Structure and viscoelastic properties of segmented polyurethane blends

Structure and viscoelastic properties of segmented polyurethanurea (SPU) blends were investigated. The glass transition temperature (T_g) of poly(tetramethylene glycohol) (PTMG) in a soft-segment block of the component SPU increased with decreasing molecular weight of PTMG. The blend samples showed two T_gs of PTMG in the temperature dispersions of the loss modulus (E″) and loss tangent (tan δ). The value of E′ in the leathery region for the blend specimens was trongly affected by the morphology. The blends were considered to have a morphology where PTMG differing in molecular weight was localized. © 1996 John Wiley & Sons, Inc.     

Fracture properties of rigid polyurethane foams

The fracture behavior of rigid polyurethane foams has been investigated and is shown to obey the Griffith criterion for fracture in so far as the predicted behavior of tensile strength on the size of artificially introduced cracks is concerned. The energy for crack propagation (fracture surface energy) has been measured as 91.4J/m². From this result, the intrinsic flaw size of the material is calculated. This value was found to be within the range of cell dimensions of the material.     

Some mechanical properties of rigid polyurethane structural foam

The mechanical response of integral-skin rigid polyurethane foam, with an average density of 300 to 700 kg/m³, to constant rate and creep loading was determined. Sandwich specimens were modeled by layers of a core material and two skins, whose secant moduli had been determined experimentally by separate tests and approximated by linear functions of the density. The effective rigidities of the sandwich in tension and flexure were calculated and compared favorably to experimental measurements. The sandwich structure improved the flexural rigidity of homogeneous foam by a factor of more than 2.20. Tensile creep tests of sandwich specimens at relatively low stress levels (up to about 38 percent of their strength) showed that the creep was nonlinear, but a single creep curve could represent creep of specimens of various densities, provided the relative load on them was the same. A limited number of flexural creep tests led to similar conclusions, but the creep rate was smaller than in tension. Results from torsion tests of core material, compressive tests of sandwich specimens, and tension and compression tests of nonskin rigid foam are included in this article.     

Estimation of mechanical properties for rigid polyurethane foams

Rigid plastic foams find application in construction mainly as core materials for loaded sandwich structures—in buildings, ground vehicles, and airplanes. This work provides an equation for the mechanical behavior of polyurethane foams as a function of foam density. Starting from a model conception and the qualitative microscopic consideration of the deformation and failure mechanism, simple relations are found for the tensile, compressive and shear strength and the elastic modulus, which sufficiently express the measured results.     

Preparation and properties of rigid polyurethane foams containing modified cornstarches

Rigid polyurethane foams were prepared containing 20% (based on weight of polyol) unmodfied or modified cornstarches. The cornstarches had been modified by breeding or conversion methods and included waxy, acid-modified waxy, malto-dextrin, and canary dextrin. Due to its more favorable role as an extender, canary dextrin was added to additional foam formulations at 10–40%. Foams containing dextrins responded to compressive stress as control foams with yield points before 10% deformation. Foams filled with the unmodified or waxy cornstarches did not give clearly defined yield points and were measured at 10% deformation. After 14 days under 70°C and ambient conditions, volume increases for the filled foams were 4.0–7.1% vs. 4.6% for the control. The foams filled with canary dextrin increased in volume 4.3%. With the addition of 40% canary dextrin, the volume increases for the foams were 4.4% under thermal conditions and 4.5% under humid conditions (38°C and 98% relative humidity). Under humid conditions for 14 days, the foams containing canary dextrin increased in weight as dextrin content increased (1.5, 3.2, 3.4, and 7.6% with 10, 20, 30, and 40% dextrin, respectively). with 40% canary dextrin in the foams, thermal conductivity was 0.0235 vs. 0.0242 W/mK (0.163 vs. 0.168 Btu in/ft²h°F) for the control.     

