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.
Related reading recommendations:
Foaming Catalysts in Action: Unraveling the Role of Catalysts in Polyurethane Foam Production
Introduction
Polyurethane foams are a versatile class of materials widely used in various applications, including insulation, cushioning, and packaging. The production of polyurethane foams involves a reaction between polyols and isocyanates, which generates carbon dioxide gas, leading to the formation of a cellular structure. Foaming catalysts play a crucial role in this process, accelerating the reaction and influencing the properties of the resulting foam. This article delves into the role of foaming catalysts, their types, mechanisms, and the impact they have on the polyurethane foam industry.
Understanding Foaming Catalysts and Their Mechanisms
Foaming catalysts are substances that promote the formation of polyurethane foams by accelerating the reaction between polyols and isocyanates, as well as the decomposition of blowing agents, which generate the gas responsible for foam expansion. They work by increasing the nucleophilicity of the polyol, facilitating its reaction with the isocyanate, and enhancing the decomposition of blowing agents. Foaming catalysts can also influence the structure and properties of the resulting foam, such as its density, cell size, and mechanical properties.
Types of Foaming Catalysts
Foaming catalysts can be classified into three main categories based on their chemical nature:
Amines: Amines are the most commonly used foaming catalysts, and they can be further divided into tertiary amines and secondary amines. Tertiary amines, such as triethylenediamine (TEDA) and N,N-dimethylcyclohexylamine (DMCHA), are strong catalysts for both the gelation and blowing reactions. Secondary amines, such as N,N-dimethylethanolamine (DMEA), primarily catalyze the gelation reaction but have a weaker effect on the blowing reaction.
Metal Salts: Metal salts, such as tin, bismuth, and lead salts, are also used as foaming catalysts. They are typically more active in the gelation reaction than amines but less active in the blowing reaction. Examples of metal salt catalysts include dibutyltin dilaurate (DBTDL), stannous octoate, and bismuth neodecanoate.
Organometallic Compounds: Organometallic compounds, such as alkyl tin compounds and organotin mercaptides, are used as foaming catalysts due to their high activity and selectivity. They primarily catalyze the gelation reaction and can be used in combination with amine catalysts to achieve desired properties.
Impact of Foaming Catalysts on the Polyurethane Foam Industry
The use of foaming catalysts offers numerous benefits to the polyurethane foam industry, including:
Enhanced Foam Production Efficiency: Foaming catalysts accelerate the reaction between polyols and isocyanates, as well as the decomposition of blowing agents, enabling faster foam production times and increased productivity.
Improved Foam Properties: By influencing the structure and properties of polyurethane foams, catalysts can help achieve desired characteristics, such as improved mechanical strength, better insulation, and enhanced durability.
Customization of Polyurethane Foams: The selection of appropriate catalysts and their combinations allows for the customization of polyurethane foams to suit specific applications, such as flexible foams for furniture, rigid foams for insulation, or specialty foams for packaging.
Reduced Environmental Impact: Foaming catalysts can contribute to greener production processes by minimizing waste, reducing energy consumption, and enabling the use of renewable resources in polyurethane foam synthesis.
Foaming Catalysts in Action: The Polyurethane Foam Production Process
The polyurethane foam production process typically involves the following steps:
Mixing of Polyols and Isocyanates: Polyols and isocyanates are mixed together, along with other additives, such as surfactants, flame retardants, and blowing agents.
Catalyst Addition: Foaming catalysts are added to the mixture, accelerating the reaction between polyols and isocyanates and the decomposition of blowing agents.
Foam Expansion: The generated gas expands the mixture, creating a cellular structure.
Curing: The polyurethane foam is allowed to cure, forming a solid material with the desired properties.
Ongoing Research and Future Prospects
The field of foaming catalysts is continuously evolving, with researchers exploring new materials, designs, and applications. Some of the exciting developments in this area include:
Green Catalysts: The search for environmentally friendly foaming catalysts is an ongoing effort, aiming to minimize the use of toxic materials and promote sustainable production processes.
Nanotechnology: The incorporation of nanomaterials in foaming catalysts offers the potential for improved catalytic performance, enhanced foam properties, and new applications.
Computational Design: Advanced computational tools and techniques are being employed to predict and optimize the performance of foaming catalysts, accelerating the discovery and development of new materials.
Conclusion
Foaming catalysts play a vital role in the production and performance of polyurethane foams, offering numerous benefits to the polyurethane foam industry. As research continues to uncover new catalysts and applications, the role of foaming catalysts will undoubtedly expand, contributing to the development of innovative, sustainable, and high-performance polyurethane foam products.
Recommended Reading?
NT CAT U28
NT CAT U26
NT CAT K-15
NT CAT D60
TMPEDA
TEDA
Morpholine
2-(2-Aminoethoxy)ethanol
DMAPA
NT CAT A-1
