Biobased Polyamide Ecomaterials and TheirSusceptibility to Biodegradation

Mariya Kyulavska, Natalia Toncheva-Moncheva, and Joanna Rydz

AbstractWidely used petrochemical polymers have negative impact on the environment,so the use of biobased material should become widespread due to growinginterest in sustainability and environmental issues. The use of renewable rawmaterials substantially improves the carbon footprint and has a positive impact onthe life-cycle assessment of plastic products; thus, the development of polyamidesfrom renewable resources – one of the largest industrial scale engineering plasticsof great significance – is very important. This review focuses on recent researchand development of biobased polyamides. Environmental impact of polyamidesis described in view of the potential applications in various fields. Biodegradationof polyamides and some factors affecting their biodegradability are alsopresented.

ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Polyamides: Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Biobased Polyamides: Synthesis, Properties, and Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Polyamide “Inks” for 3D Printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Biodegradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Future of Polyamide Ecomaterials: Final Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

M. Kyulavska • N. Toncheva-MonchevaBulgarian Academy of Sciences, Institute of Polymers, Sofia, Bulgariae-mail: mkyulavska@polymer.bas.bg; ntoncheva@polymer.bas.bg

J. Rydz (*)Centre of Polymer and Carbon Materials, Polish Academy of Sciences, Zabrze, Polande-mail: jrydz@polymer.bas.bg; jrydz@cmpw-pan.edu.pl

# Springer International Publishing AG 2017L.M.T. Martínez et al. (eds.), Handbook of Ecomaterials,https://doi.org/10.1007/978-3-319-48281-1_126-1

1

Introduction

Materials known as environmentally friendly materials (ecomaterials) help toimprove the environment by at least one property that minimizes environmentaldamage during the use of such materials. Ecofriendly polymer materials are charac-terized not only by their origin from renewable sources, but also by easy disposal,recycling such as reuse of waste, biodegradation or composting, health-safe andreducing impact on human health, lightweightness, energy efficiency, reduction ofpollution, and material usage [1]. Recently, much attention is paid to the concept ofsustainable development at all levels. To introduce this concept, it is necessary tointegrate economic, social, and environmental aspects and make a number ofchanges. Significant advances have been made in the development of alternativeresources of raw materials. The use of renewable raw materials substantiallyimproves the carbon footprint of the raw material itself and thus has a positiveimpact on the life-cycle assessment (LCA) of plastic products.

Polyamides (PA)s have been widely investigated for decades. They comprisegood balance of properties. They are very resistant to wear and abrasion, have goodmechanical properties even at elevated temperatures, have low permeability to gases,and have good chemical resistance, dimensional stability, toughness, high strength,high impact resistance, and good flow. PAs are one of the most important syntheticpolymers produced in large quantities for high-performance engineering thermo-plastics and for fibers. In this context, the development of polyamides from renew-able resources becomes a very important field in macromolecular chemistry andmodern industry. Moreover, the sustainable monomers and polymers manufacture isbecoming increasingly important for the economic and ecological point of view.Thus, the development of environmentally friendly and sustainable production ofbiomass-based polyamides is entirely justified [2]. More green polyamides can beproduced using conventional production but with biobased alternatives for tradi-tional chemicals (elaborated of new, environmentally benign routes to existingchemicals), and coming from recycling, or more ecofriendly, made from 100%biobased monomers [3].

In this review, the recent research and development of biobased polyamides areoutlined. Environmental impact of polyamides is described in view of the potentialapplications in various fields. Degradable polymeric materials attract much attentionin view of current interest in sustainable development, recycling, environmentalprotection, and medical fields. Thus, microbial and enzymatic biodegradation ofpolyamides and some factors that affect their biodegradability are also discussed.

Polyamides: Background

Polyamides contain repeating amide linkage (–C(O)–NH–), such as naturally occur-ring proteins (collagen, silk). The amide backbone presented in polyamides makethem more hydrophilic than most polymers. Nylon is a generic name for a family ofsynthetic polymers, first produced February 28, 1935 by Wallace Carothers in the

2 M. Kyulavska et al.

DuPont laboratories and is the trade name of the manufacturer. Polyamide is athermoplastic, silky material, commercially used for the first time as a bristle in atoothbrush. Typically, PA structure is linear (aliphatic polyamides) such as Zytel®

from DuPont, US; Technyl® from Solvay Group, Belgium; Rilsan® and Rilsamid®

from Arkema S.A., France; and Radipol® from Radici Group, Italy [4, 5]. PAs couldbe also semiaromatic (polyphthalamides) such as Trogamid® T from Evonik Indus-tries AG, Germany; Amodel® from Solvay Group or aromatic (aramids, poly-aramids) such as Kevlar® and Nomex® from DuPont, Teijinconex®, Twaron®, andTechnora® from Teijin Limited, Japan; and Kermel® from Kermel, France. In Table1, selected polyamides are summarized.

Polyamides were the first engineering plastics and still represent by far the biggestand most important class of materials. Suitability of PAs as engineering materials fora particular application is a result of a combination of desirable characteristics.Economic and manufacturing considerations are also important in material selection[14]. Polyamides are very important class of polymers due to their excellent prop-erties, such as high impact and tensile strengths, electrical insulation, heat andabrasion resistances, resilience, biocompatibility, and the ability to tailor theseproperties for particular applications. PAs can be reinforced with carbon, glassfiber, or by incorporation of clay particles smaller than a nanometer in width, butlong. Such nanocomposites are more durable than untreated polyamide and retainproperties often lost with traditional reinforcements. Aliphatic polyamides producedon a much larger scale than aromatic one are amorphous or semicrystalline, but thedegree of crystallinity can be increased by orientation via mechanical stretching.Aromatic polyamides generally have higher strength, flame and heat resistance, andgreater dimensional stability, but are much more expensive and more difficult toobtain. PAs are more resistant to alkaline hydrolysis than polyesters but not asresistant to acid hydrolysis. They also have better solvent resistance to many organicliquids when compared with poly(ethylene terephthalate) or polycarbonates. PAsalso have good barrier properties against oxygen, smells, and oils. Different PAshave different properties, and therefore different applications. They are used toproduce a variety of plastic products, but only PA 6 and PA 66 are used for fabricsand they are the two most common petroleum-based polyamides available commer-cially. A wide range of applications in the automotive engineering, transportation,electrical engineering and electronics, textile, machinery, packaging, cosmetic,housing and consumer goods industries, and the medical sectors makes the totalannual production of all types of PAs in the region of 5.5 million tonnes worldwide.More than 60% of all manufactured polyamides are used to produce carpets, otherfurnishing products, garments, seatbelts, upholstery, ropes, and tire reinforcements.In the automotive industry, PAs are used for wire and cable jacketing, cooling fans,air intake, turbo air ducts, valve and engine covers, brake and power steeringreservoirs, gears for windshield wipers, and speedometers. In food packaging, PAsare used as films. In electrical engineering and electronics, PAs are used for powertool housings, valves and vending for various machines, pumps, switches, sockets,plugs, and antenna-mounting devices [15]. In medicine, PAs are important syntheticpolyamides for clinical use. Because of its high tensile strength, it is used as suture

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 3

Table

1Selectedtypesof

polyam

ides

[6–1

3]

(Co)

polya

mide

Nam

esMon

omer(s)

Formula

Nylon

3PA

3Poly[im

ino(1-ox

o-1,3-prop

anediyl)],po

ly(propano

-3-

lactam

),po

ly(β-alanine)

