Thermoplastic Urethane Elastomers Research Articles

Highly Compressible Polymer Composite Foams with Thermal Heating-Boosted Electromagnetic Wave Absorption Abilities.

Polymer composite foams are desirable materials for electromagnetic (EM) energy attenuation. However, a number of challenges limit improvement in the EM energy attenuation properties of foams. In this study, a simple microcellular injection molding method was used to fabricate highly compressible thermoplastic urethane (TPU)/carbon nanotube (CNTs) composite foams, which also had increased conductivity with an increase in CNT content. Compared to unfoamed composites, foamed composites exhibited higher conductivity and EM attenuation properties because of the presence of a microcellular structure. Moreover, the TPU/CNT foam with 4 wt % CNTs (F(4)) demonstrated strong EM dissipation and an optimal reflection loss (RL) value of -30.4 dB. Furthermore, stimulated by thermal heating and cyclic compression, EM attenuation was observed to increase because of the higher conductivity. Note that F(4) foam having a small thickness of 1.3 mm when treated at 333 K had the highest EM dissipation and the lowest RL value of -51.8 dB. Enhanced polarization and ohmic losses and multiscattering were responsible for the increased EM absorption. This behavior is attributed to the movement of CNTs within the TPU elastomer walls via thermal or compression stimulation. For designing stimulation-dependent multifunctional materials, composite foams with response to thermal heating were proved to be an alternative approach.

Controlling Thermoplastic Elastomer Optical Properties by Mechanical Processing

ABSTRACTWe demonstrate that the extrusion speed of thermoplastic urethane elastomer can modify its optical transmission by a factor of more than 100. Varying extrusion speed at constant temperature may tune optical properties along the axis of a filament, for example creating absorbent regions that are sensitive to length and diameter changes, surrounded by more transmissive segments that carry the sensor signal over long distances. Such waveguiding in a stretchable optical fiber requires a stretchable cladding with lower refractive index than the core. In experiments toward a rugged, stretchable fiber cladding, we investigated whether solvents could modify the outer structure of the filaments. Soaking the filaments in NMP (n-methyl-2-pyrrolidone), then stretching the filaments while the solvent dried, turned out to modify the filaments in a way that solvents alone did not, creating porosity and reducing the appearance of optical clarity.

Synthesis and characterization of PMMA/PEG-TPE semi-interpenetrating polymer networks

Two-component semi-interpenetrating polymer networks (Semi-IPNs) of thermoplastic urethane elastomer based on poly(ethylene glycol) and polymethyl methyacrylate were synthesized by the sequential technique. The Semi-IPNs obtained were characterized with respect to their mechanical properties such as tensile strength, elongation. Glass transition temperatures were carried out using dynamic mechanical thermal analysis. Phase morphology was studied by scanning electron microscopy. The effect of the compositional variation on the above-mentioned properties was examined. The results demonstrate that the components are immiscible, phase separation at the micrometer scale is observed, the extent of interpenetrating is dependent on variations in composition.

The effect of moisture on the properties of thermoplastic urethane elastomers in molten state

The effect of moisture on the properties of thermoplastic urethane elastomers in molten state

Thermoplastic urethane elastomers. VI. Dilute solution properties in various solvents

AbstractA thermoplastic urethane elastomer prepared from a polycaprolactone diol, 4,4′‐diphenylmethane diisocyanate, and 1,5‐pentanediol was fractionated and the solution properties of the fractions were characterized in terms of viscosity and sedimentation. Mark‐Houwink relations were established for data obtained at 30° in various solvents: In dimethylacetamide, tetramethylurea, and N‐methyl pyrrolidone, the value of Kθ increased systematically in the range (1.7 to 2.0) × 10−3. Lower values of Kθ were obtained in dimethylformamide (0.8 × 10−3) and meta‐cresol (0.9 × 10−3). The molecular expansion coefficients in the various solvents were approximated from the experimental viscosity data. Short‐range interactions between the solvent molecules and polymer chains are suggested as possible causes for differences in the hydrodynamic parameters.

