Search

The hydrogenolysis of polymers is emerging as a promising approach to deconstruct plastic waste into valuable chemicals. Yet, the complexity of plastic waste, including multilayer packaging, is a significant barrier to handling realistic waste streams. Herein, we reveal fundamental insights into a new chemical route for transforming a previously unaddressed fraction of plastic waste – poly(ethylene‐co‐vinyl alcohol) (EVOH) and related polymer blends – into alkane products. We report that Ru/ZrO2 is active for the concurrent hydrogenolysis, hydrogenation, and hydrodeoxygenation of EVOH and its thermal degradation products into alkanes (C1−C35) and water. Detailed reaction data, product analysis, and catalyst characterization reveal that the in‐situ thermal degradation of EVOH forms aromatic intermediates that are detrimental to catalytic activity. Increased hydrogen pressure promotes hydrogenation of these aromatics, preventing catalyst deactivation and improving alkane product yields. Calculated apparent rates of C−C scission reveal that the hydrogenolysis of EVOH is slower than low‐density polyethylene. We apply these findings to achieve hydrogenolysis of EVOH/polyethylene blends and elucidate the sensitivity of hydrogenolysis catalysts to such blends. Overall, we demonstrate progress towards efficient catalytic processes for the hydroconversion of waste multilayer film plastic packaging into valuable products. [ABSTRACT FROM AUTHOR]

Cadmium oleate is widely used as a cation precursor in the synthesis of cadmium chalcogenide nanocrystal quantum dots (QDs) for a broad range of photonic and optoelectronic applications. Cd oleate can noncovalently assemble to form a supramolecular coordination gel, or metallogel, in solvents commonly used to disperse oleate-capped QDs. The gelation severely impedes the purification of oleate-capped QDs from excess Cd oleate, resulting in a gelled product that cannot be reliably characterized or used in further synthesis reactions. Here, we investigate the Cd oleate gel to gain insights into its viscoelastic properties and behavior under conditions relevant to QD synthesis, purification, and storage. We then examine how to effectively mitigate gelation by adding oleylamine as an additional ligand to disrupt noncovalent assembly. We synthesize PbS/CdS core/shell QDs via cation exchange as a case study to illustrate gelation of the reaction product and further demonstrate how this issue can be resolved through a better understanding of the supramolecular gel. [ABSTRACT FROM AUTHOR]

The reinforcement of mechanically‐weak hydrogels to yield composites with increased stiffness, strength, or toughness is a well‐established approach. In particular, introducing electrospun nanofibers into hydrogels is a common strategy for biomedical applications, as the resulting hierarchical structure mimics biology and allows for control over fiber diameter and alignment and tuning of mechanical properties. However, further study of the link between the constituent materials and the mechanical properties of the composite is uncommon. One potential model to understand the mechanical properties of fiber‐reinforced hydrogels involves the Halpin–Tsai equations, which relate the modulus values of the fibers and hydrogel matrix and the fiber volume fraction, to the modulus of the composite. To assess the application of this model to fiber‐reinforced hydrogels, predicted values were compared with experimental values from mechanical testing of a poly(ethylene glycol) (PEG) matrix reinforced with an electrospun polycaprolactone (PCL) fiber mat. Although the equations described these systems well in tension, providing a facile approach to identify a fiber volume fraction that will achieve a desired modulus, the Halpin–Tsai approach was less successful under compression. This study motivates additional investigation of the role of structural features of hydrogel composites in determining mechanical properties to enable design of materials for specific applications. [ABSTRACT FROM AUTHOR]

Mechanical stretching of a partially cross-linked gel or elastomer followed by additional cross-linking to fix the alignment is the most widely employed method to synthesize aligned LCEs.[[14]] This technique can be applied to a large range of synthetic approaches. Liquid crystal elastomers (LCEs) are a class of materials where liquid crystalline order and rubber elasticity combine to yield interesting properties.[1] These elastomers can exhibit a variety of liquid crystalline phases, which results in materials with distinct functional properties. Wei, P. Shiller, J. V. Selinger, R. L. B. Selinger, and O. D. Lavrentovich, "Dynamically morphing microchannels in liquid crystal elastomer coatings containing disclinations", J. Appl. Phys. 10.1063/5.0039965 43 A. Sharma, A. M. Stoffel, and J. P. F. Lagerwall, "Liquid crystal elastomer shells with topological defect-defined actuation: Complex shape morphing, opening/closing, and unidirectional rotation", J. Appl. Phys. [Extracted from the article]

Polymer nanocomposites are an important class of materials.[[1], [3], [5]] They combine the many desirable physical properties of polymers, such as their mechanical properties and ease of processing, with functionalities provided by a nanoparticle component. A common example is using thiol-terminated polymers to graft to the surface of Au nanoparticles.[[10]] The "grafting-to" approach may be easier to accomplish experimentally but typically results in lower grafting densities, especially for high molecular weight polymers. The particles are not unlike those formed by surfactants in solution; in fact, polymer chains can self-assemble in solution to form micellar structures that behave like PGNPs in many ways.[13] Recently, virus-like particles have been synthesized and functionalized with a polymer brush.[14] Finally, nanoparticles can be synthesized by crosslinking single chains into small, dense nanoparticles. [Extracted from the article]