An experimental correlation between the non‐linear behaviour of commercial polyethylene melts in LAOS flow, and the pressure fluctuations associated with melt flow instabilities developed in capillary rheometry are presented. Polyethylene melts with enhanced non‐linear behaviour under LAOS conditions present larger pressure fluctuations during capillary extrusion, and consequently, larger surface distortions on the extrudate. The combination of both methods can be a tool to predict the development of melt flow instabilities in the extrusion process of polyethylene melts, and can elucidate their correlation with material structural properties ( , MWD and topology).
An aqueous dispersion of gold nanoparticles was added to an acrylic resin and UV‐cured. The photopolymerization process was followed by means of real‐time FT‐IR spectroscopy. Nanostructured coatings containing a homogeneous dispersion of gold nanoparticles with an average size range of 20–25 nm were achieved. Macroscopic aggregation during polymerization was avoided due to the rapid initiation and kinetic associated with the photopolymerization technique, which allowed the medium to quickly solidify around the dispersion particles.
The influence of molecular weight and comonomer content on the mechanical properties of several melt‐processable polytetrafluoroethylene (MP PTFE) materials is studied. Additionally, a comparison of mechanical properties including tensile properties and their dependence on environment as well as fatigue life of PTFE, MP PTFE and perfluoroalkoxy copolymer (PFA) is made. PTFE homopolymer and PTFE copolymers exhibit considerably different mechanical properties. The small strain deformation behaviour up to yielding correlates with the degree of crystallinity and comonomer content, whereas the large strain deformation was found to depend on intercrystalline connections, such as tie molecules and chain entanglements. The special role of these elements in determining the fatigue life and sensitivity to environmental stress cracking is also demonstrated.
Epoxy‐networked materials containing N,N'‐dioctadecylimidazolium iodide are prepared by curing a mixture of DGEBA and different ratios of the ionic liquid with MCDEA at high temperature. The presence of ionic liquid results in an increase of the storage modulus and a decrease of the glass transition temperature, as indicated by DMA. Also, the onset curing temperature decreases as the amount of IL increase indicating that IL also takes part on the curing process. DSC and FTIR analyses confirm that the imidazolium‐based ionic liquid is able to promote the crosslink of the epoxy pre‐polymer without the presence of external curing agent.
Toughness enhancement of S‐(S/B)‐S triblock copolymers via a molecular‐weight‐controlled pathway is demonstrated. The post‐yield crack toughness behavior of the triblock copolymers uniquely reveal a brittle‐to‐semiductile‐to‐ductile transition with increasing while keeping the basic molecular architecture fixed. TEM and SAXS investigations indicated three distinct morphologies as a function of χeffN as a consequence of the increase in : (i) a homogeneous structure without phase‐separation, (ii) a weakly segregated structure, and (iii) a lamellar structure. The increase in crack toughness is also reaffirmed from kinetic and strain field analysis studies concerning dynamics of crack growth in block copolymers with high PS content.
MWCNT‐based composites have been successfully synthesized via layer‐by‐layer self‐assembly of crosslinked polyphosphazene nanoparticles on the surface of MWCNTs. The amino‐terminated CNTs were characterized by XPS, FT‐IR spectroscopy, EDS, XRD and TEM. The degree of functionalization could be controlled by simply changing the mass of hexachlorocyclotriphosphazene with 4,4′‐diaminodiphenyl ether. The activity of the surface amino groups was confirmed by the reaction of these groups with HAuCl4. In addition, the effects of the mass of HCCP and ODA ratios on the content of the surface amino groups was also investigated.
scCO2 was used to assist in the preparation of PP/CNT composites. Two types of CNTs were used: MWNTs with and without HDPE coating (cMWNTs). The morphology of the nanocomposites and their mechanical and thermal properties were investigated and compared with samples made by traditional melt compounding. The use of cMWNT leads to better dispersion and properties in melt‐compounded nanocomposites. For systems prepared using scCO2‐assisted mixing, however, better properties were obtained using pristine MWNTs, avoiding the additional costs of nanotube modification. It was also shown that observed improvements in the mechanical properties for these materials were due to a combination of matrix modification and nanotube reinforcement, rather than a reinforcement effect caused solely by MWNTs.
