Structural changes in blends of linear polymers during their physical aging

Abstract

125Aging of polymers is a combination of physical and chemical processes occurring during storage, process ing, and exploitation of polymeric materials and resulting in a change in their properties [1]. Depend ing on which processes prevail, chemical and physical aging of polymers can be distinguished. Under the action of oxygen, ozone, high temperature, light, pen etrating radiation, mechanical stress, etc., degradation processes may occur in polymers; they entail decom position of polymer chains and lead to formation of low molecular mass products. The improvement of known polymers and the creation of polymeric mate rials with new valuable properties are based on achievements in the chemical physics of aging and sta bilization of polymers [2,3]. However, owing to the thermodynamically nonequilibrium structure of poly mers (even in the absence of chemical transforma tions), relaxation processes occur in them; as a result, the polymers tend toward the state close to equilib rium. This process is referred to as "physical aging" [4] and is accompanied by change in local supramolecular structures [5]. Various factors responsible for aging of materials act both individually and jointly [6].Investigations of physical aging have been per formed for a very large amount of amorphous and semicrystalline polymers, and the main publications in this field concern the study of their nonequilibrium glassy states [7][8][9][10][11][12][13][14][15][16][17]. It is shown that the time and ther mal prehistory strongly affect the physical aging of polymeric materials [3,13,18,19]. Evidently, almost all composite materials are subjected to aging; how ever, little is known about the effect of physical aging on the properties of multicomponent heterogeneous systems. For example, it has been found that the pres ence of a filler in the polyvinylbutyral matrix during aging may initiate crosslinking processes in the system [20]. Thus, in manganese containing segmented poly urethanes, the redistribution of coordination bonds occurs during physical aging [21]. For compatible blends of atactic poly(methyl methacrylate) and sta tistical styrene-acrylonitrile copolymers, the rate of volume relaxation depends on the aging temperature and blend composition [22].For heterogeneous systems, such as interpenetrat ing polymer networks (IPNs), physical aging pro cesses possess their own specifics related to phase sep aration; that is, they occur independently in each phase and have different times [23][24][25]. As was shown in [25], during aging of semi interpenetrating polymer networks (semi IPNs) based on network PU and lin ear PS, there are structural and phase transformations that are related to an increase in the amount of topo logical entanglements in the system due to of fluctua tions of polymer chains and redistribution of segmen tal mobility with a change in the rate of relaxation pro cesses of each phase. Since the main factors of physical aging are by determined by relaxation pro cesses occurring in the system, which in turn depend on its str...

Terahertz dielectric spectroscopy based thermal‐oxidative aging analysis of polyvinyl chloride

“…Thermal analysis includes thermogravimetric analysis (TG), differential scanning calorimetry (DSC), dynamic thermomechanical analysis (DMA), and so on, which are relatively mature. [4][5][6] However, thermal analysis involves the physical and chemical parameters of the sample at different temperatures, which is a destructive test of the sample not allowed in the industry field. Infrared spectroscopy, ultraviolet spectroscopy, and Raman spectroscopy are the representative methods that work nondestructively by detecting carbonyl groups, conjugated structures, and energy level transitions to determine the degree of material aging, respectively.…”

“…The observation of the color, hardness, and gloss of the material is an experience‐based method in the field, which is an inaccurate qualitative judgment. Thermal analysis includes thermogravimetric analysis (TG), differential scanning calorimetry (DSC), dynamic thermomechanical analysis (DMA), and so on, which are relatively mature 4–6 . However, thermal analysis involves the physical and chemical parameters of the sample at different temperatures, which is a destructive test of the sample not allowed in the industry field.…”

Physical aging of PC:PS blends: Dynamic mechanical analysis and nuclear magnetic resonance studies

“…[1] This phenomenon, which is thermo-reversible, affects several physical properties such as density, impact strength, permeability, modulus, specific enthalpy, and so forth. [1][2][3][4][5] This is valid for polymers, [6][7][8][9][10][11][12][13][14] polymer blends, [15][16][17][18][19][20] and polymer nanocomposites. [21][22][23] It is thus highly important to study the physical aging of polymer systems to determine their long-term evolution.…”

“…[7][8][9][10][11]13,14] The most recent works focused on studying the effect of aging over blends miscibility. [16][17][18][19][20] Chang et al [19] performed stress relaxation measurements to compare the effect on neat PS with its blend with poly(p-phenylene oxide) PS:PPO and poly(vinyl methyl ether) (PS:PVME). The results showed that the stress relaxation time of the blends decreased, indicating higher free volume content compared to PS alone.…”

“…A study carried out on a blend of polyurethane and polystyrene showed that aging induced topological entanglements leading to different rates of relaxation in both phases. [ 16 ] This effect was found to be highly dependent on the aging temperature. It was concluded that immiscible or partially miscible blends behave differently under physical aging, because each phase is independently affected under specific conditions and to different degrees.…”