Production, functionalization and application of carbon materials.

The work of this thesis was structured into 2 main activities: (1) to devise a surface functionalization technique for commercial carbon fibres (CFs) based on lignin precursor developed under the European Union FP7 Project “Functionalized Innovative Carbon Fibres Developed from Novel Precursors with Cost Efficiency and Tailored Properties” (FIBRALSPEC), grant agreement No. 604248. (2) To perform the exploration of low cost carbon fillers for application to polymer composites. 1st chapter presents a general introduction of the different carbon materials and their applications. 2nd chapter is concerned with the existing commercial carbon fibre manufacturing techniques and precursors. A small portion on the surface modification techniques is also added in this chapter. The 3rd chapter deals with the production techniques and limitations of Carbon nano tubes as a filler for the application to composites. A brief introduction on biochar materials has been added as well. The 4th chapter deals with functionalization study of commercial carbon fibres and lignin based carbon fibres. Commercial carbon fibres T700 were purchased from Toray, Japan to study the surface modification through low pressure oxygen plasma at Polito. Treatment parameters in an oxygen environment such as holding time (1~10 minutes), plasma power (100~200 W), flow rate (250 Standard Cubic Centimeters) and plasma chamber pressure (53 Pa) were set. Morphology of the carbon fibres before and after plasma treatment was studied through Field Emission Scanning Electron Microscopy (FESEM). Chemical nature of the functional groups formed on the carbon fibres surface after the treatment was studied through Fourier Transform Infrared (FTIR) spectroscopy and atomic percent was quantified through X-Ray Photoelectron Spectroscopy (XPS). Raman spectroscopy was carried out to study the structural changes in the carbon fibres. Wettability test was carried out to study the interaction of the surface functional groups with epoxy matrix. Tensile strength of the CFs was determined after the plasma treatment to ensure optimum mechanical performances of the treated fibres in the subsequent composites. In order to ensure the effectiveness of the plasma treatment the same samples were studied after six months of storage in ambient conditions. On the basis of the obtained results from the activities above, optimum plasma treatment parameters such as treatment time, plasma power, oxygen flow rate, plasma chamber pressure were singled out and applied on the lignin based carbon fibres. The lignin based CFs were plasma treated for 5 minutes at 100 W and 200W at a flow rate of 250 SCCM and 53 Pa plasma chamber pressure. Surface morphology was studied through FESEM. Plasma treated fibres showed canals and pits on the surface. The fibre started to damage at a plasma power of 200W. Also the oxygen pickup reduced at this treatment power as depicted by the XPS analysis. The 200 W, 5 minutes treatment was identified as an upper limit for the treatment parameter. The treated fibres were shredded finely and dispersed in epoxy resin using an overhead mixer to produce composites. Mechanical and tribological analysis was carried out and compared with the neat epoxy and untreated CFs composites. The plasma treated carbon fibre composites outperformed their counterparts. Based on the observations we recommended low pressure oxygen plasma treatment for the surface modification of the lignin based carbon fibres intended for commercial use. To further support our recommendations we produced carbon fibers from waste cotton clothes in Polito and applied the same treatment to them. The temperature profile for the thermal treatment was deduced from thermogravimetric analysis of cotton fibres in argon environment. XPS and FTIR analysis was carried out to ensure the absence of any impurity in the cotton fabrics. Carbonization process was carried out in a Carbolite furnace (TZF12/65/550) at the temperatures of 400o C, 600o C and 800o C for one hour in nitrogen environment at a ramp rate of 15o C/minute. The sample prepared at 800o C was selected to study the plasma treatment due to its more ordered structure and high carbon content as depicted by the Raman and XPS analysis respectively. The carbon fibres were treated with oxygen plasma at 100 W and 200 W for 5 minutes. Surface morphology and structure of the treated CFs were studied via FESEM and Raman spectroscopy. Surface of the treated fibres showed pits and canals confirming the action of the plasma elements while a degradation of the ID/IG ratio in the Raman spectra evidenced the effects of the plasma elements on the structure of the CFs. The functional groups on the surface of the plasma treated CFs were studied through X-Ray Photoelectron Spectroscopy and Fourier Transform Infrared spectroscopy. Chemical groups like alcohols, carboxyl and carbonyl were found on the surface of the treated CFs. BET analysis showed that surface area of the fibers increased after treatment. The plasma treated CFs retained higher amount of the epoxy resin in the wettability test. The plasma treated fibres were applied in composites. Epoxy based composites were fabricated with the pristine and treated CFs in 1% and 3% by weight. Mechanical and tribological analysis was carried out on all composites. The composites of the plasma treated fibres showed superior mechanical and tribological properties when compared to their untreated CFs counterparts. Morphology of the mechanical and tribological specimen were studied with FESEM to investigate the interaction of the filler with the matrix. Above results supported our earlier argument and low pressure oxygen plasma was recommended as a suitable treatment for the modification of the carbon fibres. The 2nd part of the thesis emphasizes the application of cheap precursor based carbon materials for the tailoring of composites properties. In recent years, low-cost carbons derived from recycled materials have gained a lot of attention for their potentials as filler in composites and in other applications. The electrical, frictional and mechanical properties of polymer composites can be tailored using different percentages of these fillers. In the Carbon lab at Polito we synthesized carbon nano materials (CNMs) from waste polyethylene bags in two different morphologies namely carbon nano beads (CNBs) (P1) and a mix of carbon nano tubes (CNTs) and carbon nano beads (P2) using chemical vapour deposition (CVD) technique by varying the carrier gas pressure. Morphology of the CNMs were studied through FESEM and their purity through Thermogravimetric Analysis (TGA) and Raman spectroscopy. Epoxy based composites were fabricated using these CNMs as filler in 1% and 3 % by weight. Mechanical properties and tribological properties were compared with the epoxy composites of commercial Multi Walled Carbon Nano Tubes (MWCNT). It is observed that the in house generated CNMs composites show overall better mechanical and tribology properties compared to the neat epoxy and the commercial MWCNTs based composites. Morphology of the composites was analysed through FESEM to study the interaction of the filler with the matrix that lead to improved performances. A model on the fracture behaviour was proposed on basis of FESEM analysis. Chapter 6 is concerned with this activity. In chapter 7, the maple based biochar has been explored as a cheap alternative filler to enhance the polymer properties. In this regard, the mechanical, tribological and electrical behavior of composites with two types of biochar based on maple wood namely biochar and biochar HT were investigated and compared with those of a composite containing multiwall carbon nanotubes. HT is heat treated at 900o C in nitrogen at 1 hour. Superior mechanical properties (ultimate tensile strength, Young modulus and tensile toughness) were noticed at low biochar concentrations 2~4 wt. %). Biochar based composites showed equivalent tribology properties to the composites fabricated with MWCNTs. Furthermore, dielectric properties in the microwave range comparable to low carbon nanotubes loadings can be achieved by employing larger but manageable amounts of biochar (20 wt. %) rending the production of composites for structural and functional application cost-effective. Conclusive remarks and future plans are compiled in chapter 8

