Mechanical Properties Of Polyurethane Research Articles

Acoustic and mechanical properties of polyurethanes based on polybutadiene soft segment

Mechanical and acoustic properties of castable polyurethane elastomers comprising polybutadiene polyol, diphenyl methane diisocyanate, and 2-ethylhexane-1,3-diol chain extender are reported. Such elastomers are used to encapsulate sonar transducers. For this application the principal acoustic requirement is that a good impedance match to water be obtained by making both sound velocity and density similar to that of water. Perfect matching would give perfect transmission of the signal from the water into the material but due to the viscoelastic nature of polymers there is always some residual mismatch. Increasing chain extender content improves strength and increases hardness and can bring about formation of phase separated structures. The stronger materials have poorer acoustic performance due to increased shear modulus and damping. A compromise must be reached between acoustic properties and strength, which depends primarily on the layer thickness and the frequency of the sound energy in the particular application.

Morphological structure and mechanical properties of polyurethane modified with methyl methacrylate

Three kinds of polyurethane-poly(methyl methacrylate) (PU-PMMA), that is, linear polymer, block copolymer, and interpenetrating polymer network (IAN ), were synthesized by a simultaneous polymerization process, respectively. The effects of several factors such as ultraviolet (UV) setting, heat setting, chemical composition, and physical structure on the morphological structure and mechanical properties of polymers were studied by scanning electron micrograph, dynamic mechanical loss spectrum, and mechanical tests. The results show that PU-PMMA is a partially compatible system with a two-phase structure; the linear polymer has the highest elongation at break, and IPN has the strongest tensile strength, while the block copolymer has poor mechanical properties. In addition, the UV setting block copolymer and IPN system, with regular microphase domain structures, have higher tensile strength and elongation at break than those of heat setting polymers. With MMA content and hard segment in PU increasing, the tensile strength increases, and the elongation decreases.

Morphological structure and mechanical properties of polyurethane modified with methyl methacrylate

Morphological structure and mechanical properties of polyurethane modified with methyl methacrylate

Mechanical and dynamic mechanical properties of polyurethane and polyurethane/polyurea elastomers based on 4,4′‐diisocyanatodicyclohexyl methane

Mechanical and dynamic mechanical properties of polyurethane and polyurethane/polyurea elastomers based on 4,4′‐diisocyanatodicyclohexyl methane

Mechanical and dynamic mechanical properties of polyurethane and polyurethane/polyurea elastomers based on 4,4?-diisocyanatodicyclohexyl methane

The physical and thermal properties of hand-cast polyurethane and polyurethane/polyurea elastomers prepared from prepolymers of 20 and 97% trans,trans-4,4′-diisocyanatodicyclohexyl methane (t,t-rMDI) and C3- and C4-polyethers chain extended with either 1,4-butanediol (XB) or a commercial mixture of diethyl toluenediamine isomers (DETDA) were determined. The influence of the distribution of geometric isomers of the diisocyanate and of the chain-extender building blocks on these properties is significant. Urethane/ureas are harder and have higher modulus than polyurethanes formed from the same prepolymer. The polyurethane/polyurea elastomers all have somewhat high compression set. Dynamic Mechanical Analysis (DMA) suggests that DETDA extended systems based on 20% t,t-rMDI are phase separated, as illustrated by extended rubbery plateau regions and significantly higher softening points than the corresponding XB extended ones. Uniquely, these elastomers are transparent rather than opaque as typical with most other phase-segregated elastomers. Polyurethanes based on 97% t,t-rMDI are harder and have higher modulus than those based on 20% t,t-rMDI (Desmodur™ W). They have good phase separation and high softening points but they are opaque. Surprisingly, there is not much difference between the physical or thermal properties of polyurethane/polyureas and polyurethanes based on 97% t,t-rMDI. Replacing XB with DETDA gives only moderate improvement in properties, but it does make the elastomers optically clear. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 957–970, 1997

Thermal and Mechanical Properties of Polyurethanes Derived from Fractionated Kraft Lignin.

