Volume 54 Issue 3, March 2022

We visualized the spatial inhomogeneity of chain orientation on the submicron scale in high-density polyethylene associated with strain-induced density fluctuations using STXM and USAXS/SAXS/WAXD. Real-space images of the density fluctuations were obtained with STXM at the strain where a butterfly pattern was observed with USAXS. STXM observation also revealed that the chains in the low-density region were more often oriented parallel to the stretching direction than those in the high-density region.

The isothermal crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was evaluated using a range of models namely, Avrami, simplified Hillier, Tobin, Malkin, Urbanovici-Segal, Velisaris-Seferis and Hay. The Hay model was found to generate the best fit, closely followed by the Velisaris-Seferis parallel model, suggesting that primary and secondary crystallization occur concurrently. This work highlights the importance of selecting the most appropriate model for analyzing isothermal crystallization kinetics, especially when high levels of secondary crystallization occur.

We estimated the configurational heat capacity above a glass transition temperature (T_g) of 21 types of polymers for which molecular vibration analysis was already completed. The polymers for which the configurational heat capacity was determined are six types of linear polymers with a carbon backbone, eight types of polyesters, and seven types of poly(oxide)s. As temperature increases, the configurational heat capacity of all polymers decreases. Based on Landau’s theory, the obtained heat capacity can be well reproduced by the power and logarithmic functions.

Photoisomerization of doped azobenzene (AB) caused “photoinduced plasticization” effects such as reductions in the glass transition temperature (T_g) and Young’s modulus of the matrix polymer. The mechanism of the reduction in T_g and Young’s modulus of polycarbonate (PC) was investigated by comparing the two values with the characteristic times of the isomerization reactions. The sum of the characteristic times of trans→cis and cis→trans conversion is related to the repeating isomerization rate. The faster repeating isomerization enhanced the free volume of PC, resulting in the reduction in T_g and Young’s modulus.

The surface glass transition temperature (T_g) of polymer materials is believed to be significantly lower than the bulk value. We prepared a molecularly flat substrate of poly(methyl methacrylate) (PMMA) by thermally imprinting a PMMA plate with mica, on which polystyrene-b-PMMA was deposited by the Langmuir-Blodgett technique in a dilute state, and the thermal stability of the surface was evaluated by in situ high-temperature atomic force microscopy. Both the PMMA chains deposited on the plate and of the surface of the plate started to move close to the bulk PMMA T_g.

In this article, a series of thermo-driven self-healable organic/inorganic nanohybrid polyurethane (WMPUS-x) films were prepared with different addition amount of furfuryl modified silica nanoparticles (furan@SiO₂). The self-healable system was constructed via a DA/retro-DA process among furan@SiO₂ and maleimide-terminated waterborne polyurethane. The results exhibited the addition of furan@SiO₂ enhanced the mechanical behavior of all WPU samples.

A simplified multi-ion network is presented, which can toughen and modulate the spontaneous self-healing capability of dry-solid Zn(II)-carboxylate polyamic acid under ambient conditions.

Novel alcohol-derived degradable acetal-linkage-containing epoxy resins HBA–CHDMVG and HOBA–CHDMVG were synthesized. The thermal decomposition temperature of HOBA–CHDMVG was higher than 300 °C; moreover, HOBA–CHDMVG exhibited excellent Charpy impact strength. The cured HOBA–CHDMVG was completely decomposed during the hydrolysis reaction under acidic conditions, and the reaction products were soluble in a tetrahydrofuran/H₂O mixed solvent. Furthermore, the carbon fibers in the carbon-fiber-reinforced plastic with a HOBA–CHDMVG matrix were recovered via the complete decomposition of HOBA–CHDMVG.

Herein, we synthesize a new organic-inorganic hybrid material by direct coordination of a chain-end-functionalized naphthalene diimide (NDI)-based n-type semiconducting polymer with thiol group(s), PNDI-SH, to lead sulfide quantum dots (PbS-QDs). The synthesized hybrid n-type material, PNDI-SH:PbS-QD (70:30, w-w), was found to show good dispersibility in organic solvents and excellent atmospheric stability even after storage for 8 months. The formation of PbS-QD nanoclusters is confirmed by transmission electron microscopy (TEM) for a PNDI-SH:PbS-QD (70:30, w-w) thin film, which is also supported by ultraviolet-visible-near-infrared (UV-Vis-NIR) absorption spectroscopy.

Poly(vinyl alcohol) (PVA) was crosslinked via catalyst-free solid-state esterification at 120 °C with 2,5-furandicarboxylic acid (FDCA) at concentrations ranging from 1 to 10%. The thermal stability of PVA was improved significantly, especially at low FDCA concentrations of 1 and 5%, where degradation maximums occurred at 354 and 371 °C, respectively, compared to 267 °C for unmodified PVA. A twofold increase in tensile strength for the biodegradable PVA was achieved by crosslinking with 5% FDCA. A twofold increase in tensile strength for the biodegradable PVA was achieved by crosslinking with 5% FDCA.

Molecular dynamics simulation of chitosan and anionic oligosaccharides was conduced to elucidate the formation mechanism and structure of polyion complex (PIC) of polysaccharides. The association of oligosaccharides with scrambled structure indicated that PIC of polysaccharides takes on the structure of “Scrambled egg model”. The formation of hydrogen bond between deprotonated chitosan and anionic oligosaccharides suggested that hydrogen bonds contribute to the stabilization of PIC under neutral condition.

Effect of graphene (rGO), as the secondary filler, in rubber compounds filled with silica was investigated. Scanning electron microscopy showed that silica dispersion was improved in the presence of small quantities of rGO, but it deteriorated at higher loadings of rGO due to the formation of compact hybrid filler network. This morphological development affects dynamic-mechanical properties such that the Payne effect reduces in the presence of low concentrations of rGO. Using these observations, the underlying mechanism was explained based on how rGO hinders silica reagglomeration thermodynamically after the mixing.

The addition of a fibrous nucleating agent (MDBS) significantly enhanced the crystallization temperature of PP with the accelerated crystallization rate, which was barely affected by the applied shear flow. In the case of pure PP, rapid crystallization was detected only after the history at a high shear rate. Furthermore, the shear history enhanced the chain orientation of PP greatly especially for the sample with MDBS, which resulted in a good transparency.

Using a facile method, a gelatin hydrogel with anisotropic gel properties was prepared on a substrate via hydrogelation to induce self-assembly. Three kinds of surface properties (structural control factors) of the template induce the formation of an anisotropic gelatin network by self-assembly. The swelling behavior and mechanical properties of the anisotropic and isotropic gelatin hydrogels are different. When the hydrogel is compressed in a direction perpendicular to the tube-like gelatin network, the inner space of the network is compressed.