Resumen de Preparation and characterization of nanocomposites based on polylactide manufactured by reactive extrusion-calendering: thermal, rheological, mechanical and fracture properties
Raja Nazrul Hakim Bin Raja Nazri
PLA nanocomposites sheets that is rnodified with multi-functional epoxide reactive agent (Joncryi4300F, BASF, Germany) were manufacturad using reactive extrusion in a pilot plant. A commercial grade of PLA (PLA 40320, NatureWorks, Belgium) was reinforced with either a commercial grade of organornodified rnontrnorillonite clay (o-MMT) (Cioisite 308, Southem Clay Products, USA) or three comrnercial grades of fumed silica (nano-Si02){(CAB-0-SIL EH5,), (epoxy rnodified silica 6851HN and aminopropyl modified silica 6852HN, Skyspring Nanomaterials lnc., USA)}. PLA and reactively rnodified PLA nanocomposites sheets were preparad using co-rotating twin screw extruder using masterbatch approach. 15 rneters of non-modified and reactively modified PLA composites reinforced with o-MMT (PLA/o-MMT composites) calendered sheets (nominal thickness: 1 mm) and 15 rneters of reactively rnodified PLA nanocomposites reinforced with nano-Si02 (PLA/nano-Si02 composites) calendered sheets (nominal thickness: 0.6 mm) were manufacturad. For PLA/o-MMT composites, prematura reactions between epoxy rings from reactive agent and -OH group from o-MMT occurred, reducing chain branching in rnodifíed PLA/o-MMT composites (REX-PLA-C). FT-IR spectroscopy and SEC-DRI chrornatography verifies these findings. For PLA/nano-Si02 composites, Si02-polyrner tethering occurred in reactively rnodified PLA reinforced with either epoxy modified nano-Si02 (REX PLA/Si02-E) and amino modifíed nano-Si02 (REX-PLA/Si02-A). Conversely, this reaction is absent in reactively modified PLA composites reinforced with non-rnodified nano-Si02 (REX-PLA/Si02). However, both FT-IR and intrinsic viscosity test were unsuccessful to highlight the differences between unrnodified and surface-modified nano-Si02. SEM micrographs of PLA/o-MMT composites revealed homogenous clay distribution with coexisten ce of mixed structures, involving tactoids as well as intercalated clay layers were observed. Líkewise, PLA/nano-Si02 composites similarly exhibit a hornogeneous and sub-micron dispersion of nano-Si02. However, the improved chemical affinity of both surface modified nano-Si02 did not signifícantly improve the particle dispersion with aggregates presence were detectable. Rheological analysis of REX-PLA-C revealed that both the rnelt elasticity and the rnelt response time increased with o-MMT addition. Conversely, PLA/nano-Si02 composites exhibit therrnorheologically complex behaviour due to formation of sparsely branched structures. Cole-Cole plot revealed formation of filler inter-network in REX-PLA/Si02 which is absent in surface rnodified nano-Si02 reinforced PLA composites. Si02 presence reduces cold crystallization temperatura and increases the crystalline percentage of its composites. lsotherrnal crystallization kinetics and the activation energy of the PLA composites studied using the Avrami and Arrhenius rnethod, respectively revealed that Si02 enhances the crystallization rate and induces spherulitic growth rnechanism. Unfortunately, o-MMT and surface rnodified nano Si02 does not enhance PLA crystallization. Tensile studies show improved clay dispersion in REX-PLA-C enhances cavitation processes, notably improving PLA shear flow. However, the tensile behaviour of PLA/nano-Si02 composites remained insensitive to nano-Si02 presence. A combinad effect of physical ageing and nanofíller dispersion could be the reason for these trends. The essential work of fracture analysis revealed that o-MMT addition shows improved specific essential work of fracture parameter and specific plastic work of dissipation of both PLA and rnodified PLA composites with o-MMT. This is due to the effect of energy dissipation mechanisrns such as de-cohesion and coalescence of micro-void. However, nano-Si02 addition does not rnodify the specific essential work. An increase of specifíc plastic work accompanied with decrease in volurne of deformad material near the ligarnent length was observad.