Study of the curing process giving the rigid polyurethane foam by dynamic viscoelastic method

Dynamic viscoelastic properties of the rigid polyurethane foam, which is used in Japan as a thermal insulator for refrigerators were studied during the curing process using the RDS-7700 Dynamic Spectrometer. The curing process, in which large volume expansion and heat evolution occurred, was easily analyzed by this method. The apparent storage modulus (G′_app), the apparent loss modulus (G″_app), and the apparent loss tangent (tan δ_app) were measured as a function of cure time. The effects of the curing temperature and the amine catalyst on the curing process were investigated. It was found that the curing process proceeded through three stages: logarithm of G″_app (log G″_app) increased with increasing cure time in the first stage, log G″_app increased with increasing logarithm of cure time in the second, and the change of G″_app cannot be expressed simply in the final. Curing behavior can be estimated from changes of rheological parameters during the curing. The fluidity of reaction mixture can be also predicted from the peak time of tan δ_app.     

Preparation and properties of rigid polyurethane foam based on modified castor oil

Castor oil polyol (COP) having a hydroxyl number of 400?mg?KOH/g was prepared through the transesterification reaction of castor oil with glycerol. The effect of reaction temperature on the composition, hydroxyl number and viscosity of the COP products was studied. A series of rigid polyurethane foams were synthesised using the mixtures comprising COP and a petroleum-based polyol with various proportions as polyol component. It was found that the foaming rate, compressive strength and dimensional stability and morphology of resulting foams were dominated by the foam formulation, in a more accurate way, COP content in the polyol mixtures. The combination of expandable graphite and dimethyl methyl phosphonate exhibited stronger flame retardant function which was ascribed to the synergistic effect associated with the simultaneous presence of the two additives. An improvement in thermal stability was observed due to the inclusion of the flame retardants.     

Structure and properties of shape-memory polyurethane block copolymers

Segmented polyurethanes containing soft segments with lower molecular weight exhibit shape-memorizing properties. Structure and properties of shape-memorizing polyurethanes (S-PUs) were studied. S-PUs are characterized by a rather high glass transition temperature: T_g of S-PUs is usually in the range of 10–50°C. A Pplot of 1/T_m against–In X_A is approximately linear, indicating that the hard segments are randomly distributed along the molecular chain. S-PUs with a hard segment of 67–80 mole % form negative spheruiites; they give a faint scattering maximum in a small-angle X-ray diffraction pattern. On the other hand, S-PUs with a hard segment of 50 mole % form fine birefringent elements, giving diffuse scattering in its SAXD pattern. A cyclic test of an S-PUs above T_g indicates that the residual strain increases and the recovery strain decreases with increasing cycle and maximum strain. It has been suggested by dynamic mechanical investigation that the shape-memorizing property of the S-PUs may be ascribed to the molecular motion of the amorphous soft segments. © 1996 John Wiley & Sons, Inc.     

Flammability and thermal properties of rigid polyurethane foams with additionally introduced cyclic structures

Flammability, smoke evolution, thermal, and thermomechanical properties of low-density rigid polyurethane foams obtained from different aromatic polyols were investigated. The foams were prepared according to a standard formulation ensuring the same foam phosphorus content. Cellular polyurethanes with the best fire resistance were obtained from polyols containing disubstituted naphthalene and biphenyl rings. A linear equation was proposed to describe the influence of various structural units of the polyurethane (the content of cyclic structures C_c, nitrogen content C_N, and crosslinking equivalent M_c) upon its flammability, expressed in terms of its oxygen index (OI) Thermal stability of crosslinked polyurethanes was not found to influence significantly their thermomechanical properties, while crosslink density and the type and quantity of cyclic structures additionally introduced did have a pronounced effect upon these properties.     

原材料对聚氨酯硬泡抗压性能的影响

以环氧丙烷聚醚多元醇、苯酐聚酯多元醇、多苯基甲烷多异氰酸酯PM-200、发泡剂一氟二氯乙烷(HCFC-141b)、泡沫稳定剂硅油AK-8801等为主要原料,采用一步法合成了聚氨酯硬泡,考察了不同种类多元醇及其配比、发泡剂、泡沫稳定剂种类及用量等对聚氨酯硬泡抗压性能的影响。结果表明:高羟值、高官能度的环氧丙烷聚醚多元醇可提高泡沫的压缩强度,且当环氧丙烷聚醚多元醇4110为100份,并加入20份左右苯酐聚酯多元醇580及10份左右聚醚403,泡沫稳定剂用量1～2份,发泡剂水用量0.5～1份,HCFC-141b用量30～35份,催化剂用量0.5～1.5份时,所得聚氨酯硬泡性能较好。     

