Effect of clay modification on the mechanism of local deformations in PA6 nanocomposites

in Macromolecular Materials and Engineering (2012)

PA nanocomposites are prepared from clays organophilized with a phosphonium and an ammonium salt, and sodium montmorillonite is used as reference. The analysis of mechanical and micromechanical properties ... [more ▼]

PA nanocomposites are prepared from clays organophilized with a phosphonium and an ammonium salt, and sodium montmorillonite is used as reference. The analysis of mechanical and micromechanical properties of the composites reveal that several micromechanical deformation processes occur in the PA/MMT composites. The matrix cavitates at relatively small stress. Processes related to non-exfoliated clay structural units are initiated at larger stresses. Sound is emitted mainly by the fracture of particles, but debonding may also occur. The plastic deformation of the matrix dominates at larger stresses and deformations. The various local deformations are independent of each other and composite properties are not determined by silicate related processes but by the deformation of the matrix. [less ▲]

Effect of silica-coated poly(butyl methacrylate)-block-poly(methyl methacrylate) double-shell particles on the mechanical properties of PMMA composites

in Macromolecular Materials and Engineering (2012), 297(9), 887-893

Silica nanoparticles with average diameters of 12nm are grafted with PBMA-b-PMMA double shells through typical ATRP from a Si12-g-(PBMA)Br macroinitiator using 2-BriB as the initiator. A commercially ... [more ▼]

Silica nanoparticles with average diameters of 12nm are grafted with PBMA-b-PMMA double shells through typical ATRP from a Si12-g-(PBMA)Br macroinitiator using 2-BriB as the initiator. A commercially available PMMA homopolymer is used for the preparation of composites with unmodified, silane-modified and double-shell-modified silica particles. Good mechanical properties are obtained for silica double shell containing systems. The silica content in double shell particle systems is varied from 0 to 2.5 wt%. A significant improvement in impact properties is observed. The surface-modified silica particles are characterized by ATR-FTIR, NMR, GPC, and thermal analysis. TEM analysis is used to analyze the nature of dispersion of particles in the composites. [less ▲]

Crosslinking of star-shape PCLs through Diels-Alder reactions for the preparation of shape memory polymers

Poster (2012, May 10)

Poly(ε-caprolactone) (PCL), a semi-crystalline polymer, is one of the most widely studied polymers for the development of shape memory materials when chemically cross-linked. PCL presents several ... [more ▼]

Poly(ε-caprolactone) (PCL), a semi-crystalline polymer, is one of the most widely studied polymers for the development of shape memory materials when chemically cross-linked. PCL presents several advantages such as a melting transition temperature close to human body temperature, a high biocompatibility and is (bio)degradable. So, this polymer is highly relevant for both biomedical devices such as stents or resorbable suture wires and also for degradable packaging. However, after cross-linking, the material can not be reprocessed, preventing any reuse/recycling of the material. One of the purposes of this work is to find a solution to this major drawback, which would then allow, for example, to reshape packaging films after use or to recycle trimmings remaining after fabrication. Amongst current trends in the design of new polymer and composite materials, the use of organic reactions that are able to create and reversibly disrupt chemical bonds upon an external stimulus (temperature, irradiation,…) is currently gaining more and more attention as it can lead to applications in various areas such as remendable materials, drug delivery systems, stimulus-degrading materials or recyclable materials. This contribution aims at reporting a new concept for the preparation of well defined and recyclable PCL based reversibly cross-linked shape memory polymer by the formation of reversible carbon-carbon bonds. Amongst all the reversible links described in the literature, thermally (4+2) reversible cycloadditions present interesting features such as the creation of robust bonds and well defined reversibility conditions. As an example, the application of furan/maleimide adducts as covalent link, which cycloreversion is largely favored in the range of temperature (90-120°C), is widely reported. For this purpose, commercially-available star-shaped PCL precursors have been selected and selectively modified at their chain ends either by a diene (furan, anthracene) or a dienophile (maleimide). Typically, PCL-based shape memory materials have been prepared by mixing a stoichiometric amount of diene-bearing and maleimide-bearing PCLs in a twin-screw mini-extruder at a temperature which favors cycloreversion. The polymer blend is then cured at 65°C (just above PCL melting temperature), with the purpose to increase chains mobility and improve the formation of the adducts. Cross-linked PCLs were obtained, as evidenced by swelling experiments. The shape memory properties of the materials have been studied by cyclic tensile thermomechanical analysis. The influence of the nature of the Diels-Alder moieties on the cross-linking rate and on the shape memory properties has been studied. Reversibility of the network formation in the case of furan, used as diene, has been assessed by rheology and by recycling experiment. [less ▲]

Process for preparing electromagnetic interference shileding materials

Patent (2012)

The present invention relates to a process for preparing an electromagnetic interference shielding material, or a precursor thereof, comprising a first polymer matrix and carbon conductive loads, said ... [more ▼]

