Adhesives and coatings based on phenolic/epoxy resins

Low molecular weight epoxy resin based on bis (4‐hydroxy phenyl) 1,1 cyclohexane was prepared and modified with various types of the prepared phenolic resins. Phenol–, cresol–, resorcinol–and salicylic acid–formaldehyde resins were used. The optimum conditions of formulation and curing process were studied to obtain modified wood adhesives characterized by high tensile shear strength values. This study indicated that the more suitable conditions are 1:2 weight ratio of phenol–or cresol–formaldehyde to epoxy resin in the presence of phthalic anhydride (20 wt%) of the resin content as a curing agent at 150°C for 80 min. Resorcinol–or salicylic acid–formaldehyde/epoxy resins formulated at 1:2 weight ratio were cured in the presence of paraformaldehyde (20 wt%) at 150°C for 60 min. The effect of the structure of phenolic resins on the tensile shear strength values of formulated resin samples, when mixed with the epoxy resins and cured under the previously mentioned optimum conditions for different times, was investigated. Metallic and glass coatings from the previous resins were also prepared and evaluated as varnishes or paints. Copyright © 1999 John Wiley & Sons, Ltd.     

Development of novel flame‐retardant thermosets based on benzoxazine–phenolic resins and a glycidyl phosphinate

Modified novolac resins with benzoxazine rings were prepared and copolymerized with a glycidyl phosphinate. Their curing behavior and the thermal properties of the curing resins were studied. Copolymerization was studied with model compounds considering the functionality of the benzoxazine‐based phenolic resins and the easy isomerization of the glycidyl phosphinate. Phenolic novolac resin acts as an initiator but p‐toluensulfonic acid had to be used to decrease the curing temperature and to prevent glycidyl phosphinate from isomerizing. The materials obtained exhibited high glass‐transition temperatures and retardation on thermal degradation rates. V‐0 materials were obtained when the materials were tested for ignition resistance with the UL‐94 test. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 279–289, 2004     

Synthesis,polymerization, and thermal properties of benzoxazine based on bisphenol‐S and allylamine

A bifunctional benzoxazine monomer, 6,6′‐bis(3‐allyl‐3,4‐dihydro‐2H‐benzo[e][1,3]oxazinyl) sulfone (BS‐ala), was synthesized from bisphenol‐S, allylamine and formaldehyde via a solution method. The chemical structure of BS‐ala was confirmed by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and elemental analysis. The polymerization behavior of BS‐ala was investigated by FTIR, solid‐state ¹³C NMR, and differential scanning calorimetry (DSC). The oxazine ring opening polymerization is prior to the addition polymerization of allyl group, and the exothermic peaks corresponding to the two reactions appear partially overlapped in the DSC curve. The storage modulus of the resultant polybenzoxazine at 25°C is about 3.9 GPa, and the glass transition temperature is 254°C. The 5% and 10% weight loss temperatures of the polybenzoxazine are about 335°C and 361°C in both air and nitrogen, respectively. The char yield is about 58% at 800°C in nitrogen, whereas almost no residue is remained at 700°C in air. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanical properties of unsaturated polyester resins in relation to their chemical structure. I. Secondary relaxations and local motions

Dynamic mechanical spectroscopy has been combined with high-resolution solid-state ¹³C NMR to characterize the molecular motions responsible for the γ and β secondary relaxations in unsaturated polyester networks. In DEG networks the 7γ transition is assigned to restricted phenyl group rotation in the styrene cross-links whereas the motion of molecular groups in the vicinity of the residual maleic double bonds account for the β transition. © 1994 John Wiley & Sons, Inc.     

