Evaluation of coefficient of friction in similar conditions to ejection of molding parts

The injection molding is the technique most used for processing polymers. Nowadays, due to economic demands the ejection of the parts occur as soon as possible to lead to a short cycle times. The ejection stage is the most critical phase during the injection molding processing. During this stage, especially in deep core molding, it is possible the development high friction forces making difficult the ejection of the moldings without marks or other defects. The aim of this work is to assess the coefficient of friction between the part and the mould walls in conditions similar that occurs during the ejection in the injection molding process. The assessment of the coefficient of friction was carried out with the help of one apparatus that possibility this type of measurement. This equipment provides that measure under controlled conditions as test temperature, replication temperature, material of the mould, and superficial roughness. The obtained results with several polymeric materials (semicrystalline and amorphous) show that the tribological conditions have great influence on the coefficient of friction in static conditions

Bi-component injection moulding of carbon nanofibre /polypropylene composites for multifunctional parts

Polypropylene (PP) is a low cost commodity thermoplastic, easy to process and suitable for general applications. However, for structural and electrical applications, its properties are inadequate, demanding the use of reinforcing materials that may provide mechanical strength and/or electrical conductivity. Carbon-based nanoreinforcements are known for their ability to provide good electrical and mechanical properties to polymer matrix composites. However, the improvement depends essentially on the dispersion and adhesion of the reinforcement in the matrix. In this work PP composites with carbon nanofibres (CNF) were prepared and composite samples were produced; the morphology of the nanocomposite parts was studied and correlated with its mechanical and electrical performance, aiming at understanding the ability of the nanomaterial to be applied in multi-functional parts. The approach followed in this work consisted on the preparation of nanocomposites of PP with varying concentrations of CNF (PP + 2.7 % CNF, PP + 8 % CNF and PP + 4.8% (CNF +CNT)) by blending in a twin-screw extruder. These materials were then processed by co-injection moulding to obtain bi-material parts, producing two types of nanocomposite parts: (i) with an inner core of nanocomposite and an outer layer of PP, and (ii) with an inner core of PP and outer surface layer of nanocomposite. All materials/parts obtained were characterized in terms of their morphological, mechanical, thermal and electrical properties. The morphological results showed a preferential alignment of the nanoreinforcement along the flow direction, and a good dispersion in the polymer matrix; however, CNF adhesion to PP was weak. The mechanical and electrical properties varied with the composition of the bi-material part. Thus, the parts with an inner core of PP presented similar mechanical behavior to PP, with surface antistatic characteristics. The parts with an inner core of CNF nanocomposite presented similar mechanical properties to those of plain CNF nanocomposite parts, presenting semi-conducting characteristics for volume resistivity. It was observed that the incorporation of 1 wt% CNT in a composite with approximately 3% wt CNF lead to similar mechanical and electrical properties to composites with 8% wt CNF content

Bi-component injection moulding of carbon nanofibre /polypropylene composites : morphology evaluation and correlation with mechanical and electrical properties

The work reports the preparation of polypropylene (PP)/carbon nanofibre (CNF) composites with different compositions, a PP/CNF/carbon nanotube (CNT) composite, and the production of bi-component injection moulded plaques using these materials. The plaques were formed with a composite inner core and a surface layer of PP, and inversely, with a PP core and a composite surface layer. Samples were also prepared with plain PP and plain composite for comparison. The dispersion of CNF and CNT, the distribution of the polymer/composite layers along the plates formed, and the interaction between the layers, were studied by optical and electron microscopy (OM and SEM). Mechanical properties and electrical resistivity of samples cut from the plaques were measured, and compared with those of standard injection moulded dog-bone specimens with the same composition. OM and SEM showed good dispersion of the CNF and CNT in the polymer matrix, and the presence of some agglomerates, mostly of CNT. An increase in CNF content (max. 8 wt%) on PP composites improved the tensile strength and reduced its volume electrical resistivity to about 107 ım. However, a reduction on the maximum CNF content and the incorporation of a small amount of CNT in the composite (4,5wt% of total nanofiller content, distributed approximately as 3,5% CNF + 1% CNT) have maintained the mechanical performance of the composite and reduced its electrical resistivity to about 104 ım. All bi-component systems studied showed improved mechanical properties relative to PP itself. For the PP/4,5wt% of (CNF+CNT)/PP, the mechanical and electrical properties were equivalent to those of the model plain composite

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved

Global variation in postoperative mortality and complications after cancer surgery: a multicentre, prospective cohort study in 82 countries

© 2021 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND 4.0 licenseBackground: 80% of individuals with cancer will require a surgical procedure, yet little comparative data exist on early outcomes in low-income and middle-income countries (LMICs). We compared postoperative outcomes in breast, colorectal, and gastric cancer surgery in hospitals worldwide, focusing on the effect of disease stage and complications on postoperative mortality. Methods: This was a multicentre, international prospective cohort study of consecutive adult patients undergoing surgery for primary breast, colorectal, or gastric cancer requiring a skin incision done under general or neuraxial anaesthesia. The primary outcome was death or major complication within 30 days of surgery. Multilevel logistic regression determined relationships within three-level nested models of patients within hospitals and countries. Hospital-level infrastructure effects were explored with three-way mediation analyses. This study was registered with ClinicalTrials.gov, NCT03471494. Findings: Between April 1, 2018, and Jan 31, 2019, we enrolled 15 958 patients from 428 hospitals in 82 countries (high income 9106 patients, 31 countries; upper-middle income 2721 patients, 23 countries; or lower-middle income 4131 patients, 28 countries). Patients in LMICs presented with more advanced disease compared with patients in high-income countries. 30-day mortality was higher for gastric cancer in low-income or lower-middle-income countries (adjusted odds ratio 3·72, 95% CI 1·70–8·16) and for colorectal cancer in low-income or lower-middle-income countries (4·59, 2·39–8·80) and upper-middle-income countries (2·06, 1·11–3·83). No difference in 30-day mortality was seen in breast cancer. The proportion of patients who died after a major complication was greatest in low-income or lower-middle-income countries (6·15, 3·26–11·59) and upper-middle-income countries (3·89, 2·08–7·29). Postoperative death after complications was partly explained by patient factors (60%) and partly by hospital or country (40%). The absence of consistently available postoperative care facilities was associated with seven to 10 more deaths per 100 major complications in LMICs. Cancer stage alone explained little of the early variation in mortality or postoperative complications. Interpretation: Higher levels of mortality after cancer surgery in LMICs was not fully explained by later presentation of disease. The capacity to rescue patients from surgical complications is a tangible opportunity for meaningful intervention. Early death after cancer surgery might be reduced by policies focusing on strengthening perioperative care systems to detect and intervene in common complications. Funding: National Institute for Health Research Global Health Research Unit

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

© 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licenseBackground: Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide. Methods: A multimethods analysis was performed as part of the GlobalSurg 3 study—a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital. Findings: Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3·85 [95% CI 2·58–5·75]; p<0·0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63·0% vs 82·7%; OR 0·35 [0·23–0·53]; p<0·0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer. Interpretation: Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised. Funding: National Institute for Health and Care Research