Polyurethane Skateboard Wheels
Emmanuel Camacho Larios, Sam Hawk, Cristian Recinos
DES 040 A: Energy and Materials, Design
Instructor: Christina Cogdell
Date: December 6th, 2018
The Future of Skateboard Wheel Materials
Longboarding is a staple of the casual, short-distance commute in California. Downhill longboarding is rising in popularity as well. It’s a smoother, and often faster ride than a skateboard, which is more flip-trick oriented. What makes the longboard glide so majestically across asphalt? The wheels. Softer, larger, and more impact-absorbent than skateboard wheels, longboard wheels make casual riding smooth and effortless. These colorful, ever-abundant, cylindrical marvels are nearly all made with a substance called polyurethane (PUR). While there are many outstand, there are many more negative effects of harvesting PUR), which is why far more recycled plastic wheels need to blood the market very soon.
The current material unanimously used in the longboard wheel industry is polyurethane (PUR). While there are many different types of polyurethane, the constant throughout them is a reaction between two compounds - polyols and diisocyanates. Mixed with suitable additives and catalysts for the reaction, polyols and diisocyanates are the critical requirements of any type of polyurethane. The ingredients of polyurethane can only be extracted from crude oil and natural gas, so these resources are the principle raw materials for polyurethane wheels. Polyurethane (PUR) is an ideal material for longboard wheels, as their mechanical, thermal, and chemical properties can be controlled by the reaction of various polyols and polyisocyanates. This means that the durometer (hardness) of wheels can be manipulated easily by the chemical foundation of the matter. PUR is cheap to produce, and durable over time, saving resources with its long life cycle. Furthermore, one might argue that even though crude oil must be extracted, the wheels are overall an environmentally beneficial product because it lowers need for cars. Overall, PUR can absolutely be seen in a positive light when it comes to effectiveness, coastliness, and even greenness, depending on who you ask.
My research lead me to some shocking information about PUR as a whole. According to my resources, the demand for PUR around the globe was approximately 16 million tons in 2016, which, if statistics found in Boustead’s elaborate study are true, would mean that if the demand was filled, PUR alone would generate 22,000 MTCO2. The entire world produced around 36,000MTCO2 in 2016. This huge portion that PUR represents in one of the most grim statistics in environmental health means that, while PUR might be great for many reasons, it is time for the world to cut back.
In studies conducted by the three authors of Reactive and Functional Polymers, and the three authors of Methods for Polyurethane and Polyurethane Composites, Recycling and Recovery: A Review., there is an alternative that they argue is realistic enough to break into the longboard industry: recycled plastic. Recycled plastic, they, has the smoothness and rubberiness that PUR has when the plastic is manufactured into a wheel properly. Thomas, Martinez, and Hadfield maintain that if recycled plastics were utilized at every opportunity in the world, it would reduce the carbon footprint on longboard wheels by 50%, the embedded energy consumed by the wheel by 40%, and the economic material cost by 67%. If their subjective opinions on the smoothness and effectiveness of recycled plastic wheels is unbiased, and they are telling the truth, recycled plastic wheels could be the future of longboarding.
Wastes and Emissions: Polyurethane Skateboard Wheels
Imagine riding down on the first developed skateboard. Imagine riding down the asphalt in the early 1960s where the wheels on the board are made of a clay compound. Riding that road would be very bumpy wouldn't it?1 In this day Skateboard wheels are mostly made out of urethane compounds that allows the structure for better stability and traction 1. Like most manufactured goods, polyurethane wheels to go through a process where they are manufactured, sold to skateboard companies, and either repurposed or thrown out. In its life cycle though there are certainly going to be wastes and emissions being released. These emissions are most prominent in the remanufacturing of the polyurethane compound as well as the extraction of the natural compound. So even though the wastes in polyurethane wheels can be positive because its structure is chemically alternated for it to be durable for long periods of time, it can also be negative due to the emissions released when extracted and manufactured.
The commence of the polyurethane skateboard wheels starts with the extraction of crude oil. Crude oil as we know it is extracted using wells and fracking that allow the raw petroleum or “crude oil” to travel up. This process is highly toxic though when it comes to the emissions released. As noted in Sofia Plagakis article, “Oil and Gas Production a Major Source of Greenhouse Gas Emissions, EPA Data Reveals”, Plagakis explains that the extraction and production of gas and oil are the second largest in the world to release greenhouse gasses. She claims, “The oil and natural gas sector emitted 225 million metric tons of carbon dioxide equivalent that year, making it the second-largest major industry sector producing greenhouse gas pollution.”2. This process of gas release is due to the number of gasses trapped within the rock and sediment being drilled. Depending on which way the crude oil is being extracted through gasses can be extracted along to be used for other purposes, like the propane industry, as explained by the Department of Chemistry, University of York, UK3. The chemical compounds that are formed in the Polyurethane structure are all extracted from the fracking process. As explained on Europur.org, Polyurethane is produced by reacting polyols and diisocyanates, which come from the crude oil 4.
