Ultimate toughness of amorphous polymers

The deformation and toughness of amorphous glassy polymers is discusses in terms of both the molecular network structure and the microscopic structure at length scales of 50-300 nm. Two model systems were used: polystyrene-poly(2,6-dimethyl-1,4-phenylene ether) blends (PS-PPE; where PS possesses a low entanglement density and PPE a relatively high entanglement density) and epoxides based on diglycidyl ether of bisphenol A (DGEBA) with crosslink densities comparable with up to values much higher than the thermoplastic model system. The microscopic structure was controlled by the addition of different amounts of non-adhering core-shell-rubber particles. Toughness is mainly determined by the maximum macroscopic draw ratio since the yield stress of most polymers approximately is identical (50-80 MPa). It is shown that the theoretical maximum draw ratio, derived from the maximum (entanglement or crosslink) network deformation, is obtained macroscopically when the characteristic length scale of the microstructure of the material is below a certain dimension; i.e. the critical matrix ligament thickness between added non-adhering rubbery particles ('holes'). The value of the critical matrix ligament thickness (IDc) uniquely depends on the molecular structure: at an increasing network density, IDc increases indepent of the nature of the network structure (entanglements or crosslinks). A simple model is presented based on an energy criterion to account for the phenomenon of a critical ligament thickness and to describe its strain-rate and temperature dependency

Deformation and toughness of polymeric systems: 4 Influence of strain rate and temperature

The influence of testing speed and temperature on the brittle-to-tough transition of non-adhering core-shell rubber-modified polystyrene-poly(2,6-dimethyl-1,4-phenylene ether) (PS-PPE) blends was studied. The validity of the concept of a network density dependent, critical matrix ligament thickness (IDc, as introduced in this series and verified mainly by slow-speed uniaxial tensile testing) is demonstrated for notched high-speed (1 m s-1) tensile testing at different temperatures. The influence of testing speed and temperature on the absolute value of IDc can be quantitatively understood in terms of a strain rate and temperature dependence of the yield stress. The simple model introduced in part 2 of this series proves to be valid under all testing conditions studied varying from temperatures of 50 to 150°C below the glass transition temperature of the PS-PPE blends. The absolute value of the tensile toughness, on the contrary, is a not yet quantified function of the test geometry applied and, consequently, cannot be directly derived from a simple strain-to-break argument

The ultimate toughness of polymers : the influence of network and microscopic structure

The deformation and toughness of amorphous glassy polymers is discussed in terms of both the molecular network structure and the microscopic structure. Two model systems were taken into consideration: polystyrene-poly(2,6-dimethyl-1,4-phenylene ether) blends (PS-PPE) and epoxides based on diglycidyl ether of bisphenol A (DGEBA). The network structure of the thermoplastic PS-PPE system could be varied systematically by changing the relative volume fractions of PS (low entanglement density, v e=3 × 1025 chains m-3) and PPE (v e=13 × 10s25 chains m-3) in this miscible blend. The crosslink density, v c, of the DGEBA system could be set by selecting various epoxide monomer molecular weights (8 × 1025 ¿ v c ¿ 235 × 1025 chains m-3). The microscopic structure at length scales of 50–300 nm was controlled by the addition of different amounts of non-adhering core-shell-rubber particles having a constant diameter. Thoughness is mainly determined by the maximum macroscopic draw ratio since the yield stress of most polymers approximately is identical (50–80 MPa). It is shown, based on the analysis of experimental data published in literature, that the theoretical maximum draw ratio, derived from the maximum (entanglement or crosslink) network deformation, is obtained macroscopically when the characteristic length scale of the microstructure of the material is below a certain value, i.e., the critical matrix ligament thickness between added nonadhering rubbery particles (\s`holes\s`). The value of the critical matrix ligament thickness (IDc) uniquely depends on the network structure: at an increasing network density, IDc increases independent of the nature of the network structure (entanglements or crosslinks). A simple model is presented, based on an energy criterion, to account for the phenomenon of a critical ligament thickness

The influence of network density and material critical thickness on the ultimate toughness of polymers

The deformation and toughness of amorphous polymers is discussed in terms of their mol. network structure and morphol. Both neat and (nonadhering) core-shell-rubber modified thermoplastics and thermosets are analyzed. The thermoplastic model system consists of miscible blends of polystyrene (I) and poly(2,6-dimethyl-1,4-phenylene ether) in different vol. ratios (consequently with different entanglement densities). The thermosetting system is based on epoxides with various degrees of crosslink d. Toughness is mainly detd. by the max. macroscopic strain at break since the yield stress of all polymers is approx. const. (50-80 MPa). The theor. max. draw ratio can be derived from the max. (entanglement or crosslink) network deformation. Brittle polymers, like I, suffer from catastrophic localization of strain and macroscopically show a strain to break far below this theor. max. However, below a certain dimension of the microstructure, expressed by the crit. matrix ligament thickness between added nonadhering core-shell rubbery particles (holes), the max. network extension can be reached on a macroscopic level. The crit. thickness depends on the mol. structure: with increasing network d. the value of the crit. ligament thickness increases from 0.05 mm for I (high mol. wt. between entanglements: Me = 19.1 kg mole-1) via 0.18 mm for the I blends contg. 40 wt. I (Me = 6.7 kg mole-1) to 0.3 mm for an epoxide having a mol. wt. between crosslinks, Mc, of approx. 4.4 kg mole-

The influence of network density and material critical thickness on the ultimate toughness of polymers

The deformation and toughness of amorphous polymers is discussed in terms of their mol. network structure and morphol. Both neat and (nonadhering) core-shell-rubber modified thermoplastics and thermosets are analyzed. The thermoplastic model system consists of miscible blends of polystyrene (I) and poly(2,6-dimethyl-1,4-phenylene ether) in different vol. ratios (consequently with different entanglement densities). The thermosetting system is based on epoxides with various degrees of crosslink d. Toughness is mainly detd. by the max. macroscopic strain at break since the yield stress of all polymers is approx. const. (50-80 MPa). The theor. max. draw ratio can be derived from the max. (entanglement or crosslink) network deformation. Brittle polymers, like I, suffer from catastrophic localization of strain and macroscopically show a strain to break far below this theor. max. However, below a certain dimension of the microstructure, expressed by the crit. matrix ligament thickness between added nonadhering core-shell rubbery particles (holes), the max. network extension can be reached on a macroscopic level. The crit. thickness depends on the mol. structure: with increasing network d. the value of the crit. ligament thickness increases from 0.05 mm for I (high mol. wt. between entanglements: Me = 19.1 kg mole-1) via 0.18 mm for the I blends contg. 40 wt. I (Me = 6.7 kg mole-1) to 0.3 mm for an epoxide having a mol. wt. between crosslinks, Mc, of approx. 4.4 kg mole-

The diagnostics of thermal plasmas

A review with 30 refs. on plasma diagnostic techniques. [on SciFinder (R)

Passive and active spectroscopy on flowing plasmas

The equil. departures of two types of flowing plasmas were studied exptl. The combination of abs. emission spectroscopy with the non-intrusive active tool of Thomson/Rayleigh scattering made it possible to compare the at. state distribution function (ASDF) with its equil. form. The electron excitation kinetics (EEK) of a highly recombinative Cascaded Arc Created Magnetized Expanding Plasma was studied using time resolved laser induced fluorescence. The recombination process was found to be largely affected by heavy particle excitation kinetics (HEK). A comparable study of an inductively coupled plasma revealed that the deviations from partial local Saha equil. (pLSE) were much less pronounced. To get insight in this plasma, global active spectroscopy was performed by following the response to the power interruption