Thermal stability of polyurethane elastomers before and after UV irradiation

In this work, we investigated the thermal degradation behavior of segmented polyurethane (PUR) elastomers before and after UV irradiation. The thermal degradation of PUR elastomers was studied over the temperature range of 25–600°C in an atmosphere of nitrogen using thermal gravimetric analysis (TGA). Four series of PUR elastomers derived from poly(oxytetramethylene)glycol (PTMO) of 1000 and 2000 molecular weight and poly(caprolactone glycol) (PCL) of 1250 molecular weight, 4,4′‐diphenylmethane diisocyanate (MDI), and 4,4′‐dicyclohexylmethane diisocyanate (H₁₂MDI) and 1,4‐butanediol as an chain extender were synthesized by the prepolymer method. The derivative thermogravimetric (DTG) peaks observed in the experiments indicated that PUR elastomers degraded through two steps. We attributed the first step to degradation of the hard segment. The second degradation step could be ascribed to degradation of the soft segment. We found that the PUR elastomers based on poly(ester polyol) and aromatic diisocyanate exhibit better thermal stability than that of PUR elastomers based on the poly(ether polyol) soft segment in both steps of degradation. The thermal degradation is more prevalent in PUR elastomers based on cycloaliphatic diisocyanate. The higher values of the temperature of initial decomposition (Tⁱ) indicate a higher thermal stability of UV‐exposed elastomers on the beginning of degradation. This may be due to the formation of a crosslinking structure in the presence of UV irradiation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 864–873, 2001     

Block architecture influence on the structure and mechanical performance of drawn polyurethane elastomers

Some natural biopolymers such as spider silk exhibit superb mechanical properties, characterised by their great toughness. Synthetic polyurethane (PU) copolymers also endow great toughness but lack silk's stiffness and strength. The aim of this work was to elucidate the role of segment block architectural features that influence PU stiffness and strength after cold drawing. For this purpose PUs with varied soft segment character, crystalline versus rubbery, as well as with different hard segment chemistries, 4,4′‐diphenylmethane diisocyanate/1,4‐butanediol versus 1,6‐hexamethylene diisocyanate/1,4‐butanediol, were synthesised by a two‐step polymerisation method. We found that the architecture of both block segments has a dramatic influence on drawn PU mechanical performance, in which PUs with crystallisable soft segments and crystalline hard segments are shown to have a greater impact on developing stiffer and stronger materials. © 2013 Society of Chemical Industry     

Influence of polyurethane properties on mechanical performances of magnetorheological elastomers

Magnetorheological elastomers (MREs) are mainly composed of magnetizable particles and elastic polymer. The polymer matrix plays an important role in mechanical performances of MREs. In this study, the polyurethane (PU), which is synthesized by using toluene diisocyanate (TDI) and poly (propylene glycol) (PPG‐220), is selected as a matrix because it has better degradation stability than natural rubber and higher mechanical stability than silicone rubber. Four different MRE samples were fabricated by adjusting the reaction molar ratio of TDI to PPG to change the property of PU matrix. Structural characterization of the PU matrix was described by Fourier transform infrared analysis. The microstructures of samples were observed by using an environmental scanning electron microscope. The mechanical performances of samples, including shear modulus, magnetorheological effect (MR) effect, loss factor, and glass transition temperature (T_g), were characterized with dynamic mechanical analyzer. The results show that the shear modulus, the relative magnetic residual shear modulus and glass transition temperatures of samples increase with the increment of toluene diisocyanate, while the relative MR effects and loss factors decrease steadily. The experimental results indicate that optimal molar ratio (TDI : PPG) is 3 : 1. The field‐induced shear modulus of sample with molar ratio 3 : 1 is 4.9 MPa, and the relative MR effect is 121% under an external magnetic field of 800 mT at room temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Experimental investigation of the effect of hygrothermal aging on the mechanical performance of carbon nanotube/PA6 nanocomposite

The effect of hygrothermal aging on the mechanical behaviour of polyamide 6 (PA6) material filled with 10 wt % multi-walled carbon nanotubes (MWCNTs) has been investigated experimentally. Young’s modulus and flexural modulus of the materials are decreased by more than 30% for the conditions of 25°C/85% RH, compared to the reference conditions of 25°C/55% RH (RT), while the flexural strength by 6–17%. The decrease is larger for the conditions of 40°C/85% RH, which reveals that the effect of combined elevated temperature and moisture is more severe. The decrease in the properties is smaller for the MWCNT/PA6 specimens, which shows that the presence of MWCNTs mitigates the effect of hygrothermal aging. Finally, it is observed that the increase in the properties of the MWCNT/PA6 material is so large, for the specific MWCNT concentration, that it compensates the negative effect of hygrothermal aging.     

