Plastic deformation and performance of engineering polymer materials

The plastic deformation mechanism operating in polymer glasses is analyzed. The whole process consists of two main stages: nucleation of special shear defects, called PSTs (plastic shear transformations), and their disappearance. The important feature of plastic deformation of glasses is the storage of a large amount of internal energy ΔU_def upon straining. Such energy storage is the critical issue for mechanical performance of polymeric material: if the amount of stored energy is high, the appearance of macroscopic failure is very probable while glassy materials collecting a small amount of stored deformation energy are quite ductile. It is proposed that the rate of disappearance of PSTs is a key factor in dissipation of stored deformation energy. A parameter describing the dissipation ability of material upon deformation is introduced.     

Plastic deformation kinetics for glassy polymers and blends

Measurements of the plastic deformation kinetics for several glassy (PS, PC, PI-polyimide, PET, epoxy-amine network), semi crystalline polymers (PBT, PET) and blends (ABS, PC:ABS, PC: PBT) were performed for the unidirectional compression loading conditions by using constant temperature deformation calorimetry. The experiments have permitted us to follow the changes of the mechanical work (A), the heat of deformation (Q) and differences between these quantities, i.e., internal energy (U) stored in samples during their loading and unloading. Experiments have shown that the large portion (45–85%) of the mechanical work of deformation (A) is converted to heat (Q). The rest ofA is converted to internal energy (U) stored in deformed samples. U is quite high as compared with metals [1,2]. After complete unloading of plastically deformed samples, i.e., samples carrying irreversible atT _def plastic deformation ( _irr ), some amount (U) of stored energy disappeared. The amount of (U and (U) are different for different polymers. All data are analyzed in the framework of the model proposed in [3,4]. The experiments support the deformation model where the plasticity of glassy polymers is the process of nucleation and development of so-called PDs-plastic local shear defects of nonconformational and nondilatational nature.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday     

Synthesis of an inorganic-organic polymer blend from orthoboric acid and caprolactam

The possibility of modifying boron polyoxide with an oligomeric amide upon thermal dehydration of orthoboric acid and oligomerization of caprolactam in a common melt is shown. The products obtained after thermal pretreatment of the initial blend containing 30 wt % caprolactam are investigated. It is shown that the main processes at T < 200°C are dehydration of orthoboric acid and hydrolysis of caprolactam with the formation of ε-aminocaproic acid. At temperatures of 225–260°C, the predominant process is the formation of boron polyoxide and a caprolactam-based oligomeric product. The data of ¹¹B NMR spectroscopy show that the chemical transformations of caprolactam occur against the background of the N:B donor-acceptor interaction. The two-dimensional [¹¹B-¹H] heteronuclear correlation spectrum indicates that the systems obtained upon thermal treatment are solid solutions.     

Plasticity Mechanism for Glassy Polymers: Computer Simulation Picture

This review summarizes the data published over the past two and a half decades on the mechanism of plastic deformation of bulk isotropic linear glassy polymers in uniaxial tension, compression, and shear at low deformation temperatures (Т_def < 0.6Т_g) and moderate loading rates. The main attention is focused on studies concerning the numerical computer simulations of plasticity of organic polymer glasses. The plastic behavior of glassy polymers at nano-, micro-, and macrolevels in the range of macroscopic strains up to ≈100% is discussed. Plasticity mechanisms are compared for organic, inorganic, metallic, polymer, and nonpolymer glasses with different chemical structures and types of interparticle interactions. The general common mechanism of plasticity of glassy compounds, the nucleation of plasticity carriers in them, and the structure of such carriers and their dynamics are covered. Within the framework of the common plasticity mechanism, the specific features of deformation in glassy polymers are analyzed. Specifically, the participation of conformational transformations in macromolecules in the deformation response of polymer glasses, change in intensity of the yield peak with the thermomechanical prehistory of the sample, and the role of van der Waals interactions in the accumulation of excess potential energy by the sample under loading are considered. The role of free volume and structural and dynamic heterogeneities in the plasticity of glasses is also discussed.     

