Síntesis de polímeros organoborados retardantes a la llama

Identificador:  TDX:779

Handle: https://hdl.handle.net/20.500.11797/TDX779

Autores:  Martín Moreno, Cristina

Resumen:
Although in the last decade there has been an increase in the number of heteroelements<br/>used in flame retardants, the commercial market is still dominated by compounds containing halogens, notably chlorine and bromine. They are exceptionally efficient and may be incorporated as either additives or as reactives, but they do have such clear disadvantages as the generation of toxic and corrosive gases during thermal degradation. Recent developments in the chemistry of halogen-free flame retardant polymers involve polymers or reactive monomers that are inherently flame retarding such as those containing P, Si, B, N and other miscellaneous elements.<br/>Boric acid and borate salts have been used as flame retardant additives since the early<br/>1800s. Borates are effective flame retardants because impenetrable glass coatings form when they thermally degrade. The glass coatings form on the surface, and can contribute to the intumescent effect, because they exclude oxygen and prevent further propagation of<br/>combustion. The water of hydration is lost by endothermic decomposition and therefore both dilutes and cools, by absorbing the thermal energy from the flame. However, additives have the disadvantage that they have to be used in relatively high concentrations (typically 30% by weight, or more) and this may affect the physical and mechanical properties of the polymers.<br/>Also, additives may be leached, or may volatilise from the polymer during service. The<br/>alternative strategy is to use reactive flame retardants, via copolymerization or some other<br/>type of chemical modification (i.e. flame retardant groups that are inherently part of the<br/>polymer backbone or that are covalently attached as side groups to the polymer).<br/>The main aim of the present thesis is to develop new environment friendly flame<br/>retardant thermosets, which are halogen free and have the good thermal and mechanical<br/>properties of some standard materials. Synthetic approaches introduce boron into the<br/>backbone of various polymers, so this main aim can be divided into four subsidiary aims:<br/>&#8722; To synthesize and characterize boron-containing novolac resins obtained by<br/>modifying novolac with organoboron compounds. These polymers were further<br/>crosslinked with HMTA and DGEBA<br/>&#8722; To synthesize and characterize epoxy-novolac resins, which are then further modified<br/>with boron<br/>&#8722; To synthesize and characterize boron-containing styrene monomers, which are then<br/>further polymerized and copolymerized with styrene<br/>&#8722; To evaluate the thermal, mechanical and flame retardancy properties of all the<br/>polymeric systems synthesized<br/>The conclusions drawn from the various studies of the present thesis can be summarized<br/>as follows:<br/>&#8722; The modification of the commercial novolac resin with organoboron compound<br/>reaches a plateau at a modification degree of 65%<br/>&#8722; The crosslinking of boron-modified novolac resin with HMTA is slower and less<br/>extensive than that of commercial novolac resin because of the nitrogen coordination<br/>from intermediate species with boron<br/>&#8722; The crosslinking of commercial novolac resins with DGEBA needs a catalyst to be<br/>added while the crosslinking of boron-containing novolac resins does not because the<br/>boron itself acts as a catalyst<br/>&#8722; The epoxy-novolac resins react with boron compounds mainly through the hydroxylic groups from halohydrin and opened glycidylic groups<br/>&#8722; The thermal degradation of boron-containing novolac resins, boron-containing epoxynovolac resins and boron-containing styrenic polymers generates boric acid at high<br/>temperatures to give an intumescent char that slows down the degradation and<br/>prevents it from being total<br/>&#8722; Novolac resins modified with boron content between 2 and 4%, show high LOI values<br/>(above 38%)<br/>&#8722; Boron-containing styrenic polymers show LOI values that increase with boron content<br/>but boron contents need to be above 3% to achieve good flame retardant properties.