WO2018146670A1

WO2018146670A1 - Structural adhesives and composites comprising brominated epoxies

Info

Publication number: WO2018146670A1
Application number: PCT/IL2017/051384
Authority: WO
Inventors: Hanna Dodiuk-Kenig; Samuel Kenig; Maria SHEINBAUM; Lizzie SHEINBAUM; Orli WEIZMAN; Shay DICHTER; Eyal EDEN
Original assignee: Bromine Compounds Ltd.
Priority date: 2017-02-13
Filing date: 2017-12-26
Publication date: 2018-08-16

Abstract

Disclosed is a structural adhesive comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy. Disclosed also is a process for preparing such a structural adhesive. Further disclosed is a composite comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy compound. Disclosed also is a process for preparing such a composite.

Description

STRUCTURAL ADHESIVES AND COMPOSITES COMPRISING

BROMINATED EPOXIES

FIELD OF THE INVENTION

[0001] The invention is directed to structural adhesives and composites having high brominated epoxy contents. The invention is further directed to methods for preparing such structural adhesives and composites.

BACKGROUND OF THE INVENTION

[0002] An epoxy resin is a thermoset polymer that contains epoxied groups and forms a polymeric network by crosslinking the epoxied molecules with a curing agent. Many epoxy adhesives are prepared using diglycidyl ether of bisphenol A (DGEBA) as a monomer and amino compounds or formaldehyde-phenol condensates as curing agents.

[0003] Aromatic tetraglycidylamine (TGMDA), trifunctional epoxies based on meta and para aminophenol, epoxy novolacs, as well as epoxies based on trisphenol may also be used when high glass transition temperature (Tg) values are required. Epoxy resins are known to have high chemical resistance to various substances, enhanced dielectric and insulation properties, high chemical compatibility with a wide range of substances, low shrinkage on cure, dimensional stability, and fatigue resistance, and therefore are widely used in the formulation of adhesives and protective coatings.

[0004] Epoxy adhesives are highly cross-linked and amorphous materials when polymerized, thus providing high failure strength and modulus, high temperature durability, and low creep. Yet, such a micro structure leads to less advantageous properties, including poor resistance to crack initiation and growth that leads to brittle materials. Therefore, toughening the epoxy resins may be required to enable resistance to peel, impact, and fatigue.

[0005] Thus, although epoxy resins possess properties particularly suitable for use as structural and adhesive components, the brittleness of the epoxy resins must be overcome. The chemical modification of the epoxy chain backbone by lowering the crosslink density, decreasing the functionality of the curing agents and increasing the molecular weight of the epoxy monomers may provide a more flexible and less brittle resin. Further, the incorporation of a dispersed toughener phase in the cured epoxy resin may also provide a tougher resin. Nonetheless, such methods usually toughen the resin at the expense of reducing its glass transition temperature (Tg).

[0006] However, aliphatic and aromatic polyamines, as well as anhydride and sulfone based materials, such as diamino diphenyl sulfone (DDS), have been incorporated into epoxy resins, providing enhanced toughness, decreased brittleness, without significantly lowering the Tg.

[0007] Fillers may also be incorporated into the epoxy resin in order to improve the impact strength of the product; however the use of fillers may decrease the tensile and flexural strength and modulus of the modified epoxies.

[0008] Thus, it would be desirable to prepare an epoxy resin that is highly tough and not brittle, while still having a high Tg, high chemical resistance to various substances, enhanced dielectric and insulation properties, high chemical compatibility with a wide range of substances, low shrinkage on cure, dimensional stability, and fatigue resistance. Such an epoxy resin could be formulated as structural adhesives and/or as a matrix for composite materials.

SUMMARY OF THE INVENTION

[0009] Embodiments of the invention are directed to a structural adhesive comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy.

[0010] According to some embodiments, the epoxy component comprises between about 30-60% w/w of a brominated epoxy.

[0011] Further embodiments of the invention are directed to a process for preparing a structural adhesive comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy, wherein the process comprises: mixing a brominated epoxy with a non-brominated epoxy to provide an epoxy component, wherein the provided epoxy component comprises at least 10% w/w of the brominated epoxy;

while mixing, heating the epoxy component to a temperature in the range of 110-150°C; after heating for a predefined length of time, cooling the epoxy component to a temperature in the range of 25-60°C before adding the aliphatic curing agent and 120-150°C before adding the aromatic curing agent;

mixing the epoxy component with a stoichiometric amount of an aliphatic curing agent or an aromatic curing agent to provide an epoxy component and curing agent mixture; and

curing the epoxy component and curing agent mixture at a temperature of between about 25-130°C when the epoxy component and curing agent mixture comprises an aliphatic curing agent, and between about 170-220°C when the epoxy component and curing agent mixture comprises an aromatic curing agent.

[0012] According to some embodiments, the process of the invention further comprises: either

degassing the epoxy component and curing agent mixture under vacuum to provide a degassed mixture; and

casting the degassed mixture into a mold or bonded joint at a predefined temperature;

or

casting the epoxy component and curing agent mixture into a mold or bonded joint at a predefined temperature; and

degassing the epoxy component and curing agent mixture in the mold under vacuum to provide a degassed mixture;

and

maintaining the degassed mixture in the mold or bonded joint for a predefined length of time at a predefined temperature profile;

or applying the degassed mixture onto at least one adherent.

[0013] Some embodiments of the invention are directed to a structural adhesive prepared according to the process of the invention, as detailed herein. According to some embodiments, the curing agent is an aromatic curing agent. According to further embodiments, the curing agent is an aliphatic curing agent.

[0014] According to some embodiments, the curing agent is poly-diethyl triamine (DETA), poly-triethylenetetramine (TETA), polyoxypropylenediamine (JEFF AMINE D-230), poly-diamino diphenylsulfone (DDS), or any combination of aliphatic curing agents or any combination of aromatic curing agents.

[0015] According to some embodiments, the epoxy component comprises at least about 50% w/w of a brominated epoxy compound. According to some embodiments, the brominated epoxy compound is a polymer of brominated diglycidyl ether of bisphenol-A (BDGEBA). According to some embodiments, the epoxy component includes a polymer of no n- brominated diglycidyl ether of bisphenol-A (DGEBA). According to some embodiments, the epoxy component includes a tri-functional epoxy, a tetra-functional epoxy, or any combination thereof.

[0016] According to some embodiments, the invention is further directed to a process for preparing a structural adhesive comprising an epoxy component and a curing agent, wherein the epoxy component comprises between about 30-60% w/w of a brominated epoxy.

[0017] Further embodiments of the invention are directed to a composite comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy compound. According to some embodiments, the epoxy component comprises between about 30-60% w/w of a brominated epoxy.

[0018] In addition, some embodiments of the invention are directed to a process for preparing a composite comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy compound, the process comprising: mixing a brominated epoxy with a non-brominated epoxy to provide an epoxy component, wherein the provided epoxy component comprises at least 10% w/w of the brominated epoxy;

while mixing, heating the epoxy component to a temperature in the range of 110-150°C;

after heating for a predefined length of time, cooling the epoxy component to a temperature in the range of 25-60°C before adding the aliphatic curing agent and 120-150°C before adding the aromatic curing agent;

mixing the epoxy component with a stoichiometric amount of an aliphatic curing agent or an aromatic curing agent to provide an epoxy component and curing agent mixture; impregnating a fiber reinforcement with the epoxy component and curing agent mixture to provide a fiber reinforced epoxy component and curing agent mixture; and

curing the fiber reinforced epoxy component and curing agent mixture at a temperature of between about 25-130°C when the fiber reinforced epoxy component and curing agent mixture comprises an aliphatic curing agent, and between about 170-220°C when the epoxy component and curing agent mixture comprises an aromatic curing agent.

