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Papers by john hutchinson

Materials, 2014

Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphen... more Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphenol-A (DGEBA) epoxy resin as the matrix and organically modified montmorillonite (MMT) as the clay nanofiller. Resin-clay mixtures with different clay contents (zero, two, five and 10 wt%) were cured, both isothermally and non-isothermally, using a poly(ethyleneimine) hyperbranched polymer (HBP), the cure kinetics being monitored by differential scanning calorimetry (DSC). The nanostructure of the cured nanocomposites was characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), and their mechanical properties were determined by dynamic mechanical analysis (DMA) and impact testing. The results are compared with an earlier study of the structure and properties of the same DGEBA-MMT system cured with a polyoxypropylene diamine, Jeffamine. There are very few examples of the use of HBP as a curing agent in epoxy PLS nanocomposites; here, it is found to enhance significantly the degree of exfoliation of these nanocomposites compared with those cured with Jeffamine, with a corresponding enhancement in the impact energy for

Polymers

This work demonstrates that the application of even moderate pressures during cure can result in ... more This work demonstrates that the application of even moderate pressures during cure can result in a remarkable enhancement of the thermal conductivity of composites of epoxy and boron nitride (BN). Two systems have been used: epoxy-thiol and epoxy–diamine composites, filled with BN particles of different sizes and types: 2, 30 and 180 μm platelets and 120 μm agglomerates. Using measurements of density and thermal conductivity, samples cured under pressures of 175 kPa and 2 MPa are compared with the same compositions cured at ambient pressure. The thermal conductivity increases for all samples cured under pressure, but the mechanism responsible depends on the composite system: For epoxy–diamine composites, the increase results principally from a reduction in the void content; for the epoxy–thiol system with BN platelets, the increase results from an improved matrix-particle interface; for the epoxy–thiol system with BN agglomerates, which has a thermal conductivity greater than 10 W/m...

Polymers

When an amorphous polymer is cooled under pressure from above its glass transition temperature to... more When an amorphous polymer is cooled under pressure from above its glass transition temperature to room temperature, and then the pressure is released, this results in a densified state of the glass. This procedure applied to an epoxy composite system filled with boron nitride (BN) particles has been shown to increase the density of the composite, reduce its enthalpy, and, most importantly, significantly enhance its thermal conductivity. An epoxy-BN composite with 58 wt% BN platelets of average size 30 µm has been densified by curing under pressures of up to 2.0 MPa and then cooling the cured sample to room temperature before releasing the pressure. It is found that the thermal conductivity is increased from approximately 3 W/mK for a sample cured at ambient pressure to approximately 7 W/mK; in parallel, the density increases from 1.55 to 1.72 ± 0.01 g/cm3. This densification process is much more effective in enhancing the thermal conductivity than is either simply applying pressure ...

Materials

Epoxy resin composites filled with thermally conductive but electrically insulating particles pla... more Epoxy resin composites filled with thermally conductive but electrically insulating particles play an important role in the thermal management of modern electronic devices. Although many types of particles are used for this purpose, including oxides, carbides and nitrides, one of the most widely used fillers is boron nitride (BN). In this review we concentrate specifically on epoxy-BN composites for high thermal conductivity applications. First, the cure kinetics of epoxy composites in general, and of epoxy-BN composites in particular, are discussed separately in terms of the effects of the filler particles on cure parameters and the cured composite. Then, several fundamental aspects of epoxy-BN composites are discussed in terms of their effect on thermal conductivity. These aspects include the following: the filler content; the type of epoxy system used for the matrix; the morphology of the filler particles (platelets, agglomerates) and their size and concentration; the use of surf...

