The kinetics of the reaction between hydroxyl compounds and isocyanates – d (- NCO)/dt=K0 x (- NCO) x (- OH)
K1 is the forward reaction rate of the formation of complexes between isocyanates and hydroxyl compounds
K2 is the negative reaction rate of the formation of complexes between isocyanates and hydroxyl compounds
K3 is the forward reaction rate at which complexes react with hydroxyl compounds to form aminoformates and hydroxyl compounds.
K0=[K1 x K3 x (- OH)]/[K2+K3 x
Arrhenius equation
K=Ae ^ [- (Ea/RT)]
A: Exponential factor.
E=2.718
Ea: KJ/mol
R=8.31 (J/mol. K)
Calculation of reaction heat for the formation of functional groups such as urea, polyurethane, biuret, and urea formate:
Bond dissociation energy (KJ/mol)
C-N 205.1~251.2
C-C 230.2~293.0
C-O 293.0-314.0
N-H 351.6~406.0
C-H 364.9~393.5
O-H 422.8~460.5
C=C 418.6~523.3
C=O 594.1~694.9
Reaction formula:
RNCO+rOH → RNHCOOr
RNCO+HOH → RNHCOOH+RNCO → RNHCONHR+OCO ↑
RNHCOOr+RNCO → RNCONHRCOOr
RNHCONHr+RNCO → RNCONHRCONHr
The volume ratio of gas to the total volume of the polymerization system (Vg/Vo) in the polymerization system affects the temperature control ability: gas monomers affect the concentration (mol/L), which affects the polymerization heat [Q (KJ/L)=Rp (mol/L) * (- H)]. The heat of polymerization is transferred to the gas dispersion medium, causing the gas to absorb heat and expand (PV=NR/T). After a sudden increase in temperature in the polymerization system, the gas releases and carries away a large amount of heat (approximately in a straight line with Vg/Vo)
When preparing polyurethane in one step, the activation energy of amino acids is about 60 (mol. K), and the activation energy of urea reaction is 17 (mol. K)
The foam system is easier to implement than the solution suspension system. Dispersive polymerization exhibits the Norrish Tromasof effect at the beginning of the reaction, slowing down the rate of change of chain growth parameters over time and improving the monodispersity of the product.
Dispersion polymerization is a method of separating the polymerization system into numerous fine foam by gas, so that the polymerization components can be converted into the surface liquid film of foam and the “polyhedral boundary liquid cell” connecting multiple liquid films can form a special dispersion phase for polymerization.
The foam system uses gas as the dispersion medium, and the gas expands and cools suddenly when it is heated, and the negative pressure generated when the gas escapes will further polymerize the residual single concentration of the system, and accelerate and carry the evaporation of water molecules and the removal of small molecules.
The dispersion effect of gas on the polymerization system is not equivalent to true dilution of monomers.
General formula for half-life of non first-order reactions
T=[2 ^ (n-1) -1]/[a x k x (n-1) x A ^ (n-1)]
Second order reaction rate constant
A+B → Q+S
Kt=[1/(CA0-CB0)] x ln [(CB0 x CA)/(CA0 x CB)]
CA0 x Kt=[1/(1-M)] x ln {[M (1-xA)]/(M-xA)}, where M=CB0/CA0
Attachment:
Example of calculating the density of polyurethane soft foam
General polyether ternary alcohol Ppg: 50pop: 50tdi-80:42.8hoh: 3.17L-580:1a33:0.34sn: 0.17
Calculated: 4.34 2.17 6.51 38.2 112% 17% 5.2 1.74 122 Recalculated, 28kg/cubic meter
Example of calculation for polyurethane soft foam catalyst:
Universal polyether ternary alcohol ppg: 90 pop: 10 tdi-80:: 35.5 hoh: 2.2 L-580:0.84 Black slurry: 6
Calculated: A33:0.18 T-9:0.25
A33:0.14 T-9:0.24
A33:0.13 T-9:0.35
A33:0.12 T-9:0.30
Tolerance and turning points
Calculation of vertical foam flow rate and lifting speed:
Formula (for example only) PPG: 100, TDI: 80, HOH: 6, SI: 1.5, A33: * * *, SN: * * *, MC: 14.8
The diameter of the vertical bubble circular mold is 1.25.
Polyether flow rate is 12 kilograms per minute.
What is the speed of improvement in meters per minute
Calculate the formula density of 12 kilograms per cubic meter. The total weight of the formula is 173.5 kilograms. The formula volume is 14.46 cubic meters. Circular mold cross-sectional area: 1.23 square meters.
Set a loss rate of 5%.
Boosting speed: [14.46 x 12% x (1-5%)]/1.23=1.34 meters per minute.
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- by admin Published on 2024-04-11 17:00:45
- Reprinted with permission：https://www.ohans.cn/15503.html
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