determined in a wet analytical method (ASTM D 4274-88).
If I calculate the OH value based on the measured OHV of the components, it’s referred to as the theoretical system OHV. Or I can get a measured value for the system with a wet analytical method. In either case, it’s defined as the number of milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl content of 1.0 gram of polyol.
So now I know the hydroxyl value. I can convert that to equivalent weight with the following formula: 56,100 / OHV = Equivalent Weight. The latter is defined as molecular weight divided by the number of reactive sites taking part in the reaction. Think of it as somewhat analogous to Avogadro’s number: the equivalent weight for any polyol (or any isocyanate) is the weight in grams that has the exact same number of reactive sites.
For instance, assume two polyols: one with an equivalent weight of 165, and one with 145. That means that 165 grams of the former has the same number of reactive sites as 145 grams of the latter. Same with isocyanates.
Now I can determine how much isocyanate I need. Isocyanates have the chemical group –N:C:O, the reactive group of an isocyanate molecule. It’s measured as a weight percent, and the typical rigid isocyanate (polymeric MDI, or PMDI) has an NCO content of 31.2%. That’s converted to equivalent weight using the following formula: 4,200/NCO% = Eq.Wt. In this case, that’s an Eq.Wt. of ~135.
So, now we know that 165 grams of our polyol blend and 135 grams of PMDI have exactly the same number of reactive sites, and that a ratio (135:165 A:B) is perfect stoichiometry. That is, at that ratio, both sides have the exact same number of reactive sites, and the system is referred to as having an index of 100.
If it’s a rigid system (solid or foam), it’s usually over-indexed, meaning that there are more –N:C:O reactive sites than there are –O:H reactive sites. One reason for that is to insure that all of the components in the B side are reacted; any excess NCO will react with itself. It also improves certain physical properties.
Now the question is: What index do I want or need? Typical rigid systems usually run at 105 to 115 index, so I would use that factor on the iso side. If I want a 110 index (10% excess NCO): 1.10 x 135 = 148.5. So at an index of 110, my new ratio would be 149:165 A:B.
Many off-the-shelf systems are formulated to be mixed at 100:100 A:B. Remember that the index may or may not be 100; for rigid systems, it’s more than likely over 100. In this case, polyols are chosen and blended in proportions that achieve a 1:1 ratio at an index that the formulator has determined will yield the required physical properties (hardness, ductility, dimensional stability, etc.).
Check out my other posts, particularly the one on Index.
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VOTE
Polyurethane product is usually varnish and is used to finish natural wood. Serves to protect and add a shine to the surface. Not used over painted surfaces,but try it -it might work. Try it on a scrap piece first.
Polyurethane product is usually varnish and is used to finish natural wood. Serves to protect and add a shine to the surface. Not used over painted surfaces,but try it -it might work. Try it on a scrap piece first.
More
VOTE
I think perhaps you mean measure rather than calculate, but you would need special apparatus for that. If you want a general idea you can ask some of the major suppliers of the raw materials; Bayer was a supplier through much of my career when I dealt with PU. Or you could look up the prior art in any Patent for PU foam. The US site is brilliant for that sort of thing and is free on-line.
I think perhaps you mean measure rather than calculate, but you would need special apparatus for that. If you want a general idea you can ask some of the major suppliers of the raw materials; Bayer was a supplier through much of my career when I dealt with PU. Or you could look up the prior art in any Patent for PU foam. The US site is brilliant for that sort of thing and is free on-line.
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VOTE
Won't help you because this stuff is very dangerous when you have an accident in making it.
Won't help you because this stuff is very dangerous when you have an accident in making it.
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VOTE