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<p>Amine Curing of Epoxy Resins:Options and Key Formulation Considerationsmines and amine derivatives are the most diverse group of epoxy curing agents. The fully polymerized epoxy resins exhibit a very wide range of thermal and mechanical properties. Though other classes of compounds (e.g., anhydrides, phenolic resins and Lewis acids) are used as hardeners for some applications, the breadth of performance imparted by amine hardeners is unmatched. This paper provides an overview of the wide variety of amine hardeners, including several recent developments that can expand the capabilities of epoxy formulators into new applications.</p><p>AHistory</p><p>Amine/Formulation ChoicesAs mentioned previously, the choice of epoxy resin can be used advantageously to affect some processing, thermal and mechanical properties, but the wide diversity of amine curing agents typically allows the greatest latitude in creating formulations to fit a wide variety of application needs. In this article, unless otherwise stated, epoxy will refer to a standard DGEBA type resin having an epoxide equivalent weight (EEW, or WPE) ranging from about 182-192 grams per epoxide equivalent. The three main use criteria for creating or choosing an amine hardener (or blend) for an epoxy formulation are (in no particular order): cost, processing requirements and performance requirements. These will be addressed in sequence.</p><p>Amine compounds were among the earliest reactants used with epoxy resins to produce useful products. As epoxy resins became more widely available following their development and commercialization in the late 1940s and mid-1950s, utilization of an ever-wider variety of amine compounds ensued. Because most amines are reactive at room temperature with epoxy resins, such formulations are typically provided as two separate parts (or sides), which are mixed just prior to application. Though a variety of epoxy resin products are commercially available, liquid resins based on the diglycidyl ether of bisphenol A (also termed DGEBA or BADGE type resins) have the widest use and availability due to their relatively low price, which is partially gained from economies of scale. Because of this, the epoxy portion of epoxy formulations often remains relatively fixed, and most variations in processing and performance are obtained by making changes to the hardener side of the formulation. The wide variety of commercially available amine compounds and decades of study and formulation have helped to make this group of hardeners the most versatile and widely used of any epoxy reactants.</p><p>Amine Cost vs. ValueWhen choosing between hardeners that have nominally similar processing and performance characteristics, one should not simply go by price alone, but rather, do a calculation, taking into account the cost per pound (or perhaps, unit volume) of the final, cured material. As an example, such a calculation would reveal that a more expensive amine hardener A ($2.40 per pound), having an amine hydrogen equivalent weight (AHEW) of 44, results in a cheaper system cost than a corresponding cheaper amine B ($2.25 per pound) having an AHEW of 60, since more of the amine B must be used due to its higher AHEW. A similar argument would apply to other, non-amine hardeners.</p><p>Processing Requirements Stoichiometry and Mix RatiosAs a general rule, use of a 1:1 stoichiometric ratio of amine hydrogen to epoxide groups will, when fully reacted, ensure maximum stability of the product. Such a stoichiometry may not, however, always pro-</p><p>By Bruce L. Burton, Sr. Research Associate | Huntsman Corp., The Woodlands, TX 68JUNE 2006 | W W W . P C I M A G . C O M</p><p>vide the most desirable processing characteristics or combination of particular properties. For some formulations, being either off-stoichiometry (i.e., not a 1:1 equivalents ratio) or not achieving full reaction, provides an increase in some properties. In these instances, other properties, less important for a given application, may be sacrificed. Being off-stoichiometry and/or under-cured, can lead to higher modulus, higher density, greater hardness, more brittleness and a lower glass transition temperature. Resistance to solvents or moisture may also be decreased. Sometimes the existence of off-stoichiometric formulations is inadvertent, having been caused by the false assumption that formulations based on parts by weight are interchangeable with those based on parts by volume. Switching from parts by weight to parts by volume should not be done without recalculating the component percentages because the densities of most amine hardeners (around 0.92 to 0.98 grams per cc) are considerably lower than the densities of epoxy resins (often 1.15 to 1.20 grams per cc).