Polymere aus Cellulose

Plastics, such as polyethylene, polypropylene, and polyethylene terephthalate are part of our everyday lives in the form of packaging, household goods, electrical insulation, etc. These polymers are non-degradable and create many environmental problems and public health concerns. Additionally, these polymers are produced from finite fossils resources. With the continuous utilization of these limited resources, it is important to look towards renewable sources along with biodegradation of the produced polymers, ideally. Although many bio-based polymers are known, such as polylactic acid, polybutylene succinate adipate or polybutylene succinate, none have yet shown the promise of replacing conventional polymers like polyethylene, polypropylene and polyethylene terephthalate. Cellulose is one of the most abundant renewable resources produced in nature. It can be transformed into various small molecules, such as sugars, furans, and levoglucosenone. The aim of this research is to use the cellulose derived molecules for the synthesis of polymers. Acid-treated cellulose was subjected to thermal pyrolysis to obtain levoglucosenone, which was reduced to levoglucosenol. Levoglucosenol was polymerized, for the first time, by ring-opening metathesis polymerization (ROMP) yielding high molar mass polymers of up to ~150 kg/mol. The poly(levoglucosenol) is thermally stable up to ~220 ℃, amorphous, and is exhibiting a relatively high glass transition temperature of ~100 ℃. The poly(levoglucosenol) can be converted to a transparent film, resembling common plastic, and was found to degrade in a moist acidic environment. This means that poly(levoglucosenol) may find its use as an alternative to conventional plastic, for instance, polystyrene. Levoglucosenol was also converted into levoglucosenyl methyl ether, which was polymerized by cationic ring-opening metathesis polymerization (CROP). Polymers were obtained with molar masses up to ~36 kg/mol. These polymers are thermally stable up to ~220 ℃ and are semi-crystalline thermoplastics, having a glass transition temperature of ~35 ℃ and melting transition of 70-100 ℃. Additionally, the polymers underwent cross-linking, hydrogenation and thiol-ene click chemistry.Kunststoffe wie Polyethylen, Polypropylen und Polyethylenterephthalat sind ein großer Bestandteil unseres Alltags und finden Verwendung unter anderem als Verpackungsmaterialien, Haushaltswaren und Elektroisolierungen. Diese Polymere werden aus fossilen Ressourcen hergestellt, sind nicht abbaubar und verursachen nicht nur viele Umweltprobleme sondern können auch zu Gesundheitsschäden führen. Aufgrund dessen muss die Verwendung von erneuerbaren Ressourcen geachtet werden, wobei die hergestellten Polymere im Idealfall komplett biologisch abbaubar sind. Obwohl viele biobasierte Polymere, wie Polymilchsäure, Polybutylensuccinatadipat oder Polybutylensuccinat, bekannt sind, hat noch keines das Potential gezeigt, herkömmliche Polymere zu ersetzen. Cellulose ist einer der am häufigsten in der Natur produzierten nachwachsenden Rohstoffe und kann in verschiedene kleine organische Moleküle wie Zucker (Saccharide), Furan und auch Levoglucosenon umgewandelt werden. Ziel dieser Arbeit ist die Verwendung von Levoglucosenon als Monomer für die Synthese von Polymeren. Säurebehandelte Cellulose wurde einer thermischen Pyrolyse unterzogen, um Levoglucosenon zu erhalten, das dann weiter zu Levoglucosenol reduziert wurde. Das Levoglucosenol wurde zum ersten Mal erfolgreich über eine Ringöffnungsmetathese-Polymerisation (ROMP) polymerisiert. Die Molmassen der hergestellten Polymere erreichten Werte von bis zu ~150 kg/mol. Die thermische Analyse von Poly(levoglucosenol) zeigt, dass es bis zu einer Temperatur von ~220 ℃ stabil ist, eine Glasübergangstemperatur bei ~100 ℃ hat und ein amorphes Polymer ist. Weiterhin kann das Poly(levoglucosenol) in feuchter saurer Umgebung in kurzer Zeit abgebaut werden. Aufgrund dieser Eigenschaften kann Poly(levoglucosenol) als Alternative zu konventionellem Kunststoff, wie z.B. Polystyrol, eingesetzt werden kann. Levoglucosenol wurde weiter in Levoglucosenylmethylether umgewandelt. Levoglucosenylmethylether kann mit kationischer Ringöffnungs-Polymerisation (CROP) polymerisiert werden. Es wurden Polymere mit Molmassen von bis zu ~36 kg/mol hergestellt. Die Polymere weisen eine thermische Stabilität bis zu einer Temperatur von ~220 °C auf. Es handelt sich bei den hergestellten Poly(levoglucosenylmethylethern) um teilkristalline Thermoplaste, deren Glasüberganstemperatur bei ~35 °C und der Schmelzbereich bei 70-100 °C liegt. Die Doppelbindungen des Levoglucosenylmethylethers wurden genutzt um das Polymer zu vernetzen und zu funktionalisieren

