**3.1. Physical‐chemical and mechanical characterization**

Polylactides have a glass transition (*T*g) value around 60°C. This characteristic point refers to a change in the mobility of amorphous chains. Hence, atactic homopolymer shows a value of 60°C, but crystalline homopolymers that have some restriction in the mobility of amorphous phase could present *T*g values up to 70°C depending on the thermal treatment used for crystallization [9, 10].

Isotactic polylactides (pure PLLA and PDLA have same properties) crystallize forming a homocrystal, which melts in the range of 160–190°C depending on the molecular mass and shows a crystallinity fraction around 35% [9]. This value is calculated using one of the different values for theoretic melting enthalpy extrapolated from experimental analysis by different researches, being the most common values 93.6 [11] and 106 J/g [12].

Depending on the crystallization conditions, PLLA can crystallize in α, β or γ polymorphs [13, 14]. The most common form usually is the orthorhombic α crystal [15], while trigonal β form is obtained under high drawing conditions and high temperatures [16, 17]. Besides, γ poly‐ morph is obtained through epitaxial crystallization on special substrates with organic sol‐ vents [18]. Recently, the existence of a α' crystal has been reported, which can be identified as a disordered α form, with the same 103 helical conformation but different lateral packing [19].

As with other enantiomeric polymers occurs [20], polylactides also form thermally stable crystals when 50–50 wt.% of PLLA and PDLA enantiomers are blended [21]. The formation of stereocomplex crystals is favored with low molecular mass [22, 23] or isothermal treatments above homocrystal melting [24, 25]. These crystals melt at 50°C above the homocrystals and their formation is favored if a pretreatment at temperatures above the melting temperature of α crystals is carried out. This pretreatment allows the formation of homocrystal nuclei and increases the crystallization rate of stereocomplex during the isothermal crystallization step [26].

In regard to the mechanical properties, PLAs display high tensile modulus (3 GPa [27]) and yield strength (50–70 MPa [28]) but low elongation at break (5–7%) that result in a brittle behavior of the material.
