PBS was exclusively derived from petroleum‐based monomers, but since more recently the monomers can also be obtained by the bacterial fermentation route to produce fully bio‐based polybutylene succinate (bio‐PBS) [29, 55]. So far succinic acid has been mainly produced by electrochemical synthesis due to the high yield, low cost, high purity of the final product, and very low or no waste formation [56]. However, the production of succinic acid by bacterial fermentation uses renewable resources and consumes less energy compared to chemical process. For this reason, companies such as Corbion (Geleen, the Netherlands) and BASF are working on the scaling up of an economically feasible bio‐based succinate production process, despite the fact that these processes have traditionally suffered from poor productivity and high downstream processing costs. Other examples are the development of a biomass‐derived succinic acid production by Mitsubishi Chemical (Tokyo, Japan) in collaboration with Ajinomoto (Tokyo, Japan) to commercialize bio‐PBS or the development of a commercially feasible fermentation process for the production of succinic acid, 1,4‐butanediol, and the subsequent production of PBS by DSM (Heerlen, the Netherlands) and Roquette (Lestrem, France). Myriant (Quincy, USA) and Bioamber (Plymouth, USA) have also developed a fermentation technology to produce the monomers [57, 58]. Thus, in 2015, the annual production capacity of bio‐based succinic acid reached 200 000 tons [59]. In the case of 1,4‐butanediol, conventional production processes use fossil fuel feedstocks, such as acetylene and formaldehyde. Nevertheless, the bio‐based process to obtain the diol involves the use of glucose from renewable resources to produce succinic acid followed by a chemical reduction to produce butanediol [29]. PBS with excellent mechanical properties and processing capabilities can be then produced from the renewable monomers by transesterification, direct polymerization, and condensation polymerization reactions followed by chain extension and lipase‐catalyzed synthesis.
PBS is a semicrystalline aliphatic polyester with a good melt processability and balanced mechanical properties, closely comparable to those of PP. It is tougher than PLA and it shows similar thermal behavior than LDPE and a melting point lower than that of PLA [29, 60]. Its thermal and mechanical properties highly depend on the crystal structure and the degree of crystallinity [61]. The Tg and Tm are approximately −32 and 115 °C, respectively. In terms of mechanical properties, PBS has a good tensile and impact strength with moderate rigidity and hardness [29]. PBS has a wide processing window, which makes the resin suitable for extrusion, injection molding, thermoforming, fiber spinning, and film blowing. PBS has been employed as film, in foaming, and in food packaging containers [60]. However, the relatively poor mechanical flexibility of PBS limits the applications of 100% PBS‐based products. This issue can be overcome by blending PBS with other biopolymers and fillers to improve the mechanical properties to suit the required application and biodegradation rate [62–65]. The development of PBS copolymers can also lead to biopolymers with a decreased degree of crystallinity, depressed heat distortion temperature, and improved elongation [56, 66]. Copolymerization is achieved by adding a third monomer such as sebacic acid, adipic acid, terephthalic acid, succinic acid with substituted side groups, 1,3‐propanediol, and other substituted glycols, which can be also produced from renewable resources. Poly(butylene succinate‐co‐terephthalate) (PBST) and poly(butylene succinate‐co‐adipate) (PBSA) are the most employed copolymers, PBSA being the most common for flexible packaging applications. Additionally, the flexibility of the PBS backbone and the presence of readily hydrolyzable ester bonds, which are prone to catalytic degradation by microorganisms or enzymes, promote rapid degradation process of the PBS copolyesters [67]. Some studies have evaluated the biodegradability of biodegradable polymers in the mature compost soil and found that the biodegradability of PBS was slower than that of PBSA in compost soil [68]. However, the results of enzymatic hydrolysis as well as environmental degradation of PBS are highly dependent on the environment, the composition of the PBS grade, and its compound [55].
