Thermal and mechanical characterization of maleimide‐functionalized copoly(urethane‐urea)s

Maleimide functionalized copoly(urethane‐urea)s were prepared by the reaction of a binary mixture of dibenzyldiisocyanate and 5‐maleimidoisophthalic diisocyanate with a macrodiol (PEGA‐2000), using diethylene glycol and trimethylol‐propane as chain extender and crosslinkers in toluene‐dichloromethane solutions at the ratio NCO/OH = 1.2. Structures of polymers were confirmed by IR spectroscopy and properties were studied by thermal and mechanical analysis (dynamic mechanical analysis (DMA), differential scanning calorimetry, thermogravimetric analysis, stress‐strain) and other physical methods. Maleimide modification increased the storage modulus and Young's modulus of copoly(urethane‐urea)s, slightly increased their glass transition temperature from ?10.6°C to ?6.3°C. Copoly(urethane‐urea) networks obtained by thermal polymerization of maleimide functions showed significantly increased of the mechanical properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Properties of waterborne polyurethane‐fluorinated marine coatings: The effect of different types of diisocyanates and tetrafluorobutanediol chain extender content

Three series of waterborne polyurethane‐ (WBPU) fluorinated coatings were prepared with single aliphatic (4,4′‐dicyclohexylmethane diisocyanate, H₁₂MDI), aromatic (4,4′‐diphenylmethane, MDI) and a mixture of aliphatic and aromatic diisocyanates (1 : 1). Different contents of 2,2,3,3‐tetrafluoro1,4‐butanediol (TFBD) as a chain extender were used in the WBPU coatings. The fluoro‐enriched surface of the WBPU coatings was obtained with a combination of a high TFBD content (8.77 mol %) as well as the aliphatic or mixed diisocyanates. The tensile strength, Young's modulus, elongation at break (%) and adhesive strength were characterized with respect to the TFBD contents. The mechanical strength and adhesive strength increased with increasing TFBD content in the three series. In artificial salt water, the maximum adhesive strength of WBPU was observed for this coating, which was achieved by TFBD bonded H₁₂MDI of mixed diisocyanates with a higher TFBD content (8.77 mol %). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39905.     

Thermoset polyurethanes containing hydroquinone di(β-hydroxyethyl) ether

A thermoset polyurethane resin extended with hydroquinone di(β-hydroxyethyl) ether (HQEE) was found to have good thermomechanical properties suitable for external elastomeric automotive applications. A resin composed of diphenylmethane diisocyanate (MDI), ethylene glycol, and a primary polyol was found to have good mechanical properties but was too reactive for processing as a one-component resin. Replacing the liquid ethylene glycol extender with the solid HQEE substantially increased the pot life of the resin as well as improving the modulus properties. When catalyzed with zinc stearate this resin had sufficient pot life at room temperature, at least 4 hr, to be processed as a one-component system but still cure rapidly at elevated temperatures. The HQEE-extended materials required only 50% hard-block content (isocyanate plus extender) to have the same modulus at room temperature as ethylene glycol-extended materials containing 60% hard block. By using a graft or polymer polyol, the required hard-block content could be reduced to 40% The polyurethane of MDI/SAN graft polyol/HQEE containing 40% hard block had a flex modulus of 230 MPa, tensile strength of 18 MPa, and 240% elongation. The ratio of flex moduli measured at ?29 and +70°C was 2.7, which compared very favorably to conventional RIM systems. The modulus at elevated temperatures was particularly improved, which is important in painting operations.     

Morphology and Properties of Waterborne Polyurethane/CNT Nanocomposite Adhesives with Various Carboxyl Acid Salt Groups

Three series of waterborne polyurethane (WBPU)/carbon nanotube (CNT) nanocomposites were prepared, and their morphology and properties with various 2,2-dimethylol propionic acid (DMPA) and CNT contents were investigated. The CNTs were homogeneously dispersed up to the optimum content in WBPU/CNT nanocomposite films. The degree of homogeneous CNT dispersion increased with increasing DMPA content in WBPU/CNT nanocomposite films. The optimum CNT content showed maximum tensile strength, Young's modulus and adhesive strength of WBPU/CNT nanocomposite film. The optimum CNT contents for WBPU/CNT nanocomposite samples containing 3.61, 5.16 and 5.86 wt% DMPA were about 0.50, 1.00 and 1.50 wt%, respectively. The WBPU/CNT nanocomposite adhesive showed higher adhesive strength at moderately high temperatures (40/60/80/100°C) compared to conventional WBPU. The highest adhesive strength at moderately high temperatures was found with 5.86 wt% DMPA and 1.5 wt% CNT content.     

