Identifier: TDX:780
Authors: Mercado Roca, Luis Adolfo
Abstract:
The epoxy resins are widely used in coatings, adhesives, composites, etc. In some applications of epoxy resins special and versatile features are required, such as high adhesion to the substrates, low shrinkage, low thermal stress after curing, toughness, chemical resistance and low flammability. The flammability of epoxy resins is the main drawback in their application. Some flame retardants compounds, such as brominebased compounds, antimony oxides, phosphorous-halogen compounds etc. are incorporated in the epoxy resins to reduce their flammability. These compounds are exceptionally efficient but they have the inconvenience that they increase the smoke and toxic and corrosive gas evolution during the combustion of the polymer. For these drawbacks in the last years it has been increased the investigation of other heteroatoms like flame retardants to replace the halogens.Some approaches about epoxy resins with silicon covalently bonded to the polymeric matrix have been reported. In this way, modifications of commercial epoxy resins and copolymerizations of silicon-based monomers with commercial epoxy resins giving to good flame retardancy, thermal and mechanical properties have been reported.The aim of this thesis is the development of novel fire retardant silicon-based epoxy resins. Glycidyl monomers with silicon in their structure, prepolymers obtained by mean of growth of chain reactions between diphenyl silanediol and diglycidylether of bisphenol A (DGEBA) and a phosphorous-containing glycidyl monomer and two phosphorilated diamines were synthesized. Thermoset polymers were obtained from curing reactions of the compounds synthesized. To study the reaction kinetics of silicon-containing epoxy monomer with primary amines, a monofunctional silicon-containing epoxy monomer has been sinthesized, glycidyloxydimethylphenyl silane (GDMPS), and its reactivity with a primary amine, aniline, has been compared with that of a commercial epoxy monomer, phenylglycidylether (PGE). Kinetics studies were carried out by Near Infrared Spectroscopy (NIR) and applying to the spectral data obtained the multivariate resolution of curves methods. Likewise, the kinetic and curing behaviour studies for the difunctional silicon-containing epoxy monomer, diglycidyloxyphenylmethyl silane (DGPMS), and the mixtures of this monomer with DGEBA with a primary diamine, 4,4'- diaminediphenylmethane (DDM), have been carried out by means of isothermal and dynamic DSC. The gelation and vitrification for these systems have been studied by thermodinamechanical analysis (DMTA) with a shear sandwich clamp and modulated temperature differential scanning calorimetry (TMDSC).The relationship between the amount of silicon and the thermodinamomechanical, thermal and flame retardancy properties of the thermoset materials obtained have been established. Thermoset materials were obtained from mixtures of commercial glycidyl monomer, DGEBA, with a silicon-containing glycidyl monomer, diglycidyloxyphenylmethyl silane (DGPMS), and their properties have been evaluated.Thermodinamomechanical properties have been evaluated by DMTA using a 3-point bending clamp. The thermal stability have been analyzed by thermogravimetric analysis (TGA) in nitrogen and air atmospheres. The flame retardant properties have been evaluated by means of ASTM-D-2683, the limiting oxygen index test (LOI).Finally, the thermal degradation of the silicon-containing polymers has been investigated by means of chemiluminiscence (CL), TGA-MS, GC-MS, ATR-FTIR andDRX.From the results obtained the following conclusions can be infered: (1) The silicon occurrence increases the reactivity of the epoxide due to electronic effects. This higher reactivity also reduces the importance of the autocatalytic path in the curing reactions with primary amines. (2) The thermoset epoxy resins showed a decrease in the Tg and the crosslinking density when the amount of silicon increases. This decrease is related with an increase of the free volume due to the Si-O and Si-C bonds. (3) The siliconcontaining thermosets show an increment of the LOI for silicon contents higher than 3%. In the polymers that contain silicon and phosphorous, there are evidences of the synergyc effect. (4) During the degradation of the silicon-containing materials in both, nitrogen and air atmospheres, cyclic siloxane oligomers were released. A silicon oxide rich char is formed, probably forming an insulating layer.
Repositori URV