Dynamic mechanical and dielectric relaxations in poly(monoethylphenyl itaconate)

Dynamic mechanical and dielectric relaxational behavior of poly(monoethylphenyl itaconate) at different frequencies and temperatures was studied. Three relaxation zones are found. The dynamic mechanical response is dominated by a relaxation peak at room temperature, labeled β relaxation. Two prominent shoulders labelled as γ and α relaxations are observed. Because of the overlapping of the α and γ with the β relaxation, a deconvolution method to improve the understanding of these phenomena is proposed. In spite of the complexity of the experimental spectra, the proposed deconvolution method seems to be a convenient approach to interpret the relaxational behavior of this polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2749–2756, 1997     

Dynamic mechanical properties of epoxy/novolac system modified with reactive liquid rubber and carbon filler

This paper reports on the work carried out to evaluate the frequency dependent viscoelastic properties of epoxy/novolac compositons modified with a liquid reactive rubber and carbon filler. For epoxy systems modified with elastomer, three typical transitions were observed: the α-relaxation deeply related to the glass transition of epoxy, the β-transition of epoxy, and the glass transition of rubber appeared near to the β-relaxation of epoxy resin. Considering an Arrhenius equation, the activation energies of β-relaxation were estimated. In the region of glass transition and rubbery state the temperature dependence of the shift factor (α_T) was determined through Williams-Landel-Ferry (WLF) equation.     

Unsaturated polyester resins cure: Kinetic,rheologic, and mechanical dynamical analysis. II. The glass transition in the mechanical dynamical spectrum of polyester networks

Unsaturated polyester networks with various structures built from an orthophtalic polyester, with methyl ethyl ketone peroxide as an initiator and cobalt octoate as a promoter, were studied with dynamic mechanical thermal analysis from −50 to 200 °C to characterize changes in the mechanical properties as a function of the temperature. From these measurements, the glass‐transition temperatures of the different networks were determined, their dependence on conversion being fitted to an equation related to the Couchman and DiBenedetto equations. Finally, the different transitions were analyzed as a function of the cure conditions. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 146–152, 2001     

Synthesis and characterization of epoxy resins based on N,N′-aliphatic dicarboxyl bis(hydrazones)

A new class of epoxy resins having N—N bonds in their structure has been synthesized by reacting N,N′-aliphatic dicarboxyl bis(hydrazones) (the aldehyde/ketone derivatives of malonic, adipic, and sebacic dihydrazides) with epichlorohydrin. The reactivity of the $ ^{\backslash }_{/}\hbox{NH} $ protons as a function of the substituent group and the number of methylene spacer groups present in the hydrazone has been examined. The resins obtained have been characterized by elemental and epoxy equivalent analyses and IR and NMR spectra. All these resins are found to have adequate viscosity and cure easily with amine curatives at elevated temperatures. Relevant properties for their use as binders in propellant formulations, such as thermal stability, heat of combustion, density, temperature-dependence of viscosity, and mechanical strength of the composites, have been evaluated. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2835–2842, 1997     

Poly(vinylidene fluoride)/clay nanocomposites prepared by melt intercalation: Crystallization and dynamic mechanical behavior studies

The preparation and properties of poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported for the first time. PVDF/clay nanocomposites were prepared by melt intercalation with organophilic clay. The composites were characterized with X‐ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis. X‐ray diffraction results indicated intercalation of the polymer into the interlayer spacing. PVDF in the nanocomposites crystallized in the β form. Differential scanning calorimetry nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity, as evidenced by the melting and crystallization peaks. Isothermal crystallization studies showed an enhanced rate of crystallization with the addition of clay, as evidenced by a reduction in the crystallization time. Dynamic mechanical analysis indicated significant improvements in the storage modulus over a temperature range of ?100 to 150 °C. The tan δ peak signifying the glass‐transition temperature of PVDF shifted to higher temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1682–1689, 2002     

Reinforcement effect of carbon nanofillers in an epoxy resin system: Rheology,molecular dynamics,and mechanical studies

