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WARM Version 14 Carpet February 2016
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3 CARPET
3.1 INTRODUCTION TO WARM AND CARPET
This chapter describes the methodology used in EPA’s Waste Reduction Model (WARM) to
estimate streamlined life-cycle greenhouse gas (GHG) emission factors for carpet beginning at the point
of waste generation. The WARM GHG emission factors are used to compare the net emissions
associated with carpet in the following four materials management alternatives: source reduction,
recycling, landfilling, and combustion. For background information on the general purpose and function
of WARM emission factors, see the WARM Background & Overview chapter. For more information on
Source Reduction, Recycling, Landfilling, and Combustion, see the chapters devoted to those processes.
WARM also allows users to calculate results in terms of energy, rather than GHGs. The energy results
are calculated using the same methodology described here but with slight adjustments, as explained in
the Energy Impacts chapter.
At the end of its useful life, carpet can be recovered for recycling, sent to a landfill or
combusted. Landfilling is the most commonly selected waste management option for carpet. According
to EPA (2011), 9 percent of carpet is recycled annually. Efforts by industry, EPA, and other organizations
over the past few years have increased the fraction of waste carpet that is recycled.
WARM accounts for the four predominant materials constituting face fibers in residential
carpeting: Nylon 6, Nylon 6-6, Polyethylene terephthalate (PET) and Polypropylene (PET). Because the
composition of commercial carpet is different than that of residential carpet, the emission factors
presented in this chapter and in WARM only apply to broadloom residential carpet. The components of
nylon broadloom residential carpet in this analysis include: face fiber, primary and secondary backing
and latex used for attaching the backings.
Exhibit 3-1 shows the general outline of materials management pathways in WARM and how
they are modeled for carpet. Recycling carpet is an open-loop process, meaning that components are
recycled into secondary materials such as carpet pad, molded products and carpet backing. In WARM,
the life-cycle energy and material requirements for converting recycled carpet into these various
secondary end products were unavailable (Realff, 2010a). Therefore, in the recycling pathway, the
recycling benefits for carpet incorporate the avoided manufacture of the various virgin plastic resins
only. Carpet is collected curbside and at special recovery events, or individuals can bring it to designated
drop-off sites. Once carpet has been collected for recycling, it is sent to material recovery facilities that
specialize in separating and recovering materials from carpet. Building on Exhibit 3-1, a more detailed
flow diagram of the recycling pathway for carpet is provided in Exhibit 3-2.
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Exhibit 3-1: Life Cycle of Carpet in WARM
Since the original development of the carpet material type energy and GHG emission factors for
WARM in 2004, updated life-cycle data for the recycling pathway which more accurately reflect carpet
composition and recycling input energy have become available (Realff, 2011b). The updates include
revisions to include two additional types of plastics found in the face fibers of residential broadloom
carpets as well as the incorporation of the loss rates within the carpet recycling process. Updated
information on the source reduction and landfilling life-cycle pathways for carpet was not available.
Therefore, this update to the carpet factors in WARM includes changes only to the recycling and
combustion pathways.
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Exhibit 3-2: Detailed Recycling Flows for Carpet in WARM
3.2 LIFE-CYCLE ASSESSMENT AND EMISSION FACTOR RESULTS
The life-cycle boundaries in WARM start at the point of waste generation, or the moment a
material is discarded, and only consider upstream emissions when the production of materials is
affected by end-of-life materials management decisions. Recycling and source reduction are the two
materials management options that impact the upstream production of materials and consequently are
the only management options that include upstream GHG emissions. For more information on
evaluating upstream emissions, see the chapters on Recycling and Source Reduction.
WARM includes source reduction, recycling, landfilling, and combustion pathways for materials
management of carpet. Composting and anaerobic digestion are not included as pathways for materials
management of carpet. As Exhibit 3-3 illustrates, most of the GHG emissions from end-of-life
management of carpet occur from waste management of this product, while most of the GHG savings
occur from offsetting upstream raw materials acquisition and the manufacturing of other secondary
materials that are recovered from carpet.
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Exhibit 3-3: Carpet GHG Sources and Sinks from Relevant Materials Management Pathways
Materials Management
Strategies for Carpet
GHG Sources and Sinks Relevant to Carpet
Raw Materials Acquisition and
Manufacturing
Changes in
Forest or Soil
Carbon Storage End-of-Life
Source Reduction Offsets
· Transport of raw materials and
intermediate products
· Virgin process energy
· Virgin process non-energy
· Transport of carpet to point of
sale
NA NA
Composting Not applicable because carpet cannot be anaerobically digested
Recycling Emissions
· Transport of recycled materials
· Recycled process energy
· Recycled process non-energy
Offsets
· Emissions from producing
Nylon 6, Nylon 6-6, PET and PP
plastic resins from virgin
material
NA Emissions
· Collection of carpet and
transportation to recycling
center
· De-manufacturing and
reprocessing recovered carpet
Landfilling NA NA Emissions
· Transport to landfill
· Landfilling machinery
Combustion NA NA Emissions
· Transport to WTE facility
· Combustion-related CO2
Offsets
· Avoided electric utility
emissions
Anaerobic Digestion Not applicable because carpet cannot be anaerobically digested
NA = Not applicable.
