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).     

Disruption of soy-based adhesive treated by Ca(OH)2 and NaOH

In this paper, the mixed alkalis, namely Ca(OH)₂ and NaOH, were used to disrupt soy protein. The structure characteristics and thermal properties of soy protein treated by Ca(OH)₂ and NaOH were studied by FT-IR and Differential scanning calorimetry (DSC). The results showed that soy-based adhesive by the mixed alkalis had better dry shear strength, wet shear strength, water resistance, and heat resistance than those of soy adhesive treated by NaOH alone. That was partly proved by results of FT-IR. DSC results indicated that the optimal weight ratio of mixed alkalis Ca(OH)₂/NaOH was 2:1.     

Preparation and properties of waterborne polyurethane–urea anionomers. I. The influence of the degree of neutralization and counterion

Two series of waterborne polyurethane–urea anionomers were prepared by a polyaddition reaction with isophorone diisocyanate, poly(tetramethylene oxide) glycol (weight‐average molecular weight = 1000), dimethylol propionic acid (DMPA), and ethylene diamine as chain extenders. Triethylamine (TEA) or 28:1 mol/mol ammonium hydroxide (NH₄OH)/cupric hydroxide [Cu(OH)₂] was used as a neutralization agent [NH(C₂H₅) or NH/Cu²⁺ counterion] for the pendant COOH group of DMPA. The effects of the degree of neutralization and counterion on the particle size of the dispersions, the conductivity, and the antibacterial and mechanical properties of polyurethane–urea anionomer films were investigated. The particle sizes of the two sample series dispersions decreased with an increasing degree of neutralization. Aqueous dispersions of polyurethane–urea anionomers with particle sizes of 30–120 nm were stable for about 3 months. By infrared spectroscopy, it was found that TEA‐based samples (T series) had higher fractions of hydrogen‐bonded carbonyl groups in the ordered region than NH₄OH/Cu(OH)₂‐based samples (S series). However, the fractions of hydrogen‐bonded carbonyl groups in the disordered region of the S‐series samples were higher than those of the T‐series samples. The conductivities of the S‐series film samples were higher than those of the T‐series samples. However, the T‐series film samples commonly had higher tensile strengths and initial moduli than the S‐series samples. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2375–2383, 2002     

Preparation and properties of polydimethylsiloxane (PDMS)/polytetramethyleneadipate glycol (PTAd)-based waterborne polyurethane adhesives: Effect of PDMS molecular weight and content

Waterborne polyurethane (WBPU) dispersions were prepared by pre-polymer process using siloxane polyol, namely polydimethylsiloxane (PDMS), and polyester polyol, namely poly(tetramethyleneadipate glycol) (PTAd), as a soft segment. Three different molecular weights (M_n = 550, 6000, 110,000) of PDMS and one fixed molecular weight of PTAd (M_n = 2000) was used during preparation of WBPU dispersions. This research aims to explore the potential use of PDMS in complementing WBPU by boosting flexibility, water resistance, and adhesive strength. The water swelling (%), tensile strength, and adhesive strength of WBPUs were investigated with respect to PDMS molecular weight and PDMS content (PDMS mol %). The water swelling (%) and tensile strength decreased with increasing PDMS molecular weight at a fixed PDMS content (mol %) in mixed polyol of WBPU films. By contrast, the peel adhesive strength peaked at 6.64 mol % and 4.43 mol % with molecular weight of PDMS at 550 and 6000, respectively, while it only decreased when the molecular weight of PDMS stood at 110,000. The adhesive strength was almost unaffected with optimum content (6.64 mol %) of lower PDMS molecular weight (M_n = 550) in mixed polyol-based WBPU after immersing the adhesive bonded nylon fabrics in water for 48 h among all of the samples. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Tensile properties of polypropylene flame-retardant composites

