Molecular origins of toughening mechanism in uniaxially stretched nylon 6 films with clay nanoparticles

Poly(cannabinoid)s: Hemp-Derived Biocompatible Thermoplastic Polyesters with Inherent Antioxidant Properties

The legalization of hemp cultivation in the United States has caused the price of hemp-derived cannabinoids to decrease 10-fold within 2 years. Cannabidiol (CBD), one of many naturally occurring diols found in hemp, can be purified in high yield for low cost, making it an interesting candidate for polymer feedstock. In this study, two polyesters were synthesized from the condensation of either CBD or cannabigerol (CBG) with adipoyl chloride. Poly(CBD-Adipate) was cast into free-standing films and subjected to thermal, mechanical, and biological characterization. Poly(CBD-Adipate) films exhibited a lack of cytotoxicity toward adipose-derived stem cells while displaying an inherent antioxidant activity compared to poly(lactide) films. Additionally, this material was found to be semi-crystalline and able to be melt-processed into a plastic hemp leaf using a silicone baking mold.

Crystal Structure and Mechanical Properties of Uniaxially Stretched PA612/SiO2 Films

Stretching has a significant effect on the microstructure and ultimate performance of semi-crystalline polymers. To investigate the effect of stretching on structure and mechanical properties of uniaxial stretched PA612/SiO₂, PA612 and PA612/SiO2 films were prepared at four temperatures close to the glass transition temperature at various strain. The samples were characterized by a transmission electron microscope (TEM), wide-angle X-ray diffractometer (WAXD), Two-dimensional wide-angle X-ray Scattering (2D-WAXS), differential scanning calorimeter (DSC), dynamic mechanical analyzer (DMA), and stretching tests. The results showed that the α phase was the dominant phase in PA612 casting film, no obvious γ phase was observed, while both stretching and the presence of SiO₂ can induce the generation of α phase and improve the crystallinity of PA612. Crystals were oriented along the stretching direction and the b axis was parallel to the equatorial direction after stretching. The interplanar spacing of (010/110) decreased with the increasing stretching temperature and expanded with the increasing strain, while stretching temperature and strain present negligible effect on the interplanar spacing of (100). The grain size increased with the stretching temperature while decreased with strain. The presence of SiO₂ led to reduce the yield stress and the stress drop beyond yielding of the composite. Uniaxial stretching gave rise to a significant improvement in the fracture stress and the glass transition temperature.

Structure and properties of PA6-66/γ-aminopropyltriethoxysilane-modified clay nanocomposites prepared by in situ polymerization

In this study, PA6-66/γ-aminopropyltriethoxysilane-modified clay nanocomposites were prepared by in situ polymerization. It was found that the γ-aminopropyltriethoxysilane was chemically grafted onto clay successfully, and the covalent bond was formed between the clay and polymer chains. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) results indicated that intercalated and exfoliated nanocomposites were obtained. The PA6-66 nanocomposites exhibited improved mechanical performance compared to that of neat PA6-66. Most importantly, the PA6-66 nanocomposites showed significantly improved toughness. In comparison with neat PA6-66, the rupture stress and elongation at the break of the nanocomposite with only 0.5 wt% clay increased 91.9% and 91.8%, respectively. The excellent toughness of PA6-66 nanocomposites should be mainly ascribed to the combined effects of strong polymer-clay interaction, the intercalated-exfoliated structures of clay, refined crystalline, formation of γ-form crystals, and decreased crystallinity of PA6-66.

Synthesis and Properties Epoxy Resin/Mesoporous Silica-Sepiolite Nanocomposites

Size, shape and processing of the inorganic fillers are important for improving properties of nanocomposites. In this paper, a novel nanofiller containing mesoporous silica(MS) and fibrous sepiolite(SE) was prepared by in situ deposition method. EP/MS-SE nanocomposite was obtained by adding MS-SE to epoxy resin(EP) matrix. Morphologies and mechanical properties of the new ternary nanocomposite were investigated. For purpose of comparison, the corresponding binary nanocomposites, i.e., EP modified with either MS or SE, were tested as well. The test results of mechanical properties show that MS improves the strength of EP and SE obviously enhances the toughness of EP, but oM-MS exhibits synergistic effect on toughening and reinforcing of EP at the same time. Dynamic mechanical analysis revealed that the glass transition temperature and storage modulus of the EP/MS-SE nanocomposite was higher than those of pure EP.