WARM analyzes all of the GHG sources and sinks outlined in Exhibit 3-4 and calculates net GHG
emissions per short ton of carpet inputs. For more detailed methodology on emission factors, please
see the sections below on individual materials management strategies.
Exhibit 3-4: Net Emissions for Carpet under Each Materials Management Option (MTCO2E/Short Ton)
Material
Net Source
Reduction (Reuse)
GHG Emissions For
Current Mix of
Inputsa
Net Recycling
Emissions
Net
Composting
Emissions
Net
Landfilling
Emissions
Net
Combustion
Emissions
Net
Anaerobic
Digestion
Emissions
Carpet -3.83 -2.36 NA 0.02 1.09 NA a The current mix of inputs for carpet is considered to be 100% virgin material.
Note: Negative values denote net GHG emission reductions or carbon storage from a materials management practice.
NA = Not applicable.
3.3 RAW MATERIALS ACQUISITION AND MANUFACTURING
The components of nylon broadloom residential carpet in this analysis include: face fiber,
primary and secondary backing and latex used for attaching the backings. The face fiber used for nylon
carpet is typically made of a combination of Nylon 6, Nylon 6-6, Polyethylene terephthalate (PET) and
Polypropylene (PP). For the purpose of developing an emission factor that represents “typical”
broadloom residential carpet, WARM reflects the market share of each material in the carpet industry.
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Carpet backing for broadloom carpet typically consists of polypropylene (PP). For latex used to adhere
carpet backings, EPA modeled styrene butadiene, the most common latex used for this purpose. Styrene
butadiene latex is commonly compounded with a filler such as calcium carbonate (limestone). Inputs to
the manufacture of nylon, PP and styrene butadiene are crude oil and/or natural gas. Exhibit 3-5
provides the assumed material composition of the typical carpet used for this analysis (FAL, 2002, Realff,
2011b).
Exhibit 3-5: Material Composition of One Short Ton of Carpet
Material Application % of Total Weight
Weight (lbs.) (Assuming
2,000 lbs. of Carpet)
Nylon, PET, PP mix Face Fiber 45% 910
PP Woven for backing 15% 304
Styrene butadiene latex Carpet backing adhesive 8% 164
Limestone Filler in latex adhesive 32% 648
Total 100% 2,026 lbs.a a Note that these values total 2,026 pounds, which is greater than one short ton. This is because 26 pounds of the raw materials used to
manufacture carpet are assumed to be “lost” during the manufacturing process. In other words, producing one short ton of carpet actually
requires slightly more than one short ton of raw materials (FAL, 2002).
The main polymers that are used for the face fiber are Nylon 6-6, Nylon 6, PET, and PP with very
small amounts of wool and a growing interest in the use of bio-based fibers. The average proportion of
each of these plastic resins in carpet face fibers is provided in Exhibit 6. These components are
recovered and recycled in different ways, each consuming different amounts of energy. For example,
Nylon 6 face fiber is recycled mostly through depolymerization, whereas Nylon 6-6 face fiber is recycled
mainly through shaving the fiber followed by remelting and extrusion.
Exhibit 3-6: Residential Face Fiber Mix 1995-2000
Plastic Resin % of Total Weight
Nylon 6 40%
Nylon 6-6 25%
PET 15%
PP 20%
Total Face Fiber 100%
Source: Realff, 2011b
The process used to turn the components in Exhibit 3-5 into a finished carpet may include
weaving, tufting, needlepunching and/or knitting. According to the Carpet and Rug Institute, 95 percent
of carpet produced in the United States is tufted (CRI, 2010). During tufting, face pile yarns are rapidly
sewn into a primary backing by a wide multineedled machine. After the face pile yarns are sewn into the
primary backing, a layer of latex is used to secure a secondary backing, which adds strength and
dimensional stability to the carpet.
3.4 MATERIALS MANAGEMENT METHODOLOGIES
This analysis considers source reduction, recycling, landfilling, and combustion of carpet. It is
important to note that carpet is not recycled into new carpet; instead, it is recycled in an open loop
process. The life-cycle assessment of carpet disposal must take into account the variety of second-
generation products made from recycled carpet. Information on carpet recycling and the resulting
second-generation products is sparse; however, EPA has modeled pathways for which consistent data
are available for recycled carpet components. As described previously, due to unavailable life-cycle data
on the manufacture of second-generation products from recycled carpet, EPA modeled only the
remanufacture of the various virgin plastic resins (i.e., one step before the resins are used to
manufacture the second-generation products such as carpet pad, molded products and carpet backing).
Please see Exhibit 2 for the process flow diagram that illustrates these boundaries.
