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.
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.
A series of hydrogels based on poly(ethylenglycol) methyl ether methacrylate (PEGMEMA) is synthesized using macromonomers of three different molecular weights, in combination with varied degrees of chemical crosslinking. The effects of PEGMEMA, initiator, and crosslinker concentrations on gel yield and swelling properties are studied. In addition, the chemical structure of the gels is characterized by FTIR and solid‐state NMR spectra. The swelling and rheological behaviors of hydrogels as well as protein partitioning into the gels are discussed in terms of the network mesh size. Low protein sorption and bacteria deposition tendencies indicate that PEGMEMA‐based hydrogels could be highly beneficial for uses as fouling‐resistant materials, for instance, as protective coatings for desalination membranes.
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 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 properties of synthetic hydrogels can be tuned to address the needs of many tissue‐culture applications. This work characterizes the swelling and mechanical properties of thiol‐ene crosslinked PEG hydrogels made with varying prepolymer formulations, demonstrating that hydrogels with a compressive modulus exceeding 600 kPa can be formed. The amount of peptide incorporated into the hydrogel is shown to be proportional to the amount of peptide in the prepolymer solution. Cell attachment and spreading on the surface of the peptide‐functionalized hydrogels is demonstrated. Additionally, a method for bonding distinct layers of cured hydrogels is used to create a microfluidic channel.
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.
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.
Low density polyethylene (LDPE) was prepared into micro‐ or submicro‐spheres or nanofibers via melt blending or extrusion of cellulose acetate butyrate (CAB)/LDPE immiscible blends and subsequent removal of the CAB matrix. The sizes of the PE spheres or fibers can be successfully controlled by varying the composition ratio and modifying the interfacial properties of the blends. The surface structures of LDPE micro‐ or submicro‐spheres and nanofibers were analyzed using SEM and FTIR‐ATR spectroscopy. In addition, the crystalline structures of the LDPE nanofibers were characterized.
A simple, easily accessible solvent‐free method for the dispersion of MWCNTs into PET is proposed, based on the preparation of a microparticulate polymer/nanotube masterbatch via cryogenic impact‐milling and its subsequent melt blending with the bulk polymer. Thermal and mechanical properties of nanocomposites prepared using this method were evaluated as a function of nanotube concentration. Thermal stability was improved, and superior crystallization behavior of PET in the nanocomposites was observed. Significant improvements of around 25% in tensile strength and tensile modulus of the nanocomposites was achieved using this strategy, with only 0.25 wt.‐% MWCNT, compared to previous literature data where 1 wt.‐% MWCNT was employed.
An effective approach is presented for designing and tailoring diffusion‐controlled systems for targeted release rate profiles. The diffusion‐controlled system consists of PBA networks with precisely controlled crosslink densities via RAFT copolymerization of BA with ethylene glycol dimethacrylate, which gives a desired diffusivity. One‐dimensional releases in the crosslinked PBA matrix (CPM) slabs are evaluated with a hydrophobic dye. Fick's second law is used to model the transient mass transfers in the CPMs with a mixed Newton‐Tikhonov regularization method for determination of their diffusion coefficients. A two‐layer CPM (CPM‐2) with controlled crosslink densities is constructed. The dye release results from the CPM‐2 agreed well with theoretical predictions.
Bio‐based TPUs from dimer acid‐based polyols are synthesised by using a two‐step prepolymer process including reactive processing. The effect of the polyol on the final chemical structures, morphologies and properties of bio‐based TPUs is evaluated by different analytical techniques. It is observed that the percentage of hard segment (HS) distributed in organised and unorganised phases is a key factor to control the materials properties. DSC reveals that the percentages of HS dispersed in the soft domains are high at low experimental HS contents. Multiscale microscopies show better defined organised structures with increasing HS content in TPUs, highlighting the importance of the distribution between hard and soft segments in the material structure.
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.
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.
This paper describes a novel process that is stretching‐controlled thermal micromolding, to fabricate bionic superhydrophobic polyethylene films. Low‐density polyethylene was thermally pressed in a vacuum oven onto PDMS stamps replicated from lotus leaves. After being cooled and peeled off from the stamps, the polyethylene films with superhydrophobic surface were created, exhibiting a water contact angle of 154.1 ± 3.5° and a rolling angle of ≈7°. SEM imaging showed that the superhydrophobic surface had micro‐papillas much higher than those on the lotus leaf, demonstrating the papillas had been stretched longer from the holes on the stamp during the separating process. This study shows that micromolding is a promising technique for large scale production of superhydrophobic films, even if the holes on the mold are not deep enough.
The fabrication of tissue engineering scaffolds based on the polymerization of crosslinked polylactide using leaching and batch foaming to generate well‐controlled and interconnected biodegradable polymer scaffolds is reported. The scaffold fabrication parameters are studied in relation to the interpore connectivity, pore morphology, and structural stability of the crosslinked PLA scaffold. In vitro cell culture and in vitro degradation are used to analyze the biocompatibility and biodegradability of the scaffolds. The new crosslinked PLA thermoset scaffolds are highly suitable for bone tissue engineering applications due to their complex internal architecture, thermal stability, and biocompatibility.
The fabrication of nanocomposites by organic modification of clay during mixing into NR is reported. NR/OMMT nanocomposites show more intercalation and exfoliation at higher modifier content, increasing the tensile modulus primarily by improved filler reinforcement. Comparison with nominally identical pre‐modified OMMT shows similar microstructures and physical properties. No effect of mixing duration is observed, indicating that modification is rapid. Unlike montmorillonite, unmodified sepiolite disperses well in NR, so organo‐modification improves compatibility but does not affect the nanocomposite microstructure. This means that organo‐sepiolite offers relatively small improvements over sepiolite as a filler for NR.
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.