</p><p>Effect of Temperature on Available Processing TimeBecause the amine-epoxy reaction is exothermic, larger masses of material (e.g., a gallon can vs. a small jar) will have considerably higher exotherms, and the reaction will proceed faster as the temperature increases. As a result, particularly for the more reactive amine hardeners, application must occur before the end of an ever-shortening pot-life, and the thickness of such applications (such as castings or molded composite parts) must be limited to that which can withstand the resulting temperature rise. Otherwise, the interior of the part may burn itself. For some applications, the processing time required is very viscosity-dependent, with lower-viscosity systems being more suitable in cases where thorough wetting of fillers, fiber performs, etc., is necessary to ensure good mechanical properties of the cured products. In many such applications, the end of pot-life is signified by some maximum viscosity beyond which the resin will no longer suitably flow into a mold, wet fibers, etc.</p><p>DEFINITIONSCrosslinking: A bridging of polymer chains that creates a polymer network. Once crosslinked, the polymer will no longer flow upon heating and is termed a thermoset or thermosetting polymer or plastic. Thus crosslinking, a characteristic of most polymerized epoxy resins, is responsible for the final thermal and mechanical performance of the material. Curing (also called crosslinking): The term also may apply to the earlier stages of polymerization wherein fluids increase in viscosity prior to gellation and hardening. Epoxy, epoxide, oxirane: A threemember cyclic ether that serves as the primary reactive functional group in most lower-molecularweight epoxy systems. Higher-molecular epoxy resins may contain hydroxyl (OH) groups that may serve as reactive groups in addition to or in place of epoxy groups. Exotherm: A spontaneous evolution of heat caused by a chemical reaction, such as the curing of an epoxy resin formulation. This typically leads to an increase in temperature, which can sometimes lead to thermal degradation. Gelation: The point in the polymerization reaction at which a polymer network just begins to form as a result of crosslinking. At the gel point, polymers just begin to show resilience or elasticity. Gel Time: The time elapsed between mixing the hardener into the epoxy resin and when the mixture just starts to gel and form a crosslinked polymer network. Glass Transition Temperature (Tg): The Tg of a polymer is usually defined as the mid-point of the temperature range over which an amorphous (glassy, non-crystalline) plastic goes from being relatively hard and rigid to being relatively flexible (i.e., from glassy to rubbery). The midpoint of this range is somewhat dependent upon the method and rate of measurement. Hardener, Curing Agent, Co-reactant: These terms are often used interchangeably to describe compounds that polymerize or copolymerize with epoxy resins to produce usable materials. The polymerizing resin becomes harder than the starting material, thus the name hardener. Pot-life, Working Life (Time): The time available for application of the epoxy formulation. The end of potlife is application-dependent and may occur, for example, when the mixture gels or when its viscosity exceeds the viscosity at which it can be properly mixed or applied. Stoichiometry: The number relationship between reactive groups in a reaction. Because unreacted groups can lead to property changes over time, a one-to-one ratio of epoxy groups to aminehydrogen groups is typically desirable, though not always necessary, in epoxy formulations.</p><p>PA I N T & C O AT I N G S I N D U S T RY</p><p>69</p><p>Amine Curing of Epoxy Resins: Options and Key Formulation Considerations</p><p>Figure 1 | Viscosity vs. time comparison of new, slower polyetheraminehardeners. 50000 45000 40000 35000 JEFFAMINE D-230 amine 30000 XTJ-565 25000 XTJ-566 20000 XTJ-569 15000 10000 5000 0 0.00 1.00 2.00 3.00 Viscosity in cP</p><p>4.00</p><p>5.00</p><p>6.00</p><p>7.00</p><p>8.00</p><p>Hours at 40 C</p><p>Since higher initial mix temperatures promote faster reaction, thereby decreasing gel times, one might also expect the working times to also decrease; however, because flow, permeation and wetting are highly viscosity-dependent, increasing the temperature can decrease the necessary pot-life by more time than the amount of working time that is lost due to the faster reaction. Thus increasing, rather than decreasing, the temperature has been found to be a useful means of increasing the utility of many amine-cured epoxy resin systems.