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Evaluation of Recycled Plastic Feedstocks & Marketing Strategies
For A Solar Oven
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ACKNOWLEDGMENTS
CWC is a nonprofit organization providing
recycling market development services to both businesses and governments,
including tools and technologies to help manufacturers use recycled
materials. This research was partially
funded by CWC’s Recycling Technology Assistance Partnership (ReTAP), through a
grant from the U.S. Environmental Protection Agency.
The
CWC acknowledges the following participants for their contributions to this
project:
·
Persons Helping People (PHP) for participating in this
project and eagerly working to incorporate recycled plastic into their solar
oven products. PHP is a non profit
corporation based in St. Paul, Minnesota.
The mission of PHP is to empower people and build communities through
the support of sustainable and replaceable entrepreneurial activities that
utilize appropriate technologies. PHP
was established in 1991 using a trust fund donated by Virginia Persons.
·
BottomLine Consulting, Inc., (Ohio) provided invaluable
expertise and analysis of the viability of the recycled plastics in the
product.
·
Spirit West Management provided a market analysis and
perspective for the solar oven.
TABLE OF CONTENTS
INTRODUCTION......................................................................................................................... 1
I. RECYCLED
PLASTIC MATERIAL EVALUATION.......................................................... 9
1.0 PRODUCT DESIGN OVERVIEW..................................................................................... 9
1.1 Performance
Requirements............................................................................................... 9
2.0 SUITABILITY
OF POST-CONSUMER PET FOR USE IN SOLAR OVEN
COLLAR, CASING, AND GLAZING............................................................................................................................ 7
2.1 Determination
of Process Limitations and Solutions.......................................................... 13
2.2 Formulation
Development............................................................................................... 15
2.3 Evaluation
of Production Runs......................................................................................... 17
3.0 RECOMMENDATIONS
FOR RPET USE IN COLLAR & CASING............................. 18
4.0 RECYCLED
HDPE PLASTIC LUMBER IN SOLAR OVEN GLAZING FRAME.......... 19
4.1 Performance
and Fabrication Needs............................................................................... 20
4.2 Specifications................................................................................................................. 20
4.3 Performance
Requirements and Potential Suppliers.......................................................... 21
4.4 Cost
Analysis of an HDPE Plastic Lumber Glazing Frame................................................ 22
5.0 RECOMMENDATIONS
FOR RECYCLED HDPE PLASTIC LUMBER IN SOLAR OVEN GLAZING FRAME...................................................................................................................................... 24
II. MARKETING
STRATEGY EVALUATION....................................................................... 25
1.0 COMPANY
BACKGROUND......................................................................................... 25
2.0 CURRENT
DOMESTIC MARKET CONDITIONS........................................................ 25
3.0 CURRENT
INTERNATIONAL MARKET CONDITIONS............................................ 20
4.0 ANALYSIS
OF PHP MARKETING STRATEGY........................................................... 23
5.0 MARKETING
RECOMMENDATIONS......................................................................... 22
Persons Helping People (PHP) is a
non-profit corporation whose underlying mission is to help alleviate hunger in
developing countries by helping people help themselves.
Their primary product is a
prototype solar cooker oven. Solar
ovens have the potential to reduce the consumption of cooking fuels, such as
wood, by 50%, and have the potential for impacting conservation efforts in
developing countries. Over two billion
people in developing countries do not have enough fuel to cook their small
amounts of rice, corn or beans. Many
families spend as much (or more) on charcoal and firewood as they do on
food. Others spend up to six or seven
hours daily gathering firewood, which is scarce, for cooking. These cooking fires produce irritating
smoke. An alternative to cooking over a
fire is to use solar ovens. These solar
ovens do not create pollution and most fuel-poor countries are sun-rich and can
benefit from solar cookers.
PHP gained considerable experience
in the manufacture and distribution of solar ovens that were produced by the
Sunstove Corporation in South Africa.
Sunstoves were sold in Nicaragua, Haiti, El Salvador, Mexico, and
Honduras. The experience and expertise
gained during this project led PHP to develop a prototype solar oven model, the
“SOS Sport.” The material cost per
oven is projected to remain under $20 (U.S.) and each oven could potentially
consume the equivalent of sixty-five, 20-ounce, clear polyethylene terepthalate
(PET) bottles, one salvaged aluminum printing plate, and several feet of
recycled plastic lumber.
Key elements of a quality solar
oven are durability, efficiency, attractiveness, and low-cost. The prototype “SOS Sport” is a low-cost,
easily assembled, lightweight, durable, attractive, and efficient solar oven. Although solar ovens will not totally
replace other methods of cooking, they have the potential to reduce the
consumption of cooking fuels (such as wood) by 50%. This reduction in fuel usage is particularly important in
developing countries.
The design of PHP's prototype solar
oven, includes four potential components that could be manufactured from
recycled plastic; an injection molded casing, the collar, a thermoformed
acrylic glazing, and the rigid oven frame.
The glazing is bonded to an oriented polyester film to create an
insulating air space above the solar oven.
