Today's KNOWLEDGE Share :New reaction to create Monomers using Nickel as catalyst

Today's KNOWLEDGE Share

Chemists develop new sustainable reaction for creating unique molecular building blocks

Scripps Research chemists and additional collaborators have developed a new reaction to create unique monomers in a controlled way. This reaction, which uses nickel as a catalyst, ultimately enables scientists to create polymers with unique and modifiable properties for drug delivery, energy storage, microelectronics and more. The study was published in Nature Synthesis on August 8,2024.

"This study shows how earth-abundant metal catalysts can unlock the path toward previously unknown materials with unparalleled structural and functional diversity," says senior author Keary Engle, PhD, a professor in the Department of Chemistry and dean of Graduate and Postdoctoral Studies at Scripps Research.

The Engle lab at Scripps Research focuses on developing new chemical reactions to build a wide and diverse array of small molecules, typically with applications in drug discovery. In this study, the Scripps Research team collaborated with polymer researchers at the Georgia Institute of Technology and the University of Pittsburgh to test whether their methods could be scaled up to create unique polymers.

"The properties of polymers are very much dependent on what type of chemistry is on the backbone, so if you can modify the chemistry of the building blocks, then you can easily apply it to the macromolecular structure that you're building," says Anne Ravn, PhD, a postdoctoral researcher in the Engle lab at Scripps Research and co-first author on the paper. "With this project we wanted to test whether our strategy for developing small molecules could be applied to a bigger picture to provide new building blocks for polymer synthesis."

The paper's other first authors are Van Tran, PhD, who worked on the project as a graduate student in the Engle lab; Camille Rubel, a current graduate student in the Engle lab; Mizhi Xu, PhD, a former graduate student in the Gutekunst lab at the Georgia Institute of Technology; and Yue Fu, PhD, a former graduate student in the Liu lab at the University of Pittsburgh.

To create the new monomers, the Scripps Research team developed a chemical reaction that alters the structure of a starting molecule by using nickel as a catalyst. The nickel-catalyzed reaction added two new "functional groups" to the molecule -- small side chains that confer different chemical and physical properties on the ensuing polymer, for example, how flexible, elastic or soluble it is.

Then, the team's collaborators at Georgia Institute of Technology used another chemical reaction to link the monomers together via polymerization, resulting in polymers with a unique structure.

"Most commercial polymers have two carbons in between each functional group that are not decorated with any side chains, but in this case, the functional groups are much closer in space, which creates a material with different properties.

In the future, the team plans to explore the impact of substituting different functional groups onto the monomers.

"Our strategy allows us to 'decorate' the molecule with much more flexibility than other methods, which gives us more freedom to explore different types of functionalities in the building blocks," says Ravn. "We're now working to expand the method to explore how introducing other types of functional groups changes the properties of the material."

Because nickel is more abundant than many other metal catalysts used in this type of chemical reaction, the researchers say that their method holds promise as an environmentally sustainable method for polymer production. They're also exploring ways to make the products even more sustainable.

"From an environmental perspective, we want to find a method to degrade these long polymers so that we can get back to the original building blocks, which would allow us to reuse them," says Ravn. "This is a tool that we hope to fine-tune in the future to ultimately create new technologies that are useful for society."

"Ni-catalysed dicarbofunctionalization for the synthesis of sequence-encoded cyclooctene monomers" was co-authored by Ethan Wagner, Steven R. Wisniewski, Peng Liu, and Will Gutekunst of Scripps Research.

Support for the research was provided by the Department of Energy (DESC0023205), the National Science Foundation (CHE-2102550), the Independent Research Fund Denmark (grant ID: 10.46540/3102-00009B), and the Schimmel Family Endowed Scholarship Fund.

source:sciencedaily.com

Today's KNOWLEDGE Share :The difference between HDT and Vicat

Today's KNOWLEDGE Share

Heat deflection temperature (HDT):

HDT is a measure of the stiffness of the material as the temperature increases.

HDT test measures the temperature at which the specimen loses its “load-bearing” capability.

A material can have only “one” HDT.

HDT for material is affected by the addition of reinforcement, fillers, plasticizers, or any other type of additive.

Vicat softening temperature (VST):

The vicat test is used to identify a temperature at which a needle of specified dimensions penetrates a plastic specimen at a specified distance under a given load.

It reveals the temperature at which the specimen loses its “stability-form” and softens.

The vicat point is closer to the actual melting or softening point of the polymer. The Vicat number will typically be higher.

The difference between HDT and Vicat testing:

The main difference between heat deflection temperature testing and Vicat softening point testing is associated with the elements the material being tested is subjected to.  

