The sporting goods industry comprises of sports apparel, sports footwear, and sports equipment. This dynamic global industry sector has grown significantly over the years, while continuously trying to meet the growing demand for new and improved sports products. According to the recent market research report Sporting Goods–A Global Outlook 1 in 2006, the consumption of sporting goods in the global market was more than US$250 billion, with the following percentage breakdown of value sales by-product category: (i) sports apparel (45.45%); (ii) sports equipment (33.93%); and (iii) sports footwear (20.62%). While the global sporting goods market is large and growing, the majority of sales are still resulting from the most economically-developed countries, with emerging markets in eastern Europe, Asia, and South America slowly catching up. New sports product innovations are rapidly developed and brought to market by the manufacturers in order to accommodate the diverse needs and changing personal preferences of the users. In order to grasp the growing commercial opportunities, the industry has diversified by developing and producing lifestyle products in addition to performance products. This has resulted over the years in a shorter life cycle of sports products and increased disposal rates and waste.
Much of the innovations in sports products are associated with the application of new materials and processes, and with the rapid diffusion of advanced technologies developed by other industry sectors. However, new materials and processes used in sports products carry with them potential environmental risks. Looking at sports product innovations in the past, such risks have occurred for example in the case of ski boots, sports apparel, and packaging using PVC (polyvinyl chloride)-based materials, and athletic footwear using petroleum-based solvents and other potentially damaging compounds, such as sulfur hexafluoride in air bladders for cushioning and impact shock absorption 21. Also, composites, such as carbon fiber (CF)-reinforced polymers, typically used in tennis racquets, hockey sticks, skis, and other sports equipment, are associated with particular technological challenges at end of life, as they cannot be readily recycled at an acceptable cost or value. Similarly, it is not possible to cheaply recycle equipment made using fiberglass composites. Advances in sports products have unintentionally placed additional burdens on the environment and the societies that are forced to deal with such products at end of life.
It is estimated that approximately 80% of the environmental burden of a product is determined during the design stage, when most of the decisions are made regarding the selection of materials and processes for the new product. Thus, in modern design, environmental issues are given high priority, which has resulted in the development and application of new sustainable design methods and practices that are applicable to sports products and that can be effectively integrated in the design process 19, 20, 22. Additionally, governments and relevant agencies (particularly in Europe) have introduced a wide range of environmental legislations to help reduce the environmental burden associated with manufactured products, clearly indicating that it is no longer acceptable for products to be incinerated or dumped in landfills after their useful life, irrespective of the consequences. Sustainable design implies lower social cost of pollution control and a higher level of environmental protection through more efficient use of resources, reduced emissions, and waste.
The move towards sustainable design practices raises some critical questions that must be addressed by the sports industry. Is the development of new sports products informed by the state-of-the-art research and practice in sustainable design? What are the implications for the sporting goods industry in this regard? Are advances in recycling and reuse technologies for sports equipment and apparel keeping abreast of the growing requirements for sustainable design? This article aims to address these questions by providing a detailed review of the current research in sustainable design and environmental impacts of materials used in sports products. Special attention is given to composite materials in sports equipment and synthetic fibers used in sports apparel, which both pose major sustainability issues for the industry. The article encompasses the following three main sections that are perceived to be of highest interest in this context: (i) sustainable design framework; (ii) composites in sports equipment; and (iii) advanced textiles in sports apparel. The issues covered in this article aim to highlight the key technological challenges and opportunities facing the sporting goods industry in its quest to embrace the sustainable design paradigm.
2. SUSTAINABLE DESIGN FRAMEWORK
There is an ever-increasing need to develop, produce, and use products that are robust, reliable, of high quality, supportable, cost-effective, environmentally sustainable from a total life cycle perspective, and that are able to respond to the needs of the user/customer, industry, and society in a more sustainable manner. Different definitions of sustainability have been used in literature, with up to eight or more dimensions of sustainability reported to date, including physical, environmental, economic, social, equity, cultural, psychological, and ethical. Nevertheless, it is widely accepted today that sustainability encompasses three main domains: (i) social; (ii) economic; and (iii) environmental.
Sustainable design addresses not only the functional and aesthetic requirements of products, but more importantly, aims to meet the needs of the present, without compromising the ability of future generations to meet their needs. With increases in the number, variety, and complexity of sports products traded globally and affecting more stakeholders, sustainable sports product design has gained increased importance. Fundamental to sustainable design is comprehensive treatment of the entire life cycle of the product. The life cycle of products is typically related to raw material extraction, production, use and end of life, whereby design impacts all life cycle phases 23. Inappropriate use and disposal can have negative impacts, even when products are reasonably produced. In the case of sports products, the greatest environmental impacts are associated with the production phase, as opposed to some other products, like cars, where the greatest impact is in the use phase. With the adoption of new, more advanced materials, the impact weighting is increasingly being shifted to the end-of-life (disposal) phase due to the environmental burden associated with such materials.
