Emulsion rubbery particles

The essence of rubber-toughening a brittle plastics material is to disperse a rubber as discrete micron, or submicron, size particles in the polymer to be toughened, typically using the rubber at volume fractions in the range 0.05-0.20 [1-3]. Emulsion polymerization provides one means of preparing rubbery particles for this purpose, and this chapter gives an overview of the use of emulsion polymer particles for toughening of important plastics materials. 

Core-shell rubber (CSR) particles are prepared by emulsion polymerization, and typically exhibit two or more alternating rubbery and glassy spherical layers (Lovell 1996 Chapter 8). These core-shell particles are widely used in thermoplastics, especially in acrylic materials (Lovell, 1996), and have also been used to modify thermosets, such as epoxies, cyanates, vinyl ester resins, etc. (Becu et al., 1995). 

Figure 19 Transmission electron micrographs of thin sections cut from ABS materials. The rubbery domains appear darker, (a) An ABS material prepared by bulk polymerization showing the characteristic salami-like morphology of the toughening particl which contain several SAN domains within the rubber, (b) ABS materials prepared by emulsion polymerization showing cote-shell partides (i) widi and (ii) widiout subinclusions. (Reproduced with permission from ref. 29.)...

The glueline will have very good mechanical properties if the coalescence of the emulsion particles is optimal. However, if the isocyanate reaction proceeds too far before the glue film is formed, i.e., the glue mix is too old before it is used (cf. pot-life Section 6.1), adequate coalescence will not be possible and the glueline will have a more rubbery consistency [2], Hence, a good balance between these processes is essential. 

In a broad study to evaluate the composite properties of hetero-geneous-latex-based materials, Dickie et synthesized a series of latex semi-IPNs. A two-staged emulsion polymerization procedure was employed that yielded relatively uniform populations of heterogeneous latex particles (HLP). The glassy component was prepared from methyl methacrylate, and the rubbery component used a mixture comprising 95 mol % butyl acrylate (BA) and 5 mol % 1,3-butylene dimethacrylate (BPMA). Heterogeneous latex particles in which the rubbery component was polymerized first were referred to by Dickie et al as HLPl particles for which the order of polymerization was reversed were referred to as HLP2. 

Shaffer et al [365] have continued to modify staining techniques for TEM of latex particles. Recent work on structured latex particles prepared by seeded emulsion polymerization focused on the effects of changes in polymerization variables, such as batch versus semicontinuous, core-shell ratio, shell thickness and shell composition. In this system the core was poly(n-butyl acrylate) and the shell was poly(benzyl methacrylate-styrene). A few drops of the latex was combined with a few drops of a 2% uranyl acetate solution which serves as a negative stain. A drop of that mixture was deposited on a stainless steel formvar-coated grid. After drying it was stained in ruthenium tetroxide vapor to differentiate the rubbery core, which is not... 

It is intended to toughen poly(methyl methacrylate) (PMMA) by the addition of particles of rubbery poly[(n-butyl acrylate)-co-styrene] made by emulsion polymerization. In order to retain the good optical clarity of the PMMA it is necessary to match the refractive indices, n, of the PMMA and copolymer particles. Estimate the relative proportions of the two comonomers required in the particles given that at room temperature the refractive index of PMMA is 1.489 and n is 1.466 for poly(n-butyl acrylate) and 1.591 for polystyrene. Would you expect the material to retain its clarity if the temperature were changed from ambient ... 

Mechanical Properties of the Latex Films. Figure 13.18 shows a noteworthy effect of the addition of Laponite on the mechanical properties of the nanocomposite film. A remarkable increase in the storage modulus at the rubbery plateau was observed with the addition of only 5 wt% Laponite. This improvement of the mechanical properties of the poly(styrene-co-butyl acry-late)-Laponite film was expected, considering the good dispersion of the clay platelets inside the polymeric matrix and the armored morphology of the hybrid particles. It is worth remembering here that similar results were reported by Ruggerone and co-workers" and Faucheu et al. for PS-Laponite films obtained from latexes prepared by emulsion and miniemulsion polymerization, respectively (see Sections 13.3.2.1 and 13.3.2.2). 

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