Thermoplastic urethane elastomers based on optically active poly(oxy-1,2-propylene)-α,ω-diol

Thermoplastic urethane elastomers based on optically active poly(oxy-1,2-propylene)-α,ω-diol

Castable Thermoplastic Urethane Elastomers I. Formulation and Applications as Removable Encapsulants

Castable thermoplastic polyurethane formulations with im proved upper and lower temperature capability have been developed for use as removable electronics packaging matenals. Two formulations have been developed employing a two step prepolymer processing technique. One consists of 58/42 ratio of polyether to polyester diols reacted with bitolylene diisocyanate to form a prepolymer; this step is followed by reaction with 1,4 butanediol. The second contained a 64/36 ratio of poly ether to polyester diol reacted in the same manner as above. The first formulation exhibited a tensile strength of 13.1 MPa, an elongation of 500%, and a modulus of 145 MPa; the second gave a tensile strength of 7.58 MPa, elongation 275%, and modulus of 124 MPa. These property differences resulted from differences in microphase structure between hard and soft segments in these linear polyurethanes. Both formulations were essentially free of creep over an 80 hour period at 70°C. These casting resins can be processed with a filler (e.g., Al2O3) which reduces the coeffi cient of thermal expansion from ∼ 160 × 10-6 to ∼ 100 × 10 -6 /°C. The formulations are soluble in polar organic solvents such as dimethyl formamide and tetrahydrofuran. Functional electronic components have been successfully potted and depotted using these solvent-removable formulations.

Domain structure and time‐dependent properties of a crosslinked urethane elastomer

AbstractThe morphology of a chemically crosslinked urethane elastomer is correlated with its time‐dependent mechanical properties. Evaluation of this amorphous elastomer by electron microscopy and small‐angle x‐ray scattering reveals that incompatible chain segments cluster into separate microphases having a periodicity in electron density of about 90 Å. This observed domain structure is similar to that seen previously in uncrosslinked, thermoplastic urethane elastomers. As in earlier studies on such linear system, thermal pretreatment of the crosslinked elastomer causes a time‐dependent change in its room temperature modulus. However, the magnitude of this modulus change (about 20%) is generally less than observed previously with the linear systems. Another contrast with previous findings is that this time‐dependent phenomenon is apparently not caused by thermally activated changes in microphase segregation. Rather, the observed time dependence in modulus is believed to be caused by molecular relaxation resulting in densification of amorphous packing within the hard‐segment domains. The validity of this proposed mechanism is supported by differential scanning calorimetry experiments showing evidence of enthalpy relaxation during room‐temperature aging of the elastomer. This relaxation is qualitatively similar to that observed previously during sub‐Tg annealing of single‐phase glassy polymers.

Thermoplastic urethane elastomers V. Compatible and incompatible blends with various polymers

AbstractVarious blends over extended compositional ranges have beer, prepared for combinations of a thermoplastic urethane elastomer with polystyrene, a styrene‐acrylonitrile copolymer, a polyhydroxyether (Phenoxy A), and poly(vinyl ethyl ether). The thermoplastic urethane elastomer was based on a polycaprolactone diol of approximately 2100 number average molecular weight, 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol at a molar ratio of 1/2/1, respectively. At ambient temperature, the tensile properties of the blends typically are intermediate between the values of the two separate components. Characterizations of the dynamic mechanical properties of the blends show the relative degree of compatibility for the thermoplastic urethane elastomer and the respective polymers. Two separate glass transitions are obtained for blends of polystyrene and the styrene‐acrylonitrile copolymer with the thermoplastic urethane elastomer. This behavior demonstrates that these blend systems are incompatible. The blends of Phenoxy A and the thermoplastic urethane elastomer exhibit a single glass transition for which the temperature is dependent on the respective concentration of the components. These mixtures are considered to be compatible in nature.

Thermoplastic urethane elastomers. III. Effects of variations in isocyanate structure

AbstractThe dynamic mechanical properties of thermoplastic urethane elastomers have been compared for materials based on different diisocyanate structures, either 4,4′‐diphenylmethane diisocyanate (MDI) or an isomeric ratio of tolylene diisocyanate (TDI). Two comparable series of polymers were prepared with a polycaprolactone diol as the soft segment and varying concentrations of hard segments based on the respective diisocyanates and 1,4‐butanediol. Over the composition range studied, the polymer glass transition temperatures increased for the TDI‐based polyurethanes, but remained relatively constant for the series containing MDI. Differences in the degree of macroscopic order within the hard segments, due to variations in the symmetry of the diisocyanate structures, are suggested as an explanation of these dynamic mechanical properties.