Thermochimica Acta, 2002

The purpose of this paper is a rather general overview of the principles of temperature modulated... more The purpose of this paper is a rather general overview of the principles of temperature modulated differential scanning calorimetry (TMDSC). The technique is compared to conventional DSC, and particular attention is paid to whether or not the heat flow in TMDSC may be separated into so-called thermodynamic and kinetic components. It is shown that in general it is not valid

Thermochimica Acta, 1999

The enthalpy relaxation behaviour of polycarbonate has been studied by alternating differential s... more The enthalpy relaxation behaviour of polycarbonate has been studied by alternating differential scanning calorimetry (ADSC). Samples have been annealed at 125°C, about 20°C below their glass transition temperature, for periods up to 2000h, and then scanned in the ADSC using the modulation conditions: heating rate=1Kmin−1; temperature amplitude=1K; period=1min. The data have been analysed in terms of total, reversing and non-reversing

The Journal of Physical Chemistry B, 2008

Kinetic data for structural relaxation in silver iodomolybdates at the glass transition temperatu... more Kinetic data for structural relaxation in silver iodomolybdates at the glass transition temperature (Tg) are obtained by high-pressure differential scanning calorimetry (HP-DSC) and are compared with activation energies (EA) and volumes (VA) obtained earlier from conductivities below Tg. The results are fitted to an empirical equation, EA = MVA, and displayed in the form of a master plot of EA versus VA, an approach previously applied to strongly coupled systems, including polymer electrolytes and molten salts above their glass transition temperatures. The parameter M emerges as a localized modulus, expressive of interatomic forces within the medium, linking together EA,sigma, VA,sigma and EA,s, VA,s, the "apparent" activation parameters for ionic conductivity and structural relaxation, respectively. The VA and EA values for ion transport are much smaller than the corresponding values for structural relaxation. However, remarkably close agreement emerges between the "process parameters", Ms and Msigma, both close to 8 GPa, thus establishing a quantitative link between ion transport and structural relaxation in this highly decoupled system. A new EA versus VA master plot is constructed, which points the way to a unified approach to ion transport in polymers and glasses.

Polymer Engineering & Science, 1996

... France PILAR CORTES and SALVADOR MONTSERRAT Laboratori de Temodinhica ETS Enginyers Industria... more ... France PILAR CORTES and SALVADOR MONTSERRAT Laboratori de Temodinhica ETS Enginyers Industrials de Terrassa Universitat Politknica de Catalunya 08222 Terrassa, Spain JOHN M. HUTCHINSON Department of ...

Macromolecules, 1999

ABSTRACT The effect of annealing polycarbonate at 125 °C (≈Tg − 20 K) for aging times up to almos... more ABSTRACT The effect of annealing polycarbonate at 125 °C (≈Tg − 20 K) for aging times up to almost 2000 h has been investigated by differential scanning calorimetry, and the kinetics of the enthalpy relaxation process are compared with the effects of aging at the same temperature on the creep response and on the yield behavior. The enthalpy relaxation is analyzed by the peak shift method, and the following kinetic parameters are obtained: nonlinearity parameter x = 0.46 ± 0.02; apparent activation energy Δh* = 1160 kJ mol-1; nonexponentiality parameter β is in the range 0.456 < β < 0.6. The similarities and/or differences between these results and others quoted in the literature are discussed. The creep response is analyzed by the commonly accepted procedure of horizontal and vertical shifting of deflection vs log(creep time) curves, and a shift rate of μ = 0.87 is obtained, with an excellent master curve. It is shown that a similar shift rate for enthalpy relaxation can be defined, and a value of μH = 0.49 is found. The difference between these two shift rates suggests that the time scales for the aging process are different when probed by the two techniques of creep and enthalpy relaxation. Similarly, it is found that the yield stress of annealed samples depends on log(aging time) in quite a different way from its dependence on log(strain rate), and it is argued that this provides further support for the contention that the time scales and rates of physical aging will be different when probed by different techniques.

