SeungYeon Kang Applied Physics, G1
Fun facts on soft matter
Good references: Polyelectrolytes in Solution and the Stabilization of Colloids : 
Final Project: Fire Retardant Polymers
- “Flame-retardant”/ “Flame resistance”: understood to be resistant to catching on fire, but level of resistance varies
- Implied meaning: self-extinguishing
- “Flame-retardant” does NOT mean noncombustible
- Risk still present in materials (but lower than in other materials)¹
- Clothing: fire-retardant for a certain length of time. Usually a short length of time in casual clothing. Higher level of resistance required in fire fighter uniforms.
- children’s sleepwear / Casual shirts, pants, etc. / Fire fighting overalls
- construction: “Fire doors” and other materials in buildings to retard fire.
General Material Properties
- Different ways to describe material behavior, among other tests, you can test for:
- Ease of ignition / Flame spread / Fire endurance / Fuel contribution / Smoke evolution
- Can get a different perspective of material from different tests on small, medium and large scales depending on which property is most important for the application.
Theory & Mechanism
- Flame generated heat → polymer surface → produces volatile fragments, combust → feed to the heat
- Two general ways to achieve flame resistance:
Solid phase inhibition: by extensive crosslinking at the surface when in presence of heat (form a char) → insulates the underlying polymer from flame - Endothermic degradation: Some compounds break down endothermically when subjected to high temperatures. Magnesium and aluminium hydroxides are an example, together with various hydrates. The reaction removes heat from the surrounding, thus cooling the material. The use of hydroxides and hydrates is limited by their relatively low decomposition temperature, which limits the maximum processing temperature of the polymers.
- Dilution of Fuel: Inert fillers, eg. talc or calcium carbonate, act as diluents, lowering the combustible portion of the material, thus lowering the amount of heat per volume of material it can produce while burning.
- Thermal shielding: A way to stop spreading of the flame over the material is to create a thermal insulation barrier between the burning and unburned parts. Intumescent additives are often employed; their role is to turn the polymer into a carbonized foam, which separates the flame from the material and slows the heat transfer to the unburned fuel.
Vapor phase inhibition: incorporate materials that when released into flame inhibit the flame (quench the flame) → flame requires increased energy to stay lit since its initial radical reactions are inhibited - Dilution of gas phase: Inert gases (most often carbon dioxide and water) produced by thermal degradation of some materials act as diluents of the combustible gases, lowering their partial pressures and the partial pressure of oxygen, and slowing the reaction rate.
- Gas phase radical quenching: Chlorinated and brominated materials undergo thermal degradation and release hydrogen chloride and hydrogen bromide. These react with the highly reactive H* and OH* radicals in the flame, resulting in an inactive molecule and a Cl* or Br* radical. The halogen radical has much lower energy than H* or OH*, and therefore has much lower potential to propagate the radical oxidation reactions of combustion. Antimony compounds tend to act in synergy with halogenated flame retardants. The HCl and HBr released during burning are highly corrosive, which has reliability implications for objects (especially fine electronics) subjected to the released smoke.
- Both methods of inhibition used in typical flame-resistant materials<math>^1</math>