Microwave characterization of polymer composite based on Biochar: A comparison of composite behaviour for Biochar and MWCNTs

In this work, Biochar is used as a filler in Epoxy resin for composite preparation. The electrical characteristics of composites are analyzed in function of different filler percentages. Results obtained are compared with composites based on multi-wall carbon nanotubes

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

Surgical site infection after gastrointestinal surgery in high-income, middle-income, and low-income countries: a prospective, international, multicentre cohort study

Background: Surgical site infection (SSI) is one of the most common infections associated with health care, but its importance as a global health priority is not fully understood. We quantified the burden of SSI after gastrointestinal surgery in countries in all parts of the world. Methods: This international, prospective, multicentre cohort study included consecutive patients undergoing elective or emergency gastrointestinal resection within 2-week time periods at any health-care facility in any country. Countries with participating centres were stratified into high-income, middle-income, and low-income groups according to the UN's Human Development Index (HDI). Data variables from the GlobalSurg 1 study and other studies that have been found to affect the likelihood of SSI were entered into risk adjustment models. The primary outcome measure was the 30-day SSI incidence (defined by US Centers for Disease Control and Prevention criteria for superficial and deep incisional SSI). Relationships with explanatory variables were examined using Bayesian multilevel logistic regression models. This trial is registered with ClinicalTrials.gov, number NCT02662231. Findings: Between Jan 4, 2016, and July 31, 2016, 13 265 records were submitted for analysis. 12 539 patients from 343 hospitals in 66 countries were included. 7339 (58·5%) patient were from high-HDI countries (193 hospitals in 30 countries), 3918 (31·2%) patients were from middle-HDI countries (82 hospitals in 18 countries), and 1282 (10·2%) patients were from low-HDI countries (68 hospitals in 18 countries). In total, 1538 (12·3%) patients had SSI within 30 days of surgery. The incidence of SSI varied between countries with high (691 [9·4%] of 7339 patients), middle (549 [14·0%] of 3918 patients), and low (298 [23·2%] of 1282) HDI (p < 0·001). The highest SSI incidence in each HDI group was after dirty surgery (102 [17·8%] of 574 patients in high-HDI countries; 74 [31·4%] of 236 patients in middle-HDI countries; 72 [39·8%] of 181 patients in low-HDI countries). Following risk factor adjustment, patients in low-HDI countries were at greatest risk of SSI (adjusted odds ratio 1·60, 95% credible interval 1·05–2·37; p=0·030). 132 (21·6%) of 610 patients with an SSI and a microbiology culture result had an infection that was resistant to the prophylactic antibiotic used. Resistant infections were detected in 49 (16·6%) of 295 patients in high-HDI countries, in 37 (19·8%) of 187 patients in middle-HDI countries, and in 46 (35·9%) of 128 patients in low-HDI countries (p < 0·001). Interpretation: Countries with a low HDI carry a disproportionately greater burden of SSI than countries with a middle or high HDI and might have higher rates of antibiotic resistance. In view of WHO recommendations on SSI prevention that highlight the absence of high-quality interventional research, urgent, pragmatic, randomised trials based in LMICs are needed to assess measures aiming to reduce this preventable complication

