Modification Of Cyanate Ester Resin/Epoxy Resin Matrix And A Positron Annihilation Study Of Its Microstructure

Cyanate ester resins (CE) and epoxy resins (EP) are superior on comprehensive properties within all thermoset resins. So far, large amount of papers has been reported on the research of modification of CE or EP individually. However, few focuses have been taken on the modification of a CE/EP matrix. In fact, blends composed of CE and EP will extend the applications of both CE and EP. To satisfy high requires of the composites, CE/EP matrix also needs further modification to improve the mechanical properties (especially the toughness). Third dispersion phases, such as functional liquid rubbers or inorganic particles, are often in favor in the improvement in the toughness of the matrix. The most used functional liquid rubber is butadiene-acrylonitrile rubber with active functional group (hydroxyl-terminated liquid butadiene-acrylonitrile rubber HTBN or carboxyl-randomized liquid butadiene-acrylonitrile rubber CRBN). A third phase (liquid rubber or inorganic particles) has been added to CE/EP matrix for achieving excellent performances in mechanical properties. In addition, the microstructure of the composites was characterized by positron annihilation lifetime spectroscopy. The main contents are as follows:1,Effect of the functional liquid rubbers (HTBN and CRBN) on the properties of CE/EP systemThe CE/EP/HTBN and CE/EP/CRBN composites were prepared by direct-blending approach. The toughness of the matrix of CE/EP can be improved effectively with the addition of rubbers. When the rubber content is 8%, modification in the toughness is the best. SEM and TEM results show that HTBN has better compatibility and dispersion than CRBN within CE/EP matrix. Curing behavior and mechanism of CE/EP/HTBN and CE/EP/CRBN composites were analyzed according to the FT-IR and DSC results. The curing products of the composites (CE rich case) are triazine, oxazoline structure and oxazolidinone. The curing products of the composites (EP rich case) are polyesters network, oxazolidinone and isocyanurate. Although the thermal stability of rubber is usually poorer, the TGA results showed that the addition of reactive rubbers didn't have negative effects to the thermal stability of CE/EP. Different reactivity and compatibility between the rubbers and CE/EP matrix is the most determining factor for the thermal stability of the blends.2. Effect of inorganic particles (nano-CaCO3) on the properties of CE/EP(70/30) systemThe CE/EP (70/30)/nano-CaCO3 composites were prepared by nano-CaCO3 as modifier for CE/EP (70/30) system. Mechanical performance testing results showed that addition of a appreciate amount of nano-CaCO3 is favorable in enhancing the impact strength and tensile modulus of CE/EP (70/30) system. If the amount of nano-CaCO3 is excessive, mechanical performance of CE/EP (70/30)/nano-CaCO3 composites will then decrease. SEM observation showed that nano-CaCO3 particles is well-dispersed in CE/EP (70/30) resin matrix when the content of nano-CaCO3 is low Thus mechanical properties of the composites will be improved effectively. However, when nano-CaCO3 content is excessive, it is easy to agglomerate and the mechanical properties of CE/EP (70/30)/nano-CaCO3 composites will then decrease. The DSC and TGA results showed that curing temperature of CE/EP (70/30) resin matrix didn't have obvious changes for addition of/nano-CaCO3. The heat-resistant of CE/EP/nano-CaCO3 composites is better than CE/EP because of a strong interfacial interaction between the two phases and high thermal stability of nano-CaCO3 itself.3,Study on free-volume properties of compositesThe free-volume properties and interfacial properties of CE/EP/BN composites were analyzed by PALS. The results proved the toughening mechanism of CRBN and HTBN to CE/EP matrix. The well-dispersed HTBN chain can enter the free volume holes in CE/EP matrix, leading to a partition effect to the free volume size of CE/EP matrix. CRBN bigger particles have also from fairly strong interaction with CE/EP matrix, inducing a deformation of crossliking net. And this will restrict the segmental chain motion. This is the main reason determining the decrease in the mean the free volume size of CE/EP/rubber composites. The changes of chemical environment were discussed owing to addition of different modifier in CE matrix by positron age-momentum correlation (AMOC) of positron annihilation spectroscopy. The S parameter is sensitive to chemical environment changes in the composites.