[0019] According to some embodiments, the fiber reinforced epoxy component and curing agent mixture is cured under vacuum, thereby providing a degassed and cured fiber reinforced epoxy component and curing agent mixture. According to some embodiments, the vacuum is provided by way of an autoclave or a vacuum bag.

[0020] Embodiments of the invention are directed to a composite prepared according to the process of the invention, as detailed herein.

[0021] According to some embodiments, the curing agent in the composite is an aromatic curing agent. According to some embodiments, the curing agent in the composite is an aliphatic curing agent. According to some embodiments, the curing agent in the composite is poly-diethyl triamine (DETA), poly-triethylenetetramine (TETA), polyoxypropylenediamine (JEFFAMINE D-230), poly-diamino diphenylsulfone (DDS), or any combination of aliphatic curing agents or any combination of aromatic curing agents.

[0022] According to some embodiments, the epoxy component in the composite comprises at least about 50% w/w of a brominated epoxy compound. According to some embodiments, the brominated epoxy compound in the composite is a polymer of brominated diglycidyl ether of bisphenol-A (BDGEBA). According to some embodiments, the epoxy component in the composite includes a polymer of non- brominated diglycidyl ether of bisphenol-A (DGEBA).

[0023] According to some embodiments, the epoxy component in the structural adhesive includes a tri-functional epoxy, a tetra-functional epoxy, or any combination thereof. According to some embodiments, the epoxy component in the composite includes a tri-functional epoxy, a tetra-functional epoxy, or any combination thereof. [0024] According to some embodiments, the invention is further directed to a process for preparing a composite comprising an epoxy component and a curing agent, wherein the epoxy component comprises between about 30-60% w/w of a brominated epoxy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanied drawings. Embodiments of the invention are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like reference numerals indicate corresponding, analogous or similar elements, and in which:

[0026] Figure 1 presents the initial storage modulus of DGEBA1/BDGEBA1 blends with TETA, obtained from a DMA test (25°C RT);

[0027] Figure 2 presents the flexural stress curve obtained by a three-point bending test for DGEBA1/BDGEBA1 with DETA and TETA curing agents;

[0028] Figure 3 presents the flexural elongation to break for DGEBA1/BDGEBA1 with DETA and TETA curing agents;

[0029] Figure 4 presents the flexural modulus curve obtained by a three-point bending test for DGEBA1/BDGEBA1 with DETA and TETA curing agents;

[0030] Figure 5 presents the flexural stress curve obtained by a three-point bending test for DGEB A 1 /B DGEB A 1 / JEFF AMINE D-230 blends;

[0031] Figure 6 presents the flexural strain curve obtained by a three-point bending test for DGEB A 1 /B DGEB A 1 / JEFF AMINE D-230 blends;

[0032] Figure 7 presents the flexural modulus curve obtained from a three-point bending test for DGEB A 1 /B DGEB A 1 /JEFF AMINE D-230 blends;

[0033] Figure 8 presents the glass transition temperature (Tg (°C)) curve obtained from a DMA test for DGEBA1/BDGEBA1/JEFF AMINE D-230 blends; [0034] Figure 9 presents the storage modulus of the DGEBAl/BDGEBAl blend, when DDS was used as the curing agent;

[0035] Figure 10 presents the flexural stress curve obtained from a three-point bending test for DGEBA1/BDGEBA1/DDS blends;

[0036] Figure 11 presents the flexural strain curve obtained from a three-point bending test for DGEBA1/BDGEBA1/DDS blends;

[0037] Figure 12 presents the flexural modulus curve obtained from a three-point bending test for DGEBA1/BDGEBA1/DDS blends;

[0038] Figure 13 presents the Tg, flexural modulus, flexural strength, elongation to brake and E' (storage modulus) at 25°C ratios, compared to the control group results (neat DGEBA), using the DDS curing agent;

[0039] Figure 14 presents the effect of the temperature on the viscosities of the DGEBAl/BDGEBAl blends at different ratios;

[0040] Figures 15 A, 15B, 15C and 15D present SEM micrographs of the fracture surface of DGEBAl/BDGEBAl blends, cured with DETA, wherein the epoxy component in the blend comprises (Figure 15A) BDGEBA1 0 wt%, (Figure 15B) BDGEBA1 40 wt%, and (Figure 15C) BDGEBA1 50 wt%, (Figure 15D) BDGEBA1 60 wt%, prepared by mechanical mixing;

[0041] Figures 16 A, 16B and 16C present SEM micrographs of the fracture surfaces of DGEBAl/BDGEBAl blends, cured with TETA, wherein the epoxy component in the blend comprises (Figure 16A) BDGABEl 40 wt%, (Figure 16B) BDGABEl 50 wt%, and (Figure 16C) BDGABEl 60 wt%, prepared by mechanical mixing;

[0042] Figure 17 presents the tensile shear strength values obtained from a lap shear test for DGEBAl/BDGEBAl/JEFFAMINE D-230 mixtures;

[0043] Figures 18A and 18B present T-peel average adhesive strength values of the prepared DGEBAl/BDGEBAl/JEFFAMINE D-230 blend (Figure 18 A) and of the prepared DGEBAl/BDGEBAl/JEFFAMINE T-403 blend (Figure 18B);

[0044] Figure 19 presents the Tg, stress at max. load, stress at break, modulus and % elongation at brake, of neat DGEBA and DGEBAl/BDGEBAl blends, when the JEFF AMINE T-403 curing agent was used; [0045] Figure 20 presents the Tg, tensile shear strength, T-PEEL max. strength and T- PEEL avg. strength, of neat DGEBA and DGEBA1/BDGEBA1 blends, when the JEFF AMINE T-403 curing agent was used;

[0046] Figures 21A, 21B and 21C present SEM micrographs of the fracture surface of DGEBA1/BDGEBA1 blends, cured with JEFF AMINE T-403, wherein the epoxy component in the blend comprises (Figure 21A) BDGEBAl 10 wt%, (Figure 21B) BDGEBAl 40 wt%, and (Figure 21C) BDGEBAl 60 wt%, prepared by mechanical mixing; and

[0047] Figures 22A, 22B, 22C and 22D present SEM micrographs of the fracture surface of DGEBA1/BDGEBA1 blends, cured with DDS, comprising (Figure 22A) BDGEBAl 0 wt%, (Figure 22B) BDGEBAl 50 wt%, (Figure 22C) BDGEBAl 70 wt%, (Figure 22D) BDGEBAl 90 wt%.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0048] As used herein, the term "about" is defined to cover a range of +10% of the disclosed values. As used herein, unless specifically mentioned otherwise, the terms "blend", "mixture" and the like, are interchangeable. It is noted that, unless mention otherwise, the wt% provided relate to the percentages of the brominated and non- brominated epoxies as part of the epoxy component, without taking the curing agent, or other possible additives, into account. Further, unless mentioned otherwise, or unless would have been understood otherwise by a person skilled in the art, the terms "brominated epoxy compounds", "brominated epoxy" and "brominated epoxies" are interchangeable. Likewise, the terms "epoxy compounds", "epoxies" and "epoxy" are interchangeable.

[0049] Embodiments of the invention are directed to structural adhesives and composites comprising an epoxy component and a curing agent, wherein at least 10% w/w of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 15% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 20% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 25% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 30% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 35% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 40% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 50% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 60% of the epoxy component is brominated epoxy compounds. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 5-65%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 5-15%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 15-25%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 25-35%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 35-45%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 45-55%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 55- 65%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 30-60%.

[0050] According to some embodiments, at least 70% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 80% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 90% of the epoxy component is brominated epoxy compounds.

