Strength SMAs

Styrene maleic anhydride SMA is a copolymer made with or without rubber modifiers. They are sometimes alloyed with ABS and offer good heat resistance, high impact strength and gloss but with little appreciable improvement in weatherability or chemical resistance over other styrene based plastics. 

Figure 5 shows the dependences of tensile strength of the cocured DAP resins on monomer composition the tensile strength decreased with an increase in the mole fraction of comonomers and its dependency tended to be remarkable in the order VL < DOF < LMA < SMA. Particularly, the addition effects of LMA and SMA were quite great, being comparable to the result of PEGBAP as the dotted line in Figure 5. 

Thus, the introduction effect of long-chain alkyl groups into the DAP resins was reflected in the improved flexibiiity. In particular, LMA and SMA as comonomers showed a remarkable effect for example, the DAP resin cocured with 10 mol% of LMA had the tensile strength of 600 kg/cm and the elongation of 9.0%, although the DAP resin obtained by homopolymerization was quite brittle and, therefore, could not even be subjected to the measurement of mechanical properties as mentioned above. 

Figure 5. Dependences of tensile strength on monomer composition for the DAP resins cocured with (O ) VL, ( (J ) DOF, (O ) LMA, ( ) SMA, and (-----) PEGBAP.

Polycarbonate is blended with a number of polymers including PET, PBT, acrylonitrile-butadiene-styrene terpolymer (ABS) rubber, and styrene-maleic anhydride (SMA) copolymer. The blends have lower costs compared to polycarbonate and, in addition, show some property improvement. PET and PBT impart better chemical resistance and processability, ABS imparts improved processability, and SMA imparts better retention of properties on aging at high temperature. Poly(phenylene oxide) blended with high-impact polystyrene (HIPS) (polybutadiene-gra/f-polystyrene) has improved toughness and processability. The impact strength of polyamides is improved by blending with an ethylene copolymer or ABS rubber. 

To design a resin with the property enhancements of AN without the cross-linking problem, it was found that SMA copolymers and terpolymers could be blended with ABS resins to form miscible blends with properties of HHABS. A fundamental look at the miscibility of SMA copolymers with SAN copolymers indicated that the optimum thermodynamic interaction occurs when the AN content of the SAN is nearly equal to the MA content of the SMA [72]. Kim et al. also found low impact strengths at all modifier levels when blending SMA with SAN-g-polybutadiene (GRC = grafted rubber concentrate) [73]. Blends of SMA with SAN and GRC (SAN + GRC = emulsion ABS) exhibited ductility behavior similar to HHABS. The impact strengths of the polymers were 2-5 ft-lb/in, in a notched Izod test at ambient temperature. 

Studies of gabapentin in individuals with SMA II and III showed improvement in muscle strength but not in motor or respiratory function [45, 46]. 

CP VC and PMMA, methylstyrene-acrylonitrile-methyl methacrylate, methylstyrene-acrylonitrile-styrene, imidized-PMMA, imidized-SMA, and SAN economy, high HDT and impact strength Soby et al., 1994... 

PC with ABS and rubber-modified SMA processability, impact strength, heat resistance Henton, 1980, 1982... 

The largest group comprises the impact modified PEST s — these were summarized while discussing commodity resin blends. The commercial blends with, e.g., SMA or acrylic rubber, show good processability, rigidity, impact and tensile strength, as well as excellent weatherability, viz. Arloy 2000, Bexloy , Celanex , Pibiter HI, Rynite , Ultradur KR. 

Although the unmodified styrenics, viz. polystyrene, SAN and SMA copolymers, exhibit good clarity, strength and rigidity, they are invariably brittle for many applications. Hence the rubber modified styrenics such as HIPS and ABS, which combine a good level of impact strength with... 

A commercial blend of SMA and polycarbonate (Arloy , ARCO) was offered for some time, but recently it was discontinued. The polarity of SMA copolymer may account for the good degree of compatibility between the two resins. The blend contained the polybutadiene rubber normally used in SMA resins for impact strength. It exhibited good low temperamre impact strength (Table 15.8) and in many properties was similar to ABS/PC blend. 

A commercial blend of SMA and polybutylene terephthalate (Table 15.8) was also offered for applications requiring solvent resistance, which the crystalline PBT provided. This blend lacked adequate compatibility and hence its impact strength is relatively poor. 

Blends of polycarbonate with other styrenic resins are relatively new and therefore their current market volume is low. They have been developed primarily to upgrade the performance of such styrenic resins as styrenic-maleic anhydride (SMA), styrene-methyl methacrylate (S-MMA), acrylic-sty-rene-acylonitrile (ASA) resins primarily for impact strength and to some extent for DTUL improvement (Tables 15.7, 15.8 and 15.23). These blends uniquely combine high notched Izod impact strengths (ranging from 500 J/m to > 1000 J/m) with better UV resistance or weatherability than ABS. 

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. 

Thermoplastic alloy of styrene maleic anhydride copolymer and polybutylene terephthalate. Has improved dimensional stability and tensile strength. Processed by injection molding. Also called SMA PBT Alloy. 

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