JOURNAL OF MATERIALS SCIENCE 38 (2003) 3903 – 3914
An experimental investigation of modified
and unmodified flax fibres with XPS,
ToF-SIMS and ATR-FTIR
N. E. ZAFEIROPOULOS,
∗
,
†
P. E. VICKERS, C. A. BAILLIE
Department of Materials, Imperial College of Science and Technology,
Prince Consort Road, London, SW7 2BP, UK
E-mail: zafeiropoulos@ipfdd.de
J. F. WATTS
Surface Analysis Laboratory, School of Engineering, University of Surrey,
Guildford, Surrey, GU2 5XH, UK
Natural fibres are envisaged today as potential candidates for replacing glass fibres in
composite materials. Although natural fibres have a number of advantages over glass
fibres, the strong polar character of their surface is a limiting factor as, compatibility with
strongly apolar thermoplastic matrices is very low. Such problems of incompatibility may
be overcome with fibre pre-treatments, which can enhance compatibility although having a
negative impact on the economics of using such materials. In this study two fibre
pre-treatment methods, acetylation and stearic acid treatments, have been applied on flax
fibres. The effect of these two pre-treatments has been examined by use of XPS, ToF-SIMS
and FTIR spectroscopic methods. It was found that the fibre surface before treatment is
very different to what may have been expected for cellulose materials. There is an
appreciable coverage of the flax fibre surface with hydrocarbon compounds, possibly waxy
substances, but no aromatic compounds were detected. All three spectroscopic methods
revealed that the fibre surface chemistry has been altered after the treatments, and
especially for acetylation it was found that ester bonds are present on the fibre surface after
treatment. For the stearic acid treatment the situation still remains less conclusive. Finally,
ToF-SIMS experiments revealed that the coverage of the fibre surface with acetyl groups
and stearic acid is highly heterogeneous.
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2003
Kluwer Academic Publishers
1. Introduction
Over the last few years there has been an increasing
interest in using natural fibres as reinforcing agents in
composite materials [1–7]. A combination of proper-
ties, such as low cost, low density, non-toxicity, high
specific properties, no abrasion during processing, and
recycleability, all contribute to a rising interest from
the manufacturing industry of low cost, low weight
composites. However, there are a number of prob-
lems associated with incorporating such fibres into
thermoplastic matrices, most notably fibre-matrix in-
compatibility where apolar polymers are concerned,
and thermal stability of the fibres where relatively
high processing temperatures are required. The com-
patibility problem may be further complicated by di-
mensional instability of the resulting composites in
humid conditions. When water is absorbed the ma-
trix is placed under stress by the swelling of the fi-
bres. Since no significant bonding exists between the
∗
Author to whom all correspondence should be addressed.
†
Current address: Institute for Polymer Research, Dresden, 01069, Germany.
fibres and the matrix, when the material is dried a
rapid shrinkage of the fibres takes place that results
in propagation of debonding cracks and severe de-
terioration of mechanical properties [8]. In addition,
the poor interface contact between cellulose fibres
and thermoplastic may contribute to phase separation
under stress, especially at subzero temperatures, and
lead again to the degradation of mechanical properties
[9].
Fibre pre-treatments, although increasing the cost,
are potentially able to overcome these limitations. In
the past many attempts have been made to modify the
surface properties of cellulose fibres in order to en-
hance adhesion with the matrix. Various methods such
as corona treatment [10], plasma treatment [11], mer-
cerisation [12], heat treatment [13], graft copolymeri-
sation [14, 15], silane treatment [12, 16] and treat-
ments with other chemicals [17–20], to mention just
a few, have been reported to affect the compatibility
0022–2461
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2003 Kluwer Academic Publishers
3903