PBAT (short for polybutylene adipate terephthalate) is a

biodegradable Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegrada ...

random

copolymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are som ...

, specifically a copolyester of

adipic acid Adipic acid or hexanedioic acid is the organic compound with the formula C6H10O4. It a white crystalline powder at standard temperature and pressure. From an industrial perspective, it is the most important dicarboxylic acid at about 2.5 billion ...

, 1,4-butanediol and

terephthalic acid Terephthalic acid is an organic compound with formula C6H4(CO2H)2. This white solid is a commodity chemical, used principally as a precursor to the polyester PET, used to make clothing and plastic bottles. Several million tons are produced annuall ...

. PBAT is produced by many different manufacturers and may be known by the brand names ecoflex'', ''Wango, Ecoworld, Eastar Bio, and Origo-Bi. It is also called poly(butylene adipate-co-terephthalate) and sometimes polybutyrate-adipate-terephthalate (a misnomer) or even just "polybutyrate". It is generally marketed as a fully biodegradable alternative to low-density polyethylene, having many similar properties including flexibility and resilience, allowing it to be used for many similar uses such as plastic bags and wraps. The structure is a random-block polymer consisting of butanediol–adipic acid and butanediol-terephthalic acid blocks.

History

Production of plastics for use in the industrial sector around the world makes up a very large market. PET (

polyethylene terephthalate Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in synthetic fibre, fibres for clothing, packaging, conta ...

) is one of the dominant plastics within this market. It is commonly used for bottles because it makes a rigid container that is very lightweight. However, because of the stability of PET, it is also highly resistant to biodegradation, posing a significant environmental problem because of the amount of PET produced, sold, used and thrown away on a daily basis. An estimated 30% of the world production of PET goes into making these plastic bottles and only from 15% to 35% is recycled; the rest usually end up in a landfill. This has stimulated research into polymers that function comparably to PET, but are

. As with all developments in the realm of materials there are several requirements for the 'ideal' material. For biodegradable plastics, they would be: cheap, renewable, easy to produce and eco-friendly. In addition to these, the polymer should be resistant enough to be functional, such as handling the strain of being put under pressure, and flexible so that it is easy to mold. There are no homopolymers that perfectly provide every one of these features. Therefore, researchers have turned their attention to

copolymers In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are som ...

: combinations of polymers that have chemical and mechanical properties that complement each other. This led to identifying poly(butylene adipate-co-terephthalate) (PBAT) as a potential copolymer for blending. PBAT is a random copolymer known for being flexible and tough. This makes it ideal for combination with other

polymers that have high

elastic modulus An elastic modulus (also known as modulus of elasticity (MOE)) is a quantity that describes an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. Definition The elastic modu ...

and strength, but are very

brittle A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. ...

. This allows for the production of blended copolymers that can replace industry-standard plastics with environmentally safe and biodegradable plastics that will harmlessly disappear in a short period of time.

Properties

PBAT is classified as a random copolymer due to its random structure. This also means that it cannot crystallize to any significant degree due to the absence of any kind of structural order. This leads to several physical properties: wide melting point, low

and stiffness, but high flexibility and toughness. The flexibility and toughness of this polymer makes it ideal for blending with another biodegradable polymer that is strong and rigid for bottle production. The drawback of this polymer is that if it has high flexibility and toughness, then it will not be strong and rigid. This makes it non-ideal for any situation in which a strong, rigid container is desired. An example of this would be transparent barriers, such as those made of plexiglass (

Poly(methyl methacrylate) Poly(methyl methacrylate) (PMMA) is a synthetic polymer derived from methyl methacrylate. It is a transparent thermoplastic, used as an engineering plastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and bran ...

), a transparent glass substitute. PBAT is fully biodegradable when composted due to the presence of butylene adipate groups. The high stability and mechanical properties come from the terephthalate portions. Does not degrade in marine and fresh water.

Preparation

PBAT is synthesized from the polymer of 1,4-butanediol and

and the polymer of

dimethyl terephthalate Dimethyl terephthalate (DMT) is an organic compound with the formula . It is the ester, diester formed from terephthalic acid and methanol. It is a white solid that melts to give a distillable colourless liquid. Production Dimethyl terephthalat ...

