Roberto J. J. Williams

Reaction-induced phase separation in modified thermosetting polymers

Thermosetting polymers are frequently used in formulations, including rubbers, thermoplastic polymers or oils, etc, in an amount of the order of 2–50 wt% with respect to the thermoset. This extra component, called the modifier, may initially be immiscible or may phase-separate during cure. This last process, i.e the reaction-induced phase separation, is the subject of this review. A thermodynamic description of the process is made, using the Flory-Huggins equation at two approximation levels, i.e. a quasi-binary approach and a multicomponent treatment taking polydispersity of constituents into account. Thermodynamic factors affecting the phase separation process are thus established. Nucleation and growth (NG) and spinodal demixing (SD) are considered as possible phase separation mechanisms. Factors promoting one or the other process are discussed. The control of morphologies generated is analyzed on the basis of thermodynamic and kinetic arguments. Ideas for obtaining particular morphologies enhancing particular properties are put forward.

Epoxy polymers : new materials and innovations

Preface . List of Contributors . 1 General Concepts about Epoxy Polymers ( Jean-Pierre Pascault and Roberto J.J. Williams). 1.1 Polymerization Chemistry of Epoxy Monomers . 1.2 Transformations During the Formation of an Epoxy Network . 1.3 General Properties of Epoxy Networks . References . Part One New Polymers/Materials . 2 Thermoplastic Epoxy Polymers ( Jerry E. White). 2.1 Introduction . 2.2 Synthesis and Characterization of Epoxy Thermoplastics . 2.3 Fundamental Properties of Epoxy Thermoplastics . 2.4 Conclusions . Acknowledgments . References . 3 Epoxy Functional Acrylic Polymers for High Performance Coating Applications ( Carmen Flosbach and Roger Fugier). 3.1 Introduction . 3.2 Epoxy Functional Acrylic Polymers (Epoxy Acrylates) . 3.3 Synthesis of Epoxy Acrylates . 3.4 Design of Epoxy Acrylates as Film-forming Components in Coatings . 3.5 Cross-linking Reactions in Coating Systems . 3.6 Conclusions . References . 4 Epoxy Polymers Based on Renewable Resources ( Alessandro Gandini). 4.1 Introduction . 4.2 Synthesis and Polymerization of Monomers and Macromonomers Bearing Multiple Epoxy Functions . 4.3 Synthesis and Polymerization of Monomers Bearing a Single Epoxy Group . 4.4 Conclusions . References . Part Two (Nano)Structured Epoxy Networks . 5 Nanostructured Epoxies by the Use of Block Copolymers ( Sixun Zheng). 5.1 Introduction . 5.2 Formation Mechanisms of Nanostructures in Thermosets . 5.3 Morphologies of Epoxy Thermosets Modified With Block Copolymers . 5.4 Thermomechanical Properties of Nanostructured Thermosets . 5.5 Conclusions . References . 6 Self-Assembly of Epoxy-Based Polymers ( Cristina E. Hoppe and Roberto J.J. Williams). 6.1 Introduction . 6.2 Linear Nanostructured Epoxies . 6.3 Crosslinked Nanostructured Epoxies . 6.4 Possible Applications of Nanostructured Epoxies . References . 7 Polymer Dispersed Liquid Crystal, Thermotropic and Other Responsive Epoxy Polymers ( Agnieszka Tercjak and Inaki Mondragon). 7.1 Epoxy-Based Polymer Dispersed Liquid Crystal . 7.2 Polymer Dispersed Liquid Crystal Prepared by PIPS . 7.3 Block Copolymers Used as a Polymer Dispersing Agent for Liquid Crystal . 7.4 Epoxy Polymers Based on Azo-Benzene Organic Molecules . 7.5 Conclusions and Perspectives . References . 8 POSS and Other Hybrid Epoxy Polymers ( Libor Matejka). 8.1 Introduction . 8.2 Epoxy-Silica Hybrids . 8.3 Epoxy - POSS Hybrids . 8.4 Conclusions . Acknowledgment . References . 