Investigation of the oxidative degradation mechanisms and melt stabilisation of a new generation metallocene polytehylene

The two main objectives of the research work conducted were firstly, to investigate the processing and rheological characteristics of a new generation metallocene catalysed linear low density polyethylene (m-LLDPE), in order to establish the thermal oxidative degradation mechanism, and secondly, to examine the role of selected commercial stabilisers on the melt stability of the polymers. The unstabilised m-LLDPE polymer was extruded (pass I) using a twin screw extruder, at different temperatures (210-285°C) and screw speeds (50-20rpm) and was subjected to multiple extrusions (passes, 2-5) carried out under the same processing conditions used in the first pass. A traditional Ziegler/Natta catalysed linear low density polyethylene (z-LLDPE) produced by the same manufacturer was also subjected to a similar processing regime in order to compare the processability and the oxidative degradation mechanism (s) of the new m-LLDPE with that of the more traditional z-LLDPE. The effect of some of the main extrusion characteristics of the polymers (m-LLDPE and z-LLDPE) on their melt rheological behaviour was investigated by examining their melt flow performance monitored at two fixed low shear rate values, and their rheological behaviour investigated over the entire shear rates experienced during extrusion using a twin-bore capillary rheometer. Capillary rheometric measurements, which determine the viscous and elastic properties of polymers, have shown that both polymers are shear thinning but the m-LLDPE has a higher viscosity than z-LLDPE and the extent of reduction in viscosity of the former when the extrusion temperature was increased from 210°C to 285°C was much higher than in the case of the z-LLDPE polymer. This was supplied by the findings that the m-LLDPE polymer required higher power consumption under all extrusion conditions examined. It was fUliher revealed that the m-LLDPE undergoes a higher extent of melt fracture, the onset of which occurs under much lower shear rates than the Ziegler-based polymer and this was attributed to its higher shear viscosity and narrower molecular weight distribution (MWD). Melt flow measurements and GPC have shown that after the first extrusion pass, the initial narrower MWD of m-LLDPE is retained (compared to z-LLDPE), but upon further multiple extrusion passes it undergoes much faster broadening of its MWD which shifts to higher Mw polymer fractions, paliicularly at the high screw speeds. The MWD of z-LLDPE polymer on the other hand shifts towards the lower Mw end. All the evidence suggest therefore the m-LLDPE undergoes predominantly cross-linking reactions under all processing conditions whereas z-LLDPE undergoes both cross-linking and chain scission reactions with the latter occurring predominantly under more severe processing conditions (higher temperatures and screw speeds, 285°CI200rpm). The stabilisation of both polymers with synergistic combinations of a hindered phenol (Irganox 1076) and a phosphite (Weston 399) at low concentrations has shown a high extent of melt stabilisation in both polymers (extrusion temperatures 210-285°C and screw speeds 50-200rpm). The best Irganox 1076/Weston 399 system was found to be at an optimum 1:4 w/w ratio, respectively and was found to be most effective in the z-LLDPE polymer. The melt stabilising effectiveness of a Vitamin E/Ultranox 626 system used at a fraction of the total concentration of Irganox 1076/Weston 399 system was found to be higher in both polymers (under all extrusion conditions). It was found that AOs which operate primarily as alkyl (Re) radical scavengers are the most effective in inhibiting the thermal oxidative degradation of m-LLDPE in the melt; this polymer was shown to degrade in the melt primarily via alky radicals resulting in crosslinking. Metallocene polymers stabilised with single antioxidants of Irganox HP 136 (a lactone) and Irganox E201 (vitamin E) produced the highest extent of melt stability and the least discolouration during processing (260°C/1 OOrpm). Furthermore, synergistic combinations of Irganox HP I 36/Ultranox 626 (XP-60) system produced very high levels of melt and colour stability (comparable to the Vitamin E based systems) in the mLLDPE polymer. The addition of Irganox 1076 to an Irganox HP 136/Ultranox 626 system was found not to result in increasing melt stability but gave rise to increasing discolouration of the m-LLDPE polymer. The blending of a hydroxylamine (lrgastab FS042) with a lactone and Vitamin E (in combination with a phosphite) did not increase melt stability but induced severe discolouration of resultant polymer samples

