Structure and Mechanical Properties of iPP-Based Nanocomposites Crystallized under High Pressure.

The unique nonparallel chain arrangement in the orthorhombic γ-form lamellae of isotactic polypropylene (iPP) results in the enhancement of the mechanical properties of γ-iPP. Our study aimed at the investigation of the mechanical properties of γ-iPP nanocomposites with 1-5 wt.% multiwall carbon nanotubes (MWCNT) and 5 wt.% organo-modified montmorillonite prepared by melt-mixing and high-pressure crystallization. Neat iPP and the nanocomposites were crystallized under high pressures of 200 MPa and 300 MPa, and for comparison under 1.4 MPa, in a custom-built high-pressure cell. The structure of the materials was studied using WAXS, SAXS, DSC, and SEM, whereas their mechanical properties were tested in plane-strain compression. Under a small pressure of 1.4 MPa, polymer matrix in all materials crystallized predominantly in the α-form, the most common monoclinic form of iPP, whereas under high pressure it crystallized in the γ-form. This caused a significant increase in the elastic modulus, yield stress, and stress at break. Moreover, due to the presence of MWCNT, these parameters of the nanocomposites exceeded those of the neat polymer. As a result, a 60-70% increase in the elastic modulus, yield stress, and stress at break was achieved by filling of iPP with MWCNT and high-pressure crystallization.

A New Look at the Mechanism of Cocrystal Formation and Coformers Exchange in Processes Forced by Mechanical and/or Thermal Stimuli - ex situ and in†situ Studies of Low-Melting Eutectic Mixtures.

Three different devices: ball mill, hot stage melting, and magic angle spinning (MAS) NMR rotor were used for the preparation of ethenzamide (ET) cocrystals with glutaric acid (GLU), ethylmalonic acid (EMA) and maleic acid (MAL) as coformers. In each case, well-defined binary systems (ET:EMA, ET:GLU, ET:MAL) were obtained. The common features of the two solvent free methods of cocrystal formation (grinding, melting) are presented on the basis of arguments obtained by solid state NMR spectroscopy. Thermal analysis (Differential Scanning Calorimetry) proved that the eutectic phase arises over a wide range of molar ratios of components for each of the binary systems. NMR techniques, supported by theoretical calculations, allowed to provide details about the pathway of the reaction mechanism with atomic accuracy. It was found that the formation of ET cocrystals is a complex process that requires five steps. Each step has been recognized and described. Variable temperature 1D and 2D MAS NMR experiments allowed to track physicochemical processes taking place in a molten state. Moreover, it was found that in a multicomponent mixture consisting of all four components, ET, EMA, GLU, and MAL, ET in the molten phase behaves as a specific selector choosing only one partner to form binary cocrystals according to energy preferences. The process of exchange of coformers in binary systems during grinding, melting, and NMR measurements is described. The stabilization energies (Estab ) and molecular electrostatic potential (MEP) maps computed for the cocrystals under discussion and their individual components rationalize the selection rules and explain the relationships between individual species.

Electrical Conductivity and Antibacterial Activity of Woven Fabrics through Quercetin-Assisted Thermal Reduction of a Graphene Oxide Coating.

Cotton and poly(ethylene terephthalate) (PET) woven fabrics were coated with graphene oxide (GO) using a padding method and the GO deposited on the fiber surfaces was thermally reduced to impart electrical conductivity to the fabrics. To assist the thermal reduction of GO, quercetin (Q)-a natural flavonoid-was used. To this end, before the reduction, the GO-padded fabrics were immersed in Q solutions in ethanol with different Q concentrations. Q enhanced the thermal reduction of GO. Depending on the Q concentration in the solutions, electrical surface resistivities of the cotton fabric of 750 kΩ/sq to 3.3 MΩ/sq and of the PET fabric of 240 kΩ/sq to 730 kΩ/sq were achieved. The cotton and PET fabrics also became hydrophobic, with water contact angles of 163° and 147°, respectively. In addition to the electrical conductivity, the presence of Q resulted in antibacterial activity of the fabrics against Escherichia coli and Staphylococcus aureus.

Electrically conductive crystalline polylactide nonwovens obtained by electrospinning and modification with multiwall carbon nanotubes.

