Epoxy Clay Nanocomposites Research Articles

Thermoset Epoxy–Clay Nanocomposites: The Dual Role of α,ω-Diamines as Clay Surface Modifiers and Polymer Curing Agents

Diprotonated forms of polyoxypropylene diamines of the type α,ω-[NH3CHCH3CH2(OCH2CHCH3)xNH32+ with x=2.6, 5.6, and 33.1, have been intercalated into montmorillonite and fluorohectorite clays and subsequently evaluated for the formation of glassy epoxy–clay nanocomposites. The intercalated onium ions functioned concomitantly as a clay surface modifier, intragallery polymerization catalyst, and curing agent. Depending on the chain length of the diamine, different orientations of the propylene oxide chains were adopted in the clay galleries, resulting in basal spacings from ∼14 Å (lateral monolayer, x=2.6) to ∼45 Å (folded structure, x=33.1). The initial clay basal spacings were correlated with the formation of intercalated and exfoliated clay–epoxy nanocomposites with improved mechanical properties and high thermal stabilities. In comparison to clay–monoamine intercalates, the use of diamine intercalates greatly reduced the plasticizing effect of the alkyl chains on the polymer matrix, resulting in improved mechanical properties while at the same time reducing the cost and time needed for nanocomposite fabrication.

Thermoset Epoxy–Clay Nanocomposites: The Dual Role of α, ω-Diamines as Clay Surface Modifiers and Polymer Curing Agents

Diprotonated forms of polyoxypropylene diamines of the type α, ω-[NH 3CHCH 3CH 2(OCH 2CHCH 3) x NH 3 2+ with x=2.6, 5.6, and 33.1, have been intercalated into montmorillonite and fluorohectorite clays and subsequently evaluated for the formation of glassy epoxy–clay nanocomposites. The intercalated onium ions functioned concomitantly as a clay surface modifier, intragallery polymerization catalyst, and curing agent. Depending on the chain length of the diamine, different orientations of the propylene oxide chains were adopted in the clay galleries, resulting in basal spacings from ∼14 Å (lateral monolayer, x=2.6) to ∼45 Å (folded structure, x=33.1). The initial clay basal spacings were correlated with the formation of intercalated and exfoliated clay–epoxy nanocomposites with improved mechanical properties and high thermal stabilities. In comparison to clay–monoamine intercalates, the use of diamine intercalates greatly reduced the plasticizing effect of the alkyl chains on the polymer matrix, resulting in improved mechanical properties while at the same time reducing the cost and time needed for nanocomposite fabrication.

Synthesis of epoxy–clay nanocomposites. Influence of the nature of the curing agent on structure

Epoxy–clay nanocomposites were synthesised by swelling an organophilic montmorillonite in a diglycidyl ether of bisphenol A resin with subsequent polymerisation. Three different curing agents were used: an aliphatic diamine and two cycloaliphatic diamines. The cure kinetics of these systems was evaluated by differential scanning calorimetry and the structure of the nanocomposites was characterised by X-ray diffraction and transmission electron microscopy. Successful nanocomposite synthesis was dependent not only on the cure kinetics of the epoxy system but also on the rate of diffusion of the curing agent into the galleries because it affects the intragallery cure kinetics. The nature of the curing agent influences these two phenomena substantially and therefore the resulting structure of the nanocomposite. The curing temperature controls the balance between the extragallery reaction rate of the epoxy system and the diffusion rate of the curing agent into the galleries. Thus, the choice of curing agent and curing conditions controls the extent of exfoliation of the clay in the material.