Once the Polyurethane is processed chemically it can be shipped to different companies depending on how they want they want it. It is important to acknowledge though how the polyurethane is being shipped as it too can be a factor to the wastes and emissions produced. As stated before companies that manufacture the wheels themselves were private and were inaccessible, but it can be presumed that the wheels were transported by shipment trucks if in the same place. In the time for change webpage, it is explained that “modern lorry and trucks” produce 60 to 150 g” of carbon dioxide 5. This amount is dispensed for every metric ton. If done continually, which it is can be a very negative effect on the environment.
Polyurethane is in many things other than wheels, and are most prominent in insulation material for appliances like fridges. Different catalysts or additives are added to the polyurethane in order to create different effects and uses 6. In the case of the wheels, the additive that is most commonly used is butyrate 430-A-ORO-43-MS. This chemical compound allows for “good frictional characteristics, tear, and tensile strength, and, partly by virtue of its resilience, being relatively quiet”. As explained in the patent, the combination of these chemical compounds allows faster production time due to the time it takes to dry as well as reducing material costs 7. Throughout the molding process, there seems to be little to no waste of materials. The casts used throughout the process also seem to exhibit little waste. This information is not as valid though because of the lack of knowledge in this area. As exhibited in the “ How Its Made - 1405 Skateboard Wheels” very little information regarding the waste and emissions 8. Different companies were also contacted throughout the research process but because they were private companies, we were unable to receive further information concerning the wastes and emissions throughout the production process. From the acquired information though it can be inferred that while the wheels are in use little waste will be emitted. This is due to the compounds creating “strength” and “resilience”.
Even though there was a lack of information in manufacturing, when it came to the end of the wheel life cycle, information was more accessible. Polyurethane is considered a type of plastic, and as is known plastics are some of the slowest biodegradables. As examined before in the manufacturing process the compound created by polyurethane and butyrate creates a strong and resistant product. This is necessary when it comes to using as the consumer would want their wheels to last for large amounts of time when commuting on them. When it comes to disposing of the wheels it can have a rather negative effect. This is negative because in a landfill this takes longer to degrade leaving more waste. There is research though that has found that the polyurethane can degrade much quicker. In Gary T. Howard’s “Biodegradation of polyurethane: a review” Dr. Howard explains that scientists have found ways to weaken the structure of polyurethane to increase biodegradation. He explains “By changing and varying the polyhydroxy and polyfunctional nitrogen compounds, different PUs can be synthesized” 7. This is important as it can help reduce excess waste. Recently though due to changing regulations, there has been an alteration in just dumping used polyurethane in the landfill. Recycling has become an important factor in its life cycle.
At the beginning of the life cycle analysis, it was explained that polyurethane is extracted from crude oils, this is not the only way that polyurethane wheels can be made though. In Khalid Mahmood Zia, Haq Nawaz Bhatti, and Ijaz Ahmad Bhatti article, “Methods for polyurethane and polyurethane composites, recycling and recovery: A review” there are examples of the types of manufacturing processes that are used in recycling this material. In the article, it is explained that the methods of recycling polyurethane are mechanical recycling, chemical processing, thermochemical processing, and energy recovery. It is explained that mechanical engineering involves regrinding the existing polyurethane to a powder form to be reused. Chemical processing as explained uses chemicals to repurpose the product. The article does explain though that these forms of repurposing old polyurethane are, “Nevertheless, they remain of considerable interest for their long-term potential” 9. After going through every type of recycling method the article comes to a conclusion. It states that even though many forms of recycling have been developed, “but still requires more development in order to tolerate more contamination” 9. This contamination is demonstrated thermal processing which “poses the risk of formation of nitrogen oxides (NOx, N2O), ammonia, pyridines, and other hazardous or toxic nitrogen compounds as a result of the high nitrogen content of the material” 10. This statement is found in an article published by the Helinski University of Technology. The article also explains that the polyurethane that is being sent to landfills isn’t even happening in the countries where that polyurethane is being produced. It states, “These shipments may soon suffer from competition from Latin America and Asia and it is questionable whether an additional 70000 tons of scrapped PU foam from ELVs can be disposed of by exporting them to outside the US as well”7. Even though the polyurethane can be recycled it is also important to recognize that it isn’t as sustainable as we expect it to be.
