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Stress relaxation and thermogravimetric studies on room temperature vulcanised polysiloxane rubbers

日期:2018年01月15日 编辑: 作者:无忧论文网 点击次数:1468
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论文地区:其他 论文语种:中文 论文用途:硕士毕业论文 Master Thesis
Stress relaxation and thermogravimetric studies on room temperature vulcanised polysiloxane rubbers
Mogon Patela,*, Mark Soamesa, Anthony R. Skinnera, Thomas S. Stephensb
aAtomic Weapons Establishment, Aldermaston, Reading RG7 4PR, UK
bLos Alamos National Laboratory, New Mexico, USA
帮写留学生论文Received 19March 2003; accepted 17 May 2003
Abstract
The stress relaxation properties of foamed polysiloxane rubbers are important as they can influence the useful life of components
made from such a polymer system. Of particular interest is understanding the changes in properties with time and temperature and
whether the mechanisms responsible for stress relaxation are able to induce other material property changes. The stress relaxation
properties of Dow Corning S5370 polysiloxane samples, aged under controlled conditions, have been measured using a Thermomechanical
analyser (TMA) at a number of different temperatures. The results were assessed using the principle of Time-Temperature
Superposition. Derived acceleration factors showed good adherence to the Arrhenius relationship and showed two regions
where processes with different activation energies dominate. A transition region where there is a change in the predominant
degradation process is evident at around 120 C. Thermogravimetric analysis (TGA) studies were used to provide an improved
understanding of the degradation at elevated temperatures (>120 C). Time-temperature superposition and Arrhenius treatment of
the TGA results reveal an activation energy (756 kJ/mol) which correlates closely to that derived from stress relaxation (655 kJ/
mol). Overall, these observations suggest that the degradation processes at elevated temperatures which influence stress relaxation
also induce significant weight loss. The dominant degradation process at elevated temperatures(>120 C) is most probably silicone
head to tail unzipping reactions resulting in the production of volatile cyclic species.
# 2003 Elsevier Ltd. All rights reserved.
Keywords: Polysiloxane rubber; Stress Relaxation; Weight loss
1. Introduction
The properties of rubbers may change as a result of
ageing, eventually to the point where the material is no
longer capable of satisfying its function. The amount of
ageing is dependent on many factors including formulation,
polymer type, and environmental conditions
[1]. Ageing will take place at normal ambient temperatures
and increasing the temperature will accelerate the
rate of underlying degradation processes. Low temperatures
may cause elastomers to lose their rubber-like
properties and sealability. There are also synergistic
effects which must be considered. For example, materials
resistant to UV light alone or to moisture alone may
fail when exposed to a combination of UV light and
moisture [2]. Furthermore, rubbers are often operating
under conditions where factors such as fatigue, creep,
stress relaxation and chemical attack are significant. Such
materials can fail by progressive degradation resulting
in hardening, softening, set, crack growth or fracture.
Cellular packaging materials, such as S5370 rubber (a
hydrogen blown polysiloxane foam), play an important
stress absorbing role and therefore help minimise the
risk of damage to components. Such materials require
good long term load retention capability as they often
experience significant compression in service. Furthermore,
sufficient elastic recovery in the short term is
necessary in order to prevent the formation of gaps
within the system. The recovery properties of a material
0141-3910/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0141-3910(03)00231-3
Polymer Degradation and Stability 83 (2004) 111–116
www.elsevier.com/locate/polydegstab
§ # Crown Copyright (2000) This document is of United Kingdom
origin and contains proprietary information which is the property of
the Secretary of State for Defence. It is furnished in confidence and
may not be copied, used or disclosed in whole or in part without prior
written consent of the Directo