The reinforcing effect of carbon nanoparticles in an epoxy resin has been estimated with different approaches based on rheology, molecular dynamics (evaluated by differential scanning calorimetry, dielectric relaxation spectroscopy, and thermally stimulated depolarization current), and dynamic mechanical analysis. Carbon particles aggregate as the volume increases and form a fractal structure in the matrix polymer. The dispersion microstructure has been characterized by its viscoelastic properties and relaxation time spectrum. The scaling of the storage modulus and yield stress with the volume fraction of carbon shows two distinct exponents and has thus been used to determine the critical carbon volume fraction of the network formation (Φ*) for the carbon/epoxy dispersions. At nanofiller concentrations greater than Φ*, the overall mobility of the polymer chains is restricted in both dispersions and solid nanocomposites. Therefore, (1) the relaxation spectrum of the dispersions is strongly shifted toward longer times, (2) the glass‐transition temperature is increased and (3) the relaxation strength of both the secondary (β) and primary (α) relaxations increases in the nanocomposites, with respect to the pure polymer matrix. The dispersion microstructure, consisting of fractal flocs and formed above Φ*, is proposed to play the main role in the reinforcement of nanocomposites. Moreover, the network structure and the interface polymer layer (bond layer), surrounding nanoparticles, increases the relaxation strength and slows the cooperative α relaxation, and this results in an improvement of the mechanical properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 522–533, 2005     

Bio-based tri-functional epoxy resin (TEIA) blend cured with anhydride (MHHPA) based cross-linker: Thermal,mechanical and morphological characterization

A novel renewable resource based tri-functional epoxy resin from itaconic acid (TEIA) was blended with petroleum based epoxy resin (DGEBA) and fabricated at different ratios. Then, it was by thermally cured with methylhexahydrophthalic anhydride (MHHPA) in presence of 2-methylimidazole (2-MI) catalyst. The tensile, modulus, strength of virgin epoxy resin (41.97 MPa, 2222 MPa) increased to 47.59 MPa, 2515 MPa, respectively, with the addition of 30% of TEIA. The fracture toughness parameter, critical stress intensity factor (K_IC) revealed enhancement of toughness in the TEIA bio-based blends system. The thermomechanical properties of TEIA (tri-functional epoxy resin from itaconic acid) modified petroleum-epoxy networks were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The fracture morphology was also studied by the scanning electron microscopy and atomic force microscopy respectively.     

High carbon yield thermoset resin based on phenolic resin,hyperbranched polyborate,and paraformaldehyde

Hyperbranched polyborate (HBPB) is a new hyperbranched polymer with excellent thermal resistance, which can be used to improve the thermal stability, especially carbon yield, of phenolic resin (PR). In the present paper, thermal properties and curing degrees of the blends of PR and HBPB (PR–HBPB blends) are investigated. It is found that the curing degrees of PR–HBPB blends would be decreased, and the decrease of curing degree can be attributed to the improper ratio of phenol groups of HBPB to hydroxymethyl groups of PR. Paraformaldehyde (PFM) is introduced to remedy the deficiency of hydroxymethyl groups in PR–HBPB blends. The curing degrees of PR–HBPB blends are improved and the carbon yields of the blends of PR, HBPB, and PFM (PR–HBPB–PFM blends) can be up to 75–80% at 800°C in nitrogen. PR–HBPB–PFM blends can be explored as novel precursors for carbon materials with excellent properties, ease of preparation and low cost. Copyright © 2010 John Wiley & Sons, Ltd.     

Control of reaction mechanisms in cationically polymerized epoxy resins facilitates the adjustment of morphology and mechanical properties

Structure–property relations of cationically polymerized epoxy thermosets with different morphologies are examined. The morphology adjustment of amorphous epoxy based copolymers and partially crystalline polymer alloys is carried out with star‐shaped poly(ε‐caprolactone) (SPCL) bearing various numbers of hydroxyl end groups. These hydroxyl groups are known for their reactivity toward epoxides following the activated monomer (AM) mechanism. For this reason, four‐armed SPCL was synthesized with four hydroxyl end groups (SPCL‐tetraol) and, in addition, with successively esterified ones down to a SPCL with four ester end groups (SPCL‐tetraester). SPCL species bearing fewer or no hydroxyl end groups segregate into needle‐like nanodomains within the epoxy networks and, if the concentration is high enough, also into crystalline domains. The stronger phase separation of SPCL‐tetraester within the epoxy network compared with SPCL‐tetraol is due to a reduction of the AM mechanism. The mechanical properties resulting from different morphologies lead to a trade‐off between higher storage moduli and T_g values in the case of the more phase separated (and partially crystalline) polymer alloys and higher strain at break in the case of the amorphous copolymers. Nevertheless, in both cases toughness is improved or at least kept on the same level as for the pure epoxy resin. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2188–2199     

