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A new mechanism-based thermo-viscoelastic model for unidirectional polymer matrix composites based on Cartan decomposition

A new mechanism-based thermo-viscoelastic model for unidirectional polymer matrix composites based on Cartan decomposition

A new three-dimensional thermo-viscoelastic constitutive model for uni- directional fiber reinforced, polymer composite materials is developed in this work. The key point is to introduce the viscoelastic behavior only where ap- propriate, based on the constitutive behavior of the underlying constituents, elastic fibers and viscoelastic (in shear) matrix. In order to achieve this, an irreducible Cartan decomposition for the stress and strain tensors under the hypothesis of transverse isotropy is derived. The integrity basis for the de- composition is used to formulate the energy functional, which enables us to define uncoupled constitutive laws in which the contributions of the under- lying constituents are easily identified. In order to describe the viscoelastic behavior in shear of the matrix, a generalized Maxwell model is applied to the appropriate terms of the stress and strain decomposition, in agreement with the underlying physical mechanism. Thermal strains and temperature effects on the viscoelastic behavior are introduced through the time-temperature su- perposition principle. Various numerical simulations are performed to show
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The effect of moisture-induced swelling on the absorption capacity of transversely isotropic elastic polymer-matrix composites

The effect of moisture-induced swelling on the absorption capacity of transversely isotropic elastic polymer-matrix composites

Coupling between stresses and diffusion has been the subject of a very elabo- rate theory by Weitsman (1987), where a viscoelastic behavior at finite strain was considered. Few years later, Wu (2001) limited his work to finite strain elasticity but highlighted the role of the Eshelby stress tensor. Small strain elasticity was considered by Neogi et al. (1986), who used a chemical potential of the Flory-Huggins-Regner type, and by Derrien and Gilormini (2006) who insisted upon coupling-induced non-Fickian effects. Of course, viscous flow is likely to play a part during the diffusion process, as stressed by Weitsman (1990) for instance, but the present work focuses on steady state, when pos- sible transient viscous effects have vanished and the stress-strain relation is governed by small-strain linear elasticity only. This assumes the polymer is kept far enough from its glass transition temperature, even if the latter de- creases when the solvent content increases. More precisely, this study concerns steady states where concentration flux is zero everywhere, in order to avoid the additional complexity mentioned above of a non-Fickian diffusion law. All the above papers include transient diffusion and are limited to non-reinforced polymers (or, more generally, classes of homogeneous materials). The the- ory of stress-diffusion coupling in composites has been considered scarcely, but Aboudi and Williams (2000) did propose a complex analysis for transient regimes, whereas Derrien and Gilormini (2007) focused more simply on steady state. The present study is limited to composites with transverse isotropy, which includes many frequent cases where long fibers are used as reinforce- ments. In addition, the simpler case of isotropic composites, already studied by Derrien and Gilormini (2007), is also considered briefly for comparisons. Temperature is assumed uniform and constant in the material, in order to put emphasis on stress-diffusion coupling and to keep the analysis as simple as possible. Within these limits, the results can nevertheless be applied to various situations. For instance, it is shown how nonlinear sorption, departing from Henry’s law, can be treated. Even if water is considered here, the analy- sis extends to other solvents that may induce swelling of a polymer, provided that small-strain linear elasticity still applies.
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Extended Mean-Field Homogenization of Viscoelastic-Viscoplastic Polymer Composites Undergoing Hybrid Progressive Degradation Induced by Interface Debonding and Matrix Ductile Damage

Extended Mean-Field Homogenization of Viscoelastic-Viscoplastic Polymer Composites Undergoing Hybrid Progressive Degradation Induced by Interface Debonding and Matrix Ductile Damage

5 Numerical Results In order to assess the correctness of the modified Mori-Tanaka TFA damage framework in simulating progressive damage in heterogeneous materials, the present mean-field predictions are compared with the full-field finite-element homogenization simulations in Abaqus which is a gold standard. Further assessment and experimental validation of the proposed framework will be performed elsewhere in our future studies. To this end, the constitutive law implemented into the Abaqus code for the polymer matrix phase is exactly the same as that employed in the modified Mori-Tanaka TFA approach. The inelastic behavior is characterized by the viscoelastic- viscoplastic with ductile damage model; hence it is not repeated in this section. The reader can refer to the work by Praud et al. (2017a) for the numerical details of the implementation using a UserMATerial subroutine (UMAT). In the interphase layer, a viscoelastic-viscoplastic model with micromechanics-based damage described in the following is developed to characterize the nonlinear behavior and the damage in the interphase layer.
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Parameter Optimization of the Steam Thermolysis: A Process to Recover Carbon Fibers from Polymer-Matrix Composites

