Degradation and Stabilisation of Aromatic Polyesters

280 Pages·2009·0.85 MB·English

by  Fairgrieve, Stuart F.

Degradation and Stabilisation
of Aromatic Polyesters
Stuart Fairgrieve
Smithers Rapra Update
Degradation and
Stabilisation of
Aromatic Polyesters
Stuart Fairgrieve
iSmithers – A Smithers Group Company
Shawbury, Shrewsbury, Shropshire, SY4 4NR, United Kingdom
Telephone: [phone] Fax: [phone]
http://www.rapra.net
First Published in 2009 by
iSmithers
Shawbury, Shrewsbury, Shropshire, SY4 4NR, UK
©2009, Smithers Rapra
All rights reserved. Except as permitted under current legislation no part
of this publication may be photocopied, reproduced or distributed in any
form or by any means or stored in a database or retrieval system, without
the prior permission from the copyright holder.
A catalogue record for this book is available from the British Library.
Every effort has been made to contact copyright holders of any material
reproduced within the text and the authors and publishers apologise if
any have been overlooked.
ISBN: 978-1-84735-457-0 (Hardback)
978-1-84735-458-7 (ebook)
Typeset by Argil Services
Printed and bound by Lightning Source Inc.
C
ontents
1 Background ..........................................................................1
1.1 Historical Development ..............................................1
1.2 Structure and Morphology .........................................9
1.2.1 Introduction ................................................9
1.2.2 PET ...........................................................10
1.2.3 PTT ...........................................................11
1.2.4 PBT ...........................................................12
1.2.5 PCT ...........................................................13
1.2.6 PEN ...........................................................14
1.2.7 LCP ...........................................................15
2 Thermal Degradation .........................................................21
2.1 Poly(ethylene terephthalate) (PET) ............................21
2.2 Poly(butylene terephthalate) (PBT) ...........................35
2.3 Poly(trimethylene terephthalate) (PTT) .....................42
2.4 Other Poly(alkylene terephthalate)s ..........................44
2.5 Poly(alkylene naphthalate)s (PAN) ...........................47
2.6 Poly(alkylene phthalate)s and
Poly(alkylene isophthalate)s ......................................48
2.7 Poly(p-phenylene alkanedioate)s ...............................48
2.8 Highly Aromatic Polyesters ......................................49
3 Thermo-Oxidative Degradation .........................................65
3.1 Poly(ethylene terephthalate) (PET) ............................65
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Degradation and Stabilisation of Aromatic Polyesters
3.2 Poly(butylene terephthalate) (PBT) ...........................73
3.3 Poly(trimethylene terephthalate) (PTT) .....................77
3.4 Other Aromatic Polyesters ........................................80
4 Photodegradation and Radiation Degradation ..................85
4.1 Photodegradation and Oxidation of Poly
(ethylene terephthalate) (PET)...................................85
4.2 Photodegradation and Oxidation of Other
Poly(alkylene terephthalate)s ....................................93
4.3 Photodegradation and Oxidation of
Poly(alkylene naphthalate)s ......................................94
4.3.1 Formation of a naphthalic acid end group .95
4.4 Radiation Degradation .............................................96
5 Chemical Degradation and Recycling ...............................107
5.1 Hydrolytic Degradation ..........................................107
5.2 Ester Interchange ....................................................109
5.3 Aminolysis ..............................................................110
5.4 Biodegradation .......................................................110
5.5 Chemical Recycling ................................................112
6 Thermal and Hydrolytic Stabilisation ...............................143
6.1 Introduction ...........................................................143
6.2 Thermal Stabilisation ..............................................144
6.3 End-capping ...........................................................153
6.4 Chain Extension .....................................................156
6.4.1 Without Additives ...................................156
6.4.2 Chain Extenders ......................................157
7 Thermo-oxidative Stabilisation .........................................181
7.1 Introduction ...........................................................181
7.2 Studies on Antioxidants ..........................................183
7.3 Potential New Chemistries ......................................187
iv
Contents
7.4 Patents ....................................................................188
8 Stabilisation Against Ultraviolet and Ionising Radiation ...199
8.1 Introduction to Ultraviolet (UV) Stabilisation .........199
8.2 UV Screeners and Absorbers ...................................200
8.2.1 Background .............................................200
8.2.2 Salicyclates ..............................................202
8.2.3 Benzophenones ........................................203
8.2.4 Benzotriazoles. ........................................204
8.2.5 Cinnamates and Related Types ................206
8.2.6 Oxanilides ...............................................209
8.2.7 Cyclic Imino Esters ..................................209
