percentage of regrind plastic mixed with virgin
plastic significantly affects the performance
of plastic parts in electrical and electronic
equipment. Underwriters Laboratories Inc.
has worked with the industry to develop the criteria
and test methodology to ensure the safe use of
Regrind materials include
ground or chopped flash, runners, sprues and non-contaminated
rejected parts that are produced in-house by the
molder in initial molding processes. These
materials are crushed to smaller size and recycled
with virgin materials. Regrind excludes
materials that are chemically reconstituted or
repolymerized, or regrind bought in bulk and used
by another company. It only applies to post-industrial
(pre-consumer) waste from the same manufacturer.
Materials from regrind processes are used for cost
saving and environmental consideration.
are the limitations for using regrind?
In 1980, with input from the industry, UL established
the current limit on the use of regrind materials under
the Standard for Safety of Polymeric Materials - Fabricated
Parts, UL 746D. It was accepted that the use of thermoplastic
regrind at levels less than 25% by weight (0% for thermosets)
does not significantly compromise the properties of
the virgin material and does not require further investigation.
The use of thermoplastic regrind at levels exceeding
25% by weight requires a separate investigation to verify
that the material meets minimum levels of performance
with regard to critical properties.
adverse effects does increasing regrind proportion
have on plastic properties?
deterioration of the mechanical performance of
the resultant part is expected from increased
regrind percentage used with virgin materials.
1 shows the effect of increasing proportion
of regrind thermoplastic material to virgin material.
After a threshold, the properties of the resulting
material begin to degrade. This degradation
can cause hazards in the use of the plastic part
that is installed in equipment. Therefore,
for applications where mechanical properties are
important, the margin of safety decreases as the
proportion of regrind to virgin materials increases.
are becoming more commonly used for applications
- Mechanical loading - Engineering applications
- Direct contact with current carrying conductors
- Exposure to ultraviolet (UV) light, moisture,
chemicals, heat, etc.
these applications, properties such as strength,
impact resistance, softening temperature, optical
clarity, insulation, and outdoor weatherability
are very important. The molecular weight of certain
materials is an important factor for many of these
properties. Regrind material tend to result in
lower molecular weight than virgin material mainly
due to chain scission brought by the multiple
thermal exposures of the mold history. Therefore,
the overall average molecular weight of the mixture
of virgin and regrind will be less than that of
100% virgin material; as a result, too much regrind
will negatively affect key properties of the material.
example of how regrind percentage can affect performance
of plastic parts - Wire & Cable
the above, consider the application of plastics
as an insulating material for current-carrying
conductorsówires and cables.
property requirements for the plastic for this
- Good mechanical strength to support the conductor
- Good insulation properties
- Good tracking resistance
above properties for regrind material will be
lower than those of pure virgin material due to
lower molecular weight. The insulation given on
the conductor with regrind material will fail
at lower levels when compared to insulation comprised
of 100% virgin material.
2 shows the dependence of Mechanical Properties
on Molecular Weight. The material with lower molecular
weight will lose strength very fast and may eventually
crack or craze under severe conditions. Such damage
to the insulation exposes the conductor and could
in turn cause fire, shock, or injury hazards.
degradation of the properties may occur if the
plastics are fiber-reinforced and repeatedly blended
with virgin material. Long fiberglass, used to
provide reinforcement, is mechanically broken
into shorter segments after each regrind cycle,
resulting in a reduction in the strength of the
final product. This may reduce the
performance of the plastic part to an unacceptable
is UL's recommendation on the use of regrind?
regrind is accepted for thermosets, thermoplastic
elastomers and recycled materials.
other applications, UL allows regrind up to a
maximum of 25% by weight with the same grade of
thermoplastic virgin at the same molder facility
without further testing. For regrind levels
exceeding 25%, UL requires a special evaluation
be done, which includes relevant performance verification
tests such as Strength, Impact, Softening Temperature,
Flammability, Ignition, Tracking and Long Term
Aging tests. Information on evaluations of regrind
percentages over 25% that have resulted in compliance
is available on the UL iQ(TM) for Plastics
database at ul.com/plastics.
addition, UL's Follow-Up Service affirms the key
controls in the molding system for the plastics.
This system ensures the proper usage of
regrind, colorants, flame retardants, mold release
lubricants and other additives which may affect
the properties of plastics.
Field Representatives have been working with manufacturers
under UL's Follow-Up Service program for Molders
to confirm the compliance to the regrind levels
during their periodic visits.
should molders do when using regrind materials?
- Use thermoplastic regrind
materials in quantities only less than
25% by weight unless UL has verified
that higher percentages can be used (see below)
- If more than 25% regrind for thermoplastic
materials is required, use only plastics grades
available with higher regrind percentage as
documented in the UL iQ(TM) for Plastics
database at ul.com/plastics.
- DO NOT use any
thermoset, elastomeric, or thermoplastic recycled
- Grind the material immediately upon processing
or put the waste into a sealed container to
avoid contamination via dust due to the static
charges developed over the surface of the material.
- DO NOT use purged regrind
should end product manufacturers do when using
parts made from regrind materials?
with UL Follow-up Service requirements, if the
molding takes place at the end product location,
the manufacturing records should be made available
to the UL Representative(s) upon their request
to verify the percentage of regrind utilized.
molded parts came from an outside source not covered
by UL's Follow-Up Service Program, a Certificate
of Compliance (C of C) should be made available.
UL Follow-up Service Filed Representatives will
verify the regrind percentage information on the
C of C. The information should declare that the
reprocessed material content of the received thermoplastic
molded parts does not exceed 25% by weight. UL's
Representative(s) will also accept a procurement
requirement on Purchase Orders to molders. A conformance
statement should appear on the documentation accompanying
each shipment. This documentation must be traceable
to the individual lot(s) of the delivered molded
parts. All verification information should be
formatted according to accepted business practices
and comprehensible to the UL Representative(s).
manufacturers of ITE, the Web site at ul.com/ite/regrind.htm
provides an overview of regrind thermoplastic
issues related to the ITE Industry.