Posts
FLAME RETARDENT FINISHES
Anju Singh
Pursuing M.Sc. in Fabric and Apparel Science
Delhi University, India
Email: anjusingh292@gmail.com
Pursuing M.Sc. in Fabric and Apparel Science
Delhi University, India
Email: anjusingh292@gmail.com
1. Explain mechanism of combustion of fire:
Combustion is an exothermic process that requires three components
- Heat
- Oxygen
- A suitable fuel
- When left unchecked, combustion becomes self catalyzing and will continue until the oxygen, the fuel supply or the excess heat is depleted.
- When heat is applied, the fiber’s temperature increases until the pyrolysis temperature, Tp, is reached. At this temperature, the fiber undergoes irreversible chemical changes, producing non flammable gases (carbon dioxide, water vapor and the higher oxides of nitrogen and sulfur), carbonaceous char, tars (liquid condensates) and flammable gases (carbon monoxide, hydrogen and many oxidisable organic molecules).
- As the temperature continues to rise, the tars also pyrolyse, producing, more non- flammable gases, char and flammable gases. Eventually, the combustion temperature, Tc, is achieved. At this point, the flammable gases combine with oxygen in process called combustion, which is a series of gas phase free radical reactions.
- These reactions are highly exothermic and produce large amounts of heat and light. The heat generated by the combustion process provides the additional thermal energy needed to continue the pyrolysis of the fiber, thereby supplying one more flammable gases for combustion and perpetuating the reaction. The burning behavior of textiles is determined more by the speed or rate of heat release than by the amount of this heat.
2. What are the various approaches used for disruption of combustion cycle:
The various methods for disruption of combustion cycle are: A. To provide a heat sink on or in the fiber by use of materials that thermally decomposes through strongly endothermic reactions. If enough heat can be absorbed by these reactions, the pyrolysis temperature of the fiber is not reached and no combustion takes place. Examples of this method are the use of aluminium hydroxide or ‘alumina trihydrate’ and calcium carbonate as fillers in polymers and coatings. (FIG.8.3)
C. To achieve flame retardancy is to influence the pyrolysis reaction to produce less flammable volatiles and more residual char. This ‘condensed phase’ mechanism can be seen in the action of phosphorous- containing flame retardants which, after having produced phosphoric acid through thermal decomposition, crosslink with hydroxyl-containing polymers thereby altering the pyrolysis to yield less flammable by-products. FIG* 8.5
 |
Compare Condensed and Gas Phase Mechanism for Flame Retardancy:
| Type of mechanism | Condensed phase | Gas phase |
| Type of chemistry involved | Pyrolysis chemistry | Flame chemistry |
| Typical type of synergism | P/N | Sb/Br or Sb/Cl |
| Effective for fiber type | Mainly cellulose, also wool, catalyzing their dehydration to char | All kinds of fibers, because their flame chemistry is similar (radical transfer reactions) |
| Particularities | Very effective because dehydration and carbonization decrease the formation of burnable volatiles | Fixation with binder changes textiles properties such as handle and drape, preferably for back coating for example of furnishing fabrics and carpets |
| Application process | If for durable flame retardancy then demanding multi step process | Relatively simple, standard methods of coating, but viscosity control is important |
| Environment toxicity | With durable flame retardancy, formaldehyde emission during curing and after finishing ,phosphorous compounds in the waste water | Antimony oxide and organic halogen donators (DBDPO and HCBC) are discussed as problems (for eg.Possibility of generating poly halogenated dioxins and furans) |
No Responses to "Mechanism of Flame Retardant Finishes"