Volume 14, Issue 3

The swelling behavior of biocompatible and biodegradable polymers is important for the delivery and release of cells and drugs in biomedical applications. This study reported the swelling characteristics of photo-cross-linked gelatin methacrylate (GelMa) spherical microgels. Spherical microgels were generated in a microfluidic system consisting of a co-axial flow-focusing device for microdroplet generation and an ultraviolet (UV) irradiation apparatus for polymerization. At a low flow rate ratio (<0.14), the 9 wt.% GelMa spherical microgels were smaller than the 6 wt.% ones. In contrast, at a high flow rate ratio (>0.14), the results were reversed. Overall, a proportional relationship was observed between the flow rate ratio and the droplet size. The increased GelMa concentration improved the mechanical properties and increased the swelling ratios. The possibility of bioencapsulation was demonstrated, with good viability of 3T3 cells encapsulated in the spherical microgels.

Based on the geometries from molecular dynamics simulations and a package compiled by us, the interactions between graphene nanosheet (GNS) and nine types of flexible polymers have been investigated with force field. Both the van der Waals (vdW) interaction and the electrostatic interaction (EI) for two same polymer chains and between a polymer and a GNS were calculated and compared. The effect of cut-off distance was explored. It was found that the cut-off distance plays a significant role in EI energy, but a less important role in vdW energy when the cut-off distance is over 9.5 Å. The reasonable cut-off distances for EI and vdW interactions for simulation are suggested.

In this study, thermally and mechanically stable poly(methyl methacrylate) (PMMA)-based nanocomposites were produced through the reinforcement of electrospun aramid-silica - grafted multi-walled carbon nanotube-based nanofibers (MWCNT-Ar-Si). The multi-walled carbon nanotube was initially modified to prepare an isocyanatopropyltriethoxysilane-grafted MWCNT via the sol-gel route using 3-isocyanatopropyl-triethoxysilane and tetraethoxysilane (TEOS). The silica network was developed and linked to MWCNT by hydrolysis and condensation of TEOS. The said isocyanatopropyltriethoxysilane-grafted MWCNT was electrospun with the aramid solution. The electrospun MWCNT-Ar-Si nanofibers (0.1–1 wt.%) were then reinforced in a PMMA matrix. For comparative analysis, PMMA was also reinforced with 0.1–1 wt.% of aramid nanofibers. The tensile modulus of PMMA/MWCNT-Ar-Si 0.1 was 5.11 GPa, which was increased to 13.1 GPa in PMMA/MWCNT-Ar-Si 1. The 10% decomposition temperature of PMMA/MWCNT-Ar-Si 0.1–1 hybrids was in the range of 479–531°C. The glass transition temperature, determined from the maxima of tan δ data using dynamic mechanical thermal analysis, showed an increase with the filler loading and was maximum (301°C) for PMMA/MWCNT-Ar-Si 1 with 1 wt.% of MWCNT-Ar-Si nanofibers. In contrast, PMMA/Ar 0.1–1 hybrids showed lower values in the thermal and the mechanical profile depicting the combined effect of nanotube and aramid in electrospun nanofibers.

In this work, we reported the synthesis of copolymers of poly(styrene-co-acrylonitrile) via single-electron transfer-living radical polymerization using CCl 4 as an initiator and Zn(0)/2,2′-bipyridine (Bpy)/FeCl 2 as catalyst complexes. The polymerization was carried out at 25°C. The polymerization proceeded in a living fashion based on “nascent” Fe(0) as the source of the transition metal, which was prepared by Zn(0)/FeCl 2 in situ. The kinetic experimental results showed that the copolymerization is first-order kinetics. The molecular weights increased linearly with respect to monomer conversion, and narrow polydispersity index values were obtained. The effect of the molar ratio of [Zn(0)] 0 /[FeCl 2 ] 0 on polymerization was investigated. In addition, the polymerization carried out in different solvents was also investigated. The obtained random copolymer was characterized by 1 H NMR and gel permeation chromatography. The living characteristic was demonstrated by chain extension experiment.

Aluminium diethylphosphinate (AlPi-Et) and inorganic aluminium phosphinate with resorcinol-bis(di-2,6-xylyl phosphate) (AlPi-H+RXP) were compared with each other as commercially available halogen-free flame retardants in poly(butylene terephthalate) (PBT) as well as in glass-fibre-reinforced PBT (PBT/GF). Pyrolysis behaviour and flame retardancy performance are reported in detail. AlPi-H+RXP released phosphine at very low temperatures, which can become a problem during processing. AlPi-Et provided better limiting oxygen index (LOI) values and UL 94 ratings for bulk and PBT/GF than AlPi-H+RXP. Both flame retardants acted via three different flame-retardancy mechanisms in bulk as well as in PBT/GF, namely, flame inhibition, increased amount of char, and a protection effect of the char. AlPi-Et was more efficient in decreasing the total heat evolved of PBT in the cone calorimeter test. AlPi-H+RXP reduced the peak heat release rate of PBT more efficiently than AlPi-Et. An optimum loading of AlPi-Et in PBT/GF was found, which was below the supplier’s recommendation. This loading provides a maximum increase in LOI and a maximum decrease in total heat evolved.

This article highlights the microwave absorption and dielectric attributes of synthesized polyaniline (PAni)-yttrium trioxide (Y 2 O 3 ) composites. Temperature-dependent conductivity measurements were carried out in the temperature range of 300–473 K, which indicates the presence of hopping conduction. The PAni-Y 2 O 3 composites showed semiconductor behavior with the exponential variation of inverse temperature dependence of electrical conductivity. Microwave measurements were carried out in the X-band (8–12 GHz) frequency; the composites exhibit absorption-dominated shielding effectiveness (SE A ) in the range -33 to -35 dB (>99% microwave attenuation) and minimum electromagnetic reflection. The ε ′ and ε ″ values of the composites are in the range of 81.5–97.5 and 80–118.5, respectively. The PAni-Y 2 O 3 composites showed significant improvement in microwave SE and complex permittivity of the composites, indicating the influence of Y 2 O 3 in PAni.

Carbon fibers (CFs) were prepared using low-cost, textile-grade polyacrylonitrile fibers, which were 200% to 400% drawn in a hot water bath at 90°C or/and in a tubular furnace at 180°C. X-ray diffractograms confirmed that the drawing process led to higher crystallinity and molecular orientation. These fibers were stabilized in a convection oven at 25–255°C for 390 min. After stabilization, carbonization was performed to obtain carbon fibers. The tensile strength of CFs without drawing was ∼0.8 GPa; however, CFs with 200% and 200% drawing in a hot water bath at 90°C and in a tubular furnace at 180°C, respectively, showed a tensile strength of ∼1.7 GPa. These results suggest that the drawing process of precursor fibers affected the tensile properties of the resulting CFs significantly.