Design Life-Cycle

Dorothy Hung

Minh Tham, Kiara Cowderoy

DES 040A Kahui A05

Professor Cogdell

Are the Materials in Non-Woven Polypropylene Grocery Bags as “Green” as They Seem?

1. Introduction

Reusable bags were created as an alternative to plastic and paper bags in an effort to reduce waste. Among the variety of reusable grocery bags out on the market, those made from a hybrid of plastic and fabric seem to be high in demand. Understanding the production of non-woven polypropylene bags will allow consumers to assess whether this is an ideal option compared to other materials. The purpose of this review is to detail the material processes involved in the life cycle of non-woven polypropylene bags. By analyzing the beneficial characteristics of the materials required to produce non-woven polypropylene bags, one can see through a cradle to grave standpoint that the frequency of use determines the environmental viability of the bags.

2. Why Polypropylene is a Choice Material for Reusable Bags

The duality of this polymer, containing properties of both plastic and fabric, makes polypropylene the optimal material for household and healthcare products. Its durability makes it a practical material for producing insulation, medical equipment, and food containers. (Polymer Science Learning Center). The versatility of propylene can be attributed to its isotactic property, meaning all the methyl groups are lined up on the same side of the polymer chain (Polymer Science Learning Center). Isotactic polypropylene is generally used for commercial purposes due to its high melting point; its ability to withstand heat makes for a better alternative to plastic. This heat-resistant polymer is beneficial for reusable grocery bags, which are expected to carry items of varying temperatures. Polypropylene falls under the category of thermoplastics, meaning it can be softened and molded when it is heated while retaining its structure and durability. Polypropylene naturally repels water, therefore making grocery bags easy to clean. A material that can be easily disinfected is especially important since reusable bags are often exposed to bacteria when carrying raw foods. A review done on the spun bonded process acknowledges isotactic polypropylene as the most economically efficient material, as it is the most cost effective and produces the most fibers per kilogram (Lim 2). Since the order of the fibers doesn’t matter, more fabric is yielded as all the material ends up getting pressed together (Kansal 9).

3. Raw Materials Involved in Producing Polypropylene

The manufacturing and production of polypropylene involves the use of fossil fuels – specifically petroleum and natural gas that are rich in hydrocarbons that make up propylene (C3H6). The goal is to extract the hydrocarbon chains from the petroleum or natural gas by filtering out other particles and debris (Diringer 4). This can be achieved through a few methods: one involves desalting and reheating petroleum, and the other uses natural gas that must be heated, cooled, then pressurized to filter out unrelated matter and non-hydrocarbon gases (Diringer 4). Both eventually reach the fractional distillation phase, which splits up hydrocarbon chains into homogenous fractions by categorizing the chains according to size (Diringer 5). They are reduced to shorter-chain molecules to be polymerized and form extended polymer chains. Larger, longer-chain polymers are reduced through a process called “cracking,” which heats the molecules and causes vaporization to produce shorter-chain molecules (Diringer 5). The propylene monomer must then go through polymerization by coming in contact with either a Ziegler-Natta catalyst – consisting of titanium (IV) chloride and aluminum alkyls – or a metallocene based catalyst to break the existing double bonds in the monomer (Diringer 6). The polymerization stops when it is exposed to water, causing the catalyst to dissolve. The polymer precipitates into polypropylene pellets (Diringer 6). 

4. Turning Polypropylene into Non-Woven Fabric

The polypropylene granules must undergo an intense process to be formed into filaments and joined into a fabric. Rather than weaving or knitting – as the name “non-woven polypropylene” infers – the bits of polypropylene fibers are bonded together. The following steps demonstrate thermal-bonding, which is considered the most economically practical method, but polypropylene can also be bonded through chemical processes, mechanical entanglement, or hydro entanglement that uses water jets (Diringer 6-7).