High strength poly(vinyl alcohol) films obtained by drying and then stretching freeze/thaw cycled gel

The mechanical properties of stretched poly(vinyl alcohol) (PVA), which is formed by stretching a film prepared from a freeze/thaw cycled gel, were investigated as a function of the stretching ratio. The tensile strength and Young's modulus of 800% stretched PVA annealed at 130°C were 3.4 and 119 GPa, respectively. These values were much higher than those for a PVA film prepared without freeze/thaw cycling. For a film stretched more than 600% before annealing, two melting peaks, assignable to folded and extended chain crystals, were observed around 220°C and 230°C, respectively. This indicates that a shish‐kebab structure is formed as the stretching ratio increases. After annealing at 130°C, the folded‐chain crystal transformed to an extended‐chain crystal if an extended‐chain crystal was present in the stretched film before annealing. High tensile strength and Young's modulus after annealing were due to the formation of extended‐chain crystal. Therefore, the presence of extended‐chain crystal for annealing is important to provide good mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41318.     

High-strength polyethylene

Polyethylene (PE) continuous filaments having high tensile strength as well as high Young's modulus have been obtained from several linear polyethylene materials by stretching a partially oriented spun yarn to a draw ratio of ?30. The high draw ratio was readily attained for linear PE fiber extruded at a temperature of at least 250°C and quenched in air while under some intermediate tension. The number average molecular weight of the polymer was found to have the predominant effect on the ultimate tensile strength of the drawn fiber. Yarn with a tensile strength of 19 gpd (167 kg/mm²) and a Young's modulus of 854 gpd (7380 kg/mm²) was produced. Yarn with a Young's modulus of 1145 gpd (9890 kg/mm²) was made by sacrificing some tensile strength.     

Synthesis of triazole ring‐containing pentol chain extender and its effect on the properties of hyperbranched polyurethane‐urea coatings

This article describes the synthesis and property evaluation of different hyperbranched polyurethane‐urea (HBPUU) coatings based on a newly synthesized triazole ring‐based pentol chain extender. For this initially, the chain extender was synthesized using acetylene azide click reaction and the structure of the intermediate compounds were confirmed by ¹H‐, ¹³C‐NMR, FTIR, and ESI‐mass spectrometry. In the further steps, the required HBPUU coatings were prepared by a systematic three‐step reaction process. In the first step, a isocyanate terminated prepolymer resin was synthesized at NCO/OH ratio of 1.2 : 1, while the second and third step involves the partially chain extension followed by moisture curing. The excess NCO content in the prepolymer was calculated by standard dibutylamine titration method and partially (10, 20, 30, 50, and 70% of the excess NCO content) chain extended with the pentol chain extender and remaining was moisture cured. The structure property relation of different HBPUU coating films were analyzed by FTIR peak deconvulation technique using Gaussian curve fitting procedure while, their viscoelastic and thermo‐mechanical properties were measured by dynamic mechanical thermal analysis, thermo gravimetric analysis, differential scanning calorimetric, and universal testing machine instruments. These results showed that thermal stability, glass transition temperature (T_g), elongation at break increases but the storage and tensile modulus decreases with increasing the percent loading of the triazole chain extender. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Modification of Free Volume in Epoxy Adhesive Formulations

Additives are described which modify the free volume available for segmental motion in epoxy adhesives. Such a mechanism can produce an increase in the tensile modulus of conventional epoxy-amine systems of>60% (e.g. to>4.1 GPa) and in tensile strength of>50% (e.g. to 125 MPa), while also producing a ductile mode of failure (stress-strain curve has negative slope before failure). At low strains, a reduction in free volume hinders polymer segmental motion and so increases the modulus. However, these materials also exhibit a very low Poisson's ratio and strains of ca. 5% cause a sufficient increase in free volume that ductile failure can occur. Improvements in low temperature cure properties (e.g. 118 MPa tensile strength at 60°C cure) together with reductions in the coefficient of thermal expansion and water uptake are also reported. These improvements in bulk adhesive properties are shown to translate into improved adhesive joint performance.     

