This is an editorial article. It has no abstract.
Hard X-ray photoelectron spectroscopy (HAXPES) has been utilized to study chemical state and kinetics of sulfur species in a rubber compound by examining thermally induced changes of S 1s core-level spectra. Two peaks at 2470 and 2472 eV together with the 2479 eV peak from SO42– are resolved in the S 1s spectrum. As the rubber compound is heated at 374, 412, and 440 K, the former two peaks show different thermal behaviors; the peak at 2472 eV is swiftly decreased in its intensity with heating time because of thermal desorption of the sulfur species, whereas the intensity of the 2470 eV peak shows a slight increase especially in the surface region of the rubber compound. On the basis of these thermal behaviors, the peaks at 2470 and 2472 eV are, respectively, associated with S atoms bonded directly to the C atoms and those bonded only to other S atoms. An Arrhenius plot analysis of the 2470 eV peak intensity variation reveals that the S–C bond formation and scission reactions compete with each other with a slightly smaller activation energy in the bond formation than in the bond scission.
The impact resistance of polypropylene (PP)/wood composites was improved either by the traditional approach of adding an elastomer or by the use of poly(ethylene terephthalate) (PET) fibers. Composites were prepared with various elastomer and PET fiber contents at a constant wood content of 20 wt% for all hybrid composites. Interfacial adhesion was improved by the addition of a maleic anhydride modified PP (MAPP). The components were homogenized in a twin-screw compounder and injection molded into standard tensile bars. Properties were characterized by tensile and impact testing, while scanning electron microscopy (SEM) was applied for studying the structure. A combination of acoustic emission measurements (AE) and SEM was used to understand local deformation processes, the results showing that the traditional route of impact modification with elastomers does not work in wood reinforced PP, since the simultaneous fracture of large wood particles and the cavitation of the elastomer result in limited fracture toughness. On the other hand, polymeric fibers (PET) increase the impact resistance of rigid PP homopolymer matrices reinforced with wood fibers, because they initiate new local deformation processes. The concept of using polymeric fibers for the impact modification of rigid PP/wood composites is an efficient way to extend the field of application of such reinforced materials.
Structural characterization and mechanical properties of dextrin-graft-poly(butyl acrylate-co-styrene) copolymers
A. David, J. Meimoun, T. Delaunay, V. Wiatz, R. Saint-Loup, J. Parcq, N. Descamps, A. Favrelle, F. Bonnet, G. Stoclet, D. Lourdin, P. Zinck, V. Gaucher
Vol. 13., No.3., Pages 235-247, 2019
Vol. 13., No.3., Pages 235-247, 2019
Dextrin/starch-graft-poly(butyl acrylate-co-styrene) copolymers have been synthesized by radical graft copolymerization and their structure and mechanical properties are reported. High molecular weight grafted chains formation is favored, leading to a low degree of substitution of starch hydroxyl groups. Wide-Angle-X-ray Scattering (WAXS) analysis indicates that all materials are amorphous and Transmission Electron Microscopy (TEM) investigations reveal a two-phase morphology. This is further confirmed by the presence of two glass transitions, one related to the starch/dextrin macromolecules and sensitive to water content, and one assigned to the grafted polymers that is composition dependent. Water uptake is controlled by dextrin/starch content but diffusivity increases with the butyl acrylate ratio. The mechanical behavior is dependent on monomer ratio, and water content. Increasing butyl acrylate ratio improves the ductility of the sample while materials become brittle as soon as styrene ratio is predominant in the grafted chains. While no effect of molecular weight of starch substrate on structure and thermal behavior is evidenced, dextrin-based materials are slightly more ductile than starchbased ones. The interest of using dextrin instead of starch is further highlighted by a lower viscosity of the reactive medium, together with an improved processability, as structural materials can be obtained over a wider range of composition than with native starch.