The polypropylene (PP) flame-retardant composites filled with aluminum hydroxide (Al(OH)₃), magnesium hydroxide (Mg(OH)₂), zinc borate (ZB), nanometer calcium carbonate (nano-CaCO₃), and polyolefin elastomer (POE) were prepared using a twin-screw extruder, and the tensile properties were measured at room temperature by means of an electronic universal test machine (Model CMT4104) in this paper, to identify the influence of the flame-retardant content on the tensile properties. The results showed that the tensile strength decreased roughly nonlinearly while the tensile elongation at break decreased nonlinearly with increasing the flame-retardant weight fraction. The Young’s modulus and the tensile fracture strength increased nonlinearly with an addition of the flame-retardant weight fraction. The tensile ductility of PP/Al(OH)₃/Mg(OH)₂/ZB/Nano-CaCO₃/POE composite was the best in the three kinds of the composite systems. Moreover, good agreement was showed between the predictions and the measurements of the tensile strength.     

Sintering and grain growth behaviour of magnesium aluminate spinel: Effect of lithium hydroxide addition

Lithium hydroxide, LiOH, in the amounts ranging from 0.1 to 1.2 wt% has been used as a sintering aid to improve the densification of MgAl₂O₄. The addition of 0.3 wt% LiOH promotes densification and limits grain growth. The activation energy of sintering, calculated using master sintering curve approach, decreases from 790 ± 20 kJ.mol^?1 to 510 ± 20 kJ.mol^?1 with the addition of 0.3 wt% of LiOH. In addition, MgAl₂O₄ was also mixed with 10 wt% of LiOH to amplify the formation of reaction products. High-temperature XRD results showed that secondary phases (MgO and LiAlO₂) are produced above 1040 °C. The secondary phases start to disappear at T > 1200 °C, and MgAl₂O₄ is produced. While adding small amounts of LiOH, up to ca. 0.3 wt%, is beneficial for densification and suppressing grain growth, there exists a critical concentration of Li⁺ that is accounted for by the preferential incorporation of lithium ions into MgAl₂O₄ crystal lattice.     

Characterization of waterborne polyurethane/clay nanocomposite adhesives containing different amounts of ionic groups

A series of waterborne polyurethane (WBPU)/clay nanocomposite dispersions containing different amounts of 2,2-dimethylol propionic acid (DMPA) and clay were prepared. It was found that the properties of WBPU/clay nanocomposites were highly dependent on both clay content and DMPA content. The WBPU/clay nanocomposite dispersion with a higher clay content showed a larger mean particle size and a less negative zeta potential. The optimum clay content, which increased with increasing DMPA content, showed maximum tensile strength, Young's modulus and adhesive strength of WBPU/clay nanocomposite. The optimum clay concentrations for WBPU/clay nanocomposite samples containing 3.75, 5.41 and 6.17 wt% DMPA were about 0.5, 1.0 and 2.0 wt%, respectively.     

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.     

Reactivity of Heteropolytungstate and Heteropolymolybdate Metal Transition Salts in the Synthesis of Dimethyl Carbonate from Methanol and CO2

A series of Keggin-type heteropoly compounds (HPC) having different countercations (Co, Fe) and different addenda atoms (W, Mo) were synthesized and characterized by means of Fourier-Transform Infrared Spectrometer (FT-IR) and X-ray powder diffraction (XRD). The catalytic properties of the prepared catalysts for the dimethyl carbonate (DMC) synthesis from CO₂ and CH₃OH were investigated. The experimental results showed that the catalytic activity is significantly influenced by the type of the countercation and addenda atoms transition metal. Among the catalysts examined, Co_1.5PW₁₂O₄₀ is the most active for the DMC synthesis, owing to the synergetic effect between Co and W. Investigating the effect of the support showed that the least acidic one (Al₂O₃) enhanced the conversion but decreased the DMC selectivity in favor of that of methyl formate (MF), while that of dimethoxy methane remained stable.     