Adiposity and Health Status among Adult Male Mundas and Oraons of Paschim Medinipur, West Bengal, India

The present cross-sectional study was conducted among two male tribal groups Munda (n=106) and Oraon (n=104) aged 18–73 years of Paschim Medinipur, West Bengal. Objective was to evaluate the health status based on body mass index (BMI) and percent body fat (PBF). Measurements of weight, height, circumferences, and skinfolds were recorded. Results revealed that mean age of Mundas (36.2±13.3) and Oraons (35.1±15.3) in years were similar. Significant (P<0.05) ethnic differences in mean chest circumference and anterior thigh skinfold were observed. Both Munda (50.0%) and Oraon (46.2%) males suffered from very high degree of chronic energy deficiency (CED) based on BMI. Similarly, for percent body fat (PBF), Mundas (29.3%) and Oraons (35.4%) had unhealthy (too low) PBF (i.e., ≤5%) levels. Significantly negative correlations were observed between age and BMI and positive correlations between age, waist-hip ratio (WHR), and conicity index (CI) (only Mundas) among Mundas and Oraons. In Linear regression, age had a significant impact on all derived central and overall adiposity measures. Prospective studies are required to determine the associations between health status and PBF as well as nutrition status and BMI in different indigenous ethnic groups of India and elsewhere

Trialkylsulfonium-based reprocessable polyurethane thermosets

We report the development of a solvent-free protocol to produce colorless, highly transparent, and glassy polyurethane-based networks containing thioether bonds using commercially available building blocks. These polyurethane networks are converted into reprocessable networks by partial alkylation of the thioether bonds, giving dynamic trialkylsulfonium bonds that are able to exchange via transalkylation at elevated temperatures, thus inducing viscoelastic flow. Reprocessability of the trialkylsulfonium networks was demonstrated for three cycles without significant degradation of material properties. Interestingly, these materials were found to be highly processable at elevated temperatures (similar to 140 degree celsius) and showed excellent creep suppression up to 100 degree celsius, a combination that is rare among dynamic covalent polymer networks. The suppression of creep can be further controlled by changing the alkylating additive. In addition, as a result of their excellent transparency and high clarity, we investigated their optical properties to assess their potential use in smart coatings and optical devices

A Highly Dynamic Covalent Polymer Network without Creep: Mission Impossible?

Dynamic covalent polymer networks provide an interesting solution to the challenging recyclability of thermosets and elastomers. One of the remaining design constraints, however, is balancing thermal reprocessability in the form of material flow with dimensional stability during use. As a result, many chemistries are being investigated in order to improve bond reactivity control and material robustness. This Minireview highlights a number of promising concepts, with a particular emphasis on disconnecting chemical reactivity in low and high temperature regimes to obtain creep resistant, yet highly dynamic polymer networks. In addition, we will highlight the impact of sharp reactivity changes when applying extrapolation-based approaches during rheological analysis. As a result, we are confident that abandoning the myth of "permanent" reactivity will aid in the development of sustainable polymeric materials that can truly combine the benefits of thermoplastic and thermoset behaviour

Structural characterization and photoelectrochemistry of coordination polymer of Pb(II)-naphthyl-isonicotinohydrazide Schiff base

An organic-inorganic hybrid Pb(II)-based 1D coordination polymer, {Pb(NSB)NO3.DMF]}(n) (CP) (H-NSB = isonicotinic acid (2-hydroxy-naphthalen-1-ylmethylene)-hydrazide; DMF = N,N-dimethylformamide), is structurally characterized by single crystal X-ray diffraction measurement and other spectroscopic data. The structure shows that the ligand, H-NSB serves as a monoanionic tetradentate N2O2 chelating linker of mu(3)-kappa N,kappa O;kappa O,N,O type, where kappa O (phenolato-O) brings two Pb(II) centres together and the tridentate NO2 unit chelates (kappa O,N,O) with one Pb(II) unit followed by its pyridyl-N links (kappa N) with nearest Pb(II) centre for propagating as a seven coordinated distorted pentagonal bi-pyramidal PbO5N2 core (one O donor comes from DMF and another O from NO3-). Thus, 1D chain is constructed that is thermally stable. The noncovalent interactions (pi center dot center dot center dot pi, H-bonding and C-H center dot center dot center dot pi) amongst the 1D chains make supramolecular 3D architecture. The Hirshfeld surface analysis approves the existence of several noncovalent interactions for the formation of 3D network. The reasonable band gap of 3.04 eV for the CP lies in the semiconducting region, which simulates fabrication of photoelectrochemical device with high magnitude of photocurrent (current density: similar to 2.5 mu A cm(-2)). Mott-Schottky analysis indicates the n-type semiconducting behaviour, and chronoamperometry plot also shows the stability of the material against photo corrosion. Present elucidation would decipher an encouraging pathway for harvesting next-generation energy resources based on a novel Pb(II)-naphthyl-isonicotinohydrazide Schiff base-based CP

