Methods Discussion and ConclusionsIntroduction

Sustainable Footwear

Three different common footwear stuctures are evaluated for their physical attributes using sustainable yarns and environmentally-concious product development (Figure 5). Then, knit structures are developed from common knit structures found in the foot-wear industry (Figure 6). The structures are evaluated for their yarn content, burst strength, tenacity, weight, thickness, air permeability, abrasion resistance, moisture regiain and fabric elongation. While current testing parameters for footwear are inter-nal to many companies and not published, the array of tests covers many important considerations in footwear development. The fabrics were developed using the Shima Seiki APEX Software.

Research objectives inlcluded comparing existing footwear products for their contribu-tion to sustainability in the textile industry, developing novel knit structures with hemp yarns, analyzing existing footwear fabrics against hemp-rich fabrics, and evaluatinghemp as an alternative fiber to synthetic yarns. The yarns used in this study may be seen below in Table 1, while the fabrics developed may be seen in Table 2.

Thank you to my advisor, Dr. Andre West, for his support throughout this project. Thank you to Leah Resneck the knitting lab manager, for helping me with knit pro-gramming. Thank you Guy Carpenter (Bear Fiber) for your donation of Hemp yarn.

A COMPARISON OF NATURAL AND SYNTHETIC YARNS IN COMMON KNIT FOOTWEAR STRUCTURES

100% Hemp 10/1 Bleached, waxed

1 end

ASTM Method D-1777-96, 2015

ASTM Method D-3776, option C*

*modified method, 3x3”

ASTM Method D-4966

ASTM Method D-737-16* ASTM Method D-629-15**

ASTM Method D-3789*

Researchers were limited to Shima Seiki weft flatbed machinery. Additionally, not all synthetic or natural yarns were available for testing. Physical testing standards for footwear uppers and not open-source and were not able to be found. While working with natural and synthetic yarns, yarn sizes were controlled for the most appropriate fabric hand and feel for knit footwear. Finally, a final product was not developed or tested due to COVID-19 safety precautions and limitations. Regarding assumptions, aesthetics were not a concern at this stage in the development process. It may also be assumed that the knit structures from this study may be reproduced by using ap-propriate materials/machinery. The current application of this footwear is low-impact, and it must be noted that this is not a direct comparison between natural and synthetic yarns in footwear, but rather an evaluation of the replacement of one with the other.

Zoe Newman¹North Carolina State University Wilson College of TextilesDepartment of Textile and Apparel,

Technology and Management

Figure 1. Hemp vs. THC (Alphagreen, 2020) Figure 2. U.S. Industrial Hemp Market Size, by product, 2016-2027. (USD Million). (Grand View Research, 2020)

Microplastics from runoff are commonly ingested by fish and other aquatic organisms as they are confused with food (Wang, 2020). Microsplastics come from products such as plastic containers and bottles. Humans created plastics, and have been using them as yarns in the textile industry for decades. The worldwide consumption of synthetic apparel and accessories has increased the release of microplastics into the environment. The textile industry has used synthetic fibers for their inherent strength, durability, and low cost. However, the environmental crisis and climate change movement has demanded the industry to reconsider their raw materials and develop sus-tainable initiatives. Many companies have instituted the recycling of plastic bottles as yarns used in products. While the recycling of polyester yarn is a step in the right direction for the industry, the microfibers will ultimately reach a degree of processing in which they will be unable to be recycled again - resulting in waste at the end of the product life cycle. Thus, we must focus on developing a completely biodegradable shoe, otherwise the waste cycle will not end. The integration of hemp fiber into the knit footwear industry may contribute to the development of a completely biodegrad-able shoe. Currently, the majority of hemp fiber production is located in China and imported into the United States. Hemp has been outlawed in the United States due to it’s confusion with mari-juana, however industrial hemp has a different THC content than marijuana, thus it is not capable of producing any psychoactive effects. The 2018 and 2019 consecutive introduction of the Farm Bill and North Carolina Senate Bill 315 officially authorized and regulated statewide hemp farm-ing. North Carolina has the appropriate climate to grow this fiber, and in particular, North Carolina State University is well positioned to research this fiber with partnerships between the Wilson Col-lege of Textiles and the College of Agriculture and Life Sciences. The inclusion of hemp in the tex-tile industry will allow for large strides in the United States as, creating economic development and sustainable solutions in our future.

[1] adidas. (n.d.). Adidas Stories. Retrieved September 30, 2020, from https://www.adidas.com/us/blog[2] Alphagreen. (2020, July 29). CBD vs Hemp: Exploring The Difference - Alphagreen | CBD Blog | Educate, Empower, Enhance. The Medium. https://medium.com/alphagreen/cbd-vs-hemp-ex-ploring-the-difference-a01ffa0f6679[3] Baby doll pattern shoes. (2001). Doll Maker. https://dollmaker.nunodoll.com/boy/pattern17.gif[4] Grand View Research. (2020, February). Industrial Hemp Market Size, Share & Trends Analysis Report By Product (Seeds, Fiber, Shives), By Application (Animal Care, Textiles, Food & Bev-erages, Personal Care), And Segment Forecasts, 2020 -2027.https://www.grandviewresearch.com/industry-analysis/industrial-hemp-market[5] Lu, Z., Jiang, G., Cong, H., & Yang, X. (2016). The Development of the Flat-Knitted Shaped Uppers based on Ergonomics. Autex Research Journal, 16(2), 67–74. https://-doi.org/10.1515/aut-2015-0029[6] Peters, A. (2014, March 25). The Race To Create Knitted Shoes That Cut The Wastefulness Of Our Footwear. Fast Company. https://www.fastcompany.com/3027386/the-race-to-create-knit-ted-shoes-that-cut-the-wastefulness-of-our-footwear[7] Waller, T., & Ma, F. (2018, February 20). Athletic Footwear Strides Into Sustainability, Waste Reduction. Womens Wear Daily. https://wwd.com/accessories-news/footwear/foot wear-take-the-lead-on-sustainably-and-innovation-1202934927/[8] Wang, Y. (2006). Recycling in Textiles (Woodhead Publishing Series in Textiles) (1st ed.). Woodhead Publishing.