Journal of Polymer Science Part B: Polymer Physics, 1998

In this work, we have investigated by DSC the structural relaxation of amorphous polymethyl(a-n-a... more In this work, we have investigated by DSC the structural relaxation of amorphous polymethyl(a-n-alkyl)acrylates in which it is possible to change the length of the alkyl chain. We have evaluated the Narayanaswamy parameter, x, which controls the relative contribution of temperature and of structure to the relaxation time, the apparent activation energy, Dh*, and the nonexponentiality parameter, b, of the stretched exponential response function. The results suggest that x increases while Dh* decreases and b remains constant as the length of the side chain increases. This allows us to comment on the effect of chemical modification on the relaxation kinetics.

Journal of Applied Polymer Science, 2008

ABSTRACT The cure reaction kinetics of epoxy resin, with organically modified montmorillonite loa... more ABSTRACT The cure reaction kinetics of epoxy resin, with organically modified montmorillonite loadings of up to 20 wt % and with stoichiometric conditions, has been studied by differential scanning calorimetry with a view to understanding further the fabrication of epoxy-based polymer layered silicate nanocomposites. The kinetic analysis of isothermal and nonisothermal cure shows that the autocatalytic model is the more appropriate to describe the kinetics of these reactions, and it is observed that a dominant effect of the montmorillonite is to catalyze the curing reaction. However, it was not possible to model the reactions over the whole range of degrees of conversion, in particular for nonisothermal cure. This attributed to the complexity of the reactions, and especially to the occurrence of etherification by cationic homopolymerization catalyzed by the onium ion of the organically modified montmorillonite. The homopolymerization reaction results in an excess of diamine in the system, and hence in practice the reaction is off stoichiometric, which leads to a reduction in both the heat of cure and the glass transition temperature as the montmorillonite content increases. Small angle X-ray scattering of the cured nanocomposites shows that an exfoliated nanostructure is obtained in nonisothermal cure at slow heating rates, whereas for nonisothermal cure at faster heating rates, as well as for isothermal cure at 70°C and 100°C, a certain amount of exfoliation is accompanied by the growth of d-spacings of 1.4 nm and 1.8 nm for dynamic and isothermal cure, respectively, smaller than the d-spacings of the modified clay before intercalation of the resin. A similar nanostructure, consisting of extensive exfoliation accompanied by a strong scattering at distances less than the d-spacing of the modified clay, is also found for resin/clay mixtures, before the addition of any crosslinking agent, which have been preconditioned by storage for long times at room temperature. The development of these nanostructures is attributed to the presence of clay agglomerations in the original resin/clay mixtures and highlights the importance of the quality of the dispersion of the clay in the resin in respect of achieving a homogeneous exfoliated nanostructure in the cured nanocomposite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Journal of Applied Polymer Science, 2006

Three different protocols for the preparation of polymer layered silicate nanocomposites based up... more Three different protocols for the preparation of polymer layered silicate nanocomposites based upon a tri-functional epoxy resin, triglycidyl para-amino phenol (TGAP), have been compared in respect of the cure kinetics, the nanostructure and their mechanical properties. The three preparation procedures involve 2 wt% and 5 wt% of organically modified montmorillonite (MMT), and are: isothermal cure at selected temperatures; pre-conditioning of the resin-clay mixture before isothermal cure; incorporation of an initiator of cationic homopolymerisation, a boron tri-fluoride methyl amine complex, BF 3 •MEA, within the clay galleries. It was found that features of the cure kinetics and of the nanostructure correlate with the measured impact strength of the cured nanocomposites, which increases as the degree of exfoliation of the MMT is improved. The best protocol for toughening the TGAP/MMT nanocomposites is by the incorporation of 1 wt% BF 3 •MEA into the clay galleries of nanocomposites containing 2 wt% MMT.

