MANUFACTURING & MATERIALS INNOVATION

We are all familiar withsweetcorn or corn on thecob and many of us enjoyeating it boiled and coated

in butter. Americans in particular areespecially fond of it although less than1% of all the corn grown annually in theUSA is for human consumption. Theremaining 99% is industrial corn ormaize which is used for animal feed andfor processing into a variety of otherproducts. Among these is Bio-PDO or, togive it its commercial name, Susterrapropanediol produced by DuPont Tate &Lyle Bio Products, which is used as abasis for a number of environmentallyfriendly materials, increasingly used infootwear manufacture.The variety of corn involved is known

as yellow dent and has a high starchcontent. After harvesting and drying, it istransported to Tate & Lyle’s wet mill atLoudon, Tennessee. Using a wet millingprocess, the corn is separated into itsfour basic components: starch, germ,fibre and protein. The nutrient richcomponents are used for animal feedwhile glucose is derived from theremaining starch fraction and is the rawmaterial used for making 1.3-propanediol. The process starts off with

a culture of a special microorganism in asmall flask with the glucose. As it grows,it is transferred to a seed fermenter,followed by a ten-story high productionfermenter. Fermentation takes placeunder exact temperature conditions andinvolves a patented process where themicroorganism functions as abiocatalyst, converting glucose into bio-based 1.3-propaneidol.The resulting product is filtered to

remove deactivated microorganisms,unfermented glucose and excess water.After separation, it is then passedthrough a bed of charged resin thatattracts and removes any residual salts.The product is then steam distilled to ahighly-purified state, removing anytrace impurities. The resulting material,highly purified bio-based 1.3-propanediol, is checked against productspecifications before being shipped foruse in a variety of high-performanceapplications. This includes customerssuch as DuPont which makes Soronafibres, personal care and cosmeticcustomers who make skin-friendlyhumectants and industrial customerswho use Bio-PDO as the building blockfor a variety of high performance bio-based polyurethanes.

STRONG POINTSThe company says that what is so

good about it as a building block is thatit is not only plant-based but is alsosustainably produced. It has published acradle to gate life cycle analysis (Tables1 and 2) showing that it produces 47%less greenhouse gas emissions andconsumes 49% less renewable energythan petroleum-based 1.3-propanediol.Compared with propylene glycol (PG),the reductions are 42% and 41%, andcompared to butanediol (BDO), 48% and46% respectively. At full capacity(scheduled for mid-2019) the processwill achieve a greenhouse gas emissionreduction equivalent to taking 40,000passenger cars off the road for one year.As regards non-renewable energy it willsave enough energy to power onemillion 100W incandescent lightbulbsfor one year.As Susterra propanediol is a building

block for bio-based polyurethanechemistry, any footwear material orcomponent that is currently made usingpolyurethane-based on traditionalpetroleum routes can now be bio-based. This includes microfibres andother synthetic upper materials,outsoles, insoles and waterproof

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Plant-based footwear

CREDIT: MAILSONPIGNATA / SHUTTERSTOCK

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breathable membranes. DuPont is notonly the parent company of DuPont Tate& Lyle Bio Products but, as mentioned,is also a customer which uses Susterrapropanediol as the basis for its Soronafibre. This is a bio-based PTT(polytrimethylene terephthalate) that ismade from 37% Bio-TPU. It has a verysoft hand, very good elasticity and at thesame time is very long-lasting.Susterra has been very much a story

about performance and solvingproblems for different parts of a shoe.Paired with the right chemistry, DuPontsays it can perform as well as–or betterthan–traditional TPUs based on thoseperformance requirements, “Due to itsunique molecular structure and lowglass transition temperature, itprovides increased flexibility inoutsoles even at low temperatures.”For the same reasons, it can alsoenhance abrasion resistance andsoften the hand of microfibres andother synthetic upper materials. TheLalo Tactical boot developed for use byUS Navy Seals is a good example of ahigh-performance outsole that hasbeen developed in conjunction withDuPont to exploit the added flexibilitySusterra provides to cope with adverseconditions as varied as the wet deck ofa ship or sand on a beach. It also helpsto reduce the overall weight of the bootand lessen physical fatigue.

