The influence of the nanofiller on thermal properties of thermoplastic polyurethane elastomers

Pure Fe₃O₄ and Mn-doped Fe₃O₄ nanoparticles were synthesized by simple wet chemical reduction technique using nontoxic precursors. Manganese doping of two concentrations, 10 and 15%, were employed. All the three synthesized nanoparticles were characterized by stoichiometry, crystal structure, and surface morphology. Thermal studies on as-synthesized nanoparticles of pure ferrite (Fe₃O₄) and manganese (Mn) doped ferrites were carried out. The thermal analysis of the three as-synthesized nanoparticles was done by thermogravimetric (TG), differential thermogravimetric, and differential thermal analysis techniques. All the thermal analyses were done in nitrogen atmosphere in the temperature range of 308–1233 K. All the thermocurves were recorded for three heating rates of 10, 15, and 20 K min^?1. The TG curves showed three steps thermal decomposition for Fe₃O₄ and two steps thermal decompositions for Mn-doped Fe₃O₄ nanoparticles. The kinetic parameters of the three as-synthesized nanoparticles were evaluated from the thermocurves employing Kissinger–Akahira–Sunose (KAS) method. The thermocurves and evaluated kinetic parameters are discussed in this paper.     

Structure and thermal stability of aliphatic polyoxamides

A homologous series of aliphatic polyoxamides, nylon 122, 102, 82, and 62, were prepared by the bulk polycondensation of dialkyl oxalates with diamines. Infrared spectroscopy, x-ray diffraction, differential thermal analysis, thermogravimetric analysis, and gas chromatography were used to study the structure and thermal stability of these polyoxamides. From the fiber pattern of nylon 122, a structural repeat distance of 19.5 Å was measured. This was in close agreement with the expected value for an extended planar, zigzag chain conformation. With the exception of the expected decrease in the structural repeat distance along the chain axis resulting from the different number of methylene groups, nylons 122, 102, and 82 were isostructural. Nylon 62 appeared to pack in a similar manner to the other materials studied. However, there were differences in the diffraction pattern of this polymer; these may be indicative of a different chain conformation or of strain in the crystalline regions of the polymer. The infrared spectra indicate the presence of strong hydrogen bonding in all the polymers. Thermal analysis and pyrolysis data revealed catastrophic polymer degradation between 400 and 500°C in nitrogen, with appreciable homolytic cleavage of the oxamide group.     

Influence of fillers on the thermal stability of elastomers. Thermogravimetric study

The thermal degradation of hydrocarbon elastomers and polychloroprene in the presence of silica, clay, precipitated calcium carbonate and carbon black has been studied using dynamic thermogravimetry. The influence of fillers on degradation parameters of elastomers and activation energy was discussed.

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Zusammenfassung Mittels DTG wurde der thermische Abbau von Kohlenwasserstoffelastomeren und Polychloropren in Gegenwart von Siliziumdioxid, Tonerde, gefälltem Calciumcarbonat und Ruß untersucht. Weiterhin wurde der Einfluß der Streckmittel auf den Abbau der Elastomere und auf die Aktivierungsenergie besprochen.

     

Synthesis, characterization and mechanical properties of polyester-based aliphatic polyurethane elastomers containing hyperbranched polyester segments

Aliphatic polyester-based polyurethane (PU) elastomers with hyperbranched polyester segments were synthesized from polyester diol, hydroxyl-terminated hyperbranched polyester (HB-20), isophorone diisocyanate (PDI) and 1,4-butanediol. The crosslinking density of the PU elastomer was calculated by using Flory-Rehner equation. The degree of hydrogen bonding, the microstructure and the morphologies of these PU materials were characterized by means of FT-IR, WAXD and DSC, respectively. The experimental results showed that the PU elastomers containing small amount of HB-20 exhibited the enhanced hydrogen bonding and mechanical properties. As compared with the comparable PU specimen, the tensile strength of the polyester-based aliphatic PU containing 6 wt% HB-20 increased by 71.2 times, up to 36.1 MPa, and the elongation at break was still as high as 333.1%, resulting from the dual effects of the hydrogen bonding and the crosslinking density in the PU system.     

