Green esterification: A new approach to improve thermal and mechanical properties of poly(lactic acid) composites reinforced by cellulose nanocrystals

Cellulose nanocrystal (CNCs)‐reinforced poly(lactic acid) (PLA) nanocomposites were prepared using twin screw extrusion followed by injection molding. Masterbatch approach was used to achieve more efficient dispersion of CNCs in PLA matrix. Modified CNCs (b‐CNCs) were prepared using benzoic acid as a nontoxic material through a green esterification method in a solvent‐free technique. Transmission electron microscopy images did not exhibit significant differences in the structure of b‐CNCs as compared with unmodified CNCs. However, a reduction of 6.6–15.5% in the aspect ratio of b‐CNCs was observed. The fracture surface of PLA‐b‐CNCs nanocomposites exhibited rough and irregular pattern which confirmed the need of more energy for fracture. Pristine CNCs showed a decrease in the thermal stability of nanocomposites, however, b‐CNCs nanocomposites exhibited higher thermal stability than pure PLA. The average storage modulus was improved by 38 and 48% by addition of CNCs and b‐CNCs in PLA, respectively. The incorporation of b‐CNCs increased Young's modulus, ultimate tensile stress, elongation at break, and impact strength by 27.02, 10.90, 4.20, and 32.77%, respectively, however, CNCs nanocomposites exhibited a slight decrease in ultimate strength and elongation at break. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46468.     

Morphology,mechanical properties and electromagnetic shielding effectiveness of poly(styrene‐b‐ethylene‐ran‐butylene‐b‐styrene)/carbon nanotube nanocomposites: effects of maleic anhydride,carbon nanotube loading and processing method

Nanocomposites based on poly(styrene‐b‐ethylene‐ran‐butylene‐b‐styrene) (SEBS) and carbon nanotubes (CNTs) (SEBS/CNT) as well as SEBS grafted with maleic anhydride (SEBS‐MA)/CNT were successfully prepared for electromagnetic shielding applications. Both SEBS/CNT and SEBS‐MA/CNT nanocomposites were prepared by melt compounding and were post‐processed using two different techniques: tape extrusion and compression moulding. The different nanocomposites were characterized by Raman spectroscopy and rheological analysis. Their mechanical properties, electrical properties (10^-2–10⁵ Hz) and electromagnetic shielding effectiveness (8.2–12.4 GHz) were also evaluated. The results showed that the CNT loading amount, the presence of MA in the matrix and the shaping technique used strongly influence the final morphologies and properties of the nanocomposites. Whilst the nanocomposite containing 8 wt% CNTs prepared by compression moulding presented the highest electromagnetic shielding effectiveness (with a value of 56.73 dB, which corresponds to an attenuation of 99.9996% of the incident radiation), the nanocomposite containing 5 wt% CNTs prepared by tape extrusion presented the best balance between electromagnetic and mechanical properties and was a good candidate to be used as an efficient flexible electromagnetic interference shielding material. © 2018 Society of Chemical Industry     

Mechanical reinforcement of a high-performance aluminium alloy AA5083 with homogeneously dispersed multi-walled carbon nanotubes

Dense and homogeneous multi-walled carbon nanotube/metal composites are prepared by powder metallurgy. The distribution of the nano-reinforcements in the matrix is studied by scanning electron microscopy and Raman spectroscopy. The mechanical properties of the composites are determined by means of static tensile tests and Vickers micro-hardness measurements. We show that a homogeneous dispersion of the nanotubes at the micron scale is required in order to improve the mechanical properties of the metal matrix composite. This can be achieved using ball-milling through the mechanisms of plastic deformation and cold-welding. Accordingly, we report significant improvements to the mechanical properties of composites prepared with a high-performance aluminium alloy AA5083 matrix.     

In Vivo Delivery and Activation of Masked Fluorogenic Hydrolase Substrates by Endogenous Hydrolases in C. elegans

Protein expression and localization are often studied in vivo by tagging molecules with green fluorescent protein (GFP), yet subtle changes in protein levels are not easily detected. To develop a sensitive in vivo method to amplify fluorescence signals and allow cell‐specific quantification of protein abundance changes, we sought to apply an enzyme‐activated cellular fluorescence system in vivo by delivering ester‐masked fluorophores to Caenorhabditis elegans neurons expressing porcine liver esterase (PLE). To aid uptake into sensory neuron membranes, we synthesized two novel fluorogenic hydrolase substrates with long hydrocarbon tails. Recombinant PLE activated these fluorophores in vitro. In vivo activation occurred in sensory neurons, along with potent activation in intestinal lysosomes quantifiable by imaging and microplate and partially attributable to gut esterase 1 (GES‐1) activity. These data demonstrate the promise of biorthogonal hydrolases and their fluorogenic substrates as in vivo neuronal imaging tools and for characterizing endogenous C. elegans hydrolase substrate specificities.     

