Deformation mechanisms in polylactic acid/natural rubber/organoclay bionanocomposites as revealed by synchrotron X-ray scattering

7 p.: gráf.The micromechanical deformation mechanisms of a polylactic acid (PLA)/natural rubber (NR) blend(PLA/NR 90/10 wt%) and its organoclay filled bionanocomposites have been investigated by small and wide angle X-ray scattering (SAXS–WAXS) under tensile conditions. The addition of NR to a PLA matrix changed the brittle fracture of PLA to a ductile deformation through the debonding of the rubber droplets. Otherwise, the formation of cavities between PLA and NR was hampered by the nanoclays since they were mainly located at the polymer blend interface. In this case, the nanoclays acted as craze nucleation sites. At 1 wt% of filler concentration, the crazes were able to fully develop in the blend and to evolve into stable microvoids, which kept growing and orienting in the tensile direction. These mechanisms also explained the progressive plastic deformation of the polymer chains and the preferential orientation of the nanoclay platelets.© Royal Society of Chemistry 2012Supported by the Spanish Ministry of Science and Innovation(MICINN) under projects MAT2010-18749, MAT2009-07789 and MAT2008-03232. JAE-Pre grant. Project FIS 2010-15502 (Direccion general de Investigación , Spain).Peer reviewe

Structure and properties of polylactide/natural rubber blends

Polylactide, PLA, is a biodegradable thermoplastic polyester derived from biomass that has restricted packaging applications due to its high brittleness and poor crystallisation behaviour. Here, new formulations based on natural rubber-PLA blends have been developed. The processing windows, temperature, time, and rotor rate, and the rubber content have been optimised in order to obtain a blend with useful properties. The rubber phase was uniformly dispersed in the continuous PLA matrix with a droplet size range from 1.1 to 2.0 μm. The ductility of PLA has been significantly improved by blending with natural rubber, NR. The elongation at break improved from 5% for neat PLA to 200% by adding 10 wt% NR. In addition, the incorporation of NR not only increased the crystallisation rate but also enhanced the crystallisation ability of PLA. These materials are, therefore, very promising for industrial applications. © 2011 Elsevier B.V. All rights reserved.The work was supported by the Spanish Ministry of Science and Innovation (MICINN) under project MAT 2007-61116. NB thanks the CSIC for a JAE-Pre grant. RV also acknowledges a Ramon y Cajal contract from MICINNPeer reviewe

Recent Advances in Clay/Polymer Nanocomposites

Smectite clays (e.g. montmorillonite), belonging to the structural family called 2:1 phyllosilicates, are the main choice for designing polymer nanocomposites due to their low cost and rich intercalation chemistry allowing them to be chemically modified (organoclays) and to improve the compatibility with the polymer matrix. These hybrid materials, normally called polymeric nanocomposites (PNC), represent a radical alternative to conventional polymer composites and have focused the attention of both academia and industry because of their unexpected properties, and their straightforward synthesis and processing. Such materials on the nanoscale level show signifi cant improvements in mechanical properties, heat distortion temperatures, thermal stability, fl ame retardancy and enhanced barrier properties. The combination of enhanced properties, weight reduction, and low cost has led to interesting commercial applications such as automotive and packaging, among others. All this justifi es the growing interest of both academia and industry in the development of these hybrid materials. In this paper we describe the most signifi cant fi ndings in the clay/polymer nanocomposites fi eld considering three polymer families: elastomers, thermosets and polymers from natural resources or biopolymers.Financial support provided by the Ministerio de Ciencia e Innovación (MCINN) through the Project MAT 2010-18749. N.B. thanks the CSIC for a JAE-pre contract.Peer Reviewe

Poly(lactic acid)/natural rubber/cellulose nanocrystal bionanocomposites. Part II: Properties evaluation

International audienceThe crystallization, mechanical and biodegradation properties of poly(lactic acid)/natural rubber/cellulose nanocrystals (CNC) bionanocomposites were evaluated. Three types of CNC were used in this study, one unmodified (CNC), long alkyl chain grafted CNC (C18-g-CNC) and PLA grafted CNC (PLA-g-CNC). The CNC modifications determined the affinity of the nanocrystals toward the polymers and reflected on the ultimate properties. Interestingly, PLA-g-CNC acted as a nucleating agent for the PLA matrix in the bio-based PLA/NR blend. Good mechanical properties were reported, as the bionanocomposites maintained a high elongation at break for a concentration up to 3 wt.% of cellulose nanocrystals. Moreover, the disintegration study confirmed that the materials completely disintegrated after one month in compost