Propano

-3-lactam

[�NH(CH2) 2CO–]

n

Nylon

4PA

4Poly[im

ino(1-ox

o-1,4-bu

tanediyl)],po

lybu

tyrolactam

,po

lypy

rrolidinon

ePyrrolid

one

[�NH(CH2) 3CO–]

n

Nylon

6PA

6Poly[im

ino(1-ox

o-1,6-hexanediyl)],p

olycaprolactam

,po

lycaproamide

e-Caprolactam

[–NH(CH2) 5CO–]

n

Nylon

8PA

8Poly[im

ino(1-ox

o-1,8-octanediyl)],po

lycapryllactam

,po

ly(octano-8-lactam

)ω-Caprylolactam

[–NH(CH2) 7CO–]

n

Nylon

10PA

10Poly[im

ino(1-ox

o-1,10

-decanediyl)],po

ly(ω-

decanamide),p

oly(decano

-10-lactam

)10

-Aminod

ecanoicacid

ordecano

lactam

[–NH(CH2) 9CO–]

n

Nylon

11PA

11Poly[im

ino(1-ox

o-1,11-und

ecanediyl)],

polyun

decano

lactam

,polyu

ndecanoamide

11-A

minou

ndecanoicacid

[–NH(CH2) 10CO–]

n

Nylon

12PA

12Poly[im

ino(1-ox

o-1,12

-dod

ecanediyl)],

polylauryllactam

,polyd

odecanolactam,

polydo

decanamide

Laurolactam

[–NH(CH2) 11CO–]

n

Nylon

136

PA13

6Poly[im

ino-1,13

-tridecanediylim

ino(1,6-diox

o-1,6-

hexanediyl)]

1,13

-tridecanediam

ineþ

adipicacid

[–NH(CH2) 13NHCO

(CH2) 4CO–]

n

Nylon

46PA

46Poly[im

ino-1,4-bu

tanediylim

ino(1,6-diox

o-1,6-

hexanediyl)],p

oly(tetram

ethy

lene

adipam

ide)

1,4-Diaminob

utane

(tetramethy

lenediam

ine)

þadipicacid

[–NH(CH2) 4NHCO

(CH2) 4CO–]

n

Nylon

410

PA41

0Poly[im

ino-1,4-bu

tanediylim

ino(1,10

-dioxo

-1,10-

decanediyl)],p

oly(tetram

ethy

lene

sebacamide)

1,4-Diaminob

utane

(tetramethy

lenediam

ine)

þsebacicacid

[–NH(CH2) 4NHCO

(CH2) 8CO–]

n

Nylon

510

PA51

0Poly[im

ino-1,5-pentanediylim

ino(1,10

-dioxo

-1,10-

decanediyl)]

1,5-Diaminop

entane

(1,5-

pentanediamine)

þsebacicacid

[–NH(CH2) 5NHCO

(CH2) 8CO–]

n

Nylon

64PA

64Poly[im

ino-1,6-hexanediylim

ino(1,4-diox

o-1,4-

butanediyl)]

Hexam

ethy

lenediam

ineþ

succinicacid

[–NH(CH2) 6NHCO

(CH2) 2CO–]

n

(con

tinued)

4 M. Kyulavska et al.

Table

1(con

tinue

d)

(Co)

polya

mide

Nam

esMon

omer(s)

Formula

Nylon

66PA

66Poly[im

ino-1,6-hexanediylim

ino(1,6-diox

o-1,6-

hexanediyl],po

ly(hexam

ethy

lene

adipam

ide)

Hexam

ethy

lenediam

ineþ

adipicacid

[–NH(CH2) 6NHCO

(CH2) 4CO–]

n

Nylon

69PA

69Poly[im

ino-1,6-hexanediylim

ino(1,9-diox

o-1,9-

nonanediyl)],p

oly(hexamethy

lene

azelam

ide)

Hexam

ethy

lenediam

ineþ

azelicacid

[–NH(CH2) 6NHCO

(CH2) 7CO–]

n

Nylon

610

PA61

0Poly[im

ino-1,6-hexanediylim

ino(1,10

-dioxo

-1,10-

decanediyl)],p

oly(hexamethy

lene

sebacamide)

Hexam

ethy

lenediam

ineþ

sebacicacid

[–NH(CH2) 6NHCO

(CH2) 8CO–]

n

Nylon

612

PA61

2Poly[im

ino-1,6-hexanediylim

ino(1,12

-dioxo

-1,12-

dodecanediyl)],p

oly(hexamethy

lene

dodecanediam

ide)

Hexam

ethy

lenediam

ineþ

1,10

-decanedicarbox

ylicacid

(1,12-do

decanedioic

acid)

[–NH(CH2) 6NHCO

(CH2) 10CO–]

n

Nylon

1010

PA10

10

Poly[im

ino-1,10

-decanediylim

ino(1,10

-dioxo

-1,10-

decanediyl],po

ly(decam

ethy

lenesebacamide)

1,10

-Diaminod

ecane

(decam

ethy

lenediam

ine)

þsebacicacid

[–NH(CH2) 10NHCO

(CH2) 8CO–]

n

Nylon

1012

PA10

12

Poly[im

ino-1,10

-decanediylim

ino(1,12

-dioxo

-1,12-

dodecanediyl)],d

ecam

ethy

lenediam

inedo

decanedioic

acid

polymer

1,10

-Diaminod

ecane

(decam

ethy

lenediam

ine)

þ1,10

-decanedicarbox

ylicacid

(1,12-do

decanedioic

acid)

[–NH(CH2) 10NHCO

(CH2) 10CO–]

n

Nylon

1212

PA12

12

Poly[im

ino-1,12

-dod

ecanediylim

ino(1,12

-dioxo

-1,12-

dodecanediyl)],p

oly(do

decamethy

lene

dodecanediam

ide),d

odecanedioicacid,p

olym

erwith

1,12

-dod

ecanediamine

1,12

-Dod

ecanediamineþ

1,10

-decanedicarbox

ylicacid

(1,12-do

decanedioic

acid)

[–NH(CH2) 12NHCO

(CH2) 10CO–]

n

Nylon

6IPA

6IPoly[im

inocarbo

nyl-1,3-ph

enylenecarbo

nylim

ino-1,6-

hexanediyl),po

ly(hexam

ethy

lene

isop

hthalamide)

Hexam

ethy

lenediam

ineþ

isop

hthalic

acid

[–NH

(CH2) 6NHCOC6H4CO–]

n

Nylon

6TPoly(im

inocarbo

nyl-1,4-ph

enylenecarbo

nylim

ino-1,6-

hexanediyl),po

ly(hexam

ethy

lene

tereph

thalam

de)

Hexam

ethy

lenediam

ineþ

tereph

thalicacid

[–NH

(CH2) 6NHCOC6H4CO–]

n

Nylon

6(3)

T TMDT

Poly(trim

ethy

lhexamethy

lene

tereph

thalam

ide),1,4-

benzenedicarbo

xylic

acid,p

olym

erwith

2,2,4-

Trimethy

lhexam

ethy

lenediam

ineþ

tereph

thalic

acid

[–NHCH2C(CH3) 2CH2CH

(CH3)

(CH2) 2NHCOC6H4CO–]

n

(con

tinued)

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 5

Table

1(con

tinue

d)

(Co)

polya

mide

Nam

esMon

omer(s)

Formula

trim

ethy

l-1,6-hexanediam

ineand2,4,4-trim

ethy

l-1,6-

hexanediam

ine

Nylon

MXD

6,PA

RA

Poly[im

inom

ethy

lene-1,3-pheny

lenemethy

leneim

ino

(1,6-dioxo

-1,6-hexanediyl)],po

ly(m

-xyleneadipam

ide),

hexanedioicacid

polymer

with

1,3-

benzenedim

ethanamine

m-xylenediamineþ

adipicacid

[–NHCH2C6H4CH2NHCO

(CH2) 4CO–]

n

Para-

aram

idPPDT/

PPTA

Poly(im

ino-1,4-ph

enyleneiminocarbo

nyl-1,4-

phenylenecarbo

nyl),p

oly(

p-ph

enylene

tereph

thalam

ide)

p-Pheny

lenediam

ineþ

tereph

thalicacid

[–NHC6H4NHCOC6H4CO–]

n

MPDI

Poly(im

ino-1,3-ph

enyleneiminoterephthaloyl),po

ly(m

-ph

enylenetereph

thalam

ide)

m-Pheny

lenediam

ineþ

m-phthaloyl

chloride

[–NHC6H4NHCOC6H4CO–]

n

6 M. Kyulavska et al.

material, hemodialysis membranes, and vascular catheters. The balloons of inter-ventional catheters are typically made of PA 11 and PA 12 [16]. Recycling as wastemanagement, due to high dissemination of PAs, is the best option and is becomingincreasingly common with PA products. Thermoplastic PAs can be remelted andpelleted for reuse. The pellets are used, for example, for injection molding of vehiclecomponents. PAs can also be depolymerized to obtain the monomers from whichthey were originally produced [15, 3, 17].

