Antimicrobial polymers containing melamine derivatives. II. Biocidal polymers derived from 2-vinyl-4,6-diamino-1,3,5-triazine

Current plastics pollution threats due to COVID-19 and its possible mitigation techniques: a waste-to-energy conversion via Pyrolysis

BACKGROUND

The extensive use and production of PPE, and disposal in the COVID-19 pandemic increases the plastic wastes arise environmental threats. Roughly, 129 billion face masks and 65 billion plastic gloves every month are used and disposed of on the globe. The study aims to identify the polymer type of face masks and gloves and sustainable plastic waste management options.

RESULTS

The identification of polymers, which can help for fuel conversion alternatives, was confirmed by FTIR and TGA/DTA analysis and confirms that the polymeric categories fit for the intended purpose. Moreover, the handling technique for upcycling and the environmental impacts of the medical face mask and glove were discussed. The FTIR result revealed that face masks and gloves are polypropylene and PVC thermoplastic polymer, respectively and they can be easily transformed to fuel energy via pyrolysis. The endothermic peaks around 431 ℃ for medical glove and 175 ℃ for surgical is observed tells that the melting point of the PVC and polypropylene of plastic polymers, respectively. The pyrolysis of the face mask and glove was carried out in a closed reactor at 400 ℃ for 1 h. Conferring to lab-scale processes, liquid, and wax fuel rate of 75%, char of 10%, and the rest non-condensable gases were estimated at the end.

CONCLUSIONS

It can be concluded that the medical plastics can be recycled into oil due to their thermoplastics nature having high oil content and the waste to energy conversion can potentially reduce the volume of PPE plastic wastes.

Surgical face masks as a potential source for microplastic pollution in the COVID-19 scenario

Although there have been enormous reports on the microplastic pollution from different plastic products, impacts, controlling mechanisms in recent years, the surgical face masks, made up of polymeric materials, as a source of microplastic pollution potential in the ecosystem are not fully understood and considered yet. Current studies are mostly stated out that microplastics pollution should be a big deal because of their enormous effect on the aquatic biota, and the entire environment. Due to the complicated conditions of the aquatic bodies, microplastics could have multiple effects, and reports so far are still lacking. In addition to real microplastic pollutions which has been known before, face mask as a potential microplastic source could be also researching out, including the management system, in detail. It is noted that face masks are easily ingested by higher organisms, such as fishes, and microorganisms in the aquatic life which will affect the food chain and finally chronic health problems to humans. As a result, microplastic from the face mask should be a focus worldwide.

Fabrication of Polypropylene-g-(Diallylamino Triazine) Bifunctional Nonwovens with Antibacterial and Air Filtration Activities by Reactive Extrusion and Melt-Blown Technology

Air filtration materials such as protective masks can protect humans from airborne pathogens; however, most of the existing protective filtration materials are aimed to intercept bacteria. Therefore, in this work, modified polypropylene- (PP-) based melt-blown nonwovens with antibacterial property were prepared for reducing the infection rate during the filtering process. Firstly, an N-halamine precursor, 2,4-diamino-6-diallylamino-1,3,5-triazine (NDAM) monomer, was grafted with PP polymers (PP-g-NDAM) by reactive extrusion method, and the grafting effect was confirmed by nitrogen analysis and FTIR spectra. Then, the obtained PP-g-NDAM was mixed with pristine PP resins in different ratios to prepare the filter materials by melt-blown technology. Finally, the new PP-g-NDAM melt-blown filter materials were finishing treated by the chlorination and electrostatic process, which showed a high filtration efficiency with low pressure drop and a potent antibacterial effect against Escherichia coli (E. coli). This work provides an innovative method for manufacturing antibacterial filtration nonwovens, which can improve the quality of conventional filtration products.

Antibacterial Properties of Four Novel Hit Compounds from a Methicillin-Resistant Staphylococcus aureus-Caenorhabditis elegans High-Throughput Screen

There is an urgent need for the discovery of effective new antimicrobial agents to combat the rise of bacterial drug resistance. High-throughput screening (HTS) in whole-animal infection models is a powerful tool for identifying compounds that show antibacterial activity and low host toxicity. In this report, we characterize the activities of four novel antistaphylococcal compounds identified from an HTS campaign conducted using Caenorhabditis elegans nematodes infected with methicillin-resistant Staphylococcus aureus (MRSA). The hit compounds included an N-hydroxy indole-1, a substituted melamine derivative-2, N-substituted indolic alkyl isothiocyanate-3, and p-difluoromethylsulfide analog-4 of the well-known protonophore carbonyl cyanide m-chlorophenyl hydrazone. Minimal inhibitory concentrations (MICs) of the four compounds ranged from 2 to 8 μg/ml against MRSA-MW2 and Enterococcus faecium and all were bacteriostatic. The compounds were mostly inactive against Gram-negative pathogens, with only 1 and 4 showing slight activity (MIC = 32 μg/ml) against Acinetobacter baumanii. Compounds 2 and 3 (but not 1 or 4) were found to perturb MRSA membranes. In phagocytosis assays, compounds 1, 2, and 4 inhibited the growth of internalized MRSA in macrophages, whereas compound 3 showed a remarkable ability to clear intracellular MRSA at its MIC (p < 0.001). None of the compounds showed hemolytic activity at concentrations below 64 μg/ml (p = 0.0021). Compounds 1, 2, and 4 (but not 3) showed synergistic activity against MRSA with ciprofloxacin, while compound 3 synergized with erythromycin, gentamicin, streptomycin, and vancomycin. In conclusion, we describe four new antistaphylococcal compounds that warrant further study as novel antibacterial agents against Gram-positive organisms.

