Sustainable polymers

peer reviewedSustainable polymers are materials derived from renewable, recycled and waste carbon resources and their combinations, which at the end of life can be recycled, biodegraded or composted. Sustainable polymers also exhibit reduced environmental impact throughout their life cycle. This Primer presents an overview of the research in and potential of sustainable polymers, with a focus on their life cycle, synthetic routes from renewable carbon feedstocks, production, material characterization, applications, end of life, data reproducibility and limitations faced, and provides a brief outlook. The Primer also briefly covers other carbon feedstocks such as carbon dioxide and wastes, including agricultural and woody residues. Although still in their infancy, new sustainable polymers are already finding applications in packaging, automotive parts and 3D printing. This Primer also discusses the headwinds facing the adoption of sustainable polymers, including complexities of recycling and composting, manufacturing scale-up, data reproducibility, deposition and potential solutions. Development of sustainable polymers will accelerate the age of sustainable polymers and create a truly circular economy for plastics by reducing production and use of virgin plastics from finite resources

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Super Toughened Poly(lactic acid)-Based Ternary Blends via Enhancing Interfacial Compatibility

Novel super toughened bioplastics are developed through controlled reactive extrusion processing, using a very low content of modifier, truly a new discovery in the biodegradable plastics area. The super toughened polylactide (PLA) blend showing a notched impact strength of ∼1000 J/m with hinge break behavior is achieved at a designed blending ratio of PLA, poly­(butylene succinate) (PBS), and poly­(butylene adipate-co-terephthalate) (PBAT), using less than 0.5 phr peroxide modifier. The impact strength of the resulting blend is approximately 10 times that of the blend with the same composition without a modifier and ∼3000% more than that of pure PLA. Interfacial compatibilization among the three biodegradable plastics took place during the melt extrusion process in the presence of a controlled amount of initiator, which is confirmed by scanning electron microscopy and rheology analysis. The synergistic effect of strong interfacial adhesion among the three blending components, the decreased particle size of the most toughened component, PBAT, to ∼200 nm, and its uniform distribution in the blend morphology result in the super tough biobased material. One of the key fundamental findings through the in situ rheology study depicts that the radical reaction initiated by peroxide occurs mainly between PBS and PBAT and not with PLA. Thus, the cross-linking degree can be controlled by adjusting renewable sourced PLA contents in the ternary blend during reactive extrusion processing. The newly engineered super toughened PLA with high stiffness and high melt elasticity modulus could reasonably serve as a promising alternative to traditional petroleum plastics, where high biobased content and biodegradability are required in diverse sustainable packaging uses

3D printing in upcycling plastic and biomass waste to sustainable polymer blends and composites: A review

Mishandling of waste plastics and biomasses is a major global concern. Every year, around 380 million tonnes of plastic are produced, with only 9% being recycled, leading to widespread pollution. Similarly, waste biomass generation from agricultural and forestry sectors accounts for 140 billion metric tonnes, in addition to 2.01 billion tonnes from municipal solid waste. This review paper addresses the gap regarding the integration of 3D printing, upcycling of recycled plastics, and the utilization of waste biomass in sustainable composites. 3D printed parts from recycled plastic have shown comparable mechanical properties compared to virgin materials, which have been further improved by the addition of waste biomass-derived fillers. The paper acknowledges that different printing parameters have substantial influence on the strength, ductility, crystallinity, and dimensional accuracy of printed parts. Therefore, optimizing these parameters becomes crucial for achieving improved mechanical performance. Moreover, incorporating reinforcing agents, stabilizers, chain extenders, compatibilizers, and surface modifiers in plastic recycling and 3D printing presents an excellent opportunity to enhance mechanical properties, thermal stability, adhesion, and dimensional stability. Additionally, the review identifies research gaps and proposes the integration of machine learning and artificial intelligence for enhanced process control and material development, further expanding the possibilities in this field

Alkali and Peroxide Bleach Treatments on Spring Harvested Switchgrass for Potential Composite Application

Natural fibers are desirable in composite applications for their sustainability. However, improving upon the interfacial adhesion between the fiber and matrix is a major challenge. Chemical surface modification is a method used to improve compatibility of the fiber by exposing or adding functionalities to the surface, and removing non-cellulosic components in order to enhance mechanical and thermal properties. Switchgrass, an abundant natural fiber, has potential for use as a reinforcing material in composite applications. Surface modifications were conducted on switchgrass via alkali and peroxide bleaching treatments in order to remove surface impurities and create a rougher surface, as observed in scanning electron micrographs. Fourier transform infrared spectroscopy and compositional analysis showed that non-cellulosic components were reduced following the alkali and bleach treatments. Reduction of hemicellulose and lignin improved thermal stability by increasing the onset temperature of degradation from 258 °C to 289 and 281 °C for alkali and bleach treatments, respectively. The crystallinity index (CI) of untreated and treated fibers was calculated from x-ray diffraction analyses. An increase of 48% and 38% for the alkali and bleach treated fibers, respectively, was seen in the CI, compared to the untreated switchgrass. The surface of switchgrass was successfully modified using alkali and peroxide bleach treatments for composite applications