Polyurethane (PU) sheets were prepared from fractionated kraft lignin (KL) samples having molecular weights (MW's) of 1420 and 860, polyethylene glycol having a MW of 400 (PEG 400) and diphenylmethane diisocyanate (MDI). KL contents in weight %, in a mixture of KL and PEG 400, were varied from 10 to 50%. The thermal and mechanical properties of PU's were studied by thermogravimetry (TG), differential scanning calorimetry (DSC) and tensile tests. The thermal decomposition temperatures slightly decreased with increasing KL contents. The glass transition temperatures (Tg's) increased, the temperature range of glass transition (ΔT) increased, and the heat capacity difference between the glass and rubbery states at Tg's (ΔCp) decreased, with increasing KL contents. Tensile properties such as strength at break (σ), elongation at break (ε), and Young's modulus (E) were measured at 25°C. The obtained results were highly dependent on the state, i.e. the glassy state and the rubbery state. The effect of molecular weight of KL on thermal degradation and tensile properties was not prominent. However, Tg's apparently increased with decreasing molecular weights of KL when the same amounts in weight % of KL were introduced into PU molecules.

Thermal and Mechanical Properties of Polyurethanes Derived from Mono- and Disaccharides

Department of Polymer Technology, Royal Institute of Technology, S-100 44 Stockholm, Sweden(Received 1 February 1996; revised version received 3 April 1996; accepted 8 July 1996)Abstract: Thermal and mechanical properties of polyurethane (PU) sheets pre-pared from the glucose/fructose/sucroseEpolyethylene glycol (PEG)Ediphenylmethane diisocyanate (MDI) system were examined by di†erential scan-ning calorimetry, thermogravimetry, dynamic mechanical analysis and tensiletests. The saccharide content was varied at a constant NCO : OH ratio of 1E0.The glass transition temperature increased with increasing saccharide(Tg)content. The incorporation of saccharides into the PU structure results in ahigher crosslinking density and a higher content of hard segments. The thermaldecomposition was dependent on the saccharide content, an increase leading to alower thermal decomposition temperature The dissociation of saccharide(Td).OH groups and NCO groups is a major part of the thermal decomposition ofthese PUs. Dynamic mechanical analysis revealed two kinds of relaxation: thehigh temperature relaxation corresponds to main chain motion and the other is alocal mode relaxation due to non-reacted isocyanate groups. The tensile stressand YoungIs modulus increased with the saccharide content.Key words: Polyurethane, mono- and di-saccharide, decomposition, glass tran-sition, DMA, tensile properties.* To whom all correspondence should be addressed¤ IRC in Polymer Science and Technology, University of Bradford, Bradford, BD7 1DP, UK.

Concept of hard clusters in the interpretation of thermal and mechanical properties of polyurethane and polyurethane acrylate networks

Polyurethane (PU) and polyurethane acrylate (PUA) networks based on hydroxyl-terminated polycaprolactone (PCL), 1,3-bis-2,2′(2-isocyanatopropyl)benzene (m-TMXDI), trimethylolpropane (TMP) for PU or hydroxyethyl methacrylate (HEMA) for PUA were synthesized. Glass transition temperature, Tg, dynamic mechanical relaxation, α, and equilibrium tensile modulus, E′, were measured to compare the two kinds of networks. To explain thermal and mechanical properties of networks, the concept of hard clusters has been introduced. PU networks exhibit a single-phase structure with modulus and Tg dependent on the concentration of elastically active network chains (EANC) per unit volume calculated by considering hard crosslink clusters. The rigidity of the clusters comes from small diisocyanate and trimethylolpropane units connected by urethane bonds. They are embedded in a continuous soft phase of macrodiol urethane. Physical equivalence between several kinds of network models has been demonstrated for full conversion of isocyanate-alcohol reaction. PUA networks exhibit thermodynamically one-phase structures that become a two-phase structure for high molar mass of macrodiol when the molar fraction of isocyanate groups increases. For those networks, the calculated modulus considering clusters based on polyacrylate chains seems to be a good way to approach the experimental value of the equilibrium modulus. For the same molar ratio of OH to NCO groups the range of dynamic moduli is larger for PUA than for PU. This difference can be explained by a different concentration of crosslinks in the networks. © 1996 John Wiley & Sons, Inc.