A Gelation-Induced Enhanced Emission Active Stimuli Responsive and Superhydrophobic Organogelator: “Turn-On” Fluorogenic Detection of Cyanide and Dual-Channel Sensing of Nitroexplosives on Multiple Platforms

A pyrene-based highly emissive low-molecular-weight organogelator, [2-(4-fluorophenyl)-3-(pyren-1-yl)acrylonitrile] (F1), is presented, which divulges thixotropic and thermochromic fluorescence switching via reversible gel-to-sol transition and tremendous superhydrophobicity (mean contact angles: 149–160°), devoid of any gelling and/or hydrophobic units. The rationale for the design strategy reveals that the restricted intramolecular rotation (RIR) in J-type self-assembly promotes F1 for the prolific effects of aggregation- and gelation-induced enhanced emission (AIEE and GIEE). Meanwhile, hindrance in charge transfer via the nucleophilic reaction of cyanide (CN–) on the CC unit in F1 facilitates the selective fluorescence “turn-on” response in both solution [9:1 (v/v) DMSO/water] and solid state [paper kits] with significantly lower detection limits (DLs) of 37.23 nM and 13.4 pg/cm2, respectively. Subsequently, F1 discloses CN– modulated colorimetric and fluorescence “turn-off” dual-channel response for aqueous 2,4,6-trinitrophenol (PA) and 2,4-dinitrophenol (DNP) in both solution (DL = 49.98 and 44.1 nM) and solid state (DL = 114.5 and 92.05 fg/cm2). Furthermore, the fluorescent nanoaggregates of F1 in water and its xerogel films permit a rapid dual-channel “on-site” detection of PA and DNP, where the DLs ranged from nanomolar (nM) to sub-femtogram (fg) levels. Mechanistic insights reveal that the ground-state electron transfer from the fluorescent [F1-CN] ensemble to the analytes is responsible for anion driven sensory response, whereas the unusual inner filter effect (IFE) driven photoinduced electron transfer (PET) was responsible for self-assembled F1 response toward desired analytes. Additionally, the nanoaggregates and xerogel films also detect PA and DNP in their vapor phase with reasonable percentage of recovery from the soil and river water samples. Therefore, the elegant multifunctionality from a single luminogenic framework allows F1 to provide a smart pathway for achieving environmentally benign real-world applications on multiple platforms

Resorcinol-derived vitrimers and their flax fiber-reinforced composites based on fast siloxane exchange

Natural fiber-reinforced composites are gaining increased interest for their significantly reduced carbon footprint compared to conventional glass or carbon fiber-based counterparts. In this study, natural fibers are used in a resorcinol-based epoxy resin that is thermally reshapable at higher temperatures (>180 degrees C) by using fast exchanging siloxane bonds, catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene. Stress relaxation times of only about 6 s at 220 degrees C can be reached. A resorcinol-based epoxy compound is selected because it can be derived from cellulose, opening ways for more sustainable and reshapable composite materials. In a last step of the research, the low viscosity vitrimer formulation (<200 mPa s) is applied to make a flax fiber-reinforced composite using an industrially relevant vacuum-assisted resin infusion process. A section of this composite is successfully reshaped, which allows for envisioning a second life for natural fiber-reinforced composites

MANUFACTURING AND MECHANICAL CHARACTERISATION OF ADVANCED RE-FORMABLE FIBRE-REINFORCED VITRIMER COMPOSITES

Vitrimers are a new category of polymers with a dynamic covalently cross-linked network. This gives to vitrimers the chemical resistance and high mechanical properties of thermosets as they have a cross-linked structure, and the re-processability of thermoplastics thanks to the dynamic character of their network bonds. Such a unique combination of features makes vitrimers interesting for composite applications. However, the research on manufacturing and reprocessing of vitrimer composites is limited. In this work, a new epoxy-based vitrimer was used for the production of fibre-reinforced composites. Glass-Fibre-Reinforced Vitrimers (GFRVs) were produced by Vacuum Assisted Resin Infusion (VARI) and their quality was visually evaluated. The re-processability of the composite was assessed by means of thermoforming after curing and the quality of the thermoformed specimens was evaluated by digital microscopy