Foreword:
For the preparation of polyurethane foam, there are generally three reactions: isocyanate-hydroxyl reaction, isocyanate-water reaction, and isocyanate-isocyanate reaction. Therefore, catalysts of different types and functions are required to meet different demands.
Polyurethane catalysts are generally divided into tertiary amine catalysts and metal catalysts, and tertiary amine catalysts are the most widely used catalysts for the manufacture of polyurethane foam. According to the structure, they can be divided into aliphatic tertiary amines such as: bis( Dimethylaminoethyl) ether BDMAEE, aromatic/alicyclic tertiary amines such as N-methylmorpholine NEM and heterocyclic tertiary amine triethylenediamine TEDA
Function:
Tertiary amine catalysts have reaction selectivity: promoting the reaction of isocyanate and water is generally considered as a foaming catalyst; tertiary amines that promote the reaction of isocyanate and polyol are generally considered as gel catalysts. But most of the foaming tertiary amine catalysts also contribute to the gel reaction, and the gel-type tertiary amine catalysts also contribute to the foaming reaction.
One or more types of tertiary amine catalysts can be selected, and the amount can be used to meet the process requirements, such as milk white time, rising curve, gel time and even skin aging. In polyurethane foam systems, combinations of various amines are used in order to balance the gelling and foaming reactions so that the foaming process can be properly controlled.
Introduction:
Gel Catalyst: Triethylenediamine TEDA
In the early two-step method (prepolymer method) to produce polyurethane flexible foam, because The isocyanate-terminated urethane prepolymer must first be prepared, and then reacted with water for foaming, which is difficult to control. Since the invention of DABCO 1,4-diazabicyclo[2,2,2]octane (also known as triethylenediamine TEDA), it has been used as a unique catalyst and silicone surfactant to replace the prepolymer by one-step method craft. The emergence of these raw materials for the first time allowed the polyurethane foam industry to grow considerably. For details, please refer to the article: “Science Popularization Lesson 1 – What is Polyurethane Material”.
Triethylenediamine TEDA accelerates the reaction of secondary OH groups with NCO groups, accelerates the chain growth and the release of carbon dioxide under the appropriate balance of the reaction, and eliminates the time-consuming preparation of prepolymers to enter a step law era.
Due to the relatively high cost of triethylenediamine TEDA at the initial stage, other catalyst combinations, such as amine-tin composite catalysts, were developed. However, due to technological progress and localization, triethylenediamine TEDA has become the standard gel catalyst benchmark in the polyurethane industry.
Foaming catalyst: bis(dimethylaminoethyl) ether BDMAEE
In molding high resilience and soft block formulations, bis(dimethyl Aminoethyl) ether BDMAEE was used as blowing catalyst. Because its chemical structure is highly alkaline, it can complex with water, which strongly promotes the reaction between isocyanate and water, and produces a large amount of carbon dioxide gas, which can reduce the foam density.
Bis(dimethylaminoethyl) ether BDMAEE has high foaming catalytic activity, which can increase the early reaction time of polyurethane foaming and improve fluidity. Bis(dimethylaminoethyl) ether BDMAEE is about 80% effective in controlling the gas-generating reaction (foaming reaction) and about 20% effective in controlling the gelling reaction (gelling reaction). The vast majority of foam formulations use BDMAEE in combination with the well-known gelling catalyst triethylenediamine TEDA to balance the foaming reaction.
Development:
Low Odor Requirement:
Some tertiary amine catalysts can leave a residual odor in the foam due to the residual odor in the foam structure Tertiary amine catalysts evaporate and release amine odors, which may limit their use in applications such as automotive interiors, bedding and upholstered furniture. Many catalyst suppliers have introduced catalysts containing isocyanate-reactive groups to aid in the incorporation of molecules into the polymer network, but often at the expense of the catalytic efficiency of tertiary amine catalysts.
Delayed Catalyst:
The need for better in-mold flow and faster cure, and the need to balance foam reactivity in a dual hardness foaming process has led to development of delayed action catalysts.
Summary:
Tertiary amine catalyst is the most widely used catalyst for the preparation of polyurethane foam, and its catalytic activity depends on its structure and basicity.
The choice of tertiary amine will affect the foam properties such as physical performance parameters, rebound rate, open/closed cells, surface curing, etc. Too strong blowing catalyst/higher blowing catalyst level will cause foam collapse, while too strong gelling catalyst/higher gelling catalyst level will result in closed cell foam resulting in shrinkage.
A well-balanced gel and foaming reaction can form an open-cell, well-performing foam.
Tag:   Polyurethane catalyst