Polylactide nonwovens were electrospun from solutions and then crystallized, one in α-form, and another, S-PLA, made of poly(l-lactide) and poly(d-lactide) 1:1 blend, in scPLA crystals with high melting temperature, close to 220 °C. To make the nonwovens electrically conductive, they were coated with multiwall carbon nanotubes (MWCNT) by padding and dip-coating with an aqueous dispersion of MWCNT. The electrical conductivity evidenced the formation of the electrically conductive MWCNT network on the fiber surfaces. Depending on the coating method, the surface resistivity (Rs) of S-PLA nonwoven of 1.0 kΩ/sq and 0.09 kΩ/sq was reached. To study the effect of surface roughness, before the modification the nonwovens were etched with sodium hydroxide, which additionally made them hydrophilic. The effect of etching depended on the coating method and led to an increase or decrease of Rs, in the case of padding or dip-coating, respectively. All MWCNT-modified nonwovens, unetched and etched, were hydrophobic with water contact angles of 138-144°. Scanning electron microscopy corroborated the presence of MWCNT on the fiber surfaces. Impedance spectroscopy confirmed the dominant role of the network of MWCNT direct contacts on the electrical properties of MWCNT-modified nonwovens in a broad frequency range.

Antibacterial Electroconductive Composite Coating of Cotton Fabric.

Graphene oxide (GO) was deposited on a cotton fabric and then thermally reduced to reduced graphene oxide (rGO) with the assistance of L-ascorbic acid. The GO reduction imparted electrical conductivity to the fabric and allowed for electrochemical deposition of Ag° particles using cyclic voltammetry. Only the Ag°/rGO composite coating imparted antibacterial properties to the fabric against Escherichia coli and Staphylococcus aureus. Ag°/rGO-modified fibers were free of bacterial film, and bacterial growth inhibition zones around the material specimens were found. Moreover, Ag°/rGO-modified fabric became superhydrophobic with WCA of 161°.

Modification of Polylactide Nonwovens with Carbon Nanotubes and Ladder Poly(silsesquioxane).

Electrospun nonwovens of poly(L-lactide) (PLLA) modified with multiwall carbon nanotubes (MWCNT) and linear ladder-like poly(silsesquioxane) with methoxycarbonyl side groups (LPSQ-COOMe) were obtained. MWCNT and LPSQ-COOMe were added to the polymer solution before the electrospinning. In addition, nonwovens of PLLA grafted to modified MWCNT were electrospun. All modified nonwovens exhibited higher tensile strength than the neat PLA nonwoven. The addition of 10 wt.% of LPSQ-COOMe and 0.1 wt.% of MWCNT to PLLA increased the tensile strength of the nonwovens 2.4 times, improving also the elongation at the maximum stress.

Phase Structure and Properties of Ternary Polylactide/Poly(methyl methacrylate)/Polysilsesquioxane Blends.

Ternary blends of polylactide (PLA, 90 wt.%) and poly(methyl methacrylate) (PMMA, 10 wt.%) with functionalized polysilsesquioxanes (LPSQ-R) were obtained by solution blending. R groups in LPSQ containing hydroxyethyl (LPSQ-OH), methylglycolic (LPSQ-COOMe) and pentafluorophenyl (LPSQ-F5) moieties of different chemical properties were designed to modify PLA blends with PMMA. The effect of the type of LPSQ-R and their content, 1-3 wt.%, on the structure of the blends was studied with scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (SEM-EDS), dynamic mechanical thermal analysis (DMTA) and Raman spectroscopy. Differential scanning calorimetry (DSC) and tensile tests also showed various effects of LPSQ-R on the thermal and mechanical properties of the blends. Depth-sensing indentation was used to resolve spatially the micro- and nano-scale mechanical properties (hardness and elastic behaviour) of the blends. The results showed clearly that LPSQ-R modulate the structure and properties of the blends.

PLA/ß-CD-based fibres loaded with quercetin as potential antibacterial dressing materials.

Microbial infections lead to elevated inflammatory responses, which usually result in prolonged and incomplete wound healing. Therefore, there is an increasing demand for biodegradable fibres that are effective against a different range of microorganisms, especially those with antibiotic resistance. Herein, quercetin-(Q)-loaded polylactide-based fibres were developed using the electrospinning technique. Since Q exhibits low chemical stability, we used star-shaped polylactides (PLAs) with a ß-CD core to host Q by inclusion complexation. To enhance the stability of the fibres and additionally entrap the Q between polymeric chains, we adapted supramolecular cross-linking by the stereocomplexation of PLAs with opposite configurations. As a control, we prepared an additional formulation of star-shaped/commercial PLA/Q for the preparation of nonwovens in which the ß-CD moiety was not present. All developed fibres were smooth and continuous, with an average diameter of 37 µm. Although nonwovens did not possess diffusible activity, good antibacterial effects against Staphylococcus aureus (S. aureus), Escherichia coli (E.coli) and Klebsiella pneumoniae (K. pneumoniae) were observed. All these features validate the proposed approach, in which different supramolecular interactions were used to modify the properties of PLA-based fibres and, most importantly, show their great potential usefulness against microbial infections.