Polymer/layered silicate nanocomposites: a review from preparation to processing

http://staff.ulsu.ru/moliver/ref/polymers/pott11.pdf

Graphene-based polymer nanocomposites

A review on polymer–layered silicate nanocomposites

https://cyberleninka.org/article/n/768408.pdf

Mechanical properties of graphene and graphene-based nanocomposites

Recently, polymer nanocomposites reinforced with lower volume fraction of nanoceramics and carbon nanotubes have attracted steadily growing interest due to their peculiar and fascinating properties as well as their unique applications in commercial sectors. The incorporation of nanoceramics such as layered silicate clays, calcium carbonate or silica nanoparticles arranged on the nanometer scale with a high aspect ratio and/or an extremely large surface area into polymers improves their mechanical performances significantly. The properties of nanocomposites depend greatly on the chemistry of polymer matrices, nature of nanofillers, and the way in which they are prepared. The uniform dispersion of nanofillers in the polymer matrices is a general prerequisite for achieving desired mechanical and physical characteristics. In this review article, current development on the processing, structure, and mechanical properties of polymer nanocomposites reinforced with respective layered silicates, ceramic nanoparticles and carbon nanotubes will be addressed. Particular attention is paid on the structure–property relationship of such novel high-performance polymer nanocomposites.

Structural and mechanical properties of polymer nanocomposites

This is the first of a two-part series investi- gating the degradation mechanisms of PBO fiber and approaches to alleviating degradation and improving fiber properties. Poly-p-phenylenebenzobisoxazole (PBO) fiber is a high strength and modulus fiber with remarkable ther- mal stability. Recent in-service failures of this fiber have revealed that the fiber degrades rapidly in relatively mild environmental conditions of moisture and heat. In this work the mechanisms of degradation due to moisture, the presence of acid, and the effect of radiation from the UV-vis spectrum are investigated. It is found that expo- sure to moisture results in the loosening of the fiber morphology leading to an increase in the number and size of defects. The presence of aqueous acid causes both loosening of the fiber structure and hydrolysis of the oxa- zole ring structure. The effect of UV-vis radiation is pri- marily hydrolysis of the material near the fiber surface with attendant formation of amide linkages. 2006 Wiley

Environmental effects on poly-p-phenylenebenzobisoxazole fibers. I. Mechanisms of degradation

A series of epoxy networks were made with molecular weights between crosslinks, Mc, ranging from 380 to 1790 g mol-1. Resins were cast into thin walled hollow cylinders and tested in stress states ranging from uniaxial compression to biaxial tension. These tests elucidated the effects of stress state, strain rate, and Mc on the yield and fracture response of epoxy networks. Throughout the study, the strain rate along the octahedral shear plane, γoct, was maintained constant independent of stress state, for each failure envelope. The hollow cylinder tests showed that the yield behaviour of epoxy networks can be described by a modified von Mises criterion, τocty=τocty0−μσm where τoctg is the octahedral shear stress at yield, τocty0 is the octahedral shear stress at yield in pure shear, μ is the coefficient of internal friction and Vm is the hydrostatic tensile stress imposed on the sample. Furthermore, these tests showed that changes in γoct and Mc only affect τocty0, while μ remains constant. Standard tensile and compression tests were run to confirm the hollow cylinder result and to test the effect of temperature on the yield and brittle response. Tensile tests showed that changes in Mc only affect the glass transition temperature, Tg, of the materials, and the glassy modulus remained independent of Mc. With regard to the yield strength, changes in Mc cause a shift in the Tg of the materials, and the yield strengths of all the materials collapse together at a constant temperature relative to Tg. Finally, yielding of these epoxies was shown to follow an Eyring type flow model over the range of temperatures and strain rates tested.

Deformation and yield of epoxy networks in constrained states of stress

The non-isothermal crystallization of intercalated poly(trimethylene terephthalate) (PTT)/clay nanocomposites was investigated quantitatively by different methods. Non-isothermal crystallization of pure PTT can be described by the Ozawa equation, but the Ozawa theory is not valid for PTT/clay nanocomposites. The addition of clay into PTT decreases the crystallization half-time while increasing the crystallinity and crystallization rate. The PTT/modified clay nanocomposites, in turn, have a higher crystallization rate parameter, k l/n , and a lower crystallization half-time compared to unmodified clay/PTT composites. The crystallization activation energy, calculated from Kissinger equation, of PTT, PTT/unmodified clay, and PTT/modilied clay composites are 100, 180, and 198-230 kJ.mol -1 respectively. Similarly, the nucleating activities of the unmodified clay and modified clays are 0.73 and 0.51-0.58, respectively. Although the addition of clay increases the crystallization activation energy, the clay still acts as an effective nucleating agent and increases the crystallization rate are crystallinity of PTT. Further, the modified nanoscale clays rate more effective nucleating agents than the unmodified counterpats, and the most effective nucleating concentration of nano-clay is between 1.0-3.0 wt.-%.

Non-isothermal crystallization of Poly(trimethylene terephthalate) (PTT)/clay nanocomposites.

Non-Isothermal Crystallization of Poly(trimethylene terephthalate) (PTT)/Clay Nanocomposites

A series of epoxy networks with controlled molecular weight between crosslinks (MJ was constructed with a difunctional epoxy resin and a mixture of aliphatic amines. The glass transition and yield strengths decreased as M c increased, while the elastic properties were independent of M c , In determining the effect of M c on fracture toughness, the fracture behavior changed from a brittle fracture to a ductile fracture as M c increased. The tests and analyses used to evaluate the fracture energy changed from a linear elastic fracture mechanics approach for brittle failures to an elastic-plastic fracture mechanics approach for ductile failures. The ductile responses also showed an increasing fracture resistance with crack extension. Two popular models were used to describe the fracture energy as a function of yield strength. The analysis showed that a change in fracture energy by a thermally induced change in yield strength was equivalent to a change in fracture energy by a chemically induced change in yield strength. In addition, comparisons between the two models allowed insightful relationships to be drawn.

Alan J. Lesser

Papers

Environmental effects on poly-p-phenylenebenzobisoxazole fibers. I. Mechanisms of degradation

Deformation and yield of epoxy networks in constrained states of stress

Non-isothermal crystallization of Poly(trimethylene terephthalate) (PTT)/clay nanocomposites.

Non-Isothermal Crystallization of Poly(trimethylene terephthalate) (PTT)/Clay Nanocomposites

Brittle to ductile : Fracture toughness mapping on controlled epoxy networks