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Issue 05/2016

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bioplasticsMAGAZINE_1605_

Basics Co-Polyester By:

Basics Co-Polyester By: Hans-Josef Endres, A. Siebert-Raths, Michael Thielen (ed.) Based on Chapter 4.1.2.2 of the book [1] PLA is a biobased polyester that enjoys already a significant role in the market. Besides PLA, several other polyesters can be generated from biogenic raw materials. In most cases, these polyesters are manufactured from a diol (bivalent alcohol: HO C n H m OH) and a dicarboxylic acid (HOOC-C n H m -HOOC) or from an ester generated from the diacids. Bivalent alcohols (BDO, PDO) The diol-components used for such polyesters are usually propanediols (PDO) such as 1,3-propanediol, or butanediols (BDO) such as 2,3-butanediol or 1,4-butanediol (Fig 1). In the past, 2,3-butanediol was generated exclusively petrochemically, even though it has been known for a long time that it can also be generated by fermentation. A wide variety of bacteria excrete butanediol as an end product. In principle, a wide spectrum of substrates can be used, such as hexoses, pentoses, sugar alcohols, glycerine, starch, cellulose hydrolysate, melasses, whey, and others. However, in order to economically generate 2,3-butanediol by fermentation further process optimizations are necessary. 1,4-butanediol can also be generated as bio- 1,4-butanediol from bio-based succinic acid by catalytic conversion. However, butanediol is usually generated on a petrochemical basis as an important base component for various polyesters, especially PBT. Until a few years ago, 1,3-propanediol (PDO) was generated exclusively on a petrochemical basis. The commercialization of a new conventional polyester (polypropylene terephthelate PPT), also known as polytrimethylene terephthelate (PTT) created increased demand for 1,3 propanediol. This also led to interest in the possibility of generating bio-based PDO (Bio- PDO). There is no single organism occurring in nature that can perform the entire synthesis from glucose to PDO. However, several enterobacteria and clostridia microorganisms can convert glycerine into PDO. The increase in biodiesel production in recent years has led to increasing availability of the biodiesel by-product glycerine and a drop in glycerine prices. Industrial crude glycerine significantly inhibits cell growth due to the salts released a) HO CH 2 CH 2 CH 2 OH 1,3 propanediol b) HO CH 2 CH 2 CH 2 CH 2 OH 1,4 butanediol OH OH c) H 3 C CH CH CH 3 2,3 butanediol Figure 1: propanediol (a) and butanediols (b,c) during transesterification, therefore it is necessary to use pure glycerine. However, such high-quality glycerines are too expensive as basic material for manufacturing PDO on an industrial scale [2, 3]. Other processes via glycerine showed to be too complicated and cost-prohibitive or simply not economical due to low throughputs and/or conversion rates. Therefore, DuPont together with Genencor developed a genetically modified organism capable of converting glucose from wet-milled corn in a single step into Bio-PDO as a feedstock material for manufacturing a renewably sourcedpolyester. During the fermentation process, the genetically engineered E. coli microorganism metabolizes the glucose, creating 1,3-propanediol in the presence of water, minerals, vitamins, and oxygen. An important focus in the development of commercially useable Bio-PDO fermentation processes is on establishing cost-efficient purification processes for isolating propanediol. Yet another current research field is the use of Bio-PDO in applications such as thermoplastic elastomers. Acid Components Aside from the bivalent alcohols described in the previous section, the most important monomer units used as copolymer building blocks for bioplastics are carboxyl acids, such as terephthalic acids, succinic acid (HOOC (CH 2 ) 2 COOH), and adipic acid (HOOC-(CH 2 ) 4 -COOH). In bio-polyesters the aliphatic alcohol components are mostly biogenic, i. e., of fermentative origin. However, the second reaction component is still a petrochemical based dicarboxylic acid, such as purified terephthalic acid (PTA) or terephthalic acid dimethylester (dimethyl terephthalate, DMT). Succinic acid as the second aliphatic copolymer component can already be manufactured biotechnologically on an R&D scale, based on starch, sugar, or glycerine. Currently, joint ventures e.g. between DSM and Roquette, or between BASF and Corbion, are developing and already offering fermentation-based succinic acid. Therephthalic acid (PTA) can also potentially be manufactured using bio-based feedstock such as xylene produced by depolymerization of lignin. Biopolyesters If terephthalic acid or dimethyl terephthalate are used as acid components besides bio-glycols, the resulting polyalkylene terephthalates are aliphatic-aromatic polyesters. By contrast, the polyesters made from aliphatic, petro- or biobased dicarboxylic acids and diols are entirely aliphatic biopolyesters. The polymerization processes correspond to those of the known petrochemical esters, such as PET or PBT. The detailed chemical structures of the most important aliphatic and aromatic bio-co- and terpolyesters are presented below. PTT (PTT = polytrimethylene-terephthalate-copolyester = aliphatic-aromatic copolyester made from terephthalic acid and bio-propanediol) is one representative example for the resulting basic structures of these bio-copolyesters. 60 bioplastics MAGAZINE [05/16] Vol. 11

