Acidic oxidation methods have been widely reported as an effective method to purify and functionalize the surface of carbon nanotubes (CNTs). Although effective, the strong acids typically employed ...and the high sonication power used to disperse the nanotubes in the solution frequently cause nanotube damage, limiting their great potential as mechanical and electrical reinforcements. This work examines the use of HNO
3, H
2SO
4 and H
2O
2 at relatively low concentrations, short treatment times and low sonication power, in an attempt to achieve experimental conditions which efficiently functionalize the surface of multiwalled CNTs minimizing nanotube damage. A low power sonochemical treatment employing 3.0
M HNO
3 for 2
h followed by 2
h of identical treatment with H
2O
2 proved to be the most effective for this aim.
The cyclic piezoresistive behavior of multiwall carbon nanotube/segmented polyurethane (MWCNT/SPU) composites is investigated by varying the amount of rigid segment (RS) content (15, 30 and 50 wt% ...RS) of the polymer and MWCNT concentration (2, 4 and 6 wt% MWCNT). The mechanical and piezoresistive responses during the first loading-unloading cycle are quite different to those of the subsequent cycles, and become repeatable as the number of cycles increases. The cyclic piezoresistive response of the elastomeric MWCNT/SPU composites showed nonlinear, non-monotonic and hysteretic behavior during loading-unloading to 10% strain, showing positive and negative piezoresistive effects, which depend strongly on the RS content and, to a less extend, on the MWCNT weight content. It is shown that the strain sensing capabilities of this kind of composites under large strains can be tailored based on the RS and MWCNT contents.
The aim of this study was to gain some fundamental knowledge on the thermal degradation pathways of poly(
N
-vinyl pyrrolidone) using Thermogravimetry coupled with Fourier Transform Infrared ...Spectroscopy (TG–FTIR) in addition to IR and
1
H NMR spectroscopic studies of the partially degraded samples. It was found that the vinyl pyrrolidone is the main volatile products of the thermal degradation of PVP which implies that the predominant mechanism during thermal degradation of this polymer is the depolymerization to monomer of the polymeric main chain; however, it is evident that simultaneous reactions may be involved yielding oligomers. FTIR and
1
H NMR spectra of partially degraded samples of PVP exhibited very similar characteristics to that observed for undegraded samples although the
1
H NMR spectra suggest the presence of simultaneous reactions as the fragmentation of polymeric main chain.
•Plasma treatment was used as an adhesive tool for PDMS/collagen composite preparation.•Response surface methodology was used for statistical optimization.•A microscopic roughness can also lead to a ...mechanical interlocking between materials.•Hydroxyl groups on the PDMS surface contribute to the enhanced chemical interactions.•PDMS/collagen composite obtained by plasma treatment exhibited higher peel strength.
Direct chemical bonding of biomolecules to the surface of chemically inert polymers such as polydimethylsiloxane (PDMS) is not easily achieved. Therefore, pre-activation of such materials, followed by attachment of the biomolecule is necessary.
This paper describes a procedure to functionalize a PDMS surface by oxygen-based plasma followed by the adhesion of collagen type I for the preparation of adhesive-free bilayer composite intended as skin substitute. Plasma treatments between 40 and 120W for 5 to 15min were used and the extent of surface modification was followed by contact angle, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM) and adhesion test. It was found that as the plasma power and time were increased, PDMS contact angle decreased while surface roughness increased as revealed by SEM and AFM. The formation of oxygen-containing functional groups at the surface was detected by FTIR. T-peel tests, performed on PDMS treated at 80W/13min and covered with collagen showed maximum peel strength of 0.1N/mm which was 3 times higher than that measured for the untreated bilayer composite. The observed enhancement in the adhesion strength was attributed to the increased mechanical interlocking driven by the increased roughness and the formation of hydrophilic functional groups.
Display omitted
•Electrospun PCL nanofibers were superficially modified by air plasma treatment.•Effect of power level and discharge times on physicochemical properties was studied.•Surface changes ...were followed by FTIR, EDX, XPS, SEM, AFM, contact angle and o-TBO.•Carboxyl groups measured by XPS were correlated with those obtained by TBO analysis.
Polycaprolactone (PCL) is a biocompatible polymer approved by the FDA for using in medical devices but it is generally considered as hydrophobic material. In order to improve this drawback, electrospun PCL microfibers were superficially modified by air plasma treatments at three power levels (10, 20, 30W) and three discharge times (1, 3, 5min). The changes undergone by the microfibers were followed using spectroscopic and microscopic techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM); contact angle and surface energy were also determined and the concentration of carboxylic groups was estimated by means of the o-toluidine blue method (TBO). SEM and AFM images demonstrated that the electrospun microfibers did not suffer morphological or topographical changes after the treatment. The contact angle in water diminished, whereas with diiodomethane, it increased after air plasma treatment. FTIR spectra did not show evidence that the plasma treatment modified the surface chemical composition of the microfibers, although the results from EDX and XPS showed an increase in oxygen–containing species and in the O/C ratio after treatment. Deconvolution of the O1s signals in the XPS spectra demonstrated that the carboxylic groups (COOH) increase with treatment time, which was confirmed and quantified with the TBO method. The percentage of the COOH groups measure by XPS was correlated with the concentration obtained in the TBO analysis.
