CTBN, epoxy toughness

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]. 

Our interest in PDMS as an epoxy modifier lies partly in its low Tg relative to the ATBN and CTBN modifiers. Up to this time, however, improvements in K,c through copolymerization of dimethyl siloxane with TFP and DP siloxane require raising the Tg of the siloxane modifier above that of PDMS, as shown by Table 1. It is hoped that increased understanding and control of the synthesis and morphologies of siloxane-modified epoxies will make it possible to retain the low Tg of the modifier while raising the fracture toughness of the resin. The true value of this objective could eventually be shown by measurement of Klc at temperatures below ambient. 

For epoxy networks modified by liquid reactive rubbers, it is not so easy to discuss these parameters separately, because they are interdependent. For example, an increase in the acrylonitrile content of the carboxy-termi-nated butadiene acrylonitrile rubber (CTBN) induces a size reduction of the rubbery domains but also a higher miscibility with the epoxy-rich phase, leading to a higher amount remaining dissolved in the matrix at the end of cure (Chapter 8). It is not possible to separate the influence of these two effects on toughness. 

Epoxy-nitrile Nitrile-epoxy adhesives are composed of solid epoxy resin modified with carboxyl-terminated butadiene nitrile (CTBN) copolymer. The CBTN is introduced into die epoxy resin at elevated temperatures. The modification provides toughness and high peel strength without sacrificing heat and chemical resistance. The film adhesives are widely used in the aerospace industry in the construction of jetliners. 

However, newer adhesives systems having moderate temperature resistance have been developed with improved toughness but without sacrificing other properties. When cured, these structural adhesives have discrete elastomeric particles embedded in the matrix. The most common toughened hybrids using this concept are acrylic and epoxy systems. The elastomer is generally a amine- or carboxyl-terminated acrylonitrile butadiene copolymer (ATBN and CTBN). 

The use of rubbers (particularly epoxy-terminated butadiene nitrile, ETBN, rubber or carboxy-termi-nated butadiene acrylonitrile, CTBN, rubber) to toughen thermoset polymers is perhaps the most widely explored method and has been applied with some measure of success in epoxy resins. Phase separation of the second rubbery phase occurs during cure and its incorporation in the epoxy matrix can significantly enhance the fracture toughness of the thermoset. Although the rubber has a low shear modulus, its bulk modulus is comparable to the value measured for the epoxy, ensuring that the rubber inclusions introduced... 

The incorporation of elastomers into epoxy resins has been an active area of research over the past decade (1-11). The primary reason for this interest has been the improved toughness of the modified materials. We have limited our work to the carboxy-terminated butadiene-acrylonitrile copolymers (CTBN) produced by... 

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