Synthesis of epoxy–clay nanocomposites: influence of the nature of the clay on structure

Epoxy–clay nanocomposites were synthesised using two montmorillonite clays (MMT) with different cation-exchange capacities (CEC) (94 and 140meq/100g). The purpose was to investigate the influence of the CEC of the clay on the synthesis and structure of epoxy–clay nanocomposites. The dispersion of the 1nm thick clay layers was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Although XRD data did not show any apparent order of the clay layers in the nanocomposite, TEM revealed parallel clay layers with interlamellar spacing of 90Å (MMT of high CEC) and 110Å (MMT of lower CEC) and the presence of remnant multiplets of non-exfoliated layers. A mechanism responsible for the influence of CEC on nanocomposite interlamellar spacing is discussed. The dispersion of the clay was investigated by SEM and found to be finer in the nanocomposites as compared with in conventional composites although the nanocomposites still have clay aggregates at the microscale rather than a monolithic structure.

Stiffness Improvements and Molecular Mobility in Epoxy-Clay Nanocomposites

ABSTRACTConventional composites filled with clay as well as intercalated nanocomposites, and exfoliated nanocomposites based on a glassy epoxy matrix have been synthesised. Flexural moduli of these materials were measured in three-point bending at various clay contents. For a given clay content, stiffness improvements depended not only on the dispersion of the clay on the microscale, but also on the exfoliation of the clay layers at the nanolevel. Dynamic mechanical measurements indicated a decrease of intensity in the glass transition peak with the extent of exfoliation of the clay and the clay content, suggesting a restriction of the molecular mobility of the polymer in the vicinity of the clay layers. A shift in Tg of 20°C towards lower temperature for the epoxy resin cured at 160°C was possibly caused by thermal degradation of compatibilizing agents at high temperature.

Clay Nanolayer Reinforcement of a Glassy Epoxy Polymer

ABSTRACTGlassy epoxy-clay nanocomposites (Tg ≈ 82 °C) have been prepared by the reaction of diglycidyl ether of bisphenol A and a polyoxyalkylene amine curing agent in the presence of organo cation exchanged smectite (montmorillonite) clays. Commercially available AMS and CWC montmorillonites purified on the industrial scale (Nanocor, Inc.) afforded nanocomposites with performance properties comparable to those obtained from montmorillonite purified by laboratory methods. We provide the first evidence for clay nanolayer reinforcement of a glassy epoxy matrix under compressive strain. Compression stress - strain experiments revealed substantial improvements in the modulus and yield strength when the clay nanolayers were exfoliated in the glassy matrix. However, no improvement in the modulus or yield strength was observed when the clay component was merely intercalated by the epoxy matrix, signifying that nanolayer exfoliation is an essential feature of reinforcement. Furthermore, the mechanical properties of epoxy-clay nanocomposites prepared with the C18H37NH3+ - exchanged forms of the AMS and CWC clays have been tested by dynamic mechanical analysis and thermal mechanical analysis. The nanocomposites exhibit improved dynamic storage modulus above and below the glass transition temperature, as well as lower coefficients of thermal expansivity compared to the pure polymer. In addition, the solvent resistant properties of the nanocomposites are substantially improved compared to the pristine polymer.

Nanolayer Ordering in an Epoxy-Exfoliated Clay Hybrid Composite

A new class of epoxy-clay nanocomposites have been prepared from alkylammonium exchanged fluorohectorite clays. These nanocomposites have usually large and regular basal spacings up to 105 {angstrom} platelet separation. The extra large separation of the clay nanolayers results in reinforcement of the polymer matrix, the reinforcing effect being comparable to that of disordered phased nanocomposites. It is now possible to define two general classes of exfoliated clay nanocomposites, namely those with long range nanolayer ordering, and those with little or no long range ordering. Long range ordering is indicated by the XRD patterns that have multiple 00l harmonies whereas disordered composites exhibit little or no 00l diffraction. Regardless of the presence of X-ray Bragg diffraction, exfoliated polymer-clay nanocomposites form when adjacent clay nanolayers are separated by a distance that precludes the possibility of interlayer communication through the association of galleries cations.

Mechanism of Clay Tactoid Exfoliation in Epoxy-Clay Nanocomposites

Mechanism of Clay Tactoid Exfoliation in Epoxy-Clay Nanocomposites