Effects of organophilic‐modified attapulgite nanorods on thermal and mechanical behavior of segmented polyurethane elastomers

The effects of different grafting content of 4,4′‐methlenebis(phenyl isocyanate)‐modified attapulgite (ATT‐MDI) on thermal and mechanical properties of segmented polyurethane (PU) elastomers were investigated. The ATT‐MDI nanorods with different grafting content were prepared by treating ATT with heat and acid followed by grafting with MDI molecules. MDI‐modified ATT were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy. TGA analysis revealed that at least 30 wt % of MDI was grafted/adsorbed on the surface of ATT following the modification. Three PU/ATT‐MDI nanocomposites were in situ synthesized using ATT with different grafting contents, and the materials were characterized by TEM, thermal analysis, and mechanical testing. The tensile strength and modulus increased with increasing grafting content of MDI molecules, and the crystallinity of soft and hard segments was increased by ATT‐MDI. POLYM. COMPOS., 31:1890–1898, 2010. © 2010 Society of Plastics Engineers.     

A novel synthesis of reactive nano‐clay polyurethane and its physical and dyeing properties

This study is about polyurea prepolymer, which was synthesized from the extender (N‐(2‐hydroxyethyl) ethylene diamine, HEDA or ethylene diamine, EDA) with 4,4′‐diphenylmethane diisocyanate (MDI), as an intercalative agent to intercalate the organic modified montmorillonite clay. Then, it is further reacted with the polyurethane prepolymer, which is polymerized from the polytetramethylene glycol (PTMG) and MDI, to proceed the intercalative polymerization to form a polyurethane/clay nanocomposite polymer. The experimental parameters contain the use of polyurea intercalative prepolymer extender and also the contents of organo‐clay in the prepolymer etc. We expect to get better mechanical property and also to improve the dyeing properties of nano‐clay polyurethane. The polyurethane/clay polymer is synthesized using two‐step method: synthesizing the polyurethane prepolymer from PTMG and MDI and then extended with the polyurea prepolymer modified with the organo‐clay. Because the extender HEDA contains side chain of hydroxyl groups, the modified PU can further react with the reactive dye. From the experimental results of the fine structure (X‐ray and FT‐IR) and mechanical analysis, it is found that the intercalation is successfully achieved. Thedistance of interlayer spacing is manifestly enlarged. The mechanical properties are significantly improved as the content of organo‐clay is increased. Besides, although thedye up‐take is decreased with the increasing content oforgano‐clay, but the water‐resistant fastness is improved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Reaction kinetics,thermal properties of tetramethyl biphenyl epoxy resin cured with aromatic diamine

Epoxy resins, 4, 4′‐diglycidyl (3, 3′, 5, 5′‐tetramethylbiphenyl) epoxy resin (TMBP) containing rigid rod structure as a class of high performance polymers has been researched. The investigation of cure kinetics of TMBP and diglycidyl ether of bisphenol‐A epoxy resin (DGEBA) cured with p‐phenylenediamine (PDA) was performed by differential scanning calorimeter using an isoconversional method with dynamic conditions. The effect of the molar ratios of TMBP to PDA on the cure reaction kinetics was studied. The results showed that the curing of epoxy resins contains different stages. The activation energy was dependent of the degree of conversion. At the early of curing stages, the activation energy showed the activation energy took as maximum value. The effects of rigid rod groups and molar ratios of TMBP to PDA for the thermal properties were investigated by the DSC, DMA and TGA. The cured 2/1 TMBP/PDA system with rigid rod groups and high crosslink density had shown highest T_g and thermal degradation temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Terminally functionalized polyethylenes as compatibilizers for wood–polyethylene composites

Isocyanate‐terminated polyethylenes (PE), PE‐MDI and PE‐PMDI, were synthesized by reacting polyethylene monoalcohol (PEA) with 4,4′‐methylenediphenyl diisocyanate (MDI) and polymeric methylene diphenyl diisocyanate (PMDI), respectively. Effects of PEA, PE–MDI, and PE–PMDI on the mechanical properties and water resistance of wood–PE composites were investigated. All three compatibilizers increased the strength of the wood–PE composites. Composites containing PE–MDI or PE–PMDI exhibited a higher modulus of rupture (MOR) than those with PEA. The addition of PE–MDI and PE–PMDI decreased the water uptake rate of the composites while PEA increased this rate. The superior compatibilization effects of PE–MDI and PE–PMDI were attributed to the formation of covalent bonding between isocyanate and wood. This covalent bonding was demonstrated by the FTIR spectra of the wood residues after a p‐xylene extraction. Scanning electron microscope (SEM) images revealed that isocyanate‐terminated PE samples improved the interfacial adhesion between wood and PE. POLYM. ENG. SCI., 46:108–113, 2006. © 2005 Society of Plastics Engineers     

