All issues / Volume 6 (2012) / Issue 4 (April)
This is an editorial article. It has no abstract.
Rubber composite fibers containing silver nanoparticles with high morphological stability were prepared through combination of electrospinning and in-situ chemical crosslinking. The composite fibers included those of Ag/polybutadiene rubber (BR), Ag/polyisobutylene-isoprene rubber (IIR), and Ag/silicon rubber (SiR). During the study, Ag nanoparticles (Ag NPs) were first generated through reducing the Ag+ ions in rubber/N,N-dimethyformamide/tetrahydrofuran solutions upon ultraviolet-irradiation; subsequently, rubber composite fibers with uniform diameters from hundreds of nanometers to several micrometers were made by electrospinning the above solutions. The electrospinning was carried out with in-situ chemical crosslinking. The results indicated that chemical crosslinking during (and shortly after) electrospinning was able to improve substantially the morphological stability of rubber fibers. As indicated by the results acquired from UV absorption spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscope, Ag nanoparticles with sizes of 10~20 nm were uniformly dispersed in rubber fibers. It was believed that, in addition to the protection of polyvinyl pyrrolidone, a rapid solvent evaporation and limited motion space for a very fine fiber during electrospinning could prevent/mitigate the aggregation of Ag NPs, resulting in a very uniform dispersion. The electrospun Ag NPs/BR composite fibers made of the solution containing very low loading amount (3 wt%) of AgNO3 demonstrated strong antimicrobial activity.
Mechanical properties and drug release behavior were studied for three biodegradable polyester matrices (polycaprolactone, poly(nonamethylene azelate) and the copolymer derived from 1,9-nonanediol and an equimolar mixture of azelaic and pimelic acids) reinforced with polylactide (PLA) fibers. Electrospinning was used to produce suitable mats constituted by fibers of different diameters (i.e. from micro- to nanoscale) and a homogeneous dispersion of a representative hydrophobic drug (i.e. triclosan). Fabrics were prepared by a molding process, which allowed cold crystallization of PLA micro/nanofibers and hot crystallization of the polyester matrices. The orientation of PLA molecules during electrospinning favored the crystallization process, which was slightly enhanced when the diameter decreased. Incorporation of PLA micro/nanofibers led to a significant increase in the elastic modulus and tensile strength, and in general to a decrease in the strain at break. The brittle fracture was clearer when high molecular weight samples with high plastic deformation were employed. Large differences in the release behavior were detected depending on the loading process, fiber diameter size and hydrophobicity of the polyester matrix. The release of samples with the drug only loaded into the reinforcing fibers was initially fast and then became slow and sustained, resulting in longer lasting antimicrobial activity. Biocompatibility of all samples studied was demonstrated by adhesion and proliferation assays using HEp-2 cell cultures.
Chemically derivatized graphene/poly(vinyl alcohol) (PVA) nanocomposites were successfully fabricated by combination of solution processing and compression molding. SEM imaging combined with XRD measurements revealed that graphene platelets were fully incorporated into the polymer matrix after their chemical modification through adsorption of amphiphilic copolymer. The chemical functionalities onto the graphitic surface prevented particle aggregation and provided compatibility with the polymer matrix. Thermogravimetric analysis demonstrated enhanced thermal stability for the composites containing modified graphenes at loading above 1 wt%. Differential scanning calorimetry thermograms showed that graphene nanoplatelets induced the crystallization of matrix with optimum loading at 2 wt%. Dielectric spectroscopy measurements showed enhanced electrical permittivity for the graphene oxide/PVA system, compared to the one of graphene/copolymer/PVA. This could be attributed to the formation of an insulating coating between graphite inclusions and PVA because of the presence of the copolymer.
In this paper a bio-based epoxy with outstanding thermal and mechanical properties was synthesized using a rosin-based epoxy monomer and a rosin-based curing agent. The chemical structures of rosin based epoxy monomer and curing agent were confirmed by Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FT-IR) spectra. The flexural mechanical and dynamic mechanical properties as well as thermal stability of the cured epoxy were investigated. The results showed that the cured epoxy exhibited a glass transition temperature (Tg) of 164°C and its flexural strength and modulus were as high as 70 and 2200 MPa, respectively. This indicated that a wholly bio-based epoxy resin possessing high performance was successfully obtained.