Structure and plastic deformation of aromatic main-chain mesomorphic copolyesters

Thermodynamic characteristics of inelastic deformation (work W _def, heat Q _def, and stored energy ΔU _def) are studied for aromatic main-chain copolyesters (CPEs) based on p-hydroxybenzoic acid and poly(ethylene terephthalate) (Rodrun and SKB-1), p-hydroxybenzoic acid, naphthalene carboxylic acid, and terephthalic acid with hydroquinone and dioxyphenyl (HX-6000 and HX-7000). The samples are deformed under an active uniaxial compression by ?_def ≈ 50% at room temperature. All CPEs are semicrystalline polymers; their degree of crystallinity is (depending on their prehistory) 5–30%, and the melting temperature of crystallites is 275–350°C. Seemingly, the glassy component of CPEs includes two interpenetrating glassy structures, S-1 and S-2, with different glass-transition temperatures Tg: 90–120 and 250–270°C, respectively. During loading, all coexisting crystalline and glassy structures of CPEs store residual strain ?_res. The kinetics of the temperature-stimulated strain recovery of ?_res is measured. In component S-1, strain recovery occurs in the temperature interval ranging from T _room to 120°C. In the crystalline phase, this process occurs in the melting-temperature interval. In component S-2, strain recovery ?_res commences at T > 120°C. In CPEs, all structural components are involved in deformation at different ?_def. At small strains only component S-1 is deformed; then, at ?_def ≈ 10–15%, component S-2 is involved in the deformation. Crystallites join this process at ?_def > 20–25% (? _y = 8–10%). In CPE, two modes of deformation arise: reversible elastic (retarded elastic) and true plastic irreversible deformation. True plastic permanent strain always exists in the deformed CPEs. Deformation of all CPEs proceeds easier than that of all “common” glassy polymers (polystyrene, poly(methyl methacrylate), etc.). In CPEs, the yield stress and compressive modulus appear to be ≈40–50% lower than in “common” glassy polymers. It seems that the mesomorphic structure of LC CPEs enhances the elementary plastic processes in them. Thermodynamic characteristics of the S-1 phase plasticity are compared with the behavior of “common” glassy polymers. At the early stages of loading, nearly all mechanical work of deformation W _def spent is stored in phase S-1 in the form of δU _def, as in all “common” glassy polymers. This fact implies that the inelastic deformation of LC glasses commences with the nucleation of small-scale and localized intermolecular transformations of the nonconformational type. In both mesomorphic and “common” glassy polymers, the stage of nucleation of such transformations controls the overall kinetics of the inelastic and plastic deformation. Nucleation does not depend on chain rigidity, a circumstance that conflicts with the model of forced elasticity. It seems that crystallites in CPE are deformed according to crystallographic mechanisms. Currently, neither the structure nor the deformation mechanism of component S-2 is known.     

Heat and stored energy of plastic deformation of solid polymers and heterogeneous blends

Measurements of the mechanical work (A), the heat of deformation (Q) and differences between these quantities, i.e. the internal energy (U) stored in samples were performed under the unidirectional compression loading conditions by using constant temperature deformation calorimetry. It is shown for several glassy (PS, PC, PI-BD, PET, epoxy-amine network, ABS) semi crystalline (PBT, PET) polymers and blends (PC: ABS, PC: PBT), that 45–85% of the mechanical work of deformation is converted to internal energy stored in deformed samples U is quite high as compared with metals.

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Zusammenfassung Mittels Konstanttemperatur-Deformationskalorimetrie wurden bei gerichteter Kompressionsbelastung Messungen der mechanischen Arbeit (A), der Deformations-wärme (Q) und der Differenz beider Größen, d.h. der in den Proben enthaltenen inneren Energie (U) durchgeführt. Für einige amorphe Polymere (PS, PC, PI-BD, PET, Epoxy-Amine-Netzwerk, ABS), halbkristalline Polymere (PBT, PET) und Gemische (PC:ABS, PC:PBT) wurde gezeigt, daß 45–85 % der mechanischen Deformationsarbeit in den Proben als innere Energie gespeichert wird.