Biocomposites
Rene Herrmann 2011
Biological Fibers
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There are 2 different types of biological fibers, animal and
floral
Biological fibers differ from their synthetic counter parts in
that they can be hollow. This makes them in some cases
very light.
Synthetic fibers have a diameter of about 15 microns and
can be made to great length. Biological fibers have
ticknesses of about 100 microns which makes the spaces
between the fibers much larger than in laminates made in
synthetic fibers. The total resin usage is larger than in
syntetic laminates
Fiber length
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Biological fibers are short, about some cm. This is
a real problem. The fibers absorb the mechanical
load in the composite.
 The load must be transferred from one fiber to the
next, the resin matrix is doing this. For this to
work the fibers have to overlap in the laminate.
The overlap is a large part of the fibers length. The
statistical chance for fibers to not overlap
sufficiently increases the shorter the fiber.
Fiber types
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There are many fibers but flax (linen) and hemp
are the most potential competitors to glas fiber.
Another fiber is RAMIE. This fiber could
outpreform glas fiber in strength.
 Our tests have shown that wool is not strong but
the most ductile laminate results, with strain limit
at 7%.
 Silk has proven to deliver visually appealing
laminates but with less strength than hemp and
flax, however also high strain limit (5%). Silk was
difficult to wet with resin.
Fiber durability
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Biological fiber can rott, to prevent this
protection is needed before the end of
product life is reached. This can be coatings
of the product. Since all laminates must be
protected from UV light (to prevent matrix
decomposition) this is not a problem.
Textiles and fabrics
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biological fiber can be woven exactly the same
way as synthetic fibers
 biological fibers have a lower density and
therefore mass than fiber glas, because of this are
strand mat spray gun laminations not feasable.
 biological textiles are available in colored form,
this can be a problem because the coloring may
influence the resin wettability negatively.
Fiber strength
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Biological fibers come in a variety of sizes, due to
this also their mechnical properties vary.
 The measurement of youngs modulus and strain
limit is possible but difficult on the fiber itself.
The problem is the attachment of the fiber and the
measurement of the fiber diameter. It is therefore
better to measure a statistical amount of fibers and
deterime an average property.
Average fiber strength
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The procedure starts with cutting a textile to a defined size
and weighting its mass. You get a value for g/m^2 of the
fabric.
You laminate with resin whos density is known. After
lamination you weight the laminates total mass and find
resin mass and volume, calculate fiber volume and fiber
volume fraction.
You measure the E modulus of the laminate and using
volume fraction find the youngs modulus of the fiber only.
Due to the number of calculations (subtraction) the result
will have an large relative error.
Experiment1
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Make a laminate and deterime
experimentally the fibers youngs modulus
and strain limit and the textiles mass per
area. Deliver an estimate for resin uptake
and laminate thickness per layer.
Experiment2
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Take a yawn of a bilogical fiber, find the
number of k (number of tousend fibers in
the yawn). Measure the average diameter of
the fibers in the yawn and calculate an
average total cross section and test the
material in a tensile test.