Toughening modifiers

These blends can take a number of different forms. The added resin may be reacted with the epoxy resin, or it may be included as an unreacted modifier. The modifier may be blended into a continuous phase with the epoxy resin (epoxy alloys) or precipitated out as a discrete phase within the epoxy resin matrix (as is generally done in the case of toughening modifiers). Epoxy hybrid adhesives are often used as film (supported and unsupported) or tape because of the ease with which formulated systems can be dissolved into solvent and applied to a carrier or deposited as a freestanding film. Some systems, notably epoxyurethanes and epoxy-poly sulfides, can be employed as a liquid or paste formulation because of the low-viscosity characteristics of the components. 

Jan Jansen, B. J. P., Tamminga, K. Y., Meijer, H. E. H., Lemstra, P. J. Preparation of thermoset rubbery epoxy particles as novel toughening modifiers for glassy epoxy resins. Polymer 40... 

DuPont (2010) DuPont Biomax Strong PLA Toughening Modifier, http //www2. dupont.com/Biomax/en US/assets/ downloads/Biomax%20Strong.pdf (accessed 29 September 2014). 

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. 

Mechanical Properties. Properties of typical grades of PBT, either as unfiUed neat resin, glass-fiber fiUed, and FR-grades, are set out in Table 8. This table also includes impact-modified grades which incorporate dispersions of elastomeric particles inside the semicrystalHne polyester matrix. These dispersions act as effective toughening agents which greatly improve impact properties. The mechanisms are not fiiUy understood in all cases. The subject has been discussed in detail (171) and the particular case of impact-modified polyesters such as PBT has also been discussed (172,173). 

Fig. 10. Preparation and morphology of toughened PVC (a) secondary PVC grain (50—250 flm) (b) modified PVC with coherent primary grain (ca 1 -lm) (220). CPE = chlorinated polyethylene EVA = ethylene—vinyl acetate copolymers ABS = acrylonitrile—butadiene—styrene MBS = methyl...

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). 

R. Siebert, "Rubber-Modified Thermoset Resins," in C. K. Riew and J. K. GiUham, eds., ACS Advances in Chemistry Series 208, American Chemical Society, Washington, D.C., 1983, p. 179 W. D. Bascom and D. L. Hunston, "Rubber Toughened Plastic," Adv. Chem. Ser. No. 222, American Chemical Society, Washington, D.C., 1989. 

Blends of isobutylene polymers with thermoplastic resins are used for toughening these compounds. High density polyethylene and isotactic polypropylene are often modified with 5 to 30 wt % polyisobutylene. At higher elastomer concentration the blends of butyl-type polymers with polyolefins become more mbbery in nature, and these compositions are used as thermoplastic elastomers (98). In some cases, a halobutyl phase is cross-linked as it is dispersed in the polyolefin to produce a highly elastic compound that is processible in thermoplastic mol ding equipment (99) (see Elastomers, synthetic-thermoplastic). ... 

Polymers below the glass transition temperature are usually rather brittle unless modified by fibre reinforcement or by addition of rubbery additives. In some polymers where there is a small degree of crystallisation it appears that the crystallines act as knots and toughen up the mass of material, as in the case of the polycarbonates. Where, however, there are large spherulite structures this effect is more or less offset by high strains set up at the spherulite boundaries and as in the case of P4MP1 the product is rather brittle. 

Bauman, A.D., High-value engineering materials from scrap rubber. Rubber World, 212, 30, 1995. Bagheri, R., Wilbams, M.A., and Pearson, R.A., Use of surface modified recycled rubber particles for toughening of epoxy polymers, Polym. Eng. Sci., 37, 245, 1997. 

Improve both impact strength and rigidity of thermoplastics by using up the energy of crack propagation. Elastomers are prototypical toughening additives. Examples of high-polymeric impact modifier/thermoplastic matrix systems are EVA, CPE and MBS in PVC, EP(D)M and SBS in PA, and acrylic rubbers in polyesters. 

To assess the effect of elastomer degradation on composite performance, additional composites were fabricated with the same 121°C cure epoxy without any addition of the elastomer (211. The expansion behavior of the modified epoxy composite was similar to the toughened material. For electron doses less than 10 rads the CTE of the toughened and untoughened composites were essentially the same which suggests that the epoxy matrix and not the elastomeric component controls the thermal expansion behavior. 

Hourston, D. J., Lane, S. and Zhang, H. X., Toughened thermoplastics Part 2 impact properties and fracture mechanisms of rubber modified PBT, Polymer, 32, 2215-2220 (1991). 

Reactive impact modifiers are preferred for toughening of PET since these form a stable dispersed phase by grafting to the PET matrix. Non-reactive elastomers can be dispersed into PET by intensive compounding but may coalesce downstream in the compounder. Reactive impact modifiers have functionalized end groups. Functionalization serves two purposes - first, to bond the impact modifier to the polymer matrix, and secondly to modify the interfacial energy between the polymer matrix and the impact modifier for enhanced dispersion. Some examples of commercially available reactive impact modifiers for PET are shown in Table 14.3. An example of a non-reactive elastomer that can be used in combination with reactive impact modifiers is ethylene methyl acrylate (EMA), such as the Optema EMA range of ethylene methyl acrylates manufactured by the Exxon-Mobil Chemical Company (see Section 4.2). 

Most non-reactive (unfunctionalized) elastomeric impact modifiers such as general purpose rubbers, are not highly effective at toughening polyesters because they are unable to adequately interact with the polyester matrix so as to achieve... 

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