Anodic oxidation of copper in alkaline solutions 2—the open-circuit potential behavior of electrochemically formed cupric hydroxide films

Copper electrodes covered with Cu(OH)₂ films grown in 1 mol dm⁻³ LiOH solution have been examined using X-ray diffractometry, scanning electron microscopy and electrochemical techniques. A sharp change in potential on open-circuit, due to a change in phase from Cu(OH)₂ to Cu₂O, was observed. This phase change is accompanied by a substantial amount of film dissolution. The time required for transformation, and the final amount of Cu₂O formed, are functions of both hydroxide ion concentration and electrode rotation speed. A mechanism involving Cu(OH)₂ dissolution, disproportionation (Cu²⁺+Cu→2Cu⁺) and Cu₂O precipitation, is proposed to explain these observations.     

Effects of a small addition of Mn on the corrosion behaviour of Zn in a mixed solution

The effects of a small addition of Mn (0.4 wt%) on the corrosion behaviour of pure Zn (99.995 wt%) in a mixed solution (0.1 M NaCl + 0.1 M Na₂SO₄ + 0.01 M NaHCO₃, pH 8.4) were investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and X-ray photoelectron spectroscopy (XPS). The electrochemical impedances of both Zn and Zn–0.4Mn have been successfully fitted with a suitable EIS equivalent circuit model. Fitted impedance results revealed that 0.4 wt% Mn improved both the pore resistance and charge transfer resistance of Zn in the mixed solution. As a result, both anodic and cathodic reaction rates were reduced. X-ray photoelectron spectroscopy (XPS) analysis showed that the corrosion films formed in the mixed solution consisted of zinc oxide (ZnO), zinc hydroxide (Zn(OH)₂) and zinc hydrozincite (Zn₅(CO₃)₂(OH)₆). The role of small addition of Mn is that it promotes the precipitation of hydrozincite in the pores of corrosion film. An “alleviation of local acidification” mechanism is proposed to explain the investigated results.     

Thermal and mechanical properties of melt processed intercalated poly(methyl methacrylate)–organoclay nanocomposites over a wide range of filler loading

BACKGROUND: Poly(methyl methacrylate) (PMMA)–organoclay nanocomposites with octadecylammonium ion‐modified montmorillonite, prepared via melt processing, over a wide range of filler loading (2–16 wt%) were investigated in detail. These hybrids were characterized for their dispersion structure, and thermal and mechanical properties, such as tensile modulus (E), break stress (σ_brk), percent break strain (ε_brk) and ductility (J), using wide‐angle X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile and impact tests. RESULTS: Intercalated nanocomposites were formed even in the presence of 16 wt% clay (high loading) in PMMA matrix. PMMA intercalated into the galleries of the organically modified clay, with a change in d‐spacing in the range 11–16 Å. TGA results showed improved thermal stability of the nanocomposites. The glass transition temperature (T_g) of the nanocomposites, from DSC measurements, was 2–3 °C higher than that of PMMA. The ultimate tensile strength and impact strength decreased with increasing clay fraction. Tensile modulus for the nanocomposites increased by a significant amount (113%) at the highest level of clay fraction (16 wt%) studied. CONCLUSION: We show for the first time the formation of intercalated PMMA nanocomposites with alkylammonium‐modified clays at high clay loadings (>15 wt%). Tensile modulus increases linearly with clay fraction, and the enhancement in modulus is significant. A linear correlation between tensile strength and strain‐at‐break is shown. Thermal properties are not affected appreciably. Organoclay can be dispersed well even at high clay fractions to form nanocomposites with superior bulk properties of practical interest. Copyright © 2007 Society of Chemical Industry     

