- About
-
The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
provided by the
Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
Search results
Showing 1 to 3 of 3 (0.017 seconds)| 1 |
Strength of hydroentangled fabrics manufactured from photo-irradiated poly para-phenylene terephthalamide (PPTA) fibresWright, T.M., Carr, C.M., Grant, Colin A., Lilladhar, V., Russell, S.J. 30 August 2014 (has links)
No / Photo-irradiation of poly para-phenylene terephthalamide (PPTA) fibre is normally associated with
deterioration of physical properties. Nonwoven fabrics produced from 100% photo-irradiated PPTA fibres
might therefore be expected to yield fabrics with poorer mechanical properties compared to those
produced from non-irradiated fibres. To test this hypothesis, the bursting strength of hydroentangled
fabrics manufactured from photo-irradiated PPTA fibres was explored. Prior to fabric manufacture, virgin
PPTA staple fibres were photo-irradiated under controlled lighting conditions (xenon short arc lamp with
a luminous flux of 13,000 lm) for 0, 5, 10, 20, 40, 60 and 100 h. The photo-irradiated fibres were then
hydroentangled to produce nonwoven fabrics. Photo-irradiation exposure of PPTA fibre up to 30 MJ m 2
was not found to be detrimental to fabric bursting strength and at irradiation energies of 5e10 MJ m 2 a
small, but statistically significant increase in fabric bursting strength was observed compared to fabrics
manufactured from non-irradiated fibre. This may be linked to a change in the surface and skin properties
of the PPTA photo-irradiated fibres identified by atomic force microscopy (AFM) following photoirradiation.
|
| 2 |
Detection of Early Stages of Degradation on PPTA Fibers Through the Use of Positron Annihilation Lifetime SpectroscopyNelyan Lopez-Perez (7038068) 14 August 2019 (has links)
<p>High-performance fibers used for
ballistic protection are characterized by having outstanding mechanical properties
such high modulus and strength. These mechanical properties are granted by the
fiber’s chemical and physical structure as well as their high degree of
orientation. Twaron fibers are one of the most commonly used fibers on soft
body armors such as bulletproof vests. They are made from poly (p-phenylene
terephthalamide) (PPTA), a rigid-rod and highly crystalline polymer. Although
these fibers are crystalline and have great mechanical properties, their
performance can decrease when they are exposed to different degradation
factors. Free volume is the unoccupied space between the polymer molecules. It
is responsible for characteristics such as diffusion and viscosity. Hence, the
free volume changes as the polymer degrades.
This thesis focuses on the effects of sonication, pH changes, and sweat
on the free volume of PPTA fibers. </p><p><br></p>
<p>A non-destructive technique
known as positron annihilation lifetime spectroscopy (PALS) was used to measure
the free volume in PPTA. Changes in the free volume of fibers degraded under
different conditions were compared to their mechanical performance. Degradation
in DI water, pH 4 and pH 10 aqueous solutions was conducted for 10 weeks at 80<sup>o</sup>C. Sweat degradation of PPTA fibers was also
conducted for 10 weeks at 25<sup>o</sup>C, 50<sup>o</sup>C, and 100<sup>o</sup>C.
Fibers degraded in pH4 and sweat solutions had greater loss of mechanical
performance and changes in the free volume.
PALS was able to detect changes in the nanostructure of PPTA fibers at
early stages of degradation. This data was supported by mechanical tests and is
complementary to other characterization techniques such as small angle X-ray
scattering (SAXS). Results of this research are a steppingstone for future
studies on lifetime predictions of bulletproof vests and the development of the
next generation of soft body armors. </p>
|
| 3 |
Summerhill school is it possible in Aotearoa ??????? New Zealand ???????: Challenging the neo-liberal ideologies in our hegemonic schooling systemPeck, Mikaere Michelle S. January 2009 (has links)
The original purpose of this thesis is to explore the possibility of setting up a school in Aotearoa (New Zealand) that operates according to the principles and philosophies of Summerhill School in Suffolk, England. An examination of Summerhill School is therefore the purpose of this study, particularly because of its commitment to self-regulation and direct democracy for children. My argument within this study is that Summerhill presents precisely the type of model Māori as Tangata Whenua (Indigenous people of Aotearoa) need in our design of an alternative schooling programme, given that self-regulation and direct democracy are traits conducive to achieving Tino Rangitiratanga (Self-government, autonomy and control). In claiming this however, not only would Tangata Whenua benefit from this model of schooling; indeed it has the potential to serve the purpose of all people regardless of age race or gender. At present, no school in Aotearoa has replicated Summerhill's principles and philosophies in their entirety. Given the constraints of a Master's thesis, this piece of work is therefore only intended as a theoretical background study for a much larger kaupapa (purpose). It is my intention to produce a further and more comprehensive study in the future using Summerhill as a vehicle to initiate a model school in Aotearoa that is completely antithetical to the dominant neo-liberal philosophy of our age. To this end, my study intends to demonstrate how neo-liberal schooling is universally dictated by global money market trends, and how it is an ideology fueled by the indifferent acceptance of the general population. In other words, neo-liberal theory is a theory of capitalist colonisation. In order to address the long term vision, this project will be comprised of two major components. The first will be a study of the principal philosophies that govern Summerhill School. As I will argue, Summerhill creates an environment that is uniquely successful and fulfilling for the children who attend. At the same time, it will also be shown how it is a philosophy that is entirely contrary to a neo-liberal 3 mindset; an antidote, to a certain extent, to the ills of contemporary schooling. The second component will address the historical movement of schooling in Aotearoa since the Labour Party's landslide victory in 1984, and how the New Zealand Curriculum has been affected by these changes. I intend to trace the importation of neo-liberal methodologies into Aotearoa such as the 'Picot Taskforce,' 'Tomorrows Schools' and 'Bulk Funding,' to name but a few. The neo-liberal ideologies that have swept through this country in the last two decades have relentlessly metamorphosised departments into businesses and forced ministries into the marketplace, hence causing the 'ideological reduction of education' and confining it to the parameters of schooling. The purpose of this research project is to act as a catalyst for the ultimate materialization of an original vision; the implementation of a school like Summerhill in Aotearoa. A study of the neo-liberal ideologies that currently dominate this country is imperative in order to understand the current schooling situation in Aotearoa and create an informed comparison between the 'learning for freedom' style of Summerhill and the 'learning to earn' style of our status quo schools. It is my hope to strengthen the argument in favour of Summerhill philosophy by offering an understanding of the difference between the two completely opposing methods of learning.
|
Page generated in 0.0218 seconds