HELPING THE ENVIRONMENTWarnings of the dire implications of

global warming are on the increasedespite what certain world leaders

would have us believe. A recent reportby the United Nations suggests that wemay have only some 12 years left to cutCO2 emissions by around 45%. If we donot, ice caps will shrink leading to risingsea levels and increased flooding. Therewill also be severe heat waves on aregular basis. Indeed, it may proveimpossible to get climate change backunder control and, if this happens assome predict, global temperaturescould rise by as much as 5% by the end

of the century, leading to massmigrations to the northern hemisphereas other parts of the planet becomeincreasingly uninhabitable. It is also estimated that we produced

somewhere between 21 and 22 millionpairs of footwear in 2018. Most of thesewere made from petrochemical-basedmaterials where the manufacturingprocesses create large amounts ofcarbon dioxide which contributes to thealready serious effects of climate

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PLANT-BASED FOOTWEAR

MARCH/APRIL 2019 | www.footwearbiz.com

GH

G E

mis

sion

s (k

g C

O

equi

vale

nt/k

g)2

6

5

4

3

2

1

0Bio-based

1.3-propanediol (DuPont Tate & Lyle)

BDOPropanediol (PO route)

Propylene Glycol

Greenhouse Gas Emissions47% less than Propanediol42% less than Propylene Glycol48% less than BDO

2.5

4.74.3

4.8

Non-Renewable Energy Use49% less than Propanediol41% less than Propylene Glycol46% less than BDO

Non

-Ren

ewab

le E

nerg

y (M

J/kg

)

120

100

80

60

40

20

0Bio-based

1.3-propanediol (DuPont Tate & Lyle)

BDOPropanediol (PO route)

Propylene Glycol

56

109.0

95.0104.0

Table 1: Greenhouse gas emissions. Table 2: Non-renewable energy use.

CREDIT: DUPONT TATE & LYLE BIO PRODUCTS

The Lalo Tactical boot uses Susterra toadd flexibility and save weight. CREDIT: LALO FOOTWEAR

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change. The fact that the use of leatheras an upper material is declining quiterapidly, is only making the situationworse as far as the footwear industry isconcerned. While many prefer to turn ablind eye and say its adverse impact issmall compared to many otherindustries, a few visionaries haveviewed things differently.One of these is UK brand

Vivobarefoot that not only producesshoes that the company claims ‘willallow the feet to move like feet’ but alsouses plant-sourced materials to thegreatest extent possible in its new BIOrange available from March this year inorder to minimise environmentalimpact. Part of its quest to make earthpositive shoes has been to look at

alternative materials. These bio-basedshoes, first launched at outdoor retailerin Denver last autumn, are currently40-50% made from plant basedmaterials and it says that every 50,000pairs is equal to saving greenhouse gasemissions from 247,948 miles driven byan average passenger vehicle orreducing CO2 emissions from 11,286gallons of gasoline consumed.Susterra-based materials feature

prominently in the equation as ananalysis of its Primus Light Bio modelclearly shows (Table 3). This analysisdemonstrates how far the use of plant-based material can extend in asneaker/athleisure shoe. The inclusionof Bloom EVA is also significant as thisis derived from toxic algae harvested

from lakes in China and used toproduce a sustainable natural additiveto EVA (ethylene vinyl acetate) toimprove its performance while at thesame time removing an environmentalmenace (see World FootwearSeptember/October 2017). The veryfact that shoes of this type will bemainly worn by Millennials makes theuse of such materials not only positivein an environmental sense but alsosensible commercially as it is this groupof consumers that is most sensitive toenvironmental issues. They are oftenalso increasingly concerned aboutanimal welfare issues and possiblysympathetic to veganism, so Susterra-based materials would cover thisaspect too.

