Volume 17, Issue 6

Basic paths towards fully green flame retarded kenaf fiber reinforced polylactic acid (K-PLA) biocomposites are compared. Multicomponent flame retardant systems are investigated using an amount of 20 wt% such as Mg(OH) 2 (MH), ammonium polyphosphate (APP) and expandable graphite (EG), and combinations with silicon dioxide or layered silicate (LS) nanofillers. Adding kenaf fibers and flame retardants increases the E modulus up to a factor 2, although no compatibilizer was used at all. Thus, in particular adding EG and MH decreases the strength at maximum elongation, and kenaf fibers, MH, and EG are crucial for reducing the elongation to break. The oxygen index is improved by up to 33 vol% compared to 17 vol% for K-PLA. The HB classification of K-PLA in the UL 94 test is outperformed. All flame retarded biocomposites show somewhat lower thermal stability and increased amounts of residue. MH decreases the fire load significantly, and the greatest reduction in peak heat release rate is obtained for K-PLA/15MH/5LS. Synergistic effects are observed between EG and APP (ratio 2:1) in flammability and fire properties. Synergistic multicomponent systems containing EG and APP, or MH with adjuvants offer a promising route to green flame retarded natural fiber reinforced PLA biocomposites.

Unsaturated polyester resins (UPR) were prepared by the melt condensation method based on adipic acid, o-phthalic anhydride, maleic anhydride and ethylene glycol in the presence of PSS-(2,3-propanediol)propoxy-heptaisobutyl substituted (PSS-POSS) or/and 9 wt% [(6-oxide-6H-dibenz(c,e)(1,2)oxaphosphorin-6-yl)methyl]butanedioic (DDP). We synthesized UPR containing DDP (DDP-UPR) and UPR containing both DDP and PSS-POSS (DDP-PSS-POSS-UPR series). The chemical structures of the modified polyesters were characterized and confirmed by Fourier transform infrared (FTIR) and 31 P nuclear magnetic resonance ( 31 P NMR). The thermal stability and flammability behaviors of UPR were evaluated by thermogravimetric analysis (TGA) and limited oxygen index (LOI) and the vertical burning test. The morphology of residual char of UPR was shown by scanning electron microscopy (SEM). The results indicate that the incorporation of PSS-POSS has little influence on the thermal stability of DDP-UPR, but enhances the flame retardance of DDP-UPR, and when the PSS-POSS content reaches 10 wt%, the DDP-PSS-POSS-UPR has better flame retardance.

The present study deals with the one-pot synthesis of acrylate copolymers/silica latexes through the use of simultaneous radical polymerization of acrylic monomers and a silica sol-gel precursor. In presence of 3-methacryloxypropyltrimethoxysilane (γ-MPS) and 3-aminopropyltriethoxysilane (APTS), compatibility of acrylate chains to the silica species was improved by the chemical bonds as revealed by Fourier transform infrared spectroscopy (FTIR) analysis. Transmission electron microscopy (TEM) demonstrated the successful formation of p(acrylic acid-co-2-ethylhexyl acrylate)/silica nanohybrids with core-shell morphology. The nanohybrids have been used to modify a glassy carbon electrode (GCE). Cyclic voltammetry and electrochemical impedance spectra were utilized to investigate the properties of the modified electrode in a 1.0 m KCl solution that contained 1.0 m m K 4 [Fe(CN) 6 ]/K 3 [Fe(CN) 6 ], and the interface properties of electrode surfaces. The result showed a dramatic decrease in redox activity as compared to the bare GCE electrode. This revealed a slight increase in electron transfer resistance and the conductivity of the copolymer oligomers and silica species in the hybrid nanostructure. All the electrochemical results illustrated that the p(acrylic acid-co- 2-ethylhexyl acrylate)/silica nanohybrids could immobilize the selective analytes on the electrodes, which had electrochemical catalytic activity. The barrier properties of the hybrid films were also examined via ultraviolet (UV) absorption capacity of the films. It could be concluded that the adsorption capacity was a function of the silica content and uniform dispersion of the nanoparticles in the resultant films.

A polyterthiophene-titanium oxide (P3T+TiO 2 ) composite material was electrochemically synthesized in dichloromethane-tetrabutylammonium perchlorate CH 2 Cl 2 /TBAP containing a monomer (terthiophene) and semiconductor (TiO 2 ) nanoparticles. The obtained material was characterized using electrochemical methods (cyclic voltammetry and electrochemical impedance spectroscopy) and spectrometry analysis [scanning electron microscopy (SEM), spectrophotometer ultraviolet (UV)-visible, energy dispersive X-ray spectroscopy (EDX) and force atomic microscopy (AFM)]. The effect of TiO 2 nanoparticles on the photoelectrochemical and optical characteristics of P3T composite films was also studied. The results confirmed the presence of TiO 2 nanoparticles in the polyterthiophene matrix. The surface morphology of the (P3T+TiO 2 ) composite films revealed that adding TiO 2 nanoparticles increase the film’s roughness values. The addition of TiO 2 nanoparticles improve the absorbance of P3T composite films. Moreover, the photocurrent of the composite increased with the TiO 2 nanoparticles concentration and showed that this composite material could be used in photoelectrochemical applications such as photovoltaic cells.

