Polyurethanes (PUs) from Polyethylene glycol (PEG) and polycaprolactone diol (PCL) and a crosslinker, Pentaerythritol (PE), were synthetized with isophorone diisocyanate (IPDI). In this study, we investigated the effect of polyol and crosslinker composition on phase separation and thermo-mechanical properties. The properties were studied through dynamic mechanical analysis, X-ray scattering, atomic force microscopy (AFM), and thermogravimetric analysis (TGA). The results showed changes in PUs properties, microphase structure, and separation due to the composition of polyol/crosslinker blend. So, the largest concentration of PE produced multimodal loss factor patterns, indicating segment segregation while PUs with a PEG/PCL = 1 displayed a monomodal loss factor pattern, indicating a homogeneously distributed microphase separation. Additionally, the increase of the PEG concentration enhanced the damping capacity. On the other hand, agglomeration and thread-like structures of hard segments (HS) were observed through AFM. Finally, the thermal behavior of PUs was affected by chemical composition. Lower concentration of PE reduced the crosslinking; hence, the temperature with the maximum degradation rate.Polymers 2020, 12, 666 2 of 13 separation can lead to property changes because SS are responsible for the softness, flexibility, and rubbery behavior, while HS are related to stiffness and mechanical behavior. The elastomeric behavior of PUs results from embedding HS in SS, where the HS acts as crosslinker due to hydrogen bonding [5]. Hence, the segregation of HS and SS mediate PU properties. Aforesaid segregation can be studied by several microscopic, spectroscopic and crystallographic techniques like Atomic force microscopy (AFM), infrared spectroscopy (IR), both small (SAXS) and wide (WAXS) angle X-ray scattering.Previous research has described this segregation as a function of the composition and chemical structure of monomers, and its effect on PU properties. e.g., Klinedinst, D. et al. [4] studied the effects of varying the SS molecular weight and overall HS content thermoplastic segmented PUs. They used AFM and dynamic mechanical analysis (DMA) to identify a thread-like microphase separated structure in chain-extended systems. A higher polyol molecular weight increased the partial crystallization of SS at lower temperatures than room temperature, and larger SS/HS incompatibility, which induced greater microphase separation and a larger storage modulus plateau magnitude. The larger HS mass also increased the temperature at which HS melting occurred, broadening the storage modulus plateau.Some works have focused on the study of the chain extender or crosslinker structure. Like, Kim, H-N., et al.[1] who compared PU microphases with three chain extenders: isosorbide (ISB), isomannide (IMN), and 1,4-butanediol (BD). According to the SAXS results, the scattering widths of IMN and ISB-based PUs were larger than those of BD-based PUs, indicating that the HS domain sizes in the IMN and ISB-based PUs were smaller. It als...

In the present study, polyurethane materials were obtained from castor oil, polycaprolactone and isophorone diisocyanate by incorporating different concentrations of chitosan (0.5, 1.0 and 2.0% w/w) as an additive to improve the mechanical properties and the biological activity of polyurethanes. The polyurethanes were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, stress/strain fracture tests and swelling analysis, and the hydrophilic character of the surface was determined by contact angle trials. The objectives of the study were to evaluate the effect of the incorporation of chitosan on the changes of the physico-chemical and mechanical properties and the in vitro biological activity of the polyurethanes. It was found that the incorporation of chitosan enhances the ultimate tensile strength of the polyurethanes and does not affect the strain at fracture in polyurethanes with 5% w/w of polycaprolactone and concentrations of chitosan ranging from 0 to 2% w/w. In addition, PCL5-Q-PU formulations and their degradation products did not affect cell viability of L929 mouse fibroblast and 3T3, respectively. Polyurethane formulations showed antibacterial activities against Staphylococcus aureus and Escherichia coli bacteria. The results of this study have highlighted the potential biomedical application of this polyurethanes related to soft and cardiovascular tissues.

CeO2-, ZrO2-, and La2O3-supported Rh-Pt catalysts were tested to assess their ability to catalyze the steam reforming of ethanol (SRE) for H2 production. SRE activity tests were performed using EtOH:H2O:N2 (molar ratio 1:3:51) at a gaseous space velocity of 70,600 h −1 between 400 and 700 °C at atmospheric pressure. The SRE stability of the catalysts was tested at 700 °C for 27 h time on stream under the same conditions. RhPt/CeO2, which showed the best performance in the stability test, also produced the highest H2 yield above 600 °C, followed by RhPt/La2O3 and RhPt/ZrO2. The fresh and aged catalysts were characterized by TEM, XPS, and TGA. The higher H2 selectivity of RhPt/CeO2 was ascribed to the formation of small (~5 nm) and stable particles probably consistent of Rh-Pt alloys with a Pt surface enrichment. Both metals were oxidized and acted as an almost constant active phase during the stability test owing to strong metal-support interactions, as well as the superior oxygen mobility of the support. The TGA results confirmed the absence of carbonaceous residues in all the aged catalysts.

Polyurethanes (Pus) were synthesized from castor oil and modified through transesterification by pentaerythritol, poly(e-caprolactone)diol (PCL), and isophorone diisocyanate to form PU coatings. The ratio of NCO/OH groups used was 1:1. The effect of varying the PCL content on the physical properties of wood panel PU coatings was determined. The PU coatings were characterized using Fourier transform infrared spectroscopic analysis, and the physicochemical properties, such as tensile strength, elongation at the break, shore A hardness, and the results of a lap shear test, were reported. Thermal properties of the PU coatings were evaluated using differential scanning calorimetry and thermogravimetric analysis. In vitro PU degradation was related to the hard segment structure and polymer hydrophilicity.

The objective of this study was to assess the effects of type of polyol and concentration of polycaprolactone (PCL) in polyurethanes (PUs) on microbial degradability, cytotoxicity, biological properties and antibacterial activity to establish whether these materials may have biomedical applications. Chemically modified and unmodified castor oil, PCL and isophorone diisocyanate in a 1:1 ratio of NCO/OH were used. PUs were characterized by stress/strain fracture tests and hardness (ASTM D 676-59). Hydrophilic character was determined by contact angle trials and morphology was evaluated by scanning electron microscopy. Degradability with Escherichia coli and Pseudomonas aeruginosa was evaluated by measuring variations in the weight of the polymers. Cytotoxicity was evaluated using the ISO 10993-5 (MTT) method with mouse embryonic fibroblasts L-929 (ATCC® CCL-1) in direct contact with the PUs and with NIH/3T3 cells (ATCC® CRL-1658) in indirect contact with the PUs. Antimicrobial activity against E. coli and P. aeruginosa was determined. PUs derived from castor oil modified (P0 and P1) have higher mechanical properties than PUs obtained from castor oil unmodified (CO). The viability of L-929 mouse fibroblasts in contact with polymers was greater than 70%. An assessment of NIH/3T3 cells in indirect contact with PUs revealed no-toxic degradation products. Finally, the antibacterial effect of the PUs decreased by 77% for E. coli and 56% for P. aeruginosa after 24 h. These results indicate that PUs synthesized with PCL have biocidal activity against Gram-negative bacteria and do not induce cytotoxic responses, indicating the potential use of these materials in the biomedical field.