Changes of the hole volume in model epoxy networks

Liu, Yang; Hristov, Hristo; Yee, Albert F.; Gidley, David W.; Bauchiere, Didier; Halary, Jean Louis; Monnerie, L.

doi:10.1016/0032-3861(95)90978-b

Cited by 28 publications

(31 citation statements)

References 22 publications

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“…10,27 Our result perhaps emphasizes the influence of the flexibility of the -(CH 2 ) 6 -moities on the value of the thermal expansion coefficient. To some extent, the fact that the values of ␣ r found for A-1-HA60, A-1-DMHMDA60, and O-1-HMDA are unambiguously higher than that of their aromatic counterpart A-1-BAN60, A-1-DMDDM60, and O-1-DDM, respectively (Table II) might corroborate this tentative conclusion.…”

mentioning

confidence: 65%

“…The influence of network architecture on the properties of the matrices has been clarified by using series of model systems, designed to present a systematic variation of the network rigidity while keeping the crosslink density constant, and vice versa. 4 -7 Thus, unambiguous results were obtained dealing with the glass transition temperature T g , 5,[7][8][9] , the free volume, 10 the secondary relaxation ␤, 5,11,12 and the antiplasticization phenomenon. 13,14 In the case of composites, additional pending questions refer to the interaction between matrix and fiber.…”

Section: Introductionmentioning

confidence: 83%

“…With the exception of the network A-1-HMDA, the range of measured values is quite narrow (from 55 ⅐ 10 Ϫ6 K Ϫ1 to 64 ⅐ 10 Ϫ6 K Ϫ1 ), and in satisfactory agreement with previous determinations. 10,27 Considering the accuracy on the measurements (Ϯ3 ⅐ 10 Ϫ6 K Ϫ1 ), this prevents any suitable statement on the possible connection of ␣ r with crosslink density and presence of dangling moities. The quite peculiar value observed for the network A-1-HMDA (83 ⅐ 10 Ϫ6 K…”

Section: Thermal Characteristics Of the Networkmentioning

confidence: 99%

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Relationships between thermally induced residual stresses and architecture of epoxy-amine model networks

Bauchiere

Halary

Monnerie

et al. 2000

J. Appl. Polym. Sci.

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ABSTRACT:The capability of epoxy-amine resins to develop residual stresses was studied as a function of temperature and network architecture. These residual stresses were induced while cooling epoxy-glass bilayers from temperatures higher than the network glass transition temperature, T g . This behavior was the result of the marked differences (␣ r Ϫ ␣ g ), in linear thermal expansion coefficient of the two components, as evidenced by the measurement of ␣ r for the epoxy networks under study. Various network architectures were selected, resulting from variation of (1) the chemical nature of both epoxide and curing agent, (2) the nature and relative amount of the chain-extensor agent, and (3) the stoichiometric ratio. Three ranges of cooling temperature were observed systematically: first, the range of temperatures above T g , where no stress has been detected, then an intermediate temperature range (from T g to T*), where stresses develop quite slowly, and finally, the low temperature range (T Ͻ T*), where a linear increase in stress accompanies the decrease of temperature. The two latter regimes were quantitatively characterized by the extent, T g Ϫ T*, of the first one and by the slope, SDR, of the second one. T g Ϫ T* values were shown to be governed by the T g of the network: the higher the T g , the larger the gap between T g and T*. This result was interpreted by accounting for the variation of relaxation rate at T g from one network to the other. It was also shown that a semiempirical relationship holds between SDR and T g : SDR decreases monotonically as T g increases. By inspecting the effects of network architecture in more details, it turned out that SDR is governed by the Young's moduli, E r (T Ϫ T g ), of the epoxy resins in the glassy state: the lower E r (T Ϫ T g ), the lower SDR in a series of homologous networks. As E r (T Ϫ T g ) values are known to be related to the characteristics of the secondary relaxation ␤, which depends, in turn, on crosslink density, SDR values were finally connected to the amplitude of the ␤ relaxation processes. This finding was corroborated by the measurements on an antiplasticized dense network. Finally, data relative to thermoplastic-filled networks showed that the addition of thermoplastic reduces the development of residual stresses, whatever the system, is homogeneous or biphasic.

