Crystallization Behavior of Poly(lactic acid)/Titanium Dioxide Nanocomposites

Abstract

In this study, a poly(lactic acid) (PLA) with various titanium dioxide (TiO 2) nanoparticles loading were prepared by a manual laboratory mixing method. The effect of TiO 2 nanoparticles on the non-isothermal and the isothermal crystallization behavior of PLA was investigated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The presence of TiO 2 nanoparticles decreased the spherulite growth rate of PLA, whereas it initiated faster crystallization through the heterogeneous nucleation process as observed by optical microscopy. The results of DSC analyzes confirmed that the TiO 2 nanoparticles act as an efficient nucleating agent for PLA crystallization. The cold crystallization temperature and crystallization half-time of PLA decreased, while the degree of crystallinity of PLA increased in relation to increases of TiO 2 nanoparticles.

Thermal transitions and stability of melt mixed TiO2/Poly(L‐lactic acid) nanocomposites

“…According to Table , the melting enthalpy of PLLA phase follows the same pattern with the exothermic enthalpy of cold crystallization, suggesting that the crystallinity of the polymer mainly originates from the cold crystallization process. The crystallinity formed during the cooling cycle of all materials is low, ranging from 0 to 3.6%, but it slightly increases with TiO 2 content, implying that TiO 2 nanoparticles promote the crystallization process of PLLA during cooling . The crystallinity formed during cold crystallization ( X cc ) of PLLA matrix in nanocomposites is lower than that of pure PLLA and slightly increases with the increase of TiO 2 loading.…”

“…Polylactic acid (PLA) is a semicrystalline aliphatic polyester that draws attention as a biocompatible and biodegradable material with many medical and tissue engineering applications, including controlled‐release systems, medium or long‐term implants and scaffolds . This polymer shows very interesting characteristics, including high mechanical strength and modulus, excellent thermoforming ability, and capability of maintaining good mechanical integrity until degraded .…”

“…The incorporation of reinforcing fillers is an efficient method to improve physical properties and yet control PLA's thermal and mechanical performance . Such fillers and nanofillers are silica, graphite and graphene oxide, modified and unmodified clays, nanotubes and titanium dioxide (TiO 2 ) and can be incorporated by employing various techniques (e.g., in situ polymerization, solvent casting or melt‐mixing methods) . TiO 2 belongs to the family of transition metal oxides .…”

“…When irradiated with ultraviolet (UV) light, TiO 2 can act as a photocatalyst . Its versatility (due to photo‐catalytic activity, innate ability to join with human bone, properties of enhancing cell attachment and proliferation, antibacterial, antiviral and antifungal activity, as well as UV sensitivity) , makes it a very promising candidate as an inorganic nanostructured filler for thermoplastic polymeric matrices. In fact, it has already been used in orthopedic titanium rods, pins and plates, scaffolds for bone tissue engineering, drug delivery systems and devices with antibacterial properties .…”

“…The aforementioned properties have intrigued a number of studies, dedicated to examining the effectiveness of TiO 2 in the adjustment of PLLA's crystallization performance, necessary for numerous biomedical applications. Nomai et al studied the isothermal crystallization kinetics of PLA and PLA/TiO 2 nanocomposite films with 1, 2, and 4 vol% of TiO 2 , using optical microscopy and Differential scanning calorimetry (DSC). They reported that the decrease of crystallinity of PLA after processing, can partially be eliminated by the addition of nanosized TiO 2 .…”