Isocyanate–epoxy reactions in bulk and solution

The reaction between diisocyanates and diepoxides can produce polyoxazolidones. However, the reaction may be accompanied by concurrent cyclization of isocyanate to produce trimeric isocyanurate. Studies were performed with pure phenyl isocyanate or diphenylmethane-4,4′-diisocyanate (MDI) and the diglycidyl ether of bisphenol-A (DGEBA). Reactions were followed by FT-IR and differential scanning calorimetry in order to determine relative rates of conversion to polyoxazolidone and isocyanurate. Various catalysts were utilized, with the most effective being 2-ethyl-4-methylimidazole (EMI). Bulk reactions between MDI and DGEBA at 150°C resulted in considerable amounts of trimerization, thus giving crosslinked polymers. Solution reactions at 180–185°C in dry N-methylpyrrolidone using 0.1% EMI gave soluble and moldable polyoxazolidones.     

Synthesis and characterization of a liquid crystalline epoxy containing azomethine mesogen for modification of epoxy resin

A novel liquid crystalline epoxy monomer, 1,1′‐bis [4‐(2,3‐epoxypropoxyphenyleneininomethyl)]‐2,2′‐dimethylbiphenylene (BMPE) was synthesized and characterized by infrared (IR) and Nuclear magnetic resonance (NMR) spectroscopy. The effect of BMPE content on mechanical and thermal properties of its blends with Diglycidyl Ether of Biphenol A (DGEBA) was investigated. BMPE presented a Schlieren texture in the range of 150 to 215°C as observed by differential scanning calorimeter (DSC) and polarizing optical microscope (POM). The improvement of mechanical properties of DGEBA modified with BMPE was achieved without sacrificing thermal resistance. Scanning electronic microscopy (SEM) graphs of fracture surfaces of the cured blends showed that microfiber‐like structure formed in the cured blends, which would be a result of self‐oriented alignment of azomethine mesogen component. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Structure–property relationship of starch‐filled chain‐extended polyurethanes

Chain‐extended polyurethane (PU) elastomers were prepared using castor oil with 4,4′‐methylene bis (phenyl isocyanate) (MDI) as a crosslinker and 4,4′‐diamino diphenyl sulphone (DDS) as an aromatic diamine chain extender. A series of starch‐filled (from 5 to 25% wt/wt) diamines chain‐extended PUs have been prepared. The starch‐filled PU composites were characterized for physico‐mechanical properties viz, density, surface hardness, tensile strength, and percentage elongation at break. Thermal stability of PU/starch have been carried out by using thermogravimetric analyzer (TGA). Thermal degradation process of PU/starch were found to proceed in three steps. TGA thermograms of PU/starch shows that all systems were stable upto 235°C, and maximum weight loss occur at temperature 558°C. The microcrystalline parameters such as crystal size (〈N〉) and lattice strain (g in %) of PU/starch have been established using wide‐angle X‐ray scattering (WAXS) method. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2945–2954, 2003     

Fracture and adhesion behaviors of epoxy resins modified with poly(amine‐quinone)

An amine‐quinone monomer, i.e. 2,5‐bis(4,4′‐methylenedianiline)‐1,4‐benzoquinone (BB), was synthesized by the Michael addition of 4,4′‐diaminodiphenyl methane with 1,4‐benzoquinone. To evaluate the effect of BB content on the glass transition temperature (T_g) and crosslinking density (ρ) of cured diglycidyl ether of bisphenol A (DGEBA)/BB systems, storage modulus and loss factor measurements were obtained using dynamic mechanical analysis. The mechanical properties of the systems were determined in terms of the fracture toughness, impact strength, and adhesion strength. As a result, the ρ values of the systems were found to decrease systematically as the BB content increased. The fracture toughness and adhesion strength of the systems increased with increasing BB content. These results indicate that the addition of BB into epoxy resins increases the free volume of the epoxy network and absorbs the deformation energy, resulting in an improvement of the mechanical properties of the DGEBA/BB systems. Copyright © 2006 Society of Chemical Industry     