Thermoplastic urethane elastomers. II. Effects of variations in hard-segment concentration

The dynamic mechanical properties of thermoplastic urethane elastomers have been charac-terized for polymers composed of varying hard-segment concentrations and for two different molecular weight polyester diols as soft segments. The urethane polymers based on an 830 M̄n polycaprolactone diol exhibited a progressive increase in glass transition temperature at increased levels of hard segments. In contrast, a similar series of polymers prepared with a 2100 M̄n polycaprolactone diol as the soft segment maintained a relatively constant glass transition temperature. These differences are attributed to the relative degree of phase separation between the constitutive blocks of the copolymer. The polymers of both series possessed two lower-temperature, secondary relaxations, which are ascribed to methylene sequence mobility within the polycaprolactone units and to possible disruption of interfacial associations between the hard- and soft-segment structures.

Thermoplastic urethane elastomers IV. Effects of cycloaliphatic chain extender on dynamic mechanical properties

AbstractThe dynamic mechanical properties of a series of thermoplastic urethane elastomers have been studied as a function of molecular composition and temperature. Polymers based on polycaprolactone diol, an isomeric mixture of tolylene diisocyanate and hydrogenated Bisphenol‐A as the chain extender were prepared at various relative concentrations of hard and soft segments. The glass transition temperatures of these polymers progressively shifted to higher temperatures as the relative hard segment content was increased. This variation was accurately described by the Fox relationship for amorphous copolymers. These results can be interpreted in terms of the relative degree of segregation between the segment of the block copolymers.

Thermoplastic urethane elastomers. I. Effects of soft-segment variations

A series of thermoplastic urethane elastomers with soft segments of varying sequence length was prepared and their dynamic mechanical properties were characterized over a wide temperature range. The polymers were prepared using various molecular weight polycaprolactone diols as the soft segment and 4,4′-diphenylmethane diisocyanate and 1,4-butanediol as the hard segment. The urethane elastomer exhibited soft-segment crystallization when a polycaprolactone diol greater than 3000 Mn was used. The glass transition temperature of these materials progressively shifted to lower temperatures as the chain length of the soft segment was increased. This dependence was interpreted in terms of a molecular weight relationship similar to that associated with amorphous homopolymers. The dynamic mechanical properties of these polyurethanes appear to be consistent with responses observed for compatible copolymers.

Polyurethane networks

AbstractThermoplastic urethane elastomers are interesting materials, to work with when physical and mechanical properties of plastics are being studied. This is due to the frequently large or sometimes, exclusive participation of the secondary bonding. Measurements were taken in order to establish the size and extent of reaction of the primary and secondary bonds in thermoplastic urethane elastomers obtained from polyethylene adipate, 4,4 diphenylmethane diisocyanate, and the following chain extenders: ethylene glycol, propylene glycol 1,3; propylene glycol 1,2; butylene glycol 1,4. Through a series of simple stress‐strain measurements at different temperatures, and by using the swelling equilibrium method in different solvents, the crosslinking density with primary and secondary bonds was determined; in addition, we have also found the activation energy of secondary bonds in thermoplastic urethane elastomers.

New Dimensions in Automotive Use of Thermoplastic Urethane Elastomers

New Dimensions in Automotive Use of Thermoplastic Urethane Elastomers

Phase separation in urethane elastomers as Judged by low-angle X-Ray scattering. II. Experimental Results

Abstract Supposing complete segregation, volume and density of the hard segment domains in thermoplastic urethane elastomers are easily calculated from the chemical composition of the elastomers. These hypothetical values may be compared with experimental small-angle X-ray findings, resulting in a realistic picture of the actual state of segregation. A similar situation holds true for the specific surface area of the domains. With respect to elastomers of MDI, hydrazine, and a linear polyester or a polyether with a hard segment volume fraction of about 15%, specific surface areas of the domains of about 220 m2/cm3 were found. They are characterized by diffuse transition zones, the width of which was about 20 A. The segregation was further more incomplete due to isolated MDI blocks dissolved in the soft segment matrix as well as to soft segments included in the domains.

Phase separation in urethane elastomers as judged by low-angle X-ray scattering. I. Fundamentals

Abstract In thermoplastic urethane elastomers, phase separation between hard and soft segments resulting in a domain structure is an essential condition for a sufficiently high heat distortion temperature. The state of segregation, i.e., the domain structure, is characterized by the following aspects: 1) the size distribution, i.e., the dispersion level of the domains; 2) the sharpness of diffuseness of the domain boundaries, and 3) hard segments dissolved in the soft segment matrix or soft segments included in the domains. The state of segregation may be evaluated by means of low-angle X-ray scattering. The fundamental theory, based on Porod's theory of low-angle scattering, is given in this paper. Experimental findings will be discussed in a later paper.