[0051] According to some embodiments, the brominated epoxy compound is a polymer of brominated diglycidyl ether of bisphenol-A (BDGEBA), formulated as follows:

wherein the molecular weight of the polymeric BDGEBA is between about 300 to 10000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 300-1000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 1000-2000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 2000-3000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 3000-4000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 4000-5000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 5000-6000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 6000-7000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 7000-8000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 8000-9000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 9000-10000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 500-900 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 600- 8000 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is between about 650-750 daltons. According to some embodiments, the molecular weight of the polymeric BDGEBA is about 700 daltons.

[0052] According to some embodiments, the brominated epoxy compound is a polymer of halogenated epoxies, such as chlorinated epoxy. According to some embodiments, the brominated epoxy compound is a curable epoxy resin having at least two functional epoxide groups, wherein the epoxy resin may be grafted with a bromine atom. According to some embodiments, the brominated epoxy compound may be selected from brominated bisphenol F, brominated novo lac epoxy, brominated glycidyl ether of tetraphenolethane epoxy, or any combination thereof.

[0053] According to some embodiments, practically all of the epoxy compounds in the epoxy component are brominated. According to other embodiments, the epoxy component comprises brominated and non-brominated epoxy compounds.

[0054] According to some embodiments, the non-brominated epoxy compound is a polymer of diglycidyl ether of bisphenol- A (DGEBA), formulated as follows: o O

/ \ / \

H₂C-CH— H₂C-0 O— CH₂-HC— CH₂

[0055] According to some embodiments, the epoxy compound is a curable epoxy resin having at least two functional epoxide groups. According to some embodiments, the epoxy compound may be selected from bisphenol F, novo lac epoxy, glycidyl ether of tetraphenolethane epoxy, an aliphatic epoxy, or any combination thereof.

[0056] According to some embodiments, the structural adhesives and composites further comprise an epoxy curing agent selected from poly-diethyl triamine (DETA), poly-triethylenetetramine (TETA), polyoxypropylenediamine (JEFFAMINE D-230 and JEFFAMINE T-403), poly-diamino diphenylsulfone (DDS), or any aliphatic, aromatic or anhydride curing agent, or any combination of aliphatic curing agents or any combination of aromatic curing agents.

[0057] According to some embodiments, the structural adhesives and composites comprise stoichiometric amounts of an epoxy component and a curing agent, wherein the stoichiometric amount is calculated according to the following equations:

Calculation of the curing agent equivalent weight:

MW of Amine

Amine hydrogen equivalent weight (AHEW) =

Amine functionality

Calculation of the epoxy equivalent weight:

MW of Epoxy

Epoxy equivalent weight (EEW)

Epoxy functionality

Calculation when using a blend of epoxies:

total weight

EEW mix

wt_a/EEW_a + wt_b/EEW_b + wt_c/EEW_c +.. .

Content of amine per lOOgr of epoxy:

AHEW

PPH = * 100

EEW [0058] According to some embodiments, the structural adhesives and composites further comprise a toughening agent selected from carboxy-terminated polybutadiene/acrylonitrile (CTBN), poly amine terminated butadiene acrylonitrile (ATBN) or any combination thereof.

[0059] According to some embodiments, the Tg is increased significantly, while preserving the elongation, as exemplified with a formulation cured by DDS in Figure 13. It is noted that, unlike the blends in the instant formulation, usually when the Tg increases, the elongation is decreased; however, in the formulations of the invention, the fracture morphology is such that nodules are formed and therefore, the elongation is preserved.

[0060] According to some embodiments, the use of brominated epoxy according to the present invention, provides an increase in the Tg, when curing the aromatic or polyetheramine curing agents.

[0061] According to some embodiments, while the Tg of neat DGEBAl cured using aromatic curing agents, such as DDS, is about 172-185°C, the Tg of the DGEBA1/BDGEBA1 blends, prepared according to this invention, is between about 203-208°C. According to some embodiments, while the Tg of neat DGEBAl, cured using aliphatic curing agents, is about 80-115°C, the Tg of the DGEBA1/BDGEBA1 blends, prepared according to this invention, is in the range of about +10°C compared to neat DGEBAl.

[0062] According to some embodiments, the storage modulus at 25°C is increased by about 40%, for formulations comprising 50wt% BDGEBA1, cured with DDS. For example, the storage modulus at 25°C of 50wt% BDGEBA1 formulation cured with DDS is about 2650 Mpa while the storage modulus at 25°C of neat epoxy cured with DDS is about 1890 Mpa.

[0063] According to some embodiments, when formulations are cured with polyetheramine, the Tg and the elongation are increased (see, e.g., Figure 6). The Tg of the neat DGEBAl is about 8TC and the Tg of all BDGEBA1 blends is in the range of 82°C to 100 °C. Elongation of 40wt% BDGEBA1 formulation of JEFF AMINE T- 403 presented values of about 13% while neat epoxy presented elongation of about 8%. [0064] According to some embodiments, when TETA is used as the curing agent, an increase in the BDGEBAl w/w% results in higher stress at yield, while preserving the elongation.

[0065] Embodiments of the invention are directed to a process for preparing a structural adhesive comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy, said process comprising: mixing a brominated epoxy with a non-brominated epoxy to provide an epoxy component, wherein the provided epoxy component comprises at least 10% w/w of the brominated epoxy;

curing the epoxy component and curing agent mixture at a temperature of between about 25-130°C when said epoxy component and curing agent mixture comprises an aliphatic curing agent, and between about 170-220°C when said epoxy component and curing agent mixture comprises an aromatic curing agent.

[0066] Optionally, the process for preparing a structural adhesive comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy further comprises: either

degassing the epoxy component and curing agent mixture under vacuum to provide a degassed mixture; and casting the degassed mixture into a mold or bonded joint at a predefined temperature;

or

degassing the epoxy component and curing agent mixture in the mold or bonded joint under vacuum to provide a degassed mixture;

and

maintaining the degassed mixture in the mold or bonded joint for a predefined length of time at a predefined temperature profile; or applying the degassed mixture onto at least one adherent.

[0067] According to some embodiments, the brominated epoxy and non-brominated epoxy are mixed and heated, possibly in an oil bath, for about 5-15 minutes, until fusion is completed.

[0068] According to some embodiments, the epoxy component comprises at least 15% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 20% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 25% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 30% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 35% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 40% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 45% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 50% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 55% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 60% w/w of a brominated epoxy. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 5-65%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 5-15%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 15-25%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 25-35%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 35-45%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 45- 55%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 55-65%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 30-60%.

[0069] According to some embodiments, the epoxy component comprises at least 65% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 70% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 75% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 80% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 85% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 90% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 95% w/w of a brominated epoxy.

[0070] According to some embodiments, the epoxy component is heated to a temperature of between about 120-130°C.

[0071] According to some embodiments, after heating for a predefined length of time, the epoxy component is cooled to a temperature of between about 55-65°C.

[0072] According to some embodiments, the epoxy component and curing agent mixture is degassed using a vacuum pump or in a vacuum oven for about 15 minutes to one hour.

[0073] According to some embodiments, when the curing agent is DETA or TETA, the degassed mixture may be maintained in the mold for about 24 hours at room temperature, after which it may be post-cured for about three hours at a temperature between about 70-90°C. According to some embodiments, when the JEFF AMINE D- 230 curing agent is used, the degassed mixture may be maintained in the mold at a temperature of about 60-80°C for about three hours, after which it may be let to cool to room temperature and may be maintained at room temperature for about 20 hours. Post-curing may then be performed for about three hours at a temperature between about 100-120°C.