Concept of hard clusters in the interpretation of thermal and mechanical properties of polyurethane and polyurethane acrylate networks

Concept of hard clusters in the interpretation of thermal and mechanical properties of polyurethane and polyurethane acrylate networks

Dynamic mechanical properties of polyurethane grafted onto styrene–styrene sulfonic acid copolymers

AbstractThe object of this study was the exploration of the dynamic mechanical properties and thereby also of the phase behavior of partly sulfonated polystyrenes containing polyurethane grafts. The synthesis was accomplished by stepwise grafting onto the partly sulfonated polystyrene of N‐methyldiethanoloamine, via ionic interactions resulting from proton transfer followed by chain growth on the hydroxyl sites of the polyurethane structures. NMR spectra confirmed that the protons of the sulfonic acid groups had been transferred exclusively to the tertiary nitrogen of the N‐methyldiethanoloamine. If the grafts consist of only hard segments, then a single glass‐transition temperature is observed that depends on the length of attached hard segment. If, on the other hand, soft segments are also included in the grafts, then these phase‐separate and yield a new glass‐transition temperature. For the phase‐separated systems, the grafts yield a low Tg phase of higher purity than blending of sulfonated polystyrene with the preformed polyurethane of the same composition. © 1993 John Wiley & Sons, Inc.

Thermal and dynamic mechanical properties of polyurethane modified with poly(m-phenylene isophthalamide)

Thermal and dynamic mechanical properties of polyurethane modified with poly(m-phenylene isophthalamide)

Mechanical properties of solvolysis lignin‐derived polyurethanes

AbstractIn order to study the tensile properties of solvolysis lignin polyurethanes, polyurethane (PU) films were prepared from the solvolysis lignin (SL)–polyethylene glycol (PEG)–diphenylmethane diisocyanate (MDI) system, and in addition to this further PU films were also prepared from the SL–MDI system. In the SL–PEG‐MDI system, the SL content, the molecular weight of PEG and the NCO:OH ratio were varied in order to control the physical properties. The tensile stress and Young's modulus of the PUs of the SL–PEG–MDI type increased with increasing SL content and NCO:OH ratio. The tensile properties of the PUs from the SL–MDI system showed no NCO:OH ratio dependency; i.e. the mechanical properties of PUs are not influenced by the change in crosslinking. It is possible to control the tensile properties of PUs of the SL–PEG–MDI type by changing the content of PEG and SL at a constant NCO:OH ratio.

植物材料からの新しいポリウレタン

New types of polyurethanes were synthesized from kraft lignin, solvolysis lignin and wood meal by polymerization with polyethylene glycol (PEG) and diphenylmethane diisocyanate (MDI). The results obtained are as follows.(1) Polyurethane films were made by solvent casting, and their tensile properties were measured. It was found that kraft and solvolysis lignins contributed effectively to an improvement in the mechanical properties of polyurethanes. Polyurethanes of considerable toughness were obtained, under specific conditions of the isocyanate/hydroxyl group ratio (NCO/OH) and also depending on either kraft or solvolysis lignin content. At high kraft and solvolysis contents, the obtained polyurethanes were hard and brittle, regardless of the NCO/OH ratio used in the experiment.(2) Polyurethane foams were synthesized from a three-component system consisting of PEG, MDI and kraft lignin. Polyurethane foams having kraft lignin contents of up to 40% and apparent densities ranging from 0.04 to 0.22 g/cm3 were prepared by controlling the kraft lignin content, NCO/OH ratio and water content. The compressive strength and elasticity of the polyurethane foams increased with increasing kraft lignin content and NCO/OH ratio.(3) Polyurethane films and foams, which were synthesized by using wood meal as a raw material, generally showed similar mechanical properties to those of polyurethanes which were synthesized from kraft and solvolysis lignins.

Effect of chemical crosslinking of hydrogen bonds in urethane block copolymers

A study was made of the variation of the degree of self-association of urethane groups and mechanical properties of polyurethanes, according to the length of flexible and rigid segments, the type and density of chemical crosslinking networks. In polyurethanes obtained from trifunctional polyethers with M⩾5000 chemical crosslinking does not change the degree of self-association, compared with linear polyurethanes. When introducing low-molecular weight crosslinking agents crosslinking reduces the degree of self-association to a greater extent than a network of the same density formed with polyester. Results confirm the structural micro-heterogeneity of polyurethanes with high density of crosslinking.

