530

34 Agri and Food Waste Valorization Through the Production of Biochemicals and Packaging Materials

34.7.4.2

Copolymerization

It is a process of synthesizing new compounds (copolymers) using different

types of monomers. The copolymers are also called as biopolymers. PLA was

copolymerized with glycolic acid, caprolactone, [113] and D,L-lactide to synthesize

poly(lactic-co-glycolic acid) (PLGA), PCL, PLA and poly(ethylene glycol) (PEG)

copolymers [114], respectively. The work indicated that the rates of drug release and

biodegradation of copolymer could be tailored by adjusting polymer composition.

The material was suggested to have medical applications as biodegradable sutures.

Bigg [115] copolymerized PLA with PET to produce flexible, tough and clear

fibers/films.

34.7.4.3

Green Composites

Green composites are fabricated using bioplastics and the fibers extracted from nat-

ural resources. The natural fibers can be divided into three categories: plant fibers

(jute, coir, husk, bamboo, palm leaf, etc.), animal fibers (silk, wool and hair) and

mineral fiber (asbestos). The green composites are the best example to fulfill the

concept of valorization of AFW for food packaging as the fibers required for com-

posites formation are mostly derived from unutilized or discarded materials. The

reason behind imparting reinforcement to bioplastic by fiber is the presence of uni-

directional cellulose microfibril in the matrix of lignin and hemicellulose [116]. The

natural fibers improve the mechanical properties and provide several environmen-

tal benign characters to composites. These fibers are easily available, can be recy-

cled, decomposed without any toxic emission and keep the composite lightweight

because of their low-density property. Purkayastha et al. [117] developed fluores-

cent carbonaceous nanoparticles (FCDs) from the “end-of-pipe” (spent material) of

oilseed-press cake. The protein was extracted from the oilseed-press cake and the

environmental-friendly method was used to convert the remaining fibrous mate-

rial into composites. Banana fibers and stem wastes have been used to increase the

water absorption capacity and improve the impact strength of epoxy materials and

polyvinyl composites [118] and hence can be thought of to have polymer-reinforcing

capacities. Hammajam et al. [119] studied the importance of chemical treatment on

the natural fiber (millet fiber) to form green composites and its degradability in the

municipal soil. The alkalization of millet fiber enhanced its mechanical property

and reduces the rate of degradation. Wahit et al. [120] reviewed, in detail, the use of

natural fibers such as ramie, hemp, bagasse, rice husk, palm, wood and flax in the

preparation of PLA and PCL composites to enhance their mechanical properties.

In today’s time of nanoscience and technology, the composite matrix has also been

incorporated with nanoparticles (<100 nm) to drastically improve its mechanical

property, toughness, electrical and thermal conductivity [121]. There are several

film-making techniques where modifications were done to make nanocomposites

like injection molding [122]. Extrusion was followed by injection molding [123],

melt compounding followed by compression molding [99], direct melting and solid-

ification [124], solution casting after gelatinization [125] and one-step in situ inter-

calative solution polymerization [126]. The in situ polymerization method is mostly

preferred because of facile processing of material and better performance of product.