Flexural properties of moldings of rigid polyurethane made by reaction injection molding

Flexural properties of moldings made by Reaction Injection Molding (RIM), which are structural foams consisting of high density skin and low density core, were investigated by three-point bending tests. Two failure modes were observed in bending tests of the moldings made by RIM, and they are classified as follows according to the density ratio of skin layer to core layer: the opposite side of the skin layer to which load was subjected failed by tensile stress: and the same side of the skin layer to which load was subjected failed by compressive stress, causing wrinkling or buckling. Then the conventional composite beam theory was applied to the former failure mode and Hoff s buckling theory to the latter, and equations were derived to predict the flexural properties of the structural foams, which involved buckling from the flexural properties of solid construction. In addition, it has been shown that there exists a density distribution that maximizes the flexural strength of the moldings made by RIM with a given overall density. The results obtained here should be useful to the optimum structural design of moldings made by RIM.     

Fracture properties of a rigid polyurethane foam over a range of densities

Single edge notch fracture tests have been carried out on rigid polyurethane foam in the density range 32 to 360 kg/m³. Fracture properties were characterized in terms of the fracture toughness parameter (K_Ic), the critical strain energy release rate (G_Ic) and crack opening displacement (c.o.d.). The values of crack opening displacement lead to a proposed mechanism of crack propagation in foams of density greater than about 140 kg/m³.     

静电纺丝抗菌聚氨酯纳米纤维的结构与性能

在聚氨酯/四氢呋喃-N,-二甲基甲酰胺(PU/THF-DMF)溶液中分别添加质量分数为5%的TiO_2-Ag,HM-98,三氯均二苯胺(TCC),4-氯-3,5-二甲基苯酚(PCMX),2,4,4'-三氯-2'-羟基二苯酚(DP 300),ε-聚赖氨酸(ε-PLYS)抗菌剂通过静电纺丝技术制备了PU抗菌纳米纤维,并对其性能和结构进行了研究。结果表明:含ε-PLYS,HM-98,TiO_2-Ag,DP300抗菌剂的抗菌PU纳米纤维对金黄色葡萄球菌和大肠杆菌的抗菌效果较为优良,抗菌率均达到了99.9%以上,TCC、PCMX抗菌剂的抗菌效果较差;添加HM-98抗菌剂降低了纺丝溶液的可纺性,但纤维直径有所下降;抗菌剂在PU中的分散性好。     

Influences of copolymer polyol on structural and viscoelastic properties in molded flexible polyurethane foams

In this study, the viscoelastic and morphological properties of molded foams were investigated to determine the influence of the presence or absence of reinforcing particulate copolymer polyols (CPP). The molded foams were based on toluene diisocyanate (TDI) and glycerol‐initiated ethylene‐oxide endcapped polypropylene oxide and, in most samples, some amount of copolymer polyol. Two series of foams were studied. In Series 1, as CPP is added to the formulation, the amount of TDI fed is kept constant. This results in a constant amount of hard‐segment content as the filler in the system displaces, by weight, the polyether polyol in the foam, and it increases the hard segment to soft segment ratio (HS/SS). In Series 2, the amount of hard‐segment material is proportionally decreased as CPP is added, resulting in a constant HS/SS ratio. Structural investigations of the foams displayed rather similar textures. The cellular structures of a CPP‐containing foam was very similar to a foam lacking the copolymer polyols. Transmission electron microscopy revealed that the CPP particles were well dispersed and that they possessed significant rigidity even at high temperature and under high compression. Although all of the foams were microphase‐separated, they varied slightly in that the copolymer polyol containing foams exhibited higher weight fractions of extractables in both Series 1 and Series 2. This suggests that not all of the CPP material is covalently bonded into the polyol matrix. It was found that temperatures above ambient as well as humidity plasticized the viscoelastic behavior of all the molded foams evaluated. It was also found that the copolymer polyol particles, as added to the molded foams of Series 1, increased load‐bearing capabilities but had a negative effect on the stress relaxation, creep, and compression set properties. In particular, the viscoelastic properties of the CPP‐containing foam were distinctly more time‐dependent than those of the foam lacking these particles. However, the Series 2 foams show that most of these effects are a result of the increased HS/SS ratio and not a result of the CPP particulate. It was shown that adding CPP while maintaining a constant HS/SS ratio improves percent load loss and load bearing under high‐humidity conditions, two important properties in flexible polyurethane foams. Finally, it was shown that at high temperatures (ca. 100°C), an additional relaxation mechanism occurs which cannot be attributed to changes in the HS/SS ratio, but must be a result of the CPP components themselves. This additional mechanism results in higher rates of load relaxation and creep in foams containing CPP at high temperatures for foams of both series. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 766–786, 2000     