[0074] According to some embodiments, when the DDS curing agent is used, the epoxy component and curing agent mixture may be cast into a mold that is preheated to about 130-150°C. The epoxy component and curing agent mixture may then be degassed in the mold for about 30-50 minutes at a temperature between about 140- 160°C. The degassed mixture may then be cured in the mold at a temperature between about 160-180°C for about two hours, possibly followed by post-curing at a temperature of between about 190-210°C for about one hour.

[0075] Further embodiments of the invention are directed to a structural adhesive prepared according to the process provided herein.

[0076] Embodiments of the invention are directed to a composite comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy. According to some embodiments, at least 15% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 20% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 25% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 30% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 35% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 40% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 50% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 60% of the epoxy component is brominated epoxy compounds. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 5-65%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 5-15%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 15-25%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 25- 35%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 35-45%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 45-55%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 55- 65%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 30-60%.

[0077] According to some embodiments, at least 70% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 80% of the epoxy component is brominated epoxy compounds. According to some embodiments, at least 90% of the epoxy component is brominated epoxy compounds. According to some embodiments, about 95-100% of the epoxy component is brominated epoxy compounds.

[0078] Embodiments of the invention are directed to a process for preparing composites comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy, said process comprising: mixing a brominated epoxy with a non-brominated epoxy to provide an epoxy component, wherein the provided epoxy component comprises at least 10% w/w of the brominated epoxy;

mixing the epoxy component with a stoichiometric amount of an aliphatic curing agent or an aromatic curing agent to provide an epoxy component and curing agent mixture;

impregnating a fiber reinforcement with the epoxy component and curing agent mixture to provide a fiber reinforced epoxy component and curing agent mixture; and

curing the fiber reinforced epoxy component and curing agent mixture at a temperature of between about 25-130°C when said fiber reinforced epoxy component and curing agent mixture comprises an aliphatic curing agent, and between about 170-220°C when said epoxy component and curing agent mixture comprises an aromatic curing agent.

[0079] Optionally, the process for preparing composites comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy further comprises curing the fiber reinforced epoxy component and curing agent mixture under vacuum, thereby providing a degassed and cured fiber reinforced epoxy component and curing agent mixture. According to some embodiments, the vacuum is provided by way of an autoclave or a vacuum bag.

[0080] Further embodiments of the invention are directed to a composite prepared according to the process provided herein.

[0081] According to some embodiments, the epoxy component comprises at least 15% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 20% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 25% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 30% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 35% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 40% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 45% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 50% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 55% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 60% w/w of a brominated epoxy. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 5-65%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 5-15%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 15-25%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 25-35%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 35-45%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 45- 55%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 55-65%. According to some embodiments, the amount of the brominated epoxy compounds in the epoxy component is between about 30-60%.

[0082] According to some embodiments, the epoxy component comprises at least 65% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 70% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 75% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 80% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 85% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 90% w/w of a brominated epoxy. According to some embodiments, the epoxy component comprises at least 95% w/w of a brominated epoxy.

[0083] Unless explicitly stated or unless obvious to a person skilled in the art, the method or process embodiments described herein are not constrained to a particular order or sequence. Additionally, some of the described method embodiments or elements thereof may occur or be performed simultaneously, at the same point in time, or concurrently.

[0084] In order to better understand how the present invention may be carried out, the following examples are provided.

EXAMPLES

Materials

[0085] The materials detailed in Table I below were used in the examples:

Table I

Monomer Chemical formulation Molar F (Trade name) weight

Diaminodiphenyl

Preparation of the low molecular weight non-brominated epoxy (DGEBAl) blends with aliphatic or aromatic curing agents

[0086] The stoichiometric formulation for the epoxy and curing agent blends, using PPH values (calculated according to the equations provided above) are summarized in Table II below.

Table II

Stoichiometric formulation of curing agents for blends with DGEBRA1

DETA JEFF AMINE JEFF AMINE TETA DDS

T-403 D-230

PPH 11.02 45.91 30.21 Ϊ3 Ϊ 33.16

[0087] The DGEBAl/TETA and DGEBAl/DETA blends were thoroughly mixed for 15 minutes, after which they were placed in a vacuum pump for 20 minutes, and finally casted into silicone molds. After 24 hours at room temperature and an additional three hours of post curing at 80°C in the molds, the prepared structural adhesives were removed from the molds.

[0088] The DGEBAl/Jeffamine D-230 and DGEBAl/Jeffamine T-403 blends were also thoroughly mixed for 15 minutes, degassed in a vacuum pump for 20 minutes and casted into molds. The molds were maintained at 70°C for three hours, then at room temperature for 20 hours. The formulations were then post-cured in the molds for three hours at 110°C, after which the prepared structural adhesives were removed from the molds.

Preparation of the low molecular weight brominated epoxy (BDGEBAl) and non-brominated epoxy (DGEBA1) blends with aliphatic amine curing agents

[0089] Mixtures of DGEBA1 and BDGEBAl were prepared using the following ratios, respectively: 100/0, 90/10, 80/20, 70/30, 60/40, 50/50 and 40/60 (DGEBA1/BDGEBA1). For homogenization, the blends were mixed and heated to 125°C in an oil bath for 10 minutes until obtaining absolute fusion. It is noted that some of the samples were mixed manually and some were mixed using a mechanical stirrer, as detailed below. The aliphatic curing agents were added in a stoichiometric amount, as detailed in Table I above and as calculated according to the equations provided above. The curing agents were added when the mixture was approximately at 60°C. The curing process was the same as described above regarding the neat DGEBA1 blends.

Preparation of the low molecular weight brominated epoxy (BDGEBAl) and non-brominated epoxy (DGEBA1) blends with aromatic amine curing agents

[0090] Mixtures of DGEBA1 and BDGEBAl were prepared in the following ratios: 100/0, 70/30, 50/50, 30/70, 20/80, 10/90 (DGEBA1/BDGEBA1). The DDS curing agent was added to the mixtures and then, for homogenization, the blends were thoroughly stirred using a mechanical stirrer at 60 rpm and heated to approximately 125°C in an oil bath for 30 minutes to obtain a transparent liquid pre-polymer. The obtained pre-polymer was poured into a silicone mold that was preheated to 140°C, degassed in a vacuum oven at 150°C for 40 min, and than cured at 170°C for two hours, followed by a post-curing at 200°C for one hour. The aromatic curing agent was added in a stoichiometric amount according the epoxy equivalent mix equation. [0091] Once removed from the molds, the surfaces and edges of the structural adhesives, prepared as described above, were smoothed using sandpaper to remove surface defects and to provide products with flat and parallel surfaces. The average dimensions of the prepared structural adhesives were 30x6x3mm; however, various sized samples were prepared according to the necessary ASTM specifications for the different tests, as detailed below.

Tests and analyses performed on the prepared structural adhesives

Shore D hardness

[0092] Hardness tests were performed on the prepared samples based on ASTM D2240 using a Shore D hardness tester (Duro meter). The samples were tested five times in different locations on the samples. The measurements were then compared to the DOE Company database to ensure that the samples were cured to a satisfactory level prior to running further tests on the samples.

Dynamic Mechanical Analysis (DMA)

[0093] The silicone rubber molds used were fit to the DMA test standard. Accordingly, DMA samples were obtained directly from casting. Before testing, the surface and edges of the samples were smoothed using sandpaper in order to remove any surface defects as well as to guarantee that the samples had flat and parallel surfaces. The average dimensions of the test samples used was 30x6x3mm. Each sample was tested using a model Q 800 TA Instruments DMA equipment, operating at its three point flexural mode at lHz of frequency, according to standard ASTM D4065, set to a heating rate of 3°C/min, at temperature range of 25-150°C. The results were registered as curves of the storage modulus (Ε'), loss modulus (E") and tangent delta (tan δ).

