Effect of modification on the physical, mechanical and relaxation properties of the polymer - nanodispersed graphite system

The paper analyzes the physical, mechanical and relaxation properties of the polychlortrifluoroethylene (PCTFE) - modified nanodispersed graphite (TEG) system. It has been shown that the modification of the surface of conducting carbon nanoplates with ultradispersed dielectric silicon dioxide (SiO2) (30%) leads to a nontrivial effect - an increase in the electrical conductivity of the PCTFE - 2.5% TEG/30% SiO2 composite by more than two orders of magnitude in comparison with the PCTFE - TEG composites, containing unmodified carbon nanoplates. The functionalization of carbon nanoplates was carried out by treating the particle surface with an active solution of chlorosilane in an organic solvent, that in case of hydrophobization of the filler surface, leads to an increase in the system percolation threshold. It is shown that the method of hydrolyzation of the filler surface can be highly effective due to a directed change in some, in particular, shielding, properties of polymer composites based on nanocarbon. It is established that the modification of the nanofiller (dispersed thermoexpanded graphite) increases the intermolecular interaction of the filler-matrix. Depending on the concentration of the filler, the structure of the matrix and the system as a whole demonstrates dynamic transformations in the size of the heterogeneity of the structure. Ultrasonic studies of composites have shown that the smallest size of structure inhomogeneity is achieved in the range of concentrations of percolation development, and the change in the size of system structure inhomogeneity is associated with the transition from inhomogeneity as the size of crystallites activated by nanofiller at low concentrations associated with coagulation of nanoparticles at concentrations exceeding the percolation threshold. Thus, in the case of nanofillers, it is impractical to use concentrations that significantly exceed the percolation threshold, as this leads to coagulation of the filler particles and the relative loosening of the matrix.

ANALYSIS OF THE INFLUENCE OF THE NATURE OF THE FILLER SURFACE ON THE PROPERTIES OF HYBRID ORGANIC-INORGANIC NANOCOMPOSITES BASED ON EPOXY OLIGOMER

The aim of this work was to investigate the influence of the chemical nature of the filler surface on the properties of hybrid organo-inorganic nanocomposites based on epoxy oligomer ED-20 in the presence of nanoscale functional filler of inorganic origin - aerosil, with different surface nature. The influence of the chemical nature of the surface of highly dispersed aerosil on the thermal properties of nanocomposites based on epoxy oligomer ED-20 has been studied. The peculiarities of the process of thermooxidative destruction have been studied. It is shown that the introduction of highly dispersed aerosil in the amount of 0.5% in the epoxy matrix does not lead to changes in the thermal properties of composites, and the nanofiller in the amount of 5% improves thermal stability of composites. The kinetics of the curing process of epoxy nanocomposites was studied by IR-spectroscopy. The influence of the presence of functional groups on the nanofiller surface on rate and the degree of conversion of epoxy groups was determined. The presence of hydroxyl groups on the surface of A-300 contributes to the rate of conversion of epoxy groups to a greater extent, compared with aerosil with a modified surface, which contains on the surface methyl groups capable of blocking reactive groups. It is established that the rate of conversion of epoxy groups in the presence of aerosil decreases in the range of ED-20 > ED-20 + A-300 > ED-20 + AM-300. The sorption properties of epoxy nanocomposites have been studied. It is established that the sorption process proceeds at a higher rate when the matrix is filled with unmodified aerosil. The mechanism of influence of the chemical nature of the filler surface and content on formation and properties of epoxy nanocomposites is discussed.

