Epoxy resins

Top PDF Epoxy resins:

Formulation of anticorrosive paints employing conducting polymers

Formulation of anticorrosive paints employing conducting polymers

This chapter reports an innovative study about the performance of a nanostructured CP to act as anticorrosive additive in the formulation of conventional organic coatings. We presented a comprehensive study about the synthesis of PNMPy microspheres that have been prepared using the LbL self-assembly strategy. The LbL templating technique has been proved to be a highly versatile method to produce nanostructured PNMPy. Raman and XPS spectroscopies are excellent tools for characterization of nanolayers made of CPs. After the successful preparation and characterization of PNMPy/PSS core-shell microspheres, we have examined the ability of this CP to protect steel from corrosion. Unfortunately, this nanostructured CP has been found to be incompatible with the epoxy resins typically used in the formulation of solvent-borne organic primers. Thus, PNMPy/PSS microspheres tend to agglomerate giving place to the apparation of dark spots at the coating surface and precluding their application as anticorrosive additive. This behavior has been attributed to the high charge density at the microsphere surface.
Mostrar más

197 Lee mas

Development of epoxy nanocomposites based on carbon nanostructures

Development of epoxy nanocomposites based on carbon nanostructures

initial isotropic liquid system is transformed during the curing reaction in a polymer network with non-isotropic movements. The formation of enough cross-links and topological constraints promote the persistence of some RDCs at the measured temperature. We can define this moment as the NMR induction time of the curing reaction. Opposite to other complementary techniques (e.g. FT-IR or DSC), during the induction time (measured by DQ-NMR) there are numerous initial reactions between monomers and curing agent that have no relevance in the NMR signal because the formed products (at that reaction time) are non-dipolar coupled low molecular weight oligomers. The subsequent reactions after the induction time increase the total amount of constraints, limiting the conformational space of the polymer segments and increasing the RDCs. Therefore, the NMR signal increases with the curing time according to the reaction rate, giving molecular evidences about the structural evolution. At larger curing times, the curves exhibit a decrease on the extent of reaction associated to the vitrification of the system. This process is difficult to characterize by FT-IR and DSC because of the small number of reactions involved in the process (as compared with the initial stages) and also it is quite problematic to follow it by rheology measurements because of the dramatic rise of viscosity. However, DQ-NMR is a more sensitive approach to characterize these latest stages of the reaction or even the structure of epoxy resins when they are completely cured.
Mostrar más

299 Lee mas

Highly thermally conductive flame-retardant epoxy nanocomposites with reduced ignitability and excellent electrical conductivities

Highly thermally conductive flame-retardant epoxy nanocomposites with reduced ignitability and excellent electrical conductivities

In our present work, to further broaden the application of the epoxy resins in the high tech fi elds of the microelectronics (elec tronic packing), electronic information and electronic shielding, we developed a novel highly thermally conductive epoxy resins nanocomposites with reduced ignitability and excellent electrical conductivities. Phenylphosphonic dichloride (PPDCl) and allyl amine (AA) were fi rstly performed to synthesize reactive phenylphosphonate based fl ame retardant FP1, which were then introduced into epoxy matrix to fabricate the fl ame retardant epoxy resin (FREP). And the surface functionalized graphite nano platelets (fGNPs) fi llers were then performed to fabricate the fGNPs/ FREP nanocomposites via mixing followed by casting method. Herein, the “ two step ” method of methanesulfonic acid/ g glyci doxypropyltrimethoxysilane (MSA/KH 560) was performed to functionalize the surface of GNPs (fGNPs). The mass fraction of fGNPs fi llers in fl uencing on the thermal conductivities, fl ame retardancy, electrical conductivities, thermal stabilities and strength of the fGNPs/FREP nanocomposites was discussed and investigated in detail. In addition, the relationship between experimental thermal conductivities of the fGNPs/FREP nano composites and fGNPs fi llers concentration was also compared with the predictions of theoretical models.
Mostrar más