The level of environmental impact of the design on the life cycle phases of the product must be assessed using an informed, science-based approach based on standardized criteria and approaches. This allows the different products and phases of the life cycle to be compared on the same scale. The life cycle assessment (LCA) method is typically used to calculate and analyze the environmental impact and/or damages of a product across the entire life cycle. There are four main phases in an LCA study, as follows:
Goal and scope definition phase
Inventory analysis phase
Impact assessment phase
Interpretation of the LCA results could lead to particular product design improvement strategies, strategic planning of new product development, policy making, marketing, and others. Experience shows that the materials and processes used in products typically have the greatest impact on the LCA results. The following case study involving composite tennis racquets will illustrate the LCA process, type of results obtained, and typical recommendations for sustainable design stemming from such a study.
2.1 LCA of Composite Tennis Racquets
Composite tennis racquets consist of several different materials, depending on the model and the manufacturer. The manufacturing techniques used to produce tennis racquets are generally the same, with minor changes introduced from manufacturer to manufacturer, each having their own trade secrets. Although it is not possible to obtain or publish the details of these processes in full, the main steps that make up the majority of the construction can be retrieved from literature 18. In order to gather more accurate information on the materials, it is necessary to either work closely with a tennis racquet manufacturer or adopt a reverse engineering or forensic engineering approach.
In this case study, four different tennis racquets (with two different designs and two different manufacturing techniques used) will be assessed. The goal is to identify the materials and processes that give rise to the main differences in the respective environmental impacts of the racquets. The scope and boundaries, as well as the functional unit of the product system considered in this analysis, have been described in detail by Subic and Paterson 20. The functional unit is a measure of the function of the studied system, and it provides a reference to which the inputs and outputs can be related. Thus, two different products can be compared if they have the same functional unit. The functional unit of a tennis racquet requires assumptions to be made about how long it will be used for. For example, if an average casual player is considered, the average racquet's useful lifespan can be assumed to be 5 years, with each racquet requiring four replacement grips and two sets of replacement strings. A racquet will probably last much longer than this, but it is usual for new models to replace existing racquets before their useful life has been exceeded due to the changing personal preferences of the user.
A detailed material and process inventory for the four racquets has been completed, with Figure 1 showing the inventory tree (including the processing steps used for the construction of the racquets and estimates of the waste), whereby Table 1 indicates the weightings and types of materials found in the racquets (including estimations for the waste material and accurate data for packaging). There are many similarities between the materials used in the different racquets, as might be expected. For clarity, the materials that exhibit differences are indicated in bold.
Table 1. Materials inventory for four tennis racquets; model no. 1
There are five main areas where the racquets differ in material weights. The bumpers, for example, are a plastic component used to protect the frame and attach the strings. The lead alloy tape is used as additional weight in various places around the frame. It is acknowledged that this tape would require an adhesive, as with many other components of the racquet. Because the adhesive mass is negligibly small, it is expected to contribute very little to the overall environmental impact of the racquet. The two materials that contribute significantly to the overall difference in racquet weight are the CF and glass fiber sheet molding compound (SMC) used in the frame. The final material that exhibits differences depending on design is the method B finish. A particular polyamide is used only in method B to provide a better, more resilient finish to the frame décor. The environmental impact of materials used and the waste by-products of the processes have been calculated in detail in this study.
The impact assessment stage involves technical, quantitative, and qualitative efforts to determine the effects or impacts of the inventory, such as what type of damage the use of resources or output of emissions has on the environment. The main purpose of this stage is to allow a comparison of processes, emissions, and other waste on the same scale, thus determining an overall environmental impact of the product. The principal aim here is to provide a quantitative indicator of environmental impact that can be used for a relative comparison between different racquet designs. Figure 2 shows a comparison of the environmental impact determined for the four tennis racquets considered in this study. Racquet 1B is clearly the worst in terms of its environmental impact, followed by the other model 1 constructed by method A, and then the two model 2s in the same order.
Figure 3 shows how the various components contribute to the overall environmental impact of composite tennis racquets. The frame has the largest contribution to each racquet's overall environmental impact. The remaining components (end-cap, bumpers, handle) of the actual racquets contribute little, with the separate components, such as grip, strings, and packaging contributing slightly more. To put the impact in some perspective, the work of Goedkoop and Spriensma 17 should be considered. Simpson states that 1 EI-99 Pt is approximately equal to 1/1000th of the average European citizen's yearly environmental load, which equates to 114.2 mPts/h. Thus, the racquets analyzed can be equated with the average environmental load of a European citizen over a period of 3 h.
The two B models include additional materials as part of the construction process to provide a better finish, which contributes to the higher environmental impact of the frames than the model A counterparts, but only by approximately 20 mPts. This is clearly not the largest contribution to the frames' environmental impact, as seen in Figure 4, which shows the environmental impact for the parts that make up the frame, with materials and secondary processes included.
The study shows that the most significant material for all racquets is the CF SMC. The second-highest contributors to the frames' environmental impact are lead alloy, used for additional weight in model 1 racquets, and nylon, used in the blow-molding process of all racquets. The nylon material, plus the molding process, equals 26 mPt, and in model 1, where 37 g of lead alloy is present, the lead material, plus the rolling process, equals 31 mPt. Both of these materials with their respective secondary processes seem to be important.
