SynopsisThe ceric ion-cellulose redox system has been studied for grafting acrylonitrile on cotton fibers. Grafting yields are very high as compared to the persu1fat)ethiosulfate redox system reported earlier. Traces of copper sulfate in the reaction mixture do not increase grafting yields, unlike the persulfate-thiosulfate system. The high polymerization rate on cotton fibers is shown to be due to the reducing action of cellulose and not to the large surface area of cotton fibers. The Ce+4 consumption during grafting is higher than during oxidation of cellulose, indicating formation of homopolymer during the grafting reaction. Studies on the consumption of Ce+4 by model compounds siich as D-glucose and a-methyl-D-glucoside show that the hemiacetal group in D-glucose is responsible for a faster rate of Ce+' Consumption. Formation of a Ce+'-alcohol complex also contributes to the initial fast rate of Cef4 consumption. Studies on the oxidation of celldose by Ce+4 indicate that the initial oxidative attack occurs on carbon atom 2, with the formation of a >C=O group. On further oxidation, cleavage of the C2-G bond occurs as shown by the presence of glycol aldehyde determined chromatographically. Cellulose-polyacrylonitrile grafts have been isolated by an acetolysis treatment followed by extraction with dimethylformamide. Number-average molecular weight,s of the isolated fractions are approximately 50,000-55,000. A theoretical method to calculate the number-average molecular weights, based on the PAN and the COOH contents of the grafted cellulose, is described.
Poly(l-lactide) (PLA), a biodegradable and biorenewable polymer, has many excellent properties that are equivalent to those of petroleum-derived plastics such as polystyrene, aromatic polyesters, etc. However, a major disadvantage of PLA which limits its processability is its poor melt elasticity. In this work we explore the possibility of improving the viscoelastic properties of PLA melt by incorporating ionic groups on the polymer. Specifically, we demonstrate the synthesis of star telechelic PLA anionomers by a three-step procedure involving synthesis of Star PLA, converting the hydroxyl end groups into carboxylic acid end groups, and finally converting these into ionic groups. Rheology data showed a dramatic increase in the elasticity of the star telechelic ionomer melts relative to the Star PLA melts. The viscoelasticity of star telechelic ionomers melts could be modulated by varying the number of ionic groups per molecule.
We are facing a rapidly growing plastic pollution crisis, which is adversely affecting communities and ecosystems across the globe. Polymer scientists have an urgent obligation to develop and implement strategies for reutilizing plastic waste streams instead of continually relying on virgin feedstocks in plastic manufacturing. Postconsumer and postindustrial plastic items should be treated as valuable resources instead of discarding them. In order to do this, technological outlets must be developed to produce renewed materials using plastic waste as an input. Polyesters represent one of the largest plastic waste streams because they are commonly used in single-use beverage and food containers as well as textiles. Polyesters are also ideal candidates to exploit through chemical diversification, owing to the wide variety of functional derivatives that can be synthetically accessed via ester reactivity. This work highlights some recent developments related to diversifying polyester waste, with a focus on poly(ethylene terephthalate) (PET) as waste stream. The strategies encompass the production of both valuable small molecules prepared via degradation of PET and high-performance polymeric scaffolds derived from reactions with PET. Taking the recent ingenuity into consideration, based on these technological developments, an outlook is provided for the future of polyester waste streams. What are the next steps that are needed? Where are these trends headed? What gaps still exist, particularly with respect to assessment of sustainability and life cycle analysis? Collectively considering the examples highlighted here, there is great promise in the field of reutilizing waste streams as feedstocks for value-added materials.
Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries.
With a sodium thiosulfate–potassium persulfate redox system, in situ polymerization of acrylonitrile was studied in cellulosic materials. Traces of copper are found to accelerate the rate of polymerization, giving higher yields on the treated materials. Other variables studied were (a) material/liquor ratios, (b) monomer concentrations, and (c) initiator concentrations. It is found that high material/liquor ratios and higher initiator concentrations cause increased polymer yields on cotton fabrics. Fabrics containing polyacrylonitrile (PAN) are resistant to microbial degradation. Acrylonitrile was polymerized in secondary cellulose acetate, mercerized cotton, and cellophane. Studies of the insolubility behavior of the treated cellulose acetate samples in acetone and dimethylformamide, and of mercerized cotton and cellophane in cuprammonium hydroxide, were carried out for the purpose of examining the presence of cellulose‐PAN grafts. In the latter case, a constant ratio of cellulose to PAN was obtained in the cuprammonium hydroxide‐insoluble fraction over a wide range of polymer add‐ons. Alkaline saponification of the nitrile groups in the treated cotton fabrics, followed by a treatment with formaldehyde at pH 9–9.5 and subsequent curing in the presence of an acid catalyst, yield highly crosslinked fabrics which exhibit a considerable improvement in the wet crease recovery with slight loss in tensile and tear strengths. It is believed that these changes are brought about by the formation of a CO · NH · CH2. Ocellulose type of crosslink. These results strongly support the presence of a cellulose‐PAN graft.
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