8.2.8 Triazines ..................................................210
8.2.9 Miscellaneous ..........................................211
8.3 Excited State Quenching .........................................212
8.4 Radical Scavengers .................................................213
8.4.1 Background .............................................213
8.4.2 HALS ......................................................214
8.4.3 Other Radical Scavengers ........................219
8.5 Ionising Radiation Stabilisation ..............................219
Appendix – Commercial Additive Structures ............................241
Abbreviations ...........................................................................261
Index ........................................................................................263
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Degradation and Stabilisation of Aromatic Polyesters
vi
P
reface
While over the years there have been many books and review articles
published on the subject of polymer degradation and stabilisation,
most have been rather wide-ranging studies, covering either polymers
in general, or a range of polymers and/or additives. Even in cases
where specific polymers or classes of polymers have been covered,
the literature contains few specific reviews of the degradation
and stabilisation of condensation polymers such as the aromatic
polyesters.
There appear to be a number of reasons for this. Firstly, there are the
factors of tonnage and range of application. The most used polymers,
such as the polyolefins and styrenics, tended to attract the most
attention simply as a consequence of their ubiquity. Secondly, there is
the factor of rate of deterioration. In general, polyolefins and styrenics
degrade noticeably faster than, for example, Nylon 6 or poly(ethylene
terephthalate) under equivalent conditions of heat or light exposure,
so that the need for effective stablisation against such reactions
seemed to be more urgent for the former. A third factor, I would
tentatively suggest, was the perception that the degradation and
stabilisation of condensation polymers was a study that was somehow
more ‘difficult’ due to their very different chemistry compared to that
of addition polymers such as the polyolefins. Indeed, in some quarters
the view has been expressed that the condensation polymers might
not, in fact, require stabilisation, or that the reactions undergone by
such polymers during degradation did not lend themselves to being
suppressed by known stabilisation pathways.
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Degradation and Stabilisation of Aromatic Polyesters
As we head towards the second decade of the 21st century, I feel
that the points raised in the previous paragraph no longer apply to
aromatic polyesters, hence the decision to produce this review of
the state of the art of degradation and stabilisation of this class of
polymer.
In terms of tonnage and use, poly(ethylene terephthalate) is these
days virtually a commodity plastic, with widespread, large volume,
use in food packaging, beverage bottle and fibres. Other aromatic
polyesters have increased in volume production over the last decade
or so, such as poly(butylene terephthalate) and poly(ethylene
naphthalate). There is also the promise of large quantity use of the
most recently commercialised member of the family, poly(trimethylene
terephthalate).
All such polyesters are also being increasingly pushed into more
demanding environments in their applications, including greater
heat exposure (for example in hot-fill food packaging applications
and ovenable containers) and outdoor applications, where long term
stability towards sunlight and oxygen are a prerequisite. The need
for a full understanding of the degradation mechanisms, and means
of suppressing these, are thus now more required than in the past
While some controversies remain, the study of aromatic polyester
degradation in the last few years has begun to untangle the
mechanisms involved, particularly through the use of analytical
techniques previously unavailable. The study of stabilisation has
also moved on, with examination of why the established commercial
stabilisers (largely developed for use in polyolefins and rubbers) are
not as effective in aromatic polyesters, and also attempts to develop
new stabilisers specifically for use in such polymers.
I have also included in this book information on the chemical
recycling of aromatic polyesters, which may be regarded as controlled
degradation of these polymers. With the increasing emphasis on
conservation of non-renewable resources, the recovery of various
useful chemicals from materials which have reached the end of their
viii
Preface
useful lives, or are off-specification for their intended use, is a process
which needs to be considered. Especially useful is the recovery of
starting materials which may then be used to manufacture further
polyesters, and the study of the means for carrying out such processes,
and their industrial implementation, are important topics in the
current ‘green’ climate.
Finally, I would like to express my appreciation to the publishing team
at iSmithers, Shawbury, for their assistance with the compilation of
this book. Especial thanks go to Frances Gardiner for commissioning
this work, and to Eleanor Carter for assistance, above and beyond
the call of duty, with literature searches and the supply of papers.
Dr. Stuart Fairgrieve
SPF Polymer Consultants
Kidlington
July 2009
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