The racquet frame represents the most important component with respect to the environmental impact. The strings, packaging, and the grips are also important. Although these components contribute much less to the overall environmental impact during the racquet life cycle, they have the important property of easy disposal because they are easily detached from the racquet by the user. This means that compared with the racquet frame, these components are easily separated and potentially recycled, which has the potential to improve the environmental design of the racquets. Design for end of life incorporates these types of objectives. There are already environmentally-friendly initiatives in the design of strings, and particularly packaging plastics. For example, Gosen's Bio-gut Multi-oil 16 biodegradable tennis strings, made partly from corn starch, are an environmentally-friendly option that would reduce the environmental impact considerably. Chlorine-free polythene packaging is suitable for recycling, as is cardboard and paper, both of which would improve the environmental design of the product system.
The frame is the most complicated of the components and not easily recycled. This means that the most common form of racquet disposal is most probably through municipal waste at present. More work is required to identify and evaluate the various end-of-life strategies for a tennis racquet, which should enable the feasibility of frame recycling to be considered. Specifically, the recycling chain would have to be analyzed, and specialist composite recycling plants would need to be involved, which is difficult because there are only few in existence. Ideally, this could also lead to improvements in the recyclability of the frame. Recycling of fiber-reinforced composites uses solvents to dissolve the resin matrix. Anastas and Lankey 16 notes that it might be possible to develop and use less chemically-hazardous solvents in conjunction with polymer matrices. The sustainability issues associated with the use of composites in sports equipment will be discussed in greater detail in the following section.
3. COMPOSITES IN SPORTS EQUIPMENT
Fiber–polymer composites are used to make a wide variety of sports equipment due to a combination of physical and mechanical properties that provide athletes with the opportunity to improve their performance. Composites have several key advantages over other materials, such as metal alloys, including lighter weight, higher stiffness and strength, and better impact vibration damping. Composites are commonly used in equipment as diverse as cricket helmets, hockey stick handles, snowboards, ski poles, wind surfers, archery, bicycles, tennis rackets, and golf clubs 12, 14, 21.
The competitive advantage gained by using composites has made them the highest value material in the sports goods industry. Figure 6 shows the value in US dollars of different groups of advanced materials–composites, metal alloys, polymers, and other materials–to the industry 2. Composites account for approximately 50% of the entire market, and their current value is approximately US$ 370 million. The value of composites is nearly double the next highest group of advanced materials (polymers), and is approximately triple the value of metals. The market-dominant position held by composites is expected to remain for many years, despite ongoing developments in new materials, such as higher-strength polymers. Figure 5 also shows that the usage of composites and other advanced materials is not expected to increase substantially over the next few years. The projected annual growth rate in composite usage is only a few percent, mainly due to their saturation in the biggest markets, such as golf, tennis, and cycling. However, the use of nanomaterials, which are nano-sized particles added to composites to improve mechanical performance, is growing at a phenomenal rate due to their rapid uptake in the production of racing bicycles, snow skis, baseball bats, and other sports equipment. While established materials, such as composites, polymers, and metals, are projected to grow in usage by several percent each year over the next 5 years, the annual growth rate in the use of nanoparticles is above 200% 2.
Composites are used in various forms in sports equipment, which is one of their competitive advantages over plastics and metals, because by careful design and fabrication, their properties can be tailored to suit a particular sport. Composites are used in two basic forms: monolithic laminates and sandwich materials. Monolithic composites consist of a polymer matrix reinforced with particles, whiskers, or fibers. Most sports equipment are made using thermoset resin (e.g. epoxy, polyester) for the polymer matrix, although thermoplastics (e.g. polycarbonate) are used occasionally when high-impact toughness is required. The majority of composite sports equipment is reinforced with continuous fibers–carbon (graphite), glass, aramid–which provide the highest stiffness and strength. Examples of products made using monolithic composites are golf club handles, ski poles, and archery bows and arrows. Sandwich composites are constructed with thin, laminate skins encasing a light-weight core material, such as foamed polymer or syntactic foam. Sports equipment made using sandwich composites include bicycle frames, snowboards, and handles for hockey sticks and baseball bats.
Monolithic and sandwich composite materials have been used for many years in sports equipment, and their dominant position is entrenched in the market place. The most significant development in the current use of composites is the addition of nanoparticles, which is expected to broaden the applications for these materials. Nano-sized clay particles or carbon nanotubes are added to the polymer matrix to improve stiffness, strength, and toughness. Nanoparticle-reinforced composites are currently used in the latest snow skis, baseball bats, and bicycle frames, and as mentioned, their usage is projected to grow at over 200% per annum as they penetrate other sectors of the sports goods industry.
Composite sports equipment, such as golf clubs, racing bicycles, and tennis rackets are produced in many hundreds of thousands of units per year. The environmental impact of using composites in mass-produced products is emerging as a critical sustainability issue for the sporting goods industry. Composites are manufactured using energy-intensive processes that generate significant amounts of greenhouse gas. Composites are produced using non-renewal resources, and require the use of chemicals and reagents which are harmful to the environment. Significantly, composites are not easily recycled and do not biodegrade when disposed as landfill.