Thermal properties and adhesion strength of modified soybean storage proteins

Soy proteins have shown great potential for adhesive and resin applications. This investigation characterized the thermal and adhesive properties of the major soy protein components conglycinin (7S) and glycinin (11S) after chemical modification. These globulins were extracted from defatted soy flour, then modified with either sodium hydroxide, sodium dodecyl sulfate (SDS), or urea. Modified 7S, 11S, and mixtures of 7S and 11S at varying ratios were evaluated for gluing strength with cherry veneer plywood and for thermal denaturation using DSC. Adhesive strength and water resistance were significantly improved for all proteins modified with sodium hydroxide. Gluing strength and water resistance were improved for SDS- and ureamodified proteins containing greater portions of 7S globulins. The opposite behavior was observed for proteins containing large amounts of 11S globulins. DSC results showed that the temperatures of denaturation (T _d ) decreased for the proteins modified with sodium hydroxide or urea, whereas the T _d values of proteins modified with SDS were similar to the unmodified proteins. These results suggested that, at the concentrations studied, sodium hydroxide or urea could denature soybean protein more effectively than SDS, resulting in lower protein thermal stability. Soybean proteins with high ratios of 11S had more ordered structures, as evidenced by the high enthalpy values of protein denaturation observed in DSC measurements.     

Properties of Waterborne Polyurethane Adhesives with Aliphatic and Aromatic Diisocyanates

A series of waterborne polyurethane (WBPU) adhesives were prepared with various ratios of aliphatic/aromatic diisocyanates, namely 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI) as an aliphatic diisocyanate and 4,4′-diphenylmethane diisocyanate (MDI) as an aromatic diisocyanate with poly(tetramethyleneoxideglycol) (PTMG), ethylene diamine (EDA) and dimethylol propionic acid (DMPA). ¹H-NMR spectroscopy was utilized to investigate the side reaction at the dispersion step during synthesis of WBPU dispersions with respect to aliphatic, aromatic and mixed diisocyanates. The tensile strength, Young's modulus, elongation at break (%), storage modulus, glass transition temperature and adhesive strength were measured with respect to aliphatic/aromatic diisocyanate contents. The adhesive strength was maximum using mixed diisocyanates containing 25 mol% MDI in WBPU adhesives.     

Interface modification and characterization in linear low-density polyethylene highly loaded with aluminium hydroxide

Fire-retardant linear low-density polyethylene (LLDPE) composites were prepared by combining this polymer with uncoated and surface treated forms of aluminum hydroxide (Al(OH)₃). The poor toughness and ductility of polyethylene highly filled with Al(OH)₃ can be significantly improved by addition of a small amount of silicon oil. It is found that silicon oil improves elongation at break of the composite remarkably, but this is accompanied by the deterioration of tensile strength. Silane crosslinked polyethylene substituting for polyethylene as the matrix in Al(OH)₃-filled polyethylene improves the tensile strength of the composite. Fractured surface analysis and limiting oxygen index (LOI) of the composites were also studied. Possible mechanisms accounting for these effects are discussed.     

Properties of Waterborne Polyurethane/Clay Nanocomposite Adhesives

A series of waterborne polyurethane (WBPU)/clay nanocomposite dispersions using two different organically modified clays, namely Cloisite 15A and Cloisite 30B, were prepared. It was found that the properties of WBPU/clay nanocomposites were highly dependent on both the clay content and the clay surface characteristic (hydrophilic/hydrophobic). A WBPU/clay nanocomposite dispersion with a higher clay content showed a less negative zeta potential. A lower zeta potential for dispersion with Cloisite 30B compared to Cloisite 15A was observed indicating a higher stability of the dispersion. The tensile strength, Young's modulus and adhesive strength of WBPU/clay nanocomposite containing Cloisite 30B were also higher than those of nanocomposite containing Cloisite 15A. The optimum clay contents, with respect to these properties, for nanocomposites with Cloisite 15A and Cloisite 30B were found to be 2 wt% and 3 wt%, respectively.     