Nanocomposites prepared with segmented polyurethane (SPU) and commercially available nanoclays (Cloisite™ Na
+, Cloisite™ 15A, Cloisite™ 30B) were studied using thermogravimetric analysis coupled ...with Fourier Transform Infrared Spectroscopy (TGA/FTIR). The results showed that the thermal degradation of unfilled SPU and the 4, 6 and 10
wt% hand mixed nanocomposites occurred in two stages being the first due to degradation of hard segments and the second due to the degradation of soft segments. It was also found that the thermal stability of these nanocomposites was not improved by increasing nanoclay concentration except for SPU/Cloisite™ 15A nanocomposites were a 40
°C increase was observed. In a similar manner, FTIR spectra of the evolved gases obtained after the thermal degradation of these nanocomposites were qualitatively similar to the unfilled polymer except in those containing Cloisite™ 30B where isocyanate absorptions were detected. In contrast, SPU/Cloisite™ 30B nanocomposites prepared by
in-situ polymerization, exhibited higher thermal stability than the corresponding hand mixed nanocomposites. In addition, these nanocomposites exhibited the presence of carbon dioxide in the evolved gases during its second degradation stage which was not observed in the hand mixed nanocomposites. In this case, it can be said that the presence of clays in the nanocomposites has a significant effect on the thermal degradation pathways.
Biodegradable segmented polyurethanes (BSPUs) were prepared with poly(caprolactone) as a soft segment, 4,4′-methylene bis (cyclohexyl isocyanate) and either butanediol (BSPU1) or dithioerythritol ...(BSPU2) as a chain extender. BSPU samples were characterized in terms of their physicochemical properties and their hemocompatibility. Polymers were then degraded in acidic (HCl 2
N), alkaline (NaOH 5
M) and oxidative (H
2O
2 30
wt.%) media and characterized by their mass loss, Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Undegraded BSPU1 and BSPU2 exhibited different properties, such as the glass transition temperature
T
g of the soft segment (−25 vs. 4
°C), mechanical properties (600% vs. 900% strain to break) and blood coagulating properties (clotting time
=
11.46 vs. 8.13
min). After acidic and alkaline degradation, the disappearance of the 1728
cm
−1 band of polycaprolactone (PCL) on both types of BSPU was detected by FTIR. However, the oxidative environment did not affect the soft segment severely as the presence of PCL crystalline domains were observed both by DSC (melting temperature
T
m
=
52.8
°C) and XRD (2
θ
=
21.3° and 23.7°). By TGA three decomposition temperatures were recorded for both BSPU samples, but the higher decomposition temperature was enhanced after acidic and alkaline degradation. The formation of the porous structure on BSPU1 was observed by SEM, while a granular surface was observed on BSPU2 after alkaline degradation.
Thermal degradation of three biodegradable polyesters: poly(caprolactone), poly(lactic acid), and poly(hydroxybutyrate), was studied by thermogravimetry coupled to Fourier Transform Infrared ...Spectroscopy TGA/FTIR before and after they were partially degraded. TGA curves and Gram–Schmidt plots showed only one decomposition stage for both poly(caprolactone), PCL, and poly(lactic acid), PLA. In contrast, poly(hydroxybutyrate), PHB, exhibited two degradation stages by TGA, but only one region of evolved gases was appreciated in the Gram–Schmidt plot. It was established that hexenoic acid, ε-caprolactone, and small fragments of polymeric chains are the main degradation products of PCL, which were simultaneously released during thermal decomposition of this polymer. Meanwhile, carboxylic acid, aldehydes, and lactide monomer and/or oligomers were evolved from degradation of PLA. Finally, carboxylic acids and ester moiety were detected in the course of degradation of PHB; thus, random chain scission reaction took place during thermal decomposition of this polymer. Results from the spectroscopic characterization (FTIR and
1
H NMR) of partially degraded samples supported the degradation mechanisms suggested by TGA/FTIR studies.
The electrical, mechanical and piezoresistive responses of vinyl ester nanocomposites made of two types of multilayer graphene sheets (GSs) and multiwall carbon nanotube hybrid fillers at different ...relative concentrations is presented. Two types of GSs are used in order to evaluate the role of their physicochemical properties. The best mechanical properties were achieved with hybrids at 75% relative concentration of GSs. Collaborative effects were also observed in the electrical conductivity of the hybrids at this relative concentration. The flexural piezoresistive response yielded low sensitivity (with both, positive and negative gage factors) at the compression side of the flexural coupon. On the contrary, the tensile side of the coupon always presented positive resistance changes and significantly higher piezoresistive sensitivity. The highest piezoresistive sensitivity was found for hybrid materials with 75% relative concentration of GSs, using the graphenic sheets with larger lateral dimensions and higher structural quality (lower Raman ID/IG ratio).