The sustainability issues with using composites is a major challenge to the sports industry in the face of government limits on pollution and the consumer demanding ‘greener’ products. The issues to the sustainable use of composites are different to other advanced materials, such as metals. For example, the environmental impact of manufacturing sports equipment from composites can be less than using aluminum. Unlike metals, however, composites are expensive to recycle in a sustainable way. The sports equipment sector (and every other industry using composites) generally has a poor understanding of the sustainability issues, and how they are effectively managed and controlled. This chapter examines the sustainability of composites used in sports equipment, the development of environment-friendly recycling processes, and materials.
3.1 Sustainable Manufacturing of Composite Sports Equipment
The environmental impact of producing the fibers and polymers used in composites, and then manufacturing these materials in the finished piece of sports equipment, is not well understood. Assessments of the sustainable manufacture of composite products are few, and there is poor understanding of the energy consumption, pollution, and other environmental issues. It is well known that producing carbon and glass fibers is energy intensive; the production of polymer resins involves using non-renewal hydrocarbon resources and environmentally-harmful chemicals. The manufacturing processes used to form the fibers and polymer into composite products require thermal energy and yield waste material. What is not well known, however, is the quantification of the manufacturing processes in terms of energy consumption and resultant greenhouse gases, the usage of harmful chemicals, and the disposal of waste byproduct materials into landfill. What is also not well understood is the environmental impact of producing a sports product using composites, compared to other advanced materials, which is important for material selection towards sustainable design.
The production of carbon and glass fibers is energy intensive. CF are produced by pyrolysis (heating in the absence of oxygen) of carbon-rich precursor material, such as pitch, rayon, or polyacrylonitrile. These materials are produced using non-renewal hydrocarbons derived from petroleum, although the fiber industry is increasingly using recycled, carbon-rich materials. The precursor material is pyrolysed at a high temperature inside a gas- or electric-powered furnace, while being stretched and deformed into fine carbon filaments. The mechanical properties of CF are determined by the pyrolysis temperature: high-strength fibers are produced at temperatures between 1000 and 1400°C, whereas high-modulus fibers are processed above 1800–2000°C. The energy requirement for producing high-strength and high-modulus CF is estimated at approximately 25 and 50 MJ/kg, respectively. The most common fiber reinforcement used in sports equipment is high-modulus carbon because it provides exceptionally high stiffness, but it is also the most energy intensive to produce. The production of CF also generates greenhouse and other polluting gases. The precursor material contains 40–55% by weight of impurities (such as nitrogen), which are transformed in the pyrolysis process into gaseous byproducts or tar. The gases are scrubbed before being released into the atmosphere, although they still pose an environmental problem.
The production of glass fibers is also energy intensive. Silica sand is heated inside a refractory furnace to melt and refine the material into glass. The glass is then melt spun into solid filaments. The furnace is heated by gas, fuel, or electricity, which generates greenhouse gas. Gases are also produced during the refining of the silica sand. The energy requirement for producing fiberglass is expected to be similar to high-strength carbon (approximately 20–30 MJ/kg).
The energy used in the production of polymer resins, such as epoxies, is mainly in the form of heat to drive the chemical reactions and the mechanical work for stirring. The base resin, catalysts, promoters, and other reagents used to polymerize the polymer are mostly derived from non-renewal hydrocarbon fuel. The energy requirements in producing many of the polymers (both thermosets and thermoplastics) used in structural composite materials is not known, although it is estimated that epoxy resin, the most commonly used polymer in composite sports equipment, is approximately 80 MJ/kg 8. The other environmental issue in the production of polymers is the liquid waste products, particularly wash water effluent, which must be treated before disposal.
An important issue in the sustainable design of composite sports equipment is the energy consumed by the manufacturing processes used to consolidate and cure the fibers and polymer matrix into the finished product. A variety of manufacturing processes are used to produce sports equipment from thermoset composites, including vacuum bagging, resin transfer molding, and autoclave curing. Equipment made using thermoplastic composites is usually produced using thermoforming processes. Most of the energy consumed during manufacture is heat, which is required to cure the polymer matrix. The amount of heat needed to cure the composite is dependent on the resin chemistry, volume fraction of the polymer matrix, and geometry of the product, although the temperatures are typically in the range of 80–180°C. The sports industry is producing an increasing number of products using low-temperature cure epoxy to reduce manufacturing times, costs, and energy consumption. However, data on the energy requirements for the different manufacturing processes and resin systems used in the production of sports equipment are not readily available.
Material selection in the sustainable design of sports equipment requires quantitative data on the energy requirements and waste products for the candidate materials. Unfortunately, energy data for most of the materials are lacking. Even when data is available, they are often impossible to make accurate comparisons between composites and other materials. In a rare study of this type, Lee et al.8 performed a comparative assessment of the energy consumption and environmental impact of composite material against aluminum. The study contains important data, which are relevant to the sustainable manufacture of sports equipment. The production of metal is an energy-intensive process that produces large amounts of greenhouse gas. Aluminum production is among the most energy intensive of the metals used in sports equipment. An extremely large amount of electricity is needed to convert aluminum oxide (present in bauxite ore) into aluminum metal. Lee et al. 8 estimate that the energy used in the production of aluminum, which includes the mining, refinement (Bayer process), and smelting (Hall–Heroult process), is approximately 284 MJ/kg. In comparison, the energy required to produce a composite material (carbon–epoxy) is only approximately 42 MJ/kg, or just 15% of the energy requirements for aluminum.
