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|Title: ||Weathering of plastics glazing materials|
|Authors: ||Halliwell, Susan M.|
|Issue Date: ||1996|
|Publisher: ||© S M Halliwell|
|Abstract: ||Plastics glazing materials have properties which allow their widespread use in
construction, for example as rootlights. However, they are more susceptible than is glass to
degradation by weathering, notably the combined effects of ultraviolet light, heat and
moisture. Examples of unacceptable durability have been seen in practice, particularly when
high operating temperatures occur in sunlight.
Artificial weathering tests are used to assess plastics glazing materials in a reasonably
short time, two main types being utilised in this study. The applicability of ultra-fast methods
of accelerated degradation has been shown to depend on the extent to which the mechanisms
of degradation simulate practical weathering, since different procedures were found to
promote different mechanisms in the materials tested. Misleading information was obtained
when the full spectrum of solar UV and much of the visible was not adequately reproduced in
the accelerated tests. In particular an established grade of PVC-U performed unexpectedly
poorly under fluorescent lamps. Procedures based on xenon arc sources were found to be the
most generally applicable because they better reproduce the full solar spectrum range and,
hence, the typical effects observed in plastics materials in practice.
Several analytical techniques were used to characterise the virgin polymers and to assess
the weathered materials. Two commercial grades of each polymer type (poly[vinylchloride],
polycarbonate and poly[methylmethacrylate]) were studied, and measured changes explained
in terms of initial polymer properties. Profiling of chemical (e.g. carbonyl index measured by
photo-acoustic fourier transform infrared), physical (e.g. molecular weight, surface
gloss/roughness), optical (e.g. colour, light transmission) and mechanical properties (e.g.
impact resistance) as a function of exposure period and environmental conditions enabled
degradation rates and mechanisms to be established for each material. In conducting these
tests particular attention was given to the control and effects of sample temperature during
weathering, and to the wavelength range of the light source used. Poly(vinylchloride) was
affected much more by weathering at higher temperatures, and by exposure to short
wavelength radiation, than was polycarbonate, with acrylic being the most durable overall.
Practical applications of this work are through Standards committees primarily. in
particular with plastics rootlights (B/542/8 and CEN/TCI28/SC9).|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Materials)|
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