Effect of the molecular structure of polyurethane elastomers on the thermomechanical properties of PUE/PC blends

Polyurethane elastomers (PUEs) based on 4,4′‐diphenylmethane diisocyanate (MDI), 1,4‐butanediol (BDO) and two kinds of aliphatic polycaprolactone (PCL) diols with molecular weight of 1000 Da and 2000 Da have been synthesized and melt‐blended with polycarbonate (PC). The compatibility of PC and PUEs was investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). The results indicated that the glass transition temperature (T_g) of PC decreased by 0–40°C when 0–10 wt % of PUEs incorporated into the PC matrix. Phase separation in the blends was not detected by means of DSC characterization, but measurements of DMA and SEM indicated that phase separation existed in the blends of PC and PUEs synthesized with 1000 Da PCL‐diol. As for PUEs/PC blend in which 2000 Da PCL‐diol as PUEs' soft segments, it turned from completely compatible to partially when the NCO/OH ratio for the PUEs prepolymer was increased from 2 : 1 to 4 : 1. The compatibilities of PC and PUEs were greatly influenced by the molecular weight of polyols and the ratio of NCO/OH in the PUE prepolymer, higher molecular weight of polyols and lower NCO/OH ratio resulted in better compatibility. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

端羟基液体橡胶聚氨酯弹性体与金属粘接的研究

端羟基液体橡胶聚氨酯弹性体为柔性材料,丁羟聚氨酯弹性体硬度比丁腈羟聚氨酯弹性体小,前者的拉伸强度比后者稍大．伸长率也大;其作为粘合剂与金属粘接时,金属表面在分别经过酸化、磷化,喷砂、清洗,喷砂、清洗、涂偶联剂（KH-550）3种方法处理,其中金属表面进行喷砂、清洗、涂覆偶联剂时粘接性能最好。     

三官能度聚醚型聚氨酯弹性体的力学性能研究

以三官能度的聚醚多元醇、1,4-丁二醇和二苯基甲烷二异氰酸酯(MDI)为主要原料合成了聚氨酯弹性体。研究表明,硬段质量分数超过50%以后,伸长率降低,交联时间对聚氨酯(PU)弹性体整体的力学性能影响不大。在保持异氰酸酯指数为1.0和MDI含量不变的条件下,把1,4-丁二醇和聚醚多元醇的羟基摩尔比提高到1.50:0.33,材料的力学性能最佳。随着交联时间的增加,拉伸强度及硬度先增大后减小,伸长率呈减小的趋势。     

Stress-strain curves for polyurethane elastomers: A statistical assessment of constitutive models

Polyurethane elastomers (PUEs) are broadening applications attributed to their highly tunable mechanical properties, and the stress–strain curve is one of the most important characters. Theoretically, dozens of constitutive models have been developed to interpret the stress–strain curve for rubber-like materials but their applicability on PUEs is still suspicious, which results in the selection of models and the initialization of model parameters need expertise experience. We performed a statistical assessment of 25 constitutive models (10 physical and 15 phenomenological) based on a comprehensive dataset with 529 stress–strain curves for PUEs. The average coefficients of determination for the whole curve can be improved from 0.676 for the phantom model (1 parameter) to 0.990 for the Bechir model (6 parameters), and the percentage of well-fitted curves increases from 6% to 92%. Constitutive models with both the first- and the second-invariant, in logarithmic or exponential expression for strain perform better.     

Application of blocked isocyanate in preparation of polyurethane(urea) elastomers

High-performance casting polyurethane elastomers (CPUe) were successfully synthesized by the reaction of polyurethane prepolymer (PUP) blocked by methyl ethyl ketone oxime (MEKO) with diamine chain extenders. The effects of blocking agent were systematically studied on the structures, thermal stabilities, mechanical properties, and processability of polyurethane. The addition of MEKO significantly improved the tensile strength and toughness. The maximum tensile strength was 35.6 MPa, and the maximum elongation at break was 1065%. The high strength and toughness were attributed to the fact that under mild reaction conditions, the reaction tended to extend the molecular chains, which indicated that the formation of long chains was conducive to the extension and self-reinforcement of chain segments. Crystallization and strong hydrogen bonds between molecules also led to low loss factor. This deblocking polymerization strategy solves the gel problem in the polymerization process, and provides a new idea for the preparation of CPU.     