9 Lamellar Silicate-Modified Epoxies ( Jannick Duchet-Rumeau and Henry Sautereau). 9.1 Introduction . 9.2 Structure and Properties of Lamellar (Phyllo) Silicates . 9.3 Morphologies of Lamellar Silicates-Polymer Nanocomposites . 9.4 Chemical Modification of Lamellar Silicates for Epoxy Networks . 9.5 Dispersion and Structuration of Lamellar Silicates in the Initial Formulation . 9.6 Structuration of Lamellar Silicates in a Reactive Medium . 9.7 Mechanical Properties of Lamellar Silicates-Modified Epoxies . 9.8 Ternary Blends Based on Epoxy/Layered Silicates . 9.9 Barrier Properties of Nanoclay-Modified Epoxies . 9.10 Conclusions . References . 10 Epoxy/Carbon Nanotube Nanocomposites ( Luyi Sun and Hung-Jue Sue). 10.1 Introduction . 10.2 Preparation of Epoxy/CNT Nanocomposites . 10.3 Properties of Epoxy/CNT Nanocomposites . 10.4 Summary and Outlook . References . Part Three Innovative Formulations and Processing . 11 Epoxy Adhesives: A View of the Present and the Future ( Senen Paz Abuin). 11.1 Introduction . 11.2 Requirements and Conditions for the Design of an Epoxy Formulation . 11.3 Criteria for Selecting Adhesive Formulations . 11.4 Conclusions and Perspectives . Acknowledgments . References . 12 UV-Cured Nanostructured Epoxy Coatings ( Marco Sangermano). 12.1 Introduction . 12.2 Organic-Organic Nanocomposite Epoxy Coatings . 12.3 Organic-Inorganic Nanocomposite Epoxy Coatings . 12.4 Conclusions . Acknowledgments . References . 13 Electron Beam Curing of Epoxy Composites ( Felipe Wolff-Fabris and Volker Altstadt). 13.1 Introduction to Electron Beam Curing . 13.2 Materials Features . 13.3 Manufacturing Process . 13.4 Perspectives . References . 14 Composite Processing: State of the Art and Future Trends ( Stephan Costantino and Urs Waldvogel). 14.1 Introduction . 14.2 Infusion . 14.3 Resin Transfer Molding . 14.4 Prepreg . 14.5 Alternative Mold Heating Methods . 14.6 Sheet Molding Compound (SMC)/Bulk Molding Compound (BMC) . 14.7 Filament Winding . 14.8 Pultrusion . 14.9 Expandable Epoxy Systems . 14.10 Conclusions and Trends for the Future . References. 15 Thermoplastic Curable Formulations ( Thomas Fine, Raber Inoubli, Pierre Gerard, and Jean-Pierre Pascault). 15.1 Introduction . 15.2 Typical Preparation of Thermoplastic Curable Formulations . 15.3 Rheological Behavior of Blends of Block Copolymer and Thermoset Precursors . 15.4 Choice of the Hardener . 15.5 Processing and Properties . 15.6 Conclusions . Acknowledgments . References . 16 Structural Epoxy Foams ( Lisa A. Mondy, Rekha R. Rao, Harry Moffat, Doug Adolf, and Mathew Celina). 16.1 Background . 16.2 Continuum-Level Model for Foaming Materials . 16.3 Material Models and Experiments to Populate Numerical Model . 16.4 Numerical Method . 16.5 Model Validation . 16.6 Discussion and Suggested Improvements to the Model . 16.7 New Foaming Strategies to Minimize Gravity-Induced Density Gradients . 16.8 Summary . Acknowledgments . References . 17 Self-Healing Epoxy Composites ( Michael W. Keller). 17.1 Introduction . 17.2 Sequestered Healing-Agent Systems . 17.3 Intrinsically Healing Materials . 17.4 Potential Applications of Self-Healing Materials in a Bio-Engineering Setting . 17.5 Outlook for Self-Healing Materials . References . Part Four Conclusions and Perspectives . 18 Conclusions and Perspectives ( Jean-Pierre Pascault and Roberto J.J. Williams). 18.1 Definitions of Epoxy Polymers . 18.2 New Monomers and Formulations . 18.3 Nanostructured Epoxies . 18.4 Engineering Properties . 18.5 Functional Properties . 18.6 Health-Related Issues . 18.7 Life-Cycle Assessment . References . Index .

