Issue 04/2018

Automotive
Surr
complex
of
10
Years ago
Published in
bioplastics MAGAZINE
Electronics
Surround system of loudspeaker boxes with
spherical shape: housing material Arboform
of 10 mm wall thickness, lacquer coated
Lignin Matrix Composites
for Loudspeaker Boxes
Article contributed by
H. Nägele, J. Pfitzer, both of Tecnaro
GmbH, Ilsfeld-Auenstein, Germany
N. Eisenreich, W. Eckl, E. Inone-
Kauffmann, E. Walschburger all
Fraunhofer-ICT, Pfinztal,Germany
B
iocomposites obtained exclusively from renewable
resources meet the requirements of sustainable
processes and eco-innovation, and will expand future
material research for engineering applications in industry.
The properties, treatment and processing of these
materials have to meet industrial standards concerning
raw materials from biomass, fibres, wood extraction constituents
and biopolymers, to enable their supply to mass
consumer goods manufacturers, the construction industry,
and the automotive and electronics industries. Thermoplastic
matrices of composites include biopolymers such as
polylactide (PLA), polyhydroxy-butyrate (PHB) and starch,
as well as lignin from the paper industry. Reinforcement is
carried out by the use of natural short fibres from hemp,
flax and wood 1-4 . The natural polymer lignin is generated
as a by-product of the pulp and paper industry, at a rate
of approximately 60 million tonnes in chemical pulp mills
every year, worldwide. This biomass extraction can also be
carried out in an environmentally friendly way by using only
water 5,6 . Thermal use of lignin for the power supply of the
chemical pulp mills dominates its current utilisation rather
than its use as a material for components. Its integration as
a component in engineering materials has proven to be difficult
7,8 . However, recent work has succeeded in establishing
lignin as the main component of a new class of engineering
materials: Arboform®, based only on renewable resources,
applicable for use in industrial equipment parts 9,10 . Technical
advantages of these materials over synthetic polymers,
such as the acoustic properties of lignin matrix composites
(Arboform), could strongly support their application.
The material consists of lignin, natural fibres for
reinforcement, and natural additives to support processing
and performance. It exhibits wood-like properties. Various
sources of lignin - from different pulping procedures - and
of natural fibres such as wood, hemp, flax, sisal, kenaf
etc. - can be used. The choice of the lignin depends on the
application field of the product. However, the material can
be processed like a thermoplastic material and used for
various engineering products. The processing includes:
• Mixing of the constituents: ligni
(30-60%) and natural additives
mixer.
• Pelletizing of the mixture at amb
granules. This step avoids comp
used for plastic compounds
• Processing of the granules at rela
by standard injection moulding (
facture parts
This processing of lignin com
on standard industrial injection m
synthetic plastic resins. The tempe
from 100°C in zone 1 to 170°C in z
temperature can be between 155 and
nozzle (2.5 – 4.0 mm). The back-pr
high enough to enable a smooth rotat
injection pressure is relatively high (>1
injection speed. The holding pressure
of the machine’s capacity and the rela
seconds. The cooling time must be ext
compared to that of a synthetic thermo
The mould tools should be desig
production of special materials. Impor
design should take into account:
• The shrinkage on injection moulding i
not exceed 0.3%
• Core-pullers should be foreseen for d
are useful to achieve fast working cycle
• Hot runner nozzles work only in limited
Depending on the fibre content the
can vary between 2 and 8 GPa and th
Strength between 2 and 6 kJ/m 2 , but the
be extended to 16 by the use of impac
elongation at fracture is between 0.3-0.6
expansion coefficient establishes below 5
no resonance frequencies are found and a
of vibration leads to excellent acoustic pr
enables the material to be used in loudspeak
Two types of loudspeaker housings wer
manufactured according to the procedures d
The material itself exhibits a unique structu
from part to part (see fig. 1). Original colour
brown, green and red. Figures 2 and 3 show
boxes including a lacquered surface finish.
info@tecnaro.de
eri@ict.fraunhofer.de
Housing parts of the complex loudspeaker
design as obtained directly from the mould
16 bioplastics MAGAZINE [04/08] Vol. 3
52 bioplastics MAGAZINE [04/18] Vol. 13