EVA copolymer/organoclay nanocomposites were prepared using melt‐compounding. Organoclays were obtained using wet and semi‐wet modification methods. These methods enable us to obtain organoclays with adequate modifier incorporation, but organoclays with a homogeneous and narrow agglomeration size distribution were obtained only with the wet method. TS and EB were higher for nanocomposites obtained with organoclays prepared using the wet method. Analysis of Limiting Oxygen Index, UL94 test and Cone Calorimeter test showed that the retardant properties of nanocomposites were also influenced by the kind of modifiers and the modification method.
UHMWPE/MWCNT and UHMWPE/GNS composites with a segregated network are prepared. TEM and SEM images indicate that the conducting fillers are distributed on the UHMWPE surface and form a segregated conducting network. The percolation threshold of UHMWPE/GNS composites is ≈0.25 wt% and that of UHMWPE/MWCNT composites is 0.20 wt%. The electrical conductivity of UHMWPE/GNS composites is almost four orders of magnitude lower than that of the UHMWPE/MWCNT composites. For equivalent concentrations of GNS and MWCNT, the composites with hybrid fillers exhibit a lower percolation threshold and a higher conductivity than that with GNS or MWCNT alone. Due to the high strength of the fillers and the segregated network structure, the mechanical properties of the composites first increase and then decrease with increasing filler content.
Novel nanocomposites prepared by melt mixing of MWCNTs in a hot‐melt adhesive PCL‐based polyurethane are investigated. The nucleating effect of MWCNTs and the confinement they cause to polymer chains are considered. The broadening of the glass transition is indicative of a growth of the immobilized amorphous fraction adhered to MWCNTs. In the molten state the formation of a combined polymer/MWCNT network is observed. Practical requisites of hot melt adhesives, such as adequate melting temperature, crystallization degree, and viscosity are preserved when MWCNTs are added. Improvement of strength at room temperature and welding rate during cooling, are observed.
In order to enhance the molecular orientation of electrospun nanofibers, a novel collection technique is proposed and applied to the spinning of polyethylene from high temperature solution. The technique makes use of a parallel‐electrode collector that acts before solidification of the fiber occurs. The resulting multiple‐necking morphology is composed of fine nanofibrils with very small diameter and narrow size distribution. The crystalline orientation of the nanofibrils was analyzed by TED. The formation mechanism of the nanofibrils is discussed. The strong elongational effect of the electric‐field‐induced stretching force in the parallel‐electrode collector is demonstrated by the orientational analysis and by observation of the multiple‐necking morphology.
A novel zirconia polyester nanocomposite is prepared using an in situ approach. Surface‐functionalized zirconia nanoparticles are obtained by attaching 3‐phosphonopropionic acid to the metal oxide. Neat and surface‐covered metal oxide particles are incorporated at the beginning of the polyesterification reaction of isophthalic acid and neopentyl glycol resulting in zirconia/poly(neopentyl isophthalate) (PNI) nanocomposites. TEM shows that the dispersibility of the inorganic filler is improved by covering the zirconia surface with carboxylic acid groups. These results are verified by SAXS. Rheological measurements reveal that the viscosities are increasing compared to pristine PNI at particle loads of 10 wt% (neat zirconia) and 5 wt% (phosphonic‐acid‐capped zirconia), respectively.
A processing method based on stretching of molten polymer nanocomposites was applied to prepare dichroic films. First, dodecanethiol‐capped gold particles were embedded in low density polyethylene. The resulting isotropic films were stretched in the melt under uniaxial loading using an elongational rheometer. The melt elongation technique resulted in reproducible characteristics of the optical properties and can be directly transferred to an industrial scale. The organic coating of the metal particles plays an important role in the generation of the dichroism. A reactive surface (adsorbed perfluorophenyl azide) led to strongly agglomerated particles which obviously did not lead to dichroic films.
