Common modification methods of epoxy resin

  1. Flow control:
 

  a. Viscosity reduction: The viscosity of epoxy resin varies greatly according to different applications, such as painting, lining, casting, and impregnation. To reduce the viscosity, diluents can be added, which can be classified into non-reactive diluents and reactive diluents according to their functions.

  - Non-reactive diluents are advantageous in applications such as coatings, while reactive diluents are beneficial for applications like bonding and casting under sealed conditions.
 

  - Typical reactive diluents include butyl glycidyl ether (BGE), allyl glycidyl ether (AGE), 2-ethylhexyl glycidyl ether (EHAGE), styrene oxide (SO), phenyl glycidyl ether (PGE), and others.

  b. Viscosity increase: Increasing the molecular weight or adding inorganic fillers can increase the liquid viscosity. Among the inorganic fillers, rheological additives yield the best effect, while common inorganic fillers have a relatively poor effect.

  c. Thixotropy: Introducing fillers might bring about thixotropic properties, and those with significant thixotropic effects are referred to as thixotropic agents. Typical thixotropic agents include talc, asbestos, silica fume, precipitated silica, and organic-inorganic composites.

  2. "Alloy" modification:

  a. Softness is often required in epoxy materials for the following purposes:
  - Improving impact strength by increasing elongation at break
  - Enhancing resistance to thermal shock caused by the different coefficients of thermal expansion of materials linked together
  - Improving adhesion by mitigating the internal stress caused by curing shrinkage
 

  b. Types of plasticizers:
  - They can be categorized into reactive and non-reactive types, with further subdivisions such as epoxy, non-epoxy, polythiols, polycarboxylic acids, polyols, and aminoalkyl ester prepolymers.
 

  c. Plasticizing effect: While achieving plasticization, certain other material properties such as water absorption may be compromised, requiring comprehensive consideration.

  3. Rubber compound modification:

  The modification involves dispersing rubber particles in a cured epoxy resin matrix, contributing to toughening the composite.

  a. Modification mechanism: The mechanism of rubber-modified epoxy materials can be explained using the theory of thermoplastic resins, highlighting the importance of rubber particle size, modulus of elasticity, and adhesion to the matrix.

  b. Factors affecting modification effect: The formation of solid rubber particles, adhesion between rubber particles and the matrix, and the toughness of rubber particles.

  c. Effect of modification: The modification enhances toughness, impact strength, and adhesion, while reducing heat resistance (HDT), tensile strength, and resistance to solvents.

  4. Modification with fillers:

  Fillers are widely used as reinforcing agents to reduce production costs and improve specific properties of epoxy resins. Surface treatment with coupling agents is an effective method to enhance the adhesion between fillers and the resin matrix.

  a. Types and uses of fillers: A wide variety of fillers are employed, and their adaptability depends not only on their chemical composition but also on their shape and particle size.

  b. Common inorganic fillers: Asbestos, alumina, chlorite, kaolin, volcanic ash, carbon black, graphite, silica fume, calcium silicate, diatomaceous earth, magnesium oxide, titanium dioxide, iron oxide, and more.

  c. Surface treatment with coupling agents: Silane-based and titanate-based coupling agents are commonly used to improve adhesion between fillers and the matrix.

  d. Effect of fillers modification: Improvement in mechanical properties such as tensile strength, flexural strength, impact strength, dimensional stability, wear resistance, and hardness; enhancement of heat resistance, electrical properties, resistance to chemicals, and processing characteristics.