Fully aromatic PAs are defined as homo- or copolyamides consisting of at least80 mol% aromatic monomer units. They have very high melting points and shownematic liquid crystalline behavior. Therefore, these materials are processed fromsolutions, in which the para-linked aramids exhibit lyotropic behavior, making themsuitable for high-strength fiber production. Typical examples are polyaramids basedon p-phenylenediamine and terephthalic acid (Kevlar®, Twaron®) and based on m-phenylenediamine and isophthalic acid (Nomex®). Aramids are used in moredemanding applications such as ropes and cables, tennis strings, hockey sticks (asa composites), snowboards, jet engine enclosures, brake and transmission frictionparts, and gaskets. Kevlar® is used to make bulletproof vests and puncture-resistantbicycle tires. Blends of Nomex® and Kevlar® are used to make fireproof clothingand fibers. Nomex® protects firefighters, race car drivers, and monster truck andtractor drivers from getting burned. It is worthy to mark that the global marketresearch and consulting company MarketsandMarkets, US recently announced thatthe global polyamide market was $22 billion in 2012 and is estimated to reach $27billion by 2018, growing at a compound annual growth rate of 3.2% from 2013 to2018. The high demand across the industries such as automotive industry, electricaland electronics, and consumer goods will increase the overall polyamide consump-tion [15, 18, 19].

In PAs, intermolecular interactions, which determine their properties, decreasewith an increasing length of polymer chain. Long-chain biobased polyamides suchas PA 11, PA 1010, and, to a lesser extent, PA 610 have lower density, lower waterabsorption but also significantly lower strength and stiffness, lower melting temper-ature (Tm), and continuous operating temperature than PA 6 [20]. In order to improvemechanical performance and thermal stability of long-chain biobased polyamides,different fillers, both synthetic and natural, can be used. Nanocomposites of PA 1010with montmorillonite prepared by intercalating polymerization, multiwalled carbonnanotubes-reinforced PA 1010 composites, and composites of PA 11 with nanoclayprepared by melt-compounding method had higher modulus of elasticity and onsettemperature of decomposition compared with neat polyamides. Also was reportedmajor increase of mechanical properties, hardness, friction, and wear properties ofPA 11 filled with 20 wt% of short glass fibers and copper or 6% of bronze powdersprocessed by extrusion followed by injection molding [21–24]. In the case of PAswith the highest performances as PA 6, PA 46, or PAs reinforced with glass fibers,their stiffness can compete with metals, so polyamides are often consideredto replace applications for metal [25]. However, all polyamides tend to absorbmoisture due to the amide moiety. Their moisture sensitivity requires an efficientdrying process. Insufficient drying will lead to splays and anesthetics marks on part

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 7

surfaces, as well as lower mechanical properties due to material degradation (heatand water lead to oxidation).

Biobased Polyamides: Synthesis, Properties, and Applications

Most of the currently used polymers come from crude oil and other fossil fuels, suchas natural gas and coal [26]. In recent years, rapid development of polymers fromrenewable sources has taken place. The most dynamic development in green poly-mers is provided for the polyhydroxyalkanoates (PHA). PHA’s production capacitywas small in 2016, but it is expected to triple by 2021. The second most dynamicdevelopment is expected for PAs (double by 2021) [27]. Global biobased productioncapacity in 2013 and current biobased carbon content of polyamides amounts to850,000 tonnes and 40% to 100%, respectively [28]. Generally, biobased poly-amides are polyamides fully or partially derived from renewable resources (Fig. 1)[29].

Biobased polymers are materials in which at least a part of the polymer is arenewable material. They are obtained by several methods: (i) from natural poly-mers, or chemical/physical modification of natural polymers; (ii) from a mixture ofbiobased molecules having similar functionalities that are converted from biomass;

Fig. 1 Polyamides entirely and partially derived from renewable resources

8 M. Kyulavska et al.

(iii) through the synthesis of biobased polymers via various polymerization path-ways of biobased monomers with tailored chemical structures [30].

Although there are many commercial biobased products obtained by chemical orphysical modification of nature polymers and it is a method of great environmentalimportance, however, it encounters many difficulties such as poor solubility of thesepolymers, hard to remove impurities, and diverse and undesirable chemical struc-tures that might influence their properties and applications. Currently, the last twomethods of production biobased polyamides are more promising. Very often on anindustry scale, those two routes are interconnected and their differentiation isdifficult (e.g., PA-based industrial products developed by DSM Engineering PlasticsCompany) [31].

Many different products based on plant oils and fats have been developed forvarious uses. They have, among others, great potential as an alternative resource forthe production of polymeric materials. Polyamides based on castor oil are the oldestman-made polymers from renewable raw materials (Fig. 2) [32–34].

In production of commercially available biobased polyamides, castor oil fromRicinus communis plant is used as a renewable feedstock. Ricinus communis is aunique natural material, which grows in tropical regions. It is grown in relativelypoor soil conditions, and its production does not compete with the food-chain.Among other industrial plant oils, castor oil exhibits unique chemical structure andproperties. Castor beans have an abnormally high oil content (from 40% to 60%) that

Fig. 2 Biobased acids from natural oils, fats, and biomass

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 9

consists mainly (90%) of the ricinoleic acid. The double bond and hydroxy group ofricinoleic acid provide different possibilities for chemical modifications [35, 36 ].Modifications can lead to building blocks such as sebacic acid, aminoundecane acid,or decamethylenediamine [37, 38].

PAs are mostly obtained by polycondensation of diamines with dicarboxylicacids, polycondensation of amino acids, or by ring-opening polymerization oflactams. Polyamide monomers are manufactured in different ways, most of whichare from crude oil, but more often also from biomass [4]. Polyamides can besynthesized in the following processes [39]:

– Polycondensation of diamines and dicarboxylic acids with elimination of water– Polycondensation of amino carboxylic acids as bifunctional monomers (e.

g., PA 11)– From biobased acid and petroleum-based amine (e.g., PA 410, PA 610) or from

both components obtained from biomass (e.g., PA 510, PA 1010)– Ring-opening polymerization of lactams (e.g., PA 4, PA 6, PA 66)

Polyamide 6 is one of the most widely used engineering thermoplastics and itsworld production scale is 4 million tonnes annually. PA 6 has high stiffness andstrength in dry conditions, high heat distortion temperature, toughness, excellentchemical resistance and electrical properties, good abrasion resistance, good pro-cessability, and high melting point of about 220 �C. The plasticization effectenhances PA 6’s impact toughness due to a drop of the glass transition temperature.Its disadvantage is the relatively high moisture absorption, which limits dimensionalstability, tensile strength, and stiffness in humid environment. PA 6 found applica-tions in the automotive, electrical, and consumer goods industries. This polymer isvery often used to replace metal in automotive parts where design flexibility as wellas temperature and chemical resistance are critical. PA 6 applications in automotivecomprise of manufacturing door handles, radiator grilles, airbag containers, air-intake manifolds, relay boxes, engine covers, etc.

