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 work probes a hypothesis for predicting a critical stress associated with of environmental stress cracking (ESC). The hypothesis is based on a thermodynamic criterion for localized swelling induced by stress on the polymer. The surface-active liquids chosen for study are oleic acid and dibutyl phthalate and the polymer is polycarbonate (PC). An experimental technique involving contact angle measurements of a sessile drop as a function of stress is used to probe the hypothesis. A new method for measuring contact angle using refraction is also introduced. No significant change in contact angle as function of stress is observed in either system, though the kinetics of craze initiation and inelastic strain at craze initiation do show a shift in response to stress at levels similar to those predicted by the hypothesis.

Evaluating environmental stress cracking thresholds by contact angle measurements

Anisotropy in naturally occurring or synthetic microcellular structures is an important feature for the development of materials with high specific stiffness and strength, in addition to creating materials with unique physical properties. Polymeric foams constitute a broad class of materials that are widely used for their advantages of low density, high specific mechanical properties and high insulative properties. Traditional synthetic routes are slow, energy demanding processes that employ the use of high temperature ovens, freezers, or high-pressure equipment. Herein we present a convenient and energy efficient method to produce anisotropic high performance polymeric foams via rapid radically induced cationic frontal polymerization coupled with chemical blowing agents. The degree of pore orientation and degree of anisotropy are a result of the propagating front working in concert with the foam volume expansion. This paper presents results into FP foam formation to illustrate how changes in boundary conditions and front initiation position affect both the microcellular structure and their resulting physical and mechanical properties. Additionally, results are presented to show how changes in resin formulation, such as the addition of nanoparticles affect both properties as well as the microcellular structure and anisotropy. 

High performance foams and their nanocomposites generated via liquid state frontal polymerization

Upcycling by grafting onto semi-crystalline polymers using supercritical CO2

Frontal polymerization (FP) is a solvent-free, energy-efficient process where a self-propagating polymerization reaction with a characteristic sharp temperature gradient at the front head propagates through the resin to provide the curing conditions. It relies on the enthalpic balance, which spreads the reaction to unreacted resin in the neighborhood. Therefore, the FP is sensitive to the presence of non-reactive volumes, such as boundaries, fillers, or other additives, that retain heat from the front but produce no enthalpy in return. On the other hand, the front's high temperature could be used to initiate other processes, such as foaming, incorporating them into a simple single-step fabrication procedure. This study used silica particles of two different sizes (14 nm and 200-300 nm) in an epoxy-based FP foam as a representative filler to probe the constraints imposed by non-reactive additives. The presence of particles visibly hindered the front propagation, increased the foam density and even corrupted the frontal regime in some cases. We show that preheating or chemical composition changes are viable approaches to address the fillers' adverse effects. Furthermore, we present evidence that the reduced reaction enthalpy caused by silica nanoparticles, was balanced by the lower heat capacity of our model system. At the same time, the front hindrance was attributed to changes in reaction kinetics and the heat distribution around the front. These results set up essential narratives for the design and practical applications of frontally polymerized foams with non-reactive fillers.

/pdf/frontally-polymerized-foams-thermodynamic-and-kinetical-21r6f7jw.pdf

Frontally polymerized foams: thermodynamic and kinetical aspects of front hindrance by particles.

Disclosed herein is a method comprising masticating a molten polymer; where the polymer is semicrystalline polymer prior to melting; where the masticating polymer is conducted at an elevated temperature of Tm−15K to Tm+90K; where Tm is the crystalline melting point of the polymer; masticating the molten polymer while it is cooled from the elevated temperature to a temperature of Ta; where Ta is a temperature that is greater than Tc−10K, where Tc is the crystallization temperature of the polymer; and masticating the polymer at the temperature of Ta for a time period of 0.1 to 50 minutes.

Alan J. Lesser

Papers

Evaluating environmental stress cracking thresholds by contact angle measurements

High performance foams and their nanocomposites generated via liquid state frontal polymerization

Upcycling by grafting onto semi-crystalline polymers using supercritical CO2

Frontally polymerized foams: thermodynamic and kinetical aspects of front hindrance by particles.

Semi-crystalline thermoplastic polymers and articles manufactured therefrom