Table 2 presents the results of a comparative study performed by Lee et al. 8 of the energy efficiency for carbon–epoxy and aluminum. The energy efficiency for specific stiffness and strength is much higher for the composite.
Table 2. Comparison of the energy efficiency for carbon-epoxy composite and aluminium (data adapted from 8).
*Aluminium energy requirements based on 70% primary production and 30% recycled.
While the production of metal from ore is energy intensive, the sports industry is increasingly using recycled metals, which are much less energy demanding. The energy requirements for recycled aluminum is only 14 MJ/kg (or ∼35% of carbon–epoxy), and recycled steel is 26 MJ/kg (or 62%) 8. The notable exception is recycled titanium, which is used in golf club heads and racing bicycle frames, which is approximately 10 times more energy intensive to recycle than producing composite material. However, comparisons such as these have limited use for the sports designer because they are based on the raw materials produced. Important data on the energy required to consolidate and cure composites and to deform and shape metal ingots into finished products are lacking. These data are essential for sustainable design because it is a significant proportion of the total energy needs for producing sports equipment. The designer needs energy data for both the material and manufacturing processes to select the most sustainable material.
3.2 Sustainable Recycling of Composite Sports Equipment
The disposal of composite products in an environmentally-friendly way is one of the most daunting challenges facing the sports goods industry. Composites are more expensive to recycle and reprocess than most metals used in sports equipment, such as aluminum. Unlike metals, the cost of recycling composite material is not competitive against the cost of using new material. Furthermore, the mechanical properties of reprocessed composite are much lower than the original material, and are usually too low to find application in high-performance sports equipment requiring high stiffness and strength. For these reasons, the current practice for disposing of most composite products is landfill. Not only does this pose an environmental problem because of the many hundreds of thousands of products that occupy landfill, but the polymers and fibers are extremely durable and take many decades (or centuries) to break down in soil.
Despite the challenges with recycling, the composite industry has invested in the development of various reprocessing techniques, which are classified as regrinding, thermal, and chemical processes 4, 5, 10. Regrinding is the simplest and cheapest recycling process, and basically involves cutting, grinding, or chipping the waste composite down to a suitable size to be used as filler material in new molded composite products. The maximum particle size for most products is under several millimeters. The problem with using regrinded material is the continuous fibers are broken down into small fragments, and thereby lose their ability to provide high stiffness and strength. Most sports equipment must contain continuous fibers for maximum mechanical performance, and this cannot be achieved using regrinded material.
Thermal recycling involves the incineration of composite to reclaim the fibers for reuse 3, 6, 9. Waste composite is ground into fine powder and then incinerated using a rotary kiln or fluidized bed. The composite is thermally degraded at temperatures above 500–600°C in the absence of oxygen to break the polymer down into oil/wax, char, and gas. The oil and wax have a high calorific value and can be burnt to provide energy for the incineration process. The gases produced include hydrogen, methane, ethane, and propane, which are flammable volatiles that also provide energy. The process also generates significant amounts of greenhouse gas. The fibers are recovered for reuse; however, their mechanical strength is severely reduced by the high temperature needed to decompose the matrix. The strength of both carbon and glass fibers decreases rapidly with increasing temperature above approximately 400°C, and the typical temperatures used to incinerate epoxy matrix composites (500–600°C) result in strength loss of 80–95% 7, 15. The large reduction to the mechanical properties of recycled fibers means they are not suitable for reuse in high-performance sports equipment. Demand for reclaimed fibers is small but growing, and they are increasingly being used as filler material in outer cases for cellular phones and laptop computers. An added problem is the cost to recycle composites by high-temperature incineration, which is often greater than the original cost of the material, and there is no financial incentive to reclaim fibers. Recycling at low incineration temperatures is currently under development to minimize the loss in fiber strength; however, the process is not ready for large-scale processing.
Chemical processing is another approach to reclaim fibers in composite materials 6, 10, 11. The process involves using strong acid (e.g. nitric acid, sulfuric acid) or base solvent (e.g. hydrogen peroxide) to dissolve the polymer matrix, leaving the fibers for recovery and reuse. Acid or base digestion processes are less harmful to CF than thermal recycling, with only a 5–10% loss in strength. However, the solvents are corrosive and potentially harmful to the environment should they leak out during processing. Another problem is that the chemical dissolution of the polymer matrix is slow–much slower than pyrolysis–and therefore, large digestion facilities are required for commercial-scale recycling.
Problems exist with the regrinding, thermal, and chemical processes for recycling composite materials. The composite industry is investing in the development of new, more environmentally-friendly and cost-effective processes. At the moment, however, the commercial recycling of composite sports equipment is not environmentally friendly or economically feasible.