Miscibility of epoxy monomers with carboxyl-terminated butadiene-acrylonitrile random copolymers

Abstract Cloud-point curves for mixtures comprising epoxy monomers of the DGEBA type (diglycidyl ether of bisphenol A), rubbers of the CTBN type (carboxyl-terminated acrylonitrile-butadiene random copolymers) and, eventually, hardeners such as diamines are reported. It is shown that the miscibility of epoxy monomers with a particular rubber is very sensitive to the molar mass of the epoxy molecule. The application of a simple Flory-Huggins lattice model, regarding both components as monodisperse, leads to the location of the critical point, coexistence curves and the estimation of the interaction parameter per unit volume (Λ). A correlation of the type Λ=Λ0 + ΛTT was found, with a negative ΛT. The decrease in miscibility observed when using a CTBN containing less acrylonitrile is explained from the change in the solubility parameter. Using CTBN as an adduct with the epoxy monomer leads to an increase in miscibility, which is explained by the copolymer effect. Systems based on epoxy-diamine copolymers prepared in the presence of CTBN adducts showed a complex behaviour including two maxima in cloud-point curves.

Thermal properties of gelatin films

Abstract Thermal properties of dehydrated ‘hot-cast’ gelatin films, obtained from hake skin, were studied using differential scanning calorimetry (d.s.c.) and thermal mechanical analysis (t.m.a.). Two glass transition temperatures, at 120°C and at 180°–190°C, were obtained. The low-temperature transition is assigned to the devitrification of blocks rich in α-amino acids, while the high-temperature transition is attributed to the devitrification of blocks rich in imino acids. For hydrated gelatins both transitions are shifted to lower temperatures. Differences in the behaviour of fish and mammalian gelatins were found. The influence of crosslinking with formaldehyde upon the thermal properties is analysed. The crosslinked fish gelatin devitrifies progressively in the 100°–200°C temperature range.

Thermodynamic analysis of the phase separation in polyetherimide-modified epoxies

The miscibility of polyetherimides (PEIs) with epoxy monomers based on diglycidylether of bisphenol-A (DGEBA), and with reactive mixtures based on stoichiometric amounts of DGEBA and an aromatic diamine (DA) {either 4,4′-diaminodiphenylsulfone (DDS) or 4,4′-methylenebis[3-chloro 2,6-diethylaniline] (MCDEA)}; was experimentally studied. Cloud-point curves (temperature vs. composition) are reported for PEI-DGEBA and PEI-DGEBA-DA initial mixtures. Cloud-point conversions are reported for the reactive mixtures, for various PEI amounts and polycondensation temperatures. A thermodynamic model based on the Flory-Huggins-Staverman approach, taking polydispersity of both components into account, was used to analyze the experimental information. A single relationship between the interaction parameter and temperature, χ(T), could fit experimental results of mixtures of two commercial PEIs with DGEBA. The addition of DDS led to a decrease in miscibility whereas MCDEA improved the initial miscibility. In both cases, the interaction parameter decreased with conversion, meaning that PEI was more compatible with oligomeric species than with the mixture of starting monomers. The phase separation process in initially miscible rubber- or thermoplastic-modified thermosetting polymers is the result of two factors: increase in the average molar size of the thermosetting oligomer (main driving force favoring demixing), and variation of the interaction parameter with conversion, which may act to increase or decrease the cloud-point conversion determined by the first factor.

Rubber-modified thermosets: Prediction of the particle size distribution of dispersed domains

Abstract A model predicting the particle size distribution of dispersed domains in rubber-modified thermosets was developed on the basis of a thermodynamic description of the variation of free energy of mixing with conversion and a phase-separation analysis through constitutive equations for nucleation and growth rates. The model includes experimental information illustrating its application to a bisphenol-A diglycidyl ether epoxy resin cured with diaminodiphenylsulphone and containing a carboxyl-terminated acrylonitrile-butadiene random copolymer. Reasonable agreement between predicted and experimental cumulative particle size distributions is shown. Most of the morphological characteristics of the rubber-modified thermoset depend on the location of the reaction extent at which phase separation begins to take place (pc), with respect to gel conversion (pgel). Increasing the span of the (pgel – pc) range leads to: (a) an increase in the concentration of dispersed particles, (b) an increase in the volume fraction of the dispersed phase, (c) a decrease in the final amount of rubber remaining in the matrix, (d) a decrease in the average concentration of rubber in dispersed particles, and (e) an increase in the concentration of small particles in the overall distribution (a bimodal distribution may result).