7 Lee mas

Hyperbranched poly(ethyleneimine) derivatives as modifiers in epoxy networks

Hyperbranched poly(ethyleneimine) derivatives as modifiers in epoxy networks

chain stiffness of the cured network leads to low impact resistance, which places a limitation on their potential range of applications. In addition, when epoxy resins are used as coatings, the curing shrinkage promotes the appearance of internal stresses, which can lead to the generation of microvoids and microcracks, the loss of adhesion and deformation due to warping. Stresses can also appear during their processing and service life due to the mismatch between the thermal expansion coefficients of the polymer coating and the metallic substrate, the former being significantly higher. These drawbacks reduce the protection capability and durability of the coating materials and allow corrosion of the substrate to take place as a result of the penetration of moisture. On the other hand, it is difficult to recycle or repair coated devices at the end of their service life because the thermosetting coating cannot be easily removed by solvents or thermal treatment; only pyrolysis can be used, which involves a significant waste of energy in addition to some other problems.
Mostrar más

309 Lee mas

Wear and cavitation effect in an epoxy filled with boron and silicon nanocarbides

Wear and cavitation effect in an epoxy filled with boron and silicon nanocarbides

In many systems like hydraulic equipment, fluid pump impellers, ship propellers, hydrodynamic bearings, fluid seals, inlets to heat-exchanger tubes, diesel engine wet cylinder liners, hydrofoils, liquid metal power plants, steam turbines, etc., mechanical erosion could be a great problem, induced by the pulse pressure exerted by the collapse of vapour bubbles, causing surface damage [1,2]. Such process of the formation of vapour bubbles in low pressure regions within a fluid (when the hydrostatic pressure acquires a value lower than the saturation vapour pressure) is called cavitation. The mechanical erosion brought about by the cavitation is called cavitation erosion [3]. A great variety of materials and many different surface engineering processes have been applied to increase the cavitation resistance [1,3,4]. Many metallic and intermetallic compounds have been used as coatings due to their good cavitation erosion resistance by their high work hardening rate, high hardness, good oxidation and corrosion resistance [1]; also, many ceramics compounds have been used by their excellent wear resistance and high hardness and they are considered to be potencial candidates for applications needing high resistance to cavitation erosion [4]. Some authors [5,6] have provided useful data related to erosion rates for many materials, including polymers, but there is still a lack of specific information related to polymer coatings for potential use in tribological applications. Epoxy resins have shown been good results when used as coating on stainless steels by Garcia et al. [7].
Mostrar más

7 Lee mas

Liquefied wood as a partial substitute of melamine-urea-formaldehyde and urea-formaldehyde resins

Liquefied wood as a partial substitute of melamine-urea-formaldehyde and urea-formaldehyde resins

Wood liquefaction is usually done at high pressure and temperature. Recently due to the lack of oil derived products there have been several studies on liquefaction processes using moderate temperatures and a catalyst. The main liquefaction agents are phenol (Zhang et al. 2007, Lin et al. 2014) with a base or acid catalyst, polyhydric alcohols usually with an acid catalyst (Hrastnik et al. 2013) and also cyclic carbonates (Xie and Chen 2005), ionic liquids and dibasic esters. According to the liquefaction process different resins can be produced. When liquefaction is done with phenol, phenolic resins can be produced. Pan et al. (2009) used liquefied wood with phenol an acid catalyst to prepare phenolic Novolac type resins while Hassan et al. (2009) produced Resol type resins. Alma et al. (1998) and Zhang et al. (2005) produced the same type of resins but using alkali catalysts. Using polyhydric alcohols as liquefaction agents produces different kinds of resins. Lee and Lin (2008) used liquefied wood to produce a polyurethane adhesive. Also epoxy resins were prepared by Kobaiashi et al. (2000) from liquefied wood with polyhydric alcohols. Mansouri et al. (2007) studied the possibility of using liquefied wood as lignin-based wood panel adhesives without formaldehyde. The adhesives yielded a bending strength enough to pass relevant international standard specifications for exterior-grade panels and also showed sufficient reactivity to yield panels in press times comparable to those of formaldehyde-based commercial adhesives. The bond performance of specimens of beech wood, bonded with an adhesive mixture made of liquefied wood and phenolic resin, was investigated by Ugovsek et al. (2010). The shear strength increased when replacing 25% of the phenol-formaldehyde by liquefied wood, but decreased when immersing or boiling the specimens in water. So for non-structural applications
Mostrar más

8 Lee mas

Influence of graphene nanoplatelets on curing and mechanical properties of graphene/epoxy nanocomposites.

Influence of graphene nanoplatelets on curing and mechanical properties of graphene/epoxy nanocomposites.