Effect of UV aging on the tensile and fracture mechanical response of syndiotactic polypropylenes of various crystallinity

Syndiotactic polypropylene (sPP) sheets of various crystallinities were subjected to accelerated ultraviolet (UV) aging. The chemical modification of the polymer was followed by FTIR spectroscopy measuring the carbonyl index in transmittance (film) and diffuse reflectance (powder) modes. Both the tensile stress and strain, suitable indicators of the UV aging, changed linearly with the carbonyl index in semilogarithmic representation. The essential work of fracture (EWF) method proved to be less suitable for characterization, as the UV irradiation resulted in surface embrittlement of the polymer. This caused brittle fracture of the notched specimens instead of the required ductile one. On the other hand, the term of the specific work of fracture related to yielding may adequately reflect the structural and morphological changes of sPP caused by UV irradiation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3462–3469, 2004     

Synthesis and properties of liquid crystalline polyurethane elastomers

Novel type of mesogenic chain extenders used in this study are N,N′‐bis(4‐hydroxyphenyl)‐3,4,3′,4′‐biphenyldicarboxyimide (BPDI) and N,N′‐bis[4‐(6‐hydroxyhexyloxy) phenyl]‐3,4,3′,4′‐biphenyldicarboxyimide (BHDI). BHDI has a flexible spacer of 6‐methylene units but BPDI does not. The liquid crystalline polyurethane elastomers were synthesized from BPDI or BHDI as a mesogenic chain extender, 4,4′‐diphenylmethane diisocyanate, and poly(oxytetramethylene)glycol (MW 1000) as a soft segment. Polyurethane based on BHDI exhibited two melting transitions. However, any melting behavior was not shown in the BPDI‐based polyurethanes because of higher melting temperature than decomposition temperature. The composition of polyurethanes was varied as a means of manipulating liquid crystalline behavior and physical properties. The BHDI‐based polyurethanes containing above 50 wt % of hard segment content exhibited nematic liquid crystal behaviors. As the hard segment content of the BHDI‐based polyurethanes increased, the glass transition temperature (T_g), strength, modulus, and the amount of hydrogen bonding increased. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 577–585, 2000     

Influence of the synthesis conditions on the properties of thermoplastic polyurethane elastomers

Thermoplastic polyurethane elastomers (TPUs) of constant composition were prepared by using the prepolymer method and by changing the reaction conditions (prepolymerization and chain‐extension time) to study the influence of these conditions on the final TPU properties. The TPUs were characterized by gel permeation chromatography, differential scanning calorimetry, strain–stress measurements, and contact‐angle measurements. To test the adhesion properties of the TPUs, poly(vinyl chloride) strips were bonded to each other by using TPU solutions and the T‐peel strength of the adhesive joints was measured. It was found that provided a threshold is crossed, the prepolymerization time markedly influences the final properties of the TPUs (viscosity of solutions, molecular weight, mechanical and adhesive behavior), whereas the chain extension time does not. Therefore, it is possible to prepare TPUs with specific properties by playing with the prepolymerization conditions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1590–1595, 2000     

Rheological characterization of thermoplastic polyurethane elastomers

The relationship between the rheological properties and composition of eight thermoplastic polyurethane elastomers (TPUEs) was evaluated using a stress‐controlled rheometer. The composition of the TPUEs was changed by varying the OH/NCO ratio, the chain extender and the molecular weight of the macroglycol used in the synthesis. A high molecular weight macroglycol and a low OH/NCO ratio improved the rheological properties of the TPUEs due to the formation of longer or more abundant soft segments, respectively. The nature of the chain extender influenced the rheological properties to a lesser extent. © 2000 Society of Chemical Industry     