Parameter Optimization of the Steam Thermolysis: A Process to Recover Carbon Fibers from Polymer-Matrix Composites

around 3,636 MPa, which is almost 100 % of the value of virgin AS4C fibers (Fig. 11 ). Conclusion and Perspectives In this paper, the effects of process parameters on two key responses encountered in the steam-thermal recycling of the CFRP materials have been investigated. For the pur- pose of reclaiming clean carbon fibers without severe reduction in tensile strength, experimental designs using Taguchi method were realized successively on two epoxy based CFRP samples. Sample A contains a most thermally stable aromatic resin system while sample B, embeds BPA resin and non-aromatic amine curing agents. The resin matrices of both samples degrade within the same tem- perature range but sample B yields fewer char residues than sample A (sample B has a higher H/C atomic ratio of its resin matrix). The effects of three factors (target heating temperature, steam flow-rate and heating duration) were initially investigated. The ANOVA and standard least squares linear regression of the experimental results shows that, for sample A: the decomposition rate of epoxy resin is directly related with the steam flow-rate (or rather the mass
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Elastic-strain distribution in metallic film-polymer substrate composites

Elastic-strain distribution in metallic film-polymer substrate composites

Understanding the mechanical behavior of nanostruc- tured thin films in relation to their microstructure is of ut- most importance for the development of technological applications. 1 At nanometer length scales, mechanical prop- erties are significantly altered. 2 The processes responsible for these changes are not fully understood yet and are believed to be caused by grain-surface and grain-boundary volumes becoming dominant over the bulk. In a film, changes are further caused by boundary conditions at the free surface and interfaces. 1 , 2 Mechanical failure of metallic stiff thin films attached to a compliant polymeric substrate poses a significant challenge in the development of integrated structures such as flexible and stretchable electronics. Me- chanical behavior studies of metallic thin films deposited onto polymeric substrates mainly focused on rather large deformations. 3 , 4 In order to enhance the adhesion of the me- tallic film, either the substrate surface is activated by an oxy- gen plasma, 5 , 6 or an adhesion layer is deposited onto the polymer substrate with strongly reactive metals such as Ti, Cr, and Al. 7 , 8 Generally, the authors supposed that the inter- face is strong enough to assume that deformation 共in the elastic regime兲 is continuous through either the substrate-film interface or the interfaces within multilayers. Both from the fundamental and applicative points of view, it is of utmost importance to clarify this question. Elastic behavior can be studied by x-ray diffraction 共XRD兲. 9 , 10 High intensity syn- chrotron x-rays allow characterizing small volumes of mate- rial in a time schedule acceptable for in situ loading. 7 , 11 Tests were generally carried out loading uniaxially a film-substrate composite, the film being stressed biaxially because of the mismatch between the Poisson’s ratios of either the film and the supporting substrate 7 , 11 or the different sublayers. 12 Mul- tiphase materials are a key area of study for diffraction-based stress or strain measurement techniques. Polymer-matrix composites have been avoided because of the difficulty in obtaining accurate diffraction data from a hydrogen- containing material. The development of synchrotron x-ray techniques offers exciting possibilities for such composite materials. Hence, we demonstrate that synchrotron XRD can
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Coupling Mechanical and Electrical Properties in Spin Crossover Polymer Composites