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The data source used to develop the emissions factor for source reduction is a 2002 report
published by Franklin Associates Limited (FAL) on energy and GHG emission factors for the manufacture
and end-of-life management of carpet (FAL, 2002). These data were based on a number of industry and
academic data sources dating from the 1990s and 2000s. The background data for the development of
the source reduction carpet emission factors are available in an EPA background document associated
with the FAL 2002 report (EPA, 2003). The data source used to develop the open-loop recycling emission
factor for carpet is based on updated data from Dr. Matthew Realff of Georgia Institute of Technology
(Georgia Tech). His findings were informed by the 2009 Carpet America Recovery Effort (CARE) 2009
annual report, which provided a breakdown of the components of carpet face fiber polymer (CARE,
2009). In 2011, Dr. Realff collected data in collaboration with the carpet industry that provided the
energy inputs used to recycle carpet face fiber into plastic constituents (Realff, 2011b). Dr. Realff
provided the life-cycle data for recycling carpet in a spreadsheet designed for incorporation into WARM
(Realff, 2011c).
3.4.1 Source Reduction
Source reduction activities reduce the amount of carpet that is produced, thereby reducing GHG
emissions from carpet production. Source reduction of carpet can be achieved through using less
carpeting material per square foot (i.e., thinner carpet) or by finding a way to make existing carpet last
longer through cleaning or repair. For more information on this practice, see the Source Reduction
chapter.
Exhibit 7 outlines the GHG emission factor for source reducing carpet. GHG benefits of source
reduction are calculated as the avoided emissions from raw materials acquisition and manufacturing
(RMAM) of new carpet.
Exhibit 3-7: Source Reduction Emission Factor for Carpet (MTCO2E/Short Ton)
Material
Raw Material
Acquisition and
Manufacturing
for Current Mix
of Inputs
Raw Material
Acquisition and
Manufacturing
for 100% Virgin
Inputs
Forest Carbon
Storage for
Current Mix of
Inputs
Forest Carbon
Storage for
100% Virgin
Inputs
Net Emissions
for Current
Mix of Inputs
Net
Emissions
for 100%
Virgin Inputs
Carpet -3.82 -3.82 NA NA -3.82 -3.82
Note: Negative values denote net GHG emission reductions or carbon storage from a materials management practice.
Information on the share of recycled inputs used in production is unavailable or is not a common practice; EPA assumes that the current mix is
comprised of 100% virgin inputs. Consequently, the source reduction benefits of both the “current mix of inputs” and “100% virgin inputs” are
the same.
NA = Not applicable.
Post-consumer emissions are the emissions associated with materials management pathways
that could occur at end-of-life. Source reducing carpet does not involve post-consumer emissions
because production of the material is avoided in the first place. Forest products are not used in the
production of carpet; therefore, forest carbon storage is not applicable to carpet and thus does not
contribute to the source reduction emission factor.
3.4.1.1 Developing the Emission Factor for Source Reduction of Carpet
To calculate the avoided GHG emissions for carpet, EPA looks at three components of GHG
emissions from RMAM activities: process energy, transportation energy and process non-energy GHG
emissions. Exhibit 8 shows the results for each component and the total GHG emission factor for source
reduction. More information on each component making up the final emission factor is provided in the
remainder of this section.
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Exhibit 3-8: Raw Material Acquisition and Manufacturing Emission Factor for Virgin Production of Carpet
(MTCO2E/Short Ton)
(a) (b) (c) (d) (e)
Material
Process Energy
Transportation Energy
Process Non-Energy
Net Emissions
(e = b + c + d)
Carpet 3.22 0.10 0.50 3.82
FAL (2002) reports the amount of energy required to produce one short ton of carpet as 60.32
million Btu. FAL (2002) also provided the fuel mix that makes up this energy estimate. To estimate GHG
emissions, EPA multiplied the fuel consumption (in Btu) by the fuel-specific carbon contents. Summing
the resulting GHG emissions, by fuel type, gives the total process energy GHG emissions, including both
CO2 and CH4, from all fuel types used in carpet manufacture (Exhibit 3-9).
Exhibit 3-9: Process Energy GHG Emissions Calculations for Virgin Production of Carpet
Material
Process Energy per Short Ton Made
from Virgin Inputs (Million Btu)
Process Energy GHG Emissions
(MTCO2E/Short Ton)
Carpet 60.32 3.22
Transportation energy emissions come from fossil fuels used to transport carpet raw materials
and intermediate products. The methodology for estimating these emissions is the same as that for
process energy emissions. Based upon estimated total carpet transportation energy in Btu, EPA
calculates the total emissions using fuel-specific carbon coefficients (Exhibit 3-10).
Exhibit 3-10: Transportation Energy Emissions Calculations for Virgin Production of Carpet
Material
Transportation Energy per Short Ton
Made from Virgin Inputs (Million Btu)
Transportation Energy GHG Emissions
(MTCO2E/Short Ton)
Carpet 1.36 0.10
Note: The transportation energy and emissions in this exhibit do not include retail transportation.
Process non-energy GHG emissions occur during manufacture but are not related to combusting
fuel for energy. For carpet, non-energy GHGs are emitted in the use of solvents or chemical treatments.
FAL provided data on GHG emissions from non-energy-related processes in units of pounds of native gas
(2002). We convert pounds of gas per 1,000 lbs of carpet to metric tons of gas per short ton of carpet
and then multiply that by the ratio of carbon to gas to produce the emission factor in MTCO2E per short
ton of carpet, as detailed in the example below, showing the calculation of CH4 process non-energy
emissions for carpet. Exhibit 3-11 shows the components for estimating process non-energy GHG
emissions for carpet.