Diaminobisbenzothiazole chain extended polyurethanes as a novel class of thermoplastic polyurethane elastomers with improved thermal stability and electrical insulation properties

This work was devoted to the development of a new class of modified polyurethane as an electrical insulating material. For this purpose, NCO‐terminated urethane prepolymers at different NCO contents were prepared and chain extended by 6,6′‐oxybis(2‐aminobenzothiazole) (ABT) to produce thermoplastic polyurethane elastomers. All of the polymers were characterized by FTIR and ¹HNMR spectroscopies and examined for their thermal, mechanical, and electrical properties. The dynamic mechanical measurements results showed two glass transitions indicating phase separation. A considerable improvement in the thermal and electrical properties in comparison to common polyurethanes was detected for these polymers. The level of enhancement in the measured properties was related to the polyol molecular weight, hard segment content, and consequently the amount of the introduced urea and benzothiazole moieties. These findings indicated the improved high service temperature performance of these materials as electrical insulator for metallic surfaces. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of iron content on thermal stability of magnetic polyurethane foams

Magnetorheological (MR) materials are a group of smart materials which have the controllable magnetic properties with an external magnetic field. Magnetic foams, a specific type of MR solids, were synthesized from flexible polyurethane (PU) foams and carbonyl iron particles. Effects of the carbonyl iron particles on the thermal stability of the magnetic foams have been studied. Thermogravimetric analysis (TGA) was applied to characterize the thermal degradation process of the magnetic foams and then the apparent activation energy of degradation was calculated by using Ozawa's method [Ozawa T. A new method of analyzing thermogravimetric data. Bulletin of the Chemical Society of Japan 1965; 38: 1881-1886.]. The carbonyl iron particles were found to improve the thermal stability of magnetic foams in nitrogen by showing higher 10 wt% loss temperature, slower weight loss rate and higher apparent activation energy than pure PU foams. But the magnetic foams were observed to have slightly worse thermal stability in air than pure PU foams at the earlier degradation stage. At the later degradation stage, the magnetic foams exhibited the higher activation energy than pure PU foams in air.     

The thermal degradation of some fluorine-containing elastomers

Polymers containing both hydrogen and fluorine atoms can give rise to the evolution of hydrogen fluoride (HF) on thermal and thermo-oxidative degradation. This evolution has been studied with the aid of a fluoride ion specific electrode. The effect of formulation has been examined in some detail for a hydrofluoro-elastomer and it has been shown that the yield of HF is greatly affected by changes in formulation. The effect of variation in chemical structure has also been studied by comparing the degradation of hydrofluoro-, perfluoro-, phosphazene- and fluorine-containing siloxane elastomers. The perfluoro elastomer is the most stable, and the phosphazene elastomer the least stable of the polymers examined, although they both give low yields of HF.     

Thermal analysis of polyurethane elastomers matrix with different chain extender contents for thermal conductive application

Polyurethane elastomers (PUR) based on polypropylene glycol and 4,4′-diphenylmethane diisocyanate were prepared with various monoethylene glycol (mEG) contents. The aim of this study is to find a reliable polymer matrix for composites of improved thermal conductivity and testing fully in order to collect knowledge about its structure. Thermal conductivity was improved from 0.255 to 0.329 W m^?1 K^?1 when increasing chain extender content. This attributed to a high appearance crystalline ordering level when adding high mEG content. Differential scanning calorimetry revealed a low transition temperature of soft segment at the same temperature around ??64 °C, due to constant polyol content. The enthalpy of melting increases with increasing mEG content. This is due to the increasing crystalline phase and hard segment phase separation within the PUR structure. Dynamic mechanical analysis results show the glass transition temperature of soft segment in the same temperature range between ??57 and ??52 °C and intensity peak of tanδ tends to decrease when mEG content was increased. On the other hand, the glass transition temperature of hard segment tends to increase from 10 to 93 °C and has high intensity peak of tanδ with increasing mEG content. Increasing the chain extender content can be enhancing the hard segment length in PUR structure and affecting both soft segment motion and hard segment motion. Increasing hard segment length might be obstructing soft segment motion and influence hard segment motion which is hard to move at low temperatures. Phase separation of soft and hard segment clearly observed using the DMA technique.

     

Improving thermal stability of biodegradable aliphatic polycarbonate by metal ion coordination

Poly(propylene carbonate) (PPC), a typical aliphatic polycarbonate, has attracted much attention during the last two decades due to its biodegradability and commercializing perspective. However, the application of this material as thermoplastics has been limited by its poor thermal stability. Metal soaps, such as calcium stearate (CaSt₂), are important processing additives in plastics industry. In the present work, PPC-CaSt₂ complexes were prepared, the thermal stability of which was investigated by thermogravimetric analysis (TGA). The results show that the complexes are more thermal stable than pure PPC material. Supramolecular lamellar mesomorphous structures of the complexes were corroborated by the combination of small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and polarizing optical microscopy (POM). Metal ion coordination of CaSt₂ to flexible PPC chains was determined by Fourier transform infrared spectroscopy (FT-IR). This coordination interaction plays the key role in improving the thermal property of PPC and constructing the self-organized structure of the complexes.     