Three different protocols for the preparation of polymer layered silicate nanocomposites based up... more Three different protocols for the preparation of polymer layered silicate nanocomposites based upon a tri-functional epoxy resin, triglycidyl para-amino phenol (TGAP), have been compared in respect of the cure kinetics, the nanostructure and their mechanical properties. The three preparation procedures involve 2 wt% and 5 wt% of organically modified montmorillonite (MMT), and are: isothermal cure at selected temperatures; pre-conditioning of the resin-clay mixture before isothermal cure; incorporation of an initiator of cationic homopolymerisation, a boron tri-fluoride methyl amine complex, BF 3 •MEA, within the clay galleries. It was found that features of the cure kinetics and of the nanostructure correlate with the measured impact strength of the cured nanocomposites, which increases as the degree of exfoliation of the MMT is improved. The best protocol for toughening the TGAP/MMT nanocomposites is by the incorporation of 1 wt% BF 3 •MEA into the clay galleries of nanocomposites containing 2 wt% MMT.

Progress in Polymer Science, 1995

The general area of physical aging of polymers is reviewed. Various phenomenological aspects are ... more The general area of physical aging of polymers is reviewed. Various phenomenological aspects are introduced and discussed in terms of bulk structural changes evidenced by dilatometric and calorimetric studies, and are compared with the wide variety of information available from microstructural investigations involving spectroscopic and scattering techniques. Current models for describing the relaxation kinetics of the non-equilibrium glassy state are compared. Finally, the effects of physical aging on mechanical properties are reviewed, highlighting especially those areas which remain controversial.

Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphen... more Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphenol-A (DGEBA) epoxy resin as the matrix and organically modified montmorillonite (MMT) as the clay nanofiller. Resin-clay mixtures with different clay contents (zero, two, five and 10 wt%) were cured, both isothermally and non-isothermally, using a poly(ethyleneimine) hyperbranched polymer (HBP), the cure kinetics being monitored by differential scanning calorimetry (DSC). The nanostructure of the cured nanocomposites was characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), and their mechanical properties were determined by dynamic mechanical analysis (DMA) and impact testing. The results are compared with an earlier study of the structure and properties of the same DGEBA-MMT system cured with a polyoxypropylene diamine, Jeffamine. There are very few examples of the use of HBP as a curing agent in epoxy PLS nanocomposites; here, it is found to enhance significantly the degree of exfoliation of these nanocomposites compared with those cured with Jeffamine, with a corresponding enhancement in the impact energy for

Materials, 2014

Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphen... more Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphenol-A (DGEBA) epoxy resin as the matrix and organically modified montmorillonite (MMT) as the clay nanofiller. Resin-clay mixtures with different clay contents (zero, two, five and 10 wt%) were cured, both isothermally and non-isothermally, using a poly(ethyleneimine) hyperbranched polymer (HBP), the cure kinetics being monitored by differential scanning calorimetry (DSC). The nanostructure of the cured nanocomposites was characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), and their mechanical properties were determined by dynamic mechanical analysis (DMA) and impact testing. The results are compared with an earlier study of the structure and properties of the same DGEBA-MMT system cured with a polyoxypropylene diamine, Jeffamine. There are very few examples of the use of HBP as a curing agent in epoxy PLS nanocomposites; here, it is found to enhance significantly the degree of exfoliation of these nanocomposites compared with those cured with Jeffamine, with a corresponding enhancement in the impact energy for

Polymers

This work demonstrates that the application of even moderate pressures during cure can result in ... more This work demonstrates that the application of even moderate pressures during cure can result in a remarkable enhancement of the thermal conductivity of composites of epoxy and boron nitride (BN). Two systems have been used: epoxy-thiol and epoxy–diamine composites, filled with BN particles of different sizes and types: 2, 30 and 180 μm platelets and 120 μm agglomerates. Using measurements of density and thermal conductivity, samples cured under pressures of 175 kPa and 2 MPa are compared with the same compositions cured at ambient pressure. The thermal conductivity increases for all samples cured under pressure, but the mechanism responsible depends on the composite system: For epoxy–diamine composites, the increase results principally from a reduction in the void content; for the epoxy–thiol system with BN platelets, the increase results from an improved matrix-particle interface; for the epoxy–thiol system with BN agglomerates, which has a thermal conductivity greater than 10 W/m...