Coupling Mechanical and Electrical Properties in Spin Crossover Polymer Composites

values of d 33 are generally observed in composites with nonfer- roelectic loads. [37] This decrease of d 33 may be attributed to the action of depoling field generated by space charges on the par- ticles during poling. Another explanation is a disruption of the connectivity of the polymer matrix related to the existence of particle agglomerates. We can recall here that the piezoelectric coefficient in ferroelectric polymers is, for the most part, lin- early controlled by the polarization and the compressibility (sec- ondary piezoelectric effect), unlike ferroelectric ceramics where the primary piezoelectric effect at constant volume dominates. In the composites both parameters are lower. In particular the reduced breakdown voltage allows for smaller sample polariza- tion. Using different sample preparation (thickness, annealing, etc.) we were able to increase d 33 up to −9.0 pC N −1 (with a
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Polymer-cholesteric liquid-crystalline composites with a broad light reflection band

Polymer-cholesteric liquid-crystalline composites with a broad light reflection band

BROAD WAVELENGTH BANDGAP CLCs with a helical pitch gradient are found in living matter [1]. The cuticle of crustaceans and insects is a composite material made of an organic matrix, mainly proteins and chitin (a linear polymer of acetylglucosamine), and a mineral (mainly calcite). After decalcification the chitin fibrils exhibit a twisted organization, which is nothing else than the biological version of the CLC structure. The cholesteric organization is found in the organic matrix of many beetles and is responsible for their iridescent colors. The cuticle of the beetle Plusiotis boucardi exhibits reflections in the green and red [5]. Investigation of cross-sections of the elytra by transmission electron microscopy (TEM) has revealed these reflections come from two CLC structures with distinct pitches. The structure of the cuticle of the crab Carcinus mænas exhibits a pitch gradient [6]. The distribution of the pitch varies greatly, even in the most regular regions, from 0.25 to 10 Pm, and reflection mainly occurs in the IR. TEM investigations of pitch gradient structures in several insect cuticles have been reported [1].
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Mechanical effects of oxidation induced shrinkage on organic matrix composites

Mechanical effects of oxidation induced shrinkage on organic matrix composites

oxidation process, through Eshelby-Kröner self-consistent homogenization procedure (Eq. 2) (curve "KESC"). The results were compared to the corresponding properties estimated according to the finite element method (FEM "curve"). Figure 4 shows the evolutions obtained for the effective macroscopic coefficients of thermal expansion of a composite ply, according to equation (3), during the thermal oxidation process experienced by the epoxy. According to figures 2 and 4, the longitudinal effective properties (i.e. in the direction parallel to axis of the reinforcing fibers), are, in first approximation, independent from the state of thermal oxidation process of the polymer matrix constituting the considered composite ply. Actually, a relative deviation weaker than 1 % is observed at the end of the oxidation process for the Young’s modulus, while the longitudinal macroscopic coefficient of thermal expansion remains almost constant (and tends towards zero).
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Characterization of Polyoxometalate/Polymer photo-composites: a Toolbox for the Photodegradation of Organic Pollutants

Characterization of Polyoxometalate/Polymer photo-composites: a Toolbox for the Photodegradation of Organic Pollutants

in photocatalytic applications. 4. Conclusion: In the present paper, a simple and mild approach was introduced to prepare inorganic/organic hybrid composites based on polyoxometalates by photopolymerization under visible light using Light Emitting Diodes LED@405 nm as a cheap and safe irradiation source. The new proposed POM/polymer composites were characterized by several techniques. More particularly, SEM, TEM and EDX revealed the successful embedding of POMs nanoparticles which are present in aggregates in the polymer matrix. Indeed, self-assembly of POMs nanoparticles at the surface improves its mechanical properties as shown by AFM analysis. Moreover, hybrid POM/Polymer composites present high rigidity, a relatively low surface area (BET surface area is lower than 10 m².g -1 ), exhibit redox properties and a regeneration ability under air.
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Double-walled carbon nanotube-based polymer composites for electromagnetic protection

Double-walled carbon nanotube-based polymer composites for electromagnetic protection

