Epoxy/CTBN

In general, the elastomer must be prereacted (adducted) with the epoxy for the toughening effect to take place. Adducts reduce the likelihood of early phase separation and maintain the solubility of the elastomer in the uncured resin system. For CTBN the reaction is carried out at high temperatures (150 to 160°C) and usually in the presence of a catalyst, such as tris-dimethylamino phenol or piperidine. The resulting epoxy-CTBN adducts are available from several suppliers, and they can be easily formulated into epoxy adhesives. 

Formulation components Unmodified epoxy CTBN modified epoxy... 

ADDUCTS OF LIQUID EPOXY, CTBN AND DIMER ACID... 

Fig. 24 TEM micrographs of ternary epoxy, CTBN rubber and octadecyl ammonium-treated montmorillonite nanocomposites which were investigated with different polarity rubbers, (a) shows a broad view of the less polar rubber and the clay tactoids, clearly separated and (b) shows a close up of the more polar rubber close to silicate layers...

An intense interest, currently without abatement, in the characterization of rubber-toughened thermosets in general, and rubber-toughened epoxy resins in particular, has surfaced over the last several years. Riew (18) summarized work leading to the optimization of toughness in an epoxy/CTBN/piperidine model. Concurrently, Kaelble (19) reported on such systems from a block copolymer orientation and examined properties related to adhesive... 

By using EMI itself as curing agent at a level from 1 phr to 10 phr, the reaction leading to the formation of epoxy-CTBN-epoxy block copolymer was practically completed long before the gelation or the appearance of the phase... 

Epoxy/CTBN Printed circuit boards Tough, dimensionally stable... 

Siebert and Riew [1781 first described the chemistry of rubber particle formation in an admixed model involving CTBN, a DGEBA (diglycidyl ether of bis-phenol A) liquid epoxy resin, and a selective catalyst. They proposed that the composition of the rubber particles in the dispersed phase critically depended on the epoxy—CTBN-epoxy adduct being formed in situ and then further chain-extended and crosslinked with additional resin. 

CTBN Carboxylic acid Epoxy/CTBN Ring opening Impact 222, 223... 

Siebeif, A.R., Tolle, L.L. and Drake, R.S., CTBN-modified epoxies work in poor bonding conditions. Adhes. Age, 29, 19 (1986). 

Composite Particles, Inc. reported the use of surface-modified rubber particles in formulations of thermoset systems, such as polyurethanes, polysulfides, and epoxies [95], The surface of the mbber was oxidized by a proprietary gas atmosphere, which leads to the formation of polar functional groups like —COOH and —OH, which in turn enhanced the dispersibility and bonding characteristics of mbber particles to other polar polymers. A composite containing 15% treated mbber particles per 85% polyurethane has physical properties similar to those of the pure polyurethane. Inclusion of surface-modified waste mbber in polyurethane matrix increases the coefficient of friction. This finds application in polyurethane tires and shoe soles. The treated mbber particles enhance the flexibility and impact resistance of polyester-based constmction materials [95]. Inclusion of treated waste mbber along with carboxyl terminated nitrile mbber (CTBN) in epoxy formulations increases the fracture toughness of the epoxy resins [96]. 

CTBN type elastomers (carboxyl-terminated butadiene acrylonitrile) used to toughen this epoxy system. The Tg peak of the elastomer (-30°Q was shifted to higher temperatures suggesting that electron interaction resulted in crosslinking. The fact that the Tg peak disappeared at 10 rads suggests that crosslinking in the elastomer was extensive at high dose levels. 

Table VII summarizes the solubility parameters of MEK, the CTBN elastomers, and an epoxy resin of similar EEW.

It is clear, that MEK is a "good" solvent for both the elastomers and the epoxy resin. Note that at 10% rubber, the MEK absorption nearly doubles. This implies that a much higher concentration of MEK is present in the rubber phase than in the epoxy phase. This is possible because the MEK diffuses more rapidly into the rubbery CTBN phase owing to its greater segmental thermal motion. 

Solvent absorption measurement has been shown to be a sensitive and useful test method in the manufacture of epoxy powder coatings. A test method was defined and the effects of time and temperature of immersion described. It was shown that solvent absorption is a measure of raw material properties (EEW of the epoxy resin, and CTBN elastomer type and concentration), the homogeneity of the extrudate, as well as the state of cure. The information obtained from solvent absorption measurements has proven to be extremely important not only in quality control analysis but also in providing an insight into the structure function relationships in epoxy resin chemistry. 

Other papers reported the phase separation behavior for the composition showing dual phase morphology [7,20,21,43-45], Delides et al. [43] proposed that the viscosity at the point of phase separation is sufficiently large enough to inhibit diffusion of the epoxy through the rubber (CTBN) and result in the generation of the occluded phase, which is the inclusion of epoxy domains within the rubbery phase. 

The anhydride cured epoxies displayed a prominent carbonyl group of HHPA. The peak at 70 ppm was assigned to the products of the reacted epoxide groups. This peak was predominant in all four groups, piperidine-CTBN, MPDA, HHPA and NMA-DMBA. 

The control resin network used in this study was a diglycidyl ether-based epoxy resin crosslinked with a cycloaliphatic diamine. Cooligomeric modifiers were prepared having varying percentages of TFP and DP siloxane and aminoethylpiperazine end groups. Both siloxane and ATBN and CTBN elastomers were used as epoxy modifiers, the latter two having been included to facilitate direct comparisons between modifiers in similarly prepared networks. 

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