(DMT) with 1,4-butanediol. Adipic acid and 1,4-butanediol are polymerized to create their

polyester Polyester is a category of polymers that contain one or two ester linkages in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include some natura ...

(plus water). DMT and 1,4-butanediol are also reacted to form their polyester (plus

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

). This polyester is then added to the butylene adipic acid polyester by using tetrabutoxytitanium (TBOT) as a

transesterification Transesterification is the process of exchanging the organic functional group R″ of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst. Strong acids catalyze the r ...

catalyst; an overabundance of 1,4-butanediol influences chain lengths. The result is a copolymer of the two previously prepared polymers. This is a random copolymer, because there is no control on the

dispersity In chemistry, the dispersity is a measure of the heterogeneity of sizes of molecules or particles in a mixture. A collection of objects is called uniform if the objects have the same size, shape, or mass. A sample of objects that have an inconsi ...

of the

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

chain lengths or block structuring in the copolymerization reactions; repeat positions are not controlled. If A =

of adipic acid and B = polyester of DMT, each with 1,4-butanediol, then the chain structuring could look like any of these: AABABBABA or ABABAAAABB or ABABABBBBA; there is no selectivity for A and B reacting with themselves or each other.

Commercial sources

PBAT is produced commercially by

BASF BASF SE (), an initialism of its original name , is a European Multinational corporation, multinational company and the List of largest chemical producers, largest chemical producer in the world. Its headquarters are located in Ludwigshafen, Ge ...

under the trademark ecoflex and in a blend with poly(lactic acid) called ecovio, by Novamont as Origo-Bi and in a blend with starch called Mater-Bi, by Zhuhai Wango Chemical Co Ltd under the name Wango, by JinHui Zhaolong as Ecoworld and in a blend with starch called Ecowill, and by

Eastman Chemical Eastman Chemical Company is an American company primarily involved in the chemical industry. Once a subsidiary of Kodak, today it is an independent global specialty materials company that produces a broad range of advanced materials, chemicals an ...

as Eastar Bio. Furthermore, suppliers in China and other nations now produce PBAT. These companies include Zhejiang Biodegradable Advanced Material Co. Ltd, Dongguan Xinhai Environmental Protection Material Co., Ltd., Hangzhou Ruijiang Chemical Co., Ltd., and Jiangsu Torise Biomaterials Co., Ltd. in China as well as Green Chemical Co., Ltd. and WILLEAP in South Korea.

Current and future uses

PBAT is marketed commercially as a fully biodegradable plastic, with BASF's ecoflex showing 90% degradation after 80 days in testing. Particular applications that are highlighted by the manufacturers include cling wrap for

food packaging Food packaging is a packaging system specifically designed for food and represents one of the most important aspects among the processes involved in the food industry, as it provides protection from chemical, biological and physical alterations ...

, compostable plastic bags for gardening and agricultural use, and as water resistant coatings for other materials, as in paper cups. Due to its high flexibility and biodegradable nature, PBAT is also marketed as an additive for more rigid biodegradable plastics to impart flexibility while maintaining full biodegradability of the final blend. PBAT is already widely marketed and used for all of the above applications, but is also being investigated as a component in antimicrobial films. In such films, PBAT serves as the bulk of the film with the antimicrobial agent being incorporated during processing. The antimicrobial films would be used in food packaging to inhibit bacterial growth, helping to preserve food products safely.{{cite journal, author=Luis Bastarrachea , author2=Sumeet Dhawan , author3=Shyam S. Sablani , author4=Jae-Hyun Mah , author5=Dong-Hyun Kang , author6=Jinwen Zhang , author7=Juming Tang, title=Biodegradable Poly(butylene adipate-co-terephthalate) Films Incorporated with Nisin: Characterization and Effectiveness against Listeria innocua, journal=Journal of Food Science, year=2010, volume=75, issue=4, pages=E215–E224, url=http://www.bsyse.wsu.edu/tang/main/publications/pdfdocs/articles-published/tang184.pdf, access-date=14 February 2014, doi=10.1111/j.1750-3841.2010.01591.x, pmid=20546402

References

Polyesters Terephthalate esters