16.Milky time
At the end of zone I, milky white appears in the liquid ammonia mixture.This time is called cream time in the production of polyurethane foams.
17.Chain expansion coefficient
Refers to the ratio of the amount of amino and hydroxyl groups (unit: mo1) in the chain extender components (including mixed chain extenders) to the amount of NCO in the prepomer, which is the ratio of the molar number (equivalent number) of the active hydrogen group to the NCO.
18.Low unsaturated polyether
Mainly developed for PTMG, the price of PPG and the degree of unsaturation are reduced to 0.05mol/kg, which is close to the performance of PTMG. DMC catalyst is used, and the main variety is Bayer's Praise series products.
19.Ammonia grade solvent
The solvent used in the production of polyurethane should consider the solubility and volatilization speed, but the solvent used in the production of polyurethane should focus on the medium weight NC0 group of polyurethane.Solvents such as alcohol, ether alcohol, etc. that react with the NCO group cannot be used.The solvent cannot contain impurities such as water and alcohol, and cannot contain alkali substances, which will deteriorate the polyurethane.
Ester solvents are not allowed to contain moisture, nor free acids and alcohols. They will react with NCO groups.The ester solvents used in polyurethane should be "ammonia-grade solvents" with high purity.The solvent is about to react with the excess isocyanate, and then the amount of unreacted isocyanate is measured with dibutylamine to test whether it is suitable for use.The principle is that it is not applicable to those who consume more isocyanates, because it shows that the total value of the isocyanate will be consumed by the water, alcohol, and acid in the ester. If it is expressed in grams of solvent required to consume the leqNCO group, the value is large and the stability is good.
Isocyanate equivalent less than 2500 or less is not used as a polyurethane solvent.
The polarity of the solvent has a great impact on the reaction of the resin.The greater the polarity, the slower the reaction. For example, the difference between toluene and methyl ethyl ketone is 24 times. The polarity of this solvent molecule is large, and it can form a hydrogen bond with the hydroxyl group of the alcohol and make the reaction slow.
It is better to choose aromatic solvents for polyvinyl chloride solvents, and their reaction speed is faster than esters and ketones, such as xylene.During the construction of Shuangniu polyurethane, the use of ester and ketone solvents can extend its service life.In the production of coatings, the selection of the "ammonia ester-grade solvent" mentioned earlier is beneficial to the stable parts stored.
Ester solvents have strong solubility, moderate volatilization speed, low toxicity and are used more, cyclohexanone is also used more, hydrocarbon solvents have low solid solubility, are less used alone, and are mostly used in combination with other solvents.
20.Physical foaming agent
Physical foaming agent means that foam pores are formed through changes in the physical form of a certain substance, that is, through the expansion of compressed gases, the volatilization of liquids, or the dissolution of solids.
21.Chemical foaming agent
Chemical foaming agents are those compounds that can release gases such as carbon dioxide and nitrogen after heating and decomposition, and form fine pores in the polymer composition.
22.Physical crosslinking
There are some hard chains in the soft chain of the polymer, and the temperature of the hard chain below the softening point or melting point has the same physical properties as the chemically crosslinked vulcanized rubber.
23.Chemical crosslinking
Refers to the process by which macromolecular chains are connected by chemical bonds under the action of light, heat, high-energy radiation, mechanical force, ultrasonic waves, and crosslinking agents to form a mesh or bulk structure polymer.
24.Foaming index
The number of parts of water equivalent to 100 parts of polyether is defined as the foaming index (IF).
25.What are the types of commonly used isocyanates from the structural point of view?
Aliphatic group: HDI; alicycle group: IPDI, HTDI, HMDI; aromatic group: TDI, MDI, PAPI, PPDI, NDI.
26.What are the commonly used isocyanates?
Toluene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI), polyphenylmethane polyisocyanate (PAPI), liquefied MDI, hexamethylene diisocyanate (HDI).
27.What is the meaning of TDI-100 and TDI-80?
TDI-100 refers to all composed of toluene diisocyanate with 2,4 structure; TDI-80 refers to a mixture composed of 80% toluene diisocyanate with 2,4 structure and 20% 2,6 structure.
28.What are the characteristics of TDI and MDI in the synthesis of polyurethane materials?
For the reactivity of 2,4-TDI and 2,6-TDI, the reactivity of 2,4-TDI is several times higher than that of 2,6-TDI. This is because the 4-position NCO in 2,4-TDI is far away from the 2-position NCO and the methyl group, and there is almost no steric resistance, while the NCO of 2,6-TDI is affected by the steric resistance of the ortho-methyl group. The effect is greater, and the reactivity is affected.
The two NCO groups of MDI are far apart and there are no surrounding substituent groups, so the activity of these two NCOs is greater, even if one of the NCO participates in the reaction, the activity of the remaining NCO has decreased, but the overall activity is still large, so the reactivity of MDI polyurethane prepromers is larger than that of TDI prepromers.
29.Which of HDI, IPDI, MDI, TDI, and NDI are better resistant to yellowing?
HDI (belongs to the non-yellowing aliphatic diisocyanate), IPDI (polyurethane resin made of excellent optical stability and chemical resistance, generally used in the manufacture of high-grade non-discoloration polyurethane resin).
30.The purpose of MDI modification and commonly used modification methods
Purpose of modification: Liquefied pure MDI is MDI modified by liquefaction. It overcomes some defects of pure MDI (solid at room temperature, melting when used, multiple heating affects performance), and it also provides a basis for the improvement and improvement of the properties of MDI-based polyurethane materials for a wide range of modifications.
method：
①carbamate (urethane) modified liquefied MDI.
② Carbonized diimide (carbodiimide) and uretonimine (uretonimine) type modified liquefied MDI.