The interface between either Micronised Rubber Powder (MRP) or Crumb Rubber Powder (CRP) fillers in either Natural Rubber (NR) or Butadiene Rubber (BR) matrices has been studied using Transmission Electron Microscopy (TEM) ‘network visualisation’. The convoluted structure of CRP provides better interfacial adhesion than MRP. The weak interface between the MRP networks and the rubber matrix was confirmed by the lower physical bonding. The crescent tear strength test was able to characterise the possible weak interaction of MRP in unfilled NR or NR/BR blend matrix. The Akron test was used for carbon black-filled matrix.
Development of mesoporous polysaccharide/sol-gel composites with two different templating agents: Surfactants and choline chloride-based deep eutectic solvents
V. R. A. Ferreira, M. A. Azenha, A. C. Pinto, P. R. M. Santos, C. M. Pereira, A. F. Silva
Vol. 13., No.3., Pages 261-275, 2019
Vol. 13., No.3., Pages 261-275, 2019
Mesoporous sorbent composites, evolving from previous work on microporous composites of polyanionic polysaccharides were developed with the purpose of increasing the sorptive features of the materials. Using the widely successful classical surfactant micelle approach, it was observed, in this particular case, that the composites remained essentially microporous. The alternative consisted on the application of deep eutectic solvents (DES). The most common DES (choline chloride + neutral hydrogen bond donor), were tested because of their advantages over other possibilities such as imidazolium-based ionic liquids: lower cost, easy in-house preparation, safe constituents and water stability and solubility. Possible mechanisms underlying the observed mesoporosity were discussed. The surface area ranged between 76 and 267 m2/g and the average pore size was in the range 3–5 nm. DES had not a negative effect on synthesis yields and, in the case of fucoidan, composites bearing a higher content of the biopolymer were produced. As a consequence and in line with the initial expectations these new composites revealed highly enhanced Pb (II) sorptive features comparatively to their microporous predecessors: chondroitin sulfate composites - up to a 5 fold capacity enhancement; fucoidan composites- up to a 3.5 fold capacity enhancement. The highest capacity was observed for the fucoidan composite prepared with choline chloride-ethyleneglycol DES, 79 mg Pb (II)/g, which is slightly above the highest value (77 mg Pb (II)/g) found in the literature for Pb (II) sorbents based on polysaccharides, sol-gels or their composites.
The time evolution of organoclay particle size and volume fraction, as well as the shear viscosity, are measured in-line for a series of Poly(lactic acid)/organoclay composites, using a rheo-optical die coupled to a prototype modular corotating twin screw extruder. The small angle light scattering patterns and light attenuation recorded during transient experiments indicate that clay dispersion develops through melt intercalation between the clay galleries, thereby expanding the aggregates size, and eventually leads to aggregates break-up, i.e., exfoliation. The simultaneous recording of shear viscosity also indicates that smaller viscosities promote a faster melt intercalation and exfoliation but hinder the extent of clay dispersion. The methodology used in the present study validates the well accepted mechanism for clay dispersion and can be applied straight away for the monitoring of PNC manufacturing during practical production.
The two-stage mechanochemical amination of graphite by dry ball milling of graphite in a planetary ball mill under Ar followed by NH3 yields aminated multilayer graphene (AMFG) as intermediates for carbon/polymer hybrids and nanocomposites. Opposite to efficient edge-selective graphene functionalization under Ar, CO2 and N2 pressure, the onestage ball milling under NH3 pressure affords rather low N content (<0.5 wt%) and fails to reduce the graphite platelet size. According to DFT (Density Functional Theory) calculations NH3 exhibits low mobility between graphene layers and forms weak bonds to carbon which impair breakage of carbon bonds. In the two-stage ball-milling of graphite under Ar affords reactive carbon nanoparticles which react with NH3 in the second stage. With increasing milling duration of the second stage the nitrogen content increases to 3.2 wt%. As verified by XPS (X-ray photoelectron spectroscopy) measurements primary amine groups are formed which couple with various dicarboxylic anhydride groups including maleated PP to produce imidefunctionalized graphene. This is of interest to produce compatibilizers and dispersing agents for carbon/PP nanocomposites exhibiting improved mechanical properties. Two-stage mechanochemistry holds promise for carbon nanoparticle functionalization well beyond amination.