Amorphous Phase of PLA

The glass transition temperature (Tg) of amorphous PLA lies between 55 and 60°C [5, 19, 46, 47] and is a function of the PLA molecular weight and 

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The crystallization is induced by the diffusion of the acetone into the amorphous phase of PLA. The diffusion obeys a Pick type diffusion, as suggested by polarized optical photomicrograph measurements. The crystallization behavior is shown in Table 3.4. 

On the other hand, when the effects of aging on calcium sulfate-filled PLA composites were studied for 1 year under a normal environment, molecular, thermal, and viscoelastic properties showed that the performance of the PLA-calcium sulfate composites was maintained after aging [25]. The storage modulus of the samples actually increased after aging. The structural reorganization of the PLA material in terms of increase of local order in the amorphous phase of PLA was thought to be responsible for such behavior. 

At 871 and 756 cm" appear two bands that can be attributed to the amorphous and crystalline phases of PLA, respectively. The bands that appear below 300 cm" are mainly due to the CH3 torsion modes and the skeletal C-C torsions [7, 34-37]. 

PHBHHx in the PLA matrix improves the toughness and imparts ductility to the blends [132]. PHBHHx particles were dispersed in the amorphous phase of the PLA matrix below 20 wt% concentration. Good dispersion was associated with low interfacial energy between PLA and PHA. 

PLA 15 wt%/v HMW PCL, XRD peaks of PLA PCL occur at diffraction angles of 2 = 20.11° and 23.2°, which correspond to the crystal planes (101) and (200), respectively. As indicated from Table 4.1, a higher degree of crystallinity (Xc) is presented for PLA 15wt%/v HMW PCL as opposed to PLA 15wt%/v LMW PCL, which is ascribed to HMW PCL with moderate crystallinity relative to amorphous-phase-dominant PLA with low crystallinity. 

The TEM image of the MN-270-Pt nanocomposite after incorporation of pla-tinic acid is presented in Fig. 3.15. One can see that the material contains nanoparticles with a diameter exceeding 0.7 nm (the estimated resolution of the microscope). The mean particle diameter calculated from a particle size histogram is 1.6nm and standard deviation is 0.6 nm. Evidently, since HPS is a very hydrophobic matrix, Pt species do not dissipate within a polymer matrix but form well defined clusters. light colored areas in the TEM image indicate macropores. The XRD profile of this sample confirms the absence of the Pt-containing crystaUine phase, but suggests the presence of Pt amorphous scatterers. 

When taking into account that at 37°C, the total weight for the PHB films with MWs equal 350 500 and 1,000 kDa, and the PHBV film with MW equals 1,050 are invariable, a possible reason of the small increase in crystallinity is recrystallization described earlier for PLA [26], Recrystallization (or additional crystallization) happens in semicrystalline polymers where the crystallite portion can increase using polymer chains in adjoining amorphous phase [22]. 

Like other semi-crystalline polymers, the glass transition of PLA is influenced by physical aging [150], crystallinity, morphology, and impurities [151, 152]. Other properties of PLA such as the mechanical strength also depend on the morphology, crystallinity, and orientation. It was found by Wong et al. [153] that the orientation of the crystalline phase was always higher than that of the amorphous phase. 

SMP based on miscible blends of semicrystalline polymer/amorphous polymer was reported by the Mather research group, which included semicrystalline polymer/amorphous polymer such as polylactide (PLA)/poly vinylacetate (PVAc) blend [21,22], poly(vinylidene fluoride) (PVDF)/PVAc blend [23], and PVDF/polymethyl methacrylate (PMMA) blend [23]. These polymer blends are completely miscible at all compositions with a single, sharp glass transition temperature, while crystallization of PLA or PVDF is partially maintained and the degree of crystallinity, which controls the rubbery stiffness and the elasticity, can be tuned by the blend ratios. Tg of the blends are the critical temperatures for triggering shape recovery, while the crystalline phase of the semicrystalline PLA and PVDF serves well as a physical cross-linking site for elastic deformation above Tg, while still below T ,. 

Further, the thermal properties of PL A vary with crystal polymorphism. Similar to other semicrystalline polymers, PLA exhibits a three-phase structure, consisting of the crystal phase and two amorphous fractions which vitrify/devitrify in different temperature ranges [45]. Chain segments in the bulk amorphous phase... 

The Tg of the amorphous phase, composed of both PLA and PEG, served to select the Both Rf and R increased with increasing amount of the... 

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