SPORTS SHOE BRANDSSome major sports shoe brands are

also taking steps down this road.Reebok has launched its first shoeunder the Cotton + Corn sustainableproducts initiative that it announced in2017 with the aim of producingfootwear from ‘things that grow’ ratherthan from non-renewables such asthose derived from hydrocarbons.Named NPC after the Newport Classic,an iconic 1980s Reebok product, it hasan upper constructed entirely fromcotton and a sole made from TPU(thermoplastic polyurethane) thatincorporates Susterra propanediol. Inaddition, the insole uses materialderived from castor oil and packagingis 100% recycled.Bill McInnis, head of Reebok Future

says that with some 20 million pluspairs of shoes being produced per yearand athletic footwear made usingpetroleum to create synthetic rubberand foam cushioning systems, the

20 WORLD FOOTWEAR | MARCH/APRIL 2019

TABLE 3 – PRIMUS LIGHT BIO COMPOSITION AND BIO CONTENT

Upper

100% Sorona fibre bio mesh knit 37%

50% Sorona fibre bio single mesh 19%

30% Susterra Bio-PDO TPU 30%

50% Sorona fibre bio webbing + Lace 19%

Lining

50% Sorona fibre bio non-woven 19%

100% Bloom algae EVA 30%

Insole

100% Bloom algae EVA 30%

50% Sorona fibre bio single mesh 19%

Outsole

70% Susterra Bio-PDO TPU 70%

Branding

70% Susterra Bio-PDO TPU 70%

Vivobarefoot’s Primus Lite Bio shoe.CREDIT: VIVOBAREFOOT

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situation is no longer sustainable.Reebok says it also cares about whathappens to its shoes when people arefinished with them and claims thatusing plant-based raw materials suchas corn and cotton allow for easiercompostability. The ultimate goal is tocreate a broad selection of bio-basedfootwear that will be composted afteruse and the compost returned to thesoil to help grow the materials for moreshoes. Reebok says that the NPC UKCotton + Corn is the only footwearproduct on the market with such a highproportion of its content–75% in total–certified by the US Department ofAgriculture as bio-based.Chinese brand Anta Sports has also

entered the fray with its A-Flashfoamsneaker which uses Sorona instead ofspandex. The yarn used is actually 80%

viscose and 20% Sorona bico fibre sothe plant-based content is effectively84%. When cellulose-based fibres suchas viscose are combined with Soronafibres, the result is an extremely softfabric with greater resilience in stretch,recovery and dimensional stability.Whilst Spandex replacement is nothingnew as far as Sorona fibres areconcerned, this is the first time afootwear company has done so with aknitted footwear fabric. The shoe is saidto be extremely comfortable to weareven without socks and to offer long-lasting stretch and recovery formaximum shape retention. In January,Anta launched its NASA co-brandingshoe where the upper is made from afabric that has 33% Sorona bico filamentas a backing fibre with the other 67%being golden/silver PET fibre.

With leather losing ground as theupper material of choice and withmore more new manufacturingtechnologies appearing, theopportunities for new footwearmaterials has never been greater.While oil-based materials–particularlyfor soling applications–are still themost widely used, there is growinginterest in renewable plant-basedtechnologies. Cork has been used forcenturies but more recentdevelopments include Tencel (viscose),Pinatex (pineapple leaf fibre) bamboo,rice husks, etc. These all havelimitations as to what part of the shoecan be produced from them. Susterra’sstrength lies in the diversity of itspotential footwear applications asdemonstrated by Vivobarefoot’s/bio-based products.

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The upper on Anta’s NASA co-branding shoe uses Sonora bico filament backing fibre. CREDIT: ANTA SPORTS

Reebok’s Cotton + Corn shoe has a TPUsole containing Susterra propanediol.CREDIT: REEBOK

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