In this paper, we present a microwave absorber based on carbon nanotubes (CNT) dispersed inside a BenzoCycloButenw (BCB) polymer. The high aspect ratio and remarkable conductive characteristics of CNT give rise to good absorbing properties for electromagnetic protecting in microelectronic devices with very low concentration. In this article, nanocomposites are pre- pared using a solution-mixing method and are then evaluated and modeled by means of coplanar test structures. First, CNT concentrations are quantified by image processing. The nanocomposites implemented with coplanar test waveguides are then characterized using a vector network analyzer from 40 MHz to 20 GHz. An algorithm is developed to calculate the propa- gation constant “g”, attenuation constant “a”, and relative effective complex permittivity (1reff ¼ 1 reff ′ 2 j1reff ′′ ) for each CNT concentration. The extracted effective parameters are verified using the electromagnetic FEM-based Ansoft’sw high fre- quency structure simulator (HFSS). Power absorption (PA) of 7 dB at 15 GHz is obtained with only 0.37 weight percent of CNT concentration in the polymer matrix. The resulting engineerable and controllable composite provides consequently a novel degree of freedom to design and optimize innovative microwave components.
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Electrical conductivity and Raman imaging of double wall carbon nanotubes in a polymer matrix

Electrical conductivity and Raman imaging of double wall carbon nanotubes in a polymer matrix

the melt viscosity is 90 Pa s at 400 °C. From differential scanning calorimetry (DSC) a PEEK melting temperature of 341 °C and crys- tallinity of 32% were determined. The PEEK powder was added to a CNTs/acetone suspension and then submitted to a short pulse of sonication probe for 10 s, corresponding to a dissipated power of 50 W. The PEEK/CNTs/acetone suspension was then heated to 50 °C to evaporate most of the acetone. The remaining paste was compression molded in a Carver hydraulic hot press at 400 °C for 30 min under about 0.01 MPa. With this process, composites con- taining 0.16, 0.3, 0.5, 0.8, 1.2, 1.5 and 2 wt% were prepared. 2.1. Electrical measurements
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Piezoelectric properties of polymer/lead-free ceramic composites

Piezoelectric properties of polymer/lead-free ceramic composites

dispersion of NN P’s within the matrix might explain this result. For such NN contents, composites remain ductile. It should be noted that for hybrid composites, the piezoelectric state is reached with mild poling fields which is not the case for piezoelectric polymers. It is interesting to note that the Curie temperature of NN ceramic is higher than the processing temperature of high performance polymers. Further studies may give rise to a wide variety of multifunctional polymer/NN P’s piezo- electric composites. The major interest of these composites is their ductility, easy poling and thermal stability of the piezoelectricity.
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Identification of moisture diffusion parameters in organic matrix composites

Identification of moisture diffusion parameters in organic matrix composites

problem through the development of dedicated scale- transition models providing adequate homogenization relations between the effective macroscopic coefficients of diffusion and their microscopic counterparts. According to the literature, the authors agree about the scale transition relation that should be applied in order to realistically estimate, by comparison with experimental data, the effective moisture diffusion coef- ficient in the direction parallel to the reinforcement axis in the case that uni-directional fiber-reinforced polymer matrix composites are considered. 28 Regarding the identification of the effective moisture diffusion coeffi- cients of a composite ply in the direction perpendicular to the reinforcement axis, the problem is very different. For example, a wide variety of homogenization laws can be found about it: the Shen and Springer model, 29 the analogy to the electrical conductibility expression, established by Rayleigh, 30 and the analogy between diffusivities and the effective shear modulus expression from Shirel and Halpin, 31 as examples. Other methods have been proposed: purely numerical approaches, involving the finite differences methoda- chieved by Augl and Berger 32 leading to consistent pre- dictions with Rayleigh model. Another electrical analogy was investigated by Woo and Piggott 33 : the authors considered the diffusivity as the analogous of the inverse of electrical resistivity. One of the principal interests of this paper is assessing the effects of an added interphase with specific properties between the organic matrix and reinforcing fibers. Subsequently to most of the initial work in this field, Kondo and Taki 34 corrected an erroneous fundamental hypothesis con- sidered by their predecessors. Despite this, the applica- tion of the various, above–mentioned, numerical models, dedicated to the identification of moisture dif- fusion coefficients in the direction perpendicular to the reinforcing fibers in organic matrix composites, provides scattered values depending heavily on the considered scale transition model.
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Electrical conductivity and Raman imaging of double wall carbon nanotubes in a polymer matrix