Global economic burden of unmet surgical need for appendicitis

Background: There is a substantial gap in provision of adequate surgical care in many low-and middle-income countries. This study aimed to identify the economic burden of unmet surgical need for the common condition of appendicitis. Methods: Data on the incidence of appendicitis from 170 countries and two different approaches were used to estimate numbers of patients who do not receive surgery: as a fixed proportion of the total unmet surgical need per country (approach 1); and based on country income status (approach 2). Indirect costs with current levels of access and local quality, and those if quality were at the standards of high-income countries, were estimated. A human capital approach was applied, focusing on the economic burden resulting from premature death and absenteeism. Results: Excess mortality was 4185 per 100 000 cases of appendicitis using approach 1 and 3448 per 100 000 using approach 2. The economic burden of continuing current levels of access and local quality was US $92 492 million using approach 1 and$73 141 million using approach 2. The economic burden of not providing surgical care to the standards of high-income countries was $95 004 million using approach 1 and$75 666 million using approach 2. The largest share of these costs resulted from premature death (97.7 per cent) and lack of access (97.0 per cent) in contrast to lack of quality. Conclusion: For a comparatively non-complex emergency condition such as appendicitis, increasing access to care should be prioritized. Although improving quality of care should not be neglected, increasing provision of care at current standards could reduce societal costs substantially

Pooled analysis of WHO Surgical Safety Checklist use and mortality after emergency laparotomy

Background The World Health Organization (WHO) Surgical Safety Checklist has fostered safe practice for 10 years, yet its place in emergency surgery has not been assessed on a global scale. The aim of this study was to evaluate reported checklist use in emergency settings and examine the relationship with perioperative mortality in patients who had emergency laparotomy. Methods In two multinational cohort studies, adults undergoing emergency laparotomy were compared with those having elective gastrointestinal surgery. Relationships between reported checklist use and mortality were determined using multivariable logistic regression and bootstrapped simulation. Results Of 12 296 patients included from 76 countries, 4843 underwent emergency laparotomy. After adjusting for patient and disease factors, checklist use before emergency laparotomy was more common in countries with a high Human Development Index (HDI) (2455 of 2741, 89.6 per cent) compared with that in countries with a middle (753 of 1242, 60.6 per cent; odds ratio (OR) 0.17, 95 per cent c.i. 0.14 to 0.21, P <0001) or low (363 of 860, 422 per cent; OR 008, 007 to 010, P <0.001) HDI. Checklist use was less common in elective surgery than for emergency laparotomy in high-HDI countries (risk difference -94 (95 per cent c.i. -11.9 to -6.9) per cent; P <0001), but the relationship was reversed in low-HDI countries (+121 (+7.0 to +173) per cent; P <0001). In multivariable models, checklist use was associated with a lower 30-day perioperative mortality (OR 0.60, 0.50 to 073; P <0.001). The greatest absolute benefit was seen for emergency surgery in low- and middle-HDI countries. Conclusion Checklist use in emergency laparotomy was associated with a significantly lower perioperative mortality rate. Checklist use in low-HDI countries was half that in high-HDI countries.Peer reviewe

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract 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

Global variation in anastomosis and end colostomy formation following left-sided colorectal resection

Background End colostomy rates following colorectal resection vary across institutions in high-income settings, being influenced by patient, disease, surgeon and system factors. This study aimed to assess global variation in end colostomy rates after left-sided colorectal resection. Methods This study comprised an analysis of GlobalSurg-1 and -2 international, prospective, observational cohort studies (2014, 2016), including consecutive adult patients undergoing elective or emergency left-sided colorectal resection within discrete 2-week windows. Countries were grouped into high-, middle- and low-income tertiles according to the United Nations Human Development Index (HDI). Factors associated with colostomy formation versus primary anastomosis were explored using a multilevel, multivariable logistic regression model. Results In total, 1635 patients from 242 hospitals in 57 countries undergoing left-sided colorectal resection were included: 113 (6·9 per cent) from low-HDI, 254 (15·5 per cent) from middle-HDI and 1268 (77·6 per cent) from high-HDI countries. There was a higher proportion of patients with perforated disease (57·5, 40·9 and 35·4 per cent; P < 0·001) and subsequent use of end colostomy (52·2, 24·8 and 18·9 per cent; P < 0·001) in low- compared with middle- and high-HDI settings. The association with colostomy use in low-HDI settings persisted (odds ratio (OR) 3·20, 95 per cent c.i. 1·35 to 7·57; P = 0·008) after risk adjustment for malignant disease (OR 2·34, 1·65 to 3·32; P < 0·001), emergency surgery (OR 4·08, 2·73 to 6·10; P < 0·001), time to operation at least 48 h (OR 1·99, 1·28 to 3·09; P = 0·002) and disease perforation (OR 4·00, 2·81 to 5·69; P < 0·001). Conclusion Global differences existed in the proportion of patients receiving end stomas after left-sided colorectal resection based on income, which went beyond case mix alone