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Densification:
A process that lowers the volume-to-weight ratio in
order to reduce shipping costs. Baling is the most common
form of densification, although some handlers of post-consumer
plastic plastics granulate or grind collected material.
(The Blueprint for Plastics Recycling, The Council for
Solid Waste Solutions, 1991).
Design for Recycling:
This concept aims to encourage pre-production planning
for safe and efficient recycling by the elimination,
to the extent possible, of hazardous and non-recyclable
materials from the production process. (Design For Recycling:
The Scrap Recycling Industry's Perspective, Institute
of Scrap Recycling Industries, Inc. (ISRI), 1991).
Dioxin:
Dioxin is a naturally occurring compound and a by-product
of environmental events such as volcanoes and forest
fires. man-made processes such as manufacturing, paper
and pulp bleaching, and exhaust emissions also yield
dioxin. To find out more, go to the Chlorine Chemistry Council.
Discards:
The components of Municipal Solid Waste (MSW) remaining
after recovery for recycling and composting. These discards
are presumably combusted or disposed of in landfills,
although some MSW is littered, stored, disposed of on
site or burned on site, particularly in rural areas.
(Characterization of Municipal Solid Waste in the United
States: 1995 Update, prepared for U.S. EPA Municipal
and Industrial Solid Waste Division Office of Solid
Waste, March 1996).
Drop-Off Center:
A centrally located depot to which consumers bring recyclables
that does not provide payment for delivered materials.
(The Blueprint for Plastics Recycling, The Council for
Solid Waste Solutions, 1991).
Durable Goods:
Consumer products with a useful life of three years
or more that include major appliances, furniture, tires,
lead-acid automotive batteries, consumer electronics,
automobiles and other items. (Characterization of Municipal
Solid Waste in the United States: 1995 Update, prepared
for U.S. EPA Municipal and Industrial Solid Waste Division
Office of Solid Waste, March 1996).
Density
An important parameter for polyethylene, affecting most
end product physical properties like stiffness, impact
strength and optical properties. The density is normally
given in g/cm3, although the correct SI unit would be
kg/m3. Two basic measuring methods are used: (a) Density
gradient column is the basic method for density measurement.
In it a density gradient is prepared by mixing two liquids
of different densities so that density increases uniformly
from top to bottom. Small test pieces are immersed into
this density gradient, and the density of the polymer
is determined based on the equilibrium position of the
pieces and calibration floats. (b) Pyknometer measurements
rely on calibrated volumes and the density difference
to a reference fluid; compression-moulded samples are
normally used here.
Die
C-Tear Strength
The maximum force required to cause a rupture by tearing
action of the right angle test specimen; the force divided
by the thickness of the specimen. The force acts parallel
to the tab ends of the specimen or at 45¡Æ
to the 90¡Æ center angle. Refer to ASTM
Method D624.
Differential
Scanning Calorimetry (DSC)
In DSC the sample and a reference material are heated
and cooled in a defined manner. DSC provides a rapid
method for the determination of the temperature profile
of a polymeric material. This includes e.g. measurement
of heat capacity, specific heat, melting, crystallisation
and glass transition temperatures, heat (enthalpy) of
fusion, crystallization, study of thermal stability
or reaction kinetics and in certain cases identification
of the polymer or polymer mixture.
Double-strand
polymer
Ladder polymer: a polymer, the macromolecules of which
are double-strand chains.
Durometer
An instrument for determining the hardness of polymer
by measuring it's resistance to the penetration (without
puncturing) of a blunt indented point impressed on the
rubber surface against the action of a spring. A hand
and a special scale indicate the resistance to penetration
or "hardness". The scale of the Shore hardness
testers reads from 0 to 100, 0 being very soft and 100
being very hard. There are several Shore hardness gauges
available and the proper durometer depends on the hardness
of the surface being measured (Shore A, D and 00).
Dynamic
Mechanical Thermal Analysis (DMTA)
Many polymeric materials exhibit time-dependent, reversible
viscoelastic properties in deformation. Dynamic mechanical
tests are characterized by an application of a small
stress in sinusoidal fashion and a continuous scan of
resonant frequency of vibration and damping vs. temperature
is produced. This is transformed into dynamic storage
modulus, dynamic loss modulus and damping factor by
the instrument software.
Dynamic
rheometry
Dynamic rheometry gives information both about flow
and elastic properties of polymer melts. In a dynamic
measurement the sample is put between two round plates
or between a cone and a plate in the oven. The system
is heated to a desired temperature and a sinusoidal
deformation at different frequencies is applied. As
a result we get storage and loss modulus as a function
of frequency. Storage modulus is connected with elastic
energy, while loss modulus corresponds to viscose energy.
From the above parameters we can calculate complex viscosity
as a function of frequency.
With most of polyolefin products this is the same as
the conventional viscosity function, which is viscosity
as a function of shear rate. The dynamic measurements
are limited to relatively low shear rates. On the other
hand, a benefit compared to capillary rheometry is,
that we get reliable information also about elasticity.
In addition, the obtained properties are much more sensitive
for small differences in polymer structure which play
an important role in processing and end-use properties.
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Plastic
Brief