Antibacterial oil‐based polyurethane films for wound dressing applications

As an alternative to petroleum‐based polyol, hydroxyl containing material was prepared from linseed oil for polyurethane synthesis. Hexamethylene di‐isocyanate (HMDI) and/or 4, 4′‐methylene diphenyl di‐isocyanate (MDI) were used as isocyanate source. The polymerization reaction was carried out without catalyst. Polymer films were prepared by casting‐evaporation technique. The MDI/HMDI‐based polyurethane and its films had higher T_g and better thermal property than that of the HMDI‐based one because of the existence of benzene ring in the polymer chain. Static water contact angle was determined to be 74° and 77.5° for HMDI and MDI/HMDI‐based films, respectively. Water adsorption was found to be around 2.6–3.6% for both films. In vitro degradation of polyurethanes in phosphate buffered saline at 37°C was investigated by gravimetric method. Fourier transform infrared spectroscopy and scanning electron microscopy were used for confirmation of degradation on the polymer surface. The degradation rate of the HMDI‐based polyurethane film was found higher than that of the MDI/HMDI‐based film. Both the direct contact method and the MMT test were applied for determination of cytotoxicity of polymer films, and the polyurethane films investigated here was not cytotoxic. Silver‐containing films were prepared using Biocera A® as filler and were screened for their antibacterial performance against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and/or Bacillus subtilis. The films prepared with and without Biocera A® exhibited antibacterial activity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphology–properties relationship in high‐renewable content polyurethanes

The effect of diisocyanate nature and hard segment content on the morphology and properties of high‐renewable content segmented thermoplastic polyurethanes was studied. Vegetable oil‐based polyether diol and corn sugar derived chain extender were used as renewable reactants together with an aliphatic (1,6‐hexamethylene diisocyanate, HDI) or aromatic (4,4′‐diphenylmethane diisocyanate, MDI) diisocyanate as hard segment. Segmented thermoplastic polyurethanes were synthesized by two‐step bulk polymerization. Morphology and physicochemical, thermal and mechanical properties were analyzed by Fourier‐transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, atomic force microscopy, and mechanical testing. The effect of mechanical deformation over the microstructure was also analyzed. Changes in crystallinity and hard segment hydrogen bonding after mechanical testing were evaluated by Fourier‐transform infrared spectroscopy and differential scanning calorimetry. The increase of physical crosslinking sites by aromatic diisocyanate and chain extender ratio in the polyurethane results in hard segment crystalline domains with spherulitic morphology, which enhance the stiffness and hardness whereas percentage elongation at break diminish. The flexible, linear aliphatic nature of HDI favors the arrangement of urethane groups thus creating strong hard segment interactions and hard segment crystal microdomains composed of fibrillar morphology are observed. POLYM. ENG. SCI., 54:2282–2291, 2014. © 2013 Society of Plastics Engineers     

Studies on urethane–allophanate networks based on hydroxyl‐terminated polybutadiene: Modeling of network parameters and correlation to mechanical properties

Hydroxyl‐terminated polybutadiene (HTPB)‐based allophanate–urethane networks were prepared by reacting HTPB with di‐isocyanates, such as toluene–di‐isocyanate (TDI), isophorone–di‐isocyanate (IPDI), and 4,4′‐di(socyanatocyclohexyl)methane (H₁₂MDI) at stoichiometric ratios (r‐values) ranging from 1.0 to 1.5. The networks were characterized for mechanical and swell properties. The network parameters, such as “X,” which is the fraction of urethane groups involved in the allophanate formation, and effective chain length (L_x) were calculated from experimental crosslink density values determined from swell data, using α‐model equations developed by Marsh. Excellent linear correlations were obtained between mechanical properties and the calculated network parameters. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2986–2994, 2006     

Mechanical and morphological properties of organic–inorganic,hybrid, clay‐filled,and cyanate ester/siloxane toughened epoxy nanocomposites

Organic–inorganic hybrids involving cyanate ester and hydroxyl‐terminated polydimethylsiloxane (HTPDMS) modified diglycidyl ether of bisphenol A (DGEBA; epoxy resin) filled with organomodified clay [montmorillonite (MMT)] nanocomposites were prepared via in situ polymerization and compared with unfilled‐clay macrocomposites. The epoxy‐organomodified MMT clay nanocomposites were prepared by the homogeneous dispersion of various percentages (1–5%), and the resulting homogeneous epoxy/clay hybrids were modified with 10% HTPDMS and γ‐aminopropyltriethoxysilane as a coupling agent in the presence of a tin catalyst. The siliconized epoxy/clay prepolymer was further modified separately with 10% of three different types of cyanate esters, namely, 4,4′‐dicyanato‐2,2′‐diphenylpropane, 1,1′‐bis(3‐methyl‐4‐cyanatophenyl) cyclohexane, and 1,3‐dicyanato benzene, and cured with diaminodiphenylmethane as a curing agent. The reactions during the curing process between the epoxy, siloxane, and cyanate were confirmed by Fourier transform infrared analysis. The results of dynamic mechanical analysis showed that the glass‐transition temperatures of the clay‐filled hybrid epoxy systems were lower than that of neat epoxy. The data obtained from mechanical studies implied that there was a significant improvement in the strength and modulus by the nanoscale reinforcement of organomodified MMT clay with the matrix resin. The morphologies of the siloxane‐containing, hybrid epoxy/clay systems showed heterogeneous character due to the partial incompatibility of HTPDMS. The exfoliation of the organoclay was ascertained from X‐ray diffraction patterns. The increase in the percentage of organomodified MMT clay up to 5 wt % led to a significant improvement in the mechanical properties and an insignificant decrease in the glass‐transition temperature versus the unfilled‐clay systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Modification of novel bio‐based resin‐epoxidized soybean oil by conventional epoxy resin