4. ADVANCED TEXTILES IN SPORTS APPAREL
The design of modern sports apparel is primarily performance oriented and is based on highly-functional textiles for both performance and leisure applications. Recent developments in materials for sportswear have led to the customization of specialized performance properties for different sports, for example, good thermal properties for cold-weather sport, aerodynamic properties for hi-speed sports, breathable waterproofing for outdoor sports, strength, and durability. In addition to the new requirements relating to materials and functionality, there are also increasing environmental demands placed upon sportswear design.
4.1 Sustainable Raw Materials for Sports Apparel
Textile fibers are the raw materials used for all textiles and apparel. These are natural or synthetic. The demand for textile fibers worldwide is increasing, with two fibers dominating the market at present: cotton (natural) and polyester (synthetic). Polyester has been adopted as the main raw material for sports apparel, whereby the demand for this material has doubled over the last 15° years and has now overtaken cotton as the single most popular textile material 34. Synthetic fibers are derived from polymers produced from basic chemicals (primarily petrochemicals) by typically employing an energy-intensive process.
There is currently a lack of understanding of sustainability impacts of different textile raw materials, both in industry and among consumers. Synthetic fibers are commonly seen as ‘bad’, and natural fibers as ‘good’. The reality, however, is not this simple. While there is no dispute about the environmental impacts of synthetic fibers, natural fiber cultivation and processing can also have a high environmental impact. Thus, the following considerations for the selection of raw materials for sports apparel have to be made: (i) large quantities of water and pesticides required for growing conventional cotton and some of the other natural fibers; (ii) adverse impacts on water during natural fiber conversion; and (iii) significant use of energy and non-renewable resources for synthetics.
Due to these and other concerns, such as carbon emissions, rapidly reducing oil reserves, and overflowing landfill sites, attempts are being made to move away from oil-based synthetic fibers, such as polyester and nylon, which are non-renewable and non-biodegradable, to a range of alternative natural fibers, such as organic cotton and bamboo, and new breeds of biodegradable synthetics made from plants, such as poly lactic acids.
The shift in the natural fiber sector is mainly towards organic fibers. Available research indicates that using organic cotton, for example, would significantly reduce the life cycle toxicity of cotton products 35. Generally, for fibers to be certified as organic, there should be no synthetic commercial pesticides/fertilizers used and no antibiotics and hormones for livestock, and no genetic modifications and organic feedstuffs at the farm for 3 years 36. These organic growing methods support biodiversity and healthy ecosystems, improve the quality of soil, and often use less water 37. A recent range of eco-yarns including Ecowool and Ecobambu (organic wool/bamboo blend) by Zegna Baruffa, eco-life branded yarns (organic cotton and its blends with milk fiber) by Alpes, and others were exhibited at the 2009 European Yarn Trade Fairs 47.
Today, there is a growing number of alternative textile fibers used in sportswear that are eco-friendly and sustainable, that aim to provide manufacturers with the benefits of polymer-based thermoplastic fibers, and at the same time, eliminate adverse environmental impacts. This is achieved primarily by alternative ecologically-sustainable polymers for fiber and yarn production.
Poly lactic acids are a biopolymer polyester derived from 100% renewable sources, presently corn 38. Unlike conventional polyester, which is made from fossil fuels and is non-biodegradable, poly lactic acid fibers are derived from annually-renewable crops and are compostable. The sustainability benefits of these fibers stem from their biocompatible and biodegradable nature. These fibers can be readily broken down by hydrolysis and are available from renewable agricultural resources. There is also a reduction in carbon dioxide emissions in comparison with conventional petroleum-based commodity synthetic fibers. According to Cicero and Dorgan 40, the ability to engineer the particular physical properties of poly lactic acid fibers is also important. There are also some negative environmental impacts associated with the poly lactic acid fibers, such as large-scale, intensive agriculture and the problems associated with landfilled biopolymers and the generation of methane. Some other concerns relate to the possibility that corn used for its production could contain some genetically-modified parent materials. It has been reported that manufacturers of the fiber, such as NatureWorks are working towards third-party certification to guarantee genetically modified-free fibers 39.
Bamboo fibers are suitable for sports apparel, due to ts softness and thermal and moisture management properties 41. They are made of cellulose derived from fast-growing bamboo plants, but the processing uses the same ecologically, high-impact route as a conventional viscose, although it has the benefit of being sourced from a rapidly-regenerating raw material. There are many claims made regarding bamboo fibers, including health-giving properties and antibacterial resistance, but there is little research evidence available to support these claims.
Soya protein fibers are regenerated proteins from soya beans or milk (casein), and their production involves bioengineering techniques to modify the soya bean protein structure. Similar to the processing of starch, the processing of protein-based materials (in particular, thermal extrusion) is much more complex than that of conventional polymers 42. With its biodegradable, non-flammable moisture management and non-electrostatic properties, soy protein based fibers are used in ‘green composites’ 43 and provide unique and attractive features for use in sports apparel.
The use of activated carbonized fibers and fabrics for filtration and absorption of organic micropollutants is not new in technical textile applications 44. For example, Cocona developed technology that incorporates carbonized particles, made by carbonizing recycled coconut shells into synthetic polymer fibers, such as polyester and nylon, and then processed it into fabrics suitable for apparel. Carbonized bamboo incorporated into PET composites or fibers at spinning is also being developed 45.
