Reactive toughened systems

Unaccelerated medium-to-high reactive, toughened system with reduced danger of microcracks when used for pultruded profiles. c 900-1300 n 1.8%... 

Acryhc stmctural adhesives have been modified by elastomers in order to obtain a phase-separated, toughened system. A significant contribution in this technology has been made in which acryhc adhesives were modified by the addition of chlorosulfonated polyethylene to obtain a phase-separated stmctural adhesive (11). Such adhesives also contain methyl methacrylate, glacial methacrylic acid, and cross-linkers such as ethylene glycol dimethacrylate [97-90-5]. The polymerization initiation system, which includes cumene hydroperoxide, N,1S7-dimethyl- -toluidine, and saccharin, can be apphed to the adherend surface as a primer, or it can be formulated as the second part of a two-part adhesive. Modification of cyanoacrylates using elastomers has also been attempted copolymers of acrylonitrile, butadiene, and styrene ethylene copolymers with methylacrylate or copolymers of methacrylates with butadiene and styrene have been used. However, because of the extreme reactivity of the monomer, modification of cyanoacrylate adhesives is very difficult and material purity is essential in order to be able to modify the cyanoacrylate without causing premature reaction. 

E-EA-GMA (see Table 14.3) and EEA are often used in combination as a toughening system. The optimum blend ratio of reactive elastomers non-reactive elastomers (e.g. Lotader Lotryl) is 30/70. Since the E-EA-GMA terpolymer and EEA copolymer are mutually miscible, when blended together with PET the mixture acts as a single elastomeric phase, which is interfacially grafted to the PET continuous phase. 

Figure 14.11 Variation of the notched Izod impact strength of PET containing 20 % of an elastomeric toughening system as a function of the ratio of reactive to non-reactive modifier. It can be seen that the 30 70 reactive non-reactive mixture provides the optimum balance. The reactive modifier acts more as a compatibilizer in this system. Note units for impact strength (kJ m 2) can be converted to J nr1 by multiplying by 10...

In multiphase polymeric systems, the properties of the end products do not solely depend on the properties of the pure components, but other various parameters also have a great impact (Fig. 1). In order to emphasize these factors, the following systems are taken into consideration (I) elastomer toughened styrene system, (2) elastomer toughened polycarbonate blends, and (3) direct reactive blend processing. 

Pecorini and Calvert [28] attribute the role of small particles and a small interparticle distance to inducing high toughness in PET by promoting massive shear yielding in the matrix. Their study showed that the non-reactive impact modifier gives a system in which the rubber phase is not well dispersed. It was shown that this is not effective in toughening PET at levels of either 10 or 20%. The... 

J This result was obtained by a reaction-driven phase separation. An advantage of this system compared to the more conventional ones is that no filtering of toughener during fiber-impregnation can take place. The phase separation is accomplished by carefully designing the reactivities of the different components as well as the surface polarity of the hyperbranched resin [120-122]. 

Liquid reactive rubbers were also used for UP and vinyl ester formulations (Suspene et al., 1993 Siebert et al., 1996). Increases in fracture energy and fatigue- crack resistance were reported for some systems, although no significant improvements were observed for some other systems. These different behaviors are probably related to the heterogeneous structure of the matrix (Chapter 7). Toughening mechanisms in three-phase systems are not yet well established. 

In many systems, such as epoxy resins, the rubber toughener may be soluble in the other phase, such as epoxy resin, so the phase separation must be achieved during cure. This is an example of phase separation during reactive processing. 

In the 1950 s, the core-shell, emulsion type methylmethacrylate-butadiene-styrene terpolymer (MBS) was developed to toughen PVC or PC. These blends could also contain other polymers, viz. SAA [Murdock et al., I960] SMM and PS [Murdock et al., 1962] SMM-AN [Schmitt et al., 1967] high heat ABS [Kanegafuchi Chemical Industry, 1967] HIPS [Ward, 1970] MMVAc-AA [Holland et al., 1970] SMMA [Blasius, 1992], etc. Table 1.34 traces evolution of these systems. Later, these multipolymers were modified by incorporation MA, AA, or GMA units to serve as reactive compatibilizers and toughening agents for PA, PEST or PC blends. 

An unusual type of two component system has recently been introduced in the adhesive industry (1,). These are called reactive adhesives, second generation acrylics, toughened acrylics, modified acrylics (2) or "honeymoon adhesives" (in Europe). 

Compositions of these adhesives are suggested in a number of recent patents (5- )- All of these reactive adhesive patents indicate essentially the same concept an elastomer is colloidally dispersed in a monomer, or a monomer/oligomer/polymer solution. The system is then polymerized using a free radical mechanism. What occurs is a rapid, "in situ" polymerization of a (typically) methyl methacrylate system, toughened by elastomeric domains which have beer, incorporated into the structure by grafting. 

Consequent to documentation surrounding methods of employing reactive nitrile elastomers to modify epoxy resins is a growing body of literature which serves to characterize and elucidate these systems. Such topics as morphology in the cured and uncured state, transitions from toughening to flexlbilization, viscoelastic effects, equilibrium physical properties and phase structure are available to the investigator (12-17). 

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