Time-resolved shear behavior of end-tethered Nylon 6–clay nanocomposites followed by non-isothermal crystallization

Abstract. Low density polycarbonate foams containing different amounts of graphene nanoplatelets with variable cellular morphologies were prepared using a supercritical carbon dioxide two-step foaming process, which consisted of the dissolution of supercritical CO 2 into moulded foam precursors and their later expansion by double contact restricted foaming. The effects of the processing conditions and graphene content on the cellular morphology of the obtained foams were investigated, showing that the addition of increasingly higher amounts of graphene nanoplatelets resulted in foams with increasingly smaller cell sizes and higher cell densities, due on the one hand to their effectiveness as cell nucleating agents and on the other to their platelet-like geometry, which limited CO 2 loss during foaming due to a barrier effect mechanism. Especially significant was the addition of 5 wt% graphene nanoplatelets, as the high concentration of graphene limited CO 2 escape and cell coalescence during expansion, enabling to obtain highly expanded microcellular foams.Keywords: polycarbonate foams, graphene nanoplatelets, supercritical carbon dioxide, two-step foaming.Page 2 of 24 2 IntroductionGraphene-filled polymer foams have recently aroused a great interest in the scientific and industry communities [1][2][3][4], as the incorporation of graphene can dramatically enhance the electrical, physical, mechanical and barrier properties of polymers at extremely low loadings and, as a consequence, extend their potential applications to fields such as electronics, aerospace, automotive, green energy, among others [5]. The use of supercritical carbon dioxide (scCO 2 ) dissolved into a given polymer has become one of the most common strategies used to prepare graphene-filled polymer foams [2][3][4]6]. Carbon dioxide acts as polymer plasticizer, decreasing its glass transition temperature and facilitating expansion due to decreased polymer viscosity [7], in some cases even leading to cell coalescence and as a result to a decrease in cell density [8]. Thus, foaming processing conditions play an essential role in the final morphological/microstructural characteristics of the resulting foams. On the other hand, several studies have indicated that a small amount of well-dispersed nanoparticles can act as cell nucleation sites and that nucleation efficiency is dependent on particle size, shape, surface properties and dispersion quality [2,4,9]. In addition, it has been shown that the combination of graphene nanoplatelets and scCO 2 during foaming may have remarkable effects on the microstructure of the developed foams [10].It is known that polymer foaming using carbon dioxide in supercritical conditions can be done in one [11][12] Experimental Compounding and moulding of foam precursorsPolycarbonate (Lexan-123R-PC), supplied by Sabic in the form of pellets, with a density of 1.2 g/cm 3 and melt flow index (MFI) of 17.5 dg/min, measured at 300 ºC and 1.2 kg, was meltcompounded with 0.5 and 5 wt% of graphene nanoplatelets (GnP) using a B...

show abstract

“…It has previously been reported that the stretching of polymer molecules due to shear promotes polymer ordering [22][23][24][25].…”

Section: Influence Of the Heating Time On The Cellular Structurementioning

confidence: 99%

Effects of graphene nanoplatelets on the morphology of polycarbonate–graphene composite foams prepared by supercritical carbon dioxide two-step foaming

Gedler

Antunes

Velasco

2015

The Journal of Supercritical Fluids

View full text Add to dashboard Cite

show abstract

“…However, martensiticlike transformations of the crystalline phase have been observed only in selected polymer-clay combinations. The most well explored examples of this type are the development of γ phase in Nylon 6 at the expense of the α phase in the neat polymer [12,13] and the evolution of β phase instead of the α form in PVDF [14][15][16][17][18][19][20][21][22][23][24]. The latter has a considerable impact in applications where pyroelectric, piezoelectric, ferroelectric or magnetostrictive response is desirable [25], given that the all-trans configuration of β phase imparts a high dipole moment (7.0 10 -30 Cm /repeat unit) due to the alignment of the polar C-F bonds perpendicular to the polymer axis chain.…”

Section: Introductionmentioning

confidence: 99%

Clay nanocomposites based on poly(vinylidene fluoride-co-hexafluoropropylene): Structure and properties