Other natural polymers, such as seed of the castor oil plant, have been used in plant fiber ‘green composites’ 46, and are currently being developed into fibers and yarns that can be used for apparel fabrics, including sportswear. For example, Greenfil yarn, developed by the French spinner Sofila, and Caston polyamide 11 by Kuraray described as ‘eco-nylon’, are suitable for swimwear and other sport applications 47. There is also a number of new and somewhat exotic fibers marketed for their sustainable nature and eco-friendliness, for example, patented ‘S.Cafe’ fabric produced by Singtex Industrial that is made from coffee grounds. It is touted as offering fast-drying properties, odor control, and UV protection, but again, the company's claims have not been supported by available research data to date.
4.2 Reusable, Recycled Materials and Waste Reduction
Due to fashion-driven purchasing behavior, millions of tons of textiles and clothing waste are generated annually. For example, in the USA, 16.6 billion tons of textiles and clothing are thrown away, and only 15% is collected for reuse or recycling at present. Nevertheless, focus on recycling has been growing in recent years. This is driven by factors, such as ‘green consumerism’, rising waste disposal costs, an explosion of legislative initiatives and mandates, and the evolution of waste recycling into a more effective commodity industry.
Traditionally, fibers are extracted mechanically from garments and fabrics and then reused. Garments made from synthetic fibers can also be recycled chemically, where the fiber is broken down to the molecular level and then repolymerized. Several LCA studies have been conducted comparing reuse/recycling of textile waste with virgin materials 32, 33. This research quantified the energy burden associated with the processing and transportation of collected (donated) domestic clothing for potential reuse or reprocessing, and showed that all processes, including the energy burden associated with retailing and distribution of the donations, have been insignificant compared with the energy consumed during the manufacture of these items from virgin materials. For example, the reuse of 1 ton of polyester garments only uses 1.8% of the energy required for manufacture of these goods from virgin materials, and the reuse of 1 ton of cotton clothing only uses 2.6% of the energy required to manufacture those from virgin materials.
The most commonly recycled synthetic fiber is polyester made from plastic bottles. Repreve by Unify Fibres, and Eco Circle Garment Association, established by Teijin Fibres, Japan (Figure 6) are examples of such recycling that is widely available to sportswear manufacturers. Another concept of reuse and recycling is the closed-loop supply chain illustrated in Figure 7.
For the successful operation of closed-loop supply chains, product acquisition from customers plays a key role. In cases where products still have a considerable marginal value of time or short life cycles, it is more likely that customers would return products at the end of their life cycle. However, for a wide range of products, such as sports apparel, the opposite is the case. The research based on the Ecolog recycling network case study, where transaction cost economics are used to evaluate the behavior of end-customers regarding end-of-life returns, demonstrated that low transaction costs are vital for acquiring products at the end of their life, thus it is important to include the final customer in planning such product return channels 24.
Another example of closed-loop supply chains is the ‘Capilene’ supply loop 29. Through this loop, unwanted polyester garments, including those made by their competitors, are collected from customers through Patagonia's Common Threads Recycling Program and then transformed into fiber for use as new garments. The garments that are manufactured through this program have information on their environmental footprint, including energy consumption, distance travelled, carbon dioxide emissions generated by the garment production, and waste generated per garment. Since the launch of this program in 2005, the company has collected more than 450 kg of used Capilene base layers to be recycled into new garments.
4.3 Sportswear and Eco-Design
There is a significant number of eco-textile standards applicable to some or all of the stages of the production of fibers, fabrics, and garments, including sportswear. They include such broad measures as using environmentally-safe and healthy raw materials, design for material reutilization (such as recycling or composting), the use of renewable energy and energy efficiency, the efficient use of water, and maximum water quality associated with production, as well as instituting strategies for social responsibility where the certification of responsible bodies plays a key part 28. By far the most widely used is the Oeko-Tex Standard 100, with over 65,000 product certificates issued to date 28. This standard is primarily concerned with the safety of textile products for the consumer and the elimination of dangerous substances along the processing route. Oeko-Tex Standard 1000 and Oeko-Tex Standard 100 Plus are much more inclusive and far reaching, as is the Bluesign standard, which combines aspects of consumer safety, water and air emissions, and occupational health into a single standard. Major sportswear brands and their suppliers who have already signed as Bluesign supporters include Eschler, Everest Textile, Patagonia, Polartec, Schoeller Textil, The North Face, Vaude, Deuter, Mammut, Haglöfs, Helly Hansen, and Ortlieb. Perhaps more complex is the cradle-to-cradle design framework. This assumes a new approach to manufacturing and product design based on the cradle-to-cradle cycle, where materials are perpetually circulated in closed loops. Maintaining materials in closed loops maximizes material value without damaging ecosystems'.
Dewberry 27 proposed three eco-design approaches: (i) Green Design has a single-issue focus, perhaps incorporating the use of some new material or considers energy consumption; (ii) Ecodesign adopts the product life cycle management approach, exploring and tackling all of the greatest impacts across the products life cycle; and (iii) the Sustainable Design concept which is much more complex and moves design concerns outwards to societal conditions, regional development, and ethics.