Polymers

When an amorphous polymer is cooled under pressure from above its glass transition temperature to... more When an amorphous polymer is cooled under pressure from above its glass transition temperature to room temperature, and then the pressure is released, this results in a densified state of the glass. This procedure applied to an epoxy composite system filled with boron nitride (BN) particles has been shown to increase the density of the composite, reduce its enthalpy, and, most importantly, significantly enhance its thermal conductivity. An epoxy-BN composite with 58 wt% BN platelets of average size 30 µm has been densified by curing under pressures of up to 2.0 MPa and then cooling the cured sample to room temperature before releasing the pressure. It is found that the thermal conductivity is increased from approximately 3 W/mK for a sample cured at ambient pressure to approximately 7 W/mK; in parallel, the density increases from 1.55 to 1.72 ± 0.01 g/cm3. This densification process is much more effective in enhancing the thermal conductivity than is either simply applying pressure ...

Materials

Epoxy resin composites filled with thermally conductive but electrically insulating particles pla... more Epoxy resin composites filled with thermally conductive but electrically insulating particles play an important role in the thermal management of modern electronic devices. Although many types of particles are used for this purpose, including oxides, carbides and nitrides, one of the most widely used fillers is boron nitride (BN). In this review we concentrate specifically on epoxy-BN composites for high thermal conductivity applications. First, the cure kinetics of epoxy composites in general, and of epoxy-BN composites in particular, are discussed separately in terms of the effects of the filler particles on cure parameters and the cured composite. Then, several fundamental aspects of epoxy-BN composites are discussed in terms of their effect on thermal conductivity. These aspects include the following: the filler content; the type of epoxy system used for the matrix; the morphology of the filler particles (platelets, agglomerates) and their size and concentration; the use of surf...

Thermochimica Acta, 2002

The purpose of this paper is a rather general overview of the principles of temperature modulated... more The purpose of this paper is a rather general overview of the principles of temperature modulated differential scanning calorimetry (TMDSC). The technique is compared to conventional DSC, and particular attention is paid to whether or not the heat flow in TMDSC may be separated into so-called thermodynamic and kinetic components. It is shown that in general it is not valid

Thermochimica Acta, 1999

The enthalpy relaxation behaviour of polycarbonate has been studied by alternating differential s... more The enthalpy relaxation behaviour of polycarbonate has been studied by alternating differential scanning calorimetry (ADSC). Samples have been annealed at 125°C, about 20°C below their glass transition temperature, for periods up to 2000h, and then scanned in the ADSC using the modulation conditions: heating rate=1Kmin−1; temperature amplitude=1K; period=1min. The data have been analysed in terms of total, reversing and non-reversing

The Journal of Physical Chemistry B, 2008

Kinetic data for structural relaxation in silver iodomolybdates at the glass transition temperatu... more Kinetic data for structural relaxation in silver iodomolybdates at the glass transition temperature (Tg) are obtained by high-pressure differential scanning calorimetry (HP-DSC) and are compared with activation energies (EA) and volumes (VA) obtained earlier from conductivities below Tg. The results are fitted to an empirical equation, EA = MVA, and displayed in the form of a master plot of EA versus VA, an approach previously applied to strongly coupled systems, including polymer electrolytes and molten salts above their glass transition temperatures. The parameter M emerges as a localized modulus, expressive of interatomic forces within the medium, linking together EA,sigma, VA,sigma and EA,s, VA,s, the "apparent" activation parameters for ionic conductivity and structural relaxation, respectively. The VA and EA values for ion transport are much smaller than the corresponding values for structural relaxation. However, remarkably close agreement emerges between the "process parameters", Ms and Msigma, both close to 8 GPa, thus establishing a quantitative link between ion transport and structural relaxation in this highly decoupled system. A new EA versus VA master plot is constructed, which points the way to a unified approach to ion transport in polymers and glasses.

Polymer Engineering & Science, 1996

... France PILAR CORTES and SALVADOR MONTSERRAT Laboratori de Temodinhica ETS Enginyers Industria... more ... France PILAR CORTES and SALVADOR MONTSERRAT Laboratori de Temodinhica ETS Enginyers Industrials de Terrassa Universitat Politknica de Catalunya 08222 Terrassa, Spain JOHN M. HUTCHINSON Department of ...

