Abstract:The reduction of polylactide acid (PLA) molecular weight for amorphous and semicrystalline grade nanocomposites with 5 wt% load of organomodified montmorillonite Cloisite30B (C30B) was investigated in periods of up to 360 h under artificial weathering. A correlation between artificial and natural weathering was established. The nanocomposites were prepared by mixing the C30B in PLA matrix using two stages of extrusion followed by injection molding. In addition, we also studied materials without C30B in PLA matrix prepared by a single stage of injection, as well as with two stages of extrusion followed by injection, in order to assess thermal effects. XRD (X-ray diffraction) and TEM (Transmission electron microscope) were used to determine the layer dispersion of the C30B within the PLA. An increase in the interlayer spacing of a sandwich structure corresponding to a partial exfoliation of the C30B was found, leading to the creation of OPEN ACCESSPolymers 2015, 7 761 small particles at nanoscale of one (1.29 nm) to eight (11.76 nm) platelets. Also, GPC (Gel permeation chromatography) was used to evaluate the molecular weight decay of neat PLA and its nanocomposites due to thermal processing and subsequent artificial weathering exposure. From thermal processing, a more significant decrease of polydispersity in amorphous PLA than in semicrystalline PLA counterparts could be observed. First order fitting of molecular weight decay of samples versus time of exposure under artificial weathering was found for all materials tested. It was observed that the addition of clay favored PLA degradation in amorphous PLA, in comparison with semicrystalline PLA in both thermal processing and artificial weathering. Moreover, a possible effect of C30B interactions with PLA chains under artificial weathering could be postulated.

Thermal stability as well as enhanced mechanical properties of poly-lactide (PLA) can increase PLA applications for short-use products. The conjunction of adequate molecular weight (M W ) as well as satisfactory thermo-mechanical properties, together, can lead to the achievement of suitable properties. However, PLA is susceptible to thermal degradation and thus an undesired decay of M W and a decrease of its mechanical properties during processing. To avoid this PLA degradation, nanofiller is incorporated as reinforcement to increase its thermo-mechanical properties. There are many papers focusing on filler effects on the thermal stability and mechanical properties of PLA/nanocomposites; however, these investigations lack an explanation of polymer/filler interactions. We propose interactions between PLA and Cloisite30B (C30B) as nanofiller. We also study the effects on the thermal and mechanical properties due to molecular weight decay after exposure to artificial weathering. PLA blank and nanocomposites were subjected to three time treatments (0, 176, and 360 h) of exposure to artificial weathering in order to achieve comparable materials with different M W . M W was acquired by means of Gel Permeation Chromatography (GPC). Thermo-mechanical properties were investigated through Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Dynamic Mechanical Thermal Analysis (DMTA) and Fourier Transform Infrared Spectroscopy (FTIR).

Zinc oxide (ZnO) is an attractive material for many applications in electronics, photonics, sensing, among others [1]. There are a number of techniques for preparing ZnO powders including thermal decomposition, precipitation, spay pyrolysis, hydrothermal synthesis, and mechanochemical processes [2-3]. However, nanocrystalline ZnO is difficult and inconvenient to obtain due to its high degree of agglomeration. Mechanical milling has proved to be an effective and simple technique to produce nanocrystalline powders and the possibility to obtain large quantities of materials. Some studies have shown the effect of highenergy ball milling on the structural and microstructural changes in monoclinic zirconia. [4] The aim of this investigation is to show the transition from the initial laminates of Zn mesh 20 through different milling times into ZnO. The milled powders were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The initial materials was Zn mesh 20, the mechanical milling parameters was 500 rpm, 0.5 ml of methanol as a control agent and a weight ratio for ball to powder of 5:1.