The casing and collar pieces are currently manufactured from
polypropylene and nylon resins. The lid
frame is constructed from natural lumber.
Although natural lumber is suitably rigid for this application, it is
relatively expensive, generates considerable sawdust during fabrication, has
limited weatherability, and is prone to use as firewood in underdeveloped
countries.
The CWC worked
with PHP and two consultants to evaluate the “SOS Sport” solar oven model with
respect to:
·
Use of recycled PET in the collar and casing of the oven;
·
Use of recycled plastic lumber in the framing of the
oven; and
·
Marketing strategies.
The estimated maximum temperature
inside a solar oven is 300°F, so internal components must withstand exposures
to this temperature for extended time periods and service life. The objectives of this project were to: (1) verify whether product performance
requirements can be met subsequent to substituting post-consumer polyethylene
terephthalate (PET) for the oven collar and casing; (2) evaluate the
performance and viability of plastic lumber for the oven frame; and (3)
determine appropriate domestic and international marketing strategies for the
current solar oven model.
PHP
retained the services of Bottom Line Consulting, Inc. (BLC), of Lake
Barrington, Illinois, to provide technical assistance for evaluating and
testing recycled PET plastic for use in the casing and collar of the solar
oven, and for evaluating and testing the use of recycled HDPE plastic lumber
for the framing. In addition, BLC
served as the technical consultant to two PHP manufacturers during the
development of process conditions to maximize material properties for
pre-production test runs. Section I
describes the evaluation of recycled plastic materials for use in the product
components.
CWC retained the services of
Spiritwest Management, of Seattle, Washington, to evaluate PHP’s current
marketing strategy for this product, based on the anticipated use of recycled
content components and PHP’s long-term business goals. Subsequent to this analysis, PHP decided to
produce ovens as a not-for-profit entity, with a major focus on being
cost-effective. Section II describes
the marketing strategy evaluation and recommendations from Spirit West, as well
as the plans and market perspectives that PHP has gained over the years.
I. RECYCLED PLASTIC MATERIAL EVALUATION
1.0 PRODUCT DESIGN OVERVIEW
The solar oven model, the “SOS Sport”, is designed to be a
low-cost, easily assembled, lightweight, durable, and efficient oven. It is comprised of an exterior shell, an
inner liner forming an oven cavity, and an insulation barrier between the inner
liner and exterior shell. The oven
cavity is covered with a clear glazing.
When the sun penetrates the glazing, dark colors on the exterior of
cooking pots and the floor of the oven cavity will transform the light rays
into heat. The glazing and insulation
hinder the longer heat rays from escaping the oven cavity. The current oven design has a recycled
polypropylene plastic exterior casing and collar, and aluminum plates for the
inner liner. The unit has a foam
insulation layer and a double-glazed lid.
The rigid exterior frame is constructed of natural lumber.
Bottom Line Consulting, Inc. (BLC) evaluated the
suitability of using post-consumer PET, including specification of the
particular grade and formulation required, based on performance standards for
each component. Solar oven performance
requirements are established by the operating conditions and environment in
which this solar oven is used.
The performance requirements for the oven and the
various components are categorized and presented below. Table 1 provides the performance
requirements for the applicable oven components for stiffness, heat deflection
temperature and aesthetics. The
remaining specifications are presented in Table 2.
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Stiffness
·
Heat deflection temperature (an indicator of the
maximum operating temperature at which the plastic can perform and not degrade)
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Aesthetics
·
Impact resistance
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UV Resistance
·
Chemical Resistance
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Moisture Resistance
·
Shipping Durability
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Durability
Table 1 Oven
Performance Requirements for Stiffness,
Heat Deflection Temperature and Aesthetics
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Oven Component
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Requirement
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Stiffness of Flex Modulus
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Heat Deflection Temperature
(Assumed load of 66
pounds per square inch)
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Aesthetics
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Casing:
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As
clear as possible but UV efficient.
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Collar:
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Black
with matte finish preferred. External
texturing desirable to minimize appearance of scratches, etc.
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Glazing:
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Must not bow at cooking temperatures of up to 300°F.
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Must withstand temperature of 300°F (although it is
exposed to temperature lower than 300 °F due to the air space
between it and the protective PET film).
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Black
with matte finish preferred. External
texturing desirable to minimize appearance of scratches, etc.
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Framing:
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Minimum of 200,000 psi.
Unfilled HDPE plastic lumber will generally be about 265,000 psi. It cannot compete with wood on a strength
basis -- the stiffness of most wood is at least 1,000,000 psi.
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Not applicable.
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Not applicable.
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Table 2
Oven Performance
Requirements for Impact Resistance, UV Resistance, Chemical Resistance,
Moisture Resistance, Shipping Durability and Service Life
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Performance Measure
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Discussion of Requirement
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UV Resistance
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Ten-year life
under UV exposure for oven and components.
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The plastic components typically
are not directly in contact with food or oils. However, the oven should be mildew resistant for environments
where ambient temperatures are constantly above 60°F.
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Shipping Durability
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Service Life
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Usage of three
to four times per week for four to six hours (or 620 to 1250 hours per year)
for 10 years.
