Design for the Environment/Office Chair Foam

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This page is part of the Design for the Environment course

File:Mainpic harrington.jpg
Teknion Inc. Office Chairs - Harrington Series

Company Website: Teknion Inc.

More than 60% of the 2.1 billion pounds of flexible polyurethane foam (FPF) produced worldwide is used in the home/office furnishings sector [1]. FPF is a polymeric foam consisting of two main components: petroleum derived polyols and man-made, amine based isocyanates [2]. FPF production consumes 6.6 million tonnes of petroleum yearly, 0.2% of the world’s yearly oil supply [3]. It is desirable to find a more sustainable and environmentally friendly alternative to be used in the production of office furniture.

The goal of furniture companies such as Teknion Inc. is to reduce the environmental impacts of the office furniture sector by replacing petroleum constituents in foam cushioning with renewable alternatives. The two alternatives under consideration are soy -based polyurethane foam (soy foam or soy FPF) and natural latex foam (latex foam). The soy based alternative reduces the total amount of petroleum products used in manufacturing FPF by direct substitution of petrol-derived polyether polyols with polyols derived from soy oil[4]. Although development of high percentage soy-based FPF is currently being pursued by companies such as Woodbridge Group, Lear Corporation, and Bayer, the analysis will focus on soy FPF with 15% soy polyol content. For latex foam, the natural latex resin used to produce the foam is extracted from the Hevea Brasiliensis tree [5] and transformed to latex foam through the Dunlop process.

Foam Cushion Example: Soy-Based Foam (15% Soy Polyol Content)

Office chair cushion sample, courtesy of Comp-Tech Mfg., Obtained: Feb 2008 Plant Tour

Project Information[edit]

Section 1 Group 18
A. Marangoni (A_Marangoni)
P. Mitassov (Pmitassov)
S. Memme (Smemme)

Background[edit]

Both FPF foams use the same manufacturing process: the two primary chemical ingredients (polyols and isocyanates) are injected into a mold using a multiple stream, high pressure mixing head attached to a robotic arm. Flame retardants, stabilizers and water are also added to this mix. The water and isocyanates react to produce CO2, which creates the characteristic bubbles of the foam. Each mold is lined with a release agent (to ensure that the products can be easily removed). No further curing processes are needed once the final product is removed from the mold [2]. Approximately 10 000 FPF cushions can be produced daily on a typical manufacturing line [6].

Latex foam is created through the Dunlop process which uses an Oakes mixer: a mixing machine which combines the ingredients with air bubbles through high speed mixing [7]. Additives such as ethyl zimate, zetax, potassium oleate, sulphur and zinc oxide are required during the latex foaming process to induce vulcanization, stabilization, frothing, etc [8]. The liquid latex compound is then injected into mold pallets, which progress along a conveyor belt through a steam curing chamber, washing chamber and finally a drying oven.

Highlights and Recommendations[edit]

Functionally, polyurethane, soy-based and latex foam behave similarly, with latex foam possessing slightly higher performance than the FPF alternatives (see density verses compression plots below for more information). Latex foam is more resilient than FPF, but does not show significant benefits in the long term. Overall, the differences in the performance of the foam alternatives as cushioning materials are not significant; any of the three is suitable for use as office chair padding. It should also be noted that the life expectancy of the three foams is not factored into the performance analysis since the useful life of the foam is typically greater than that of the office chair (which is usually discarded for reasons other than foam performance, such as mechanical failures, aesthetics, etc) [4] . Please see the Functional Analysis section for more detail.

The lifecycle assessment of the three alternatives resulted in the conclusion that latex foam was the most environmentally friendly product. It was also shown that the major impacts arose from the pre-manufacturing and manufacturing lifecycle stages of the foams, with the use, delivery and end of life phases being virtually identical (please see the SLCA section for details).

