Phenol formaldehyde resin:

Phenol formaldehyde resins (PF) are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Phenolic resins are mainly used in the production of circuit boards. They are better known however for the production of molded products including pool balls, laboratory countertops, and as coatings and adhesives. In the form of Bakelite, they are the earliest commercial synthetic resin.

Chemical reactions for manufacturing of phenol formaldehyde resin:

This is a batch process which takes place for about eight hours. Phenol and formaldehyde are taken from the raw material storage room. Vacuum is first created in the reactor kettle, and then charging of phenol is done. Before adding phenol, vacuum pressure is created and cooling water supply is started. After charging phenol, formaldehyde is charged into the kettle. The molar ratio of phenol to formaldehyde is of 1:1.5. Now, sodium hydroxide, which is the catalyst, is added. It is mixed with necessary amount of water. Charging of raw materials in the reactor kettle takes place at 30°C. Reactor consists of an outer jacket and a coil around its circumference. The outer jacket carries the cooling oil for the first two hours of the reaction and the cooling water is circulated in the coil within the reactor for the same time.

Now, after the entire charging section is complete, condenser valve is opened. As the stirring continuously takes place, the reaction temperature increases to about 102º C, the reaction being an exothermic one. The cooling oil and cooling water helps to control the reaction temperature at about 60-70ºC. Now, the reaction continues for about 2 hours at the same temperature. The extent of the reaction or amount reacted is tested by Water Tolerance Test also known as Gel Time Test. The water tolerance reduces from infinity to 600 as the reaction continues.

Step 1:

$C_6 H_5\ OH+2CH_2 O→C_8 H_{10} O3$

Step 2:

$2nC_8 H_{10} O_3→[C_8H_8O_2 ]n+nH_2 O$

Overall reaction:

$2nC_6H_5OH + 4nCH_2O→nC_8H_7O_2Na + nH_2 O{NaOH}$

Now, after two hours of reaction, the reactor behaves as a distillation column and continuous condensation takes place. Cooling is cut off and hot water and oil is circulated through the coils and outer jacket respectively. Distillation continues for about 6 hours at about 60 - 70°C. The distilled water is collected in the receiver. Condensation takes place in the condenser; thereby changing the phase of vapour to liquid and directing it towards the distillation receiver. As the condensation takes place, the resin is checked for its viscosity periodically.

Properties:

• Excellent ablative properties
• Good flame resistance
• Low smoke properties
• High strength and modulus properties
• Dimensional stability at elevated temperatures
• Excellent flame Resistance (UL94-V0 Rating)
• Outstanding durability (UV Resistant)
• High strength-to-weight ratio
• Creep resistant

• Resistant to corrosion

   

Applications:

• Space, Aerospace & Defense Composites in ablative liners
• Carbon-Carbon Composites
• Pre pregging applications