Applications and Limitations of Suction Assisted Transverse Medial Thigh Lift

Aims and objectives: Skin laxity or excess can be a part of ageing process and weight loss. Skin laxity or excess is commonly experienced following weight loss around arms, thighs, face and neck, breast and abdomen. Various methods and techniques are described to address these excess skin issues. Liposuction assisted abdominoplasty has been described by Saldanha along with Colour Doppler studies of the superior and inferior epigastric arteries. Similarly DJ Hurwitz has described liposuction assisted brachioplasty. The process allows honeycombing of the subcutaneous tissue when suction lipectomy is performed using blunt tipped cannulas. Process allows creation of a safe plane superior to the deep fascial layer with preservation of the important nerves and vessels. Skin excess is removed without the need of sharp dissection or risks to the underlying structures. Postoperative bleeding and bruising is minimal and most of the instances the procedure is performed as a day case without drains. Patient postoperative analgesia requirements are minimal and allows patient to ambulate early with a quick recovery. Methods: Between 2009 and 2018, 153 suction assisted procedure were performed on various parts of the body. Of the 153 procedures 22 patients had thigh lifts as an outpatient. Results: There was no skin loss, DVT, PE or motor nerve damage. All patients retained sensation of the distal limbs

Teacher’s Questioning Effects on Students Communication in Classroom Performance

Classroom questioning has been more of a puzzle regarding its role in learning output among school students. Research studies point to its significance in affecting students’ performance and achievement. The purpose of this study is to investigate how students perceive teachers’ questions in the classroom and relate them to their academic participation. The study also inquires question-types that are more or less favorably received and their consequences. The study is conducted in three schools (Grade V to VIII), and a sample of 50 students was purposively selected and interviewed through semi-structured interviews. A qualitative method is used to analyze the data; where the primary data is supported by secondary information and previous scholarly arguments. The discussion reveals that questioning in the classroom is positively associated. The study recommends that training sessions and workshops should be organized for teachers along with induction of practical courses on how to use effective questions in the classroom. Furthermore, developmental questions can be used by developmental managers in the workplace as they encourage their employees to think for themselves when taking care of customers and increasing productivity. Keywords: Teachers, classroom, questioning, high-order question, low-order question, wait time

The dormancy of empowerment: An analytical study of various impediments to women’s education in Khyber Pakhtunkhwa province of Pakistan

Education is a key to empower women, control their lives and a source to overcome the oppressive customs and traditions which are resisting their educational participation.The present study describes the socio-cultural, economic and religious impediments to women’s education in Malakand Division, Khyber Pakhtunkhwa province, Pakistan. The data was collected from 320 respondents categorized in different segments with proportional allocation method of stratified random sampling technique using questionnaire as a tool of data collection.The data has been analyzed by applying Chi-square test, correlation technique and processed in the form of tables and bar-charts, while discussions have been made on the basis of findings and results.The results show that socio-cultural, economic, religious and political constraints exist in women’s education, which has adversely affected the developmental process.The study suggests that proper policy making, implementation, availability of educational institutions etc.would promisingly increase women’s education in Pakhtun society

Temporal–spatial variability of grazing behaviors of yaks and the drivers of their intake on the eastern Qinghai-Tibetan Plateau

IntroductionGrassland-livestock balance is an important principle of sustainable development of grassland livestock production and grassland ecosystem health. Grassland degradation becomes more serious at global scales and especially at the area that is sensitive to climate change and human activities. Decreases in pasture biomass and shifts in plant community composition in degraded grasslands can largely affect grazing behaviors of livestock. Up to date, however, it is unclear that whether livestock behaviors change across spatial and temporal scales and what key factors are to shape observed behavioral patterns of livestock.MethodsHere, yak behaviors including grazing, rumination and walking on the eastern Qinghai-Tibetan Plateau (QTP) were monitored by a continuous visual observation, to investigate temporal and spatial variations of grazing behavior of yaks (Bos grunniens); based on the data from public database in the past 18 years, a meta-analysis was conducted to examine the main factors that affect grazing behaviors and intake of yaks.ResultsWe showed that grazing behaviors of yaks differed significantly within hours, among hours of each day and among days as well as across different observation sites. Intake rate of yaks was higher in the morning than in the afternoon, but walking speed showed an inverse trend compared with intake rate. Resting, altitude, the mean annual precipitation (MAP), the mean annual temperature (MAT), forage ash, yak age and season were the main predictors for yak intake, and forage and yak individual characteristics had direct effects on grazing behaviors and intake of yaks.DiscussionThe findings confirm that grazing behaviors of yaks can vary even at small temporal scales and regional scales, which is closely related to the shift in forage quality and biomass caused by environmental changes. The study suggests that multiple factors can be responsible for the variation in livestock behaviors and shifts in behavioral patterns may consequently lead to positive or negative feedback to grassland ecosystems through plant-animal interactions

Augmentation mastopexy and augmentation mammoplasty: an analysis of 1,406 consecutive cases