Some of the main PA 6 producers are BASF SE, Germany (Ultramid B®,Capron®); DuPont (Zytel®, Maranyl B), RTP Co. US; Lanxess AG, Germany(Durethan®); Radici Group, DOMO Engineering Plastics GmbH; DSM EngineeringPlastics Company, the Netherlands (Akulon® and Novamid®); Toray Industries,Inc., Japan (Amilan®); EMS-Chemie Holding AG, Switzerland (Grilon®);Ube Industries Ltd., Japan; Solvay Group (Technyl®), Aquafil, Italy (Aquamid®);Azoty Tarnów, Poland (Tarnamid®); China Petrochemical DevelopmentCorporation, China; Radici Group (Radipol®), Hualon Corporation Vietnam;etc. [40–44]

Unlike most other polyamides, PA 6 is not a condensation polymer, but instead isformed by ring-opening polymerization. There is a patented method of PA 6synthesis by ring-opening polymerization of e-caprolactam produced by glucosefermentation from entirely renewable feedstocks as crops or sugar (Fig. 3) [45, 46].

The same biobased route can be applied to obtain PA 66. Likewise, glucosemay be used as feedstock to produce PA 4 by fermentation to glutamate, its

10 M. Kyulavska et al.

decarboxylation to γ-aminobutyric acid (GABA), which is then heated to produce 2-pyrrolidone, and finally by ring-opening polymerization of 2-pyrrolidone [37, 47].

Another biobased strategy for catalytic e-caprolactam production using cellulose-and hemicellulose-derived γ-valerolactone was also developed. The strategy is basedon a corn stover which is catalytically converted to γ-valerolactone. The γ-valerolactone is then upgraded to e-caprolactam as a reaction intermediate. Experi-mental studies showed high yields biomass to γ-valerolactone (41%) and γ-valerolactone to e-caprolactam (30%). Moreover, the biobased process proposed isdeveloped for commercial-scale production and it was evaluated as economicfriendly [48].

Polyamide 66 is valued for its good thermal and mechanical properties. It has amelting point of 265 �C, making it the second aliphatic polyamide having the highestmelting point. Moisture absorption according to ISO 1110 [49] is relatively high(8–9 wt%) but lower than that for PA 6 (10 wt%) and PA 46 (13 wt%) [50]. Thermalstability makes PA 66 suitable for industrial yarns, airbags, radial tires, and under-the-hood automotive applications such as specific applications as intake manifolds,engine covers or consumer goods as home mirrors, and door handles. PA 66 is thesecond largest aliphatic polyamide in the world production scale (3.4 million tonnesannually). At present, 55% of PA 66 production is used as fibers and the rest isapplied as engineering thermoplastics.

The important PA 66 manufacturers are DuPont (Zytel®, Maranyl A), Invista,BASF SE (Ultramid® A), DSM Engineering Plastics Company (Akulon® S), SolvayGroup (Technyl®), and Ascend Group, Thailand (Vydyne®), Akro-Plastic GmbH,Germany (Akromid® A), Lanxess AG (Durethan®), Honeywell International Inc.,US, etc. [51, 52]

The production of PA 66 involves the use of two monomers: adipic acid obtainedthrough fermentation of plant-oil or glucose and hexamethylenediamine (HMD),which can be readily obtained from biomass (Fig. 4) [53].

Commercially biobased routes from renewable feedstocks were developed toobtain the monomers for PA 66 production. Rennovia Inc., US biobased chemicalbrand, developed the first in world 100% biobased PA 66 (Rennlon™). Thiscompany makes from entirely renewable monomers, Rennlon adipic acid andRennlon hexamethylenediamine. The production of biobased adipic acid is alreadywell known, while production of biobased hexamethylenediamine from widelyavailable and renewable feedstocks, using proprietary chemical catalytic processtechnology, is completely new development platform process. The development of

Fig. 3 Polyamide 6

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 11

biobased HMD opens a unique ability to create technological breakthroughs in theproduction of biobased chemical products, with projected significant cost advan-tages versus products produced from petroleum-based feedstocks. As an example,production of biobased HMD costs for Rennovia Inc. 20–25% below that ofconventional petroleum-based HMD, with a significantly lower per-pound capitalcost. Additional benefits include a 50% reduction in greenhouse gas (GHG) emis-sions compared to conventional petroleum-derived HMD [54].

Polyamide 11 and polyamide 12 are suitable for extrusion and injection moldingapplications. The lower moisture absorption of PA 11 and PA 12 compared to PA 6and PA 66 provides better dimensional stability. Despite this, the market of PA 11and PA 12 are small. In contrast to traditional biobased polymers, biosourced PA 11and PA 12 exhibit excellent chemical resistance, superior durability and ageing,flexibility, gold impact, and thermal resistances. These properties are responsible fortheir commercial success despite the fact that the price is significantly higher than PA6 and PA 66. PA 11 and PA 12 are the materials of choice for applications wheresafety, durability, or reliability is critical. Transparent grades are also available,allowing high flexibility in terms of design and creation. PA 11 and PA 12 areused in automotive industry as fuel and fluid systems, fuel-resistant quick connec-tors, bearings for windshield wiper arms and other car parts, air brake tubing forheavy trucks, in electrical and electronic industry as high-performance cables, aswell as in oil and gas industries as hoses, pipes, and pump parts for the offshorepetroleum production industry, natural gas distribution networks, food packaging,precision moldings for engineering uses, medical articles and monofilaments forscreen fabrics and bristles, sports articles (e.g. ski boots), and (after blending withcarbon black or carbon fibers) antistatic housings for electrical switches, lamps, ormining equipment [40].

Polyamide 11 has been commercially available for over 60 years. PA 11 is the firstbiobased high-performance engineering polyamide. PA 11 is obtained by polymer-ization of 11-aminoundecanoic acid from entirely renewable resources (castorplants) produced mainly by Cathay Industrial Biotech Ltd. and also by AtoFinaCompany, US (Fig. 5).

Fig. 4 Polyamide 66

12 M. Kyulavska et al.

Ultrahigh-performance PA 11 resins is produced by Arkema S.A. (Rilsan® B),alloys or polyamide fine powders by Agiplast (AGIMID® PA 11/NYLON 11),Plastim Ltd., and Plastica S.p.a. Italy. PA 11 products, unlike other PAs, absorbvery little moisture. Thus, their moisture content does not influence its shockresistance. In addition, the PA 11 products have all good mechanical features ofpolyamides as tremendous toughness and durability in extreme environments andhigher temperatures. PA 11 has excellent self-lubricating properties, lack of hygro-scopicity (thus, its electrical properties are stable and it is widely used for electricalapplications such as insulators). PA 11 is physiologically inertness and used in foodprocessing machinery. All these features make PA 11 also ideal for 3D printing ofhighly durable parts [55–59].

Star-shaped PA 11 structures were obtained via one-pot copolycondensationof 11-aminoundecanoic acid with a multifunctional agent, either trifunctionalbishexamethylentriamine or tetrafunctional 2,2,6,6-tetra[(β-carboxyethylcy)clohexanone]. This copolycondensation of 11-aminoundecanoic acid with selectedmultifunctional comonomers provides a very convenient and industrially scalablemethod for the production of star-shaped PA 11 polymers containing a concentrationof star-type chains that can be tuned to yield the desired rheological and solid-stateproperties products [60].

Polyamide 12 shows performance similar to PA 11 and properties betweenpolyamide 6 and polyamide 66 and is produced by Arkema S.A. (Rilsamid® PA12), RTP Co., Bada Hispanaplast S.A., Spain (Badamid PA 12), Evonik IndustriesAG (Vestamid® L-Polyamide 12), EMS-Chemie Holding AG (Grilamid L) and UbeIndustries Ltd.

PA 12 can be derived from both petroleum and renewable sources. Petroleum-based monomer, laurolactam, has been used to manufacture PA 12 via ring-openingpolymerization most frequently with anionic initiators (Fig. 6).