The initial stages of production mirror that of plastic film, as the polypropylene resin goes through an extruder to form molten polymer. Another filtering process takes place – the material must be near to completely uniform; any foreign particles left in the molten polymer can lead to damage in the machinery or flaws in the final product (Lim 3). Consistency is key not only among the particles, but in the temperature throughout the molten polymer. The insulated metering pump ensures that there is a constant volumetric flow rate before the molten polymer proceeds to the die block assembly, also known as the spin pack (Lim 3). This stage involves a polymer feed distribution that continues to maintain the balance of temperature in the flow of material. It gets passed onto the spinneret, a perforated metal plate or block that the fibers must go through to form continuous filaments (Kansal 10). As the molten polymer is pumped out of the nozzle of the spin pack, it comes in contact with the quench chamber where the bunches of filaments are cooled and solidified. The filaments are stretched by encountering high velocity air, which contributes to the flexibility of the polypropylene by expanding the fibers (Lim 4). The method and rate at which the material is spun depends on the polymer – polypropylene is spun at 2,000 m/min, and melt spinning is typically the option in spun bonding (Lim 4). After the filaments are formed, it lands on a conveyor belt and begins its transformation into a web. From here the material is pressed into sheets as it passes through calendar rollers; the embossed patterns on the rollers bond the filaments together, forming a fabric (Kansal 10). The non-woven polypropylene fabric is then ready to be shipped to another factory where the material is cut, screen printed, sewn and packaged (Muthu 13). 

5. Environmental Impacts of Materials and Production

A majority of the detrimental effects occur when obtaining the raw materials from natural resources as opposed to producing the bags themselves. Extracting the material to make polypropylene accounts for over 90% of the bags’ contribution to abiotic depletion, and about 75% of its impact on eutrophication (chart from Edwards & Fry 43). Though non-woven polypropylene bags reportedly have the “least carbon-intensive” process compared to other materials, they are the only bags that use a specific industrial furnace to burn heavy fuel oils (Edwards & Fry 43). This results in greater nickel and vanadium emissions, causing the raw material acquisition to make up about 75% of the bags’ overall global warming impact (Edwards & Fry 44). 

Transitioning to a renewable source of energy or exchanging the fabric between factories that are closer to each other would be the most effective solution to reducing carbon emissions during the transport stage (Muthu 15). A majority of the waste from the entire production of the fabric and the use of corrugated cardboard adds onto the bags’ effects on human toxicity and fresh water ecotoxicity (Edwards & Fry 43-44). 

Manufacturing websites and other sources claim that non-woven propylene bags are recyclable through reclaiming fibers or re-melting polypropylene. That material can be salvaged to create new fabric and produce more reusable grocery bags. However, scholarly articles that report on the life cycle assessment of non-woven polypropylene bags say that most fabric waste can be recycled, but lack information on what happens to the bags after they are disposed of (Muthu 15).

6. On the Environmental Viability of Reusable Bags

The primary goal of reusable grocery bags can only be fulfilled if they are reused enough to counterbalance the amount of materials and energy used in production. The production of non-woven polypropylene has been noted as “less costly than cotton” compared to other materials (Thompson).  Even so, the economic cost doesn’t compensate for the environmental costs unless these bags are used regularly. In a study assessing the environmental impact of both disposable and reusable grocery bags, the global warming potential is measured “based on the weight of CO2 equivalents generated per kg of each bag,” where the value decreases the more times someone reuses a bag (Edwards & Fry 53). An unused bag produced an equivalent of 21.51 kg of CO2 compared to a bag that has been used 14 times, which comes out to about 1.536 kg of CO2 equivalency; the unused bag generated nearly 20 times more CO2 that the bag that was reused (Edwards & Fry 44). The data also charted the significant difference in waste equivalency for other categories such as abiotic depletion, acidification, and eutrophication (Edwards & Fry, 44 and attached chart). Most sources support the claim that a non-woven polypropylene bag should be used at least 11-14 times before it outweighs the environmental costs of producing the bag (Thompson). Though many people actually do bring their reusable bags to the store, some will resort to old habits by continuing to accumulate (and pay for) disposable plastic bags because they either forget or are too lazy to bring their reusable ones.