Electrical conductivity and Raman imaging of double wall carbon nanotubes in a polymer matrix

to external pressure [24] . We assume that individual double wall tubes in a polymer matrix have a split G band like individual tubes on surfaces in air or in liquids. The splitting is explained by the interaction of the outer tubes with their environment. This means that the interaction of the outer tubes with the polymer matrix can be used as a local sensor for the dispersion of the DWNTs in the PEEK matrix: the splitting of G band indicates an interaction of out- er tubes with the polymer matrix that is characteristic of a better dispersion. When the G band is observed at the same spectral posi- tion in pristine DWNTs and in composites, the nanotubes are orga- nized in bundles or in agglomerates. The G band Raman spectrum in Fig. 4 a is characteristic of DWNTs agglomerates because no split-
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Piezoelectric properties of polymer/lead-free ceramic composites

Piezoelectric properties of polymer/lead-free ceramic composites

dispersion of NN P’s within the matrix might explain this result. For such NN contents, composites remain ductile. It should be noted that for hybrid composites, the piezoelectric state is reached with mild poling fields which is not the case for piezoelectric polymers. It is interesting to note that the Curie temperature of NN ceramic is higher than the processing temperature of high performance polymers. Further studies may give rise to a wide variety of multifunctional polymer/NN P’s piezo- electric composites. The major interest of these composites is their ductility, easy poling and thermal stability of the piezoelectricity.
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Quantification of nanoparticle dispersion within polymer matrix using gap statistics

Quantification of nanoparticle dispersion within polymer matrix using gap statistics

5. Conclusion A method was developed for deductively quantifying dispersion and agglomeration within particle reinforced polymer composites. The approach was successfully applied to simulated models and validated with SEM images. It was observed that for a comprehensive determination of the dispersion state of a system, the dispersion parameters, the gap factor, particle spacing and particle size dispersity are vital components as standard deviation data alone was not sufficient for accurate assessment. In theory, as (D) approaches 100%, the state of dispersion improves. The current technique is versatile and capable of analysing optical and electron microscopy images. The results can be used as a platform for introducing some measure of standardisation aimed at benchmarking dispersion quality. This proposed method can be modified to analyse 3D images with ease. The aim of the composite design is to manufacture superior performance materials using optimal parameters. This study has shown that optimisation of the degree of dispersion within composites is possible since a reliable numerical measurement for accurate quantification has been provided. The new approach avoids the limitations of previous methods such as the over-reliance on standard deviation, means and varied
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Strain-induced inverse magnetostriction measured on a single contacted Ni nanowire in a polymer matrix Strain-induced inverse magnetostriction measured on a single contacted Ni nanowire in a polymer matrix

Strain-induced inverse magnetostriction measured on a single contacted Ni nanowire in a polymer matrix Strain-induced inverse magnetostriction measured on a single contacted Ni nanowire in a polymer matrix

2 Introduction The physical properties of nanostructured composites are the object of intense investigations for the fabrication of smart materials, nano-sensors and other electronic devices. [1-5] In this context, magnetic materials are especially interesting not only for their response to a magnetic field, but also for their sensibility to mechanical forces. In particular, the possibility of controlling the magnetization with piezoelectric means (especially through the so called inverse magnetostriction effect) is a promising technique for data storage and data processing applications [6-10]. On the other hand, the nanotechnology approach based ion-track shaping of polymer templates has proven to be very efficient for investigating the physical properties of magnetic nanostructures [11-17]. A systematic study of the physical properties of single- contacted magnetic nanowires embedded in an active thermoelastic and piezoelectric polymer matrix is reported. It is shown that a nanowire (NW) embedded in a matrix plays the role of a nanoscopic probe, which is sensitive to the amplitude and the direction of the mechanical stress.
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Elastic-strain distribution in metallic film-polymer substrate composites