Mechanical Behavior of Lightly Crosslinked Polyurethanes

Abstract Polyurethane elastomers are a numerous group of polymeric materials of wide practical application. They are usually formed by polyaddition of diisocyanates with hydroxyl-terminated polyesters or polyethers in the presence of low molecular weight diols or diamines as chain extenders. One may consider urethane elastomers to be block copolymers, consisting of moderately flexible long linear polyester or polyether segments and relatively stiff segments of aromatic and urethane groups. The length and structure of each block can be easily controlled. Crosslinking by an excess of diisocyanate can occur only at the stiff segments, and the number of branch points can also be controlled. The properties of these elastomers can be widely changed using components of different structures and varying their quantitative ratios. They are the results of a combination of segment flexibility, crosslinking, chain entanglement, orientation of segments, hydrogen bonding and other van der Waals forces, as well as rigidity of aromatic units. In the urethane systems, hydrogen bonding and other van der Waals forces, play a much more pronounced role than in familiar olefin-derived elastomers. Although polyurethane elastomers have very good mechanical properties at room temperature, their application is strongly limited by rapid deterioration of properties which takes place at elevated temperatures. The decay of mechanical properties of polyurethane is caused by the breaking of hydrogen and other secondary bonds, as well as by the presence of relatively weak crosslinks that make up their network. The properties of polyurethanes at elevated temperatures may, perhaps, be improved by forming additional crosslinks, besides the typical ones. Some efforts concerning this problem have been published. The aim of our study was to obtain and check the properties of polyurethane elastomers having unsaturated bonds, on which some additional crosslinks were expected to be formed in the presence of a suitable crosslinking agent.

Mechanical Properties of High Density Cellular Urethanes

The use of cellular polyurethanes either as microporous foams in shoe upper materials (poromerics) or in closed cell form as soling materials has increased rapidly during the last few years in the footwear industry. Compared with vulcanised rubbers, these materials have high strength over an extended temperature range, high set and good resistance to cut growth. The research now presented.has been concerned with determining the reasons for these mechanical properties of polyurethane as compared with compounded conventional vulcanised rubbers. The supplementary contribution to the thesis presents a review of earlier work on the strength and reinforcement of crystalline, amorphous and filled vulcanised rubbers and includes a short section on the effect of crosslinking on ultimate failure properties of natural rubber. This study has been extended by the author into the effect of chain branching in polyurethane elastomers on the failure properties. The viscoelastic properties of natural and artificial leathers are also discussed in order to demonstrate similarities between the different materials and show how a cellular polyurethane sheet has hysteresial properties similar to those of a natural material of fibrous structure. It is shown that a cubical lattice model can be applied to explain the differences between such mechanical properties as modulus, tensile and tear strength of a cellular polyurethane and the corresponding solid material of the same polymer. This model, which has previously been applied to the mechanical properties of a natural rubber latex foam, indicates that the strength of cellular polyurethanes is due to the very high strength of the solid material. An extensive investigation into the effect of time and temperature on the tensile properties of cellular and solid polyurethanes is presented in order to show that polyurethanes of the type used in poromerics have a very broad relaxation spectrum extending over 18 decades of time. Because of this response to deformation, the failure properties remain fairly constant over the temperature range from 21 – 160°c. Above 160°c, the tensile properties fall quite markedly. Stress softening in these polyurethanes is very high and can only be reversed by heating to temperatures above 160°c. The cut growth and fatigue properties of cellular and solid polyurethanes are considered. Following a brief review of the investigation on cut growth and fatigue of vulcanised rubbers involving the use of tearing energy theory, it is shown that cut growth and hysteresis properties of vulcanised .rubbers can be correlated. The lower limit of tearing energy (To) below which no cut growth takes place in the absence of chemical effects is found to be higher for polyurethanes than for vulcanised rubbers. Fatigue failure of cellular polyurethanes is found to be due to cut growth from the largest pore in the sample. These data are also compared with measurements on other two phase elastomer systems such as styrene butadiene copolymer vulcanisates with high styrene content and polystyrene-polybutadiene thermoplastic rubbers. From an extensive review of the literature on the structure of polyurethane elastomers, it is deduced that polyurethanes of the type used in poromerics consist of a segmented structure of long polyester chains connected to very minute (25A) hard urethane segments. The cohesion of the hard segments is primarily due to hydrogen bonding and other physical forces. It is concluded that the high strength, good cut growth resistance and broad relaxation spectrum of polyurethanes are due to the reinforcement given by the hard urethane segments which act as well dispersed minute filler particles in the polyester rubber matrix. The hydrogen bonding between the hard segments dissociates at approximately 170°c so giving a degree of thermoplasticity which produces a very high permanent set. An appendix discusses some of the practical applications in the footwear industry of the work presented, such as forming of poromerics, tearing from stitch-holes and flex cracking of solings