Silicone resins are traditional thermoset polymers with an inorganic backbone, affording chemical inertness and high thermal stability, which also makes them inherently difficult to recycle by traditional methods. Here, we demonstrate that catalytic amounts of fluoride ion at room temperature solubilize highly cross-linked silicone resins initially cured up to 250 °C. After solubilization equilibria are achieved, solvent is removed to reform the polymer network. Coatings on aluminum substrates and monoliths of virgin and recycled silicone resins were evaluated for hydrophobicity, wear resistance, substrate adhesion, and thermal stability. Silicones recycled under optimized conditions retained nearly 100% wear resistance, thermal stability, and adhesion properties. In some instances, the recycled coatings offer properties superior to the initial materials.
Polycrystalline silicon, with impurity levels lower than those of the SEMI III standard for solar grade silicon feedstock (≈99.9999% pure), was produced using rice hull ash (RHA) as a biogenic silica source. The RHA is first purified using very simple, low cost, low energy, acid milling/boiling water wash purification steps and pelletization followed by carbothermal reduction using an experimental 50 kW electric arc furnace (EAF) operated at 1700-2100°C in batch mode. Typical processing involves adding 3.6 kg of pellets to the EAF followed by introduction of an additional 3.6 kg charge every 6 h after the start of carbothermal reduction. This approach produces up to 1.6 kg of silicon per batch. Purities, determined by inductively coupled plasma optical emission spectrometry (ICP-OES), were reproducibly found to be 99.9999 wt% (6 Ns) with B contents of ≈0.1 part per million by weight. This process escapes multiple process steps including the intermediacy of metallurgical grade silicon and the production and reduction of chlorosilanes as currently used in the Siemen's process. Furthermore, burning rice hulls to produce electricity and RHA, generates more energy than required for the overall process. Finally, the carbon footprint for the process discussed here is very low. The rice plant "fixes" CO 2 as it grows. The recovered hull contains sufficient amounts of this carbon that it can be burned to generate electricity returning part of this carbon to the atmosphere as CO 2 . The carbon retained in the RHA is still from fixed CO 2 and provides the carbon source (especially in the Path 2 process) for carbothermal reduction returning the remaining carbon to the atmosphere as CO 2 . A further point is that the alternative of landfilling with RHA or especially rice hulls would lead to generation of methane, a known green house gas. Thus, one might even argue that the carbon footprint for the process described here is actually negative.
There have been many successful efforts to enhance the water shedding properties of hydrophobic and superhydrophobic coatings, but durability is often a secondary concern. Here, we describe durable and hydrophobic coatings prepared via fluoride catalyzed rearrangement reaction of dodecaphenylsilsesquioxane [PhSiO] (DDPS) with octamethylcyclotetrasiloxane (D). Hydrophobic properties and wear resistance are maximized by incorporating both low surface energy moieties and cross-linkable moieties into the siloxane network. Water contact angles as high as 150 ± 4° were achieved even after 150 wear cycles with SiC sandpaper (2000 grit, 2 kPa). These hybrid organic-inorganic copolymers also have high thermal stabilities after curing at 250 °C (T ≥ 340 °C in air) due to the siloxane network with a maximum T of >460 °C measured for the system with the highest silsesquioxane content. The coating systems presented here offer a unique combination of hydrophobicity and mechanical/thermal stability and could greatly expand the utility of water repellent coatings.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.