Conventional epoxy resin (DGEBA), in varying proportion, was used to modify epoxidized soybean oil (ESO) based systems, crosslinked by phthalic anhydride. The properties of DGEBA modified ESO systems were investigated by dynamic mechanical analysis, impact testing, tensile and flexural testing, scanning electron microscopy, and thermogravimetric analysis. Single loss factor tan δ peak was obtained for all of the modified systems. The results show the improvement in mechanical properties from their high crosslinking densities through the introduction of DGEBA with increase in initial degradation temperature, as obtained from thermogravimetric analysis. Results approaches to an ideal composition which gives the optimum property. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Studies of surface functional modification of nanosized α-alumina

Surface functional modification of nanosized α-alumina is an effective way to improve its dispersion in polymer and to enhance interfacial agglutinate force between particles and polymer. In this paper, diphenylmathane-4,4'-diisocyanate(MDI) was used as a surface grafting agent to react with the hydroxyl group on the surface of nanosized α-alumina. The surface properties of the grafted α-alumina were studied by FT-IR spectra X-ray photoelectron spectroscopy(XPS), surface tensiometer and transmission electron microscope (TEM). It was found that the reaction between the isocyanate group and the hydroxyl group on the surface of α-alumina nanoparticles was attribute to additional reaction of the double bond between C and N in the isocyanate group. The surface of MDI grafted α-alumina nanoparticles showed an extremely hydrophobic property and good dispersibility in ethanol. The most important influence was that there was a quantity of isocyanate groups with an active chemical property on the surface of the grafted particles, which could readily react with compounds containing -OH, -NH₂ or -COOH groups.     

Polyurethane triblock copolymers with mono‐disperse hard segments. Influence of the hard segment length on thermal and thermomechanical properties

Polyurethane triblock copolymers were synthesized by reacting 4,4′‐methylenebis(phenyl isocyanate) (MDI)‐endcapped poly(tetramethylene oxide) (PTMO) with mono‐amine‐amide (MMA) units. Four different MMA units were used, i.e. no‐amide (6m), mono‐amide (6B), di‐amide (6T6m) and tri‐amide (6T6B), based on hexylamine (6m), 1,6‐hexamethylenediamine (6), terephthalic acid (T), and benzoic acid (B). The PTMO had a molecular weight of 2000 g/mol. Thermal and thermo‐mechanical properties were studied by means of differential scanning calorimetry and dynamic mechanical analysis, respectively. The structure of the carbonyl bond was explored by infra‐red analysis and the elastic behavior of the materials by compression set experiments. The triblock polyurethanes with mono‐disperse, hard end‐segments displayed low molecular weights (3200–3800 g/mol). The crystallinity of the MDI urethane‐urea group was found to depend on the structure of the amide. Increasing the number of amide bonds in the mono‐disperse hard segment increased the modulus and the hard segment melting temperature, and decreased the compression set values. The low temperature properties were hardly affected by the amide length. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Surface modification and physical properties of various UHMWPE‐fiber‐reinforced modified epoxy composites

Two surface modification methods—plasma surface treatment and chemical agent treatment—were used to investigate their effects on the surface properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers. In the analyses, performed using electron spectroscopy for chemical analysis, changes in weight, and scanning electron microscope observations, demonstrated that the two fiber‐surface‐modified composites formed between UHMWPE fiber and epoxy matrix exhibited improved interfacial adhesion and slight improvements in tensile strengths, but notable decreases in elongation, relative to those properties of the composites reinforced with the untreated UHMWPE fibers. In addition, three kinds of epoxy resins—neat DGEBA, polyurethane‐crosslinked DGEBA, and BHHBP‐DGEBA—were used as resin matrices to examine the tensile and elongation properties of their UHMWPE fiber‐reinforced composites. From stress/strain measurements and scanning electron microscope observations, the resin matrix improved the tensile strength apparently, but did not affect the elongation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 655–665, 2007     