7. Conclusion

Reusable bags serve as a solution to the planned obsolescence of disposable grocery bags. The production of any tangible good will lead to some waste, but the magnitude of waste is ultimately determined by how the resources are utilized. The life of a reusable tote doesn’t just end at the market, but the actual effectiveness of these bags is assessed by how often the consumers use them.

Works Cited

Edwards, C., Fry, J.M. Life Cycle Assessment of Supermarket Carrier Bags. Environment Agency, 2011, pp. 12–27, Life Cycle Assessment of Supermarket Carrier Bags. References

Bisinella, Valentina, et al., editors. “Life Cycle Assessment of Grocery Carrier Bags.” The Danish Environmental Protection Agency, 2018, pp. 25–52.

Diringer, Jeremy Alan. “Evaluation of Durability of Nonwoven Polypropylene Grocery Bags Under Routine Use.” Graduate School of Clemson University, Aug. 2016, pp. 14–24. All Theses. 2476. tigerprints.clemson.edu/all_theses/2476/?utm_source=tigerprints.clemson.edu%2Fall_theses%2F2476&utm_medium=PDF&utm_campaign=PDFCoverPages.

“Eco Bag Plastic Inserts - The Low Down.” 1 Bag at a Time, 15 Jan. 2016, 1bagatatime.com/learn/plastic-inserts-the-low-down/.

Edwards, C., Fry, J.M. “Life Cycle Assessment of Supermarket Carrier Bags.” Environment Agency, 2011, pp. 12–27.

“HOW ARE NON-WOVEN POLYPROPYLENE BAGS ECO-FRIENDLY?” Bagfactory, 24 Jan. 2017, www.bagfactory.eu/how-are-non-woven-polypropylene-bags-eco-friendly-carrier-bags/.

Kansal, Harsh. “Experimental Investigation of Properties of Polypropylene And Non-Woven Spunbound Fabric.” Journal of Polymer and Textile Engineering (IOSR-JPTE), 2016, Vol. 3, No. 5, pp. 8–14., doi:10.9790/019X-03050814.

Lim, Hosun. “A Review of Spun Bond Process.” Journal of Textile and Apparel, Technology and Management, 2010, Vol. 6, Issue 3. NC State University.

Maddah, Hisham A. “Polypropylene as a Promising Plastic: A Review.” American Journal of Polymer Science. 6(1): 1-11. 

Muthu, Subramanian Senthikannan, et al. “Carbon Footprint of Production Processes of Polypropylene Nonwoven Shopping Bags.” 92nd ed., vol. 3, FIBRES & TEXTILES in Eastern Europe, 2012, pp. 12–15.

“Nonwoven Manufacturing Process, Nonwoven Fabric Making Process.” Process, Nonwoven Fabric Making Process, www.technicaltextile.net/articles/nonwoven-manufacturing-7188.

“Polypropylene.” The Polymer Science Learning Center, pslc.ws/macrog/pp.htm.

Sayed, U. and Sneha Parte. “Recycling of Non Woven Waste.” International Journal of Advanced Science and Engineering. Vol. 1, No. 4, 67-71 (2015). 

“The Definitive Guide to Polypropylene (PP) .” Polypropylene (PP) Plastic: Types, Properties, Uses & Structure Info, omnexus.specialchem.com/selection-guide/polypropylene-pp-plastic.

Thompson, Claire. “Paper, Plastic or Reusable?” STANFORD Magazine, Sept. 2017, stanfordmag.org/contents/paper-plastic-or-reusable.