Poly(lactic acid)/natural rubber/cellulose nanocrystal bionanocomposites Part I. Processing and morphology

PLA/NR/cellulose nanowhisker composites were prepared using three types of cellulose nanocrystals (CNC), i.e. unmodified CNC obtained from acid hydrolysis of microcrystalline cellulose and two surface modified CNC. The two modification reactions, consisting on the grafting of long alkyl chains and of PLA chains onto the cellulose nanocrystals were carried out in order to facilitate the incorporation of the nanocrystals in the PLA/NR blend. A novel processing method was optimized combining solvent casting and extrusion in order to obtain a homogeneous dispersion of the nanofillers in the blend. The CNC modifications determined their location in the PLA/NR blend and influenced its morphology. © 2013 Elsevier Ltd. All rights reserved.NB thanks the CSIC for a JAE-Pre grant. EF gratefully acknowledges the financial 436 support from the National Consortium of Materials Science and Technology (INSTM).Peer reviewe

Fluid dynamics of evolving foams

The physical properties of many multiphase systems are determined by coarsening phenomena. From raindrops to polycrystal grains and foams, the formation and stability of these systems continuously evolve towards lower-energy configurations through events such as coalescence, Ostwald ripening and drainage. Here we propose a procedure to identify and characterise key topological transformations of coarsening phenomena using a physically-based fluid dynamic framework. In situ, real-time foaming processes of a polymeric matrix reinforced with two morphologically different nanofillers, carbon nanotubes and graphene sheets were observed by synchrotron X-ray radioscopy. We obtained detailed information on the evolution of the growth patterns and coarsening events. Filled samples showed differences in both trend and speed compared with the unfilled sample. Furthermore, we found different dominating coarsening phenomena due to the wetting nature of carbon nanoparticles. Our procedure can be extended to sequences of any type of 2D projection or 3D images and to other multiphase systems. © the Owner Societies 2009.We thank the European Synchrotron Radiation Facility (ESRF, beamline ID19) for providing beam time and support (MA641). RV acknowledges a JAEDoc contract from CSIC. The work at ICTP-CSIC was supported by the Spanish Ministry of Science and Innovation under project MAT 2007-35 61116. The work at the UCLM was funded by research grants PAI06-0102-7466 (Regional Government of Castilla-La Mancha), CGL2006-03611 (MiCInn), and the Ramon y Cajal programme.Peer Reviewe

Poly(lactic acid)/natural rubber/cellulose nanocrystal bionanocomposites. Part II: Properties evaluation

The crystallization, mechanical and biodegradation properties of poly(lactic acid)/natural rubber/ cellulose nanocrystals (CNC) bionanocomposites were evaluated. Three types of CNC were used in this study, one unmodified (CNC), long alkyl chain grafted CNC (C18-g-CNC) and PLA grafted CNC (PLA-g-CNC). The CNC modifications determined the affinity of the nanocrystals toward the polymers and reflected on the ultimate properties. Interestingly, PLA-g-CNC acted as a nucleating agent for the PLA matrix in the bio-based PLA/NR blend. Good mechanical properties were reported, as the bionanocomposites maintained a high elongation at break for a concentration up to 3 wt.% of cellulose nanocrystals. Moreover, the disintegration study confirmed that the materials completely disintegrated after one month in compost. © 2013 Elsevier Ltd. All rights reserved.NB thanks the CSIC for a JAE-Pre grant. EF gratefully acknowl-edges the financial support from the National Consortium of Materials Science and Technology (INSTM). The Authors acknowl-edge Gesenu S.p.a. for compost supplPeer reviewe

Thermal and bio-disintegration properties of poly(lactic acid)/natural rubber/organoclay nanocomposites

The crystallisation behaviour of a poly(lactic acid) (PLA)/natural rubber (NR) blend compatibilised through the addition of organoclays located at the interface between both polymers was evaluated by differential scanning calorimetry (DSC), rheological and wide angle X-ray diffraction (WAXD) measurements. NR acted as a nucleating agent for the PLA matrix, leading to a decrease of PLA cold crystallisation temperature during dynamic DSC measurements and an increase of the crystallisation rate followed by rheological measurements during isothermal crystallisation. Nevertheless, this effect was suppressed when adding 3. wt.% of organoclays due to the particular morphology of the nanocomposites. Moreover, the organoclays increased the thermal degradation temperature of the PLA/NR blend and delayed its disintegration in compost, without affecting the disintegration percentage after one month of experiment. © 2014 Elsevier B.V.Peer Reviewe