Controlled immobilisation of active enzymes on the cowpea mosaic virus capsid

Immobilisation of horseradish peroxidase (HRP) and glucose oxidase (GOX) via covalent attachment of modified enzyme carbohydrate to the exterior of the cowpea mosaic virus (CPMV) capsid gave high retention of enzymatic activity. The number of enzymes bound per virus was determined to be about eleven for HRP and 2-3 for GOX. This illustrates that relatively large biomacromolecules can be readily coupled to the virus surface using simple conjugation strategies. Virus-biomacromolecule hybrids have great potential for uses in catalysis, diagnostic assays or biosensors.     

Influence of granulometry and organic treatment of a Brazilian montmorillonite on the properties of poly(styrene‐co‐n‐butyl acrylate)/layered silicate nanocomposites prepared by miniemulsion polymerization

The influence of granulometry and organic treatment of a Brazilian montmorillonite (MMT) clay on the synthesis and properties of poly(styrene‐co‐n‐butyl acrylate)/layered silicate nanocomposites was studied. Hybrid latexes of poly(styrene‐co‐butyl acrylate)/MMT were synthesized via miniemulsion polymerization using either sodium or organically modified MMT. Five clay granulometries ranging from clay particles smaller than 75 μm to colloidal size were selected. The size of the clay particles was evaluated by specific surface area measurements (BET). Cetyl trimethyl ammonium chloride was used as an organic modifier to enhance the clay compatibility with the monomer phase before polymerization and to improve the clay distribution and dispersion within the polymeric matrix after polymerization. The sodium and organically modified natural clays as well as the composites were characterized by X‐ray diffraction analysis. The latexes were characterized by dynamic light scattering. The mechanical, thermal, and rheological properties of the composites obtained were characterized by dynamical‐mechanical analysis, thermogravimetry, and small amplitude oscillatory shear tests, respectively. The results showed that smaller the size of the organically modified MMT, the higher the degree of exfoliation of nanoplatelets. Hybrid latexes in presence of Na‐MMT resulted in materials with intercalated structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A Highly Potent and Cellularly Active β‐Peptidic Inhibitor of the p53/hDM2 Interaction

New and improved : The incorporation of a 6‐chlorotryptophan (6‐Cl‐Trp) into a β‐peptide (M)‐3₁₄ helix leads to a high‐affinity hDM2 inhibitor, as demonstrated by fluorescence fluctuation analysis at single molecule resolution. When conjugated to penetratin, the newly derived hDM2 binder specifically inhibits tumour cell growth in vitro.

     

Spray deposited fluoropolymer/multi-walled carbon nanotube composite films with high dielectric permittivity at low percolation threshold

High performance perfluoro alkoxy (PFA) and chemical vapor deposition-grown multi-walled carbon nanotube (MWCNT) composite films with thicknesses of 30 μm were prepared using a scalable spray deposition technique. A homogeneous distribution of MWCNTs within the PFA matrix was confirmed by electron and optical microscopy. Dielectric and AC conductivity measurements showed a significant enhancement of dielectric permittivity for PFA/MWCNT films at low frequencies, and a very weak dependence of dielectric permittivity on temperature in the range 25-230 °C. Very low percolation threshold volume fractions of ca. 0.0043 and 0.0017 were attained for MWCNTs with two different aspect ratios, which have been explained by an inherent feature of spray route, a microcapacitor model and percolation theory. The combination of PFA/MWCNT composites and the spray deposition route provides a promising approach for the fabrication of industrial scale composite films with well-controlled dielectric properties for micro-electronic and high temperature applications.     

Intelligent gripper technology for the handling of carbon fiber material

Nowadays, the serial production of Carbon Fiber-Reinforced Polymers remains a challenge for the industry. Their production and application have been limited by the intensive manual work required to produce them and the resulting elevated manufacturing costs. Moreover, the production handling tasks are fulfilled to a limited extent by the gripping systems currently available in the market. The delicate process and specific material requirements of these polymers compromise the feasibility and use of automated gripper systems. An innovative solution for the automated material handling of carbon fiber textiles developed by the wbk Institute for Production Science in cooperation with J. Schmalz GmbH will be presented in this paper. The main focus of this study deals with measuring principles to increase energy efficiency, process reliability and adaptability of a gripping system using low pressure grippers. This study presents suitable solutions for the implementation of low pressure grippers in a production environment.