Effect of Artificial Weathering on PLA/Nanocomposite Molecular Weight Distribution

Abstract

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.

Plasticizing effect of coconut oil on morphological, mechanical, thermal, rheological, barrier, and optical properties of poly(lactic acid): A promising candidate for food packaging

“…Also, the PDI ( M w /M n ) revealed a low stability with values 1.83 and 2.09. This strongly suggest that chain scission randomly occurred in PLA and plasticized PLA under thermo‐oxidative and shear forces during processing . Plasticizer improves the segmental mobility of PLA chains and as the CO content increases the molecular weight is reduced which indicates that the mobility of amorphous part has enhanced …”

Insight on the influence of nano zinc oxide on the thermal, dynamic mechanical, and flow characteristics of Poly(lactic acid)– zinc oxide composites

“…The number average molecular weight ( M n ) and the weight average molecular weight ( M w ) have a huge influence on different properties in polymeric materials such as rheological, viscoelastic, thermal characteristics as well as processability. The linear structure in PLA structure makes this polymer so susceptible to manufacturing process, revealing a decline in M n and M w as a result of thermal degradation and high shear in different processing techniques . Table summarizes the comparative evaluation of molecular structure ( M w , M n , and dispersity index [ M w / M n ]) of pure PLA and composites pellets after extrusion process.…”

Investigation of the Influence of PLA Molecular and Supramolecular Structure on the Kinetics of Thermal-Supported Hydrolytic Degradation of Wet Spinning Fibres

“…The results presented in these works testify that hydrolytic degradation of polymer structures lasts up to many weeks and it is favourable to conduct it in conditions close to the glass transition temperature of the polymer [24][25][26]. Other investigations of PLA degradation carried out under laboratory conditions are thermal degradation [27,28], artificial weathering [29,30] and composting [31,32].…”