2.72 lbs CH4/1,000 lbs carpet × 2,000 lbs carpet/1 short ton carpet × 1 metric ton CH4/2,205 lbs CH4 =
0.0025 MT CH4/short ton carpet
0.0025 MT CH4/short ton carpet × 25 MTCO2E/metric ton CH4 = 0.06 MTCO2E/short ton carpet
Exhibit 3-11: Process Non-Energy Emissions Calculations for Virgin Production of Carpet
Material
CO2
Emissions
(MT/Short
Ton)
CH4
Emissions
(MT/Short
Ton)
CF4 Emissions
(MT/Short
Ton)
C2F6
Emissions
(MT/Short
Ton)
N2O
Emissions
(MT/Short
Ton)
Non-Energy
Carbon
Emissions
(MTCO2E/Short
Ton)
Carpet 0.01 0.00 – – 0.00 0.50
– = Zero emissions.
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3.4.2 Recycling
This section describes the development of the recycling emission factor, which is shown in the
final column of Exhibit 3-12. For more information on recycling in general, please see the Recycling
chapter. As mentioned previously, updated life-cycle data for recycling carpet were available from Dr.
Matthew Realff of Georgia Tech. His findings were informed by the 2009 Carpet America Recovery Effort
(CARE) 2009 annual report, which provided a breakdown of the components of carpet face fiber
polymers in conjunction with the collaboration with the carpet industry to collect data that provided the
energy inputs used to recycle carpet face fiber plastic constituents.
Exhibit 3-12: Recycling Emission Factor for Carpet (MTCO2E/Short Ton)
Material
Raw Material
Acquisition and
Manufacturing
(Current Mix of
Inputs)
Materials
Managemen
t Emissions
Recycled
Input
Credita
Process
Energy
Recycled Input
Credita –
Transportation
Energy
Recycled
Input
Credita –
Process
Non-Energy
Forest Carbon
Sequestration
Net
Emissions
(Post-
Consumer)
Carpet – – -1.41 -0.01 -0.94 – -2.36 a Includes emissions from the virgin production of secondary materials.
Note: Negative values denote net GHG emission reductions or carbon storage from a materials management practice.
NA = Not applicable.
In WARM, EPA models open-loop recycling of carpet into a mixture of following plastic resins:
Nylon 6, Nylon 6-6, PET and PP. The resulting plastic resins produced from the open-loop recycling
process will then be converted into a number of products including new carpet fiber, molded or
extruded plastics and plastic pellets. The additional energy and resultant GHG emissions from the
conversion of the recycled plastic resins into these final secondary products were not available.
Therefore, the recycling benefits for carpet are limited to the avoided energy and GHG emissions
associated with virgin plastic resin manufacture.
The recycled input credits shown in Exhibit 3-12 include all of the GHG emissions associated with
collecting, transporting, processing and recycling or remanufacturing carpet into secondary materials.
None of the upstream GHG emissions from manufacturing the carpet in the first place are included;
instead, WARM calculates a “recycled input credit” by assuming that the recycled material avoids—or
offsets—the GHG emissions associated with producing the same amount of secondary resins from virgin
inputs. The eventual secondary products those resins are then used to manufacture are not factored
into WARM’s calculations. Consequently, GHG emissions associated with management (i.e., collection,
transportation and processing) of end-of-life carpet are included in the recycling credit calculation. Since
carpet does not contain any wood products, there are no recycling benefits associated with forest
carbon storage. The GHG benefits from the recycled input credits are discussed further below.
EPA calculates the GHG benefits of recycling carpet by comparing the difference between the
emissions associated with manufacturing a short ton of each of the four resins derived from recycled
carpet and the emissions from manufacturing the same ton from virgin materials, after accounting for
losses that occur in the recycling process. WARM assumes that both recycled Nylon 6-6 fiber and Nylon
6-6 pellets displace the virgin production of Nylon 6-6 resin. These results are then weighted by the
distribution shown in Exhibit 3-13 to obtain a composite emission factor for recycling one short ton of
carpet. This recycled input credit is composed of GHG emissions from process energy, transportation
energy and process non-energy.
Exhibit 3-13: Secondary Resins Produced from Recycled Carpet Fibers
Material Percent of Recovered Carpet Face Fiber
Nylon 6 Fiber 54.02%
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Material Percent of Recovered Carpet Face Fiber
Nylon 6-6 Fiber 6.72%
Nylon 6-6 Pellet 23.07%
PET Fiber 7.71%
PP Fiber 8.62%
Source: Realff, 2011b
To calculate each component of the recycling emission factor, EPA follows five steps, which are
described in detail below.
Step 1. Calculate emissions from virgin production of one short ton of secondary resin.
We apply fuel-specific carbon coefficients to the life-cycle data for virgin RMAM of each
secondary resin (FAL, 2010, Plastics Europe, 2005). The life-cycle data for virgin production of Nylon 6
and Nylon 6-6 were unavailable for production of these resins in the United States. Thus, life-cycle data
for the production of these resins in the European context were used as a proxy (Plastics Europe, 2005).
