Isothermal Crystallization and Melting Behavior of Composites Composed of Poly(L-lactic Acid) and Poly(glycolic Acid) Fibers

Several composites of poly (L-lactic acid) (PLLA) with poly (glycolic acid) (PGA) fibers were prepared. The isothermal crystallization kinetics and melting behavior of PLLA and all of the composites were characterized by using differential scanning calorimetry. The experimental data were processed by using the Avrami equation. The relative parameters, such as the Avrami exponent and half-time crystallization, revealed that PGA fibers had positive effects on the crystallization of PLLA, but these effects had only a minimal dependence on the PGA fiber content. Moreover, at low isothermal crystallization temperatures (85°C～110°C), recrystallization during the heating scan was observed, which could lower the melting point of the samples to a certain extent.     

Some characteristic features of formation of composite material based on KDP single crystal with incorporated Al2O3·nH2O nanoparticles

Composite material based on KDP (KH₂PO₄) crystal matrix with incorporated aluminum oxyhydroxide Al₂O₃·nH₂O nanoparticles is obtained and peculiarities of the formation of KDP:Al₂O₃·nH₂O composite structure are studied by selective etching, optical and scanning electron microscopy. Influence of the nanoparticles on the formation of defect subsystem is analyzed. The obtained material is shown to have a zonal structure with a period independent of the concentration of nanoparticles. By means of FTIR‐spectroscopy, interaction of nanoparticles with KH₂PO₄ solution is studied. A model of the capture of nanoparticles by the {100} KDP crystal face is proposed.     

Active and Passive LC Based Polarization Elements

Passive and active polarization elements were created by surface and bulk photo-alignment of LCs, reactive LCs, photo-sensitive LCP and photo-curable monomer/LC composites. The use of different photo­sensitive liquid crystalline materials for the development of highly anisotropic elements with high spatial resolution and stability or, alternatively, fast switch ability will be discussed. Photo-active and voltage tunable polarization and diffraction elements are presented. For active micro-optic application a photo-addressed patterned retarder was created. Electrically switchable diffraction gratings were generated by interference exposure of photo-curable LC composites at room temperature characterized by droplet free morphology. These polarization sensitive diffraction elements are characterized be excellent optical properties and low switching times.     

High microwave absorption performances for single-walled carbon nanotube–epoxy composites with ultra-low loadings

Microwave-absorbing polymeric composites based on single-walled carbon nanotubes(SWNTs) are fabricated via a simple yet versatile method, and these SWNT–epoxy composites exhibit very impressive microwave absorption performances in a range of 2 GHz–18 GHz. For instance, a maximum absorbing value as high as 28 dB can be achieved for each of these SWNT–epoxy composites(1.3-mm thickness) with only 1 wt% loading of SWNTs, and about 4.8 GHz bandwidth,corresponding to a microwave absorption performance higher than 10 dB, is obtained. Furthermore, such low and appropriate loadings of SWNTs also enhance the mechanical strength of the composite. It is suggested that these remarkable results are mainly attributable to the excellent intrinsic properties of SWNTs and their homogeneous dispersion state in the polymer matrix.     

Pyridyl‐Dicarboxylate Tuned Cadmium(II) Complexes and Their Fluorescence Emission Properties

To investigate the effect of organic anions on coordination frameworks, the complexes [Cd(2, 6‐pydc)(bibix)₂(H₂O)₂]_n ( 1 ) and {[Cd₄(2, 5‐pydc)₄(bibix)₄(H₂O)₄](H₂O)₈}_n ( 2 ) were isolated by the reactions of 1‐{4‐[(1H‐benzoimidazol‐1‐yl)methyl]benzyl}‐1H‐benzoimidazole (bibix) and two distinct pyridyl‐dicarboxylates as organic anions with d¹⁰ metal salts. In the resulting structures, bibix adopts different coordination modes affected by the aromatic anions, which have distinct geometric structure and bonding modes. Thus, complex 1 has a 1D chain structure, whereas complex 2 has a 2D architecture. Both complexes 1 and 2 have a strong fluorescence emission, which may be tentatively assigned to metal‐perturbed intraligand interactions.     

Mechanical and biodegradation performance of short natural fibre polyhydroxybutyrate composites

The work outlined in this paper describes the evaluation of polyhydroxybutyrate (PHB) based natural fibre composites via an extrusion – injection moulding process. Virgin PHB was compounded with two different naturally occuring plant fibres, hemp and jute, and a third, regenerated cellulose fibre, lyocell. Composite materials containing 10–30 wt% of each type of fibre were obtained by twin screw extrusion and the resultant material was injection moulded to produce tensile samples suitable for mechanical characterisation. Mechanical properties were determined using tensile, impact and flexural testing. Melt flow index and water absorption studies were also carried out on the biocomposite materials, and Fourier transform infrared spectroscopy was used to examine the bonding between the polymer and each fibre type. The rate of biodegradation was also observed by placing composite samples in compost and measuring weight loss weekly. The biocomposites produced using this method were shown to have increased rates of biodegradation whilst exhibiting significantly improved flexural properties.     

Effect of electrospun polyamide 6 nanofibres on the mechanical properties of a glass fibre/epoxy composite

Recently, several types of nanoparticles are frequently incorporated in reinforced epoxy resin composites. A homogeneous dispersion of these nanoparticles is still a problem. Thermoplastic nanofibrous structures can tackle this dispersion issue. Therefore, this paper investigated the effect of electrospun polyamide 6 nanofibrous structures on the mechanical properties of a glass fibre/epoxy composite. The nanofibres were incorporated in the glass fibre/epoxy composite as stand-alone interlayered structures and directly spun on the glass fibre reinforcement. Both ways of nanofibre incorporation have no negative effect on the impregnation of the epoxy. Moreover, the nanofibres remain well dispersed within the matrix. Incorporation of nanofibres increases the stress at failure in the 0°-direction, the best results are obtained when the nanofibres are directly electrospun onto the glass fibres. Optical microscopic images also demonstrate that nanofibres prevent delamination when a 90° crack reaches a neighbouring 0° ply. Furthermore, mode I tests showed a small improvement when a thin nanofibrous structure is deposited directly onto the glass fibres. When the composites are loaded under 45°, it is proven that, for an identical stress, the glass fibre composite with deposited nanofibres has less cracks than when interlayered nanofibrous structures are incorporated. Generally, it can be concluded that the addition of polyamide 6 nanofibres improves some mechanical characteristics of a glass fibre/epoxy composite.