Graphene oxide coated silica hybirds (SiO2-GO) were fabricated through electrostatic assembly in this work, then blended with poly(vinylidene fluoride) (PVDF) by solution mixing to make PVDF nanocomposites. The interfacial interaction was investigated by scanning electron microscopy (SEM), polarized optical microscopy (POM) and Fourier transform infrared spectroscopy (FTIR). The results showed that the interfacial interaction was enhanced by adding of SiO2-GO and strong hydrogen bonds were observed. The as-made nanocomposites were investigated using standard tensile test and dynamic mechanical analysis (DMA) measurements, mechanical properties of PVDF with SiO2-GO hybrids showed limited improvement.
New fully aromatic poly(phosphazene-aryl amides) were prepared by polycondensation reaction of our synthesized aromatic diamine: 1,1,3,5-tetraphenoxy-4,6-bis(4-aminophenoxy)oligocyclotriphosphazene (monomer 1) with terephthaloyl dichloride. Their chemical structure and composition were characterized by elemental analysis, 1H and 31P NMR (Nuclear Magnetic Resonance), and FT-IR (Fourier transform infrared) spectroscopy, whereas their thermal degradation properties were determined by DSC (Differential Scanning Calorimetry) and TGA (Thermal Gravimertic Analysis) techniques. The solid residues of all samples were analysed by FT-IR and SEM (Scanning Electron Microscopy). Compared to conventional PPTA (poly(p-phenylene terephthamide)), PPAA (poly(phosphazene-aryl amide)) shows excellent thermal stability and solubility in polar protic solvents. All poly(phosphazene-aryl amides) show two thermal degradation in the temperature range 150–600°C. The monomer 1, due to its structure, shows the first maximum rate of thermal decomposition temperature around 150–350°C, which may be due to the decomposition of the P–O–C bone. Morphology of the solid residues by Scanning Electron Microscope exhibit that the granular of the solid residues gradual disappearance with the increase of monomer 1 content. The surface layer of PPAA solid residues has been grumous, for the syneresis of P–O–P took place.
Carbon/polymerized cyclic butylene terephthalate (pCBT) composites were prepared through a modified film stacking technique. Three crystalline morphologies of carbon/pCBT composites were obtained at different crystallization temperatures. Tensile, flexural, short beam shear and impact tests were conducted. The low crystallinity carbon/pCBT samples were crystallized at 185°C with spherulitic structure which leads to form the large area spherulite/transcrystalline boundary regions. Consequently, the crack initiated and propagated along with ‘weak’ spherulite/transcrystalline boundary regions, which were resulted low mechanical properties. Carbon/pCBT sample crystallized at 210°C with high crystallinity and highly disordered spherulitic crystallites without spherulite/transcrystalline boundary lines or boundary crystals exhibits the highest mechanical properties.
Composites based on resorcinol formaldehyde latex (RFL) coated aramid short fiber and a polyolefin based thermoplastic elastomer, namely ethylene octene copolymer (EOC) were prepared by melt mixing technique. The effects of both fiber loading and its length on the mechanical and thermal characteristics of the composite under natural and sheared conditions were investigated. Both the low strain modulus and Young’s modulus were increased as a function of fiber loading and length. However, thermal stability of the composite was found to enhance with increase in fiber loading and was independent of fiber length. Due to poor interfacial interaction between the fiber and the matrix and the formation of fiber aggregation especially with 6 mm fiber at high loading, the elongation and toughness of the composite were found to decrease drastically. In order to solve this problem, a maleic anhydride adducted polybutadiene (MA-g-PB) was applied on the aramid fiber. The improvements in tensile strength, elongation at break, toughness to stiffness balance and a good quality of fiber dispersion especially with 6 mm short fiber were achieved. These results indicate the potential use of maleic anhydride adducted PB as a multifunctional interface modifying coupling agent for the aramid short fiber reinforced polymers to enhance the mechanical properties as well as fiber dispersion. FTIR analyses of the treated fiber and SEM analyses of the tensile fractured surfaces of the composite strongly support and explain these results.