Polycarbonates impact modifiers

Phosphorus -bromine flame retardant synergy was demonstrated in a 2/1 polycarbonate/polyethylene blend. These data also show phosphorus to be about ten times more effective than bromine in this blend. Brominated phosphates, where both bromine and phosphorus are in the same molecule, were also studied. In at least one case, synergy is further enhanced when both phosphorus and bromine are in the same molecule as compared with a physical blend of a phosphorus and a bromine compound. On a weight basis, phosphorus and bromine in the same molecule are perhaps the most efficient flame retardant combination. The effect of adding an impact modifier was also shown. 

A 2/1 blend of polycarbonate and polyethylene terephthalate (PC/PET) was flame retarded with bromine, phosphorus, a blend of bromine and phosphorus, and compounds containing both phosphorus and bromine in the same molecule. All compositions contained 0.5 % Teflon 6C as a drip inhibitor and where specified 5 % of an impact modifier. 

Table 6 shows the flamability characteristics of an impact modified 2/1 polycarbonate/PET blend containing 6 % of the various flame retardants. The composition containing the brominated phosphate 60/4 is the only one which is V-0 by the UL-94 vertical burn test. At 10 % add-on, the all-bromine containing resin is V-1 and at 13 % add-on the all-phophorus containing resin is V-0. 

Table 6. Flame Retarding Impact Modified 2/1 Polycarbonate/PET Blend...

Data concerning the xenon arc exposure of PECT have been reported [2], Note that comparison is made to general purpose polycarbonate and impact modified acrylic for the color development. The PECT copolymer obviously changes much more rapidly in b value [3] than either of these materials. Flatwise impact testing (see below) showed the PECT sample to be ductile at the test start and brittle at the first exposure interval of 800kJ/m2 exposure. 

B. Perret and B. Schartel, The effect of different impact modifiers in halogen-free flame retarded polycarbonate blends - ii. fire behaviour, Polym. Degrad. Stab., In Press, Corrected Proof, 2009. 

Core-shell emulsion polymers with a core or rubbery stage based on homopolymers or copolymers of butadiene are used as impact modifiers in matrix polymers, such as ABS, for styrene acrylonitrile copolymer methyl methacrylate (MMA) polymers, poly(vinyl chloride) (PVC), and in various engineering resins such as polycarbonate) (PC) poly(ester)s, or poly(styrene)s, further in thermosetting resins such as epoxies. 

We have tested the following polymers polycarbonate (PC), poly-carbonate/4% polyethylene blend (PC/PE), poly (ethylene terephthal-ate) (PET), ABS, and impact modified polystyrene (HIPS). All materials except PC were compression molded into nominal Vs-inch sheets. The PC used was an Vs-inch extruded sheet heat-treated in a manner previously described (22). These PC specimens were considered to be... 

Polybutylene therephthalate (PBT) has been used as a blend component to provide chemical resistance in various systems, but the most interesting one results from a combination with polycarbonate and, eventually, an Impact modifier of the coreshell type. Polyester blends containing polycarbonate exhibit ester interchange chemical reactions, which add to the complexity of property control of these materials. DEVAUX and co-workers (14) have examined the transesterification reaction catalysed by residual catalysts in PBT which can lead to the formation of block and random copolymers. They have shown that allyl or aryl phosphites inactivate the residual titanium catalyst and minimise the transesterification reaction. HOBBS et al. (15) reported a way of controlling miscibility behaviour, morphology and deformation mechanisms, in order to obtain blends compati-bilisation and excellent mechanical properties. 

Polycarbonate has been found to lose its toughness when aged at temperatures below its T and impact modifiers are often added to counteract this effect of physical aging. Blends of PC with... 

The commercial grades of polyamide/polycarbonate blend (Dexcarb ) exhibit high notched Izod impact strength comparable to that of impact modified polyamides and polycarbonate (Table 15.24). It is believed that an elastomeric impact modifier was included in these compositions. Patent claims the use of a polyetheramide and a maleated polypropylene or EPR as the compatibilizing/ impact modifying additives [Perron, 1988]. The commercial grades contain varying amounts of PC, PA-66 (or 6) and the impact modifier. 

Impact modified polycarbonates Improve notch sensitivity... 

Table 15.25. Properties of commercial impact modified polycarbonate vs. polycarbonate...