Aim: Simultaneous augmentation mastopexy is a challenging operation for esthetic plastic surgeons. Complication and revision rates following augmentation mammoplasty or mastopexy are less commonly seen when these two procedures are performed separately. However, when the two procedures are combined, the complication rate is reported exponentially higher when compared with its individual component carried out separately. The current retrospective chart review is a comparative analysis of the two procedures performed by a single surgeon.Methods: Retrospective data were collected using patient’s charts. All patients who had augmentation mammoplasty (Group A) or simultaneous augmentation with mastopexy (Group B) in muscle splitting biplane using round cohesive gel textured silicone implants by a single surgeon were included.Results: A total of 1,406 patients had consecutive augmentation mammoplasty or simultaneous augmentation mastopexy. Augmentation mammoplasty (Group A) included 1,298 and simultaneous augmentation with mastopexy (Group B) had 108 patients, respectively. The mean age of the patients in Group A and B was 29.6 years and 32.2 years, respectively (P = 0.006). The mean size of the implants in Group A and B was 340 mL and 308 mL (P = 0.001), respectively. Wound infection in Group A and B was seen in 0.6% and 3.7%, respectively. Wound breakdown was seen in 1.1% in Group A as compared to 6.5% in Group B (P = 0.001). Revision surgeries were performed in 1.4% and 11.1% of Group A and B, respectively (P = 0.001).Conclusion: There was a statistically and clinically significant higher rate of complications and revision rate noted in simultaneous augmentation with mastopexy (Group B) as compared to augmentation mammoplasty alone (Group A). However, the rise in complications rate is sum of the complications of the two individual components performed and not exponential

Preoperative planning and breast implant selection for volume difference management in asymmetrical breasts

Aim: To assess volume management in patients presenting with breast asymmetry and ptosis.Methods: Retrospectively collected data was analysed. The patients were divided into 3 groups. Group A included patients who had volumetric difference alone and had different size implants alone. Group B included patients who had volumetric difference with breast ptosis requiring mastopexy with different size implants. Group C included patients who presented with breast asymmetry with ptosis and had same size implants on both sides with different volume breast reduction.Results: Subgroup A1 included 145 patients who had larger implants placed on right side. Subgroup A2 included 95 patients who had larger implants on the left side. Subgroup B1 included 7 patients who had larger implants on the right. Subgroup B2 included 13 patients who had larger implant on the left side. Subgroup C1 included 7 patients who had larger reduction on right side. Subgroup C2 included 11 patients who had larger reduction on left.Conclusion: When different volume implants are used, the vast majority of the patients do not require a volume difference of more than 60 mL. When the breast is larger on the right then larger mean volumes are used on left side to offset the larger right breast

A long term review of augmentation mastopexy in muscle splitting biplane

Aim: Simultaneous or single stage mastopexy with augmentation is challenging, unique and commonly performed by a plastic surgeon. In this procedure pocket for implant placement, marking for envelope reduction and type of implants used can affect the outcome of the procedure. Muscle splitting pocket for mastopexy is a plane described by the author for implant placement with a short term follow up. The use and outcome of the technique is presented with a larger series and a long term follows up to evaluate the efficacy of the procedure.Methods: Retrospective data was collected. Augmentation was performed using muscle splitting technique and periareolar, vertical scar and wise pattern were used for skin reduction and mastopexy. A single surgeon performed all procedures.Results: In total 108 patients mastopexy with augmentation in muscle splitting technique. The mean age of the patient was 32.2 years (range: 18-67 years) with an average follow up of 4.5 years (range: 3 months to 10 years). All patients had round textured cohesive gel silicone implants with a mean size of 308 cc (range: 200-555 cc). Wound infection was seen in 4 (3.7%), wound breakdown in 7 (6.5%) patients. Drains were used in 25 (23.1%). All patients were treated as day cases and revision surgery was performed in 12 (11.1%). There was no hematoma, deep venous thrombosis (DVT) or nipple areolar complex in the series.Conclusion: Simultaneous augmentation mastopexy in muscle splitting pocket can be performed with good aesthetic results along with an acceptable revision rate

Pathogenesis, presentation and classification of late autoinflation of the breasts: case report and literature search

Aim: Autoinflation of the breast following mammoplasty using breast implants can be divided into early and late. Early autoinflation of the breast is commonly due to haematoma. Late autoinflation of the breast is an uncommon complication and its true incidence is not known due to the paucity of its reporting.Methods: A retrospective review was performed of the available charts for 2,772 consecutive bilateral primary, secondary augmentation mammoplasties and mastopexy with augmentation mammoplasties by the author between April 1999 and February 2015. Each breast was taken as a single unit for a total of 5,544 breasts.Results: There were 2,334 patients in primary augmentation mammoplasty, 258 in secondary augmentation mammoplasty and 180 in simultaneous mastopexy with augmentation mammoplasty. There were three autoinflation of breasts due to late seromas identified in the series. All patients presented at least six months following augmentation mammoplasty and all had textured implants place in muscle splitting submuscular pocket. There was no late seroma noted in secondary augmentation mammoplasty or simultaneous mastopexy with augmentation mammoplasty. All patients were treated conservatively without a recurrence.Conclusion: Late autoinflation of the breast due to seroma is an uncommon clinical complication and can be treated conservatively in the first instance