</p><p>times grouped, for convenience, with those amines whose performance or reactivity characteristics it shares. As a starting point, the categories are proposed as indicated in Sidebar 2, and some of their performance and reactivity characteristics are described. It should be noted that the Tg range assigned to each category is intended to indicate the range of fully cured DGEBA-type resins, based on different hardeners within the category. No common cure schedule should be inferred. Hardeners with higher Tg values, such as aromatic amines, may require elevated temperatures to achieve full curing and attain their maximum Tg. Other hardener types, such as Mannich bases, may typically only be cured at ambient conditions, though if they were baked, higher Tgs might be obtainable. Additionally, some amines such as imidazole and its derivatives are used as catalytic or co-curing agents, as are some guanidine derivatives such as dicy (dicyandiamide or cyanoguanidine).</p><p>Performance RequirementsFor those formulations that have met the necessary cost and processing requirements, the final performance/suitability of amine-cured epoxy formulations will depend upon their mechanical, thermal and physical properties. In this discussion, thermal properties are singled out from other physical properties because of their significant effect on the cured resin mechanical properties. Foremost of concern among the thermal properties of a cured epoxy system is the glass transition temperature, designated as Tg (T-sub-g).</p><p>Pot-life vs. Curing TimeEvery epoxy user likes plenty of pot-life or processing time, and the available range of amine hardeners fills most of these needs, but sometimes new applications create needs that stretch beyond the boundaries of the available products. As an example, in one relatively recent development, new amine hardeners exhibiting particularly long pot-lives were produced to meet needs created by the molding of extremely large composites. Figure 1 shows an example of the viscosity build vs. time at 40 C for a few such new materials, compared against a standard, long commercialized polyetheramine known for its particularly long pot-life. As hardeners providing increased pot-life (and decreased reactivity) are used, curing time, or the time to achieve the desired level of properties prior to putting the part or coating into (or back into) service, is also extended. Though there are some formulation tricks that can narrow the time for sufficient curing while still providing a usefully long pot-life, these are outside the scope of the current article. In general, for applications where the applied epoxy cannot reasonably be heated, formulating to obtain faster cure times will come at the expense of shorter pot-lives.</p><p>Thermal PerformanceFor some applications, such as fiber-reinforced composites, Tg is one of the first measurements made on a cured epoxy, to determine whether the hardener even qualifies for further work. In other applications, such as coatings, many customers never think in terms of Tg, or measure it. Despite the latter, an understanding of the Tg can aid in solving formulation and/or performance problems. Many properties of plastics vary greatly, depending upon whether the measurement/use temperature is above or below the plastics Tg. As a result, much of the formulation of epoxy systems involves selecting combinations of different amine hardeners to change the Tg of the cured epoxy, thus modifying its properties. For many blends, use of the Fox Equation can provide a reasonable estimate of the Tg of the fully cured resin. This equation states that the reciprocal of the Tg of the blend is equal to the sums of the weight fraction of each polymer segment times the reciprocal of that segments Tg. This is illustrated in the following equation for a two-component amine blend:</p><p>Classes of Amine HardenersThe wide variety of commercially available amines may be grouped by chemical structure. In cases where an amine has a combination of structures, it is some70JUNE 2006 | W W W . P C I M A G . C O M</p><p>Polyetheramines 25 100 C Tg Moderate Tg, thus flexible Long pot-life Slow curing, low exotherm Only slight odor Very low color Low viscosity Ethyleneamines and their Adducts 110 130 C Tg Somewhat brittle Short pot-life Fast curing, high exotherm Handling concerns/odor Low viscosity Polyamides and Amidoamines 40 100 C Tg Moderate pot-life Fast curing, high exotherm Colored</p><p> Very good corrosion resistance Handling concerns/odor Higher viscosity Arylyl Diamines Somewhat brittle when fully cured Fast curing Low temperature curing Chemical and water resistance Cycloaliphatic Amines 145 175 C Tg (baked cure) Somewhat brittle when fully cured Intermediate pot-life Moderate exotherm Some odor Very low color Often low viscosity Aromatic Amines Higher Tg, 160 220 C</p><p>(baked cure) Somewhat brittle Slow curing, higher temperatures High strength Colored Toxicity concerns High viscosity or solid at room temperature Mannich Bases and Phenalkamines 50 55 C Tg (ambient cure) Somewhat brittle Curing as low as freezing temperatures Colored Chemical resistance High viscosity Lewis Bases/Catalytic Curing Agents</p><p>Table 1 | Relative Tgs of a DGEBA-type resin cured with various types ofamines.</p><p>1/Tg = X1/Tg1 +X2/Tg2Amine Type Polyetheramines (PEAs) Polyamides & Amidoamines Ethyleneamines Examples of Amine Type JEFFAMINE T-403 amine JEFFAMINE D-230 amine VERSAMID 125 polyamide GENAMID 490 amidoamine DETA (diethylenetriamine), TETA (triethylenetetramine), TEPA (tetraethylenepentamine), AE...</p>