The Streamlined Lifecycle Assessment (SLCA) results demonstrated that natural latex foam was the most environmentally-friendly of the three alternatives thanks to its extremely clean premanufacturing lifecycle stage. In comparison to a natural latex resin, regular and soy FPF use virgin petroleum to produce polyols, and hazardous materials in the production of isocyanates (includes toluene, phosgene, HCl, CO)[2]. The gathering of latex resin also uses far less energy than the extraction of the oil and coal that used in the production of the polyols and isocyanates [5][9][10], or the energy used in soybean farming (farming equipment, electricity for irrigation pumps, fertilizer pridyction etc [11]). Latex also produces virtually no liquid, solid or gaseous residues compared to the alternatives (please see the SLCA - Premanufacturing section).

It should be noted that the latex foam has the least environmentally friendly manufacturing stage, due to the high amount of energy used to manufacture the latex foam. (Since each cushion needs to be cured, washed and dryed [8]). However, the almost ideal pre-manufacturing stage of the latex foam makes the alternative with the cleanest overall lifecycle.

Economic Input-Output Life Cycle Assessment (EIOLCA) - Total Energy Consumption & Air Releases For All Three Alternatives

Based on the EIOLCA, polyurethane foam was considered the most environmentally friendly alternative since it emits lower amounts of air pollutants and consumes less energy. Although latex and soy are renewable, farming and energy use substantially hinders them in terms of environmental compatibility.

According to Economic Input-Output Life Cycle Analyses for each alternative, the primary conventional air pollutants emitted during foam production are carbon monoxide (CO), nitrogen oxides (NOx), sulphur dioxide (SO2) and volatile organic compounds (VOCs). The soy and latex alternatives are by far the worst in terms of the production of air pollutants due to higher NOx, SO2 and CO emissions in comparison to conventional FPF.
For each of the foam products, CO is the largest pollutant, with soy foam having the highest overall output of CO. However, the NOx, SO2 and VOC emissions are also significant (please see EIOLCA section for more information).

As seen in the the total energy consumption chart to the right, latex uses by far the most energy. Each alternative relies most heavily on natural gas as an energy source. This is especially true for latex foam manufacturing, which uses natural gas heaters and furnaces. Since large amounts of electric energy are also required, coal is also a major energy source for the process (since many electric power plants run on coal).

Based on an economic analysis of the three foam alternatives FPF is the most economically viable option for an office furniture manufacturer since its costs are substantially less than the other alternatives. The producer prices of the foam alternatives are shown in the table below [4].

Office Chair Foam Alternatives -
Producer Prices ($US/Cushion)
FPF 6
Latex 14
Soy 9.75


Since purchasing the foam is the only expense incurred by the manufacturer during the product’s lifecycle, (ie. no maintenance, identical recycling methods - Please see Details - End of Life), the decision of FPF as the most economic choice was based solely on its low relative cost to the other alternatives. The additional cost associated with latex foam in comparison to FPF arises from the time required for the rubber trees to produce large quantities of latex. The rubber tree only starts to produce latex once it is approximately 8 years old [5], resulting in large periods of unproductivity. Likewise, farming equipment, water, fertilizers, distillation etc, contribute to the high cost of soy FPF. Refer to Details- Cost Analysis for more reasons as to why the soy and latex foam alternatives are more expensive than FPF.

Foam Alternative Final Scoring Table

The table above demonstrates the conclusions of the completed analysis. Since FPF is less than half the price of a natural latex cushion, and 60% of a soy FPF cushion, it is not justifiable for a office chair manufacturer to pay so much more for soy or natural latex foams while seeing only marginal decreases in the total environmental impacts of the product. With current technology, FPF is the alternative which demonstrates the lowest cost, while having comparable environmental impacts to the other alternatives. Therefore, our group recommends that FPF be used for office furniture padding.