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2.0 SUITABILITY OF POST-CONSUMER PET FOR USE
IN SOLAR OVEN COLLAR, CASING, AND GLAZING
BottomLine
Consulting, Inc. (BLC) reviewed two comprehensive papers on solar ovens, which
provided important background information on solar cooking and ovens. Potential grades of post-consumer resins
were identified that would produce solar oven components meeting the
performance requirements of Section 1.1, be cost-effective, and compatible with
standard plastic manufacturing equipment.
CASING: Unmodified post-consumer PET for the casing
will meet all but one of the performance requirements; the drop impact strength
requirement of 100 ft-lb. The casing on
the oven will primarily absorb any impact.
To ensure the proper toughness over the service life of the solar oven,
a small percentage of impact modifier must be added to the PET formulation.
COLLAR: During operation, a portion of the collar
piece is subjected to high temperature (up to 300°F) and humidity. Due to the low glass transition temperature
of unmodified post-consumer PET, at 170°F, PET is unsuitable for
this application. However, glass-filled
grades of post-consumer PET are available for high heat applications. At 15% glass content, these grades are thermally
stable up to 400°F. Such a material is suitable for the solar
oven collar piece.
GLAZING: The glazing must transmit visible and near
infrared wavelengths without discoloration and withstand the relatively high
temperatures (up to 300°F). The current
design, consisting of acrylic sheet bonded at the perimeter to polyester film,
has performed extremely well. A
10-millimeter air space between the bubble of acrylic and flat film provided
excellent insulation across the glazing surface. The acrylic sheet thickness of 0.093 inches provided a good
balance of strength and
rigidity. The only problem that has
occurred with this component is sagging and clouding of the acrylic when used
alone. This issue can be corrected by
incorporating an acrylic that has higher heat resistance, or by improving the
design of the double-wall glazing.
Based on the stringent performance requirements for the glazing, no
further analysis was conducted for conversion to use of a recycled plastic in
this component.
A
working relationship was established by PHP with two plastic manufacturers in
Minnesota who produce injection molded plastic products. Both have manufactured the prototype casings
and collars for the current PHP oven model.
BottomLine Consulting contacted key personnel at both plants to
determine their processing capabilities, and to evaluate the feasibility of
running recycled PET in their existing equipment. Discussions included a detailed review of drying, blending,
material handling, grinding, weight feeding, molding, and tooling operations.
One
facility lacked adequate drying equipment for running post-consumer PET. This facility primarily molds polyethylene
and polypropylene, neither of which is dried prior to molding. PET is extremely hygroscopic and wet resin
degrades rapidly at normal molding temperatures. Therefore, inadequate drying results in inferior properties, such
as reduced impact strength, and increases molding problems such as drooling,
sticking, flashing, and splay. The
company borrowed a desiccant dryer from another nearby plastic manufacturer to
run the PET test product trials. PET
pellets were used, rather than PET regrind, since pellets have much lower
moisture than regrind, and can be adequately dried in a desiccant drier. (A crystallizing dryer is typically
recommended for PET regrind.)
Although
not a limiting factor with respect to the testing, both molding machines
available for the casing and collar molding trials were oversized, i.e., shot
capacities were above the desirable ratio of 2:1 to 3:1 of part weight. This exposes the melted resin to long
residence times in the machine barrel, thereby diminishing material
properties. This potential
performance-degrading factor was noted as the trials proceeded.
2.2 Formulation
Development
Successful
molding of post-consumer PET requires tailoring the resin chemistry and molding
conditions to meet the performance properties at the lowest possible piece-part
cost. Given the performance
requirements established above, BLC developed the most cost-effective
formulations for the solar oven casing and collar.
CASING
The target for incorporation of recycled
PET (RPET) in the casing was to enhance performance while using a recycled
feedstock. The key performance
properties for the casing are:
Stiffness
of Flex Modulus >375,000
psi
Drop
Impact Strength 100
foot-pounds
HDT
at 66 psi >130
degrees F, preferably about 170 degrees F
RPET
has limited impact strength for injection-molded parts. An impact-modified grade of post-consumer
PET from beverage bottles was used to meet the casing performance
specifications. Carbon black was added
to provide ultraviolet light stability for the casing. The recommended blend of RPET and additives
must be desiccant dried and kept bone dry until molding, otherwise degradation
from hydrolysis will occur. This type
of degradation can result in brittle parts, altered melt viscosity, and changes
in mechanical properties.
The
injection mold previously used for the casing was intended for a different
resin, and did not hold up to a production run using the post-consumer
PET. A new mold is required to be able
to utilize recycled PET in the casing.
In
order to optimize the production run for the casing, settings were recommended
for the melt temperature, nozzle temperature, increasing temperature profile,
mold temperature and injection speed.
COLLAR
The target for incorporation of
recycled PET (RPET) in the collar was to enhance the stiffness, UV resistance,
dimensional stability, and heat resistance, while using a recycled
feedstock. The key performance properties
for the collar are:
·
Stiffness
of Flex Modulus >650,000
– 800,0