100% biobased monomer has been used to manufacture PA 12 from 12-aminododecanoic acid derived from entirely renewable source (palm kernel oil) byone-step fermentation production. The monomer serves as an alternative to

Fig. 5 Polyamide 11

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 13

laurolactam and further to manufacture of high performance and biobased PA 12 bypolycondensation (Fig. 7).

The resulting biobased PA 12 shows the same outstanding properties as theconventional, petrobased one [61].

PA 12 has a lower amide group concentration than any other commerciallyavailable polyamides what affects its properties: absorbs very little moisture andhas an excellent resistance to chemicals including hydraulic fluids, oil, fuels, grease,salt water and solvents, dampens noise and vibration, the lowest melting point, buthas a superior flexibility and is highly processable. It is also characterized by highstrength, stiffness, strong resistance to cracking under stress, and an excellent long-term constant behavior. On the other hand, PA 12 is exceptionally strong even at verylow temperatures. PA 12 has a broad range of applications; it is mainly used for filmsfor packing material in the food industry and sterilized films and bags for use in thepharmaceutical and medical fields. It is also prepared as sheets and sintered powderfor coating metals. In the electronics field, it is used for covering cables and asinsulating material, while in the automobile industry, it is used to prepare oil- andgasoline-resistant tubes. In the cosmetic and personal care industries, it is used asbulking and opacifying agents in face and body powders, and skin creams. PA 12has also found applications in the textile industry and in the sports and leisure goods[61–66].

Until 1991, polyamide 1212 was commercially manufactured by DuPont by step-growth polymerization of 1,12-dodecanediamine and 1,12-dodecanedioic acid(DDDA) (Fig. 8). Currently, major manufacturers of PA 1212 are ANID Co. andCathay Industrial Biotech Ltd. (Terryl®).

Fig. 7 Polycondensation of 12-aminododecanoic acid

Fig. 6 Ring-opening polymerization of laurolactam

14 M. Kyulavska et al.

Properties, processing characteristics, and also applications of PA 1212 arevery similar to those of PA 11 and PA 12; however, it offers better shape retentionat elevated temperatures. The low water solubility of PA 1212 salt requires handlingat high pressure and temperature for the first prepolymerization step. For thepolycondensation step, both batch and continuous reactors can be applied. PA1212 and related products find applications as electric insulation in electrical engi-neering, constructional and antifriction materials, radio engineering, vehiclemanufacturing and aviation, oil extracting, instrument making, medical, and otherindustries [4, 67–70].

Polyamide 46 has the highest melting point (295 �C) of aliphatic polyamides.The symmetrical chain structure of this polycondensation copolymer leads to ahigh degree of crystallinity and a high speed of crystallization. These features givePA 46 a technical edge over other engineering plastics like PA 6 and PA 66, polyestersand polyphthalamides, and has therefore found numerous applications such as sur-face-mounted device components in which PA 46 is more resistant to high solderingtemperatures (electrical and electronic industry), chain tensioners in which the highcrystallinity results in excellent wear and fatigue behavior (automotive industry), gearwheels and bearings in which the combination of temperature, oil, and chemicalresistance, low friction and wear of PA 46 corresponds to the requirements (technicaluses). The worldwide manufacturer of PA 46 (Stanyl®) is DSM Engineering PlasticsCompany. Because of outstanding flow properties of PA 46 and its easier andconvenient processing, Stanyl® delivers economical and commercial benefits throughreduced cycle time and increased design freedom. By the proper combinationbetween the short 1,4-diaminobutane block and adipic acid, DSM EngineeringPlastics Company succeeded reducing of carbon dioxide (CO2) emission. The invest-ment is less than 1 € per g/km CO2 reduction (Fig. 9) [71–75].

Petroleum and biobased global adipic acid market is approximately $6 billion peryear, predicted to grow at 3–4% compound annual growth rate to 2022. Adipic acidis a key component of different polyamides production. Everyday products thatcontain adipic acid include clothing, footwear, furniture, carpets, automobile parts,and PA fabric. Recently, companies such as Verdezyne Inc., US, Rennovia Inc.,BioAmber Inc., US, Celexion LLC, US, and Genomatica, US have developed anddemonstrated production and recovery of biobased adipic acid at pilot scale throughfermentation of economically available plant oil or glucose, sourced by renewablefeedstocks. The invented processes are competitive comparing to petroleum

Fig. 8 Polyamide 1212

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 15

production of adipic acid in context to lower cost, employing sustainable, low carbonfootprint, environmentally friendly process technologies [76]. Stanyl® TW371 isheat-stabilized, wear and friction-modified PA 46 providing extra benefits in terms ofreduced CO2 emissions and improved fuel economy [71].

The typical applications of polyamide 410, polyamide 69, polyamide 610, andpolyamide 612 are bushings, cams, electrical connectors, industrial parts, tubings,rods, profiles, sheets, and extruded monofilaments for bristles (e.g., toothbrushes). Inparticular, PA 410 is used for a variety of demanding automotive and electricalapplications. PA 610 and PA 612 have better performance than PA 6, PA 66, PA 11,and PA 12, with respect to improved bend recovery and higher resistance againstdeformation under load in wet environment. The combination of stiffness, abrasionresistance, low moisture absorption, good dimensional stability, and good chemicalresistance enables the manufacturing of precision injection molding parts for theautomotive, electrical, and electronic industries. Pipes made of PA 612 are stiffer,have a higher resistance against burst, and exhibit slightly better chemical resistanceagainst fuel and lower oxygen permeability in comparison with PA 11 and PA 12.Ascend Group is manufactured PA 69 with the Vydyne® trade name [8, 77].

Long-chain polyamide 410 as EcoPaXX® is produced by DSM EngineeringPlastics Company from 1,4-diaminobutane obtained from biomass and sebacicacid obtained from castor oil [78] (Fig. 10).

It is unique combination of biobased and high-performance engineering plastic.This product possesses excellent high-temperature stiffness under moist conditionswith high melting point (highest of all biobased plastics) and high crystallization rate(typical for engineering plastics such as PA 66 and PA 46). Approximately, 70% ofthe polymer consists of building blocks derived from castor oil as a renewableresource. EcoPaXX® has been shown to be 100% carbon neutral from cradle togate, which means that the CO2, which is generated during the production process ofthe polymer, is fully compensated by the amount of CO2 absorbed in the growthphase of the castor beans [79, 80].

PA 410 can be modified by copolymerization of 1,4-diaminobutane, sebacic acid,and C36 dimerized fatty acid. Resulting polyamide 410/436 (76/24 mol/mol)

Fig. 9 Polyamide 46

16 M. Kyulavska et al.

copolymer possess better hydrophobicity, additional benefit is the increasedbiobased content (from 70 to 80 wt%) [81–84].

Polyamide 510 is produced by BASF SE, Cathay Industrial Biotech Ltd., China,and Evonik Industries AG. PA 510 has similar properties of PA 66. It is suitable forinjection and extrusion and possesses stable mechanical properties for automotiveapplications. Cathay Industrial Biotech Ltd. product line currently offers also newrenewable polyamides as PA 56 (45% renewable), PA 511 (31% renewable), PA 512,PA 513, and PA 514 (from 26 to 100% renewable) under the trade name Terryl™. PA510 dicarboxylic acid part is synthesized from castor oil, while 1,5-diaminopentaneis obtained from lysine (product of glucose fermentation). Thus, PA 510 is 100%biobased (Fig. 11) [29, 85–87].