Thermal analysis of the structure of segmented polyurethane elastomers

Polyurethanes were prepared from 4,4′-methylenebis (phenyl isocyanate) (MDI), 1,4-butanediol (BD), and poly(tetrahydrofurane) polyether polyol (PTHF) by melt polymerization. The –OH functional group ratio of polyol/total diol was kept constant at 0.4, while the ratio of the isocyanate and hydroxyl groups (NCO/OH) changed between 0.940 and 1.150. The thermal analysis of the polymers by DSC and DMTA measurements indicated several transitions. The three glass transition temperatures observed were assigned to the relaxation of the aliphatic –CH₂– groups of the polyol, and to that of the soft and hard segments, respectively. The glass transition temperature of the soft and hard phase changed with the NCO/OH ratio indicating changes in phase structure and composition confirmed also by the maximum in the number of relaxing soft segments. Changes in the relatively small number of end-groups result in considerable modification of mechanical properties. Strength is determined by molecular mass and interactions, while stiffness depends mainly on phase structure. Surprisingly enough, –OH excess yields stiffer polymers, since the interaction of the –OH groups results in a decrease in the amount of the soft phase. A unique correlation was found between tensile modulus and the number of relaxing soft segments.     

Tensile deformation behaviour of the polymer phase of flexible polyurethane foams and polyurethane elastomers

The change in micromorphology of the polymer phase (single strut) of a flexible polyurethane foam during deformation has been investigated by attenuated total reflection infrared spectroscopy - linear dichroism and by atomic force microscopy. Deformation and, therefore, orientation take place mainly in the soft rubbery phase. This two-phase elastic deformation process has been translated into a mathematical model, which correctly predicts the shape of a single-strut stress-strain curve. The theory also predicts the ultimate shape of stress-strain curves of polyurethane elastomers at various hard phase contents and of low-density polyethylene at various temperatures. Deviations from the elastic behaviour could be ascribed to yielding in combination with the rubbery behaviour.     

聚酯的序列结构对聚氨酯弹性体形貌的影响

以己二酸(AA),1,4-丁二醇(BDO),乙二醇(EG)分别采用一步法、二步法合成分子量为3000的聚酯PAEB-R和聚酯PAEB-A.再分别与二苯基甲烷二异氰酸酯(MDI)、扩链剂1,4-丁二醇(BDO),乙二醇(EG)反应分别合成固含量30%与粘度为20000的聚氨酯(PAEB-R)-MDI-TPU和聚氨酯(PAEB-A)-MDI-TPU.SEM、AFM表明不同工艺所合成的聚氨酯均存在微相分离,且聚氨酯(PAEB-R)-MDI-TPU微相分离程度高于(PAEB-A)-MDI-TPU.     

The study of regenerated cellulose films toughened with thermoplastic polyurethane elastomers

Regenerated cellulose blend film with thermoplastic polyurethane (TPU) was successfully prepared by coagulating cellulose/TPU solution with water in the presence of a thermoplastic polyurethane elastomer (TPU). Compared with pristine regenerated cellulose film, the toughness and thermal stability of the blend film was significantly improved. For example, the elongation at break was increased from 11% of pristine cellulose film to 51% of blend film with 20 wt. % TPU. The 50% weight loss temperature of this blend film was increased by 33 °C compared to neat cellulose. The relaxation transition temperature of cellulose was decreased with the addition of TPU through dynamic mechanical thermal analysis. The oxygen permeability was decreased from 2.3 × 10⁻¹⁰ cm³ cm/cm² s Pa of pristine cellulose film to 0.08 × 10⁻¹⁰ cm³ cm/cm² s Pa of the blend film with 20 wt.%. TPU The X-ray diffraction spectra showed that the crystallinity of cellulose decreased with incorporation of TPU. The images of scanning electron microscope discovered that there was good compatibility between cellulose and TPU. TPU was nano-dispersed in cellulose matrix. The blend film still maintained quite good transparency.     