Figure 3. Upper Components of a Shoe (Doll Maker, 2001).

Sustainability in the the footwear market has increased since the 2012 introduction of Nike’s Flyk-nit sneaker and the Adidas Primeknit shoe. The U.S. Department of the Interior reports 300 million pairs of shoes get thrown out every year, eventually ending up in landfills (Waller & Ma, 2018). The introduction of knitted shoes to the market allow for streamlined processing, resulting in less cut-and-sew while simultaneously reducing waste in the footwear industry. The effect is a reduc-tion of waste by approximately 80% (Peters, 2015). The yarn for footwear must present robust properties with respect to weight, abrasion resistance, and strength. Research for the develop-ment of sustainable alternatives to synthetic fibers must be conducted in order for progress to be made in the industry. This study evaluates knit structures for sustainable footwear using natural yarns, specifically focusing on hemp. The intention is that the final fabrics may be integrated into fully fashioned, shaped footwear uppers.

Figure 4. Fully Fashioned knit footwear upper, shoe. Image courtesy of adidas. (adidas, n.d)

References

Figure 5. (a) Tubular knit structure with cross-tucks for increased stability, (b) Mock Mesh structure for increased breathability, (c) Tubular knit structure with floating yarn (Lu, et. al., 2016).

(a) (b) (c)

Figure 6. Knit structure development program models, diagrams, and simulations developed using the Shima Seiki APEX system. Designs based off Figure 5.

(a) Cross-Tuck Knit Structure (b) Mock-Mesh Knit Structure (c) Inlay yarn with cross-tuck structure

100% Repreve®1/150/96 Tri-Set Poly Neon Green - 3 ends

100% Cotton20/1 Jupiter Orange

2 ends

100% Hemp10/1 bleached, waxed

1 endStyle 1 Cross-Tucks

Style 2Mock Mesh

Style 3Tubular, Tuck, and Inlay

100% Cotton20/1 Jupiter Orange

2 ends

Repreve®1/150/96 Tri-Set Poly, Neon

Green3 ends

Yarn Repreve® Cotton HempContent 100% polyester

(tri-set) 100% cotton 100% hemp

Yarn Type Filament Staple StapleColor Neon Green Jupiter Orange Natural (Undyed)

Denier 156 (3 ends) = 468 denier

221 (2 ends) = 442 denier

489 (1 end) = 489 denier

Table 2. Extrapolated yarn size based on number of ends used in knitting. Own work.

Table 2. Photographs of the fabrics developed and evaluated for the study. Own work.Length of Skein

(yd)Weight of Skein (g)

Denier Cotton Count

Repreve® 120.0 1.90 156 34.1Cotton 120.0 2.70 221 24.0Hemp 120.0 5.96 489 10.9

Table 1. Yarn Count Specifications

ASTM Method D-5035

Acknowledgements

Tables may be seen below, measuing parameters deemed important in the develop-ment of knit footwear uppers. ASTM Methods were used in every instance, and modified as-needed due to limitations in the amount of fabric produced.Firstly, the tenacity of the yarn used in this study was evaluated, showing the stron-gest yarn as the synthetic contender (Figure 7a). Understanding the tenacity of the individual yarns allow further understaning of the following parameters evaluated. Tenacity is a numerical calculation of the ultimate breaking force of a yarn, and may ultimately impact abrasion resistance, air permeability, and fabric elongation. As ex-pected, the Repreve yarn has a stronger breaking force than the natural fibers due to it’s more crystalline composition. In the evaluation of other parameters, the yarn contents are listed on the x-axis, while the styles evaluated are color-coded to the right of the graph.

Figure 7. Testing outcomes from (a) Tenacity, (b) Fabric Thickness, (c) Fabric Weight, (d) Abrasion, (e) Air Permeabil-ity, (f) Moisture Regain, (g) Burst Strength, (h) Fabric Elongation. Test methods used are noted in the upper right corner of each graph. Bars represent mean +/- STD.

* modified method, performed 5 tests intead of 10, test area 2.75” ** modified method, test performed once

* Burst strength >500 for Repreve (style 2)

ASTM Method D-2256

Hemp provides the greatest degree of air permeability and moisture regain attri-butes. A combination of appropriate knit structures and natural fibers allow for desir-able properties to be achieved. While fabric elongation, burst strength, and abrasion resistance were not desirable, there is room for improvement with the development of stronger knit structures and different yarn sizes. Waste can be further reduced through the integration of natural fibers in footwear through careful placement of certain yarns, integration of intimate blend yarns, and the use of possible compos-ites made from hemp. The integration of natural yarns into footwear will allow for a more friendly contributions to the environment and our ecosystems.

instep

inner sole

filler

soleside

sole

1 - Under the direction of Dr. Andre J. West