Recently, pioneering studies have enabled 1,5-diaminopentane production fromsugar in engineered cells of the soil bacterium Corynebacterium glutamicum [88].These synthesize the desired chemical from the natural amino acid lysine throughheterologous expression of the Escherichia coli lysine decarboxylase CadA orLdcC. The production of a novel biobased polyamide PA 510 through an integrationof biological and chemical approaches was reported. First, systems metabolic engi-neering of Corynebacterium glutamicum was used to create an effective microbialcell factory for the production of 1,5-diaminopentane as the polymer building block.In this approach, a hyperproducer, with a high 1,5-diaminopentane yield of 41%

Fig. 11 Polyamide 510

Fig. 10 Polyamide 410

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 17

in shake flask culture was generated. Subsequent fed-batch production of Coryne-bacterium glutamicum DAP-16 allowed a molar yield of 50%, a productivity of 2.2gl�1 h�1, and a final titer of 88 gL�1. The streamlined producer accumulated 1,5-diaminopentane without generating any byproducts. Solvent extraction fromalkalized broth and two-step distillation provided highly pure 1,5-diaminopentane(99.8%), which was then directly accessible for polycondensation. Chemical poly-merization with sebacic acid, a C10 dicarboxylic acid derived from castor plant oil,yielded the biobased PA 510. In a pure form and reinforced with glass fibers, thenovel 100% biobased polyamide achieved an excellent Tm and the mechanicalstrength of the well-established petrochemical polymers (PA 6 and PA 66) [89].

The main producers of commercial polyamide PA 610 are Solvay Group (SpecialTechnyl® grades), Toray Industries, Inc. (Amilan®), Akro-Plastic GmbH (Akromid®

S), BASF SE (Ultramid® S Balance), RTP Co. (RTP 200 B), ANID Co., RussianFederation, Arkema S.A. (Hiprolon® 70), EMS-Chemie Holding AG (Grilamid 2S),Evonik Industries AG (Vestamid®), Terra HS DuPont, and Suzhou Hipro, China. PA610 is produced with about 70% of renewable-source content and carbon footprint4.6 kg CO2eq., which has recently met with a great interest (Fig. 12) [90–92].

PA 610 is synthesized from hexamethylenediamine readily obtained from bio-mass and sebacic acid on the base of castor oil. PA 610 combines high mechanicalproperties (characteristic such as of PA 6, PA 66, and PA 12) with low density andhigh chemical resistance (such as for PA 1010) [93]. Although, PA 610 can beprocessed like all common polyamides, the materials from this product family arefurther characterized by exceptional dimensional stability, good surface quality,good abrasion resistance wear behavior, and an improved carbon footprint. It isused in automotive sector (connectors, housings, nonreturn valves, power steering-fluid reservoirs), machine construction and tool building (gears, door handles,fittings, office equipment), and sports and leisure (components in high-end gardentools, bicycle accessories). Another important application of this polyamide is in aircleaners industry. The worldwide companies such as BASF SE, Robert BoschGmbH, Germany, Daimler AG, Germany, Mann þ Hummel Group, Germanyfocus its activities on this biobased polyamide for automotive applications. Inorder to improve mechanical performance and thermal stability of PA 610, differentfilters, both synthetic and natural, can be used [90–92].

Fig. 12 Polyamide 610

18 M. Kyulavska et al.

Polyamide 612 is supplied by Arkema S.A. (Hiprolon® 90) RTP Co. (RTP 200D), Evonik Industries AG (Vestamid® D), and DuPont (Zytel® 150 series). PA 612 isthe polycondensation product of hexamethylenediamine and 1,12-dodecanedioicacid obtained through fermentation of plant oil or glucose by EMS-Chemie HoldingAG (Grilamid® 2D) (Fig. 13) [94–96].

PA 612 is more than 62% biobased and possesses carbon footprint 4.6 kg CO2eq.Some yeasts, such as Candida tropicalis, can oxidize terminal aliphatic carbons tocarboxylic acids such as DDDA. Biotechnology offers an innovative way to over-come the limitations and disadvantages of the chemical processes, transforminglong-chain fatty acids readily available from renewable feedstock to long-chaindicarboxylic acids [97]. Verdezyne Inc. produced Biolon™ DDDA from renewablefeedstocks [98]. Although the carbonamide group concentration is slightly higherthan in PA 12, it is significantly lower than in PA 6 or PA 66. PA 612 is anotherspecial long-chain polyamide, designed for high added value applications requiringspecific performances. PA 612 is exclusively used for injection molding. Anotherbenefits of PA 612 are good UV and chemical resistance, excellent resistance togreases, oils, fuels, hydraulic fluids, water, alkalis, and salt solutions, excellentresistance to stress cracking, even when subjected to chemical attack and whenused to encapsulate metal parts, low sliding friction coefficient, and high abrasionresistance even under dry conditions. The advantages over PA 12 are higher heatdeflection temperature, higher tensile and flexural strength, and excellent reboundresilience combined with high wet strength. The excellent rebound resilience isadvantageous in the bristles of toothbrushes, as the high heat deflection temperaturesfor short-term temperature spikes occur, for example, in hydraulic clutch lines invehicles. This property also makes VESTAMID® D polyamide compounds suitablefor plastic-rubber composites, as in door lock casings, housing covers with seals, andseals for spark plug tubes [94–96, 99].

The Verdezyne Inc.'s feedstock strategy is the use of nonfood plant oils, soapstocks, and distillates and other oil coproducts, which under fermentation-basedproduction gives high quality products, mainly biobased succinic, adipic, sebacic,and dodecanedioic acids. Rennovia Inc. is also using renewable feedstocks. Theyproduced 270 Kta biobased adipic acid and more than 1500 Kta biobased hexa-methylenediamine by glucose fermentation [100]. Another leading and global man-ufacturer certified (ISO 9001:2008) of biobased sebacic acid production is Hebei

Fig. 13 Polyamide 612

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 19

Casda Biomaterials Co. Ltd., China. The Cathay Industrial Biotech Ltd. is also aworldwide company that developed bioprocess of long-chain diacids and greendiamines industrial production [101].

Polyamide 1010 produced by Arkema S.A. (major producer, Rilsan® T),DuPont (Zytel® PA1010), Evonik Industries AG (Vestamid® Terra DS andTEGOLON® ECO 10–10), Agiplast, Italy (Agimid® Polyamide 10.10/NYLON10.10), EMS-Chemie Holding AG (Grilamid® 1S), Bayer AG, Germany, and SuzhouHipro is a long-chain polyamide having properties similar to those of PA 11 and maybe used as alternative to high-performance polyamides such as PA 11, PA 12, and PA1212. PA 1010 is the polycondensation product of decamethylenediamine and 1,10-decanedoic diacid (sebacic acid). Both monomers are derived from castor oil, makingPA 1010 100% biobased polymer (Fig. 14) [102, 103].

PA 1010 exhibits excellent degree of rigidity (especially when reinforced withglass fiber), thermal stability, permeability to petrol and gas, and processability[104]. Various PA 1010 grades find applications in automotive (monolayer ormultilayer brake lines for trucks and fuel lines for cars), industrial pipes, cables,and injection molded parts for sports or electronics applications [105]. PA 1010 canbe used for cable jacketing, in optical fibers, toothbrush bristles, and in dish washersas a thermoplastic powder-coating material due to its low moisture uptake andexcellent resistance against hydrolysis. Zytel® PLUS is high-performance PAwhich resists aging in high-heat automotive engine parts. Zytel® HTN is used forapplications requiring stiffness, such as hand-held consumer electronics [106].TEGOLON® ECO 10-10 is the first purely plant-based PA 1010 powder withexcellent mattifying properties and compatibility, high oil absorption andhigh covering power, and can be used in cosmetic formulations. The CO2 footprintof PA 1010 is 4.0 kg CO2eq. A life-cycle assessment confirms that TEGOLON®

ECO 10-10’s carbon footprint is significantly lower compared to petrochemicalbased PAs [77, 92, 107–110].

Polyamide 1012 is an innovative long-chain polymer that contains monomerswhich can be obtained from castor oil, by this reason it could be defined as biobasedpolymer (Fig. 15).