Differential Scanning Calorimetry (DSC)

[0094] The cured DGEBA1 and DGEBA1/BDGEBA1 samples, cured with four different curing agents, as detailed above, were further studied using a Temperature Modulated scanning calorimetry (TMDSC) technic. The calorimetric measurements were collected using a DSC Q200 differential scanning calorimeter, based on ASTM D3417. TMDSC experiments were performed to determine the glass transition temperature, Tg, of the cured products. TMDSC measurements were carried under "Quasi- linear heating rate" conditions, with a sinusoidal temperature modulation; the tests were performed under a nitrogen atmosphere at a 5°C/min heating rate with a modulation amplitude of 0.5 °C, between 0°C and 200°C, for aliphatic amine curing agents, and between room temperature and 280°C, for aromatic amine curing agent.

Three Point Flexural test

[0095] The flexural tests were performed using an Instron, model 4481, a universal testing machine. The samples were shaped using a silicone cavity mold yielding the sample geometry of approximately 38x12.7x2mm³. The test yielded values of flexural stress, flexural modulus, and flexural strain. All measurements were conducted at three-point bending using a crosshead speed of 1 mm/min, with a span equal to 32 mm. The dimensions of the sample, span and speed of test were based on ASTM D 790-03 protocol. Measurements were performed for each sample at 50% relative humidity at 23°C, and the results average value was taken with standard deviation.

Tensile test

[0096] Tensile tests were performed using an Instron, model 4481. The tests were performed to measure tensile strength and elongation of cured DGEBA1/BDGEBA1 mixtures and of neat DGEBA1 samples. Test samples were shaped using dog-bone silicone molds, of the above cured blends. The sample dimensions as well as the span and speed of the test were based on the ASTM D 638-02a protocol for rigid plastics.

Scanning electron microscopy image and energy-dispersive X-ray spectrum (SEM-EDX)

[0097] An analysis using a scanning electron microscope (SEM) with energy- dispersive X-ray (EDX) was performed to investigate the morphology and chemical composition of the DGEBA1/BDGEBA1 mixtures and of neat DGEBA1 samples. Samples were mounted on sample stubs and coated with an alloy of 95%wt gold and 5%wt palladium, under an argon environment. An Aspex Explorer machine was used to observe the samples using an accelerated voltage of 13 kV.

Parallel plate viscometer

[0098] A Discovery- HR- 1 (hybrid rheometer) was used to determine the viscosities of DGEBA1/BDGEBA1 sample at different ratios of brominated epoxy, in temperature rump mode. A 25mm diameter parallel plate and a 2mm gap mode were used. The viscosities were measured by applying a 1 Hz fixed frequency, heating rate of 2°C/min, at a temperature range of 25 °C to 90°C.

Lap shear adhesion strength

[0099] The Lap shear adhesion strength tests were performed using an Instron, model 4481. Anodized treated alumina plates, having the size of approximately 25 x 101 x 1.6 mm³, were used as adherents. The plates were used in two different forms: with no surface pretreatment and with epoxy silane surface treatment. Then, the various prepared adhesive mixtures, as detailed above, were coated onto two adherents having a surface area of 25 x 13 mm² before curing. The coated adherents were adhered and pressed together with a thickness of 0.1 mm and were then cured according to the curing conditions for each mixture, as detailed above. The sample dimensions as well as the span and speed of the test were based on the ASTM D 1002 protocol for metal adherents.

T-peel adhesion strength

[00100] The T-peel adhesion strength tests were performed using an Instron, model 4481. Anodized treated alumina plates, having the size of approximately 25x305x1.6 mm³, were used as adherents. The samples were prepared as follows: first, the plates were surface treated with epoxy silane at pH=4 surroundings. Then, the different adhesive mixtures were coated onto two adherents having a surface area of 241x25 mm². The coated adherents were adhered and pressed together to a standard gap of 0.5mm and were then cured according to the curing conditions for each sample, as detailed herein. Prior to the test, the un-bonded ends were bent away from one another, perpendicular to the adhesion line, for clamping in the grips of the testing machine. The tension test machine was set to a crosshead speed of 250 mm/min. Measurements were performed four times at least and the averages were calculated for the T-peel adhesion strength.

Results and Discussion

Thermal properties

[00101] Loss modulus (E") data at glass transition temperature (Tg), from

DMA test, is presented in Table III below. The Tg of the neat DGEBA1 adhesives prepared is within range of temperatures found in the literature. When the TETA curing agent was used, raising the bromine content did not lead to large differences in the Tg. The use of DETA showed a 10% decrease in Tg when increasing the bromine content. When JEFF AMINE D-230 was used, an increase in the Tg was obtained with an increase in bromine content.

[00102] It seems that the shorter structure of DETA, in comparison to TETA, having fewer methylene groups, may lead to brittleness properties. Consequently, the brominated epoxy with DETA mixtures has a toughening effect that causes the decrease in Tg. When JEFF AMINE D-230 is used, the phenomena of the increase in Tg can be described in terms of "antiplastization". The polar bromine atoms and stiffness of the epoxy chains reduce the free volume available, thus reducing the molecular motion in the thermoset network. JEFF AMINE D-230 has an etheric group that provides flexibility to the chains in the thermoset backbone, corresponding to the assumption that antiplasticization can occur in thermoset networks containing a small amount of a flexible component.

[00103] Regarding the DDS results, as presented in Table III, it is possible that the initial increase in Tg can be related to the electronegativity of the C^~Br bond, resulting in the increase of the dipole moment in the molecule, which leads to stronger interactions, increased Tg and improved strength, hardness and stiffness.

Table III

Glass transition temperature (Tg) of DGEB Al/BDGEB Al blends, with TETA, DETA, JEFF AMINE d-230, JEFF AMINE T-403 and DDS curing agents, obtained from DSC and DMA tests

Mixture JEFF AMINE

TETA DETA D- DDS by weight T-403

230

DGEB A 1

Tg Tg Tg Tg Tg Tg Tg Tg Tg /BDGEBA1 (°C) (°C) (°C) (°C) (°C) (°C) (°C) (°C) (°C)

DMA DSC DMA DSC DMA DMA DSC DMA DSC

100:0 110 N/A 115 102 81 82 85 184 163

90: 10 106 N/A N/A N/A N/A N/A N/A N/A N/A

80:20 107 N/A N/A N/A N/A 88 85 N/A N/A

70:30 103 93 104 90 82 N/A N/A 208 205

60:40 101 93 104 N/A 87 93 88 N/A N/A

50:50 105 94 102 N/A 89 N/A N/A 203 198 40:60 109 N/A 104 N/A N/A 100 94 N/A N/A

30:70 N/A N/A N/A N/A N/A N/A N/A 205 198

20:80 N/A N/A N/A N/A N/A N/A N/A N/A N/A

10:90 N/A N/A N/A N/A N/A N/A N/A 203 191

0: 100 N/A N/A N/A N/A N/A N/A N/A N/A N/A

DMA results determined by loss modulus curves

Shore D hardness

[00104] Shore D values of DGEBAl/BDGEBAl blends are presented in Table

IV below. All samples achieved hardness values in and above the range mentioned in the literature for epoxies, which is between 70-90D.

Table IV

Shore D hardness values for DGEBAl/BDGEBAl blends with aliphatic and aromatic amine curing agents for 1/1 equivalent ratio

Mixture by weight Curing agent

TETA DETA JEFF AMINE DDS

DGEBAl/BDGEBAl D230 T-403

88.0+1. 89.1+2. 89.6+1.

