Keywords: phenol formaldehyde resins, PF, phenolic resins, phenolic foam
Phenol formaldehyde resins (PF) or phenolic resins are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Phenolic foam (PF), an excellent fire insulation composite, has reached the standard of Class B1 flame-retardant foam without modification, obtained by foaming phenolic resin. It has a uniform closed pore structure, low thermal conductivity, and good thermal insulation performance, and is therefore better than PS and PU. Even in the event of a fire, phenolic foam shows no dripping and less smoking, and the char layer formed on its surface can protect the internal structure. Phenolic foam is a thermal insulation composite with great development potential; it is known as a third-generation emerging thermal insulation composite. It is suitable for electrical appliances, meters, and buildings, petrochemical and other industries as ideal insulation materials, so it has received extensive attention.
Raw materials of Phenolic foam
The key indicators of resin are viscosity, moisture, solid content and free monomer. Foam resins are mainly thermosetting phenolic resins. Thermosetting resins have active functional groups and will be cured under the action of heat or acid. Thermosetting resin will continue to react in storage, which will increase viscosity and speed up curing, and the reaction speed will double for every 10°C increase in temperature. Therefore, thermosetting resin must be stored under low temperature conditions to maximize its life.
The cross-linking of the resin is accomplished by adding organic sulfonic acid or inorganic acid. Common acids include toluene sulfonic acid, benzene sulfonic acid, phosphoric acid, etc. The type of acid and the acid strength affect the foaming and curing speed.
3. Foaming agent
Blowing agents are used to provide gas that can generate foam. The amount and type of blowing agent affects the density of the foam.
Surfactants, cell regulators, play an important role in reducing surface tension, and it can improve the compatibility between the foaming agent and the resin. Choosing the right surfactant helps to produce a uniform fine foam cell structure. Too little surfactant produces unstable foam quality, and too much will cause cell collapse.
5. Other additives
Used to improve foam properties, such as flame retardancy, water absorption, toughness, etc. Including aluminum hydroxide, ethylene glycol, wood flour, polyphosphate, etc.
Foam production process
The production of foam can be divided into batch type or continuous type. Block mold square foams are produced in batches, while continuous production is usually used to produce heat-preserving panels, compounding various surface materials when foaming, such as aluminum foil, color steel plates, and non-woven fabrics. Since phenolic foam uses strong acid in the production process, all foam contact equipment should be acid resistant, such as stainless steel or rigid plastic equipment.
Phenolic foam is a foamed plastic obtained by foaming phenolic resin under the action of a catalyst. Compared with organic foams such as polystyrene foam and polyurethane foam, it has the characteristics of heat resistance, flame resistance, flame penetration resistance, low smoke and toxicity, low thermal conductivity, wide operating temperature, corrosion resistance, aging resistance, and dimensional stability. Compared with inorganic insulating materials such as rock wool and glass wool, it has the advantages of light weight, low thermal conductivity and good sound insulation effect.
In terms of cell structure, there are two types of phenolic resin foam, namely open-cell floral mud foam and closed-cell insulation foam. The flower mud foam is used to store flowers and is usually dyed green with paint. It should absorb water quickly, be slow, easy to cut but not too brittle. Closed-cell insulation phenolic foam is used in the field of insulation and traditional polyurethane foam, but phenolic foam has better heat resistance, dimensional stability, and flame retardancy. The production of phenolic foam is very complicated. The success of the production depends not only on the raw materials used, but also on the stability and reproducibility of the production process, which requires very strict control of every parameter.
Phenolic foam is used in the insulation of building walls, fire doors, ceilings, chemical equipment and pipelines, flower arranging mud, air-conditioning duct insulation, underground filling reinforcement and other fields.
However, it is difficult to use phenolic foam in the direct preparation of thermal insulation exterior wall materials due to the defects of the material itself; it exhibits poor mechanical properties, high brittleness, and a high pulverization rate, which seriously affect its application. Therefore, reinforcement has been an important research direction of phenolic foam composites.
One of OKCHEM strategy manufacturer Hangmo New Materials Group Co., Ltd. can supply phenolic resins used in Phenolic foam. This series of phenolic resin is a foamed thermosetting phenolic resin with the characteristics of stable activity and good foaming effect. It is mainly used in thermal insulation materials, sound insulation materials, flower mud, etc. Click here to know more.