Isothermal Crystallization Kinetics of Poly(lactic acid) Stereocomplex/Graphene Nanocomposites

Abstract

The isothermal crystallization kinetics of PLA stereocomplex (scPLA) and scPLA/graphene oxide nanocomposites was investigated. scPLA was prepared by symmetric blending the two isomers, PLLA and PDLA and the scPLA nanocomposite by polymerization of the respective lactides in presence of commercial graphene oxide nanoplatelets (GNPO + ) followed of blending the two composites. The effect of the filler on the crystallization behavior and thermal properties of scPLA was investigated by using differential scanning calorimetry (DSC). Avrami equation was used to describe the isothermal crystallization kinetics and melting behavior. Addition of 0.5 wt% GNPO + to PLA matrix increases the crystallization rate, lowering the half-time of crystallization t 1/2 to around 5.5 min for scPLA nanocomposites, which is about 2.7 min below that found for scPLA when isothermally crystallized at 165ºC. During the isothermal crystallization, homochiral and stereocomplex crystals are formed, depending on the crystallization temperature. As crystallization temperature reaches 160 and 165ºC, the crystallization of homocrystals become prevented and only stereocomplex crystals are formed.

Development of Stereocomplex Polylactide Nanocomposites as an Advanced Class of Biomaterials—A Review

“…Specific properties can be conferred to stereo-nano PLA depending on the type of nanoparticles used. Some nanoparticles work as nucleating agents to improve the crystallinity of PLA, in turn enhancing its mechanical and thermal properties [ 89 , 90 , 91 , 92 , 94 , 99 , 100 , 101 , 102 , 126 , 127 , 130 ]. PDLA grafted onto lignin supports the formation of s-PLA crystallites, improves lignin dispersion, accelerates the crystallization rate, and results in the greater hydrolysis resistance of PLLA/PDLA blends [ 130 ].…”

“…In crystallization studies, the presence of graphene oxide lowers the crystallization activation energy of s-PLA crystallites, reduces chain mobility and hinders crystal growth as a consequence of the exfoliation of graphene oxide sheets [ 89 ]. The presence of graphene oxide nanoplatelets accelerates the crystallization time by 2.7 min compared to the half-time crystallization of s-PLA [ 92 ]. The D-lactide chains on graphene nanoplatelets promote the formation of s-PLA crystallites at the interface of the PLLA matrix and exhibit a synchronous enhancement in thermal conductivity, heat distortion temperature, and mechanical properties [ 125 ].…”

Thermal performances and optical property of poly(L-lactic acid) under the influence of N,N'-dodecanedioic bis(3-phenylpropionic acid) dihydrazide as a crys­tal­lization promoter

“…And the current typical nucleating agents include talc [12,13], montmorillonite [14,15], silicon dioxide [16], calcium carbonate [17,18], phenylphosphonate metals [19,20], metallic phenylmalonate salts [21], 1H-benzotriazole derivatives [22,23], benzoyl hydrazine derivatives [24,25], etc. For examples, upon the addition of 0.5 wt % commercial graphene oxide nanoplatelets, the half-time of crystallization of the PLA stereocomplex lower to around 5.5 min at 165°C [26]. Even then, the current nucleating agents for PLLA are still not able to meet the commercial requirements.…”