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Synthetic boehmite alumina (BA) has been incorporated up to 8 wt% in low density polyethylene (LDPE) and high density polyethylene (HDPE), respectively, by melt compounding. The primary nominal particle size of these two BA grades was 40 and 60 nm, respectively. The dispersion of the BA in polyethylene (PE) matrices was investigated by scanning and transmission electron microscopy techniques (SEM and TEM). The thermal (melting and crystallization), thermooxidative (oxidation induction temperature and time), and rheological behaviors of the nanocomposites were determined. It was found that BA is nanoscale dispersed in both LDPE and HDPE without any surface treatment and additional polymeric compatibilizer. BA practically did not influence the thermal (melting and crystallization) and rheological properties of the parent PEs. On the other hand, BA worked as a powerful thermooxidative stabilizer for LDPE, and especially for HDPE nanocomposites.
Cationic polyacrylamide (CPAM) was synthesized by aqueous two-phase polymerization technique using acrylamide (AM) and dimethylaminoethyl methacrylate methyl chloride (DMC) as raw materials, aqueous polyethylene glycol 20000 (PEG 20000) solution as dispersant, 2,2′-azobis(2-amidinopropane) dihydrochloride (V-50) as initiator and poly(dimethylaminoethyl methacrylate methyl chloride) (PDMC) as stabilizer. The polymer was characterized by infrared (IR) spectroscopy, 1H-NMR spectrum and transmission electron microscopy (TEM). The copolymer composition was analyzed. The effect of monomers concentration, PEG 20000 concentration and stabilizer concentration on copolymer were investigated, respectively. The optimum reaction conditions for obtaining a stable CPAM aqueous two-phase system were monomers concentration 8~15%, PEG 20000 concentration 15~25%, and PDMC concentration 0.5~1.5%. Finally, the formation process of copolymer particles was investigated by optical microscope.
Effect of solution-blended poly(styrene-co-acrylonitrile) (SAN) copolymer on crystallization of poly(vinylidene fluoride) (PVDF) was investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). Acrylonitrile segment in SAN copolymer was partially miscible with PVDF. Styrene segment in SAN reduced the copolymer’s polarity and its miscibility with PVDF. FTIR and WAXD tests both showed as-prepared PVDF was mainly β-phase. We employed an index Aβdivided by Xc, suggesting that blended SAN could decrease the content of β-phase of PVDF. By DSC, the smaller content of PVDF made the system more miscible so that the Tg,SAN of pure SAN decreased from 86.6 to 81.6°C of sample PVDF/SAN = 20/80; further increase PVDF to 50/50, the Tg,SAN had a relative increase to be 84.2°C. However, for SAN by melt molding, Tg,SAN increased with the increase of PVDF content, which might be due to the incorporation of SAN into inter-spacing of PVDF lamellae, because PVDF molecular chains had not enough mobility to retreat from the SAN’s embrace and crystallize despite of the exit of SAN.
Electrical conductivity of 150–200 µm thick polysulfone films loaded with 0.05–0.75% w/w multiwall carbon nanotubes was systematically investigated for two types of dispersion states, uniformly dispersed and agglomerated at the micro-scale. The percolation threshold was found at 0.11% and 0.068% w/w for the uniformly dispersed and agglomerated films, respectively. Overall, the conductivity of the films with agglomerated nanotubes was higher than that of the uniformly dispersed ones, with marked differences of 2 to 4 orders of magnitude for carbon nanotubes loadings in the upper vicinity of the percolation threshold (0.1–0.3% w/w). The increased conductivity of the agglomerated state is explained by the increased nanotube-to-nanotube contact after the percolating network has formed, which facilitates electron transfer.
The electric modulus properties of solid polymer electrolyte based on chitosan: AgCF3SO3 from 303 to 393 K have been investigated by using impedance spectroscopy. The shift of the M'' peak spectra with frequeny depends on the dissociation and association of ions. The lowest conductivity relaxation time τσ, was found for the sample with the highest conductivity. The real part of electrical modulus shows that the material is highly capacitive. The asymmetric peak of the imaginary part of electric modulus M'', predicts a non Debye type relaxation. The distribution of relaxation times was indicated by a deformed arc form of Argand plot. The increase of M' and M'' values above 358 K can be attributed to the transformation of silver ions to silver nanoparticles. The complex impedance plots and ultraviolet-visible (UV-vis) absorption spectroscopy indicate the temperature dependent of silver nanoparticles in chitosan-silver triflate solid electrolyte. The formation of silver nanoparticles was confirmed by transmission electron microscopy (TEM). The scaling behavior of M'' spectra shows that the dynamical relaxation processes is temperature independent for aparticular composition. The β exponent value indicate that the conductivity relaxation is highly non exponential.
Although starch foams are well known as biodegradable alternatives to foamed polystyrene, starch-lignin foams have not previously been reported. Lignin is an abundant byproduct of paper manufacture usually burned as fuel for lack of higher-value uses. We have prepared novel starch-kraft lignin foams with a known technique similar to compression molding. Replacing 20% of the starch with lignin has no deleterious effect on density or morphology as indicated by scanning electron microscopy: a thin outer layer of approximately 100 µm encloses a region of cellular structure containing 100–200 µm voids, with the major internal region of the foam consisting of large voids of up to 1 mm in size. Powder X-ray diffraction shows residual structure in both starch and starch-lignin foams. Differential scanning calorimetry displays endothermic transitions in the starch foam but not in the starch-lignin foam, indicating that lignin stabilizes the residual starch structure. Lignin decreases water absorption; diffusion constants for the starch and starch-lignin foams are 2.68•10–6 and 0.80•10–6 cm2/sec, respectively. The flexural strength of the starch-lignin foam is similar to that of foamed polystyrene, the strain at maximum stress is smaller, and the modulus of elasticity is larger.
Polyaspartic acid/silk fibroin/hydroxyapatite (PASP/SF-HA) composites have been synthesized by biomimetic processing. SF solution was mixed with different contents of PASP to prepare the PASP/SF blend membranes. After ethanol treatment and premineralization process, the blend membranes were immersed into 1.5 simulated body fluid (1.5 SBF) for 24 h to induce apatite deposition at 37±0.5°C. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results revealed that a conformation transition of SF occurred after the addition of PASP and ethanol treatment. The FTIR and XRD results also confirmed that the main component of apatite deposition was HA. Scanning electron microscopy (SEM) showed that the content of HA increased with increasing PASP concentration .Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP) results revealed that the Ca/P molar ratio could reach 1.45, which was close to the Ca/P ratio of apatite. It was appropriate to conclude that the increasing content of PASP had a distinct effect on HA deposition in the blend films.