issue 05/2021

Fibres, Textiles
Targeted control of
biodegradability
New test methods and development of multi filament and nonwoven
production processes
In a project of the Institute of Textile Technology at RWTH
Aachen University (ITA) and the Fraunhofer Institute for
Environmental, Safety and Energy Technology UMSICHT
possibilities for targeted control of the biodegradability of
multi filament yarns and nonwovens were investigated. To
achieve sustainability goals such as a circular economy,
it can be reasonable to use biodegradable plastics in
applications, where products enter and remain in the
environment e.g., geotextiles for the reinforcement of
embankments [1]. During their product life, the materials
must fully meet the required technical properties and
should subsequently biodegrade completely.
Aim
It is known that there are many factors involved in the
biodegradability process of polymers [2]. The surface
area and crystallinity can be regulating parameters to
make targeted control of biodegradability possible. A high
crystallinity slows down the biodegradation process of
the polymer [2]. The aim of the project “DegraFib” was to
investigate how fibre crystallinity and fibre surface area
influence the degradation of fibres and textiles. In the
project, different cross-section geometries of filaments and
therefore different surface areas were produced to test the
influence on the biodegradation process of filaments and
nonwovens.
Melt spinning and ageing trials
At first, suitable biobased and biodegradable polymers
such as polylactic acid (PLA) grades from NatureWorks,
Minnetonka, USA and polybutylene succinate (PBS)
grades from Mitsubishi Chemical Performance Polymers,
Düsseldorf, Germany were selected and a melt spinning
process for multi filament yarns was developed [3, 4].
Filaments were extruded successfully in the melt spinning
process, varying the cross-section geometry to adjust
the available filament surface area. Round, flat, crossshaped
and star-shaped filaments were produced with yarn
counts between 200–700 dtex (see Figure 1). The influence
of the filament surface at constant yarn count on the
biodegradability of multifilament yarns and nonwovens was
investigated.
To determinate the correlation between filament
parameters and the degradation rate of filaments in
substrate, a new test method was developed inspired by
testing standards [5, 6, 7]. Additionally, a transfer of the
findings to the textile level was carried out by producing
nonwovens from selected multifilament yarns (weight:
approx. 300 g/m 2 ) and developing a new test method to
determine the degradation rate of the nonwovens. An
example of the nonwoven degradation test method is shown
in Figure 2.
Analytics and results
During the degradation trials, the temperature was varied
between 20 and 58 °C in different trials to simulate industrial
as well as home composting conditions. The optical and
mechanical properties of the multi filament yarns and
nonwovens produced were analysed before and after ageing
in substrate. Additionally, a thermal analysis via differential
scanning calorimetry (DSC) was carried out for the filaments.
Degradation or ageing of the filaments and nonwovens could
be detected. The results of the degradation tests indicate
that filament relaxation and polymer crystallinity have a
complex influence on the degradation rate of fibres.
Some results of the nonwovens made from PBS fibres
are shown in figure 3. For each tested sample group means
of the tensile strength as well as standard deviations were
calculated and statistical analyses were performed.
Figure 1: Cross-sectional geometries of the extruded multi filament yarns [a) star-shaped, b) cross-shaped]
22 bioplastics MAGAZINE [05/21] Vol. 16