Elastomeric modifier

Elastomeric Modified Adhesives. The major characteristic of the resins discussed above is that after cure, or after polymerization, they are extremely brittie. Thus, the utility of unmodified common resins as stmctural adhesives would be very limited. Eor highly cross-linked resin systems to be usehil stmctural adhesives, they have to be modified to ensure fracture resistance. Modification can be effected by the addition of an elastomer which is soluble within the cross-linked resin. Modification of a cross-linked resin in this fashion generally decreases the glass-transition temperature but increases the resin dexibiUty, and thus increases the fracture resistance of the cured adhesive. Recendy, stmctural adhesives have been modified by elastomers which are soluble within the uncured stmctural adhesive, but then phase separate during the cure to form a two-phase system. The matrix properties are mosdy retained the glass-transition temperature is only moderately affected by the presence of the elastomer, yet the fracture resistance is substantially improved. 

The use of elastomeric modifiers for toughening thermoset resias generally results ia lowering the glass transition temperature, modulus, and strength of the modified system. More recendy, ductile engineering thermoplastics and functional thermoplastic oligomers have been used as modifiers for epoxy matrix resias and other thermosets (12). 

Commercial thermoplastics are the engineering materials containing two or more compatibilized polymers that are chemically bounded in a way that creates a controlled and stable morphology with a unified thermodynamic profile. In view of multiplicity and contradictory requirements of various properties for most of the applications, almost all the commercial PBAs are made of two or more thermoplastics, elastomeric modifiers along with a series of compatibilizers with modifiers compounded together. A considerable number of blends have been appearing in the market regularly, some of which are listed in Table 9. 

The addition of the polysulfide resin acts as both an elastomeric modifier and a diluent for the epoxy resin. The low viscosity of LP-3, for example, can drastically reduce the viscosity of the overall formulation. This provides greater ease of mixing and application and the ability to be applied and sprayed without a solvent. 

Elastomeric modifiers Noveon (formerly B.F. Goodrich) www.noveon.com... 

The principle rheological properties which reflect the polymer process dynamics are the loss modulus (C), storage modulus (G"), dynamic complex viscosity (n ), and tan delta parameters. In simplified form the loss modulus describes the viscous or fluid component of viscosity. That is, how easily the molecules can move past each other. The storage modulus describes the elastic or network entanglement structure of the polymers. It is, therefore, sensitive to cross linking, reaction formation and the elastomeric modifiers. The complex dynamic viscosity is the combined effect of both moduli discussed. It, therefore. 

The lower molecular weight LP-3, LP-33 and ZL-1400 C polymers are used as elastomeric modifiers, particularly for epoxy coatings and adhesives. Owing to their low molecular weight these polymers have the lowest viscosities of commercially available LPs. This low viscosity is particularly beneficial under cold conditions. Even at 4°C the polymers have viscosities which are considerably lower than those associated with standard unmodified bisphenol A [diglycidyl ether of bisphenol A (DGEBA)] epoxy resins at 25°C. 

If the hydrolyses in organosilicate-polymer systems are carried out with sufficiently large amounts of the silicate, then the silica generated can become the continuous phase, with the polymer dispersed in it. The result is a polymer-modified ceramic, variously called an "ORMOCER",23-25 "CERAMER",26 or POLYCERAM". - - It is obviously of considerable interest to determine how the polymeric phase, often elastomeric, modifies the ceramic in which it is dispersed. 

Mechanical stren fth tensile, flexural, impact and compressive strength Mechanical properties such as tensile and flexural strength are mainly affected by reinforcements but the addition of these materials (especially glass fiber) may also create a more brittle compound (as with reinforced polyamides), and an elastomeric modifier may often be added to counter this tendency. Elastomeric additives are also widely used to improve impact strength, especially at subzero temperatures. Mineral fillers can improve compressive strength. 

The use of elastomeric or flexibilizing modifiers occurred and grew with epoxy resins first. Various aspects of toughened epoxy adhesives have been covered in reviews by the present authors (2,3), where the elastomeric modifiers have essentially been carboxylic, liquid and solid butadiene/acrylonitrile polymers. There has not been a systematic review, however, of these and other reactive liquid polybutadiene/acrylonitriles in the burgeoning areas of acrylic, anaerobic and radiation-curable systems. Thus, this paper s intent. 

In addition to the stress concentrations upon loading, which arise from a difference in stiffness of the matrix and elastomeric modifier, there are thermal stresses generated around particles due to the difference in thermal expansion... 

In rubber toughening, an elastomeric modifier is incorporated into the epoxy matrix as a second phase (as discussed in Chapter 4), which is why improvement in toughness is achieved without a significant sacrifice of the and mechanical properties. The toughening agents reported so far can be classified as commercial, other rubber-based, acrylate-based and hyperbranched polymer-based modifiers. 

By the authors [26] the novolac-epoxy networks was modified with reactive epoxy functional polysiloxane oligomers containing various levels of polar nitrile pendent groups was investtigated. It was shown that the using with high content of polysiloxanes as an elastomeric modifiers component in epoxy-novolac networks exhibited micro phase separation. 

It is supposed that cavities (in elastomeric modifier particles) form wherever fiy > five. The volume strain y in the vicinity of a sharp crack (in the plane of the crack, for opening mode I and for small strains) can be expressed as... 

The use of different classes of additives, such as stabilizers, inert fillers, elastomeric modifiers, and compatibilizers can improve the processability, enhancing the thermomechanical resistance of the polymers, and the mechanical properties. 

A thermal cure hot melt phenolic resin providing adequate stability and viscosity and developed for the manufacture of aerospace prepregs. Cured glass composites (60 minutes 135 C) demonstrate excellent flexural, tensile and compressive properties. The resin can be modified with GP413D41 and GP464D20 elastomeric modifiers to produce composites with improved toughness while maintaining superior fire resistance and low smoke density. 

The above described polymers show a good combination of chemical, mechanical and process properties, and are particularly useful, either alone or as mixtures, as high-tenacity thermoplastic polymers and as elastomers or elastomeric modifiers. One can control both the incorporated amount of carbon monoxide and the ratio of cyclopentanones/cyclo-hexanones and, consequently, the properties of the desired polymer. This makes such a class of new materials of great potentid interest. 

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