Minh Tham

Professor Cogdell

Kahui Lim

DES 40A A05

4 November 2019

From Natural Gas to Non-Woven Polypropylene Bags: Embodied Energy

Introduction

Grocery bags are essential to the modern human lifestyle.  They provide a way to efficiently organize and transport groceries, along with many alternative uses.    These bags can be produced from a wide variety of materials - oftentimes plastic, paper, fabric, and other alternative materials.  A quote from The Australian Bureau of Statistics describes the functionality of traditional grocery bags, “Plastic bags are popular with consumers and retailers because they are a functional, lightweight, strong, cheap, and hygienic way of transporting food and goods. Additionally, the manufacture of plastic bags uses little energy. However, research has shown that energy use and greenhouse gas emissions can be reduced by switching from the commonly used bags to larger, reusable bags, by expanding the Code, and introducing a levy” (Australian Bureau of Statistics, 1).  There has been a push in the recent years to eliminate plastic bags and replace them with alternative more eco-friendly grocery bags.  One type of grocery bag stands out among the rest, reusable non-woven polypropylene (NWPP) grocery bags provide a more environmentally conscious alternative to plastic ones.  There are varying types of energy processes that go into the extraction of materials, manufacturing, and transportation of NWPP grocery bags. By looking at the embodied energy during the lifecycle of a non-woven polypropylene reusable grocery bag, it is evident that energy is an integral part of almost every stage of the NWPP bags lifecycle. 

What is Non-Woven Polypropylene?

One of the more popular alternatives to the classic plastic or paper bag is the NWPP bag. Propylene, the raw material base for non-woven polypropylene, was originally discovered by an Italian chemist by the name of Giulio Natta. (The Editors of Encyclopaedia Britannica) To clarify, polypropylene is a material that is made from a plastic-like substance called propylene monomers which is very versatile due to its unique chemical structure.  A segment from the article, Everything You Need to Know about Polypropylene (PP) Plastic, defines the nature of polypropylene, “Polypropylene is classified as a “thermoplastic” (as opposed to “thermoset”) material which has to do with the way the plastic responds to heat. Thermoplastic materials become liquid at their melting point (roughly 130 degrees Celsius in the case of polypropylene). A major useful attribute about thermoplastics is that they can be heated to their melting point, cooled, and reheated again without significant degradation.” (Creative Mechanisms Staff, 1) In addition to being used for grocery bags, it is used for packaging, vehicle parts, different types of containers, and many other things.   

Energy Necessary in Raw Materials Acquisition

Polypropylene is made from propylene gas, a raw material that is found underground.   Extraction of the raw materials for NWPP bags requires the use of coal as well as fossil fuels to power the machinery needed to drill into the earth.  Use of a vertical drill requires coal and fossil fuels to generate chemical as well as thermal energy. There is also a need for mechanical energy, human workers, in order to operate the machinery.  Chemical energy provides the means of transportation for these raw materials of NWPP grocery bags. Fossil fuels provide the necessary energy to power the trucks, planes, and ships to transport raw materials from overseas to the factories to the manufacturing plants.  The manufacturing processes that take place in order to produce NWPP bags creates the need for high amounts of primary energy sources which produces chemical and thermal energy.  

Energy in Manufacturing, Processing, and Formulation

Non-woven polypropylene requires a more strenuous manufacturing process than that of traditional plastic and paper bags, but in turn, they are much longer functioning because of their chemical structure.  As opposed to traditional bags being created with mechanical energy, NWPP uses thermal energy using a high temperature to manipulate the material. (Muthu, 2) An article titled, Woven vs. Non-Woven PP from the website 1 bag at a time describes the manufacturing of NWPP by stating, “Non-woven PP is made by taking polypropylene polymers and spinning them using heat and air into long fluffy threads, like cotton candy, then pressing the threads together between hot rollers to get a flexible but solid fabric with a weave-like texture similar to canvas” (1bagatatime, 1). This quote describes the manufacturing process that occurs when producing NWPP bags, which differs from that of traditional grocery bags.   Polypropylene’s high melting point at 130 degrees Celsius requires a high amount of coal and fossil fuels to provide an immense amount of thermal energy necessary to break down the compounds as the first step in the manufacturing process. These threads are then pressed with heated rollers to flatten out the material so that it can be assembled as sort an alternative fabric. Manufacturing NWPP requires a high amount of thermal energy, to heat the polymers, along with chemical energy in changing the structure of polypropylene.  Heating mechanisms, fueled by coal and fossil fuels, use both thermal and chemical energy in order to manipulate the chemical structure of the raw materials of NWPP. There is also a need for mechanical energy, namely human labor, in order to operate the machinery in the NWPP manufacturing factories. Electricity, a secondary energy source, to power factory lights and machinery such as conveyor belts. A life cycle assessment of NWPP describes the variation in the need for energy in manufacturing and production: “The energy demand for these processes is mainly met by grid electricity and this energy consumption depends on the polymer type, density, production equipment and capacity.” (Kimmel, 1) Since these NWPP manufacturing plants require a high amount of energy, the energy density of fossil fuels is one of the primary fuel sources.  Variation in the polymers types requires specialized machinery which in turn results in a fluctuating amount of energy usage. Another segment from an article titled, How are Non-Woven Polypropylene Bags Eco-Friendly (Carrier Bags) describes the physical properties of NWPP, “It is rough and resistant to other chemicals. Polypropylene is tough, but also flexible. This makes the material to be used easily for chemical and plastic engineering experiments. Polypropylene fabric can be translucent, but because it does not fade very easily, most people use polypropylene as dyed colored fabric.” (Bag Factory, 1) Factories that produce NWPP bags often appear in areas near supermarkets and grocery stores, so the distribution of these goods does not require as much energy as transportation of raw materials.  

