The effect of various clay nanoparticles and their synergy on the properties of polylactic acid for advanced applications

Abstract

The study investigates the effect of clay(s) on the properties of the poly (lactic acid) (PLA). Nanocomposites having 3% of clays (viz. halloysite, montmorillonite (MMT), and kaolin) were fabricated using melt mixing method. Furthermore, zinc borate was added into the PLA/Clay(s) nanocomposites with the aim of enhancing the properties of nanocomposites. Techniques such as the transmission electron microscopy (TEM), X-ray diffractogram (XRD), thermogravimetric analysis (TGA), rheology, and UL-94 were adopted. TEM was used to investigate the dispersion of the clays within the PLA polymer matrix. The incorporation of the MMT into PLA resulted into an intercalation and exfoliation of the nanoclay within the polymer matrix when compared with kaolin and halloysite clays. As the ZnB was not modified, its nanoparticles were found to be agglomerated into the PLA matrix. Furthermore, the synergy of the other clays with MMT seems to have formed intercalation and exfoliation, which seems to verify that MMT acted as a modifier for other clays within the PLA matrix. It was further observed that the presence of ZnB and clays such as halloysite, and kaolin clays resulted in immiscibility between the nanoparticles and the PLA matrix. According to the XRD, the incorporation of the MMT in the PLA systems acted as a steric hindrance; and as a result, crystallization was restricted, thus causing a reduction in the intact crystalline region. Thermal stability of the tubular halloysite clay-based nanocomposite was found to be higher when compared with the silicate clay-based nanocomposites (viz. MMT and kaolin). One can realize that the synergistic effects of the nanoclays showed better thermal stability than all the single clays reinforced PLA matrix. Additionally, the majority of the synergistic nanoparticles were found to have a high thermal stability when compared with single filler-based nanoparticles/polymer composites. Halloysite in the PLA/ZnB system improved the complex viscosity of the system more than all the clays systems and PLA due to a stable and tubular structure of the halloysite. Halloysite, and its synergy with the other clays seemed to dominate in terms of improving the flammability resistance of the PLA matrix with V-0 UL-94 rating. The pollutant removal efficacy was found to be depended on the filler-type. Fillers with stronger interaction with PLA resulted in poor adsorption properties due to limited accessibility to the available active sites.