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Aug 29, 2014 In the 1980’s he was also Chairman of the Epoxy Resin Formulators Division of the Society of the Plastics Industry, Inc. And contributed to the definitive work (at the time) for formulating epoxies “The Epoxy Resin Formulators Training Manual”. Technical Library BioRenewable Epoxy Resins from Raw Materials. And require a method of toughening for use in structural adhesives. Traditional methods for toughening epoxy resins, such as the incorporation of carboxyl terminated butadiene. Presented at a meeting of the Thermoset Resin Formulators Association in Chicago, IL Tuesday. Home » Application of epoxy resins in consolidation of ornamental stone. Application of epoxy resins in consolidation of ornamental stone. At the same time, another characteristic will be weakened, such as chemical resistance. If the level of epoxy resin is increased outside the mix ratio, the system will not cure, and in this.
1. A biaxially oriented film prepared from a curable composition comprising
(A) at least one resin having an average of more than one vicihal epoxide or vicinal thiirane group per molecule; and
(B) at least one curing agent and/or curing catalyst for said epoxy or thiirane resin; and wherein
(1) at least one of (A) or (B) contains one or more rodlike mesogenic moieties which provides said film with liquid crystal domains prior, during or after curing;
(2) component (B) is present in a quantity sufficient to cure component (A);
(3) said liquid crystalline domain(s) have been biaxially oriented to provide a molecular grating throughout the film thickness; and
(4) optionally, said curable mixture has been B-staged.
2. A biaxially oriented film of claim 1 wherein
(1) component (A) is a diglycidyl ether of a bisphenol containing one or more rodlike mesogenic moieties; and
(2) component (B) is an adduct formed by reacting a compound containing an average of more than one, but not more than about 2 vicinal epoxide groups per molecule with a stoichiometric excess of a compound containing an average of more than one, but not more than two hydrogen atoms reactive with an epoxide group, said adduct containing one or more rodlike mesogenic moieties.
3. A biaxially oriented film of claim 1 wherein
(1) component (A) is 4,4'-diglycidyloxy-α-methyl stilbene; and
(2) component (B) is an aniline adduct of 4,4'-diglycidyloxy-α-methyl stilbene.
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4. A biaxially oriented film of claim 1 which has been B-staged.5. A biaxially oriented film of claim 2 which has been B-staged.
6. A biaxially oriented film of claim 3 which has been B-staged.
7. The product resulting from curing the biaxially oriented film of claim 1.
8. The product resulting from curing the biaxially oriented film of claim 2.
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9. The product resulting from curing the biaxially oriented film of claim 3.Epoxy Resin Formulators Training Manual Download
10. The product resulting from curing the biaxially oriented film of claim 4.
11. The product resulting from curing the biaxially oriented film of claim 5.
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12. The product resulting from curing the biaxially oriented film of claim 6.
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13. The product resulting from curing the biaxially oriented film of claim 1 said product being a laminate or composite, adhesive or coating.14. The product resulting from curing the biaxially oriented film of claim 2 said product being a laminate or composite, adhesive or coating.
15. The product resulting from curing the biaxially oriented film composition of claim 3 said product being a laminate or composite, adhesive or coating.
16. The product resulting from curing the biaxially oriented film of claim 4 said product being a laminate or composite, adhesive or coating.
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17. The product resulting from curing the biaxially oriented film of claim 5 said product being a laminate or composite, adhesive or coating.
18. The product resulting from curing the biaxially oriented film of claim 6 said product being a laminate or composite, adhesive or coating.