Izod impact, blends

Most of the polymer s characteristics stem from its molecular stmcture, which like POE, promotes solubiUty in a variety of solvents in addition to water. It exhibits Newtonian rheology and is mechanically stable relative to other thermoplastics. It also forms miscible blends with a variety of other polymers. The water solubiUty and hot meltable characteristics promote adhesion in a number of appHcations. PEOX has been observed to promote adhesion comparable with PVP and PVA on aluminum foil, cellophane, nylon, poly(methyl methacrylate), and poly(ethylene terephthalate), and in composite systems improved tensile strength and Izod impact properties have been noted. 

The brittleness of isotactic polystyrenes has hindered their commercial development. Quoted Izod impact strengths are only 20% that of conventional amorphous polymer. Impact strength double that of the amorphous material has, however, been claimed when isotactic polymer is blended with a synthetic rubber or a polyolefin. 

Elliot [38] has reported that interfacial adhesion in the NR-PP blend can be enhanced by the addition of small amounts of HOPE. Addition of HDPE does give some improvement in the notched Izod impact strength of NR-PP blend (Fig. 7). The effect of HDPE on the impact modification of NR-PP is associated with the improved crystallinity of PP, enhanced by HDPE. During the mill mixing of NR and PP, chain scission may occur to give polymeric radicals that, on reaction with... 

Figure 7 Effect of addition of HOPE on Izod impact strength of NR-PP blend. (O) 20 80 NR-PP homopolymer, (V) 20 67 13 NR-PP-homopolymer-HDPE, ( ) 15 85 NR-PP copolymer grade, and (x) 15 75 10 NR-PP-copo-lymer-HDPE.

Rubber particle size (/i.m) Large particles in blends (%) Rubber phase volume fraction Notched Izod impact strength ft. Ibs/in. Gloss... 

Heterogeneous compatible blends of preformed elastomers and brittle plastics are also an important route for the development of blends of enhanced performance with respect to crack or impact resistance. Polycarbonate blends with preformed rubber particles of different sizes have been used to provide an insight into the impact properties and the fracture modes of these toughened materials. Izod impact strength of the blends having 5-7.5 wt% of rubber particles exhibits best overall product performance over a wide range temperature (RT to -40°C) [151-154]. 

Figure 2 Notched Izod impact strength of ternary PA-PP-SEBS-g-MAH blends with 0 wt%, 5 wt%, and 10 wt% SEBS-g-MAH. Source Ref. 44.

Figure 6 Dependence of Izod impact strength on the DMAE concentration in 80 20 PS-bromo butyl rubber blends. Source Ref. 53.

When 10 % PTT is blended with PET, it suppressed the PET Tg such that it can be dyed at atmospheric boil without using a carrier [109], A similar phenomenon was also found be Oppermann et al. [110]. Kelsey etal. [Ill] found that the addition of 9 % PTT to poly(cyclobutane terephthalate) (PCBDOT) improves its impact strength without too much sacrifice to the Tg. The 9/93 PTT/PCBDOT blend has a Tg of 100 °C and a notched Izod impact of 75 J/m. 

The notched Izod impact strength of PET at room temperature is only 45 J/m. Supertough PET with notched impact strengths up to 1000 J/m can be prepared by melt blending PET with 20wt% of a reactive elastomeric terpolymer (e.g. E-MA-GMA). Pecorini and Calvert [28] have attributed this supertoughness phenomenon to two distinct toughening mechanisms, as follows ... 

Fig. 3. Dependence of Izod impact strength on temperature for (-) polycarbonate, (—) ABS, and (-) polycarbonate-ABS blends. To convert J to cal,...

Figure 1. Effect of concentration of PTHF on notched Izod impact strength of PVC-PTHF blends. Intrinsic viscosity of PTHF is 3.2 dl/ gram (C6H6 at 25°C)...

Incompatible Mixtures. Even at very low levels, many of the poly-ether additives led to incompatible mixtures. These blends were not successfully milled to a smooth sheet under any conditions tried. Instead, a mass of crumbs was obtained. These crumbs could be molded into a coherent mass, but the physical properties were poor. For example, addition of 8.75 parts of polybutene-1 oxide to Masterbatch B for CPVC alone gave a brittle, free-flowing material with these properties notched Izod impact strength, 0.7 lb/in notch, flow rate 452 g/10 min. This is a particularly interesting result, since PBO has the same chemical formula as PTHF but structurally is a substituted ethylene oxide polymer rather than a linear homopolymer. No further studies were made of such blends. 

Blends of iso- and terephthalates give amorphous, transparent resins, mosdy yellow in color. Heat-deflection temperatures are higher than those of 100% PC resins and depend on the iso- to terephthalate ratio. For example, a resin with a 1 1 ratio has a value of 160°C. These resins are flame retardant mechanical and electrical properties are similar to those of PC resins. The notched Izod impacts are lower at 150—300 J/m (4.7—5.6 fflbf/in.), even in thick sections. Long-term uv radiation stabilities are excellent, but yellowness increases during initial exposure owing to photo-Fries rearrangements (80), wherein 0-hydroxy-benzophenone units are produced along the polymer chains. 

However, the kind of technique used to mold these blends seems to be important in determining their mechanical properties. In fact, mechanical tests carried on injection molded samples [37] show, with respect to compression molded samples, a significant enhancement of the energy to break for all samples (Tables 20.2 and 20.3). Moreover the addition of 10wt% of SEBS to an 80 20 wt% sPS/HDPE blend involves in the injection molded samples an increase in both the energy at break and the Izod impact strength, whereas in the thermo-compressed samples no improvement is observed. Differences between compression and injection molded samples are widely acknowledged [38] and... 

New grades of SMMA are being developed that have shown tremendous potential for blends in SBC. These new grades result in very high impact in the blends with higher loadings of SMMA. Notched Izod impact values of almost 5 ft-lb/in have been reported for injection molded test specimens containing 50 % SMMA [22]. 

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