# Valorization of Agri-Food Waste into PHA and Bioplastics: From Waste Selection to Transformation
## 3 Production of Bioplastics from Volatile Fatty Acids
### Physico-Chemical Properties of Bioplastics and Their Applications
#### 3.3.2 Other Bioplastics  
(a) Poly(lactic acid) (PLA)  
PLA can be produced from renewable resources. The carbohydrates extracted from plants (lignocellulosic biomass [208]) or waste materials (brewer's spent grain [209]) are subjected to fermentation, resulting in the production of lactic acid [210]. Polysaccharides from the cell wall of lignocellulosic materials can be converted to fermentable sugars after going through pretreatment and hydrolysis steps [211]. For example, lactic acid can be produced from the fermentation of dextrose, which can be derived from plant starch by bacteria. Examples of agricultural products that are employed in the preparation of PLA include sugar cane, corn, and sugar beet [212]. Also, in their study, [PERSON] et al. obtained lactic acid from whey under controlled fermentation conditions, achieving lactose consumption levels of 94.6% [213]. It is semi-crystalline if the proportion of enantiomerically pure monomers exceeds 85-88%. At lower purities, the material is amorphous and exhibits a reduced melting temperature. Semi-crystalline PLA exhibits a melting temperature between 170 and 180 \({}^{\circ}\)C, with a glass transition temperature between 55 and 60 \({}^{\circ}\)C. Furthermore, the properties of PLA are contingent upon its molar mass. In accordance with their respective properties, amorphous, low-molecular-weight DL-PLA is employed in medical applications that necessitate drug release, where good degradability is a requisite. In contrast, high-molecular-weight L-PLA (>100,000 g/mol) is utilized in packaging applications where superior thermomechanical properties are paramount [214; 215]. In recent years, research has been conducted as part of the European InnOREX project with the objective of investigating its potential as a substitute for polypropylene [216]. Lactic acid, the monomer which is employed in the polymerization of PLA, can be obtained through either a chemical or a biotechnological process. The former is based on the reaction of acetaldehyde with hydrocyanic acid (HCN) to give lactonitrile, which can be hydrolyzed to lactic acid. Another type of reaction is based on the high-pressure reaction of acetaldehyde with carbon monoxide and water in the presence of sulphuric acid as a catalyst. This method of production has the disadvantage that the lactic acid produced is a mixture of D and L, optically inactive lactic acids [217; 218]. In contrast, biotechnological production is based on the fermentation of carbohydrate-rich substrates by microorganisms, resulting in the formation of optically active D(+) or L(+) enantiomers, which is an advantage over chemical production. The microorganisms employed are preferably thermophilic, capable of rapid and complete fermentation of inexpensive substrates with minimal nitrogenous nutrient supplementation. They thrive in conditions of low pH, exhibit minimal biomass production, and generate negligible by-products. The most utilized bacterial genera for production are _Lactobacillus_, _Carnot bacterium_, _Leuconostoc_, _Pedicococcus_, _Streptococcus_, _Tetragencococcus_, _Lactococcus_, _Vagococcus_, _Enterococcus_, and _Aerococccus_. However, it is also possible to employ fungal strains such as Rhizopus that are capable of producing L(+) lactic acid [219]. (b) Poly(butylene succinate) (PBS). PBS is predominantly produced by polycondensation of succinic acid (SA) and 1,4-butanediol (BDO). It can be produced either by monomers derived from petroleum sources or by biological (bacterial) fermentation [220]. Regarding biological synthesis, BioAmber Inc. started the commercialization of bio-based succinic acid in 2010. Then, in 2016, Novamont S.p.A. started the production of 1,4-butanediol from renewable resources [221]. PBS is a semi-crystalline polymer that exists in two crystalline forms, designated \(\alpha\) and \(\beta\).