1.3.5 Bio‐based Polyethylene
Bio‐based polyethylene (bio‐PE), also called “microbial” or “green” polyethylene, can be produced by the catalytic dehydration of bioethanol obtained by microbial fermentation, followed by normal polymerization to produce polyethylene (PE) [69, 70]. Bio‐PE is not biodegradable and has the same properties as PE made from natural gas or oil feedstocks [29]. Conventional PE is manufactured by polymerization of ethylene under pressure, temperature, in the presence of a catalyst. Traditionally, ethylene is produced through steam cracking of naphtha or heavy oils or ethanol dehydration. However, the concept of producing PE from bioethanol is not particularly new. In the 1980s, Braskem (São Paulo, Brazil) had already made bio‐PE from bioethanol, however, the limitations of the biotechnology processes made the technology unattractive at that time [71]. Currently, bio‐PE produced on an industrial scale from bioethanol is derived from renewable feedstocks, including sugarcane and beet, starch crops such as maize, wood, wheat, corn, and other plant wastes through microbial strain and biological fermentation process. In a typical process, extracted sugarcane juice with high sucrose content is anaerobically fermented to produce ethanol. At the end of the fermentation process, ethanol is distilled in order to remove water and to yield an azeotropic mixture of hydrous ethanol. Ethanol is then dehydrated at high temperatures over a solid catalyst to produce ethylene and, subsequently, bio‐PE [69, 72]. Figure 1.4 shows a schematic flow diagram of the bio‐PE production.
Figure 1.4 Schematic flow diagram of the production of bio‐based polyethylene (bio-PE) from sugarcane via fermentation into ethanol and subsequent dehydration into ethylene.
Source: From Koopmans [73]. © 2013, John Wiley & Sons.
Braskem is the largest producer of bio‐PE, mainly bio-based high-density polyethylene (bio-HDPE), with 52% market share, with an annual production capacity of 200 000 tons per year made from ethanol obtained from sugarcane [71] and this is the first certified bio‐PE in the world. Similarly, Braskem is developing other bio‐based polymers such as bio‐based polyvinyl chloride (bio‐PVP), bio‐based polypropylene (bio‐PP), and their copolymers with similar industrial technologies. Braskem's current bio‐based PE grades are mainly targeted toward food packaging, cosmetics, personal care, automotive parts, and toys. Dow Chemical (Midland, USA) in cooperation with Crystalsev (São Paulo, Brazil) is the second largest producer of bio‐PE, having 12% market share. Solvay (Brussels, Belgium), another producer of bio‐PE, has 10% share in the current market. However, Solvay is a leader in the production of bio‐PVC with similar industrial technologies. China Petrochemical Corporation (Pekin, China) also plans to set up production facilities in China to produce bio‐PE from bioethanol [74]. LyondellBasell (Rotterdam, The Netherlands) and Neste (Espoo, Finland) have recently announced the first parallel production of bio‐PP and bio‐based low‐density polyethylene (bio‐LDPE) at a commercial scale, being marketed under the trade names Circulen and Circulen Plus [75].
Bio‐PE can replace all the packaging applications of current fossil derived PE because of its low price, good lifetime performance, and especially recyclability [75]. The price of bio‐PE is currently about 50% higher as compared with petrochemical PE, but it will take advantage from the scale‐economy. Current upcoming applications by multinationals include yogurt cups produced by Danone (Paris, France), fruit juice bottles by Odwalla (Atlanta, USA), and plastic caps and closures for aseptic paperboard cartons by Tetra Pak (Lund, Sweden) [76].
1.3.6 Bio‐based Polyethylene Terephthalate
PET is a copolymer of monoethylene glycol (MEG) and terephthalic acid, and one of the most studied polymers to be transformed in commercial bio‐based plastics, which can be derived from plant‐based sugars and agricultural residues. This interest gave life to a technological collaboration between several companies, such as Coca‐Cola (Atlanta, USA), Ford (Detroit, USA), Heinz (Sharpsburg, USA),