Sporicidal/bactericidal textiles via the chlorination of silk

Bacterial spores, such as those of the Bacillus genus, are extremely resilient, being able to germinate into metabolically active cells after withstanding harsh environmental conditions or aggressive chemical treatments. The toughness of the bacterial spore in combination with the use of spores, such as those of Bacillus anthracis, as a biological warfare agent necessitates the development of new antimicrobial textiles. In this work, a route to the production of fabrics that kill bacterial spores and cells within minutes of exposure is described. Utilizing this facile process, unmodified silk cloth is reacted with a diluted bleach solution, rinsed with water, and dried. The chlorination of silk was explored under basic (pH 11) and slightly acidic (pH 5) conditions. Chloramine-silk textiles prepared in acidified bleach solutions were found to have superior breaking strength and higher oxidative Cl contents than those prepared under caustic conditions. Silk cloth chlorinated for ≥1 h at pH 5 was determined to induce >99.99996% reduction in the colony forming units of Escherichia coli, as well as Bacillus thuringiensis Al Hakam (B. anthracis simulant) spores and cells within 10 min of contact. The processing conditions presented for silk fabric in this study are highly expeditionary, allowing for the on-site production of protein-based antimicrobial materials from a variety of agriculturally produced feed-stocks.

Surface functional polymers by post-polymerization modification using diarylcarbenes: introduction, release and regeneration of hydrogen peroxide and bactericidal activity

Functionalized diarylcarbenes are excellent reactive intermediates suitable for the direct surface modification of organic polymers, and these may be used to introduce urea and thiourea functions onto polystyrene at loading levels of up to 2.3 x 10(13) molecules/cm(2). These functions are capable of the reversible binding and release of peroxide at loading levels of up to 0.6 mmol/g and give polymers that display biocidal activity against a spectrum of gram-positive and gram-negative bacteria.

Control of arrangement for s-triazine group in comb copolymers by the Langmuir-Blodgett method and its structural estimation by NEXAFS spectroscopy

We investigated the molecular orientation of organized molecular films with regard to solid-state structures for newly synthesized comb copolymers with 2-vinyl-4,6-diamino-1,3,5-triazine (VDAT) by surface pressure-area (pi-A) isotherms, in-plane and out-of-plane X-ray diffraction (XRD), atomic force microscopy (AFM), and polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Since VDAT has adsorption ability to an adenine-thymine base pair of a DNA molecule, control of orientation for VDAT units in monolayers is possible to form surface patterning of biomolecules and construct candidates of new biochip materials. In the bulk state, hydrogenated and fluorinated comb copolymers containing VDAT form side-chain crystals for a two-dimensional lattice spacing of 4.2 and 5.0 A, respectively. From the results of the differential scanning calorimetric (DSC) measurements, sharp-shaped melting peaks appear on the relatively lower temperature side of the thermograms. This result supports the formation of side-chain crystals in the synthesized comb copolymers. These monolayers of copolymers on the water surface were extremely condensed, except for the VDAT:OA = 5:1 copolymer. From the in-plane XRD measurement of multilayers on solids, changes in the two-dimensional lattice structure of fluorinated comb copolymer films containing VDAT units, as opposed to their bulk state, were confirmed. It seems that these structural changes are caused by the stronger pi-pi interaction between the s-triazine rings rather than the van der Waals interaction between fluorocarbons. Polarized NEXAFS spectroscopy showed highly ordered orientation of s-triazine groups in the films based on the incident angle dependency of C and N1s-pi*(CN) transitions with synchrotron radiation. These experimental findings relate to well-ordered arrangement of functional groups supporting the side-chain rearrangement caused by the pi-pi interaction between the s-triazine rings.

N-halamine-based chitosan: Preparation, characterization, and antimicrobial function

Upon chlorine bleach treatment, amino groups in chitosan were transformed into N-halamine structures. The transformation was confirmed by UV/VIS, XPS, DSC, and TGA evaluation and iodimetric titration. The N-halalmine-based chitosan provided total kill of 10(8)-10(9) colony forming units (CFU/mL) of E. coli (gram-negative bacteria) and S. aureus (gram-positive bacteria) in 10 and 60 min, respectively. SEM observations demonstrated that the chlorinated chitosan effectively prevented the formation of bacterial biofilms. The antimicrobial activity and bio film controlling function were stable for longer than 1 month; when the functions were lost due to extensive use and/or prolonged storage, they could be readily recharged by another bleach treatment. The antimicrobial mechanism was also discussed.

Biocidal efficacy, biofilm-controlling function, and controlled release effect of chloromelamine-based bioresponsive fibrous materials

In this study, 2-amino-4-chloro-6-hydroxy-s-triazine (ACHT) was synthesized through controlled hydrolysis of 2-amino-4,6-dichloro-s-triazine (ADCT). A simple pad-dry-cure approach was employed to immobilize ACHT onto cellulosic fibrous materials. After treatment with diluted chlorine bleach, the covalently bound ACHT moieties were transformed into chloromelamines. The structures of the samples were fully characterized with NMR, UV/VIS, DSC, TG, iodometric titration and elemental analyses. The chloromelamine-based fibrous materials provided potent, durable, and rechargeable biocidal functions against bacteria (including multi-drug resistant species), yeasts, viruses, and bacterial spores. SEM studies demonstrated that the new fibrous materials could effectively prevent the formation of biofilms, and controlled release investigations in vitro suggested that the biocidal activities were bioresponsive. Biocidal mechanisms of the chloromelamine-based fibrous materials were further discussed.