Core-shell impact modifier

For the core-shell impact modifiers of interest here, the rubber core can be regarded as an impenetrable wall where one end of each chain is grafted to this 

The use of core-shell impact modifiers for sPS is also patented in EP 318793 [15] (see Table 19.1). These impact modifiers are usually prepared using the emulsion polymerization process, although other methods such as the microsuspension polymerization process are possible. The core usually consists of polymers prepared from an acrylate, especially butyl or 2-ethylhexyl acrylate or butadiene. These rubber particles are then grafted with vinyl monomers, where 

The use of core-shell impact modifiers combined with styrene-hydrogenated poly butadiene block copolymers in sPS is described by Rohm and Haas [24]. The core of the former type is of polybutadiene or its copolymer, the shell consists predominately of polystyrene. Rohm and Haas found that a synergistic effect is present and that the Izod notched impact strength is higher when both rubber types are used instead of only one. 

It would appear that these rubbers have a similar toughening effect as the S-EB-S block copolymers. However, a synergistic effect is present when a mixture of both impact modifiers is employed [27]. 

as in the preceding examples, if the sPS in the specimen is given sufficient time to relax after injection moulding and to crystallize, then the notched impact strength is reduced. 

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Safety precautions Before this experiment is carried out, Sect. 2.2.5 must be read as well as the material safety data sheets (MSDS) for all chemicals and products used. This example describes the concept of core/shell impact modifiers for thermoplastic polymers (see Sect. 5.51). 

Aerdts et al. [1997] prepared stabilized PA blends with a functionalized core-shell impact modifier having grafted epoxide groups in the shell. Specifically, 75 parts PA-6 was extraded on a mini-extruder with 25 parts SB core/MMA-GMA shell impact modifier at 240°C. Blends were characterized by TEM. Dispersed phase agglomeration was examined as a function of epoxide concentration on the shell surface. Koulouri et al. 

KAV 96] Kavano Y., Keskkula H., Paul D.R., Effect of polycarbonate molecular weight and processing conditions on mechanical behaviour of blends with a core-shell impact modifier , Po/ywer, vol. 37, no. 20, pp. 4505 518,1996. 

Acrylic copolymers (i.e., core-shell impact modifiers with a shell of PMMA and a core of butyl acrylate elastomer) have been developed mainly for impact modification of PVC for outdoor applications. Butadiene-styrene copolymers are used exclusively for PVC, PC or styrene-acrylonitrile (SAN). Thermoplastic elastomers in the form of styrenic copolymers, e.g., SBS, are used preferably for styrenics and PA. Polyolefins, like EVA, are used for impact modification of technical polymers. 

There are several factors which determine the results of impact modification. They include PVC molecular weight, condition of material surface, materials thickness, temperature of service, type and structure of impact modifier, its particle size and concentration, UV degradation and stabilization of impact modifier, method of incorporation (dispersion mechanism), shell thickness of core-shell impact modifiers, interaction with other components of formulation (fillers, ther-... 

The shell thickness of core-shell impact modifier was found to be the most important property, controlling its effectiveness as the impact modifier. Figure 3.28 shows that if the shell thickness is too small (smaller than 4.9 nm) or too large (above critical value of 15.8 nm), impact strength is rapidly reduced. Within the range of 4 to 15.8 nm, the thickness of the shell does not seem to matter. 

PA-6 (75)/SMA (20 % MA) (0-5)/ SB core -I- MMA shell impact modifier (20-25) Mini-extruder at 240 °C/TEM/ comparison to blends containing core-shell impact modifier with GMA grafted onto shell Aerdts et al. 1997... 

C. A. Cruz-Ramos, Core-shell impact modifiers, in Polymer Blends, Vol. 2 Performance, ed. by... 

Bio-based PHAs (polyhydroxyalkanoates) show improved mechanical and environmental performance over PVC. Since some versions may be miscible with PVC, it is possible to produce blends that have superior plasticization, impact strength, and processability. Acting as a plasticizer in the PVC, the PHA provides low migration and extractability, volatile loss, and staining. Toughness can exceed that afforded by traditional MBS core/shell impact modifiers without compromising transparency or UV stability (Anon 2013a). 

So-called core-shell impact modifiers have a less damaging effect on the modulus and HDT. They are made by emulsion graft polymerisation, and consist of two parts. As their name implies, one part is an outer shell of a hard acrylic polymer-like PMMA, in direct contact with the polymer that needs toughening the two must be compatible. (In the case of SAN copolymers, the compatibility depends on the polarity, and hence on the nitrogen content of the copolymer.)... 

The third and fourth digit indicate the Tg plus 100 C. Example PARALOID EXL 4260, a copolymer without polar groups with a Tg of 160 C. Blends were prepared with polyamide-6, polyamide-12 and with clear ABS. In some cases a newly developped reactive, all acrylic Rohm and Haas core/shell impact modifier (PARALOID EXL 3386) was also included in the evaluation (2,3). 

Figure 4.51 Schematic illustration of an emulsion-made core-shell impact modifier particle...

Applications core-shell impact modifier (automotive parts, housings for electronic components, thermoset adhesives), electrical parts, sheet ... 

Recently, Wills et al. [16,17] proposed a novel agglomeration method. Core/shell impact modifiers, useful in toughening polyfvinyl chloride) and other thermoplastics, are prepared at small particle size by an emulsion polymerization process, agglomerated by the novel technique which has little effect on emulsion solid, are further encapsulated by a final shell, and are isolated by spray drying or coagulation. The isolated particles are readily redispersed to their original particle size in the matrix polymer. 

Core-shell impact modifiers have also been reported as impact modifiers for engineering polymers. MBS impact modifiers with a SBR core, a polystyrene middle layer and an outer layer of MMA copolymers with glycidyl methacrylate, acrylamide or methacrylic acid functional monomers were evaluated in PC/PBT blends [104]. Optimal results were obtained with 60 wt% SBR content in the MBS and a modest amoimt of a functional monomer in the MMA copolymer shell. Core-shell impact modification of polycarbonate [105] (PMMA grafted on poly(n-butyl acrylate) and PBT[106] (SAN grafted onto a butadiene based rubber) have been reported. A comprehensive review of core-sheU impact modification of various polymers (PMMA, PVC, PC, PBT, PET, polyamides, thermoplastic blends, thermosets) has been presented by Cruz-Ramos [107]. 

Core-shell impact modifiers produced via emulsion polymerization involve the grafting of acrylate or styrenic monomers onto elastomers (PB, SBR, acrylate rubbers). These materials can be recovered from the emulsion as dry powders for subsequent extrusion blending with various thermoplastics. Impact modified PVC blends are the major use of core-shell impact... 

A core-shell impact modifier is probably the best model to illustrate the utility of emulsion polymerization technology. The core polymer is based on a low glass transition temperature (Tg) mbber and is surrounded by a hard polymeric shell (high Tg material). The core rubber is made in the first stage of the emulsion polymerization. 

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