Crosslinked PDMS elastomers and coatings from the thermal curing of vinyl‐functionalized PDMS and a diazide aliphatic crosslinker

The crosslinking of poly(dimethylsiloxane) elastomers and coatings by the thermal curing of poly(dimethylsiloxane‐co‐methylvinylsiloxane) and 1,12‐diazido‐dodecane was studied. This crosslinking pathway relies on the cycloaddition of azides and alkenes as well as the thermal generation of nitrene transient radicals, which react with alkenes, yielding respectively 1,2,3‐triazoline and aziridine crosslinking knots. The influence of temperature and the ratio of azide and vinyl functionalities has been investigated by rheological, swelling, and insoluble fraction measurements for materials crosslinked in bulk and by comparison of the thickness before and after extraction of the soluble materials by soxhlet extraction for the crosslinked coatings. The preparation of highly crosslinked PDMS‐based elastomers and coatings has been demonstrated, even if the fraction of elastically effective crosslinks in bulk remained below 160 mol/m³. Advantageously, this system does not require additional initiator or catalyst, is not sensitive to moisture or oxygen, and can be extended to a wide range of unsaturated polymers as well as different organic or inorganic solid substrates. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Comparison of the characteristics of polyurethane elastomers based on DMC- and traditional polyethers

The results of the study of replacement of traditional polyether polyols with DMC polyols based on the new DMC technology in formulas of polyurethane (PU) elastomer adhesives and sealants are presented. It is shown that the physical and mechanical characterisrics of PU elastomers are improved in many cases.     

Synthesis and characterization of second-order nonlinear optical polyurethane with high thermal stability

A second-order nonlinear optical polyurethane was formed with an X-type multi-dimensional charge-transfer (CT) chromophore (DNPIPDHPI) and 3,3^′-dimethoxy-4,4^′-diphenyl diisocyanate. Simultaneous poling and polymerization and in situ second harmonic generation (SHG) measurement technique was carried on to evaluate the thermal stability of the poling induced orientation. The SHG signal of the poled polymer film was not decay below 150 °C and remains 90% of relative d₃₃ value at 200 °C, which is better than the results reported in literature. Comparison of thermal stability indicates that the X-type chromophores possess better property in controlling the decay of the SHG activity than classic chromophores.     

Mechanical behavior during different weathering tests of the polyurethane elastomers films

Segmented poly(ester-urethane)elastomers (PU) based on poly(ethylene diethylene adipate) diols as a soft segment and aromatic diisocyanates in the hard segment were synthesized by a conventional method. The precipitated and compact polyurethane films have been degraded after a limited exposure to natural weathering. The effects on mechanical properties of precipitated and compact polyurethane films were found to be a measure of the degradation due to weathering. The present study attempts to correlate the physical-mechanical properties of the precipitated polyurethane and compact films with time of weathering. In all cases a certain amount of oxidative change had been initiated. This was probably associated with enzyme adsorption on surfaces. We compared natural weathering of PU films carried out in earth, seawater and exposure to sunlight with untreated samples. In common with other weathering tests, the effect was to decrease the ultimate tensile strain, except seawater. It was found that enzymatic degradation in the earth occurred only after, the ageing process was continuous and practically linear with a relatively short initial period of increase in degradation rate.     

The physical crosslinking of polyurethane elastomers studied by X-ray investigation of model urethanes

Polyurethane elastomers extended with aliphatic glycols or diamines, show a characteristic fluctuation in their thermal and hydrothermal properties which is dependent on the number of CH₂ groups in the chain extender (even or odd).The causes of this behavior are examined in the following report using X-ray crystallographic analyses of single crystals of model urethanes. These model compounds were prepared by reaction between diphenylmethane -4-mono-isocyanate and glycoles of the HO-(CH₂)_n-OH structure withn=2 to 6.Whilst strain-free hydrogen bonds can form between neighboring molecules in urethanes with even chain extenders, significant strains occur in urethanes containing odd chain extenders which result in reduced stability of the physical crosslinking system.In memoriam to Prof. Dr. Dr. h. c. mult. Otto Bayer.     

The effect of processing conditions on the mechanical properties and thermal stability of highly oriented PP tapes

It has previously been shown possible to use highly oriented polypropylene (PP) tapes to create self-reinforced (all-PP) composites. It is desirable to understand the relationship between tape processing parameters and the mechanical properties and thermal stability of the tapes, as these tape properties will govern the ultimate properties of the all-PP composite. In this paper, the effects of the tape drawing parameters such as draw ratio (λ), drawing temperature and thermal annealing on the final mechanical properties, density and dimensional thermal stability of the tapes are presented. PP tapes drawn to λ = 17 possess tensile moduli of ～15 GPa and tensile strengths of ～450 MPa. PP tapes with high draw ratios, λ > 9.3, show a decrease in density, a change from transparent to opaque appearance and increased dimensional thermal stability with increasing draw ratio. The results of an investigation into the effects of a thermal annealing step, targeted at improving the dimensional thermal stability of these highly oriented PP tapes, are also presented.