**3. Techniques for the preparation and synthesis of biopolymers**

Due to biopolymers' biodegradability and substantially, their applications are environmentally friendly [30]. Biopolymers properties influence the shelf-life and the product's biodegradability. The possibility of increasing the strength of bio-polymers and bio-composites have been studied without decreasing the biodegradability [31].

Poly (butylene succinate-co-butylene terephthalate) co-polyesters have much better thermal stabilities in nitrogen compare to air [32]. It was reported that "Poly(butylene succinateco- ethylene succinate-co-ethylene terephthalate)"can be polymerized from three pre-polymers of ethylene succinate, butylene succinate, and ethylene terephthalate by direct poly-condensation [33]. An ideal random copolymer (Poly(butylene terephthalate-succinate-adipate) from aliphatic units (BA and BS) has a rubber-like tenacity curve [34]. Aliphatic aromatic copolyester (AAC) could potentially modify the basic BTA (1,4-butanediol, adipic acid, and terephthalic acid) structure and may become commercialized [35, 36]. Development of biodegradable aliphatic-aromatic co-polyesters began with the study of different modes of degradation [37, 38]. Aliphatic biopolymers are biodegradable and sensitive to hydrolysis; their flexible chain fits easily into the active site of an enzyme [39]. Aromatic biopolymers have favorable physical properties such as resistance to bacterial, fungal and hydrolysis attack [40] but degrade if they are co-polymerized with aliphatic bio-polymers [41]; breaking down by means of hydrolytic or/and enzyme degradation [42]. It was reported that inclusion and/or incorporation of aromatic monomer groups in the aliphatic polyesters' main chain, can potentially enhance their mechanical properties [43]. The randomness and the length of the polymer chains aid in understanding the biodegradation behavior for aliphatic-aromatic co-polyesters [44]. Polyester-based nano-particulates could be easily prepared by solvents diffusion or evaporation methods. The degradability of the oligomers would decrease by increasing chain length [45], thus the amorphous part of the polymer would become that which is degraded [46].