Details[edit]

Functional Analysis[edit]


Comfort/Durability[edit]

The comfort, durability and ability to support weight are characteristics that are directly related to the density of the foam [1]. Most low density polyurethane and soy FPF used in furniture have a density between 14.2 kg/m3 and 40.5 kg/m3 (0.9 lb/ft3 - 2.5 lb/ft3), which has been proven to be sufficiently resilient while remaining comfortable for the user [12]. Soy foam density is known to increase with increased biomass [13]. The density of latex foam generally varies between 25 kg/m3 and 300 kg/m3 (1.56 lb/ft3 and 18.97 lb/ft3) [14], with the lower values in this range being more commonly used for seating applications.

Flammability[edit]

All three foam alternatives pass the regulated smouldering cigarette test, during which the upholstered furniture must not ignite in the presence of a smouldering cigarette [2]. The cellular structure of the FPF alternatives makes it quite flammable even after the addition of phosphorus containing flame retardants. However, flame retardants help these materials meet all fire related regulations [12]. Natural latex foam, on the other hand, surpasses all fire safety and flammability requirements without needing fire-repelling additives [15]

Toxicity/Allergic Reactions[edit]

Solid state FPF (regular and soy based) is non-toxic, and completely inert when in contact with the human body [16]. Like most other materials, fine FPF dusts may cause coughing and skin irritation at concentrations higher than 6mg/m3 [3]. Similarly, latex foam is naturally hypoallergenic and non-toxic. The open cell structure of latex foam, combined with a careful washing process, ensures removal of most or all of the protein culprits in latex allergic reactions [17]. Latex foam is also dust mite resistant, which is beneficial for some allergy sufferers (those allergic to dust mite excrement) [18].

Odour[edit]

Soy based FPF may produce odours in a solid state when made with high concentrations of soy (>50%). If an ultraviolet (UV) process is used for treating the soy polyol, no odour is created, whereas using a heat treatment creates an odour [19]

Streamlined Lifecycle Analysis (SLCA)[edit]


SLCA Table.JPG

The Streamlined Lifecycle Assessment (SLCA) technique is a method of evaluating the environmental impact of a product or process over its entire lifecycle. For products, five life stages (pre-manufacturing, manufacturing, delivery, use and end of life) are evaluated based on five categories of environmental impacts (materials choice, energy use, solid residues, liquid residues and gaseous residues). A set of guidelines and scoring criteria are used to aid the evaluation, these can be found in various reference books such as "Streamlined Life Cycle Assessment" by T.Graedel. [20] The results of the SLCA analyses for each of the alternatives are shown in the following table.

Pre-Manufacturing Stage[edit]

Solid Residues[edit]

The production of natural latex does not leave any solid residues, resulting in a perfect score for the process. Polyurethane foam premanufacturing produces more solid residues than the latex foam due to the large sulphur releases associated with mining of the coal used in FPF production. This results in the acidification of the soil and surrounding bodies of water[10]. Conversely, the primary residue of soy farming is the plant stover, which does not have any substantial impact, and is used primarily as animal feed [21].

Liquid Residues[edit]

The possible leaks/spills that occur in both the extraction/transportation of oil [22] and runoff from coal mines are the primary causes of liquid residues in FPF production. These possible spills are far more hazardous than spilling natural latex since latex is a natural substance. A major liquid residue, and the largest environment impact of soy farming, is the nitrogen-rich agricultural runoff which is responsible for large dead zones in the aquatic bodies it enters [23][24][25][26]. The disruption of the ecosystem in nearby bodies of water due to the algal blooms produced by the runoff, and the contamination of the ground water are severe effects which reduce soy foam’s score for this section.

Gaseous Residues[edit]

Emissions from transporting raw materials are the only gaseous residues associated with latex foam. However, since these emissions are also present for the other alternatives, they were disregarded when formulating the scores. The primary contributor of gaseous residues in the production of the FPF alternatives is the production of isocyanates, which releases small amounts of isocyanate into the atmosphere, usually much lower than the accepted limits (scrubbers remove more than 98% of all isocyanate from the escaping air) [2]. Finally, the emissions from the machinery used in the production of soybeans are also considered adverse gaseous residues.