Toughening and polymerization stress control in composites using thiourethane-treated fillers

Filler particle functionalization with thiourethane oligomers has been shown to increase fracture toughness and decrease polymerization stress in dental composites, though the mechanism is poorly understood. The aim of this study was to systematically characterize the effect of the type of filler surface functionalization on the physicochemical properties of experimental resin composites containing fillers of different size and volume fraction. Barium glass fillers (1, 3 and 10 µm) were functionalized with 2 wt% thiourethane-silane (TU-Sil) synthesized de novo and characterized by thermogravimetric analysis. Fillers treated with 3-(Trimethoxysilyl)propyl methacrylate (MA-Sil) and with no surface treatment (No-Sil) served as controls. Fillers (50, 60 and 70 wt%) were incorporated into BisGMA-UDMA-TEGDMA (5:3:2) containing camphorquinone/ethyl-4-dimethylaminobenzoate (0.2/0.8 wt%) and 0.2 wt% di-tert-butyl hydroxytoluene. The functionalized particles were characterized by thermogravimetric analysis and a representative group was tagged with methacrylated rhodamine B and analyzed by confocal laser scanning microscopy. Polymerization kinetics were assessed by near-IR spectroscopy. Polymerization stress was tested in a cantilever system, and fracture toughness was assessed with single edge-notched beams. Fracture surfaces were characterized by SEM. Data were analyzed with ANOVA/Tukey's test (α = 0.05). The grafting of thiourethane oligomer onto the surface of the filler particles led to reductions in polymerization stress ranging between 41 and 54%, without affecting the viscosity of the composite. Fracture toughness increased on average by 35% for composites with the experimental fillers compared with the traditional methacrylate-silanized groups. SEM and confocal analyses demonstrate that the coverage of the filler surface was not homogeneous and varied with the size of the filler. The average silane layer for the 1 µm particle functionalized with the thiourethane was 206 nm, much thicker than reported for traditional silanes. In summary, this study systematically characterized the silane layer and established structure–property relationships for methacrylate and thiourethane silane-containing materials. The results demonstrate that significant stress reductions and fracture toughness increases are obtained by judiciously tailoring the organic–inorganic interface in dental composites.

“Toughening and stress-reducing effects in composites formulated with thiourethane-treated fillers: systematic evaluation of the influence of filler size, loading and surface treatment”

Objectives: Filler particle functionalization with thiourethane oligomers has been shown to increase fracture toughness and decrease polymerization stress in dental composites, though the mechanism is poorly understood. The aim of this study was to systematically characterize the effect of the type of filler surface functionalization on the physicochemical properties of experimental resin composites containing fillers of different size and volume fraction. Methods: Barium glass fillers (1, 3 and 10 µm) were functionalized with 2 wt% thiourethane-silane (TU-Sil) synthesized de novo and characterized by thermogravimetric analysis. Fillers treated with 3-(Trimethoxysilyl)propyl methacrylate (MA-Sil) and with no surface treatment (No-Sil) served as controls. Fillers (50, 60 and 70 wt%) were incorporated into BisGMA-UDMA-TEGDMA (5:3:2) containing camphorquinone/ethyl-4-dimethylaminobenzoate (0.2/0.8 wt%) and 0.2 wt% di-tert-butyl hydroxytoluene. The functionalized particles were characterized by thermogravimetric analysis and a representative group was tagged with methacrylated rhodamine B and analyzed by confocal laser scanning microscopy. Polymerization kinetics were assessed by near-IR spectroscopy. Polymerization stress was tested in a cantilever system, and fracture toughness was assessed with single edge-notched beams. Fracture surfaces were characterized by SEM. Data were analyzed with ANOVA/Tukey's test (α = 0.05). Results and Conclusions: The grafting of thiourethane oligomer onto the surface of the filler particles led to reductions in polymerization stress ranging between 41% and 54%, without affecting the viscosity of the composite. Fracture toughness increased on average by 35% for composites with the experimental fillers compared with the traditional methacrylate-silanized groups. SEM and confocal analyses demonstrate that the coverage of the filler surface was not homogeneous and varied with the size of the filler. The average silane layer for the 1 µm particle functionalized with the thiourethane was 206 nm, much thicker than reported for traditional silanes. In summary, this study systematically characterized the silane layer and established structure-property relationships for methacrylate and thiourethane silane-containing materials. The results demonstrate that significant stress reductions and fracture toughness increases are obtained by judiciously tailoring the organic-inorganic interface in dental composites.