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mentioning

confidence: 65%

Section: Introductionmentioning

confidence: 83%

Section: Thermal Characteristics Of the Networkmentioning

confidence: 99%

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Relationships between thermally induced residual stresses and architecture of epoxy-amine model networks

Bauchiere

Halary

Monnerie

et al. 2000

J. Appl. Polym. Sci.

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“…This means that, in spite of the great variation in crosslink density and in the amounts of dangling chains, the average hole size is not affected by either q or f PGE . A comparison between our findings and literature results is not straightforward due to the great variability of epoxy formulations (which does not allow to separate the effect of chemistry from that of free volume) and to the different methods of analysis for the annihilation spectra (distributed o‐Ps component, chosen by us and Goyanes et al or discrete components ). However, the fact that variations of crosslink density were not mirrored by a systematic change in hole sizes was already shown for epoxy systems by Monnerie et al .…”

Section: Resultsmentioning

confidence: 59%

Thermomechanical and large deformation behaviors of antiplasticized epoxy resins: Effect of material formulation and network architecture

Pandini

Bignotti

Baldi

et al. 2017

Polymer Engineering & Sci

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A series of amine-hardened epoxies were prepared by systematically varying the stoichiometric ratio and the relative amounts of diepoxide and monoepoxide resin to chemically control the material composition and macromolecular architecture (chain segments flexibility; crosslink density; amounts of dangling groups). Positron Annihilation Lifetime Spectroscopy was used to investigate the free volume associated to the various epoxy formulations, while dynamic-mechanical analysis was employed to investigate their network density and their primary and secondary mechanical relaxations. The mechanical behavior at small and large strain was studied by means of tensile and compression tests. The results pointed out that deviations from the ideal stoichiometric composition and the addition of monoepoxide resins lead to significant room temperature stiffening, together with a reduction of the crosslink density and glass transition temperature. This behavior, phenomenologically associated to antiplasticization, was interpreted according to the specific macromolecular architecture and ascribed to chain mobility hindrance, as revealed by secondary transitions, whereas no significant contribution from the free volume could be evidenced. Furthermore, it was shown that depending on the strain scale and on the corresponding deformational mechanisms, the mechanical response may be differently influenced either by the presence of dangling groups or by the network density

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“…It is well known that the most important factors influencing their performance are molecular architecture, epoxy/hardener ratio, and curing conditions [1][2][3]. As a matter of fact, it is an useful thinking that by choosing monomers with appropriate molecular structure the rigidity of epoxy networks can be controlled, while stoichiometry and curing conditions predominantly affect crosslinking density, free volume but also mechanical properties.…”

mentioning

confidence: 99%

PALS study of epoxy matrices: self‐assembly of block copolymers and its capability for nanostructuring thermosetting systems

Ramos

Serrano

Tercjak

et al. 2007

Phys. Status Solidi (c)

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The free volume in epoxy systems based on diglycidyl ether of bisphenol-A (DGEBA) fully cured with aminic hardeners having different chemical structures has been studied by means of positron annihilation lifetimes spectroscopy. The results are compared with those obtained from the analysis of the macroscopic specific volume changes by using pressure-volume-temperature (PVT) experimental technique. An excellent correlation between the volumes measured at macro and nanoscales was found for the epoxy systems fully cured with aminic hardeners. On the other hand, a systematic study on the dependence of the volumes at nano-scale in epoxy systems cured with two selected aminic hardeners at different pre-cure temperatures revealed that the pre-cure temperature, as well as, the structure of the hardeners governs the packing of the molecular chains of the epoxy network and its influence in the volume and number density of the nanoholes. In the second part of this work, a systematic study of the effect of several epoxidation degrees of butadiene block in a commercial polystyrene-polybutadiene star block copolymer (SB) has been carried out to control nano-ordering in thermosetting epoxy systems. For this purpose, blends of DGEBA cured with 4,4´-methylenebis(3-chloro-2,6-diethylaniline) (MCDEA) containing 30 wt % neat SB and several epoxidized SB star block copolymers have been synthesized. At low epoxidation degrees, interactions with the epoxy matrix are not sufficiently favorable and macroscopic phase separation takes place, leading to a phase-inverted morphology where the block copolymer may become the matrix. For high epoxidation degrees, however, nanostructured thermosetting systems, being the epoxy-rich phase the matrix of the blends, have been obtained. It has been proved that, in blends containing SepB61 and SepB76 star block copolymers, the copolymer self-assembles into a well-defined hexagonally ordered structure, where cylinders are formed by PS arranged in an epoxy matrix containing both epoxidized and nonepoxidized butadiene units. SAXS experiments show that there are not strong differences in the long spacing between the different systems because the repeated distance between PS cylinders for all the blends is around 41-42 nm.

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Changes of the hole volume in model epoxy networks

Cited by 28 publications

References 22 publications

Relationships between thermally induced residual stresses and architecture of epoxy-amine model networks

Relationships between thermally induced residual stresses and architecture of epoxy-amine model networks

Thermomechanical and large deformation behaviors of antiplasticized epoxy resins: Effect of material formulation and network architecture

PALS study of epoxy matrices: self‐assembly of block copolymers and its capability for nanostructuring thermosetting systems

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