Life-cycle data for the production of PET and PP resins are the same as used in the development of the
PET and PP emission factors in WARM (FAL, 2011). The upstream life-cycle data also incorporate
transportation and process non-energy data. The calculations for virgin process, transportation and
process non-energy emissions for the secondary resins are presented in Exhibit 14, Exhibit 15, and
Exhibit 16, respectively.
Exhibit 3-14: Process Energy GHG Emissions Calculations for Virgin Production of Carpet Secondary Resins
Material
Process Energy per Short Ton Made
from Virgin Inputs (Million Btu)
Energy Emissions (MTCO2E/Short Ton
Carpet)
Nylon 6 112.16 6.60
Nylon 6-6 122.40 7.45
PET 28.43 1.74
PP 23.72 1.17
Exhibit 3-15: Transportation Energy Emissions Calculations for Virgin Production of Carpet Secondary Resins
Material
Transportation Energy per Short Ton
Made from Virgin Inputs (Million Btu)
Transportation Emissions
(MTCO2E/Short Ton Carpet)
Nylon 6 1.05 0.07
Nylon 6-6 0.82 0.05
PET 1.00 0.07
PP 2.36 0.13
Exhibit 3-16: Process Non-Energy Emissions Calculations for Virgin Production of Carpet Secondary Resins
Material
CO2
Emissions
(MT/Short
Ton Carpet)
CH4
Emissions
(MT/Short
Ton Carpet)
CF4
Emissions
(MT/Short
Ton Carpet)
C2F6
Emissions
(MT/Short
Ton Carpet)
N2O
Emissions
(MT/Short
Ton Carpet)
Non-Energy
Carbon Emissions
(MTCO2E/Short
Ton)
Nylon 6 1.04 0.00 – – 0.01 3.43
Nylon 6-6 0.84 0.00 – – 0.00 1.08
PET 0.27 0.00 – – – 0.39
PP 0.07 0.01 – – 0.00 0.21
– = Zero emissions.
Step 2. Calculate emissions from recycled production of one short ton of the secondary resin.
EPA then applies the same carbon coefficients to the energy data for the production of the
secondary resin production from recycled carpet. Personal correspondence with Dr. Matthew Realff
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(2011a) indicated that no non-energy process emissions occur in recycled production of secondary
resins from carpet. The same amount of energy is required to remix HMA from recycled asphalt
concrete as is required to produce HMA from virgin materials (Levis, 2008); therefore, the analysis uses
data on virgin HMA production from the Canadian Program for Energy Conservation as described in the
source reduction section (Natural Resources Canada, 2005).
Exhibit 1-10Exhibit 3-17 and Exhibit 3-18 present the emission calculation components for
recycled secondary product process energy emissions and transportation energy emissions, respectively.
Exhibit 3-17: Process Energy GHG Emissions Calculations for Recycled Production of Carpet Secondary Resins
Material
Process Energy per Short Ton
Made from Recycled Inputs
(Million Btu)
Energy Emissions (MTCO2E/Short
Ton)
Nylon 6 Fiber 74.24 3.93
Nylon 6-6 Fiber 3.13 0.16
Nylon 6-6 Pellet 13.39 0.70
PET Fiber 1.24 0.06
PP Fiber 10.55 0.56
Exhibit 3-18: Transportation Energy GHG Emissions Calculations for Recycled Production of Carpet Secondary
Resins
Material
Transportation Energy per Short
Ton Made from Recycled Inputs
(Million Btu)
Transportation Emissions
(MTCO2E/Short Ton)
Nylon 6 Fiber 0.85 0.07
Nylon 6-6 Fiber 2.56 0.21
Nylon 6-6 Pellet 3.67 0.003
PET Fiber 3.24 0.003
PP Fiber 0.84 0.001
Note: The transportation energy and emissions in this exhibit do not include retail transportation.
Step 3. Calculate the difference in emissions between virgin and recycled production.
To calculate the GHG reductions associated with replacing virgin production with recycled
production of secondary products, we then subtract the emissions from recycled production (Step 2)
from the emissions from virgin production (Step 1). These results are shown in Exhibit 1-12.
Exhibit 3-19: Differences in Emissions between Recycled and Virgin Carpet Manufacture (MTCO2E/Short Ton)
Material/
Product
Product Manufacture Using
100% Virgin Inputs
(MTCO2E/Short Ton)
Product Manufacture Using 100%
Recycled Inputs
(MTCO2E/Short Ton)
Difference Between Virgin and
Recycled Manufacture
(MTCO2E/Short Ton)
Process
Energy
Transpor-
tation
Energy
Process
Non-
Energy
Process
Energy
Transpor-
tation
Energy
Process
Non-
Energy
Process
Energy
Transpor-
tation
Energy
Process
Non-
Energy
Nylon 6 Fiber 6.60 0.07 3.43 3.93 0.07 – -2.67 -0.01 -3.43
Nylon 6-6 Fiber 7.45 0.05 1.08 0.16 0.21 – -7.28 0.16 -1.08
Nylon 6-6 Pellet 7.45 0.05 1.08 0.70 0.003 – -6.75 -0.047 -1.08
PET Fiber 1.74 0.07 0.39 0.06 0.003 – -1.68 -0.067 -0.39
PP Fiber 1.17 0.13 0.21 0.56 0.001 – -0.61 -0.129 -0.21
Note: Negative values denote net GHG emission reductions or carbon storage from a materials management practice.