Manufacturing[edit]

Material Choice[edit]

Chemicals of relatively low toxicity are added to the primary raw materials to increase the stability of all three foam alternatives. Likewise, both processes use readily available, natural blowing agents (see SLCA Manufacturing - Basics) to produce the characteristic bubbles of the foam. FPF requires the addition of flame retardants, whereas latex foam is able to complete the task naturally. However, since the flame retardants have little if any environmental effects [27], both processes merit a score of 2, due to the relatively low toxicity of the materials used.

Energy Use[edit]

The production of latex foam is more energy intensive than that of FPF since latex foam must pass through steam curing and washing chambers and finally a drying oven, each of which consume a lot of energy due to their high operating temperatures [8]. The production of molded FPF does not require any curing since the chemical reaction which produces the CO2 is exothermic and produces all the energy needed to cure the foam [16]. Additionally, the latex foam production process does not attempt to utilize a single heating system for the drying oven and the steam curing chamber; a design that would have increased the overall energy efficiency.

Solid Residues[edit]

The only solid residues produced while manufacturing the foam alternatives are small scrap pieces. Since the products are molded in both manufacturing processes, it is assumed that only about 1% of the foam material becomes scrap, with the majority being recycled [6].

Liquid Residues[edit]

Latex foam manufacturing produces substantially more liquid residues than the FPF manufacturing process due to the need to wash the molds after the production of each latex foam cushion, thereby diluting the mold release agents into the cleaning water. This water is neither treated nor reused. In comparison, the FPF manufacturing process produces no liquid residues directly related to the manufacturing line [8].

Gaseous Residues[edit]

For both processes, the main contributor to VOC emissions are the naphtha based mold release agents [2]. Additional gaseous residues for FPF foam include carbon dioxide produced in the chemical reaction between isocyanates and water, and the emissions of isocyanates themselves. Though these residues have low environmental impacts due to their low relative concentrations and the treatment of the emissions [28], they do not exist in latex foam production, resulting in the latter being given a slightly higher score.

Delivery[edit]

The delivery of the final molded foam part to the client is generally the same for polyurethane, soy and latex based foams. Corrugated fiberboard (cardboard) boxes are the preferred packaging material in the foam padding industry due to their low cost and ability to contain multiple parts [29]. Since corrugated fiberboard is paper-based, a functioning recycling infrastructure also exists [30].

Depending on the location of the customer, transportation of the product may require air, land or sea vehicles. Since transportation is a major component of the delivery phase, numerous gaseous emissions (i.e. CO2) are expelled from the various vehicles. The size of an order may also influence the mode of transportation and in turn the amount of emissions due to weight considerations[29].

Use[edit]

Once manufactured and assembled, the three alternatives do not require any form of maintenance or care over the course of their useful life. Therefore no material or energy inputs are required, and no liquid, gaseous or solid residues are created with the exception of polyurethane [8]. Generally, the various foams are encased with fabric in office chair use. Therefore, chunking or tearing of the foam is usually not a concern [4].

In the case of polyurethane foam, it has been found that trace amounts of VOCs may be released into the atmosphere over the course of the products life. Therefore, health risks ranging from acute anaesthesia to long term illnesses are possible, though in the vast majority of cases, they pose negligible risks due to low concentrations [31].

End of Life[edit]

The non-chemical recycling options are the same for all three foam alternatives. One option is to grind up old cushions and mix the resulting powder with the various ingredients required during virgin foam manufacturing, thus creating new foam. Another option is to bond and re-mold old foam strips together to produce a new product. More than 80% of all carpet underlay, for example, comes from recycled FPF [32].

The recycling of soy and polyurethane foams may also be completed using hydrolosis, glycolosis, and pyrolosis to extract the polyols from the scrap foam [33]. However, these recycling processes require great deals of energy and generate an increased amount of liquid residues [3]. Latex foam recycling focuses on regrinding, rebonding and stuffing [8][29]. Adhesives used to bond scrap pieces of foam together end up in waste water when the molds are washed, generating more liquid residue than the original manufacturing process (since adhesives are not originally required) [8]

Note that even with multiple recycling techniques, the sheer volume of scrap foam that is generated (mainly due to old cushions) is greater than the rate at which it can be recycled. Therefore, a fair portion of the scrap is land-filled [33].