Effect of fillers on thermal and mechanical properties of polyurethane elastomer

The effects of five different types of fillers on the thermal and mechanical properties of hydroxyl-terminated polybutadiene-based polyurethane elastomers were explored to develop a filled polyurethane elastomeric liner for rocket motors with hydroxyl-terminated polybutadiene-based composite propellants. Two type of carbon black, silica, aluminum oxide, and zirconium(III) oxide were used as filler. Based on the improvement in the tensile properties and the erosion resistance achieved in the first part of the study, an ISAF-type carbon black was selected to be used as the main filler in combination with an additional filler. The second part involves the investigation of polyurethane elastomers containing a second filler in various amounts in addition to the ISAF-type carbon black used as the main filler. In addition to the thermal and mechanical properties, the processability of the uncured polyurethane mixtures were also explored by measuring the viscosity in this second part of the study. The studied fillers do not considerbly change the thermal degradation temperatures and the thermal conductivity of the polyurethane elastomers with a filler content up to 16 wt %. The best improvement in the erosion resistance and tensile strength of the polyurethane elastomers with additional fillers is also achieved when filled with the ISAF-type carbon black, whereas the use of zirconium(III) oxide as additional filler provides almost no improvement in these properties. Viscosity of the uncured polyurethane mixtures increases with the increasing filler content and with the decreasing particle size of the filler. Aluminum oxide-filled elastomers seem to be the most suitable compositions having sufficiently high thermal and mechanical properties, together with the processability of uncured mixtures. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1057–1065, 1998     

聚氨酯弹性体耐热性的影响因素

讨论了多异氰酸酯，聚合物多元醇，扩链剂，分子内基团，杂环，离子基团对聚氨酯弹性体耐热性能的影响。指出开发新原料，引入热稳定杂环，严格控制反应条件和原料的纯度及配比，是提高聚氨酯弹性体耐热性的有效途径。     

聚四氢呋喃类聚氨酯弹性体的热氧老化过程

以聚四氢呋喃( PTMG)预聚物为原料,3,3′-二氯-4,4′-二氨基二苯甲烷(MOCA)为扩链剂,对制备的PTMG类聚氨酯弹性体进行了热氧老化研究.结果表明,聚氨酯弹性体经过100℃、50 d的热氧老化后,产生了醇、羧酸类和酯;聚氨酯弹性体在热空气中发生了氧化反应,并伴随着降解过程,试样老化后最大失重速率温度由老化...     

Polyurethane microcellular elastomers: 2. Effect of chain extender on the mechanical properties

The influence of ethylene glycol, triethanol amine and a rigid polyol on the tensile strength, elongation at break and tear resistance of a microcellular elastomer (used in RIM technology), have been studied using multiple linear regression analysis. Using the statistical Student-t test, the importance of the above parameters has been established. It has been found that the moulded density has the biggest influence on the tensile strength; so that the tensile strength is increased by the ethylene glycol and rigid polyol content, while triethanol amine reduces it. All the chain extenders studied have a negative influence on the elongation at break. Similarly the moulded density and the ethylene glycol content have a beneficial effect on the tear resistance, while triethanol amine and the rigid polyol reduce this property.     

UV固化聚氨酯丙烯酸酯预聚体的合成及其性质

聚氨酯丙烯酸酯预聚体的制备是由二步反应完成,本文对预聚体合成过程中各种影响因素进行分析比较,确定最佳合成聚氯酯丙烯酸酯预聚体的工艺条件为：第一步反应温度为60-65℃,时间为4h,n(NCO)：n(OH)=3,催化剂为物料总量的0．4％,第二步反应温度为70．75℃,时间为4h。     

紫外光固化脂肪族聚氨酯丙烯酸酯的合成研究

以异佛尔酮二异氰酸酯(IPDI),季戊四醇(PETL)和丙烯酸羟乙酯(HEA)合成了可紫外光固化的四官能团脂肪族聚氨酯丙烯酸酯低聚物。研究了催化剂用量、反应物配比、合成反应温度和反应时间等对反应的影响。确定了最佳合成工艺条件:二月桂酸二丁基锡为催化剂;第1步反应用量为IPDI和PETL总质量的0.05%~0.08%;对羟基苯甲醚为阻聚剂,用量为总投料质量的1%;反应物配比n(PETL)∶n(IPDI)∶n(HEA)=1∶4∶4.12;第1步反应温度控制在55~75℃,反应时间2 h,第2步反应温度65~70℃,反应时间2~2.5 h。     

Water resistance of the membranes for UV curable waterborne polyurethane dispersions

The water absorption of the membranes made from UV curable waterborne polyurethane dispersions (UV-PUDs) was investigated systematically and correlated with the nature of the polymer and its gel content after curing. It was found that the water absorption of the membranes was reduced significantly by using polyester polyols, reducing the COOH content and increasing the gel content through a higher CC level. In particular, the membranes made from polyurethanes having hydroxyl-terminated polybutadiene (HTPB) or modified with dihydroxybutyl-terminated polydimethylsiloxane (PDMS) presented a superior water resistance. The results showed a linear relationship between the water absorption and the surface tension of the membrane.