The aim of this thesis is to modify flax pulp fibres (Linum usitatissimum) by more
friendly environmental processes. Pulp and paper research is focussing through
enzyme systems investigation for developing green chemistry technologies due to
existing environmental concerns and to legal restrictions. Moreover, it exists also an
increasing strategic interest in using flax fibres to obtain high-quality specialty papers.
That is why we study the application of biotechnology as an efficient alternative to
traditional industrial processes based on the use of chemical agents.
This work is framed by two of the main research topics of the Paper and Graphic
Specialty Laboratory in the Textile and Paper Engineering Department of the
Universitat Politècnica de Catalunya. One research line is based on pulp bleaching and
is focused basically on the study of enzymatic systems as biobleaching agents; the
other research topic that has been recently introduced in our investigation group is the
use of enzymes as functionalisation agents by promoting the grafting of several
compounds. Laccase is the main enzyme used in this thesis; it is an oxidoreductase that
can assist reactions in an eco-friendly way since laccase uses air and produces water as
the only by-product. Moreover, laccase can work under mill conditions and has wide
application potential.
The first part of this thesis involved the use of enzymes to bleach flax pulp. The aim
was to explore the potential of various natural mediators (lignin-derived compounds)
for delignifying flax fibres in order to identify the most efficient and ecofriendly choice
among them. Afterwards, we assessed the use of various enzyme delignification stages
in an industrial bleaching sequence. The ensuing totally chlorine free (TCF) sequence
comprised various laccase-mediator system treatments (L stage) followed by a by a
chelating stage (Q stage) and a subsequent bleaching step with hydrogen peroxide (Po
stage). A xylanase pretreatment was additionally carried out. Laccases used came from
the fungi Pycnoporus cinnabarinus and Myceliophthora thermophila; the performance
of several natural mediators was compared with the obtained with the application of
various synthetic mediators. In addition, the lack of studies on the properties of
effluents from the treatment of non-wood pulp with laccase and natural mediators led
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us to examine effluent properties upon biotreatments and after different bleaching
stages. The results obtained warrant upscaling any of the biobleaching sequences for
flax pulp as they provide sustainable flax fibre with a high cellulose content and
brightness above 80% ISO. The use of xylanase pretreatment was found to efficiently
remove HexA and enhance delignification by laccase.
Premi extraordinari doctorat curs 2010-2011, àmbit d’Enginyeria Enginyeria Industrial
