Search

The polyester diol obtained from the glycolysis of the recycled PET flakes was used to synthesize the polyurethanes of PU-1, PU-1.7, and PU-2 that the numbers indicate the isocyanate to hydroxyl groups (NCO/OH) molar ratios. The nanocomposites of PUs with hydroxylated multiwalled carbon nanotube (MWCNT) (PUCNT-1.7 and PUCNT-2) were synthesized via in situ polymerization, while the PUCNT-1 was not synthesized due to the steric hinderance effect of MWCNT. It was shown that the NCO/OH molar ratios and the added MWCNT govern the crosslink degree of the samples. Because, the good creep–recovery behavior of the under-loaded polymers in long time applications has remarkable importance for polymer engineers, the creep–recovery behavior of PUs and their nanocomposites was studied by dynamic mechanical analysis (DMA). Nevertheless, there has been no report on the creep–recovery behavior of these PET originated polyurethanes. The well-known models of Power law and Burgers (for fitting the creep experimental data), and Weibull model (for fitting the recovery experimental data) showed the good agreements with the empirical data. The creep strain of the samples was in the order PU-1 > PUCNT-1.7 > PU-2 > PU-1.7 > PUCNT-2. It was found that the crosslink-degree of the samples and also the opposing effects of MWCNT (the reinforcing and hindrance effects) are the important parameters that govern Young modulus, creep, and recovery of the samples. PU-1.7 due to its higher crosslink-degree showed the lower creep–recovery strain in comparison to PU-2 and PU-1. The lower creep–recovery strain of PUCNT-2 as compared to other samples can be attributed to the dominant reinforcing effect of MWCNT in this sample, whereas the high creep–recovery strain of PUCNT-1.7 was assigned to the dominant hindrance effect of MWCNT. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers

Disposal of plastics in the environment has become a core of anxiety in developing countries, while in the developed countries the focus has additionally been placed on design and manufacture of emerging products from plastic wastes—a somewhat vague yet promising horizon. Central to environmental concerns are poly(ethylene terephthalate) (PET) wastes, mainly from post-consumer bottles. Because of a considerable drop in molecular weight in the course of recycling, recycled PETs are not suitable for engineering uses. An efficient yet reasonably green synthesis route is employed here to convert PET wastes into polyurethane, and then carbon nanotubes (CNTs) was added at different levels to obtain nanocomposites with high mechanical properties. The effects of isocyanate (NCO)/hydroxyl (OH) molar ratio and CNTs content on the morphology, physical and mechanical properties were discussed. Chemical/physical crosslink density was calculated from initial slope of stress–strain curves, Mooney–Rivlin plots, strain-hardening modulus, rubbery-plateau storage modulus and swelling data. High tensile strength (300 MPa) and breaking elongation (160%) of polyurethane/CNTs nanocomposites born from PET wastes seemed promising. Microscopic analyses by AFM, SEM, and TEM gave useful information about distribution of CNTs in polyurethane. Lastly, structural changes were correlated to mechanical properties improvement.

In this work, an attempt is made to present an in-depth investigation on the temperature and frequency dependences of viscoelastic properties of polyurethanes and PU nanocomposites containing multi-walled carbon nanotubes (CNTs) obtained from polyethylene terephthalate (PET) waste through dynamic mechanical analysis. The experimental results indicate that NCO/OH molar ratios and nanoparticles can have a marked effect on the ultimate properties and performance of the polyurethanes and their corresponding nanocomposites produced from PET waste. The opposite effects of the reinforcing and steric hindrance of CNT in the studied nanocomposites can be the reason for the observation of some unexpected results. Relaxation spectra were also subsequently calculated by means of two consecutive approximation methods. Good conformity was observed between the data from storage modulus (E′) and loss (modulus) E″ by the second approximation in relaxation spectra which confirmed the internal consistency of the experimental data. In the end, TEM images confirmed the effect of the reinforcing of CNT in the PUCNT-2 as demonstrated by DMA results. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