100:0 9 90.0+1.2 89.0+1.1 9 8

90: 10 92.4+3 89.4+0.9 83.0+0.4 N/A N/A

88.8+1. 85.5+1. N/A

80:20 3 88.4+2.3 81.0+0.8 1

89.6+0. N/A N/A

70:30 9 85.0+1.8 84.0+3

86.0+0. 84.4+3. N/A

60:40 7 93.0+2.8 N/A 6

89.8+5.

50:50 N/A N/A N/A N/A 0

91.6+2.

30:70 N/A N/A N/A N/A 8

20:80 N/A N/A N/A N/A 88.8+4. 8

92.8+3.

10:90 N/A N/A N/A N/A 4

0: 100 N/A N/A N/A N/A N/A

Storage modulus

[00105] As presented in Figure 1, similarly to the results detailed in Table III, presenting a similar Tg for the tested blends, the storage modulus values at 25°C do not show a certain trend depending on the bromine content of the tested sample.

Flexural strength, elongation and modulus for manually mixed mixtures containing an aliphatic curing agent

[00106] Reference is now made to Figure 2, presenting flexural strength data of cured DGEBA1/BDGEBA1 blends as a function of the BDGEBAl content comprising DETA and TETA curing agents, wherein the control sample comprises 0% BDGEBAl. When TETA was used as the curing agent, the cured DGEBA1/BDGEBA1 blends show a higher flexural strength than the control. When DETA is the curing agent, cured DGEBA1/BDGEBA1 blends under 50wt% BDGEBAl show a higher flexural strength than the control 50% also seems higher if 0% is what you're considering the control. Although at blends with 40wt% BDGEBAl a turning point can be seen, blends with less than 40 wt% BDGEBAl show a decrease in flexural strength, while blends with 60wt% show lower flexural strength than the control. The control related to herein is the sample comprising 0% BDGEBAl.

[00107] Reference is now made to Figure 3, presenting flexural elongation to break results of cured DGEBA1/BDGEBA1 blends as a function of the BDGEBAl content, using DETA and TETA as the curing agent. The results of cured blends with the TETA curing agent show similar behavior to the control (0% BDGEBAl). When DETA is used as the curing agent, blends with 30wt% and 40wt% BDGEBAl show a higher elongation percentage than the control, while, blends with 50wt% BDGEBAl exhibit similar elongation as the control and blends with 60wt% BDGEBAl present a remarkably low elongation value. [00108] Reference is now made to Figure 4, presenting flexural modulus results of cured DGEBAl/BDGEBAl blends as a function of the BDGEBA1 content, using DETA and TETA as the curing agents. The flexural modulus is increased for both DETA and TETA curing agents in all tested DGEBAl/BDGEBAl blends. As shown in Figure 4, when TETA is used, the modulus values increase with the increase of the BDGEBA1 content, while when DETA is used, there is no specific correlation between the modulus values and the BDGEBA1 content. As shown, when DETA is used, blends with 40wt% BDGEBA1 present the highest flexural modulus values.

[00109] Reference is now made to Figure 5, presenting flexural strength results of cured DGEBAl/BDGEBAl blends as a function of BDGEBA1 content, when using the JEFF AMINE D-230 curing agent. The tested DGEBAl/BDGEBAl blends show lower flexural strength than the control; however, there is a trend of increase of the flexural strength with the increase of the BDGEBA1 content.

[00110] Reference is now made to Figure 6, presenting the flexural elongation to yield (%) results obtained from cured DGEBAl/BDGEBAl blends as a function of the BDGEBA1 content, when JEFF AMINE D-230 was used as the curing agent. As shown in Figure 6, the DGEBAl/BDGEBAl blends show a higher elongation to yield percentage than the control.

[00111] Reference is now made to Figure 7, presenting the flexural modulus results obtained from cured DGEBAl/BDGEBAl blends, as a function of BDGEBA1 content, using JEFF AMINE D-230 as the curing agent. As presented in Figure 7, the DGEBAl/BDGEBAl blends show a lower flexural modulus than the control; however, there is a trend of increase in the flexural modulus with the increase of the BDGEBA1 content.

[00112] Reference is now made to Figure 8, presenting thermal results of

DGEBAl/BDGEBAl blends, when the JEFF AMINE D-230 curing agent was used, obtained from DMA analysis, compared to the control. An increase in Tg values was observed for all blends containing BDGEBA1, compared to the control.

Dynamic mechanical thermal analysis results for a DGEBAl/BDGEBAl blend using DDS as the curing agent

[00113] The measured storage modulus (Ε') obtained from a dynamic mechanical analysis, which measures the ability of a material to store energy, was preformed. As shown in Figure 9, the storage modulus of DGEBA1/BDGEBA1 mixtures at 30, 50, 70, 90 wt% BDGEBAl were found to be 935, 1484, 926, and 1415, respectively, at a temperature of about 200°C. it is noted that the drop in the graph defines the Tg of the material. As can be seen in the graph for the neat samples the Tg was about 160°C, while by mixing with BDGEBA, the Tg was increased to about 200°C.

Flexural strength, elongation and modulus for DGEBA1/BDGEBA1 mixtures using DDS as the curing agent

[00114] Reference is now made to Figure 10, presenting the flexural strength results obtained from cured DGEBA1/BDGEBA1 blends, as a function of BDGEBAl content, using the DDS curing agent. As shown in Figure 10, at 30, 50, and 70wt% the DGEBA1/BDGEBA1 blends present flexural strengths similar to that of the control, while the 90wt% BDGEBAl blend presents lower flexural strength than the control.

[00115] Reference is now made to Figure 11, presenting the flexural elongation results obtained from cured DGEBA1/BDGEBA1 blends, as a function of the BDGEBAl content, when DDS was used as the curing agent. As presented in Figure 10, the cured DGEBA1/BDGEBA1 blends, having a 30, 50, and 70wt% BDGEBAl content, have similar elongation results to the control, while the 90wt% BDGABE1 blend shows a decrease in the observed elongation values.

[00116] Reference is now made to Figure 12, presenting the flexural modulus results obtained from cured DGEBA1/BDGEBA1 blends, as a function of BDGEBAl content, when DDS was used as the curing agent. While most blends show similar flexural modulus to the control, the 90wt% BDGABA1 blend presented an increase in flexural modulus.

[00117] Reference is now made to Figure 13, presenting mechanical and thermal results of DGEBA1/BDGEBA1 blends, when the DDS curing agent was used, obtained from a three point bending test and DMA analysis, compared to the control. An increase in Tg values was observed for all blends containing BDGEBAl, compared to the control. The blend with 50wt% BDGEBAl presented a higher E' at 25°C compared to the control, as opposed to the other blends that presented a lower E' than the control. The blend with 90wt% BDGEBAl presented lower elongation to yield and flexural strength, and higher flexural modulus, compared to the control. These results may be caused by the toughening effect of the BDGEBA. Blends with 50wt% and 70wt% BDGEBAl showed similar elongation percentages and flexural modulus compared to the control, while the 30wt% blend showed a decrease in the flexural modulus. All flexural strength ratios exhibited lower values than the control. Blends with 50wt% BDGEBAl exhibit a similar elongation to the control, while blends with 90wt% BDGEBAl present a much lower value.

[00118] Table V below presents tensile properties, including tensile strength, tensile elongation, and Young's Modulus, wherein the DDS curing agent was used to cure the DGEBA1/BDGEBA1 mixtures.

Table V

Results from tensile test of DGEBA1 /BDGEBAl blends, cured with DDS.

5 specimens were taken for every mechanical test (10%).

[00119] As presented in Table V, at the 50:50 DGEBA1/BDGEBA1 ratio, the tensile strength and tensile elongation were increased, while Young's Modulus was decreased, in comparison to the control (0% BDGEBAl).