HDT testing :

HDT testing subjects a standard sized test specimen to stress, while also raising the temperature at a uniform rate. The temperature at which deflection occurs is recorded, which allows you to determine the heat the sample is able to withstand. The result is also dependent on factors such as the load, the speed the temperature is raised and the flexure chosen. This data can be used to compare samples and create an accurate picture of the ways paints and polymer coatings may behave under both heat and stress.  

Vicat softening point testing :

The Vicat softening point method was introduced as a way of determining the softening point of a material or coating. It’s essential because thermoplastic doesn’t have a melting point where solids become liquids, instead they are subject to softening. In Vicat testing, a circular indenter of 1 mm² in section penetrates exactly 1 mm into the specimen under a standardized load of 10 N or 50 N. The indentation is used to calculate how much the specimen has softened.  

 

Meeting industry standards for HDT and Vicat:

HDT testing should be carried out according to testing standards ISO 75 (parts 1, 2 and 3) and ASTM D648 while Vicat testing is ISO 306 and ASTM D1525.  

source:industrialphysics.com/omnexus.specialchem.com

Photo:Amde-Tech

Today's KNOWLEDGE Share: PFAS REMOVAL

Today's KNOWLEDGE Share

Researchers Claim New Process Destroys Forever Chemicals — Forever!

You may not be familiar with Ritsumeikan in Kyoto, Japan, but researchers there say they may have an answer to the curse of so-called “forever chemicals,” also known at PFAS, the class of chemicals used in many commercial applications that are so durable that they resist breaking down for decades, or longer. That might not be a problem were it not for the fact that they have been identified as risk factors that contribute to a variety of human health concerns such as cancer. They also are thought to affect the development of human embryos in the womb, and not in a good way.

The scientists at Ritsumeikan say they have developed a groundbreaking, eco-friendly method to eliminate harmful forever chemicals using visible LED light. The process has achieved a nearly complete breakdown of perfluoroalkyl substances (PFAS), a persistent pollutant, at room temperature. This innovative approach not only eliminates these persistent pollutants but also recovers valuable fluorine, addressing both environmental and economic concerns. The conclusions have been published in the journal Angewandte Chemie International Edition.

The new process has achieved a 100% breakdown of perfluorooctanesulfonate (a type of PFAS) in just eight hours and an 81% breakdown of Nafion (a fluoropolymer) in 24 hours. Since the invention of Teflon in 1938, PFASs and perfluorinated polymers (PFs) have been widely used for their exceptional stability and resistance to water and heat. These properties made them ideal for countless applications, from cookware and clothing to firefighting foam.

However, this very stability has become a major problem. These forever chemicals do not easily break down in the environment, so they accumulation in water, soil, and even the bodies of humans, where they are known to cause carcinogenic effects and hormonal disruptions. Today, these forever chemicals can be found in drinking water supplies, food, and even in the soil of Antarctica. Although there are plans to phase out PFAS production, treating them remains challenging as they decompose only at temperatures exceeding 400° C. As a result, products containing PFASs and PFs end up in landfills, potentially creating future contamination risks.

“The proposed methodology is promising for the effective decomposition of diverse perfluoroalkyl substances under gentle conditions, thereby significantly contributing towards the establishment of a sustainable fluorine-recycling society,” says Professor Yoichi Kobayashi, the lead author of the study. In case you missed it, the current method of breaking down forever chemicals involves heat — quite a lot of heat, in fact. 400º C translates to 752º F. The only way of reaching temperatures like that today usually involves burning fossil fuels, which involves its own set of health and environmental issues.

The method for breaking down forever chemicals created by the researchers in Japan involves irradiating visible LED light onto cadmium sulfide (CdS) nanocrystals and copper-doped CdS (Cu-CdS) nanocrystals with surface ligands of mercaptopropionic acid (MPA) in a solution containing PFAS, FPs, and triethanolamine (TEOA). The researchers found that irradiating these semiconductor nanocrystals generates electrons with a high reduction potential that break down the strong carbon-fluorine bonds in PFAS molecules.

For the photocatalytic reaction, the researchers added 0.8 mg of CdS nanocrystals (NCs), 0.65 mg of PFOS, and 20 mg of TEOA to 1.0 ml of water. They then exposed the solution to 405-nanometer LED light to initiate the photocatalytic reaction. This light excites the nanoparticles, generating electron-hole pairs and promoting the removal of MPA ligands from the surface of the nanocrystals, creating space for PFOS molecules to adsorb onto the NC surface.