– = Zero emissions
Step 4. Adjust the emissions differences to account for recycling losses.
For almost every material that gets recycled, some portion of the recovered material is
unsuitable for use as a recycled input. This portion is discarded either in the recovery stage or in the
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manufacturing stage. Consequently, less than one ton of new material is typically made from one ton of
recovered materials. Material losses are quantified and translated into loss rates. Exhibit 20 shows the
relative amounts of each plastic resin recovered from a given ton of recycled carpet and their end uses.
Associated with each of these end uses are different recycling routes. For example Nylon 6 face fiber is
recycled mostly through depolymerization, whereas Nylon 6-6 face fiber is recycled mainly through
shaving the fiber followed by remelting and extrusion.
The distribution of end uses for carpet material is shown in Exhibit 3-20 and illustrates the total
amount of plastic resins recovered and ultimately remanufactured per 1000 kg of recycled carpet. Note
that the recovery and remanufacture of plastic resins per 1000 kg of incoming carpet material is less
than 50 percent by mass indicating a high loss rate for recycling carpet. Furthermore, due to lack of data,
EPA did not factor in the recovery of plastic pellets and molded plastics made from recovered PP resin.
Exhibit 3-21 shows the recovery rates for each plastic resin recovered from carpet face fiber. The
recovery rates add up to less than 100 percent due to the low overall recovery rate outlined in Exhibit
3-20.
Exhibit 3-20: End Uses for Recycled Carpet based on 1000 kg of Incoming Carpet Material
Per 1000 kg Recycled Carpet
Material Total Nylon 6 Nylon 6-6 PET PP
New Carpet 233.3 207.5 25.8 – –-
Plastic Pellets 171.1 – 88.6 – 82.5* Molded or
Extruded Plastics 25.9 – – –
25.9*
Carpet Padding 62.2 – – 29.6 33.1 Total Polymer
Weight 492.5 207.5 114.4 29.6 141.5
Note: The recycled flows indicated by an asterisk (*) are not accounted in the recycling pathway in WARM because the life-cycle data
associated with recovering these flows in the recycling process were not available.
Source: Realff, 2011b
Each product’s process energy, transportation energy and process non-energy emissions are
weighted by the percentages in Exhibit 3-21 and then they are summed as shown in the final column of
Exhibit 3-22.
Exhibit 3-21: Calculation of Adjusted GHG Savings for Carpet Recycled into Secondary Products
Material Rate of Recovery per Short Ton Carpet Collected
Nylon 6 Fiber 20.7%
Nylon 6-6 Fiber 2.58%
Nylon 6-6 Pellet 8.85%
PET Fiber 2.96%
PP Fiber 3.31%
Source: The WARM Model – Analysis and Suggested Action (Realff, 2011b).
Step 5. Weight the results by the percentage of recycled carpet that the secondary products
comprise.
Exhibit 3-22: Carpet Recycling Emission Factors (MTCO2E/Short Ton)
Material
Recycled Input Credit for Recycling One Short Ton of Carpet
Weighted Process Energy
(MTCO2E/Short Ton
Product)
Weighted Transport Energy
(MTCO2E/Short Ton
Product)
Weighted Process Non-
Energy (MTCO2E/Short
Ton Product)
Total
(MTCO2E/Short
Ton Product)
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Material
Recycled Input Credit for Recycling One Short Ton of Carpet
Weighted Process Energy
(MTCO2E/Short Ton
Product)
Weighted Transport Energy
(MTCO2E/Short Ton
Product)
Weighted Process Non-
Energy (MTCO2E/Short
Ton Product)
Total
(MTCO2E/Short
Ton Product)
Nylon 6 Fiber -0.55 -0.00 -0.80 -1.35
Nylon 6-6 Fiber -0.19 0.00 -0.03 -0.21
Nylon 6-6 Pellet -0.60 -0.00 -0.10 -0.70
PET Fiber -0.05 -0.00 -0.01 -0.06
PP Fiber -0.02 -0.00 -0.01 -0.03
Carpet Total -1.41 -0.01 -0.94 -2.36
Note: Negative values denote net GHG emission reductions or carbon storage from a materials management practice.
3.4.3 Composting
Carpet is not subject to aerobic bacterial degradation and therefore cannot be composted. As a
result, WARM does not consider GHG emissions or storage associated with composting carpet.
3.4.4 Combustion
Combustion results in both direct and indirect emissions: direct emissions from the combustion
process itself and indirect emissions associated with transportation to the combustor. To the extent that
carpet combusted at waste-to-energy (WTE) facilities produces electricity, combustion offsets GHG
emissions that would have otherwise been produced from non-baseload power plants feeding into the
national electricity grid. These components make up the combustion factor calculated for carpet. The
tables presented here are based on the national average grid mix, rather than on any of the regional grid
mixes also available in the Excel version of WARM.
For further information on combustion, see the Combustion chapter. Because WARM’s analysis
begins with materials at end-of-life, emissions from RMAM are zero. Exhibit 3-23 shows the components
of the emission factor for combustion of carpet. Further discussion on the development of each piece of
the emission factor is discussed below.