Rheological properties

Parallel plate viscometer

[00120] Reference is now made to Figure 14, presenting the viscosity results of cured DGEBA1/BDGEBA1 blends, as a function of temperature. As shown in Figure 14, as the BDGEBAl content was increased, the viscosity was higher. This may be caused by the higher molecular weight of the BDGEBAl in comparison to the DGEBA1.

Morphological properties HR-SEM

[00121] Reference is now made to Figure 15, presenting the SEM micrographs of the fracture surfaces of various DGEBA1/BDGEBA1 blends, cured by DETA Figures 15 A, 15B, 15C and 15D present the effect of the amount of the brominated epoxy on the morphology of the prepared DGEBA1/BDGEBA1 blend. Figure 15A shows that the surface of the control, in which 100 wt% of the epoxy component is DGEBA1, is a smooth surface having longitudinal lines that characterize neat epoxy at break. As shown in Fig. 15B, the fracture surface of the DGEBA1/BDGEBA1 blend, in which 40% of the epoxy component is BDGABEl, presents a spherical shape containing structures different from the surrounding surface areas. Further, Figures 15C and 15D reveal that 50 and 60% w/w of the epoxy component provide surfaces having a nodular- like structure. As shown in Figures 15C and 15D, the circular border lines encompass a center point from which lines extend in a radial direction towards the circular border lines. Such structures, as shown in Figures 15C and 15D are known to be obtained by a toughening mechanism, which appears during crack propagation, in epoxy systems.

[00122] The effect of the amount of the brominated epoxy on the blend morphology, when cured by TETA, was studied using SEM microscopy. Figure 16A presents nodular-like shapes (40 wt% BDGEBAl). Figure 16B (50 wt% BDGEBAl) also shows nodular shaped structures; however, they are realized only at a higher magnification. Figure 16C (60 wt% BDGEBAl), snow-flake like structures are presented.

Thermal properties

[00123] Loss modulus (E") results at glass transition temperature (Tg), obtained from the DMA and MDSC tests are presented in Table VI below, wherein the DETA curing agent was used to cure the DGEBA1/BDGEBA1 mixtures. As presented in Table VI, when the DGEBA1/BDGEBA1 blend is manually prepared, the Tg is decreased when the BDGEBAl content is increased. When prepared mechanically, all Tg values are similar and all are lower than the control (0% BDGEBAl).

Table VI Glass transition temperature (Tg) obtained by DSC and DMA tests (DMA determined by loss modulus curves) for mechanically and manually prepared

DGEBA1/BDGEBA1/DETA mixtures

Mixture

Manual Mechanical

by weight

Tg (°C) Tg CO Tg CO Tg CO

BDGEBAl (%) DMA MDSC DMA MDSC

0 115 102 115 102

30 104 90 104 N/A

40 72 N/A 104 96

50 61 51 102 93

60 N/A N/A 104 99

Adhesive properties

[00124] Reference is now made to Figure 17 and to Table VII below, presenting the tensile shear strength results of DGEB A 1 /B DGEB A 1 / JEFF AMINE D- 230 blends, as a function of the BDGEBAl content. As presented, anodized alumina panels, pre-treated with silane, show an increase in tensile shear strength, indicating a better adhesion between the panel surface and the adhesion layer, compared to anodized alumina panels not pre-treated with silane. Further, the non-treated anodized alumina panels present a trend of increase in the tensile shear strength values with the increase of the BDGEBAl content, while the pre-treated anodized alumina panels do not exhibit a certain trend. The 40wt% BDGEBAl blend presents the highest tensile shear strength mean value.

Table VII

Tensile shear strength (lap shear) for DEGEBA1/BDGEBA1/ JEFF AMINE D-230

blends conducted according to ASTM D 1002

bTensile ^bFailure shear mode

BDGEBAl Tensile shear strength Failure

(%wt) strength (Mpa) (Mpa) mode

0 19.1 11.5 M M

10 N/A 10.2 M N/A

20 14.6 11.6 M M

30 N/A 15.1 M N/A

40 20.1 N/A N/A M 50 N/A N/A N/A N/A

60 16/7 N/A N/A M

Anodized alumina panels with silane pre-treatment

b Anodized alumina panels without silane pre-treatment

Curing conditions: 3 hr, 70°C; 3 hr, 110°C

5 specimens were taken for every test (+ 10%)

Adhesive failure- A; Cohesive failure- C; Mixed- M

[00125] Reference is now made to Figure 18A and Table VIII, presenting the

T-peel adhesion average strength values of cured DGEBAl/BDGEBAl/JEFF AMINE D-230 blends, as a function of BDGEBA1. A remarkable increase in the T-peel adhesion maximum strength is found in 60wt% BDGEBA1. All T-peel average strength values for DGEBAl/BDGEBAl blends are higher than in the control.

Table VIII

Max. and average T- peel adhesive strength values for DEGEBAl/BDGEBAl/JEFFAMINE D-230 blends, conducted according to ASTM D

1876

T-peel avg.

strength Failure

BDGEBA1(%) (N/mm) mode Remarks

0 0.27 C

40 0.31 C

60 0.31 C

Anodized alumina panels with silane pre-treatment

Curing conditions: 3 hr, 70°C; 3 hr, 110°C

5 specimens were taken for every test (+ 10%)

Adhesive failure- A; Cohesive failure- C; Mixed- M

Conclusions

[00126] As detailed above, various neat DGEBA1 and DGEBA1/BDGEBA1 blends were prepared and cured using the DETA, TETA, JEFF AMINE D-230 and DDS curing agents, wherein the curing conditions were dependent on the type of curing agent used.

[00127] The Shore D hardness characterization reveals that using JEFFAMINE

D-230 as curing-agent, lowered the hardness values of the epoxy matrix compared to the other curing agents, possibly due to the presence of etheric groups. Further, an increase in brominated epoxy weight percentage resulted in higher viscosity of the BDGEBA1/DGEBA1 blend. Mechanical mixing resulted in changing the curing behavior, as shown in the results above, possibly attributed to a uniform dispersion of the solid brominated epoxy in the liquid neat epoxy.

[00128] It was also shown that when using TETA as the curing agent, an increase in the BDGEBA1 weight% resulted in higher stress at yield while preserving the Tg and elongation values. When using DDS as the curing agent, an increase in Tg value was observed for all blends containing BDGEBA1, followed by preserving the elongation in the 30, 50, 70 wt% BDGEBA1 blends (toughness). When using JEFFAMINE D-230 as the curing-agent, an increase in lap shear adhesive strength was observed at higher concentrations of brominated epoxy. Further, the presence of brominated epoxy at all concentrations resulted in an increased T-peel strength, compared to the control, which was neat DGEBA1.

[00129] The enhanced mechanical properties, including, stress at yield, modulus and adhesive strength, observed in all types of mixtures containing brominated epoxy, was attributed to the dipole moment that the C-Br bond induces, which strengthens the intermolecular bonds in the molecular network. Furthermore, the preservation of the elongation and Tg values is attributed to the free volume that the bulkiness of the bromine atom provides to the network. Thus, the addition of brominated epoxy increases the mobility of the molecules and enhances the properties of the prepared adhesive.

Physical properties for DGEBAl/BDGEBAl blends prepared using the JEFFAMINE T-403 curing agent

[00130] The DGEBAl/BDGEBAl blends were prepared using the JEFFAMINE

T-403 curing agent as detailed above. The physical results obtained from those blends are presented in Tables IX and X below, as well as in Figure 18B).

