It is particularly difficult to prepare a foam CPC material because its porous structure makes it hard to form a conductive network. We utilized acetone‐assisted dispersion to disperse CNTs into PU foam and successfully prepared a lightweight conductive CNT/assembled PU foam composite. The NTC effect, which exclusively exists in the melt state CPC materials, has unexpectedly been observed in the solid‐state lightweight conductive CNT/sPU composite. Higher gas fraction and lower matrix modulus could result in stronger NTC effect. The mechanism that thermal expansion of gas wrapped in the cellular structure induces more perfect conductive paths has been proposed to satisfactorily elucidate the NTC effect and its gas fraction and matrix modulus dependence.
Orthopedic‐grade PMMA bone cement, admixed with prophylactic antibiotics, is widely used in hip and knee replacement surgery. There is a critical need to improve its structural integrity and to control antibiotic release. In this study, clay nanotubes are loaded with the antibiotic gentamicin sulfate and the cement is doped with 5–8 wt% nanotubes. The halloysite nanotubes isolate the drug from the cement monomers and serve as nanocontainers for sustained release of the antibiotic. Gentamicin‐loaded clay nanotubes admixed in PMMA cement provide sustained release up to 300–400 h and with enhanced release at cement cracks. The PMMA/halloysite/gentamicin composite tensile strength does not deteriorate as compared with pure cement and its adhesion to bone is significantly increased.
A new, nickel‐coated graphite resistance‐change‐based method for gel‐point determination for epoxy‐based thermoset resins is presented and compared with DSC and rheological methods. Gelation times determined by this new method are in very good agreement with conventional techniques; this new method is potentially simpler and less time consuming than existing ones.
Novel fluoroalkyl end‐capped oligomer/hydroxyapatite nanocomposites have been easily prepared by the reaction of disodium hydrogenphosphate and calcium chloride in the presence of self‐assembled molecular aggregates formed by fluoroalkyl end‐capped oligomers in aqueous media. The fluorinated hydroxyapatite nanocomposites thus obtained were found to exhibit a good dispersibility in a variety of media, and were applied to the surface modification of glass.
The timescale at which ductile failure occurs in loaded glassy polymers can be successfully predicted using the engineering approach presented in a previous publication. In this paper the influence of progressive physical ageing on the plastic deformation behaviour of unplasticised poly(vinyl chloride) (uPVC) is characterised and incorporated in the existing approach. With the modification it is possible to quantitatively predict long‐term failures which show a so‐called endurance limit. The predictions are compared with failure data of uPVC specimens which were subjected to constant or dynamic loads. In dynamic loading conditions a second type of failure mode was observed: fatigue crack growth. A brief study on the influence of the frequency and stress ratio of the applied stress signal shows that crack growth failure is not expected to occur within experimentally reasonable timescales for constant loading conditions.
Temperature‐responsive PVCL homopolymers and functional PVCL polymers containing carboxylic acids are prepared in organic and aqueous solutions. PVCL bulk polymers are characterized using 1H NMR, photometry, ATR‐FTIR, and thermal analysis. A finite phase transition at 37–40 °C occurs in aqueous solutions of PVCL and PVCL‐COOH. PVCL and PVCL‐COOH polymers are electrospun into fibers ranging from 100 to 2300 nm in diameter. PVCL/cellulose bi‐component films are obtained by electrospinning of CA and PVCL followed by alkaline hydrolysis. These tunable thermo‐responsive PVCL/cellulose nanofibers have potential applications in developing affinity membranes.
This paper demonstrates how the electric‐field‐assisted thermal annealing of octadecylamine‐functionalized SWNT/PMMA films induces an increase in the composite transversal conductivity of several orders of magnitude and a decrease in the lateral conductivity. This difference has been rationalized in terms of the nanotube alignment into the polymer matrix along the electric field direction. This result provides an initial understanding of how electric fields can be used to control the bulk physical properties of such nanocomposites.
Lipase‐catalyzed polycondensation of two biobased diacids, 1,12‐dodecanedioic acid and 1,14‐tetradecanedioic acid, with 1,8‐octanediol was achieved using immobilized Lipase B from Candida antarctica. The procedure resulted in partially renewable prepolymers, while poly(octylene adipate) from petroleum‐based adipic acid was also synthesized for comparison reasons, revealing a dependence of the enzymatic polymerization degree on monomer composition. The prepolymers were further submitted to bulk postpolymerization at temperatures in the vicinity of their melting point under flowing nitrogen. The intrinsic viscosity increase was found up to 12%, with no significant impact on the polyesters thermal properties.
A facile and easily industrialized approach for preparing highly dispersed MMT/polymer nanocomposites is developed by combining the latex compounding method and a spray‐drying process. Clay particles are successfully delaminated into layers, and layer re‐stacking is effectively prevented. HR‐TEM and XRD results confirm that MMT layers achieve exfoliated or nearly exfoliated dispersion in both MMT/styrene‐butadiene rubber and MMT/PS nanocomposites. Compared with melt‐blended MMT/SBR composites, MMT/SBR nanocomposites prepared by this new strategy exhibit extremely high dynamic modulus.