Fatigue crack propagation and related failure in modified,andhydride-cured epoxy resins

The fatigue crack propagation (FCP) of neat and modified, anhydridecured epoxy resin (EP) was studied in tensile-tensile mode at ambient temperature. As modifiers, liquid carboxyl-terminated acrylonitrile-butadiene (CTBN) and silicon rubber (SI) dispersions were used. The latter modifier in a defined particle size distribution was produced by a special latex technology, whereas the former developed in situ in the EP by phase separation during curing. The dispersion-type morphologies of the EPs were characterized by using polished sections and viewing them in a scanning electron microscope (SEM). The resulting frequency distribution curves were compared with those analyzed from fatigue fracture surfaces. Probable failure mechanisms were also studied by SEM-fractography.Both modifiers improved the resistance to FCP by shifting the curves to higher stress intensity factor ranges (K) in relation to the reference curve determined for the neat EP-matrix. The failure mechanisms, summarized also schematically, differed basically for the various modifiers. According to this, rubber-induced cavitation and shear yielding of the matrix seemed to be dominant for CTBN, which did not affect the principal crack plane. In contrast to this, crack bifurcation, branching and, hence, a forced deviation in the fatigue crack path induced by debonded SI-particles in the EP-matrix were concluded for the SI modifier. The common use of both modifiers yielded a positive synergistic effect due to the superposition of the above failure mechanisms.Dedicated to the 60th birthday of Prof. H. H. Kausch     

Preparation,mechanical properties,and in vitro biocompatibility of novel nanocomposites based on polyhexamethylene carbonate fumarate and nanohydroxyapatite

In the current study a new biodegradable nanocomposite based on poly hexamethylene carbonate fumarate (PHMCF) and nano‐sized hydroxyapatite (nano‐HA) has been developed. A silane coupling agent γ‐methacryloxypropyltrimethoxy silane, was used to achieve a good interfacial adhesion between nano‐HA and PHMCF matrix. PHMCF with different nano‐HA contents were characterized using dynamical mechanical thermal analysis (DMTA) and hardness test. The effect of frequency on storage modulus, glass transition temperature (T_g) and the damping were investigated. In vitro cytotoxicity and proliferation were performed using G292 cell lines by MTT assay. The addition of nano‐HA resulted in an increment on the storage modulus and decrement on the damping. Along with improvement in mechanical properties of composites, the addition of nano‐HA resulted in enhanced cell proliferation. Following these results, the newly developed nano‐PHMCF composite scaffold may be considered for bone tissue engineering applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Poly(ether ether ketone)‐bischromenes: Synthesis,characterization, and influence on thermal,mechanical, and thermo mechanical properties of epoxy resin

Poly(ether ether ketone) s with terminal propargyl groups (PEEK‐PR) were synthesized from hydroxyl terminated PEEK (PEEKTOH) and characterized. The heat‐triggered polymerization of PEEK‐PR to poly bischromenes having PEEK backbone was confirmed by Fourier transform infrared spectroscopy and differential scanning calorimetric studies. PEEK‐PR was blended with a bisphenol based epoxy resin‐diamino diphenylsulphone system in different proportions and cured to form PEEK‐bischromene‐interpenetrated‐epoxy‐amine networks. Tensile strength and elongation of the cured blends increased up to 10‐phr loading of PEEK‐PR and then declined. Tensile moduli of all formulations were comparable. Fracture toughness increased by a maximum of 33%, and the fractured surface morphology showed a ductile fracture. The blends exhibited slightly lower glass transition temperature to that of the neat epoxy‐amine system. A reference sample of epoxy‐amine was processed with the optimum loading of the precursor polymer, PEEKTOH, and compared its properties with the PEEK‐PR incorporated epoxy systems. In this way, it is found that the incorporation of addition curable propargylated PEEK increases the strength characteristics with adequate thermal stability and fracture toughness for high‐performance structural applications.     