Elastic-strain distribution in metallic film-polymer substrate composites

Understanding the mechanical behavior of nanostruc- tured thin films in relation to their microstructure is of ut- most importance for the development of technological applications. 1 At nanometer length scales, mechanical prop- erties are significantly altered. 2 The processes responsible for these changes are not fully understood yet and are believed to be caused by grain-surface and grain-boundary volumes becoming dominant over the bulk. In a film, changes are further caused by boundary conditions at the free surface and interfaces. 1 , 2 Mechanical failure of metallic stiff thin films attached to a compliant polymeric substrate poses a significant challenge in the development of integrated structures such as flexible and stretchable electronics. Me- chanical behavior studies of metallic thin films deposited onto polymeric substrates mainly focused on rather large deformations. 3 , 4 In order to enhance the adhesion of the me- tallic film, either the substrate surface is activated by an oxy- gen plasma, 5 , 6 or an adhesion layer is deposited onto the polymer substrate with strongly reactive metals such as Ti, Cr, and Al. 7 , 8 Generally, the authors supposed that the inter- face is strong enough to assume that deformation 共in the elastic regime兲 is continuous through either the substrate-film interface or the interfaces within multilayers. Both from the fundamental and applicative points of view, it is of utmost importance to clarify this question. Elastic behavior can be studied by x-ray diffraction 共XRD兲. 9 , 10 High intensity syn- chrotron x-rays allow characterizing small volumes of mate- rial in a time schedule acceptable for in situ loading. 7 , 11 Tests were generally carried out loading uniaxially a film-substrate composite, the film being stressed biaxially because of the mismatch between the Poisson’s ratios of either the film and the supporting substrate 7 , 11 or the different sublayers. 12 Mul- tiphase materials are a key area of study for diffraction-based stress or strain measurement techniques. Polymer-matrix composites have been avoided because of the difficulty in obtaining accurate diffraction data from a hydrogen- containing material. The development of synchrotron x-ray techniques offers exciting possibilities for such composite materials. Hence, we demonstrate that synchrotron XRD can
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Preparation and characterization of olive pit powder as a filler to PLA-matrix bio-composites

Preparation and characterization of olive pit powder as a filler to PLA-matrix bio-composites

This study is focused on recycling potential of some waste materials, such as olive pits, i.e. the solid phase derived from an olive oil mill, blended with thermoplastic polymers and used for the production of new materials applied in manufacturing containers and formworks. The olive pit powders are described and characterized. Then the powder is introduced in a bio-based and biodegradable matrix (polylactic acid, PLA) at various percentages. In this study, a comparison of the size distribution and the densities of olive pit powders according to the grinding methods (planetary mill and centrifugal mill) was made. The analyses showed that olive pits can be further stud- ied as additive for the production of green materials. The development of an agricultural based polymer matrix compatible with olive pits and consequently a fully biodegradable composite system is the future and ultimate goal of the research undertaken. For that purpose, composite samples made out of PLA matrix, reinforced with olive pit powders were manufactured and mechanically characterized. With filler loading, an increase in the ten- sile modulus but a decrease of the flexural strength may be due to the poor interfacial bonding between olive pit powder and PLA.
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Humid Ageing of Organic Matrix Composites

Humid Ageing of Organic Matrix Composites

In the former studies of the process, the authors supposed that the small mol- ecules were mainly catalyst residues and other additives. These products are, however, in too small concentrations to reach the value of 8 mol.L -1 calculated above. Various studies, in the 1980s–1990s showed the importance of certain matrix structural characteristics, as well the nature and concentration of ester groups [ 129 , 130 ]. Mortaigne et al. [ 131 ] confirmed the influence of the ester nature, but showed also that the induction time of osmotic cracking is almost proportional to the reciprocal of the prepolymer molar mass, i.e. almost propor- tional to the concentration of polyester chain ends. Osmotic crack propagation was well understood but the mechanism of crack initiation remained unexplained. The hypothesis of the presence of micro-pores is not proven. Osmotic cracking can occur in highly homogeneous polymer glasses as, for instance, polycarbonate [ 132 ], where the presence of porosities is not obvious. Gautier et al. [ 128 ] pro- posed the following synthetic explanation: solutes can be effectively present but the most important part results from hydrolysis events near polyester chain ends that explains the result cited above of Mortaigne et al. [ 131 ]. Indeed random hydrolysis generates new chain ends and, then, contributes also to the process. These small molecules remain dissolved in the matrix until the time when their concentration becomes higher than their solubility threshold. Then, they demix and form highly hydrophilic micro-pockets able to initiate cracking. Then, the induction time of osmotic cracking would be the time at which the concentration of small molecules reaches its solubility limit. This reasoning leads to the fol- lowing equation:
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