A review of phenolic resin and its modification methods

Reaction of phenolic resin with benzoxazine
Benzoxazines are heterocyclic compounds obtained by the reaction of phenols with amines and formaldehyde. Examples of benzoxazine synthesized based on bisphenol A and aniline are shown in the figure below.

Synthesis of bisphenol-based benzoxazine

Benzoxazines are key components in the curing reaction of Novalac resins with hexamine. The crosslinking of benzoxazine monomers at high temperatures will improve the above properties in the network structure of the resin, which includes the following.

• Reduce free space on the network
• Increase of glass transfer temperature compared to resin resin network
• Increasing the thermal resistance of the network
• Increase flame retardant properties
• Reduction of toxic gases during the cooking process

Hydroxybenzylamine is formed from the rapid reaction of benzoxazine and the free ortho positions of the phenolic resin and is facilitated by the formation of hydrogen bonds between the hydrogen of the hydroxyl phenol group and the oxygen of the benzoxazine as shown below.

Reaction of phenolic resin with cyanide

The hydroxyl groups of Novalac resin react with cyanogen bromate under play conditions as shown below to produce a cyanate ester resin.

Synthesis of phenolic triazine resin

Cyanate ester, by applying heat, creates a network free of free space, and in its structure, triazine rings are also observed, and as a result, a combination with a high glass transition temperature produces a suitable coal at 900 ° C. Also, thermal degradation of this network occurs at high temperatures.

Also, by adding cardanol to Novalac resins, cyanate ester is produced, but adding cardanol to the resin reduces charcoal and the thermal stability of the resin network.

Reaction of phenolic resin with diacids

The toughness of Novalac resins is modified by reaction with carboxylic acids such as adipic acid. Novalac modified with these compounds, after curing with hexamethylenetetramine, form a low-density, lattice lattice and flexible aliphatic chains. The following figure shows the reaction of a two-factor acid and Novalac resin. Using

7000 /. Mol of adipic acid, the hardness of the resin will reach a desirable value, and thus the strain will increase from 3% to 7% and the compressive strength from 99 to 142MPa.

Chemical modification of phenolic resin by diacids

Alloy rubber compounds can be used as a refractory agent in phenolic resins. In this case, the issue that matters is the compatibility of phenolic resin with rubber.

For example, nitrile butadiene rubber (NBR) after fusion with resin resin and sintering process creates a fuzzy separation that the adhesion and interaction of these areas in the joint will be very low, which reduces the mechanical properties with has it.