Structure and viscoelastic properties of epoxy resins prepared from o-cresol novolacs

The relation between the structure and viscoelastic properties of the epoxy resins prepared from o-cresol novolacs was studied. Our model epoxy resins were two kinds of epoxy compounds synthesized from three-nuclei and four-nuclei o-cresol novolacs. In addition to these models, a commercially available o-cresol novolac-type epoxy resin was also studied. Each of the three epoxy compounds was cured with one of three kinds of novolacs, which were starting materials of the above-mentioned epoxy resins. Characteristic properties of the cured resins, such as glass transition temperature (T_g), average molecular weight between crosslinking points (M¯_c), and front factor (?) were obtained. It was concluded that the number of functional groups contained in the curing system almost dominated the viscoelastic properties of the cured resins.     

Stress relaxation of glass-fiber-reinforced rigid polyurethane foam

Flexural stress relaxations were measured for rigid polyurethane foams (PUF) and glass-fiber-reinforced rigid polyurethane foams (FRU). The results were successfully analyzed in terms of the five element Maxwell model: (1) Samples reinforced with longer fibers exhibit reduced stress relaxation and reduced temperature dependency of stress relaxation; (2) The increased expansion ratio reduces the flexural modulus of both reinforced and non-reinforced materials, but the stress relaxation tends to increase greatly at the higher temperature for PUF, while not so greatly for FRU; (3) The temperature dependency of E₁ decreases as longer fibers are used to reinforce the polyurethane. The dependency is minimal for the polyurethane reinforced with continuous fibers, where the reinforcing effect is maximal; and (4) The activation energy calculated from τ₂ according to the Arrhenius plot is smaller for the longer fiber reinforced polyurethane foams.     

Thermal and viscoelastic behavior of polyurethane/polyvinylchloride blends

The potential of melt processing polymer blends to prepare damping materials was investigated. Binary and ternary blends of polyvinylchloride (PVC) with thermoplastic polyurethane elastomers (TPU) were studied. The soft segments of the polyurethanes for the first series were of the ether type and of the ester type for the second series of blends. A series of polymer blends were prepared by mechanical melt mixing and the apparent miscibility was evaluated from the thermal, dielectric, and dynamic mechanical behavior as well as from transmission electron microscopy. Some samples exhibited a single damping peak at low PVC content, indicating miscibility of the blends at the detection scale of the test method. The relationship between the properties and the morphology of the blends was studied.     

无氟里昂聚氨酯硬质泡沫及应用

介绍了水发泡无氟里昂聚氨酯硬质泡沫的研制、工业应用以及水和ＨＣＦＣ－１４１ｂ复合发泡剂无氟里昂聚氨酯硬质泡沫在冰柜中的应用     

Structure and viscoelastic properties of epoxy resins prepared from four-nuclei novolacs

The relation between the structure and the viscoelastic properties of seven kinds of epoxy resins was studied. Seven tetraglycidylethers were synthesized from four-nuclei novolacs in which the positions of methylene linkage or number of kind of substituents were different. These epoxy compounds were cured with diaminodiphenylmethane as a hardener. From the viscoelastic properties of the fully cured resins with the hardener, characteristic properties such as glass transition temperature (T_g), average molecular weight between crosslinking points (M̄_c), and front factor (ϕ) were obtained. It was concluded that higher linearity in the main chain of epoxy resins gave a cured resin with a higher T_g, a smaller M̄_c, and a larger ϕ.     

The mechanical properties of high-density rigid polyurethane foams in compression: I. Modulus

A series of rigid polyurethane foams of densities varying from 65 kg/m^?3 to 400 kg/m^?3 have been tested in compression as a function of rate and temperature. It has been found that a linear relation exists between density and modulus if the data is referred to a constant thermodynamic temperature.