To prevent photoexcited electrons from recombining with holes, TEOA is added to capture the holes and prolong the lifetime of the reactive electrons available for PFAS decomposition. These electrons undergo an Auger recombination process, where one exciton (an electron-hole pair) recombines non-radiatively, transferring its energy to another electron, and creating highly excited electrons. These highly excited electrons possess enough energy to participate in chemical reactions with the PFOS molecules adsorbed on the NC surface. The reactions lead to the breaking of carbon-fluorine (C-F) bonds in PFOS, resulting in the removal of fluorine ions from the PFAS molecules.

The presence of hydrated electrons, generated by Auger recombination, was confirmed by laser flash photolysis measurements, which identified transient species based on the absorption spectrum upon laser pulse excitation. The defluorination efficiency depended on the amount of NCs and TEOA used in the reaction and increased with the period of light exposure. For PFOS, the efficiency of defluorination was 55%, 70–80%, and 100% for 1-, 2-, and 8-hour light irradiation, respectively. Using this method, the researchers also successfully achieved 81% defluorination of Nafion, a fluoropolymer, after 24 hours of light irradiation. Nafion is widely used as an ion-exchange membrane in electrolysis and batteries.

Fluorine is a critical component in many industries, from pharmaceuticals to clean energy technologies. By recovering fluorine from waste PFAS, we can reduce reliance on fluorine production and establish a more sustainable recycling process. “This technique will contribute to the development of recycling technologies for fluorine elements, which are used in various industries and support our prosperous society,” concludes Professor Kobayashi.

Forever chemicals have become a political issue in the United States, where the EPA has issued new rules that require public drinking water agencies to limit the amount of them in the water they supply to their customers. Taking crud out of the water we drink is supposed to be what drinking water companies do, but because the cost of removing forever chemicals by traditional methods is high, states like Wisconsin and the manufacturers who make this stuff have sued the EPA for doing its job. Oh, the horror!

Americans are suddenly obsessed with reproductive health, but when it comes to spending money to ensure the birth of healthy babies, suddenly they want to snap their wallets shut and let the chips fall where they may. Such stunning levels of hypocrisy are difficult to reconcile with common sense, but there you are. There is a good chance the US Supreme Court will rule favorably on any challenges to the forever chemicals rules as part of its full frontal assault on the administrative infrastructure first created by FDR. The Supremes, in their infinite wisdom, believe it is better to waste years in endless litigation so judges can substitute their non-profession judgment for that of actual scientists who may actually know a thing or two about their field of expertise.

The prospect of being able to break down some forever chemicals at room temperature using visible light is hopeful. Humans have a way of ignoring the harm done to their environment by things that make life easier. Who wants to live without nonstick cookware? These researchers are offering us a possible way of addressing the forever chemical problem. We should seize this opportunity with both hands and bring it to commercial viability as soon as possible. We really have to learn that putting crud into our air, our water, and our earth is not a sustainable path forward for humanity.

source:https://cleantechnica.com

Today's KNOWLEDGE Share : Epoxy Resin Composites properties Modified by Nanofiller

Today's KNOWLEDGE Share

Mechanical Properties of the Epoxy Resin Composites Modified by Nanofiller under Different Aging Conditions

Epoxy resin (EP) is a typical cross-linked thermosetting polymer material, which has many outstanding advantages, such as good mechanical properties, strong stability and bonding ability, low shrinkage, excellent heat resistance, chemical resistance, and fire-retardant. Therefore, it is widely used in the field of surface coating, adhesives, composite manufacturing, civil engineering, etc.. However, the performance of EP is degraded in harsh environments, including humidity, high-temperature, hygrothermal, and radiation conditions, which decreases their lifetime and durability.

The hygrothermal aging condition has strongly deteriorated the mechanical performance of the EP. Under the hygrothermal aging condition, EP will absorb water, leading to the deterioration in the physical and chemical properties of the resin because of hydrolysis, plasticization, and matrix swelling. To reduce the damage and deterioration of the resin in a hygrothermal environment, some nanofillers are used, such as carbon nanotube (CNT), graphene nanoplatelet (GNP), graphene oxide (mGO), nanoclay, and nano-silicon carbide (n-SiC). Nanoclay is one of the commonly used nanofillers to improve multiple properties of the EP because of its low cost, high aspect ratio, unique chemical properties, high mechanical properties, and thermal stability. Halloysite nanoclay is from silicate minerals and is also named halloysite nanotube (HNT) due to its hollow nanotube structure. Due to its excellent properties, HNT is widely used in the research of composite materials. Previous research work shows that the addition of HNTs into polymers can significantly enhance mechanical properties, which improves the tensile strength, flexural strength, and durability of EP, and delay the degradation behavior of the EP in a humid environment.