However, the tensile strength values show a decrease with the increase in GNPs content. In a composite material, an increase in strength is expected when strong adhesion takes place between components and no defects are pre- sent; thus, the simultaneous decrease in tensile strength and increase in modulus of GNP/epoxy nanocomposites sug- gest the presence of defects due to the graphene load. The strain at break and toughness of epoxy are almost unchanged with the addition of 1 mass% of GNPs, but show a significant decrease with the addition of 5 mass% GNP. A decrease in toughness has been reported for low graphene (2 mass%) content in another graphene/epoxy nanocomposite [22].
Mostrar más

8 Lee mas

Restauraciones compuestas Bulk Fill Descripcin paso a paso de las tcnicas de restauracin clnica Informes de casos

Restauraciones compuestas Bulk Fill Descripcin paso a paso de las tcnicas de restauracin clnica Informes de casos

In the effort to reduce shrinkage stress, it has been indicated that composite resins should be inserted in the cavity in increments of 2 mm maximum thickness (the incremental technique). By means of this technique, a lower number of walls are united, diminishing the cavity configuration factor, known as C factor (7,11,13). However, the incremental insertion method has some disadvantages, such as the possibility of the incorporation of air bubbles, bond failures and contamination among the composite increments,

9 Lee mas

Synthesis and mechanical properties of laminates based on phenolic resins modified with sodium lignosulfonate.

Synthesis and mechanical properties of laminates based on phenolic resins modified with sodium lignosulfonate.

The synthesis of base phenol-formaldehyde resins using sodium lignosulfonate as partial replacement of phenol was studied. The resins obtained were used for the pro- duction of industrial and laboratory laminates. The properties of the modified laboratory laminates were evaluated and compared with those of traditional lami- nates. For this purpose, tests such as tensile, bending and impact resistance were performed and final proper- ties such as boiling water resistance and ball drop im- pact were measured. The mechanical tests were com- bined with statistics techniques to a better assessment of the mechanical properties. Materials with good proper- ties according to the industrial specifications were ob- tained employing a weight ratio lignosulfonate:phenol of 10:90.
Mostrar más

6 Lee mas

Furanic Copolymers With Synthetic And Natural Phenolic Materials For Wood Adhesives - A Maldi Tof Study

Furanic Copolymers With Synthetic And Natural Phenolic Materials For Wood Adhesives - A Maldi Tof Study

MALDI-TOF mass spectroscopy highlighted some of the main differences in comparative oligomers distribution of phenol-formaldehyde, P-Furan and Tannin-Furan resins for wood adhesives and other applications. In parallel to tannin-furan coreacted oligomers furan homopolymers are also formed in noticeable quantities due to the self condensation of furfuryl alcohol. This does not appear to be the case in P-Furan resins which are prepared in a different fashion. These latter are also different from PF resins.

6 Lee mas

Fluoride adsorption capacity of composites based on chitosan-zeolite-algae

Fluoride adsorption capacity of composites based on chitosan-zeolite-algae

Fluoride is considered beneficial in drinking water at levels about 0.7 mg / L, but hazardous if it exceeds 1.5 mg / L which is the maximum permissible limit proposed by the World Health Organization (WHO, 1984). Some health damage caused by water intake with a high fluoride concentrations are: dental cavities, dental and skeletal fluorosis (Mohapatra et al., 2009). The methods used to remove excessive fluoride from drinking water are ion exchange resins, coagulation, electrochemical methods, unfortunately the high cost of these technologies make them unviable in developing countries (Miretzky and Cirelli, 2011).Many technologies have been developed to remove fluoride from water, that are based on the adsorption process using di ff erent adsorbents materials such as activated alumina, double layered hydroxides, carbon nanotubes, bone char, clays, among others (Leyva Ramos, et al, 2001; Medellin Castillo et al., 2007; Viswanathan and Meenakshi, 2010). In recent years, there has been special attention to adsorbents containing natural polymers such as chitosan, which is the second most abundant natural polymer on earth. Chitosan a cationic copolymer consisting of 2-glucosamine and N-acetyl- glucosamine-2 (Fig. 1), which is derived from chitin by demineralization processes, deproteinization and deacetylation (Navarro et al., 2010). This polymer is characterized by its high content of amino groups. Which are responsible of the interaction among metal ions by chelation mechanisms (Guibal et al., 1999; Kawamura et al., 1993). Chitosan can be found with the shape of flakes and powder, this has been a drawback for application in studies of columns, as it presents low mechanical strength. Thus, it has been looking for alternatives to overcome this disadvantage. Chitosan based microspheres have been prepared by using di ff erent type of support material that can give a greater mechanical strength. For example clay minerals, hydroxyapatite, and double layered hydroxide (Boddu et al., 2008; Dalida et al., 2011; Sairam Sundaram et al., 2008; Viswanathan and Meenakshi, 2010). Furthermore, chitosan has a pk ≈ 6.5, therefore, it is soluble in acid medium. Chitosan shows a tendency to form a gel in acetic acid and this gel may be precipitated in an alkaline solution to obtain microspheres (Salazar Leyva, 2014). The natural zeolites are microporous crystalline aluminosilicates, with structures formed by tetrahedrons of [SiO 4 ] 4− and [AlO 4 ] 5− that are
Mostrar más