Energy in Distribution and Transportation

Transportation and distribution of the NWPP bags is the next step in the lifecycle.  After being manufactured, NWPP grocery bags are distributed to grocery stores such as Trader Joe’s, Walmart, and FoodMaxx.  There is a need for varying amounts of fossil fuels, namely petroleum, in order to provide the chemical energy necessary to power the semi-trucks and distribution facilities.  In addition to this, mechanical energy or human power is needed just as before to operate the vehicles to distribute NWPP grocery bags to stores. More human labor is also necessary in unloading the bags from distributors and stocking them into stores.  At this point, the NWPP bags have reached the stage where they can finally be used. 

Energy in Use, Re-Use and Maintenance

Grocery stores often offer alternatives to the traditional plastic bag in the form of paper bags, canvas totes, and of course non-woven polypropylene bags.  Non-woven polypropylene bags often range between 99 cents to 5 dollars and are reusable for many years. This eliminates the need to purchase paper or plastic for 10 cents every time while purchasing groceries.  Primarily, these NWPP bags are used for to carry groceries but they can be used to carry and organize many different items. The energy that goes into using these bags is predominantly mechanical because of the people that use the non-woven propylene bags.  A human exerts on average about 100 watts a day. Lifting a bag full of groceries exerts about 10 watts of energy but it can vary depending on how heavy the contents are in the bags. When reusing these non-woven polypropylene bags, it is easy to wipe them down and clean them because of the waterproof and durable material.  (Thompson, 1) A segment from NRDC’s article, NRDC Lauds Passage of New York City Council Legislation Requiring Groceries, Retails to Provide Plastic Bag Recycling for Consumers, describes the magnitude of the plastic bag epidemic, “’The average American family takes home almost 1,500 plastic shopping bags a year, clogging our cabinets, kitchen drawers and landfills. They’re hanging from trees, and littering our beaches,’” said NRDC Urban Program co-director, Eric A. Goldstein. (NRDC, 1) Plastic bag usage and consumption is detrimental to the environment because of the fact they are difficult to recycle without the correct resources.  When comparing plastic bags to non-woven polypropylene bags there is a difference in the reusability and sustainability of the product. Traditional plastic bags are oftentimes used only once before being discarded, on the other hand, non-woven polypropylene reusable can sustain many years of use if maintained properly thus reducing the need to purchase new grocery bags all the time.  