Electrically conductive, cationically UV‐cured composites were prepared using exfoliated graphite plates (EGP) with cycloaliphatic epoxy resin and polyalcohol binder system. Exfoliated graphite (EG) was obtained from natural flake graphite through chemical and thermal treatment. Sonication of EG in solvent produced EGP. Characterization of graphite samples by XRD showed structural similarity between original graphite and EGP. UV curing behavior was characterized using photoDSC. Electrical resistivity measurements of the composites as a function of EGP concentration showed that at low filler concentration the binder system can influence the electrical percolation behavior. Some formulations showed electrical percolation at less than 1 vol.‐% of EGP filler.
A detailed finite‐element analysis of possible influences on the stiffness reduction of layered laminates due to tolerable IFF has been carried out and the IFF accumulation has been calculated. It is shown that both the transverse Young modulus and the in‐plane shear modulus are degraded independently with increasing IFF density. The calculations show that the thickness of the layer affected by IFF has only a minor influence on the resulting degradation. In addition, it has been shown that the IFF accumulation can be calculated by applying the Puck criterion on the numerically calculated stresses.
CNT based elastomer‐hybrid‐nanocomposites prepared by melt mixing have been investigated showing promising results in technologically relevant electrical, mechanical, and fracture‐mechanical properties. It is demonstrated that the incorporation of CNT in silica‐filled natural rubber results in a good dispersion of the CNT. The materials show an enhanced mechanical stiffness and tensile strength, an increased modulus, and a high electrical conductivity with quite low amounts of CNT, though the tear resistance under dynamical loading is slightly reduced. Using DMA and dielectric spectra, a better understanding of the conduction mechanism, the polymer/tube interaction, and the filler networking in CNT nanocomposites is achieved.
A difunctional methacrylate oligomer was mixed with a variable amount of a MAPTMS precursor in the presence of both a radical and a cationic photoinitiator. The simultaneous photolysis of both photosensitive molecules upon UV irradiation allowed the single‐step generation of a type‐II polymethacrylate/polysiloxane nanocomposite film. Methacrylate and methoxysilyl conversions during irradiation were efficiently monitored by FTIR spectroscopy. The inorganic structure of the resulting silica‐based hybrid films was characterized using 29Si solid‐state NMR. Finally, the reinforcement ability of the resulting hybrid films was also assessed by using a unique range of characterization techniques: DMA, scratch test, and nanoindentation.
Continuous and uniform yarns of thermoplastic nanofibers were prepared via direct melt extrusion of immiscible blends of thermoplastic polymers with CAB and subsequent extraction removal of CAB. Ratios of thermoplastic/sacrificial polymers, melt viscosity, and interfacial tensions affect the formation of nanofibers. Dominating sacrificing polymer content in the blends and low interfacial tensions between thermoplastic polymer and CAB are two key factors. This fabrication process possesses features of high productivity, versatility of thermoplastics, controllability, and environment friendliness in manufacturing thermoplastic nanofibers.
Copolymers of 3,4‐ethylenedioxythiophene and 3‐methylthiophene have been prepared by recurrent potential pulses using monomer mixtures with various concentration ratios, their properties being compared with those of the corresponding homopolymers. In addition, different technological applications have been tested for the generated copolymers. Results indicate that the properties of the copolymers are closer to those of poly(3,4‐ethylenedioxythiophene) than to those poly(3‐methylthiophene). Furthermore, the ability of the copolymers to store charge and to interact with plasmid DNA suggest that they are very promising materials.
The preparation of nanofibrillar composite (NFC) materials using single‐polymer nanofibrils as starting materials is described. Such a possibility is offered by (i) the concept of polymer/polymer NFCs, which have recently been manufactured and represent a further development in the field of microfibril‐reinforced composites, and (ii) the opportunity to isolate neat nanofibrils through selective dissolving of the second blend component. The resulting nanofibrillar single‐polymer composites are characterized by superior mechanical properties (the tensile modulus and strength are improved up to 350%), competing with glass‐fiber‐reinforced PET.