PTMG／TDI型聚氨酯弹性体的制备及力学性能研究

以聚四氢呋喃醚二醇（PTMG）、2,4-甲苯二异氰酸酯（TDI）、3,3’-二氯-4,4’-二胺基二苯甲烷（MOCA）或3,5-二甲硫基甲苯二胺（E-300）为主要原料,采用预聚体法合成浇注型聚氨酯弹性体（PUE）。分析了预聚体NCO基含量、PTMG软段相对分子质量、两种扩链剂以及扩链系数对PUE力学性能的影响。结果表明,随着预聚体NCO基含量增加,PUE的硬度、拉伸强度、300％定伸应力和撕裂强度提高,扯断伸长率下降,扯断永久形变发生微小变化;随着软段相对分子质量的不断提高,PUE的硬度、拉伸强度、300％定伸应力和撕裂强度缓慢下降,而扯断伸长率和扯断永久形变升高;在其它条件相同时,扩链剂E-300与MOCA相比,综合力学性能较好。     

The effect of pre-carbonization on the properties of PAN-based carbon fibers

A continuous stabilization and two-stage carbonization process was used to prepare polyacrylonitrile (PAN)-based carbon fibers, The effect of pre-carbonization (300 to 550°C) on the final properties and microstructure of carbon fibers was measured. Experimental results using an X-ray diffractometer indicated the presence of a less ordered structure at 2Θ from 5 to 18° in the pre-carbonized fibers and the final carbon fibers. This study found that the pre-carbonization process strongly affects the microstructure of the resulting carbon fibers. The results also showed that a suitable pre-carbonization was very conducive to improvement in tensile strength or in Young's modulus of the final carbon fibers. When the final carbon fiber was pre-carbonized at 300 and 550°C, respectively, these fibers had a higher tensile strength and higher Young's modulus than carbon fibers pre-carbonized at other conditions.     

Hyperbranched waterborne polyurethanes

A hyperbranched polyol (HBP), viz. hyperbranched 2,2-bis(hydroxymethyl) propionic acid (MPA) polyester-16-hydroxyl, was incorporated chemically into waterborne polyurethane by a covalent bond as a multifunctional chain extender or chemical crosslink for isocyanate (NCO)-terminated PU prepolymers. In addition, the effects of HBP incorporation on the particle size, tensile properties in the glassy and rubbery states, thermal stability, contact angle, and hardness were examined. After HBP incorporation, the particle size initially decreased during the dispersion step. With time, the particle size increased due to the swelling of HBP, and there was an increase in the contact angle, initial modulus, break strength, and decomposition temperature of the dispersion cast film. In particular, the largest increases in these properties were obtained when the NCO index was unity.     

Effect of incorporation of graphene oxide and graphene nanoplatelets on mechanical and gas permeability properties of poly(lactic acid) films

Nanocomposite thin films of poly(lactic acid) (PLA) were produced incorporating small amounts (0.2 to 1 wt%) of graphene oxide (GO) and graphene nanoplatelets (GNP). The films were prepared by solvent‐casting. Mechanical properties were evaluated for plasticized (by residual solvent) and unplasticized films. Plasticized nanocomposite films presented yield strength and Young's modulus about 100% higher than those of pristine PLA. For unplasticized films improvements in tensile strength and Young's modulus were about 15 and 85%, respectively. For both film types, a maximum in mechanical performance was identified for about 0.4 wt% loadings of the two filler materials tested. Permeabilities towards oxygen and nitrogen decreased, respectively, three‐ and fourfold in films loaded with both GO or GNP. The glass transition temperature showed maximum increases, in relation to unloaded PLA films, of 5 °C for 0.4 wt% GO and 7 °C for 0.4 wt% GNP, coinciding with the observed maxima in mechanical properties. Copyright © 2012 Society of Chemical Industry     

Mechanical and thermal properties of epoxy resins with reversible crosslinks

The tensile properties: Young's modulus, ultimate tensile strength, ultimate elongation, the glass transition temperature, and the dynamic mechanical properties (dynamic shear modulus (G'), loss tangent (Tan δ)), of three epoxy resins (Epon 828, Epon 836, Epon HPT 1071) cured with the disulfide-containing crosslinking agent—4.4-dithiodianilme (DTDA) have been characterized. The results show that DTDA is a satisfactory crosslinking agent for the epoxide resins that have been studied as compared to the well-known curing agent methylene dianiline (MDA). There are no significant differences between the properties of Epon 828 cured with DTDA at stoichiometric ratio (2:1) and Epon 828 cured with DTDA at small amine excess ratio (1.75:1). The glass transition temperature of the cured tetrafunctional epoxy resin Epon HPT 1971 (235°C) is significantly higher than that of difunctional epoxy resins such as Epon 828 (T_g–175°C), but the product is too brittle to be used without plasticizer.     