Energy in Recycling

Recycling these bags is also an important part of the life cycle as well.  In terms of reuse and recycling, non-woven polypropylene bags can be used for many other things.  They can be used to carry toys, books, clothes, shoes, along with many other supplies. When comparing the potential for recycling of plastic bags, paper bags, and NWPP bags, non-woven polypropylene stands out among the rest.  The most important form of energy for recycling in this case would be mechanical, or human energy. Mechanical energy is used in order to physically move these bags to the correct recycling facilities as opposed to discarding them in the trash in which they will inevitably end up in a landfill.  (Greene,1) In addition, polypropylene can be broken down into its original raw materials, approximately the same amount of energy can be put into recycling the NWPP bags. This requires thermal, chemical, and mechanical energy as well, just like before. Non-woven polypropylene bags are entirely recyclable so there is no need for energy in waste management as opposed to plastic and paper bags which oftentimes end up in landfills.

Why Choose Non-Woven Polypropylene?

Energy is an essential part of the life cycle of any product.  For reusable non-woven polypropylene grocery bags, most of the energy goes into the acquisition of raw materials, manufacturing processes, and transportation of the materials to and from one place to another.  Embodied energy sources for the life cycle of non-woven polypropylene include thermal, chemical, and mechanical energy. The amount of energy saved by using reusable non-woven polypropylene grocery bags outweighs the cost and potential waste caused by traditional plastic and paper bags.  NWPP bags are much more efficient and sustainable because they are much more durable and require less energy in the long run.

Works Cited

1bagatatime. “NWPP: The Most Popular Bag Material.” 1bagatatime, 2019, https://1bagatatime.com/learn/nwpp/.

Australian Retailers Association. “How Much Energy Is Used to Make a Plastic Bag?” Australian Bureau of Statistics, 2004, https://www.abs.gov.au/ausstats/abs@.nsf/Previousproducts/1301.0Feature Article212004

Creative Mechanisms Staff. “Everything You Need To Know About Polypropylene (PP) Plastic.” Creative Mechanisms Staff, 4 May 2016, https://www.creativemechanisms.com/blog/all-about-polypropylene-pp-plastic.

Greene, Joseph. Life Cycle Assessment of Reusable and Single-Use Plastic Bags in California. California State University Chico Research Foundation, 2011.

“HOW ARE NON-WOVEN POLYPROPYLENE BAGS ECO-FRIENDLY?” Bagfactory, 24 Jan. 2017, www.bagfactory.eu/how-are-non-woven-polypropylene-bags-eco-friendly-carrier-bags/.

Kimmel, Robert M. “Life Cycle Assessment of Grocery Bags in Common Use in the United States.” Clemson University TigerPrints, 2014, pp. 1–194.

Muthu, Subramanian Senthikannan, et al. Carbon Footprint of Production Processes of Polypropylene Nonwoven Shopping Bags. 92nd ed., vol. 3, FIBRES & TEXTILES in Eastern Europe, 2012, pp. 12–15, Carbon Footprint of Production Processes of Polypropylene Nonwoven Shopping Bags.

 NRDC. “NRDC Lauds Passage of New York City Council Legislation Requiring Groceries, Retailers to Provide Plastic Bag Recycling for Consumers.” Natural Resources Defense Council, 9 Jan. 2008, https://www.nrdc.org/media/2008/080109. 

The Editors of Encyclopaedia Britannica. “Polypropylene.” Encyclopædia Britannica, 23 July 2009, https://www.britannica.com/science/polypropylene.

Thompson, Claire. “Paper, Plastic or Reusable?” Standford Magazine, Standford University, Sept. 2017, https://stanfordmag.org/contents/paper-plastic-or-reusable.

Kiara Cowderoy

Professor Cogdell

Kahui Lim

Design 040A - A05

4 December 2019

The True Impact of Non-Woven Polypropylene: Waste and Emissions

Introduction

As greenhouse gas emissions increase and the idea of global warming looms over the world, people have begun to question the products they consume on a daily basis. A shocking image that has been circulating through the media is a picture of a sea animal struggling for its life with none other than the common plastic bag. With the increased realization of this daily commodity’s harmful impact, there have been many movements for consumers to start using reusable options; one of the most popular being non-woven polypropylene bags for its durability and recyclability. After researching more about different substitutions, it is clear that non-woven polypropylene bags leave a much smaller carbon footprint with their greater use over time ratio, but in order to find out if these bags are truly “sustainable,” one must look at its complete life cycle.