Cellulose microfibers were modified with two different bi‐functional monomers. Composites of EVA copolymer with modified and unmodified cellulose were prepared by melt mixing. The samples were analyzed by SEM, XRD, FT‐IR, DSC, TGA, DMTA and tensile mechanical tests. SEM showed that the presence of reactive groups on cellulose surface enhanced the compatibility, improving the fiber/matrix interfacial adhesion. FT‐IR disclosed the occurrence of chemical reactions between the functionalized cellulose and polymer chains. The incorporation of fibers affected the crystallization behaviour and crystallinity of the polymer matrix. Composites with GMA modified cellulose displayed better compatibility, higher thermal and mechanical properties.
The influence of the flow history experienced during injection molding on the mechanical properties of amorphous polymers is investigated. It is demonstrated that flow‐induced molecular orientation only causes a small anisotropic effect on the yield stress, which can be regarded as insignificant with respect to its absolute value. Its influence on the post‐yield strain‐hardening response is also shown to be imperceptible, in contrast to a orientation which is applied during deformation below the glas transition.
A dual‐cure latex is prepared by mixing an amide‐functionalized latex with a latex that has both acetoacetoxy and unsaturated acrylic functionalities. The amide‐functionalized latex provides a thermal cure with the acetoacetoxy groups of the other latex via Michael addition. The partially polymerized triacrylates in the acrylate‐functionalized latex provide active sites for photocuring. Thermoset latex films are prepared by blending amide‐ and acrylate‐functionalized latexes in varying amounts. The effect of the photosensitizer (camphorquinone) concentration on thermal and mechanical properties is studied. The highest tensile modulus and elongation is observed in a 50:50 wt% amide/acrylate‐functionalized latex blend.
Based on an in situ template method, branched phosphazene‐containing nanotubes were synthesized via a controlled two‐step adding technique of acid acceptors. Structural and morphological characterizations of the as‐synthesized products were performed by SEM, TEM, EDX and FTIR. The results showed that the branched nanotubes were had inner and outer diameters of 8 and 50–150 nm, respectively. In addition, a formation mechanism for the nanostructures was proposed.
Novel nanocomposites based on conductive Ag nanoparticles and a self‐assembled polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) block copolymer were investigated. Good confinement of the nanoparticles into polystyrene microphase was achieved by the addition of DT as surfactant. The polymeric matrix kept its hexagonal order packed cylindrical structure up to 7 wt.‐% content of Ag nanoparticles. An electrostatic force microscopy (EFM) analysis of well‐dispersed metal‐organic hybrid Ag/SBS films was used to characterize the electric behavior of the conductive nanocomposites.
The effect of OMLS incorporation on the thermal properties of PET/LCP blends is studied. Pure and OMLS‐modified PET/LCP blends were prepared by melt‐extrusion using twin‐screw extruder. The morphological analyses of PET/LCP blends show that OMLS addition enhances the phase‐separated structure of the pure blend. A detailed study on the thermal properties of the pure and OMLS‐modified PET/LCP blends were carried out by means of DSC in both conventional and modulation modes. Results show a complex melting behaviour comprises of successive melting and re‐crystallisation. Finally, non‐isothermal crystal‐growth kinetics of pure and OMLS‐modified blends were investigated.
A new completely biodegradable shape‐memory elastomer consisting of PLLCA reinforced by in situ PGA fibrillation is described. The manufacturing processes and shape‐memory effects of the composites are discussed. DMA results reveal a strong interface interaction between in situ PGA fibrillation and PLLCA. Compared with the SMP‐based composites that are commonly used, the shape‐memory test shows that in situ PGA fibrillation can improve the recovery properties of PLLCA; in fact, the shape‐recovery rate increases from 80.5 to 93.2%.
Porous cellulose acetate butyrate foams with a bimodal cell size distribution were produced using supercritical carbon dioxide as a blowing agent. It is demonstrated that the cell size distribution is tunable, due to the semi‐crystalline nature of the polymer. The resulting morphology will either be homogeneous or bimodal, depending on the depressurization rate. Mercury intrusion porosimetry shows that the produced cellulose acetate butyrate foams possess an open cellular structure.
A recently developed electrohydrodynamic printing method is described that can be used to create ordered structures and complex patterns using coarse processing needles and two polymeric materials. The results highlight the method's potential for direct 3D writing of biomedical polymers and composites for a variety of biomedical applications.
This review presents the state of the art regarding the improvement of scratch resistance of polymeric coatings. In particular, our attention is focused on the effect of inorganic nanometric fillers on the scratch resistance of organic coatings. Two main strategies are described for the achievement of such nanostructured hybrid organic/inorganic coatings: either a top‐down or a bottom‐up approach.