The present invention relates to a process for preparing an electromagnetic interference shielding material, or a precursor thereof, comprising a first polymer matrix and carbon conductive loads, said process comprises the steps of: (a) Forming a reaction mixture comprising carbon conductive loads and a polymerizable medium said polymerizable medium comprising one or more monomers dissolved in a solvent, (b) Exposing the reaction mixture to polymerization conditions to polymerize said polymerizable medium and thus form a polymer, and (c) Forming a precipitate or an agglomerate of an electromagnetic interference shielding material made of less than 50 wt.% carbon conductive loads dispersed in the first polymer matrix formed in step (b), characterized in that, said polymer is insoluble in said solvent and in that a fraction of the polymer chains thus formed are grafted on part of the surface of the carbon conductive loads. [less ▲]

Multifunctional poly( ε-caprolactone)-forming networks by Diels–Alder cycloaddition: effect of the adduct on the shape-memory properties

in Macromolecular Chemistry and Physics (2012), 213(2), 187-197

Star-shaped poly(e-caprolactone)s are functionalized by various dienes (furan and anthracene) and a dienophile (maleimide), and the kinetics of network formation by melt-blending is compared for both ... [more ▼]

Star-shaped poly(e-caprolactone)s are functionalized by various dienes (furan and anthracene) and a dienophile (maleimide), and the kinetics of network formation by melt-blending is compared for both Diels–Alder adducts. When curing at 60 °C, the anthracene–maleimide network forms more rapidly and gives rise to a more crosslinked material than with the furan–maleimide adduct. Shape-memory properties of the networks are compared in terms of Diels–Alder adduct stability. Both materials exhibit excellent fixity and recovery ratios, but the relatively low retro Diels–Alder temperature of the furan–maleimide adduct perturbs the mechanical stability of the network during cyclic tensile testing between 0 and 60 °C, whereas the anthracene–maleimide adduct is shown to be stable up to 150 °C. [less ▲]

Thermo-reversible reactions for the preparation of smart materials: recyclable covalently-crosslinked shape memory polymers

in Macromolecular Symposia (2011), 309/310(1), 154-161

[4+2] thermoreversible Diels-Alder cycloaddition has been used to crosslink star-shaped poly(ε-caprolactone) in order to produce networks based on strong carbon-carbon covalent bondings. Depending on the ... [more ▼]

[4+2] thermoreversible Diels-Alder cycloaddition has been used to crosslink star-shaped poly(ε-caprolactone) in order to produce networks based on strong carbon-carbon covalent bondings. Depending on the nature of the Diels-Alder reactants, these bonds can be thermoreversibly broken, allowing re-processing of the polymer matrix. [less ▲]

Morphology and mechanical properties of bisphenol A polycarbonate/poly(styrene-co-acrylonitrile) blends based clay nanocomposites

in Composites Science & Technology (2011), 71(16), 1893-1897

Two organic modified clays (Cloisite®30B (CL30B) and PCL/Cloisite®30B masterbatch (MB30B)) were used to improve the mechanical properties of polycarbonate (PC)/poly (styrene-co-acrylonitrile) (SAN) blends ... [more ▼]

Two organic modified clays (Cloisite®30B (CL30B) and PCL/Cloisite®30B masterbatch (MB30B)) were used to improve the mechanical properties of polycarbonate (PC)/poly (styrene-co-acrylonitrile) (SAN) blends. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurements of the melt blended nanocomposites revealed that partially exfoliated and partially degraded structure was obtained and the clay platelets were located mostly in the SAN phase and at the two-phase boundary. Dispersion of the clay platelets is better when MB30B were used. The mechanical properties of the clays filled nanocomposites vary accordingly and when MB30B is used better mechanical properties can be achieved. Tensile strength increases 41% at maximum as the CL30B loading is 5 wt.%, while elongation at break decreases dramatically. Impact strength can be improved up to 430% compared to the pure blend when 1 wt.% MB30B was used. [less ▲]

PMMA/ carbon nanotube nanocomposite foams for EMI shielding application

Conference (2011, August 30)

Thermoreversibly crosslinked poly(ε-caprolactone) as recyclable shape-memory polymer network

in Macromolecular Rapid Communications (2011), 32(16), 1264-1269

A new concept to build shape memory polymers (SMP) combining outstanding fixity and recovery ratios (both above 99% after only one training cycle) typical of chemically crosslinked SMPs with ... [more ▼]

A new concept to build shape memory polymers (SMP) combining outstanding fixity and recovery ratios (both above 99% after only one training cycle) typical of chemically crosslinked SMPs with reprocessability restricted to physically crosslinked SMPs is demonstrated by covalently bonding, through thermoreversible Diels–Alder (DA) adducts, star-shaped poly(epsilon-caprolactones) (PCL) end-functionalized by furan and maleimide moieties. A PCL network is easily prepared by melt-blending complementary end-functional star polymers in retro DA regime, then by curing at lower temperature to favour the DA cycloaddition. Such covalent network can be reprocessed when heated again at the retro DA temperature. The resulting SMP shows still excellent shape memory properties attesting for its good recyclability. [less ▲]

Locating carbon nanotubes (CNTS) at the surface of polymer microspheres using poly(vVinyl alcohol)-grafted CNTS as dispersion co-stabilizers

Poster (2011, June 30)