The physical properties of nonionic waterborne polyurethane with a polyether as side chain

A series of nonionic waterborne polyurethanes (WPU) based on hydrogenated methylene diphenylene diisocyanate, polybutylene succinate diol, polybutylene adipate diol, polyethylene glycol, and diethylene glycol as chain extender were synthesized with a polyether, MPEG‐(OH)₂, as side chain. The physical properties such as tensile strength, elongation, hardness, molecular weight, kinetic viscosity, and so on were detected. The WPUs made with polyesters have the best tensile strength but the lowest elongation. Because of the hydrophilic property of MPEG‐(OH)₂ grafted on the WPUs, they have obvious increases of solid contents and water absorptions with the ratio of MPEG‐(OH)₂. The functional group ratio of NCO/OH is another reason affecting the hydrophilic properties of the WPUs. In addition, the water ratios of the dispersions dramatically affect the stability of WPU systems. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Tensile shear strength of wood bonded with urea–formaldehyde with different amounts of microfibrillated cellulose

Urea–formaldehyde (UF) adhesive mixtures with a 5% suspension of microfibrillated cellulose (MFC) at 0.5, 1, 3, and 5 wt% loading levels based on the solid weight (62.4%) of the UF adhesive were prepared. Beech lamellas with dimensions of 5 mm×20 mm×150 mm were prepared from beech lumbers using a planer saw. The UF adhesive (E0 class) was mixed with the MFC using a magnetic stirrer to achieve a proper distribution of the MFC in the UF adhesive. The tensile shear strength of single lap-joint specimens bonded with UF adhesive containing MFC was determined in accordance with EN 205 (2003). The specimens bonded with UF adhesive containing the MFC showed better tensile shear strengths as compared to the control. As compared to the control specimens, the tensile shear strength of the specimens increased by 5.7% as 3 wt% of the MFC was incorporated into the UF adhesive. However, a further increment in the MFC content up to 5 wt% decreased the tensile shear strength of the specimens (−14.3% of control specimen). The MFCs were well dispersed in the UF resin and were cross-linked to form a network to reinforce the bond line, improving bonding performance.     

Eco-Friendly Adhesives Based on Tannin and N,N-Bis(2-Hydroxy-Ethyl) Fatty Amides (HEFAs) from Non-Traditional Oils for Wood Bonding

Abstract

Wood adhesives were formulated using tannin and N,N-bis(2-hydroxyethyl) fatty amides (HEFAs). The natural tannin-based adhesives can be used to replace formaldehyde-based adhesive systems and thereby reduce formaldehyde and volatile organic compound (VOC) emissions from adhesives used for plywoods. Performance properties of the adhesively bonded wood joints viz., tensile strength, impact strength and chemical resistance were measured. N,N-bis(2-hydroxyethyl) fatty amides (HEFAs) from non-traditional oils were mixed with a pure tannin-based adhesive as a crosslinker, and this increased the tensile strength, impact strength and chemical resistance of wood joints. The results revealed that a high performance and eco-friendly adhesive system for wood can be successfully formulated using tannin and HEFA.     

Effect of nAl(OH)3 on thermal, mechanical and morphological properties of millable polyurethane (MPU) rubber

Aluminium hydroxide nanoparticles [nAl(OH)₃] were synthesized using continuous ultrasonic cavitation technique. The size and shape of synthesized nanoparticles were confirmed using X-ray diffraction and transmission electron microscopy, which was found to be ~55 nm in diameter with needle shape. Millable polyurethane (MPU) rubber nanocomposites were prepared with nAl(OH)₃ as a filler (0.5–2.5 wt% loading) using two-roll mill and moulded on compression moulding machine. Dicumyl peroxide was used as a curing agent. Mechanical property and abrasion resistance was determined using universal testing machine (UTM) and abrasion resistance tester, respectively. Physical (hardness and swelling index) and thermal (flammability and stability) properties were also studied on shore A hardness tester, flammability tester and thermo gravimetric analyzer, respectively. The extent of dispersion of nAl(OH)₃ in MPU matrix was studied using scanning electron microscope (SEM) and atomic force microscope (AFM). MPU rubber:nAl(OH)₃ nanocomposites show improved mechanical, physical and thermal properties compared to pristine MPU composite. This dramatic improvement in properties was due to very small grain size of nAl(OH)₃, which facilitates uniform dispersion of nanoparticles within the chains of MPU rubber. This improvement in properties were up to 2 wt% and decreases subsequently (2.5 wt%) due to agglomeration. nAl(OH)₃ behaves like an ordinary filler at higher wt% loading.