EIO-LCA[edit]

Background[edit]

By quantifying the amount of economic activity that the purchase of a foam seat cushion stimulates in the entire economy, the Economic Input-Output LCA model [34] outputs a list of environmental impacts divided into 4 main categories: Conventional Air Pollutants, Greenhouse Gases, Energy, and Toxic Releases [35].
Notes:

  • Model based on the US economy in 1997; all dollar inputs into the model were converted to 1997 dollars using a Consumer Price Index Inflation Calculator [36].
  • Use, delivery and recycling life cycle stages for each of the three alternatives have similar environmental impacts and therefore were not analyzed in the model (see SLCA Delivery, Use and End of Life).

Conventional Air Pollutants[edit]

High CO emissions are attributed to transportation needed in foam production since CO is a by-product of combustion [37]. As seen in the table below, these emissions are significantly higher for latex and soy based foams since their raw materials are delivered from tropical climates such as Brazil for latex, for example.


EIOLCA CO Emissions
(mt/1mill cushions)
FPF 37.4
Latex 76.1
Soy 82.2


NOx and SO2 coming from the power generation sector were also significant contributors to air pollution during production, with latex having the largest overall emissions. Coal fired power plants in this sector are estimated to produce more than 10 000 tonnes of NOx and SO2 in an average year in the United States [38]. Latex foam is a larger producer of these two compounds due to its heavier dependence on electricity use in its manufacturing stage ( see SLCA Manufacturing - Basics).


VOC emissions were approximately equal to 7% of the total conventional air pollutants for each alternative. The primary sources of VOC production for the alternatives were the manufacturing of organic chemicals and transportation sectors. VOCs are also largely emitted when using petroleum distillates in the foam manufacturing sector (solvents, fuel) and in the production of organic chemicals [39], all of which are facets of regular and soy FPF production (i.e. petroleum based polyols, naphtha mold release agents, isocyanate production).

Greenhouse Gases[edit]

The CO2 emissions of the foam are detailed below. As can be seen, latex foam has the highest emissions, closely followed by the soy foam.


Greenhouse Gas Emissions
(mt/1mill cushions)
FPF 4300
Latex 15360
Soy 11000


Economic Input-Output Life Cycle Assessment (EIOLCA) - Nitrous Oxide (NO2) Releases For All Three Alternatives

Part of this total owes to the electricity used in running a foam manufacturing process (a large portion of electricity generation still depends on fossil fuels). While the synthetic rubber manufacturing sector contributes to CO2 production for latex foam, this is due to the inclusion of petroleum based products that are not applicable to natural latex foam. Therefore, the actual CO2 emissions of latex foam are lower than displayed.

Soy foam produces a large amount of N2O which is a direct result of soy bean farming (see the bar chart to the right). This N2O primarily comes from nitrogen runoff from farms, which in turn comes from fertilizer that does not get consumed by the plants and instead gets washed off by rainwater. [40]

Energy[edit]

Natural gas is the primary source of energy for all three alternatives, contributing approximately 46%, 42% and 61% of the total energy used for polyurethane, soy-based and latex foam respectively. In the case of polyurethane foam, a large natural gas contribution may be attributed to the fact that ethylene, a primary component of many plastics including polyurethane is derived from natural gas [3]. Various fertilizers (which are often made from natural gas) are also needed to stimulate and facilitate the growth of the soy plants, thus contributing to the amount of natural gas used during the life of the product [11][41]. Lastly, the large energy contribution of natural gas during latex foam production is due to the various heating and steaming procedures required during manufacturing. Many of the water boilers and ovens use natural gas as a fuel to generate heat [8].