Table IX

Mechanical & adhesive properties of DGEBAl/BDGEBAl blends, cured with

JEFFAMINE T-403.

Tensile shear T-peel max. T-peel avg.

BDGEBA1 (%) strength (MPa) strength (N/mm) strength (N/mm)

0 17.8±1.9 ^b 2.6+0.6 ^a 0.25+0.05 ^a

20 16.9+0.8 ^b 1.8+0.5 ^a 0.29+0.02 ^a

40 13.0+2.9 ^b 2.1+0.4 ^a 0.29+0.01 ^a

60 11.2+1.7 ^b 2.4+0.4 ^a 0.26+0.03 ^a

5 specimens were taken for every mechanical and adhesive test (10%).

Cohesive Failure mode in all specimens.

b Adhesive Failure mode in all specimens.

Work time: 15min at RT.

Table X

Results from tensile test of DGEBAl/BDGEBAl blends, cured with JEFFAMINE

T-403.

Young's

Stress at Maximum Stress at Break % Strain at Modulus

BDGEBA1 (%) Load (MPa) (MPa) Break (GPa)

0 60.5+0.8 12.1+0.2 8.4+1.5 1.8+0.4

20 61.6+2.3 12.3+0.5 5.4+0.9 1.8+0.1

40 65.6+3.1 13.1+0.6 13.5+3.8 1.5+0.2

60 65.1+3 13.0+0.6 6.7+2.3 1.3+0.4

5 specimens were taken for every mechanical and adhesive test (10%).

Work time: 15min at RT. [00131] Reference is now made to Figure 19, presenting the Tg, stress at max. load, stress at break, modulus and % elongation at brake, of neat DGEBA and DGEBA1/BDGEBA1 blends, when the JEFF AMINE T-403 curing agent was used. Reference is further made to Figure 20, presenting the Tg, tensile shear strength, T- PEEL max. strength and T-PEEL avg. strength, of neat DGEBA and DGEBA1/BDGEBA1 blends, when the JEFF AMINE T-403 curing agent was used.

[00132] As shown in Tables IX and X, as well as in Figure 19 and 20, blends of

BDGEBA1/DGEBA1, prepared using the JEFF AMINE T-403 curing agent, exhibited a significant increase in Tg values with an increase of BDGEBA1 content. All blends displayed higher strength values than the control. Blend with 40wt% BDGEBA1 demonstrated an outstanding improvement of elongation (-60%). Peel strength exhibited similar average strength with a cohesive failure mode for all blends. Shear strength values of blends were low compared to control. It should be noted that most of the specimens presented adhesive failure mode. It is suggested that higher viscosities of brominated blends resulted in poor wetting of the aluminum substrates, which caused poor adhesion of the brominated epoxy blends to the substrate. The 60wt% BDGEBA1 blend was the highest brominated epoxy content applicable blend.

[00133] Further, SEM micrographs revealed that blends with BDGEBA1 presented a rough fracture surface. Figure 21 A presents smooth fracture surface of control sample. While adding BDGEBA1 to the mixtures increased surface roughness The particle size in the rough phases [Figures 21A and 21B] was in the range of 0.5- Ιμιη. It should be emphasized that rubber modification in epoxy results in phase separation of the rubber with sub-micron particles that lead to toughening of the epoxy matrix. The main drawback in rubber modification of epoxy is that the Tg is lowered. Contrarily, the phase separation in blends of BDGEBA1/DGEBA1, prepared using the JEFF AMINE T-403 curing agent, provided enhanced Tg values.

SEM of cryogenic fractured surfaces of DGEBA1/BDGEBA1/DDS networks

[00134] Figures 22A, 22B, 22C and 22D presents SEM micrographs of the fracture surface of DGEBA1/BDGEBA1 blends, cured with DDS. The Brominated Epoxy component in the blend comprises (Figure 22A) BDGEBA1 0 wt%, (Figure 22B) BDGEBA1 50 wt%, (Figure 22C) BDGEBA1 70 wt%, (Figure 22C) BDGEBA1 90 wt%. The fracture surface of all of the blends, including the control (Figure 22A), presented an abundance of nodular structures. Moreover, control specimen exhibited rougher fracture surface compared to all BDGEBA1 blends.

[00135] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents may occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

CLAIMS:

1. A structural adhesive comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy.

2. A process for preparing a structural adhesive comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy, said process comprising:

mixing a brominated epoxy with a non-brominated epoxy to provide an epoxy component, wherein the provided epoxy component comprises at least 10% w/w of the brominated epoxy;

3. The process according to claim 2, further comprising:

either

or casting the epoxy component and curing agent mixture into a mold or bonded joint at a predefined temperature; and

degassing the epoxy component and curing agent mixture in the mold or bonded joint under vacuum to provide a degassed mixture; and

4. A structural adhesive prepared according to the process of claim 2.

5. The structural adhesive according to claim 1, wherein the curing agent is an aromatic curing agent.

6. The structural adhesive according to claim 1, wherein the curing agent is an aliphatic curing agent.

7. The structural adhesive according to claim 1, wherein the curing agent is poly-diethyl triamine (DETA), poly-triethylenetetramine (TETA), polyoxypropylenediamine (JEFFAMINE D-230), poly-diamino diphenylsulfone (DDS), or any combination of aliphatic curing agents or any combination of aromatic curing agents.

8. The structural adhesive according to claim 1, wherein the epoxy component comprises at least about 50% w/w of a brominated epoxy compound.

9. The structural adhesive according to claim 1, wherein the brominated epoxy compound is a polymer of brominated diglycidyl ether of bisphenol-A (BDGEBA).

10. The structural adhesive according to claim 1, wherein the epoxy component includes a polymer of non-brominated diglycidyl ether of bisphenol-A (DGEBA).

11. A composite comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy compound.

12. A process for preparing a composite comprising an epoxy component and a curing agent, wherein the epoxy component comprises at least 10% w/w of a brominated epoxy compound, said process comprising: mixing a brominated epoxy with a non-brominated epoxy to provide an epoxy component, wherein the provided epoxy component comprises at least 10% w/w of the brominated epoxy;

impregnating a fiber reinforcement with the epoxy component and curing agent mixture to provide a fiber reinforced epoxy component and curing agent mixture;

and

13. The process according to claim 12, wherein the fiber reinforced epoxy component and curing agent mixture is cured under vacuum, thereby providing a degassed and cured fiber reinforced epoxy component and curing agent mixture.

14. A composite prepared according to the process of claim 12.

15. The composite according to claim 11, wherein the curing agent is an aromatic curing agent.

16. The composite according to claim 11, wherein the curing agent is an aliphatic curing agent.

17. The composite according to claim 11, wherein the curing agent is poly-diethyl triamine (DETA), poly-triethylenetetramine (TETA), polyoxypropylenediamine (JEFFAMINE D-230), poly-diamino diphenylsulfone (DDS), or any combination of aliphatic curing agents or any combination of aromatic curing agents.

18. The composite according to claim 11, wherein the epoxy component comprises at least about 50% w/w of a brominated epoxy compound.

19. The composite according to claim 11, wherein the brominated epoxy compound is a polymer of brominated diglycidyl ether of bisphenol-A (BDGEBA).

20. The composite according to claim 11, wherein the epoxy component includes a polymer of non-brominated diglycidyl ether of bisphenol-A (DGEBA).

21. The composite according to claim 11, wherein the epoxy component includes a tri- functional epoxy, a tetra-functional epoxy, or any combination thereof.

22. The structural adhesive according to claim 1, wherein the epoxy component includes a tri- functional epoxy, a tetra-functional epoxy, or any combination thereof.

23. The process according to claim 13, wherein the vacuum is provided by way of an autoclave or a vacuum bag.