Exhibit 3-23: Components of the Combustion Net Emission Factor for Carpet (MTCO2E/Short Ton)
Raw Material
Acquisition and
Manufacturing
(Current Mix of
Inputs)
Transportation to
Combustion
CO2 from
Combustion
N2O from
Combustion
Avoided
Utility
Emissions
Steel
Recovery
Net
Emissions
(Post-
Consumer)
– 0.01 1.67 – -0.59 – 1.09 Note: Negative values denote net GHG emission reductions or carbon storage from a materials management practice.
3.4.4.1 Developing the Emission Factor for Combustion of Carpet
EPA estimates that carpet has a weighted carbon content of 51 percent and that 98 percent of
that carbon is converted to CO2 during combustion. These estimates are based on the carbon that is
contained within the various plastics and the limestone in carpet. These carbon contents and resulting
direct CO2 emissions from combustion of carbon in carpet are presented in Exhibit 3-24.
Exhibit 3-24: Carpet Combustion Emission Factor Calculation
Components
% of Total
Weight
Carbon
Content
Carbon Content %
of Total Weight
Carbon Converted
to CO2 during
Combustion
Total
MTCO2E/Short
Ton
Styrene-butadiene (latex) 10% 90% 9% 98% 0.29
WARM Version 14 Carpet February 2016
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Components
% of Total
Weight
Carbon
Content
Carbon Content %
of Total Weight
Carbon Converted
to CO2 during
Combustion
Total
MTCO2E/Short
Ton
Limestone 37% 12% 4% 98% 0.13
Backing Fiber (PP) 11% 86% 9% 98% 0.29
Face Fibers:
Nylon 6 and Nylon 6-6 28% 64% 18% 98% 0.59
PP 8% 86% 7% 98% 0.23
PET 6% 63% 4% 98% 0.13
Carpet (Sum) NA NA 51% 98% 1.67
Sources: Styrene-butadiene carbon content calculated from chemical formula; limestone carbon content (Kantamaneni, 2002); polypropylene
and nylon carbon contents (EPA, 2001, Ch. 7). Face fiber plastic component distribution from personal communication with Matthew Realff
(Realff 2011a).
Totals may not sum due to independent rounding.
NA = Not applicable.
EPA estimates CO2 emissions from transporting carpet to the WTE plant and transporting ash
from the WTE plant to the landfill using data provided by FAL (2002). Transportation-related CO2
emissions were estimated to be 0.03 MTCO2E per short ton of carpet combusted.
Most utility power plants use fossil fuels to produce electricity, and the electricity produced at a
WTE plant reduces the demand for fossil-derived electricity. As a result, the combustion emission factor
for carpet includes avoided GHG emissions from utilities. We calculate the avoided utility CO2 emissions
based on the energy content of carpet, the combustion efficiency of the WTE plant including
transmission and distribution losses, and the national average carbon-intensity of electricity produced
by non-baseload power plants. EPA utilized the energy content from recent analysis, which presents the
energy content that is more representative of the current carpet composition (Realff, 2010b). Exhibit
3-25 shows the estimated utility offset from combustion of carpet.
Exhibit 3-25: Utility GHG Emissions Offset from Combustion of Carpet
(a) (b) (c) (d) (e)
Material
Energy Content
(Million Btu per
Short Ton)
Combustion
System Efficiency
(%)
Emission Factor for Utility-
Generated Electricity
(MTCO2E/
Million Btu of Electricity
Delivered)
Avoided Utility GHG per
Short Ton Combusted
(MTCO2E/Short Ton)
(e = b × c × d)
Carpet 15.2* 17.8% 0.22 0.59
* Calculated from the “Carpet 1” architecture in Table 2 of Realff 2010b using the heat of combustion (20% solid) value
3.4.5 Landfilling
Typically, the emission factor for landfilling is composed of four parts: landfill CH4; CO2 emissions
from transportation and landfill equipment; landfill carbon storage; and avoided electric utility
emissions. However, as with other non-biodegradable materials in WARM, there are zero landfill
methane emissions, landfill carbon storage or avoided utility emissions associated with landfilling
carpet, as shown in Exhibit 3-26. GHG emissions associated with RMAM are not included in WARM’s
landfilling emission factors. As a result, the emission factor for landfilling carpet represents only the
transportation emissions associated with collecting the waste and operating the landfill equipment. For
more information on landfilling, refer to the Landfilling chapter.
WARM Version 14 Carpet February 2016
3-14
Exhibit 3-26: Landfilling Emission Factor for Carpet (MTCO2E/Short Ton)
Material
Raw Material
Acquisition and
Manufacturing
(Current Mix of Inputs)
Transportation
to Landfill
Landfill
CH4
Avoided CO2
Emissions from
Energy
Recovery
Landfill
Carbon
Storage
Net
Emissions
(Post-
Consumer)
Carpet – 0.02 NA NA NA 0.02
NA = Not applicable.
– = Zero emissions.
3.4.6 Anaerobic Digestion
Because of the nature of carpet components, carpet cannot be anaerobically digested, and thus,
WARM does not include an emission factor for the anaerobic digestion of carpet.