Cooperative relaxations in semicrystalline fluoropolymers studied by thermally stimulated currents and ac dielectric

Semicrystalline fluoropolymers including poly(tetrafluoroethylene) (PTFE), a 8 mol % hexafluoropropylene (HFP)/92% TFE random copolymer (FEP), and poly(vinyl fluoride) (PVF) were studied using thermally stimulated current depolarization (TSC), ac dielectric, and other thermal analysis techniques. The TSC thermal sampling (TS) technique is emphasized here for the detection of broad and weak “cooperative” relaxations with all three of the polymers studied exhibiting two cooperative (i.e., relatively high apparent activation energy) transitions. The well-studied low-temperature γ relaxation in PTFE at ca. −100°C is characterized by this method as well as the γ relaxation in the less crystalline FEP sample. Higher temperature cooperative glass transitions, associated with constrained noncrystalline regions, are found at ca. 100°C in PTFE and ca. 80°C in FEP at TSC frequencies. Comparisons with relaxation studies of linear polyethylene are made, and the effects of crystallinity on the various transitions are discussed. The unique characterization by the TSC-TS technique in the detection of multiple “cooperative” relaxations, even in the case of overlapping transitions, is emphasized here. An example is the low-temperature relaxation in FEP. Two cooperative transitions were detected in PVF. The higher temperature one at ca. 45°C is the glass transition, as is well known in the literature. More information is needed to confirm the molecular origin and the effects of crystallinity and chemical structure on the low-temperature cooperative transition in PVF. © 1996 John Wiley & Sons, Inc.     

Effect of ionic liquid on dielectric, mechanical and dynamic mechanical properties of multi-walled carbon nanotubes/polychloroprene rubber composites

This paper focuses on the influence of ionic liquid on carbon nanotube based elastomeric composites. Multi-walled carbon nanotubes (MWCNTs) are modified using an ionic liquid at room temperature, 1-butyl 3-methyl imidazolium bis (trifluoromethylsulphonyl) imide (BMI) and modified MWCNTs exhibit physical (cation–π/π–π) interaction with BMI. The polychloroprene rubber (CR) composites are prepared using unmodified and BMI modified MWCNTs. The presence of BMI not only increases the alternating current (AC) electrical conductivity and polarisability of the composites but also improves the state of dispersion of the tubes as observed from dielectric spectroscopy and transmission electron microscopy respectively. In addition to the hydrodynamic reinforcement, the formation of improved filler–filler networks is reflected in the dynamic storage modulus (E′) for modified MWCNTs/CR composites in amplitude sweep measurement upon increasing the proportion of BMI. Hardness and mechanical properties are also studied for the composites as a function of BMI.     

Curing kinetics,thermal, mechanical,and dielectric properties based on o‐cresol formaldehyde epoxy resin with polyhedral oligomeric (N‐aminoethyl‐γ‐amino propyl)silsesquioxane

The curing reaction and kinetics of o‐cresol formaldehyde epoxy resin (o‐CFER) with polyhedral oligomeric silsesquioxane of N‐aminoethyl‐γ‐amino propyl group (AEAP‐POSS) were investigated by differential scanning calorimetry (DSC). The thermal, mechanical, and dielectric properties of o‐CFER/AEAP‐POSS nanocomposites were investigated with thermogravimetric analysis (TGA), torsional braid analysis (TBA), tensile tester, impact tester, and electric analyzer, respectively. The results show that the activation energy (E) of curing reaction is 58.08 kJ/mol, and the curing reaction well followed the ?esták‐Berggren (S‐B) autocatalytic model. The glass transition temperature (T_g) increases with the increase in AEAP‐POSS content, and reaches the maximum, 107°C, when the molar ratio (N_s) of amino group to epoxy group is 0.5. The nanocomposites containing a higher percentage of AEAP‐POSS exhibited a higher thermostability. The AEAP‐POSS can effectively increase the mechanical properties of epoxy resin, and the tensile and impact strengths are 2.84 MPa and 143.25 kJ m^?2, respectively, when N_s is 0.5. The dielectric constant (ε), dielectric loss factor (tan δ), volume resistivity (ρ_v), and surface resistivity (ρ_s) are 4.98, 3.11 × 10^?4, 3.17 × 10¹² Ω cm³, and 1.41 × 10¹² Ω cm², respectively, similarly at N_s 0.5. Copyright © 2009 John Wiley & Sons, Ltd.