Polyurethane wheels are a great product when riding due to its resilience to wear and tear. The chemical compounds produced by the additives make a product that will last forever. When focusing on the waste of this specific product there is very little waste occurring. There seems to be an issue when it comes to the emissions be released though. Like other raw materials extracted there will be an environmental conflict. As noted the fracking process of the crude oils has a major impact, as well as the transportation involved. Although the research was restricted, due to companies being private, we were still able to find or closely assume some of the emissions released during production. Through this process, we also became aware that the fight for a sustainable and ecological way of repurposing old polyurethane hasn’t really been found. Although recycling is being used to repurpose instead of allowing the material to decay, there are still negative emissions being released in this process. It can be concluded that even though the product of polyurethane skateboard wheels are a strong product due to their structure, their life cycle allows emissions to released, making it ecologically and sustainably unreliable.
Embodied Energy and Environmental impact of Polyurethane Skateboard Wheels
Since 1937, the creation of polyurethane has become an essential plastic that has reached virtually every branch of industry. Polyurethane, like most plastics, replaced or enhanced thousands of products due to its versatility and durability. Polyurethane’s complex molecular compound allows it to have plasticity which makes it a malleable material. Its durability allows it be used in products that need to have longevity. Such product is the skateboard wheel. Polyurethane wheels spawned an entire new movement of skateboarding culture, forever becoming a stable in pop culture. However, to better understand polyurethane wheels, I examined the manufacturing process of attaining the raw materials to its final form. With embodied energy in mind, the energy used in the production is essential to understand the life cycle of polyurethane wheels. By considering the types of energy that is needed to the operate machinery that extracts, refines, transports and recycles polyurethane wheels, we can see a complex parasitic relationship between the environment and the industries that are dependent of its natural resources. This helps clarify the true impact industries have on our ailing earth.
Polyurethane (PU) is part of the “Polymer Family” which all are derived from crude oil. Crude oil exists several thousands of feet beneath the Earth’s crust in pocket reservoirs on land and sea. Seismic exploration tools that produce sound waves are used to find the location of crude oil reservoirs by having the sound waves bounce back to creating an image, mapping the ground underneath. I focused on pump jacks in my research because they are most common instruments to pump and extract crude oil from wells. Pump jack vary from big to small depending on how shallow a well is. A standard pump jack uses 298 kWh to pump approximately 100 barrels per day. 1 barrel equals to 42 US liquid gallons (“California 2009 Oil and Gas Production,” 2009). A pump jack is moved by kinetic energy of the lever and wheel that acts as a counter weight for the sucker rod pump. In 2009, California used 3.7 million kWh of electricity to produce 253 million barrels of oil including off and on shore drilling (“California 2009 Oil and Gas Production,” 2009). Although pump jacks are the leading providers for most of the fossil fuel consumed by the United States, there are drawbacks. Hydraulic fracturing is the result of pumping water, chemicals or minerals to break up earth’s shallow rock and extract oil or gas. Fracking the shallow rock underneath allows for unstable rock beds to create seismic tremors that could cause collateral damage to nearby cities. Nonetheless, after crude oil is pumped to the surface, it gets transported to refineries through pipelines all across the U.S.
The United States have over 3000 miles of pipeline transporting oil, petroleum, natural gas and milk. (“Transportation of Oil, Gas, and Refined Products,” 2018). Crude oil is transported to refineries because the oil extracted has different sulfurs and other impurities. Crude oil travels roughly over 1600 miles of pipeline up to 3-6 mph taking 10-20 days to reach a refinery (“Transportation of Oil, Gas, and Refined Products,” 2018). Electric motors or gas turbines Figure 1. Oil pump jacks on Canadian Prairie at dusk provide the sufficient energy to pump the crude oil across states. However, pipelines have been under heavy scrutiny because of their effect on the surrounding land. Because over 90% of crude oil is transported by pipeline, leaks and spills are prone to happen. Oils spills on land and sea have significant impact; gas leaks emit methane which contributes to ozone pollution; oil spills damages surrounding land and leaks can potentially taint freshwater reservoirs. Since it’s the most economical transpiration of hazardous liquids, pipelines will not go away so soon. Once the crude oil finds its way to a refinery, up to 80-85% of the crude oil becomes gasoline, diesel and jet fuel. The other 20-15% are different variations of hydrocarbons (“Polyurethane Production, Pricing and Market Demand”). When you mix different variations of hydrocarbons from natural gas or crude oil and other additives like sodium chloride and Sulphur, polyols and isocyanate molecular compounds are created. In simplest form, these two compounds, polyol and isocyanate go through chemical reaction with other additives that make-up of polyurethane (I Boustead, 2005). A finding was published on September 1976 by V.O. Haynes from the Oak Ridge National Laboratory energy division stated that the annual usage of U.S. refineries was 3x10^15 Btu of energy which is 8.8x10^11kWh, about 4% of the U.S. energy consumption. Also, it was stated the “plant size, product, and location affect the refinery energy consumption” (Haynes, 1976). Nonetheless, refining oil and natural gas creates air pollutions. Greenhouse gasses like carbon dioxide and methane is released into our ozone. In addition, acidic chemicals like sulfur get released into the atmosphere producing acidic rain, causing havoc on surrounding environments.