The PA 1012 is between 45% and 100% biobased and it can be an alternative toPA 12 and PA 1212. Produced by Arkema S.A. (Hiprolon® 400 and Addibio®

Renew), Castello Italia srl, Italy, Evonik Industries AG (VESTAMID® Terra DD)

Fig. 14 Polyamide 1010

20 M. Kyulavska et al.

has carbon footprint 5.2 kg CO2eq. Its chemical characteristic is similar to those ofPA 11 and PA 12; due to this fact, the tubes of this copolymer are used in automotiveand industrial applications, since they offer very good dimensional stability, chem-ical, and mechanical resistances, flexibility, large working temperature interval, andvery low water absorption. In contrast to other semicrystalline polyamides, PA 1012can be processed to films with good transparency [92, 111, 112].

Polyamide 136 was successfully synthesized from 100% biobased monomers1,13-tridecanediamine and adipic acid (Fig.16). Melting temperature and glasstransition temperature are 206 �C and 60 �C, respectively, while the equilibriummelting temperature is 248 �C. Characterization of the crystallization kineticsshowed that PA 136 exhibits very fast crystallization compared to the industriallyimportant polyamides, PA 6 and PA 66. In addition, the moisture absorption of PA136 is much lower than PA 6 and PA 66 which is consistent with the much loweramide content of PA 136 [113, 114].

There are also other polyamides that could be made from plant oil derivatives[115, 116]. In Table 2, current biobased carbon content of biobased polyamides andproducers is summarized.

Polyamide “Inks” for 3D Printing

Three-dimensional (3D) printing (also additive manufacturing) in essence is theprocess of fabrication of 3D object by using CAD (computer aided design) file oranother electronic data source as design origin. In practice, by additive processes,

Fig. 15 Polyamide 1012

Fig. 16 Polyamide 136

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 21

successive layers of initial material (liquid, powder, paper, or polymers) are depos-ited under 3D printer computer program control. Thus, the two main improvementdirections are focused on the tooling with the relevant software and differentmaterials usage as starting point. There is a growing interest for laser sintering(LS) technology because it provides quick identification of design issues and easilyproduces durable complex parts with great mechanical properties [117, 118]. Find-ing the right material toward final application easily pass through investigation ofvariety of polymers such as polyamides, polyesters, poly(vinyl alcohol), poly(eth-ylene terephthalate), photopolymers, etc. One can say that polyamides are thereference materials in powder bed fusion processes like LS [119].

Arkema S.A. offers a comprehensive range of fine polyamide 11 powders forpowder bed fusion as Orgasol® and Rilsan® invent powders. Rilsan® is a high-performance polyamide 100% sourced from entirely renewable resources. Theyhave been specially developed for 3D printing, with good control of particle size

Table 2 Current biobased carbon content of biobased polyamides with producers of biobasedpolyamides (or their monomers).

Biobasedpolyamides

Current biobased carbon content(fraction of carbon derived frombiomass) [%] Companies

PA 6 100 DuPont, Solvay Group, Bayer AG, BASFSE, DSM Engineering Plastics Company,Toray Industries, Inc.

PA 11 100 AtoFina, Arkema S.A.

PA 12 100 Arkema S.A., Evonik Industries AG, RTPCo., Bada Hispanaplast S.A.

PA 46 56–70 DSM Engineering Plastics Company

PA 410 100 DSM Engineering Plastics Company

PA 56 47 BASF SE, Cathay Industrial Biotech Ltd.

PA 510 100 BASF SE, Cathay Industrial Biotech Ltd.

PA 511 36 BASF SE, Cathay Industrial Biotech Ltd.

PA 512 34–100 BASF SE, Cathay Industrial Biotech Ltd.

PA 513 32–100 BASF SE, Cathay Industrial Biotech Ltd.

PA 514 31–100 BASF SE, Cathay Industrial Biotech Ltd.

PA 66 100 DuPont, Rhodya, Bayer AG, BASF SE,DSM Engineering Plastics Company,Honeywell International Inc.

PA 610 >60 BASF SE, Evonik Industries AG, SolvayGroup, DuPont, Arkema S.A.

PA 612 >62 Evonik, Arkema S.A., RTP Co.

PA 1010 100 Bayer AG, Evonik Industries AG,DuPont, Arkema S.A.

PA 1012 46–100 DSM Engineering Plastics Company,Evonik Industries AG

PA 1212 Up to 100 EMS-Chemie Holding AG, ANID Co.

PA 136 100 Laboratory scale

22 M. Kyulavska et al.

and thermal properties, providing a very good processability in LS machines.Rilsan® invent parts display superior mechanical properties compared to PA 12,with outstanding impact resistance, higher ductility, and elasticity [120].

Polyamide 12 fine powders (Rilsamid®) is also used for 3D printing with fuseddeposition modeling (FDM). PA 12 parts built on a Fortus 3D production system arethe toughest in the industry, exhibiting 100–300% better elongation at break andsuperior fatigue resistance over any other additive manufacturing technology. PAoffers the best Z-axis lamination and highest impact strength of any FDM thermo-plastic, as well as excellent chemical resistance. FDM PA 12 is ideal for applicationsthat demand high fatigue endurance, including repetitive snap fits, and friction-fitinserts as aerospace and automotive applications. Arkema S.A. has a collaborationwith HP Inc., US (Multi Jet Fusion Open Platform is a new business model for theindustry). Their strategy is to design new materials and uncover diversity of newapplications. As an example, 3D-printed eyeglasses (which include both sunglassesand corrective-lens glasses) are made with selective laser sintering (SLS) 3D printingtechnology and polyamide 3D printing material [121, 122].

In the very recent years, polyamide 6 material opens up a new and broadopportunity for 3D printing and respective products fabricated. Key moment of theapplication of pointed material in 3D printing solutions is novel sintering approachesas SLS. Core technological advancement of using laser (highly condensed energy) isthe flexibility of shape creation just by beam focusing on the polyamide powder anddesired 3D object to be produced layer by layer. Sintering aspect was successfullytouched by others as Prodways Group, France while developing advanced LSprinters. PA 6 is used to have better heat-distortion stability compared to objectsmade of the previously used PA 12. Thus, by applying different sintering strategies,wide range of polymer powders could be used for design/tailoring of materials withunique even impossible to be created up to nowadays. Balance equilibrium/optimumbetween materials limits industrial needs and covering customer expectationsbecame quite achievable. Another key aspect is the mechanical properties asmechanical toughness, resistance combined with elasticity, and minor materialerosion (i.e., superior tribology behavior) with chemical resistivity [123, 124].

PA 6 has a lots of positives such as powder and phases not sintered in theproduction process, could be reused to a high degree, and it has good aestheticproperties (color and transparency) and close to unlimited time stability overdecades’ usage (what can be also disadvantage for environment). Industrial aspectsof PA 6 along with other polymers can be summarized as quite cost-effectiveexpressed due to manufacturing versatile/flexibility, energy-saving, superior manu-facturability with high productiveness. Moreover, also beneficial is the ability onproduced complex parts on a small volume having still competitive price anddevelopment cycle could be easily reduced. This fulfils all customer requirementsand expectations. And, last but not least, variety of opportunities for hybrid andcomposite materials is created by using 3D printing and polyamide as core additive.All result in a high interest and possible (even unforeseen ones) design applicationsin the areas of medical instruments and health care, aeronautics, automotive, sportsmanufacturing, and much more [123, 125–132].

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 23

Quite easily could be foreseen the industrial evolution in polymers manufacturingby replacement of injection molding process (characterized with huge annual capitalinvestment in tooling and their maintenance) with 3D printing solution starting fromprototypes to serial production. Expanded opportunities are also expressed by theworld’s first drone made almost entirely from 3D-printed parts (shown by Airbus onthe June 2016 Berlin air show) [123, 133, 134].

