Effects of glycerol content on structure and molecular motion in thermoplastic starch-based nanocomposites during long storage.

Thermoplastic starch-based nanocomposites with varying glycerol content and montmorillonite as a nanofiller were studied using dynamic-mechanical analysis (DMA), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) during one-year storage. DMA results showed that starch-rich and glycerol-rich domains were present in the samples and during storage for up to one year the content of the amorphous phase decreased and molecular mobility changed. 13C NMR and XRD measurements confirmed that ordered structures were formed during storage and its content was larger for samples with higher glycerol content and increased with the storage time. The data obtained from deconvolutions of 1H broad line NMR spectra indicate increased overall molecular mobility in the samples up to four months of storage, while after nine months the trends were opposite. Lower free water content compared to the total water content in the samples determined according to deconvoluted 1H MAS (magic-angle spinning) NMR spectra indicated that a part of water molecules was immobilized in the ordered structures.

A Comprehensive Study of Polyurethane Potting Compounds Doped with Magnesium Oxide Nanoparticles.

Recently, polyurethanes (PURs) have become a very promising group of materials with considerable utilization and innovation potential. This work presents a comprehensive analysis of the changes in material properties important for PUR applications in the electrical industry due to the incorporation of magnesium oxide (MgO) nanoparticles at different weight ratios. From the results of the investigations carried out, it is evident that the incorporation of MgO improves the volume (by up to +0.5 order of magnitude) and surface (+1 order of magnitude) resistivities, reduces the dielectric losses at higher temperatures (-62%), improves the thermal stability of the material, and slows the decomposition reaction of polyurethane at specific temperatures (+30 °C). In contrast, the incorporation of MgO results in a slight decrease in the dielectric strength (-15%) and a significant decrease in the mechanical strength (-37%).

Influence of Air Humidity Level on the Structure and Mechanical Properties of Thermoplastic Starch-Montmorillonite Nanocomposite during Storage.

Thermoplastic starch (TPS) consisting of corn starch and glycerol as a plasticizer, and TPS-montmorillonite (MMT) nanocomposite were stored at room temperature in the air with relative humidities (RH) of 11, 55 and 85% for seven weeks. Mechanical testing and dynamic mechanical thermal analysis (DMTA) were performed to detect changes in their mechanical properties. Solid-state NMR spectroscopy monitoring the changes in molecular mobility in the samples provided an insight into relations between mechanical properties and local structure. The results of mechanical testing indicated that the addition of MMT results in the increase in the tensile strength and Young's modulus while elongation at break decreased, indicating the reinforcing effect of MMT. DMTA experiments revealed a decrease in glass transition temperature of starch-rich phase below room temperature for samples stored at higher RH (55 and 85%). This indicates that absorbed water molecules had additional plasticizing effect on starch resulting in higher mobility of starch chain segments. Recrystallization in these samples was deduced from the shape of cross-polarization magic-angle spinning 13C NMR spectra. The shape of broad-line 1H NMR spectra reflected changes in molecular mobility in the studied samples during seven weeks of storage and revealed that a high amount of water molecules impacts the starch intermolecular hydrogen bond density.

Influence of Nanoparticles on the Dielectric Response of a Single Component Resin Based on Polyesterimide.

The influence of various types of nanoparticle fillers with the same diameter of 20 nm were separately incorporated into a single component impregnating resin based on a polyesterimide (PEI) matrix and its subsequent changes in complex relative permittivity were studied. In this paper, nanoparticles of Al2O3 and ZnO were dispersed into PEI (with 0.5 and 1 wt.%) to prepare nanocomposite polymer. Dielectric frequency spectroscopy was used to measure the dependence of the real and imaginary parts of complex relative permittivity within the frequency range of 1 mHz to 1 MHz at a temperature range from +20 °C to +120 °C. The presence of weight concentration of nanoparticles in the PEI resin has an impact on the segmental dynamics of the polymer chain and changed the charge distribution in the given system. The changes detected in the 1H NMR spectra confirm that dispersed nanoparticles in PEI lead to the formation of loose structures, which results in higher polymer chain mobility. A shift of the local relaxation peaks, corresponding to the α-relaxation process, and higher mobility of the polymer chains in the spectra of imaginary permittivity of the investigated nanocomposites was observed.