Jatropha oil (JO) is an inedible oil mainly used in biodiesel. We have attempted to prepare a JO-based polyesteramide/clay composite using a one-pot, two-step reaction, for application as a protective coating. The aim of the work is to utilize JO for its value-added application by preparing a JO polyesteramide/clay composite, to investigate the potential of the prepared composite as a protective coating, and also to study the effect of loaded clay on the structure, morphology, thermal stability and coating properties of the composite. The formation of composites was confirmed by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and atomic force microscope (AFM) studies. The coating properties were studied by standard physico-mechanical and corrosion resistance tests in corrosive media (3.5 wt% HCl, 3.5 wt% NaCl and tap water). The thermal stability was assessed by differential scanning calorimetry (DSC), thermogravimetric (TGA) and derivative thermogravimetric (DTG) analyses. The coatings showed good physico-mechanical and corrosion resistance performance and can be safely used up to 275°C. The approach paves way towards an alternate value addition to a non-edible oil.

This study demonstrates a simple two-step post-treatment method for improving the thermoelectric power factor of low-cost poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) films. The dry re-dispersible PEDOT:PSS pellets are cost-effective, however, they exhibit extremely low thermoelectric performance. On treating with ethylene glycol followed by hydrazine, the power factor of the PEDOT:PSS films increased from 0.0632±0.0097 μW m −1 K −2 to 13.3±1.5 μW m −1 K −2 . The enhancement might be attributed to the effective removal of the free, non-complexed PSS chains and fine control of the oxidation level of PEDOT by the two-step post-treatment.

Polymer electrolytes composed of an acrylonitrile and polyethylene glycol methacrylate copolymer poly(AN-co-PEGMA) with addition of NaClO 4 are studied by impedance spectroscopy, differential scanning calorimetry (DSC), fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Hexagonal boron nitride (hBN) particles are having increasing interest owing to mechanical properties, thermal stability, chemical stability and good lubrication property. In this study, hBN was used as an inorganic filler. FTIR spectroscopy was used to examine the interactions between the host polymer and both NaClO 4 salt and nano hBN particles. The thermal properties of the composites were studied using TGA and DSC tests. TGA results showed that all the composites membranes were thermally stable till 300°C with one step degradation. Surface morphology of the films was examined with SEM which also reveals the homogeneous dispersion of nano hBN in the polymer matrix. Ionic conductivity was studied with impedance spectroscopy, the results showed that the ionic conductivity increases with increasing PEGMA ratio. ANcoPEGMA 11 20Na (EO:Na ratio=20) sample showed maximum ion conductivity of approximately 3.6×10 −4 S cm −1 at 100°C. This is because ANcoPEGMA 11 20Na has highest percentage of PEGMA and highest number of Na + ion per EO groups.

The present study emphasizes the reinforcement of rigid polyurethane foam (RPUF) by the addition of glass fibers (GFs) for diverse engineering applications. In contrast to the conventional RPUF, the foam developed in this case is castor oil based. The developed reinforced foam was tested for its mechanical properties such as hardness, tensile, flexural and compressive strength and for its morphology. Mechanical properties of the resulted reinforced RPUF were found to be improved with addition of the GF content. The foam density was also observed to be increased with the insertion of GF. The SEM results clearly indicated the decreased cell size in the reinforced RPUF.

A series of azo-based diblock copolymers (DBCs) with various compositions were successfully synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization in anisole with PCAEMA-CTA (macro-CTA), DOPAM (new acrylamide monomer) and AIBN (initiator). Kinetic studies on diblock copolymerization manifested a controlled/living manner with good molecular weight control. Structures and properties of monomers and DBCs were determined by 1 H nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). Liquid crystalline (LC) phases and morphological properties were investigated using optical polarizing microscope (OPM), atomic force microscopy (AFM), scanning electron microscopy (SEM) and small-angle X-ray scattering (SAXS). Experimental results demonstrated that the prepared PCAEMA-CTA and DBCs possessed low polydispersity index (≤1.37). All DBCs revealed sharp endothermic transition peaks corresponding to the smectic-to-nematic phase. DBCs with high azo contents showed batonnet textures of the smectic phase whereas DBCs of low azo segments displayed threaded textures of the nematic phase. DBC with 49 wt% of azo side-chains generated a lamellar compared to DBCs with low azo block (≤41 wt%) or non-azo block (≤38 wt%) which produced hexagonal-type nanostructures. In addition, all DBCs exhibited reversible trans-cis photoisomerization behavior under UV irradiation and dark storage at different intervals of time.