In order to improve both the thickness sensitivity and low temperature sensitivity of the impact strength, polycarbonate has been blended with a variety of low T, elastomeric impact modifiers. More important among these are the core-shell rubbers like PMMA-g-polybutadiene, PMMA-g-SBR (MBS), PMMA-g-n-butylacrylate (acrylic core-shell), all normally composed of 0.1/core particles. These modifiers improve both the thick-section (6.4 mm) and low temperature notched Izod impact properties of polycarbonate [Witman, 1981 Neuray and Ott, 1981 Bussink et al., 1977] (Figures 15.13 and 15.14). The blends are of course opaque. Impact modified polycarbonate also shows better retention of impact strength with heat-aging. 

Commercial impact modified (elastomer blended) polycarbonates are used for the production of protective headgear, sporting goods, bobbins for textile industry and automotive components requiring high toughness. Impact modified PC has to compete with the more solvent resistant impact modified PBT/PC, PET/PC blends and polyamides in some of the applications. 

Figure 15.13. Effect of sample thickness on the notched impact strength of unmodified (I) vs. impact modified (II) polycarbonates P reitag et al., 1985].

SMA PC blend. This blend (Arloy , Arco) contained SMA grafted with polybutadiene as the impact modifier. The properties of SMA/PC blend were similar to ABS/PC blend with slightly higher heat distortion temperatures (107 to 117°C) but comparable impact strength (> 500 J/m). However, it was discontinued from the market due to unfavorable economics relative to ABS/PC blend. The partial miscibility between the styrene-maleic anhydride and polycarbonate accounts for the adequate compatibility of this blend as evidenced by the high level of tensile and impact strengths. 

Several research investigations have been made to compatibilize PET or PBT with PPE both by reactive and non-reactive routes of compatibiliza-tion [Brown et al., 1990 and 1991 Akkapeddi and VanBuskirk, 1992]. Compatibilized binary blends of PPE/polyesters still lacked adequate toughness and invariably required the addition of rubbery impact modifiers (reactive or compatible type) and polycarbonate. The addition of polycarbonate presumably suppresses the crystallization of the thermoplastic PET or PBT phase, due to its... 

Modification of Engineering Resins Specific interaction of the phosphonium ionomer from Exxpro elastomer with selected engineering resins such as Polycarbonates(PC), Polyesters(PET), Polyacrylates(PAE), Polyamides(PA), Polyphenylene Oxide(PPO), and Acetals(PAc) can be utilized to compatibilize, impact modify or nucleate the above resin in blends with similar polymers. Typical examples are ... 

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. 

The physical mixing of two or more polymers to crate a material with properties different from each of the components has become an increasingly popular route to new materials development. The resulting blend or alloy greatly reduces the associated time and costs while permitting improved processibility and enhanced properties tailored to specific application areas. Many commercial examples of two-phase polyblends consist of a matrix polymer impact modified by the addition of rubber particles. Recently, however, TLCPs have received increasing attention in the scientific and technical literature as in situ reinforcements in polymer blends and microcomposites. The matrices examined in the literature include polyimides, PES, PEI, PEEK, polycarbonate, PET, PPS, and polyarylate. 

Most of the discussion has been centered around just the neat polymer or the polymer plus a modifier or additive. Coloring issues further escalate when polymer blends are used or when multiple additives are incorporated. Would it be difficult, and would the color gamut be somewhat restricted, if one was to color an impact modified, flame retardant, glass reinforced PBT/polycarbonate alloy The answer now better be a resounding YES ... 

Super-tough poly(sulfone)s can be produced by blending PES with acrylate rubber and a polycarbonate as an impact modifier. From this high impact strength composition, films and molded articles are useful in automotive applications, durable goods and appliances, medical and plumbing applications where resistance to hot, humid environments may be particularly important, and safety equipment and protective gear. 

Polycarbonate / Polyester Blends. Contour maps of the temperature-frequency variation of complex relative permittivity have been obtained for impact-modified PC/PBT and PC/PET blends [3,43] and for their constituent polycarbonate [3], PBT [44] and PET [45] homopolymers. In the impact-modified PC/PBT blend (Figure 7), as in each of the blends, a single broad p-absorption is observed but the separate a-absorptions of the constituents persist. 

For impact-modified PC/PBT and PC/PET blends evidence has been presented for partial miscibility of the component polymers and for a two-phase blend morphology with a polyester-rich dispersed phase in a continuous matrix rich in polycarbonate. Other absorptions are attributed respectively to MWS interfacial polarization, to the presence of the impact modifier and to a phosphite processing stabilizer. 

---