Recycling Thermoset Glass Fiber Composites Improving Properties of Bulk Molding Compounds Containing Recycled Sheet Molding Compounds

1
Recycling Thermoset Glass Fiber
CompositesImproving Properties of Bulk Molding
Compounds Containing Recycled Sheet Molding
Compounds
Introduction
Unlike their thermoplastic cousins, thermoset
polymers are difficult to recycle. Once they are
formed to shape and crosslinked, they cant be
remolded or melted. When they are used as matrix
materials for composites the recycling problem
becomes more difficult because of the multi-phase
nature of the composite. As thermoset composites
become more widely used in large volume
industries, such as the automotive industry, the
need to recycle them comes to the forefront.

Use of SMC Recyclate in BMC Both filler and
reinforcement materials produced from SMC
recycling can be used in Bulk Molding
Compound (BMC). BMC is similar to SMC but
contains either no fiber or shorter fiber
reinforcement. BMC is used for many of
the same applications as SMC, especially
for thick parts. Problems with Using
Reinforcement Grade Recyclate As virgin
fibers are replaced with reinforcement grade
recyclate strength properties of the BMC are
lowered. 30 replacement causes up to a
40 reduction in flexural strength2 .

Infrared Spectra of BMC Component Materials

Spectra were taken using an FTIR
with an attenuated total reflectance
accessory.

Spectra of the SMC
recyclate shows the particle surfaces consists
mainly of polyester resin and CaCO3 filler.
Little to no fiber can be seen in the spectra.
The small amounts of loose
fibers in the recyclate have spectra similar to
virgin fibers, but have small peaks due to resin
and filler.
Calcium Carbonate Filler (CaCO3 )
CO3 Stretching (asymmetric)
CO3Wagging
CO3 Combined stretching bending
Recycling Methods for Thermosets Thermoset
Composites Incineration The reclaiming of the
energy content of the polymer. It is
not useful for composites because of the
high inorganic content.
Pyrolysis Thermal break down of polymer or
composite in an inert atmosphere.
Produces useful gases and can
potentially reclaim fibers and fillers.
Currently has not proved
economically viable. Hydrolysis Chemical break
down of matrix materials. Polymer
specific and has seen limited use in
composites. Regrinding Entails grinding up of
the bulk composite scrap into smaller
pieces. Produces new composite reinforcement
and filler materials.
Currently this is the only
commercially applied
method. How Regrinding Works Bulk parts
are broken up into 5 to 20 cm pieces.
Pieces are put through either a
knife granulator or hammer mill.
Resulting materials go through a
separation process. Large pieces
are removed and reintroduced into grinding
process. Sieves are then used to separate
the materials into reinforcement and filler
grades.
Virgin E-Glass Fiber Used for BMC
Initial Investigation Determine the
surface make up of the recyclate using
optical electron microscopy and FTIR.
Conduct strength testing on BMC - Get baseline
strength properties of virgin fiber and
recyclate reinforced BMC for
comparison to BMC containing treated
recyclate. - Investigate fracture
surfaces of composites.
Si-O bonds Broadened by Coupling Agent
Polyester Resin
Meta Sub Aromatic Ring (698)
Meta Sub Aromatic Ring
CO stretching
C-CO-OC
Mono Sub Aromatic Ring
Optical Microscopy
An image of the loose fibers that make up one
portion of recyclate. Clearly the fibers have
both resin and filler bonded to them.
Mecelec Recycled SMC
Filler CO3 Stretching (asymmetric)
Resin Meta Sub Aromatic Ring (693 cm-1) Filler
Combined CO3 stretching and bending
(712 cm-1)
.
Filler CO3Wagging
The other particles making up the recyclate are
larger particles of resin, filler, and fiber.
Unlike the loose fibers, the particles included
of a significant portion of resin and filler.

Polyester Resin CO stretching
Strength Testing of BMC BMC bars were
molded and tested in 3 point bending to
find their flexural strength. Different
virgin fiber lengths were tested to
determine which one best imitates the
recyclate. ¼ fiber matches the
recyclate best. As expected, flexural
strength decreased by a factor of 3 when
recyclate replaced ¼ virgin fiber in the
BMC. Two factors may cause the strength
decrease - Poor bonding between recyclate and
new matrix. Recyclate pulls out of new
matrix at fracture surface.
- Recyclate contains significant amount of
filler and resin so actual fiber content is
lower.
Conclusion Strength is significantly
reduced when untreated recyclate is
substituted for virgin fiber. Strength
reduction appears to be caused by poor
recyclate matrix bonding and lower effective
fiber content. Bonding
between recyclate and matrix needs to be
improved and fiber content of recyclate needs to
be determined.

Composites Recycled by Regrinding Sheet
Molding Compound (SMC) In 1995, 200 million
pounds of SMC were used by the auto
industry alone making it one of the highest
volume composites and therefore most in
need of recycling1. What is SMC?
SMC is highly filled,
chopped fiber reinforced thermoset
composite sheets. Polymer matrix -
Thermoset polyester - Low cost.

Filler material -Calcium carbonate most
common. Chopped glass fiber reinforcement
(1 to 5 cm lengths) Some applications include
car body panels, car bumper beams, heat
shields, showers, stadium seating, and
circuit boards.
Continued Work
Surface Treatments for
Recyclate Treatments need to functionalize
the surface of the recyclate to improve
bonding. Potential
treatments include NaOH and O2 plasma.
Effectiveness will be based on changes in surface
chemistry and improvement of strength
properties.
Fiber Content of
Recyclate Thermal gravimetric analysis
separation techniques will be used to
determine fiber, resin, and filler content
in recyclate.
I would like to thank CEER, my advisors,
Gabrielle Gaustad for her microscopy work, and
Mecelec Recycling Co., Composites One, and AOC
Resins for supplying materials
1. E.K. Jost, "Sheet Molding Composite
recycling," Automotive Engineering, 1038 40-41
(1995).






2. A.K.
Bledzki, Goracy, K., "The use of Recycled Fibre
Composites as Reinforcement for Thermosets,"
Mechanics of composite materials, 294 352-356
(1993).








Recycling of Glass Fiber Composites Eric
Telfeyan Advisors
Dr. Rebecca DeRosa and Dr. Steve Mayes
NYS College of Ceramics Alfred University