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.
In this study, the relationship between structural hierarchy in PVDF/PMMA blends as altered by melt casting and annealing and electrical properties was investigated. PVDF was blended with PMMA in three crystallizable compositions: 50/50, 60/40 and 70/30 of PVDF/PMMA using twin screw extrusion followed by film casting. The films were characterized structurally through offline birefringence measurements as well as WAXS, SAXS, IR Dichroism and DSC to understand the processing induced structural changes and their effect on electrical properties. The addition of PMMA to PVDF suppressed crystalization during casting of films. This opened a low temperature film deformation window between T g and cold crystallization temperatures allowing for development of high preferential chain orientation in the films. Crystallinity in cast films was shown to correlate directly with breakdown strength. Systemic annealing experiments were carried out to enhance crystallinity and the effect of annealing induced structural changes on the dielectric properties were studied. It was found that upon annealing, the amorphous PMMA tends to undergo relaxation that is detrimental to the breakdown properties. As annealing progresses, the mismatch in the kinetics between crystallization/recrystallization and the amorphous relaxation causes density gradients within the bulk of the films and dictate the overall orientation levels in the films, as well as have implications on the dielectric properties.
In this study, the effect of organically modified clay on the orientation enhancement in Nylon 11 in melt casting was investigated. Nylon 11 was mixed with 1 and 3 wt% Cloisite 20A using twin screw extrusion and they were cast into films with varying take‐up speeds. The addition of clay in Nylon 11 helped increase orientation levels substantially in melt cast films, both as a function of clay concentration as well as take‐up speeds. This was primarily due to shear amplification effect caused by the movement of adjacent clay nanoparticles due to the shear flow gradient within the die. At low clay concentrations, the sub‐Tm stretchability, and electrical breakdown strength improve as the presence of clay reduces inter/intrachain hydrogen bonding. At higher clay concentrations, both orientation and electrical breakdown levels decrease. The latter is primarily caused by increased percolation path of charge carriers. Nevertheless, clay nanoplatelets were very effective in their role as melt processing aids, as they enhance orientation levels of Nylon 11 thin films by shear amplification effect where they increase local chain orientation of chains trapped between clay platelets while their orientation relaxation is suppressed.
In this study, the effect of processing on the structural and dielectric properties of Nylon 11 melt cast film was studied. Capacitor grade thin films were cast using a film extruder and stretched uniaxially and real-time mechano-optical data were acquired at temperatures ranging from solid state all the way to partially molten state. These studies were supplemented with offline WAXS, SAXS, and DSC to develop a complete understanding of processing induced structural changes and their relation to dielectric properties. When stretched in the solid-state, preferential crystalline and amorphous chain orientation levels increased as a function of strain while the long spacing remained constant due to lamellar slippage. Processing in the partially molten state led to the formation of new lamellae with larger long spacings. It was also observed that the dielectric properties of Nylon 11 were strongly dependent on the crystallinity and crystal phase, with higher crystallinity of the α 0 phase giving higher electrical breakdown strength. When films were stretched to 3X solid and partially molten states, together with crystallinity, the breakdown strength is increased, while the dielectric constant and loss decrease. Since crystalline regions are stiffer, they form effective barriers to hot carriers, retarding the electric breakdown.
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