Biodegradation

Peptides or proteins, like all natural polymers, are susceptible to biodegradation.Polyamides contain the same amide moiety, but, due to the strong chain interactions(hydrogen bonds between molecular chains), less polarity than proteins and highcrystallinity are considered nonbiodegradable polymers. However, degradation ofPA homopolymers synthesized from amino acids or low-molar-mass polyamidesinto oligomers under the action of microorganisms (biodegradation) or isolatedenzymes (enzymatic degradation) has been described [135–140]. Bacterium-degraded monomers and their oligomers were also found [141]. It should be keptin mind that according to IUPAC terminology, biodegradable polymer is able toundergo chain scissions, resulting in a decrease of molar mass due to enzymaticprocess from the action of cells; however, in vitro activity of isolated enzymescannot be considered as biological activity. Despite the fact that biobased materialis composed or derived in whole or in part of biological products issued from thebiomass , it does not mean that the material is biodegradable [142, 143].

Certain aliphatic polyamides are susceptible to biodegradation by microorgan-isms (fungi or bacterium). Thermophilic bacteria with optimum growth at 55 �Cisolated from soil by enrichment culture technique at 60 �C found to degrade PA 12and PA 66. Biodegradation was assumed to be due to endogenous enzymatichydrolysis of amide bond [144]. Marine bacteria such as Bacillus cereus, Bacillussphericus, Vibrio furnisii, and Brevundimonas vesicularis were shown to degradePA 6 and PA 66 in mineral salt medium with the polymer as the carbon source at35 �C [145]. It has been shown that some white rot fungal strains degrade PA 66[146]. These strains produce some type of nonspecific peroxidase, which has founduse in the bioremediation of many types of environmental pollutants, which givessome possibility to use them for recycling of PA 66. Also, the lignolyticfungi Phanerochaete chrysosporium can cause degradation of PA 6, which isa direct analogue of biodegradable polyester – poly(e-caprolactone). The mechanismof polyamide biodegradation by fungi occurs by oxidation of the methylene groupadjacent to the nitrogen atom in the PA main chain with the peroxidase enzyme,and the obtained radical then undergoes a stepwise oxidation with releasingdegradation products [147]. Selected microorganisms which degrade polyamidesare presented in Table 3.

Biodegradation of high-molar-mass polyamides can be forced by introducingside groups such as hydroxy (�OH), carboxy (�C(O)OH), hydroxyalkyl,methyl (�CH3), benzyl (�CH2C6H5), and formyl (�CH(O)) moieties or ester

24 M. Kyulavska et al.

Table 3 Selected microorganisms degraded PA 6, PA 12, and PA 66

Polyamide Microorganisms Conditions Reference

Bacteria

PA 6 Bacillus cereus pH 7.5 temp. 35 �C, mineral saltmedium under submerged enrichmentconditions with the polymer as the solecarbon source, 31% molar massdecrease (Mn0 = 58,000), moietiesformed in 90 days: NHCHO, CH3, C(O)NH2, CHO, and COOH

[145]

Bacillus sphericus,Vibrio furnisii,Brevundimonasvesicularis

pH 7.5 temp. 35 �C, mineral saltmedium under submerged enrichmentconditions with the polymer as the solecarbon source, less than 10% molarmass decrease (Mn0 = 58,000), moietiesformed in 90 days: NHCHO, CH3, C(O)NH2, CHO, and COOH

[145]

Neighboring species toBacillus pallidus, strain26

pH 7.0, temp. 60 �C, molar massdecrease in 20 days (Mv0 = 39,000),strain 26 recognized an amide linkagebased on ω-amino acid

[148]

PA 12 Neighboring species toBacillus pallidus, strain26

pH 7.0, temp. 60 �C, molar massdecrease in 20 days (Mv0 = 41,000),strain 26 recognized an amide linkagebased on ω-amino acid

[148]

Geobacillusthermocatenulatus

pH 7.0, temp. 60 �C, 73% molar massdecrease in 20 days (Mv0 = 41,000)

[144]

PA 66 Geobacillusthermocatenulatus

pH 7.0, temp. 60 �C, 60% molar massdecrease in 20 days (Mv0 = 43,000)

[144]

Bacillus cereus pH 7.5, temp. 35 �C, mineral saltmedium under submerged enrichmentconditions with the polymer as the solecarbon source, 42% molar massdecrease (Mn0 = 55,000), moietiesformed in 90 days: NHCHO, CH3, C(O)NH2, CHO, and COOH

[145]

Bacillus sphericus,Vibrio furnisii,Brevundimonasvesicularis

pH 7.5, temp. 35 �C, mineral saltmedium under submerged enrichmentconditions with the polymer as the solecarbon source, less than 10% molarmass (Mn0 = 55,000), moieties formedin 90 days: NHCHO, CH3, C(O)NH2,CHO, and COOH

[145]

Fungi

PA 6 Phanerochaetechrysosporium

pH 6.25, temp. 30 �C, 50% molar massdecrease in 90 days (Mn0 = 16,900)

[149]

PA 66 Trametes versicolor Temp. 30 �C, nitrogen starvation, 68%molar mass decrease (Mw0 = 85,000),moieties formed in 20 days: CHO,NHCHO, CH3, and C(O)NH2,

[146]

(continued)

Biobased Polyamide Ecomaterials and Their Susceptibility to Biodegradation 25

linkage (–C(O)O–). Structural elements such as unsaturated moieties, straight alkanechains of longer than nine carbons, lower number of halogen substituents, and orthoor para substituents on a benzene ring reduce susceptibility to biodegradation. Alsolack of aromatic units, water solubility, or copolymerization promotes biodegrada-tion. Copolymers of polyamides with polyesters show better biodegradability[150–155].

Future of Polyamide Ecomaterials: Final Conclusion

Polymers are carbon-based materials. In natural ecosystem, carbon is part of thebiological life cycle, so it is important how carbon-based polymeric materials areadapted to the global carbon cycle. The conversion rate of biomass into fossilresources (petroleum-based materials) is in total imbalance with the rate at whichthey are consumed and renewed. This way, more CO2 is released than transformsinto fossil resources and carbon is not managed sustainably and ecologically.However, using annual renewable resources of crops or biomass as raw materialsfor polymer production, the rate at which CO2 is renewed equals its consumption,which is sustainable [156].

Annually, there is a growing number of green materials with low environmentalimpact. Development of environmentally friendly and sustainable production ofpolyamides from renewable feedstock is justified, since ecomaterials are becomingincreasingly important from the economic and ecological point of view. With thegrowth of the consumer markets, polyamide production is also growing. It isassumed that global polyamide market is growing 3% a year and is expected tocontinue at this rate to 2020, so the polyamide sector is an area of great potential forthe biobased industry [157].

Ecomaterials are not only biobased and reusable (recycling) materials but alsosustainable, energy-efficient, should minimize plastic waste, and first of all be (bio)degradable. Nonbiodegradable polymers, for what polyamides are considered, can

Table 3 (continued)

Polyamide Microorganisms Conditions Reference

degradation through oxidation byperoxidase

White rot fungi, IZU-154 Temp. 30 �C, nitrogen or carbonstarvation, 93% molar mass decrease in20 days (Mw0 = 85,000), CHO,NHCHO, CH3, and C(O)NH2,degradation through oxidation byperoxidase

[146]

Phanerochaetechrysosporium

Temp. 30 �C, nitrogen starvation, 86%molar mass decrease in 20 days(Mw0 = 85,000), CHO, NHCHO, CH3,and C(O)NH2, degradation throughoxidation by peroxidase

[146]

26 M. Kyulavska et al.

potentially be biodegradable if suitable microorganisms are found [149]. Microor-ganisms by adaptation can acquire completely new metabolic abilities towardxenobiotic compounds. Stimulated expansion of microorganisms’ diversity intovarious synthetic compounds is important in the context of environmental pollution,such as byproducts of PA production (factory waste). However, to find suitablemicroorganisms does not ensure that such a polymer will become susceptible toorganic recycling or will degrade in the environment. Nonetheless, biobased poly-amides have a future and should become widespread displacing those from petro-chemical sources [158, 159].

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