Waste recycling is considered a major concern for industry due to the environmental regulations imposed on industry to protect the environment. In this regard, chemical methods are not only helpful in the decomposition of wastes but also in upgrading them into worthwhile commercial materials. In this investigation, soft-drink bottles composed of polyethylene terephthalate (PET) were depolymerized via glycolysis using 2-methyl-1,3-propanediol (MPD) to obtain oligomeric dioles (diol). Nevertheless, there has been no report on the use of MPD in PET degradation. Diol can be reacted with adipic acid to lengthen the chains to obtain a polyester diol. This polyester diol has the potential for further reactions to produce various products. Here, the diol and polyester diol were characterized using FT-IR, 1H-NMR spectroscopy, and viscosity-Brookfield tests. Moreover, the molecular weight and concentration of the hydroxyl groups were determined. In the second step, novel value-added polyurethanes (cross-linked and non-cross-linked) and carbon nanotube-based polyurethane composites with different molar ratios of diisocyanate to diol (NCO/OH) were prepared using hexamethylene diisocyanate (HDI), polyester diol, and carbon nanotubes. Fourier transform infrared spectra, the thermal transitions, and degradation of the synthesized polyurethanes and nanocomposites were investigated. The swelling characteristics of the cross-linked polyurethanes were fully studied in a wide variety of non-polar to polar solvents. The diffusion profile in different solvents and the absorption kinetics were evaluated as well. The transportation of the solvents showed a Fickian sorption mechanism, while the absorption kinetics followed a pseudo-second-order model. The influence of the NCO/OH molar ratio on the swelling behavior was also investigated. The polyurethane samples, obtained from PET waste, could be used in various applications, such as industrial parts, membranes and O-rings.

Many polyols or diols have been used for the synthesis of polyurethanes (PU), however, to the best of our knowledge, PU-graphene oxide (GO) nanocomposites synthesized with ester-based polyols have been rarely studied. In this work ester-based polyol synthesized by the reaction of adipic acid and 1,4 butane diol, was in-situ polymerized with hexamethylene diisocyanate (HDI) and GO to prepare PU-GO nanocomposites. The content of GO was changed from 1 to 2.5 wt% and its effect on the mechanical, thermal and electrical properties of the samples were examined. The presence of GO more than 1.5% in the nanocomposites resulted in brittle samples and reduced the tensile strength, however, the Young’s modulus of the samples containing 1 and 1.5% was increased to 11 and 12.08-fold (275 and 302 MPa) compared to the neat PU (25 MPa), respectively. The shore A hardness of the samples was increased from 86 for PU to 96 for PUGO-1.5. The abrasion resistance of the samples was decreased by increasing the GO content. Results of the thermogravimetric analysis showed that higher amounts of GO increase the thermal stability of the samples. The chemical and physical interactions between the surface of GO nanolayers and the PU chains were confirmed by FTIR spectroscopy. The dynamic mechanical analysis of the samples showed that GO nanolayers decreased the molecular motions of the PU chains in the nanocomposites which were noticed by shifting the glass transition to the higher temperatures.

Polyurethanes (PUs) were prepared by in situ polymerization of three diisocyanate with three synthesized low cost ester-based polyols. The effect of diisocyanate type, diol structure, and molar ratio of diisocyanate to polyol on the mechanical properties was examined and the optimum chemical structure was introduced regarding the superior mechanical properties. Also, in presence of well dispersed hydroxylated multi-walled carbon nanotubes (CNT), PU/CNT nanocomposites were synthesized and fully characterized. The results showed that PU synthesized based on 1,4-butane diol (BDO) has the best mechanical properties and thermal stability. Also, the PU samples synthesized from 1,6-hexamethylene diisocyanate (HDI) were more profitable than aromatic diisocyanate structures due to higher crystallinity and microstructure packing. The nanocomposite sample containing 1.5% CNT was the optimum composition for the maximum tensile strength and electrical conductivity. This result was related to the uniform dispersion and bonding of CNTs to PU chains at this composition, while aggregates were formed at higher concentration of CNTs which increased the defects and reduced the uniformity of the structure. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44567.

Chemical recycling of PET has been developed by various methods. Aminolysis is one of chemical recycling methods of PET has been developed recently. The obtained product using aminolysis, Bis (2-hydroxy ethylene) terephthalamide (BHETA), has the potential for further reactions to obtain useful products. There are few reports on usage of recycled BHETA from PET waste to synthesis of polyurethanes. On the other hand, various biodegradable polyurethanes have been synthesized using polycaprolactone diol. Therefore, caprolactone is a new potential in synthesis of biodegradable polyurethanes from PET waste. In this work, novel biodegradable polyurethanes have been synthesized using BHETA. In this order, at first polyols with different molecular weights have been synthesized through ring opening polymerization of caprolactone by BHETA, then urethane linkages were formed using HDI (Hexamethylene Diisocyanate) without chain extender. Chemical, thermal, mechanical and dynamic mechanical properties, biodegradability, morphology and UV resistance of synthesized polyurethanes have been investigated.