Kelarakis

Hayrapetyan

Ansari

et al. 2010

Polymer

View full text Add to dashboard Cite

The introduction of organically modified clays to poly(vinylidene fluoride-cohexafluoropropylene) matrix promotes an α to β transformation of the crystalline phase in a manner that critically depends upon the nature of the clay surface modifier. In addition, the presence of nanoclay facilitates an energy dissipation mechanism that gives rise to extensive enhancements in mechanical toughness. At ambient and elevated temperatures the dielectric permittivity of nanocomposites dramatically increases compared to the neat polymer. The rheological, mechanical and dielectric properties of hybrids directly reflect the morphological and structural changes induced by clays.2

show abstract

“…In the intermediate region, the clay layers, presumably owing to their higher aspect ratio, still orient parallel to the surface and the nylon 6 crystallites assume an orientation perpendicular to the silicate. Very recently, Medellin-Rodriguez et al 53 reported that the molten N6CN samples showed planar orientation of silicate layers along the flow direction, which is strongly dependent on shear time as well as clay loading, reaching a maximally orienting level after being sheared for 15 2). The edges of the silicate layers laying along the z axis (marked with the arrow (a)) or parallel alignment of the silicate edges to the shear direction (x axis) (marked with the arrow (b)) rather than assumingly random orientation in the nylon 6 matrix is observed, but in fact, these faces in this plane can be seen (Fig.…”

Section: Alignment Of Silicate Layersmentioning

confidence: 99%

“…31 The essential difference between c form and a form is the molecular packing; in the a form, hydrogen bondings are formed between antiparallel chains, while the molecular chains have to twist away from the zigzag planes to form the hydrogen bonds among the parallel chains in c form giving rise to lesser interchain interaction as compared with a form.…”

Section: Flexibility Of Single Clay Layermentioning

confidence: 99%

Recent advances in polymer/layered silicate nanocomposites: An overview from science to technology

Okamoto¹

2006

Materials Science and Technology

140

View full text Add to dashboard Cite

Polymer/layered silicate nanocomposites (PLSNCs) offer remarkably improved mechanical and other properties with low inorganic filler loading. The major development in this field has been carried out over the last one and a half decades. However, the authors are far from the goal in terms of understanding the mechanisms of the enhancement effect in the nanocomposites. Continued progress in nanoscale controlling and an improved understanding of the physicochemical phenomena at the nanometre scale have contributed to the rapid development of novel PLSNCs. The present paper describes recent advances in PLSNCs with the primary focus on these advances from basic science to technology.Keywords: Nanocomposite, Layered silicate Introduction A decade of research has shown that nanostructured materials have the potential to significantly impact growth at every level of the world economy in the twenty-first century. This new class of materials is now being introduced in structural applications, such as gas barrier film, flame retardant product and other load bearing applications (see Table 1). 1Of particular interest is recently developed nanocomposites consisting of a polymer and layered silicate (LS), because they often exhibit remarkably improved mechanical and other properties 2 when compared with pure polymer or conventional composites (both micro and macrocomposites). A primary progress in polymer/ layered silicate nanocomposites (PLSNCs), a nylon 6/LS hybrid 3 reported by Toyota Central Research & Development Co. Inc. (TCRD), was successfully prepared by in situ polymerisation of e-caprolactam in a dispersion of montomorrillonite (MMT). The silicate can be dispersed in liquid monomer or a solution of monomer. It has also been possible to melt and mix polymers with layered silicates, avoiding the use of organic solvents. The latter method permits the use of conventional processing techniques such as injection moulding and extrusion.Continued progress in nanoscale controlling and an improved understanding of the physicochemical phenomena at the nanometre scale have contributed to the rapid development of novel PLSNCs. The present paper describes current research on PLSNCs with the primary focus on recent advances from basic science to technology. Historical point of viewEarlier attempts of preparing polymer/LS composites are found in almost half a century old patent literatures. 4,5 In such cases, incorporation of 40-50 wt-% clay mineral (bentonite, hectorite, etc.) into a polymer was attempted but ended up with unsatisfactory results: the maximal modulus enhancement was only y200%, although the clay loading was as much as 50 wt-%. The failure was obvious, because they failed to achieve good dispersion of clay particles in the matrix, in which silicate minerals existed as agglomerated tactoids. Such a poor dispersion of the silicate particles could improve the material rigidity, but certainly sacrificing the strength, the elongation at break and the toughness of the materials. 4,5 A major reason for this impossibil...

show abstract

Time-resolved shear behavior of end-tethered Nylon 6–clay nanocomposites followed by non-isothermal crystallization

Cited by 108 publications

References 19 publications

Effects of graphene nanoplatelets on the morphology of polycarbonate–graphene composite foams prepared by supercritical carbon dioxide two-step foaming

Effects of graphene nanoplatelets on the morphology of polycarbonate–graphene composite foams prepared by supercritical carbon dioxide two-step foaming

Clay nanocomposites based on poly(vinylidene fluoride-co-hexafluoropropylene): Structure and properties

Recent advances in polymer/layered silicate nanocomposites: An overview from science to technology

Contact Info

Product

Resources

About