Emissions in Raw Material Acquisition

To start, it is important to look holistically at polypropylene’s origins from extraction to creation. Beginning at the very heart of what these bags are made out of is propylene. First, shale naptha must be obtained. This is done by using a chemical destructive distillation process which decomposes unprocessed material with a high temperature. Specifically for propylene, the distilled product is a bituminous shale; a sedimentary rock containing organic material (Pandey, 2004). A low-temperature fractional distillation method is then used to separate the propylene from the other materials. Throughout the starting phase, there are already many instances of harmful waste emissions. For example, oil refining pollutes the air, water, and land through harmful gases, discharged chemical pollutants, and solid waste respectively (Ohrui, 1976). Then, there is the actual process of creating polypropylene. It was first polymerized in 1951 by Paul Hogan and Robert Banks, and by 1957, its popularity exploded starting in Europe (Bpf). The polymerization process requires the propylene monomer to be treated with heat and pressure, thus generating a translucent material (Bpf). Overall, raw material acquisition for non-woven polypropylene does leave an environmental impact with abiotic depletion, freshwater ecotoxicity, and acidification (Edwards & Fry, 2011). Nonetheless, non-woven polypropylene bags still use less material than the common high-density polyethylene at 718 grams versus 7,570 grams, thus being more sustainable in the case of obtaining raw materials (Muthu, 2014).

Manufacturing, Processing, and Formulation Waste

After examining extraction, one must investigate the manufacturing stage of non-woven polypropylene bags as it is the main contributor to its waste emissions. There are five main stages of the manufacturing process; spun bonding, cutting, screen printing, thermal bonding, and packaging (Edwards & Fry, 2011). Spun bonding takes the polypropylene pellets, sets them to a high heat, and spins them almost like cotton candy so the outcome is a thread-like texture (Bpf). Because polypropylene has such a high melting point at 130℃, the industrial furnace burns a significant amount of oil and subsequently releases a large number of harmful gases into the atmosphere (Bpf). Moreover, spun bonding also uses other processes such as filtering and extrusion that add to the total amount of emissions (Muthu, 2014). Another impactful stage is screen printing. It often relies on harmful, toxic chemicals and the thermal and catalytic oxidizer exhaust from these inks are hazardous air pollutants (EPA, 2018). Besides chemicals, unsafe practices in printing facilities can contribute to water and airborne emissions. For example, the hazardous chemicals previously mentioned are sometimes not properly taken care of and swept up into the trash. This results in toxic waste polluting the waters and affecting the quality of life for sea creatures (EPA, 2018). After the non-woven polypropylene bags are printed and ready, they are packaged and shipped using paper and cardboard materials. One ton of cardboard produces “emissions amounting to 538 kg of CO2 equivalent” comprised of recycled process energy, transportation, and production (Containers, 2016). Even though this production process has a smaller impact, it still leaves behind a carbon footprint and should be considered. Overall, after examining the phases, it is clear that the manufacturing process of non-woven polypropylene bags is the most detrimental in its life cycle as it emits a significant amount of waterborne, airborne, and solid waste.

Airborne Emissions in Distribution and Transportation

Once the non-woven polypropylene bags are packaged and ready to ship, the distribution process contains many instances of airborne waste emissions. The majority of these bags are manufactured in China due to low labor costs so transportation to and through the United States by lorries, freight ships, and freight rail produces a high amount of greenhouse gas emissions (Morris & Seasholes, 2014). Additionally, after being processed through distribution centers, they are sent to various stores such as Trader Joes for consumers to purchase. The exact amount of emissions is unclear, yet there is no doubt that these transportation methods produce a significant amount of CO2. 