Properties of Waterborne Polyurethane/CNT Nanocomposite Adhesives: Effect of Countercations

Two series of waterborne polyurethane (WBPU)/carbon nanotube (CNT) nanocomposites were prepared with various CNT contents (0–1.50 wt%). We used a metal-hydroxide (copper hydroxide, Cu(OH)₂) and amine (triethylamine, TEA) as the countercation in the nanocomposites. The interaction of the countercations with the CNTs in the nanocomposite was characterized by TEM, and the interaction effects on the properties, such as the glass transition temperature (T_g), storage modulus, tensile strength, Young's modulus and adhesive strength, were investigated. The CNTs were homogeneously (optimum) dispersed at concentrations of up to 1.25 and 1.00 wt% for the metal-hydroxide and amine series, respectively. At the optimum CNT content, the tensile strength and adhesive strength were maximized in each series. However, the adhesive strength of the WBPU/CNT nanocomposite with the metal-hydroxide countercation was less affected than with the amine-countercation after immersing the adhesive bonded nylon fabrics in water (for up to 48 h).     

Microstructure evolution and mechanical behavior of a mullite fiber heat-treated from 1100 to 1300°C

In this paper, the effect of phase transformation on microstructure evolution and mechanical behaviors of mullite fibers was well investigated from 1100 to 1300°C. In such a narrow temperature range, the microstructure and mechanical properties showed great changes, which were significant to be studied. The temperature of the alumina phase transformation started at below 1100°C. The main phases in fibers were γ-Al₂O₃ and δ-Al₂O₃ with amorphous SiO₂ at 1150°C. The stable α-Al₂O₃ formed at 1200°C. Then the mullite phase reaction occurred. As the alumina phase reaction took place, the tensile strength increased with the increasing temperature. In particular, the filaments achieved the highest strength at 1150°C with 1.98 ± 0.17 GPa, and the Young's modulus was 163.08 ± 4.69 GPa, showing excellent mechanical performance. After 1200°C, the mullite phase reaction went on with the crystallization of orthorhombic mullite. The density of surface defects increased rapidly due to thermal grooving, which led to mechanical properties degrade sharply. The strength at 1200°C was 1.01 ± 0.15 GPa with a strength retention of 63.13%, and the Young's modulus was 184.14 ± 10.36 GPa. While at 1300°C, the tensile strength was 0.64 ± 0.14 GPa with a strength retention of only 40.00%.     

High‐tensile‐strength polyvinyl alcohol films prepared from freeze/thaw cycled gels

The mechanical properties and molecular structure of a poly(vinyl alcohol) (PVA) film, which was obtained by eliminating water from a PVA hydrogel using repeated freeze/thaw cycles, were investigated by tensile tests, thermal analysis, and X‐ray diffraction measurements. The mechanical properties of PVA with 99.9% saponification were measured as a function of the number of freeze/thaw cycles performed. The tensile strength and Young's modulus increased and the elongation at break decreased with increasing freeze/thaw cycles. The tensile strength and Young's modulus of PVA films obtained after seven freeze/thaw cycles were as high as 255 MPa and 13.5 GPa after annealing at 130°C. Thermal analysis and X‐ray diffraction measurements revealed that this is because of a high crystallinity and a large crystallite size. A good relationship between the tensile strength and the glass transition temperature was obtained, regardless of the degree of saponification and annealing conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40578.     

Continuous carbonization of polyacrylonitrile-based oxidized fibers: Aspects on mechanical properties and morphological structure

By following the progression of continuous carbonization (300–1250°C) of polyacrylonitrile (PAN)-based oxidized fibers, variations in tensile mechanical properties and morphological structure are reported in detail along the carbonization line. The tensile strength and Young's modulus of the fibers generally increase throughout the carbonization stage. Meanwhile, the fiber diameter displays a significant decrease. The preferred orientation of carbon layer planes is observed to increase remarkably for temperatures over 400°C. In a similar manner, the stacking size increases significantly but reaches saturation around 600°C, a changing point corresponding to that observed for the variation of the Young's modulus. However, beyond about 1200°C, the stacking size again displays a marked increase. Results thus obtained are interpreted in relation to each other. Possible implications are also discussed. © 1994 John Wiley & Sons, Inc.     