Finally, the chemical compounds, polyols and isocyanates, are bought and transported to skateboard factories. Transportation for these chemicals vary depending where and how far third party buyers are. Skateboard wheel manufactures have a series of equipment to pour, to heat, to cure and to shape polyurethane into skateboard wheels. There are several formulations of polyurethane materials available to be designed to suit different applications. The manufacturing of skateboard wheels begins with mixing polyol, isocyanate and other additives. The ratio of each compound is critical for the tensile strength and abrasion resistance of the wheel (Reynolds, 2015). During the chemical reaction when mixing, the chemicals are heated up to 140-170 F. The thermal energy that concurs in this process helps in the pouring the now liquefied polyurethane into molds. The liquefied polyurethane in the molds are moved onto trays to be inserted in industrial ovens to be cured and solidified. The ovens bake the polyurethane up to 190-240 F, depending on the molecular structure of the polyurethane. During baking, any bubbles rise up and expel; leaving a solidified wheel with no weak spots. After, the wheels are tempered and cooled to be pulled from their mold. Using compressed air, the wheels are popped out of the mold. The wheels are then shaped by being placed on a lath and spun while an automatic cutter cuts the excess polyurethane. This creates a softer and rounder profile. The polyurethane wheels are to be packaged and sealed ready to be shipped (“1405 Skateboard wheels,” 2015). Depending on the machinery and the type of polyurethane product being made, the energy usage fluctuates. For the polyurethane pour equipment, the energy data is inconclusive. However, the baking of polyurethane reaches its heating to 240 F. That equal to 456 Watts. This is a rough estimate because finding how much the exact energy intake from these machines is inconclusive. When the skateboard wheels are packaged, they are transported to skateboard shops and other big department store retailers to be sold. Semi-trucks that are sued for transportation use diesel fuel. The same fuel that comes from refineries. The exact composition of exhaust from diesel fuel depends on “operational parameters, such as speed, motor load, engine and vehicle type, fuel composition, ambient air temperature, and relative humidity” (Lloyd, Crackette). But one thing is clear, diesel fuel is no different from gasoline. Even though you get more mileage for a gallon than gasoline, it still releases greenhouse gasses to the atmosphere.
To reduce the greenhouse gasses that escape during the process of making skateboard wheels, recycling is valent effort. Although Polyurethane cannot be melted and reused, it can be shredded to be rebonded and compressed to be used in various padding products. In an article published in the Reactive and Functional Polymer, it states that in 2008, 830 million pounds of polyurethane were used to make carpet cushion, of which all was polyurethane scrap (Zia, H. Bhatti, I. Bhatti; 2007).
Polyurethane skateboard wheel forever changed the landscape of the skateboarding culture. Because of its low- cost, durability and longevity of the wheels, skateboarding became accessible to everyone. Now, polyurethane wheels are an essential part for the skateboard companies. Polyurethane is very high in demand because of its versatility. it versatility. Plastic Insight charted that in 2016 15 million tons of polyurethane was demanded and rapidly increasing every year. Still, any product that is plastic is not beneficial for the environment. Oil and gas companies have a parasitic relationship with our environment because they benefit from the energy provided by the fuels while harming the planet. Our planet thrived from the greenhouse effect, warming our planet enough to have liquid water. The molecular compound essential for life. However, when we contribute to the effect, it could become a run-away greenhouse effect. When our planet has reached a point of no return. Our oceans would become acidic, hurricanes more powerful, extensive wild fire major flooding, etc. This future can be prevented if we all contribute to reduce our energy intake and recycle.
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