3.5 LIMITATIONS
As outlined in the Recycling section (3.4.2), the open-loop recycling process is a complicated
end-of-life process for carpet. There are some limitations associated with modeling the GHG emissions
from open-loop carpet recycling, including limited availability of representative life-cycle inventory (LCI)
data for carpet and the materials recovered from them.
Given the complex open-loop recycling process and a lack of more complete information on
carpet recycling, the recycling factor for carpet is subject to important limitations. A primary data gap is
the availability of representative LCI data for carpet in the closed-loop recycling process, and the
materials recovered from them in the open-loop recycling process. For this analysis, we use life-cycle
data to represent the recovery of various plastic resins from recycled carpet but do not incorporate the
additional energy and material requirements for converting these plastic resins into secondary products.
Since the WARM carpet emission factor was initially developed, manufacturers have increased their
capacity to recycle carpet into different end products including new carpet, plastic pellets, molded
plastics and carpet padding. According to the CARE Annual Report for 2009, 47 percent of carpet
recovered for recycling is used to manufacture new carpet, 35 percent was used to manufacture plastic
pellets, 13 percent was used to manufacture carpet padding, and 5 percent was used to manufacture
molded or extruded plastics (CARE, 2009). Updated LCI data on the conversion of plastic resins into final
secondary products for carpet could have important effects on our results for the recycling benefits
associated with carpet. EPA is investigating the availability of data necessary to develop a more
representative open-loop recycling emission factor for carpet.
Finally, the open-loop recycling pathways for each carpet type vary significantly (Realff, 2010a).
WARM currently assumes that the same average mix of carpet types is recycled by each of the three
open-loop recycling pathways, since at the time the emission factors were created, no further
information was available. However, more recent data show that some carpet types are rarely or never
recycled into some open-loop products. For example, Nylon 6 carpet is exclusively recycled into new
Nylon 6 carpet, PET carpet is exclusively recycled into new carpet padding, and Nylon 6-6 carpet is only
recycled into new Nylon 6-6 carpet and plastic pellets (CARE, 2009).
Emissions associated with retail transport of carpet from manufacturing to point of sale were
not developed in the original WARM analysis as the representative transportation mode/distance data
were not available. EPA is investigating the availability of these data through the U.S. Census and will
likely incorporate emissions from retail transport in the next version of the carpet emission factor in
WARM.
WARM Version 14 Carpet February 2016
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For the source reduction pathway, the LCI data to estimate GHG emissions from the
manufacture of carpet from virgin materials are slightly outdated. EPA is investigating the availability of
updated life-cycle data and will revise the source reduction emission factor accordingly in WARM.
3.6 REFERENCES
CARE. (2009). Annual Report 2009. Carpet America Recovery Effort. Retrieved from
https://carpetrecovery.org/wp-content/uploads/2014/04/09_CARE-annual-rpt1.pdf.
CRI. (2010). Carpet and Rug Construction. Carpet and Rug Institute. Retrieved from http://www.carpet-
rug.org/commercial-customers/selecting-the-right-carpet/carpet-and-rug-construction.cfm.
EPA (2006). Solid Waste Management and Greenhouse Gases: A Life-Cycle Assessment of Emissions and
Sinks. Washington, DC: U.S. Environmental Protection Agency. Retrieved October 22, 2008, from
http://epa.gov/epawaste/conserve/tools/warm/SWMGHGreport.html.
EPA (2003). Background Document for Life-Cycle Greenhouse Gas Emission Factors for Carpet and
Personal Computers. EPA530-R-03-018. November 21, 2003.
FAL. (2011). Cradle-to-Gate Life Cycle Inventory of Nine Plastic Resins and Two Polyurethane Precursors.
Revised Final Report. Prairie Village, KS: Franklin Associates, Ltd.
FAL. (2002). Energy and Greenhouse Gas Factors for Personal Computers. Final Report. Prairie Village,
KS: Franklin Associates, Ltd. August 7, 2002.
Kantamaneni , R. (2002) Expert opinion of Ravi Kantamaneni, ICF Consulting, April 2002.
Plastics Europe. (2005). Eco-profiles of the Plastics Industry—Polyamide (Nylon 6). Brussels, Belgium:
Plastics Europe. March 2005.
Plastics Europe. (2005). Eco-profiles of the Plastics Industry—Polyamide (Nylon 66). Brussels, Belgium:
Plastics Europe. March 2005.
Realff, M. (2010a). Personal communication with Matthew Realff, Associate Professor of Chemical and
Biomolecular Engineering, Georgia Tech, September 9, 2010.
Realff, M. (2010b). “The role of using carpet as a fuel in carpet recovery system development.” Delivered
to ICF International via email on September 9, 2010.
Realff, M. (2011a). Personal communication with Matthew Realff, Associate Professor of Chemical and
Biomolecular Engineering, Georgia Tech, September 15, 2011.
Realff, M. (2011b). The WARM Model – Analysis and Suggested Action. September 15, 2011.
Realff, M. (2011c). “WARM_information_FINAL.xls”. Excel spreadsheet with life-cycle data provided to
ICF International and EPA on July 12, 2011.