10 Lee mas

Physico-Mechanical Properties Of Plywood Bonded By Nano Cupric Oxide (Cuo) Modified Pf Resins Against Subterranean Termites

Physico-Mechanical Properties Of Plywood Bonded By Nano Cupric Oxide (Cuo) Modified Pf Resins Against Subterranean Termites

Nano CuO and alkane surfactant modified phenol Formaldehyde (PF) resins were applied to manufacture plywood, and physical and mechanical properties, such as shear strength, tensile property, modulus of rupture (MOR), modulus of elasticity (MOE), as well as termite resistance were evaluated. The result showed that the combination of nano CuO and alkane surfactantplayed different effect on tensile strength, and especially on shear strength as evaluated at different test conditions. But it was confirmed to improve the water resistance of treated plywood specimens. The introduction of nano CuO and surfactant did not influence the flexural properties significantly by statistically. The result of termite tests indicated that the weight loss decreases gradually from 31,12% to less than 10,37%, and the mortality increases from 32,61% to higher than 86,35%. And the AWPA rating also rises from 4 (very severe attack) to 7 (moderate attack).
Mostrar más

10 Lee mas

Influence of uron resins on the performance of uf resins as adhesives for plywood

Influence of uron resins on the performance of uf resins as adhesives for plywood

Th e contamination from formaldehyde emission on the environment limits the wide application of urea-formaldehyde (UF) resin. Th us, considerable eff orts have been paid on reducing formaldehyde emission level from UF bonded wood composites, such as mending the prescription and procedure of UF resin synthesis, optimizing the application craft of adhesives, as well as the use of formaldehyde scavengers with adhesives (Abdullah and Park 2010) . Uron initially aroused interest due to its lower formaldehyde emission eff ect on UF resin which was synthesized at very acid pH (Gu et al. 1995). Th e following research confi rmed that the introduction at lower reaction temperatures of the additional strongly acid condensation step was the formation of sometime considerable quantities of Uron (Gu et al. 1995). Th us, the critical parameters for maximizing the portion of Uron present at the end of the UF resin synthesis was proposed, and the particle board bonded with uron-rich resins showed the considerable bond strength (Soulard et al. 1999). However, the preparation of UF resins containing high proportion of urons is not feasible in practice simply because the quantity of free formaldehyde left at the end of the reaction is too high and would lead to a very high formaldehyde emission from panels. Futher, little is known about the mechanisms of the reduction eff ect of uron structure on reducing free formaldehyde content and formaldehyde emission levels.
Mostrar más

10 Lee mas

Taste masked orodispersible tablet of atomoxetine hydrochloride

Taste masked orodispersible tablet of atomoxetine hydrochloride

In the present work, orodispersible tablets of atomoxetine HCl were designed by preparing tasteless complexes of atomoxetine HCl with weak cation ion exchange resins (Kyron T 134).. IR a[r]

1 Lee mas

Experimental analysis of reinforced concrete beams strengthened with steel bars and epoxy structural adhesive

Experimental analysis of reinforced concrete beams strengthened with steel bars and epoxy structural adhesive