Use, Re-use, and Maintenance of Non-Woven Polypropylene

At the utilization stage, there are no primary waste emissions from the non-woven polypropylene bags themselves, but from other sources. Non-woven polypropylene is a popular material for its durability, moisture absorption, and strength but that does not mean they are indestructible (Staff). In the case of breakage, the main source of emissions comes from transportation to recycling centers and the entire process following (discussed in more detail in the next stage). These CO2 emissions contribute to non-woven polypropylene’s carbon footprint although not a significant or identifiable amount. Additionally, maintenance could be a questionable source of harmful byproducts. To care for non-woven polypropylene and any recycled material for that matter, hand wash with soap and water is the most effective and safe route. Only in large amounts can the common cleaner become harmful to aquatic life, yet, it is always important to consider more environmentally friendly options when choosing these products (Lenntech). In the long run, the use of non-woven polypropylene bags is more sustainable compared to their counterparts. Because of its mentioned durability, the average person only consumes around 10 of these bags per year versus 1000 high-density polyethylene bags (Muthu, 2014). So when choosing what bag to use, the average use over time is important to consider as it determines the number of emissions and carbon footprint one leaves behind.

The Impact of Recycling 

Non-woven polypropylene bags are completely recyclable, yet large amounts of CO2 pollutants come from the process of transporting bags to designated recycling facilities and the processes thereafter. As mentioned before, non-woven polypropylene has a high melting point so once it is at the recycling centers, they must use fossil fuel burning machinery to melt it back down into pellets and remove all coloring (Ruibag). That is not to discredit the impact of recycling though. The very act of recycling non-woven polypropylene bags reduces the amount of wasted plastic by 25% (Ruibag). In this regard, it is in the hands of the consumer to determine the positive impact of reusable bags. Non-woven polypropylene bags need to be used 11 times to have lower Global Warming Potential than high-density polyethylene bags, so to truly make a change and reduce one’s carbon footprint, each bag must be reused as many times as possible (Melnik, et al, 2017).

Emissions in Waste Management

Even though non-woven polypropylene bags are recyclable, a large portion still ends up in landfill sights. This degradation is low impact with polypropylene being non-toxic and having a weak chemical structure. Although, this does lead to other issues. Polymeric materials amount to around 30% of solid waste disposal and despite it not producing harmful emissions, it ends up becoming “semi-permanent residue” (Longo, et al, 2011). As mentioned in the recycling stage, to maximize the eco-friendliness of polypropylene, one must prevent the entry of these products into landfill sights until it is practically useless. 

Conclusion

With this examination the lifecycle of non-woven polypropylene bags, it is clear that they do have a significant environmental impact mainly due to raw material acquisition and manufacturing processes. Yet, in terms of choosing the more sustainable option, their overall use outweighs the costs in the long run. The entire process from acquisition to transportation produces 5 kilograms of greenhouse gas emissions as opposed to high-density polyethylene’s 12.8 kilograms (Melnik, et al, 2017). With that being said, even though they are one of the most sustainable in its category, it is up to the end-user to minimizing its global warming potential through constant reuse and recycling.

References

Bpf. “British Plastics Federation.” Polypropylene (PP), https://www.bpf.co.uk/plastipedia/polymers/pp.aspx#development.

“Documentation for Greenhouse Gas Emission and Energy Factors Used in the Waste Reduction Model .” Containers, Packaging, and Non-Durable Good Materials Chapters, Feb. 2016.

Edwards, Chris, and Jonna Meyhoff Fry. Environment Agency, Feb. 2011.

Longo, Carina, et al. "Degradation study of polypropylene (PP) and bioriented polypropylene 

    (BOPP) in the environment." Materials Research 14.4 (2011): 442-448.

Melnik, Alyson, et al. “Reusable Campus Bag.” Appropriate Technology and Sustainability, 20 Apr. 2017, p. 3.

“Monitoring Information By Industry - Printing and Publishing.” EPA, Environmental Protection Agency, 31 July 2018, https://www.epa.gov/air-emissions-monitoring-knowledge-base/monitoring-information-industry-printing-and-publishing.

Morris, J. & Seasholes, B. 2014. How Green Is that Grocery Bag Ban? An Assessment of the 

    Environmental and Economic Effects of Grocery Bag Bans and Taxes. Policy Study 437,        

    http://reason.org/files/how_green_bag_ban.pdf 

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