The aging behavior of resin composites is related to several variables, such as temperature, corrosion medium, additives, and aging time. Uthaman et al.  considered the effects of water and acid solutions at different temperatures on the properties of EP. The reduction in tensile strength of the resin is depending on the soaking time and temperature, and a long soaking time and high temperature accelerate the aging behavior. Shettar et al. studied the effect of thermal shock cycling (TSC) on the properties of EP. Under the condition of TSC, the tensile strength of neat EP was reduced by 6%-11%, and the bending strength decreased by 8%-15%. The tensile strength and bending strength of EP added with nanoclay decreased by 7%-13% and 9%-17%, respectively. It can be attributed to stress formation at the nanoclay/epoxy interface due to the mismatch coefficient of thermal expansion, and therefore, the addition of nanoclay is not helpful to improve aging resistance under thermal shock cycling (TSC) conditions. Ulus et al. investigated the effect of the addition of halloysite nanoclay on the properties of the resin in a saltwater environment. They found that after 6 months of aging, the tensile strength and flexural strength of neat EP decreased by about 37.4% and 41.9%, respectively, while the tensile strength and flexural strength of EP with halloysite nanoclay decreased by about 28% and 35.1%, respectively.

Although some studies have investigated the aging behavior of resin composites under hygrothermal and thermal shock cycle conditions, there is little research on coupled aging factors, e.g., a combination of soaking aging and thermal shock cycle; therefore, the effects of single condition aging and coupling aging on the mechanical properties of neat EP and HNT/EP nanocomposites were investigated. The accelerated aging conditions were set as water soaking (20°C, 40°C, and 60°C), thermal shock cycling (TSC), and soaking coupled with subsequent thermal shock cycling (composite aging). The degradation in mechanical properties under these conditions was studied to obtain a comprehensive understanding of the effects of the aging condition and nanofiller on EP in a variety of applications.

source:S. J. Lu, T. Yang, X. Xiao, X. Y. Zhu, J. Wang, P. Y. Zang, J. A. Liu

Today's KNOWLEDGE Share :Chemical Substances Undergoing Prioritization

 Today's KNOWLEDGE Share

Chemical Substances Undergoing Prioritization

As required under section 6(b) of the Toxic Substances Control Act (TSCA), EPA must conduct a prioritization process to determine if chemical substances are a high- or low-priority for risk evaluation. 

2023-2024 Prioritization Process

On July 26, 2024, EPA proposed to designate five chemicals as High-Priority Substances for risk evaluation under TSCA. If EPA finalizes these designations the Agency will begin risk evaluations for these chemicals.

In December 2023, EPA initiated the process of prioritizing five chemicals as candidates for high-priority designation and subsequent risk evaluation:

Acetaldehyde (CASRN 75-07-0);

Acrylonitrile (CASRN 107-13-1);

Benzenamine (CASRN 62-53-3);

Vinyl Chloride (CASRN 75-01-4) , and ;

4,4’-Methylene bis(2-chloroaniline) (MBOCA) (CASRN 101-14-4). 

All five chemicals were selected from the 2014 TSCA Work Plan, which is a list of chemicals identified by EPA for further assessment based on their hazards and potential for exposure.  

In selecting these five chemicals, EPA considered numerous factors including how they are used, their known hazards and exposures, and the availability of information on each chemical to allow for fulsome risk evaluations to be completed. Between September and November 2023, EPA met with federal partners, industry, environmental organizations, labor organizations, state and local governments, and Tribes to discuss the prioritization process and presented a list of 15 chemical substances EPA was considering for prioritization. EPA took feedback from these discussions into consideration when selecting this set of five chemicals for prioritization. 

Upon publication of the Federal Register Notice in December 2023, EPA received comments and requested further information on these factors, as well as any other information relevant to the potential risks of these chemicals to will inform the Agency’s review of these chemicals. In March 2024, EPA extended the comment period for MBOCA by an additional 30 days.

Comments on MBOCA can be submitted to docket ID number EPA-HQ-OPPT-2018-0464 on www.regulations.gov until April 17, 2024. Comments on the other four chemicals were submitted until March 18, 2024. EPA received public comments on topics such as manufacturing, processing, and consumer/commercial uses and products; release and exposure information; and potential hazards of these chemical substances, as well as previously conducted hazard assessments. For more information, please see the Federal Register Notice at EPA-HQ-OPPT-2023-0601.

During this second 90-day public comment period, EPA is particularly interested in relevant information for any of the prioritization considerations, such as chemicals’ uses conditions of use and encourages the public to submit comment. EPA will accept public comments on the proposed designations for 90 days after publication via docket EPA-HQ-OPPT-2023-0601 at the Regulations.gov page.

source:EPA