Polyurethane Rigid Foam Insulation Material Flame Retardant Technology

Polyurethane Rigid Foam Insulation Material Flame Retardant Technology

I. Polyurethane rigid foam insulation material combustion process

Polyurethane rigid foam insulation material combustion process and general polymer material combustion process is similar, can be roughly divided into five stages:

• Heat accumulation.

• Thermal decomposition or degradation and volatilization.

• Fire.

• Heat transfer.

• Spreading.

II. Common Flame - Retardant Technologies for Rigid Polyurethane Foam Insulation Materials

At present, the main technical approaches for achieving the flame retardancy of polymer materials include degradation and oxidation inhibition technology, catalytic flame retardant technology, smoke - reducing technology, gaseous flame retardant technology, heat - insulating carbon - layer technology, grafting and cross - linking modification technology, and cooling and temperature - reducing technology.

III. There are three primary methods for the flame retardancy of polyurethane materials:

1. Adding compounds containing elements such as chlorine, bromine, and phosphorus during synthesis, which are commonly known as additive flame retardants.

2. Introducing atoms such as chlorine, bromine, phosphorus, and antimony onto the isocyanate or organic polyol links in the raw materials to produce inherent flame - retardant foam plastics, referred to as reactive flame retardants.

3. Incorporating groups with high heat resistance into polyurethane materials to enhance their flame retardancy.

IV. Additive Flame Retardants

Additive flame retardants are physically dispersed in the polyurethane matrix without undergoing chemical reactions with the matrix or its reactive raw materials. They are currently widely used in flame - retardant applications for rigid polyurethane foam insulation materials and are available in liquid and solid forms. Liquid flame retardants have poor stability and their flame retardancy decreases over time. However, they offer a wide selection range, are easy to use, have minimal impact on polyurethane foam reactions, are economical, and have a simple process, so they remain important flame retardants for rigid polyurethane foam insulation materials.

Additive flame retardants can be divided into organic additive flame retardants and inorganic additive flame retardants. Inorganic additive flame retardants mainly include antimony oxide, aluminum hydroxide (ATH), ammonium phosphate, borates, expandable graphite, etc. Organic additive flame retardants mainly consist of tris (2 - chloropropyl) phosphate (TCPP), tris (2 - chloroethyl) phosphate (TCEP), tris (dichloropropyl) phosphate (TDCPP), tetra (2 - chloroethyl) ethylene diamine diphosphate, dimethyl methylphosphonate (DMMP), polybrominated diphenyl ethers, etc.

1. Inorganic Additive Flame Retardants

Inorganic flame retardants typically involve filling the rigid polyurethane foam insulation material matrix with inorganic compounds. When heated, these compounds decompose and absorb a large amount of heat, achieving flame retardancy. The advantages of inorganic additive flame retardants are low toxicity, non - volatility, good thermal stability, non - extraction, persistent flame - retardant effects, low cost, and low smoke generation. However, their disadvantages include the impact of dosage and particle size on the material's flame retardancy and physical properties, as well as a tendency to reduce the forming and processing properties and physical properties of polymers. These flame retardants are generally solid, have strong polarity and hydrophilicity, and have poor compatibility with non - polar polymer materials. Their interfacial interaction with the rigid polyurethane foam insulation material matrix is poor, making it difficult to form good bonding and adhesion. Some flame retardants can significantly affect the flame - retardant performance of rigid polyurethane foam insulation materials when directly added. Therefore, chemical treatment of these flame retardants is required, such as surface modification, ultrafine processing, and macromolecular bonding. This can reduce the dosage of flame retardants, lower smoke generation, and improve the performance of foam plastic products.

2. Organic Additive Flame Retardants

Common organic additive flame retardants are organic compounds containing flame - retardant elements such as phosphorus, bromine, chlorine, and nitrogen. Among these, organic phosphorus compounds are widely used in the flame - retardant research of rigid polyurethane foam insulation materials. They offer high flame - retardant efficiency, low viscosity, good compatibility with polyether polyols, moderate thermal stability, and resistance to "coking."

Tris (2 - chloroethyl) phosphate (TCEP) was one of the earliest and most cost - effective varieties used in rigid polyurethane foam insulation materials. However, it is prone to migration and volatilization, resulting in poor flame - retardant persistence. To reduce volatilization losses, highly chlorinated (poly) phosphates and high - molar - mass oligomeric phosphates can be selected, such as tris (dichloropropyl) phosphate and halogenated bisphosphonates. Adding up to 20% tris (2,2 - dichloropropyl) phosphate to a rigid foam formulation can increase the oxygen index of the foam to 26%.

Researchers investigated the use of dimethyl methylphosphonate (DMMP) as a flame retardant to improve the flame retardancy of rigid polyurethane foam insulation materials. DMMP is a halogen - free, high - phosphorus liquid flame retardant with a phosphorus mass fraction as high as 25%. Therefore, a small amount is required. Adding 5% to rigid foam provides the same flame - retardant effect as adding 14% TCEP or 18% tris (2,3 - dichloropropyl) phosphate.

V. Synergistic Effects of Flame Retardants

In the flame - retardant system of rigid polyurethane foam insulation materials, a commonly used synergistic system combines solid and liquid flame retardants. Since solid flame retardants increase material viscosity while liquid ones decrease it, their combined use can adjust the viscosity of reactive materials, resulting in highly flame - retardant rigid polyurethane foam insulation materials.

VI. Reactive Flame Retardants

Reactive flame retardants incorporate flame - retardant elements into the synthetic reaction of polyurethane, making them part of the main chain structure of the polyurethane material. This endows rigid polyurethane foam insulation materials with excellent flame - retardant properties. The main flame - retardant elements are halogens, phosphorus, antimony, etc. Phosphorus - and/or halogen - containing diols or chloro - or bromine - containing cyanic esters are reactive flame retardants for polyurethane. In the formulation for producing rigid polyurethane foam insulation materials, adding multi - hydroxy compounds with flame - retardant elements such as phosphorus, chlorine, bromine, boron, and helium, or introducing flame - retardant elements into the polyether polyol or isocyanate molecules used in rigid polyurethane foam production, incorporates flame - retardant elements into the rigid polyurethane foam molecules. This achieves flame retardancy. Although this method offers advantages such as good flame - retardant persistence and minimal impact on physical and mechanical properties, it requires specialized equipment for introducing flame - retardant elements into polyether polyol or isocyanate and involves a more complex production process.