Search results for "COMPOSITE"
showing 10 items of 4584 documents
Linear–dendritic block copolymers: The state of the art and exciting perspectives
2011
Concurrent with the rapid development of both dendrimers and hyperbranched polymers, a novel class of block copolymer architectures has emerged from the combination of these dendritic architectures with linear chains, the “linear–dendritic block copolymers” (LDBCs). This review gives a comprehensive summary of the state of the art in this rapidly developing field from pioneering early work to promising recent approaches.The different strategies leading to these hybrid architectures with either perfect dendrimer/dendron building blocks or imperfect, yet more conveniently accessible hyperbranched segments, are reviewed and compared. The consequences of the unusual polymer topology for supramo…
Ferroelectric LC-elastomers
1997
Ferroelectric liquid crystalline elastomers combine the rubber elasticity of polymer networks with liquid crystalline phases and ferroelectric ordering. Ferroelectric switching leads therefore to a deformation of the polymer network and an elastic stress. The coupling between both effccts can be varied by changing the topology of the netpoints.
Nanoscale mechanical characterization of polymers by AFM nanoindentations: Critical approach to the elastic characterization
2006
AFM nanoindentations show a dependence of penetration, i.e., the relative motion between the sample and the tip (indenter), on material elastic properties when using the same load. This elationship becomes visible by using of samples being homogeneous down to the scale of nanoindentation. They were prepared from materials covering a broad range of mechanical behavior: from rubbery networks to glassy and semicrystalline polymers. The elastic modulus can be obtained applying Sneddon’s elastic contact mechanics approach. To do this, some calibrations and instrumental features have to be measured accurately. All the polymers tested show that the contact between the tip and the sample is dominat…
Mechanical relaxation in miscible polymer systems: the glass transition regime in poly(vinylmethylether) (PVME)-cross-polystyrene (PS) semi-interpene…
1990
Abstract Miscible semi-interpenetrating polymer networks (semi-IPN) of varying composition are prepared by crosslinking polystyrene containing few maleic anhydride groups with a diamine in the presence of linear poly(vinylmethylether) (PVME). The resulting PVME-c-P(ScoMA) semi-IPNs are characterized by their thermal and thermomechanical behaviour. Comparison with the corresponding uncrosslinked material proves that weak crosslinking has a negligible effect on the location of the glass transition as measured by d.s.c. Both the Tg data and the temperatures of the loss modulus maximum E″ (at 1 rad/s) show the same non-linear curved composition dependence. Contrary to this the tan δ maximum var…
Improvement of the mechanical properties of photo-oxidized films after recycling
2002
Mechanical recycling of post-consumer plastics gives rise, in most cases, to secondary materials with mechanical properties worse than those of the reclaimed polymer. This is mostly due to the thermomechanical treatment undergone during the melt reprocessing operations. In this work, low density polyethylene films have been photo-oxidized in artificial accelerated ageing conditions and then the brittle films have been melt reprocessed. It is shown that the secondary material, after reprocessing, shows mechanical properties, in particular elongation at break, better than those of the photo-oxidized films. This behaviour has been attributed to the fact that the melt reprocessing has the effec…
Closed-loop recycling. A case study of films for greenhouses
2010
Abstract The degradation undergone by plastic films used for greenhouse coverage is the main cause of the worsening of the processability, of the mechanical properties and of the durability of secondary materials obtained by their recycling. This means that this secondary material cannot be processed to produce films for the same applications (closed-loop recycling). In this work different strategies are proposed to improve the processability, some mechanical properties and the resistance to photo-oxidation of these secondary materials. In particular, homopolymer blends or multilayer films where the secondary material is used in combination with virgin polymer give the best results.
Complete in-plane elastic characterisation under tensile tests of angle-ply laminates composed of polymer-matrix layers
2002
In this paper we present a new strategy to completely characterise the in-plane elastic properties of a large range of angle-ply laminates using only unidirectional tests. We consider laminates having the same number of identical plies in the α and – α directions. This new method uses some preceding results found by Verchery for orthotropic laminates, namely the conditions of existence of a specific direction ω, in which the shear-extension coupling is null. The characterisation of the laminate is then made using the results of three tensile tests: two in the orthotropy axes, and the third one in the ω direction, in order to have always a pure one-dimensional state of stress. We show that …
Composite films of natural clay nanotubes with cellulose and chitosan
2014
Composite films based on cellulose, chitosan and halloysite clay nanotubes were prepared using a solution casting method, which allowed for a uniform distribution of nanotubes within the material and provided control over the morphology of the composite. The mechanical performance of these bio nanocomposites is influenced by humidity and the nanotubes showed a plasticisation effect on the polymeric matrix. The composites of chitosan and halloysite nanotubes (HNTs), with modified hydrophobic inner lumens, resulted in a technique for controlled and sustainable surface cleaning. Lignocellulose wood microfibres modified with HNTs were also produced by a layer-by-layer assembly. The obtained ma…
Strategy for good dispersion of well-defined tetrapods in semiconducting polymer matrices.
2014
The morphology or dispersion control in inorganic/organic hybrid systems is studied, which consist of monodisperse CdSe tetrapods (TPs) with grafted semiconducting block copolymers with excess polymers of the same type. Tetrapod arm-length and amount of polymer loading are varied in order to find the ideal morphology for hybrid solar cells. Additionally, polymers without anchor groups are mixed with the TPs to study the effect of such anchor groups on the hybrid morphology. A numerical model is developed and Monte Carlo simulations to study the basis of compatibility or dispersibility of TPs in polymer matrices are performed. The simulations show that bare TPs tend to form clusters in the m…
Transmission of mechanical energy through polymeric liquid crystals and their blends
1988
Molecular composites, also called polymeric liquid crystals (PLC), are contrasted with the traditional composites; the name heterogeneous composites is proposed for the latter. Advantages of blending PLCs with ordinary engineering polymers are discussed. Results reported for blends of poly(ethylene terepthalate) (PET) with a PLC containing sequences of PET and p-hydroxybenzoic acid (PHB) include thermophysical properties, melt rheology, mechanical properties of solid blends, and scanning electron microscopy of fracture surfaces. A model called the island model was developed to explain the results: One assumes that the lines of force as well as propagating cracks tend to concentrate in the p…