Experimental investigation and optimization of printing parameters of 3D printed polyphenylene sulfide through response surface methodology

Today fused filament fabrication is one of the most widely used additive manufacturing techniques to manufacture high performance materials. This method entails a complexity associated with the selection of their appropriate manufacturing parameters. Due to the potential to replace poly-ether-ether-ketone in many engineering components, polyphenylene sulfide (PPS) was selected in this study as a base material for 3D printing. Using central composite design and response surface methodology (RSM), nozzle temperature (T), printing speed (S), and layer thickness (L) were systematically studied to optimize the output responses namely Young's modulus, tensile strength, and degree of crystallinity. The results showed that the layer thickness was the most influential printing parameter on Young's modulus and degree of crystallinity. According to RSM, the optimum factor levels were achieved at 338°C nozzle temperature, 30 mm/s printing speed, and 0.17 mm layer thickness. The optimized post printed PPS parts were then annealed at various temperatures to erase thermal residual stress generated during the printing process and to improve the degree of crystallinity of printed PPS's parts. Results showed that annealing parts at 200°C for 1 hr improved significantly the thermal, structural, and tensile properties of printed PPS's parts.     

Properties of Waterborne Polyurethane Adhesives: Effect of Chain Extender and Polyol Content

A series of waterborne polyurethane (WBPU) adhesives were prepared with various ratios of polyol, poly(tetramethylene oxide glycol) (PTMG), and chain extender, ethylene diamine (EDA), at a fixed content of diisocyanate, 4,4-dicyclohexylmethane diisocyanate (H₁₂MDI) and hydrophilic agent, 2,2-dimethylol propionic acid (DMPA). WBPU adhesives were characterized by IR and ¹H-NMR spectroscopies, X-ray diffraction (XRD) and gel permeation chromatography (GPC). It was found that the extent of hydrogen bonds between hard–hard segment (i.e., hydrogen bonds between the NH and carbonyl groups) increased with increasing chain extender content (decreasing polyol content). Moreover, the disordered hydrogen bond of carbonyl group (hydrogen bond of urethane groups in the interfacial region) increased with increasing chain extender content (decreasing polyol content). The cyclic urea and allophanate group, which are attributed to the side reaction and cross-linking reaction, respectively, were found above a molar ratio 0.17 of chain extender to diisocyanate. The adhesive strength was maximum with 0.95 wt% and 63.10 wt% chain extender and soft segment (PTMG), respectively (H2 sample) at room temperature for the WBPU adhesive. However, with increasing application temperature the adhesive strength decreased for all samples.     

Synthesis of polyurethanes from solvolysis lignin using a polymerization catalyst: Mechanical and thermal properties

Two methods of synthesis, namely, using a polymerization catalyst versus a non-catalytic route, were investigated to produce lignin-based polyurethanes. The films were characterized with respect to crosslink density, ultimate tensile behavior and glass transition temperature. The results indicated that use of the catalyst for polymerization is an effective way for producing films with consistent properties, even at lignin contents as high as 45 to 50 wt%. To illustrate the catalyst effectiveness, crosslink densities of catalyzed films with 20 wt% of lignin content increased drastically from 0.2-0.3 to 1.7-2.7 mmol/cm 3 when the NCO/OH molar ratio increased from about 1.3 to 3.0, without much increase in the corresponding crosslink densities of the non-catalyzed films. Also, when the NCO/OH molar ratio increased from 1.2 to 3.2, the tensile strength increased from 1.9 MPa to a maximum of 55 MPa (NCO/OH=2.6) before decreasing. Also, for same NCO/OH ratios, ultimate strain decreased drastically from 174.4% to 4.3%, with a corresponding increase in Young's Modulus from 0.03 GPa to 2.8 GPa. The glass transition temperatures of the catalyzed films also increased from 35°C to 89°C. Without the catalyst, only polyurethanes with low NCO/OH ratios, low lignin contents, and inferior mechanical properties, could be synthesized.