Macromolecules, 1999

ABSTRACT The effect of annealing polycarbonate at 125 °C (≈Tg − 20 K) for aging times up to almos... more ABSTRACT The effect of annealing polycarbonate at 125 °C (≈Tg − 20 K) for aging times up to almost 2000 h has been investigated by differential scanning calorimetry, and the kinetics of the enthalpy relaxation process are compared with the effects of aging at the same temperature on the creep response and on the yield behavior. The enthalpy relaxation is analyzed by the peak shift method, and the following kinetic parameters are obtained: nonlinearity parameter x = 0.46 ± 0.02; apparent activation energy Δh* = 1160 kJ mol-1; nonexponentiality parameter β is in the range 0.456 < β < 0.6. The similarities and/or differences between these results and others quoted in the literature are discussed. The creep response is analyzed by the commonly accepted procedure of horizontal and vertical shifting of deflection vs log(creep time) curves, and a shift rate of μ = 0.87 is obtained, with an excellent master curve. It is shown that a similar shift rate for enthalpy relaxation can be defined, and a value of μH = 0.49 is found. The difference between these two shift rates suggests that the time scales for the aging process are different when probed by the two techniques of creep and enthalpy relaxation. Similarly, it is found that the yield stress of annealed samples depends on log(aging time) in quite a different way from its dependence on log(strain rate), and it is argued that this provides further support for the contention that the time scales and rates of physical aging will be different when probed by different techniques.

Journal of Polymer Science Part B: Polymer Physics, 1998

In this work, we have investigated by DSC the structural relaxation of amorphous polymethyl(a-n-a... more In this work, we have investigated by DSC the structural relaxation of amorphous polymethyl(a-n-alkyl)acrylates in which it is possible to change the length of the alkyl chain. We have evaluated the Narayanaswamy parameter, x, which controls the relative contribution of temperature and of structure to the relaxation time, the apparent activation energy, Dh*, and the nonexponentiality parameter, b, of the stretched exponential response function. The results suggest that x increases while Dh* decreases and b remains constant as the length of the side chain increases. This allows us to comment on the effect of chemical modification on the relaxation kinetics.

Journal of Applied Polymer Science, 2008

ABSTRACT The cure reaction kinetics of epoxy resin, with organically modified montmorillonite loa... more ABSTRACT The cure reaction kinetics of epoxy resin, with organically modified montmorillonite loadings of up to 20 wt % and with stoichiometric conditions, has been studied by differential scanning calorimetry with a view to understanding further the fabrication of epoxy-based polymer layered silicate nanocomposites. The kinetic analysis of isothermal and nonisothermal cure shows that the autocatalytic model is the more appropriate to describe the kinetics of these reactions, and it is observed that a dominant effect of the montmorillonite is to catalyze the curing reaction. However, it was not possible to model the reactions over the whole range of degrees of conversion, in particular for nonisothermal cure. This attributed to the complexity of the reactions, and especially to the occurrence of etherification by cationic homopolymerization catalyzed by the onium ion of the organically modified montmorillonite. The homopolymerization reaction results in an excess of diamine in the system, and hence in practice the reaction is off stoichiometric, which leads to a reduction in both the heat of cure and the glass transition temperature as the montmorillonite content increases. Small angle X-ray scattering of the cured nanocomposites shows that an exfoliated nanostructure is obtained in nonisothermal cure at slow heating rates, whereas for nonisothermal cure at faster heating rates, as well as for isothermal cure at 70°C and 100°C, a certain amount of exfoliation is accompanied by the growth of d-spacings of 1.4 nm and 1.8 nm for dynamic and isothermal cure, respectively, smaller than the d-spacings of the modified clay before intercalation of the resin. A similar nanostructure, consisting of extensive exfoliation accompanied by a strong scattering at distances less than the d-spacing of the modified clay, is also found for resin/clay mixtures, before the addition of any crosslinking agent, which have been preconditioned by storage for long times at room temperature. The development of these nanostructures is attributed to the presence of clay agglomerations in the original resin/clay mixtures and highlights the importance of the quality of the dispersion of the clay in the resin in respect of achieving a homogeneous exfoliated nanostructure in the cured nanocomposite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Journal of Applied Polymer Science, 2006