Development of bicontinuous morphologies in polysulfone-epoxy blends

The development of bicontinuous morphologies in 10 wt% polysulfone (PSu)‐epoxy (DGEBA)/anhydride (MTHPA) blends, was followed by optical and scanning electron microscopy. Blends cured at 808C revealed the formation of large epoxy-rich domains surrounded by a PSu-rich matrix, soon after the cloud point. Advancing the cure led to an increase in the volume fraction and the coalescence of epoxyrich domains. A bicontinuous primary morphology was thus generated. A secondary phase separation was observed in both primary phases from the very beginning of the phase-separation process. While spinodal demixing was clearly the mechanism by which the primary morphology was generated, nucleation-growth could be responsible of the secondary phase separation. Postcure steps produced a change in the composition of phases as revealed by DMA, and in the secondary morphology as observed by SEM. A postcure at 1208C led to a single Tg at 1158C with a small shoulder at higher temperatures. A postcure at 2008C led to a Tg at 1088C for the epoxy-rich phase and a Tg at 1378C for the PSu-rich phase. The partial purification of the thermoplastic phase produced a significant enhancement of toughness.KIC was increased from 0.65 MPa m 1/2 for the neat thermoset to 1.10 MPa m 1/2 for the blend postcured at 2008C. q 1999 Elsevier Science Ltd.

Statistical structural model for the build-up of epoxy-amine networks with simultaneous etherification

Abstract A statistical structural model is developed to describe a diepoxy-diamine cure, taking into account the possibility of simultaneous epoxy-hydroxy reaction (etherification). Expressions for the number- and weight-average molecular weights, gel conversion, sol fraction, mass fraction of pendant and elastically active network chains (EANC) and concentration of EANC are derived. The different reactivity of primary and secondary amine hydrogens is taken into account, but intramolecular reactions in the pregel stage are neglected. The model is applied to the cure of bisphenol A diglycidyl ether with diaminodiphenyl sulphone, where a previous kinetic analysis showed the presence of etherification. It is shown that, for stoichiometric formulations, etherification acts to decrease both the gel conversion and the concentration of EANC at full epoxy conversion. However, the elastic modulus of the material is not expected to change significantly. Instead, for formulations containing a 100% epoxy excess, the predicted elastic modulus at full epoxy conversion is 50% higher than that predicted for a stoichiometric mixture.

Rubber-modified cyanate esters : thermodynamic analysis of phase separation

Abstract Cloud-point curves were determined for blends of a rubber (butadiene—acrylonitrile random copolymer terminated in non-functional groups, NFBN) and a cyanate ester (4,4′-dicyanate-1,1′-diphenylethane, CE). Measurements were made in the initial blend and in partially polycondensed blends (thermal polycyclotrimerization of the CE monomer). Cloud-point conversions and temperatures were determined for different rubber fractions in the initial formulation. A thermodynamic analysis based on a Flory-Huggins equation, taking polydispersity of both components into account, led to the following conclusions. (1) Phase separation was the result of the change in two different contributions to the free energy of mixing: (a) a decrease in the entropic contribution due to the increase in the oligomer size; (b) a decrease in the enthalpic contribution as a result of the decrease in the cohesive energy density of the CE-oligomer in the course of polycondensation. (2) Spinodal demixing was excluded as a possible mechanism of phase separation during polycondensation in solutions containing less than 12% rubber by volume.

Phase separation induced by a chain polymerization : Polysulfone-modified epoxy/anhydride systems

The reaction-induced phase separation in a blend of a commercial polysulfone (PSu) with diepoxide-cyclic anhydride monomers, was studied. The diepoxide was based on diglycidylether of bisphenol A (DGEBA) and the hardener was methyl tetrahydrophthalic anhydride (MTHPA), used in stoichiometric proportion. Benzyldimethylamine (BDMA) was used as initiator. PSu had no influence on the polymerization kinetics, the gel conversion, and the overall heat of reaction per epoxy equivalent. A kinetic model including initiation, propagation, and termination steps was used to estimate the distribution of linear and branched species in the first stages of the chain-wise copolymerization. This distribution, together with the PSu distribution, were taken into account in a thermodynamic model of the blend. The interaction parameter was fitted from experimental determinations of conversions at the start of phase separation, obtained under different conditions. The thermodynamic model was used to explain the complex morphologies developed in materials containing different PSu concentrations as well as their dynamic mechanical response. The shift in glass transition temperatures was explained by the fractionation of different species during the phase separation process. Phase inversion produced a significant decrease of the elastic modulus in the glassy state and a thermoplastic-like behavior of the material in the rubbery region.