Analysis of the strengthened and reference beams revealed that Beams E2 and E4 were under superior ultimate loads compared to the other beams. However, it can be concluded that in this study, the addition of the clips to Beams E3 and E5 damaged their strength. Moreover, the unbonding of the strengthening, which occurred in all the strengthened beams, was because the epoxy resin has an elasticity modulus significantly lower than of the other materials of the system. Therefore, when a strengthened beam was loaded, because of insufficient stiffness, the resin did not transfer all the tension that it received from the lower face of the beam. This resulted in the unbonding of the strengthening, indicating that only steel works. The scenario would be different if the materials had similar elasticity moduli. Thus, despite Beams E2, E3, and E4 having larger ultimate loads than the reference beam, the system does not operate efficiently. Therefore, it is not recommended to use this type of strengthening because it is ineffective and can be dangerous. It is important to emphasize that the conclusions of this work are limited only to the results of the tests of the five beams presented here. Other future research studies with more tests of beams and with and without strengthening are necessary for a better validation of this research.
Mostrar más

14 Lee mas

Mechanical evaluation of laminates based on phenolic resins using lignins as partial substitutes for phenol

Mechanical evaluation of laminates based on phenolic resins using lignins as partial substitutes for phenol

High-pressure decorative laminates (HPLs) are composite materials comprised of a paper-based decorative surface and a substrate impregnated with formaldehyde resins. The decorative surface consists of -cellulose paper impregnated with a base melamine- formaldehyde resin (MF), and the substrate consists of a set of kraft-type papers impregnated with a base resol-type phenol-formaldehyde (PF) resin. The curing of resins imparts special mechanical and physical properties to the laminates, enhancing the matrix properties. However, postforming HPLs are partially cured in order to impart some flexibility to the material, allowing for a tailored fit to curved surfaces. Currently, the use of environmentally friendly plasticizers is preferred over the use of high initial phenol-to- formaldehyde (P/F) molar ratios (Pilato 2010).
Mostrar más

14 Lee mas

Aptasensors based on electrochemical impedance spectroscopy

Aptasensors based on electrochemical impedance spectroscopy

In this paper we report a novel labelfree electrochemical DNAzyme based biosensor for the detection of copper ions using avidin–graphite epoxy composite electrodes.35 Electrochemical imp[r]

365 Lee mas

Experimental analysis of reinforced concrete beams strengthened with steel bars and epoxy structural adhesive

Experimental analysis of reinforced concrete beams strengthened with steel bars and epoxy structural adhesive

This work was aimed at analyzing the efficiency of the strengthening of reinforced concrete beams with the addition of steel bars and epoxy adhesive. Five beams were produced, out of which four beams were strengthened to flexure. In two of them, “U” clips were also used to improve the anchorage of the strengthening. The tests demonstrated that the clips reduced the resistances of the beams compared to those without clips. The strengthened beams without clips yielded better results, but the largest limiting factor was the adherence between the epoxy and beam. The use of clips for solving the problem of adherence made this research original. The conclusions were based on the comparisons of the tested beams.
Mostrar más

14 Lee mas

Experimental analysis of reinforced concrete beams strengthened with steel bars and epoxy structural adhesive

Experimental analysis of reinforced concrete beams strengthened with steel bars and epoxy structural adhesive

This work was aimed at analyzing the efficiency of the strengthening of reinforced concrete beams with the addition of steel bars and epoxy adhesive. Five beams were produced, out of which four beams were strengthened to flexure. In two of them, “U” clips were also used to improve the anchorage of the strengthening. The tests demonstrated that the clips reduced the resistances of the beams compared to those without clips. The strengthened beams without clips yielded better results, but the largest limiting factor was the adherence between the epoxy and beam. The use of clips for solving the problem of adherence made this research original. The conclusions were based on the comparisons of the tested beams.
Mostrar más

14 Lee mas

Polymer Bisphenol-A, the Incorporation of Silica Nanospheres into Epoxy–Amine Materials and Polymer Nanocomposites

Polymer Bisphenol-A, the Incorporation of Silica Nanospheres into Epoxy–Amine Materials and Polymer Nanocomposites

The applications of the product above are: epoxy curing agent, it reacts with carboxylic acids to form hot-melt adhesives, it reacts quickly with isocyanates and salts may be formed readily for surfactant use. The benefits of the product above are: low viscosity coefficient, colour and vapour pressure, completely miscible with a wide variety of solvents, including water, it provides tough, clear, impact-resistant coatings, castings and adhesives, as well as coatings are free of surface blush prevalent with many amine curing agents (cf. Table 2).

8 Lee mas

Show all 65 documents...