To date, the most widely applied eco-design approaches in sportswear are Green Design and Ecodesign.
Sportswear designers and brands readily adopted the new ‘environmentally-friendly’ raw materials as the easiest way of introduction of eco-improvement to the product, where the product concept and design stays the same, but parts of the product are developed further or replaced by others.
A number of brands also adopted the Ecodesign approach that mainly utilizes LCA as a tool for product design and development. At the LCA stage in sports apparel engineering, the following environmental considerations must be addressed: idea generation and analysis (versatility, lifespan, durability, appropriate certification, and close-loop supply chain), material selection (durability, minimal care, organic or sustainable fibers, and yarns containing no harmful chemicals), construction (amount of waste generated, reuse/recycling of waste, and the ethical treatment of workers), labeling (certification, appropriate care labeling, and end-of-life information for reuse or recycling), finishing processes (ecologically sustainable, impact on recycling, and disassembly), and packaging (amount used, materials used, and recyclability/reuse).
The Ecodesign approach and design strategy for improved environmental performance has its technological possibilities for product innovation in product concept and/or structure. As a starting point, only the products' functionality is in principle fixed, and the realization that this functionality could be done in numerous ways. An example of this approach in sportswear engineering is employing Ecodesign in changing the conventional way the sports garments are engineered and constructed to be more ecologically effective. Traditionally, sportswear garments are manufactured by ‘fully-cut’ methods, which incorporate relatively high-waste factors (17–50%) that occur even with small garment pieces, and high labor/process intensity of assembly of the garment.
A number of brands adopted the so-called ‘seam-free’ method, where skin and mid-layers of sports apparel are produced as engineered tubes with zoned functional structures and yarns incorporated into the garment. There is a minimal number of seams (normally in armholes, gusset, and neck), which reduces the waste to 10–20% and the process intensity of the garment assembly. Normally, due to technological limitations, these garments are produced from synthetic fibers, with special application of the moisture management treatment. The integral seam-free technology allows engineering and manufacturing of the whole garment without any seams and with engineered biomapped functional zones (Figure 8).
This technology produces minimal waste and results in minimal garment finishing and resources required. Current technological limitations are in garment engineering methods for the perfect fit and freedom of movement.
Examples of a broader Sustainable Design concept include Design for Recycling and Design for Disassembly, widely used in industrial design and product development 25. The possibility of disassembling products into recyclable fractions and the issue of the material quality is central to the subject of optimal recycling. The difficulty in applying these methods to sports apparel is that there are numerous structural and functional components in a sports garment that are difficult to extract and disassemble after use. Some companies and brands embarked on this path. For example, German brand Vaude developed an Ecolog recycling network working with their garment component suppliers, and is putting together a range of materials and components (fabrics, zips, labels, cords etc.) to be used in their garment designs. The totally consistent garment could be disassembled and recycled for making new products 24. A similar approach is taken by Teijin through its Eco Circle Garment Association, where all the components and accessories of the garment are accredited.
In general, sustainable design of sports equipment poses significant challenges to the sporting goods industry. Growth in manufacturing of a wider range of sports and lifestyle products, coupled with fashion-driven purchasing behavior, have led to shorter product life cycles, increased disposal rates, and waste. Millions of tons of sports equipment, sports shoes, and apparel waste are generated annually worldwide. The present article examined the issues and challenges associated with sustainable design and the environmental impact of materials in sports products, focusing in particular on composite materials in sports equipment and natural and synthetic fibers in sports apparel. The extensive use of composites in sports equipment, produced in many hundreds of thousands of units per year, requires the industry to tackle the sustainability challenges associated with the use of these materials. A key challenge is making designers of sports equipment aware of the benefits and problems of using composites. Typical benefits include lower energy requirements, and therefore, less greenhouse emissions when making an item from composites rather than from metal alloy refined from ore. However, this benefit is lost when recycled metals are used, which generally require less energy than composites. The greatest challenge is the recycling and disposal of composites. The current recycling processes are expensive and yield recycled material that can only be used in low-performance items, and not in sports equipment. Most composite products are disposed as landfill, where they take many decades or hundreds of years to break down. The composites industry is continually seeking new recycling processes that yield better-quality reusable material at lower cost and new materials that rapidly biodegrade when disposed into landfills. Much more research and development is required in the recycling and disposal of composites. Similarly, the use of textiles in sports apparel also involves significant sustainability challenges. The demand for textile fibers worldwide is increasing, with cotton (natural) and polyester (synthetic) dominating the market at present. The use of polyester in sports apparel has doubled over the last 15 years and has now overtaken cotton as the single most popular textile material. While synthetic fibers are commonly seen as ‘bad’ and natural fibers as ‘good’, the reality, however, is not that simple, as this article demonstrated. While there is no dispute about the environmental impacts of synthetic fibers, natural fiber cultivation and processing can also have a high environmental impact. Until the problems associated with the use of advanced materials in sports products are resolved, the sporting goods industry must be made aware of the challenges associated with the sustainable use of these materials in their equipment.
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