Preparation and thermo‐mechanical properties of heat‐resistant epoxy/silica hybrid materials

Diglycidyl ether of bisphenol‐A (DGEBA) based epoxy/silica hybrid materials filled with various amounts of 3‐glycidoxypropyltrimethoxysilane (GPTMS) and silica nanoparticles were prepared, using 4,4′‐diaminodiphenyl sulfone (DDS) as curing agent. The obtained hybrid materials were analyzed by means of Fourier‐transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results indicated that the introduction of GPTMS and silica nanoparticles had synergistic effect. The addition of GPTMS not only ameliorated the compatibility between silica and the epoxy matrix but also increased the crosslinking density of the epoxy system; meanwhile the nano‐silica further reinforced the inorganic network of the hybrid system. Consequently, the hybrid materials showed much improved heat‐resistant properties. The storage modulus of the hybrid systems showed no obvious decrement in the glass transition region and kept at a high value even in the temperature region up to 300°C. The integral thermal stability of the resulting hybrid materials was also improved compared with the corresponding pure epoxy resin. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

The effect of the soft segment of prepolymers on properties of poly(urethane‐ester) and its biodegradability

The influence of soft‐segment prepolymers prepared through the polymerization of δ‐valerolactone (VL) and 2,2‐dimethyl‐1,3‐propandiol (DP) monomers on the structure and properties of poly(urethane‐ester) as well as its biodegradability were investigated. Poly(urethane‐ester) was prepared in two steps. The first step was the preparation of prepolymers with various chain lengths by polymerizing VL and DP monomers in the presence of a distannoxane catalyst at 100 °C under nitrogen atmosphere. The second step was the preparation of poly(urethane‐ester) by polymerizing 4,4′‐methylene‐bis(phenyl isocyanate) (MDI) and prepolymers with various chain lengths in the absence of catalysts. The poly(urethane‐ester) was characterized through an analysis of functional groups (FTIR), thermal properties (differential thermal analysis/TGA), mechanical properties (tensile tester), crystallinity (XRD) and biodegradability. An increased chain length of the prepolymer used in polymerization with MDI leads to an increase in the thermal properties and crystallinity of poly(urethane‐ester). However, the maximum biodegradability in the activated sludge was observed in the poly(urethane‐ester) prepared by polymerizing MDI and prepolymers with a molar VL/DP ratio of 20/1. The amorphous parts of polymers were more easily decomposed by microorganism enzymes than were the crystalline parts after an incubation period of 30 days. Copyright © 2011 Society of Chemical Industry     

Flavoenzyme‐Catalyzed Oxygenations and Oxidations of Phenolic Compounds

Flavin‐dependent monooxygenases and oxidases play an important role in the mineralization of phenolic compounds. Because of their exquisite regioselectivity and stereoselectivity, these enzymes are of interest for the biocatalytic production of fine chemicals and food ingredients. In our group, we have characterized several flavoenzymes that act on phenolic compounds, including 4‐hydroxybenzoate 3‐hydroxylase, 3‐hydroxyphenylacetate 6‐hydroxylase, 4‐hydroxybenzoate 1‐hydroxylase (decarboxylating), hydroquinone hydroxylase, 2‐hydroxybiphenyl 3‐monooxygenase, phenol hydroxylase, 4‐hydroxyacetophenone monooxygenase and vanillyl‐alcohol oxidase. The catalytic properties of these enzymes are reviewed here, together with insights obtained from site‐directed and random mutagenesis.     

Synthesis and characterization of organically modified attapulgite/polyurethane nanocomposites

Polyurethane (PU) nanocomposites filled with attapulgite (ATT) nanorods were synthesized and characterized with thermal analysis, dynamic mechanical analysis (DMA), and mechanical testing. The formulations were based on 4,4′‐methylene bis(phenyl isocyanate) (MDI), polytetrahydrofuran, 1,4‐butanediol, and inorganic ATT premodified with MDI. The original and premodified ATT (ATT–OH and ATT–MDI) nanorods were characterized with thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The analysis revealed that 17 wt % MDI was grafted/adsorbed onto the surface of ATT as a result of the modification. Pristine PU and ATT–MDI/PU nanocomposites were characterized with scanning electron microscopy, differential scanning calorimetry, and TGA. The mechanical tests and DMA showed an increase in the storage modulus and Young's modulus with increasing ATT–MDI content. The crystallinity of the hard and soft segments and thermal stability showed enhancements over those of the neat resin. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008