Dynamics of Phase Separation in Poly(acrylonitrile-butadiene-styrene)-Modified Epoxy/DDS System: Kinetics and Viscoelastic Effects

RHEOKINETIC AND MORPHOLOGICAL FEATURES OF THE REACTION FORMATION OF A POLYMER COMPOSITE MATERIAL BASED ON IMPACT-RESISTANT POLY(METHYL METHACRYLATE). MODEL AND APPLIED ASPECTS

Based on the experimental data on the rheology of dispersions of hydrophobic aerosil (Am) in a low molecular weight hydrocarbon medium, the possibility of using a «micellar» mechanism for the formation of a bulk structure for such dispersions is considered. A model of such a structure before, during and after shear deformation is proposed, which makes it possible to interpret experimental data on the rheology of dispersed systems. The results of the study of rheokinetics are presented in a new visio – from the point of view of self-organization under the influence of the shear field. The PMMA–PU–Am system was considered as a polymer composite (PC), in which the matrix is the poly(methyl methacrylate) (PMMA) being modified, and the dispersed phase is a mixture of polyurethane (PU) with Am. It has been shown that during the reaction formation of this composition, the conditions of shear deformation of the system correspond to those at which self-organization and fixation of the coagulation rheopex structure of the nanofiller in PC is possible at the moment of reaching very high viscosity values (gel-point), when diffusion processes will be practically frozen. Two concentration regions of Am were predicted (before and after the percolation threshold), where an enhancement of the mechanical characteristics of PMMA can be expected. The relationship between the rheokinetics of the formation of a linear PMMA–crosslinked PU mixture in the presence of different amounts of oligomeric azo-initiator containing fragments of the polyurethane chain and groups capable of initiating radical polymerization of methyl methacrylate and the process of phase separation, morphology and mechanical properties of the final products has been established. It was shown that the time of phase separation and gelation are interrelated and there is in a simple dependence on the concentration of the azo-initiator. Such an initiator affects the structural-rheological transitions in the system and leads to the formation of morphology with smaller domains. The most stable system with the best dispersion of polyurethane in polymethyl methacrylate is a mixture containing 0.002 mol/L of azo-initiator, which has improved mechanical properties and increased impact viscosity.

An overview of viscoelastic phase separation in epoxy based blends

The viscoelastic effects during reaction induced phase separation play an important role in toughening epoxy-based blends. The large difference in molecular weight/glass transition temperature between the blend components before the curing reaction results in dynamic asymmetry, causing viscoelastic effects during phase separation accompanying the curing reaction. This review will focus on the key factors responsible for viscoelastic phase separation in epoxy-based blends and hybrid nanocomposites. Time-resolved characterization techniques such as rheometry, small angle laser light scattering, optical microscopy etc., are mainly used for monitoring the viscoelastic effects during phase separation. Incorporation of nanofillers in epoxy thermoplastic blends enhances the viscoelastic phase separation due to the increase in dynamic asymmetry. Different theoretical models are identified for the determination of processing parameters such as temperature, viscosity, phase domain size, and other parameters during the viscoelastic phase separation process. The effect of viscoelastic phase separation has a very strong influence on the domain parameters of the blends and thereby on the ultimate properties and applications.

Dual effects of mesoscopic fillers on the polyethersulfone modified cyanate ester: enhanced viscoelastic effect and mechanical properties

Enlarging the filler content and decreasing the filler size contribute to enhancing both viscoelastic effect and mechanical property of polyethersulfone modified cyanate system.

Investigation of Cure Reaction, Rheology, Volume Shrinkage and Thermomechanical Properties of Nano-TiO2 Filled Epoxy/DDS Composites

The cure reaction, rheology, volume shrinkage, and thermomechanical behavior of epoxy-TiO2 nanocomposites based on diglycidyl ether of bisphenol A cured with 4,4′-diaminodiphenylsulfone have been investigated. The FTIR results show that, at the initial curing stage, TiO2 acts as a catalyst and facilitates the curing. The catalytic effect of TiO2 was further confirmed by the decrease in maximum exothermal peak temperature (DSC results); however, it was also found that the addition of TiO2 decreases the overall degree of cure, as evidenced by lower total heat of reaction of the cured composites compared to neat epoxy. The importance of cure rheology in the microstructure formation during curing was explored by using rheometry. From the PVT studies, it was found that TiO2 decreases the volume shrinkage behavior of the epoxy matrix. The mechanical properties of the cured epoxy composites, such as tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength, and fracture toughness of the polymer composites, were examined. The nanocomposites exhibited good improvement in dimensional, thermal, and mechanical properties with respect to neat cross-linked epoxy system. FESEM micrographs of fractured surfaces were examined to understand the toughening mechanism.

Effect of Attapulgite Nanorods and Calcium Sulfate Microwhiskers on the Reaction-Induced Phase Separation of Epoxy/PES Blends

The influence of two kinds of mesoscale inorganic rod fillers, nanoscale attapulgite and micron-sized CaSO4whisker, on the reaction-induced phase separation of epoxy/aromatic amine/poly- (ether sulfone) (PES) blends has been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and time resolved light scattering (TRLS). By varying the PES concentration and curing temperature, we found that the incorporation of attapulgite and CaSO4had dramatic impact on the phase separation process and the final phase morphology of blends. In blends at higher content than critical concentration, the process of phase separation was retarded by the incorporation of nanoscale fillers but accelerated by that of the micron-sized fillers, mainly due to the enhanced viscoelastic effect and the preferential wettable effect, respectively. Meanwhile both mesoscale fillers could change the cocontinuous phase structure of blends with lower PES content than critical concentration into PES-rich dispersed structure due to the surface affinity of fillers to epoxy matrix.