Economic Input-Output Life Cycle Assessment (EIOLCA) - Natural Gas Consumption For All Three Alternatives

Energy generated through coal is also a significant contributor for all three alternatives. The power generation sector is responsible for the majority of the coal used during the life of the foams.

Energy sources such as kerosene, jet fuel, etc, are not significant contributors during FPF production. It should be noted, however, that the dominant consumer of electricity in the FPF manufacturing process is the foam production sector itself. Latex foam is similar to polyurethane foam since only natural gas and coal are significant contributors to environmental pollution.

Unlike its two competitors, soy-based foam requires noticeable amounts of energy from sources such as distillates (alcohol, ethanol, butanol, etc) and liquefied petroleum gases (propane, butane, etc). The main consumer of such fuels is the grain farming sector. The aforementioned fuels are required since some farming equipment use internal combustion propulsion systems (ie. tractors).

Cost Analysis[edit]

Soy vs FPF[edit]

Since the soy FPF being studied is 85% petrol based (and therefore still incurs 85% of the costs associated with regular FPF), the primary difference in cost between regular and soy FPF are the expenses associated with soy recovery and processing. Farming equipment, water, fertilizers, distillation etc, all contribute to the cost of the final product, while regular FPF does not incur these expenses.

Latex vs FPF[edit]

The rubber tree only continues to produce latex until approximately age 30[5]. The distance raw latex must be transported (since rubber trees are strictly grown in tropical environments) also contributes to the higher cost associated with latex foam[5]. The latex foam manufacturing process also requires various ovens, heaters and boilers for the washing and steaming procedures, which are capital costs not incurred by regular and soy-based FPF manufacturers (see SLCA - Manufacturing). The high energy use associated with these processes also contribute to the overall higher price of latex foam.

Future Prospects[edit]

Since petroleum prices are predicted to rise due to diminishing supplies [42](thus increasing the cost of polyurethane foam ingredients), companies can be expected to invest into improving the soy refinement and latex collection methods, in an effort to replace the expensive petroleum polyols . This is already demonstrated by the efforts being put forth by companies such as Woodbridge Group and Lear Corporation to develop FPF foams containing very high percentages of biologically-derived polyols [43][44]. These investments in production technology can be expected to eventually make soy processing more efficient, thus decreasing the cost of polyol manufacturing .

Density Verses Compression Plots[edit]

Polyurethane Foam

Polyurethane Foam Density Vs. Compression Plot

Reference: Woods, G. Flexible Polyurethane Foams: Chemistry and Technology. Essex: Applied Science Publishers, Inc, 1982.


Latex Foam

Latex Foam Density Vs. Compression Plot

Reference: Daniel Klempner and Vahid Sendijarevic, Handbook of Polymeric Foams and Foam Technology 2nd Edition. Cincinnati: Hanser Gardner Publications, 2004.

See also[edit]

References[edit]

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  2. 2.0 2.1 2.2 2.3 2.4 2.5 Woods, G. The ICI Polyurethanes Book: Second Edition. Chichester: ICI Polyurethanes and John Wiley & Sons, 1990.
  3. 3.0 3.1 3.2 3.3 Uhlig, K. Discovering Polyurethanes. Cincinnati: Hanser/Gardener Publications, 1999.
  4. 4.0 4.1 4.2 4.3 Reddy Vatti, P.Eng, Design/Manufacturing, Teknion Inc., (private communication), 2008.
  5. 5.0 5.1 5.2 5.3 5.4 Microsoft Encarta Encyclopaedia, “Hevea Brasiliensis (rubber) tree,” 2002 ed.
  6. 6.0 6.1 Dr. Hamdy Khalil, Director, Product Development, Woodbridge Group., (private communication), February 2008
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  8. 8.0 8.1 8.2 8.3 8.4 8.5 8.6 8.7 Daniel Klempner and Vahid Sendijarevic, Handbook of Polymeric Foams and Foam Technology 2nd Edition. Cincinnati: Hanser Gardner Publications, 2004
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