Three different protocols for the preparation of polymer layered silicate nanocomposites based up... more Three different protocols for the preparation of polymer layered silicate nanocomposites based upon a tri-functional epoxy resin, triglycidyl para-amino phenol (TGAP), have been compared in respect of the cure kinetics, the nanostructure and their mechanical properties. The three preparation procedures involve 2 wt% and 5 wt% of organically modified montmorillonite (MMT), and are: isothermal cure at selected temperatures; pre-conditioning of the resin-clay mixture before isothermal cure; incorporation of an initiator of cationic homopolymerisation, a boron tri-fluoride methyl amine complex, BF 3 •MEA, within the clay galleries. It was found that features of the cure kinetics and of the nanostructure correlate with the measured impact strength of the cured nanocomposites, which increases as the degree of exfoliation of the MMT is improved. The best protocol for toughening the TGAP/MMT nanocomposites is by the incorporation of 1 wt% BF 3 •MEA into the clay galleries of nanocomposites containing 2 wt% MMT.

Three different protocols for the preparation of polymer layered silicate nanocomposites based up... more Three different protocols for the preparation of polymer layered silicate nanocomposites based upon a tri-functional epoxy resin, triglycidyl para-amino phenol (TGAP), have been compared in respect of the cure kinetics, the nanostructure and their mechanical properties. The three preparation procedures involve 2 wt% and 5 wt% of organically modified montmorillonite (MMT), and are: isothermal cure at selected temperatures; pre-conditioning of the resin-clay mixture before isothermal cure; incorporation of an initiator of cationic homopolymerisation, a boron tri-fluoride methyl amine complex, BF 3 •MEA, within the clay galleries. It was found that features of the cure kinetics and of the nanostructure correlate with the measured impact strength of the cured nanocomposites, which increases as the degree of exfoliation of the MMT is improved. The best protocol for toughening the TGAP/MMT nanocomposites is by the incorporation of 1 wt% BF 3 •MEA into the clay galleries of nanocomposites containing 2 wt% MMT.

Progress in Polymer Science, 1995

The general area of physical aging of polymers is reviewed. Various phenomenological aspects are ... more The general area of physical aging of polymers is reviewed. Various phenomenological aspects are introduced and discussed in terms of bulk structural changes evidenced by dilatometric and calorimetric studies, and are compared with the wide variety of information available from microstructural investigations involving spectroscopic and scattering techniques. Current models for describing the relaxation kinetics of the non-equilibrium glassy state are compared. Finally, the effects of physical aging on mechanical properties are reviewed, highlighting especially those areas which remain controversial.

Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphen... more Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphenol-A (DGEBA) epoxy resin as the matrix and organically modified montmorillonite (MMT) as the clay nanofiller. Resin-clay mixtures with different clay contents (zero, two, five and 10 wt%) were cured, both isothermally and non-isothermally, using a poly(ethyleneimine) hyperbranched polymer (HBP), the cure kinetics being monitored by differential scanning calorimetry (DSC). The nanostructure of the cured nanocomposites was characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), and their mechanical properties were determined by dynamic mechanical analysis (DMA) and impact testing. The results are compared with an earlier study of the structure and properties of the same DGEBA-MMT system cured with a polyoxypropylene diamine, Jeffamine. There are very few examples of the use of HBP as a curing agent in epoxy PLS nanocomposites; here, it is found to enhance significantly the degree of exfoliation of these nanocomposites compared with those cured with Jeffamine, with a corresponding enhancement in the impact energy for