Basics The polymerization processes are similar to the production of PET. PTT is commercially available under DuPont’s brandname Sorona and is used for textile fibers as well as injection moulding applications with high surface qualities [4]. Another polyester that shall not be dealt with here, as it has been reported abundantly in the recent past is PET. Bio-based PET can be produced by a polycondensation reaction of biobased monothylene glycol (MEG) and petrobased or potentially biobased PTA. In Fig. 3 the chemical constitution of PBAT (polybutylene-adipate-terephthalate = aliphaticaromatic terpolyester made from adipic acid, terephthalic acid and butane diol) is presented as another typical example of bio-copolyesters. A different approach for developing a fully biobased aromatic polyester involves the production of polyethylene furanoate (PEF) [5]. This is a promising new type of polyester developed specifically by Avantium Co. in collaboration with Mitsui and put on the market using the buzzword “yxy technology”. Here also, one of the polymer components is biobased MEG on the basis of bio-ethanol. The other component is biobased FuranDiCarboxylicAcid FDCA on the basis of methoxymethyl furfural (MMF) resp. hydroxymethylfurfural (HMF). The result is a new type of polymer, seemingly with a somewhat different property profile compared to bio-PET. First comments suggest that PEF has much better barrier properties for CO 2 , O 2 and H 2 O compared to PET and also has improved mechanical properties as well as better heat resistance. A similar path is being followed by DuPont Industrial Biosciences in cooperation Archer Daniels Midland (ADM). They have developed a method for producing furan dicarboxylic methyl ester (FDME) from fructose. FDME is a high-purity derivative of furandicarboxylic acid (FDCA). Utilizing FDME one of the first polymers under development is polytrimethylene furandicarboxylate (PTF) based on FDME and also DuPont’s Bio-PDO (1,3-propanediol). Other potential candidates for partially or completely bio-based polyesters are polybutylene succinate (PBS) and polybutylene-succinateadipate (PBSA). Currently, PBS is polymerized by a condensation process of succinic acid and 1,4-butandiol, both typically derived from maleic anhydride. Succinic acid and BDO can also be produced via different bio-routes (see above). The chemical structures of the most important bio-copolyesters and bio-terpolyesters are presented in more detail in Section 4.2.4 of the book [1]. These polyesters contain varying amounts of bio-based material components, depending on their composition and feedstock basis. At the same time, their biological degradability varies strongly. Therefore, there is no clear mechanism to distinguish between bio-polyesters and non bio-polyesters. Other examples of newly developed biopolyesters include polybutylene succinate-co-lactates (PBSL, GS Pla) by Mitsubishi Chemical Corp., and polyethylene isosorbide terephthalate (PEIT) by Roquette Frères. Isorbide can be obtained via acid catalyzed cyclic dehydration of sorbitol based on hydrogenated glucose or sucrose. References [1] Endres, H.-J.; Siebert-Raths, A.: Engineering Biopolymers, Carl Hanser- Publishers, 2011 [2] Witt, U.; Müller, R.J., Deckwer, W.-D.: Biodegradation of Polyester Copolymers containing aromatic compounds [3] Wolf, O. (Editor) et.al.:Techno-economic Feasibility of Largescale Production of Bio-Based Polymers in Europe. (=Technical Report EUR 22103 EN), Brüssels, 2005 [4] PTT for Automotive Air Outlet, bioplastics MAGAZINE issue 04/2011 [5] PEF, a biobased polyester with a great future, bioplastics MAGAZINE issue 04/2015 Glycerin HOOC Fermentation Glucose Fermentation (genetically modified microorganisms) Bio-Propanediol Bio-PDO BPDO Fermentation Glycerin Fermentation Glucose Fermentation (mixed culture) Glucose Figure 2: Fundamental approaches to generating bio-propanediol Therephthalic acid Butanediol (BDO) Adipic acid O COOH + HO (CH 2) 4 OH + HOOC (CH 2) 4 COOH O C C O (CH 2) 4 O C (CH 2) 4 Polybutylene adipate therephthalate (PBAT) Figure 3: Terpolyester synthesis of polybutylene adipate terephthalate (PBAT) O O C bioplastics MAGAZINE [05/16] Vol. 11 61

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